JPH06262849A - Reversible thermal recording material - Google Patents

Abstract

PURPOSE:To prevent the lowering of opacity even when the printing and erasing operations due to a thermal head are repeated by constituting an org. monomeric substance of at least two components and crosslinking a resin matrix. CONSTITUTION:An org. monomeric substance pref. consists of at least one kind of compd. selected from 16C or more higher fatty acid and a compd. with an m.p. of 50 deg.C or more and one kind of a compd. selected from fatty acid saturated dicarboxylic acid and sulfide. A resin matrix is formed into a layer having the org. monomeric substance uniformly dispersed and held therein and largely exerts effect on the transparency of a recording layer at a transparent time. Therefore, as the resin matrix, a resin high in transparency and mechanically stable and excellent in film forming properties is pref. Further, it is desirable that this resin can be crosslinked by a crosslinking agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible heat-sensitive recording material capable of reversibly repeatedly forming and erasing an image by heating means such as a thermal head.

[0002]

2. Description of the Related Art In recent years, with the spread of thermal heads, the demand for heat-sensitive recording materials has expanded rapidly. Particularly in prepaid cards, which are rapidly becoming popular in the fields of communication, transportation, distribution, etc., magnetic information is often displayed on the card as visible information. Such magnetic cards are widely used as highway cards, prepaid cards for department stores, supermarkets, and JR Orange cards.

However, in such a recording material, the area in which the visible information can be displayed is limited. For example, in the case of a high-priced prepaid card, the information may not be displayed when the balance is additionally recorded. In such a case, conventionally, a new card is reissued to deal with the problem, which causes a problem of high cost.

In order to solve such a problem, studies have been made on a reversible recording material capable of repeatedly recording and erasing in the same area. When such a material is used, old unnecessary information can be erased and new information can be displayed, so that the information cannot be displayed and a new card need not be reissued. Further, by using such a recording material as, for example, a facsimile sheet, it becomes possible to save resources and help to solve environmental problems.

Conventionally, as a heat-sensitive recording material capable of reversibly recording and erasing such information, a high-grade material is used in a resin base material such as polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyester and polyamide. Those having a heat-sensitive layer in which an organic low molecular weight substance such as alcohol or higher fatty acid is dispersed have been proposed (JP-A-54-119377, 5).
5-154198 and JP-A-2-1363).

The principle of image formation and erasure of such a reversible thermosensitive recording material lies in the change in transparency of the thermosensitive layer when the temperature is raised to different temperatures and returned to room temperature. That is, such a recording material shows a transparent state when it is heated to a certain temperature and returned to room temperature, and shows a cloudy state when it is heated to another temperature and returned to room temperature.

A thermal head is preferable as a method of recording on such a heat-sensitive recording layer, and a heat roll, a hot stamp, a thermal head or the like is preferable as an erasing method.

However, from the viewpoint of versatility of the recording / erasing apparatus, it is desirable to use the thermal head for erasing. In this case, JP-A-55-154198
In the recording materials disclosed in Japanese Patent Publication No. JP-A-2003-242, the erasable proper energy range is extremely narrow and erasing is practically impossible. In order to solve such a problem, it is proposed to add various additives to broaden the erasing energy range (Japanese Patent Laid-Open Publication No. Sho 6-62).
3-39378, 63-104879, JP-A-3-2
No. 089 and Japanese Patent Application Laid-Open No. 4-78573), the practicality of the reversible thermosensitive recording material is improved.

[0009]

However, even with such a recording material, printing with a thermal head,
When the erasing operation is repeated, the white turbidity gradually decreases, and the readable contrast is no longer obtained.

[0010]

As a result of further research on the above problems, the present inventors have found that such deterioration is caused by using a crosslinked resin as a resin matrix used in a reversible thermosensitive recording material. The present invention has been completed based on the finding that the occurrence of the phenomenon is less likely to occur.

The present invention is a reversible thermosensitive recording material which comprises a resin matrix and an organic low molecular weight substance as main components and can be repeatedly recorded and erased by heating, and the organic low molecular weight substance comprises at least two components. Further, the present invention provides a reversible thermosensitive recording material characterized in that the resin base material is crosslinked.

It is considered that the conventional mechanism of deterioration of this type of reversible thermosensitive recording material due to repeated use is due to the simultaneous application of heat and shearing force by the thermal head. It is considered that the effect of simultaneous application of heat and shear force is reduced by the crosslinked resin.

The above-mentioned organic low molecular weight substance is (i) at least one compound selected from higher fatty acids having 16 or more carbon atoms and ketones having a melting point of 50 ° C. or more, and (ii) fatty acid saturated dicarboxylic acid and general _{formula: HOOC (CH 2) m -S-} (CH 2) n COOH (m and n are each an integer of 1 to 5) is preferably at least one compound selected from sulfides represented by.

Next, the reversible thermosensitive recording material of the present invention will be described.

The resin base material forms a layer in which an organic low molecular weight substance is uniformly dispersed and held, and greatly affects the transparency of the recording layer when it is transparent. Therefore, the resin base material is preferably a resin having high transparency, mechanical stability, and excellent film-forming property. Further, it is desirable that thermal crosslinking with a crosslinking agent is possible. Examples of such a resin include vinyl chloride-
Vinyl chloride-based copolymers such as vinyl acetate-vinyl alcohol copolymer, vinyl chloride acrylate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, epoxy modified vinyl chloride-vinyl acetate copolymer; phenoxy resin Examples thereof include resins such as epoxy resin and acrylic resin. These resin base materials may be used alone or in combination of two or more kinds, or may be used by mixing with other resins.

In the present invention, the recyclability of the recording material is improved by crosslinking the resin base material. As a method of such crosslinking, it is preferable to perform thermal crosslinking so as not to impair other characteristics such as recording characteristics. Examples of the crosslinking agent used here include amino resins, phenol resins, isocyanates, amines, and epoxy compounds. Examples of the amino resin include melamine resin (eg hexamethoxyethylmelamine), benzoguanamine, urea resin and the like. Examples of the phenol resin include trimethylolphenol. Examples of the isocyanates include 2,4- or 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate. Further, examples of amines include polymethylenediamine, diaminophenylmethane, diaminophenylsulfone, o-toluidine, benzyldimethylamine and the like. Examples of the epoxy compound include triglycidyl isocyanurate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and epoxidized melamine resin. In addition, an acid anhydride, methyl acrylic acid glycolate methyl ether, etc. may be used. Cross-linking is preferably carried out using these cross-linking agents and catalysts.

The amount of the cross-linking agent added to the resin base material is 0.5.
˜50.0 phr, preferably 1.0 to 30.0 phr. If the amount of the cross-linking agent is less than 0.5 phr, the cross-linking is insufficient and the deterioration due to long-term use is not sufficiently prevented. Again 50 phr
If the amount is larger, the crosslinking agent acts as a plasticizer and the recyclability is deteriorated, which is not preferable.

The organic low molecular weight substance used in the present invention is composed of at least two components. The first component thereof is a higher fatty acid, particularly a higher fatty acid having 16 or more carbon atoms, and a melting point of 5
Ketones at 0 ° C. or higher are preferably used.

Specific examples of the higher fatty acids having 16 or more carbon atoms include palmitic acid, margaric acid, stearic acid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, behenic acid, lignoceric acid, pentacosanoic acid, serotic acid, heptacosanoic acid, montan. Acid, triacontanoic acid, nonacosanoic acid, mericinic acid, 2-hexadecynoic acid, trans-
3-hexadecenoic acid, 2-heptadecenoic acid, trans-
2-octadecenoic acid, cis-2-octadecanoic acid, trans-4-octadecenoic acid, 2-heptadecenoic acid, cis-6-octadecenoic acid, elaidic acid, vacenic acid, trans-gondoinic acid, erucic acid, brassic acid, brassic acid , Ceracoleic acid, trans-Ceracoleic acid,
Trans-8, trans-10-octadecadienoic acid,
Linoelaidic acid, α-eleostearic acid, β-eleostearic acid, pseudoeleostearic acid, 12,
20-heneicosadienoic acid and the like.

When a ketone is used as the first component, it preferably has a melting point of 50 ° C. or higher. Melting point 5
When Kents below 0 ° C. are used, they are unstable at room temperature, and the energy required for recording or erasing changes during storage. Therefore, erasing cannot be performed with a constant set energy, which is not preferable. This kind of melting point is 50
The ketones above ℃ are listed below.

1) Dialkyl ketone General formula CH ₃ (CH ₂ ) _n-1 CO (CH ₂ ) _n-1 CH ₃
n ≧ 8 2) Methyl alkyl ketone General formula CH ₃ CO (CH ₂ ) _n-3 CH ₃
n ≧ 17 3) Phenylalkylketone General formula C ₆ H ₅ CO (CH ₂ ) _n-1 CH ₃
n ≧ 10

4) Macrocyclic ketone

[Chemical 1] 5) Symmetrical α-diketone General formula RCOCOR R = C _n H _{2n + 1}
n ≧ 7 6) acyloine general formula RCH (OH) COR R = C _n H _{2n + 1}
n ≧ 9

7) Cyclic acyloine

[Chemical 2]

8) Ketene dimer

[Chemical 3] Then, the organic low as the second component of the molecular substances aliphatic saturated dicarboxylic acid or the formula _{HOOC (CH 2) m -S- (} C
_{H 2) n COOH (m,} n sulfides are preferably used represented by each an integer from 1 to 5).

Specific examples of the aliphatic dicarboxylic acid include the following substances represented by the general formula HOOC (CH ₂ ) _n-2 COOH.

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ n Material quality name n Material quality name ───── ───────────────────────────── 2 oxalic acid 15 pentadecanedioic acid 3 malonic acid 16 hexadecanedioic acid 4 succinic acid 17 heptadecanedioic acid 5 Glutaric acid 18 Octadecanedioic acid 6 Adipic acid 19 Nonadecanedioic acid 7 Pimelic acid 20 Eicosanedioic acid 8 Suberic acid 21 Heneicosandioic acid 9 Azelaic acid 22 Docosandioic acid 10 Sebacic acid 23 Tricosandioic acid 11 Undecanedioic acid 24 Tetracosanodioic acid 12 Dodecanoic acid 26 Hexacosanedioic acid 13 Tridecanedioic acid 30 Nonacosanedioic acid 14 Tetradecanedioic acid 34 Dotriacontanedioic acid ━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━━━━━

Further, the general formula HOOC (CH ₂ ) _m --S-(C
Specific examples of the sulfide represented by H ₂ ) _n COOH (m and n are each an integer of 1 to 5) include (1,1′-dicarboxy) dimethyl sulfide and (2,2′-dicarboxy) diethyl sulfide. [Thiodipropionic acid],
(3,3′-dicarboxy) dipropyl sulfide,
(1,2′-dicarboxy) methyl ethyl sulfide,
(1,3′-dicarboxy) methylpropyl sulfide,
(1,4′-dicarboxy) methylbutyl sulfide,
(2,3′-dicarboxy) ethylpropyl sulfide,
(1,4′-dicarboxy) methylbutyl sulfide,
Examples thereof include (5,5′-dicarboxy) dipentyl sulfide, with thiodipropionic acid being particularly preferable.

The blending ratio of the second component to the first component of the organic low molecular weight substance is preferably 95: 5 to 5:95 (weight ratio). When the blending ratio of the second component is too small, the transparentizing energy region is narrowed, which is not preferable, and when the blending ratio is too large, sufficient contrast cannot be obtained and both are not preferable.

Furthermore, the total amount of these organic low molecular weight substances mixed with the resin base material is 1 per 100 parts by weight of the resin base material.
It is preferably from 0 to 170 parts by weight. If the amount of the low-molecular organic compound is too small, the contrast becomes low, and if it is too large, the film-forming property deteriorates, which is not preferable.

The solvent used for forming the heat-sensitive recording layer may be variously selected depending on the types of the base material and the organic low molecular weight substance, and for example, tetrahydrofuran, methyl ethyl ketone,
Methyl isobutyl ketone, chloroform, carbon tetrachloride,
Examples thereof include ethanol, toluene, benzene and the like.

If desired, the recording material of the present invention may further contain a lubricant, an antistatic agent, a plasticizer, a dispersant, a stabilizer, a surfactant, an inorganic or organic filler, and the like.

To form the heat-sensitive recording layer, generally, a solution in which two components of a resin base material and an organic low molecular weight substance are dissolved is prepared, or a solvent which does not dissolve at least one of the organic low molecular weight substances is used. A solution of a resin base material is prepared, and an organic low-molecular substance is dispersed in the form of fine particles, and these are coated on a substrate and dried to form a heat-sensitive recording layer. Next, the resin base material is cured under appropriate heat treatment conditions. The thickness of the heat-sensitive recording layer is usually 1 to 20 μm, and if it is thicker than this, the sensitivity decreases and a temperature gradient occurs in the thickness direction, which is not preferable. On the other hand, if it is thinner than this, the contrast is lowered, which is not preferable. Pulse width 2msec especially using thermal head
When recording and erasing at the following high speeds, the thickness of the thermosensitive recording layer is preferably 10 μm or less.

If desired, an overcoat layer may be provided on the heat-sensitive recording layer directly or through an undercoat layer for protection thereof. The overcoat layer may be made of an organic material such as acrylic, silicone, fluorine, or epoxy, and may be SiO ₂ , SiO, Mg.
An inorganic substance such as O, ZnO, TiO ₂ , Al ₂ O ₃ , AlN or Ta ₂ O ₅ may be used.

For forming the overcoat layer, conventionally known coating methods and vacuum thin film forming methods (vacuum vapor deposition method, etc.) are used.
Thickness is 0.1-5.0 μm, preferably 0.5-3.0 μm
And If the thickness of the overcoat is thinner than this, the protective effect is not sufficient, and if it is thicker than this, the amount of energy required for recording becomes large, which is not preferable either.

[0035]

EXAMPLES Next, the present invention will be described more specifically by way of Examples and Comparative Examples. In the following, "parts" means "parts by weight".

Example 1 Composition by weight Lauron (CH ₃ (CH ₂ ) ₁₀ CO (CH ₂ ) ₁₀ CH ₃ ) 30 parts Eicosane diacid 10 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 60 parts Coronate L (75% isocyanate cross-linking agent) 8 parts Tetrahydrofuran 400 parts The solution was applied with a wire bar onto a metal reflective substrate (a polyethylene terephthalate film 188 μm on which a 0.1 μm thick Al layer was formed by vacuum deposition). Then, it was dried by heating to form a thermosensitive recording layer having a thickness of 5 μm. Then,
The resin base material was cured by aging at 40 ° C. for 24 hours. Further, a silicone type thermosetting resin layer (2 μm thick) was formed as a protective layer on the heat sensitive layer.

[Example 2] A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that behenic acid was used instead of laurone and thiodipropionic acid was used instead of eicosanedioic acid.

Example 3 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that an epoxy compound crosslinking agent (tetrad) was used instead of Coronate L.

Comparative Example 1 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that Coronate L was omitted.

Comparative Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 2 except that Coronate L was omitted.

[Comparative Example 3] A reversible thermosensitive recording material was prepared in the same manner as in Example 3 except that tetrad was omitted.

[Test Method] The recyclability of the reversible thermosensitive recording materials obtained in the above Examples and Comparative Examples was evaluated by the following method.

An 8 dot / mm line type head is used, and the application time is changed under a constant applied voltage (pulse period 2.0 m
s), the application time showing the maximum white turbidity was determined, and this condition was defined as the application condition. Then, with respect to the sample after printing, the stamp temperature was changed with a hot stamp at a contact time of 0.1 sec (contact pressure 1 kg / cm ² ), and the temperature showing the maximum transparency was determined to be an erasing condition. Hereinafter, printing and erasing were repeated under these conditions, and the number of recycles was once when printing and erasing were performed once. The white turbidity and the transparency were evaluated by the reflection temperature of a Macbeth reflection densitometer (RD-914), and the smaller the numerical value, the more the white turbid state (the larger the numerical value, the transparent state). The results are shown in Table 1.

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Initial stage after 1000 times of recycling ─ ─────────────────────────── Print density contrast Print density contrast (OD erase-OD print) (OD erase-OD print) ━━━━ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Example 1 0.60 1.00 1.00 0.70 0.80 〃 20 .50 0.80 0.60 0.70 〃 3 0.60 0.90 0.75 0.75 ────────────────────────── ─────────── Comparative Example 1 0.60 1.00 1.00 1.30 0.05 〃 2 0.50 0.80 1.20 0.02 〃 3 0.60 0.90 1. 35 0.04 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━━━

[0045]

INDUSTRIAL APPLICABILITY The reversible thermosensitive recording material of the present invention is composed of at least two components of an organic low molecular weight substance, and the resin base material is cross-linked. Therefore, the white turbidity does not decrease due to repeated printing and erasing, and the recyclability is high. Greatly improved.

Claims (5)

[Claims] 1. A reversible thermosensitive recording material comprising a resin base material and an organic low-molecular substance as main components and capable of being repeatedly recorded and erased by heating, wherein the organic low-molecular substance comprises at least two components, A reversible thermosensitive recording material characterized in that the resin base material is crosslinked. 2. An organic low molecular weight substance is (i) at least one compound selected from higher fatty acids having 16 or more carbon atoms and a ketone having a melting point of 50 ° C. or higher, and (ii) fatty acid saturated dicarboxylic acid and a general formula: _{HOOC (CH 2) m -S- (} CH 2) n COOH (m and n are each an integer of 1 to 5) reversible sense of claim 1, wherein at least one compound selected from sulfides represented by Thermal recording material. 3. The reversible thermosensitive recording material according to claim 1, wherein the resin base material is thermally crosslinked. 4. The crosslinking agent is an amino resin, a phenol resin,
4. The reversible thermosensitive recording material according to claim 3, which is at least one resin selected from isocyanates, amines and epoxy compounds. 5. The main component of the resin matrix is vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-acrylate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, epoxy-modified vinyl chloride. The reversible thermosensitive recording material according to claim 1, which is at least one resin selected from a vinyl acetate copolymer, a phenoxy resin, an epoxy resin and an acrylic resin.