JP4321174B2 - Reversible multicolor recording medium and recording method using the same - Google Patents

Description

  The present invention relates to a reversible multicolor recording medium for recording an image or data, and a recording method using the same.

  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.

  As an example of a display medium that replaces printed matter, a recording medium capable of reversibly recording and erasing information by heat, a so-called reversible thermosensitive recording medium, has been widely used for various types of prepaid cards, point cards, credit cards, IC cards, In addition, it has been put into practical use in applications such as visualization and reading of balances and other recorded information, and further in applications such as copying machines and printers.

  Various proposals have been made regarding the reversible thermosensitive recording medium and the recording method using the same (see, for example, Patent Documents 1 to 4). These are so-called low-molecular dispersion types, that is, recording media in which organic low-molecular substances are dispersed in a resin base material, which changes the scattering of light by the thermal history and changes the recording layer to cloudy or transparent. Therefore, since the contrast between the image forming portion and the image non-forming portion is insufficient, only a medium whose contrast is improved by providing a reflective layer under the recording layer has been put into practical use. Yes.

  On the other hand, a leuco dye type, that is, a recording medium having a recording layer in which a leuco dye that is an electron donating color developing compound and a developer / color-reducing agent are dispersed in a resin base material, and a recording method using the same Disclosure has been made (see, for example, Patent Documents 5 to 9). In these, as the developing / color-reducing agent, an amphoteric compound having an acidic group for developing a leuco dye and a basic group for decoloring the developed leuco dye, a phenol compound having a long-chain alkyl, or the like is used. Since this recording medium and recording method utilize the color developed by the leuco dye itself, the recording medium and the recording method have better contrast and visibility than the low molecular dispersion type, and have been widely put into practical use in recent years.

In the prior art disclosed in each of the above patent documents, only two types of colors, that is, the color of the base material, that is, the background color, and the color changed by heat can be expressed. However, in recent years, in order to improve visibility and fashionability, there has been a great demand for displaying multicolor images and recording various data by color identification.
On the other hand, various recording methods that apply the above-described conventional method and display a multicolor image have been proposed.

  For example, a recording medium that performs multicolor display by visualizing or concealing layers and particles separately coated in multiple colors with a low molecular dispersion type recording layer, and a recording method using the same are disclosed ( (See Patent Documents 10 to 12.) However, in the recording medium having such a configuration, the recording layer cannot completely hide the color of the lower layer, the color of the base material is transparent, and high contrast cannot be obtained.

  Although other disclosures have been made on reversible thermosensitive multicolor recording media using leuco dyes (see, for example, Patent Documents 13 and 14), these have repeating units having different hues in the plane. Therefore, since the area ratio in which each hue is actually recorded is small, there is a problem that a recorded image can be obtained only in a very dark or thin image.

Also disclosed is a reversible thermosensitive multicolor recording medium having a structure in which recording layers using leuco dyes having different color development temperature, decoloring temperature, cooling rate, etc. are separated and formed independently (for example, patents). Reference 15-23).
However, there are problems that it is difficult to control the temperature with a recording heat source such as a thermal head, a good contrast cannot be obtained, and color fog cannot be avoided. Furthermore, it is very difficult to control the increase of three or more colors only by the difference in heating temperature and / or cooling rate after heating with a thermal head or the like.

In addition, in a reversible thermosensitive multicolor recording medium having a structure in which a recording layer using a leuco dye is separated and formed independently, only an arbitrary recording layer is heated by light-to-heat conversion by laser light irradiation, and color development The recording method to be performed is also disclosed (for example, refer to Patent Document 24). According to this method, due to the wavelength selectivity effect of the light-to-heat conversion layer, only an arbitrary recording layer can be colored, and the problem of color fog, which has been a problem with conventional reversible multicolor recording media. May be resolved.
However, in this reversible thermosensitive multicolor recording medium, since the light-heat conversion layer is provided independently of the recording layer, the number of constituent layers increases and the manufacturing process becomes complicated. Have. Further, there is a problem that energy converted into light-heat by laser light irradiation is not efficiently transmitted to the recording layer, sufficient color development cannot be obtained, and the time required for recording becomes long.
Furthermore, since the light-to-heat conversion layer (laser light absorption layer) is formed by depositing a light-absorbing material that does not contain a binder and is dissolved in an organic solvent, laser light can be emitted in an extremely wide wavelength region. In other words, the display accuracy is deteriorated. In addition, the laser light absorption layer formed by such a method has light absorption even in the visible region, so that the transparency of the recording layer is deteriorated in the erased state, and the recording accuracy is deteriorated. Also have.

JP 54-119377 A JP 55-154198 A JP-A-63-39377 JP-A-63-41186 JP-A-2-188293 JP-A-2-188294 JP-A-5-124360 Japanese Patent Laid-Open No. 7-108761 JP 7-188294 A Japanese Patent Laid-Open No. 5-62189 JP-A-8-80682 JP 2000-198275 A JP-A-8-58245 JP 2000-25338 A JP-A-6-305247 JP-A-6-328844 JP-A-6-79970 JP-A-8-164669 JP-A-8-300825 Japanese Patent Laid-Open No. 9-52445 JP 11-138997 A JP 2001-162941 A JP 2002-59654 A JP 2001-1645 A

  As described above, there is a great demand for multicolor thermal recording, and various studies have been actively conducted in the past, but a recording medium or a recording method that is practically satisfactory has not yet been realized.

  Therefore, in the present invention, in view of such problems of the prior art, stable color development / contrast, contrast, and practically excellent image stability can be realized in daily life. An erasable reversible multicolor thermal recording medium and a recording method using the same are provided.

In the present invention, a plurality of reversible thermosensitive color forming compositions each having a plurality of reversible thermosensitive color developing compositions having different color tone in the surface direction of the support substrate are separated and laminated to form a plurality of reversible thermosensitive color forming compositions. The material contains a light-to-heat conversion material that generates heat by absorbing infrared rays in different wavelength ranges, and the recording layer has a color-forming compound having an electron donating property and a visible / subtractive color having an electron accepting property. And at least one of the color developing / color-reducing agents having electron accepting properties is a compound represented by the following general formula (4), a color-forming compound having electron donating properties, and electron accepting properties: There is provided a reversible multicolor recording medium adapted to reversibly change the recording layer into two states of color development or color erasure by a reversible reaction between the developer and the color-reducing agent.

  However, R5 and R6 are hydrocarbon groups having a total carbon number of 8 to 26, and n is an integer of 5 or less.

  Further, in the recording method of the present invention, a plurality of reversible thermosensitive color-forming compositions having different color tones are separated and laminated in the surface direction of the support substrate, and a plurality of reversible layers are formed. The heat-sensitive color-forming composition contains a light-to-heat conversion material that generates heat by absorbing infrared rays in different wavelength ranges, and the recording layer has a color-forming compound having electron donating properties and an electron accepting property. A color developing compound having an electron donating property, wherein at least one of the color developing / color reducing agents having electron acceptability is a compound represented by the following general formula (4): And a reversible multicolor recording medium in which the recording layer is reversibly changed into two states of color development or decoloration by a reversible reaction between the color developing agent and the color-reducing agent having electron acceptability. , Decolorize the whole recording layer in advance by heat treatment Depending on the desired image information, exposure is performed by irradiating infrared rays of a selected wavelength region corresponding to the selected one of the recording layers, and the recording layer is heated to selectively develop color. By doing so, image information is recorded.

  However, R5 and R6 are hydrocarbon groups having a total carbon number of 8 to 26, and n is an integer of 5 or less.

  Further, in the recording method of the present invention, a plurality of reversible thermosensitive color-forming compositions having different color tones are separated and laminated in the surface direction of the support substrate, and a plurality of reversible layers are formed. The heat-sensitive color-forming composition contains a light-to-heat conversion material that generates heat by absorbing infrared rays in different wavelength ranges, and the recording layer has a color-forming compound having electron donating properties and an electron accepting property. A color developing compound having an electron donating property, wherein at least one of the color developing / color reducing agents having electron acceptability is a compound represented by the following general formula (4): And a reversible multicolor recording medium in which the recording layer is reversibly changed into two states of color development or decoloration by a reversible reaction between the color developing agent and the color-reducing agent having electron acceptability. , Preheat the entire recording layer. In accordance with the desired image information, exposure is performed by irradiating with infrared rays of a wavelength region selected corresponding to the selected one of the recording layers, causing the recording layer to generate heat and selectively erase. It is assumed that image information is recorded by colorization.

  However, R5 and R6 are hydrocarbon groups having a total carbon number of 8 to 26, and n is an integer of 5 or less.

  According to the present invention, it is possible to control various conditions such as solubility in a solvent or polymer, melting point, temperature capable of color development / decoloring, etc. Sensitivity is improved.

  According to the present invention, the developer / color-reducing agent contained in the recording layer is specified to have an arbitrary chemical structure, so that an arbitrary recording layer can be heated accurately when irradiated with wavelength-selected infrared rays. Therefore, it is possible to quickly and accurately convert between a reversible coloring state and a decoloring state, and thus excellent reproducibility, contrast, and fineness can be obtained when information is repeatedly recorded and erased. The resulting reversible multicolor recording medium was extremely sensitive.

  Further, according to the present invention, a stable and clear color erasing and decoloring and clear contrast can be obtained, and a recording method capable of high-speed recording and high-speed erasing can be realized with practically sufficient image stability.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. However, the reversible multicolor recording medium of the present invention is not limited to the following examples.
FIG. 1 is a schematic sectional view of a reversible multicolor recording medium according to the present invention.
In the reversible multicolor recording medium 10, a first recording layer 11, a second recording layer 12, and a third recording layer 13 are laminated on a support substrate 1 via heat insulating layers 14 and 15, respectively. The protective layer 16 is formed as the uppermost layer.

  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. However, for purposes other than transmission applications such as overhead projectors, the support substrate 1 is white or metallic in order to improve the visibility when information is recorded on the finally obtained reversible multicolor recording medium 10. It is preferably formed of a material having a high reflectance with respect to visible light having a color.

The first to third recording layers 11 to 13 are formed using a material capable of controlling a decoloring state and a coloring state, which enables stable repeated recording.
The first to third recording layers 11 to 13 contain light-heat conversion materials that generate heat by absorbing infrared rays having different wavelengths (λ ₁ , λ ₂ , λ _{3 in} FIG. 1). Each of the first to third recording layers 11 to 13 has a reversible thermosensitive color-developing composition, that is, a color-forming compound having electron donating properties, such as a leuco dye, and a visible / photosensitive material having a predetermined electron accepting property. It is assumed that it is formed by applying a paint in which these are contained in a resin base material.

Further, the first to third recording layers 11 to 13 apply a predetermined leuco dye corresponding to a desired color to be colored. For example, if the three primary colors are developed in the first to third recording layers 11 to 13, a full color image can be formed as the entire reversible multicolor recording medium 10.
As the leuco dye, which is a color-forming compound having an electron donating property, for example, an existing thermal paper dye can be applied.

  A compound represented by the following general formula (1) may be applied as the electron accepting developer / color-reducing agent contained in the recording layers 11 to 13 of the reversible multicolor recording medium 10 of the present invention. it can.

However, X consists of any one of OH, COOH, halogen, and H, Y is -NHCO-, -CONH-, -NHCONH-, -CONHCO-, -NHNHCO-, -CONHNH-, -CONHNHCO-,- NHCONCONH-, -NHCONHCO-, -CONHCONH-, -NHNHCONH-, -NHCONHNH-, -CONHNHCONH-, -NHCONHNHCO-, -CONHNHCONH-, R1 and R2 are each a hydrocarbon having 2 to 26 carbon atoms And the total number of carbon atoms of R 1 and R 2 is 9 to 30, and Z is —COO—, —OCO—, —O—, —CONH—, —NHCO—, —NHCONH—, —NHNHCO—. , -CONHNH -, - CH (C n H 2n OH) - or (where, n = 0 to 5) Rinari, a is assumed to be 0 or 1.

X, Y, Z, R1, and R2 constituting the chemical formula of the developer / color reducing agent are recording / erasing sensitivities required for the target reversible multicolor recording medium 10, that is, solubility in a solvent or polymer, melting point, Select and combine them appropriately according to various conditions such as the temperature at which coloring and decoloring are possible.
For example, compounds represented by the following general formulas (2) to (4) can be applied as the developer / color-reducing agent having electron acceptability.

  However, R3 shall represent a C8-24 hydrocarbon group.

  R4 is a hydrocarbon group having 8 to 24 carbon atoms.

  However, R5 and R6 are hydrocarbon groups having a total carbon number of 8 to 26, and n is an integer of 5 or less.

The first to third recording layers 11 to 13 contain light-to-heat conversion materials having absorption in different wavelength ranges.
As the light-heat conversion material, for example, the first recording layer 11 emits infrared light with a wavelength λ ₁ , the second recording layer 12 emits infrared light with a wavelength λ ₂ , and the third recording layer 13 emits infrared light with a wavelength λ ₃ . A material that absorbs heat and generates heat can be applied.

Examples of the light-to-heat conversion material contained in the first to third recording layers 11 to 13 include, for example, phthalocyanine dyes and cyanine dyes that are generally used as infrared absorbing dyes that hardly absorb in the visible wavelength range. Dyes, metal complex dyes, diimonium dyes, and the like can be applied.
Furthermore, in order to generate heat only in an arbitrary light-heat conversion material, it is preferable to select a combination of materials having a narrow light absorption band and not overlapping each other.

  Examples of the resin for forming the first to third recording layers 11 to 13 include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, and polyester. , Aromatic polyester, polyurethane, polycarbonate, polyacrylic acid ester, polymethacrylic acid ester, acrylic acid copolymer, maleic acid polymer, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, starch and the like. . Various additives such as an ultraviolet absorber may be used in combination with these resins as necessary.

  The first to third recording layers 11 to 13 are prepared by using the above-mentioned resin using a solvent for the reversible thermosensitive coloring composition composed of the leuco dye, the developer and the color reducing agent, the light-heat conversion material, and various additives. It can form by apply | coating the coating material dissolved and adjusted in each predetermined | prescribed formation surface. The solvent used at this time is preferably a solvent having high solubility of the developer / color reducing agent.

  The first to third recording layers 11 to 13 are each preferably formed to a thickness of about 1 to 20 μm, and more preferably about 3 to 15 μm. If these film thicknesses are less than 1 μm, a sufficient color density cannot be obtained, and if the film thickness exceeds 20 μm, the heat capacity of the recording layers 11 to 13 increases, and the color developability and decoloring properties deteriorate. .

  Translucent heat insulating layers 14 and 15 are formed between the first recording layer 11 and the second recording layer 12 and between the second recording layer 12 and the third recording layer 13, respectively. Is desirable. As a result, heat conduction from the adjacent recording layer is avoided, and so-called color fogging can be prevented.

The heat insulation layers 14 and 15 can be formed using a conventionally known translucent polymer. For example, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polyacrylic acid ester, polymethacrylic acid Examples include esters, acrylic acid copolymers, maleic acid polymers, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, and starch. These polymers may be used in combination with various additives such as ultraviolet absorbers as necessary.
Moreover, the heat insulation layers 14 and 15 can also be formed using a translucent inorganic film. For example, when porous silica, alumina, titania, carbon, or a composite thereof is used, the thermal conductivity is lowered and the heat insulating effect is high, which is preferable. These can be formed by a sol-gel method capable of forming a film from a liquid layer.

  The heat insulating layers 14 and 15 are preferably formed to a thickness of about 3 to 100 μm, and more preferably about 5 to 50 μm. If these film thicknesses are too thin, a sufficient heat insulating effect cannot be obtained, and if the film thickness is too thick, the thermal conductivity deteriorates when the entire recording medium is uniformly heated in the recording method to be described later, or the translucency is low. It is because it falls.

The protective layer 16 can be formed using a conventionally known ultraviolet curable resin or thermosetting resin, and the film thickness is preferably about 0.1 to 20 μm, more preferably about 0.5 to 5 μm.
This is because if the film thickness of the protective layer 16 is less than 0.1 μm, a sufficient protective effect cannot be obtained, whereas if the film thickness exceeds 20 μm, there is a disadvantage that the thermal conductivity deteriorates.

  Next, the principle of performing multicolor recording using the reversible multicolor recording medium 10 shown in FIG. 1 will be described.

First, the first principle of multicolor recording will be described.
The reversible multicolor recording medium 10 shown in FIG. 1 is entirely heated at a temperature at which each recording layer is erased, for example, at a temperature of about 120 ° C., and the first to third recording layers 11 to 13 are erased in advance. Leave in color. That is, in this state, it is assumed that the color of the support substrate 1 is exposed.

Next, an arbitrary part of the reversible multicolor recording medium 10 is irradiated with infrared light having an arbitrarily selected wavelength and output by a semiconductor laser or the like.
For example, when the first recording layer 11 is colored, an infrared ray having a wavelength λ ₁ is irradiated with energy that the first recording layer 11 reaches the coloring temperature, and the light-to-heat conversion material is heated to donate electrons. The color development reaction between the color developing compound and the electron donating developer / color-reducing agent is caused to color the irradiated portion.
Similarly, the second recording layer 12 and the third recording layer 13 are also irradiated with energy having a wavelength of λ ₂ and λ ₃ to reach the coloring temperature, respectively, so that each light-heat conversion material generates heat. To color the irradiated area.
As described above, an arbitrary portion of the reversible multicolor recording medium 10 can be colored, and a full-color image can be formed and various information can be recorded.

  By the way, when the first recording layer 11 or the second recording layer 12 is recorded, the transparency of the recording layer formed on the upper layer greatly affects the recording sensitivity of the lower recording layer. That is, when the recording layer is poorly soluble in the polymer of the developer / color reducing agent used in the recording layer formed on the upper layer of the predetermined recording layer and the recording layer is dispersed and cloudy, the irradiation is performed. Since the infrared rays are reflected and scattered by the upper layer, the recording sensitivity is remarkably lowered. For this reason, in the multilayer reversible multicolor recording medium 10 having the configuration shown in FIG. 1, it is possible to use a developing / color-reducing agent having a high solubility in a solvent or polymer for forming the recording layer. is important.

  Further, in the predetermined recording layer colored as described above, an infrared ray having an arbitrary wavelength is further irradiated with energy at which each recording layer 11 to 13 reaches the decoloring temperature, and the light-heat conversion material generates heat. Thus, the recording can be erased by causing a decoloring reaction between the coloring compound and the developer / color-reducing agent.

  Further, the entire reversible multicolor recording medium 10 partially colored as described above is uniformly heated at a temperature at which all the recording layers are decolored, for example, 120 ° C. Information and images can be erased, and recording can be repeated by performing the operations described above.

Next, the second principle of multicolor recording will be described.
First, the reversible multicolor recording medium 10 shown in FIG. 1 is heated on the entire surface at a temperature at which each of the recording layers 11 to 13 develops color, for example, at a high temperature of about 200 ° C., and then cooled. All of the recording layers 11 to 13 are colored in advance.

Next, an arbitrary part of the reversible multicolor recording medium 10 is irradiated with infrared light having an arbitrarily selected wavelength and output by a semiconductor laser or the like.
For example, when the first recording layer 11 is decolored, the recording layer 11 is irradiated with infrared light having a wavelength λ ₁ with such energy that the first recording layer 11 is decolored to generate heat. Is decolored.
Similarly, the second recording layer 12 and the third recording layer 13 are each irradiated with infrared rays having wavelengths λ ₂ and λ ₃ with energy to reach the decoloring temperature, and the respective light-to-heat conversion materials are applied. The irradiated portion can be decolored by generating heat.
As described above, an arbitrary portion of the reversible multicolor recording medium 10 can be erased, and a full-color image can be formed and various information can be recorded.

  In each of the recording layers 11 to 13 decolorized as described above, an infrared ray having an arbitrary wavelength is further irradiated with energy at which the recording layers 11 to 13 reach the coloring temperature, and the light-heat conversion material generates heat. Thus, by causing a color development reaction between the color forming compound and the developer / subtractor, any portion of the recording layer can be colored.

  Further, the entire reversible multicolor recording medium 10 partially erased or developed as described above is uniformly heated at a temperature at which all the recording layers are colored, for example, 200 ° C. Then, the recording information and the image can be erased by cooling, and the recording can be repeated again by performing the operation described above.

Which of the recording methods shown in the first principle and the second principle is applied to the reversible multicolor recording medium 10 of the present invention depends on the characteristics of the recording layer and the recording light source. Select appropriately according to the performance.
For example, the recording layer may be formed as a so-called positive type layer that develops color at a high temperature and erases at a temperature lower than that, or a so-called negative type layer that erases at a high temperature and develops color at a temperature below that. (For example, JP-A-8-197853).

Next, the reversible multicolor recording medium of the present invention will be described with specific examples and comparative examples. However, the reversible multicolor recording medium of the present invention is not limited to the following examples. . In addition, Examples A1 to 8, B1 to 4, and C1 to C4 in [Experiment A] to [Experiment C] shown below are examples corresponding to reference examples not belonging to the scope of the present invention. .

[Experiment A]
[Example A1]
In this example, as shown in FIG. 1, the first recording layer 11, the heat insulating layer 14, the second recording layer 12, the heat insulating layer 15, the third recording layer 13, and the protective layer are formed on the support substrate 1. A reversible multicolor recording medium having a so-called three-layer recording layer in which 16 is sequentially laminated is manufactured.

As the supporting substrate 1, a white polyethylene terephthalate substrate having a thickness of 1 mm was used.
As the first recording layer 11, a recording layer that can be colored yellow by applying a coating containing the following composition on the support substrate 1 with a wire bar and subjecting it to a heat drying treatment at 110 ° C. for 5 minutes. The film thickness was 5 μm. The absorbance of the first recording layer 11 with light having a wavelength of 915 nm was 1.0.

(Composition)
Leuco dye (fluorane compound: λmax = 490 nm): 1 part by weight developer / color-reducing agent (substance shown in the following chemical formula (5)): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, average molecular weight (M.W.) 115000)
Cyanine-based infrared absorbing dye: 0.10 parts by weight (Yamamoto Kasei, YKR-2081, absorption wavelength peak in recording layer: 910 nm)
Tetrahydrofuran (THF): 140 parts by weight

  On the first recording layer 11 formed as described above, an aqueous polyvinyl alcohol solution was applied and dried to form a heat insulating layer 14 having a thickness of 20 μm.

  On the heat insulation layer 14, the following composition as a second recording layer 12 is applied with a wire bar, and heat-dried at 110 ° C. for 5 minutes to form a layer capable of developing cyan in a thickness of 6 μm. did. The absorbance of the second recording layer 12 with light having a wavelength of 830 nm was 1.0.

(Composition)
Leuco dye (manufactured by Yamada Chemical Co., Ltd., H-3035): 1 part by weight developer / color-reducing agent (substance shown in the following chemical formula (5)): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, MW 115000)
Cyanine-based infrared absorbing dye: 0.08 parts by weight (manufactured by Yamamoto Kasei, YKR-2900, absorption wavelength peak in recording layer 830 nm)
Tetrahydrofuran (THF): 140 parts by weight

  On the second recording layer 12 formed as described above, a polyvinyl alcohol aqueous solution was applied and dried to form a heat insulating layer 15 having a thickness of 20 μm.

  A coating layer containing the following composition as a third recording layer 13 is applied to the heat insulating layer 15 with a wire bar, and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a recording layer capable of coloring magenta. The film thickness was 6 μm. The absorbance of the third recording layer 13 with light having a wavelength of 785 nm was 1.0.

(Composition)
Leuco dye (manufactured by Hodogaya Chemical Co., Ltd., Red DCF): 2 parts by weight developer / color-reducing agent (substance shown in chemical formula (5) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, MW 115000)
Cyanine-based infrared absorbing dye: 0.08 part by weight (Nippon Kayaku CY-10, absorption wavelength peak in recording layer 790 nm)
Tetrahydrofuran (THF): 140 parts by weight

  A protective layer 16 having a film thickness of about 2 μm was formed on the third recording layer 13 using an ultraviolet curable resin, and the intended reversible multicolor recording medium 10 was produced.

A specific example of the method for synthesizing the developer / color-reducing agent represented by the chemical formula (5) contained in the first to third recording layers 11 to 13 will be described.
In a 500 ml flask equipped with a stirrer, 13.8 g of 4-Hydroxybenzoic Acid, 29.9 g of Steric Hydrazide, 12.6 g of N, N'-Diisopropylcarbodiimide, 13.5 g of 1-Hydroxybenzotriazole, and tetrahydrofuran (THF) 250 ml of each was charged and refluxed at 90 ° C. for 6 hours. Then, it cooled to room temperature and filtered the deposit. The filtered reaction mixture was recrystallized with IPA to obtain the desired product. The yield was 85%, and the melting point of the target product was 155 ° C.

  The reversible multicolor recording medium 10 produced as described above is uniformly heated using a ceramic bar heated to 120 ° C., and the first, second and third recording layers 11, 12 and 13 are erased. A sample in a color state was used.

[Example A2]
The developing / color-reducing agent applied in Example A1 described above was changed to a compound represented by the following chemical formula (6). Other conditions were the same as in Example A1, and a sample was produced.
The synthesis method of the compound represented by the following chemical formula (6) is the same except that 4-Hydroxybenzoic Acid is changed to 3-Hydroxybenzoic Acid in the method of synthesizing the developer / color-reducing agent of the above chemical formula (5).

[Example A3]
The developing / color-reducing agent applied in Example A1 described above was changed to a compound represented by the following chemical formula (7). Other conditions were the same as in Example A1, and a sample was produced.
The method for synthesizing the compound represented by the following chemical formula (7) is the same except that 4-Hydroxybenzoic Acid in the method for synthesizing the developer / color-reducing agent represented by the chemical formula (5) is changed to 3,5-Dihydroxybenzoic Acid.

[Example A4]
The developing / color-reducing agent applied in Example A1 described above was changed to a compound represented by the following chemical formula (8). Other conditions were the same as in Example A1, and a sample was produced.
The method for synthesizing the compound represented by the following chemical formula (8) is the same except that 4-Hydroxybenzoic Acid is changed to 3,4-Dihydroxybenzoic Acid in the method for synthesizing the developer / color-reducing agent of the chemical formula (5).

[Example A5]
The developing / color-reducing agent applied in Example A1 described above was changed to a compound represented by the following chemical formula (9). Other conditions were the same as in Example A1, and a sample was produced.
The synthesis method of the compound represented by the following chemical formula (9) is the same except that 4-Hydroxybenzoic Acid is changed to 3-Chloro-4-hydroxybenzoic Acid in the method of synthesizing the developer / color-reducing agent of the above chemical formula (5). To do.

[Example A6]
The developing / color-reducing agent applied in Example A1 described above was changed to a compound represented by the following chemical formula (10). Other conditions were the same as in Example A1, and a sample was produced.
A method for synthesizing the compound represented by the following chemical formula (10) is shown below.
In a 500 ml flask equipped with a stirrer, 29.6 g of n-Octadecyl Isocyanate, 14.4 g of 4-Amino-3-Chlorophenol, and 250 ml of tetrahydrofuran (THF) were charged and refluxed at 90 ° C. for 5 hours. Then, it cooled to room temperature and filtered the deposit. The filtered reaction mixture was recrystallized with IPA to obtain the desired product. The yield was 95%, and the melting point of the target product was 133 ° C.

[Example A7]
The developing / color-reducing agent applied in Example A1 described above was changed to a compound represented by the following chemical formula (11). Other conditions were the same as in Example A1, and a sample was produced.
A method for synthesizing the compound represented by the following chemical formula (11) is shown below.
In a 500 ml flask equipped with a stirrer, 29.6 g of n-Octadecyl Isocyanate, 16.8 g of 2,4-dihydroxybenzoic acid hydradide, and 250 ml of tetrahydrofuran (THF) were charged and refluxed at 90 ° C. for 5 hours. Then, it cooled to room temperature and filtered the deposit. The filtered reaction mixture was recrystallized with IPA to obtain the desired product. The yield was 95%, and the melting point of the target product was 200 ° C.

[Example A8]
The developing / color-reducing agent applied in Example A1 described above was changed to a compound represented by the following chemical formula (12). Other conditions were the same as in Example A1, and a sample was produced.
The synthesis method of the compound represented by the following chemical formula (12) is the same as the synthesis method of the developer / color-reducing agent of the above chemical formula (11) except that 2,4-Dihydroxybenzoic acid hydrazide is changed to 3,5-Dihydroxybenzoic acid hydrazide. The same shall apply.

Each recording medium sample produced as described above was evaluated for recording line width, reflection density, recording layer transparency, and erasing characteristics.
Evaluation methods and evaluation results are shown below.

(Recording line width measurement)
(1) An arbitrary position of the sample was irradiated with a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW and a spot diameter of 80 μm while scanning at a speed of 300 mm / sec, and the recording line width was measured.
(2) Further, the recording line width was measured when the output of the semiconductor laser light was 100 mW and the scanning speed was 300 mm / sec.
(3) Further, the recording line width was measured when the output of the semiconductor laser light was 70 mW and the scanning speed was 150 mm / sec.

(Reflectance density measurement)
(1) Recording a solid image at an arbitrary position of the sample by recording a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 80 μm at a scanning speed of 300 mm / s at an interval of 10 μm. Went. The reflectance of the recorded sample was measured with a self-recording spectrophotometer equipped with an integrating sphere, and the reflection density (reflectance) at the peak wavelength was determined. In addition, the peak wavelengths at the time of laser beam irradiation with wavelengths of 785 nm, 830 nm, and 915 nm were 490 nm, 660 nm, and 530 nm, respectively.
(2) Further, the reflection density at the peak wavelength when the output of the semiconductor laser light was 100 mW and the scan speed was 300 mm / sec was obtained.
(3) Further, the reflection density was determined when the output of the semiconductor laser light was 70 mW and the scan speed was 150 mm / sec.

(Evaluation of recording layer transparency)
Each recording layer was formed with a single layer thickness of 6 μm, and was evaluated in four stages: ◎, ○, Δ, × from the one with good transparency.

(Erase characteristics evaluation: reflection density measurement after erasure)
(1) Recording a solid image at an arbitrary position of the sample by recording a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 80 μm at a scanning speed of 300 mm / s at an interval of 10 μm. Went.
Thereafter, the sample was irradiated with semiconductor laser light having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 250 μm while scanning at a speed of 200 mm / sec to erase the recording portion.
About the sample after erasure | elimination, the reflectance was measured with the self-recording spectrophotometer equipped with the integrating sphere, and the reflection density (reflectance) in a peak wavelength was calculated | required.
(2) At the time of erasing, the scanning speed of the semiconductor laser beam was set to 100 mm / sec, and the recording part was erased. About the sample after erasure | elimination, the reflectance was measured with the self-recording spectrophotometer equipped with the integrating sphere, and the reflection density (reflectance) in a peak wavelength was calculated | required.

(Evaluation results)
For the recording medium of [Examples A1 to A8], a recording line when recording a solid image using a laser beam with an output of 70 mW, a scanning speed of 300 mm / sec, a spot diameter of 80 μm, wavelengths of 915 nm, 830 nm, and 785 nm Table 1 below shows the evaluation results of the width, the reflection density at the obtained peak wavelength, and the transparency of the recording layer.
Table 2 below shows the measurement results of the recording line width when the output is 100 mW and the scanning speed is 300 mm / sec, and the obtained reflection density at the peak wavelength.
Further, the measurement results of the recording line width when the output is 70 mW and the scanning speed is 150 mm / sec and the obtained reflection density at the peak wavelength are shown in Table 3 below.

As shown in Tables 1 to 3, the line width recorded on the recording media of [Examples A1 to A8] is sufficiently wide for practical use under any conditions and has excellent recording sensitivity. all right.
Also, it was found that the reflection density of the solid image was sufficiently high for practical use under any conditions, and the irradiation light was converted into heat with high efficiency, and the recording layer was colored.
In addition, the recording layers constituting the recording media of [Examples A1 to A8] had very good transparency evaluation. Therefore, the recording layer constituting the recording medium of the present invention has high solubility of the developer / color reducing agent, high light-heat conversion efficiency and coloring efficiency in the solvent and the polymer, and realizes excellent recording sensitivity. I understood that I was able to do it.

Next, with respect to the erasing characteristics evaluation in the recording media of [Examples A1 to A8], the measurement results when the output of the semiconductor laser light at the time of erasing is 70 mW and the scanning speed is 200 mm / s are shown in [Table 4] below. Shown in
The measurement results when the output of the semiconductor laser light is 70 mW and the scanning speed is 100 mm / s are shown in Table 5 below.

  As shown in [Table 4] and [Table 5], the reflection density after erasure in the recording media of [Examples A1 to A8] was 0.10 or less at each wavelength and was almost colorless. This is because the recording layers used in [Examples A1 to A8] have good transparency and can perform light-to-heat conversion efficiently, so that sufficient erasure can be performed.

[Experiment B]
[Example B1]
In this example, as shown in FIG. 1, the first recording layer 11, the heat insulating layer 14, the second recording layer 12, the heat insulating layer 15, the third recording layer 13, and the protective layer 16 are formed on the support substrate 1. A reversible multi-color recording medium having a so-called three-layer recording layer in which are sequentially laminated is prepared.

  As the support substrate 1, a white polyethylene terephthalate substrate having a thickness of 1 mm was prepared. Next, as the first recording layer 11, the following composition is applied on the support substrate 1 with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a recording layer capable of developing yellow. The thickness was 6 μm. At this time, the absorbance in light having a wavelength of 915 nm was 1.0.

(Composition)
Leuco dye (fluorane compound: λmax = 490 nm): 1 part by weight developer / color-reducing agent (substance shown in chemical formula (13) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, average molecular weight (M.W.) 115000)
Cyanine infrared absorbing dye: 0.10 parts by weight (manufactured by Yamamoto Kasei, YKR-2081, absorption wavelength peak in recording layer 910 nm)
Tetrahydrofuran (THF): 140 parts by weight

  On the first recording layer 11 formed as described above, an aqueous polyvinyl alcohol solution was applied and dried to form a heat insulating layer 14 having a thickness of 20 μm.

  On the heat insulation layer 14, the following composition was applied as a second recording layer 12 with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a layer capable of developing cyan in a thickness of 6 μm. . At this time, the absorbance in light having a wavelength of 830 nm was 1.0.

(Composition)
Leuco dye: 1 part by weight (manufactured by Yamada Chemical Co., Ltd .: H-3035, a substance represented by the following chemical formula (14))

Developer / color-reducing agent (substance shown in chemical formula (13) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, MW 115000)
Cyanine-based infrared absorbing dye: 0.08 parts by weight (manufactured by Yamamoto Kasei, YKR-2900, absorption wavelength peak in recording layer 830 nm)
Tetrahydrofuran (THF): 140 parts by weight

  On the second recording layer 12 formed as described above, a polyvinyl alcohol aqueous solution was applied and dried to form a heat insulating layer 15 having a thickness of 20 μm.

  On the heat insulation layer 15, the following composition as a third recording layer 13 was applied with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a layer capable of developing magenta with a film thickness of 6 μm. . At this time, the absorbance in light having a wavelength of 785 nm was 1.0.

(Composition)
Leuco dye: 2 parts by weight (manufactured by Hodogaya Chemical Co., Ltd .: Red DCF (substance shown in chemical formula (15) below)

Developer / color-reducing agent (substance shown in chemical formula (13) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, MW 115000)
Cyanine-based infrared absorbing dye: 0.08 part by weight (Nippon Kayaku CY-10, absorption wavelength peak in recording layer 790 nm)
Tetrahydrofuran (THF): 140 parts by weight

  A protective layer 16 having a film thickness of about 2 μm was formed on the third recording layer 13 using an ultraviolet curable resin, and the intended reversible multicolor recording medium 10 was produced.

  The reversible multicolor recording medium 10 manufactured as described above is uniformly heated using a ceramic bar heated to 120 ° C., and the first to third recording layers 11 to 13 are decolored. Was used as a sample.

Next, a specific example of the method for synthesizing the developer / color-reducing agent shown in the chemical formula (13) contained in the first to third recording layers 11 to 13 will be shown.
In a 500 ml flask equipped with a stirrer, 15.3 g of 5-aminosalicylic acid, 28.4 g of stearic acid, 13.5 g of 1-hydroxybenzotriazole, 12.6 g of N, N′-Diisopropylcarodiimide, and tetrahydrofuran (THF) were added. 250 ml each was charged and refluxed at 90 ° C. for 5 hours.
After completion of the reaction, the reaction mixture was filtered to collect crystals, and then recrystallized with IPA to obtain the desired product. The yield was 70%.

[Example B2]
The developing / color-reducing agent applied in Example B1 described above was changed to a compound represented by the following chemical formula (16). Other conditions were the same as in Example B1, and a sample was produced.
The synthesis method of the compound represented by the following chemical formula (16) is the same except that the 5-Aminosalicylic acid in the method for synthesizing the developer / color-reducing agent represented by the chemical formula (13) is changed to 4-Aminosalicylic acid.

[Example B3]
The developing / color-reducing agent applied in Example B1 described above was changed to a compound represented by the following chemical formula (17). The other conditions were the same as in Example B1, and a sample was produced.
The method for synthesizing the compound represented by the following chemical formula (17) is the same except that 5-Aminosalicylic acid in the method for synthesizing the developer / color-reducing agent represented by the chemical formula (13) is changed to 3-Aminosalicylic acid.

[Example B4]
The developing / color-reducing agent applied in Example B1 described above was changed to a compound represented by the following chemical formula (18). The other conditions were the same as in Example B1, and a sample was produced.
The method for synthesizing the compound represented by the following chemical formula (18) is the same except that 5-Aminosalicylic acid in the method for synthesizing the developer / color-reducing agent represented by the chemical formula (13) is changed to 3-Hydroxy-4aminobenzoic acid.

[Example B5]
The reversible multicolor recording medium produced in Example B1 described above was heated using a ceramic bar heated to 180 ° C., then cooled, and the first recording layer 11, the second recording layer 12, and the third recording medium were then cooled. Each of the recording layers 13 was colored in advance as a sample.

[Test Example B1]
The developing / color-reducing agent applied in Example B1 described above was changed to a compound represented by the following chemical formula (19). The other conditions were the same as in Example B1, and a sample was produced.

[Comparative Example B1]
The developing / color-reducing agent applied in Example B1 described above was changed to a compound represented by the following chemical formula (20). The other conditions were the same as in Example B1, and a sample was produced.

[Test Example B2]
In Example B1 described above, the developer / color reducing agent was changed to a compound represented by the following chemical formula (21). The other conditions were the same as in Example B1, and a sample was produced.

[Comparative Example B2]
In Example B1 described above, the developing / color-reducing agent was changed to a compound represented by the following chemical formula (22). The other conditions were the same as in Example B1, and a sample was produced.

[Test Example B3]
In Example B1 described above, the developer / color reducing agent was changed to a compound represented by the following chemical formula (23). The other conditions were the same as in Example B1, and a sample was produced.

Each recording medium sample produced as described above was evaluated for recording line width, reflection density, recording layer transparency, and erasing characteristics.
Evaluation methods and evaluation results are shown below.

(Recording line width measurement)
(1) An arbitrary position of the sample was irradiated with a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW and a spot diameter of 80 μm while scanning at a speed of 300 mm / sec, and the recording line width was measured.
(2) Further, the recording line width was measured when the output of the semiconductor laser light was 100 mW and the scanning speed was 300 mm / sec.
(3) Further, the recording line width was measured when the output of the semiconductor laser light was 70 mW and the scanning speed was 150 mm / sec.

(Reflectance density measurement)
(1) Recording a solid image at an arbitrary position of the sample by recording a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 80 μm at a scanning speed of 300 mm / s at an interval of 10 μm. Went. The reflectance of the recorded sample was measured with a self-recording spectrophotometer equipped with an integrating sphere, and the reflection density (reflectance) at the peak wavelength was determined. In addition, the peak wavelengths at the time of laser beam irradiation with wavelengths of 785 nm, 830 nm, and 915 nm were 490 nm, 660 nm, and 530 nm, respectively.
(2) Further, the reflection density at the peak wavelength when the output of the semiconductor laser light was 100 mW and the scan speed was 300 mm / sec was obtained.
(3) Further, the reflection density was determined when the output of the semiconductor laser light was 70 mW and the scan speed was 150 mm / sec.

(Evaluation of recording layer transparency)
Each recording layer was formed with a single layer thickness of 6 μm, and was evaluated in four stages: ◎, ○, Δ, × from the one with good transparency.

(Erase characteristics evaluation: reflection density measurement after erasure)
(1) Recording a solid image at an arbitrary position of the sample by recording a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 80 μm at a scanning speed of 300 mm / s at an interval of 10 μm. Went.
Thereafter, the sample was irradiated with semiconductor laser light having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 250 μm while scanning at a speed of 200 mm / sec to erase the recording portion.
About the sample after erasure | elimination, the reflectance was measured with the self-recording spectrophotometer equipped with the integrating sphere, and the reflection density (reflectance) in a peak wavelength was calculated | required.
(2) At the time of erasing, the scanning speed of the semiconductor laser beam was set to 100 mm / sec, and the recording part was erased. About the sample after erasure | elimination, the reflectance was measured with the self-recording spectrophotometer equipped with the integrating sphere, and the reflection density (reflectance) in a peak wavelength was calculated | required.

(Evaluation results)
With respect to the recording media of [Examples B1 to B4], [Test Examples B1 to B3], and [Comparative Example B1], using a laser beam with an output of 70 mW, a spot diameter of 80 μm, wavelengths of 915 nm, 830 nm, and 785 nm, a scanning speed of 300 mm / Table 6 below shows the evaluation results of the recording line width, the reflection density at the obtained peak wavelength, and the transparency of the recording layer when a solid image was recorded in sec.
Table 7 below shows the measurement results of the recording line width when the output is 100 mW, the scanning speed is 300 mm / sec, and the obtained reflection density at the peak wavelength.
Further, the measurement results of the recording line width when the output is 70 mW and the scanning speed is 150 mm / sec and the obtained reflection density at the peak wavelength are shown in Table 8 below.

As shown in Tables 6 to 8, the line width recorded on the recording medium of [Examples B1 to B4] is wider than that of [Test Examples B1 to B3] and [Comparative Example B1] in any condition. It was found that the recording sensitivity was excellent.
Also, it was found that the reflection density of the solid image was sufficiently high for practical use under any conditions, and the irradiation light was converted into heat with high efficiency, and the recording layer was colored.
The recording layers constituting the recording media of [Examples B1 to B4] had very good transparency evaluation. Therefore, the recording layer constituting the recording medium of the present invention has high solubility of the developer / color reducing agent, high light-heat conversion efficiency and coloring efficiency in the solvent and the polymer, and realizes excellent recording sensitivity. I understood that I was able to do it.

  In the recording media of [Test Examples B1 to B3], when the semiconductor laser conditions are a power of 70 mW and a scanning speed of 300 mm / s, as shown in Table 6, the recording line width is narrow and the reflection density is low. However, when the laser power was increased to 100 mW or the scan speed was decreased to 150 mm / s, the recording media of [Examples B1 to B4] The same recording line width was obtained, the reflection density was good, and excellent recording sensitivity was realized.

  On the other hand, the recording layer using the developing / color-reducing agent shown in [Comparative Example B1] was inferior in solubility in the polymer, dispersed and clouded, and the transparency was deteriorated. As a result, in the order of the third, second, and first recording layers, the lower the recording line width, the lower the sensitivity. This is because the irradiated laser light is reflected and scattered by the undissolved developing / color-reducing agent in the upper layer, and the efficiency of light-heat conversion is lowered. It has been found that the transparency of the recording layer has a great influence on the recording sensitivity in the optical writing type thermal recording medium.

Next, for the erasing characteristics evaluation in the recording media of [Example B1], [Test Examples B1, B3], and [Comparative Example B2], the output of the semiconductor laser light at the time of erasing is 70 mW, and the scanning speed is 200 mm / second. The measurement results when s is shown in Table 9 below.
The measurement results when the output of the semiconductor laser light is 70 mW and the scanning speed is 100 mm / s are shown in Table 10 below.

  As shown in Tables 9 and 10, the reflection density after erasure in the recording medium of [Example B1] was 0.02 or less at each wavelength and was almost colorless. This is because the transparency of the recording layer used in [Example B1] was good and the light-heat conversion could be performed efficiently, so that sufficient erasure could be performed.

  On the other hand, in [Comparative Example B2], since the alkyl chain length of the compound of the developer / color-reducing agent was short and the cohesive force between the molecules was lowered, the erasing characteristics were deteriorated.

  In [Test Examples B1 and B3], the cohesive force between molecules increased and the solubility was reduced, leading to a decrease in light-heat conversion efficiency, and a semiconductor laser scanning speed of 200 mm / s. In Table 1, the erasing characteristics deteriorated as shown in Table 9. However, when the scanning speed was set to 100 mm / s, practically sufficient erasing characteristics were obtained as shown in Table 10.

In addition, since the recording medium according to the present invention having a high light-to-heat conversion efficiency using a compound of a developer / color reducing agent having high solubility in a solvent and a polymer can obtain excellent erasing characteristics, The reversible multicolor recording medium produced in Example B5] was heated using a ceramic bar heated to 180 ° C., then cooled and pre-colored, and then each of wavelengths 915 nm, 830 nm, and 785 nm. It was confirmed that it is possible to obtain a recorded image of multicolor recording by irradiating a laser beam and erasing the recording portion.
It was confirmed that the image thus obtained showed color development, contrast, and fineness equivalent to those of a multicolor recording image recorded from a previously decolored state as in [Example B1].

[Experiment C]
[Example C1]
In this example, as shown in FIG. 1, the first recording layer 11, the heat insulating layer 14, the second recording layer 12, the heat insulating layer 15, the third recording layer 13, and the protective layer 16 are provided on the support substrate 1. A reversible multicolor recording medium having a so-called three-layer recording layer sequentially laminated was produced.

  As the support substrate 1, a white polyethylene terephthalate substrate having a thickness of 1 mm was prepared. Next, as the first recording layer 11, the following composition is applied on the support substrate 1 with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a recording layer capable of developing yellow. The thickness was 6 μm. At this time, the absorbance in light having a wavelength of 915 nm was 1.0.

(Composition)
Leuco dye (fluorane compound: λmax = 490 nm): 1 part by weight developer / color-reducing agent (substance shown in chemical formula (24) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, average molecular weight (M.W.) 115000)
Cyanine infrared absorbing dye: 0.10 parts by weight (manufactured by Yamamoto Kasei, YKR-2081, absorption wavelength peak in recording layer 910 nm)
Tetrahydrofuran (THF): 140 parts by weight

  On the first recording layer 11 formed as described above, an aqueous polyvinyl alcohol solution was applied and dried to form a heat insulating layer 14 having a thickness of 20 μm.

  On the heat insulation layer 14, the following composition was applied as a second recording layer 12 with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a layer capable of developing cyan in a thickness of 6 μm. . At this time, the absorbance in light having a wavelength of 830 nm was 1.0.

(Composition)
Leuco dye: 1 part by weight (manufactured by Yamada Chemical Industry: H-3035 (substance shown in chemical formula (25) below)

Developer / subtractor (substance shown in chemical formula (24) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, MW 115000)
Cyanine-based infrared absorbing dye: 0.08 parts by weight (manufactured by Yamamoto Kasei, YKR-2900, absorption wavelength peak in recording layer 830 nm)
Tetrahydrofuran (THF): 140 parts by weight

  On the second recording layer 12 formed as described above, a polyvinyl alcohol aqueous solution was applied and dried to form a heat insulating layer 15 having a thickness of 20 μm.

  On the heat insulation layer 15, the following composition as a third recording layer 13 was applied with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a layer capable of developing magenta with a film thickness of 6 μm. . The absorbance of the third recording layer 13 with light having a wavelength of 785 nm was 1.0.

(Composition)
Leuco dye: 2 parts by weight (manufactured by Hodogaya Chemical Co., Ltd .: Red DCF (substance represented by the following chemical formula (26))

Developer / subtractor (substance shown in chemical formula (24) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, MW 115000)
Cyanine-based infrared absorbing dye: 0.08 part by weight (Nippon Kayaku CY-10, absorption wavelength peak in recording layer 790 nm)
Tetrahydrofuran (THF): 140 parts by weight

  A protective layer 16 having a film thickness of about 2 μm was formed on the third recording layer 13 using an ultraviolet curable resin, and the intended reversible multicolor recording medium 10 was produced.

  The reversible multicolor recording medium 10 manufactured as described above is uniformly heated using a ceramic bar heated to 120 ° C., and the first to third recording layers 11 to 13 are decolored. Was used as a sample.

Next, a specific example of the method for synthesizing the developer / color reducing agent represented by the chemical formula (24) contained in the first to third recording layers 11 to 13 will be described.
In a 500 ml flask equipped with a stirrer, 15.3 g of 5-aminosalicylic acid, 29.5 g of n-Octadecyl isocyanate, and 250 ml of tetrahydrofuran (THF) were charged and refluxed at 90 ° C. for 6 hours.
After completion of the reaction, the reaction mixture was recrystallized to obtain the desired product.
The yield was 75%, and the melting point of the target product was 210 ° C.

[Example C2]
The developing / color-reducing agent applied in Example C1 described above was changed to a compound represented by the following chemical formula (27). Other conditions were the same as in Example C1, and a sample was produced.
The method for synthesizing the compound represented by the following chemical formula (27) is the same except that 5-Aminosalicylic acid in the method for synthesizing the developer / color-reducing agent represented by the chemical formula (24) is changed to 4-Aminosalicylic acid.

[Example C3]
The developing / color-reducing agent applied in Example C1 was changed to the compound represented by the following chemical formula (28). The other conditions were the same as in Example C1, and a sample was produced.
The method for synthesizing the compound represented by the following chemical formula (28) is the same except that 5-Aminosalicylic acid in the method for synthesizing the developer / color-reducing agent represented by the chemical formula (24) is changed to 3-Aminosalicylic acid.

[Example C4]
The developing / color-reducing agent applied in Example C1 was changed to the compound represented by the following chemical formula (29). The other conditions were the same as in Example C1, and a sample was produced.
The synthesis method of the compound represented by the following chemical formula (29) is the same except that 5-Aminosalicylic acid in the synthesis method of the developer / color-reducing agent of the above chemical formula (24) is changed to 3-Hydroxy-4aminobenzoic acid.

[Example C5]
The reversible multicolor recording medium produced in Example C1 described above was heated using a ceramic bar heated to 180 ° C., then cooled, and the first recording layer 11, the second recording layer 12, and the third recording medium were then cooled. Each of the recording layers 13 was colored in advance as a sample.

[Test Example C1]
The developing / color-reducing agent applied in Example C1 was changed to the compound represented by the following chemical formula (30). The other conditions were the same as in Example C1, and a sample was produced.

[Comparative Example C1]
The developing / color-reducing agent applied in Example C1 described above was changed to a compound represented by the following chemical formula (31). The other conditions were the same as in Example C1, and a sample was produced.

[Test Example C2]
In Example C1 described above, the developing / color-reducing agent was changed to a compound represented by the following chemical formula (32). The other conditions were the same as in Example C1, and a sample was produced.

[Comparative Example C2]
In Example C1 described above, the developing / color-reducing agent was changed to a compound represented by the following chemical formula (33). The other conditions were the same as in Example C1, and a sample was produced.

[Test Example C3]
In Example C1 described above, the developing / color-reducing agent was changed to a compound represented by the following chemical formula (34). The other conditions were the same as in Example C1, and a sample was produced.

Each recording medium sample produced as described above was evaluated for recording line width, reflection density, recording layer transparency, and erasing characteristics.
Evaluation methods and evaluation results are shown below.

(Recording line width measurement)
(1) An arbitrary position of the sample was irradiated with a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW and a spot diameter of 80 μm while scanning at a speed of 300 mm / sec, and the recording line width was measured.
(2) Further, the recording line width was measured when the output of the semiconductor laser light was 100 mW and the scanning speed was 300 mm / sec.
(3) Further, the recording line width was measured when the output of the semiconductor laser light was 70 mW and the scanning speed was 150 mm / sec.

(Reflectance density measurement)
(1) Recording a solid image at an arbitrary position of the sample by recording a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 80 μm at a scanning speed of 300 mm / s at an interval of 10 μm. Went. The reflectance of the recorded sample was measured with a self-recording spectrophotometer equipped with an integrating sphere, and the reflection density (reflectance) at the peak wavelength was determined. In addition, the peak wavelengths at the time of laser beam irradiation with wavelengths of 785 nm, 830 nm, and 915 nm were 490 nm, 660 nm, and 530 nm, respectively.
(2) Further, the reflection density at the peak wavelength when the output of the semiconductor laser light was 100 mW and the scan speed was 300 mm / sec was obtained.
(3) Further, the reflection density was determined when the output of the semiconductor laser light was 70 mW and the scan speed was 150 mm / sec.

(Evaluation of recording layer transparency)
Each recording layer was formed with a single layer thickness of 6 μm, and was evaluated in four stages: ◎, ○, Δ, × from the one with good transparency.

(Erase characteristics evaluation: reflection density measurement after erasure)
(1) Recording a solid image at an arbitrary position of the sample by recording a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 80 μm at a scanning speed of 300 mm / s at an interval of 10 μm. Went.
Thereafter, the sample was irradiated with semiconductor laser light having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 250 μm while scanning at a speed of 200 mm / sec to erase the recording portion.
About the sample after erasure | elimination, the reflectance was measured with the self-recording spectrophotometer equipped with the integrating sphere, and the reflection density (reflectance) in a peak wavelength was calculated | required.
(2) At the time of erasing, the scanning speed of the semiconductor laser beam was set to 100 mm / sec, and the recording part was erased. About the sample after erasure | elimination, the reflectance was measured with the self-recording spectrophotometer equipped with the integrating sphere, and the reflection density (reflectance) in a peak wavelength was calculated | required.

(Evaluation results)
For the recording media of [Examples C1 to C4], [Test Examples C1 to C3], and [Comparative Example C1], using a laser beam with an output of 70 mW, a spot diameter of 80 μm, wavelengths of 915 nm, 830 nm, and 785 nm, a scanning speed of 300 mm / [Table 11] shows the evaluation results of the recording line width, the reflection density at the obtained peak wavelength, and the transparency of the recording layer when a solid image is recorded in sec.
The measurement results of the recording line width when the output is 100 mW, the scanning speed is 300 mm / sec, and the obtained reflection density at the peak wavelength are shown in Table 12 below.
Furthermore, the measurement results of the recording line width when the output is 70 mW and the scanning speed is 150 mm / sec and the obtained reflection density at the peak wavelength are shown in Table 13 below.

As shown in Tables 11 to 13, the line width recorded on the recording medium of [Examples C1 to C4] is wider than that of [Test Examples C1 to C3] and [Comparative Example C1] under any conditions. It was found that the recording sensitivity was excellent.
Also, it was found that the reflection density of the solid image was sufficiently high for practical use under any conditions, and the irradiation light was converted into heat with high efficiency, and the recording layer was colored.
The recording layers constituting the recording media of [Examples C1 to C4] had very good transparency evaluation. Therefore, the recording layer constituting the recording medium of the present invention has high solubility of the developer / color reducing agent, high light-heat conversion efficiency and coloring efficiency in the solvent and the polymer, and realizes excellent recording sensitivity. I understood that I was able to do it.

In the recording media of [Test Examples C1 to C3], as shown in Table 11, when the power of the semiconductor laser is 70 mW and the scan speed is 300 mm / s, the recording line width is narrow and the reflection density is as shown in Table 11. However, when the laser power was increased to 100 mW or the scan speed was decreased to 150 mm / s, the recording media of [Examples C1 to C4] The same recording line width was obtained, the reflection density was good, and excellent recording sensitivity was realized.

  On the other hand, the recording layer using the developing / color-reducing agent shown in [Comparative Example C1] was inferior in solubility in the polymer, dispersed and clouded, and the transparency was deteriorated. As a result, in the order of the third, second, and first recording layers, the lower the recording line width, the lower the sensitivity. This is because the irradiated laser light is reflected and scattered by the undissolved developing / color-reducing agent in the upper layer, and the efficiency of light-heat conversion is lowered. It has been found that the transparency of the recording layer has a great influence on the recording sensitivity in the optical writing type thermal recording medium.

Next, for the erasing characteristics evaluation in the recording media of [Example C1], [Test Examples C1, C3], and [Comparative Example C2], the output of the semiconductor laser light at the time of erasing is 70 mW, and the scanning speed is 200 mm / The measurement results when s is shown in Table 14 below.
The measurement results when the output of the semiconductor laser light is 70 mW and the scanning speed is 100 mm / s are shown in Table 15 below.

  As shown in Tables 14 and 15, the reflection density after erasure in the recording medium of [Example C1] was 0.02 or less at each wavelength and was almost colorless. This is because the recording layer used in [Example C1] has good transparency, can perform light-to-heat conversion efficiently, and can perform sufficient erasure.

  On the other hand, in [Comparative Example C2], the alkyl chain length of the compound of the developer / color-reducing agent was short and the cohesive force between the molecules was reduced, so that the erasing characteristics deteriorated.

  In [Test Examples C1 and C3], the solubility between the molecules of the compound of the developer / color-reducing agent increased, so that the solubility was reduced. When the semiconductor laser scan speed was 200 mm / s, As shown in Table 14, the erasing characteristics deteriorated. However, when the scanning speed was set to 100 mm / s, practically sufficient erasing characteristics were obtained as shown in Table 15.

In addition, since the recording medium according to the present invention having a high light-to-heat conversion efficiency using a compound of a developer / color reducing agent having high solubility in a solvent and a polymer can obtain excellent erasing characteristics, The reversible multicolor recording medium produced in Example C5] was heated using a ceramic bar heated to 180 ° C., then cooled and pre-colored, and then each of wavelengths 915 nm, 830 nm, and 785 nm. It was confirmed that it is possible to obtain a recorded image of multicolor recording by irradiating a laser beam and erasing the recording portion.
It was confirmed that the image thus obtained showed color development, contrast, and fineness equivalent to those of a multicolor recording image recorded from a previously decolored state as in [Example C1].

[Experiment D]
[Example D1]
In this example, as shown in FIG. 1, the first recording layer 11, the heat insulating layer 14, the second recording layer 12, the heat insulating layer 15, the third recording layer 13, and the protective layer 16 are formed on the support substrate 1. A reversible multicolor recording medium having a so-called three-layer recording layer in which are sequentially stacked.

  As the support substrate 1, a white polyethylene terephthalate substrate having a thickness of 1 mm was prepared. Next, as the first recording layer 11, the following composition is applied on the support substrate 1 with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a recording layer capable of developing yellow. The thickness was 6 μm. At this time, the absorbance in light having a wavelength of 915 nm was 1.0.

(Composition)
Leuco dye (fluoran compound: λmax = 490 nm): 1 part by weight developer / color-reducing agent (substance shown in chemical formula (35) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, average molecular weight (M.W.) 115000)
Cyanine infrared absorbing dye: 0.10 parts by weight (manufactured by Yamamoto Kasei, YKR-2081, absorption wavelength peak in recording layer 910 nm)
Tetrahydrofuran (THF): 140 parts by weight

  On the first recording layer 11 formed as described above, an aqueous polyvinyl alcohol solution was applied and dried to form a heat insulating layer 14 having a thickness of 20 μm.

  On the heat insulation layer 14, the following composition was applied as a second recording layer 12 with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a layer capable of developing cyan in a thickness of 6 μm. . At this time, the absorbance in light having a wavelength of 830 nm was 1.0.

(Composition)
Leuco dye: 1 part by weight (manufactured by Yamada Chemical Industries: H-3035 (substance shown in chemical formula (36) below)

Developer / color-reducing agent (substance shown in chemical formula (35) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, MW 115000)
Cyanine-based infrared absorbing dye: 0.08 parts by weight (manufactured by Yamamoto Kasei, YKR-2900, absorption wavelength peak in recording layer 830 nm)
Tetrahydrofuran (THF): 140 parts by weight

  On the second recording layer 12 formed as described above, a polyvinyl alcohol aqueous solution was applied and dried to form a heat insulating layer 15 having a thickness of 20 μm.

  On the heat insulation layer 15, the following composition as a third recording layer 13 was applied with a wire bar and subjected to a heat drying treatment at 110 ° C. for 5 minutes to form a layer capable of developing magenta with a film thickness of 6 μm. . The absorbance of the third recording layer 13 with light having a wavelength of 785 nm was 1.0.

(Composition)
Leuco dye: 2 parts by weight (manufactured by Hodogaya Chemical Co., Ltd .: Red DCF (substance represented by the following chemical formula (37))

Developer / color-reducing agent (substance shown in chemical formula (35) below): 4 parts by weight

Vinyl chloride vinyl acetate copolymer: 10 parts by weight (90% vinyl chloride, 10% vinyl acetate, MW 115000)
Cyanine-based infrared absorbing dye: 0.08 part by weight (Nippon Kayaku CY-10, absorption wavelength peak in recording layer 790 nm)
Tetrahydrofuran (THF): 140 parts by weight

  A protective layer 16 having a thickness of about 2 μm was formed on the third recording layer 13 using an ultraviolet curable resin, and the intended reversible multicolor recording medium 10 was produced.

  The reversible multicolor recording medium 10 manufactured as described above is uniformly heated using a ceramic bar heated to 120 ° C., and the first to third recording layers 11 to 13 are decolored. Was used as a sample.

Next, a specific example of the method for synthesizing the developer / color reducing agent represented by the chemical formula (35) contained in the first to third recording layers 11 to 13 will be described.
In a 1000 ml flask equipped with a stirrer, 5-Aminosalicylic acid: 15.3 g, 12-Hydroxystearic acid: 30.0 g, Diphenylphosphoryl azide: 27.5 g, Triethylamine: 10.1 g, and tetrahydrofuran (THF): 500 ml, respectively Charged and refluxed at 90 ° C. for 6 hours.
After completion of the reaction, the reaction mixture was cooled to room temperature and filtered to obtain a desired product by recrystallization from IPA. The yield was 55%.

[Example D2]
The developing / color-reducing agent applied in Example D1 described above was changed to a compound represented by the following chemical formula (38). Other conditions were the same as in Example D1, and a sample was produced.
The synthesis method of the compound represented by the following chemical formula (38) is the same except that the 5-Aminosalicylic acid in the synthesis method of the developer / color-reducing agent represented by the chemical formula (35) is changed to 4-Aminosalicylic acid.

[Example D3]
The developing / color-reducing agent applied in Example D1 described above was changed to a compound represented by the following chemical formula (39). Other conditions were the same as in Example D1, and a sample was produced.
The method for synthesizing the compound represented by the following chemical formula (39) is the same except that 5-Aminosalicylic acid in the method for synthesizing the developer / color-reducing agent represented by the chemical formula (35) is changed to 3-Aminosalicylic acid.

[Example D4]
The developing / color-reducing agent applied in Example D1 described above was changed to a compound represented by the following chemical formula (40). Other conditions were the same as in Example D1, and a sample was produced.
The synthesis method of the compound represented by the following chemical formula (40) is the same except that 5-Aminosalicylic acid in the method for synthesizing the developer / color-reducing agent of the above chemical formula (35) is changed to 3-Hydroxy-4aminobenzoic acid.

[Example D5]
The reversible multicolor recording medium produced in Example D1 described above was heated using a ceramic bar heated to 180 ° C., then cooled, and the first recording layer 11, the second recording layer 12, and the third recording medium were then cooled. Each of the recording layers 13 was colored in advance as a sample.

[Test Example D1]
The developing / color-reducing agent applied in Example D1 described above was changed to a compound represented by the following chemical formula (41). Other conditions were the same as in Example D1, and a sample was produced.

[Comparative Example D1]
The developing / color-reducing agent applied in Example D1 described above was changed to a compound represented by the following chemical formula (42). Other conditions were the same as in Example D1, and a sample was produced.

[Test Example D2]
In Example D1 described above, the developing / color-reducing agent was changed to a compound represented by the following chemical formula (43). Other conditions were the same as in Example D1, and a sample was produced.

[Comparative Example D2]
In Example D1 described above, the developing / color-reducing agent was changed to a compound represented by the following chemical formula (44). Other conditions were the same as in Example D1, and a sample was produced.

[Test Example D3]
In Example D1 described above, the developing / color-reducing agent was changed to a compound represented by the following chemical formula (45). Other conditions were the same as in Example D1, and a sample was produced.

[Test Example D4]
In Example D1 described above, the developer / color reducing agent was changed to the compound represented by the following chemical formula (46). Other conditions were the same as in Example D1, and a sample was produced.

Each recording medium sample produced as described above was evaluated for recording line width, reflection density, recording layer transparency, and erasing characteristics.
Evaluation methods and evaluation results are shown below.

(Recording line width measurement)
(1) An arbitrary position of the sample was irradiated with a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW and a spot diameter of 80 μm while scanning at a speed of 300 mm / sec, and the recording line width was measured.
(2) Further, the recording line width was measured when the output of the semiconductor laser light was 100 mW and the scanning speed was 300 mm / sec.
(3) Further, the recording line width was measured when the output of the semiconductor laser light was 70 mW and the scanning speed was 150 mm / sec.

(Reflectance density measurement)
(1) Recording a solid image at an arbitrary position of the sample by recording a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 80 μm at a scanning speed of 300 mm / s at an interval of 10 μm. Went. The reflectance of the recorded sample was measured with a self-recording spectrophotometer equipped with an integrating sphere, and the reflection density (reflectance) at the peak wavelength was determined. In addition, the peak wavelengths at the time of laser beam irradiation with wavelengths of 785 nm, 830 nm, and 915 nm were 490 nm, 660 nm, and 530 nm, respectively.
(2) The reflection density was determined when the output of the semiconductor laser light was 100 mW and the scan speed was 300 mm / sec.
(3) Further, the reflection density was determined when the output of the semiconductor laser light was 70 mW and the scan speed was 150 mm / sec.

(Evaluation of recording layer transparency)
Each recording layer was formed with a single layer thickness of 6 μm, and was evaluated in four stages: ◎, ○, Δ, × from the one with good transparency.

(Erase characteristics evaluation: reflection density measurement after erasure)
(1) Recording a solid image at an arbitrary position of the sample by recording a semiconductor laser beam having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 80 μm at a scanning speed of 300 mm / s at an interval of 10 μm. Went.
Thereafter, the sample was irradiated with semiconductor laser light having a wavelength of 785 nm, 830 nm, 915 nm, an output of 70 mW, and a spot diameter of 250 μm while scanning at a speed of 200 mm / sec to erase the recording portion.
About the sample after erasure | elimination, the reflectance was measured with the self-recording spectrophotometer equipped with the integrating sphere, and the reflection density (reflectance) in a peak wavelength was calculated | required.
(2) At the time of erasing, the scanning speed of the semiconductor laser beam was set to 100 mm / sec, and the recording part was erased. About the sample after erasure | elimination, the reflectance was measured with the self-recording spectrophotometer equipped with the integrating sphere, and the reflection density (reflectance) in a peak wavelength was calculated | required.

(Evaluation results)
With respect to the recording media of [Examples D1 to D4], [Test Examples D1 to D3], and [Comparative Example D1], a scanning speed of 300 mm / mm was used using a laser beam with an output of 70 mW, a spot diameter of 80 μm, wavelengths of 915 nm, 830 nm, and 785 nm. Table 16 below shows the evaluation results of the recording line width, the reflection density at the obtained peak wavelength, and the transparency of the recording layer when a solid image was recorded in sec.
The measurement results of the recording line width when the output is 100 mW, the scanning speed is 300 mm / sec, and the obtained reflection density at the peak wavelength are shown in Table 17 below.
Furthermore, the measurement results of the recording line width when the output is 70 mW and the scanning speed is 150 mm / sec and the obtained reflection density at the peak wavelength are shown in Table 18 below.

As shown in Tables 16 to 18, the line width recorded on the recording medium of [Examples D1 to D4] is wider than that of [Test Examples D1 to D3] and [Comparative Example D1] under any conditions. It was found that the recording sensitivity was excellent.
It was also found that the reflection density of the solid image was sufficiently high for practical use under any condition, and the irradiation light was converted into heat with high efficiency, and the recording layer was colored.
The recording layers constituting the recording media of [Examples D1 to D4] had very good transparency evaluation. Therefore, the recording layer constituting the recording medium of the present invention has high solubility of the developer / color reducing agent, high light-heat conversion efficiency and coloring efficiency in the solvent and the polymer, and realizes excellent recording sensitivity. I understood that I was able to do it.

  In the recording media of [Test Examples D1 to D3], when the conditions of the semiconductor laser are 70 mW and the scanning speed is 300 mm / s, as shown in Table 16, the recording line width is narrow and the reflection density is low. However, when the laser power was increased to 100 mW or the scan speed was decreased to 150 mm / s, the recording media of [Examples D1 to D4] The same recording line width was obtained, and the reflection density was practically good.

  On the other hand, the recording layer using the developing / color-reducing agent shown in [Comparative Example D1] was inferior in solubility in the polymer, dispersed and clouded, and the transparency was deteriorated. As a result, in the order of the third, second, and first recording layers, the lower the recording line width, the lower the sensitivity. This is because the irradiated laser light is reflected and scattered by the undissolved developing / color-reducing agent in the upper layer, and the efficiency of light-heat conversion is lowered. It has been found that the transparency of the recording layer has a great influence on the recording sensitivity in the optical writing type thermal recording medium.

Next, for the above erasing characteristics evaluation in the recording media of [Example D1], [Test Examples D1, D3, D4], and [Comparative Example D2], the output of the semiconductor laser light at the time of erasing is 70 mW, and the scanning speed is The measurement results at 200 mm / s are shown in [Table 19] below.
The measurement results when the output of the semiconductor laser light is 70 mW and the scanning speed is 100 mm / s are shown in Table 20 below.

  As shown in Tables 19 and 20, the reflection density after erasure in the recording medium of [Example D1] was 0.02 or less at each wavelength and was almost colorless. This is because the recording layer used in [Example C1] has good transparency, can perform light-to-heat conversion efficiently, and can perform sufficient erasure.

  On the other hand, in [Comparative Example D2], the alkyl chain length of the compound of the developer / color-reducing agent was short and the cohesive force between the molecules was reduced, so that the erasing characteristics were deteriorated.

In [Test Examples D2 and D3], since the alkyl chain length of the compound of the developer / color-reducing agent is long, the cohesion between molecules is increased, and the solubility is reduced, the light-heat conversion efficiency is reduced, and the semiconductor When the laser scanning speed was set to 200 mm / s, the erasing characteristics deteriorated as shown in Table 19, but when the scanning speed was set to 100 mm / s, as shown in Table 20, it was practically sufficient. Erase characteristics were obtained.
Further, in [Test Example D4], the alkyl chain length of the compound of the developer / color-reducing agent has a branched structure, and the cohesive force between the molecules is reduced, leading to deterioration of the erasing characteristics, and the scanning speed of the semiconductor laser is increased. In the case of 200 mm / s, the erasing characteristics deteriorated as shown in Table 19, but when the scanning speed was set to 100 mm / s, practically sufficient erasing characteristics were obtained as shown in Table 20. It was.

  In addition, since the recording medium according to the present invention having a high light-to-heat conversion efficiency using a compound of a developer / color reducing agent having high solubility in a solvent and a polymer can obtain excellent erasing characteristics, The reversible multicolor recording medium produced in Example D5] was heated using a ceramic bar heated to 180 ° C., then cooled and pre-colored, and then each of wavelengths 915 nm, 830 nm, and 785 nm. It was confirmed that it is possible to obtain a recorded image of multicolor recording by irradiating a laser beam and erasing the recording portion.

  It was confirmed that the image thus obtained showed color development, contrast, and fineness equivalent to those of a multicolor recording image recorded from a previously erased state as in [Example D1].

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Support substrate, 10 ... Reversible multicolor recording medium, 11 ... 1st recording layer, 12 ... 2nd recording layer, 13 ... 3rd recording layer, 14, 15 ... Heat insulation layer , 16 …… Protective layer

Claims (5)

Recording layers each containing a plurality of reversible thermosensitive color-developing compositions with different color tones in the surface direction of the support substrate are separated and laminated.
The plurality of reversible thermosensitive color-developing compositions contain light-to-heat conversion materials that generate heat by absorbing infrared rays in different wavelength ranges,
The recording layer contains a color developing compound having electron donating properties and a developer / color-reducing agent having electron accepting properties.
At least one of the above-described electron accepting developer / color-reducing agent is a compound represented by the following general formula (4):
Reversible reaction between the electron donating color former and the electron accepting developer / color-reducing agent so that the recording layer is reversibly changed into two states of color development and decoloration. A reversible multicolor recording medium.

(R5 and R6 are hydrocarbon groups having a total carbon number of 8 to 26, and n is an integer of 5 or less.) Recording layers each containing a plurality of reversible thermosensitive color-developing compositions with different color tones in the surface direction of the support substrate are separated and laminated.
The plurality of reversible thermosensitive color-developing compositions contain light-to-heat conversion materials that generate heat by absorbing infrared rays in different wavelength ranges,
The recording layer contains a color developing compound having electron donating properties and a developer / color-reducing agent having electron accepting properties.
At least one of the above-described electron accepting developer / color-reducing agent is a compound represented by the following general formula (4):
Reversible reaction between the electron donating color former and the electron accepting developer / color-reducing agent so that the recording layer is reversibly changed into two states of color development and decoloration. Using the reversible multicolor recording medium that has been made,
Apply heat treatment to pre-decolor the entire recording layer,
In accordance with desired image information, exposure is performed by irradiating infrared rays of a wavelength region selected corresponding to the selected one of the recording layers,
A recording method for a reversible multicolor recording medium, wherein the image information is recorded by causing the recording layer to generate heat and selectively develop color.

(R5 and R6 are hydrocarbon groups having a total carbon number of 8 to 26, and n is an integer of 5 or less.) Recording layers each containing a plurality of reversible thermosensitive color-developing compositions with different color tones in the surface direction of the support substrate are separated and laminated.
The plurality of reversible thermosensitive color-developing compositions contain light-to-heat conversion materials that generate heat by absorbing infrared rays in different wavelength ranges,
The recording layer contains a color developing compound having electron donating properties and a developer / color-reducing agent having electron accepting properties.
At least one of the above-described electron accepting developer / color-reducing agent is a compound represented by the following general formula (4):
Reversible reaction between the electron donating color former and the electron accepting developer / color-reducing agent so that the recording layer is reversibly changed into two states of color development and decoloration. Using the reversible multicolor recording medium that has been made,
Apply heat treatment to make the entire recording layer in a colored state in advance.
In accordance with desired image information, exposure is performed by irradiating infrared rays of a wavelength region selected corresponding to the selected one of the recording layers,
A recording method for a reversible multicolor recording medium, wherein the image information is recorded by causing the recording layer to generate heat and selectively decoloring.

(R5 and R6 are hydrocarbon groups having a total carbon number of 8 to 26, and n is an integer of 5 or less.) The reversible multicolor recording medium according to claim 1, wherein the recording layer is laminated in the surface direction of the support substrate via a heat insulating layer. The reversible multicolor recording medium according to claim 1, wherein a protective layer is formed on the outermost surface.

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