JP2655038B2 - Reversible thermosensitive recording medium - Google Patents

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 capable of recording and erasing images reversibly by heating.

[0002]

2. Description of the Related Art JP-A-55-154198 and JP-A-55-154198.
Japanese Patent Application Laid-Open No. 1-257883 proposes a reversible thermosensitive recording medium in which the transparency after cooling changes reversibly due to the difference in the temperature reached upon heating, thereby enabling an image to be recorded and erased. I have. These reversible thermosensitive recording media, as a thermosensitive recording layer, those in which organic low-molecular substances such as higher fatty acids are dispersed in fine particles in an organic polymer resin such as vinyl chloride-vinyl acetate copolymer, It has a layer configuration provided on a support.

[0003] The relationship between the transparent state of these reversible thermosensitive recording media and the thermal history applied thereto will be described with reference to FIG.
FIG. 1 is a state diagram showing the relationship between temperature and transparency in a reversible thermosensitive recording medium. An opaque (white turbid) portion is heated to a certain temperature range T1 to T2 and gradually cooled to room temperature TR. Can be made transparent (→→→).
Conversely, in order to make the transparent portion opaque (cloudy), the transparent portion may be heated to a temperature of T3 or higher and then cooled to room temperature (→→
→→). In this case, the transparent state and the cloudy state are
It is kept stable at room temperature TR. In the traditional way,
Heating temperature range T1 to make opaque (opaque) parts transparent
Since the width of T2 (clearing temperature width TW) is very narrow and cannot be arbitrarily controlled, strict control of the temperature is necessary to make the opaque reversible thermosensitive recording medium transparent. Thus, practical use was very difficult.

[0004]

When the reversible thermosensitive recording medium in the opaque state is made transparent, a heating medium having a sufficient heat capacity, such as an oven or a heat block, is used as a heating means for a sufficient time. When the reversible thermosensitive recording medium is heated by heating, the transparentizing temperature range TW
Need not be very wide. However, when the heating means at the time of transparency does not have a sufficient heat capacity, or when heating cannot be performed for a sufficient time, for example, when heating is performed on the order of several milliseconds using a thermal head or a laser, reversible heating occurs. Since a temperature gradient occurs in the thickness direction of the thermosensitive recording layer of the thermosensitive recording medium and it is difficult to heat the recording medium to a uniform temperature, it is necessary to set the transparency temperature TW sufficiently wide. However, the conventional reversible thermosensitive recording medium has a considerably narrow transparentizing temperature range, and it has been difficult to use a thermal head or the like as a heating medium for image erasing. Further, the conventional reversible recording medium has a sufficient heat capacity, such as a thermal head, or a sufficient erasability when erasing a cloudy printed portion to make it transparent by a heating means that cannot be heated for a sufficient time. Was not a problem. Therefore, an object of the present invention is to solve the above-mentioned problems in the prior art and to increase the transparency temperature range TW, that is, to easily control the temperature and to achieve good erasing characteristics of the white turbid printing portion. Is to provide.

[0005]

The reversible thermosensitive recording medium of the present invention is obtained by dispersing an organic low-molecular substance in a resin composition comprising an organic polymer resin and a plasticizer on a support,
It has a heat-sensitive recording layer whose transparency can be reversibly changed with temperature, and has a melting point of 50 as an organic low-molecular substance.
At least one of the long-chain alkyl group-containing compounds at a temperature of
And at least one of saturated aliphatic bisamides having a melting point of 120 ° C. or higher in a ratio of 98: 2 to 80:20, and containing a plasticizer in an amount of 1 to 10% by total solid content of the heat-sensitive recording layer. It is characterized by having.

Hereinafter, the structure of the reversible thermosensitive recording medium of the present invention will be described. As a support, a synthetic resin film or paper provided with a colored coating layer on the front or back surface,
A synthetic resin film kneaded with a color pigment can be used, for example, a black film kneaded with carbon black can be used. Further, a transparent organic polymer resin film, for example, a film of polyvinyl chloride, polyester, polycarbonate, polyacetate, polyimide, or the like, or a film provided with a reflective layer made of a metal layer is used.

As the organic polymer resin used for the heat-sensitive recording layer, those having good transparency, excellent mechanical strength, and good film-forming properties are preferable. For example, polyvinyl chloride, vinyl chloride-
Vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer , Vinylidene chloride-acrylonitrile copolymer, polyester resin, polyamide resin, acrylic resin, silicone resin and the like.

In the present invention, the compound having a long-chain alkyl group used as one of the organic low-molecular substances in the heat-sensitive recording layer generally refers to a substance called wax or wax, which is solid at room temperature. , A compound containing a long-chain alkyl group of about C _{14 to} C ₅₀ , having a melting point of 50 to 1
As long as the temperature is 00 ° C., any material can be used, but an ester, an amide or a ketone containing a long-chain alkyl group is preferable. Specifically, examples of the ester include stearyl stearate, behenyl stearate, behenyl behenate, behenyl montanate, C ₃₀ alcohol stearate, and C ₃₀ behenate.
Alcohol, stearic acid C ₅₀ alcohol, behenic acid C ₅₀ alcohol esters, Eikosanji stearyl alcohol diesters; the amides, for example, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, N- stearyl stearic acid amide , N-oleyl palmitic amide, N-stearyl erucic acid amide, N-stearyl oleic acid amide and the like; Examples of the ketone include, but are not limited to, distearyl ketone and dibehenyl ketone. These compounds having a long-chain alkyl group include 1
Species may be used, but two or more may be used.

A saturated aliphatic bisamide used as another organic low molecular weight substance has a melting point of not less than 120 ° C.
It is preferably in the range of 130 to 150 ° C. and is an acid amide of a long-chain saturated fatty acid and an alkylenediamine, or an acid amide of a saturated aliphatic dicarboxylic acid and a saturated aliphatic amine. Specifically, for example, ethylene bisstearic acid amide m.p. p. 143 ° C. (C ₁₇ H ₃₅ CONH) ₂ (CH ₂ ) ₂ ethylenebisbehenamide m. p. 141 ° C. (C ₂₁ H ₄₃ CONH) ₂ (CH ₂ ) ₂ hexamethylene bisstearic acid amide m. p. 146 ° C. (C ₁₇ H ₃₅ CONH) ₂ (CH ₂ ) ₆ hexamethylenebisbehenamide m. p. 143 ° C. (C ₂₁ H ₄₃ CONH) ₂ (CH ₂ ) ₆ N, N′-distearyl adipamide m. p. 144 ° C. (C ₁₈ H ₃₇ NHCO) ₂ (CH ₂ ) ₄ N, N′-distearyl eicosandiamide m. p. _{128 ℃ (C 18 H 37 NHCO} ) 2 (CH 2) 18 N, N'- distearyl sebacic acid amide m. p. 138 ° C. (C ₁₈ H ₃₇ NHCO) ₂ (CH ₂ ) ₈ N, N′-dilauryldecanediamide m. p. 138 ° C. (C ₁₂ H ₂₅ NHCO) ₂ (CH ₂ ) ₁₀ N, N′-dilauryleicosandiamide m. p. 130 ° C. (C ₁₂ H ₂₅ NHCO) ₂ (CH ₂ ) _{18 and the} like, but are not limited thereto. One of these saturated aliphatic bisamides may be used, or two or more thereof may be used. In this case, if the melting point of the saturated aliphatic bisamide is lower than 120 ° C., there is a problem that a substantial increase in the clearing temperature range cannot be obtained.

In the present invention, the compounding ratio of the compound containing a long-chain alkyl group and the aliphatic bisamide is 9% by weight.
It is necessary to be in the range of 8: 2 to 80:20. When the proportion of the aliphatic bisamide in the organic low molecular weight substance is lower than 2% by weight, no effect is obtained on the expansion of the clarification temperature range, while when it is higher than 20% by weight, a good contrast is obtained. Can not be. In the present invention, the compounding amount of the organic low-molecular substance dispersed in the organic polymer resin is 5 parts in total of the long-chain alkyl group-containing compound and the saturated aliphatic bisamide per 100 parts by weight of the organic polymer resin.
To 100 parts by weight, preferably 10 to 100 parts by weight.
It is preferably in the range of from 50 to 50 parts by weight. When the amount of the organic low-molecular substance is less than 5 parts by weight, the opaque (white turbidity) of the heat-sensitive recording layer is not sufficient, and good contrast cannot be obtained. Film formability deteriorates.

As the plasticizer, an appropriate one is used. Specifically, the following are exemplified. Phosphates such as tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di-n-octyl phthalate, diisooctyl phthalate, fucapryl phthalate, phthalate Fats such as di-2-ethylhexyl acid, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, dibutoxyethyl phthalate, butyl oleate, tetrahydrofurfuryl oleate, glycerin monooleate, etc. Group-basic acid esters, dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, di-2-ethylbutyl azelate, di-2-ethylhexyl azelate, dibutyl sebacate,
Fatty acid dibasic acid esters such as di-2-ethylhexyl sebacate and dicapryl sebacate, and dihydric alcohols such as diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, and triethylene glycol di-2-ethylhexoate Esters, oxyesters such as methyl acetyl ricinoleate, butyl acetyl ricinoleate, methoxyethyl acetyl ricinoleate, butyl phthalbutyl glycolate, acetyl tri (2-ethylhexyl), chlorinated paraffin, chlorinated biphenyl-2-nitro Biphenyl, dinonylnaphthalene, show brain, methyl abietic acid and the like. These can be used alone, or two or more can be appropriately selected and used.

The amount of the plasticizer added is preferably in the range of 1 to 10% of the total solid content of the heat-sensitive recording layer. When the addition amount of the plasticizer is less than the above range, the effect of adding the plasticizer is lost, and when the addition amount is too large than the above range,
The cloudy print density decreases, and the contrast (visibility) between the cloudy print portion and the transparent background portion deteriorates. The contrast can be improved by providing a light reflecting layer made of a thin film of a metal such as aluminum between the heat-sensitive recording layer and the support. In this case, the reflection density (Macbeth reflection density) between the white turbid portion and the transparent portion is improved.
Is preferably 0.7 or more. The type and amount of the plasticizer to be used can be appropriately selected in the above range in consideration of these.

The heat-sensitive recording layer in the present invention may be a solution of an organic polymer resin containing a plasticizer and a compound containing a long-chain alkyl group and a saturated aliphatic bisamide, or a solution of an organic polymer resin containing a plasticizer. Disperse a compound containing a long-chain alkyl group and a saturated aliphatic bisamide, or melt-mix a compound containing a long-chain alkyl group and a saturated aliphatic bisamide in an organic polymer resin containing a plasticizer. It can be provided by coating or printing the support on a support and forming a film. In the formed heat-sensitive recording layer, the organic low-molecular substance is present in the organic polymer resin in a state of being dispersed in the form of particles, and the particle size is distributed in a range of about 0.5 to 2 μm.

[0014] The thickness of the heat-sensitive recording layer is preferably in the range of 1 to 20 µm, more preferably in the range of 3 to 10 µm. When the thickness is less than 1 μm, the heat-sensitive recording layer is not sufficiently opaque (opaque) and
If the thickness is larger, the thermal conductivity is deteriorated at the time of printing or erasing with a thermal head or the like, and the sensitivity of the heat-sensitive recording layer to heat is deteriorated.

In the heat-sensitive recording medium of the present invention, the following layers can be provided as necessary. For example, when recording and erasing an image using a thermal head, in order to improve the heat resistance of the thermosensitive recording layer and to maintain the matching property with the thermal head, a thermoplastic or thermosetting A heat-resistant protective layer mainly composed of a resin such as a photo-curable or electron beam-curable urethane-acrylate resin such as a polymethacrylate resin, a silicone resin, an acrylic resin, and an alkyd resin may be provided. . Further, an intermediate layer between the heat-sensitive recording layer and the protective layer for preventing migration of the organic low-molecular substance in the heat-sensitive recording layer to another layer or for enhancing the adhesiveness between the heat-sensitive recording layer and the protective layer. It may be provided.

Further, a magnetic recording layer can be provided on the surface of the support opposite to the heat-sensitive recording layer or between the support and the heat-sensitive recording layer. When the magnetic recording layer is provided on the surface of the support opposite to the heat-sensitive recording layer, to prevent abrasion of the magnetic recording layer, a thermoplastic resin or a thermosetting resin on the surface of the magnetic recording layer, For example, a heat-resistant protective layer mainly composed of a photo-curable or electron beam-curable urethane-acrylate resin or epoxy-acrylate resin such as a polymethacrylate resin, a silicone resin, an acrylic resin, and an alkyd resin may be provided.

[0017]

The difference between the transparent state and the white turbid state in the reversible thermosensitive recording medium of the present invention is considered to be due to the difference in the crystal state of the organic low-molecular substance dispersed in fine particles in the thermosensitive recording layer. That is, the transparent state can be described as follows. The thermosensitive recording layer of the reversible thermosensitive recording medium is heated to a clearing temperature T1 to T2. At this time, the organic low-molecular substance dispersed in the heat-sensitive recording layer melts,
It remains without being completely melted. Next, when cooled, a large crystal grows with the unmelted organic low-molecular substance as a nucleus in the cooling process. The organic low-molecular substance dispersed in the heat-sensitive recording layer after cooling is a large crystal, so that when light enters, the degree of light scattering at the interface is small, and thus the heat-sensitive recording layer is in a transparent state. Caught as The opaque (cloudy) state can be explained as follows. The thermosensitive recording layer is heated above the temperature TW. At this time, the organic low-molecular-weight substance dispersed in the heat-sensitive recording layer is in a completely molten state, and when cooled, there is no nucleus for crystal growth in the cooling process. It cannot grow and becomes an aggregate of fine microcrystals after cooling. Therefore, the light incident on the heat-sensitive recording layer is scattered at the interface between the microcrystals and is regarded as an opaque (cloudy) state. The reversible thermosensitive recording material of the present invention utilizes the reversible change in transparency as described above to record and erase images, and according to the present invention, it is possible to increase the temperature range for the transparency. Things.

In the conventional reversible recording medium,
There has been a problem that the erasability is not sufficient when the white turbid print portion is to be made transparent by a sufficient heat capacity such as a thermal head or a heating means that cannot be heated for a sufficient time. It is considered that the cause is that the organic polymer resin of the heat-sensitive recording layer becomes harder with time due to the rearrangement of the molecules, and the heat energy required for the transparency is increased, thereby significantly lowering the sensitivity. However, in the present invention, since a plasticizer is contained, in addition to the effect of widening the above-mentioned transparency temperature range, the intermolecular force of the organic polymer resin in the heat-sensitive recording layer is reduced, and the organic polymer resin is reduced. It is considered that this also has the effect of suppressing the hardness of the white portion and improving the erasing characteristics of the white turbid printed portion.

In the heat-sensitive recording layer of the present invention, a long-chain alkyl group-containing compound having a melting point of 50 to 100.degree. C. and a saturated aliphatic bisamide having a melting point of 120.degree. Because, when heated for clarification, even when the temperature is higher than the melting temperature of the long-chain alkyl group-containing compound, the saturated aliphatic bisamide is not melted but remains in the heat-sensitive recording layer, The remaining saturated aliphatic bisamide fine particles serve as crystal nuclei during the cooling process. Therefore, the upper limit T2 of the clearing temperature is shifted to the higher temperature side. As a result, the reversible thermosensitive recording medium of the present invention has a wider transparent temperature range.

[0020]

The present invention will be described below with reference to examples. In addition, "part" means a weight ratio. Example 1 Using a 188 μm transparent polyethylene terephthalate film on which aluminum was deposited on one side as a support, the following heat-sensitive recording layer paint was applied using a wire bar on the opposite side of the aluminum deposit side of the support. After drying, a thermosensitive recording layer having a thickness of 10 μm was formed. Behenyl montanate 95 parts N, N'-distearyldodecanediamide 5 parts Vinyl chloride-vinyl acetate copolymer 300 parts Di-2-ethylhexyl phthalate (plasticizer) 20 parts Tetrahydrofuran 1600 parts After coating and drying on the thermosensitive recording layer, a protective layer having a thickness of 3 μm was formed to obtain a reversible thermosensitive recording medium of the present invention. Silicon resin YR3370 (Toshiba Silicone Co., Ltd.) 400 parts Catalyst CR15 (Toshiba Silicone Co., Ltd.) 1 part Isopropyl alcohol 1600 parts

Example 2 A reversible thermosensitive recording medium was obtained in the same manner as in Example 1 except that the plasticizer in Example 1 was replaced with 10 parts of dibutyl adipate. Example 3 The plasticizer in Example 1 was replaced with diisodecyl phthalate 10
A reversible thermosensitive recording medium was obtained in the same manner as in Example 1 except that the recording medium was replaced with a part. Example 4 A reversible thermosensitive recording medium was obtained in the same manner as in Example 1, except that the plasticizer in Example 1 was replaced with 10 parts of di-2-ethylhexyl sebacate. Example 5 A mixture of 150 parts of a vinyl chloride-vinyl acetate-vinyl alcohol copolymer (manufactured by Sekisui Chemical Co., Ltd .: Esrec A) and 150 parts of a polyester resin (manufactured by Toyobo Co., Ltd .: Byron 290) was used as the organic polymer resin for the heat-sensitive recording layer. A reversible thermosensitive recording medium was obtained in the same manner as in Example 1 except that the above conditions were satisfied.

Comparative Example 1 A reversible thermosensitive recording medium was obtained in the same manner as in Example 1 except that a coating material for a thermosensitive recording layer having the following composition was used. 100 parts of behenyl montanate 300 parts of vinyl chloride-vinyl acetate copolymer Comparative Example 2 1600 parts of tetrahydrofuran Comparative Example 2 Reversibility was obtained in the same manner as in Comparative Example 1 except that 100 parts of N-stearyl oleamide was used instead of behenyl montanate. A thermal recording medium was obtained. Comparative Example 3 Distearyl ketone 10 instead of behenyl montanate
A reversible thermosensitive recording medium was obtained in the same manner as in Comparative Example 1 except that 0 part was used. Comparative Example 4 A reversible thermosensitive recording medium was obtained in the same manner as in Example 1, except that the amount of the plasticizer was changed to 80 parts.

The sample of the reversible thermosensitive recording medium produced in this manner is sufficiently heated in an oven at 130 ° C. to completely turn the medium completely opaque, and then, using a thermal gradient tester manufactured by Toyo Seiki Co., Ltd. At a pressure of 400 g / m ² , a heat block was pressed against the sample for 1 second to perform color development and decoloration tests. Since the portion where the heat block at the clearing temperature was pressed was made transparent, the range of the clearing temperature was measured. In addition, the number of the reversible recording medium is 8 / mm.
The white turbid portion was made transparent with a thin film type thermal head, and the erasing characteristics were evaluated. Table 1 shows the results.
Shown in The evaluation of the erasing characteristics is to completely clear the entire surface of the reversible recording medium with a dryer, then perform solid white printing with a thermal head, and perform transparency with the thermal head when the maximum cloudy printing density is exhibited. It is.
The erasing rate (R) was calculated from the following equation as a measure of the erasing characteristics. R = [(B−C) / (A−C)] × 100 (%) However, A, B, and C are those obtained by measuring the following reflection densities with a Macbeth reflection densitometer (RD-914). A: Transparent background density (reflection density when the entire surface is transparentized by a dryer) B: Transparency density (reflection density at a part transparentized by a thermal head) C: Maximum opaque print density 80% as a criterion ≦ R is Δ, 70% <R <
80% was evaluated as Δ, and 70%> R was evaluated as ×. However, in Comparative Example 4, the difference (contrast) between the maximum white turbid print density and the transparent background density was small, and the image quality was poor.

Table 1 shows the clearing temperature range measured by the above method.
Shown in

[Table 1]

As is evident from the measurement results in Table 1, the samples of the present invention to which the saturated aliphatic bisamide was added were more transparent than those of Comparative Examples 1 to 3 to which no saturated aliphatic bisamide was added. It was confirmed that the temperature range was significantly wide and the erasing rate was improved. Further, it was clarified that the addition of a plasticizer to the heat-sensitive recording layer further improved the clearing temperature range and the erasing rate. It was also confirmed that the contrast (visibility) was greatly affected.

[0026]

As described above, in the reversible thermosensitive recording medium according to the present invention, the long-chain alkyl group-containing compound and the saturated aliphatic bisamide are contained in a weight ratio of 98: 2 to 80 as the organic low-molecular substance of the thermosensitive recording layer. : 20, the transparency temperature range of the recording medium can be widened,
As a result, it is possible to provide a reversible thermosensitive recording medium in which an image can be easily erased when a heating medium having a small heat capacity such as a thermal head is used.

[Brief description of the drawings]

FIG. 1 is a state diagram showing the relationship between temperature and transparency in a reversible thermosensitive recording medium.

Continuation of the front page (72) Inventor Riki Murata 3-1 Yosoba-cho, Shizuoka City, Shizuoka Prefecture Inside the Electronic Materials Research Laboratories of Hamakawa Paper Mill Co., Ltd. (56) References JP-A-3-180389 (JP, A)

Claims (4)

(57) [Claims] 1. A heat-sensitive recording layer in which a low-molecular organic substance is dispersed in a resin composition comprising an organic high-molecular resin and a plasticizer and whose transparency can be reversibly changed depending on temperature. In the reversible thermosensitive recording medium, at least one kind of the long-chain alkyl group-containing compound having a melting point of 50 to 100 ° C. and at least one kind of the saturated aliphatic bisamide having a melting point of 120 ° C. or more are used as the organic low-molecular substances. ~ 8
A reversible thermosensitive recording medium which is used in a ratio of 0:20 and contains the plasticizer in an amount of 1 to 10% by total solid content of the thermosensitive recording layer. 2. The long-chain alkyl group-containing compound,
2. The reversible thermosensitive recording medium according to claim 1, wherein an ester comprising a higher fatty acid and a higher alcohol is used. 3. The long-chain alkyl group-containing compound,
The reversible thermosensitive recording medium according to claim 1, wherein a higher aliphatic amide is used. 4. The reversible thermosensitive recording medium according to claim 1, wherein a higher aliphatic ketone is used as the long-chain alkyl group-containing compound.