JP2000351275A - Heat-sensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly heat-sensitive recording medium having outstanding print color developing properties by using a 4,4'-dihydroxydiphenyl sulfone as a color developer in the heat-sensitive recording layer containing a colorless or paled-colored basic dye and a color developer which develops a color through a chemical reaction with the basic dye and a sensitizer, formed on a support. SOLUTION: This heat-sensitive recording medium uses a 4,4'- dihydroxydiphenyl sulfone as a color developer and a salicylanilide and dibenzyloxalate. In addition, a fatty amide, preferably at least one kind selected from among an amide stearate, an amide N,N'-ethylenebisstearate and an amide palmitate, is added to a heat-sensitive recording 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 using 4,4'-dihydroxydiphenylsulfone as an electron-accepting developer, and more particularly to a heat-sensitive recording material having high sensitivity and excellent printing color development. It is about.

[0002]

2. Description of the Related Art Generally, a thermosensitive recording medium is provided on a support with an electron-donating colorless or light-colored basic dye (hereinafter referred to as a color-forming substance) and an electron-accepting developer (hereinafter referred to as a color-developing substance). ) Is provided with a thermosensitive recording layer. By heating with a thermal head, a hot pen, a laser beam, or the like, the coloring substance and the developing substance react instantaneously to obtain a recorded image, JP-B-43-4160, JP-B-45-14039
Publication No. JP-A-2005-133125 discloses a heat-sensitive recording material.

[0003] Such a thermosensitive recording medium has the advantages that recording can be obtained with a relatively simple apparatus, maintenance is easy, and there is no noise. For example, a measuring recorder, a facsimile, a printer, Computer terminals, labels,
It is used in a wide range of fields such as automatic ticket vending machines such as tickets.

[0004] The heat-sensitive recording layer of a heat-sensitive recording medium that forms an image by heating to form an image contains a color-forming substance and a color-developing substance that reacts with the color-forming substance to form a color when heated. As the coloring substance, for example, a colorless or light-colored leuco dye having a lactone, lactam or spiropyran ring is used, and as the coloring substance, 4,4′-isopropylidene diphenol, 4,4′-dihydroxydiphenyl sulfone, Various acidic substances such as 2,4'-dihydrocosidiphenylsulfone, 4-hydroxy-4'isopropoxydiphenylsulfone and 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone are used.

A color image formed by combining such a color-forming substance and a color-developing substance has been applied to more heat-sensitive recording materials than ever since its color tone is clear. Among these color-developing substances, 4,4'-dihydroxydiphenylsulfone has useful aspects such as high whiteness and clear color development after printing, but has a very high melting point (24
6 ° C.), and therefore has poor thermal responsiveness and low sensitivity, and is inferior in color development in high-speed facsimile and various printers due to recent energy-saving technology. At present, improvements are strongly desired.

In order to improve the color-forming performance, it is common to add a so-called sensitizer such as 2-benzyloxynaphthalene which functions as a melting point depressant for the color-developing substance. Various studies have been made on -benzyloxy-naphthalene, hydroxydiphenylsulfone derivatives, benzyl oxalate derivatives, etc., but at present, sufficient effects have not yet been obtained.

[0007]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a heat-sensitive recording material having high sensitivity and excellent color development by using 4,4'-dihydroxydiphenyl sulfone as a color developing substance. And

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors contain a color-forming substance, a color-developing substance, and a sensitizer that plays a role in accelerating and promoting the color-forming reaction. In the heat-sensitive recording material, 4,
By using 4'-dihydroxydiphenyl sulfone and using salicylanilide and dibenzyl oxalate as sensitizers, it has been found that high sensitivity and excellent print coloring property can be obtained, and the present invention has been achieved.

Further, by adding a fatty acid amide to the heat-sensitive recording layer containing the color-developing substance, it was possible to obtain a heat-sensitive recording material having higher sensitivity and excellent print coloring property.
As fatty acid amides, stearic acid amide, N,
N'-ethylenebisstearic acid amide, palmitic acid amide and the like were the most preferred compounds.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
That is, the present invention relates to a thermosensitive recording medium in which a coating layer containing a color-forming substance, a color-developing substance and a sensitizer is provided on a support: 1) 4,4'-dihydroxydiphenylsulfone as a color-developing substance And salicylanilide and dibenzyl oxalate as sensitizers. 2) Add fatty acid amide to the heat-sensitive recording layer. 3) As fatty acid amide, stearic acid amide,
At least one fatty acid amide selected from N, N'-ethylenebisstearic acid amide and palmitic acid amide is added. 4) At least one or more overcoat layers are provided on the heat-sensitive recording layers 1) to 3).

In the present invention, the amount of the sensitizer in the heat-sensitive recording layer is from 50 to 300% by weight, and preferably 7 to 300% by weight, based on the color developing material.
It is used in the range of 5 to 250% by weight. If the amount is less than 50% by weight, the sensitizing effect is hardly obtained, and if it exceeds 300% by weight, no further improvement in the sensitizing effect is observed, and the amount of the heat-meltable substance including the sensitizer and the color developing substance increases. As a result, the amount of hot melt adhering to the heating element head increases (adhesion of scum), and there is fear that printing troubles or the like may occur.

In the present invention, the addition amount of stearic acid amide, N, N'-ethylenebisstearic acid amide or palmitic acid amide in the heat-sensitive recording layer is used in the range of 5 to 150% by weight based on the color developing substance. More preferably, it is in the range of 10 to 75% by weight. If the content is less than 5% by weight, it is difficult to obtain the effect of improving color development,
No further greater effect can be obtained by adding more than.

The use of 4,4'-dihydroxydiphenyl sulfone used as a color-developing substance in the present invention is disclosed in Japanese Patent Application Laid-Open No. Sho 57-11088. The substance itself has a melting point of 235 to 250 ° C. It is a fusible substance. As for the method of use as a color-developing substance, see JP-A-57-169393 and JP-A-58-1261.
Nos. 89 and 61-160292 disclose the use of other color developing substances in combination.

Salicylanilide used as a sensitizer is a compound having a melting point of about 135 ° C., and dibenzylaxalate is a compound having a melting point of about 80 ° C. Although both compounds are known as sensitizers, The fact that excellent effects can be obtained in combination with 4,4'-dihydroxydiphenylsulfone has not been known before.

As the fatty acid amide used in the present invention, various commercially available fatty acid amides can be used. For example, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, erucic acid amide N, N'-ethylenebislauric acid amide, N, N'-methylenebisstearic acid amide, N, N'-ethylenebisstearic acid amide, N, N'-ethylenebisoleic acid amide,
N, N′-ethylenebisbehenamide, methylol amide stearate, N, N′-distearyl stearic acid amide, N, N′-dioleyl adipate amide and the like can be mentioned, but the present invention is not limited thereto. It is not limited.

The fatty acid amide has a melting point of about 8
Compounds at 0 ° C. or higher are suitable, and among the above compounds, stearic acid amide, N, N′-ethylenebisstearic acid amide and palmitic acid amide can be mentioned as particularly preferred compounds.

In the present invention, the color-forming substance constituting the recording layer of the thermosensitive recording medium is used alone or as a mixture of two or more as necessary. What is applied is applied arbitrarily,
For example, leuco compounds of dyes such as triallylmethane, fluoran, thiazine, spiropyran, and lactam are preferably used, and fluoran leuco dyes are particularly widely used, and specific examples thereof include: The following are mentioned.

3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,3-bis (p
-Dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindole -3-yl)
-5-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl)- Triallylmethane dyes such as 6-dimethylaminophthalide, 6 '-[ethyl (3-methylbutyl) amino] -3'-methyl-2'-(phenylamino) -spiro [isobenzylfuran-1-9 ' −
Xanthen] -3-one, 3-dibutylamino-6-methyl-7-anilinofluoran, 3- (N-methyl-N
-Propylamino) -6-methyl-7-anilinofluoran, 3- (N-cyclohexyl-N-methylamino)
-6-methyl-7-anilinofluoran, 3-dimethylamino-6-methyl-7-chlorofluorane, 3-dimethylamino-7-methyl-7-chlorofluorane, 3-
Dimethylamino-6-methyl-7-anilinofluoran, 3,3-bis (4-dimethylaminophenyl) 6-
Diethylaminophthalide, 3-diethylamino-7 (2
-Chloroanilino) fluoran, 3-dibutylamino-
Fluoran dyes such as 7 (2-chloroanilino) fluoran; thiazine dyes such as benzoylleucomethylene blue and p-nitribenzoylleucomethylene blue;
Spiropyrans such as -methyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho- (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran And lactam dyes such as rhodamine (p-nitroanilino) lactam and rhodamine (o-chloroanilino) lactam.

Further, in the present invention, various binders as shown below are applied as a binder for binding and supporting the heat-sensitive recording layer on the support.

Polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methylcellulose, hydroxymethylcellulose, carboxymethylcellulose and ethylcellulose, polyvinylpyrrolidone, polyacrylamide, sodium polyacrylate, acrylamide /
Acrylic ester copolymer, acrylamide / acrylic ester / methacrylic acid terpolymer, styrene /
Maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, sodium alginate,
In addition to water-soluble polymers such as gelatin, casein, and gum arabic, polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, polymethacrylate, vinyl chloride / vinyl acetate copolymer, ethylene / vinyl acetate copolymer An aqueous emulsion such as coalesced or polybutyl methacrylate can be used as a binder.

The heat-sensitive recording material of the present invention may contain, in the heat-sensitive recording layer, together with the above-described color-forming substance and color-developing substance, if necessary, auxiliary additives commonly used in this type of heat-sensitive recording medium, for example, fillers, Surfactants, lubricants and the like can be used in combination. In this case, examples of the filler include inorganic fine powder such as calcium carbonate, silica, alumina, magnesium carbonate, talc, barium sulfate, zinc oxide, titanium oxide, surface-treated calcium carbonate and silica, and urea /
Examples include organic fine powders such as formalin resin, styrene / methacrylic acid copolymer, and polystyrene.
Examples of the lubricant include higher fatty acids or esters thereof, amide compounds and metal salts, various waxes, condensates of aromatic carboxylic acids and amines, benzoic acid phenyl esters, higher linear glycols and other heat-fusible agents. Organic compounds may be mentioned. Add fine powder such as aluminum stearate to improve the clarity of the color image, and add lubricants such as linseed oil, tung oil, wax, paraffin, polyethylene wax, paraffin chloride, metal salts of higher fatty acids, etc. The traveling performance of the head can be further improved.

To form the overcoat layer in the present invention, for example, polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, casein, gum arabic, Water-soluble resins or aqueous emulsions such as oxidized starch, etherified starch, esterified starch, styrene-butadiene copolymer emulsion, vinyl acetate-ethylene copolymer emulsion, methacrylate-butadiene copolymer, and styrene-acryl copolymer emulsion Is used.

Further, in the overcoat layer, if necessary, surfactants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, alginates, fatty acid metals, etc. (as dispersants and wetting agents) ), Glyoxal, methylolmelamine, potassium persulfate, sodium persulfate,
A water-resistant agent such as ammonium persulfate, an ultraviolet absorber such as benzophenone and triazole, an antifoaming agent, and various assistants such as a fluorescent dye and a coloring dye can be added.

A pigment can be added to such an overcoat layer in order to impart suitability for writing implements and fixability for printing. Such pigments include light calcium carbonate,
Heavy calcium carbonate, talc, kaolin, silica, magnesium carbonate, clay, zinc oxide, aluminum oxide,
Examples include inorganic pigments such as aluminum hydroxide, organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formaldehyde resin filler, and raw starch.

As the support, paper is generally used, but resin films, synthetic papers, nonwoven fabrics and the like can also be used. It should be noted that various known techniques in the field of heat-sensitive recording material production can be added, such as providing a protective layer on the back surface of the support and further applying an adhesive process to the back surface of the support.

An undercoat layer may be provided between the support and the thermosensitive recording layer. As an apparatus used for coating the undercoat layer and the heat-sensitive recording 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, an apparatus such as a machine calender, a super calender, a gloss calender, and brushing can be used. Further, the amount of coating when the undercoat layer is provided is not particularly limited, but 3 to 20 g / m ^2, preferably 5 to 10 g / m ² is appropriate. The coating amount of the heat-sensitive recording layer on the support is not limited, but usually 3
To 15 g / m ^2, preferably 4 to 10 g / m ² .

[0028]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In addition, all the parts and% shown below are based on weight.

Example 1 [Adjustment of Undercoat Layer] Water 107 parts by weight 10% sodium hexametaphosphate 8 parts by weight Calcined kaolin (trade name: Ansilex manufactured by Engelhard Co.) 100 parts by weight 25% starch oxide solution 24 parts by weight 48 % SBR latex 25 parts by weight An undercoat layer solution having a solid content ratio of 45% was prepared from the above composition.

[Formation of Undercoat Layer] The obtained undercoat layer coating solution was applied to 50 g / m ² base paper by a blade coater so as to have an application amount of 6 g / m ² and dried to form an undercoat layer. did.

[Adjustment of Thermosensitive Recording Layer] (1) Adjustment of Liquid A Liquid A and Liquid B having the following component compositions were obtained by dispersing for 10 hours. 80% by weight of a 10% modified polyvinyl alcohol solution (Goseiran L3266, Nippon Gosei Co., Ltd.) 100 parts by weight of 3-dibutylamino-6-methyl-7-anilinofluoran 180 parts by weight of water 180 parts by weight of the solution A to Dynomill (Shinmaru Enterprises) Pulverized so as to have a volume average particle size of 1.5 μm. (2) Preparation of Solution B 15% styrene maleic anhydride copolymer ammonium salt (Arakawa Chemical Co., Ltd., Polymalon 1318) 34 parts by weight 4,4'-dihydroxydiphenyl sulfone (Nichika Chemical Co., Ltd., BPS -P) 40 parts by weight Dibenzyl oxalate (HS2046 manufactured by Dainippon Ink and Chemicals, Inc.) 30 parts by weight Salicylanilide (Yoshitomi Fine Chemical Co., Ltd., Tomirac SA) 30 parts by weight Water 130 parts by weight Dynomill (Shinmaru Enterprises Co., Ltd.) so that the volume average particle diameter was 1.5 μm. (4) Preparation of solution C 15% styrene maleic anhydride copolymer ammonium salt 34 parts by weight 4,4'-dihydroxydiphenyl sulfone 40 parts by weight 2-benzyloxy-naphthalene (BON manufactured by Ueno Pharmaceutical Co., Ltd.) 60 parts by weight 130 parts by weight of water Solution C was pulverized using a Dynomill (manufactured by Shinmaru Enterprises) so that the volume average particle size became 1.5 μm.

[Formation of Thermal Recording Layer] [A]
Liquid] and [Liquid B] to prepare a coating solution for the heat-sensitive recording layer comprising the following components, and coat the undercoat layer with an air knife coater so that the dry weight is 5 g / m ^2.
Dry coating was performed at m / min. Thereafter, the coated paper was calendered and finished so that the Beck smoothness became 400 to 600 seconds, thereby obtaining a thermosensitive recording medium of Example 1. Polyvinyl alcohol solution (10% aqueous solution) 500 parts by weight Calcium carbonate 100 parts by weight Liquid A 100 parts by weight Liquid B 264 parts by weight 40% zinc stearate dispersion 40 parts by weight Water 250 parts by weight

Example 2 [Preparation of Overcoat Liquid] An overcoat liquid was prepared according to the following formulation. Water 115 parts by weight 5% PVA 100 parts by weight 20% Acrylic emulsion resin (Barrier Star OM1050 manufactured by Mitsui Chemicals, Inc.) 50 parts by weight Fine silica powder (Mizukasil P527 manufactured by Mizusawa Chemicals, Inc.) 10 parts by weight 40% zinc stearate dispersion 5 parts by weight of liquid

[Preparation of Overcoat Layer] The prepared overcoat liquid was coated on the heat-sensitive recording layer prepared in Example 1 with a rod coater so that the dry coating amount was 2 g / m ^2, and then dried. The coated paper was calendered and finished so as to have a Beck smoothness of 700 to 1000 seconds. Thus, a thermosensitive recording medium of Example 2 was obtained.

Example 3 A 20% stearic acid amide dispersion (Chukyo Yushi Co., Ltd., Hydrin G270) was added to the composition of the heat-sensitive recording layer of Example 1.
A thermosensitive recording material of Example 3 was obtained in the same manner as in Example 1 except that 0 parts by weight was added and the coating was dried so that the dry coating weight was 5.5 g / m ² .

Example 4 Fifty parts by weight of the 20% stearic acid amide dispersion of Example 3 was mixed with N, N'-ethylenebisstearic acid amide 28.
% Dispersion (Chukyo Yushi Co., Ltd., Hydrine B961) 36
A thermosensitive recording medium of Example 4 was obtained in the same manner as in Example 3 except that the amount was changed to parts by weight.

Example 5 Example 3 was repeated except that 50 parts by weight of the 20% stearic acid amide dispersion of Example 3 was changed to 56 parts by weight of 18% palmitic acid amide dispersion (K646, manufactured by Chukyo Yushi Co., Ltd.). In the same manner as in the above, a thermosensitive recording medium of Example 5 was obtained.

Comparative Example 1 Example 1 was repeated except that solution C was used in place of solution B of example 1.
In the same manner as in Example 1, a thermosensitive recording medium of Comparative Example 1 was obtained.

Comparative Example 2 A heat-sensitive recording material of Comparative Example 2 having an overcoat layer was obtained in the same manner as in Example 2 except that the heat-sensitive recording material of Comparative Example 1 was used instead of the heat-sensitive recording material of Example 1. .

The following items were evaluated for the thermosensitive recording materials obtained in the above Examples and Comparative Examples, and the results are shown in Table 1. [Sensitivity evaluation] Head resistance 1 with a test machine manufactured by Okura Electric Co., Ltd.
10ms using 335Ω head (Kyocera head)
/ Line was printed at an energy of 0.25 mj / dot, and the print density of the image portion at that time was measured. The results are shown in Table 1. The print density was measured using Macbeth RD918.

[0041]

[Table 1]

[0042]

According to the above results, in a thermosensitive recording medium containing a coloring material and a coloring material, 4,4'-dihydroxydiphenyl sulfone was used as the coloring material,
By using salicylanilide and dibenzyl oxalate as the sensitizer, a heat-sensitive recording material having high sensitivity and excellent print coloring properties can be obtained. In addition, stearic acid amide, N, N'-ethylenebisstearic acid can be obtained. At least one fatty acid amide such as amide and palmitic acid amide.
By adding the kinds, it was possible to obtain a heat-sensitive recording medium having higher sensitivity and excellent print coloring property.

Claims (4)

[Claims] 1. A thermosensitive recording medium comprising a support having thereon a thermosensitive recording layer containing a colorless or light-colored basic dye and a color developer and a sensitizer capable of forming a color by reacting with the dye. A heat-sensitive recording material comprising 4,4'-dihydroxydiphenylsulfone as a coloring agent and salicylanilide and dibenzyloxalate as sensitizers. 2. The heat-sensitive recording material according to claim 1, wherein at least one fatty acid amide is added to the heat-sensitive recording layer. 3. The heat-sensitive recording material according to claim 2, wherein the fatty acid amide is at least one selected from the group consisting of stearic acid amide, N, N'-ethylenebisstearic acid amide, and palmitic acid amide. 4. The heat-sensitive recording material according to claim 1, wherein at least one overcoat layer is provided on the heat-sensitive recording layer.