JP2000071624A - Reversible thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible thermal recording material for effectively erasing or displaying a visible image by a thermal head even in the state of warming to a using environmental temperature particularly in summer or human body temperature by sufficiently extending a clarifying temperature area of the material. SOLUTION: In the reversible thermal recording material for displaying or erasing a visible image by blending a crystalline organic low molecular compound in a resin base material in a dispersing state and reversibly changing transparency of the blend according to a temperature, the compound contains a higher fatty acid ester and an aliphatic dibasic acid as main components, and contains 10 to 40 pts.wt. of an organic low molecular compound made of a higher fatty acid or higher ketone having a higher melting point than that of the fatty acid ester to 100 pts.wt. of the fatty acid ester.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording material capable of displaying and erasing a visible image according to temperature, and more particularly to a commuter pass, an admission permit, cards such as various prepaid cards, OHP sheets and the like. The present invention relates to a reversible thermosensitive recording material that can be used.

[0002]

2. Description of the Related Art In general, a commuter pass used by a user of a transportation system, an admission permit to an event hall or a predetermined building, and other repeatedly used cards are written on the surface by characters such as characters printed by an administrator. The device is checked with the naked eye or magnetically recorded information recorded on cards is read by a device to prevent unauthorized use.

However, if the contents written on the surface of the cards do not match the magnetically recorded information, the administrator cannot immediately judge the correctness of the information only on the front surface, and the reading device of the magnetic recording is erroneous. In some cases, it was difficult to completely prevent unauthorized use of cards and the like.

[0004] Further, even with a magnetic recording card such as a prepaid card or an IC card provided with an IC chip, information recorded on the card, such as a past payment amount or a balance, cannot be visually confirmed every time the card is used. Therefore, both the administrator and the user were inconvenient.

In order to eliminate such inconvenience, a card-type recording apparatus that displays visually recognizable recording information by a reversible thermosensitive recording layer (Japanese Patent Laid-Open No. 54-19377,
JP-A-55-154198) is known.

In this apparatus, a recording material in which a crystalline organic low-molecular substance is dispersed in a polymer resin base material is provided in a layer form,
The step of heating the recording material to a specific temperature area (T1) to make it transparent and the step of heating the recording material to an area (T2) above the specific temperature area to make it cloudy are selectively used to form a layered recording material. It has a mechanism of displaying or erasing a visible image by causing a difference in contrast at a key point.

[0007]

However, the above-mentioned conventional reversible thermosensitive recording material has a narrow temperature region where transparency is high, that is, a temperature region where a visible image can be erased. It is difficult to control the temperature.

That is, the conventional reversible thermosensitive recording material is as follows:
It is possible to erase images using a heating stamp or heating bar that heats a large area with a large amount of heat. However, in particular, in the case of instantaneous heating processing in units of dots (points) using a thermal head, the temperature distribution in the thickness direction of the recording layer Is large, it is difficult to completely erase the image.

As a prior art which addresses the above problem by expanding the transparent temperature range, there is disclosed a reversible thermosensitive recording material in which a higher fatty acid and an aliphatic saturated dibasic acid are dispersed (JP-A No. 2-13 / 1990).
No. 63) is known, but even with such a technique, a visible image cannot be reliably erased using a thermal head.

Further, as a technique for expanding the low-temperature side of the clearing temperature range, the above-mentioned crystalline organic low-molecular substance is used.
A reversible thermosensitive recording material employing a higher fatty acid ester having a low melting point (about 60 ° C.) is also known.

However, when a higher fatty acid ester having a low melting point (about 60 ° C.) is used, a high-temperature use environment such as a summer temperature (about 30 ° C. or more) or a reversible thermosensitive recording material cannot be used as a human body temperature (about 36 ° C. on average). In such a case, the crystallization becomes difficult when heated or the like, and a problem arises in that an image cannot be displayed reliably due to printing or the like.

Under the above-mentioned high-temperature use conditions, an image that is not completely clouded cannot be erased even if it is heated to a clearing temperature range, so that not only the image display function but also the erase function deteriorates. did.

Therefore, an object of the present invention is to solve the above-mentioned problems, sufficiently expand the transparent temperature range of the reversible thermosensitive recording material, and set a relatively high temperature range within a temperature range assumed in normal use. A reversible thermosensitive recording material that can reliably display and erase images even at high temperatures.Reversible that can reliably erase and display visible images with a thermal head, especially when heated to the operating temperature in summer or human body temperature. To be a thermosensitive recording material.

[0014]

In order to solve the above-mentioned problems, the present invention comprises mixing a crystalline organic low-molecular compound in a dispersed state with a resin base material, and reversibly changing the transparency of the compound by temperature. In a reversible thermosensitive recording material capable of displaying and erasing a visible image by changing, the organic low molecular weight compound has a higher fatty acid ester and an aliphatic dibasic acid as main components, and has a melting point higher than the melting point of the higher fatty acid ester. An organic low-molecular-weight compound is used as the above-mentioned higher fatty acid ester 10
The reversible thermosensitive recording material contained 10 to 40 parts by weight with respect to 0 part by weight.

The melting point (mp) in the present invention is a temperature at which a compound melts when heated at a heating rate of 10 ° C./min by a differential scanning calorimeter (DSC).

As the organic low molecular weight compound having a melting point higher than the melting point of the higher fatty acid ester, a higher fatty acid or a higher ketone can be used.

The mechanism for estimating the recording / erasing of the reversible thermosensitive recording material according to the present invention will be briefly described below.

In the graph of FIG. 3, schematic diagrams (a) to (g) of the crystal phase dispersed in the resin base material are additionally shown. In the reversible thermosensitive recording material in the state shown in (a) in the figure, the hard resin base material and the crystal (dispersed phase) of the organic low-molecular compound are in close contact with each other at room temperature, and the refractive indices of both are in contact. Is in a transparent state because When heated from this transparent state, both the crystal of the dispersed phase and the resin matrix become soft as shown in (b), and when the temperature further rises, the partially melted crystal is dispersed in the resin matrix as shown in (c). In this state, all of them are in the transparent state up to this point.

Then, when the crystal is heated to a temperature exceeding the melting point of the crystal, the dispersed phase becomes completely liquid as shown in (d), and the recording material becomes semi-turbid due to the refractive index difference between the softened base material and the liquid. State. When the temperature is lowered from this state, the base material resin is gradually cured, but the recording material maintains a semi-turbid state as shown in (e) until the crystallization temperature of the dispersed phase.

When the cooling is further advanced and the temperature becomes lower than the crystallization temperature of the dispersed phase, some small crystals grown based on some seed crystal are formed, and the volume of the dispersed phase is shrunk. As shown in FIG. 3 (f), a gap is formed between the recording material and the resin base material, and the recording material becomes completely clouded.

When heated again from this cloudy state, (g)
As described above, since the resin base material softens as the temperature rises and gradually fills the gap, the recording material gradually becomes transparent. When the temperature further rises, the crystal partially melts and becomes transparent as shown in (c).

When the recording material in the transparent state (c) is cooled down to room temperature, the softened resin base material adheres to the disperse phase so that no void is formed at the boundary even if the recording material is cooled thereafter. ) Will return to the transparent state.

If the transparency and opacity are made according to the above-mentioned mechanism, the lower the melting point of the crystal of the organic low molecular weight compound, which is the dispersed phase, the more transparent the recording material can be made at a lower temperature. If the crystallization temperature of the compound is increased, crystals are more likely to be formed on the higher temperature side, resulting in a thermosensitive recording material having a display function even at a higher temperature.

The reversible thermosensitive recording material of the present invention is based on the knowledge of the above-mentioned mechanism of action, and contains a higher fatty acid ester having a low melting point and an aliphatic dibasic acid having a high melting point as main components with respect to a resin base material. By blending an organic low-molecular compound, a wide range of transparency temperature range can be secured. Further, by adding an organic low molecular weight compound having a crystallization temperature (Tc) higher than the Tc of the higher fatty acid ester, the organic low molecular weight compound can be surely crystallized even under conditions where the temperature is warmed by the outside temperature in summer or human body temperature. Thus, a reversible thermosensitive recording material that can be displayed and erased can be obtained.

The reason that the reversible thermosensitive recording material of the present invention has a wide range of transparency temperature range and has a display function even at a high temperature is that a crystalline organic low molecular weight compound in a dispersed phase is heated and melted and then cooled. It is considered that the organic low-molecular weight compound having a high crystallization temperature sometimes crystallizes first, and this crystal nucleus serves as a crystal nucleus to promote the crystallization of another fatty acid ester having a low crystallization temperature. Since the crystallization temperature is usually slightly lower than the melting point, the melting point can be referred to when comparing the crystallization temperatures of the two compounds.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The resin constituting the base resin according to the present invention has good transparency, film formability, elasticity and other heat resistance in a high temperature region, durability under repeated heating conditions, and the like. The following are examples of suitable base resin types.

That is, as the base resin species, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-alcohol copolymer, other Examples include vinyl acetate compounds, vinyl chloride copolymers, polyvinylidene chloride, vinylidene chloride copolymers, polyesters, polyamides, polystyrene, polymethyl (meth) acrylate, and copolymers thereof.

Particularly, vinyl chloride-vinyl acetate copolymer, or vinyl chloride-vinyl acetate copolymer and ultraviolet light (UV)
A mixture with a photo-curable resin such as a curable resin or a radiation-curable resin such as an electron beam (EB) curable resin has a high elastic modulus in a high-temperature region, and has a good durability when repeatedly rewritten (displayed / erased). It is.

The crystalline organic low-molecular-weight compound mixed in a dispersed state with the resin base material is a heat-sensitive recording material that can employ an erasing method using a thermal head. An aliphatic dibasic acid having a high melting point is used as a main component (50% by weight or more of all organic low molecular weight compounds).

The higher melting fatty acid ester having a low melting point is a dehydration condensate of a higher fatty acid and a monohydric or dihydric or higher alcohol, and an alkyl ester of a fatty acid having 12 or more carbon atoms is particularly preferred in view of the melting point. Preferred examples of the aliphatic dibasic acids having a high melting point include those having 10 or more carbon atoms.

Specific examples of the low melting point alkyl esters of fatty acids having 12 or more carbon atoms include fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, lignoceric acid, serotinic acid, and melicic acid.
Esters with alkyl groups such as methyl, propyl,..., Palmityl, stearyl, behenyl and the like. The melting point of these higher fatty acid esters is 50 to 80 ° C.

Specific examples of aliphatic dibasic acids having a high melting point (hereinafter, the melting point is abbreviated as mp) and having 10 or more carbon atoms include suberic acid (mp: 140 ° C.), sebacic acid (m
p: 134 ° C), dodecandioic acid (mp: 128 ° C), tetradecandioic acid (mp: 125 ° C), hexadecandioic acid (mp: 125 ° C), octadecandioic acid (mp: 125 ° C)
° C) and eicosane diacid (mp: 123 ° C).

By appropriately adjusting the mixing ratio of the fatty acid ester and the aliphatic dibasic acid, it is possible to arbitrarily change the temperature range for transparency, the degree of transparency, and the degree of turbidity in the cloudy state. . It is preferable that the mixing ratio is set in consideration of the performance of a printing / erasing apparatus using a reversible thermosensitive recording material, the sharpness of printing contrast, and the like.

By using a fatty acid ester having a low melting point and an aliphatic dibasic acid having a high melting point in combination as such a crystalline organic low-molecular compound, a eutectic crystal is formed and the dispersed phase has a wide melting point. It is considered that the material becomes a thermal recording material, and the temperature region having high transparency expands, and the applied energy region necessary for erasing using the thermal head becomes wide.

Specific examples of the organic low molecular weight compound having a melting point higher than the melting point of the higher fatty acid ester include higher fatty acids and higher ketones.

Specific examples of the higher fatty acid here include:
Stearic acid (C: 18, mp: 70 ° C.), behenic acid (C: 22, mp: 80 ° C.), lignoceric acid (C: 24, mp: 84 ° C.), cellotic acid (C: 26,
mp: 88 ° C.), melicic acid (C: 30, mp: 94)
° C) (C: 18 or more). In each case, one or more of those having a higher mp than the higher fatty acid ester mp are selected and employed.

Further, specific examples of the higher ketone include:
Millistone (14-heptacosanone, C: 27, mp:
78 [deg.] C), palmitons (16-Hentriacontanone,
C: 31, mp: 81 ° C.) and stearone (18-pentatriacontanone, C: 35, mp: 90 ° C.) (C: 27 or more).
One or more types having a mp higher than p are selected and employed.

The mixing ratio of the organic low molecular weight compound having a melting point higher than that of the higher fatty acid ester is preferably 10 to 40 parts by weight based on 100 parts by weight of the higher fatty acid ester. If the amount of the high-melting organic low-molecular-weight compound is less than the above-mentioned predetermined range, the crystallization temperature of the crystalline organic low-molecular-weight compound does not rise to the expected level, and the low-temperature below the average body temperature (36 ° C.). This is because printing (display of an image) by the thermal head can be performed only under the conditions of use. If the amount is larger than the above-mentioned predetermined range, the melting point is too high together with the crystallization temperature, so that it is difficult to erase an image with a thermal head.

An embodiment of a card type recording apparatus using the reversible thermosensitive recording material of the present invention will be described below with reference to the accompanying drawings.

In the card type recording material shown in FIGS. 1 and 2, a reflective layer 2 made of aluminum or the like for forming an optically reflective surface is provided on the surface of a card base 1 made of a synthetic resin sheet such as polyethylene terephthalate. A recording layer 3 made of a reversible thermosensitive recording material is provided on the recording layer 3, and a protective layer 4 and a printing layer 6 for forming a recording display window 5 are further provided thereon. The magnetic recording layer 7 and the protective printing layer 8 are sequentially laminated and integrated.

The reflection layer 2 is used to make the image formed on the recording layer 3 easy to see from the surface of the card. Consists of a coating layer of paint.

The recording layer 3 can be formed integrally with the reflective layer 2 by applying a solvent and adding a solvent to a liquefied reversible thermosensitive recording material, followed by drying by heating.

The protective coating layer 4 provided on the recording layer 3 is made of a transparent resin film having good heat resistance, and specific resin materials include polyethylene terephthalate, polyetherimide, polyetherketone, and polyetherether. Examples thereof include heat-resistant resins such as ketone, polysulfone, polyphenylene sulfide, polyacrylate, polyether sulfone, polycarbonate, polyethylene naphthalate, polyimide, and acrylic resin.

The card-type recording material formed as described above has a wide temperature range in which the recording layer can be made transparent, and the image can be reliably erased by instantaneous heating with a thermal head having a wide temperature distribution. Improves the speed of the re-recording process because a single thermal head can be used for both printing and erasing, and erasing and re-printing can be performed simultaneously, and overwriting that does not require initialization by erasing the entire area is possible. You can do it.

[0045]

Examples and Comparative Examples [Examples 1 to 4, Comparative Examples 1 to 4]
3) A magnetic paint was previously applied to the back surface to a thickness of 10 μm.
Aluminum is vapor-deposited on the surface of a polyethylene terephthalate resin sheet (card base material) having a thickness of 8 μm, and the composition shown in Table 1 (the resin base material (1) and the crystalline organic low-molecular compound (2) to ( 5) is dissolved in tetrahydrofuran, applied to a recording material, and dried by heating.
A recording layer having a thickness of 0 μm was formed. Among the materials used, the melting point (mp) of hexadecyl stearate was 58 ° C.
Mp of other materials is dodecane diacid (mp: 128 ° C.), stearone (mp: 90) as described above.
° C) and melicic acid (mp: 94 ° C).

Then, a protective film made of polyethylene terephthalate resin having a thickness of 2 μm is adhered on the recording layer, and printing for forming a recording display window is performed thereon, and a magnetic recording layer is formed on the back surface of the card base material. Then, a protective printing layer was sequentially superposed, and a card-type reversible thermosensitive recording material was formed by laminating and integrating these layers.

A printing test was performed on the obtained card-type reversible thermosensitive recording material under the following conditions. That is, the card-type reversible thermosensitive recording material is 0.30 mJ / d.
After printing with a thermal head and forming a cloudy image,
Heat from 0.01 mJ / dot to 0.30 mJ / dot with a thermal head at 0.01 mJ / dot intervals,
An experiment of cooling to room temperature is repeated to measure the applied energy area (mJ / dot) where the image can be erased, and the reflection density of the erasing (transparent) part and the printing (white turbid image) part of the card surface is measured using a Macbeth reflection densitometer. (RD-914), and the results are shown in Table 2. Regarding the reflection density, 0.5 or less was evaluated as a cloudy state and 1.0 or more as a transparent (erased) state.

The transparent card can be printed at room temperature (23 ° C.) with a thermal head at a stepwise ambient temperature of 30 to 50 ° C. (in air) at 0.30 mJ / do.
Heating was performed at t, and the maximum environmental temperature at which printing was possible was examined. The results are also shown in Table 2.

The crystallization temperature of the composition prepared by adding the lower melting higher fatty acid ester, the higher melting point aliphatic dibasic acid and the organic low molecular weight compound prepared in the manufacturing process was measured by a differential scanning calorimeter (DSC). The temperature was measured at a cooling rate of 10 ° C./min using Table 2. The results are also shown in Table 2.

[0050]

[Table 1]

[0051]

[Table 2]

As is clear from the results shown in Table 2, higher ketone or higher fatty acid having a higher melting point than the fatty acid ester was used in a predetermined amount (10 to 4 parts by weight per 100 parts by weight of the fatty acid ester).
(0 parts by weight) The blended recording material of the embodiment has a printable temperature of 36 ° C. or higher and can be printed with a thermal head even at an average body temperature or higher or at an environmental temperature in summer, and the image erasing characteristics, printing characteristics and contrast Was also good.

On the other hand, in Comparative Example 1 in which no higher ketone or higher fatty acid was added, the printable temperature was 30 ° C. (At least 30 ° C.) could not be printed.

In Comparative Example 2, the blending amount of higher ketone or higher fatty acid having a melting point higher than that of the fatty acid ester was 10%.
Since it is less than parts by weight, printing is possible at the ambient temperature in summer (at least 30 ° C.), but it cannot be used under the average body temperature condition (36 ° C.). Further, in Comparative Example 3, since the blending amount of the higher ketone or higher fatty acid having a melting point higher than that of the fatty acid ester is larger than 40 parts by weight, the melting point of the organic low molecular weight compound is too high,
The image could not be erased with the thermal head.

[0055]

As described above, the present invention provides an organic low molecular weight compound comprising a lower melting higher fatty acid ester and a higher melting aliphatic dibasic acid as main components and further having a melting point higher than the melting point of the higher fatty acid ester. Is added to the resin base material in a dispersed state, making it a reversible thermosensitive recording material that can reliably display and erase images even at relatively high temperatures within the temperature range expected under normal use conditions. In particular, there is an advantage that the reversible thermosensitive recording material can reliably erase and display a visible image with a thermal head even in a state where it is heated at a use environment temperature in summer or a human body temperature.

[Brief description of the drawings]

FIG. 1 is a perspective view of a card-type reversible thermosensitive recording material.

FIG. 2 is an enlarged sectional view of the card-type reversible thermosensitive recording material of FIG.

FIG. 3 is an explanatory diagram of a mechanism for estimating recording / erasing of a reversible thermosensitive recording material.

[Explanation of symbols]

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

Claims (3)

[Claims] 1. A reversible thermosensitive thermosensitive element capable of displaying and erasing a visible image by mixing a crystalline organic low-molecular compound in a dispersed state with a resin base material and reversibly changing the transparency of the compound according to temperature. In the recording material, the organic low-molecular compound is mainly composed of a higher fatty acid ester and an aliphatic dibasic acid, and has a melting point higher than the melting point of the higher fatty acid ester. A reversible thermosensitive recording material, characterized in that it contains 10 to 40 parts by weight. 2. The reversible thermosensitive recording material according to claim 1, wherein the organic low molecular weight compound having a melting point higher than that of the higher fatty acid ester is a higher fatty acid. 3. The reversible thermosensitive recording material according to claim 1, wherein the organic low molecular weight compound having a melting point higher than that of the higher fatty acid ester is a higher ketone.