JPH10175371A - Heat-sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the high sensitivity and superior water resistance and heat resistance and resistance to plasticizer of a white paper by using an aqueous dispersion liquid in which a leuco dye and 4,4'-diallyloxydiphenyl sulfone are covariance treated in a water medium so that the volume average particle diameter is a specified numerical value or under in a heat-sensitive coloring layer. SOLUTION: A heat-sensitive coloring layer is formed on one face of a substrate, on which a protective layer is formed. An aqueous dispersion liquid prepared by covariance treating a leuco dye and 4,4'-diallyloxydiphenyl sulfone is used for the heat-sensitive coloring layer. The volume average particle diameters of leuco dye and 4'-diallyloxydiphenyl sulfone are set as 2μm or less, preferably 1μm or less. The adding amount of 4,4'-diallyloxydiphenyl sulfone is 20-300wt.% to the leuco dye, and particularly it is desirable to add the amount in the range of 50-200wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, which has high sensitivity, excellent water resistance in an image area immediately after printing, and excellent heat resistance and plasticizer resistance of blank paper. It is about.

[0002]

2. Description of the Related Art Many types of thermal recording have been known for a long time. For example, a heat-sensitive recording material using an electron donating colorless dye and an electron accepting compound is disclosed in JP-B-43-4.
No. 160, No. 45-14039, etc., and in recent years, these thermal recording systems have been applied to various fields such as facsimile machines, printers, labels, and the like, and needs are expanding. In particular, in applications such as labels, with the miniaturization and high speed of the device, color development at low energy, that is, high sensitivity and image preservation, and heat resistance in microwave ovens, etc., that is, heat resistance of blank paper, are required. ing.

In order to increase the sensitivity, a low-melting compound having good compatibility between the leuco dye and the developer, a so-called sensitizer (JP-A-60-82382, JP-B-63-42590).
JP-A-58-76293, the provision of an intermediate layer of a pigment having a high oil absorption (JP-B-57-52915, etc.), or the atomization of leuco dyes and developers (JP-A-58-76293).
And various other means.

On the other hand, various methods have been proposed for improving the heat resistance of a heat-sensitive recording material. For example, JP-A-59-207283 discloses that at least the third and seventh
By combining a leuco dye having a substituted amino group at the position with parahydroxybenzoic acid ester and using at least one dispersant of hydroxyethyl cellulose and carboxyl group-modified polyvinyl alcohol as a dispersant for the dye, oil resistance, There is an improvement in heat resistance.

In Japanese Patent Application Laid-Open No. 2-577, heat response and image storability are improved by using metabis (3,4-dihydroxycumyl) benzene as a developer in a leuco-type thermosensitive color former. Heat-sensitive recording medium).

Furthermore, in recent years, there has been a demand for labels that can withstand use in microwave ovens and the like, and also for the heat resistance of blank paper. The heat resistance of white paper is greatly affected by the sensitizer.In the conventional system, when a sensitizer is used, the heat resistance of the white paper is not possible. Could not be obtained.

[0007] In addition, for food label use, since it is stored for a long time in an environment where water is present, such as during freezing transportation or refrigerated storage, the storage stability when water adheres to the image area (hereinafter referred to as water resistance). Good things are strongly demanded.

As a sensitizer, 4,4'-diallyloxydiphenyl sulfone (JP-A-60-72788) is known to be effective for background fog.
Water resistance was insufficient, and a sheet having satisfactory heat resistance and image storability of white paper could not be obtained. In order to improve such water resistance, there have been many proposals to add various preservability improvers for hindered phenols (JP-A-61-11).
289, JP-A-63-151481, JP-A-6-99661).

However, these improvement proposals are effective in improving the storage stability of the image area under high-temperature conditions, and may be accompanied by new defects such as deterioration of the heat resistance of the blank paper area. No results were obtained.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material having high sensitivity, excellent water resistance in an image area immediately after printing, and heat resistance and plasticizer resistance of a white paper. is there.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies to improve these disadvantages, and as a result, have come to invent the heat-sensitive recording material of the present invention. That is, the heat-sensitive recording material of the present invention comprises, on one surface of a support, a heat-sensitive coloring layer containing a leuco dye and a developer, and a protective layer provided thereon. And 4,4'-diallyloxydiphenylsulfone in an aqueous medium, wherein an aqueous dispersion obtained by performing a co-dispersion treatment so that the volume average particle diameter becomes 2 μm or less is used.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the heat-sensitive recording material of the present invention will be described in detail. The heat-sensitive recording material obtained by the method of the present invention is a heat-sensitive recording material in which a heat-sensitive coloring layer containing a leuco dye and a developer is provided on one surface of a support and a protective layer is provided thereon. By using an aqueous dispersion obtained by co-dispersing a leuco dye and 4,4′-diallyloxydiphenyl sulfone as the heat-sensitive coloring layer, the image portion immediately after printing is excellent in water resistance, high sensitivity, and high heat resistance of white paper. Thus, a heat-sensitive recording material was obtained.

Although the reason is not clear, the thermosensitive recording material containing 4,4'-diallyloxydiphenyl sulfone has a phenomenon that when the image area is immersed in water immediately after printing, the image area partially loses color. Occurs. This phenomenon does not disappear when the heat-sensitive recording material that has been printed for a long time is immersed in water. In addition, it tends to be improved by heating the thermosensitive recording material immediately after printing at 60 ° C. for 30 minutes. The developer and the leuco dye are melted and become amorphous when heated, and gradually crystallize with time. It is presumed that the image area formed by using a ternary system containing 4,4'-diallyloxydiphenyl sulfone as the developer and leuco dye is more stable in the crystallized state than in the amorphous state. Is done. 4,4 '
-By co-dispersing diallyloxydiphenyl sulfone with a leuco dye, since the leuco dye and 4,4'-diallyloxydiphenyl sulfone are present closer to each other, the crystallization of the melt with the color developer is promoted. It is estimated that the effect has increased.

In the present invention, the leuco dye and 4,4'-
The volume-average particle diameter of the aqueous co-dispersion of diallyloxydiphenyl sulfone is characterized in that it is 2 μm or less, preferably 1 μm or less. Can not be obtained. The thermosensitive recording material develops color when the developer and the leuco dye coloring material melted by heating diffuse and react through mutual dissolution, but the melting and mutual dissolution rates depend on the particle diameter of the coloring material. The smaller the diameter is, the higher the color density becomes. If the diameter exceeds 2 μm, the speed becomes slow.

The amount of 4,4'-diallyloxydiphenyl sulfone added is 20 to 30 with respect to the leuco dye.
0% by weight, particularly preferably in the range of 50 to 200% by weight.

The leuco dye used in the present invention includes:
There is no particular limitation as long as it is used for general pressure-sensitive recording paper, heat-sensitive recording paper, and the like. Hereinafter, specific examples will be described. (1) Triarylmethane compound 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (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-phenylindole-
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-Dimethylaminothalide, 3-
p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethyl-aminophthalide and the like.

(2) Diphenylmethane compounds 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-halophenylleuco auramine, N-
2,4,5-trichlorophenylleuco auramine and the like.

(3) Xanthene compounds rhodamine B-anilinolactam, rhodamine B-p-
Nitroanilinolactam, rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3-diethylamino-7-phenylfluoran, 3- Diethylamino-7- (3,4-dichloro) anilinofluoran, 3-diethylamino-7-
(2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-ethyl-tolylamino-6-methyl-7-ani Linofluoran, 3-ethyl-tolylamino-6-methyl-7-phenethylfluoran, 3-diethylamino-7- (4-nitroanilino) fluoran, 3-dibutylamino-6
Methyl-7-anilinofluoran and the like.

(4) Thiazine compounds Benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue and the like.

(5) Spiro compounds 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3'-dichloro-spiro-
Dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-methylnaphtho- (3-methoxy-benzo) -spiropyran, 3-propyl-spiro-dibenzopyran and the like. Alternatively, the above various mixtures can be mentioned.
These are determined by the application and desired properties.

The developer used in the present invention is preferably a phenol derivative, an aromatic carboxylic acid derivative or the like, and particularly preferably a bisphenol. Specifically, as phenols, p-octylphenol, p-tert-butylphenol, p-phenylphenol, 1,1-bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2-ethyl-hexane,
2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane and the like. As the aromatic carboxylic acid derivative, p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate,
3,5-di-tert-butylsalicylic acid, 3,5-di-α
-Methylbenzylsalicylic acid and carboxylic acids include polyvalent metal salts thereof.

The co-dispersion of the leuco dye and 4,4'-diallyloxydiphenyl sulfone and the developer dispersion are prepared by various wet pulverization methods such as a dyno mill, a sand grinder, an attritor, a ball mill, and a coball mill. The volume average particle diameter is 2.0 μm or less, preferably 1.
The process is performed until the thickness becomes 0 μm or less. Also, a water-soluble synthetic polymer compound such as a surfactant and polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol and a styrene-maleic anhydride copolymer, and hydroxyethyl, as long as the effects of the present invention are not inhibited, if necessary. A water-soluble natural polymer compound such as cellulose, starch derivative, gelatin and casein or a derivative thereof may be added, or various auxiliaries such as an antifoaming agent may be added.

In the present invention, when preparing a coating solution for a heat-sensitive recording material, the leuco dye, which is separately prepared, and 4,4'-
The co-dispersion of diallyloxydiphenyl sulfone and the developer dispersion are mixed together, and if necessary, pigments, waxes, metal soaps and, if necessary, an ultraviolet absorber are added.

The above additives may be added at the time of the dispersion operation of each dispersion.

As the pigment, an inorganic powder having an oil absorption of 50 ml / 100 g or more according to the JIS K5101 method is used. For example, calcined kaolin, activated clay, silica, calcium carbonate, diatomaceous earth and the like are mainly used. , Talc and the like can be used together. In addition, organic pigments of urea-formalin resin powder and polystyrene resin powder can also be used.

Examples of the waxes include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax and the like.

Examples of the metal soap include higher fatty acid polyvalent metal salts, that is, zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like.

The smear contains a binder (adhesive) for bonding the above components to form a thermosensitive coloring layer.
Water-soluble binders are generally used, and polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, Examples include polyacrylic acid, starch derivatives, casein, and gelatin.
For the purpose of imparting water resistance to these binders, a water-resistant agent (gelling agent, cross-linking agent) may be added, or an emulsion of a hydrophobic polymer, specifically, a styrene-butadiene rubber latex, an acrylic resin emulsion, or the like may be used. Can be added.

As the support, paper is generally used, but resin film, synthetic paper, non-woven fabric and the like can also be used. As an apparatus used for smearing the intermediate layer and the thermosensitive coloring layer, a coater head such as a blade coater, an air knife coater, a roll coater, a rod coater, and a curtain coater can be used.

Further, in order to improve the surface smoothness of the coated product, a machine calender, a super calender,
Devices such as gloss calendars and brushing can be used.

The amount of smear when the intermediate layer is provided is not particularly limited, but if the amount is too small, the effect is small.
If the amount is too large, the strength of the paper becomes weak and it is not economical, so that 3 to 20 g / m ² , preferably 5 to 10 g / m ² is suitable. Although coating amount of the support of the thermosensitive coloring layer is not limited, usually, 3 to 15 g / m ² by dry weight, preferably in the range of 4~10g / m ^2. The developer is used in an amount of 5 to 300% by weight based on the dye, and preferably 20 to 150% by weight.

As the pigment for the intermediate layer, JIS K51 which is porous and has high heat insulation from the viewpoint of improving sensitivity and adhesion of scum.
Inorganic powder having an oil absorption of 50 ml / 100 g or more according to the method 01 is used. For example, calcined kaolin, activated clay, silica, calcium carbonate, diatomaceous earth and the like are mainly used, and kaolin and talc can be used in combination.

Examples of the aqueous adhesive include styrene-butadiene latex, acrylic resin emulsion, styrene-
Maleic anhydride copolymer, polyvinyl alcohol, hydroxyethyl cellulose, starch, starch derivatives,
Casein, gelatin and the like, other, dispersant,
An antifoaming agent, a lubricant and the like can also be added, and those used for general coated paper can be used.

In the present invention, a protective layer is further provided on the thermosensitive coloring layer for solvent resistance and the like. As the adhesive for the protective layer, any of a water-soluble resin and a water-dispersible resin can be used. For example, polyvinyl alcohol,
Modified polyvinyl alcohol, hydroxyethyl cellulose
Water, starch, modified starch, casein, gelatin styrene-butadiene latex, acrylic resin emulsion, styrene-maleic anhydride copolymer, and the like. These may be used alone or in combination of two or more. Also, if necessary, further pigments,
It is possible to add a wax, a waterproofing agent and the like.

[0035]

Next, the present invention will be described in more detail with reference to examples. All parts and percentages shown below are based on weight. Unless otherwise specified, the value indicating the amount of smear indicates the amount of smear after drying.

Embodiment 1 1. Preparation of Intermediate Layer Ansilex (calcined kaolin manufactured by Engelhardt Co., Ltd., oil absorption by JIS-K5101 method 80 ml / 100 g) 100 parts 10% sodium hexametaphosphate 4 parts 20% MS4600 (Nippon Shokuhin, phosphorylated starch) 30 parts 48 % Styrene-butadiene-based copolymer latex 40 parts and water 90 parts were stirred and dispersed to prepare a coating liquid for the intermediate layer, and a base paper of 50 g / m ^{2 was} coated with a coating amount of 8.5 g / m ² using a blade coater to obtain an intermediate layer.

2. Preparation of co-dispersion of dye and 4,4'-diallyloxydiphenyl sulfone [Preparation of solution A] 3-dibutylamino-6-methyl-7-anilinofluoran 15 parts 5% polyvinyl alcohol 90 parts 4,4 ' -Diallyloxydiphenyl sulfone 50 parts Water 15 parts Solution A was pulverized using Dynomill (manufactured by Shinmaru Enterprises) to a volume average particle diameter of 0.7 µm. The particle size was measured using a Nikkiso Microtrac X-100 type particle size distribution analyzer.

3. Preparation of developer dispersion [Preparation of solution B] 2,4'-dihydroxydiphenylsulfone 50 parts 5% polyvinyl alcohol 100 parts Water 15 parts Volume B of the solution B was measured using a Dynomill (manufactured by Shinmaru Enterprises). It was pulverized to 1.0 μm.

[Formation of Recording Layer] 55 parts of solution A and 115 of solution B
Parts, 40% zinc stearate emulsion (manufactured by Chukyo Yushi, Hydrin E-366), 20 parts, calcium carbonate 3
Five parts were mixed, and a 10% aqueous polyvinyl alcohol solution was added so that the solid content was 20% of the total solid to obtain a thermosensitive coloring layer coating solution. The coating solution of the thermosensitive coloring layer was smeared on the intermediate layer with a hand coating bar so as to have a coating amount of 5 g / m ² to obtain a thermosensitive coloring layer.

Subsequently, the following protective layer coating solution was smeared on the thermosensitive coloring layer of Example 1 with a hand-coating bar so as to have a coating weight of 3 g / m ² , and the Bekk smoothness was adjusted to 600 to 800 seconds using a calendar. Thus, a heat-sensitive recording material was obtained.

[Blending of protective layer liquid] 10% polyvinyl alcohol 100 parts 40% zinc stearate emulsion liquid (manufactured by Chukyo Yushi, Hydulin E-366) 5 parts 20% silicic acid (Mizusawa Chemical, Mizukasil P527) 50 parts

Example 2 In the preparation of solution A of Example 1, 3-dibutylamino-6
Example 2 was repeated, except that -methyl-7-anilinofluoran was replaced with 3-di (n-pentyl) amino-6-methyl-7-anilinofluoran and 130 parts of solution B was used. Was obtained.

Example 3 The heat-sensitive recording material of Example 3 was obtained in the same manner as in Example 1, except that 2,4'-dihydroxydiphenylsulfone was replaced by 2,2-bis (p-hydroxyphenyl) propane. Was.

Example 4 A heat-sensitive recording material of Example 4 was obtained in the same manner as in Example 1, except that the volume average particle diameter of Solution A was changed to 1.7 μm.

[Preparation of Solution C] 3-Dibutylamino-6-methyl-7-anilinofluoran 30 parts 5% polyvinyl alcohol 60 parts Water 10 parts The volume of the solution C was measured using a Dynomill (manufactured by Shinmaru Enterprises). It was pulverized to an average particle size of 0.7 μm.

[Preparation of Solution D] 4,4′-diallyloxydiphenyl sulfone 50 parts 5% polyvinyl alcohol 100 parts Solution D was pulverized to a volume average particle diameter of 1.0 μm using Dynomill (manufactured by Shinmaru Enterprises). .

Comparative Example 1 In Example 1, 20 parts of solution A and 35 parts of solution D were used.
The heat-sensitive recording material of Comparative Example 1 was obtained in the same manner, except that the heat-sensitive recording material was replaced.

[Preparation of Solution E] 2,4′-dihydroxydiphenylsulfone 15 parts 4,4′-diallyloxydiphenylsulfone 25 parts 5% polyvinyl alcohol 40 parts 20 parts E solution was treated with Dynomill (manufactured by Shinmaru Enterprises). And pulverized to a volume average particle size of 1.0 μm.

Comparative Example 2 Comparative Example 2 was carried out in the same manner as in Example 1 except that Liquid A and Liquid B were replaced with 50 parts of Liquid C and 140 parts of Liquid E.
Was obtained.

Comparative Example 3 Example 1 was repeated except that 4,4'-diallyloxydiphenylsulfone in Solution A was replaced with di-p-methylbenzyl oxalate and that 110 parts of Solution B were used. Thus, a heat-sensitive recording material of Comparative Example 3 was obtained.

Comparative Example 4 In Example 1, 4,4′-diallyloxydiphenylsulfone in Solution A was replaced with an emulsion of stearic amide (manufactured by Chukyo Yushi, High Micron G-270, melting point 10
0 ° C.) to obtain a heat-sensitive recording material of Comparative Example 4.

Comparative Example 5 Comparative Example 5 was carried out in the same manner as in Example 1 except that 4,4′-diallyloxydiphenylsulfone in Solution A was omitted.
Was obtained.

Comparative Example 6 In Example 1, the volume average particle diameter of the solution A was 2.3 μm.
The heat-sensitive recording material of Comparative Example 6 was obtained.

Next, the following evaluations were performed on the heat-sensitive recording materials of Examples 1 to 4 and Comparative Examples 1 to 6, and the results are shown in Table 1 below. In addition, each evaluation method is as follows.

[Coloring density] Labeler (ISHIDA I)
Using P21EX), the thermosensitive recording material was colored with a pulse width of 0.65 ms and an applied voltage of 23 V, and the color density of the obtained recorded image was measured with a Macbeth densitometer RD-918. The higher the numerical value, the higher the color density, and practically, it is preferably at least 1.0 or more.

[Heat resistance of blank paper] The heat resistance of blank paper was measured by leaving the above-mentioned thermosensitive recording material at 90 ° C or 100 ° C for 1 hour, and measuring the density of the background (unprinted) portion with a Macbeth densitometer RD-. 918.

[Water Resistance] The water resistance indicates the residual ratio of an image when the heat-sensitive recording material immediately after printing is immersed in water for 24 hours. The larger the number, the better the water resistance, and practically 80%
The above is desirable.

[Storage Stability of Image] The storage stability of the image is the storage stability with a plasticizer, and three diamond wraps G (manufactured by Mitsubishi Plastics) are superimposed on the image portion at 40 ° C. for 24 hours. It indicates the residual rate of the processed image, and the larger the number is, the better the storage stability is.

[0059]

[Table 1]

As shown in Table 1, the heat-sensitive recording materials of Examples 1 to 4 use an aqueous dispersion in which a leuco dye and 4,4'-diallyloxydiphenyl sulfone are co-dispersed. The heat resistance of the blank portion at 90 ° C. and 100 ° C., the water resistance immediately after printing, and the stability of the image portion are particularly excellent.

In the heat-sensitive recording material of Comparative Example 1, since the leuco dye and 4,4′-diallyloxydiphenyl sulfone were separately dispersed, the color density and the heat resistance of blank paper were at a sufficient level, but immediately after printing. The water resistance of the image area is poor.
In Comparative Example 2, since a dispersion obtained by co-dispersing 4,4′-diallyloxydiphenyl sulfone with a color developer was used, the water resistance of an image portion immediately after printing was poor. Since the heat-sensitive recording materials of Comparative Examples 3 and 4 use a co-dispersion liquid of a leuco dye and a sensitizer other than 4,4'-diallyloxydiphenyl sulfone, the heat resistance of the blank portion is inferior. Comparative Example 5
Since 4,4′-diallyloxydiphenyl sulfone is not used, the heat resistance of the white paper portion is excellent, but the color density is low. Comparative Example 6 shows that the leuco dye of Example 1 and 4,4′-
In the co-dispersion treatment of diallyloxydiphenyl sulfone, since the co-dispersion liquid having a volume average particle diameter exceeding 2 μm and having a large volume average particle diameter is used, the water resistance immediately after printing is excellent, but sufficient. Color density is not obtained.

[0062]

As is clear from the heat-sensitive recording materials of the above Examples and Comparative Examples, the heat-sensitive recording material of the present invention has high sensitivity, heat resistance of blank paper, water resistance of the image area immediately after printing,
The image part had excellent storage stability.

Claims (1)

[Claims] 1. A thermosensitive recording material comprising a heat-sensitive coloring layer containing a leuco dye and a color developer provided on one side of a support, and a protective layer provided thereon.
-A thermosensitive recording material using an aqueous dispersion obtained by subjecting diallyloxydiphenyl sulfone to a co-dispersion treatment in an aqueous medium so that the volume average particle diameter becomes 2 μm or less.