JP3057210B2 - Reversible thermosensitive recording material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reversible thermosensitive recording material for recording and erasing by utilizing a reversible change in transparency of a thermosensitive layer depending on the temperature.

[Related Art] In recent years, a reversible thermosensitive recording material that can form a temporary image and erase the image when it becomes unnecessary has been attracting attention. A typical example is a resin matrix such as a vinyl chloride-vinyl acetate copolymer having a low glass transition temperature (Tg) of 50 to 60 ° C. to less than 80 ° C., such as a higher fatty acid. A reversible thermosensitive recording material in which various organic low-molecular substances are dispersed (Japanese Patent Laid-Open No. 54-11 / 1979).
9377, JP-A-55-154198 and the like).

However, since the temperature range for making the opaque portion transparent is as narrow as 2 to 4 ° C., the entire opaque recording material is made transparent, or a transparent image is formed on the entire opaque recording material. Temperature control at the time was difficult. In order to solve this drawback, JP-A-63-178079 proposes a reversible thermosensitive recording material containing a high boiling point solvent having a boiling point of 200 ° C. or higher.

[Problems to be solved by the invention]

The reversible thermosensitive recording material of JP-A-63-178079 has an effect of expanding the range of the temperature at which the recording material becomes transparent.However, after the recording material is heated and made transparent, the recording material is heated with a minute energy by a thermal head or the like. However, there is a problem that the turbidity decreases when printing is performed after the heating and clearing time has elapsed.

The present invention has been made in view of the above points, and has a reversibility that a clearing temperature range can be widened and a clear image can be formed even when printing with a thermal head or the like after a long time has elapsed after heating and clearing. It is intended to provide a thermal recording material.

[Means for solving the problem]

According to the present invention, in a reversible thermosensitive recording material having a heat-sensitive layer in which transparency changes reversibly depending on temperature, the heat-sensitive layer comprises a resin base material and an organic resin dispersed in the resin base material. Provided is a reversible thermosensitive recording material comprising a molecular substance as a main component and further containing an unsaturated fatty acid metal salt, and particularly a reversible thermosensitive recording material in which the unsaturated fatty acid metal salt is zinc ricinoleate. Is done.

The conventional reversible thermosensitive recording material can widen the range of the temperature at which the thermosensitive recording layer becomes transparent by mixing a high boiling point solvent into the thermosensitive recording layer and can maintain the clearing temperature range over time.

In addition, after heating this heat-sensitive recording material to make it transparent, it is possible to make it cloudy even if it is heated with a minute energy of a thermal head or the like, but several days after heating and making it transparent as described above. Similarly, even when heated by a thermal head or the like, there is a disadvantage that the turbidity is reduced as compared with immediately after heating and transparency. The present inventors have found that by further adding an unsaturated fatty acid metal salt to the heat-sensitive recording layer, it is possible to prevent a decrease in turbidity during image formation.

The mechanism is that the unsaturated fatty acid metal salt is poorly compatible with the resin base material and the organic low-molecular substance, so that it becomes finely dispersed in them and is heated from the transparent state by the thermal head, and the organic low-molecular substance is melted. Thereafter, when the crystals are precipitated by cooling, it is considered that the unsaturated fatty acid metal salt becomes a nucleus of the crystals, and fine crystals are likely to be precipitated, thereby serving to prevent a decrease in turbidity.

The amount of the metal salt of the unsaturated fatty acid is 1
0.01 to 1.0 part by weight, preferably 0.02 to 0.2 part by weight,
Part by weight is particularly preferred. If the amount is less than 0.01 part by weight, it is not possible to prevent the turbidity from decreasing over time. Also,
If it exceeds 1.0 part by weight, the transmittance in the transparent state decreases.

Specific examples of the unsaturated fatty acid of the unsaturated fatty acid metal salt used in the present invention include oleic acid, linoleic acid, linolenic acid, erucic acid, ricinoleic acid, amolenic acid, isoambretic acid, 6-octadecenoic acid, 12-Nanodecinic acid, β-oxyhydrosorbic acid, ricinoleic acid, oxynarvonic acid, 2-heptadecinic acid, 6-undecinic acid and the like, and as the metal, Ca, Zn,
Examples include Mg, Al, Pb, Co, Ni, Fe, Cu, Mn, Ti, Sn, Li, Cd, and Ba. Among unsaturated fatty acid metal salts, metal ricinoleate is
Good solubility in organic solvents and little decrease in transmittance in the transparent state. Among them, zinc ricinoleate has better solubility in an organic solvent, and there is almost no decrease in transmittance in a transparent state.

The reversible thermosensitive recording material used in the present invention utilizes a change in transparency (transparent state, cloudy opaque state) depending on the temperature of the heat-sensitive layer of the recording material as described above, and the difference between the transparent state and the cloudy opaque state is as follows. It is guessed as follows.

That is, (i) in the case of transparency, the particles of the organic low-molecular substance dispersed in the resin base material are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered and is opposite. (Ii) in the case of cloudiness, the particles of the organic low-molecular substance are composed of polycrystals in which fine crystals of the organic low-molecular substance are aggregated,
This is due to the fact that the light incident from one side is refracted many times at the interface of the crystals of the organic low-molecular-weight material particles, and appears white because it is scattered because the crystal axes of the individual crystals are oriented in various directions. .

The change in transparency of the recording material of the present invention due to heat will be described with reference to the drawings.

In Figure 1, the heat-sensitive layer of the resin matrix, mainly composed of an organic low-molecular material dispersed in the resin base material is in a white turbid opaque state, for example, T ₀ or less at room temperature. This is the temperature
T ₁ through T becomes transparent when heated to _2, and remains also clear again returned to the normal temperature of T ₀ or less in this state. This is the temperature T _{1 to} T ₂
Low-molecular organic material before reaching the T ₀ or less from the presumably because the crystal to a single crystal from a polycrystalline via a semi-molten state grows. Upon further heating to T ₃ or more temperature becomes translucent state intermediate between the maximum transparency and the maximum opacity. Next, when the temperature is lowered, the state returns to the original cloudy and opaque state without taking the transparent state again. This after low-molecular organic material is melted at a temperature T ₃ or more, presumably because the polycrystals precipitated by being cooled. 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 equal to or lower than T ₀ , an intermediate state between transparent and opaque can be obtained. Also, by returning to room temperature After heating to be again T ₃ or more temperature which became clear at the normal temperature, the flow returns to cloudy opaque state again. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be taken.

Therefore, the heat-sensitive layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent ground and a transparent image on a cloudy ground, and the change can be repeated many times. . If a colored sheet is arranged on the back of such a heat-sensitive layer, a color image of the colored sheet on a white background or a white image on a colored background of the colored sheet can be formed. Also, when projected by an OHP (overhead projector) or the like, the cloudy portion becomes a dark portion, the transparent portion transmits light, and becomes a bright portion on the screen.

In order to prepare the reversible thermosensitive recording material of the present invention, generally, (1) a solution in which two components of a resin base material and an organic low-molecular substance are dissolved, or a solution of a resin base material (a low-molecular organic substance is not dissolved as a solvent) A dispersion liquid in which an organic low-molecular substance is dispersed in the form of fine particles on a target surface such as a plastic sheet or a glass plate and dried, or (2) the two components in the presence or absence of a solvent. It is made by kneading while heating, if necessary, forming this into a sheet, and then forming a heat-sensitive recording sheet itself. In any case, a resin protective layer such as a silicone resin or a fluorine resin can be provided on the heat-sensitive recording layer as needed.

The solvent for preparing the heat-sensitive layer or the heat-sensitive recording material can be variously selected depending on the types of the resin base material and the organic low-molecular-weight substance. For example, tetrahydrofuran, methyl ethyl ketone,
Methyl isobutyl ketone, chloroform, carbon tetrachloride,
Examples include ethanol, toluene, and benzene. It should be noted that, of course, when a solution or a kneaded product is used, the organic low-molecular substance is precipitated as fine particles and exists in a dispersed state in the thermosensitive recording medium obtained when a dispersion or a kneaded material is used.

The resin base material used for the thermal recording medium is a material which forms a layer in which organic low-molecular substances are uniformly dispersed and held, and which affects the transparency at the time of maximum transparency.

For this reason, the base material is preferably a resin that has good transparency, is mechanically stable, and has good film-forming properties. Examples of such a resin include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-acrylate copolymer. Vinylidene chloride copolymers such as polyvinylidene chloride, polyvinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, vinyl chloride-acrylate copolymer; polyesters; polyamides A polyacrylate, a polymethacrylate, an acrylate-methacrylate copolymer, and a silicone resin. These may be used alone or as a mixture of two or more.

On the other hand, the organic low-molecular substance may be appropriately selected according to the selection of the temperatures T _{0 to} T ₃ in FIG. 1, and generally, a substance having a melting point of 30 to 200 ° C., preferably about 50 to 150 ° C. is used. You. Such organic low molecular weight substances include alkanols;
An alkane diol; a halogen alkanol or a halogen alkane diol; an alkylamine; an alkane; an alkene; an alkyne; a halogen alkane; a halogen alkene; a halogen alkyne; a cycloalkane; a cycloalkene; a cycloalkyne; a saturated or unsaturated mono- or dicarboxylic acid or an ester thereof; Amide or ammonium salt; saturated or unsaturated halogen fatty acid or ester, amide or ammonium salt thereof; allyl carboxylic acid or ester, amide or ammonium salt thereof; halogen allyl carboxylic acid or ester, amide or ammonium salt thereof; thio alcohol Thiocarboxylic acids or their esters, amines or ammonium salts; thioalcohol carboxylic acid esters and the like. These may be used alone or in combination of two or more. These compounds preferably have 10 to 30 carbon atoms. The alcohol group in the ester may be saturated, and may be halogen-substituted or not saturated.
In any case, organic low molecular weight substances contain oxygen, nitrogen,
At least one of sulfur and halogen, for example -OH, -COO
H, -CONH, -COOR, -NH, -NH 2, -S -, - S-S
It is preferably a compound containing-, -O-, halogen and the like.

More specifically, these compounds include lauric acid,
Higher fatty acids such as dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, araginic acid, oleic acid; methyl stearate, tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate , esters of higher fatty acids dodecyl behenate _{like; C 16 H 33 -O-C} 16 H 33, C 16 H 33 -S-C 16 H 33, C 16 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 , And ether or thioether. Among them, in the present invention, higher fatty acids, particularly higher fatty acids having 16 or more carbon atoms such as palmitic acid, stearic acid, behenic acid, and lignoceric acid are preferable, and higher fatty acids having 16 to 24 carbon atoms are more preferable.

The ratio between the organic low-molecular substance and the resin base material in the heat-sensitive layer is preferably about 2: 1 to 1:16, more preferably 1: 1 to 1: 3, by weight. When the ratio of the resin base material is less than this, it becomes difficult to form a film holding the organic low-molecular substance in the resin base material.On the other hand, when it exceeds this, the amount of the organic low-molecular substance is small, Opacification becomes difficult.

〔The invention's effect〕

The reversible thermosensitive recording material of the present invention is a thermosensitive layer mainly composed of a resin base material and an organic low-molecular substance dispersed in the resin base material, and further contains an unsaturated fatty acid metal salt. For this reason, even when printing is performed with a thermal head or the like after a long period of time after the heat-sensitive layer is transparentized by heating, a clear image can be formed without a decrease in white turbidity.

〔Example〕

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

Example 1 On a transparent PET film having a thickness of 100 μm, stearic acid 8 parts Eicosane diacid 2 parts Vinyl chloride-vinyl acetate copolymer 25 parts (UCC VYHH) Zinc ricinoleate 0.2 parts Diisodecyl phthalate 1.5 parts Tetrahydrofuran 150 A solution consisting of 17 parts of toluene and 17 parts was coated with a wire bar and dried,
By providing a thick thermosensitive recording layer, a white opaque reversible thermosensitive recording material was prepared.

Example 2 A white opaque reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that zinc ricinoleate was changed to zinc oleate.

Example 3 A white opaque reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 2.0 parts of zinc ricinoleate was used.

Example 4 A white opaque reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 0.1 part of zinc ricinoleate was used.

Example 5 A white opaque reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 10.0 parts of zinc ricinoleate was used.

Comparative Example 1 A white opaque reversible thermosensitive recording material was prepared in the same manner as in Example 1, except that zinc ricinoleate was omitted.

Next, each recording material obtained above was heated to 85 ° C. to make it transparent, and immediately after heating, a cloudy image was formed with CUVAX MJ550 (manufactured by Ricoh) three days after heating. The density was set on black paper and the reflection density was measured. Table 1 shows the results.

[Brief description of the drawings]

FIG. 1 is a graph showing the principle of the change in transparency of the reversible thermosensitive recording material of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Makoto Kawaguchi 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (72) Inventor Kunichika Moroboshi 1-3-6 Nakamagome, Ota-ku, Tokyo No. Ricoh Co., Ltd. (72) Inventor Akira Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-63-41186 (JP, A) JP-A-62 JP-A-285950 (JP, A) JP-A-57-82087 (JP, A) JP-A-2-1363 (JP, A) JP-A-64-14079 (JP, A) (58) Fields investigated (Int. . ^7, DB name) B41M 5/36

Claims (2)

(57) [Claims] 1. A reversible thermosensitive recording material having a thermosensitive layer whose transparency reversibly changes depending on temperature, wherein said thermosensitive layer comprises a resin base material and an organic low molecular weight compound dispersed in the resin base material. A reversible thermosensitive recording material characterized by comprising a substance and a metal salt of an unsaturated fatty acid. 2. The reversible thermosensitive recording material according to claim 1, wherein said unsaturated fatty acid metal salt is zinc ricinoleate.