JPH02258287A - Reversible thermal recording material - Google Patents

Abstract

PURPOSE:To prevent the accumulation of dust on a thermal head even if adhered and to form a uniform and sharp image by providing an overcoat layer having a fine uneven shape of specific surface roughness. CONSTITUTION:A solution having a resin base material and organic low molecular weight substance dissolved therein is applied to a support and dried to form a thermal layer. A solution prepared by dispersing fine particles in a resin solution is applied to said thermal layer and dried to form an overcoat layer and, continuously, unveneness having surface roughness of 0.5-3mum is formed in the overcoat layer. At this time, a method of forming uneveness on the surface of copy paper or the like is appropriately selected and used. Herein, as the resin base material, a resin having good transparency, mechanical stability and good film forming properties is used. As the organic low molecular weight substance, alkanol or alkane diol is used and, further, as the fine particles used in the overcoat layer, a colorless or transparent material such as silica, aluminum hydroxide or alumina is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a reversible thermosensitive recording material that performs recording and erasing by utilizing reversible changes in transparency of a thermosensitive member depending on temperature.

[Prior art]

As a heat-sensitive recording material capable of reversible recording and erasing, there is a heat-sensitive layer on a support in which organic low-molecular substances such as higher alcohols and higher fatty acids are dispersed in a resin such as polyester. -119377, 55-1
It is known as No. 54198. Recording with this type of recording material, that is, image formation and erasing, utilizes the change in transparency of the heat-sensitive layer depending on the temperature.

However, with conventional reversible thermosensitive recording materials, when printing and heating the surface with a thermal head etc. to form an image, sufficient adhesion cannot be achieved due to large friction with the heating means, resulting in a decrease in thermal sensitivity. However, it has been difficult to form clear images due to the unevenness of the surface.

Therefore, the present inventors have developed a reversible thermosensitive recording material in which an overcoat layer is provided to reduce surface friction in Japanese Patent Application Laid-Open No. 63-221087 and Japanese Patent Application No. 62-152550, and a hard overcoat layer is provided in Japanese Patent Application No. 62-310969. We have proposed reversible thermosensitive recording materials with a coating layer that prevents unevenness on the surface, but when these materials print many sheets with a thermal head, dust and dirt adhere to the head.
There was a drawback that printing could not be performed on that part.

He also proposed a reversible heat-sensitive recording material in which fine white powder was mixed in the heat-sensitive layer (Japanese Patent Laid-Open No. 63-28068
4) This was good not only on the surface but also in the heat-sensitive layer, and due to the presence of fine powder, the transparency was slightly low.

〔composition〕

The reversible thermosensitive recording material of the present invention comprises (a) a support, (b)
) A reversible heat-sensitive recording material comprising a resin base material and a heat-sensitive layer whose transparency changes reversibly depending on temperature, the main components of which are a resin base material and an organic low-molecular substance dispersed in the resin base material, It is characterized by having an overcoat layer as the uppermost layer, the surface of which has fine irregularities with a surface roughness of 0.5 to 3 μm.

The recording principle of the recording material of the present invention utilizes the change in transparency of the heat-sensitive layer depending on the temperature, that is, the change from transparent to cloudy and opaque, or vice versa.

The reason why the transparent part looks transparent is because the organic low-molecular substance particles dispersed in the resin base material in this part are composed of thick crystals, so light that enters from one side is not scattered. This is thought to be because the light is transmitted to the other side. Also, the reason why the opaque area appears white is that it is composed of polycrystals, which are aggregates of microcrystals of organic low-molecular substance particles dispersed in the resin base material, and the crystal axes of the individual crystals are oriented in various directions. This is thought to be because light incident from one side is refracted and scattered many times at the interface of each crystal.

The above-mentioned changes in transparency due to temperature will be explained with reference to the drawings. In FIG. 1, the heat-sensitive layer is in a cloudy, opaque state at room temperature, for example, T0 or higher.

When this is heated to a temperature between 11 and 11, it becomes transparent, and even if it is returned to room temperature below T in this state, it remains transparent.

This is considered to be because the organic low-molecular substance passes through a semi-molten state and crystals grow from polycrystals to single crystals from a temperature between 11 and 11 to a temperature T and below. If it is further heated to a temperature higher than T1, it becomes a semi-transparent state between the maximum transparency and the maximum opacity. When the temperature is then lowered, it returns to the initial cloudy and opaque state without becoming transparent again. . This is considered to be because the organic low molecular weight substance is melted at a temperature of 13 or higher and then cooled to precipitate polycrystals. Note that when this opaque state is heated to a temperature between 11 and 11 and then cooled to room temperature, that is, a temperature below T, it can assume an intermediate state between transparent and opaque. Moreover, if the above-mentioned material that becomes transparent at room temperature is heated again to a temperature of 13 or more and returned to room temperature, it will return to a cloudy, opaque state. That is, it can take both opaque and transparent forms, as well as intermediate states, at room temperature.

Therefore, by selectively heating the recording material by selectively applying heat to the surface of the heat-sensitive recording material having the heat-sensitive layer as described above, it is possible to form a cloudy image in the transparent part or a transparent image in the cloudy part. This image formation can be repeated many times. If a colored sheet is placed on the back side of a heat-sensitive recording material having such an image, an image of the color of the colored sheet can be formed on a white background, or an image of a white background can be formed on a background of the color of the colored sheet. Furthermore, when this heat-sensitive recording material is projected with a projection device such as an overhead projector, the cloudy areas appear on the screen as dark areas, and the transparent areas appear as bright areas due to the transmission of light.

However, as mentioned above, conventional reversible thermosensitive recording materials have a flat surface, so if dirt or dust adheres to the film, when printing with a thermal head, the dirt or dust will get stuck between the film and the head, resulting in an image. It causes unevenness. Therefore, the present inventors created a fine uneven surface with a surface roughness of 0.3 to 3 μm, so that even if dirt or dust adheres to it, when the film moves, the dirt or dust will move at the same time, creating a uniform surface. We discovered that it is possible to compose images.

Note that 1 surface roughness as used in the present invention means 10-point average roughness (Rz) defined in JISBO601.

If the surface roughness is less than 0.3 μl, dust will remain between the film and the head, resulting in unevenness in one image, and if it is more than 3 μl, it will be difficult for the heat from the thermal head to be transferred to the heat-sensitive layer, resulting in a decrease in thermal sensitivity.

In order to produce the reversible heat-sensitive recording material of the present invention, the following method is generally employed in which a heat-sensitive layer is formed on a support and then an overcoat layer is formed.

(1) A solution in which a resin base material and an organic low-molecular substance are dissolved, or a solution of a resin base material (use a solvent that does not dissolve the organic low-molecular substance) and an organic low-molecular substance dispersed in the form of fine particles. The dispersion is applied onto a support and dried to form a heat-sensitive layer.

(2) A liquid prepared by dispersing fine particles in a solution containing a resin is applied thereon and dried to form an overcoat layer.

(3) Other methods for forming irregularities on the overcoat layer can be appropriately selected from methods used for forming irregularities on the surface of copy paper, etc.

The thickness of the heat-sensitive layer thus formed is suitably about 1 to 30 microns. The thickness of the overcoat layer is preferably 5 μm or less.

Next, materials used for manufacturing the above heat-sensitive recording material will be explained. First, the heat-sensitive layer is as follows.

As the solvent for forming the heat-sensitive layer, various solvents can be used depending on the type of organic low-molecular substance and resin base material. For example, tetrahydrofuran, methyl ethyl ketone,
Methyl isobutyl ketone, chloroform, carbon tetrachloride,
Examples include organic solvents such as ethanol, toluene, and benzene.

In addition, in the heat-sensitive layer formed in one or more ways,
The organic low-molecular substance exists in a dispersed state as fine particles in the resin matrix.

The resin base material used for the heat-sensitive layer is a material that forms a film or sheet in which a low-molecular-weight organic substance is uniformly dispersed and holds, and also influences the transparency at maximum transparency. For this reason, the resin base material is preferably a resin with good transparency, mechanical stability, and good film-forming properties. Examples of such resins include polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, and vinyl chloride-vinyl acetate copolymer.
Vinyl acetate - vinyl alcohol copolymer, vinyl chloride -
Vinylidene chloride copolymers such as vinyl acetate-maleic acid copolymers, vinylidene chloride-vinyl chloride copolymers such as vinyl chloride acrylate copolymers, vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides;
Examples include polyacrylate, polymethacrylate, acrylate-methacrylate copolymer, and silicone resin. These may be used alone or in combination of two or more.

On the other hand, the organic low-molecular substance may be appropriately selected depending on the temperature range T1 to T shown in FIG.
Examples of such organic low-molecular substances, which are preferably about 00°C, especially about 50 to 150°C, include alkanols; alkanediols; halogen alkanols or halogen alkanediols; 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; Allyl carboxylic acids or their esters, amides or ammonium salts; Halogen allyl carboxylic acids or their esters, amides or ammonium salts; Thioalcohols;
Examples include thiocarboxylic acids or their esters, amines, or ammonium salts; carboxylic acid esters of thioalcohols, and the like. These may be used alone or in a mixture of two or more. The carbon number of these compounds is lO~60,
Preferably 10 to 38, particularly preferably 1O to 30, the alcohol group moiety in the ester may be saturated or unsaturated, and may be halogen-substituted.
In any case, organic low-molecular substances contain oxygen, nitrogen,
At least one of sulfur and halogen, such as -OH, -
C0OH, -CONH, -poOR, -NH--NH,
, -8--5-8--0+, Ha.

Preferably, it is a compound containing gen, etc.

More specifically, these compounds include lauric acid, dodecanoic acid, myristic acid, and pentadecanoic acid.

Higher fatty acids such as palmitic acid, stearic acid, behenic acid, nonadecanoic acid, arachic acid, and oleic acid; Ester; Cl5H33-0-C1&1133 I C1GN
3M-5-C1&H3MCx-Hs, -5-C-mHs
, -C-xHxs-5-C-*Hz-C,,)13. −
5-C1,I+,,, C1,H,,-5-5-C,,
H.

There are ethers and thioethers such as

The ratio of the organic low-molecular substance to the resin base material in the heat-sensitive layer is preferably about 1:0.5 to 1:16 by weight. If the ratio of the resin base material is less than this, the organic low-molecular substance is It becomes difficult to form a film retained in the base material, and on the other hand, if the amount exceeds this, it becomes difficult to make it opaque because the amount of the organic low molecular weight substance is small.

Further, in the present invention, a substance that controls the crystal growth of the organic low-molecular substance can be used in combination.

Examples of such substances include substances that are eutectic with organic low-molecular substances and can widen the temperature range in which the organic low-molecular substances are in a semi-molten state, and substances that promote crystal movement. Polyhydric alcohol higher fatty acid ester; polyhydric alcohol higher alkyl ether; polyhydric alcohol higher fatty acid ester, higher alcohol, higher alkylphenol, higher fatty acid higher alkyl amine, higher fatty acid amide,
Lower olefin oxide adducts of fats and oils or polypropylene glycol; Acetylene glycol: Na, Ca, Ba or Mg salts of higher alkylbenzene sulfonic acids; Higher fatty acids, aromatic carboxylic acids, higher aliphatic sulfonic acids,
Ca, Ba or Mg salts of aromatic sulfonic acid sulfuric acid monoesters or phosphoric acid mono- or di-esters; low sulfated oils; poly long chain alkyl acrylates; acrylic oligomers; poly long chain alkyl methacrylates; long chain alkyl methacrylates Examples include latoluamine-containing monomer copolymers; styrene-maleic anhydride copolymers; olefin-maleic anhydride copolymers; olefin-maleic anhydride copolymers. Also used as film plasticizers are tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, Phthalic acid di-n-
Octyl, di-2-ethylhexyl phthalate, diisononyl phthalate, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate, di-n-hexyl adipate, di-2 adipate
-Ethylhexyl, di-2-ethylhexyl azelate, dibutyl sepacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butylade, methyl acetyl ricinolate, butyl acetyl ricinoleate, butyl phthalyl butyl glyco ester, acetyl tributyl citrate, and the like.

Also, one of the organic low-molecular substances listed above can be used as an organic low-molecular substance, and another type of organic low-molecular substance can be used as a substance that controls crystal growth. For example, stearic acid can be used as an organic low-molecular substance. and stearyl alcohol is used as a substance to control crystal growth.

The weight ratio of the organic low-molecular substance and the substance that controls the crystal growth of the organic low-molecular substance is preferably about 1:0.01 to 1:0.8, and the substance that controls the crystal growth of the organic low-molecular substance is preferably less than this range. At this point, it is impossible to widen the temperature range or energy range at which it becomes transparent, and beyond this, the opacity decreases.

Next, the overcoat layer will be explained.

As mentioned above, a solvent or the like may be used to form the overcoat layer, and examples of the solvent in this case include the same solvents as those for forming the heat-sensitive layer.

Examples of resins used in the overcoat layer include, in addition to the resins used in the heat-sensitive layer described above, silicone rubber,
silicone resin (see JP-A No. 63-221087),
Polysiloxane graft polymer (patent application 1986-152)
No. 550), ultraviolet curing resin (patent application No. 62-31096)
No. 9) etc. can be used.

The fine particles used in the overcoat layer are preferably colorless or transparent materials such as silica, aluminum hydroxide, alumina, aluminum silicate, magnesium hydroxide, magnesium carbonate, magnesium oxide, titanium oxide, zinc oxide, and barium sulfate. , urea-formalin resin, styrene resin, and other inorganic and organic fine powders.

The appropriate amount used is 0.5 to 30 parts by weight per 1 part by weight of the resin.

Further, a reversible thermosensitive recording material to which the overcoat layer of the present invention can be applied is disclosed in Japanese Patent Application Laid-Open No. 63-3179 filed by the applicant.
0.63-39376.63-39377.63-39
378°63-41186. ft3-84978,'
63-104879.63-104879.63-10
7584.63-130380.63-132089.
63-145080゜63-145081.63-14
5091.63-178079.63-179789゜63-179795.63-221087.63-25
Known reversible thermosensitive recording materials such as No. 6481.63-280684 and Japanese patent application No. 62-152550.62-163.
962.62-171627.62-171628.6
2-171629, 62-182917.62-215
373.62-237867゜62-261321.6
2-264718.62-271715.62-283
856゜62-310969.63-14754,63
-28338,63-109601゜63-17514
3.63-234369.63-252767.63-
268203゜63-271735, -63-2720
All prior art related to the applicant's application, such as No. 16.63-272017, is covered.

Among these prior art, for example, Japanese Patent Application No. 63-1096
Although there are cases where the overcoat layer has features such as No. 01, the present invention also includes cases where the overcoat layer itself has irregularities.

〔Example〕

The present invention will be explained below by way of examples. Note that both "part" and "1%" are based on weight.

Example 1 Behenic acid 8 parts stearyl stearate 2 parts di(2-ethylhexyl) phthalate 2 parts tetrahydrofuran on a transparent polyester film
A solution consisting of 150 parts was applied with a wire bar and dried by heating to form a heat-sensitive layer with a thickness of 15 μm.

A solution consisting of 10 parts of polyamide resin (C-A8000 manufactured by Toshisha Co., Ltd.) and 90 parts of methyl alcohol was applied thereon using a wire bar, and dried by heating to form an intermediate layer having a thickness of 1 μm.

Furthermore, on top of that, 10 parts of silica particles (average particle size 0.5μ) are added.
A uniformly dispersed solution of 50 parts of the composition was applied with a wire bar, dried by heating, and then irradiated with ultraviolet light for 5 seconds using an 80 W/(Ilm) ultraviolet lamp to form a 5 μ-thick overcoat layer. The surface roughness was 0°5μ.Then, by reheating to 65°C, a transparent reversible thermosensitive recording material was prepared.

Example 2 A transparent reversible heat-sensitive recording material was prepared in the same manner as in Example 1, except that silica fine particles having an average particle diameter of 1 μm were used.

Example 3 A transparent reversible thermosensitive recording material was prepared in the same manner as in Example 1, except that fine silica particles having an average particle size of 2 to 3 μm were used and the surface roughness was set to 3 μm.

Comparative Example 1 A transparent reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that fine silica particles were not used.

The surface roughness at that time was 0.1 μm or less.

Comparative Example 2 A transparent reversible thermosensitive recording material was prepared in the same manner as in Example 1, except that fine silica particles having an average particle diameter of 3 to 4 μm were used and the surface roughness was set to 5 μm.

Next, dust was collected and placed on the reversible thermosensitive recording material prepared as described above, and then an image was formed using a thermal head.

Then, black drawing paper was placed on the back side of the recording material, and the density of the resulting image was measured using a Macbeth densitometer RD514. Also 1
The uniformity of the image was determined visually. The results are shown in the table.

(Margin below) FIG.

Claims (1)

[Claims] 1. A thermosensitive layer whose main components are (a) a support, (b) a resin base material, and an organic low-molecular substance dispersed in the resin base material, and whose transparency changes reversibly depending on temperature. 1. A reversible thermosensitive recording material comprising: a reversible thermosensitive recording material comprising, as the uppermost layer, an overcoat layer having a surface having a fine unevenness with a surface roughness of 0.5 to 3 μm.