JP3505273B2 - Reversible thermosensitive recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium capable of reversibly forming and erasing an image.

[0002]

2. Description of the Related Art In recent years, with the progress of office automation, the amount of various kinds of information has remarkably increased, and as the amount of information has increased, the opportunities for outputting information have increased.
Generally, the output of information includes a hard copy display on a paper by a printer and a display display. However, the hard copy display requires a large amount of paper as a recording medium as the output of information increases, which is problematic in terms of resource protection. In addition, since the display unit requires a large-scale circuit board in the display unit, there is a problem in portability and cost. From such a background, a rewritable recording medium (reversible thermosensitive recording medium) capable of solving these problems is expected as the third recording medium. The rewritable recording medium is an all-solid or semi-solid recording medium capable of reversibly recording / erasing an image having high visibility over a large number of times and requiring no energy to hold a display.

Conventionally, such a rewritable recording medium is a thermal printer head (hereinafter abbreviated as TPH).
There is known an organic low molecular weight / high molecular weight resin matrix system capable of recording / erasing by (for example, JP-A-55-154198).
No. 57-82086). This system has a relatively good balance of characteristics as a rewritable recording medium, and is being used for some prepaid cards. However, this organic low-molecular / polymer resin matrix system has T
There is a problem that the range of environmental temperature in which recording / erasing can be performed in a short time using PH is narrow, and the number of repetitions is relatively small, about 150 to 500 times. As a result, the field of application of this rewritable recording medium is extremely limited, and it is difficult to apply it to, for example, a station service IO card having a wide operating environment temperature. Further, this system has a problem that the visibility is insufficient because the cloudy state and the transparent state reversibly change.

The following system is known as a system in which a colored state and a decolored state reversibly change. For example, JP-A-4-50290 discloses a recording material capable of chemically repeating coloring and decoloring by supplying heat energy.
A composition comprising a leuco dye and a color developing material having an acidic group having a color developing function and a basic group having a color erasing function has been proposed. Further, JP-A-4-247985 and JP-A-4-247985.
No. 308790 and JP-A-4-344287 disclose reversible coloring by controlling thermal energy in a composition system in which a leuco dye and a long-chain phosphonic acid as a developer are mixed to change the crystal structure. It has been reported that decolorization occurs.

These coloring and decoloring type rewritable recording media using a leuco dye take advantage of the fact that the reaction rates of coloring and decoloring are largely different, and therefore, two types of thermal history of rapid cooling or slow cooling after heating are used. The applied state controls the coloring state and the erasing state. In order to realize such control, heating is performed by TPH or a laser in the coloring process requiring rapid cooling, and a hot stamp or a heat roller is used in the decoloring process requiring slow cooling. As can be seen from the above, the conventional coloring / erasing type rewritable recording medium requires at least two types of heating devices and has a problem that the erasing speed is slow.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the conventional problems, and recording / erasing can be performed by a single heating device, and both coloring and erasing speeds are extremely fast. An object is to provide a reversible thermosensitive recording medium.

[0007]

Reversible thermosensitivity according to the present invention
The recording medium is a color-developing compound, a color developing material, and a cholesterol.
Le, Stegmasterol, Pregnenolone, Methyl Anne
Drosstendiol, estradiol benzoate,
Epiandrostene, stenolone, β-sitosterone
Le, pregnenolone acetate and β-cholesterol
Supply of binary heat energy selected from the group consisting of
Or reversible changes in composition system caused by two types of thermal history
Reversible material, straight chain higher alcohol, straight chain higher polyhydric alcohol
Rucol, straight chain higher fatty acid, straight chain higher polyvalent fatty acid, it
Ester and ether bond, linear higher fatty acid amide
And higher linear fatty acid amides
Containing two or more low molecular weight organic materials
Shows a supercooling property with a difference of 10 ° C or more,
Change the phase separation rate between the color-developing compound or developer and the reversible material.
It is characterized by containing a phase separation control material to be turned into.

In the reversible thermosensitive recording medium according to the present invention
And two or more kinds of low molecular weight organic compounds that constitute the phase separation controlling material.
The materials preferably have a melting point difference of 8 ° C or more.
Yes.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. First, the action of the basic components constituting the recording medium of the present invention and the operating principle of the recording medium will be briefly described.

In a general sense, the color-forming compound refers to a precursor compound of a dye forming a display image, and the color-developing material is present by an interaction (mainly transfer of electrons) with the color-forming compound. A compound that changes the coloring state of a color compound. That is, generally, the combination of the color developable compound and the color developing material means a combination of two kinds of compounds in which a color-developing state is produced when the interaction is increased and a color-erasing state is produced when the interaction is reduced. The terms color developable compound and developer in the present invention naturally include a narrow meaning as described above, but they should be construed in a wider meaning, and when the interaction increases, a decolored state occurs and the interaction When it decreases, it becomes a coloring state 2
It also includes a combination of species compounds (a narrow combination of a dye and a decolorizer). However, in the following, in order to simplify the explanation, the discussion will be centered on the combination of the color-forming compound in the narrow sense and the developer, and the latter combination of the dye and the decolorizer in the narrow sense will be appropriately supplemented. Discuss.

The color-developing compound used in the present invention includes leuco auramines, diaryl phthalides,
Electron donating organic substances such as polyaryl carbinols, acyl auramines, aryl auramines, rhodamine B lactams, indolines, spiropyrans, fluorans, cyanine dyes and crystal violet,
Examples thereof include electron-accepting organic substances such as phenolphthalein.

More specifically, as the electron-donating organic substance, crystal violet lactone, malachite green lactone, 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- (phenyliminoethanedilidene)- 3,3-Dimethylindoline, N-
3,3-trimethylindolinobenzospiropyran,
8'-methoxy-N-3,3-trimethylindolinobenzospiropyran, 3-diethylamino-6-methyl-
7-chlorofluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-6-benzyloxyfluorane, 1,2-benzo-6-diethylaminofluorane, 3,6-di-p-toluidino-4, Examples include 5-dimethylfluorane-phenylhydrazide-γ-lactam, 3-amino-5-methylfluorane and the like. Examples of electron-accepting organic substances include phenolphthalein, tetrabromophenolphthalein, phenolphthalein ethyl ester, tetrabromophenolphthalein ethyl ester, and the like. These may be used alone or in combination of two or more.
Among the compounds described above, cyanine dyes and crystal violet may be in a decolored state when the interaction with the developer is increased, and may be in a colored state when the interaction is decreased. In the present invention, various color development states can be obtained by appropriately selecting a color-forming compound, and thus color correspondence is possible. Further, if a coloring dye or the like is used in combination with the color-forming compound, any desired coloring state can be obtained.

As the color developer in the present invention, when the color developing compound is an electron-donating organic substance, phenols, phenol metal salts, carboxylic acid metal salts, benzophenones, sulfonic acids, sulfonates, phosphoric acids, Acidic compounds such as phosphoric acid metal salts, acidic phosphoric acid esters, acidic phosphoric acid ester metal salts, phosphorous acid, and phosphorous metal salts,
On the other hand, when the color-forming compound is an electron-accepting organic substance, basic compounds such as amines can be mentioned. These may be used alone or in combination of two or more.

In the present invention, the reversible material is a low molecular weight organic compound having a property of affecting a reversible state change of a three-component system consisting of a color developable compound, a color developing material and a reversible material. When the three-component system is in a fluid state, the reversible material acts as a color developing material (or a color developing compound). Further, when this three-component system is in a solidified state, at least two long-life states shown below can be taken. (1) The reversible material dissolves the color-developing compound and the color developing material in an amount corresponding to the equilibrium solubility, and the surplus color-developing compound and the color developing material that exceed the solubility are phase-separated from the reversible material and develop color. State (equilibrium state). (2) A state in which the reversible material takes in a large amount of the color developing material (or the color developing compound) in excess of the equilibrium solubility, and the interaction between the color developing compound and the color developing material is reduced to eliminate the color ( Equilibrium). This state is metastable or unstable as compared with the state (1), but has a sufficiently long life at room temperature.

Such a three-component system typically has (1) due to the supply of binary thermal energy or the two types of thermal history.
And the reversible change (equilibrium-
Non-equilibrium changes) can occur. It is also possible to cause a reversible change between the two states by applying a stress change.

The states (1) and (2) may be crystalline or amorphous. Therefore, the mode of state change is crystalline-amorphous, amorphous-amorphous or crystalline-crystalline. There are cases. In addition, the property of the reversible material itself is not particularly limited. For example, when the reversible material has a property that it can be crystalline or amorphous, the normally colored state is a state in which the color-developing compound and the developer are eluted or segregated at the grain boundaries of the reversible material due to phase separation. The decolored state is an amorphous state in which the color-developing material (or color-developing compound) and the reversible material interact (or mutually dissolve). When the reversible material is crystalline, the coloring state is a state in which the color-developing compound and the color developing material are eluted or segregated at the grain boundaries of the reversible material, and the decolored state is the color developing material ( Or the color-developing compound) forms a mixed crystal with the reversible material and almost completely phase-separates with the color-developing compound (or the color-developing material), and the interaction between the color-developing compound and the color-developing material is reduced. Is. However, as the reversible material, a material that can be crystalline or amorphous by itself or in combination with the color developing material (or the color developing compound) is preferable.

Based on the properties of each component described above,
FIG. 1 shows a simple model of a typical coloring and decoloring mechanism in a three-component system composed of a color developing compound, a color developing material and a reversible material. In this figure, the color developable compound is represented by A, the color developing material is represented by B, and the reversible material is represented by C. This figure also shows a case where the interaction between the reversible material C and the developer B is large (specifically, the solubility of the developer B in the reversible material C during melting is high). Further, “:” indicates an interaction, and “*” indicates a fluid state.

At room temperature (Tr), the color-forming compound A
The color-developed state in which the phase of the color developing material B and the phase of the reversible material C are phase-separated is close to an equilibrium state in terms of solubility. When heating from this state to the melting point (Tm) or higher of the three-component system, the developer B loses its interaction with the color-forming compound A, while interacting with the reversible material C in a fluid state, resulting in the system. Loses color. Then, when the system is forcibly fixed by quenching from this molten state, the reversible material C interacting with the developer B incorporates the developer B in an amount exceeding the equilibrium solubility and becomes amorphous. And the system becomes colorless at room temperature. This non-equilibrium amorphous substance has a long life at a temperature below the glass transition point (Tg), and does not easily move to the equilibrium state if Tg is room temperature or higher.

Next, when the non-equilibrium amorphous substance is heated to exceed the glass transition point, the diffusion speed of the developer B in the system rapidly increases, so that the developer B is returned to the original equilibrium state. And the phase separation motion of the reversible material C is accelerated. At a temperature at which color development due to phase separation can be sufficiently achieved within a predetermined time,
Since the reversible material C phase-separated from the color developing material B crystallizes rapidly, the lower limit of the coloring temperature may be considered to be the crystallization temperature (Tc). A composition system that has passed the crystallization temperature or higher (melting point or lower) for a predetermined time has a more stable phase separation state closer to an equilibrium state, and the system is in a colored state. Therefore, the crystallization temperature Tc
Equilibrium-non-equilibrium phase changes can be reversibly repeated if binary heat energies of different magnitudes capable of heating the reversible material to a temperature above the melting point Tm and above the melting point Tm are appropriately supplied. Therefore, the coloring / decoloring state can be repeated accordingly. Strictly speaking, since the coloring state depends on the equilibrium solubility and the state of the color developing material (or the coloring compound), it is necessary to consider that the coloring density of the system is affected by the heating temperature and the heating time. .

As described above, the three-component system consisting of the color developable compound, the color developing material and the reversible material can be used as a reversible thermosensitive recording medium. However, in consideration of practicality as a recording medium, it is required that the storage stability is excellent and the coloring (recording) speed is fast. That is, if the amorphous material in the non-equilibrium state is unstable, the phase separation proceeds due to the storage at room temperature or slight heating, which causes a problem in storage stability. From this point of view, the glass transition point Tg of the three-component system and the glass transition point of the reversible material among the constituents thereof must be at least room temperature (25 ° C.) or higher, and more preferably 50 ° C. or higher. preferable. The crystallization temperature Tc of the reversible material is also affected by the heating rate,
It exists in the temperature range between the glass transition point Tg and the melting point Tm. Therefore, in order to perform recording / erasing at high speed, the glass transition point Tg of the reversible material is preferably 150 ° C. or lower.

As the reversible material satisfying the above-mentioned conditions, a compound having a nearly spherical and bulky molecular skeleton such as a steroid skeleton is preferable, and examples thereof include cholesterol, stegmasterol, pregnenolone, methylandrostenediol, estradiol benzoate, epiandro. Examples include sten, stenolone, β-sitosterol, pregnenolone acetate, β-cholesterol and the like. On the other hand, a low molecular weight compound having a molecular weight of less than 100, a linear long-chain alkyl derivative or a planar aromatic compound having a molecular weight of 100 or more is not suitable as a reversible material.

It should be noted that by only optimizing the glass transition point of a three-component system consisting of a color-developing compound, a color-developing material and a reversible material, storage stability is ensured and a sufficient color development / erasing speed is achieved. Hard to get. Therefore, in order to satisfy the storage stability and the coloring and decoloring speed required for the reversible thermosensitive recording medium, a four-component system in which a phase-separation control material is mixed with a color-developing compound, a color developing material and a reversible material is adopted. Preferably.

In the present invention, the phase separation controlling material is a low molecular weight organic material having the following properties and a molecular weight of about 1,000 or less. 1. It has a melting point lower than the melting point of the composition composed of the color developable compound, the developer and the reversible material.

2. Below the melting point, the interaction between the color-developing compound and the color-developing material has little effect on the coloring state. 3. At the melting point or higher, the developer (or color-developing compound) is dissolved.

4. The diffusion speed of the color developing material (or the color-developing compound) is significantly increased as compared with that before and after the melting point. That is, it has the effect of rapidly promoting the phase separation rate of the system near its melting point.

5. The interaction between the melted phase-separation control material and the color-developing material (or color-developing compound) is the dissolution (or melting).
It is smaller than the interaction between the reversible material and the color developing material (or the color developing compound).

FIG. 2 shows an example of a typical coloring and decoloring mechanism of a four-component system composed of a color developing compound, a color developing material, a reversible material and a phase separation controlling material. In this figure, the phase separation control material is D,
The melting point of the phase separation control material is represented by TmD. Other displays are shown in Figure 1.
Is the same as

At room temperature (Tr), the color-forming compound A
The color-developed state in which the phase of the developer B, the phase of the reversible material C, and the phase of the phase-separation control material D are close to an equilibrium state in terms of solubility. When heating from this state to the melting point (Tm) or higher of the composition system, the developer B loses its interaction with the color-developing compound A, while it interacts with the reversible material C in a fluid state, resulting in a system. Loses color. Then, when the four-component system is cooled from the molten state, the phase-reversible material C and the phase-separation controlling material D become a supercooled liquid that maintains fluidity even at a melting point or lower, and the developer B and the reversible material C in the fluidized state. Interacts with and solidifies at a low temperature below the glass transition point Tg, and the reversible material C takes in an amount of the developer B exceeding the equilibrium solubility and becomes amorphous to become a colorless nonequilibrium state. Therefore, unlike the three-component system, this four-component system can obtain a colorless non-equilibrium state by rapid cooling or slow cooling. A non-equilibrium amorphous quaternary system also has an extremely long life at a temperature below the glass transition point (Tg), and does not easily shift to the equilibrium state if Tg is room temperature or higher.

Next, when the non-equilibrium four-component amorphous material is heated to exceed the glass transition point, the diffusion speed of the developing material B rapidly increases, so that the developing material B returns to the equilibrium state. And the phase separation motion of the reversible material C is accelerated. Further, when the melting point (TmD) of the phase separation controlling material D is exceeded, the liquefied phase separation controlling material D dissolves a part of the color developing material B and a part of the reversible material C, and the diffusion speed of the color developing material B increases. Dramatically increased color developer B and reversible material C
And the color-developing compound A associate with each other in a short time. However, at this point, the developer B does not interact with 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 to the melting point of the phase separation controlling material D or less again from this state, the solubility of the developer B in the phase separating control material D sharply decreases, and the developer B and the phase separation controlling material D are instantaneously dropped. Are phase separated. The phase-separated developer B interacts with the color-forming compound A to bring the system into a more stable color-developing state closer to the equilibrium state.

The color development rate of the composition system containing the phase separation controlling material D varies 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, in the four-component system, the melting point of the system (Tm) and the melting point of the phase separation control material (TmD)
By appropriately supplying binary heat energies of different magnitudes that can be heated up to, extremely fast reversible equilibrium-nonequilibrium phase changes while significantly reducing the effects of thermal history of rapid cooling / slow cooling. Can be repeated repeatedly, and the colored / decolored state can be repeated.

The principle of operation shown in FIG. 2 is merely an example, and various other modes are possible. For example,
The position of the glass transition point (Tg) is not necessarily the freezing point (T
s) Not necessarily below. Further, it is not necessary that the reversible material be completely dissolved at the melting point (Tm) or higher of the system, and if the reversible material in an amount capable of interacting with the color developing material is dissolved, the system becomes a decolored state after cooling. Similarly, the melting point (Tm
D) In the above, it is not necessary that all of the developer material is dissolved, and if phase separation (diffusion of developer material or developer compound) is performed at a sufficiently high speed compared to the solid state, dissolution Even if the amount is about several percent, it is effective.

Further, in the composition system containing the phase separation controlling material, the reversible material does not necessarily have to be blended. For example, (1) a state in which the color-developing compound phase and the color-developing material phase are phase-separated and decolored (equilibrium state), and (2) the color-developing material exceeds the equilibrium solubility to develop color A state in which a large amount of a compound is incorporated and the two interact to develop color (non-equilibrium state)
By incorporating a phase separation control material into the two-component system capable of taking two long-life states, the diffusion speed of the color-developing compound in the color developing material is increased, and thus the decoloring speed of the composition system is improved. It may be a composition system.

In the present invention, as the phase separation controlling material corresponding to the reversible material having both crystallinity and amorphousness, a long chain alkyl group (methylene chain) and, for example, OH, CO, COOH.
A low molecular weight organic material having a strong crystallinity, such as a polar group, is preferable. Specifically, straight-chain higher alcohols, straight-chain higher polyhydric alcohols, straight-chain higher fatty acids, straight-chain higher polyvalent fatty acids, their ester-ether conjugates, straight-chain higher fatty acid amides, straight-chain higher polyvalent fatty acid amides And so on.

More specifically, 1-tetradecanol,
1-hexadecanol, 1-octadecanol, 1-eicosanol, 1-docosanol, 1-tetracosanol, 1-hexacosanol, 1-octacosanol, 1
-Straight chain higher monohydric alcohol represented by triacontanol; 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, 1,12-
Octadecanediol, 1,2-dodecanediol,
Linear higher polyhydric alcohols represented by 1,2-tetradecanediol and 1,2-hexadecanediol; palmitic acid, stearic acid, 1-octadecanoic acid, behenic acid, 1-docosanoic acid, 1-tetracosanoic acid, 1 -Higher straight chain fatty acids typified by hexacosanoic acid, 1-octacosanoic acid, etc .; higher straight chain fatty acids typified by sebacic acid, dodecanedioic acid, tetradecanedioic acid, etc .; typified by 14-heptacosanone, stearone, etc. Linear higher ketones; lauric acid ethanolamide, lauric acid n-propanolamide, lauric acid isopropanolamide,
Lauric acid butanolamide, lauric acid hexanolamide, lauric acid octanolamide, palmitic acid ethanolamide, palmitic acid n-propanolamide, palmitic acid isopropanolamide, palmitic acid butanolamide, palmitic acid hexanolamide, palmitic acid octanolamide, stearic acid ethanol Amide, stearic acid n-propanolamide, stearic acid isopropanolamide, stearic acid butanolamide, stearic acid hexanolamide, stearic acid octanolamide, behenic acid ethanolamide, behenic acid n-propanolamide, behenic acid isopropanolamide, behenic acid butanolamide , Behenic acid hexanolamide, behenic acid octanolamide, etc. Chain higher fatty acid alcohol amide; ethylene glycol lauric acid diester, propylene glycol lauric acid diester, butylene glycol lauric acid diester, catechol lauric acid diester, cyclohexane diol lauric acid diester, ethylene glycol palmitic acid diester, propylene glycol palmitic acid diester, butylene glycol palmitin Acid diester, catechol palmitic acid diester, cyclohexanediol palmitic acid diester, ethylene glycol stearic acid diester, propylene glycol stearic acid diester, butylene glycol stearic acid diester, catechol stearic acid diester, cyclohexane diol stearic acid diester, ethylene glycol ester Phosphate diesters, propylene glycol behenic acid diester, butylene glycol behenic acid diester, catechol behenic acid diester, such as straight-chain higher fatty acid diol diesters to such a representative cyclohexanediol behenic acid diester. These may be used alone or in combination of two or more. Examples of the mixture include ester wax, alcohol wax, and urethane wax, which can be used as a phase separation control material.

A particularly preferable phase separation control material is a compound having a methylene chain (maximum carbon chain length) of 20 or more, a carbon number of 36 or less, a melting point of 70 ° C. or more and 120 ° C. or less, and at least one OH group. Is preferred. The maximum carbon chain length is the polar atom (oxygen, nitrogen, etc.) of the main chain or side chain among the carbon chains present in the linear phase separation control material.
It means the number of carbon atoms contained in the longest carbon chain when the carbon atom bonded to is counted virtually as one terminal. Specifically, the linear higher alcohols exemplified above are preferably used as the phase separation controlling material.

The present inventors have blended a phase separation control material
By adopting the component system, it has been realized that the color development speed is improved 10 to 100 times as compared with the three-component system containing no phase separation control material. However, even with this four-component reversible thermosensitive recording medium, it has become clear that there is a limit to the improvement of the thermal writing speed. For example, thermal writing by TPH is a rapid heating / quenching process, and the time during which the medium is in a high temperature state is extremely short. Therefore, as the line writing speed of TPH becomes faster, the heat supply time from TPH becomes shorter, and the phase separation control material in the medium is heated above the melting point for a sufficient time to develop the color developing material necessary for color development. It has become difficult to secure the diffusion time.

As described above, in order to cause color development in the reversible thermosensitive recording medium according to the present invention, the color developing material (or the color developing compound) is diffused in the medium for a certain distance to give a color change. It is necessary that the polymerizable compound and the color developer are associated with each other. Here, the diffusion distance L of the developer (or the color-developing compound) in the medium is represented by L = D ^1/2 · t. In the equation, D is the diffusion coefficient and t is the diffusion time. In the four-component system containing the phase separation control material, the diffusion coefficient D of the developer or the like at a predetermined writing temperature is larger than that in the three-component system. As a result, the diffusion distance can be secured even if the diffusion time t is short, so that the thermal writing speed can be improved. As described above, the four-component system has a thermal writing speed of 10 to 10 as compared with the three-component system.
It is improved 100 times, which means that the diffusion coefficient D is 100-
It means that it has increased 10,000 times. Judging from this, it cannot be expected that the diffusion coefficient D will be further improved by simply selecting the optimum phase separation control material. Therefore, in order to further improve the thermal writing speed, it is necessary to lengthen the diffusion time t. As a result of further studies by the present inventors based on such knowledge, it was noted that the heat supply time and the diffusion time do not necessarily correspond to each other, and that the heat supply time to the medium is If the flow state of the separation control material can be maintained as long as possible, the effective diffusion time t
I found that you can increase.

The present invention has been made in accordance with this consideration. The phase separation control material is made to have a supercooling property, that is, the difference between the melting point and the freezing point is increased to keep the flow state of the phase separation control material for a long time. By increasing the temperature, the substantial diffusion time of the developer (or the color-developing compound) in the medium is lengthened, and the thermal writing speed is further improved. As described above, the supercooling property means a thermal property having a large difference between the dynamic melting point and the freezing point. In the present invention, the phase separation control material having supercooling property means that the difference between the melting point and the freezing point observed in the DSC analysis measured at a temperature change rate of 10 ° C. per minute is 10 ° C. or more. . further,
From the viewpoint of sufficiently prolonging the flow state of the phase separation control material, the difference between the melting point and the freezing point of the phase separation control material is preferably 20 ° C. or more.

The above-described supercooling property can be exhibited by using a mixture of two or more kinds of organic compounds as the phase separation controlling material, and in this case, especially in two or more kinds of materials constituting the phase separation controlling material. The difference in melting point is preferably 8 ° C. or higher, more preferably 15 ° C. or higher. At least one of the two or more kinds of organic compounds constituting the phase separation control material is
It is preferable to use a linear higher alcohol having a methylene chain (maximum carbon chain length) of 20 or more, a carbon number of 36 or less, a melting point of 70 ° C. or more and 120 ° C. or less, and having at least one OH group as described above. . Other organic compounds may be straight chain higher alcohols, straight chain higher polyhydric alcohols, straight chain higher fatty acids, straight chain higher polyhydric fatty acids, their ester and ether linkages, straight chain higher fatty acid amides, straight chain higher fatty acids. It may be a polyvalent fatty acid amide. That is, as the two or more kinds of materials, materials having different methylene chain lengths, different substitution positions of polar groups, or different polar groups from each other are used. Examples of the two or more kinds of materials having polar groups different from each other include a case where the polar group of one material is a hydroxyl group and the polar group of another material is a carboxyl group, an amide group or an amino group. Further, the phase separation controlling material in the present invention is preferably crystalline.

FIG. 3 shows an example of a typical coloring and decoloring mechanism of a four-component system composed of a color-developing compound, a color-developing material, a reversible material and a phase-separation controlling material having a supercooling property. In this figure, the phase separation control material is represented by D, and the melting point and freezing point of the phase separation control material are represented by TmD and TsD, respectively. The other display is the same as in FIG.

At room temperature (Tr), the color-forming compound A
The color-developed state in which the phase of the developer B, the phase of the reversible material C, and the phase of the phase-separation control material D are close to an equilibrium state in terms of solubility. When heating from this state to the melting point (Tm) or higher of the composition system, the developer B loses its interaction with the color-developing compound A, while it interacts with the reversible material C in a fluid state, resulting in a system. Loses color. Then, when the four-component system is cooled from the molten state, the phase-reversible material C and the phase-separation controlling material D become a supercooled liquid that maintains fluidity even at a melting point or lower, and the developer B and the reversible material C in the fluidized state. Interacts with and solidifies at a low temperature below the glass transition point Tg, and the reversible material C takes in an amount of the developer B exceeding the equilibrium solubility and becomes amorphous to become a colorless nonequilibrium state. The above process is the same as in the case of FIG.

Next, when the non-equilibrium quaternary system is heated to exceed the glass transition point, the diffusion speed of the developer B rapidly increases, so that the developer B is returned to the equilibrium state. And the phase separation motion of the reversible material C is accelerated. Further, when the melting point (TmD) of the phase separation controlling material D is exceeded, the liquefied phase separation controlling material D dissolves a part of the color developing material B and a part of the reversible material C, and the diffusion speed of the color developing material B increases. Dramatically increased color developer B and reversible material C
And the color-developing compound A associate with each other in a short time. However, at this point, the developer B does not interact with the color-forming compound A, and the system is in a decolored state or a semi-decolored state.

This state continues until the temperature of the system falls below the freezing point (TsD) of the phase separation controlling material. Since the phase separation controlling material D used in the present invention has a supercooling property,
The fluid state is maintained even below the melting point (TmD), and the diffusion speed of the developer B is also maintained at the same level as in the liquid phase. Then, if the freezing point (TsD) of the phase separation controlling material D is sufficiently lower than the melting point (TmD), the case of FIG. 2 using the phase separation controlling material D having almost no difference between the melting point and the freezing point. Compared to
The time (diffusion time) significant to the diffusion of the color developing material B (or the color-developing compound A) in the heat supply time becomes several times to several tens of times. Therefore, the association between the color developing material B and the color developable compound A further progresses. When the temperature of the system falls below the freezing point (TsD) of the phase separation control material D from this state, the solubility of the developer B in the phase separation control material D sharply decreases, and the phase separation control with the color developer B is instantaneously performed. Material D undergoes phase separation. The phase-separated developer B interacts with the color-forming compound A to bring the system into a more stable color-developing state closer to the equilibrium state.

As described above, in the reversible thermosensitive recording medium of the present invention, by using the phase-separation controlling material having supercooling property, the substantial diffusion time of the developer (or color-developing compound) in the medium is increased. Can be made longer, and by extension, the heat writing speed can be improved by 2 to 50 times as compared with the case where a phase separation control material having no supercooling property is used (the case of FIG. 2). Further, the stamping time by hot stamping and the line cycle by TPH can be shortened.

Next, in the reversible thermosensitive recording medium according to the present invention, the preferable compounding ratio of the color developing compound, the color developing material, the reversible material and the phase separation controlling material will be explained. Regarding the compounding ratio of the color developing compound and the color developing agent, it is preferable to set 0.1 to 10 parts by weight, more preferably 1 to 2 parts by weight of the color developing compound to 1 part by weight of the color developing compound. The reason for this is that the color developing material is 0.
If the amount is less than 1 part by weight, it is difficult to sufficiently increase the interaction between the color developable compound and the color developing material during recording or erasing. On the contrary, if the amount of the color developing material exceeds 10 parts by weight, recording or erasing is performed. This is because it is sometimes difficult to sufficiently reduce the interaction between the color-developing compound and the color-developing material, and in either case, display with an excellent contrast ratio may not be realized.

The compounding ratio of the reversible material is 1 to 1 part by weight of the color developing material.
˜200 parts by weight, more preferably 3 to 30 parts by weight. The reason for this is that if the amount of the reversible material is less than 1 part by weight, the amount of the reversible material that interacts with the reversible material is insufficient, and the residual color density at the time of erasing becomes high. This is because the

The compounding ratio of the phase separation controlling material is 1 to 50 parts by weight with respect to 1 part by weight of the color developing material, and 5 from the viewpoint of storage stability.
It is preferably about 20 parts by weight. The reason for this is that if the amount of the phase separation controlling material is less than 1 part by weight, the color development rate is not significantly improved, and if it exceeds 50 parts by weight, the glass transition point of the composition system becomes too low and the storage stability at the operating temperature is improved. This is because problems will occur.

In the present invention, a color developing compound, a color developing material,
When the film is composed only of the reversible material and the phase-separation control material, each component is a low molecular compound as described above. Therefore, when a thermal history is given, defects are likely to occur in the film due to recrystallization, and the recording medium is left as it is. Difficult to use as. Therefore, in order to realize a large area and uniform film structure while suppressing the generation of defects due to thermal defects, it is effective to hold the above-mentioned four components in a polymer compound. In this case, the four components may be dissolved and / or dispersed in a polymer matrix, or may be held in microcapsules made of a polymer compound. The compounding ratio of the polymer compound is preferably 0.01 to 100 parts by weight, more preferably 0.1 to 5 parts by weight, based on 1 part by weight of the reversible material. The reason for this is that it is difficult to obtain a uniform film when the amount of the polymer compound is less than 0.01 parts by weight, and when the amount of the polymer compound exceeds 100 parts by weight, the color density in the color-developed state decreases.

In the present invention, the film thickness of the reversible thermosensitive recording medium having a film shape is 0.5 to 100 μm, more preferably 1.5 to 100 μm.
It is preferably 20 μm. When the film thickness is smaller than the lower limit value, it is impossible to obtain the required coloring density in the coloring state. On the other hand, when the film thickness exceeds the upper limit value, a temperature difference occurs in the film thickness direction due to heating from the surface, and it becomes difficult to obtain a uniform colored state and a decolored state. In order to realize uniform and high-speed recording / erasing, the film thickness is about 100 μm for hot stamp heating, and about 20 μm for thermal printer head or laser heating.

[0050]

EXAMPLES Examples of the present invention will be described below. Example 1 Crystal violet lactone 1 as a color-developing compound
1 part by weight, 2,4,4'-trihydroxybenzophenone as a color developer, 1 part by weight as a reversible material, and 5 parts by weight of methylandrostenediol as a reversible material, and 1 as a phase separation control material.
4 parts by weight and 1 part of triacontanol (melting point 87 ° C.)
After blending 1 part by weight of tetracosanol (melting point: 73 ° C.), it was heated and melt-mixed to obtain a uniform composition. This phase separation control material has a supercooling property because the difference between the melting point and the freezing point is 10 ° C. or more.

For comparison, a uniform composition was prepared in the same manner as above except that 5 parts by weight of 1-triacontanol alone or 5 parts by weight of 1-tetracosanol alone was used as the phase separation controlling material. Obtained.

Each of the obtained compositions was heated on a hot plate to impregnate neutral paper (SZ base paper made by Daishowa Paper Co., thickness 25 μm). Then, after heating on a hot plate until the composition melts,
By cooling to room temperature, the white decolored state was obtained.
Further, a protective film made of a PET film having a film thickness of 5 μm was formed on the recording medium film to prepare a test sample.

These samples were hot stamped at 150 ° C.
Writing was performed at the color setting temperature of, and the time until reaching the saturated color density was evaluated. As a result, in the sample using 1-triacontanol alone or 1-triacontanol alone as the phase separation controlling material, the saturated color density was reached in 0.2 seconds, whereas 1-triacontanol and 1-tetracontanol were used. The sample of this example using cosanol as the phase separation control material reached the saturated color density in 0.1 seconds, and the writing speed was improved at least twice.

Example 2 Crystal Violet Lactone 1 as a color developing compound
1 part by weight, 2,4,4'-trihydroxybenzophenone as a color developer, 1 part by weight as a reversible material, and 5 parts by weight of methylandrostenediol as a reversible material, and 1 as a phase separation control material.
2 parts by weight of docosanol (melting point: 69 ° C.) and 3 parts by weight of behenic acid (melting point: 80 ° C.) were mixed and heated to be melt-mixed to obtain a uniform composition. This phase separation control material is composed of two kinds of organic compounds having different polar groups from each other, and also has a difference between the melting point and the freezing point of 10 ° C. or more and has a supercooling property.

For comparison, a uniform composition was obtained in the same manner as above except that 5 parts by weight of 1-docosanol alone or 5 parts by weight of behenic acid alone was used as the phase separation controlling material.

Using each of the obtained compositions, a test sample was prepared in the same manner as in Example 1 and was hot stamped to 15
Writing was performed at a color development setting temperature of 0 ° C., and the time until reaching the saturated color density was evaluated. As a result, the saturated color density was reached in about 0.2 seconds in the sample using only 1-docosanol and in about 2 seconds in the sample using only behenic acid.
In the sample of this example using 1-docosanol and behenic acid, the saturated color density was reached in 0.1 seconds, and the writing speed was improved at least twice.

Example 3 Crystal Violet Lactone 1 as a color developing compound
Parts by weight, 2,4,4'-trihydroxybenzophenone as a developer, 1 part by weight of methylandrostenediol as a reversible material, and an alcohol oxide wax as a phase separation control material (manufactured by Nippon Seiro Co., Ltd., trade name NPS92
After blending 5 parts by weight of the material obtained by removing the low molecular weight component containing a carboxyl group from 10), the mixture was heated and melt-mixed to obtain a uniform composition. This phase-separation control material is considered to be a mixture containing various linear higher alcohols as a main component, and also the difference between the melting point and the freezing point is 10 ° C. or more and it has supercooling property.

Using the composition thus obtained, a test sample was prepared in the same manner as in Example 1 and was hot stamped to 150
Writing was performed at a color development setting temperature of ° C, and the time required to reach the saturated color density was evaluated. As a result, the sample of this example reached the saturated color density in 0.1 seconds.

Examples 4 to 12 Reversible thermosensitive recording media were prepared in the same manner as in Examples 1 to 3 by using the compounds shown in Table 1 in combination as the phase separation controlling material, and color development was set at 150 ° C. by hot stamping. Writing was performed at the temperature, and the time required to reach the saturated color density was evaluated. As a result, all the samples reached the saturated color density in 0.1 seconds.

[0060]

[Table 1]

[0061]

As described above in detail, according to the present invention, a reversible thermosensitive recording medium which can record / erase with a single heating device and has an extremely high rate of both coloring and decoloring is provided. be able to.

[Brief description of drawings]

FIG. 1 is composed of a color-forming compound, a color-developing material and a reversible material.
The figure which shows the principle of operation of a component type | system | group reversible thermosensitive recording medium.

FIG. 2 is a diagram showing the operating principle of a four-component reversible thermosensitive recording medium comprising a color developable compound, a color developing material, a reversible material and a phase separation controlling material.

FIG. 3 is a diagram showing the operating principle of a four-component reversible thermosensitive recording medium comprising a color-developing compound, a color developing material, a reversible material and a supercooling phase separation control material according to the present invention.

Front page continuation (72) Hideyuki Nishizawa Inventor Hideko Nishizawa 1 Komukai Toshiba Town, Kouki-ku, Kawasaki-shi, Kanagawa Toshiba Research and Development Center Co., Ltd. (56) Reference JP 5-294063 (JP, A) JP 5 -69664 (JP, A) JP 59-120492 (JP, A) JP 9-71052 (JP, A) JP 3-114881 (JP, A) JP 6-270545 (JP, A) ) JP-A-3-17181 (JP, A) JP-A-4-344287 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5 / 28-5 / 34

Claims (2)

(57) [Claims] 1. A color-developing compound, a color developing agent , and cholesterol.
, Stegmasterol, Pregnenolone, Methyla
Ndrostenediol, estradiol benzoate
G, epiandrostene, stenolone, β-sitostero
, Pregnenolone acetate and β-cholestaro
It is selected from the group consisting Lumpur, reversible material expressing the reversible change in the composition system according to heat energy supply or two thermal history of the binary, linear higher alcohols, linear higher polyvalent
Alcohol, straight chain higher fatty acid, straight chain higher polyvalent fatty acid,
Ester and ether conjugates, straight chain higher fatty acid
Selected from the group consisting of amides and straight chain higher polyvalent fatty acid amides
Containing two or more kinds of low molecular weight organic materials, melting point and freezing point
And a phase separation control material that changes the phase separation rate between the color developing compound or the color developing material and the reversible material in the vicinity of the melting point. A reversible thermosensitive recording medium. 2. Two or more kinds of materials constituting the phase separation control material
The reversible thermosensitive recording medium according to claim 1 , wherein the low-molecular weight organic material has a difference in melting point of 8 ° C or more .