JP3237955B2 - Color reversible thermosensitive recording material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible color reversible thermosensitive recording material, and more particularly to a reversible color reversible thermosensitive recording material comprising a leuco dye / developer system which has remarkably improved repetition durability. The present invention relates to a color reversible thermosensitive recording material.

[0002]

2. Description of the Related Art Various types of heat-sensitive recording materials have been known in the past, and all of them will not be described. However, at present, so-called dye-coloring-type heat-sensitive recording materials have become mainstream and have become extremely popular. I have. This method is a heat-sensitive recording material in which a colorless or light-colored leuco dye and a solid organic acid (developing agent) are each made into a powder, and a layer is applied on a support using a binding agent (binder). A visible image is obtained by giving a thermal pattern and performing a color reaction at a heated site.

In such a thermosensitive recording material, once an image is formed, it is impossible to erase that portion and return to the state before image formation. I had no choice but to add. Therefore, it has not been possible to erase unnecessary image information and convert new information into an image.

[0004] In recent years, in order to cope with such a problem, several reversible thermosensitive recording materials capable of repeatedly forming and erasing images have been proposed, and are described in the literature ("Functional Materials", published by CMC Corporation, April 1993). 14), it is roughly classified into three types: polymer / low molecular composite type, polymer type (there are three types of liquid crystal polymer, polymer blend, and phase change type) and leuco dye type. The two reversibly change between a transparent state and a cloudy state, and it is impossible to select various colors such as a leuco dye type.

The present invention relates to a reversible thermosensitive recording material classified into the leuco dye type described above.
n Hardcopy '90', 147 pages (199)
(June 0, 2000), which is of the type that realizes the color development / decoloration of the leuco dye / developer system only by controlling the heat energy, and in particular, has already been proposed by the present applicant ( Japanese Patent Application No. 4-347032), a new feature in that the color development state is fixed when a thermochromic image is rapidly cooled and the color disappears when gradually cooled, which is brought about by using a novel color developer (electron accepting compound). The present invention relates to a reversible thermosensitive recording material which is capable of forming and erasing an image with good contrast and having a stable image over time in an environment of daily life, and which is superior to known reversible thermosensitive recording materials.

The reversible thermosensitive recording material of this type has the following characteristics.
Although it greatly depends on the chemical structure of the color developer in particular, the subsequent tests indicate that the number of times that the color can be repeatedly developed and erased, in particular, should not be involved in the color development reaction. It has been found that a dramatic improvement can be achieved by devising the present invention, leading to the present invention.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a reversible thermosensitive recording material of the type which realizes color development / decoloration of a leuco dye / developer system only by controlling heat energy. This is to make the number of times much larger than before.

[0008]

An object of the present invention is to provide a reversible thermosensitive recording material having a leuco dye / developer system comprising a leuco dye / color developing system on a support. The problem has been solved by forming particles having a substantially spherical or nearly spherical shape in or under the thermosensitive recording layer to form fine irregularities on the layer surface. Furthermore, a further improvement was observed by laminating an overcoat layer on the uppermost layer while maintaining the surface irregularities.

That is, a paper or a plastic film is generally used as a support for the recording material. In some cases, a coating solution for a reversible thermosensitive recording layer is directly applied thereto. It is also possible to apply an undercoat (anchor coat) once for the purpose of improving adhesiveness, heat insulation, soaking of the coating liquid, smoothness of the coating layer surface, etc., and then applying the recording layer coating liquid thereon. Often done. At this time, spherical or nearly spherical particles are present in the recording layer or below the recording layer (that is, in the undercoat layer) so that the surface of the recording layer shows fine irregularities.

Therefore, the size of the particles to be present should be at least 1.1 times the thickness of the dried recording layer when it is put into the recording layer, and after drying the undercoat layer and the recording layer when it is put into the undercoat layer. It is preferable that the total thickness is 1.1 times or more. When an overcoating layer is further applied on the remarkable coloring / reversing reversible thermosensitive recording layer of the present invention thus produced, the unevenness of the surface is maintained, and the number of times of repeated coloring / decoloring is further increased. .

The colorless or light-colored leuco dye used in the present invention is not particularly limited as long as it is generally used for pressure-sensitive recording paper or heat-sensitive recording paper. Specific examples include, for example, the following, but the present invention is not limited thereto.

(1) Triarylmethane compound 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (commonly called crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide , 3- (p-dimethylaminophenyl)-
3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-
Methylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindole-3
-Yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl)- 5-dimethylaminophthalide, 3-p
-Dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethylaminophthalide and the like.

(2) Diphenylmethane compounds 4,4′-bis (dimethylaminophenyl) benzhydryl benzyl ether, N-chlorophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine and the like.

(3) Xanthene compound rhodamine B anilinolactam, rhodamine Bp-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3- Diethylamino-7-phenylfluoran, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7- (3,4-dichloroanilino) fluoran, 3 -Diethylamino-7
-(2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3- (N
-Ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tolyl) amino-6 Methyl-7-phenethylfluoran, 3-diethylamino-7- (4-nitroanilino) fluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-propyl) amino-
6-methyl-7-anilinofluoran, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-cyclohexyl) amino-6 Methyl-7-anilinofluoran, 3
-(N-ethyl-N-tetrahydrofuryl) amino-6
-Methyl-7-anilinofluoran, and the like.

(4) Spiropyran Compounds 3-Methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3- Methoxybenzo) spiropyran, 3-propylspirobenzopyran, and the like.

The above leuco dyes are used alone or as a mixture of two or more.

In the present invention, a color developer which causes reversible color development / decoloration of the leuco dye (including a color-reducing agent, which is referred to as a color developing agent in the present invention) The following are specific examples of N- (hydroxyphenyl).
L) -N'-alkyl urea is used as a developer.

[0018] N- (hydroxyphenyl)-N'-alkyl ureas N- (4-hydroxyphenyl)-N'-n-hexyl-urea, N- (4-hydroxyphenyl)-N'-n-dodecyl urea, N -(4-hydroxyphenyl) -N'-
n-hexadecyl urea, N- (4-hydroxyphenyl) -N '-(9-octadecenyl) urea, N- (4-
Hydroxyphenyl) -N'-n-docosyl urea, and the like.

In the present invention, one type or two or more types of color developers may be used in combination, and the amount of the leuco dye used is 5 to 5000%, preferably 10 to 3000%.
It is. When two or more developers are used in combination,
Not only the combination of the developer alone but also the N- (hydroxy
(Nyl) -N'-alkyl urea
You may use it.

[0020] (1) an organic amine salt of bis organic acid (4-hydroxyphenyl) lauryl amine salt of acetic acid, stearyl amine salts of 2,2-bis (4-hydroxyphenyl) butyric acid, bis (4-hydroxyphenyl) acetic acid Palmitylamine salt, gallic acid laurylamine salt, gallic acid stearylamine salt, gallic acid palmitylamine salt, and the like.

[0021] (2) ascorbate -6-O-acyl derivatives L- ascorbic acid -6-O-butyryl, L- ascorbic acid -6-O-lauryl, L- ascorbic acid-6
O-palmityl, L-ascorbic acid-6-O-myristyl, L-ascorbic acid-6-O-stearyl, and the like.

In order to increase the mechanical strength of the reversible thermosensitive recording layer, a binder is generally added to the recording layer. Specific examples thereof include soluble starches,
Hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylamide-acrylate copolymer, acrylamide-acrylate-methacrylate terpolymer, styrene-maleic anhydride Water-soluble polymers such as copolymer alkali salts, ethylene-maleic anhydride copolymer alkali salts, or polyvinyl acetate, polyurethane, polyacrylate, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer Latex such as coalescence, ethylene-vinyl acetate copolymer and the like.

Further, as additives for controlling the color sensitivity and the color erasing temperature, waxes such as N-hydroxymethyl stearamide, stearamide, palmitamide and the like, naphthol derivatives such as 2-benzyloxynaphthalene and the like can be used. , P-benzylbiphenyl, 4-allyloxybiphenyl, etc., 1,2-bis (3-methylphenoxy) ethane, 2,2′-bis (4
-Methoxyphenoxy) diethyl ether, bis (4-
Polyether compounds such as methoxyphenyl) ether and the like, and carbonic acid or oxalic acid diesters such as diphenyl carbonate, dibenzyl oxalate, bis (p-methylbenzyl) oxalate, and the like can be added alone or in combination.

Examples of the spherical or nearly spherical particles suitable for use in the present invention include calcium carbonate, magnesium carbonate, basic magnesium carbonate, magnesium hydroxide, magnesium oxide, kaolin, calcined kaolin and clay. , Zinc oxide, zinc carbonate, titanium dioxide, silica, silica alumina, glass, talc and other inorganic particles, calcium stearate, magnesium stearate, silicon resin, melamine resin, benzoguanamine resin, polystyrene, polyethylene, polypropylene, etc. Fairs, various starch particles,
Crystalline cellulose fine powder and the like can be mentioned, and water-insoluble and heat-resistant particles are particularly preferable. The amount to be present varies depending on other materials used and purposes, but is preferably in the range of about 0.5 to 5 g / m ² .

The reason why such particles are present to make the surface of the coating layer uneven can dramatically increase the number of times the color can be repeatedly generated and erased.

The overcoat layer can be selected from the water-soluble polymers mentioned above for the binder. Further, an organic or inorganic pigment may be added to the overcoat layer.

The support used in the reversible thermosensitive recording material of the present invention includes paper, non-woven fabric, woven fabric, plastic film, synthetic resin laminated paper, synthetic paper, metal plate, glass plate, and composite sheet combining these. And the like are arbitrarily selected according to the purpose.

The reversible thermosensitive recording material according to the present invention is obtained by mixing each dispersion obtained by pulverizing each color-forming component,
It can be obtained by a method of coating and drying on a support, or mixing each solution obtained by dissolving each coloring component in a solvent, and coating and drying on a support. In this case, for example, each color-forming component may be contained one by one to form a multilayer structure. The reversible thermosensitive recording layer may be provided on the entire surface of the support, or may be provided partially by a printing machine or the like. Further, a layer capable of recording information electrically, magnetically or optically may be provided on the opposite surface of the support, or a back coating layer may be provided for the purpose of preventing curling or charging.

The thickness of the reversible thermosensitive recording layer after drying is preferably in the range of 1 to 20 μm, and is set so as to obtain a required image density.

In order to record an image on the thermosensitive coloring / decoloring reversible thermosensitive recording material of the present invention thus obtained, a thermal printer equipped with a thermal (thermal) head capable of heating in milliseconds (line head type or There is a serial head method, etc.)
Is most suitable, but other means may be used. In short, it is important to select a means capable of high-temperature heating and rapid cooling in a very short time. To erase the color image obtained by these means, heat stamp, heat roller, infrared lamp,
The image portion may be heated and allowed to cool by using an electric heater, hot air or the like at a temperature slightly higher than 100 ° C. for about 0.1 to 10 seconds. From the recording material from which the image has been erased, a color image can be obtained again by the above-mentioned means, and these can be repeated thereafter.

[0031]

Next, the present invention will be described in more detail by way of examples. The parts and percentages shown below are based on weight unless otherwise specified.

Example 1 On one side of a commercially available foamed PET film (an opaque film having a thickness of 188 μm), first, approximately spherical particles of 1 part of polyvinyl alcohol and basic magnesium carbonate (average particle size: 6.0 μm, Tokuyama Soda Co., Ltd.) Co., Ltd.) was applied and dried. According to the scanning electron microscope observation, the substantially spherical particles are scattered almost uniformly apart from each other with a part of the lower part being buried in the polyvinyl alcohol layer and the upper part being largely exposed.

Leuco dye 3-dibutylamino-6
40 parts of -methyl-7-anilinofluoran were crushed together with 90 parts of a 2.5% aqueous solution of polyvinyl alcohol in a ball mill for 24 hours to obtain a leuco dye dispersion. Separately, N- (4-hydroxyphenyl) -N'-n-
100 parts of hexadecyl urea was ground with a ball mill for 24 hours together with 400 parts of a 2.5% aqueous polyvinyl alcohol solution to obtain a dispersion. After mixing these two dispersions, 1
200 parts of 0% polyvinyl alcohol aqueous solution and 400 parts of water
Parts were added and mixed to prepare a reversible thermosensitive coating liquid.

The reversible thermosensitive coating solution was applied onto the undercoating film of spherical particles prepared above so that the coated amount after drying was 4 g / m ^2, and dried. According to the scanning electron microscope observation, the coated surface was prominent where the spherical particles were present, and the surface unevenness was clearly visible. Further, microscopic observation of the lamination section showed that the thickness of the undercoat layer in the absence of spherical particles (that is, the portion of only polyvinyl alcohol) was 1 μm, and the thickness of the reversible thermosensitive recording layer was 4 μm.

Example 2 A 10% aqueous solution of polyvinyl alcohol was further overcoated on the surface of the reversible thermosensitive recording material obtained in Example 1 and dried. According to the scanning electron microscope observation, the coated surface was prominent where the spherical particles were present, and the surface unevenness was clearly visible. Also, from microscopic observation of the laminated cross section,
The thickness of the overcoat layer was found to be 1.5 μm.

Example 3 Coating obtained by directly adding 43 parts of glutinous rice starch particles (average particle size: 4.9 μm) to the reversible thermosensitive coating liquid prepared in Example 1 directly onto one side of a high-quality paper having a basis weight of 200 g / m ^2. The liquid was applied so that the applied amount of the total solid content after drying was 5 g / m ^2, and dried. According to the scanning electron microscope observation, the coated surface was clear with irregularities on the surface, where the starch particles were present.
Microscopic observation of the lamination section showed that the thickness of the reversible thermosensitive recording layer in the portion where starch particles were absent was 4 μm.

Example 4 A 10% aqueous solution of polyvinyl alcohol was further overcoated on the coated surface of the reversible thermosensitive recording material obtained in Example 3 and dried. According to the scanning electron microscope observation, the coated surface was prominent where the spherical particles were present, and the surface unevenness was clearly visible. Also, from microscopic observation of the laminated cross section,
The thickness of the overcoat layer was found to be 1.5 μm.

Comparative Example 1 A comparative sample was prepared in the same manner as in Example 1 except that substantially spherical particles of basic magnesium carbonate were not added at all. According to the observation with a scanning electron microscope, since substantially spherical particles of basic magnesium carbonate were not added, the coating surface was flat without any irregularities.

Comparative Example 2 A comparative sample was prepared in the same manner as in Example 2 except that substantially spherical particles of basic magnesium carbonate were not added at all, and the overcoat layer was similarly provided. According to the observation with a scanning electron microscope, since substantially spherical particles of basic magnesium carbonate were not added, the coating surface was flat without any irregularities.

Comparative Example 3 A comparative sample was prepared in the same manner as in Example 3, except that no glutinous rice starch particles were added. According to the scanning electron microscope observation, since glutinous rice starch particles were not added, the surface was almost flat without any irregularities.

Comparative Example 4 A comparative sample was prepared in the same manner as in Example 4, except that no glutinous rice starch particles were added, and the other steps were performed in the same manner. According to the scanning electron microscope observation, since glutinous rice starch particles were not added, the surface was almost flat without any irregularities.

Example 5 The reversible thermosensitive recording material obtained in Examples 1 to 4 or Comparative Examples 1 to 4 was applied to a thermal print head KJT-256-8 manufactured by Kyocera Corporation.
Using an Ogura Denshi Thermal Facsimile Thermal Printing Tester TH-PMD with MGF1, thermal printing was performed with an applied pulse of 1.0 millisecond and an applied voltage of 26 volts, and the reflection density of the resulting color image was measured using a densitometer Macbeth RD918. As a result, all showed a concentration of 1.30 to 1.40. When these colored image portions were heated at 120 ° C. for 1 second using a heat stamp and allowed to cool, the color was erased to a density of less than 0.10.

A test was made as to how many times such color printing by the thermal print head / decoloring by the thermal stamp was possible repeatedly. As the number of times of use, the initial color density × 0.
The number of times the color density reached 8 was adopted (deterioration of the recording material due to repeated color development / decoloration appears first in the decrease in color density, and the increase in density after decoloration appears much later than that).

According to this test, Example 1 or Example 3
In the reversible thermosensitive recording material of No. 5, no decrease in the color density was observed even after 50 repetitions. On the other hand, in the sample without the spherical particles prepared in Comparative Example 1 or Comparative Example 3, the color density was reduced more than the specified value as early as 19 times, and the color density was further decreased as the number of times was increased. .

In the reversible thermosensitive recording material of Example 2 or 4, no decrease in the color density was observed after 100 repetitions. On the other hand, in the samples prepared in Comparative Example 2 or Comparative Example 4 in which no spherical particles were added, the reduction in the color density began to exceed the specified level already at 27 times, and as the number of times increased, the reduction in the color density became more remarkable. Was.

As described above, in the coloring / decoloring reversible thermosensitive recording material according to the present invention, the unevenness of the coated surface due to the addition of the spherical particles contributes to the improvement of the number of times of repeated use. And it turned out that an overcoat layer also contributes greatly to the further improvement of a service life.

[0047]

As is clear from the examples, the reversible thermosensitive recording material of the type which realizes the color development / decoloration of the leuco dye / developer system only by controlling the heat energy has a repetitive service life. , In or under the reversible thermosensitive recording layer, the presence of spherical or nearly spherical particles,
By forming fine irregularities on the surface of the coating layer, the durability is dramatically improved in combination with the effect of the overcoat layer.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41M 5/28-5/34

Claims (3)

(57) [Claims] 1. A reversible thermosensitive recording material having at least a color reversible thermosensitive recording layer provided on a support, a leuco dye
And N- (hydroxyphenyl) -N'-alkyl urine
Erasing characterized by the fact that substantially spherical particles having an average particle size of 1.1 times or more the thickness of the layer are present in the coloring / erasing reversible thermosensitive recording layer containing element as a developer. Color reversible thermosensitive recording material. 2. In a reversible thermosensitive recording material comprising an undercoat layer and a reversible thermosensitive recording layer laminated on a support, the undercoat layer, the leuco dye and N- ( hydr) are added to the undercoat layer.
Roxyphenyl) -N'-alkyl urea as color developer
A color-decolorable reversible thermosensitive recording material characterized in that substantially spherical particles having an average particle diameter of 1.1 times or more of the total thickness of the heat-decolorable reversible thermosensitive recording layer are contained. 3. The reversible thermosensitive recording material according to claim 1, further comprising an overcoat layer provided on the reversible thermosensitive recording layer.