JPH07172072A - Reversible thermal recording medium - Google Patents

Abstract

PURPOSE:To obtain excellent density and contrast even if image forming and erasing are repeated by a thermal head, etc., by specifying a thermal pressure difference of a thermal layer and its change rate. CONSTITUTION:A reversible thermal recording medium comprises a thermal layer in which transparency or color tone is reversibly changed depending upon a temperature and which is provided on a support, wherein a thermal pressure difference of the layer is 40% or less, and a thermal pressure difference change rate is 70% or less. A thermal pressure applying unit has an air regulator 103 of a pressure regulator, a print timer 105 of a time regulator, a temperature regulator 112 of a temperature regulator, a printing head 101 of a thermal pressure applying unit, and a sample support base 102 for supporting a recording medium. The head 101 improved for measurement of a thermal pressure difference amount is used.

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 material, and more specifically, repetitive writing and erasing of information mainly utilizing reversible transparency or color tone change depending on temperature of a thermosensitive layer (recording layer). The present invention relates to a reversible thermosensitive recording medium that can be performed and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, reversible thermosensitive recording media have attracted attention because they enable temporary image formation (writing of information) and can erase the image (erasing of information) when it is no longer needed. Typical examples thereof include higher fatty acids in a resin matrix such as a vinyl chloride-vinyl acetate copolymer having a glass transition temperature (Tg) of 50 to 60 ° C. to less than 80 ° C. and having a low glass transition temperature. A reversible thermosensitive recording medium in which various organic low-molecular substances are dispersed is known (JP-A-54).
-119377, JP-A-55-154198, etc.). However, in this reversible thermosensitive recording medium, distortion is generated in the recording layer during repeated image formation and erasure by a heating element such as a thermal head, and the image density during image formation is lowered and the contrast is lowered. There is a drawback that it will end up.

In order to solve the above-mentioned drawbacks and to improve the durability against repeated image formation / erasure by a thermal head, the present inventors have previously developed a resin such as vinyl chloride resin used in a reversible thermosensitive recording layer. We proposed a reversible thermosensitive recording medium in which the heat resistance of the resin base material was improved and the durability was improved by specifying the average polymerization degree and vinyl chloride unit content of the base material, and particularly by increasing the average polymerization degree ( JP-A-62-154
547, JP-A-5-169809, and JP-A-5-169810). Further, for the same purpose, a reversible thermosensitive recording medium having a reversible thermosensitive recording layer containing an epoxy resin was proposed (Japanese Patent Laid-Open No. 5-38872).
The use of these reversible thermosensitive recording media considerably reduces the abovementioned drawbacks.

Further, in JP-A-5-085045, a thermosetting resin comprising a hydroxyl-modified vinyl chloride-vinyl acetate copolymer and an isocyanate compound is used as a resin matrix used for a reversible thermosensitive recording layer, and heat resistance is used. A thermal recording medium has been proposed which has improved mechanical strength and improved repeated durability such as a thermal head.

By the way, in a reversible thermosensitive recording medium of a type in which an organic low molecular weight substance is dispersed in a resin, it usually becomes transparent in a certain temperature range and becomes cloudy at a higher temperature, and this state change is utilized. Although an image is recorded and erased, in order to reversibly change it to transparent and cloudy by heat, it is necessary that the range of the temperature at which the image becomes transparent be maintained to some extent wide and stable.

However, the thermosetting resin of this kind has a change in the degree of cure with time, and specifically, the degree of cure in forming the recording layer changes with the passage of time.
As the degree of hardness of the resin changes with time, the clearing temperature width also shrinks with time, making it impossible to erase in the initial image erasing temperature setting, and this erasing temperature setting becomes very complicated. is there. This problem is a new problem, and no solution has been proposed so far.

Recently, as a method of printing on such a reversible thermosensitive recording medium, printing is performed by a printer or the like under the same conditions as high energy printing on a low sensitivity thermosensitive recording medium (for example, a thermal destruction type thermosensitive recording medium). The number of systems used is increasing, and the energy applied in this case is in excess of the appropriate energy required for image formation of the reversible thermosensitive recording medium. Therefore, when printing is performed on the reversible thermosensitive recording medium with this thermal destruction type thermosensitive recording medium printer, the reversible thermosensitive recording medium is deteriorated by performing only one printing, and the density and the contrast are reduced in the subsequent printing. There is a problem that there is a tendency to run short. However, a solution to this problem has not been proposed yet.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and provides a thermal destruction type thermal recording medium printer even when image formation and erasure are repeatedly performed by a thermal head or the like. And a reversible thermosensitive recording medium having excellent durability and excellent durability even when repeatedly subjected to image formation and erasing with high energy, and having improved stability of the clearing temperature range over time. The manufacturing method is provided.

[0009]

According to the present invention, there is provided a reversible thermosensitive recording medium comprising a support and a thermosensitive layer whose transparency or color tone reversibly changes depending on temperature. A reversible thermosensitive recording medium, characterized in that the thermal pressure step is 40% or less and the thermal pressure step change rate is 70% or less, and in particular, the thermosensitive layer contains a resin and the resin is crosslinked. The reversible thermosensitive recording medium is provided. Further, in a reversible thermosensitive recording medium in which a thermosensitive layer whose transparency or color tone reversibly changes depending on temperature is provided on a support, the thermosensitive layer contains a resin, the resin is crosslinked, and a gel There is provided a reversible thermosensitive recording medium characterized by having a rate of change in fraction of 110% or less, and in particular, the reversible thermosensitive recording medium having a gel fraction value of the resin of 30% or more. Further, the resin is polyvinyl chloride,
At least one selected from chlorinated polyvinyl chloride, polyvinylidene chloride, saturated polyester, polyethylene, polypropylene, polystyrene, polymethacrylate, polyamide, polyvinylpyrrolidone, natural rubber, polyacrolein, polycarbonate, or a copolymer thereof. The resin is crosslinked using a crosslinking agent, and the resin is crosslinked by electron beam irradiation or ultraviolet rays, or
The reversible thermosensitive recording medium is characterized in that a protective layer is provided on the thermosensitive layer. Furthermore,
On the support, the transparency or color tone reversibly changes depending on the temperature, in the method for producing a reversible thermosensitive recording medium to form a thermosensitive layer containing a resin, electron beams or ultraviolet rays are irradiated multiple times, There is provided a method for producing the reversible thermosensitive recording medium, which comprises cross-linking a resin. Further, in the method for producing a reversible thermosensitive recording medium, the transparency or color tone of which is reversibly changed by heat on a support to form a thermosensitive layer containing a resin and an organic low molecular weight substance. Provided is a method for producing a reversible thermosensitive recording medium, which comprises heating at least a portion of the resin at a temperature at which it melts or higher and then crosslinking the resin.

In the present invention, the thermal pressure step amount and the thermal pressure step change rate of the thermosensitive layer which is the image display portion in the reversible thermosensitive recording medium are defined as follows. The thermal pressure step difference is a physical property that represents the hardness of the coating film when heated,
The smaller the value is, the harder the coating film is. When the value of the thermal pressure step difference is 40% or less, the durability to repetitive image formation and erasure by a thermal head or the like is remarkably improved. The reason is considered to be that the force that suppresses the aggregation and expansion of particles due to contact between organic low-molecular-weight substances suddenly increases, and as a result, the heat-sensitive layer is deformed even when heat and pressure are applied by a thermal head or the like. It is expected to decrease.

The thermal pressure step difference is measured by the following method. First, as a heat and pressure applying device, a hot stamp type air type desktop T made by Unique Machinery Co., Ltd. shown in FIG.
A C film eraser tester is used. FIG. 1A is a schematic view of the heat and pressure applying device as viewed from the front side, and FIG.
(B) is a schematic view seen from the side. As shown in this figure, the heat and pressure applying device includes an air regulator 103 as a pressure adjusting unit, a print timer 105 as a time adjusting unit, a temperature controller 112 as a temperature adjusting unit, and It is composed of a print head unit 101 in the drawing which is a thermal pressure application unit, and a sample support base 102 in the drawing which supports a recording medium. Further, the print head 101 in the figure is an improved print head for measuring the thermal pressure difference, and the print head shown in FIG. 2 is used. As the print head material, Al was used, and the surface roughness (Ry) of the portion of the projection X in contact with the surface of the heat-sensitive layer was 0.8 μm or less (JISB0
031-1982, B0601-1994. )
And the area of the protrusion is 0.225 cm ² .
Further, in order to prevent the pressure from being dispersed at the time of applying heat pressure to the sample support base 2 in the figure, as shown in FIG. 3, a 1 mm thick fluororubber (102-
2) A 1 mm-thick stainless steel plate (102-3) is placed on a support table to which (spring hardness Hs65) is attached.

Next, as a heat pressure application condition for measuring the heat pressure level difference amount, in the heat pressure application apparatus of FIG. The applied pressure is set to 0.5 kg / cm ² , then the print timer 105 in the figure is adjusted so that the application time is 10 seconds, and then the temperature controller 112 in the figure is set. It is adjusted and the applied temperature is set to 130 ° C. The applied temperature is 10 in the figure.
The value is adjusted by the heater and the temperature sensor of No. 8 and is approximately close to the temperature of the print head surface.

Next, a method of measuring the thermal pressure step difference value applied by the thermal pressure applying device will be described. As a measuring device, a two-dimensional roughness analyzer surf coder AY-41, recorder RA-60E and surf coder SE30K manufactured by Kosaka Laboratory Ltd. is used. First, the surf coder SE30K is set to a vertical magnification (V); 2000, lateral magnification (H); set to 20, and then surf coder AY-41 set to standard length (L); 5 mm, feed rate (Ds); 0.1 mm / se
The measurement result may be recorded in RA-60E after setting to c, and the thermal pressure level difference value (Dx) of the thermal pressure applying section may be read from the recorded chart. Further, these settings are examples, and can be arbitrarily changed according to the measurement.
In addition, this measurement is performed by applying a heat pressure applying part (1
The position is changed at intervals of 2 mm in the width direction of 01-1), and measurement is performed at 5 points D _{1 to} D ₅ , and the average value is set as the thermal pressure step average value (Dm).

The amount of thermal pressure step (D) is determined by the following equation from the average value of thermal pressure step (Dm) and the film thickness of the thermosensitive recording layer (DB). D: Thermal pressure step amount (%) Dm: Thermal pressure step average value (μm) DB: Thermal recording layer film thickness The thermal layer thickness (DB) is the thermal layer formed on the support as described above. And can be examined by observing a cross section of a TEM (transmission electron microscope), an SEM (scanning electron microscope) or the like as described above.

The thermal pressure step change rate is a physical property showing the degree of change in the hardness of the coating film during heating with time, and the smaller the numerical value, the more stable the coating film. When the thermal pressure step change rate is 70% or less, the effect of the present invention is remarkably exhibited, and particularly, the stability of characteristics such as the transparentizing temperature range and width of the recording medium is remarkably exhibited. It is considered that the stability of the thermal properties of the coating film is particularly improved at the boundary.

The thermal pressure step change rate is obtained by the following equation. Dc: Thermal pressure step change rate (%) DI: Initial thermal pressure step amount (%) DD: Temporal thermal pressure step amount (%) Here, the initial thermal pressure step amount (DI) is after the image display portion is formed. First, it is the value measured for the first time, and does not need to be the value immediately after formation. Next, the amount of thermal pressure difference over time (D
D) is the value measured after leaving the sample on which the image display section was formed at the same time as the initial stage in a 50 ° C. environment for 24 hours. It goes without saying that all of these are the values measured and calculated by the above-mentioned thermal pressure level difference measuring method. When measuring this thermal pressure step change rate, the above-mentioned conditions (2.
If a step is not possible at 5 kg / cm ² , 130 ° C.), it is possible to raise the pressure and temperature. This thermal pressure step difference measurement can be applied to both the reversible thermosensitive recording medium described above, 1) having only a recording layer, and 2) having a protective layer.

As for the layer structure of the reversible thermosensitive recording medium of the present invention, a thermosensitive recording layer and a magnetic recording layer containing a magnetic material as a main component are provided on a support as described in Japanese Utility Model Publication No. 2-3876. In addition to the above, a layer structure in which at least the portion directly below the heat-sensitive recording layer or the portion of the support corresponding to the heat-sensitive recording layer is colored is exemplified. Alternatively, as described in JP-A-3-130188, there may be mentioned a layer structure in which a magnetic recording layer is provided on a support, a light reflecting layer is provided thereon, and a heat sensitive layer is provided thereon. In this case, the magnetic recording layer may be provided on the back surface of the support or between the support and the heat-sensitive layer, and any other layer structure of these may be used.

Even with the layer structure of the reversible thermosensitive recording medium as described above, there is no problem in measuring the thermal pressure step amount, and even in such a structure, the thermal pressure can be applied to the surface of the thermal layer by applying the thermal pressure. The amount of step difference can be measured.

In the above-mentioned constitution, when the reversible thermosensitive layer is provided on the support and the protective layer is formed thereon, in order to expose the reversible thermosensitive layer on the surface and perform the measurement, There are the following methods. First, the film thicknesses of the reversible heat-sensitive layer and the protective layer may be checked by observing the cross section of the TEM, SEM, etc. described above, and then the film thickness of the protective layer may be removed. As shown in FIG. 5, the method of scraping off the protective layer is as follows. The medium (301) having the above structure is fixed to the support base (302) of a stainless steel plate having a thickness of 2 mm with the protective layer facing upward, and then the diameter of brass is used. Sandpaper (roughness 800
The surface-cutting member (303) wound with a No.) is placed on the above-mentioned protective layer, and is translated in a fixed direction (304) while supporting the cylinder so as not to rotate. At this time, the pressure applied from the normal direction is 1.0 to 1.5 kg / cm ² , and regarding the number of movements, first, the thickness of the medium (301) before surface cutting is measured with an electronic micrometer (film thickness meter). Then, the surface cutting may be performed, the thickness may be measured, and the surface cutting may be repeated until the thickness of the protective layer is removed. Here, it is possible that the surface becomes rough after cutting the protective layer, but even in that case, it is possible to specify the thermal pressure application part, so the surface roughness is not affected and the thermal pressure step measurement is not possible. it can.

In addition to the structure in which the protective layer is laminated on the recording layer as described above, an intermediate layer provided between the protective layer and the recording layer,
Alternatively, even in a configuration in which a printing layer provided on the protective layer, or a layer having a heat resistant film adhered on the recording layer is provided, it is possible to expose the recording layer surface by using the method described above. The pressure step amount can be measured.

The gel fraction change rate of the resin forming the heat-sensitive layer in the reversible thermosensitive recording medium of the present invention is a physical property showing the degree of change in the degree of crosslinking of the resin coating film constituting the heat-sensitive layer over time. The smaller the value, the more stable the degree of crosslinking of the coating film. When the gel fraction change rate is 110% or less, the hardness of the coating film and the stability of thermal properties are remarkably improved, and as a result, various characteristics such as the repeated durability of the recording medium and the clearing temperature are stable. It is believed that The gel fraction change rate is calculated by the following equation. Gc: change rate of gel fraction (%) GI: initial gel fraction value (%) GD: time-dependent gel fraction value (%) Here, the initial gel fraction value (GI) means the cross-linking of the heat-sensitive layer, First, it is the value measured the first time, and it need not be the value immediately after crosslinking. Next, the aged gel fraction value (GD) is 5 times the sample cross-linked at the same time as the initial gel fraction value (GI).
It is a value measured after being left in an environment of 0 ° C. for 24 hours.

In the reversible thermosensitive recording medium of the present invention, the gel fraction value of the resin in the thermosensitive layer is preferably 30% or more, and preferably 50% with respect to the effect of improving the image durability and the heat resistance by applying excess energy. % Or more, more preferably 7
It is 0% or more, particularly preferably 80% or more. As a gel fraction measuring method, a heat-sensitive layer is formed on a support to have an arbitrary thickness, and after electron beam irradiation, the film is peeled from the support and the initial weight of the film is measured. Sandwich it in a 400-mesh wire net and put it in a solvent in which the resin before cross-linking is soluble.
After soaking for a period of time and vacuum drying, the weight after drying was measured. The gel fraction is calculated by the following formula. Gel fraction (%) = [weight after drying (g) / initial weight (g)] × 100

When calculating the gel fraction by this calculation, it is necessary to exclude the weight of the organic low-molecular substance particles other than the resin component in the heat sensitive layer. In this case, the gel fraction is calculated by the following formula. . In the above, when the weight of the organic low-molecular weight substance is not known in advance, the weight ratio is calculated from the area ratio occupying per unit area and the specific gravity of each of the resin and the organic low-molecular weight substance by observing the cross section of the above-mentioned TEM, SEM, etc. The weight of the low molecular weight substance may be calculated to calculate the gel fraction value.

In addition to the above measuring method, when a reversible thermosensitive layer is provided on the support and the above-mentioned other layers are laminated on it, or between the support and the thermosensitive layer. When there are other layers as described above, first, as described above, the film thicknesses of the reversible thermosensitive layer and other layers are checked by observing the cross section of the above-mentioned TEM, SEM, etc. The surface of the layer corresponding to the film thickness is shaved to expose the surface of the reversible thermosensitive layer and the reversible thermosensitive layer is peeled off, and the gel fraction may be measured in the same manner as in the above measuring method. In this method, when there is a protective layer or the like made of an ultraviolet curable resin or the like on the upper layer of the heat sensitive layer, in order to prevent this layer from being mixed in as much as possible, the thickness of the protective layer is reduced and the heat sensitive layer surface is slightly removed. It is necessary to prevent the influence on the gel fraction value.

In addition to the above, there is the following gel fraction measuring method. First, using a Soxhlet extractor,
A method in which the uncured component in the cured film is extracted (4 hours) with a solvent in which the resin without crosslinking treatment is soluble and the weight fraction of the non-extracted residue is determined. A second method is to form a heat-sensitive layer coating film on a surface-treated PET support in the same manner as above, perform electron beam irradiation, and then immerse in a solvent to determine the film thickness ratio before and after immersion. A third method is a method similar to the second method in which a solvent is dropped by a dropper in an amount of about 0.2 cc with a dropper, left for 10 seconds, and then the solvent is wiped off to obtain the film thickness ratio before and after the dropping. In the first method, the weight of the organic low molecular weight substance may be excluded from the calculation as described above. In addition, since the second and third methods are based on film thickness measurement, it is considered that the film thickness does not change even after immersion in a solvent if the resin base material surrounding the organic low molecular weight substance is completely crosslinked. It is not necessary to consider organic low molecular weight substances as in the weight fraction method.

In the case of measuring the reversible thermosensitive layer on which another layer is provided as described above, the first method may be the same as the above-mentioned measuring method. Also, since the second and third methods are based on film thickness measurement, only the layer laminated on the reversible thermosensitive layer may be scraped and measured.

The present inventors analyzed and examined the mechanism of why the decrease in image density and contrast caused by repeated use of forming and erasing an image on a reversible thermosensitive recording medium occurs. As a result, when an image was formed by pressing a heating element such as a thermal head or a thermal destruction type thermal recording medium printer onto the surface of the recording medium, the following phenomenon was observed. In a reversible thermosensitive recording medium having a recording layer in which particles of an organic low-molecular substance are dispersed in a resin base material, the recording layer is used before the application of energy or when the number of repetitions is small during image formation and erasing by a heating element. There is no distortion that changes the state of existence of the material forming the material, and the organic low-molecular-weight substance particles are uniformly dispersed in the resin base material as shown in FIG. 6 (a). (As will be understood from the following, the recording layer of the present invention maintains the uniform dispersion state of the organic low molecular weight substance particles even after repeated recording and erasing.) However, during image formation, an image such as a heating element is formed on the recording medium. When the forming means is relatively moved while being pressed, stress is applied to the inside of the recording layer. During the repeated application of energy in the same direction, this stress is the main cause of occurrence of strain inside the recording layer in the direction of energy application, as shown in FIG. It will be in a deformed state. Then, as the energy application is further repeated in the same direction, the strain progresses, and the organic low-molecular substance particles deformed as shown in FIG. 6 (c) start to aggregate, and finally as shown in FIG. 6 (d). Then, the aggregated particles reaggregate with each other, and the organic low-molecular-weight substance particles are in a state of being maximized. In such a state, it becomes almost impossible to form an image, which is a so-called deteriorated state. It is considered that these phenomena are related to the cause of decrease in image density after repeated formation and deletion of an image on a reversible thermosensitive recording medium.

Further, the reason why the transparentization temperature range decreases with time as compared with the above-mentioned change in the curing degree is considered as follows. Here, first, before that, the mechanism of changing the cloudiness and transparency of the reversible thermosensitive recording material is presumed as follows. That is, in the case of (I) transparent, the particles of the organic low molecular weight substance dispersed in the resin base material are in close contact with the organic low molecular weight substance and the resin base material without a gap, and there is no void inside the particle. Light entering from one side is not scattered and is transmitted to the other side, so it looks transparent.
(II) In the case of white turbidity, the particles of the organic low molecular weight substance are composed of fine crystals of the organic low molecular weight substance, and there is a gap at the crystal interface or the interface between the particle and the resin base material, and the light incident from one side is It is derived from the fact that it looks white because it is refracted and scattered at the interface between voids and crystals and between voids and resin.

In FIG. 7 (representing the change in transparency due to heat), the heat-sensitive layer mainly composed of the resin base material and the organic low molecular weight substance dispersed in the resin base material is, for example, T ₀ or less. It is cloudy and opaque at room temperature. When this is heated, it gradually becomes transparent from the temperature T ₁ , and at the beginning temperatures T _{2 to} T ₃
When it is heated to ₀ , it becomes transparent, and it remains transparent even if it is returned to room temperature below T ₀ again in this state. This is because the resin begins to soften near the temperature T ₁ , and as the softening progresses, the resin shrinks to reduce the interface between the resin and the organic low-molecular substance particles or the voids in the particles, so that the transparency gradually increases and the temperature T increases. ₂
At ~ T ₃ , the organic low-molecular weight substance becomes semi-molten and becomes transparent by filling the remaining voids with the melted organic low-molecular weight substance. However, it is considered that because the resin is still in a softened state, the resin follows the volume change of the particles due to crystallization, and voids are not formed, so that the transparent state is maintained. Further heating to a temperature of T ₄ or higher results in a semitransparent state between the maximum transparency and the maximum opacity. Next, if you lower this temperature,
It returns to the first cloudy opaque state without taking the transparent state again. This is because after the organic low molecular weight substance has completely melted at a temperature of T ₄ or higher, it becomes a supercooled state and crystallizes at a temperature slightly higher than T ₀ , and at that time, the resin cannot follow the volume change accompanying the crystallization and the voids are formed. It seems to occur. However, the temperature-transparency change curve shown in FIG. 7 is only a representative example, and the transparency and the like of each state may change depending on the material by changing the material.

As described above, the softening point of the resin and the deformation behavior above the softening point are important for the change in transparency, but as described above, when the curing degree of the resin base material used in the heat-sensitive recording layer changes, As the degree of curing increases, the softening point of the resin also rises, and the deformation behavior above the softening point also changes, so the clearing temperature range will shrink over time compared to the initial stage. Conceivable.

As described above, the present inventors set the thermal pressure step difference of the thermosensitive layer of the reversible thermosensitive recording medium to 40% or less and the thermal pressure step change rate to 70% or less. I have found that the purpose is achieved. The preferred embodiment in this case is as follows. When the heat-pressure step difference of the heat-sensitive layer in the reversible heat-sensitive recording medium is 40% or less, it tends to particularly contribute to the improvement of the repeating durability. It is considered that this is because the recording medium of the present invention has a much smaller amount of thermal pressure difference in the heat-sensitive layer than the conventional one, that is, the heat resistance and mechanical strength of the heat-sensitive layer are very excellent. Thus, when an organic low molecular weight substance is contained in the heat-sensitive layer, aggregation or maximization of particles of this substance is unlikely to occur, and there is little deterioration after repeating image formation and erasing,
It is estimated that the high contrast is maintained. With respect to such effects, the thermal pressure step difference is preferably 40% or less,
It is preferably 30% or less, more preferably 25% or less, and particularly preferably 20% or less.

On the other hand, the thermal pressure step change rate of the heat sensitive layer is 70%.
The following will tend to particularly contribute to the suppression of the above-mentioned reduction in the transparentization temperature range. This is because the recording medium of the present invention has a very small thermal pressure step change rate of the heat-sensitive layer, that is, it is considered that the physical properties of the heat-sensitive layer do not change at the initial stage and the lapse of time, whereby the transparency temperature range It is presumed that the erasing characteristics will be stable without fluctuation and reduction in the clearing temperature range. In view of such effects, the thermal pressure step change rate is preferably 70% or less, preferably 50% or less, more preferably 45% or less, and particularly preferably 40%.
It is the following.

The resin used in the reversible thermosensitive recording layer is important in order to reduce the thermal pressure step change rate to 70% or less. It is necessary for this resin to maintain a certain degree of hardness when heated to a high temperature. Specifically, it is possible to use a resin having a high softening temperature, use a resin having a high softening temperature for the main chain and a resin having a low softening temperature for the side chain, or crosslink the resin. It is particularly preferable to crosslink the resin.

Further, as described above, in the present invention, the resin contained in the reversible thermosensitive layer of the reversible thermosensitive recording medium is crosslinked and the gel fraction change rate of the resin is 110.
The object of the present invention is achieved by controlling the content to be not more than%.
In this case, the gel fraction value of the resin is more preferably 30%.
By the above, it is more preferable to add a cross-linking agent to cross-link, and more preferably to cross-link by electron beam or ultraviolet irradiation, whereby these effects are further improved.

This is because the gel fraction change rate when the resin contained in the reversible thermosensitive layer is crosslinked in the recording medium of the present invention is very small, that is, the above-mentioned change in curing degree with time is very small. Therefore, it is presumed that the erasing characteristics described above are stabilized by this. To this effect, the gel fraction change rate is preferably 110% or less, preferably 90% or less, more preferably 70% or less, and particularly preferably 50% or less. Furthermore, in the recording medium of the present invention, since the gel fraction value when the resin is crosslinked is high, it is considered that the heat resistance and mechanical strength of the above-mentioned image display part are further improved. It is presumed that the print marks and crack resistance of the image display part will be further improved. For these effects, the gel fraction value is preferably 30% or more, preferably 50% or less, more preferably 70% or less.
% Or less.

The method of crosslinking the resin contained in the above reversible thermosensitive layer is carried out by heating or by irradiation with ultraviolet rays (U
V irradiation) or electron beam irradiation (EB irradiation), but ultraviolet irradiation and electron beam irradiation are preferable, and electron beam irradiation is more preferable. Among these crosslinking methods, the EB irradiation is the most excellent for the following reasons.

First, the major difference between the curing of resin by EB and that of UV is that UV curing requires a photopolymerization initiator and a photosensitizer, and UV is limited to those that are almost transparent. Is. On the other hand, in the reaction by EB,
Because the radical concentration is high, radical reaction progresses rapidly,
Polymerization may be instantaneously completed, and in EB, a larger energy may be obtained than in UV, so that the cured film thickness may be increased. Further, as described above, the UV curing requires a photopolymerization initiator and a photosensitizer, and since these additives remain in the recording layer after the crosslinking reaction, image forming, erasing and repeated durability of the recording layer There is an inconvenience that there is a concern that it may adversely affect the above.

Next, the major difference between EB curing and heat curing is that heat curing requires a catalyst and an accelerator for crosslinking, and even if these are used, the curing time is considerably slower than that of EB curing, and As for the above, since the above additives remain in the recording layer after the crosslinking reaction, the same disadvantages as in the case of UV curing may occur, and since the crosslinking reaction may occur little after the crosslinking reaction, the characteristics of the recording layer change immediately after crosslinking and over time. May occur. For these reasons, it can be said that EB irradiation is the most suitable crosslinking method. In addition, it was also confirmed that the deterioration of the image density in high-energy printing was reduced and high contrast was maintained. The present invention has been made based on these findings.

The method of the present invention will be described in more detail below.
The "thermosensitive layer (transparency or color tone reversibly changes depending on temperature)" used in the reversible thermosensitive recording medium of the present invention is a material that reversibly causes visible changes due to temperature changes. The visible change can be divided into a change in color state and a change in shape, but the present invention mainly uses a material that causes a change in color state. The change in color state includes the transmittance,
There are changes in reflectance, absorption wavelength, scattering degree, etc., and the actual reversible thermosensitive recording material displays by a combination of these changes. More specifically, anything that reversibly changes transparency and color tone by heat may be used, but for example, the first color state is reached at a first specific temperature higher than room temperature and higher than the first specific temperature. The second color state can be obtained by heating at the second specific temperature and then cooling. In particular, the one whose color state changes between the first specific temperature and the second specific temperature is preferably used. As an example of these, a transparent state is obtained at a first specific temperature and a cloudy state is obtained at a second specific temperature (Japanese Patent Laid-Open No. 55-154198).
JP-A-4-224996, JP-A-4-224996, which develops color at a second specific temperature and erases color at a first specific temperature.
No. 247985, Japanese Patent Laid-Open No. 4-267190, etc.), a cloudy state at a first specific temperature and a transparent state at a second specific temperature (Japanese Patent Laid-Open No. 3-169590), a first specific temperature. That develops black, red, blue, etc. at a second specific temperature (JP-A-2-188293,
JP-A-2-188294) and the like. Of these, the following two materials are particularly representative. A material in which the transparent and cloudy states change reversibly A material in which the color of dyes and the like changes chemically

As a typical example of the heat sensitive layer, as described in the prior art and as has been repeatedly described above, a thermosensitive layer in which an organic low molecular weight substance such as a higher alcohol or a higher fatty acid is dispersed in a resin base material such as polyester. Can be mentioned. Also,
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 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. The thermoreversible recording medium of the present invention 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 as described in FIG. 7 above. .

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 disposing 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 the white background or an image of the white background 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.

The thickness of the heat sensitive layer is preferably 1 to 30 μm,
2 to 20 μm is more preferable. If the recording layer is too thick, heat distribution will occur in the layer and it will be difficult to make it transparent uniformly. On the other hand, if the heat-sensitive layer is too thin, the white turbidity is lowered and the contrast is lowered. The white turbidity can be increased by increasing the amount of fatty acid in the recording layer.

To prepare the reversible thermosensitive recording medium (1), a thermosensitive layer is formed on a support by the following method, for example. In some cases, the sheet may be formed without using the support. 1) Dissolve a resin base material and an organic low molecular weight substance in a solvent, coat this on a support, evaporate the solvent to form a film or sheet and then crosslink, or after forming into a sheet, crosslink Method. 2) Dissolve the resin base material in a solvent that dissolves only the resin base material, pulverize or disperse the organic low molecular weight substance in the solvent by various methods, apply this on a support, and evaporate the solvent to form a film or A method in which a sheet is formed and crosslinked, or a sheet is formed and then crosslinked. 3) A method in which a resin base material and an organic low molecular weight substance are heated and melt-mixed without using a solvent, formed into a film or a sheet, cooled, and then crosslinked. As the solvent for forming the heat-sensitive layer or the heat-sensitive recording medium, various selections can be made according to the types of the resin base material and the organic low molecular weight substance,
Examples thereof include tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. The organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the heat-sensitive layer obtained not only when the dispersion liquid is used but also when the solution is used.

In the present invention, the resin used as the resin base material of the thermosensitive layer of the reversible thermosensitive recording medium is preferably a resin which can form a film or sheet, has good transparency and is mechanically stable. Such a resin is selected from polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene chloride, saturated polyester, polyethylene, polypropylene, polystyrene, polymethacrylate, polyamide, polyvinylpyrrolidone, natural rubber, polyacrolein and polycarbonate. Examples thereof include those containing at least one kind or two or more kinds, or those containing a copolymer thereof. In addition, polyacrylate, polyacrylamide, polysiloxane, polyvinyl alcohol,
Alternatively, these copolymers can also be used.

More specifically, polyvinyl chloride: vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-
Vinyl alcohol copolymer, vinyl chloride-vinyl acetate-
Vinyl chloride copolymers such as maleic acid copolymers and vinyl chloride-acrylate copolymers; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-
Vinylidene chloride-based copolymers such as acrylonitrile copolymers; polymethacrylate, methacrylate copolymers and the like.

Furthermore, when a vinyl chloride copolymer is used as the resin, the average degree of polymerization of these polymers is P = 300.
Or more, more preferably P = 600 or more, and the polymerization ratio of the vinyl chloride unit and the copolymerization monomer unit is preferably 90/10 to 60/40, and more preferably 85/15 to 65/35. . The glass transition temperature (Tg) of the resin used as the resin base material is preferably 10
It is lower than 0 ° C, more preferably lower than 90 ° C, and particularly preferably lower than 80 ° C.

On the other hand, as the organic low molecular weight substance, particles having a melting point of 30 to 200 ° C., preferably about 50 to 150 ° C. are generally used as long as they are particles in the recording layer. 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; allylcarboxylic acids or their esters, amides or ammonium salts; halogenallylcarboxylic acids or Of their esters, amides or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amines or ammonium salts; of thioalcohols Carboxylic acid esters, and the like. These may be used alone or in admixture of two or more. The carbon number of these compounds is preferably 10 to 60, preferably 10 to 38, and particularly preferably 10 to 30. 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 kind of oxygen, nitrogen, sulfur and halogen in the molecule, for example, -OH, -COOH, -CON.
_{H, -COOR, -NH, -NH 2} , -S -, - S-S
A compound containing-, -O-, halogen or the like is preferable.

In the present invention, it is preferable to use a combination of a low melting point organic low molecular weight substance and a high melting point organic low molecular weight substance as the organic low molecular weight substance because the transparency temperature range can be further expanded. . The difference in melting point between the low melting point organic low molecular weight substance and the high melting point organic low molecular weight substance is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, and particularly preferably 40 ° C. or higher. The low melting point organic low molecular weight material preferably has a melting point of 40 ° C to 100 ° C,
The thing of 50 to 80 degreeC is more preferable. The high-melting point organic low-molecular substance preferably has a melting point of 100 ° C to 200 ° C, more preferably 110 ° C to 180 ° C.

Among these organic low molecular weight substances, the low melting point organic low molecular weight substances used in the present invention are preferably the following fatty acid esters, dibasic acid esters and polyhydric alcohol difatty acid esters. These may be used alone or in combination of two or more.

The fatty acid ester used in the present invention has a melting point lower than that of a fatty acid having the same carbon number (in a two-molecule association state),
On the contrary, it has the characteristic that it has more carbon atoms than fatty acids of the same melting point. Deterioration due to repeated printing and erasing of images with the thermal head is considered to be due to the change in the dispersed state of the organic low-molecular substance particles due to the compatibility of the resin base material and the organic low-molecular substance during heating. It is considered that the compatibility of the organic low-molecular weight substance decreases as the carbon number of the organic low-molecular weight substance increases, and the deterioration in printing / erasing of an image is small. Further, the white turbidity also tends to increase in proportion to the carbon number. Therefore, in the reversible thermosensitive recording medium of the same clearing temperature (near the melting point),
By using a fatty acid ester as the organic low molecular weight substance to be dispersed in the resin base material, it is considered that the white turbidity is high, that is, the contrast is high and the repeating durability is improved as compared with the case of using the fatty acid. By mixing such a fatty acid ester with a high-melting-point organic low-molecular substance, the transparent temperature range can be widened and the erasing performance with the thermal head is high. Even if the characteristics fluctuate, it can be erased, and the repeated durability can be improved due to the characteristics of the material itself.

The fatty acid ester used in the present invention is represented by, for example, the following general formula. R ₁ —COO—R ₂ (In the formula, R ₁ and R ₂ represent an alkyl group having 10 or more carbon atoms.) The fatty acid ester preferably has 20 or more carbon atoms, more preferably 25 or more carbon atoms, and particularly preferably 30 or more carbon atoms. . When the carbon number is high, the white turbidity is high and the repeated durability is improved. The melting point of the fatty acid ester is preferably 40 ° C or higher. These may be used alone or in combination of two or more.

Specific examples of the fatty acid ester used in the present invention are shown below. Octadecyl laurate Docosyl laurate Docosyl myristate Dodecyl palmitate Dodecyl palmitate Tetradecyl palmitate Pentadecyl palmitate Hexadecyl palmitate Octadecyl palmitate Tricontyl palmitate Octadecyl palmitate Isopropyl stearate Butyric acid stearate stearate propyl stearate stearate propyl stearate stearate Heptyl Octyl stearate Tetradecyl stearate Hexadecyl stearate Heptadecyl stearate Heptadecyl stearate Octadecyl stearate Docosyl stearate Hexacosyl stearate Triaconyl stearate Dodecyl behenate Octadecyl behenate Tracosyl lignocerate tracosyl myricin melicate

The dibasic acid ester may be either a monoester or a diester and is represented by the following general formula.

[Chemical 1] (In the formula, R and R'represent a hydrogen atom or an alkyl group having 1 to 30 carbon atoms, and R and R'may be the same or different, except when they are simultaneously hydrogen atoms. n represents an integer of 0 to 40.) In the dibasic acid ester represented by the general formula (III), the alkyl group of R and R ′ preferably has 1 to 22 carbon atoms, and n has 1 to 30 carbon atoms. Preferably, 2 to 20 is more preferable. The melting point is preferably 40 ° C or higher.

Specifically, oxalic acid ester malonic acid ester succinic acid ester glutaric acid ester adipic acid ester pimelic acid ester suberic acid ester azelaic acid ester sebacic acid ester 1-, 9-nonamethylene dicarboxylic acid ester 1-, 10-deca Methylenedicarboxylic acid ester 1-, 11-undecamethylenedicarboxylic acid ester 1-, 12-dodecamethylenedicarboxylic acid ester 1-, 13-tridecamethylenedicarboxylic acid ester 1-, 14-tetradecamethylenedicarboxylic acid ester 1-, 15-Pentadecamethylenedicarboxylic acid ester 1-, 16-hexadecamethylenedicarboxylic acid ester 1-, 17-heptadecamethylenedicarboxylic acid ester 1-, 18-octadecamethylenedicarboxylic acid ester Ter 1-, 19-nonadecamethylene dicarboxylic acid ester 1-, 20-eicosamethylene dicarboxylic acid ester 1-, 21-heneicosamethylene dicarboxylic acid ester 1-, 22-docosamethylene dicarboxylic acid ester 1-, 24- Examples thereof include tetracosamethylene dicarboxylic acid ester 1-, 28-octacosamethylene dicarboxylic acid ester 1-, 32-dotriacontamethylene dicarboxylic acid ester.

Examples of the polyhydric alcohol difatty acid ester of an organic low molecular weight substance used in the present invention include those represented by the following general formula. CH ₃ (CH ₂ ) m- ₂ COO (CH ₂ ) nOOC (CH ₂ ) m- ₂ CH ₃ (In the formula, n is 2 to 40, preferably 3 to 30, and more preferably 4 to 22 is an integer. M is an integer of 2 to 40, preferably 3 to 30, and more preferably 4 to 22.) Specific examples include the following. 1,2 ethanediol dialkanoic acid ester 1,3 propanediol dialkanoic acid ester 1.4 butanediol dialkanoic acid ester 1.5 pentanediol dialkanoic acid ester 1,6 hexanediol dialkanoic acid ester 1,7 heptanediol Dialkanoic acid ester 1,8 Octanediol dialkanoic acid ester 1,9 Nonanediol dialkanoic acid ester 1,10 Decanediol dialkanoic acid ester 1,11 Undecanediol dialkanoic acid ester 1,12 Dodecanediol dialkanoic acid ester 1 , 13 Tridecanediol dialkanate 1,14 Tetradecanediol dialkanate 1,15 Pentadecanediol dialkanate 1,16 Hexadecanediol dialkanate 1, 7 Heptadecanediol dialkanate 1,18 Octadecanediol dialkanate 1,19 Nonadecanediol dialkanate 1,20 Icosandiol dialkanate 1,21 Henicosandiol dialkanate 1, 22 Docosanediol dialkanate 1,23 Tricosanediol dialkanate 1,24 Tetracosanediol dialkanate 1,25 Pentacosanediol dialkanate 1,26 Hexacosandiol dialkanate 1, 27 Heptacosanediol dialkanate 1,28 Octacosanediol dialkanate 1,29 Nonacosandiol dialkanate 1,30 Triacontanediol dialkanate 1 , 31 Hentriacontanediol dialkanate 1,32 Dotriacontanediol dialkanate 1,33 Tritriacontanediol dialkanate 1,34 Tetratriacontanediol dialkanate

The alcohol difatty acid ester having a temperature of 35 ° C. or higher includes the following. As the polyhydric alcohol, 1,4 butanediol, 1,5 pentanediol, 1,6 hexanediol, 1,7 heptanediol, 1,8 octanediol, 1,9 nonanediol,
1,10 decanediol, 1,11 undecanediol, 1,12 dodecanediol, 1,13 tridecanediol, 1,14 tetradecanediol, 1,15 pentadecanediol, 1,16 hexadecanediol,
1,17 heptadecane diol, 1,18 octadecane diol, 1,19 nonadecane diol, 1,20 icosane diol, 1,21 hen icosane diol, 1,2
2 docosanediol, 1,23 tricosanediol,
1,24 tetracosane diol, 1,25 pentacosane diol, 1,26 hexacosane diol, 1,27 heptacosane diol, 1,28 octacosane diol,
1,29 Nonacosandiol, 1,30 Triacontanediol, 1,31 Hentriacontanediol, 1,
Dilaurate using a diol selected from 32 dotriacontanediol, 1,33 tritriacontanediol, and 1,34 tetratriacontanediol,
Ditridecate, dimyristate, dipentadecate,
Examples thereof include dipalmitate, dimalgallate, distearate, dinonadecate, diarachicade, dihen icosate and dibehenate.

The polyhydric alcohol difatty acid ester is characterized in that it has a lower melting point than a fatty acid when compared with the same carbon number, and conversely has a higher carbon number than the fatty acid when compared with the same melting point. The repeated durability of printing with the thermal head is considered to be due to the compatibility of the resin and the organic low molecular weight substance during heating,
It is considered that the compatibility between the resin and the organic low molecular weight substance decreases as the carbon number of the organic low molecular weight substance increases. Further, the white turbidity also tends to increase in proportion to the number of carbon atoms. Therefore, by using a polyhydric alcohol difatty acid ester, as compared with a fatty acid in a reversible thermosensitive recording material having the same clearing temperature (which is near the melting point), Repeated durability seems to be improved.

Further, since the polyhydric alcohol difatty acid ester has a low melting point and has the same characteristics as the fatty acid having a higher melting point in terms of white turbidity and repeated durability, it is different from the organic low molecular weight substances having a higher melting point. When mixed and widened the clearing temperature range, the clearing temperature range can be expanded while having the same white turbidity and repeated durability as when using a fatty acid. Image erasing (transparency) by heating in a short time can be improved, and even if the image erasing energy fluctuates over time due to an increased image erasing margin, there is no practical problem and erasing with a thermal head is possible. Will also be possible.

Next, as the high melting point organic low molecular weight substance used in the present invention, aliphatic saturated dicarboxylic acid, ketone having a higher alkyl group, semicarbazone derived from the ketone, α-phosphono fatty acid and the like can be mentioned. The following are preferable, but not limited thereto. These are used alone or in combination of two or more.

Specific examples of these organic low molecular weight substances having a melting point of 100 ° C. or higher are shown below. Specific examples of the aliphatic dicarboxylic acid having a melting point of about 100 to 135 ° C. include, for example,
Succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid,
Dodecanedioic acid, tetradecanedioic acid, pentadecanedioic acid,
Hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, nonadecanedioic acid, eicosanedioic acid, heneicosanedioic acid, docosanedioic acid and the like can be mentioned.

The ketone used in the present invention contains a ketone group and a higher alkyl group as essential constituent groups, and may also contain an unsubstituted or substituted aromatic ring or primed ring. The total number of carbon atoms in the ketone is preferably 16 or more, more preferably 21 or more. The semicarbazone used in the present invention is derived from the above ketone. Examples of the ketone and semicarbazone used in the present invention include those shown in Table 1 below.

[0063]

[Table 1- (1)]

[Table 1- (2)]

[Table 1- (3)]

The α-phosphono fatty acid used in the present invention is, for example, E. V. Kaurer et al. Ak. Oil Che
Fatty acids were converted to Hell-Volhard-Zel according to the method of kist's Soc, 41, 205 (1964).
Bromination by the inskin reaction to α-brominated acid bromide, then ethanol was added to obtain α-promo fatty acid ester, which was further heated and reacted with triethylphosphite to give α-phosphono fatty acid ester, which was hydrolyzed with concentrated hydrochloric acid. It can be obtained by recrystallizing the product from toluene. Specific examples of the phosphono fatty acid used in the present invention are shown below. alpha-phosphono pelargonic acid CH ₃ (CH _{2) 6} CH [PO (OH) _2] COOH (mp 130-1 ℃) α- Hosuhonokapuriru acid CH ₃ (CH _{2) 7} CH [PO (OH) _2] COOH (mp 131-2 ℃, mp 16
2-4 ° C) α-phosphonolauric acid CH ₃ (CH ₂ ) ₉ CH [PO (OH) ₂ ] COOH (mp 131-2 ° C, mp 16
2-3 ℃) α-phosphonomyristylic acid CH ₃ (CH ₂ ) ₁₁ CH [PO (OH) ₂ ] COOH (mp 132-3 ℃, mp 15
3-6 ° C) α-phosphonopalmitic acid CH ₃ (CH ₂ ) ₁₃ CH [PO (OH) ₂ ] COOH (mp 132-3 ° C, mp 15
6-65 ° C) α-phosphonostearic acid CH ₃ (CH ₂ ) ₁₅ CH [PO (OH) ₂ ] COOH (mp 130-1 ° C, mp 15
7-65 ℃). It should be noted that it has two mps (melting points) other than α-phosphonoberargonic acid.

The mixing weight ratio of the low melting point organic low molecular weight substance and the high melting point organic low molecular weight substance is 95: 5 to 5:95.
Is preferable, 90:10 to 10:90 is more preferable,
80:20 to 20:80 are particularly preferable. In addition to these low melting point and high melting point organic low molecular weight substances, other organic low molecular weight substances described above may be mixed and used. These include the following.

These compounds include lauric acid and dodeca.
Acid, myristic acid, pentadecanoic acid, palmitic acid,
Stearic acid, behenic acid, nonadecanoic acid, aragic acid,
Higher fatty acids such as oleic acid; Etc., such as ether or thioether. Above all, the present invention
Higher fatty acids, especially palmitic acid, pentadecanoic acid,
Nonadecanoic acid, arachidic acid, stearic acid, behenic acid,
Higher fatty acids having 16 or more carbon atoms such as lignoceric acid are preferred.
However, higher fatty acids having 16 to 24 carbon atoms are more preferable.

As described above, in the present invention, in order to widen the range of temperature at which the material can be made transparent, the organic low molecular weight substances described in this specification may be appropriately combined, or other organic low molecular weight substances having different melting points may be used. The above materials may be combined. These are disclosed in, for example, JP-A-63-39378 and JP-A-63-130380, and Japanese Patent Application No. 63-1.
Although disclosed in the specifications such as 4754 and Japanese Patent Application No. 3-2089, the present invention is not limited to these.

The ratio of the organic low molecular weight substance to the resin (resin having a crosslinked structure) in the heat sensitive layer is 2: 1 by weight.
˜1: 16 is preferable, and 1: 2 to 1: 8 is more preferable. When the ratio of the resin is less than this, it becomes difficult to form a film in which the organic low molecular weight substance is held in the resin, and when the ratio of the resin is more than that, it is difficult to make the opacity because the amount of the organic low molecular weight substance is small. .

In addition to the above components, additives such as a surfactant and a plasticizer 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. As the plasticizer, phosphoric acid ester, fatty acid ester, phthalic acid ester, dibasic acid ester,
Glycols, polyester-based plasticizers, and epoxy-based plasticizers are mentioned, and specific examples are as follows. Tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, phthalate. Acid di-2-ethylhexyl, diisononyl phthalate, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate,
Di-n-hexyl adipate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate , Methyl acetylricinoleate, butyl acetylricinoleate, butylphthalylbutyl glycolate, tributyl acetylcitrate and so on.

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 , Oil or fat or lower olefin oxide adduct of polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salt of higher alkylbenzene sulfonic acid; aromatic carboxylic acid, higher fatty acid sulfonic acid, aromatic sulfonic acid, sulfuric acid monoester or phosphoric acid Mono- or di-ester C
a, Ba or Mg salt; low-sulfated oil; poly long-chain alkyl acrylate; acrylic orgomer; poly long-chain alkyl methacrylate; long-chain alkyl methacrylate-amine-containing monomer copolymer; styrene-maleic anhydride copolymer; Olefin-maleic anhydride copolymer etc.

Subsequently, the reversible thermosensitive recording medium of the present invention is
In addition, the heat-sensitive layer also includes a layer utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound,
What utilizes such a reversible thermochromic reaction will be described below. The color-forming reaction utilizes a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound, and a thermochromic composition comprising these compounds is When the electron-accepting compound is heated and melt-mixed, an amorphous color-forming material is formed, while when the amorphous color-forming material is heated at a temperature lower than the melting temperature, the electron-accepting compound is crystallized. This phenomenon utilizes the phenomenon that the color-developing body is decolored due to the generation of color.

The thermochromic composition instantly develops color upon heating, and the color development state thereof is stable even at room 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 decoloring, that is, image formation and image erasing when this composition is used as a heat-sensitive layer will be described with reference to the graph shown in FIG. The vertical axis of the graph represents the color density, the horizontal axis represents the temperature, the solid line represents the image forming process by heating, and the broken line represents the image erasing process by heating. A is the concentration in the completely erased state,
B is the density in a completely colored state when heated to a temperature of T ₆ or higher, C is the density at a temperature of T ₅ or lower in the completely colored state, and D is heat-erased at a temperature between T _{5 and} T ₆ . The concentration at the time is shown.

This composition according to the present invention is in a colorless state (A) at a temperature of T ₅ or lower. To perform recording (image formation), a color image (B) is formed by heating to a temperature of T ₆ 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 ₅ or less 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 _{5 and} T _{6 which} is lower than the color development temperature, whereby the colorless state (D) is obtained. In this state, the colorless state (A) is maintained as it is even if the temperature is returned to T ₅ or lower. 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 behavioral characteristics of forming and erasing 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, and further contains a binder resin if necessary. 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, the heat-sensitive layer is T ₆
By performing the process of decoloring after heating to the above temperature, the particles of the color-developing agent and the color-developing agent return to their original state, which is advantageous in forming a new color-developed state.

A composition comprising a conventional color-developing agent and a color-developing agent, 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 having a color-developing effect. When this is melt-mixed by heating, it becomes a colored 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, there is no ring closure of the lactone ring and decolorization. I don't.

On the other hand, when the composition of the color former and the developer according to the present invention is also 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 former. 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 developing and decoloring behavior observed in the thermochromic composition is the mutual solubility of the color former and the color developer by heating and melting, the strength of both actions in the color developing state, and the color developer. 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, in the reversible thermochromic composition system according to the present invention, if necessary, a third substance such as a binder resin can be present. It was confirmed that the decoloring behavior was retained.
The binder resin may be the same as the resin base material forming the heat-sensitive layer of the reversible heat-sensitive recording medium.
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, the color developing agents preferably used in the present invention are exemplified below. As described above, the color developing agents 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 R ₁ —PO (OH) ₂ (wherein R ₁ represents a linear or branched alkyl group or alkenyl group having 8 to 30 carbon atoms) Specific examples of the phosphoric acid compound include the following. 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 R ₂ —CH (OH) COOH (wherein R ₂ is a linear or branched alkyl group having 6 to 28 carbon atoms) 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, α-hydroxyeicosanoic acid, α-hydroxydocosanoic acid and the like.

The color former used here is a compound exhibiting an electron-accepting property, and is itself a colorless or light-colored dye precursor, and is not particularly limited.
There are triphenylmethanephthalide-based compounds, fluoran-based compounds, phenothiazine-based compounds, leucoauramine-based compounds, rhodamine-lactam-based compounds, spiropyran-based compounds, indolinophtalide-based compounds, and the like. To be 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-Diethylaminofluorane, 2- {3,6-bis (diethylamino) -6- (o
-Chloranilino) xanthyl benzoate lactam}, 3
-Diethylamino-6-methyl-7- (m-trichloromethylanilino) fluorane, 3-diethylamino-7
-(O-chloranilino) fluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-N
-Methyl-N-amylamino-6-methyl-7-anilinofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- Anilino Fluoran, 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'-dimethylaminophenyl) -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) fluorane, 3-diethylamino-5-
Chloro-7- (N-benzyl-trifluoromethylanilino) fluorane, 3-pyrrolidino-7- (di-p-chlorophenyl) methylaminofluorane, 3-diethylamino-5-chloro-7- (α-phenyl Ethylamino) 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) fluorene spiro (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.

The means for cross-linking the resin in the heat-sensitive layer in the present invention may be heating or irradiation with ultraviolet rays,
It can be carried out by electron beam irradiation, but among these, it is most suitable to carry out electron beam irradiation. The method of cross-linking these is specifically as follows. (I) a method of using a resin having crosslinkability, (ii) a method of adding a crosslinking agent, (iii) a method of crosslinking by irradiation with an ultraviolet ray or an electron beam, (iv) an ultraviolet ray in the presence of a crosslinking agent, Alternatively, there is a method of crosslinking by irradiation with an electron beam. The cross-linking agent includes a non-functional monomer and a functional monomer, and specific examples include the following.

Examples of non-functional monomers: (1) methyl methacrylate (MMA) (2) ethyl methacrylate (EMA) (3) n-butyl methacrylate (BMA) (4) i-butyl methacrylate (IBMA) (5) t-butyl methacrylate (TBMA) (6) 2-ethylhexyl methacrylate (EHMA) (7) lauryl methacrylate (LMA) (8) alkyl methacrylate (SLMA) (9) tridecyl methacrylate (TDMA) ( 10) Stearyl Methacrylate (SMA) (11) Cyclohexyl Methacrylate (CHMA) (12) Benzyl Methacrylate (BZMA)

Examples of monofunctional monomers: (13) Methacrylic acid (MMA) (14) 2-Hydroxyethyl methacrylate (HEMA) (15) 2-Hydroxypropyl methacrylate (HPM)
A) (16) Dimethylaminoethyl Methacrylate (DMMA) (17) Dimethylaminoethyl Methacrylate Methacrylate (DMCMA) (18) Diethylaminoethyl Methacrylate (DEMA) (19) Glycidyl Methacrylate (GMA) (20) Methacryl Tetrahydrofurfuryl acid (THFM
A) (21) Allyl methacrylate (AMA) (22) Ethylene glycol dimethacrylate (EDMA) (23) Triethylene glycol dimethacrylate (3ED
MA) (24) Tetraethylene glycol dimethacrylate (4E
DMA) (25) 1,3-butylene glycol dimethacrylate (B
DMA) (26) 1,6-hexanediol dimethacrylate (HX
MA) (27) Trimethylolpropane trimethacrylate (TM)
PMA) (28) 2-Ethoxyethyl methacrylate (ETMA) (29) 2-Ethylhexyl acrylate (30) Phenoxyethyl acrylate (31) 2-Ethoxyethyl acrylate (32) 2-Ethoxyethoxyethyl acrylate (33) 2-Hydroxy Ethyl acrylate (34) 2-Hydroxypropyl acrylate (35) Dicyclopentenyloxyethyl acrylate (36) N-vinylpyrrolidone (37) Vinyl acetate

Examples of bifunctional monomers: (38) 1,4-butanediol acrylate CH₂= CHCOO (CH₂)_FourOOCCH = CH₂ (39) 1,6-hexanediol diacrylate CH₂= CHCOO (CH₂)₆OCOCH = CH₂ (40) 1,9-Nonanediol diacrylate CH₂= CHCOO (CH₂)₉OCOCH = CH₂ (41) Neopentyl glycol diacrylate CH₂= CHCOOCH₂-C (CH₃)₂CH₂OOCC
H = CH₂ (42) Tetraethylene glycol diacrylate CH₂= CHCOO (CH₂CH₂O)_FourOCCH = CH₂ (43) Tripropylene glycol diacrylate(44) Tripropylene glycol diacrylate (45) Polypropylene glycol diacrylate(46) Bisphenol A. EO adduct diacrylate

[Chemical 2] (47) Glycerin methacrylate acrylate

[Chemical 3] (48) Diacrylate of neopentyl glycol with 2 mol addition of propylene oxide (49) Diethylene glycol diacrylate (50) Polyethylene glycol (400) Diacrylate (51) Diacrylate of ester of hydroxypivalic acid and neopentyl glycol (52) 2 , 2-Bis (4-acryloxydiethoxyphenyl) propane (53) Diacrylate of neopentyl glycol adipate

[Chemical 4] (54) Diacrylate of ε-caprolactone adduct of neopentyl glycol hydroxypivalate

[Chemical 5] (55) Diacrylate of ε-caprolactone adduct of neopentyl glycol hydroxypivalate

[Chemical 6] (56) 2- (2-hydroxy-1,1-dimethylethyl) -5-hydroxymethyl-5-ethyl-1,3-dioxane diacrylate

[Chemical 7] (57) Tricyclodecane dimethylol diacrylate

[Chemical 8] (58) ε-caprolactone adduct of tricyclodecane dimethylol diacrylate

[Chemical 9] (59) Diacrylate of diglycidyl ether of 1,6-hexanediol

[Chemical 10]

Examples of polyfunctional monomers: (60) trimethylo
Propane triacrylate (61) Pentaerythritol triacrylate (62) Glycerin PO-added triacrylate

[Chemical 11](63) Tris acryloyloxyethyl phosphate (CH₂= CHCOOCH₂CH₂O)₃PO (64) pentaerythritol tetraacrylate (65) Propylene oxide of trimethylolpropane
3-Mole adduct triacrylate (66) Glyceryl propoxy triacrylate (67) Dipentaerythritol polyacrylate (68) Caprolactone adduct of dipentaerythritol
Polyacrylate (69) Propionic Acid / Dipentaerythritol Triac
Related (70) Hydroxypivalaldehyde modified dimethylol
Ropin triacrylate  (71) Tetra of propionic acid / dipentaerythritol
Acrylate(72) Ditrimethylolpropane tetraacrylate(73) Pentaa of dipentaerythritol propionate
Crelate(74) Dipentaerythritol hexaacrylate (D
PHA)(75) ε-caprolactone adduct of DPHA

[Chemical 12]

Examples of oligomers: (76) Bisphenol A-diepoxy acrylic acid adduct

[Chemical 13]

These cross-linking agents may be used alone or in admixture of two or more. As the addition amount of these cross-linking agents,
The amount is preferably 0.001 to 1.0 part by weight, and more preferably 0.01 to 0.5 part by weight, relative to 1 part by weight of the resin.
If the amount added is 0.001 parts by weight or less, the crosslinking efficiency will be poor, and if it is 1.0 parts by weight or more, the white turbidity will decrease,
The contrast is low. As described above, in order to improve the crosslinking efficiency by adding a small amount of the cross-linking agent, among the above-mentioned cross-linking agents, a functional monomer is preferable to a non-functional monomer, and a polyfunctional monomer is more preferable than a monofunctional monomer. Monomers are preferred.

When UV irradiation is used as a means for crosslinking the resin of the heat-sensitive layer in the present invention, the following crosslinking agents, photopolymerization initiators and photopolymerization accelerators may be used. Specific examples thereof include, but are not limited to, the following.

First, the cross-linking agent can be roughly classified into a photo-polymerizable prepolymer and a photo-polymerizable monomer. The same as the functional monomer can be mentioned. Next, examples of the photopolymerizable prepolymer include polyester acrylate, polyurethane acrylate, epoxy acrylate, polyether acrylate, oligo acrylate, alkyd acrylate, and polyol acrylate. These cross-linking agents may be used alone or in admixture of two or more.
The addition amount of these crosslinking agents is preferably 0.001 to 1.0 part by weight, and more preferably 0.01 to 0.5 part by weight, relative to 1 part by weight of the resin. Addition amount is 0.001
If it is less than 10 parts by weight, the crosslinking efficiency will be poor, and if it is more than 1.0 part by weight, the white turbidity will decrease and the contrast will decrease.

Next, the photopolymerization initiator can be roughly classified into a radical reaction type and an ion reaction type, and the radical reaction type is further classified into a photocleavage type and a hydrogen abstraction type. Specific examples include those shown in Table 2 below.

[0093]

[Table 2- (1)]

[0094]

[Table 2- (2)]

These photopolymerization initiators may be used alone or in admixture of two or more. The addition amount is preferably 0.005 to 1.0 part by weight, more preferably 0.01 to 0.5 part by weight, relative to 1 part by weight of the crosslinking agent.

Next, as a photopolymerization accelerator, a hydrogen-abstraction type photopolymerization initiator such as a benzophenone type or a thioxanthone type has an effect of improving the curing rate and has an aromatic tertiary amine or an aliphatic type. There are amines. Specific examples include the following.

[Chemical 14]

[Chemical 15] These photopolymerization accelerators may be used alone or in admixture of two or more. The amount added is preferably 0.1 to 5 parts by weight, more preferably 0.3 to 1 part by weight with respect to 1 part by weight of the photopolymerization initiator.
3 parts by weight.

The ultraviolet irradiation device used in the present invention is composed of a light source, a lamp, a power source, a cooling device, and a carrying device. The light source includes a mercury lamp, a metal halide lamp, a gallium lamp, a mercury xenon lamp, and a flash lamp, and a light source having an emission spectrum corresponding to the ultraviolet absorption wavelength of the above photopolymerization initiator and photopolymerization accelerator may be used. . Regarding the ultraviolet irradiation conditions, the lamp output and the conveying speed may be determined according to the irradiation energy required to crosslink the resin.

In the present invention, the electron beam irradiation method which is particularly effective for crosslinking the resin of the thermosensitive layer of the reversible thermosensitive recording medium is as follows. First, the EB irradiation device can be roughly classified into a scanning type (scan beam) and a non-scanning type (area beam), but it may be determined according to the purpose such as the irradiation area and irradiation dose. Next, the EB irradiation condition is determined from the following formula in consideration of the electron flow, the irradiation width, and the transportation speed according to the dose required to crosslink the resin. D = (ΔE / ΔR) · η · I / (W · V) D: Required dose (Mrad) ΔE / ΔR: Average energy loss η: Efficiency I: Electron flow (mA) W: Irradiation width (cm) V: Conveyance speed (cm / s) Industrially, this is simplified, D · V = K · I / W, and the device rating is shown in Mrad · m / min. The electron flow rating is selected to be 20 to 30 mA for the experimental device, 50 to 100 mA for the pilot device, and 100 to 500 mA for the production device.

Regarding the dose required for crosslinking the resin, the crosslinking efficiency varies depending on the type and degree of polymerization of the resin, the type and addition amount of the crosslinking agent, the type and addition amount of the plasticizer, etc. Since the gel fraction of is not constant,
It suffices to determine the constituent factor level of the thermosensitive layer of these reversible thermosensitive recording media to prepare the recording layer, determine the gel fraction target value, and determine the dose accordingly. Further, here, when high energy is required to crosslink the resin, the irradiation dose is set to a plurality of irradiations in order to prevent the support or the resin from being deformed or thermally decomposed by the heat generated by the irradiation. It is preferable to prevent high heat from being applied once per irradiation. Further, it is preferable to heat at least a part of the organic low molecular weight substance contained in the recording layer at a temperature of melting or higher before the EB irradiation, and then to crosslink, and further, to a temperature at which all the organic low molecular weight substance melts. After heating above, it is preferable to crosslink. The relationship between each heat-sensitive layer constituent factor and the gel fraction is as described above. First, the above-mentioned resins can be selected as the type of resin, but the degree of polymerization of these tends to improve the gel fraction as the average degree of polymerization (P) increases, and preferably P = 300 or more. Preferably, P = 600 or more.

The type and amount of the cross-linking agent are as described above, and as the type of the plasticizer, fatty acid ester, polyester type plasticizer, epoxy type plasticizer and the like are preferable among the above-mentioned plasticizers. Epoxy plasticizers are most suitable from the viewpoint of irradiation discoloration and crosslinking efficiency. Regarding the amount of the plasticizer added, the gel fraction tends to improve as the amount of the plasticizer increases, and is 0.0% with respect to 1 part by weight of the resin.
1 to 1.0 parts by weight is preferable, and 0.05 is more preferable.
~ 0.5 parts by weight.

In addition to the above, there are the following methods for improving the repeating durability. First, durability is improved by raising the softening temperature of the heat sensitive layer to the high temperature side. The higher the softening temperature, the higher the durability. As a method of measuring the softening temperature, a membrane similar to that used in the gel fraction measurement can be used, and it can be measured using a thermomechanical analyzer (TMA) or a dynamic viscoelasticity measuring apparatus. In addition, the rigid pendulum method without peeling off the recording layer formed as described above
It can be measured by a dynamic viscoelasticity measuring device. As for the softening point, the less variation with time, the less variation in the clearing temperature width and range described above.

Secondly, as will be described later, durability is also improved by laminating the above-mentioned protective layer on the heat-sensitive layer formed on the support and increasing the interlayer strength between the layers. The stronger the interlayer strength is, the more the durability is improved. The method for measuring the interlaminar strength can be performed according to Tappi UM-403.

Thirdly, the smaller the penetration of the thermosensitive layer by the TMA penetration measurement, the better the durability. The lower the penetration, the better the durability. As a method of measuring the penetration degree, the recording layer formed on the support was used, and the TMA used for measuring the softening temperature was used. In addition, it can be heated if necessary and the amount of displacement can be measured.

Fourthly, the durability is improved when the amount of the crosslinking agent remaining in the heat-sensitive layer after EB crosslinking is small. The smaller the remaining amount, the more the durability is improved. The following method is mentioned as a residual amount measuring method. An ATR measurement accessory device attached to a Fourier transform infrared spectrophotometer was used as a measurement device, and the heat-sensitive layer coating film used in the above gel fraction measurement was used as a measurement sample.
The absorption band intensity of the acryloyl group appearing near 0 cm ^{-1 due} to the CH out-of-plane bending vibration is measured. This absorption band strength is proportional to the residual amount of the cross-linking agent. If the residual amount decreases, the strength also decreases, so that the residual amount can be known. The residual amount value is preferably 0.2 parts by weight or less, more preferably 0.1 parts by weight or less, further preferably 0.05 parts by weight or less, and particularly preferably, 1 part by weight of the resin in the thermosensitive layer. It is 0.01 part by weight or less. In this measuring method,
In addition to the above measurement, a photopolymerization initiator used in UV curing,
The residual amount of the photosensitizer and the catalyst used in the heat curing can be known, and the qualitative analysis of each residual component indicates that the crosslinking of the resin in the heat sensitive layer can be one of EB curing, UV curing, and heat curing. It is possible to determine which method was used. In either method, the smaller the residual component, the better the durability. Also, with this measurement method, since knowledge of only a thin layer of the order of several μm on the surface of the coating film can be obtained,
It is also possible to directly measure the heat-sensitive layer formed on the support.

In addition to these, if there are voids different from the refractive index of the resin and the particles in the interface between the resin and the organic low-molecular-weight substance particles in the heat-sensitive layer and / or in the particles, the image density in the white turbid state will increase. There is an effect that the contrast is improved. The effect is more remarkable when the size of the void is 1/10 or more of the wavelength of light used for detecting the opaque state.

When the image formed on this recording medium is used as a reflection image, it is desirable to provide a layer for reflecting light on the back surface of the thermosensitive layer. In addition, the presence of the reflective layer makes it possible to reduce the thickness of the heat-sensitive layer and significantly increase the contrast. Specifically, vapor deposition of Al, Ni, Sn and the like can be mentioned (described in JP-A No. 64-14079).

Further, the heat-sensitive layer may be provided with a protective layer for protecting the heat-sensitive layer. Protective layer (thickness 0.1
Examples of the material of (10 to 10 μm) include silicone rubber, silicone resin (JP-A-63-221087), and 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 hard to dissolve the resin of the recording layer and the organic low molecular weight substance. Examples of the solvent that hardly dissolves the resin of the heat-sensitive layer and the organic low molecular weight substance include n-hexane, methyl alcohol, ethyl alcohol, isopropyl alcohol, and the like, and the alcohol solvent is particularly preferable from the viewpoint of cost.

Further, these protective layers can be cured at the same time as crosslinking the resin of the heat sensitive layer. In this case, after forming the heat-sensitive layer on the support by the method described above, the protective layer is applied and dried, and then electron beam or ultraviolet irradiation is performed by the EB irradiation device and irradiation conditions or the UV irradiation device and irradiation conditions described above. And each layer may be cured.

Further, 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 (JP-A-1-13378).
1). As the material of the intermediate layer, the following thermosetting resins and thermoplastic resins can be used in addition to those listed as the material of the resin base material in the heat sensitive layer. That is, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin,
Phenol resin, polycarbonate, polyamide and the like can be mentioned. The thickness of the intermediate layer is preferably about 0.1 to 2 μm.

As mentioned above, in the present invention, a colored layer may be provided between the support and the heat-sensitive layer in order to improve visibility. The coloring layer is formed by applying a solution or dispersion containing a coloring agent and a resin binder as main components to the target surface and drying, or simply by laminating a coloring sheet.
Here, as the colorant, any change in transparency and white turbidity of the upper recording layer can be recognized as a reflection image, and red, yellow, blue,
Dyes and pigments having colors such as navy blue, purple, black, brown, grey, orange and green are used. As the resin binder, various thermoplastic, thermosetting or ultraviolet curable resins are used.

Further, an air layer, which is a non-contact portion containing air, can be provided between the support and the heat sensitive layer. When the air layer is provided, the organic polymer material used as the main component of the heat-sensitive layer has a refractive index of about 1.4 to 1.6, which is largely different from the refractive index of air of 1.0. Light is reflected at the interface between the side film and the non-adhesive portion, and the white turbidity is amplified when the heat-sensitive layer is in the white turbid state, and the visibility is improved. Therefore, it is desirable to use the non-adhesive portion as the display portion. Since the non-adhesion portion has air inside the non-adhesion portion, the non-adhesion portion serves as a heat insulating layer and the heat sensitivity is improved. Furthermore, the non-adhesive part also serves as a cushion, and even if the thermal head is pressed and pressed, the pressure actually applied to the heat-sensitive member will be low, and the heat-sensitive layer will not be deformed even when heat is applied. Repeatability is improved without expansion.

It is also possible to provide an adhesive layer or a pressure-sensitive adhesive layer on the back surface of the support and use it as a reversible thermosensitive recording label. This label sheet is attached to an adherend, and examples of the adherend include a vinyl chloride card such as a credit card, an IC card, an ID card, a paper, a film, a synthetic paper, a boarding bus, and a commuter pass. However, the present invention is not limited to these. Further, when the support is made of a material such as Al vapor-deposited layer that has a poor adhesive force to the resin, an adhesive layer may be provided between the support and the heat sensitive layer (Japanese Patent Laid-Open No. 3-7377).

When used as a thermosensitive recording image display device for displaying an image in the present invention, there are various types, and a typical one is to perform image formation / erasure on a reversible recording medium. The image forming means and the image erasing means are the same heating element, for example, a thermal head, and a thermal recording image display device capable of performing image processing by changing the energy applied to the thermal head, or the image forming means is a thermal The head, the image erasing means is a thermal head, hot stamp,
There is a heat-sensitive recording image display device selected from one of a contact pressure type means for adhering a heating element such as a heat roller and a heat block, or a non-contact type means using warm air or infrared rays.

Specifically, for example, as shown in FIGS.
The thermal recording and erasing device as shown in (c) and (d) can be mentioned. FIG. 9A is a schematic view of a contact-pressing type heating device that presses a hot stamp 402 against a reversible thermosensitive recording medium 1 that has been stationary to make it transparent. In the figure, 403 indicates a balance stand. FIG. 9B is a schematic view of a contact-type heating device that makes the heat roller 404 transparent. In the figure, 5 indicates an idle roller. In this apparatus, the heat roller 404 and the idle roller 405 rotate at the same peripheral speed, and the reversible thermosensitive recording medium 401 is moved while being nipped between them. FIG. 9 (c) is a schematic view of a non-contact type heat-sensitive device for making transparent by hot air from the dryer 406, and in the figure, 407 represents a feed roller. FIG. 9 (d)
Is a schematic diagram of a contact-pressing type heating device that is transparentized by a heat block 408. In the figure, reference numeral 407 represents a feed roller. Also, although not shown in this figure,
As a matter of course, a thermal head can be used as the image erasing device as shown in FIG.

A specific example using a heat-sensitive recording image display device for displaying an image in the present invention will be described below. First, FIG. 10A shows an example in which the image forming means and the image erasing means for forming and erasing an image on the reversible recording medium are thermal heads. Figure 10
In (a), the reversible thermosensitive recording medium 501-1 in the figure on which the image is formed is sent to the right by the platen roll 511 in the figure, and at that time, the energy is removed by the thermal head for image erasing 509 in the figure. The image is erased by being applied (at the same time, a displacement stress is generated between the contact surface of the recording medium and the thermal head, but this is extremely small because the resin of the heat-sensitive layer is cross-linked. Energy is not applied, and only the platen roll 11 in the figure is driven, and then 512, 512 in the figure
It is conveyed to the stopper 513 in FIG. In FIG. 10B, the reversible thermosensitive recording medium 501-2 in the figure, in which the image has been erased, is fed leftward by the guide roll 512 in the figure, and then further leftward by the platen roll 511 in the figure. Sent out. At that time, energy is applied by the thermal head for image formation 510 in the figure to form a new image (at the same time, a displacement stress is generated between the recording medium and the contact surface of the thermal head, but as described above, the degree is extremely small). . At this point 5 in the figure
The energy of the image erasing thermal head 09 is not applied, and only the platen roll 511 in the drawing is driven and further conveyed to the left.

It is clear that image display using a reversible thermosensitive recording medium can be carried out by using the thermosensitive recording image forming apparatus as described above. Further, in the above thermal recording image forming apparatus, the thermal heads 509 and 510 in the figure can be the same thermal head.
It is also possible to change the image erasing thermal head of No. 9 to a contact pressure type erasing device such as a hot stamp, a heat roller, a heat block, or a non-contact erasing device using warm air or infrared rays. Furthermore, in this device, 9
It is defined to provide an image erasing thermal head and an image forming thermal head at 510 in the figure, but the reverse apparatus does not matter.

Secondly, the image forming means and the image erasing means for forming and erasing an image on the reversible thermosensitive recording medium are the same thermal head, and a guide roll is provided behind the thermal head as a pressing means. Figure 11
Shown in. In FIG. 11, the reversible thermosensitive recording medium 501-1 in the figure on which the image is formed is sent out to the right by the platen roll 511 in the figure, and at that time, 51 in the figure.
The old image is erased and a new image is formed by the image forming-erasing thermal head of No. 4. Next, 501 in the figure
The reversible recording medium on which a new image of -3 is formed is further fed to the right by the platen roll 511 in the figure, passes between the guide rolls 512 and 512 in the figure, and moves to the right. As described above, it is obvious that the image display can be performed even in such a thermosensitive recording image forming apparatus. The image formation and erasure can be performed without contact. Further, between the image formation and the erasing, it is possible to employ means such as non-contact heating above the image forming temperature or heating while applying pressure above the image forming temperature.

In the above reversible thermosensitive recording medium of the present invention, since the recording layer as a whole exhibits a crosslinked structure, the recording layer does not cause distortion including the organic low molecular weight substance particles,
A good record can be erased at all times. Further, also in the reversible thermosensitive recording medium of the present invention, crosslinking the binder resin does not cause color misregistration or other inconvenience at the time of color development.

[0119]

EXAMPLES The present invention will be described in more detail based on the following examples. All parts and% herein are by weight.

Example 1 (Preparation of reversible thermosensitive recording medium) A1 was vacuum-deposited on a polyester film having a thickness of about 188 μm to a thickness of about 400 Å to form a light reflecting layer. A vinyl chloride-vinyl acetate-phosphate ester copolymer 5 parts (Denka Vinyl # 1000P manufactured by Denki Kagaku Kogyo Co., Ltd.) THF 95 parts solution was applied onto this, and dried by heating to give an adhesive layer of about 0.5 μm thickness. Was set up. Furthermore, behenic acid (NAA-22S manufactured by NOF CORPORATION) 5 parts Eicosane diacid (SL-20-99 manufactured by Okamura Oil Co., Ltd.) 5 parts trimethylolpropane triacrylate 1.25 parts (TMP3A manufactured by Osaka Organic Chemical Co.) Chloride Vinyl-vinyl acetate copolymer 25 parts (Kanefuchi Chemical Co., Ltd. No. 20-1497 vinyl chloride 80%, vinyl acetate 20%, average degree of polymerization = 500) THF 150 parts Toluene 15 parts A solution consisting of 15 parts is applied, It was dried by heating at 130 ° C. for 3 minutes to provide a heat-sensitive layer (reversible heat-sensitive recording layer) having a thickness of about 15 μm.
Next, the heat-sensitive layer prepared as described above was irradiated with an electron beam as follows. Area beam type electron beam irradiation device EB manufactured by Nisshin High Voltage Co., Ltd. as an electron beam irradiation device
Using C-200-AA2, the irradiation dose was adjusted to 15 Mrad, and electron beam irradiation was performed. Thus, a reversible thermosensitive recording medium having a thermosensitive layer formed was prepared. Next, on the heat-sensitive layer thus formed, a solution of a urethane acrylate-based UV-curable resin in 75% butyl acetate (Unidick C7-157, manufactured by Dainippon Ink and Chemicals, Inc.) 10 parts IPA 10 parts Apply with a wire bar, heat dry, then 8
A reversible thermosensitive recording medium having a protective layer with a thickness of about 2 μm was prepared by curing with a 0 w / cm ultraviolet lamp.

Example 2 In Example 1, the total irradiation dose of electron beam irradiation was 30 Mr.
A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer formed was prepared in the same manner as in Example 1 except that the irradiation was adjusted and changed so that the irradiation was performed twice.

Example 3 In Example 1, the cross-linking agent (trimethylolpropane triacrylate) in the heat-sensitive layer was eliminated, and irradiation was performed in four times so that the total irradiation dose of electron beam irradiation was 60 Mrad. A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer formed was prepared in the same manner as in Example 1 except that adjustments and changes were made.

Example 4 In Example 1, the vinyl chloride-vinyl acetate copolymer in the heat-sensitive layer was treated with No. Kanebuchi Chemical Co., Ltd. 20-1796 (vinyl chloride 80%, vinyl acetate 20%, average degree of polymerization = 30
A reversible thermosensitive recording medium having a recording layer and a protective layer was prepared in the same manner as in Example 1 except that the irradiation dose was changed to 00) and the irradiation dose was adjusted and changed to 15 Mrad.

Example 5 Formation of a heat-sensitive layer and a protective layer in the same manner as in Example 1 except that the irradiation was adjusted and changed so that the total irradiation dose was 30 Mrad. The reversible thermosensitive recording medium was prepared.

Example 6 (Preparation of reversible thermosensitive recording medium) About 100 μm as a support
An Al vapor-deposited polyester film (Metal Me 100TS manufactured by Toray Industries, Inc.) having a thickness of m was used, and 8 parts of behenic acid (SIGMA CHEMICAL CO.B-7644) and 2 parts of stearic acid (SIGMA CHEMICAL CO.S-4751) were formed on the film surface. Methylolpropane triacrylate 2 parts (TMP3A made by Osaka Organic Chemical Co., Ltd.) Vinyl chloride-vinyl acetate copolymer 37 parts (Kanefuchi Chemical Co., Ltd. No. 20-1510 Vinyl chloride 70%, vinyl acetate 30%, average degree of polymerization = 500) THF 130 parts Toluene 90 parts was applied and a solution was heated and dried at 90 ° C. for 5 minutes to provide a heat-sensitive layer (reversible heat-sensitive recording layer) having a thickness of about 10 μm. Next, in the thermosensitive layer created as described above,
Electron beam irradiation was performed. As an electron beam irradiation device, an area beam type electron beam irradiation device EBC- manufactured by Nisshin High Voltage Co., Ltd.
Using 200-AA2, the irradiation dose was adjusted to 15 Mrad, and electron beam irradiation was performed. Thus, a reversible thermosensitive recording medium having a thermosensitive layer formed was prepared.
Next, on the heat-sensitive layer thus formed, a solution of a urethane acrylate-based UV-curable resin in 75% butyl acetate (Unidick C7-157, manufactured by Dainippon Ink and Chemicals, Inc.) 10 parts IPA 10 parts Apply with a wire bar, heat dry, then 8
A reversible thermosensitive recording medium having a protective layer with a thickness of about 2 μm was prepared by curing with a 0 w / cm ultraviolet lamp.

Example 7 In Example 6, the total irradiation dose of electron beam irradiation was 30 Mr.
A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer was prepared in the same manner as in Example 6 except that the irradiation was adjusted and changed so that the irradiation was performed twice.

Example 8 In Example 6, the cross-linking agent (trimethylolpropane triacrylate) in the heat-sensitive layer was eliminated, and irradiation was performed in four times so that the total irradiation dose of electron beam irradiation was 60 Mrad. A reversible thermosensitive recording medium having a recording layer and a protective layer formed was prepared in the same manner as in Example 6 except that adjustments and changes were made.

Example 9 In Example 6, the resin in the heat-sensitive layer was vinyl chloride-vinyl acetate copolymer No. 1 manufactured by Kanegafuchi Chemical Industry Co., Ltd. 20-150
7 (vinyl chloride 70%, vinyl acetate 30%, average degree of polymerization = 3000), and the heat-sensitive layer and the protective layer were formed in the same manner as in Example 6 except that the irradiation dose was adjusted and changed to 15 Mrad. The reversible thermosensitive recording medium was prepared.

Example 10 Formation of a heat-sensitive layer and a protective layer in the same manner as in Example 6 except that the irradiation was adjusted and changed so that the total irradiation dose was 30 Mrad. The reversible thermosensitive recording medium was prepared.

Example 11 In Example 6, trimethylolpropane triacrylate in the heat-sensitive layer was replaced with DPCA-30 (DP manufactured by Nippon Kayaku Co., Ltd.).
CA-30), the addition amount was changed to 6.2 parts, and the irradiation was divided into two parts so that the total irradiation dose of electron beam irradiation was 20 Mrad, and the irradiation was performed in the same manner as in Example 6. Then, a reversible thermosensitive recording medium having a thermosensitive layer and a protective layer formed thereon was prepared.

Example 12 In Example 6, trimethylolpropane triacrylate in the heat-sensitive layer was replaced with DPHA (DPHA manufactured by Nippon Kayaku Co., Ltd.).
In the same manner as in Example 6 except that the addition amount was changed to 3.7 parts and the total irradiation dose of electron beam irradiation was 20 Mrad. A reversible thermosensitive recording medium having a protective layer formed thereon was prepared.

Example 13 In Example 6, trimethylolpropane triacrylate in the heat-sensitive layer was replaced with DPCA-30 (DP manufactured by Nippon Kayaku Co., Ltd.).
CA-30), the addition amount was changed to 12.4 parts,
A heat-sensitive layer was provided in the same manner as in Example 6. Next, the heat-sensitive layer thus prepared was irradiated with ultraviolet rays as follows without irradiation with electron beams. As a UV irradiation device, Nihon Battery Co., Ltd. HiCure 250 small conveyor type U
A V irradiation device is used, a mercury lamp is used as a light source, a lamp output is 3 kW (120 W / cm), and a conveying speed is 10 m /
Then, ultraviolet irradiation was performed 9 times. A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer was prepared in the same manner as in Example 6 except for the above.

Example 14 In Example 13, 0.6 part of 2,4-diethylthioxanthone (DETX-S manufactured by Nippon Kayaku Co., Ltd.) and P-dimethylaminobenzoic acid isoamyl ester (manufactured by Nippon Kayaku Co., Ltd.) were used in the heat-sensitive layer. A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer formed was prepared in the same manner as in Example 13 except that 0.6 part each of DMBI) was added.

Example 15 A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer was prepared in the same manner as in Example 10 except that the thickness of the thermosensitive layer was changed to 5 μm.

Example 16 A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer was prepared in the same manner as in Example 10 except that the thickness of the thermosensitive layer in Example 10 was changed to 15 μm.

Comparative Example 1 The procedure of Example 1 was repeated except that the crosslinking agent (trimethylolpropane triacrylate) in the thermosensitive layer was omitted and the electron beam irradiation was not performed. The formed reversible thermosensitive recording medium was prepared.

Comparative Example 2 Example 1 is the same as Example 1 except that the electron beam irradiation is eliminated.
A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer formed thereon (the thermosensitive layer was not crosslinked) was prepared in the same manner as in.

Comparative Example 3 The procedure of Example 6 was repeated except that the crosslinking agent (trimethylolpropane triacrylate) in the thermosensitive layer was omitted and electron beam irradiation was not performed. The formed reversible thermosensitive recording medium was prepared.

Comparative Example 4 Example 6 is the same as Example 6 except that the electron beam irradiation is eliminated.
A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer was prepared in the same manner as in.

Comparative Example 5 The procedure of Example 9 was repeated except that the crosslinking agent (trimethylolpropane triacrylate) in the heat-sensitive layer was omitted and the electron beam irradiation was not performed. The formed reversible thermosensitive recording medium was prepared.

Comparative Example 6 Example 9 is the same as Example 9 except that the electron beam irradiation is eliminated.
A reversible thermosensitive recording medium having a thermosensitive layer and a protective layer was prepared in the same manner as in.

Comparative Example 7 A support similar to that in Example 6 was used, and behenic acid 8 parts (SIGMA CHEMICAL CO.B-7644) stearic acid 2 parts (SIGMA CHEMICAL CO.S-4751) vinyl chloride-acetic acid was used. Vinyl-vinyl alcohol copolymer 30 parts (Sekisui Chemical Co., Ltd. trade name S-REC A) Isocyanate 3 parts (Asahi Kasei curing agent trade name Duranate 24A-100) Triethylenediamine (curing accelerator) 0.3 parts Toluene 30 Parts in the same manner as in Example 6 except that a solution of 120 parts of tetrahydrofuran was applied, and the mixture was heated and dried at 90 ° C. for 5 minutes and heat-cured to provide a heat-sensitive layer (reversible heat-sensitive recording layer) having a cured film thickness of about 10 μm. Thus, a reversible thermosensitive recording medium was prepared. Since this thermosensitive layer was thermosetting, electron beam irradiation and ultraviolet irradiation were not performed.

With respect to the reversible thermosensitive recording media of Examples and Comparative Examples thus obtained, the following respective performances were measured, and the results are shown in Tables 3 to 7.

(Measurement of Thermal Pressure Step Amount and Thermal Pressure Step Change Rate-1) Using the reversible thermosensitive recording medium on which the thermosensitive layer has been formed as described above, the heat of FIG. The two-dimensional roughness analysis device Surfcoder AY described above was applied with a pressure applying device under the conditions of an applied pressure of 2.5 Kg / cm ² , an applied time of 10 seconds and an applied temperature of 130 ° C.
-41, recorder RA-60E, and surf coder SE3
Using 0 K, the average value of thermal pressure step (Dm) was read to determine the initial pressure step amount (DI). Next, the reversible thermosensitive recording medium prepared at the same time as the sample used for the above measurement was heated to 50 ° C.
The sample was left for 24 hours in the constant temperature bath, cooled to room temperature, and the time-dependent thermal pressure step difference (DD) was determined by the same measurement method as above. Next, the initial thermal pressure step difference (DI) calculated above
Then, the thermal pressure step change rate (DC) was calculated from the thermal pressure step change amount (DD) over time. The results are shown in Table 3. Also, the recorder RA for measuring the initial thermal pressure step difference obtained by the above test
The surface roughness curves output by -60E are shown in FIG. 12 for the recording media of Example 7 and Comparative Example 3.

(Measurement of Gel Fraction and Gel Fraction Change Rate) Next, the heat-sensitive layer was peeled from the support using each reversible thermosensitive recording medium to determine the initial gel fraction value (GI). Next, 50 samples prepared at the same time as the sample used in the above measurement
After leaving it in a constant temperature bath at ℃, it was cooled to room temperature, and the time-dependent gel fraction value (GD) was determined by the same measurement method as above. For this measurement, the solvent is THF (tetrahydrofuran)
Was used. Next, the initial gel fraction value (G
The gel fraction change rate (G
C) was calculated. The results are shown in Table 3.

(Durability Test) Using each reversible thermosensitive recording medium, a repeated durability test of image formation and erasure was conducted as follows. A thermal head printing tester manufactured by Yashiro Denki Co., Ltd. was used as an image forming apparatus, a 8 dot / mm thermal head manufactured by Ricoh was used as a thermal head, and a pulse width of 2
A cloudy image is formed under the conditions of msec and applied voltage of 20.0 V, and a hot stamp is used for image erasing.
℃, others erase temperature 70 ℃, applied pressure 1kg /
The image was erased by setting cm ² and applying time of 1.0 sec. 1 for forming and erasing a cloudy image on a reversible thermosensitive recording medium
One cycle was considered to be repeated one by one, and the durability test was repeated under the same conditions until a total of 100 cycles. Regarding the cloudiness image density in the repeated durability test, the cloudiness density at the first cycle and the 100th cycle was measured by a Macbeth reflection densitometer (RD-914). The measurement results are summarized in Table 4.

(High Energy Application Test) Next, the following high energy application tests were carried out using the reversible thermosensitive recording media of Examples 1 to 5 and Comparative Examples 1 and 2. An image forming apparatus similar to the one used in the durability test is used,
The applied energy of the thermal head of the image forming apparatus is set to 0.
Proper energy of 4 mj / dot and 3.2 mj / dot
2 high energy conditions were set and printing was performed under each condition. After printing under these conditions, the image cloudiness density was measured with a Macbeth reflection densitometer (RD-914). The results are summarized in Table 5.

(Measurement of Transparent Temperature Range and Width) Separately from the above, the transparent temperature range and width of each reversible thermosensitive recording medium were measured as follows. First, all the recording media obtained as described above were in a transparent state. These recording materials were heated in a constant temperature bath at 120 ° C. for 1 minute and then cooled to room temperature to be white and opaque. Next, these recording materials were subjected to steps of 1 ° C. from 50 ° C. in Examples 1 to 5 and Comparative Examples 1 and 2.
Is heated to 120 ° C. for others and cooled to 80 ° C. for 1 minute, and then cooled to room temperature.
The reflection density was measured in 4). At this time, the temperature when the reflection density exceeded 0.8 was defined as the clearing temperature, and its range and width were shown. The results are shown in Table 6. Further, the sample prepared at the same time as the sample used for the above measurement was left in a constant temperature bath at 50 ° C. for 24 hours, cooled to room temperature, and the clearing temperature range and width with time were measured by the same method as above. . The results are shown in Table 6. In addition, for Example 7 and Comparative Example 7,
13 and 14 show graphs of the clearing temperature range and width obtained by the above-mentioned measurement at the initial stage and the time course (after 50 ° C. for 24 hours).

(Measurement of Thermal Pressure Step Amount and Thermal Pressure Step Change Rate-2) Next, the following tests were conducted on Example 7 and Comparative Example 3. Example 7 obtained as described above
Using the reversible thermosensitive recording medium of Comparative Example 3 on which the protective layer has been formed, the protective layer is scraped off to expose the surface of the reversible thermosensitive layer by the method shown in FIG. Thermal pressure is applied under the same conditions as above, and the thermal pressure step difference is measured, and the initial thermal pressure step difference (DI ''), the temporal thermal pressure step difference (DD '') and the thermal pressure step change rate (DC ''). I asked. The results are summarized in Table 7. Further, the surface roughness curve output by the recorder RA-60E in the initial thermal pressure step difference measurement obtained by the above test is shown in FIG.

[0150]

[Table 3]

[0151]

[Table 4]

[0152]

[Table 5]

[0153]

[Table 6]

[0154]

[Table 7]

[0155]

In the reversible thermosensitive recording medium of the present invention, the heat-pressure step difference of the photosensitive layer is 40% or less, and the heat-pressure step change rate is 70% or less. There is little deterioration of cloudy images even after repeated erasing, repeated durability is improved, and even when high energy printing is performed with a thermal destruction type thermal recording medium printer, etc., there is a difference in density compared to the image density in proper energy printing. There are few, print marks and cracks on the surface of the heat-sensitive layer after repeated durability with a thermal head, high contrast can be maintained, and it is possible to stabilize the transparent temperature range and width over time. Is. Furthermore, the heat-sensitive layer of these recording media is crosslinked to give a gel fraction change rate of 1
By setting the gel fraction value to 10% or less and the gel fraction value to 30% or more, the above-mentioned effects can be further improved.

[Brief description of drawings]

FIG. 1 is a hot stamp type air-operated tabletop TC film erasing device tester (manufactured by Unique Machinery Co., Ltd.) as a heat and pressure applying device. (A) is a schematic front view of the device (b) is a side view of the device Schematic diagram (c) is a schematic diagram of the temperature controller of the device.

2 is a front view of a print head (a) of the apparatus shown in FIG. 1 and a side view of FIG.

FIG. 3 is a sample support base when the thermal pressure application device shown in FIG. 1 is used.

FIG. 4 is an enlarged view of a portion to which heat pressure is applied by the heat pressure applying device shown in FIG.

[Fig. 5] Protective layer cutting device

6 (a), (b), (c) and (d) are diagrams showing the influence of a reversible thermosensitive recording medium by a heating element in conventional image display.

FIG. 7 is a diagram showing a change in transparency of a heat-sensitive layer according to the present invention due to heat.

FIG. 8 is a diagram showing a change in color tone due to heat of another heat-sensitive layer according to the present invention.

FIG. 9 is a diagram showing various specific examples of image erasing means in the thermosensitive recording image display device.

10A and 10B are examples in which an image is formed on and erased from a reversible thermosensitive recording medium using a thermal head according to the method of the present invention.

FIG. 11 is an example in which an image is formed on and erased from a reversible thermosensitive recording medium using a thermal head, a pressure means provided after the thermal head, and a guide roll.

FIG. 12 is a surface roughness curve output by the measurement of the initial thermal pressure step difference. (A) And (b) is a graph at the time of measuring the reversible thermosensitive recording medium of Example 7. (C) and (d) are graphs when measured for the reversible thermosensitive recording medium of Comparative Example 3.

FIG. 13 is a graph showing the transparentization temperature range and width of the reversible thermosensitive recording medium of Example 7.

FIG. 14 is a graph showing the transparentization temperature range and width of the reversible thermosensitive recording medium of Comparative Example 7.

[Explanation of symbols]

101 print head, thermal head 101-1 thermal pressure application unit 102 sample support base 102-1 Al plate 102-2 fluororubber 102-3 stainless steel plate 103 air regulator and filter 104 air gauge 105 print timer 106 ONE SHOT switch 107 print cylinder 108 Heater and temperature sensor 109 Control box 110 Hot stamp command switch 111 Power switch 112 Temperature controller 113 Temperature alarm lamp 301 Thermosensitive recording medium 302 Support base 303 Surface cutting member 304 Surface cutting member moving direction 501 Reversible thermosensitive recording medium 501 -1 Reversible thermosensitive recording medium on which image is formed 501-2 Reversible thermosensitive recording medium on which image is erased 501-3 Reversible thermosensitive recording medium on which image is newly formed 402 Stamp 403 stamp table 404 heat roller 405 idle roller 406 dryer 407 feed roller 408 heat block 509 image erasing head 510 image forming head 511 platen roll 512 guide roll 513 stopper 514 image forming-erasing head

Claims (10)

[Claims] 1. A reversible thermosensitive recording medium comprising a support and a thermosensitive layer whose transparency or color tone reversibly changes depending on temperature, wherein the thermosensitive layer has a thermal pressure step of 40% or less, A reversible thermosensitive recording medium characterized in that the rate of change in thermal pressure step is 70% or less. 2. The reversible thermosensitive recording medium according to claim 1, wherein the thermosensitive layer contains a resin, and the resin is crosslinked. 3. A reversible thermosensitive recording medium comprising a support and a thermosensitive layer whose transparency or color tone reversibly changes depending on temperature, wherein the thermosensitive layer contains a resin, and the resin is crosslinked. And a gel fraction change rate of 110% or less, a reversible thermosensitive recording medium. 4. The reversible thermosensitive recording medium according to claim 3, wherein the gel fraction value of the resin is 30% or more. 5. The resin is polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene chloride, saturated polyester, polyethylene, polypropylene, polystyrene, polymethacrylate, polyamide, polyvinylpyrrolidone, natural rubber, polyacrolein, polycarbonate,
Alternatively, the reversible thermosensitive recording medium according to claim 2 or 3, wherein the reversible thermosensitive recording medium is at least one selected from these copolymers. 6. The reversible thermosensitive recording medium according to claim 2, wherein the resin is crosslinked with a crosslinking agent. 7. The reversible thermosensitive recording medium according to claim 2, wherein the resin is crosslinked by electron beam irradiation or ultraviolet rays. 8. The reversible thermosensitive recording medium according to claim 1, wherein a protective layer is provided on the thermosensitive layer. 9. A method for producing a reversible thermosensitive recording medium in which transparency or color tone reversibly changes depending on temperature and a thermosensitive layer containing a resin is formed on a support, and an electron beam or an ultraviolet ray is applied a plurality of times. The method for producing a reversible thermosensitive recording medium according to claim 7, wherein the resin is crosslinked by irradiation. 10. A method for producing a reversible thermosensitive recording medium comprising a support, on which a transparency or a color tone is reversibly changed by heat to form a thermosensitive layer containing a resin and an organic low molecular weight substance. A method for producing a reversible thermosensitive recording medium, which comprises heating the resin at a temperature at which at least a part of the molecular substance is melted or higher and then crosslinking the resin.