JPH0717131A - Thermal recording - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a heat-sensitive recording material which is excellent in storability of a recorded image with respect to chemicals such as oil and plasticizer and excellent in light resistance. [Structure] In a heat-sensitive recording material in which a heat-sensitive recording layer and a protective layer containing an ultraviolet absorbent are sequentially provided on a support, a hydrophobic ultraviolet absorbent having an average particle diameter of 0.3 μm or less is added to the protective layer in a total solid amount. 1 to 20% by weight of the thermal recording material contained in the protective layer.

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 is excellent in color developability, background stability, recorded image storage characteristics, and particularly light resistance.

[0002]

2. Description of the Related Art A heat-sensitive recording material in which a plurality of color-forming substances are brought into contact with each other by heat to obtain a recorded image is well known.
Since such a thermosensitive recording medium is relatively inexpensive, the recording device is compact, and its maintenance is easy, it is used not only as a recording medium for facsimiles and various computers but also in a wide range of fields.

One of the fields of use thereof is, for example, POS.
(Point of sales) Thermal recording labels for systems can be cited, but with the expansion of the systemization, it is attached to products for a long period of time in addition to the conventional food labels that end their mission in a short period of time. There is an increasing use as tag paper used, or as handy terminal paper for collection and delivery, which is often handled outdoors. However, in such applications, it is often exposed to room light or sunlight for a long period of time, which causes the background portion of the thermal recording material to turn yellow, resulting in a marked loss of product image.
Therefore, there is a strong demand for a thermosensitive recording medium that does not cause yellowing of the background portion even after being exposed to room light or sunlight for a long time.

Therefore, for the purpose of preventing yellowing of the background portion due to light, an inorganic pigment having a UV-shielding effect such as zinc oxide or titanium oxide or a hydrophobic and water-soluble UV absorber is used in the heat-sensitive recording layer or the protective layer. The method of adding the above is disclosed in
0-107388, JP-A-60-112487, JP-A-60-125694, JP-A-61-193883.
No. However, since the water-soluble ultraviolet absorber forms ions such as sodium salt in order to solubilize the ultraviolet absorber in water, the thermal head is electrochemically worn. Further, an inorganic pigment having an ultraviolet shielding effect or a hydrophobic ultraviolet absorber finely pulverized to a size of several μm cannot obtain a sufficient effect because the ultraviolet absorption efficiency is poor.
If the amount of use is increased, background fog occurs, or a new defect such as concealing a recorded image and lowering the recording density occurs. In particular, among the inorganic pigments having an ultraviolet shielding effect, there are those that may physically wear the thermal head, and some cannot be contained in the protective layer. Even finely pulverized UV absorbers may cause adhesion of head shavings by being contained in the protective layer, or because these UV absorbers are organic substances, they are easy to use for chemicals such as oils, plasticizers and solvents. And the barrier property is lowered, and as a result, the storability of the recorded image cannot be maintained and the role as a protective layer is not fulfilled.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material having excellent light resistance, which solves the above problems.

[0006]

DISCLOSURE OF THE INVENTION The present inventors have found that a thermosensitive recording medium in which a thermosensitive recording layer and a protective layer containing an ultraviolet absorber are sequentially provided on a support has an average particle diameter of 0.3 μm.
By incorporating a hydrophobic ultraviolet absorber of m or less in the protective layer in an amount of 1 to 20% by weight based on the total solid amount of the protective layer, color development, stability of the background portion, storage characteristics of recorded images, particularly light resistance and head. The inventors have found that a heat-sensitive recording material having excellent matching properties can be obtained, and completed the present invention.

[0007]

In the present invention, the protective layer has an average particle size of 0.3 μm.
The following hydrophobic UV absorbers are contained in the protective layer in a total solid content of 1 to 20:
It is characterized by containing by weight%. By making the ultraviolet absorbent 0.3 μm or less, not only the ultraviolet absorption efficiency is remarkably improved, but also when the protective layer contains this particle size, the recorded image is hardly hidden and the recording density is lowered. I knew I wouldn't come. By setting the content of the above-mentioned specific ultraviolet absorber to 1 to 20% by weight in the total solid content of the protective layer, the ultraviolet absorber which is a soluble component can be dissolved even when it comes into contact with chemicals such as oil, plasticizer and solvent. It has been found that the storage characteristics of the recorded image are maintained, probably because it does not dissolve until it reaches the heat-sensitive recording layer even if it dissolves. If the content of the ultraviolet absorber is less than 1%, the desired light resistance cannot be obtained, and 2
If it exceeds 0%, the ultraviolet absorber is likely to dissolve in a solvent or the like, and the storability of a recorded image is deteriorated.

As the hydrophobic ultraviolet absorber used in the present invention, various known ones can be used, and among them, a benzotriazole type ultraviolet absorber is preferable from the viewpoint of ultraviolet absorption efficiency. Examples of the benzotriazole-based ultraviolet absorber include the following. 2- (2'-hydroxyphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole,
2- (2'-hydroxy-5'-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-
3 ', 5'-di-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'- Hydroxy-3 ', 5'-di-tert
-Butylphenyl) -5-chlorobenzotriazole,
2- (2'-hydroxy-3 ', 5'-di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-3', 5'-di-tert-butylphenyl) -5-
tert-Butylbenzotriazole, 2- (2'-hydroxy-3'-sec-butyl-5'-tert-butylphenyl) -5-tert-butylbenzotriazole, 2- (2'-hydroxy-3 ', 5 ′ -Di-tert-
Amylphenyl) -5-tert-amylbenzotriazole, 2- [2′-hydroxy-3 ′-(3 ″, 4 ″,
5 ", 6" -tetrahydrophthalimido-methyl)-
5'-methylphenyl] benzotriazole, 2-
(2'-hydroxy-5'-tert-octylphenyl)
Benzotriazole, 2- (2'-hydroxy-3'-
sec-Butyl-5'-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-methyl-5'-sec-butylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-
Amylphenyl) -5-methoxybenzotriazole,
2- (2'-hydroxy-3'-tert-amyl-5'-
Phenoxyphenyl) -5-methylbenzotriazole, 2- (2'-hydroxy-5'-n-dodecylphenyl) benzotriazole, 2- (2'-hydroxy-
5'-sec-octyloxyphenyl) -5-phenylbenzotriazole, 2- (2'-hydroxy-3 '
-Tert-amyl-5'-phenylphenyl) -5-methoxybenzotriazole, 2- [2'-hydroxy-
3 ', 5'-bis (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole and the like can be mentioned. Considering the heat resistance of the thermal recording medium among them, the melting point is 1
It is preferably 25 ° C or higher. Further, more preferable is 2- (2′-hydroxyphenyl) benzotriazole, which has a small molecular weight and can contain a large number of mols in the same solid amount.

Other ultraviolet absorbers include salicylic acid type ultraviolet absorbers such as phenyl salicylate, p-tert-butylphenyl salicylate and p-octylphenyl salicylate, 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone. Two
-Hydroxy-4-octyloxybenzophenone, 2
-Hydroxy-4-dodecyloxybenzophenone,
2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone and other benzophenone-based UV absorbers, 2-ethylhexyl -2-cyano-3,3'-diphenyl acrylate, ethyl-2-cyano-3,3'-
Cyanoacrylate UV absorbers such as diphenyl acrylate, bis (2,2,6,6-tetramethyl-4-
Piperidyl) sebacate, succinic acid-bis (2,2,2
6,6-tetramethyl-4-piperidyl) ester, 2
-(3,5-Di-tert-butyl) malonic acid-bis (1,
Examples thereof include hindered amine UV absorbers such as 2,2,6,6-pentamethyl-4-piperidyl) ester. Of course, it is not limited to these, and it is also possible to use two or more kinds in combination if necessary.

The amount of the ultraviolet absorber used cannot be determined unconditionally because it depends on the coating amount of the protective layer, but it is generally preferable that 0.05 to 2.0 g / m ^{2 be} present in the protective layer. The range is preferably 0.2 to 1.0 g / m ² . When the amount of the ultraviolet absorber in the protective layer is less than 0.05 g / m ² , the effect of preventing yellowing of the background portion of the thermosensitive recording material decreases. Further, since the protective layer inevitably exceeds 2.0 g / m ² , the protective layer becomes thick, so that the recording sensitivity is lowered.

As a method for making the ultraviolet absorbent finer, generally, water is used as a dispersion medium, and additives such as a dispersant and an antifoaming agent are added if necessary, and the mixture is stirred and ground by a ball mill, attritor, sand mill or the like. There is a method using a machine, a method of dissolving an ultraviolet absorber in a low boiling point solvent, then emulsifying it, and removing the low boiling point solvent by evaporation. Among them, a sand mill type crusher is preferable, and the average particle diameter of the dispersion medium is preferably 1 mm or less, more preferably 0.5 mm or less.

The heat-sensitive recording system to which the present invention is applied includes, for example, a combination of a basic dye and a color former, a combination of a diazonium salt and a coupler, a combination of a chelate compound of a transition element such as iron and a color former, Examples thereof include a combination of an aromatic isocyanate compound and an imino compound, and a combination of a basic dye and a colorant is preferably used because it has excellent color density and excellent background and recording sensitivity.

As the basic dye, various known colorless or pale basic dyes can be used, and specifically,
For example, 3,3-bis (p-dimethylaminophenyl)-
6-Dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide, 3-diethylamino-7-dibenzylamino-benzo [a ] Blue-coloring dyes such as fluoran, 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilinofluorane, 3
Green color-forming dyes such as diethylamino-7-anilinofluorane and 3-diethylamino-7-dibenzylaminofluorane, 3,6-bis (diethylamino) fluorane-γ-anilinolactam, 3-cyclohexylamino-
6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-
Chlorofluorane, Rhodamine (o-chloroanilino)
Lactam, rhodamine (p-chloroanilino) lactam, 3-diethylamino-7,8-benzofluorane,
Red-coloring dyes such as 3- (N-ethyl-p-toluidino) -7-methylfluorane and 3-diethylamino-6,8-dimethylfluorane, 3- (N-ethyl-N-isoamyl) amino-6. -Methyl-7-anilinofluorane,
3- (N-methyl-N-cyclohexyl) amino-6-
Methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di (n-
Butyl) amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl) amino-6-methyl-7-
Anilinofluorane, 3-diethylamino-7- (o-
Chlorophenylamino) fluorane, 3-di (n-butyl) amino-7- (o-chlorophenylamino) fluorane, 3-diethylamino-7- (o-fluorophenylamino) fluorane, 3-di (n-butyl) amino-
7- (o-fluorophenylamino) fluorane, 3-
(N-ethyl-p-toluidino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3- (N -Ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-anilinofluorane,
3- (N-methyl-Nn-propylamino) -6-methyl-7-anilinofluorane, 3-dimethylamino-
6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-m-toluidinofluorane, 3
-(N-n-hexyl-N-ethyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-)
Isobutyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-p-ethoxyanilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3- Piperidino-6-methyl-7-anilinofluorane, 2,2-bis {4-
[6 '-(N-cyclohexyl-N-methylamino)-
3'-methylspiro [phthalide-3,9'-xanthen-2'-ylamino] phenyl} propane, 3-diethylamino-7- (3'-trifluoromethylphenyl)
Black coloring dyes such as aminofluorane, 3,3-bis [1
-(4-Methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6,7-
Tetrachlorophthalide, 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-chlorofluorane,
Close to 3-p- (p-chloroanilino) anilino-6-methyl-7-chlorofluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide, etc. Dyes that have absorption wavelength in the infrared region. Of course, it is not limited to these, and two or more kinds may be used in combination as required.

Various materials are known as a colorant used in combination with the basic dye as described above. For example, activated clay, attapulgite, colloidal silica, inorganic acidic substances such as aluminum silicate, 4,4'- Isopropylidene diphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, 4 -Benzyl hydroxybenzoate, 4,
4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4 '
-Isopropoxydiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone,
3,4-dihydroxyphenyl-4'-methylphenyl sulfone, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, bis (p-hydroxyphenyl) Butyl acetate, methyl bis (p-hydroxyphenyl) acetate, 1,1-bis (4-hydroxyphenyl)-
1-phenylethane, 1,4-bis [α-methyl-α-
(4'-hydroxyphenyl) ethyl] benzene, 1,
3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-te
rt-octylphenol), 2,2'-thiobis (4-
tert-octylphenol) and other phenolic compounds,
Thiourea compounds such as N, N'-di-m-chlorophenylthiourea, p-chlorobenzoic acid, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4-
Aromatic carboxylic acids such as [3- (p-tolylsulfonyl) propyloxy] salicylic acid and 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid, and zinc, magnesium and aluminum of these aromatic carboxylic acids. , Salts with polyvalent metals such as calcium, titanium, manganese, tin and nickel, as well as organic acid substances such as antipyrine complexes of zinc thiocyanate and complex zinc salts of terephthalaldehyde acid with other aromatic carboxylic acids. It is illustrated. In particular, when 1,1-bis (4-hydroxyphenyl) cyclohexane, 4-hydroxy-4′-isopropoxydiphenylsulfone or bis (3-allyl-4-hydroxyphenyl) sulfone is used, the recorded image is generally preserved. It is preferably used because it has excellent properties.
The use ratio of the basic dye and the colorant is appropriately selected according to the type of the basic dye or the colorant used, and is not particularly limited, but generally 1 part by weight of the basic dye is used. On the other hand, about 1 to 50 parts by weight, preferably about 2 to 10 parts by weight, of the coloring agent is used.

A coating material for a heat-sensitive recording layer containing these substances is
Generally, water is used as a dispersion medium, and a ball mill, attritor,
It is prepared by dispersing the dye and the coloring agent together or separately by a stirring and crushing machine such as a sand mill. In the coating liquid, as a binder, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, silicon modified polyvinyl alcohol, diisobutylene. Maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion, urea resin, melamine resin, At least one kind of amide resin, polyurethane resin and the like is blended in the range of about 5 to 30% by weight based on the total solid content of the recording layer.

If desired, various auxiliaries can be added to the coating liquid. For example, kaolin, clay, calcium carbonate, calcined clay, calcined kaolin, titanium oxide,
Inorganic pigments such as diatomaceous earth, anhydrous silica particles, activated clay, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, organic starch particles, raw dioctyl sodium sulfosuccinate, sodium dodecylbenzenesulfonate, lauryl Dispersing agents for sodium alcohol sulfate, fatty acid metal salts, etc., waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, defoaming agents,
A coloring dye or the like is appropriately added.

Further, a sensitizer may be used in combination depending on the purpose. Specific examples of the sensitizer include stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylenebisstearic acid amide,
Behenic acid amide, methylenebisstearic acid amide, N
-Methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthylbenzyl ether, m-terphenyl, dibenzyl oxalate. , Oxalic acid-di-p-methylbenzyl, oxalic acid-di-p-
Chlorobenzyl, p-benzylbiphenyl, p-tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ethane,
1,2-di (4-methoxyphenoxy) ethane, 1,2
-Di (4-chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2-
(3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetotoluidide, p-acetophenetizide, N-acetoacetyl-p-toluidine, di (β-biphenyl) Examples include ethoxy) benzene, p-di (vinyloxyethoxy) benzene and 1-isopropylphenyl-2-phenylethane. The amount of these sensitizers used is not particularly limited, but it is generally desirable to adjust the amount within the range of about 4 parts by weight or less relative to 1 part by weight of the color developing agent.

In the present invention, it is possible to add a storability improver in the heat-sensitive recording layer. Examples of such storability improvers 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'-butylidene bis (6-tert-butyl-m-cresol), 1- [α-methyl-α- (4'-hydroxyphenyl) ethyl] -4- [α ', α'-bis (4 "-hydroxy) Phenyl) ethyl] benzene, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butyl) Phenyl) butane, 4,4′-thiobis (3-methylphenol),
4,4'-dihydroxy-3,3 ', 5,5'-tetrabromodiphenyl sulfone, 4,4'-dihydroxy-
3,3 ′, 5,5′-tetramethyldiphenyl sulfone, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-)
Hindered phenol compounds such as 3,5-dichlorophenyl) propane and 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 1,4-diglycidyloxybenzene, 4,4′-diglycidyloxy Diphenyl sulfone, 4-benzyloxy-4 '-(2-
Epoxy compounds such as methylglycidyloxy) diphenyl sulfone, diglycidyl terephthalate, cresol novolac type epoxy resin, phenol novolac type epoxy resin, bisphenol A type epoxy resin, N, N ′
-Di-2-naphthyl-p-phenylenediamine, 2,
Examples thereof include sodium or polyvalent metal salt of 2'-methylenebis (4,6-di-tert-butylphenyl) phosphate, bis (4-ethyleneiminocarbonylaminophenyl) methane and the like. Among them, 1,1,3-tris (2-
Methyl-4-hydroxy-5-cyclohexylphenyl) butane is preferably used because it has an excellent effect on water resistance and is less likely to cause background fog.

The heat-sensitive recording material of the present invention is characterized by containing a hydrophobic ultraviolet absorber having an average particle diameter of 0.3 μm or less on the heat-sensitive recording layer. It is also possible to add a binder composed of a water-soluble or water-dispersible polymer compound, and specific examples of such a binder include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, and carboxy. Modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, silicon modified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid Copolymer salt, styrene Examples thereof include butadiene copolymer emulsion, urea resin, melamine resin, amide resin, polyurethane resin, etc. Among them, acetoacetyl group-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol must form a strong film. It is particularly preferably used because it can

A pigment may be added to the protective layer, if necessary, in order to improve printability and sticking. Specific examples thereof include calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc,
Examples thereof include inorganic pigments such as kaolin, clay, calcined kaolin and colloidal silica, organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, and raw starch particles. The method for preparing the coating liquid for forming the protective layer is not particularly limited, and is generally prepared by mixing water as a dispersion medium with a fine ultraviolet absorber, a binder, a pigment added as necessary, and the like.

Further, in the coating liquid for protective layer, if necessary, a lubricant such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, etc., and a surfactant (dispersion such as sodium dioctylsulfosuccinate) (dispersion). Agent, wetting agent), defoaming agent,
Various auxiliaries such as water-soluble polyvalent metal salts such as potassium alum and aluminum acetate may be appropriately added. Further, in order to further improve the water resistance, glyoxal, boric acid,
A curing agent such as dialdehyde starch or an epoxy compound may be used in combination, and if necessary, a microencapsulated UV absorber or the like may be used in combination.

The method for forming the heat-sensitive recording layer and the protective layer is not particularly limited, and suitable examples include air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating and die coating. The coating liquid for recording layer is applied and dried on the support by the coating method, and then the coating liquid for protective layer is applied and dried on the recording layer. The support may be appropriately selected from paper, plastic film, synthetic paper, non-woven fabric, metal deposit, etc., and used.
The coating amount of the recording layer coating liquid is 2 to 12 g / dry weight.
m ² , preferably about 3 to 10 g / m ² , and the coating amount of the protective layer coating solution is adjusted to a dry weight of 0.1 to 20 g / m ² , preferably about 0.5 to 10 g / m ^2. It

If necessary, a protective layer may be provided on the back side of the thermosensitive recording medium to further improve the storage stability. Furthermore, an undercoat layer may be provided on the support, smoothing treatment such as super calendering may be applied after coating each layer, or an adhesive label may be applied to the back surface of the recording material to form an adhesive label, magnetic recording layer or printing. Various known techniques in the field of producing a heat-sensitive recording material such as a coating layer for coating and a thermal transfer recording layer may be added as necessary.

It is desirable that the surface of the protective layer be treated so that the Bekk smoothness (according to JIS P 8119) is 300 seconds or longer, preferably 500 seconds or longer. As a smoothing device used at that time, a super calender or a gloss calender in which an elastic roll and a metal roll are combined is used. As the elastic roll, the Shore D hardness specified by ASTM D-2240 is 60 to 90 °. It is preferred to use elastic rolls which are preferably at 70-90 °. The nip linear pressure during the treatment should be appropriately selected depending on the hardness of the elastic roll to be used and the desired smoothness.
It is desirable to adjust in the range of 300 kg / cm.

[0025]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, "part" and "%" in an example respectively show "weight part" and "weight%" unless there is particular notice.

Example 1 Preparation of solution A A composition consisting of 10 parts of 3-diethylamino-7- (3'-trifluoromethylphenyl) aminofluorane, 5 parts of a 5% aqueous solution of methylcellulose and 40 parts of water was averaged by a sand mill. It was pulverized to a diameter of 1.5 μm.

Preparation of Solution B A composition consisting of 30 parts of 1,1-bis (4-hydroxyphenyl) cyclohexane, 5 parts of a 5% aqueous solution of methylcellulose, and 80 parts of water was sand milled until the average particle size reached 1.5 μm. Crushed.

Preparation of Solution C A composition consisting of 20 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water was pulverized with a sand mill until the average particle size became 1.5 μm. did.

Formation of Recording Layer 55 parts of solution A, 115 parts of solution B, 80 parts of solution C, 80 parts of 10% aqueous solution of polyvinyl alcohol, and calcium carbonate 3
The coating liquid obtained by mixing and stirring 5 parts was applied and dried on one surface of a high-quality paper of 60 g / m ² so that the coating amount after drying was 6 g / m ² to form a heat-sensitive recording layer.

Preparation of Solution D 10 parts of 2- (2′-hydroxy-5′-methylphenyl) ventriazole, 5% aqueous solution of methylcellulose 5
Parts and 40 parts of water were pulverized with a sand mill until the average particle size became 0.12 μm.

Formation of protective layer 43 parts of D liquid, 125 parts of 10% aqueous solution of polyvinyl alcohol modified with acetoacetyl group, kaolin [trade name: UW-
90, manufactured by EMC] 29 parts, 30% of zinc stearate
A coating solution for a protective layer obtained by mixing and stirring a composition comprising 6 parts of a dispersion liquid and 30 parts of water was coated and dried on the recording layer so that the coating amount after drying was 6 g / m ^2, and Super calendering was performed to obtain a heat sensitive recording material.

Example 2 Example 1 was repeated except that in the preparation of solution D of Example 1, 2- (2'-hydroxy-5'-methylphenyl) bentriazole was pulverized to an average particle size of 0.23 μm. A thermal recording material was obtained in the same manner.

Example 3 In the preparation of liquid D of Example 1, 2- (2'-hydroxy-3'-tert- was used instead of 10 parts of 2- (2'-hydroxy-5'-methylphenyl) ventriazole. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 10 parts of butyl-5'-methylphenyl) -5-chlorobenzotriazole was used and the mixture was pulverized until the average particle size became 0.17 µm.

Comparative Example 1 As in Example 1 except that D-solution of Example 1 was prepared, 2- (2'-hydroxy-5'-methylphenyl) bentriazole was pulverized to an average particle size of 1.5 μm. A thermal recording material was obtained in the same manner.

Comparative Example 2 Example 1 was repeated except that in the preparation of solution D of Example 1, 2- (2'-hydroxy-5'-methylphenyl) bentriazole was ground to an average particle size of 0.56 μm. A thermal recording material was obtained in the same manner.

Comparative Example 3 In the formation of the protective layer of Example 1, the amount of liquid D used was 70
Parts, and a thermosensitive recording medium was obtained in the same manner as in Example 1 except that the amount of kaolin used was changed to 24 parts.

The following six evaluation tests were conducted on the thus obtained six kinds of thermal recording materials, and the results are shown in [Table 1] and [Table 2]. [Evaluation] [Coloring property] A thermosensitive evaluation machine [trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.] was used to color each thermosensitive recording medium at an applied energy of 0.45 mJ / dot, and the color density of the recorded image obtained. Was measured in a visual mode with a Macbeth densitometer [RD-914 type, manufactured by Macbeth Co.].

[Light Resistance] The initial density of the background portion of the thermal recording material after recording as described above and the density of the background portion after exposure to direct sunlight for 10 days were measured with a Macbeth densitometer (using a blue filter).

[Plasticizer resistance] A wrap film [trade name: KMA-W, manufactured by Mitsui Toatsu Chemicals, Inc.] was wound in three layers on a polycarbonate pipe (40 mmφ pipe), and recording was performed by the above method. A thermosensitive recording medium was placed, and a wrap film was further wound around it in three layers, and the color density after standing at 40 ° C. for 24 hours was measured with a Macbeth densitometer (visual mode) to evaluate the plasticizer resistance. .

[Oil resistance] The oil resistance was evaluated by applying edible oil on the heat-sensitive recording material after recording as described above and measuring the color density after leaving at room temperature for 8 hours with a Macbeth densitometer (visual mode). did.

[Solvent resistance] The surface of the recording paper was wiped with gauze soaked with ethanol, and the fog density was measured with a Macbeth densitometer (visual mode) to evaluate the solvent resistance.

[Head Matching Property] The degree of dirt (head residue) of the thermal head and the recorded image quality after continuous recording of 200 mm were visually evaluated. Evaluation criteria [Head residue] ○: No head residue at all. Δ: There is some head debris. X: Some amount of head debris. [Recording quality] ○: Recording quality is excellent. X: The recording image quality is poor.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

As is apparent from the results of [Table 1] and [Table 2], the thermosensitive recording medium of the present invention is excellent in color density, light resistance of the background portion, chemical resistance, and head matching property. It was an excellent thermosensitive recording medium that also served as a recording medium.

Claims (3)

[Claims] 1. A thermosensitive recording medium comprising a support, on which a thermosensitive recording layer and a protective layer containing an ultraviolet absorber are sequentially provided.
A heat-sensitive recording material, characterized in that a hydrophobic ultraviolet absorber having an average particle diameter of 0.3 μm or less is contained in the protective layer in an amount of 1 to 20% by weight based on the total solid amount of the protective layer. 2. The heat-sensitive recording material according to claim 1, wherein the hydrophobic ultraviolet absorber is a benzotriazole derivative. 3. The heat-sensitive recording material according to claim 2, wherein the heat-sensitive recording layer utilizes a coloring reaction between a colorless or light-colored basic dye and a coloring agent.