JP2006088644A - Reversible thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reversible thermal recording medium which has excellent recording repeatability, light resistance and durability. <P>SOLUTION: This reversible thermal recording medium 10 has reversible thermal recording layers 31 to 33 containing in a resin a thermal color developing composition which can reversibly change in two ways, i.e. colorless or colored, depending on temperature variations, formed in a planar direction of a supporting substrate 1. In this medium 10, a leuco dye compound added to the thermal color developing composition is specified with regard to its chemical formula. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a reversible thermosensitive recording medium for recording a desired image and various data.

In recent years, the necessity of rewritable recording technology has been strongly recognized from the viewpoint of the global environment.
With the progress of computer network technology, communication technology, OA equipment, recording media, storage media, etc., paperless is progressing in offices and homes.

  Under such circumstances, as an example of a display medium that replaces printed matter, a recording medium capable of recording and erasing information by heat is used as the remaining amount due to the spread of various prepaid cards, point cards, credit cards, IC cards, etc. And other recorded information, etc., are being put into practical use for visualization and readability, and are also being put into practical use for copying machines and printers.

Various proposals have heretofore been made regarding the recording medium as described above and a recording method using the same.
For example, a leuco dye type, that is, a recording medium having a recording layer in which a leuco dye which is a color developing compound in a resin base material and a developer / color-reducing agent are dispersed, and a recording method using the same are proposed. This has the advantage that contrast and visibility are better than those of the low molecular weight dispersion type because it utilizes the color of the leuco dye itself.

  As a method for recording the above recording medium, there is a method in which a thermal head is used to make a color by contacting the recording medium and heating.

In addition, by applying the color development principle as described above, a plurality of recording layers using leuco dyes are separated and laminated in an independent state, and a laser beam is irradiated to perform light-to-heat conversion. There has been disclosed a technique for heating only an arbitrary recording layer to develop a color (for example, see Patent Document 1).
According to this method, only an arbitrary recording layer can be colored by the effect of wavelength selectivity of the layer containing the light-heat conversion material.

JP 2001-1645 A

However, conventionally known reversible thermosensitive recording media generally do not have sufficient studies on durability to light, and particularly when mixed with a coloring material for recording, they degrade over time and gradually deteriorate in function. Therefore, when recording and erasing are repeated many times, there is a practical problem that the color development / decoloring property is remarkably deteriorated. This is due to the fact that the thermosensitive coloring composition has the property of being chemically decomposed by absorbing light.
Further, the heat-sensitive color-forming composition has a problem that when oxygen enters the layer from the outside, it is chemically decomposed by active oxygen generated by this and light.

  In view of such problems, the development of a reversible recording medium having a design that intentionally prevents the entry of oxygen from the outside, as further high-density recording and miniaturization are promoted in the future. Was desired.

Therefore, in the present invention, regarding the leuco dye, a chemical structure having excellent light resistance is specified, color developability is excellent, contrast is excellent, there is no color cast, and there is no problem in practical use. An object of the present invention is to provide a reversible recording medium that can realize practically sufficient color developability even after repetitive and decoloring.
Furthermore, the present invention provides a reversible recording medium that prevents oxygen from entering the recording layer from the outside and can maintain excellent color reproducibility over a long period of time.

  In the present invention, in the surface direction of the support substrate, a reversible thermosensitive recording layer is formed in which a thermosensitive coloring composition that reversibly changes two states of colorless and colored in accordance with a temperature change is contained in the resin. And a reversible thermosensitive recording medium comprising at least one leuco dye compound represented by the following general formula (1) in the thermosensitive coloring composition.

X and Y in the above formulas represent a carbon atom or a nitrogen atom.
R1, R2 are, -C linear _n H _n + 2: shows the (n 4 less natural number).
R3, R4 is a straight chain -C of _n H _{2n +} 1: a cyclic structure (n 4 less natural number), or R3 and _{R4 - (CH 2) 4,} - shows a (CH _{2) 5.}
A is linear —C _n H _{2n + 1} (n: natural number of 4 or less), cyclic structure — (CH ₂ ) ₄ , — (CH ₂ ) ₅ , hydrogen atom, alkoxy group, halogen group, amide group Any one of these substituents is shown.
B is linear —C _n H _{2n + 1} (n: natural number of 4 or less), cyclic structure — (CH ₂ ) ₄ , — (CH ₂ ) ₅ , hydrogen atom, alkoxy group, halogen group, amide group Any one of these substituents is shown.

  Further, the present invention provides a reversible thermosensitive recording medium having a structure in which the oxygen gas barrier layer is provided on the upper layer side and the lower layer side of the reversible thermosensitive recording layer, and the reversible thermosensitive recording layer is sandwiched between the oxygen gas barrier layers.

According to the present invention, with regard to the leuco dye, by specifying a chemical structure excellent in light resistance and including this in the heat-sensitive recording layer, decomposition by light is suppressed, color developability is good, and contrast is excellent. There is no color cast, there is no problem in practical use, and it is excellent in stability over time, which can realize practical color development even after repeated firing and decoloring many times. A reversible thermosensitive recording medium was obtained.
In addition, by providing an oxygen gas barrier layer that suppresses the entry of oxygen into the reversible thermosensitive recording layer, the generation of active oxygen in the layer can be prevented, and the chemical change of the thermosensitive coloring composition and the deterioration of the function over time. Is avoided, and even when the color conversion is repeatedly performed, the recording image quality equivalent to the initial value can be maintained over a long period of time.

Hereinafter, specific embodiments of the reversible thermosensitive recording medium of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following examples.
In the following, a reversible thermosensitive recording medium having a structure in which three reversible thermosensitive recording layers are formed will be described as an example, but the present invention is not limited to this example. Only two colors or a structure capable of color development may be used, and any structure having one or more reversible thermosensitive recording layers is within the scope of the present invention.

FIG. 1 is a schematic sectional view of a reversible thermosensitive recording medium as an example of the present invention.
In the reversible thermosensitive recording medium 10, the first to third recording layers 17 to 19 include first to third light-heat conversion layers 11 to 13 through intermediate layers 14 to 16 in the surface direction of the support substrate 1. The first to third reversible thermosensitive recording layers 31 to 33 having a laminated structure are sandwiched between oxygen gas barrier layers 21 and 21.
Further, heat insulating layers 23 and 24 are interposed between the first to third reversible thermosensitive recording layers 31 to 33, and a protective layer 25 is formed as the uppermost layer.
Hereinafter, each layer will be described in detail.

As the support substrate 1, a conventionally known material can be appropriately used as long as the material has excellent heat resistance and high dimensional stability in the planar direction. For example, it can be appropriately selected from polymer materials such as polyester and hard vinyl chloride, glass materials, metal materials such as stainless steel, and materials such as paper.
In addition, by selecting a material having low oxygen gas permeability for the support substrate 1, it is possible to effectively suppress the invasion of oxygen gas from the support substrate 1 side.
In addition, for the purpose other than the transmission use such as an overhead projector, the support substrate 1 is visible in white or metal color in order to improve the visibility when recording is performed on the finally obtained reversible recording medium 10. It is preferable to form with a material having high reflectance to light.

  The first to third light-to-heat conversion layers 11 to 13 each comprise a light-to-heat conversion composition comprising a light-to-heat conversion material, a resin polymer, and various additives that generate heat by absorbing light in different wavelength ranges. It is comprised by. When recording is performed with a laser, desired color development is performed using the wavelength selection function of the light-heat conversion layers 11 to 13.

  Light-to-heat conversion material avoids color development in the erased state and prevents color fogging to improve recording sensitivity. Therefore, it uses dyes that have almost no absorption in the visible wavelength range and a narrow absorption band as the main component. It shall be applied in a state where it is uniformly dissolved in a resin binder using a predetermined solvent.

As the light-to-heat conversion material as described above, phthalocyanine dyes, cyanine dyes, metal complex dyes, diimmonium dyes, etc., which are generally used as infrared absorbing dyes having no absorption in the visible wavelength range, can be used. Cyanine dyes are preferred.
Cyanine dyes have little absorption in the visible range and sharp absorption in the near infrared range. Since the absorption maximum wavelength varies depending on the structure, it is possible to select one suitable for the laser wavelength used for recording.

The light-to-heat conversion material is dispersed in a resin binder.
Examples of the resin binder for dispersion include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, Examples include polymethacrylic acid ester, acrylic acid copolymer, maleic acid copolymer, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, gelatin, starch, and ultraviolet curable resin and thermosetting resin. It is done.
In particular, by selecting a material having a low oxygen gas permeability, deterioration of the light-heat conversion material due to active oxygen can be effectively avoided.

Moreover, it is desirable to add various additives, such as a ultraviolet absorber and a singlet oxygen quencher, to the light-heat conversion layers 11 to 13 as necessary.
The singlet oxygen quencher contains at least one selected from the group consisting of conjugated polyenes, transition metal complexes, hindered amines, amines, aminium salts, and iminium salts.
The addition amount of these singlet oxygen quenching agents is preferably about 0.05 to 4 times by weight with respect to the light-to-heat conversion material constituting the light-to-heat conversion layer. More preferably, it is 1 to 2 times.

  The film thickness of the first to third light-heat conversion layers 11 to 13 is preferably about 0.05 to 10 μm, and more preferably about 0.1 to 5 μm. If these film thicknesses are too thick, a sufficient color density cannot be obtained. Conversely, if the film thickness is too thin, the dye as the light-heat conversion material cannot be sufficiently dissolved.

The first to third intermediate layers 14 to 16 are formed using a conventionally known light-transmitting polymer.
For example, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polymethacrylate, acrylic acid Copolymers, maleic acid-based copolymers, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, gelatin, starch, etc. can be applied, and they can be formed using ultraviolet curable resins or thermosetting resins. Good.
In addition, as a material for forming the first to third intermediate layers 14 to 16, it is preferable to select a material having a low oxygen gas permeability. For example, when polyvinyl alcohol is applied, oxygen gas permeability is suppressed to be extremely low. It is possible to effectively avoid deterioration of the light-to-heat conversion material due to generation of active oxygen.
Moreover, you may make the 1st-3rd intermediate | middle layers 14-16 contain various additives, such as a ultraviolet absorber, as needed.

  The intermediate layers 14 to 16 may be formed of a translucent inorganic film. For example, it is preferable to apply porous silica, alumina, titania, carbon, or a composite thereof to reduce thermal conductivity. These can be formed by a sol-gel method capable of forming a film from a liquid layer.

The resin constituting the intermediate layers 14 to 16 is selected from materials that are incompatible with the resin constituting the adjacent light-to-heat conversion layers 11 to 13 and the recording layers 17 to 19. It is desirable to exist in a separate and independent state.
The intermediate layers 14 to 16 preferably have a thickness of about 0.05 to 30 μm, more preferably about 0.1 to 10 μm. This is because if the intermediate layers 14 to 16 are too thin, the light-to-heat conversion material is remarkably deteriorated. On the other hand, if the intermediate layers 14 to 16 are too thick, the thermal conductivity is deteriorated, so that sufficient color density cannot be obtained.

Next, the first to third recording layers 17 to 19 will be described.
The first to third recording layers 17 to 19 are formed of a material capable of forming a stable color generation / decoloring state (colored state and transparent state) by controlling the heat state, and this is repeated. Recording and erasing are possible.

  Each of the first to third recording layers 17 to 19 includes at least a color developing compound having an electron donating property, that is, a leuco dye, and a thermosensitive coloring composition composed of a developing / color-reducing agent having a predetermined electron accepting property. Suppose that it is formed in a state of being uniformly dissolved in a resin binder using a predetermined solvent.

  As the color developable compound (leuco dye), a material corresponding to a desired color to be developed in each recording layer is applied. For example, the first to third recording layers 17 to 19 emit three primary colors. For example, a full color image can be formed as the entire reversible recording medium 10.

  The leuco dye used in the present invention contains at least one compound represented by the general formula (1).

X and Y in the above formulas represent a carbon atom or a nitrogen atom.
R1, R2 are, -C linear _n H _n + 2: shows the (n 4 less natural number).
R3, R4 is a straight chain -C of _n H _{2n +} 1: a cyclic structure (n 4 less natural number), or R3 and _{R4 - (CH 2) 4,} - shows a (CH _{2) 5.}
A is linear —C _n H _{2n + 1} (n: natural number of 4 or less), cyclic structure — (CH ₂ ) ₄ , — (CH ₂ ) ₅ , hydrogen atom, alkoxy group, halogen group, amide group Any one of these substituents is shown.
B is linear —C _n H _{2n + 1} (n: natural number of 4 or less), cyclic structure — (CH ₂ ) ₄ , — (CH ₂ ) ₅ , hydrogen atom, alkoxy group, halogen group, amide group Any one of these substituents is shown.

A leuco dye deteriorates when it absorbs light, and a long-chain alkyl group or a long-chain alkyl group bonded to an amino group is eliminated. In order to avoid such a problem, it is necessary to specify the number of carbon atoms of the alkyl group in the formula of the compound constituting the leuco dye to be 4 or less to suppress elimination.
Preferable examples of the leuco dye specified in the present invention include those represented by the following formulas (2) to (11).

  As for the developer / color-reducing agent constituting the first to third recording layers 17 to 19, organic acids having a long-chain alkyl group conventionally used in these (JP-A-5-124360, JP-A-7-108761). No. 7, JP-A-7-188294, JP-A-2001-105733, JP-A-2001-13829, etc.) can be applied.

Examples of the resin binder for forming the first to third recording layers 17 to 19 include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, modified cellulose, acetal resin, butyral resin, polystyrene, and styrene. Copolymer, phenoxy resin, polyester, aromatic polyester, polyether resin, polyurethane, polycarbonate, polyacrylate ester, polymethacrylate ester, acrylic acid copolymer, maleic acid polymer, polyvinyl alcohol, modified polyvinyl Examples include alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, starch and the like.
As the resin binder for forming the first to third recording layers 17 to 19, it is preferable to select a material having extremely low oxygen gas permeability. Thereby, generation | occurrence | production of the active oxygen in a layer is suppressed, and deterioration of a coloring compound can be prevented effectively.

The first to third recording layers 17 to 19 are prepared by dissolving or dispersing the leuco dye, the developing / color-reducing agent, and various additives in the resin binder using a solvent, and preparing a predetermined coating material. It can form into a film by apply | coating to the formation surface.
The first to third recording layers 17 to 19 are preferably formed to a thickness of about 1 to 50 μm, and more preferably about 2 to 20 μm. If the recording layers 17 to 19 are too thin, a sufficient color density cannot be obtained. On the other hand, if the recording layers 17 to 19 are too thick, the heat capacity of the layer becomes too large, and the color development and decoloring properties deteriorate, or the thermal conductivity is low. This is because it deteriorates or the translucency decreases.

Next, the oxygen gas barrier layers 21 and 22 will be described.
The oxygen gas barrier layers 21 and 22 have a function of preventing oxygen from entering the reversible thermosensitive recording layers 31 to 33 from the outside.
The reversible thermosensitive recording medium 10 of the present invention preferably has at least one oxygen gas barrier layer. In particular, it is effective that oxygen enters the light-heat conversion layers 11 to 13 from the outside. As shown in FIG. 1, it is preferable to sandwich the reversible thermosensitive recording layers 31 to 33 from both the support substrate 1 side and the protective layer 25 side, that is, from both the upper layer and the lower layer.

Regarding the oxygen gas barrier function of the oxygen gas barrier layers 21 and 22, for example, when a sample having a film thickness of 20 μm is measured under the conditions of 20 ° C. and 60% RH, the oxygen gas permeability is 20 ml / m ² .24 Hrs · It is desirable to select it to be atm or less.
Examples of the resin having an oxygen gas barrier function as described above include an ethylene-vinyl alcohol copolymer (0.2 ml / m ² .24 Hrs · atm), polyvinyl alcohol (0.2 ml / m ² .24 Hrs · atm), Examples thereof include modified polyvinyl alcohol (0.2 ml / m ² .24 Hrs · atm), polyvinylidene chloride (3 ml / m ² .24 Hrs · atm), and polyacrylonitrile (15 ml / m ² .24 Hrs · atm).
For polyesters and polyamides, oxygen gas permeability becomes higher than the above values when made into a thin film. However, if the film is applied as the support substrate 1 and has a sufficient mechanical strength, the oxygen gas barrier function is sufficient. Can also demonstrate.

The oxygen gas barrier layers 21 and 22 may be made of a resin film containing an inorganic substance such as porous silica, alumina, titania, carbon, mica, clay, kaolin, calcium carbonate, or the like.
The oxygen gas barrier layers 21 and 22 may be formed by depositing a light-transmitting inorganic material by vapor deposition. Examples of the light-transmitting inorganic material include silica and alumina. As a vapor deposition method, a PVD method or a CVD method is suitable.
In addition, you may use together various additives, such as a singlet oxygen quencher and a ultraviolet absorber, for the oxygen gas barrier layers 21 and 22 as needed.

  The oxygen gas barrier layers 21 and 22 are preferably formed to a thickness of about 0.01 to 50 μm, and more preferably about 0.1 to 20 μm. This is because if these film thicknesses are too thin, sufficient oxygen gas barrier properties cannot be obtained, and conversely if they are too thick, thermal conductivity deteriorates.

Between the first reversible thermosensitive recording layer 31 and the second reversible thermosensitive recording layer 32, and between the second reversible thermosensitive recording layer 32 and the third reversible thermosensitive recording layer 33, It is desirable to form heat-insulating layers 23 and 24 that are transparent to the near-infrared light to be irradiated.
Thereby, heat conduction to the adjacent reversible thermosensitive recording layer during recording can be avoided, and so-called color fog can be prevented.

The heat insulation layers 23 and 24 can be formed using a conventionally known translucent resin material. For example, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polyacrylate ester, polymethacrylate ester , Acrylic acid copolymer, maleic acid polymer, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, starch and the like.
The heat insulating layer is preferably formed of a material having extremely low oxygen gas permeability. Thereby, generation | occurrence | production of an active oxygen can be avoided and deterioration of the color developing compound in an adjacent layer can be prevented effectively.
It is preferable that the heat insulating layers 23 and 24 contain various additives such as an ultraviolet absorber as necessary.
Moreover, you may form the heat insulation layers 23 and 24 with a translucent inorganic film | membrane. For example, when porous silica, alumina, titania, carbon, or a composite thereof is applied, the thermal conductivity can be reduced. These can be formed by a sol-gel method in which a film is formed from a liquid layer.

  The heat insulating layers 23 and 24 are preferably formed to a thickness of about 2 to 100 μm, and more preferably about 40 to 50 μm. If the heat insulating layer is too thin, a sufficient heat insulating effect cannot be obtained, and if the film thickness is too thick, the thermal conductivity deteriorates or the translucency decreases when the entire recording medium is uniformly heated in the recording method described later. This is because

Next, the protective layer 25 will be described.
The protective layer 25 can be formed using a conventionally known ultraviolet curable resin or thermosetting resin. In addition, when a material having a very low oxygen gas permeability is applied, so-called oxygen gas barrier properties are exhibited, and deterioration of the light-heat conversion material due to generation of active oxygen can be effectively avoided. The film thickness is preferably about 0.5 to 50 μm.
If the protective layer 25 is too thin, a sufficient protective effect cannot be obtained. If the protective layer 25 is too thick, the thermal conductivity deteriorates or the translucency decreases when the entire recording medium described later is uniformly heated.

Next, a method for recording on the reversible thermosensitive recording medium of the present invention using a laser will be described.
In the following, a method for recording and erasing using the reversible thermosensitive recording medium 10 having the configuration in which the three layers of the reversible thermosensitive recording layers 31 to 33 shown in FIG. 1 are formed will be described. The present invention is not limited to this, and a reversible recording medium in which one or more reversible thermosensitive recording layers are formed and can be formed in only one color or two colors can be similarly applied.

  First, the entire surface is heated at a temperature at which each of the recording layers 17 to 19 is decolored, for example, about 120 ° C., so that the recording layers 17 to 19 are in a decolored state in advance. That is, in this state, the color of the support substrate 1 is exposed. Next, an infrared ray whose wavelength and output are arbitrarily selected is irradiated onto a desired portion with a semiconductor laser or the like.

  For example, when the first recording layer 17 is colored, infrared light near the absorption peak wavelength (λmax1) of the light-heat conversion material contained in the first light-heat conversion layer 11 is used as the first recording layer. The first light-heat conversion layer 11 is irradiated with energy at an energy enough to reach a color development temperature to generate heat, causing a color development reaction between the electron donating color developing compound and the electron accepting developer / color reducing agent, Color the irradiated area.

Similarly, for the second recording layer 18 and the third recording layer 19, the absorption peak wavelengths of the light-heat conversion materials contained in the second and third light-heat conversion layers 12, 13 respectively. Laser light in the vicinity of (wavelengths λmax2, λmax3) is irradiated to the second and third light-to-heat conversion layers with an energy sufficient for the corresponding recording layer to reach the color development temperature to generate heat, and the irradiated portion is colored.
In this way, an arbitrary portion of the reversible thermosensitive recording medium 10 can be developed in a desired hue. At this time, all hues can be recorded by using the same number of laser light sources having different oscillation wavelength bands as the number of recording layers including the light-heat conversion material.

  Further, by irradiating the same position of the reversible thermosensitive recording medium 10 with laser beams having a plurality of wavelengths, a mixed color of the corresponding colored hue can be obtained. At this time, the color tone of the mixed color can be displayed by adjusting the energy of the irradiated laser beam. That is, if each recording layer is set to develop yellow, cyan, and magenta, a full-color image and various information are recorded on an arbitrary portion of the reversible thermosensitive recording medium 10 by adopting the above method. be able to.

  Further, in the recording layer that has been colored as described above, the recording information and the image can be obtained by heating uniformly to a temperature at which the first to third recording layers 17 to 19 are decolored, for example, 120 ° C. It can be erased and repeated recording can be performed.

Hereinafter, the present invention will be described with specific examples and comparative examples.
First, paints 1 and 2 were prepared by combining the resins, solvents, and light-heat conversion materials shown in Table 1 below.
Further, leuco dyes, developer / color-reducing agents, resins, and solvents shown in Table 2 below were mixed in an appropriate combination and pulverized with a paint conditioner to 0.3 μm or less to prepare paints 3 to 10.

  Chemical formulas corresponding to the leuco dyes of the formulas (12) and (13) shown in Table 2 are shown below.

  The chemical formula corresponding to the developer / color-reducing agent of the formula (14) shown in Table 2 is shown below.

The chemical formula corresponding to the light-to-heat conversion material (near infrared absorbing dye) of formula (15) shown in Table 1 is shown below.
In the formula, Me represents a methyl group.

Next, as shown in Table 3 below, a predetermined one of the paints shown in Tables 1 and 2 above is selected and applied to a white polyethylene terephthalate support substrate having a thickness of 500 μm to form a film. The reversible thermosensitive recording media of Examples 1 to 7 and Comparative Examples 1 to 3 were produced.
Each layer was formed by applying paint with a wire bar and drying.

  Then, each optical characteristic was evaluated about the samples of Examples 1-7 of Table 3 produced as mentioned above, and Comparative Examples 1-3.

[Evaluation method of optical characteristics]
First, the reflection density (OD) of the background of each sample produced as described above was measured with a Macbeth densitometer.
Subsequently, for each recording layer constituting the sample, the absorbance of the recording layer alone at the wavelength of the laser beam used for recording was measured, and the absorption curve was measured with a spectrophotometer. As a result, it was confirmed that the absorbance of the recording layer alone in all the recording layers at the recording laser beam wavelength was about 1.0 to 1.1.

[Evaluation of storage stability of light-to-heat conversion material against oxygen gas permeability]
The oxygen permeability was measured for the samples of Examples 1 and 2 and Comparative Examples 1 and 2.
(Measurement of oxygen gas permeability)
The oxygen permeability was measured with a differential pressure type gas permeability meter. The measurement results are shown in Table 4 below.
In this measurement of oxygen gas permeability, a PE film having a thickness of 60 μm (oxygen permeability 2000 ml / m ² .24 Hrs · atm. 20 ° C. 60% RH) was used as a support substrate, A film-formed sample was applied as a measurement sample.

  As shown in Table 4 above, in Example 2 and Comparative Example 2 having an oxygen gas barrier layer, oxygen gas permeability was higher than in Example 1 and Comparative Example 1 having no oxygen gas barrier layer. Was found to be extremely low.

[Laser recording evaluation]
Using the samples of Examples 1 to 7 and Comparative Examples 1 to 3 prepared as described above, semiconductor laser irradiation was performed under the following conditions, and the recording line width and the solid image recording reflection density were evaluated. Went.
(Verification 1)
First, the reflection density (OD) of the background in the initial state was measured, and the reflection density when recording was performed by irradiating with laser light.
In this case, scanning was performed while irradiating a semiconductor laser beam having a predetermined oscillation center wavelength under the conditions of a spot shape of 30 μm × 200 μm and an output of 450 mW. The scanning conditions were a spot shape of 200 μm in the direction of the axis with a speed of 5.4 m / s and a scanning interval of 15 μm, and the reflection density of the recorded solid image was evaluated with a Macbeth densitometer.
(Verification 2)
Using a light resistance tester, the light source is a white fluorescent lamp, the intensity is 500,000 lx, light irradiation is performed for 8 hours, and after a storage test, the reflection density (OD) of the background is measured. Further, after that, recording was performed by irradiating a laser beam, and the reflection density was measured. The recording conditions are the same as above.
(Verification 3)
Next, a 120 ° C. hot stamp was pressed for 1 second using the sample after recording in the verification 1 to erase the image.
The recording and erasing operations were repeated 100 times, and the solid image when the 100th recording was performed and the reflection density when the erasing was performed for the 100th time were evaluated with a Macbeth densitometer.

〔Evaluation results〕
In Table 5 below, the evaluation results of the initial laser recording shown in the above (Verification 1) (the reflection density of the background and the reflection density of the recorded image) of the samples of Examples 1 to 7 and Comparative Examples 1 to 3 are shown. Show.
Table 6 below shows the evaluation results of the laser recording (background reflection density and recorded image) of the samples of Examples 1 to 7 and Comparative Examples 1 to 3 after the light irradiation storage test shown in (Verification 2) above. Reflection density).
Table 7 below shows a solid image when the recording and erasing operations shown in (Verification 3) of the samples of Examples 1 to 7 and Comparative Examples 1 to 3 were repeated 100 times and the 100th recording was performed. And the measurement result of the reflection density when erasing is performed for the 100th time.

As shown in Table 5 above, in Examples 1 to 7, when recording was performed using laser light having an oscillation center wavelength of 800 nm, good color development was obtained, and no color fogging occurred.
Further, after recording with laser light, all images could be erased by bringing a hot stamp at 120 ° C. into contact for 1 second, and the transparency after erasure was good.
As shown in Table 6 above, in Examples 1 to 7, even after the light irradiation test (storage test), a practically sufficient color was obtained and no color cast was generated.
In particular, in Examples 2 to 7, since the oxygen gas barrier layer was formed on the upper layer side and the lower layer side of the reversible thermosensitive recording layer and sandwiched between them, oxygen gas intrusion from outside and generation of active oxygen Therefore, it was confirmed that the color development state after the light irradiation test (storage test) was clearer than in Example 1 in which the oxygen gas barrier layer was not formed.
Further, as shown in Table 7 above, in Examples 1 to 7, even after 100 times of recording and erasing, good color development was obtained and no color cast was generated. Further, the reflection density after disappearance when the 120 ° C. hot stamp was contacted for 1 second was very small, and almost all images could be erased.

On the other hand, in Comparative Examples 1 to 3, as apparent from the comparison of the results in Table 5 and Table 6, the color developability and contrast were significantly deteriorated after the light irradiation test (storage test).
This is because in the samples of Comparative Examples 1 to 3, the chemical structure specified in the present invention was not applied as the leuco dye, so that the leuco dye was decomposed by light irradiation for a long time. is there.
In particular, in Comparative Example 1, since the oxygen gas barrier layer did not shield the reversible thermosensitive recording layer from the upper layer side and the lower layer side, oxygen gas entered from the outside, generating active oxygen, and decomposing the leuco dye. As a result, the color developability deteriorated remarkably. In addition, the reflection density of the background increased and the contrast decreased.

Further, as shown in Table 7 above, in Comparative Examples 1 to 3, a practically sufficient color development and contrast could not be obtained even after 100 times of recording and erasing were repeated.
This is because the leuco dye was decomposed by light because the chemical structure specified in the present invention was not applied as the leuco dye, and recording and erasing were repeated.
In particular, in Comparative Example 1, since the oxygen gas barrier layer did not shield the reversible thermosensitive recording layer from the upper layer side and the lower layer side, oxygen gas entered from the outside, generating active oxygen, and decomposing the leuco dye. Progressed and the color developability deteriorated remarkably. In addition, the reflection density of the background increased and the contrast decreased.

  As is clear from the results described above, according to the present invention, by specifying the chemical formula of the leuco dye constituting the thermosensitive coloring composition, an unprecedented light fast leuco dye can be obtained. As a result, even when light irradiation was performed for a long time or when conversion of color emission / decoloration was repeated, it was possible to realize the same recording image quality as the initial one.

  Furthermore, by providing an oxygen gas barrier layer on the upper layer side and lower layer side of the reversible thermosensitive recording layer, it is possible to effectively suppress the intrusion of oxygen gas into the layer and the generation of active oxygen. Even when color conversion was performed, it was possible to maintain the same recording image quality as in the initial stage.

1 is a schematic cross-sectional view of an example of a reversible thermosensitive recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Support substrate, 10 ... Reversible thermosensitive recording medium, 11 ... 1st light-heat conversion layer, 12 ... 2nd light-heat conversion layer, 13 ... 3rd light-heat conversion layer , 14, 15, 16 ... intermediate layer, 17 ... first recording layer, 18 ... second recording layer, 19 ... third recording layer, 31 ... first reversible thermosensitive recording layer, 32 ... 2nd reversible thermosensitive recording layer, 33 ... 3rd reversible thermosensitive recording layer

Claims (5)

In the direction of the surface of the support substrate,
A reversible thermosensitive recording layer is formed in which a thermochromic composition that reversibly changes between two states, colorless and colored, in response to temperature changes is contained in the resin.
A reversible thermosensitive recording medium, wherein the thermosensitive coloring composition contains at least one compound of a leuco dye represented by the following general formula (1).

X and Y in the above formulas represent a carbon atom or a nitrogen atom.
R1, R2 are, -C linear _n H _n + 2: shows the (n 4 less natural number).
R3, R4 is a straight chain -C of _n H _{2n +} 1: a cyclic structure (n 4 less natural number), or R3 and _{R4 - (CH 2) 4,} - shows a (CH _{2) 5.}
A is linear —C _n H _{2n + 1} (n: natural number of 4 or less), cyclic structure — (CH ₂ ) ₄ , — (CH ₂ ) ₅ , hydrogen atom, alkoxy group, halogen group, amide group Any one of these substituents is shown.
B is linear —C _n H _{2n + 1} (n: natural number of 4 or less), cyclic structure — (CH ₂ ) ₄ , — (CH ₂ ) ₅ , hydrogen atom, alkoxy group, halogen group, amide group Any one of these substituents is shown. An oxygen gas barrier layer having a function of preventing oxygen gas from entering is provided on the upper layer side and the lower layer side of the reversible thermosensitive recording layer,
The reversible thermosensitive recording medium according to claim 1, wherein the reversible thermosensitive recording layer is sandwiched by the oxygen gas barrier layer. 3. The oxygen gas barrier layer according to claim 2, wherein an oxygen permeability is 20 ml / m ² .24 Hrs · atm or less under conditions of a film thickness of 20 μm, 20 ° C., and a relative humidity of 60% RH. Reversible thermosensitive recording medium. Two or more reversible thermosensitive recording layers are separated and laminated in the surface direction of the support substrate,
2. The reversible thermosensitive recording medium according to claim 1, wherein each of the two or more reversible thermosensitive recording layers contains a thermosensitive coloring composition that develops colors in different colors. Two or more reversible thermosensitive recording layers are separated and laminated in the surface direction of the support substrate,
The reversible thermosensitive recording medium according to claim 2, wherein the oxygen gas barrier layer is provided between the two or more reversible thermosensitive recording layers.

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