JP2001030633A - Reversible heat sensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible heat sensitive recording medium, capable of erasing an image efficiently and surely at a high speed by heating employing a thermal head and preventing the deterioration of accuracy of the image upon developing. SOLUTION: This reversible heat sensitive recording medium is constituted of a laminated body having a reversible heat sensitive recording layer 2 and capable of indicating or erasing a visible image by changing the transparency or the color developing property of the reversible heat sensitive recording layer 2 by changing a temperature reversibly. In such a reversible heat sensitive recording medium, a temperature gradient mitigating layer 4, consisting of a light transmission synthetic resin and having the layer thickness of not less than 10 μm, is provided on the surface side of the reversible heat sensitive recording layer 2. When the medium is heated from the surface of the laminated body by a thermal head with dot unit, the wide part of the reversible heat sensitive recording layer of the reversible heat sensitive recording medium having the temperature gradient mitigating layer 4 of layer thickness of not less than 10 μm can be heated to a uniform temperature (a) compared with a conventional example (b) having a protective layer 4' of layer thickness of not more than 10 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium having a reversible thermosensitive recording layer and capable of displaying and erasing a visible image depending on temperature, and more particularly to a commuter pass, an entrance permit, various prepaid cards, etc. The present invention relates to a reversible thermosensitive recording medium that can be used for cards and OHP sheets.

[0002]

2. Description of the Related Art Generally, as a reversible thermosensitive recording material for displaying or erasing a visible image, the color tone is reversibly changed on a resin base material by, for example, an organic low-molecular compound or a heating temperature condition or a cooling rate after heating. There are known leuco dyes (also called leuco dyes) dispersed therein.

JP-A-63-41186 discloses a resin base material which reversibly changes the transparency and displays an image with a transparent / opaque contrast, and an organic low-molecular compound dispersed in the resin base material. A reversible thermosensitive recording material is described.

A leuco dye is a reduction dye composed of a colorless or light-colored electron-donating dye precursor, and one of a coloring action by an acidic group and a decoloring action by a basic group is prioritized by heating energy. Therefore, it has the effect of coloring and decoloring. A reversible thermosensitive recording material containing such a leuco dye, an amphoteric compound having an acidic group capable of developing the color and a basic group capable of decolorizing the developed leuco dye as a developer is disclosed in No. 188293.

In order to use the reversible thermosensitive recording material as described above as a reversible thermosensitive recording medium, the reversible thermosensitive recording material is dissolved in an organic solvent such as tetrahydrofuran (THF), and this is dissolved in a base material such as a synthetic resin film. , Dried and cured, and the surface is coated with a protective layer to protect the recording layer from physicochemical damage.

[0006] The protective layer covering the surface of the reversible thermosensitive recording layer in the above-mentioned conventional reversible thermosensitive recording medium usually has a thickness of less than 10 µm so that the recording medium changes as soon as possible upon contact with the thermal head. It is formed to a thickness.

[0007]

However, in the above-mentioned conventional reversible thermosensitive recording medium, when erasing an image while moving the recording medium using a thermal head, if the moving speed is increased, it is partially unreliable. There is a problem that an erased image may remain.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems and to make it possible to erase an image efficiently and at high speed by heating using a thermal head, and to reduce image accuracy when developing. An object of the present invention is to provide a reversible thermosensitive recording medium that does not allow the recording to be performed.

[0009]

In order to solve the above-mentioned problems, the present invention comprises a laminate having a reversible thermosensitive recording layer, and the transparency or coloring of the reversible thermosensitive recording layer depends on the temperature. In a reversible thermosensitive recording medium capable of displaying and erasing a visible image by reversibly changing, a temperature gradient of a layer of 10 μm or more made of a light-transmitting synthetic resin on the surface side of the reversible thermosensitive recording layer of the laminate. That is, a relaxation layer was provided.

The reversible thermosensitive recording medium of the present invention having the above-described structure, when heated by a thermal head in dot units from the surface of the laminate, forms a resin-made temperature gradient relaxation layer having a predetermined thickness. Through which the reversible thermosensitive recording layer is heated. At this time, the heat of the thermal head is transmitted through the synthetic resin having a layer thickness of 10 μm or more, and the temperature gradient in the layer thickness direction is moderated by the thermal conductivity of the synthetic resin. That is, as shown in FIG. 1, the reversible thermosensitive recording medium heated by the thermal head (T) has a larger thickness than the conventional example having a protective layer 4 ′ having a layer thickness of less than 10 μm shown in FIG. 1B. As shown in FIG. 1A, the one having the temperature gradient relaxation layer 4 having a layer thickness of 10 μm or more can heat a wide portion of the reversible thermosensitive recording layer 2 to a uniform temperature.

Therefore, the reversible thermosensitive recording layer heated by the thermal head has a wider isothermal area when heated, and the reversible thermosensitive recording layer can reliably erase an image of a larger area using the same thermal head as before. Becomes a recording medium.

In order to sufficiently supply the heat necessary for erasing and developing the image on the reversible thermosensitive recording layer with the thermal head, it is preferable to heat the thermal head to as high a temperature as possible. It is preferable that the temperature gradient relaxation layer in contact with the thermal head is formed of a heat-resistant resin.
Further, in order to clearly form an image such as a print with a thermal head, it is preferable that the temperature gradient moderating layer is formed of, for example, an acrylic resin having good transparency to a thickness of 10 to 30 μm.

As a heating means, a heating stamp or a heater bar may be used in place of the thermal head.
In that case, the thickness of the temperature gradient relaxation layer is, for example, 10 to 10.
Preferably, the thickness is 50 μm.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A reversible thermosensitive recording layer is made of a reversible thermosensitive recording material that reversibly develops or discolors color according to temperature or a reversible thermosensitive recording material that reversibly crystallizes and melts according to temperature. As the resin base material, a resin base material having excellent durability, such as heat resistance, transparency, film formability, high temperature elasticity, and the like under conditions of repeated rapid heating, is used.

Specific examples of preferable resin base materials include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-vinyl chloride.
Vinyl acetate-alcohol copolymer, other vinyl acetate compounds, vinyl chloride copolymer, polyvinylidene chloride,
Vinylidene chloride copolymer, polyester, polyamide,
Examples include polystyrene, polymethyl (meth) acrylate, and a copolymer thereof.

The organic low molecular weight compound used as the reversible thermosensitive recording material is an organic low molecular weight compound which crystallizes or melts into a non-crystalline state by heat treatment, and includes carboxylic acid, dicarboxylic acid, ketone, ether, It is a compound composed of an alcohol, an ester, a derivative thereof, and the like, and one or more of them can be used as a mixture.

Among such organic low molecular weight compounds, fatty acid alkyl esters having 12 or more carbon atoms have a low melting point (m
p), which is preferable because it crystallizes or melts by heat treatment at a relatively low temperature. Furthermore, carbon number 10
If the above aliphatic dibasic acids having a high melting point (mp) are used in combination and the mixing ratio of the fatty acid alkyl ester and the aliphatic dibasic acid is adjusted, the temperature range for clarification can be adjusted, or the The degree of transparency and the degree of cloudiness in the cloudy state can be arbitrarily changed.

Specific examples of leuco dyes (electron-donating dye precursors) used as reversible thermosensitive recording materials include triphenylmethanephthalide compounds, diphenylmethane compounds, fluoran compounds, phenothiazine compounds, leuco auramines. And indolinophthalide compounds.

Specific examples of triarylmethane compounds as leuco dyes include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone) and 3,3-bis (P-dimethylaminophenyl) phthalide, 3- (p-
Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide; and diphenylmethane compounds such as 4,4'-bis (dimethylaminophenyl) benzhydryl benzyl ether, N
-Chlorophenylleuco auramine, N-2,4,5-
Trichlorophenylleuco auramine and the like,
Rhodamine B anilinolactam, rhodamine Bp-chloroanilinolactam, 3
-Diethylamino-7-dibenzylaminofluoran; thiazine-based compounds include benzoyl leucomethylene blue; p-nitrobenzoyl leucomethylene blue; and spiro-based compounds include 3
-Methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3'-dichlorospirodinaphthopyran and the like.

As the color-reducing agent for bringing the leuco dye into a colored state or a decolored state, a structure capable of coloring the leuco dye in the molecule and a long aliphatic chain structure for controlling the cohesive force between the molecules are used. Are combined compounds, for example,
Examples thereof include an organic phosphorus compound having an aliphatic group having 12 or more carbon atoms, an aliphatic carboxylic acid compound, and a phenol compound.

Examples of the organic phosphorus compound having an aliphatic group having 12 or more carbon atoms include dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid, and tetracosylphosphonic docosylphosphonate. Acids, hexacosylphosphonic acid, octacosylphosphonic acid and the like.

Further, as the aliphatic carboxylic acid compound,
α-hydroxydecanoic acid, α-hydroxytetradecanoic acid, α-hydroxyhexadecanoic acid, α-hydroxyoctadecanoic acid, α-hydroxypentadecanoic acid, α-hydroxyeicosanoic acid, α-hydroxydocosanoic acid, α
-Hydroxytetracosanoic acid, α-hydroxyhexacosanoic acid, α-hydroxyoctacosanoic acid and the like. Further, aliphatic carboxylic acid compounds having a halogen element at the α-position or β-position carbon, or those having an oxo group at the α-position, β-position or γ-position carbon, dibasic acids, long chains It may be a tribasic acid such as citric acid acylated by a fatty acid.

Examples of the phenolic compound include:
A compound represented by the following formula 1 is exemplified.

[0024]

Embedded image

Wherein n is an integer of 1 to 3, and m is 0
Or, it represents an integer of ₁ , and R ₁ and R ₂ represent a substituent or a hydrogen atom selected from an aliphatic hydrocarbon group, an alkoxy group, and a halogen atom, and may be the same or different. R ₃ represents an aliphatic hydrocarbon group. Y
Is a group represented by the following chemical formula 2. )

[0026]

Embedded image

(In the formula, p and q each represent an integer of 0 or 1, X ₁ and X ₂ each represent a divalent group having at least one hetero atom, and Ar is an aromatic group which may have a substituent.) The reversible thermosensitive recording material as described above can be generally provided in a layer on the surface of an object by employing a solvent coating method. . In addition, a laminating method by dispersion coating with a poor solvent, extrusion coating without a solvent, or the like, or a method of laminating a reversible thermosensitive recording layer previously laminated on a release film by thermal transfer to an object can also be adopted.

Embodiments of the reversible thermosensitive recording medium of the present invention will be described below with reference to the accompanying drawings.

The card-type reversible thermosensitive recording medium shown in FIGS. 2 and 3 has a reflective layer 2 made of aluminum or the like for forming an optically reflective surface on the surface of a card base 1 made of a synthetic resin sheet such as polyethylene terephthalate. , A reversible thermosensitive recording layer 3 is superposed thereon, and a temperature-gradient moderating layer 4 made of a heat-resistant synthetic resin and having a light transmittance of 10 μm or more is further provided thereon. A printed layer 6 for forming the display window 5 is provided, a magnetic recording layer 7 and a protective printed layer 8 are sequentially laminated on the back side of the card substrate 1, and these are laminated and bonded and integrated. . The reversible thermosensitive recording layer is formed by coating a reversible thermosensitive recording material, which is liquefied by adding a solvent, as a paint on the reflective layer 2, and heating and drying the same to form an integral part with the reflective layer 2.

The reversible thermosensitive recording material referred to herein is an alkyl ester of a fatty acid having 12 or more carbon atoms and an alkyl ester of a fatty acid having 10 or more carbon atoms.
An organic low-molecular compound containing the above-mentioned aliphatic dibasic acid, or a leuco dye and a color-reducing agent are employed.

When a reversible thermosensitive recording layer containing a leuco dye is formed, for example, 3 is used as a leuco dye precursor.
-Di-n-butylamino-6-methyl-7-anilinofluoran (40 parts) was ground with a 2.5% polyvinyl alcohol aqueous solution (90 parts) in a ball mill for 24 hours to obtain a dye precursor dispersion, and then 4 ' 100 parts of hydroxy-n-heptaneanilide is pulverized together with 400 parts of a 2.5% aqueous solution of polyvinyl alcohol in a ball mill for 24 hours to obtain a dispersion. After mixing the above two dispersions, 200 parts of a 10% aqueous solution of polyvinyl alcohol and 400 parts of water are added and mixed to prepare a coating liquid of a reversible thermosensitive recording material. The solid coating amount is 4 g / m ² . The reversible heat-sensitive recording layer can be formed by coating and drying as needed.

The temperature gradient moderating layer 4 is formed of a transparent resin film having good heat resistance, such as an acrylic resin, and has a thickness of 10 μm or more.
Preferably, it is formed to a thickness of 30 μm. In this case, if the layer thickness exceeds 30 μm, the heat energy required at the time of erasing and developing the image increases, and the load on the entire layer constituting material is undesirably increased.

When a heating stamp or a heater bar that generates a large amount of heat is used as the heating means, the thickness of the temperature gradient relaxing layer 4 is about 50 μm (for example, 1 μm).
0 to 50 μm).

Thermal conductivity (× 10 ⁻⁴ cal / cm · S · ° C.) of the resin material forming the temperature gradient relaxation layer (ASTM method C-17)
7) is usually about 2.3 to 12.4, and more preferably the thermal conductivity is 3.0 to 7.0. Specific examples of the thermal conductivity of the resin material include acrylic resin (thermal conductivity; 4.2 to 5.
0), polyethylene terephthalate (thermal conductivity; 3.6), polybutylene terephthalate (thermal conductivity; 4.2 to 6.9), polyimide (thermal conductivity; 2.3 to 2.6), polyetherimide (thermal conductivity; 6.1), polystyrene ( Thermal conductivity; 3.1), polyether sulfone (thermal conductivity; 4.3), polyphenylene sulfide (thermal conductivity; 6.9), polyether ether ketone (thermal conductivity; 6.0), polycarbonate (thermal conductivity;
2.1 to 4.6), polyvinyl chloride (thermal conductivity; 2.9 to 4.1), polyethylene (thermal conductivity; 8.0 to 12.4), polytetrafluoroethylene (thermal conductivity; 6.0), etc. This is also preferable. Incidentally, the average of the thermal conductivity of the resin exemplified above is about 5.0 (× 10 ^−4).
cal / cm · S · ° C).

The reflection layer 2 is provided to make the image formed on the heat-sensitive recording layer 3 easy to see from the surface of the card. The reflection layer 2 is formed by depositing aluminum or tin, bonding foil, or removing aluminum powder. It is made of mixed light reflective paint.

When such a reversible thermosensitive recording medium is used, the heat generated by the thermal head is appropriately stored in the temperature gradient relaxing layer before it is transmitted from the surface of the medium to the thermosensitive recording layer. Therefore, the gradient of the heating temperature from the thermal head is transmitted from the thermal gradient moderating layer to the reversible thermosensitive recording layer in a gentle manner, and the temperature difference in the thickness direction of the thermosensitive recording resin layer is reduced.

Therefore, the erasing area per dot of the thermal head is increased, and even when the card type recording medium is heated at a relatively high speed, the image erasure is not uneven, and the erasing and development of the thermal head can be easily controlled.

Further, since initialization and overwriting by erasing the entire area at once can be performed reliably, the speed of the recording process can be improved, an image having a high contrast (reflection density) can be reliably obtained, and the erasing speed can be increased. It becomes to become.

The embodiments of the invention of the present application or other related matters will be listed below by dividing the items.

(1) A reversible thermosensitive recording medium comprising a laminate having a reversible thermosensitive recording layer, wherein the transparency or coloring of the reversible thermosensitive recording layer is reversibly changed depending on the temperature so that a visible image can be displayed and erased. A reversible thermosensitive recording medium, characterized in that the recording medium is provided with a temperature-gradation-reducing layer made of a light-transmitting synthetic resin and having a thickness of 10 μm or more on the surface side of the reversible thermosensitive recording layer of the laminate.

(2) The reversible thermosensitive recording medium according to the above item 1, wherein the temperature gradient relaxing layer is formed of an ultraviolet curable resin or an electron beam curable resin.

(3) The reversible thermosensitive recording medium as described in (1) or (2) above, wherein the temperature gradient moderating layer is formed of a plurality of layers.

(4) The reversible thermosensitive recording medium according to the above item 3, wherein the temperature gradient moderating layer is formed by laminating a plurality of light-transmitting heat-resistant resin films.

(5) The reversible thermosensitive recording medium according to any one of the above items 1 to 4, wherein the temperature gradient moderating layer is a temperature gradient moderating layer made of a synthetic resin containing silicone or a fluorine compound. .

(6) The reversible thermosensitive recording medium according to any one of the above items (1) to (5), wherein the temperature gradient relaxation layer is made of a synthetic resin containing fine particles having a particle size of 5 μm or less.

(7) The reversible thermosensitive recording medium according to any one of the above items (1) to (6), wherein the temperature gradient moderating layer is made of a synthetic resin containing a colorant.

[0047]

Examples and Comparative Examples [Examples 1 to 4, Comparative Examples 1 to 4]
3] Polyethylene terephthalate resin sheet base material (18
8 μm thick), and the following reversible thermosensitive recording material is dissolved in tetrahydrofuran, coated and heated and dried to form a reversible thermosensitive recording medium having a 10 μm thick reversible thermosensitive recording layer. Produced.

The reversible thermosensitive recording material is a vinyl chloride-vinyl acetate copolymer (Solvain C, manufactured by Nissin Chemical Co., Ltd.) 170
Adipic acid polyester (Dai Nippon Ink Co., Ltd .: Polysizer W-4000, solidification point 14 ° C) based on parts by weight
30 parts by weight, 70 parts by weight of hexadecyl stearate,
A blended composition consisting of 30 parts by weight of dodecane diacid was used.

As shown in Table 1, a layer having a temperature gradient of 2 μm (Comparative Example 1), 5 μm (Comparative Example 2), and 8 μm (Comparative Example 3) was formed on the reversible thermosensitive recording layer as a temperature-gradation-reducing layer. , 1
0 μm thickness (Example 1), 15 μm thickness (Example 2), 20
Urethane acrylate-based UV-curable resin material (Dainippon Ink and Chemicals, Unidick 17-824-9) to have a thickness of 30 μm (Example 3) or 30 μm (Example 4).
Was applied, dried and then cured by irradiating ultraviolet rays to form a layer having a predetermined thickness.

The obtained reversible thermosensitive recording medium (Examples 1 to 5)
4. Printing and erasing tests were performed on Comparative Examples 1 to 3 under the following conditions.

In the printing / erasing test, the reversible thermosensitive recording medium was passed through a thermal head having a printing density of 8 dots / mm at a speed of 40 mm / sec.
Printing (cloudy image formation) or erasing (clearing) is performed by adjusting the heating energy by changing the applied pulse width at 4 to 0.40 mJ / dot, and the resulting reflection density on the surface of the reversible thermosensitive recording medium is obtained. Is a Macbeth reflection densitometer (RD
−914), and the results are shown in the line graph of FIG. 4 or FIG.

The evaluation of transparency (erasing) and white turbidity (printing) was performed when the reflection density was 0.4 or less, that is, a good printing state, and when the reflection density was 1.2 or more, a good erasing state (the background was about 1.4). Table 1 shows the range (mJ / dot) of erasable heat, the width of the heat, and the minimum heat (mJ / dot) that can be printed.

Further, when the erasability of the image was actually confirmed with the naked eye, the evaluation was as follows: x (partially printed), Δ
The evaluation was made in three steps: mark (printing was almost completely erased and the allowable range of operation) and mark (completely erased).
Also described in the inside.

[0054]

[Table 1]

Next, with respect to the obtained reversible thermosensitive recording media (Examples 1 to 4 and Comparative Examples 1 to 3), the erasing characteristics and the heating when a heater bar capable of large-capacity heating was used were used. The erasing characteristics when the stamp was used were examined, and these results are shown in the table of FIG. 6 or FIG.

As is clear from the results shown in FIGS. 4 to 7 and Table 1, Comparative Examples 1, 2, and 3 in which the thickness of the temperature gradient moderating layer is less than 10 μm have a range of applied energy that can be erased.
It was a narrow range of less than 0.07 mJ / dot, and it was difficult to actually completely erase the print with the thermal head.

On the other hand, the thickness of the temperature gradient moderating layer is 1
In Examples 1 to 4 of 0 μm or more, the erasable applied energy range is as wide as 0.07 mJ / dot or more, and complete erasing can be performed by the operation of the thermal head. Printing (developing) was performed at a reflection density of 0.4 m or less at 24 mJ / dot or more, preferably 0.24 to 0.45 mJ / dot. Examples 1 to 4 also showed favorable erasing characteristics when the heater bar was used and when the heating stamp was used (0.5 second contact). However, in the fourth embodiment, the required amount of printing heat by the thermal head is larger than in the first to third embodiments, and the load on the thermal head is higher.

[0058]

As described above, the present invention provides a reversible thermosensitive recording medium comprising a laminate having a temperature-gradation-relaxed layer having a predetermined thickness on the surface side of the reversible thermosensitive recording layer.
While the heat of the thermal head is transmitted through the temperature gradient moderating layer, the temperature gradient is moderated in the thickness direction of the layer, resulting in a reversible thermosensitive recording medium capable of reliably erasing an image of a larger area.

That is, the present invention provides a reversible thermosensitive recording medium capable of efficiently and quickly erasing an image efficiently and reliably by heating using a thermal head, and which does not reduce the precision of the developed image. There are advantages.

[Brief description of the drawings]

FIG. 1A is a diagram illustrating a temperature gradient during heating according to an embodiment. FIG. 1B is a diagram illustrating a temperature gradient during heating according to a conventional example.

FIG. 2 is a perspective view of a card-type reversible thermosensitive recording medium.

FIG. 3 is an enlarged sectional view of FIG. 2;

FIG. 4 is a table showing printing characteristics of Examples and Comparative Examples, and showing a relationship between applied energy by a thermal head and reflection density.

FIG. 5 is a table showing erasing characteristics of an example and a comparative example, and showing a relationship between energy applied by a thermal head and reflection density.

FIG. 6 is a table showing erasing characteristics of Examples and Comparative Examples, and showing a relationship between applied energy by a heater bar and reflection density.

FIG. 7 is a table showing erasing characteristics of Examples and Comparative Examples, and showing a relationship between applied energy by a heating stamp and reflection density.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Card base material 2 Reflective layer 3 Reversible thermosensitive recording layer 4 Temperature gradient relaxation layer 5 Recording display window 6 Printing layer 7 Magnetic recording layer 8 Protective printing layer

Claims (1)

[Claims] 1. A reversible thermosensitive recording comprising a laminate having a reversible thermosensitive recording layer, wherein the transparency or coloring of the reversible thermosensitive recording layer is reversibly changed depending on the temperature so that a visible image can be displayed and erased. A reversible thermosensitive recording medium, characterized in that a temperature gradient-reducing layer made of a light-transmitting synthetic resin and having a thickness of 10 μm or more is provided on the surface side of the reversible thermosensitive recording layer of the laminate.