JPH07115545B2 - Reversible thermosensitive recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reversible thermosensitive recording material for performing image formation and erasing by utilizing reversible transparency change of a thermosensitive layer with temperature.

RELATED ART JP-A-54-119377 and JP-A-55-154198 disclose a reversible thermosensitive recording material having a thermosensitive layer in which an organic low molecular substance such as a higher fatty acid is dispersed in a resin matrix such as a vinyl chloride resin. Is proposed. Image formation and erasing by this type of recording material utilize reversible transparency change of the heat-sensitive layer due to temperature, but when these recording materials are actually made transparent or opaque by heating, When the amount of organic low molecular weight substance is small, the concentration of the opaque part (white part) is low, and when the amount of organic low molecular substance is large with respect to the resin base material, the concentration of the opaque part (white part) is high but the transparency is low. Therefore, we cannot get enough contrast. Further, since the temperature range in which the opaque portion becomes transparent is as narrow as about 2 to 4 ° C., the entire recording material which is at least partially opaque is made transparent, or a colorless (transparent) image is formed on the recording material which is totally opaque. At this time, it is difficult to control the temperature.

Aim of the Invention It is an object of the present invention to provide a reversible thermosensitive recording material capable of forming a high-contrast image and having easy temperature control.

Composition The reversible thermosensitive recording material of the present invention comprises a resin base material and an organic low molecular weight substance dispersed in the resin base material as main components, and the transparency reversibly changes depending on temperature. In the reversible thermosensitive recording material having a thermosensitive layer, the organic low molecular weight substance has a higher fatty acid having 16 or more carbon atoms, preferably 16 to 30, more preferably 16 to 24, and the following compound (a),
At least one of (b) and (c) is used in a weight ratio of 95: 5 to 20:80.

(A) General formula R ₁ —X—R ₂ [wherein R ₁ and R ₂ are substituted or unsubstituted alkyl groups having 10 or more carbon atoms, preferably 10 to 30, and more preferably 10 to 24, or aralkyl groups; Or −R ₃ COOR ₄ or R ₅ OCOR ₆ (
R ₃ and R ₅ have 1 or more carbon atoms, preferably 1 to 30, more preferably 1 to 24 alkylene groups, and R ₄ and R ₆ have 10 or more carbon atoms, preferably 10 to 30 and more preferably 10 to 24. A substituted or unsubstituted alkyl group or aralkyl group), and X
Represents an -O-, -NH-, -S- or -SS group. ] The compound shown by these.

(B) General formula R ₁₁ —COOR ₁₂ [wherein R ₁₁ is an alkyl group having 10 or more carbon atoms, preferably 10 to 30, more preferably 10 to 24, and R ₁₂ is 1 or more carbon atoms, preferably 1 to 30, More preferably, it represents 1 to 24 alkyl groups. ] The compound shown by these.

(C) General formula C (CH ₂ OR ₂₀ ) ₄ [wherein R ₂₀ is a hydrogen atom or -COR ₂₁ (R ₂₁ is an alkyl group having 10 or more carbon atoms, preferably 10 to 30, more preferably 10 to 24 carbon atoms)] As shown, it does not become hydrogen at the same time. ] The compound shown by these.

The recording (and erasing) principle of the recording material of the present invention utilizes the change in transparency depending on the temperature of the heat-sensitive layer (or sheet), which will be described with reference to the drawings. In FIG. 1, the resin base material and the heat-sensitive layer containing an organic low molecular weight substance as a main component in the resin base material are in a cloudy and opaque state at room temperature of T ₀ or lower, for example.
When this is heated to a temperature between T _{1 and} T ₂ , it becomes transparent, and even if it is returned to room temperature below T ₀ in this state, it remains transparent. Further
Heating to temperatures above T ₃ results in a semi-transparent state intermediate between maximum transparency and maximum opacity. Next, when this temperature is lowered, the temperature on the bottom side of the trapezoidal hysteresis curve in FIG.
When it moves from T ₃ to T ₁ and returns to room temperature below T ₀ ℃, it returns to the initial cloudy opaque state. In addition, when this opaque state is heated to a temperature between T _{0 and} T ₁ and then cooled to room temperature, that is, a temperature of T ₀ or lower, a state between transparent and opaque can be obtained. In addition, the above-mentioned transparent material that has become transparent at normal temperature is heated again to a temperature of T ₃ or higher, and when it is returned to normal temperature, it becomes cloudy and opaque again. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be obtained.

Therefore, the whole heat-sensitive layer is heated to a temperature between T _{1 and} T ₂ with a heat roll or the like, cooled to a room temperature of T ₀ or lower to be transparent, and then heated to a temperature of T ₃ or higher in an image with a thermal head or the like. By making the portion opaque, a white image is formed on this layer. on the other hand,
After heating the entire partially opaque heat-sensitive layer to a temperature of T ₃ or higher, the temperature is returned to room temperature of T ₀ or lower to make the whole cloudy and opaque, and then an image is formed between T _{1 and} T ₂ by a thermal head etc. A transparent image is formed with a white background as a background by heating the portion to make it transparent. The recording and erasing operations on the heat sensitive layer as described above can be repeated 10 ⁴ times or more.

Furthermore, it has 16 carbon atoms as an organic low-molecular substance used in the heat-sensitive layer
When the above higher fatty acid and at least one of the compounds (a), (b) and (c) are mixed and used in a specific ratio, the mixture causes a eutectic phenomenon during heating, resulting in a change in the mixing ratio. As a result, the transparentization temperature range T _{1 to} T ₂ of the heat-sensitive layer changes and expands, making it easier to control the temperature when making the recording material transparent, as described above, and the ratio of organic low-molecular substances to the resin matrix. It was found that a sufficient degree of transparency can be obtained and the contrast can be improved even when the ratio is increased.

The heat-sensitive recording material of the present invention is generally coated (or impregnated) with a heat-sensitive layer forming liquid containing a resin base material and the above-mentioned specific organic low-molecular substance on a support such as paper, plastic film, glass plate, metal plate and the like. It is prepared by drying, or by kneading the above components while heating and coating this on a support, or by forming into a film or sheet.
The heat-sensitive layer forming liquid used here usually dissolves both the resin base material and the organic low-molecular-weight substance in a solvent, or the organic low-molecular-weight substance (insoluble in the base-material solvent) is dissolved in the resin base-material solution. ) Is pulverized or dispersed by various methods. Examples of the solvent include tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. The organic low-molecular substance is precipitated as fine particles and exists in a dispersed state in the heat-sensitive layer obtained not only when the dispersion is used but also when the solution is used.

The resin base material used for the heat-sensitive layer is a material that forms a layer in which an organic low-molecular substance is uniformly dispersed and held, and has an effect on the transparency at maximum transparency. For this reason, the base material is preferably a resin having good transparency, mechanical stability, and good film forming properties. Examples of such resin include 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. Vinyl chloride-based copolymers such as; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-copolymers such as vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides; polyacrylates or polymethacrylates or acrylates Methacrylate copolymers, silicone resins, etc. may be mentioned. These may be used alone or in admixture of two or more.

On the other hand, as the organic low molecular weight substance, a mixture of a higher fatty acid having 16 or more carbon atoms and at least one of the compounds (a), (b) and (c) is used. Specific examples of such higher fatty acids 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, nonacosanoic acid,
Melisic acid, 2-hexadecenoic acid, trans-3-hexadecenoic acid, 2-heptadecenoic acid, trans-2-octadecenoic acid, cis-2-octadecanoic acid, trans-4
-Octadecenoic acid, cis-6-octadecenoic acid, elaidic acid, bassenic acid, trans-gondoinic acid, erucic acid, brassic acid, ceracoleic acid, trans-ceracoleic acid, trans-8, trans-10-octadecadienoic acid, lino Elaidic acid, α-eleostearic acid, β-
Eleostearic acid, pseudoeleostearic acid, 1
2,20-heneicosadienoic acid and the like can be mentioned. These may be used alone or in combination of two or more.

Specific examples of the compound _{(a), C 16 H 33 -O-C} 16 -H 33, C 16 H 33 -S-C 16 H 33, C 18 H 37 -S-C 18 H 37, C 12 H ₂₅ -S-C ₁₂ H ₂₅ , C ₁₉ H ₃₉ -S-C ₁₉ H ₃₉ , C ₁₂ H ₂₅ -S-S-C ₁₂ H ₂₅ , Etc.

Specific examples of the compound (b) include methyl nonadecanoate, ethyl nonadecanoate, methyl arachiate, ethyl arachiate, methyl heneicosanoate, ethyl heneicosanoate, methyl brassicinate, methyl tricosanoate, ethyl tricosanoate, methyl lignocerate, and lignocerine. Ethyl acid, methyl cerotate, ethyl cerotate, methyl octacosanoate, ethyl octacosanoate, methyl melicinate, ethyl melicinate, tetradecyl palmitate,
Pentadecyl palmitate, hexadecyl palmitate, octadecyl palmitate, triaconyl palmitate, methyl stearate, ethyl stearate, stearyl stearate, lauryl stearate, tetradecyl stearate, hexadecyl stearate, heptadecyl stearate, octadecyl stearate, stearic acid. Hexacosyl, triacontyl stearate, methyl behenate, ethyl behenate, stearyl behenate, behenyl behenate, docosyl behenate, tetracosyl lignocerate, myricyl melicate and the like can be mentioned.

Compound (c) is a higher fatty acid and pentaerythritol [C
(CH ₂ OH) ₄ ], which is obtained by an esterification reaction with higher fatty acids such as capric acid, undecanoic acid,
Lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid, arachidic acid, oleic acid, etc., 10 to 24 carbon atoms
Among these, those having 16 to 18 carbon atoms are particularly preferable. A typical example is pentaerythritol monostearate [C (CH ₂ OH) ₃ (CH ₂ OOCC
₁₇ H ₃₅ )], pentaerythritol systemate [C (CH ₂ OH) ₂ (CH ₂ OOCC ₁₇ H ₃₅ ) ₂ , pentaerythritol tristearate [C (CH ₂ OH) (CH ₂ OOCC ₁₇ H
₃₅ ) ₃ ], pentaerythritol tetrastearate [C (CH ₂ OOC ₁₇ H ₃₅ ) ₄ ], pentaerythritol monolaurate, pentaerythritol dilaurate,
Pentaerythritol trilaurate, pentaerythritol tetralaurate, pentaerythritol
Monopalmilate, pentaerythritol dipalmilate, pentaerythritol tripalmylate, pentaerythritol tetrapalmylate, pentaerythritol monobehenate, pentaerythritol dihebenate, pentaerythritol tribehenate,
Examples thereof include pentaerythril and tetrabehenate.

The mixing ratio of the higher fatty acid having 16 or more carbon atoms used as the organic low molecular weight substance and at least one of the compounds (a), (b) and (c) is in the range of 95: 5 to 20:80 (weight). Is.
If the temperature is out of this range, the temperature range of transparency is not widened.

The weight ratio of the organic low molecular weight substance to the resin base material in the heat sensitive layer is preferably from 1: 0.5 to 1:16, and more preferably from 1: 0.5 to 1: 3.
When the ratio of the base material is less than this, it becomes difficult to form a film in which the organic low-molecular weight material is retained in the base material, while when it exceeds the ratio, the amount of the organic low-molecular weight material is small, and the opacity is reduced. It will be difficult.

Hereinafter, the present invention will be described in more detail with reference to Examples. All parts are parts by weight.

Example 1 behenate 95 parts _{S (CH 2 CH 2 COOC 18} H 37) 2 5 parts of vinyl-vinyl copolymer 200 parts of acetic acid chloride (UCC Co. VYHH) consisting of tetrahydrofuran 1000 parts solution 75μm thickness on a polyester film A reversible thermosensitive recording material was prepared by coating with a wire bar and drying at 150 ° C. to provide a 15 μm thick thermosensitive layer.

Example 2 Behenic acid 95 parts to 80 parts and S (CH ₂ CH ₂ COOC ₁₈ H ₃₇ ) ₂
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 5 parts was changed to 20 parts.

Example 3 Behenic acid 95 parts to 30 parts and S (CH ₂ CH ₂ COOC ₁₈ H ₃₇ ) ₂
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 5 parts was changed to 70 parts.

Comparative Example 1 95 parts of behenic acid was 98 parts, and S (CH ₂ CH ₂ COOC ₁₈ H ₃₇ ) ₂
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 5 parts was changed to 2 parts.

Comparative Example 2 95 parts of behenic acid was made 10 parts and S (CH ₂ CH ₂ COOC ₁₈ H ₃₇ ) ₂
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 5 parts was changed to 90 parts.

Example 4 A reversible thermosensitive recording material was prepared in the same manner as in Example 2 except that stearyl stearate was used instead of S (CH ₂ CH ₂ COOC ₁₈ H ₃₇ ) ₂ .

Example 5 A reversible thermosensitive recording material was prepared in the same manner as in Example 2 except that pentaerythritol monostearate was used instead of S (CH ₂ CH ₂ COOC ₁₈ H ₃₇ ) ₂ .

Comparative Example 3 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 5 parts of S (CH ₂ CH ₂ COOC ₁₈ H ₃₇ ) ₂ was used and 95 parts of behenic acid was 100 parts.

Except for Comparative Example 4 95 parts of behenic acid, and created the _{S (CH 2 CH 2 COOC 18} H 37) a reversible thermosensitive recording material ₂ except that the 5 parts of the 100 parts in the same manner as in Example 1.

The heat-sensitive recording materials obtained as described above all had an opaque white color.

Example 6 A reversible thermosensitive recording material was prepared in the same manner as in Example 2 except that the vinyl chloride-vinyl acetate copolymer was 100 parts.

Comparative Example 5 A reversible thermosensitive recording material was prepared in the same manner as in Comparative Example 3 except that the vinyl chloride-vinyl acetate copolymer was 100 parts.

Next, each recording material was heated from 50 ° C to 2 ° C in increments of 80 ° C, allowed to cool to room temperature, placed on black drawing paper, and the reflection density was measured with a Macbeth densitometer RD514. At this time, the temperature when the reflection density exceeded 1.0 was defined as the clearing temperature, and the range (width) was shown. The minimum value of this temperature was defined as the density of the opaque part (white part), while the maximum value was defined as the density of the transparent part. The results are shown in the table below.

Effect As described above, the reversible thermosensitive recording material of the present invention contains, as an organic low molecular weight substance in the thermosensitive layer, a higher fatty acid having 16 or more carbon atoms and at least the compounds (a), (b) and (c) described above. Since the mixture with one kind was used in a specific ratio, the contrast can be improved, and as a result of widening the transparentization temperature range, temperature control can be performed when the entire recording material is made transparent or when a colorless transparent image is formed on a white background. It has the advantage of being easy.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of image formation and erasing in the heat-sensitive layer of the recording material of the present invention.

Claims (1)

[Claims] 1. A reversible thermosensitive layer comprising a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component and having a heat-sensitive layer whose transparency reversibly changes depending on temperature. In the recording material, the organic low molecular weight substance has 16 carbon atoms.
A reversible thermosensitive recording material comprising the above higher fatty acid and at least one of the following compounds (a), (b) and (c) in a weight ratio of 95: 5 to 20:80. (A) General formula R ₁ -X-R ₂ [wherein R ₁ and R ₂ are a substituted or unsubstituted alkyl group or aralkyl group having 10 or more carbon atoms; or -R ₃ COOR ₄ or -R ₅ OCOR ₆
(Here, R ₃ and R ₅ are alkylene groups having 1 or more carbon atoms, R ₄ and R ₆
Represents a substituted or unsubstituted alkyl group having 10 or more carbon atoms or an aralkyl group), and X represents -O-, -NH-, -S-.
Alternatively, it represents a -S-S- group. ] The compound shown by these. (B) General formula R ₁₁ —COOR ₁₂ [wherein R ₁₁ is an alkyl group having 10 or more carbon atoms, and R ₁₂ is 1 carbon atom]
The above alkyl groups are represented. ] The compound shown by these. (C) General formula C (CH ₂ OR ₂₀ ) ₄ [wherein R ₂₀ represents a hydrogen atom or —COR ₂₁ (R ₂₁ is an alkyl group having 10 or more carbon atoms), but it does not become hydrogen at the same time. ] The compound shown by these.