JPH10264526A - Heat sensitive recording body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat sensitive recording body, high in sensitivity of color development, good in resistance to heat, not producing powder due to aging, restrained in the deterioration of coloring density upon printing after preserving a part whereat color is not developed yet for a long period of time and prevented in the generation of adhesion of scum or sticking. SOLUTION: A heat sensitive recording body is provided with an intermediate layer and a heat sensitive color developing layer, containing the principal constituents of colorless or thin colored basic colorless dye and organic color developing agent, which are provided on a bearer. In such a heat sensitive recording body, the intermediate layer contains hollow polymer grain, having an opening unit obtained by cutting a part of hollow polymer particle, and a heat sensitive color developing layer contains 4-hydroxy-4'-n- propoxydiphenylsulfone and the derivative of sulfone amide shown by a formula (in the formula, Z shows the lower alkyl group having 1-6C or electron attractive group, (n) is an integer of 0-2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Good heat resistance, no dusting over time, and a reduction in color density (reprintability) when printing after storing uncolored areas for a long period of time, while preventing heat and sticking. It relates to a recording medium.

[0002]

2. Description of the Related Art In general, a thermosensitive recording medium is prepared by grinding and dispersing a colorless or pale-colored basic colorless dye and an organic developer such as a phenol compound into fine particles, and mixing the two. , A filler obtained by adding a sensitivity enhancer, a lubricant and other auxiliaries, to a paper, a synthetic paper, a film, a substrate such as plastic, coated with a thermal head, a hot stamp, Color is generated by an instantaneous chemical reaction caused by heating with a hot pen, laser light, or the like, and a recorded image is obtained. Thermal recording media are widely used in facsimile machines, computer terminal printers, automatic ticket vending machines, measurement recorders, and the like. In recent years, high-speed printing and high-speed image formation have become possible along with the diversification of recording apparatuses and the advancement of performance, and higher quality is required for the recording sensitivity of a thermosensitive recording medium.

As a method for satisfying this requirement, it has been proposed to use a dye and a developer together with a sensitizer. For example, when the color developer is a phenolic compound represented by bisphenol A, p-benzylbiphenyl (JP-A-60-82382), benzyl p-benzyloxybenzoate (JP-A-57-201691), benzyl Naphthyl ether (JP-A-58-87094) and the like have been used as suitable sensitizers. When using a sensitizer,
When heated, the sensitizer first melts, and it dissolves the basic dye and the developer, so that the two are mixed at the molecular level to induce a color-forming reaction. It is important to consider the color developer. When such a sensitizer is used, since a large amount of a molten substance is contained in the recording medium, a problem of scum adhesion such as adhesion of the molten substance to the thermal head after recording is likely to occur. Also,
As described in JP-A-56-144193, a method has been devised in which the color development sensitivity is increased by a method using a novel color developing agent having a high color developing ability. However, it was difficult to say that the quality was sufficient because of the drawbacks such as dusting due to the above, and a decrease in color density (reprintability) when printing after storing the uncolored portion for a long time. Accordingly, the present inventors have conducted intensive studies in order to solve the above-mentioned problems, and have found that 4-hydroxy-4'-n-
Using propoxydiphenyl sulfone and finding that it contains a sulfonamide derivative as a sensitizer,
It is disclosed in Japanese Patent Application No. 9-38104. on the other hand,
A method has been proposed in which an intermediate layer having good heat insulating properties is interposed between the heat-sensitive recording layer and the support to enhance the thermal response of the heat-sensitive recording material. For example, JP-A-54-92
No. 263 discloses a method of providing an intermediate layer made of a film-forming polymer having a glass transition point of 60 ° C. or lower,
Satisfactory thermal responsiveness has not been obtained by this method. JP-A-59-5093 discloses a method of providing an intermediate layer containing fine hollow sphere particles.
Japanese Patent No. 171685 discloses a method in which an intermediate layer comprising a thermal foaming agent and a thermoplastic polymer is provided and heated and foamed to form a sponge-like intermediate layer. A method is disclosed in which two layers, that is, a layer in which a filler is heated and foamed, and a layer containing a filler and a binder thereon are provided as intermediate layers.

However, even when an intermediate layer having minute hollows as described above is provided, for example, those using non-expandable hollow sphere fine particles can improve the sensitivity temporarily, but still have a satisfactory thermal response. Sex is not obtained. On the other hand, those provided with an intermediate layer using a foam have a sufficient heat insulating function,
Although a high-density recorded image can be obtained with minute energy,
A process for foaming the foam was required, and it was difficult to control to obtain stable quality. Japanese Patent Application Laid-Open No. 2-164580 proposes to provide an intermediate layer containing a porous non-spherical hollow filler formed by squeezing a plastic hollow sphere to form an uneven surface. However, when such an intermediate layer is provided, the thermal response is improved, but the binding force between the support and the heat-sensitive recording layer is not sufficient. Also, Japanese Patent Application Laid-Open No.
No. 73 proposes to provide an intermediate layer containing plastic spherical or oval spherical hollow particles.
The hollow particles have an average particle size of 2 to 20 μm, preferably 3 to 20 μm.
Although it is a fine hollow particle in a foamed state of 10 to 10 μm, it is difficult to prepare uniform particles having a small particle size distribution with little variation. Furthermore, Japanese Patent Application Laid-Open No. 2-57382 proposes to provide an intermediate layer containing hollow polymer fine particles having an average particle size of 5 μm or less, preferably 0.1 to 3 μm.
However, even if such an intermediate layer is provided, the recording sensitivity is not sufficient, and sticking and adhesion of scum of the thermal head occur. As described above, there is no practically satisfactory technique for providing an intermediate layer to achieve higher quality with respect to the recording sensitivity of the thermosensitive recording medium. However, the speeding up and miniaturization of the recording device are progressing further,
At present, more excellent recording sensitivity is required together with high image storability.

[0005]

SUMMARY OF THE INVENTION The present inventors have conducted various studies to solve the above problems, and as a result, have solved the problems. An object of the present invention is to provide high color development sensitivity and high heat resistance. Another object of the present invention is to provide a heat-sensitive recording medium which is free from dusting over time, suppresses a decrease in color density when printing after storing an uncolored portion for a long period of time, and prevents generation of scum and sticking.

[0006]

The gist of the present invention resides in that an intermediate layer and a thermosensitive coloring layer containing a colorless or pale-colored basic colorless dye and an organic color developer as main components are provided on a support. In the heat-sensitive recording medium, the intermediate layer contains hollow polymer particles having openings such as obtained by cutting a part of the hollow polymer particles in a plane, and the heat-sensitive coloring layer is an organic developer. A 4-hydroxy-4'-n-propoxydiphenylsulfone, and a sulfonamide derivative represented by the following general formula (I).

[0007]

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(Wherein, Z represents a lower alkyl group having 1 to 6 carbon atoms or an electron-withdrawing group; n represents an integer of 0 to 2). It is presumed to be affected by the melt dissolution diffusion rate with the color developer and the saturation solubility. In order to further improve the melt dissolution diffusion rate and the saturation solubility, various methods are added as sensitizers. The reason is that many factors such as lowering of melting point, change of polarity, lowering of activation energy, improvement of compatibility between materials work in a complicated manner, so that the melting / diffusion speed and saturation solubility are further improved, and as a result, thermal recording It is thought to contribute to the improvement of the color development sensitivity of the body. In the present invention, the thermosensitive recording material contains 4-hydroxy-4'-n-propoxydiphenylsulfone as an organic color developer and a specific ratio of a sulfonamide derivative, thereby not causing a large drop in melting point. It is thought that the color sensitivity was improved. Therefore, although the color sensitivity is improved, the heat resistant ground color is not deteriorated, and it is considered that the color development of the ground color portion does not occur. Also, by blending the sulfonamide derivative, the compatibility between each material is greatly improved, so that the coloring sensitivity is also improved, and the affinity of each material in the thermosensitive coloring layer is increased, resulting in phase instability. It is considered that the powder wiping due to the aging is suppressed, and the decrease in print density when printing is performed after the uncolored portion is stored for a long time.

In the general formula (I), Z may be any substituent that does not inhibit the sensitizing effect. Examples of such a substituent include a lower alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group, and an electron-withdrawing group such as a chlorine atom, a nitro group and a methoxy group. Specific examples of the compound represented by the general formula (I) include the following (I-1) to (I-1).
(I-30), but is not limited thereto.

[0009]

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[0010] The hollow polymer particles used in the intermediate layer of the present invention have a characteristic structure having an opening portion obtained by cutting a part of the hollow polymer particles in a plane. Specifically, FIG. 1 schematically shows an example in the case of a spherical shape, but is not limited thereto, and may take various shapes such as a pot shape or a conical shape. Referring to FIG. 1,
The hollow polymer particles used in the present invention have an opening obtained by cutting a part of the hollow polymer particles having a hollow portion in the core at a plane, and the hollow portion is hollow perpendicular to the cut surface. A cross section passing through the center of the polymer particle has a shape obtained by cutting a part of a double circle by a straight line m. In the hollow polymer particles used in the present invention, the maximum diameter of the outer circle p of the double circle is D, and the maximum value of the length H of a perpendicular drawn from any point on the outer arc to the straight line m is Hmax. When the equivalent radius of the opening that does not include the thick portion inside the double circle is d, “d
≦ D / 2 and d / Hmax ≦ 1 ”. The same applies to other shapes other than those shown in FIG. In particular, a bowl-like shape obtained by cutting a part of a spherical hollow polymer particle in a plane as shown in FIG. 2 and having the Hmax equal to or larger than D / 2 is an object of the present invention. In addition to being effective in achieving the above, it is advantageous and preferable in production. In this case, in the vicinity of the opening edge, it becomes slightly enormous inward, and has a thickness of about twice the thickness of the hollow polymer particles before the bowl-shaped particles are formed. The thick part of the bowl-shaped particles may have a flattened hollow part derived from the original hollow polymer particles, or a solid part without the hollow part. The average maximum diameter of the bowl-shaped polymerized fine particles is generally 0.3 to 5 μm.
m, preferably 0.5 to 3 μm. The ratio of the average equivalent diameter of the openings to the average maximum diameter of the particles is generally 25
-100%, preferably 60-95%.

The polymer particles having an opening used in the present invention usually have a thick-walled portion having a multilayered polymer structure. As an example of the production method, the following steps (1) to (7) And a multistage polymerization method. (1) Nucleic acid polymer particles are prepared by copolymerizing a monomer mixture of 30 to 65% by weight of an acidic group-containing monomer and 70 to 35% by weight of a monomer copolymerizable therewith,
(2) In the presence of the polymer particles, 10 to 35% by weight of an acidic group-containing monomer and a monomer 90 copolymerizable therewith.
By co-polymerizing the monomer mixture with about 65% by weight, a core polymer substantially surrounding the nucleus polymer particles is formed. The content ratio of the body is equal to or smaller than the content ratio of the acidic group-containing monomer in the nuclear polymer),
(3) In the presence of the core / core polymer particles, 1 to 12% by weight of an acidic group-containing monomer and a monomer 9 copolymerizable therewith
By copolymerizing the monomer mixture with 9 to 88% by weight, at least one intermediate polymer layer substantially surrounding the core polymer particles is formed. An aromatic vinyl monomer is used alone or in an amount of 0.5% by weight or less of an acidic group-containing monomer and an aromatic copolymerizable therewith in the presence of a polymer particle having an intermediate layer polymer formed thereon. By copolymerizing a monomer mixture comprising at least 99.5% by weight of a vinyl monomer, an outer layer polymer substantially surrounding the intermediate layer polymer was formed. A base is added to the aqueous dispersion containing the polymer particles having a layer structure to adjust the pH of the dispersion to 7 or more to form voids in the polymer particles. (6) Then, if desired, The pH was adjusted to less than 7, and the aqueous dispersion was treated with aromatic vinyl. A monomer mixture consisting of at least 90% by weight of an aromatic vinyl monomer and at most 10% by weight of a monomer copolymerizable therewith, to form the at least four-layer structure. The outermost layer polymer is formed around the outer layer polymer by polymerizing in the presence of the polymer particles having the following formula (1), and then (7) the obtained polymer particle dispersion is dried.

In the present invention, the reason why the intended effect can be obtained by including the specific hollow polymer particles in the intermediate layer is considered as follows. The specific hollow polymer particles used in the present invention have an opening obtained by cutting a part of the hollow polymer particles in a plane and have a characteristic structure. Therefore, many voids are present in the intermediate layer containing the hollow polymer particles, and an air layer having a high heat insulating effect is constructed, so that heat energy can be efficiently taken into the thermosensitive coloring layer. As a result, the recording sensitivity is improved. Further, it is presumed that the intermediate layer of the present invention using hollow polymer particles having a specific structure has extremely high cushioning properties as compared with the case where inorganic fillers or solid polymer particles are used. As a result, the contact between the thermal head and the thermosensitive recording medium is improved, and as a result, the reproducibility of the printed pixels is improved in addition to the recording sensitivity, and a good image quality of the recording section is provided. Furthermore, the specific hollow polymer particles used in the present invention have a hollow portion largely open to the outside inside, unlike a normal hollow polymer particle having no opening. For this reason, it is possible to absorb the hot melt generated at the time of recording in the hollow portion, and it is possible to suppress the adhesion of scum to the thermal head. The mixing ratio of the developer and the sulfonamide derivative used in the present invention is as follows:
When the ratio is in the range of 1: 0.1 to 1: 3, the object of the present invention is better achieved, which is preferable. When the compounding ratio of the sulfonamide derivative to the developer is 0.1 or less, the effect of improving the color sensitivity is small, and when it is 3 or more, the adhesion of scum and sticking during recording tend to increase, Some wiping is observed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In order to produce the thermosensitive recording medium of the present invention, various known production methods can be used. Specifically, for example, the hollow polymer particles having a specific structure used in the present invention are dispersed together with a binder, and the dispersion is applied to a support and dried to form an intermediate layer. next,
A dispersion in which a basic colorless leuco dye and an organic developer are respectively dispersed together with a binder is mixed, and a filler or other necessary additive is added to prepare a thermosensitive coloring layer coating material. By forming a coloring layer, the thermosensitive recording medium of the present invention can be manufactured. The above-mentioned organic developer, dye, and materials to be added as necessary are pulverized to a particle diameter of several microns or less by a pulverizer such as a ball mill, an attritor, or a sand grinder or an appropriate emulsifier, and a binder and Various coating materials are added according to the purpose to form a coating liquid. In the present invention, the specific hollow polymer particles contained in the intermediate layer,
It is also possible to partially replace the pigment. As the pigment, generally known inorganic pigments and organic pigments can be used. Such pigments include alumina, magnesium hydroxide, calcium hydroxide, magnesium carbonate, zinc oxide,
Inorganic pigments such as barium sulfate, silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, aluminum hydroxide, urea-formalin resin,
Styrene-methacrylic acid copolymer, polystyrene resin,
Organic pigments such as amino resin fillers and the like can be mentioned.
Of these various pigments, calcined kaolin is more preferably used because of its excellent heat insulating properties.

The basic colorless dye used in the present invention is not particularly limited, but is preferably a triphenylmethane type, a fluoran type, an azaphthalide type, a fluorene type or the like, and specific examples thereof are shown below. 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (CVL), 3- (4-diethylamino-2-
Methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) Blue-developing dye such as -4-azaphthalide (PB-63), 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilinofluoran (ATP), 3-diethylamino-7- Green coloring dyes such as anilinofluoran (GREEN-2) and 3-diethylamino-7-dibenzylaminofluoran (PSD-G); 3-diethylamino-7-dibenzylamino-benzo [a] fluoran (RED -3), 3, 6
-Bis (diethylamino) fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluoran (PSD-O), 3-diethylamino-6-methyl-7-chlorofluoran (PSD-V), 3- Diethylamino-7-chlorofluoran (PSD-HR), 3,
3-bis (1-ethyl-2-methylindol-3-yl) phthalide (indolyl red), rhodamine (o-
Chloroanilino) lactam, rhodamine (p-chloroanilino) lactam, 3-diethylamino-7,8-benzofluoran, 3- (N-ethyl-p-toluidino)-
7-methylfluorane, 3-diethylamino-6,8-
Red-coloring dyes such as dimethylfluoran, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran (S-205), 3- (N-methyl-N-
Cyclohexyl) amino-6-methyl-7-anilinofluoran (PSD-150), 3-diethylamino-6
-Methyl-7-anilinofluoran (ODB), 3-di (n-butyl) amino-6-methyl-7-anilinofluoran (ODB-2), 3-di (n-pentyl) amino-6 -Methyl-7-anilinofluoran, 3-diethylamino-7- (o-chlorophenylamino) fluoran (TH-106), 3-di (n-butyl) amino-7-
(O-chlorophenylamino) fluoran (TH-10
7), 3-diethylamino-7- (o-fluorophenylamino) fluoran, 3-di (n-butyl) amino-
7- (o-fluorophenylamino) fluoran, 3-
(N-ethyl-p-toluidino) -6-methyl-7-anilinofluoran (ETAC), 3- (N-ethyl-p
-Toluidino) -6-methyl-7- (p-toluidino)
Fluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3- (N-methyl-NNn-propylamino) -6-methyl-7-anilinofluoran (P
SD-300), 3-dimethylamino-6-methyl-7
-Anilinofluoran, 3-dibutylamino-6-methyl-7-m-toluidinofluoran, 3- (Nn-hexyl-N-ethyl) amino-6-methyl-7-anilinofluoran , 3- (N-ethyl-N-isobutyl) amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-p-ethoxyanilinofluoran, 3-pyrrolidino-6-methyl -7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 2,2-bis {4- [6 '-(N-cyclohexyl-N-methylamino) -3'-methylspiro [Phthalide-3,9'-xanthen-2'-ylamino] phenyl} propane, 2-anilino-3-methyl-
6-N-ethyl-N-tetrahydrofurfurylaminofluoran (CF-51), 2,4-dimethyl-6-
[(4-dimethylamino) anilino] -fluoran (P
SD-500), 3-diethylamino-7- (3'-trifluoromethylphenyl) aminofluoran (BLA
CK100), 3-dipentylamino-7- (3'-trifluoromethylphenyl) aminofluoran (H70
01) and the like, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6,7-tetrachloro Phthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2
-Yl] -4,5,6,7-tetrachlorophthalide,
3,3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3-p- (p-dimethylaminoanilino) Anilino-6-methyl-7-chlorofluoran, 3
-P- (p-chloroanilino) anilino-6-methyl-
Dyes having an absorption wavelength in the near infrared region, such as 7-chlorofluorane and 3,6-bis (dimethylamino) fluorene-9-spiro-3 ′-[6′-dimethylamino] phthalide, are exemplified. Of course, the present invention is not limited to these, and two or more of them can be used in combination, if necessary. Among them, 3-di (n-butyl) amino-6-methyl -7-anilinofluoran is preferably used, and various pigments can be used in the thermosensitive coloring layer, for example, kaolin, clay, calcium carbonate, calcined clay, calcined kaolin, aluminum hydroxide, oxide Inorganic pigments such as titanium, diatomaceous earth, particulate anhydrous silica, activated clay, styrene microballs, nylon powder, polyethylene powder,
Organic pigments such as urea / formalin resin fillers and raw starch particles are exemplified. Various auxiliary agents can be added to the heat-sensitive coloring layer as needed, for example, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, fatty acid metal salts, and stearin. Zinc acid, calcium stearate, polyethylene wax,
Waxes such as carnauba wax, paraffin wax and ester wax, antifoaming agents, coloring dyes and the like are appropriately added.

In the present invention, it is possible to add a preservability improver to the thermosensitive coloring layer. Examples of such a preservability improver include the following. 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2,
2′-methylenebis (4-ethyl-6-tert-butylphenol), 2,2′-ethylidenebis (4,6-di-
tert-butylphenol), 4,4′-thiobis (2-
Methyl-6-tert-butylphenol), 4,4′-butylidenebis (6-tert-butyl-m-cresol),
1- [α-methyl-α- (4′-hydroxyphenyl)
Ethyl] -4- [α ′, α′-bis (4 ″ -hydroxyphenyl) ethyl] benzene, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,3-tris (2-methyl-4
-Hydroxy-5-tert-butylphenyl) butane;
4,4′-thiobis (3-methylphenol), 4,
4'-dihydroxy-3,3 ', 5,5'-tetrabromodiphenylsulfone, 4,4'-dihydroxy-3,
3 ′, 5,5′-tetramethyldiphenyl sulfone,
2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,
5-dichlorophenyl) propane, 2,2-bis (4-
Hindered phenol compounds such as hydroxy-3,5-dimethylphenyl) propane, 1,4-diglycidyloxybenzene, 4,4′-diglycidyloxydiphenylsulfone, 4-benzyloxy-4 ′-(2-methylglycidyl) Oxy) diphenyl sulfone, diglycidyl terephthalate, cresol novolak type epoxy resin,
Epoxy compounds such as phenol novolak type epoxy resin and bisphenol A type epoxy resin, N, N'-di-
2-naphthyl-p-phenylenediamine, sodium or polyvalent metal salts of 2,2′-methylenebis (4,6-di-tert-butylphenyl) phosphate, bis (4-ethyleneiminocarbonylaminophenyl) methane, and the like. Can be

In the heat-sensitive recording medium of the present invention, as a binder used for the intermediate layer and the heat-sensitive coloring layer, a commonly used emulsion of a water-soluble polymer or a hydrophobic polymer can be appropriately used. As a specific example,
Cellulose derivatives such as polyvinyl alcohol, polyvinyl acetal, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, etc., starch and its derivatives, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylate copolymer, acrylamide / acrylate / Methacrylic acid copolymer, styrene / maleic anhydride copolymer alkaline salt, isobutylene / maleic anhydride copolymer alkaline salt, polyacrylamide, sodium alginate, gelatin, casein and other water-soluble polymers, polyvinyl acetate, polyurethane , Styrene / butadiene copolymer, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, It can be used styrene / butadiene / emulsion of a hydrophobic polymer such as an acrylic copolymer. Polyvinyl alcohol is most commonly used, for example, because the desensitization of color development sensitivity is small. The hollow polymer particles having a specific structure contained in the intermediate layer of the present invention, the type and amount of the pigment, the binder, and other various components are determined according to the required performance and recording suitability, but usually,
The total amount of the hollow polymer particles and the pigment is 70 to 90 in the total solid content.
% By weight and the binder is suitably from 10 to 30% by weight.
The coating amount of the intermediate layer is generally ² to 20 g / m ² , preferably about 4 to 10 g / m ² .

The amounts of the organic developer and leuco dye contained in the thermosensitive coloring layer of the present invention and the types and amounts of other various components are determined according to the required performance and recording suitability. Organic developer 1 to 8 per part
Parts and 1 to 20 parts of a filler, and the binder is suitably used in an amount of 10 to 25% based on the total solid content. As the support used for the thermosensitive recording medium of the present invention, any support such as paper, synthetic paper, plastic film, and nonwoven fabric can be used. Further, the heat-sensitive recording medium of the present invention may be provided with an overcoat layer containing a water-soluble polymer and a pigment as main components on the heat-sensitive coloring layer for the purpose of enhancing the storage stability, or formed of a water-soluble polymer on the back surface of the support. A back coat layer can be provided. In the heat-sensitive recording medium of the present invention, the method for forming the intermediate layer and the color-forming layer is not particularly limited, and can be formed according to well-known conventional techniques, for example, an air knife coater, a rod blade coater, a bill blade coater, and a roll. An off-machine coating machine or an on-machine coating machine provided with various coaters such as a coater is appropriately selected and used. In addition, after coating and drying the intermediate layer or the thermosensitive coloring layer, each layer may be subjected to a smoothing treatment such as super calendering as necessary.

[0018]

EXAMPLES Hereinafter, production examples of the hollow polymer particles used in the present invention and the present invention will be described with reference to Examples.
In the description, parts and% are based on weight. [Production Example 1 of Hollow Polymer Particles] Monomer mixture (a) 1 for forming a nuclear polymer, comprising 60% of methyl methacrylate (MMA), 5% of butyl acrylate (BA) and 35% of methacrylic acid (MAA) Parts, emulsifier (DBS)
005 parts and 0.8 parts of ion-exchanged water were mixed with stirring to prepare an emulsion (a). Separately, MMA 70%, B
An emulsion (b) was prepared by mixing 10 parts of a core polymer-forming monomer mixture (b) consisting of 10% of AA and 20% of MAA, 0.05 parts of an emulsifier (DBS) and 8 parts of ion-exchanged water with stirring. . In addition, MMA 78%, BA 16%,
Then, 25 parts of a monomer (c) for forming an intermediate layer polymer composed of 6% of MAA, 0.1 part of an emulsifier (DBS) and 35 parts of ion-exchanged water were mixed with stirring to prepare an emulsion (c). Further, 36.9 parts of styrene (ST), 0.3 part of emulsifier (DBS) and 16 parts of ion-exchanged water were mixed with stirring to prepare an emulsion (d) for forming an outer layer polymer. ST96.9% and MAA3.1%
Consisting of a monomer mixture (d) 3 for forming an outermost layer polymer
Emulsion (e) was prepared by mixing 8.1 parts, 0.3 part of emulsifier (DBS) and 16 parts of ion-exchanged water with stirring.

In a reactor equipped with a stirrer, a reflux condenser, a thermometer, and a separating funnel, 2.8 parts of ion-exchanged water, 0.04 parts of an acrylic seed latex having a particle diameter of 35 nm and a solid concentration of 12% ( (In terms of solid content), and the temperature was raised to 80 ° C. Then, 0.17 parts of a 3% aqueous solution of potassium persulfate (KPS) was added from a separating funnel, and the emulsion (a) was added continuously over 4 hours, and then 1 part of the emulsion was further added.
Polymerization was carried out for an hour to obtain a nuclear polymer emulsion. The polymer conversion of the monomer mixture (a) was 99%. Next, 28 parts of ion-exchanged water and 1.7 parts of a 3% KPS aqueous solution were added, and then the emulsion (b) was continuously added to the reactor over 3 hours. After the addition, the mixture was further polymerized for 2 hours to form an outer layer polymer. The polymerization conversion of the monomer mixture (b) was 99%.

Further, 240 parts of ion-exchanged water, KPS 3%
After the addition of 6.7 parts of the aqueous solution, the emulsion (c) was continuously added to the reactor over 4 hours. After the addition, the mixture was further polymerized for 2 hours to form an intermediate layer polymer. The polymerization conversion of the monomer mixture (c) was 99%. In addition, 8
After the temperature was raised to 5 ° C. and 6.7 parts of a 3% KPS aqueous solution was added, the emulsion (d) was continuously added to the reactor over 1.5 hours. After the addition, the mixture was further polymerized for 1 hour to form an outer layer polymer. The polymerization conversion of the monomer mixture (d) was 99%.

To the latex containing the polymer particles obtained above, 9 parts of a 10% aqueous solution of sodium hydroxide was added dropwise from a separating funnel, and then the base treatment was carried out for 30 minutes by heating at 85 ° C. for 30 minutes. At this stage, a part of latex is collected,
The pH of the latex measured at room temperature was 8.7. Next, 10 parts of a 3% aqueous solution of KPS was added, and then emulsion (e) was continuously added to the reactor over 1.5 hours. After the addition, the mixture was further polymerized for 2 hours to obtain a latex containing polymer particles in which the outermost layer polymer was formed. The polymer conversion of the monomer mixture (e) was 99%. Next, the latex containing the above polymer particles was dried with a spray drier having an inlet temperature of 160 ° C. (the outlet temperature was 60 ° C.) to obtain polymer particles. FIG. 2 shows a scanning electron micrograph (SEM) of the obtained polymer particles. When the shape of the obtained polymer particles was observed by SEM, a part of the spherical particles having an average maximum diameter of 890 nm was bowl-shaped particles forming a concave portion, and the average diameter of the opening of the concave portion was 690 nm. Met.

[Production Example 2 of Hollow Polymer Particles] The amount of the acrylic seed latex used was set to 0.0048 parts, the amount of the monomer mixture (a) for forming a nucleus polymer was set to 0.12 parts, and the core was prepared. The composition of (b) of the monomer mixture for forming a polymer for
Polymer particles were produced in the same manner as in Reference Example 1, except that MA was 60%, BA was 10%, and MAA was 30%, and the amounts used were 3 parts. The product was bowl-shaped particles in which part of spherical particles having an average maximum diameter of 1390 nm formed a concave portion, and the diameter of the opening was 1100 nm.

Example 1 (Formation of Intermediate Layer) Hollow polymer particles prepared in Production Example 1 100 parts Styrene / butadiene copolymer latex (solid content: 48%) 11 parts 10% aqueous polyvinyl alcohol solution 5 parts Water 150 parts The above composition was mixed to obtain an intermediate layer coating liquid. The coating liquid application amount after drying fine paper having a basis weight of 50 g / m ² and was applied and dried such that the 6 g / m ^2. (Production of a heat-sensitive layer coating liquid) Liquid A (developing agent dispersion liquid) 4-hydroxy-4'-n-propoxydiphenylsulfone 6.0 parts 10% aqueous polyvinyl alcohol solution 18.8 parts Water 11.2 parts Liquid B ( Dye dispersion liquid) 3-N-n-dibutylamino-6-methyl-7-anilinofluorane 2.0 parts 10% aqueous polyvinyl alcohol solution 4.6 parts Water 2.6 parts Liquid C (sensitizer dispersion liquid) P-Toluenesulfonamide 4.0 parts 10% aqueous polyvinyl alcohol solution 5.0 parts Water 3.0 parts Each liquid having the above composition was ground by a sand grinder to an average particle diameter of 1 micron. Subsequently, the dispersion liquid was mixed at the following ratio to obtain a coating liquid. Liquid A 36.0 parts Liquid B 9.2 parts Liquid C 12.0 parts Kaolin clay (50% dispersion) 12.0 parts Each of the above coating liquids is applied to one surface of a 50 g / m ² base paper 6.0.
g / m < ² > and dried, and this body was treated with a super calender so as to be smooth for 200 to 600 seconds to prepare a heat-sensitive recording sheet.

Example 2 A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that the composition of the coating solution was changed as follows. Solution C (sensitizer dispersion) P-toluenesulfonamide 8.0 parts 10% aqueous polyvinyl alcohol solution 10.0 parts Water 6.0 parts

Example 3 In the preparation of a coating solution, the P-
A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that O-toluenesulfonamide was used instead of toluenesulfonamide. Example 4 A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that P-toluenesulfonamide in Solution C was changed to O-toluenesulfonamide in the preparation of the coating solution. Example 5 A heat-sensitive recording sheet was obtained in the same manner as in Example 1, except that the formulation was as follows in the preparation of the coating liquid for the intermediate layer. Hollow polymer particles prepared in Production Example 2 50 parts Calcined kaolin 50 parts Styrene / butadiene copolymer latex (solid content: 48%) 11 parts 10% aqueous polyvinyl alcohol solution 5 parts Water 150 parts

Example 6 A heat-sensitive recording sheet was obtained in the same manner as in Example 1, except that the composition of the coating solution was changed as follows. Liquid C (sensitizer dispersion liquid) P-toluenesulfonamide 0.5 part 10% aqueous polyvinyl alcohol solution 0.63 part water 0.375 part [Example 7] In the preparation of the coating liquid, the composition of liquid C is as follows. A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that the above conditions were changed. Solution C (sensitizer dispersion) P-toluenesulfonamide 20 parts 10% aqueous polyvinyl alcohol solution 25 parts Water 15 parts

[Comparative Example 1] In the preparation of the coating solution, 4
A heat-sensitive recording sheet was obtained in the same manner as in Example 1, except that -hydroxy-4'-n-propoxydiphenylsulfone was replaced by 4,4'-isopropylidenediphenol. [Comparative Example 2] In the preparation of a coating solution, 4-hydroxy-
Example 1 except that 4'-n-propoxydiphenylsulfone was replaced by 2,4-dihydroxydiphenylsulfone
A heat-sensitive recording sheet was obtained in the same manner as described above. [Comparative Example 3] In the preparation of a coating solution, 4-hydroxy-
A heat-sensitive recording sheet was obtained in the same manner as in Example 1, except that 4'-n-propoxydiphenylsulfone was replaced with 4-hydroxy-4'-isopropoxydiphenylsulfone. Comparative Example 4 A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that P-toluenesulfonamide in Solution C was changed to parabenzylbiphenyl in the preparation of the coating solution.

Comparative Example 5 A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that the composition of the coating solution for the intermediate layer was changed as follows in the preparation of the coating solution. Calcined kaolin 100 parts Styrene-butadiene copolymer latex (solid content: 48%) 11 parts 10% aqueous solution of polyvinyl alcohol 5 parts Water 150 parts [Comparative Example 6] In the preparation of the coating liquid, the composition of the intermediate layer coating liquid was as follows. A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that the above conditions were changed. Polystyrene 50 parts Calcined kaolin 50 parts Styrene / butadiene copolymer latex (solid content: 48%) 11 parts 10% aqueous polyvinyl alcohol solution 5 parts Water 150 parts [Comparative Example 7] In the preparation of the coating liquid, the mixture of the intermediate layer coating liquid was mixed. A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that the procedure was as described below. Hollow fine particles 100 parts Styrene / butadiene copolymer latex (solid content: 48%) 11 parts 10% aqueous polyvinyl alcohol solution 5 parts Water 150 parts [Comparative Example 8] Example 1 except that no intermediate layer was provided in the preparation of the coating solution. A heat-sensitive recording sheet was obtained in the same manner as described above. Table 1 summarizes the results of quality tests performed on the thermal recording papers obtained in the above Examples and Comparative Examples.

[0029]

[Table 1]

The quality test items in Table 1 are as follows. (1) Color density: Matsushita Densen Co., Ltd.-Thermal facsimile UF-
Using 1000, applied energy 0.58mj / do
t, the image density recorded with a pulse width of 0.97 milliseconds was measured with a Macbeth densitometer. (2) Heat-resistant ground color: An uncolored portion was left in an atmosphere of 70 ° C. for 24 hours and measured with a Macbeth densitometer. (3) Powdering: The sample which had been left in an atmosphere of 105 ° C. and had developed the entire surface was allowed to stand at room temperature for one week, and it was visually confirmed whether white crystals appeared. (4) Color density over time: The uncolored sample was allowed to stand at room temperature for 3 months, and then was manufactured by Matsushita Densen Co., Ltd.—thermosensitive facsimile UF-1.
000 and an applied energy of 0.58 mj / do
t, the image density recorded with a pulse width of 0.97 milliseconds was measured with a Macbeth densitometer. (5) Stick; Matsushita Densen Thermal Facsimile UF-
22, GII communication mode, (test environment: 22 ° C, 65
%), The image recorded was visually observed, and based on the degree of line omission caused by the stick, the evaluation was evaluated as ○: good, Δ: slightly poor, x: poor. (6) Scrap: Thermal facsimile UF-60 copy mode manufactured by Matsushita Densen Co., Ltd., 20 vertical stripe originals (B4) were recorded, and the amount of scrap adhering to the thermal head was visually observed. ○: good, Δ: slightly poor, X: Evaluated as poor.

[0031]

Advantages of the present invention include the following. (1) Because of its excellent thermal response, a clear high-density image can be obtained even at high speed and high density recording. (2) The heat resistance of the ground color portion is excellent. (3) There is no occurrence of dusting or a decrease in color density over time. (4) Less scum and sticking occur during recording.

[Brief description of the drawings]

FIG. 1 schematically shows an example of a hollow polymer particle used in the present invention, and shows a cross section perpendicular to an opening surface and passing through the center of the particle.

FIG. 2 shows a scanning electron micrograph (SEM) of the hollow polymer particles obtained in Production Example 1.

[Explanation of symbols]

p The outer circle of the double circle D The maximum diameter of the outer circle p of the double circle H The length of the perpendicular drawn from any point on the outer arc to the straight line m The maximum value of Hmax H d The double at the opening Equivalent radius not including the thick part inside the circle

[Procedure amendment]

[Submission date] November 19, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

In a reactor equipped with a stirrer, a reflux condenser, a thermometer, and a separating funnel, 2.8 parts of ion-exchanged water, 0.04 parts of an acrylic seed latex having a particle diameter of 35 nm and a solid concentration of 12% ( (In terms of solid content), and the temperature was raised to 80 ° C. Then, 0.17 parts of a 3% aqueous solution of potassium persulfate (KPS) was added from a separating funnel, and the emulsion (a) was added continuously over 4 hours, and then 1 part of the emulsion was further added.
Polymerization was carried out for an hour to obtain a nuclear polymer emulsion. The polymer conversion of the monomer mixture (a) was 99%. Next, 28 parts of ion-exchanged water and 1.7 parts of a 3% KPS aqueous solution were added, and then the emulsion (b) was continuously added to the reactor over 3 hours. After the addition, the mixture was further polymerized for 2 hours to form a core layer polymer. The polymerization conversion of the monomer mixture (b) was 99%.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0025

[Correction method] Change

[Correction contents]

Example 3 In the preparation of the coating liquid, the P
A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that O-toluenesulfonamide was used instead of -toluenesulfonamide. Example 4 A heat-sensitive recording sheet was obtained in the same manner as in Example 2 , except that P-toluenesulfonamide in Solution C was changed to O-toluenesulfonamide in the preparation of the coating solution. Example 5 A heat-sensitive recording sheet was obtained in the same manner as in Example 1 except that the composition was changed as follows in the preparation of the coating liquid for the intermediate layer in the preparation of the coating liquid. Hollow polymer particles prepared in Production Example 2 50 parts Calcined kaolin 50 parts Styrene / butadiene copolymer latex (solid content: 48%) 11 parts 10% aqueous polyvinyl alcohol solution 5 parts Water 150 parts

Claims (3)

[Claims] 1. A thermosensitive recording medium comprising a support and an intermediate layer provided thereon and a thermosensitive coloring layer containing a colorless or pale basic colorless dye and an organic developer as main components. Containing a hollow polymer particle having an opening obtained by cutting a part of the hollow polymer particle in a plane, wherein the heat-sensitive color-forming layer is 4-hydroxy-4′-n- as an organic developer.
A heat-sensitive recording material containing propoxydiphenyl sulfone and a sulfonamide derivative represented by the following general formula (I). General formula (I) (In the formula, Z represents a lower alkyl group having 1 to 6 carbon atoms or an electron-withdrawing group. N represents an integer of 0 to 2.) 2. The hollow polymer particles contained in the intermediate layer have a bowl-like shape having an opening obtained by cutting a part of the spherical hollow polymer particles in a plane, and have a cut cross section. A vertical cross section passing through the center of the spherical hollow polymer particle has a shape obtained by cutting a part of a double circle by a straight line, and the maximum value of the perpendicular length drawn from the arc outside the cross section to the straight line is the above-mentioned two. 2. The thermosensitive recording medium according to claim 1, wherein the thermosensitive recording medium is equal to or larger than half of the maximum diameter of a circle outside the heavy circle. 3. The method according to claim 1, wherein the mixing ratio of 4-hydroxy-4'-n-propoxydiphenyl sulfone and the sulfonamide derivative is 1: 0.1 to 1: 3.
Or the heat-sensitive recording material according to 2.