JPH0822622B2 - Thermal recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-sensitive recording material for recording and erasing by utilizing reversible change in transparency of a heat-sensitive layer with temperature.

2. Description of the Related Art As a heat-sensitive recording material capable of reversible recording and erasing, a heat-sensitive recording material in which a low-molecular organic material such as a higher alcohol or a higher fatty acid is dispersed in a resin such as polyester or polyamide on a support is provided, for example. Kaikai 54-119377, 55-
It is known in 154198 and the like. Recording with this type of recording material, that is, image formation and erasing, utilizes the change in transparency depending on the temperature of the heat-sensitive layer. However, in conventional heat-sensitive recording materials, if the amount of organic low molecular weight substances in the heat-sensitive layer is increased in order to increase the opacity that becomes an image or background, this substance precipitates on the surface and the transparency of the heat-sensitive layer itself decreases. There was a drawback to do.

The object of the present invention is to provide a heat-sensitive recording material capable of forming a high-contrast clear image without deposition of this substance on the surface of a heat-sensitive member having this heat-sensitive body even if the amount of the organic low-molecular substance in the heat-sensitive body is increased. Is to provide.

Constitution The heat-sensitive recording material of the present invention comprises a heat-sensitive material which comprises a resin base material and an organic low-molecular substance dispersed in the resin base material as main components, and whose transparency reversibly changes depending on temperature. A resin layer is provided on one surface or both surfaces of the heat-sensitive member.

Here, the heat-sensitive member is formed by forming the heat-sensitive body as a heat-sensitive layer on a support, or by forming the heat-sensitive body in a film shape or a sheet shape without using a support.

The inventors of the present invention have conducted various studies in order to improve the above-mentioned drawbacks of the conventional thermosensitive recording materials, and as a result, as a result, a resin was further formed on this thermosensitive layer in a thermosensitive member formed by forming a thermosensitive body as a thermosensitive layer on a support. By providing a layer, or by providing a resin layer on both sides of a heat-sensitive member formed by forming the heat-sensitive material in a film shape or a sheet shape, even if the amount of the organic low molecular weight substance in the heat-sensitive material is increased, The present invention has been completed by finding out that the precipitation of the above does not occur.

FIG. 1 shows an example of the thermosensitive recording material of the present invention in which a thermosensitive layer 2 is provided on a support 1 and a resin layer 3 is provided thereon.

Next will be explained the recording principle of the present invention the recording material by the drawing, in FIG. 2, the heat-sensitive layer is in a clouded opaque state at room temperature, for example T ₀ or less. When this is heated to a temperature between T _{1 and} T ₂ , it becomes transparent, and in this state, it remains transparent even when it is returned to room temperature of T ₀ or lower. Upon further heating to T ₃ or higher,
The transparent state is between the maximum transparency and the maximum opacity. Next, when this temperature is lowered, it returns to the initial cloudy opaque state without becoming transparent again. After heating this opaque state to a temperature between T _{0 and} T ₁ , it is at room temperature, that is,
When cooled to a temperature of T ₀ or lower, it can be in a state between transparent and opaque. Also, the transparent material that has become transparent at room temperature is heated to a temperature of T ₃ or higher again, and returns to room temperature to return to a cloudy opaque state. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be obtained.

Therefore, after heating the entire heat-sensitive layer to a temperature between T _{1 and} T ₂ , it is cooled to room temperature below T ₀ to make it transparent, and then it is imagewise heated with a thermal head etc. to make that part opaque. A white image is formed on the layer. Further, if a colored layer is arranged under the heat-sensitive layer having such a white image, this image portion can recognize the color of the colored layer as a white image under the background. on the other hand,
After heating the entire partially opaque heat-sensitive layer to a temperature of T ₃ or higher, and then returning it to a room temperature of T ₀ or lower to make the whole cloudy and opaque, the temperature between T _{1 and} T ₂ is imaged by a thermal head. When heated to make the part transparent, a transparent image is formed against a white background. If a colored layer is arranged under the heat-sensitive layer having such a transparent image, this image portion can be recognized as a colored image with the white color of the heat-sensitive layer as the background. The recording and erasing operations on the thermosensitive layer as described above can be repeated at least about 10 ⁴ times.

In the present invention, a resin layer is further provided on the heat-sensitive layer, whereby no organic low molecular weight substance is deposited on the surface of the recording material, and therefore the image obtained as described above has a higher contrast.

In order to prepare the heat-sensitive recording material of the present invention, a heat-sensitive layer forming liquid containing a resin base material and an organic low molecular weight substance is generally applied on a support to form a heat-sensitive layer, and then a solution of the same or different resin as described above is applied. Coating and drying to form a resin layer, or
The resin base material and the organic low molecular weight substance are kneaded in the presence or absence of a solvent while heating, if necessary, and then formed into a film or sheet and cooled, and the resin solution is applied to both surfaces and dried. To form the resin layer. Here, the heat-sensitive layer forming liquid is a solution in which both components of the resin base material and the organic low molecular weight substance are dissolved in a solvent, or a solution in which only the resin base material is dissolved (a solvent that does not dissolve the organic low molecular weight substance is selected) It is made by pulverizing and dispersing an organic low molecular weight substance in various ways. The organic low-molecular substance is present as fine particles 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 ratio of the organic low-molecular substance used here and the resin base material is by weight.
It is 1: 0.5 to 1: 3. The thickness of the heat-sensitive layer or film or sheet thus formed is preferably about 5 to 50 μm. If it is 5 μm or less, the opacity (whiteness) is insufficient, and
When it is 50 μm or more, the transparency is insufficient and the contrast is lowered in both cases. On the other hand, the thickness of the resin overcoat layer is 0.2
About 30 μm is preferable. If it is 0.2 μm or less, it is difficult to form a uniform film, and if it is 30 μm or more, the thermal sensitivity decreases.

As the support in the heat-sensitive recording material of the present invention, paper, plastic film, matte film, glass plate,
A transparent or opaque uncolored support such as a metal plate or a colored support obtained by coloring these is used according to the application. This colored support is 1) coated (or impregnated) with a solution or dispersion containing a coloring pigment or dye and, if necessary, a binder, on the above-mentioned uncolored support, or 2) a coloring pigment or It is prepared by kneading a dye and a binder while heating and molding the mixture into a film or sheet.
Commercially available color coated papers for printing and colored films can also be used as they are. Here, all known pigments or dyes can be used.

The resin base material used for the heat-sensitive member is a material that forms a layer or film or sheet in which an organic low molecular weight substance is uniformly dispersed and held, and affects the transparency at maximum transparency. Therefore, the base material has good transparency, is mechanically stable,
A resin having a good film forming property is preferable. 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 as a mixture of two or more.

On the other hand, the organic low molecular weight substance may be appropriately selected according to the temperature T _{0 to} T ₃ shown in FIG.
C., especially about 50 to 150.degree. C. are preferred. Such organic low molecular weight substances include alkanols; alkane diols; halogen alkanols or halogen alkane diols; alkylamines; alkanes; alkenes; alkynes;
Halogen alkanes; Halogen alkenes; Halogen alkynes; Cycloalkanes; Cycloalkenes; Cycloalkynes; Saturated or unsaturated mono- or dicarboxylic acids or their esters, amides, or ammonium salts; Saturated or unsaturated halogen fatty acids or their esters, amides, Or ammonium salts; allylcarboxylic acids or their esters, amides or ammonium salts; halogen allylcarboxylic acids or their esters, amides or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amines or ammonium salts; thioalcohols And the like. These may be used alone or in admixture of two or more. The carbon number of these compounds is preferably 10 to 60, preferably 10 to 38, and particularly preferably 10 to 30. The alcohol group moiety in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, the organic low molecular weight substance is at least one of oxygen, nitrogen, sulfur and halogen in the molecule, such as --OH,
-COOH, -CONH, -COOR, -NH - , - NH 2, -S -, - S-
A compound containing S-, -O-, halogen or the like is preferable.

More specifically, these compounds include lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid,
Stearin powder, behenic acid, nonadecanoic acid, arachidic acid,
Higher fatty acids such as oleic acid; esters of higher fatty acids such as methyl stearate, tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate and docosyl behenate; 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 ₃₃ , C ₁₂ H _26- S-S-C ₁₂ H ₂₅ Etc., such as ether or thioether.

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

The weight ratio of the organic low molecular weight substance to the resin base material in the heat sensitive member is about 1: 0.5 to 1: 3. When the ratio of the resin base material is higher than this, it becomes difficult to form a film in which the organic low molecular weight substance is retained in the resin base material. Will be difficult.

As the resin used in the resin overcoat layer, in addition to the resin for the resin base material described above, thermoplastic resins such as polyethylene, polypropylene, polystyrene, ABS resin and PVA, unsaturated polyester, epoxy resin, phenol resin, etc. A thermosetting resin may be used.

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

Example 1 A solution of 20 parts of stearic acid, 10 parts of vinyl chloride-vinyl acetate copolymer (VYHH manufactured by UCC) and 70 parts of tetrahydrofuran on a 75 μm thick polyester film was coated with a wire bar, dried at 150 ° C. and dried to 15 μm. After forming a thick heat-sensitive layer, a polyester resin (Vylon 200 manufactured by Toyobo Co., Ltd.) 20 parts Toluene 72 parts Ethyl alcohol 8 parts A solution consisting of 8 parts is applied with a wire bar and dried at 130 ° C to a resin thickness of 30 μm. A thermal recording material was prepared by forming layers.

Example 2 A thermosensitive recording material was prepared in the same manner as in Example 1 except that 20 parts of stearic acid was used and 10 parts of vinyl chloride-vinyl acetate copolymer was used.

Example 3 A thermosensitive recording material was prepared in the same manner as in Example 1 except that 20 parts of stearic acid was 7.5 parts and 10 parts of vinyl chloride-vinyl acetate copolymer was 22.5 parts.

Comparative Examples 1 to 3 Thermal recording materials of Comparative Examples 1 to 3 were prepared in the same manner as in Examples 1 to 3 except that the overcoat layer was not provided.

Comparative Example 4 After forming a heat-sensitive layer on a polyester film in the same manner as in Example 1, SiO ₂ was deposited on the heat-sensitive layer by RF sputtering,
When a protective layer having a film thickness of 2 μm was formed, precipitation of stearic acid in the heat sensitive layer was observed.

All of the heat-sensitive recording materials obtained as described above were white and opaque, but when heated to 65 ° C. and allowed to cool, they showed stable transparency.

Next, 1mJ from the thermal layer side of each recording material with a thermal head
A white image was formed upon application of heat energy. Furthermore, place this recording material on black color coated paper,
When the reflection densities of the white part and the black part (the transparent part of the heat-sensitive layer) were measured with a Macbeth densitometer RD514, the results shown in the table below were obtained.

Effect As described above, in the heat-sensitive recording material of the present invention, the resin layer is provided on the heat-sensitive member. Therefore, even if the amount of the organic low-molecular substance is increased, there is no deposition on the surface, and therefore, a clear image having a higher contrast than the conventional one can be obtained. Can be formed. Of course, since the transparency of this recording material changes reversibly with temperature, repeated recording and erasing are possible. Therefore, this recording material can be used as a causative film for an overhead projector when a colorless and transparent support is used, or as a reflective display or an electronic blackboard when a colored support or a colored sheet is used.

[Brief description of drawings]

FIG. 1 is a block diagram of the heat-sensitive recording material of the present invention, and FIG. 2 is an explanatory view of the recording principle in the heat-sensitive layer of this recording material. 1 ... Support, 2 ... Heat sensitive layer 3 ... Resin layer

Claims (1)

[Claims] 1. A resin base material comprising an organic low molecular weight substance and an organic low molecular weight substance dispersed in the resin base material at a weight ratio of 1: 0.5 to 1: 3 as a main component. A heat-sensitive recording material having a resin layer on one surface or both surfaces of a heat-sensitive member having a heat-sensitive material whose transparency reversibly changes depending on temperature.