JPH06191152A - Reversible heat sensitive recording material - Google Patents

Abstract

PURPOSE:To obtain a reversible heat sensitive recording material showing high transparency extending over wide energy sphere, by a method wherein an organic low-molecular substance which is comprised of at least two components and has the first and second components incompatible with each other and a basic material are compounded with each other. CONSTITUTION:A composition for a heat sensitive recording material is prepared by compounding fixed quantities of an organic low-molecular substance which is comprised of at least two components and has the first and second components incompatible with each other and a resin basic material with each other. In this case, it is preferable that a difference in dissolution parameter between the first and second components is at least 1.20. Then ketone having the melting point of at least 50 deg.C and sulfide represented by a formula I (m, n represent an integral number of 1-5) are preferable respectively for the first and second components. Two components of the foregoing resin basic material and organic low-molecular substance are dissolved into an appropriate solvent and a coating solution for a heat sensitive recording layer is prepared. The coating solution is applied onto a substrate such as paper, synthetic paper and plastic film and dried, to which a heat sensitive recording layer is laminated and a reversible heat sensitive recording material is obtained.

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.

[0008]

However, the record-
Considering the versatility of the erasing device, it is desirable to use a thermal head for erasing. In this case, with the recording materials disclosed in JP-A-55-154198 and the like, the erasable proper energy range was extremely narrow and erasing was virtually impossible.

In order to solve such a problem, Japanese Unexamined Patent Publication No. Hei 2
In Japanese Laid-Open Patent Publication No. 1363, etc., it is proposed to increase the erasable energy range by adding a high melting point substance as a second component of an organic low molecule.

However, the above-mentioned recording material has a problem in that the apparent melting point of the high melting point substance is lowered, and as a result, the erasable energy range cannot be sufficiently expanded.

An object of the present invention is to provide a reversible thermosensitive recording material which exhibits high transparency over a wide energy range.

[0012]

As a result of further research on the above-mentioned problems, the present inventors have found that when an organic low-molecular substance is composed of at least two components and the two components are incompatible systems. The inventors have completed the present invention knowing that the above problems can be solved.

That is, the present invention is a reversible thermosensitive recording material comprising a resin base material and an organic low molecular weight substance, which can be repeatedly recorded and erased by heating, and the organic low molecular weight substance is at least two components. And a reversible sensitized heat-sensitive recording material comprising the first component and the second component which are incompatible with each other. The present invention also relates to the reversible thermosensitive recording material, wherein the difference (ΔSP) in the solubility parameter SP value between the first component and the second component, which are incompatible organic low-molecular substances, is 1.20 or more. is there.

Further, in the present invention, the first component of the organic low molecular weight substance is a ketone having a melting point of 50 ° C. or higher, and the second component is represented by the general formula: HOOC (CH ₂ ) _m -S- (CH ₂ ) _n COOH ( m and n are each a sulfide represented by 1 to 5) or an aliphatic saturated dicarboxylic acid represented by the general formula: HOOC (CH ₂ ) _P COOH (p is an integer of 0 to 8). The reversible thermosensitive recording material is provided.

As described above, the organic low-molecular substance is composed of two incompatible components as essential materials, so that the transparent erasing temperature range can be expanded and the reversible thermosensitive recording material can be erased by the thermal head. Is obtained.

FIG. 1 shows the difference in behavior between the case where two compatible components are used as the organic low molecular weight substance and the case where two compatible components are used. Each sample was heated at a contact time of 0.1 sec and then returned to room temperature to measure the optical reflection density. Two
When the component is an incompatible system, a sufficient clearing temperature range can be obtained. On the other hand, when the compatible system is a compatible system, the clearing temperature region becomes narrow, and erasing using a high-speed heating means such as a thermal head becomes difficult.

Next, each material used for the 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 has a great influence on the transparency of the recording layer at the time of transparency. Therefore, the resin base material is preferably a resin having high transparency, mechanical stability, and excellent film-forming property. Examples of such resins include polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-acrylate copolymers, and other vinyl chloride-based copolymers; Vinylidene chloride-based copolymers such as polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer; polyester; polyamide; polyacrylate or polymethacrylate; acrylate-methacrylate copolymer, silicone resin,
Examples thereof include thermoplastic resins such as polystyrene and styrene-butadiene copolymer, and other thermosetting resins. These resin base materials may be used alone or in combination of two or more kinds.

The organic low molecular weight substance used in the present invention is composed of at least two components. As the first component thereof, ketones having a melting point of 50 ° C. or higher, higher fatty acids having 16 or more carbon atoms, and the like are used.

When a ketone is used as the first component, it preferably has a melting point of 50 ° C. or higher. If the melting point is less than 50 ° C., it becomes unstable at room temperature, and the energy value required for recording changes during storage. That is, the transparent energy region shifts, and it becomes impossible to erase with a constant set energy, which is not preferable. The ketones having a melting point of 50 ° C. or higher used in the present invention are listed below.

[0021]

[Chemical 1]

Specific examples of 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, cerotic acid, heptacosanoic acid, montanic acid, triacontanoic acid,
Examples thereof include nonacosanoic acid, melissic acid, elaidic acid, bassenic acid, erucic acid, brassic acid, brassic acid, and ceracoleic acid. Next, as the second component of the organic low molecular weight substance, sulfide or aliphatic saturated dicarboxylic acid is preferably used.

The general formula HOOC (CH ₂ ) _m --S-(CH ₂ ) _n C
Specific examples of the sulfide represented by OOH (m and n are each an integer of 1 to 5) include (1,1′-dicarboxy) dimethyl sulfide and (2,2′-dicarboxy) diethylfide [thiodipropion]. Acid], (3,3'-dicarboxy) dipropyl sulfide (1,2'-dicarboxy) methyl ethyl sulfide, (1,3'-dicarboxy) methyl propyl sulfide, (1,4'-dicarboxy) Methyl butyl sulfide,
(2,3'-dicarboxy) ethylpropyl sulfide, (2,4
Examples include ′ -dicarboxy) ethyl butyl sulfide and (5,5′-dicarboxy) dipentylfide, with thiodipropionic acid being particularly preferred.

The general formula HOOC (CH ₂ ) _p COOH
Specific examples of the saturated aliphatic dicarboxylic acid represented by (p is an integer of 0 to 8) include oxalic acid, malonic acid, succinic acid,
Examples thereof include glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.

It is incompatible with the first component of the present invention and has a difference in solubility parameter (ΔSP) of 1.20 or more, 1.
It is more preferably 70 or more. The solubility parameter SP value of the organic low molecular weight substance was calculated by the Fedors method shown below. Further, the determination of the compatible system and the incompatible system was made by differential scanning calorimetry (DSC).

SP value (δ) = (E _V / v) ^1/2 = (ΣΔe
i / ΣΔvi) ^1/2 E _V : Molar evaporation energy v: Molar volume Δei: Evaporation energy of atom or atomic group Δvi: Molar volume of atom or atomic group SP of a typical organic low-molecular substance calculated from the above
Table 1 shows the values, and Table 2 shows the relationship between ΔSP and the compatible and non-compatible systems based on the combination of organic low-molecular substances.

[Table 1] SP value of each organic low molecular weight substance ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Ingredient SP value ──────────────────────────── Higher fatty acid Palmitic acid 9.19 Stearic acid 9.12 Behenic acid 9.03 ──────── ───────────────────── Ketones (dialkyl ketones) Lauron (12-tricosanone) 8.66 14-Heptacosanone 8.65 Stearone (18-pentatriacontanone) 8.63 ━━ ━━━━━━━━━━━━━━━━━━━━━━━━━━ Second component of organic low-molecular substance SP value ─────────────── ────────────── sebacic acid 11.04 thiodipropionic acid 12.64 tetracosanedioic acid 9.76 aluminum stearate 9.08 ━━ ━━━━━━━━━━━━━━━━━━━━━━━━━

[Table 2] Relationship between ΔSP and compatible system, incompatible system ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━ Organic low-molecular substance ΔSP Compatible or incompatible ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Palmitic acid / Tetracosandioic acid 0.57 Compatible system Stearic acid / Aluminum stearate 0.04〃 Behenic acid / Tetracosandioic acid 0.73〃 Lauron / Tetracosandioic acid 1.10〃 Stearone / Palmitic acid 0.40〃 ────────────── ──────────────────────── Palmitic acid / Sebacic acid 1.85 Incompatible system Stearic acid / Thiodipropionic acid 3.52 〃 Behenic acid / Sebacic acid 2.01 〃 Lauron / Sebacic acid 2.38 〃 Stearone / Thiodipropionic acid 4.01 〃 ━━━━━━━ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

The compounding ratio of the second component to the first component of the organic low molecular weight substance is preferably 90:10 to 10:90 (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.

The total amount of these organic low-molecular substances compounded in the resin base material is 5 per 100 parts by weight of the resin base material.
It is preferably about 70 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.

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 resin which does not dissolve at least one of the organic low molecular weight substances is used. A base material solution 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.

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. For example, tetrahydrofuran, methyl ethyl ketone,
Methyl isobutyl ketone, chloroform, carbon tetrachloride,
Examples thereof include ethanol, toluene, benzene and the like.

The thickness of the heat-sensitive recording layer is usually 1 to 20 μm, and if it is thicker than this, the sensitivity is lowered 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. Particularly when a high-speed energy applying means of 2 msec or less is used, the thickness of the thermosensitive recording layer is preferably 10 μm or less.

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

If desired, an overcoat layer may be provided on the heat-sensitive recording layer directly or through an undercoat layer for protecting the layer. The overcoat layer may be made of an organic material such as acrylic, silicone, fluorine, or epoxy, or may be SiO ₂ , Si.
O, MgO, ZnO, TiO ₂ , Al ₂ O ₃ , AlN, Ta ₂ O ₅
You may use inorganic substances, such as.

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.

[0037]

EXAMPLES Next, the reversible thermosensitive recording material of the present invention will be described more specifically with reference to examples. In the following, "parts" means "parts by weight".

As a sample, a reversible thermosensitive recording layer having a thickness of 5 μm formed on a metal reflective substrate was used, and it was made cloudy by heating, and this was the initial state. Next, using a thermal paper static color developing device (manufactured by Okura Electric Co., Ltd.), the optical reflection density when heated at a contact time of 0.1 sec and returned to room temperature was measured by a Macbeth reflection densitometer (Model RD-918). It was measured.

Example 1 (ΔSP = 3.98) Composition Weight part Lauron [[CH ₃ (CH ₂ ) ₁₀ ] ₂ CO] 30 parts (Melting point 73.0 ° C.) Thiodipropionic acid 10 parts Vinyl chloride- Vinyl acetate copolymer 100 parts Tetrahydrofuran 560 parts The solution was coated with a wire bar on a metal reflective substrate (a polyethylene terephthalate film 188 μm on which a 0.1 μm thick Al layer was formed by a vacuum deposition method), and dried by heating. Then, a 6 μm thick thermosensitive recording layer was provided.

Example 2 (ΔSP = 2.38) A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that sebacic acid was used instead of thiodipropionic acid.

Example 3 (ΔSP = 4.01) Instead of lauron, stearone [CH ₃ (CH ₂ ) ₁₆ ] ₂
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that CO (melting point 91.0 ° C.) was used.

Comparative Example 1 (ΔSP = 0.42) A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that aluminum stearate was used instead of thiodipropionic acid.

Comparative Example 2 (ΔSP = 0.40) A reversible thermosensitive recording material was prepared in the same manner as in Example 3 except that palmitic acid was used instead of thiodipropionic acid.

Comparative Example 3 (ΔSP = 0.73) A reversible thermosensitive recording material was prepared in the same manner as in Example 4 except that tetracosanedioic acid was used instead of thiodipropionic acid.

Regarding the recording materials obtained in the above Examples and Comparative Examples, the temperature range in which the reflection density was within the range of 0.1 from the maximum transparency (clearing temperature range), and the line type thermal head (8 dot / mm Then, an energy range (clearing energy range) in which erasure (erasure rate ≧ 80%) was possible was obtained at an application time of 1.0 msec and a pulse period of 2.0 ms. The results are shown in Table 3. The erasing rate is calculated by the following formula.

Head erase rate (%) = {erase density (OD)
-Recording density (OD)} x 100 / {background density (OD)-
Recording density (OD)}

[Table 3] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Transparent temperature range (℃) Transparent Energy range (max OD ≧ reflection density ≧ max OD-0.1) (mJ / dot) erasure rate ≧ 80 judgment ━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━━━━━━━ Example 1 36 (65-100) 0.02 ○ Example 2 40 (65-104) 0.03 ○ Example 3 29 (72-100) 0.02 ○ ──────────────────────────────────── Comparative Example 1 14 (66 to 79) Not erasable × Comparative Example 2 11 (60 to 70) Unerasable × Comparative Example 3 15 (80 to 94) Unerasable × ━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━━━━━━━━

[0048]

INDUSTRIAL APPLICABILITY The recording material of the present invention is used in combination with an incompatible organic low molecular weight substance having a solubility parameter SP value difference of 1.20 or more, so that the transparent temperature region is expanded and erasing by a thermal head or the like is possible. It became easier.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between temperature and reflection density when an organic low molecular weight substance is a compatible system and an incompatible system.

Claims (4)

[Claims] 1. A reversible thermosensitive recording material comprising a resin base material and an organic low molecular weight substance as main components, wherein the organic low molecular weight substance comprises at least two components, and the first component and the second component are non-phase. A reversible thermosensitive recording material characterized by being melted. 2. The reversible thermosensitive recording material according to claim 1, wherein the difference in solubility parameter between the first component and the second component is 1.20 or more. 3. The first component is a ketone having a melting point of 50 ° C. or higher, and the second component is a compound represented by the general formula: HOOC (CH ₂ ) _m —S— (CH ₂ ) _n COOH (m and n are each 1 to 5). The reversible thermosensitive recording material according to claim 2, which is a sulfide represented by (integer). 4. An aliphatic saturated dicarboxylic acid represented by the following formula: the first component is a ketone having a melting point of 50 ° C. or higher, and the second component is represented by the general formula: HOOC (CH ₂ ) _P COOH (p is an integer of 0 to 8). The reversible thermosensitive recording material according to claim 2.