JPH0648033A - Image recording method - Google Patents

Abstract

PURPOSE:To prevent a reversible, thermosensible recording material from its accelerated deterioration when the recording material is rewritten repeatedly with a thermal head. CONSTITUTION:In an image recording method in which a specified reversible, thermosensitive recording material is used and an image formation in which the color condition is changed from the first to the second condition is carried out by a thermal head, the thermal head and the recording material are moved relatively and the temperature of the recoding material is controlled in a range lower than the average temperature reached by heating with the thermal head at the moment of the start of the movement. In another way, the relative movement between the thermal head and the recording material is actuated intermittently so that the pulse current starts in the thermal head heater, avoiding the time overlapping of the pulse current with the start of the movement during the relative movement in a cycle of the intermittent actuation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a recording method using a reversible thermosensitive recording material capable of repeating image recording (repeating writing and erasing of information) by heating.
The present invention relates to a good recording method for a reusable heat-sensitive film or card using a reversible heat-sensitive recording material.

[0002]

2. Description of the Related Art In recent years, rewritable materials have been demanded as thermal recording materials in order to save paper resources. As the most effective material, one having a heat-sensitive layer obtained by dispersing an organic low molecular weight substance such as a higher alcohol or a higher fatty acid in a resin such as polyester on a support is disclosed in, for example, JP-A-54-54.
No. 119377 and JP-A No. 55-154198 are known. Recording (image formation) and erasing with this type of reversible thermosensitive recording material utilize the change in transparency due to the temperature of the thermosensitive layer. As with conventional irreversible thermosensitive recording materials, thermal head and hot stamping are used. It has the feature that it can form images and erase them.

By the way, as a method for heating a heat-sensitive recording material for recording, heating by a thermal head is the most general method, and repetitive rewriting (repetitive recording) by a thermal head has also been considered for recording a reversible heat-sensitive recording material. ing. However, recently, it has been pointed out that repeated rewriting by a thermal head significantly accelerates deterioration of a reversible thermosensitive recording material as compared with other rewriting methods such as hot stamping. There is.

[0004]

The present invention relates to an image recording method, and more specifically, image recording in which the reversible thermosensitive recording material is not deteriorated or hardly caused by repeated rewriting of the reversible thermosensitive recording material by a thermal head. It provides a method.

[0005]

According to one aspect of the present invention, a first color is brought into a state of a first color at a temperature higher than room temperature and a second specific temperature higher than the first specific temperature is heated and then cooled. In the image recording method in which the reversible heat-sensitive recording material in the second color state is used and the rewriting is repeatedly performed by the thermal head, the thermal head and the reversible heat-sensitive recording material are moved relatively and It is characterized in that the temperature of the reversible thermosensitive recording material is lower than the average temperature reached by heating by the thermal head at the moment of starting the movement.

According to another aspect of the present invention, the first color is brought into a first color state at a temperature higher than room temperature, and the second color is heated and cooled at a second specific temperature higher than the first specific temperature. In an image recording method in which a reversible heat-sensitive recording material having a color state of
While the thermal head and the reversible thermosensitive recording material are relatively intermittently moved, a period during which the reversible thermosensitive recording material is moving with respect to the thermal head in one cycle of intermittent driving (see FIG. (Period a), the pulse current of the heating element of the thermal head rises, and the period during which the pulse current flows and the movement start timing (the beginning of the period a in FIG. 1 described later) do not overlap. It has a feature.

The method of the present invention will be described in more detail below. The concentration of the reversible thermosensitive recording material used in the present invention does not change at room temperature, but the concentration can be changed by heating it to a certain temperature range. The temperature range in which the concentration changes is roughly divided into two, and in the present invention, the “lower temperature” range is defined as the “first specific temperature”.
Area, and the "higher temperature" area among them is called the "second specific temperature" area. The reversible thermosensitive recording material used in the present invention changes its color state when heated to the first specific temperature, and the second
It has the property of changing to another color when it is heated to a specific temperature and then cooled.

As mentioned above, the reversible thermosensitive recording material deteriorates considerably depending on the frequency of use, especially in image formation which is considered to be caused by a thermal head. The reason for this deterioration is presumed as follows. Currently, reversible thermosensitive recording materials are mainly composed of organic low molecular weight substances and resin base materials.However, at the moment of heating with a thermal head for recording, the temperature is the melting point of the organic low molecular weight substances or the resin base material. Since the softening point of the material is exceeded, the reversible thermosensitive recording material becomes very soft. Therefore, even a slight stress due to friction with the thermal head is easily deformed and the structure of the material is changed. It is considered that the accumulation of these changes appears as deterioration of the reversible thermosensitive recording material.

The strain generated inside the reversible thermosensitive recording material is determined by the stress applied inside the reversible thermosensitive recording material and the hardness of the reversible thermosensitive recording material at that time. Further, the stress applied to the inside of the reversible thermosensitive recording material is determined by the weight and frictional force between the thermal head and the reversible thermosensitive recording material. Generally, the largest frictional force is the maximum static frictional force at the moment when the reversible thermosensitive recording material starts to move. At this moment, if the inside of the reversible thermosensitive recording material is in a soft state, the internal strain becomes remarkable. become.

From these things, in order to prevent the deterioration of the reversible thermosensitive recording material by the thermal head, Lower the load between the thermal head and the reversible thermosensitive recording material. 2. The coefficient of friction (especially at high temperature) between the thermal head and the reversible thermosensitive recording material is lowered. 3. While the reversible thermosensitive recording material is not completely cooled and softened, the reversible thermosensitive recording material does not start moving. Such conditions are required.

Of these, the third condition corresponds to the printing method described in claim 1. By the way, when a pulsed current is applied to the heating element of the thermal head, the temperature transition curve has a shape similar to that of a rectangular wave passed through an analog integrating circuit. That is, when the pulse rises, the temperature rises sharply but gradually, and when the pulse falls, the temperature becomes highest. Therefore, it is considered that the temperature of the reversible thermosensitive recording material becomes the highest around the time of this pulse fall and is in a softened state.
In the first aspect, the average temperature reached by heating with the thermal head is the sum of the temperatures when the pulse is started and when the pulse is stopped and divided by two.

From the above, the above condition No. 3 can be rephrased as follows. 4. The movement of the reversible thermosensitive recording material is not started during and immediately after the pulse is applied to the heating element. In particular, the movement of the reversible thermosensitive recording material does not start when the pulse falls. From these, two methods can be considered when the printing method is specifically considered. When the relative movement between the reversible thermosensitive recording material and the thermal head is performed by intermittent driving such as a pulse motor, by adjusting the relationship between the driving timing and the pulse current timing of the thermal head heating element,
The timing at which movement starts intermittently and the timing at which the pulse current flows (particularly the timing at which the pulse falls) should not overlap. (B) Relative movement between the reversible thermosensitive recording material and the thermal head is continuously driven by a DC motor or the like, and the pulse current of the heating element of the thermal head is applied after the driving is started to stabilize the relative movement speed. Here, the former method is the printing method described in claim 3, and the latter method is the printing method described in claim 2.

In the above intermittent driving, the relative movement between the reversible thermosensitive recording material and the thermal head is schematically shown as shown in FIG. In the present invention, a in the figure
The period of time is referred to as a moving period, the period of b is referred to as a reaction period, and the period of c is referred to as a stationary period. Even when driven by a pulse motor, there may be no period b or c depending on the driving conditions. If neither b nor c is present, it can be regarded as equivalent to continuous drive by a DC motor. In continuous driving, once the driving is started, it is always regarded as a moving period until the driving is stopped. The method (1) will be described with reference to FIG. 1. The pulse current rises during the period a and the pulse current falls during the period a to c. Further, when the pulse current is made to fall between the period a and the period b in FIG. 1, the movement slightly reverses in the period b,
Since the frictional force also works in the opposite direction, even if the reversible thermosensitive recording material is not completely cold at the moment of starting the movement and distortion occurs, it can be canceled. Therefore, in particular, the printing method according to the fourth aspect has an effect of preventing deterioration even if the reversible thermosensitive recording material is not completely cooled at the start of movement. In order to make the most of this effect, it is particularly preferable to raise the pulse in the latter half of the period a and lower the pulse in the first half of the period b. Also, b
When there is not only the period of, the pulse is more preferably dropped in the first half of the period of c or the latter half of the period of a.

Up to this point, the method of recording with one pulse current on one recording dot has been described, but in the case of applying a plurality of pulse currents to one recording dot, it is possible to move within one cycle of movement. In the present invention, the period in which the temperature of the heating element rises due to the group of pulse currents
It is considered to correspond to the period when two pulse currents are flowing.

The "reversible thermosensitive recording material" in the present invention does not change its color state at room temperature, but when heated to a certain temperature, it becomes the first color state, and at a certain temperature higher than a certain temperature. It is a material that enters the second color state when it is returned to room temperature after being heated, and is a material that can repeatedly change the state of this color many times. Changes in the color state include changes in transmittance, reflectance, absorption wavelength, scattering degree, etc., and in actual reversible thermosensitive recording materials, display is performed by a combination of these changes. More specifically, a material that reversibly changes between a transparent state and a cloudy state. A material whose color such as dye changes chemically. Currently, it can be classified into two types of systems.

As a conventional technique and as repeatedly described above, a heat-sensitive layer comprising a resin base material such as polyester and an organic low molecular weight substance such as a higher alcohol and a higher fatty acid dispersed therein is provided on a support. The one provided is a typical example. As a typical example, a leuco thermosensitive recording material having enhanced reversibility can be mentioned.

The heat-sensitive layer of the type that causes a change in transparency is mainly composed of a resin base material and an organic low molecular weight substance dispersed in the resin base material. The reversible thermosensitive recording material here has a temperature range in which it becomes transparent, as described later. Further, the reversible thermosensitive recording material herein utilizes the transparency change (transparent state, cloudy opaque state) as described above, and the difference between the transparent state and the cloudy opaque state is presumed as follows. That is, in the case of (I) transparent, the particles of the organic low-molecular substance dispersed in the resin base material are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered and is opposite. When it is cloudy (II), the particles of the organic low molecular weight substance are composed of polycrystals of fine crystals of the organic low molecular weight substance. Since the light is directed in various directions, the light incident from one side is refracted many times at the interface of the crystal of the organic low molecular weight substance particles, and is scattered and thus appears white.

In FIG. 2 (representing the change in transparency due to heat), the heat-sensitive layer mainly composed of a resin base material and an organic low molecular weight substance dispersed in the resin base material is, for example, T _0.
It is cloudy and opaque at room temperature below. This is the temperature T ₂
When it is heated to ₀ , it becomes transparent, and even if it is returned to room temperature below T _{0 in} this state, it remains transparent. This is the temperature T ₂ to T ₀
It is considered that the organic low molecular weight substance is in a semi-molten state until the following and the crystal grows from a polycrystal to a single crystal.
Upon further heating to T ₃ or more temperature becomes translucent state intermediate between the maximum transparency and the maximum opacity. Next, when this temperature is lowered, the first cloudy opaque state is restored without taking the transparent state again. It is considered that this is because when the organic low molecular weight substance is melted at a temperature of T ₃ or higher, the polycrystal is deposited by being cooled. When this opaque state is heated to a temperature between T _{1 and} T ₂ and then cooled to room temperature, that is, a temperature of T ₀ or lower, an intermediate state between transparent and opaque can be obtained. Also, the transparent material that has become transparent at room temperature returns to the cloudy and opaque state again when heated to a temperature of T ₃ or higher and then returned to room temperature. That is, both opaque and transparent forms at room temperature and intermediate forms thereof can be obtained.

Therefore, the heat-sensitive layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent background and a transparent image on a cloudy background, and the change can be repeated many times. It is possible. By arranging a coloring sheet on the back surface of such a heat-sensitive layer, it is possible to form an image of the color of the coloring sheet on a white background or a white image on the background of the color of the coloring sheet. Further, when projected by an OHP (overhead projector) or the like, the cloudy portion becomes a dark portion, the transparent portion transmits light and becomes a bright portion on the screen. Furthermore,
When the image of this reversible thermosensitive recording material is used as a reflection image, a contrast can be increased by providing a light reflecting layer on the back surface of the recording layer even if the thickness of the recording layer is reduced. To form the reflective layer, specifically, vapor deposition of Al, Ni, Sn or the like can be mentioned.

To prepare the reversible thermosensitive recording material according to this type of the present invention, generally, (1) a solution in which two components of a resin base material and an organic low molecular weight substance are dissolved, or (2) a solution of the resin base material (solvent Is used that does not dissolve at least one of the organic low molecular weight substances), and a dispersion liquid in which the organic low molecular weight substance is dispersed in the form of fine particles is applied and dried on a support such as a plastic film, a glass plate or a metal plate. Then, the heat sensitive layer may be formed.

The solvent for preparing the heat-sensitive layer or the heat-sensitive recording material can be variously selected depending on the kind of the resin base material and the organic low molecular weight substance, and for example, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, Examples thereof include benzene. Of course, when using the dispersion,
Even when a solution is used, the organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the obtained heat-sensitive layer.

The resin base material used for the heat-sensitive layer is a material which forms a layer in which an organic low molecular weight substance is uniformly dispersed and held, and which affects the transparency at maximum transparency. Therefore, the resin base material is preferably a resin having good transparency, mechanical stability, and good film forming property.

Examples of such resins include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride- Vinyl chloride-based copolymers such as acrylate copolymers; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-based copolymers such as vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides; polyacrylates or polyacrylates Methacrylate or acrylate-methacrylate copolymer; silicone resin and the like can be mentioned.
These may be used alone or in combination of two or more.

On the other hand, the organic low molecular weight substance may be any substance that changes from polycrystal to single crystal due to heat in the recording layer, and generally has a melting point of 30 to 200 ° C., preferably 50 to 150.
The thing of about ℃ is used. Such organic low-molecular substances include alkanols; alkane diols; halogen alkanols or halogen alkane diols; alkylamines; alkanes; alkenes; alkynes; halogen alkanes; halogen alkenes; halogen alkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or Unsaturated mono- or dicarboxylic acids or their esters,
Amides or ammonium salts; saturated or unsaturated halogen fatty acids or their esters, amides or ammonium salts; arylcarboxylic acids or their esters, amides or ammonium salts; halogenallylcarboxylic acids or their esters, amides or ammonium salts; thioalcohols Thiocarboxylic acids or their esters,
Amine or ammonium salts; carboxylic acid esters of thioalcohol and the like. These may be used alone or in admixture of two or more. The carbon number of these compounds is 1
0-60, preferably 10-38, especially 10-30 are preferred. The alcohol group moiety in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, the organic low molecular weight substance is at least one of oxygen, nitrogen, sulfur and halogen in the molecule, for example, −
OH, -COOH, -CONH-, -COOR, -NH
_{-, - NH 2, -S -} , - S-S -, - O-, it is preferably a compound containing a halogen and the like.

More specifically, as these compounds,
Uric acid, dodecanoic acid, myristic acid, pentadecane
Acid, palmitic acid, stearic acid, behenic acid, nonadeca
Higher fatty acids such as acid, araginic acid and oleic acid; steer
Methyl phosphate, tetradecyl stearate, stearin
Acid octadecyl, octadecyl laurate, palmitin
Of higher fatty acids such as tetradecyl acid acid and dodecyl behenate
Stell; C₁₆C₃₃-OC₁₆C₃₃, C₁₆C₃₃-SC₁₆C₃₃, C₁₈C₃₇-SC₁₈C₃₇, C₁₂C_{twenty five}-SC₁₂C_{twenty five}, C₁₉C₃₉-SC₁₉C₃₉, C₁₂C_{twenty five}-S-S-C₁₂C
_{twenty five},   Etc., such as ether or thioether. Above all, the present invention
Higher fatty acids, especially palmitic acid, stearic acid,
Higher fats with 16 or more carbon atoms such as henic acid and lignoceric acid
Acids are preferable, and higher fatty acids having 16 to 24 carbon atoms are more preferable.
Good

In order to widen the range of temperatures at which the material can be made transparent, the organic low molecular weight substances described in this specification may be appropriately combined, or such organic low molecular weight substances may be combined with other materials having different melting points. . These are, for example, JP-A-63
No. 39378, Japanese Patent Application Laid-Open No. 63-130380, Japanese Patent Application No. 63-14754, Japanese Patent Application No. 1-1401.
However, the present invention is not limited thereto. The weight ratio of the organic low molecular weight substance to the resin base material in the heat sensitive layer is preferably about 2: 1 to 1:16, more preferably 1: 1 to 1: 3. When the ratio of the resin base material is less than this, it becomes difficult to form a film in which the organic low molecular weight material is retained in the resin base material. Becomes difficult.

In addition to the above components, additives such as a surfactant and a high boiling point solvent may be added to the heat-sensitive layer in order to facilitate the formation of a transparent image. Specific examples of these additives are as follows. Examples of high boiling point solvents: tributyl phosphate, tri-2-phosphate
Ethylhexyl, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate , Dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate,
Dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, di-2 azelaate
-Ethylhexyl, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetylricinoleate, butyl acetylricinoleate, butylphthalylbutyl glycolate, acetylcitric acid Tributyl.

Examples of surfactants and other additives: polyhydric alcohol higher fatty acid ester; polyhydric alcohol higher alkyl ether; polyhydric alcohol higher fatty acid ester, higher alcohol, higher alkylphenol, higher fatty acid higher alkylamine, higher fatty acid amide , Lower olefin oxide adducts of fats and oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salt of higher alkylbenzene sulfonic acid; higher fatty acid, aromatic carboxylic acid, higher fatty acid sulfonic acid, aromatic sulfonic acid, sulfuric acid monoester Or Ca, Ba or Mg salts of phosphoric acid mono- or di-esters; low-sulfated oils; poly long-chain alkyl acrylates; acrylic orgomers;
Poly long-chain alkyl methacrylate; long-chain alkyl methacrylate-amine-containing monomer copolymer; styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer.

A protective layer may be provided on the heat sensitive layer to protect the heat sensitive layer. Protective layer (thickness 0.1-5
(μm), silicone rubber, silicone resin (described in JP-A-63-221087), polysiloxane graft polymer (Japanese Patent Application No. 62-15255).
No. 0) and an ultraviolet curable resin or an electron beam curable resin (described in Japanese Patent Application No. 63-310600). In both cases, a solvent is used during coating,
It is desirable that the solvent is difficult to dissolve the resin of the heat sensitive layer and the organic low molecular weight substance. Examples of the solvent that hardly dissolves the resin and the organic low molecular weight substance in the heat-sensitive layer include n-hexane, methyl alcohol, ethyl alcohol, isopropyl alcohol and the like, and the alcohol solvent is particularly preferable from the viewpoint of cost.

Furthermore, an intermediate layer may be provided between the protective layer and the heat-sensitive layer in order to protect the heat-sensitive layer from the solvent, monomer components and the like of the protective-layer forming liquid. As the material for the intermediate layer, the following thermosetting resins and thermoplastic resins can be used in addition to those listed as the resin base material in the heat sensitive layer.
That is, polyethylene, polypropylene, polystyrene,
Examples thereof include polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate and polyamide. The thickness of the intermediate layer is preferably about 0.1 to 2 μm.

Next, a description will be given of a case where the heat-sensitive layer is formed by a reversible thermochromic composition utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound. A thermochromic composition utilizing a color-forming reaction between an electron-donating color-developing compound and an electron-accepting compound is prepared by heating and melting the electron-donating color-developing compound and the electron-accepting compound. Amorphous chromophores are formed, while when the amorphous chromophore is heated at a temperature lower than the melting temperature, the electron-accepting compound causes crystallization and the chromophore disappears. It utilizes the phenomenon of.

The thermochromic composition instantly develops color upon heating, and the color-developed state thereof is stable even at room temperature. On the other hand, the composition in the color-developed state is instantly heated by heating at a temperature not higher than the color development temperature. The color is erased, and the erased state is stable even at room temperature, and such a reversible peculiar color developing and erasing behavior is a novel and surprising phenomenon that has never been seen before.

The principle of coloring and erasing, that is, image forming and image erasing when this composition is used as a thermal recording medium is shown in FIG.
This will be explained with reference to the graph shown in. The vertical axis of the graph represents the color density, the horizontal axis represents the temperature, the solid line represents the image forming process by heating, and the broken line represents the image erasing process by heating. A is the density in the completely erased state, B is the density in the completely colored state when heated to a temperature of T ₅ or higher, C is the density at a temperature of T ₄ or lower in the completely colored state, and D is T ₄ It shows the concentration when heat erasing is performed at a temperature between T _{5 and} T ₅ .

This composition according to the invention is in the colorless state (A) at temperatures below T ₄ . To perform recording (image formation), a color image (B) is formed by heating to a temperature of T ₅ or higher with a thermal head or the like to form a recorded image. Even if the recorded image is returned to the temperature of T ₄ or lower according to the solid line, the state (C) is maintained as it is and the recording memory property is not lost.

Next, in order to erase the recorded image, the formed recorded image is heated to a temperature between T _{4 and} T _{5 which} is lower than the coloring temperature, so that a colorless state (D) is obtained. In this state, even if the temperature is returned to T ₄ or lower, the colorless state (A) is maintained as it is. That is, the process of forming the recorded image reaches C by the path of the solid line ABC and the recording is held. Next, in the process of erasing the recorded image, the erased state is maintained by reaching A through the path of the broken line CDA. The behavior characteristics of formation and erasure of the recorded image are reversible and can be repeated many times.

The reversible thermochromic composition contains a color former and a color developer as essential components. Then, the coloring state is formed by heating and melting the color-developing agent and the color-developing agent, while the coloring state is erased by heating at a temperature lower than the coloring temperature, and the coloring state and the erasing state exist stably at room temperature. Is. As described above, the mechanism of coloring and decoloring in the composition is such that when the coloring agent and the color developer are heated and melt-mixed at the coloring temperature, the composition causes an amorphization and a coloring state. On the other hand, it is based on the property that, when heated at a temperature lower than the coloring temperature, the developer of the colored composition causes crystallization to form an erased state of coloring. However, even in this case, since the heat-sensitive layer is heated to a temperature of T ₅ or higher and then decolored, the particles of the color-developing agent and the color-developing agent are restored to form a new color-developed state. Is advantageous to.

A composition comprising a conventional color former and a developer, for example, a leuco compound having a lactone ring, which is a dye precursor widely used in conventional thermal recording paper, and a phenolic compound exhibiting a color developing effect. When this is melt-mixed by heating, it becomes a coloring state based on the ring opening of the lactone ring of the leuco compound. This colored state is an amorphous state in which both are compatible. Although this colored amorphous state is stable at room temperature, it does not crystallize even when heated again, and because the phenolic compound is not separated from the leuco compound, the lactone ring is not closed and decolorized. I don't.

On the other hand, when the composition of the color former and the developer according to the present invention is melt-mixed by heating, it becomes a color-developed state, exhibits an amorphous state as in the conventional case, and is stable at room temperature. Exist. However, in the case of the present invention, when the composition in the colored amorphous state is heated at a temperature not higher than the coloring temperature, that is, at a temperature at which the molten state is not reached, crystallization of the developer occurs and the composition is compatible with the color developing agent. The bond due to the state cannot be maintained, and the color developer separates from the color developer. It is considered that due to the crystallization of the color developer from the color developer, the color developer cannot accept electrons from the color developer and the color developer is decolorized.

The above-mentioned peculiar color-development behavior observed in the thermochromic composition is the mutual solubility of the color-developing agent and the color-developing agent by heating and melting, the strength of both actions in the color-developing state, and the color-developing agent. Is related to the solubility of the color developing agent, the crystallinity of the developer, etc.
In principle, it causes amorphization by heating and melting, while
Any color former / developer system that causes crystallization by heating at a temperature lower than the color development temperature can be used as a composition component in the present invention. Further, those having such characteristics show endothermic change due to melting and exothermic change due to crystallization in thermal analysis, so that the color former / developer system applicable to the present invention can be easily analyzed by thermal analysis. You can check. Further, the reversible thermochromic composition system according to the present invention may contain a third substance, for example, the reversible decoloring behavior thereof is retained even if a polymer substance is present. Was confirmed. In the thermochromic composition of the present invention, the decolorization is due to the separation from the color former due to the crystallization of the color developer. Therefore, in order to obtain an excellent decoloring effect, the color developer should be selected. is important.

Next, examples of the color developer preferably used in the present invention are as follows. As described above, the color developer applicable to the present invention can be easily found by thermal analysis. It is not limited to ones. (1) Organic phosphoric acid compound represented by the following general formula (1) R ¹ —PO (OH) ₂ (1) (wherein R ¹ is a linear or branched alkyl group or alkenyl having 8 to 30 carbon atoms) Represents a group.) Specific examples of the organic phosphoric acid compound include the followings. Octylphosphonic acid, nonylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid, docosylphosphonic acid, tetracosylphosphonic acid.

(2) Organic acid having a hydroxyl group at the α-position carbon represented by the following general formula (2) R ² —CH (OH) COOH (2) (wherein R ² is a straight chain having 6 to 28 carbon atoms) Represents a cyclic or branched alkyl group or alkenyl group.) Specific examples of the organic acid having a hydroxyl group at the α-position carbon include the following. α-Hydroxyoctanoic acid, α-hydroxydodecanoic acid, α-hydroxytetradecanoic acid, α-hydroxyhexadecanoic acid, α-hydroxyoctadecanoic acid, α-hydroxypentadecanoic acid Acid, α-hydroxyeicosanoic acid, α-hydroxydocosanoic acid, etc.

The color former used in the present invention is a compound exhibiting an electron-accepting property, and is a colorless or light-colored dye precursor itself, and is not particularly limited, and conventionally known ones, for example, triphenylmethanephthalide-based compounds. There are compounds, fluoran compounds, phenothiazine compounds, leuco auramine compounds, rhodamine lactam compounds, spiropyran compounds, indolinophtalide compounds, and the like. Specific examples include the following. 3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-
Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis (p-dimethylaminophenyl)-
6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-
Bis (p-dibutylaminophenyl) phthalide, 3-cyclohexylamino-6-chlorofluorane, 3-dimethylamino-5,7-dimethylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7- Methylfluorane, 3-diethylamino-7,8
-Benzfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3- (Np-tolyl-N-
Ethylamino) -6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 2- {N- (3'-trifluoromethylphenyl) amino} -6-diethylamino Fluoran, 2-
{3,6-bis (diethylamino) -6- (o-chloroanilino) xanthylbenzoic acid lactam}, 3-diethylamino-6-methyl-7- (m-trichloromethylanilino) fluorane, 3-diethylamino-7- ( o-
Chloranilino) fluorane, 3-dibutylamino-7
-(O-Chloranilino) fluorane, 3-N-methyl-N-amylamino-6-methyl-7-anilinofluorane, 3-N-methyl-N-cyclohexylamino-6
-Methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N,
N-diethylamino) -5-methyl-7- (N, N-dibenzylamino) fluorane, benzoleucomethylene blue, 6'-chloro-8'-methoxy-benzoindolino-spiropyran, 6'-bromo-2'- Methoxy-benzoindolino-spiropyran, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'methoxy-5'-chlorophenyl) phthalide, 3- (2'hydroxy-4'-dimethyl Aminophenyl) -3-
(2'-methoxy-5'-nitrophenyl) phthalide,
3- (2'-hydroxy-4'-diethylaminophenyl) -3- (2'-methoxy-5'-methylphenyl)
Phthalide, 3- (2'-methoxy-4'-dimethylaminophenyl) -3- (2'-hydroxy-4'-chloro-5'-methoxyphenyl) phthalide, 3-morpholino-7- (N-propyl-). Trifluoromethylaniline)
Fluoran, 3-diethylamino-5-chloro-7-
(N-benzyl-trifluoromethylanilino) fluorane, 3-pyrrolidino-7- (di-p-chlorophenyl) methylaminofluorane, 3-diethylamino-5
-Chloro-7- (α-phenylethylamino) fluorane, 3- (N-ethyl-p-toluidino) -7- (α-
Phenylethylamino) fluorane, 3-diethylamino-7- (o-methoxycarbonylphenylamino) fluorane, 3-diethylamino-5-methyl-7- (α
-Phenylethylamino) fluorane, 3-diethylamino-7-piperidinofluorane, 2-chloro-3-
(N-methoxytoluidino) -7- (pn-butylanilino) fluorane, 3- (N-methyl-N-isopropylamino) -6-methyl-7-anilinofluorane,
3-dibutylamino-6-methyl-7-anilinofluorane, 3,6-bis (dimethylamino) fluorenspiro (9,3 ')-6'-dimethylaminophthalide, 3-
(N-benzyl-N-cyclohexylamino) -5,6
-Benzo-7-α-naphthylamino-4'-bromofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-N-ethyl-N- (2-ethoxypropyl) amino-6- Methyl-7-anilinofluorane, 3-N-ethyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-mesitidino-4 ', 5'. −
Benzofluorane, 3-N-methyl-N-isobutyl-
6-methyl-7-anilinofluorane, 3-N-ethyl-N-isoamyl-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (2 ',
4'-dimethylanilino) fluorane and the like.

Particularly preferred color formers used in the present invention are those containing halogen as a substituent. Examples of such a thing include the following. 3,3-bis (p-dimethylaminophenyl) -6
-Chlorophthalide, 3-cyclohexylamino-6-chlorofluorane, 3-cyclohexylamino-6-bromofluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-bromofluorane, 3
-Dipropylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-phenylamino-fluorane, 3-pyrrolidino-6-chloro-7-phenylamino-fluorane, 3-diethylamino-6-chloro-7
-(M-trifluoromethylphenyl) amino-fluorane, 3-cyclohexylamino-6-chloro-7- (o
-Chlorophenyl) amino-fluorane, 3-diethylamino-6-chloro-7- (2 ', 3'-dichlorophenyl) amino-fluorane, 3-diethylamino-6-
Methyl-7-chlorofluorane, 3-dibutylamino-
6-chloro-7-ethoxyethylamino-fluorane,
3-diethylamino-7- (o-chlorophenyl) amino-fluorane, 3-diethylamino-7- (o-bromophenyl) amino-fluorane, 3-diethylamino-7- (o-chlorophenyl) amino-fluorane, 3
-Dibutylamino-7- (o-fluorophenyl) amino-fluorane, 6'-bromo-3'-methoxybenzoindolino-pyrrolospirane, 3- (2'-methoxy-
4'-Dimethylaminophenyl) -3- (2'-hydroxy-4'-chloro-5'-chlorophenyl) phthalide, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2 '-Methoxy-5'-chlorophenyl) phthalide, 2- {3,6-bis (diethylamino)}-9- (o-chlorophenyl) amino-xanthyl lactam benzoate and the like.

A preferred color former for use in the present invention is a compound represented by the following general formula (3).

[Chemical 1] (However, R ³ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ⁴ is a hydrogen atom or an optionally substituted amino group, X is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenylamino group. , M is an integer of 1 or 2, Y is a carbon number of 1 to 4.
Alkyl group or alkoxy group having 1 to 2 carbon atoms, n is 1
Or represents an integer of 2. )

Specific examples of the compound represented by the general formula (3) include the followings. 3-
(N-methyl-N-phenylamino) -7-amino-fluorane, 3- (N-ethyl-N-phenylamino)-
7-amino-fluorane, 3- (N-propyl-N-phenylamino) -7-amino-fluorane, 3- {N-
Methyl-N- (p-methylphenyl) amino} -7-amino-fluorane, 3- {N-ethyl-N- (p-methylphenyl) amino} -7-amino-fluorane, 3-
{N-propyl-N- (p-methylphenyl) amino}
-7-amino-fluorane, 3- {N-methyl-N-
(P-Ethylphenyl) amino} -7-amino-fluorane, 3- {N-ethyl-N- (p-ethylphenyl)
Amino} -7-amino-fluorane, 3- {N-propyl-N- (p-ethylphenyl) amino} -7-amino-fluorane, 3- {N-methyl-N- (2 ', 4'-dimethyl) Phenyl) amino} -7-amino-fluorane,
3- {N-ethyl-N- (2 ', 4'-dimethylphenyl) amino} -7-amino-fluorane, 3- {N-propyl-N- (2', 4'-dimethylphenyl) amino}
-7-amino-fluorane, 3- {N-methyl-N-
(P-Chlorophenyl) amino} -7-amino-fluorane, 3- {N-ethyl-N- (p-chlorophenyl)
Amino} -7-amino-fluorane, 3- {N-propyl-N- (p-chlorophenyl) amino} -7-amino-fluorane, 3- (N-methyl-N-phenylamino) -7-methylamino -Fluorane, 3- (N-ethyl-N-phenylamino) -7-methylamino-fluorane, 3- (N-propyl-N-phenylamino) -7-
Methylamino-fluorane, 3- {N-methyl-N-
(P-Methylphenyl) amino} -7-ethylamino-
Fluoran, 3- {N-ethyl-N- (p-methylphenyl) amino} -7-benzylamino-fluorane, 3
-{N-methyl-N- (2 ', 4'-dimethylphenyl)
Amino} -7-methylamino-fluorane, 3- {N-
Ethyl-N- (2 ', 4'-dimethylphenyl) amino}
-7-Ethylamino-fluorane, 3- {N-methyl-
N- (2 ', 4'-dimethylphenyl) amino} -7-benzylamino-fluorane, 3- {N-ethyl-N-
(2 ', 4'-Dimethylphenyl) amino} -7-benzylamino-fluorane, 3- (N-methyl-N-phenylamino) -7-dimethylamino-fluorane, 3- (N
-Ethyl-N-phenylamino) -7-dimethylamino-fluorane, 3- {N-methyl-N- (p-methylphenyl) amino} -7-diethylamino-fluorane,
3- {N-ethyl-N- (p-methylphenyl) amino} -7-diethylamino-fluorane, 3- (N-methyl-N-phenylamino) -7-dipropylaminofluorane, 3- (N- Ethyl-N-phenylamino) -7
-Dipropylaminofluorane, 3- {N-methyl-N
-(P-Methylphenyl) amino} -7-dibenzylamino-fluorane, 3- {N-ethyl-N- (p-methylphenyl) amino} -7-dibenzylamino-fluorane, 3- {N-ethyl -N- (p-methylphenyl)
Amino} -7-di (p-methylbenzyl) amino-fluorane, 3- {N-methyl-N- (p-methylphenyl) amino} -7-acetylamino-fluorane, 3-
{N-ethyl-N- (p-methylphenyl) amino}-
7-benzoylamino-fluorane, 3- {N-methyl-N- (p-methylphenyl) amino} -7- (o-methoxybenzoyl) amino-fluorane, 3- {N-ethyl-N- (p-methyl) Phenyl) amino} -6-methyl-7-phenylamino-fluorane, 3- {N-methyl-N- (p-methylphenyl) amino} -6-methyl-7-phenylamino-fluorane, 3- {N- Methyl-N- (p-methylphenyl) amino} -6-tert
-Butyl-7- (p-methylphenyl) amino-fluorane, 3- (N-ethyl-N-phenylamino) -6-
Methyl-7- (N-ethyl-N- (p-methylphenyl) amino-fluorane, 3- {N-propyl-N-
(P-Methylphenyl) amino} -6-methyl-7-
{N-methyl-N- (p-methylphenyl) amino}-
Fluoran, 3- {N-ethyl-N- (p-methylphenyl) amino} -5-methyl-7-benzylamino-fluorane, 3- {N-ethyl-N- (p-methylphenyl) amino} -5 -Chloro-7-dibenzylamino-fluorane, 3- {N-methyl-N- (p-methylphenyl) amino} -5-methoxy-7-dibenzylamino-
Fluorane, 3- {N-ethyl-N- (p-methylphenyl) amino} -6-methyl-fluorane, 3- {N-
Ethyl-N- (p-methylphenyl) amino} -5-methoxy-fluorane and the like.

The color developer is applied alone or as a mixture of two or more kinds. Similarly, the color-developing agent can be applied alone or in a mixture of two or more kinds. The thermochromic composition can be formed as a thermosensitive layer on a support and used as a reversible thermosensitive recording material. In this case, the reversible heat-sensitive recording material can be obtained by uniformly dispersing or dissolving a color former and a developer together with a binder in water or an organic solvent according to a conventionally known method, and coating this on a substrate. .

As the binder, various conventional binders can be appropriately used. Examples thereof include polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, methoxy cellulose, carboxymethyl cellulose, methyl cellulose, cellulose acetate, gelatin, casein, starch, polyacrylic acid. Soda, polyvinylpyrrolidone, polyacrylamide, maleic acid copolymer, acrylic acid copolymer, polystyrene, polyvinyl chloride, polyvinyl acetate, polyacrylic acid esters, polymethacrylic acid esters, vinyl chloride-vinyl acetate copolymer Examples include coalesced products, styrene-based copolymers, polyesters and polyurethanes.

In the present invention, various additives, such as dispersants, surfactants, and fillers, which are used in ordinary thermal recording paper, are used for the purpose of improving coating properties or recording properties as required.
It is also possible to add a color image stabilizer, an antioxidant, a light stabilizer, a lubricant and the like.

As described above, the protective layer and the intermediate layer may be provided if necessary.

The support (base) in the present invention may be paper, synthetic paper, plastic film or a composite thereof depending on the purpose of use and is not particularly limited. Further, the reversible thermosensitive recording medium of the present invention may be a long one or an endless one.

[0051]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. Parts herein are by weight.

(Production of reversible thermosensitive recording film) Behenic acid 7 parts Eicosane diacid 3 parts Diisodecyl phthalate 2 parts Vinyl chloride / vinyl acetate copolymer resin 40 parts on a polyester film (support) having a thickness of about 100 μm (VYHH manufactured by UCC) A solution containing 150 parts of THF and 15 parts of toluene was applied and dried to provide a thermosensitive recording layer (thickness: about 7 μm) made of a reversible thermosensitive recording material. Next, apply a liquid having the following composition on the heat-sensitive recording layer, dry it, and UV.
Irradiate and protect layer made of UV curable resin (about 2μ
m) is provided so that the second specific temperature becomes approximately 100 ° C. or higher and the white turbid state occurs, and the region of the first specific temperature is approximately 70 ° C. or higher 1
A reversible thermosensitive recording film having a characteristic of becoming transparent at a temperature of up to 00 ° C was prepared. (Composition of protective layer forming liquid) 75% butyric acid acetate solution of urethane acrylate UV curable resin (Dainippon Ink and Chemicals Co., Ltd .: Unidick C7-157) 10 parts Toluene 10 parts (Repeated image recording) Thermal recording prepared Image recording was repeated on the film by the following four methods using a thermal head, and the change in recording density was measured. The results are summarized in Table 1.

Example 1 A white turbid image was formed on a thermosensitive recording film with a thermal head and was made transparent with a heat roller, and this was repeated up to 500 times. The condition for forming a cloudy image on the reversible thermosensitive recording material was that the recording was performed at a recording pulse width of 2 ms with a line cycle of 20 ms, driven at 1 step / line by intermittent driving by a step motor. Here, in FIG.
Is about 2 ms, the period of (b) is about 1 ms, the period of (c) is about 17 ms, and the relationship between the movement period and the recording pulse is 2 m after 1 ms from the beginning of FIG. 1 (a).
The recording pulse of s was started, and the temperature of the reversible thermosensitive recording material was set to be the lowest at the head position of (a), that is, at the time of starting movement.

Example 2 The movement of the reversible thermosensitive recording material was controlled by changing the gear ratio.
Driving is performed in small steps in steps / lines, and the moving speed per line does not change, but neither the period of (b) nor the period of (c) is eliminated, and continuous driving is performed. Then, under the same conditions as in Example 1 except for the above, white turbid image formation and transparency were performed at 500 times.
Repeated up to times.

Example 3 FIG. 1A has a period of about 3 ms, and FIG. 1C has a period of about 17 ms.
The drive system was adjusted so that the reaction period of (b) did not occur in ms. Other than that, under the same conditions as in Example 1, the formation of the cloudy image and the clearing were repeated up to 500 times.

Example 4 A recording pulse having a pulse width of 2 ms was started up at the end of the period shown in FIG. 1a, and otherwise the white turbid image formation and the clearing were repeated up to 500 times under the same conditions as in Example 1. I repeated.

Comparative Example 1 The reversible thermosensitive recording material was moved by the same intermittent drive as in Example 1, and the relationship between the moving cycle and the print pulse was that the recording pulse was recorded at a time 15 ms after the beginning of FIG. It was set up so that the recording pulse falls just at the beginning of (a). Other than that, under the same conditions as in Example 1, the formation of the cloudy image and the clearing were repeated up to 500 times.

COMPARATIVE EXAMPLE 2 The reversible thermosensitive recording material was moved by the same intermittent drive as in Example 1, and the relationship between the moving cycle and the print pulse was that the recording pulse was 16 ms after the beginning of FIG. It was set up so that the timing of the beginning of (a) and the period of the recording pulse were exactly overlapped. Other than that, under the same conditions as in Example 1, the formation of the cloudy image and the clearing were repeated up to 500 times.

[0059]

[Table 1]

[0060]

According to the method of the present invention, it is possible to prevent the deterioration of the reversible thermosensitive recording material which is caused by the repeated image formation by the thermal head.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a method of the present invention.

FIG. 2 is a diagram for explaining formation / erasure of an image in the reversible thermosensitive recording material according to the present invention.

FIG. 3 is a diagram for explaining image formation / erasure in another reversible thermosensitive recording material according to the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI technical display location 8305-2H B41M 5/26 102 (72) Inventor Akihide Ito 1-3-3 Nakamagome, Ota-ku, Tokyo No. 6 Ricoh Co., Ltd.

Claims (4)

[Claims] 1. A reversible device which is brought into a first color state at a first specific temperature higher than room temperature and is heated to a second specific temperature higher than the first specific temperature and then cooled to be in a second color state. In an image recording method using a thermosensitive recording material and rewriting repeatedly with a thermal head, the thermal head and the reversible thermosensitive recording material are relatively moved, and at the moment of starting the movement, the reversible thermosensitive recording material. The image recording method is characterized in that the temperature of is lower than the average temperature reached by heating with a thermal head. 2. The image recording method according to claim 1, wherein the recording is performed by relatively and continuously moving a thermal head and a reversible thermosensitive recording material. 3. A reversible device which becomes a first color state at a first specific temperature higher than room temperature and becomes a second color state by heating and cooling at a second specific temperature higher than the first specific temperature. In an image recording method using a thermosensitive recording material and rewriting repeatedly with a thermal head, the thermal head and the reversible thermosensitive recording material are relatively intermittently moved, and the reversible recording is performed in one cycle of intermittent driving. It is characterized in that the pulse current of the heating element of the thermal head rises while the thermal recording material is moving with respect to the thermal head, and the period during which the pulse current is flowing and the timing of starting movement do not overlap. Image recording method. 4. The thermal head and the reversible thermosensitive recording material are moved relatively intermittently, and the reversible thermosensitive recording material is thermally moved while the reversible thermosensitive recording material is moving with respect to the thermal head or during a recoil period. The image recording method according to claim 3, wherein the pulse current of the heating element of the head falls.