JPH10250226A - Rewritable heat sensitive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To repeatedly develop and erase color many times with satisfactory visibility, color display and color developing density by incorporating reversing agent for repeating a color developing state and an erasing state by an interaction of a coloring compound and a developer. SOLUTION: In a composition which contains coloring compound such as a leuco auramine and the like and a diarylphthalide and the like, developer such as phenol and the like, benzophenone and the like and reversing agent, a mixed ratio of the compound to the developer is preferably 0.1 to 10 pts.wt. or further 1 to 2 pts.wt. of the developer to 1 pt.wt. of the compound. A mixed ratio of the agent is preferably set to 1 to 200 pts.wt. to 1 pt.wt. or further 10 to 100 pts.wt. of the compound. As the preferable agent, compound containing alcohol group including bulky molecular skeleton near a column like steroid skeleton. More specifically, cholesterol, stigmasterol or pregnenolone is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to various cards, OA
The present invention relates to a thermal recording medium applicable to paper, OHP sheets, bills, and the like, and more particularly, to a rewritable thermal recording sheet for repeatedly writing and erasing characters and images by controlling thermal history.

[0002]

2. Description of the Related Art With the spread of OA in recent years, the data amount of various types of information has been steadily increasing, and the output of information has also increased accordingly. The output of information is represented by a hard copy display on paper by a printer and a display display. However, in recent years, as a third recording medium, a rewritable recording medium, that is, an all-solid or semi-solid recording that can record and erase an image with high visibility many times and does not require energy to maintain a display. From the viewpoint of resource protection from hard copy displays, which use a lot of paper, to display resources that require a large-scale electric circuit in the display unit, from the viewpoint of cost reduction and portability of recording media, various fields Is expected in.

Conventionally, such a rewritable recording medium is disclosed in, for example, JP-A-55-154198 and JP-A-57-157.
Organic small molecules that can be recorded and erased by a thermal printer head (TPH) as described in US Pat.
A polymer resin matrix system may be used. This system has a relatively good balance of characteristics as a rewritable recording medium, and is partly used as a prepaid card. However, in this organic low molecular weight / high polymer resin matrix system,
Because the cloudy state and the transparent state change reversibly,
The visibility is insufficient, and it is not possible to display a color picture or pattern by itself.

[0004] For this reason, for example, Japanese Patent Application Laid-Open No. Hei 4-50290 has conventionally disclosed a leuco dye and a developing function as a recording medium capable of chemically repeating coloring and decoloring by supplying heat energy. A composition comprising a developer having an acidic group and a basic group having a decoloring function has been proposed. Further, JP-A-4-247895, JP-A-4-308790 and JP-A-4-344287 disclose, in a composition system in which a leuco dye and a long-chain phosphonic acid as a color developer are mixed, the crystal structure by thermal energy is used. It has been reported that the change causes reversible coloring and decoloring.
These media are colorless in an equilibrium state, and are suitable for positive recording in printing using a thermal printer head. For this reason, these media are not suitable for displaying multicolor pictures and patterns.

On the other hand, the present inventors have disclosed in Japanese Patent Application No. 7-37001, a prior application, a recording medium suitable for displaying a multicolored picture or pattern by using a coloring compound and a developer. A recording medium in which a reversible agent was newly added to the contained composition system was obtained. This recording medium is suitable for negative recording in printing using a thermal printer head, and can display multicolor pictures and patterns in a balanced color development state.

However, since this recording medium having a reversible agent uses a general color developer such as bisphenol having no long-chain alkyl group as a color developer, it is difficult to use a recording medium such as polyethylene phthalate (PET) or polycarbonate (PC). When a polymer film is used as a base sheet or a protective film of a recording medium, the color developer easily diffuses into the polymer film, and the color density gradually decreases when the color is repeatedly developed and erased. For this reason, it was necessary to provide an intermediate layer to prevent diffusion, but it was not possible to completely prevent diffusion. Further, when an intermediate layer is provided, more energy is required for coloring and decoloring. If a polyimide film (PI) having high heat resistance is used, diffusion can be prevented. However, since the color density is reduced due to surface adsorption of the developer and the polymer film itself is colored, color display is not possible. Decreased.

[0007]

As described above, conventionally, as a rewritable recording medium, a recording medium capable of chemically repeating coloring and decoloring by supplying energy has been developed. The visibility, color display, and color density were not all satisfied.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has good visibility, color display, and color density even without an intermediate layer, and is capable of repetitive coloring and erasing many times. It is an object of the present invention to provide a thermosensitive sheet.

[0009]

According to the present invention, there is provided a base layer having a polyethylene naphthalate film, a color forming compound formed on the base layer, and an interaction between the color forming compound and the color forming compound. A rewritable type including a color developer for causing a color compound to change from a decolored state to a color-developed state, and a reversible agent for allowing the color-developed state and the decolored state to be repeated by the interaction between the color-developing compound and the color developer. A rewritable heat-sensitive sheet comprising a heat-sensitive recording layer.

The rewritable thermosensitive recording layer is preferably formed directly on a polyethylene naphthalate film.
The developer preferably has no alkyl side chain or has a linear alkyl side chain structure having 5 or less carbon atoms.

[0011] The polyethylene naphthalate film is 5
% Or less and preferably 80% or less.
The developer preferably has a molecular weight of 300 or less. Preferably, the reversible agent is a steroid compound.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The rewritable heat-sensitive sheet of the present invention comprises:
A color-forming compound, a color developer that causes the color-forming compound to change from a decolored state to a color-formed state by an interaction with the color-forming compound, and a color-developed state and a decolored state by an interaction between the color-forming compound and the color developer. And a base layer having a polyethylene naphthalate film for supporting the heat-sensitive recording layer.

First, the basic principle of the rewritable thermosensitive recording layer used in the present invention as a recording medium will be described.
Generally, in a composition system containing a color former and a color developer, the coloring state changes according to the interaction between the color former and the color developer. For example, it is known that when the interaction between the color former and the color developer increases, the color develops, and when the interaction between the color former and the color developer decreases, the color disappears. The basic principle of a rewritable thermosensitive recording medium is to control the interaction between the color-forming compound and the developer by utilizing a structural change of the medium such as a crystal-amorphous transition or a crystal-crystal transition. It is.

In the heat-sensitive recording layer used in the present invention, a reversible agent is added to a composition system containing a color former and a developer. As a result, the coloring state and the decoloring state can be reversibly repeated, and both the coloring state and the decoloring state can exist at a temperature near room temperature. This medium is particularly suitable for negative display such as printing using a thermal printer head and erasing using a hot stamp.

The term "reversing agent" as used herein means that it has a property of acting on either a color developer or a color-forming compound in a fluidized state, and at least two kinds of long-lived states upon solidification, that is, a reversing agent. The equilibrium state in which the color former compound and the developer surplus from the stationary solubility have a phase in which the color former is separated from the reversible agent to form a color, and at room temperature, the reversible agent is the other color former compound or It means a low molecular weight organic compound having the property of being able to assume a quasi-equilibrium or non-equilibrium but long-lived state in which a developer is taken out of a value of the solubility at a steady state equilibrium. As the reversible agent exhibiting an equilibrium-non-equilibrium change that can be controlled by temperature, a material having both crystalline and amorphous properties, alone or in combination with a color developer or a coloring compound, is more preferable. Alternatively, a material exhibiting a crystalline-crystalline transition or a material exhibiting an amorphous-amorphous transition can be used alone or in combination with a color developer or a coloring compound depending on the heat history.

As the reversing agent, a steroid compound is preferably used. FIG. 1 shows a simple model of a typical color development / decoloration mechanism of a three-component system composed of a color former, a color developer, and a reversible agent.

In the figure, A indicates a color-forming compound, B indicates a developer, C indicates a reversible agent, and * indicates a fluid state. At room temperature (Trt), the color-developed state in which the phase of the color former A and the developer B and the phase of the reversible agent C are phase-separated is close to an equilibrium state in terms of solubility.

When this state is heated to a temperature equal to or higher than the melting point (Tm), the developer B loses the interaction with the color-forming compound A, while interacting with the reversible agent C in a fluid state. Above the melting point, the system loses color.

Next, when the system is forcibly fixed by rapidly cooling the molten state, the reversible agent C interacting with the developer B takes in the amount of the developer B exceeding the equilibrium solubility. Amorphizes and the system becomes colorless at room temperature. This non-equilibrium amorphous state has a very long life at a temperature below the glass transition point (Tg), and does not easily transition to an equilibrium state at room temperature below Tg.

Thereafter, when the non-equilibrium amorphous is heated to exceed the glass transition point, the diffusion speed of the developer B in the system is sharply increased, so that the developer B returns to the original equilibrium state. And the phase separation movement of the reversible agent C is accelerated. At a temperature (Tc ') at which color development by phase separation can be sufficiently achieved within a predetermined time, the color developer B and the phase-separated reversible agent C crystallize rapidly, so the lower limit of the color development temperature is the crystallization temperature. (T
c) may be considered. A composition system that has spent a predetermined time above the crystallization temperature (below the melting point) becomes a phase separation state closer to the equilibrium state (more equilibrium), and the system becomes a colored state.

Therefore, by appropriately supplying binary heat energy having different magnitudes, which can heat the reversible agent to a temperature higher than the crystallization temperature Tc and lower than the melting point Tm, and to a temperature higher than the melting point Tm, Since the equilibrium-non-equilibrium phase change can be reversibly repeated, the color-developed / decolored state can be repeated accordingly. Since the state of color development depends on the equilibrium solubility and state of the color developer, it is preferable to consider that the color density of the system is affected by the heating temperature and the heating time.

In the present invention, a PEN film is used in the substrate of the rewritable thermosensitive recording layer as described above. P
EN is a polymer having a structure in which a benzene ring of polyethylene terephthalate (PET) is changed to a 2,6-naphthalene ring. There is almost no general-purpose polymer having a hydrocarbon condensed polycyclic ring such as a naphthalene ring except for PEN. PEN has a high glass transition temperature of 110 ° C. or higher and has high heat resistance and is colorless. The heat resistance is affected by the associative force between naphthalene rings, which is different from other heat-resistant polymers such as polyimide, which are mainly associated by polar groups. From these properties, polyimide, polyethylene phthalate (PET) and polycarbonate (PC)
Unlike the conventional base sheet made of the above, the interaction with the coloring compound or the developer is small. Therefore, by using PEN, even if a coloring compound having a polar group or a color developing agent is used, a decrease in color density can be suppressed.

Further, the effect of PEN is particularly remarkable when, for example, a developer made of a low molecular compound having a polar group is used in order to further increase the writing speed. When a heat-sensitive recording layer containing a color developer composed of a low molecular compound having a polar group is used together with a base sheet containing a polymer having a strong polarity, the color developer is combined with the polymer, and the color density is reduced.
In contrast, when PEN is used, the polar group carbonyl group is shielded by a bulky naphthalene ring, and the interaction between the naphthalene rings causes little interaction between the developer and the carbonyl group of PEN.

In place of PEN, a heat-resistant saturated hydrocarbon polymer (eg, norbornene resin) or silicone resin can also suppress the interaction with the color developer. However, since saturated hydrocarbon polymers and silicone resins have low surface energy, they do not adhere well to the heat-sensitive layer and are easily peeled off.

In the rewritable multicolor heat-sensitive sheet of the present invention, it is preferable to use a developer having no alkyl side chain or having a linear alkyl structure having 5 or less carbon atoms.
A developer having no alkyl side chain or having a straight-chain alkyl structure having 5 or less carbon atoms has a high diffusion speed, and can write and erase recording at high speed. This has 5 carbon atoms
This is because the linear alkyl structure of can have a cyclic structure, and has low viscosity and low diffusion due to small interaction between molecules. On the other hand, if the number of carbon atoms is 6 or more, the chain structure becomes stable and the associative force between molecules increases, so that diffusion becomes difficult.
The difference in associative power is, for example, that the melting enthalpy of n-pentane is 2.0 kcal / mol, and that of n-hexane is 3.1 kcal / mol.
mol and cyclohexane are 2.3 kcal / mol (including phase transition), which can be explained by the large value of n-hexane. Further, the linear alkyl structure lowers the melting point of the color developer, so that the thermal stability of the recording medium also decreases. However, on the other hand, a developer having no alkyl side chain or having a linear alkyl structure having 5 or less carbon atoms easily diffuses into the base material and the polymer film as a protective film, and repeatedly develops and discolors. The operation has a disadvantage that the color density gradually decreases. However, PEN used in the base material has a carbonyl group which is a polar group shielded by a bulky naphthalene ring, and the interaction between the color developer and the carbonyl group of PEN is small due to association between naphthalene rings. . Therefore, by using PEN, even if a developer having no alkyl side chain or having a linear alkyl structure having 5 or less carbon atoms is used, a decrease in color density can be sufficiently suppressed.

In the present invention, it is possible to provide a thin intermediate layer between the PEN and the heat-sensitive recording medium layer for further enhancing the adhesiveness.
The EN film is in direct contact.

The crystallinity of the PEN film used is preferably 5% or more and 80% or less. The crystallinity of the PEN film can be variously changed by the production conditions and post-treatment, and its properties vary in various ways depending on the crystallinity. The crystallinity of the PEN film is preferably from 5% to 80%. If it is less than 5%, the transparency increases, but the heat resistance tends to decrease, and the function of suppressing the diffusion of the color developer tends to decrease. On the other hand, if it exceeds 80%, the transparency is deteriorated, the flexibility of the film is reduced, and the film tends to be weak against bending or the like. Crystallinity can be determined by DSC measurement, as is generally known.

In the present invention, the molecular weight of the color developer is preferably 300 or less. When the molecular weight of the color developer is larger than 300, diffusion becomes slow, so that high-speed writing and erasing tend to be difficult.

Further, since the color development speed and the storage stability are contradictory properties, if it is difficult to simultaneously improve both properties only with the three components of the color former, the color developer and the reversible agent, the problem arises. In order to improve the viscosity, a four-component system to which a phase separation controlling agent is added can be used.

The phase separation controlling agent has a melting point lower than the melting point of a composition comprising a color former, a color developer and a reversible agent. The effect of the interaction of the compound on the color development state is small. Above the melting point, the color developer or the coloring compound is dissolved, and the diffusion rate of the color developer or the coloring compound in the medium is significantly increased around the melting point. It has the property that the interaction between the molten phase separation controlling agent and the color developer or the color developing compound is smaller than the interaction between the dissolved or molten reversible agent and the color developing agent or the color forming compound. It is a thermoplastic low molecular organic material. These materials have a function of rapidly increasing the phase separation speed of the composite system in the vicinity of its melting point when added to other materials, and are therefore called phase separation control agents.

FIG. 2 shows a simplified model of a typical coloring / decoloring mechanism of a four-component system to which a phase separation controlling agent is added. Here, the reference numerals used are the same as those used in FIG. 1 except that D represents a phase separation controlling agent.

At room temperature (Trt), the medium can take two states, a decolored state and a colored state. In these two states, due to their compatibility, the color-developed state in which the phase of the color former A, the phase of the developer B, the phase of the reversible agent C, and the phase of the phase separation controller D are close to an equilibrium state. When this state is heated above the melting point (Tml) of the composition system, the developer B loses the interaction with the color-forming compound A, while it becomes in a state interacting with the reversible agent C in a fluid state. Above the melting point, the system loses color.

Next, when the four-component system is cooled from the molten state, unlike the three-component system, the compatibilizer of the reversing agent C and the phase separation controlling agent B becomes a supercooled liquid that maintains fluidity even at a temperature lower than the melting point. B and the reversible agent C in the fluidized state coagulate at a low temperature below the glass transition point Tg while interacting, and the reversible agent C takes in the amount of the developer B exceeding the equilibrium solubility to become amorphous and becomes colorless. It becomes non-equilibrium. Therefore, in the four-component system, a colorless non-equilibrium state can be obtained by rapid cooling or slow cooling. 4
In the non-equilibrium amorphous state of the component system, the glass transition point (Tg)
At the following temperatures, the life is extremely long, and if the room temperature is equal to or lower than Tg, it does not easily shift to the equilibrium state.

Thereafter, when the quaternary non-equilibrium amorphous is heated to exceed the glass transition point, the diffusion rate of the developer B in the system rapidly increases as in the ternary system. The phase separation movement of the developer B and the reversible agent C is accelerated in a direction to return to the equilibrium state. Further, the melting point of the phase separation controlling agent D (Tm
After 2), the liquefied phase separation controlling agent D dissolves a part of the developer B and a part of the reversible agent C, and the phase separation between the developer B and the reversible agent C Alternatively, it is greatly promoted by a dramatic increase in the diffusion rate of the color former, and the association between the color developer B and the color former A is completed in a short time. However, at this time, the developer B does not act on the color-forming compound A, and the system is in a decolored state or a semi-decolored state.

When the temperature of the system is lowered again below the melting point of the phase separation controlling agent D from this state, the color-separated developer B and the color-forming compound A interact with each other, and the system is closer to an equilibrium state. An equilibrium color development state results.

The coloring speed of the composition system containing the phase separation controlling agent changes by 2 to 4 digits before and after the glass transition point, and further by 3 to 4 digits before and after the melting point. Therefore, the melting point of the system (T
ml) and the binary thermal energy of different magnitudes, which can be heated up to the melting point (Tm2) of the phase separation controlling agent, reversibly change the equilibrium-non-equilibrium phase change at an extremely high speed. Coloring and decoloring can be repeated regardless of the heat history of rapid cooling and slow cooling.

The color-forming compounds used in the present invention include leuco auramines, diaryl phthalides, polyaryl carbinols, acyl auramines, aryl auramines, rhodamine B lactams, indolines and spiropyrans. Donating organic substances such as organic compounds and fluorans. Specifically, crystal violet lactone (CVL), malachite green lactone, 2-
Anilino-6- (N-cyclohexyl-N-methylamino) -3-methylfluoran, 2-anilino-3-methyl-6- (N-methyl-N
-Propylamino) fluoran, 3- [4- (4-phenylaminophenyl) aminophenyl] amino-6-methyl-7-chlorofluoran, 2-anilino-6- (N-methyl-N-isobutylamino)- 3-methylfluoran, 2-anilino-6- (dibutylamino) -3-methylfluoran, 3-chloro-6- (cyclohexylamino) fluoran, 2-chloro-6- (diethylamino) fluoran, 7- (N , N-Dibenzylamino) -3
-(N, N-diethylamino) fluoran, 3,6-Bis (diethylamino) fluoran-γ- (4′-nitro) anilinolactam, 3-diethylaminobenzo [a] -fluoran, 3-diethylamino-6-methyl- 7-aminofluoran, 3-diethylamino-7-xyridinofluoran, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4- Azaphthalide, 3- (4-diethylaminophenyl) -3- (1-ethyl-2-methylindole
-3-yl) phthalide, 3-diethylamino-7-chloroanilinofluoran, 3-diethylamino-7,8-benzofluoran, 3,3-Bis (1-n-butyl-2-methylindole-3-
Il) phthalide, 3,6-dimethylethoxyfluoran,
3-diethylamino-6-methoxy-7-aminofluoran,
DEPM, ATP, ETAC, 2- (2-chloroanilino)
-6-dibutylaminofluoran, crystal violet carbinol, malachite green carbinol, N-
(2,3-dichlorophenyl) leuco auramine, N-benzoyl auramine, rhodamine B lactam, N-acetyl auramine, N-phenyl auramine, 2- (phenyliminoethanedylidene) -3,3-dimethylindoline, N-3,3-trimethylindolinobenzospiropyran, 8'-methoxy-N
-3,3-trimethylindolinobenzospiropyran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-methoxyfluoran, 3-diethylamino
-6-benzyloxyfluoran, 1,2-benz-6-diethylaminofluoran, 3.6-di-p-toluidino-4,5-dimethylfluoran-phenylhydrazide-γ-lactam, 3-amino-5-methylfluoran Etc. are exemplified. These can be used alone or in combination of two or more.

Since the color development of various colors can be obtained by appropriately selecting the color-forming compound, the rewritable heat-sensitive sheet of the present invention is easily applicable to colors, and can use a coloring dye in addition to the color-forming compound. When used in combination, a desired colored state can be obtained in both cases of crystalline and amorphous.

Examples of the color developing agent include phenols, phenol metal salts, carboxylic acid metal salts, benzophenones, sulfonic acids, sulfonates, phosphoric acids, metal phosphates, acid phosphates, Examples thereof include acid phosphate metal salts, phosphorous acid salts, and metal phosphite salts, and these may be used alone or in combination of two or more.

In the case where the reversible agent has both crystallinity and amorphousness, either the developer or the color developing compound interacts with the reversible agent or the developer or the color developing compound When the compound and the reversible agent are mutually dissolved, an amorphous state of the decolorized state is exhibited. For example, due to heating or a change in stress, the color developer or the color-forming compound is phase-separated from the reversible agent to form particles of the reversible agent. The color-forming compound and the developer are eluted or segregated in the field to exhibit a colored state.

When the reversible agent is crystalline, one of the color developer and the color former forms a mixed crystal with the reversible agent and almost completely forms the other with the other of the color former and the color developer. Phase-separated, the interaction between the color developing compound and the developer decreases to exhibit a decolored state, for example, by heating or a change in stress, the developer or the color developing compound undergoes phase separation from the reversible agent, The color-forming compound and the color developing agent are eluted or segregated at the grain boundary of the reversible agent to exhibit a color-developed state.

The reversible agent suitable for the present invention is a compound containing an alcohol group having a molecular skeleton such as a steroid skeleton having a bulky molecular skeleton, and conversely, a low molecular compound having a molecular weight of less than 100. Even when the molecular weight is 100 or more, linear long-chain alkyl derivatives and planar aromatic compounds are not suitable. Specific materials suitable for such reversible agents include steroidal alcohols, more specifically, cholesterol, stegmasterol, pregnenolone,
Methylandrostenediol, estradiol benzoate, epiandrostene, stenolone, β-sitosterol, pregnenolone acetate, β-cholesterol, 5,16-pregnadien-3β-ol-20-one, 5α-pregnene-3β-ol -20-one, 5-pregnene-3β, 17-diol-20-one 21-acetate, 5-pregnene-3β, 17-diol-20-one 17-acetate, 5-pregnene-3β, 21-diol-20 -One 21-acetate, 5-
Pregnene-3β, 17-diol diacetate, locogenin, tigogenin, esmilagenin, hecogenin, diosgenin and derivatives thereof, and mixtures thereof.

In the recording medium used in the present invention, the glass transition temperature Tg of the composition system is low, and when the temperature is close to room temperature, a slight rise in the ambient temperature causes a phase separation due to the diffusion of the coloring compound and the color developing agent and the system. Tends to proceed, and the thermal stability of recording tends to decrease. Therefore, the glass transition temperature Tg when the whole or a part of the composition system forms an amorphous phase in the present invention is preferably 25 ° C. or more, more preferably 50 ° C. or more. Considering this point, the color-forming compound also has a large molecular weight and a small melting enthalpy H per weight, for example, a compound having a bulky molecular skeleton close to a sphere or a compound capable of forming a hydrogen bond between molecules. It is preferable to use a compound having the following site.

Contrary to the above, if a composition system having a glass transition temperature Tg close to room temperature is used, for example, a rewritable heat-sensitive sheet that is naturally erased after the recorded information is retained for a desired period of time can be used. It can also be realized. further,
For special applications, a composition system having a glass transition temperature Tg lower than room temperature may be used. As such a special use, when the temperature of a refrigerator that stores a substance that needs to be refrigerated is increased due to failure or transportation, it is possible to indicate the change in the coloring state due to crystallization of the composition system. Conceivable.

On the other hand, in the present invention, when the glass transition temperature Tg of the composition system is too high, the composition system is heated to a temperature higher than the crystallization temperature Tc but lower than the melting point Tm or higher than the melting point Tm in recording / erasing information. When heating, large heat energy is required, which is disadvantageous in terms of energy saving. Therefore, the glass transition temperature Tg of the composition system in the present invention is 150
It is preferable that the temperature is not higher than ° C.

Here, it is known that the glass transition temperature Tg of the mixture generally indicates a weight average value of the glass transition temperature Tg of each compounded component. Therefore, in order to set the glass transition temperature Tg of the composition system of the present invention to a desired value, it is effective to control the glass transition temperature Tg of each component in the composition system. In the rewritable heat-sensitive sheet of the present invention, the color change compound, the developer and the reversible agent incorporated in the composition system each have a glass transition temperature Tg of 25.
It is preferable to use a compound having a temperature of at least 50 ° C, more preferably at least 50 ° C. In consideration of the thermal stability of recording, it is particularly desirable that the reversible agent has a melting point of 100 ° C. or higher.

The composition system in the rewritable thermosensitive sheet of the present invention and the glass transition temperature Tg of each component contained in the composition system
Can be measured, for example, using a differential scanning calorimeter (DSC) for the whole or a part of the composition system and each component in the composition system.

On the other hand, a component which easily forms an amorphous material having a clear glass transition temperature Tg generally has a glass transition temperature Tg.
And melting point Tm, Tg = a.Tm (a is 0.65-0.8;
g and Tm are absolute temperatures). Therefore, if the glass transition temperature Tg of the composition system and each component in the composition system is set high,
As a result, the melting point Tm of the composition system also increases. In this case, while the thermal stability of the recording can be improved, it is necessary to heat to a very high temperature when melting the composition system. Along with this, for example, a substrate excellent in heat resistance and the like is required, and the practicality is reduced. In order to avoid this problem, it is effective to use a composition system that forms a plurality of crystal forms. In order to prepare a composition system that specifically forms a plurality of crystal forms, for example, a component capable of forming a plurality of crystal forms may be used for a developer and a reversible agent in the composition system.

In the present invention, in a composition system containing a color former and a developer but not containing a reversible agent, the compounding ratio of the color former to the developer is 1 part by weight of the color former. On the other hand, the amount of the developer is preferably set to 0.1 to 100 parts by weight, more preferably 1 to 10 parts by weight. If the developer is less than 0.1 parts by weight,
During recording or erasing, it is difficult to sufficiently increase the interaction between the color former and the developer. Conversely, if the developer is used in an amount of 100 parts by weight, the color density in the color-developing state tends to decrease.

In the composition system containing the color developing compound, the color developing agent and the reversible agent, the mixing ratio of the color developing compound to the color developing agent is 0.1 to 0.1 part by weight of the color developing compound. It is preferably set to 10 parts by weight, more preferably 1 to 2 parts by weight. If the developer is less than 0.1 part by weight, it is difficult to sufficiently increase the interaction between the color former and the developer during recording or erasing. Conversely, if the amount of the developer exceeds 10 parts by weight, it becomes difficult to sufficiently reduce the interaction between the color former and the developer during recording or erasing. The mixing ratio of the reversible agent is preferably set to 1 to 200 parts by weight, more preferably 10 to 100 parts by weight, per 1 part by weight of the color former. When the amount of the reversible agent is less than 1 part by weight, it is difficult to cause a crystalline-amorphous transition or a change in a phase separation state of the composition system.
If the reversible agent exceeds 200 parts by weight, the color density in the color-developing state tends to decrease.

As a phase separation controlling material corresponding to a reversible steroidal alcohol having both crystalline and amorphous properties, _n- part of a long straight chain (CH ₂ ) having 8 or more carbon atoms and a polar group such as OH A low molecular weight organic material having strong crystallinity, such as CO, CO, and COOH, is preferred. Specifically, 1-docosanol, 1-tetracosanol, 1-hexacosanol,
Linear higher monohydric alcohol represented by 1-octacosanol or the like, or 1,12-dodecanediol,
Linear higher polyhydric alcohols represented by 12-octadecanediol, 1,2-tetradecanediol, 1,2-hexadecanediol, etc., or behenic acid, 1-docosanoic acid, 1-tetracosanoic acid, 1-hexacosanoic acid,
Linear higher fatty acids such as 1-octacosanoic acid,
Alternatively, linear higher polyvalent fatty acids represented by dodecane diacid, 1,12-dodecane dicarboxylic acid, linear higher ketones represented by stearone, or isopropanolamide stearate, isopropanolamide behenate, hexanolamide behenate A straight-chain higher fatty acid alcohol amide represented by ethylene glycol laurate diester, catechol laurate diester, cyclohexanediol laurate diester, etc., or a mixture of a plurality of materials. This was confirmed by experiments. Further, as an example of the mixture, there is a material that can be used as a phase separation controlling agent in ester-based wax, alcohol-based wax, and urethane-based wax.

When the recording layer used in the present invention is mixed with a phase separation controlling agent, the mixing ratio is from 0.1 to 100 parts by weight, more preferably from 1 to 50 parts by weight, per 1 part by weight of the coloring compound. Is preferred. When the amount of the phase separation controlling agent is less than 0.1 part by weight, the effect of increasing the phase separation speed of the composition system is hardly obtained. When the amount of the phase separation controlling agent exceeds 100 parts by weight, the non-equilibrium state of the composition system becomes unstable, and the thermal stability of recording may decrease.

In the recording layer used in the present invention, components other than the color former, the color developer, the reversing agent and the phase separation controlling agent include coloring dyes, fluorescent dyes, ultraviolet absorbers, heat insulators, heat storage agents and the like. May be appropriately compounded. At this time, by appropriately selecting a coloring dye or the like in accordance with the color-forming compound contained in the composition system, it is possible to obtain any desired coloring state in any of the coloring state and the decoloring state. Become.

In the rewritable thermosensitive recording sheet of the present invention, at least a part of the rewritable thermosensitive recording layer covers a cluster of the rewritable thermosensitive recording medium having a size not exceeding the pixel size or the film thickness, and covers the surface of the cluster. And a matrix material for forming a cluster into a film. It is also possible that the matrix material comprises a coating material for coating the cluster and a structural material for forming the coating cluster into a film. One of the methods for realizing these is a microencapsulation technique.

As a method for producing the rewritable thermosensitive sheet of the present invention from a rewritable thermosensitive recording medium, a thin film sheet can be obtained by stretching the melt of the recording medium thinly. On the other hand, the composition can be dissolved in an appropriate solvent and cast to form a thin film. The thickness of the thin film thus formed is preferably 0.5 μm or more and 50 μm or less. If the thickness of the thin film is too small, the resulting thermosensitive recording medium may have an insufficient color density in a colored state. Conversely, if the thickness of the thin film is too large, large heat energy is required at the time of recording / erasing, making it difficult to perform high-speed recording / erasing.

In the rewritable heat-sensitive sheet of the present invention,
From the viewpoint of improving the strength of the heat-sensitive recording medium, the above-described composition as a recording material may be inserted into an appropriate medium. Specific examples include dispersion in a binder polymer, dispersion in an inorganic glass, impregnation into a porous substrate, intercalation into a layered substance, microencapsulation, and the like.

When the composition is dispersed in the binder polymer, a melt, a solution or fine particles of the composition are prepared, and if necessary, other components are added, and the composition is dispersed together with the binder polymer by various dispersion methods. . The resulting product may be coated on a suitable substrate. Examples of the binder polymer include polyethylenes; chlorinated polyethylenes; ethylene / vinyl acetate copolymers, ethylene / acrylic acid / maleic anhydride copolymers and other ethylene copolymers; polybutadienes; polyethylene terephthalate;
Polyesters such as polybutylene terephthalate and polyethylene naphthalate; polypropylenes; polyisobutylenes; polyvinyl chlorides; polyvinylidene chlorides;
Polyvinyl acetates; polyvinyl alcohols; polyvinyl acetals; polyvinyl butyrals; ethylene tetrafluoride resins; ethylene trifluoride chloride resins: ethylene fluoride propylene resins; vinylidene fluoride resins;
Vinyl fluoride resins: tetrafluoroethylene / perfluoroalkoxyethylene copolymer, tetrafluoroethylene / perfluoroalkylvinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / Tetrafluoroethylene copolymers such as ethylene copolymers;
Fluorinated materials such as polyfluorinated polybenzoxazole; acrylic resins; methacrylic resins such as polymethyl methacrylate; polyacrylonitriles;
Acrylonitonol copolymers such as butadiene / sterene copolymers: polystyrenes; halogenated polystyrenes;
Styrene copolymers such as styrene / methacrylic acid copolymer and styrene / acrylonitrile copolymer; sodium polystyrene sulfonate; ionic polymers such as sodium polyacrylate; acetal resins; polyamides such as nylon 66; gelatin; Gum arabic; Polycarbonates; Polyester carbonates; Cellulosic resins; Phenolic resins; Urea resins; Epoxy resins; Unsaturated polyester resins; Alkyd resins; Melamine resins; Polyurethanes; Diaryl phthalate resins; Oxides; polyphenylene sulfides; polysulfones; polyphenylsulfones; silicone resins; polyimides; bismaleimide triazine resins; polyimide amides; Polymethyl pentene acids; polyetheretherketones; polyetherimides; may be a thermoplastic resin of a norbornene-based amorphous polyolefins, etc., polyvinyl carbazoles.

Examples of the dispersion method include a mixer method, a sand mill method, a ball mill method, an inverer mill method, a colloid mill method, a three-roll mill method, a kneader method, a two-roll method, a bumper mixer method, a homogenizer method, and a nanomizer method. Can be mentioned. These dispersion methods are:
It may be appropriately selected according to the viscosity of the melt or the solution, the use and form of the heat-sensitive recording medium, and the like. Furthermore, regarding the coating method on the substrate, etc., spin coating method, pull-up coating method, air doctor coating method, blade coating method, rod coating method, knife coating method, squeeze coating method, impregnation coating method, reverse roll coating method It is possible to use a transfer coating method, a gravure coating method, a kiss roll coating method, a cast coating method, a spray coating method, a curtain coating method, a calendar coating method, an extrusion coating method, an electrostatic coating method, and the like. These coating methods can be appropriately selected according to the use, form, and the like of the thermosensitive recording medium.

In the rewritable heat-sensitive sheet of the present invention, when the composition to be a recording material is dispersed in a binder polymer, the compounding ratio of the binder polymer is set to 1
The amount is preferably set to 0.01 to 100 parts by weight, more preferably 0.05 to 20 parts by weight, per part by weight. This is because when the amount of the binder polymer is less than 0.01 part by weight, the strength of the thermosensitive recording medium is little improved, and when the amount is more than 100 parts by weight, the color density in a color-developing state tends to decrease.

In the rewritable heat-sensitive sheet of the present invention, when the composition as a recording material is supported on an inorganic glass sheet, it is preferable to use an inorganic glass that can be produced by a so-called sol-gel method. At that time, it is desired that the gelling temperature is not so high. Examples of the porous substrate include various inorganic compounds, and examples of the layered material include mica, clay mineral, talc, chlorite, and the like.

In order to produce microcapsules enclosing the composition inside the film, an interfacial polymerization method, an in-situ polymerization method, a hardening-in-liquid coating method, a phase separation method from an aqueous solution system, and a phase from an organic solution system are used. A separation method, a melting dispersion cooling method, an air suspension method, a spray drying method and the like can be used. These methods can be appropriately selected according to the use and form of the thermosensitive recording medium. As the microcapsule coating,
Thermosetting properties such as condensation polymers such as melamine resin, epoxy resin, urea resin, phenol resin, and furan resin; three-dimensional crosslinked vinyl polymers such as styrene-divinylbenzene copolymer and methyl methacrylate-vinyl acrylate copolymer A resin or a thermoplastic resin disclosed as a binder polymer for dispersing the composition can be appropriately used.

Further, a multilayer coating constituting the microcapsule may be formed by using two or more kinds selected from the above-mentioned thermosetting resins and thermoplastic resins. In this case, it is preferable to use a thermosetting resin for the outermost shell of the coating from the viewpoint of improving the thermal stability of the microcapsules. The microcapsules thus obtained may be dispersed in a binder polymer or inorganic glass. in this case,
Even when the composition itself has insufficient dispersibility in a medium, a good dispersion state can be obtained by forming and dispersing microcapsules.

In the rewritable heat-sensitive sheet of the present invention, the durability of the recording layer composed of a thin film of the composition is improved, and sticking to a thermal printer head (TPH) for supplying thermal energy to the recording layer is prevented. From the viewpoint, a protective layer may be provided on the recording layer. Examples of the material for the protective layer include wax, thermoplastic resin, thermosetting resin, photocurable resin, water-soluble resin, latex, and the like. The thickness of the protective layer is preferably about 0.1 to 100 μm.

Further, a heat releasing agent, a lubricant, a heat resistant material, an antistatic material and the like may be appropriately blended in such a protective layer. Specifically, a protective layer can be formed by applying a solution obtained by dissolving or dispersing the above-described components in a solvent onto a recording layer and then drying the solution.

A protective layer may be formed by bonding a heat-resistant film, to which an adhesive has been applied in advance, to the recording layer by a dry lamination method. On the other hand, the adhesion between the substrate and the recording layer is improved,
An undercoat layer may be provided between the substrate and the recording layer in order to improve the solvent resistance and the like.

The heat-resistant film is not particularly limited as long as it has a heat distortion temperature equal to or higher than the melting point of the composition to be a recording material. For example, polyether ether ketones; polycarbonates; polyarylates; polysulfones; ethylene tetrafluoride resins; tetrafluoroethylene / perfluoroalkoxyethylene copolymers, tetrafluoroethylene / perfluoroalkylvinyl ether copolymers , Ethylene tetrafluoride / propylene hexafluoride copolymer,
Polytetrafluoroethylene copolymers such as ethylene tetrafluoride / ethylene copolymer; ethylene trifluoride chloride resins; vinylidene fluoride resins; silicone resins; fluorinated polybenzoxazoles; polypropylenes; Polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polysterenes;
Polyamides such as nylon 66; polyimides; polyimide amides; polyether sulfones; polymethylbenthenes; polyetherimides;
A sheet of a high molecular compound such as polybutadiene can be used. These can be appropriately selected and used depending on the use, form, and the like of the heat source and the heat-sensitive recording medium.

Examples of the adhesive include acrylic resins generally used in the dry lamination method; phenoxy resins; ionomer resins; ethylene-vinyl acetate copolymer, ethylene-acrylic acid-maleic anhydride copolymer, and the like. Polyethylene ethers; polyvinyl ethers; polyvinyl formals; polyvinyl butyrals; gelatin; gum arabic; polyesters;
Styrene copolymer such as styrene / acrylic acid copolymer;
Vinyl acetate resins; polyurethanes; xylene resins;
Epoxy resins; phenolic resins; urea resins, and the like.

In the rewritable heat-sensitive sheet of the present invention, in order to perform recording / erasing based on the change of the crystal quality-amorphous transition or the phase separation state, as described above, the binary thermal energy having different magnitudes from each other is used. It is possible to supply two types of heat histories having different cooling rates after supplying or heating to a temperature equal to or higher than the melting point Tm.

In order to supply thermal energy during recording, it is preferable to use a heat source such as a thermal head (for example, TPH) or a laser beam. Among them, the thermal head is not so large in resolution but can heat the thermal recording medium over a large area and is advantageous in miniaturizing the apparatus.

On the other hand, a laser beam is preferable in that the spot diameter can be reduced to facilitate high-density recording and that the recording / erasing speed can be increased. However, when laser light is used, a light absorbing layer having an absorption band at the wavelength of the laser light may be provided in order to efficiently absorb the laser light even for an amorphous composition having a good light-transmitting property. Alternatively, it is desirable to compound a compound having an absorption band at the wavelength of laser light into the composition.

In order to supply thermal energy at the time of erasing, it is preferable to use a heat source such as a hot stamper method or a hot roll method which can heat the entire thermosensitive recording medium at one time. When the heated thermosensitive recording medium is cooled, it may be allowed to cool naturally, but it is preferable to use a cold stamper, a cold roll, a cool airflow or a Peltier element for rapid cooling.

Further, in the rewritable heat-sensitive sheet of the present invention, overwrite recording can be realized by using a plurality of thermal heads having different energies or a plurality of laser beams having different spot diameters.

[0073]

The present invention will be described below in detail with reference to examples. Example 1 1.0 parts by weight of crystal violet lactone (CVL) as a blue leuco dye as a color-forming compound, and a phenolic compound represented by the following chemical formula (1) 1.
0 parts by weight, 10 parts by weight of pregrenolone represented by the following chemical formula (2) as a reversible agent, and 3 parts by weight of polymethyl methacrylate as a binder polymer were mixed, and then dispersed in toluene.

[0074]

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[0075]

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This liquid was printed on a PEN film having a thickness of 40 μm by using a screen printer to form a thin film having a thickness of about 10 μm, thereby producing a rewritable thermosensitive sheet. This film was adhered to a card made of paper with an adhesive, and a photo-curable epoxy resin was further applied thereon, followed by photo-curing to form a protective film having a thickness of 0.4 μm. After pressing a hot roll over the entire surface of the card, the recording medium was crystallized by naturally cooling at room temperature.

FIG. 3 shows a cross section of the obtained thermal recording card. As shown in the figure, the obtained thermal recording card has a paper mount 31, an adhesive layer 32 provided on the mount 31, and a PEN film 3 bonded to the mount 31 by the adhesive layer 32.
3. A rewritable thermosensitive recording layer 34 formed on the PEN film 33 and a protective layer 35 provided on the rewritable thermosensitive recording layer 34.

Using a thermal head (6 dots / mm, 380n) manufactured by Toshiba, an applied voltage of 12 V
Heat printing was performed with a pulse width of 0.8 msec. As a result, the printed portion became amorphous, and white characters were printed in the blue area.

Next, when the hot stamper was pressed on the entire surface for 4 seconds and allowed to stand at room temperature, the printed portion returned to crystalline, and the record could be erased. After 200 cycles of recording and erasing in the same manner as described above, the color density only decreased by 10% from the initial density, and the display did not deteriorate much. Further, no change was observed in the printing state even after being left at 30 ° C. for one year.

Comparative Example 1 A thermosensitive recording card was produced in the same manner as in Example 1 except that a PET film was used instead of the PEN film. Using a thermal head (6 dots / mm, 380n) manufactured by Toshiba, an applied voltage of 12 V
Heat printing was performed with a pulse width of 0.8 msec. As a result, the printed portion became amorphous and white characters were printed in the blue area.

Next, when the hot stamper was pressed on the entire surface for 4 seconds and allowed to stand at room temperature, the printed portion returned to a crystalline state, and the recording could be erased. When the same recording / erasing was performed for 200 cycles, the color density was reduced by 50% from the initial density.

Comparative Example 2 A thermal recording card was produced in the same manner as in Example 1 except that a PC film was used instead of the PEN film. Using the obtained thermal recording medium, thermal printing was carried out using a thermal head (6 dots / mm, 380 n) manufactured by Toshiba at an applied voltage of 12 V and a pulse width of 0.8 msec. As a result, the printed portion became amorphous and white characters were printed in the blue area.

Next, when the hot stamper was pressed on the entire surface for 4 seconds and allowed to stand at room temperature, the printed portion returned to crystalline and the recording could be erased. After 200 cycles of recording / erasing in the same manner as described above, the color density decreased by 30% from the initial density.

Example 2 As a color-forming compound, 1.0 part by weight of a red fluorane dye, Indrial Red (manufactured by Yamamoto Kasei), 1.0 part by weight of a phenolic compound represented by the chemical formula (3) as a color developer, 5 parts by weight of methylandrostenediol represented by the chemical formula (4) as a reversible agent, 5 parts by weight of 1-triacontanol as a phase separation controlling agent, and 3 parts by weight of polystyrene as a binder polymer are mixed, and then dispersed in toluene. Was.

[0085]

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[0086]

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This solution was applied to a 0.5 μm-thick gelatin film-coated 40 μm-thick P
On the EN film, printing was performed in the same manner as in Example 1, and a film thickness of about 10
A μm thin film was formed to produce a rewritable thermosensitive sheet.
This film was attached to a card made of paper with an adhesive, and a 3 μm-thick PEN film protected with a silicone-based hard coat agent was further laminated thereon. After pressing a hot roll over the entire surface of the card, the recording medium was crystallized by naturally cooling at room temperature.

Using a thermal head (6 dots / mm, 380n) manufactured by Toshiba, an applied voltage of 12 V
Heat printing was performed with a pulse width of 0.8 msec. As a result, the printed portion became amorphous and white characters were printed in the red area.

Next, when the hot stamper was pressed on the entire surface for 0.4 seconds and allowed to stand at room temperature, the printed portion returned to crystalline and the recording could be erased. After 200 cycles of recording and erasing in the same manner as described above, the color density only decreased by 5% from the initial density, and the display did not deteriorate much. Further, even after being left at 30 ° C. for one year, no change was observed in the printing state.

Comparative Example 3 A thermosensitive recording card was produced in the same manner as in Example 2 except that a PET film was used instead of the PEN film having a thickness of 40 μm. For the obtained thermal recording medium,
Using a Toshiba thermal head (6 dots / mm, 380n), heating printing was performed with an applied voltage of 12V and a pulse width of 0.8msec.
As a result, the printed portion became amorphous and white characters were printed in the blue area.

Next, when the hot stamper was pressed on the entire surface for 0.4 seconds and allowed to stand at room temperature, the printed portion returned to crystalline and the recording could be erased. When the same recording / erasing was performed for 200 cycles, the color density was reduced by 40% from the initial density.

Comparative Example 4 A heat-sensitive recording card was produced in the same manner as in Example 2 except that a polyimide film was laminated instead of the PEN film. The whole card was colored yellow and the color display was reduced.

Example 3 1.0 parts by weight of crystal violet lactone (CVL) which is a blue leuco dye as a color-forming compound, and a phenolic compound represented by the following chemical formula (1) as a color developing agent 1.
After mixing and melting 0 parts by weight, 5 parts by weight of pregrenolone represented by the following chemical formula (2) as a reversible agent, and 5 parts by weight of 1-triacontanol as a phase separation controlling agent, the mixture was quenched. The resulting solid was made into a fine powder having a diameter of about 5 μm using a mortar and a homogenizer, and then dispersed in an aqueous gelatin solution.

[0094]

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[0095]

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Using a screen printer, this liquid was used to print the same picture pattern as in Example 1 on a polyvinyl alcohol-coated PEN film having a thickness of 40 μm to form a thin film having a thickness of about 10 μm. A multicolor heat-sensitive sheet was produced. This film was adhered to a card made of paper with an adhesive, and a photo-curable epoxy resin was further applied thereon, followed by photo-curing to form a 0.4 μm-thick protective film. After pressing a hot roll over the entire surface of the card, the recording medium was crystallized by naturally cooling at room temperature.

An applied voltage of 15 V was applied to the obtained thermal recording medium using a thermal head (6 dots / mm, 380 n) manufactured by Toshiba.
Heating printing was performed with a pulse width of 1 msec. as a result,
The printed portion became amorphous and white characters were printed in the blue area.

Next, when the hot stamper was pressed on the entire surface for 0.5 second and allowed to stand at room temperature, the printed portion returned to crystalline and the recorded data could be erased. After 200 cycles of recording and erasing in the same manner as described above, the color density decreased only by 6% from the initial density, and the display did not deteriorate much. Further, no change was observed in the printing state even after being left at 30 ° C. for one year.

Comparative Example 5 The procedure of Example 3 was repeated except that the phenolic compound represented by the chemical formula (5) was used instead of the phenolic compound represented by the chemical formula (1) as a color developer. And a heat-sensitive recording card was produced. For the obtained thermal recording medium,
Using a Toshiba thermal head (6 dots / mm, 380 n), heating printing was performed with an applied voltage of 12 V and a pulse width of 0.8 msec.
As a result, the printed portion became amorphous and white characters were printed in the blue area.

[0100]

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Next, the hot stamper was pressed on the entire surface for 0.5 second and allowed to stand at room temperature. However, since the printed portion was still amorphous, the recording could not be erased. Seconds needed.

Example 4 1.0 parts by weight of crystal violet lactone (CVL), a blue leuco dye, as a color-forming compound, 1.0 part by weight of a phenolic compound represented by the chemical formula (1) as a color developer, and a chemical formula as a reversible agent 5 parts by weight of methylandrostenediol represented by (4), 1-phase-controlling agent
After mixing and melting 5 parts by weight of triacontanol, the mixture was rapidly cooled. One part by weight of the melamine prepolymer was mixed with 30 parts by weight of this composition and heated and melted. This melt was dropped into 200 g of a 5 wt% aqueous gelatin solution and stirred with a homogenizer so as to form fine droplets. Further, the pH was adjusted to 2 using hydrochloric acid, and stirring was continued at about 80 ° C. for 5 hours. This operation produced microcapsules 1 in which the cured melamine resin was coated with a composition comprising a color former, a developer, and a reversible agent.

[0103]

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As a color-forming compound, 1.0 part by weight of a red fluoran dye, Indo Real Red (manufactured by Yamamoto Kasei), 1.0 part by weight of a phenolic compound represented by the chemical formula (1) as a color developing agent, and After mixing and melting 10 parts by weight of pregrenolone, the mixture was rapidly cooled. One part by weight of the melamine prepolymer was mixed with 30 parts by weight of this composition and heated and melted. This melt was dropped into 200 g of a 5 wt% aqueous gelatin solution and stirred with a homogenizer so as to form fine droplets. Further, the pH was adjusted to 2 using hydrochloric acid, and stirring was continued at about 80 ° C. for 5 hours. By this operation, microcapsules 2 in which the cured melamine resin was coated with a composition comprising a color former, a developer, and a reversible agent were produced.

1.0 parts by weight of a black fluoran dye PSD-150 (manufactured by Nippon Soda) as a coloring compound, and 1.0 parts by weight of a bisphenol compound having a long-chain alkyl group represented by the chemical formula (6) as a color developer Was quenched after mixing and melting. One part by weight of the melamine prepolymer was mixed with 30 parts by weight of this composition and heated and melted. This melt was dropped into 200 g of a 5 wt% aqueous gelatin solution and stirred with a homogenizer so as to form fine droplets. Further, the pH was adjusted to 2 using hydrochloric acid, and stirring was continued at about 80 ° C. for 5 hours. By this operation, the microcapsules 3 in which the cured melamine resin was coated with the composition comprising the color former and the developer were produced.

[0106]

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The above-mentioned microcapsules were respectively dispersed in water to prepare recording medium liquids 1, 2, and 3. In addition, recording medium liquids 2 and 3 were mixed in equivalent amounts to prepare recording medium liquid 4. An aqueous dispersion of these microcapsules was printed on a 40 μm-thick PEN film using a screen printer,
A thin film having a thickness of about 10 μm was formed to produce a rewritable multicolor heat-sensitive sheet. This film was attached to a card made of paper with an adhesive, and a 3 μm-thick PEN film protected by a cone-based hard coat agent was further laminated thereon. After pressing a hot roll over the entire surface of the sheet, the recording medium was crystallized by naturally cooling at room temperature.

FIG. 4 is a model diagram schematically showing a cross section of the obtained thermal recording card. As shown in the drawing, the obtained thermal recording card is formed on a paper mount 41, an adhesive layer 42 provided on the mount 41, a PEN film 43 bonded to the mount 31 by the adhesive layer 42, and a PEN film 43. The rewritable thermosensitive recording layer 44 includes microcapsules 46 dispersed therein, and a protective layer 45 provided on the rewritable thermosensitive recording layer 44.

In this thermosensitive recording card, the area where the recording medium liquid 1 was applied consists of a blue sky, the area where the recording medium liquid 4 was applied consists of red Mt. Fuji, and the area where the recording medium liquid 3 was applied consists of white clouds and snow. The picture is displayed.

The obtained thermal recording medium was applied with a 12 V applied voltage using a thermal head (6 dots / mm, 38 On) manufactured by Toshiba.
Heat printing was performed with a pulse width of 0.8 msec. As a result, the printed portion became amorphous and white characters were printed in blue regions, black characters were printed in red regions, and black characters were printed in white regions.

Next, when the hot stamper was pressed on the entire surface for 0.2 seconds and allowed to stand at room temperature, only the white characters in the blue region returned to crystalline, and the recording could be erased.
Further, when the hot stamper was pressed on the entire surface for 2 seconds and left at room temperature, all the characters returned to the crystalline state, and the recording could be erased. Perform the same recording / erasing as above.
The display hardly deteriorated even after 0 cycles. Further, no change was observed in the printing state even after being left at 30 ° C. for one year.

[0112]

As described in detail above, according to the present invention,
A rewritable heat-sensitive sheet which does not require an intermediate layer, has good visibility, color display, and color density, and is sufficiently capable of repeatedly performing coloring and erasing many times is obtained.

[Brief description of the drawings]

FIG. 1 is a model diagram for explaining a three-component coloring / decoloring mechanism used in the present invention.

FIG. 2 is a model diagram for explaining a four-component coloring / decoloring mechanism used in the present invention.

FIG. 3 is a schematic sectional view illustrating an example of a thermal recording card using the rewritable thermal sheet of the present invention.

FIG. 4 is a schematic sectional view showing another example of a thermal recording card using the rewritable thermal sheet of the present invention.

[Explanation of symbols]

 31, 41 ... Mount 32, 42 ... Adhesive layer 33, 43 ... PEN film 34, 44 ... Rewritable thermosensitive recording layer 35, 45 ... Protective layer 46 ... Microcapsule

Claims (6)

[Claims] 1. A base layer having a polyethylene naphthalate film, and a color forming compound formed on the base layer,
A developer that causes the color compound to change from a decolored state to a colored state by interaction with the color compound; and a color developing state and a decolored state due to the interaction between the color compound and the developer. A rewritable heat-sensitive recording layer containing a reversible agent that enables the repetition of the above. 2. The rewritable thermal sheet according to claim 1, wherein the rewritable thermal recording layer is formed directly on a polyethylene naphthalate film. 3. The rewritable heat-sensitive sheet according to claim 1, wherein the color developer has no alkyl side chain or has a linear alkyl side chain structure having 5 or less carbon atoms. 4. The rewritable heat-sensitive sheet according to claim 1, wherein the polyethylene naphthalate film has a crystallinity of 5% or more and 80% or less. 5. The rewritable heat-sensitive sheet according to claim 1, wherein the color developer has a molecular weight of 300 or less. 6. The rewritable heat-sensitive sheet according to claim 1, wherein the reversible agent is a steroid compound.