JPH06183148A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance high speed recording aptitude and whiteness, in a thermal recording material for a thermal facsimile, by adding a sensitizer containing a dibenzylbenzene compd. represented by a specific formula to a thermal color forming layer. CONSTITUTION:When a thermal color forming layer consisting of a dye precursor such as triphenylmethane and a developer such as phenol is formed on a sheet like support, a sensitizer containing one or more kind of a dibenzylbenzene compd. represented by specific formula (wherein R<1>-R<5> are respectively independently a lower alkyl group, an alkoxy group, a halogen atom or a hydrogen atom and all of them are not hydrogen atoms at the same time), for example, 4-bis(p-methylbenzyl)benzene is added to the recording layer in an amt. of 10-1000% by wt. of the developer.

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, and more particularly to a heat-sensitive recording material having high whiteness and excellent suitability for high speed recording.

[0002]

2. Description of the Related Art A heat-sensitive recording material utilizing a heat-coloring reaction of a normally colorless or light-colored leuco dye with a phenol or an organic acid is disclosed, for example, in JP-B-43-4160 and JP-B-4.
It is disclosed in Japanese Patent Laid-Open No. 5-14039, Japanese Patent Laid-Open No. 48-27736 and the like, and is widely put into practical use.

In recent years, such a heat-sensitive recording material has various advantages such that a color image can be formed by simply heating it and the recording apparatus can be made relatively compact. Widely used. In particular, thermal facsimiles, thermal printers, and the like using such thermal recording media have been improved in their devices, and high-speed printing and high-speed image formation, which have been considered difficult in the past, are now possible.

With the speeding up of such equipment and hardware fields, it is required that the recording sensitivity of the thermal recording medium to be used be greatly improved as compared with the conventional one. Many proposals have been made to meet this requirement, but many of these proposals are characterized by a combination of a dye precursor and a color developer.
Alternatively, it is characterized by using a heat-fusible substance in combination with these color-forming components.

The above-mentioned heat-fusible substance is also called a sensitizer,
For example, 1-hydroxy-2-naphthoic acid phenyl ester (JP-A-57-191089), p-benzylbiphenyl (JP-A-60-82382), benzylnaphthyl ether (JP-A-58-87094), dibenzyl. Terephthalate (JP-A-58-98285), benzyl p-benzyloxybenzoate (JP-A-57-2016)
91), diphenyl carbonate, ditolyl carbonate (JP-A-58)
-136489) and m-terphenyl (JP-A-57-
89994), 1,2-bis (m-tolyloxy) ethane (JP-A-60-56588), 1,5-bis (p).
-Methoxyphenoxy) -3-oxapentane (JP-A-62-181183), benzyl oxalate (JP-A-64-1583) and the like are known.

[0006]

When the heat-sensitive recording material containing the above-mentioned heat-fusible substance is heated, the heat-fusible substance is first melted, and the dye precursor and the visible light are melted in the melt. When the colorant is dissolved, both color-forming components are mixed at the molecular level to accelerate the color-forming reaction. Therefore, these heat-fusible substances have an appropriate melting point (preferably 60 to 140).
C.), and particularly for the purpose of high sensitivity, the melting point must be lower than about 120.degree.

The heat-fusible substance must have excellent compatibility with the dye precursor and the color developer. Furthermore, it is also important that the heat-fusible substance does not reduce the whiteness of the thermosensitive recording medium.
It is desirable that it has a melting point of 60 ° C. or higher, is extremely insoluble in water, and further has properties such as low sublimability.

It is considered that the sublimability of the heat-fusible substance is deeply related to a phenomenon in which the heat-colored portion of the heat-sensitive recording material becomes dusty with time, that is, a phenomenon called whitening. This is an extremely important property to be solved in practical use of the thermal recording material. Although a large number of heat-fusible substances have been proposed in the past as described above, few of them satisfy all of the above conditions, and therefore, the emergence of new materials has been demanded.

The present invention has a thermosensitive coloring layer containing a novel heat-fusible substance, which satisfies the above-mentioned requirements together with a dye precursor and a color developer, and recording is greatly improved without deteriorating various recording performances. An object of the present invention is to provide a thermosensitive recording medium having sensitivity.

[0010]

The thermal recording material of the present invention comprises:
A sheet-like substrate, and a thermosensitive coloring layer formed on at least one surface of the sheet-like substrate and containing a colorless or light-colored dye precursor, and a developer which reacts with the dye precursor under heating to develop a color thereof. And the thermosensitive coloring layer has the following general formula (I):

[Chemical 2] (However, in the formula, R ¹ , R ² , R ³ , R ⁴ , and R
⁵ are each independently a lower alkyl group, a lower alkoxy group, a halogen atom, or a hydrogen atom,
R ¹ , R ² , R ³ , R ⁴ , and R ⁵ are not all hydrogen atoms at the same time. ), And further contains a sensitizer containing at least one dibenzylbenzene compound. The lower alkyl group of formula (I) preferably contains 1 to 4 carbon atoms, and the lower alkoxy group preferably contains 1 to 4 carbon atoms.
Further, the halogen atom is preferably selected from chlorine, bromine and fluorine atoms.

[0011]

When the heat-fusible compound represented by the general formula (I) is used as a sensitizer, the present inventors have heretofore been proposed as a typical heat-fusible substance (Japanese Patent Publication No. 50-14531).
No.) and higher fatty acid amides such as stearic acid amide and palmitic acid amide, which have been put to practical use, are used, and the whiteness of the thermosensitive coloring layer does not decrease, and the quality of the color image is improved. It was found that a whitening phenomenon that deteriorates with time does not occur, and therefore extremely high recording sensitivity can be obtained, and the present invention has been completed.

That is, according to the present invention, a colorless or monochromatic basic leuco dye (dye precursor) is reacted with a color developing agent capable of reacting with the dye precursor under heating to form a color. In a heat-sensitive recording material for recording a color-developed image by utilizing, at least 1 of the above-mentioned general formula (I) is contained in the heat-sensitive color-developing layer.
It is characterized in that a dibenzylbenzene compound of a kind is contained in a heat-fusible sensitizer.

The reason why the sensitizer containing the heat-fusible compound of the formula (I) as described above improves the color-developing sensitivity of the thermosensitive color-developing layer is not fully clear, but this compound has a low viscosity in a molten state. It is presumed that the compatibility with the dye precursor and the color developer is part of the reason. Also, the formula (I)
The reason why the sensitizer does not reduce the whiteness of the thermosensitive coloring layer is that it is hardly soluble in water, and it is extremely likely that it causes phenomena such as whitening which deteriorates the quality of recorded images. Less is believed to be due to its lower sublimation properties. However, the inventor does not stick to this interpretation.

The following can be mentioned as specific examples of the sensitizer compound of the general formula (I) used in the present invention. 1,4-bis (p-methylbenzyl) benzene, 1,4
-Bis (m-methylbenzyl) benzene, 1,4-bis (o-methylbenzyl) benzene, 1,3-bis (p-
Methylbenzyl) benzene, 1,2-bis (p-methylbenzyl) benzene, 1,4-bis (p-ethylbenzyl) benzene, 1,4-bis (o-ethylbenzyl) benzene, 1,4-bis ( p-methoxybenzyl) benzene, 1,4-bis (m-methoxybenzyl) benzene,
1,4-bis (o-methoxybenzyl) benzene, 1,
3-bis (p-methoxybenzyl) benzene, 1,2-
Bis (p-methoxybenzyl) benzene, 1,4-bis (p-ethoxybenzyl) benzene, 1,2-bis (p
-Ethoxybenzyl) benzene, 1,4-bis (2 ',
4'-dimethylbenzyl) benzene, 1,4-bis (2 ', 5'-dimethylbenzyl) benzene, 1,4-
Bis (3 ', 4'-dimethylbenzyl) benzene, 1,
4-bis (3 ', 5'-dimethylbenzyl) benzene,
1,4-bis (2 ', 4', 6'-trimethylbenzyl) benzene, 1,4-bis (2 ', 5'-dimethoxybenzyl) benzene, 1,4-bis (2', 5'-di) Ethoxybenzyl) benzene, 1,4-bis (2′-methyl-5′-methoxylbenzyl) benzene, 2,5-dimethoxy-p-dibenzylbenzene, 2,5-dimethyl-p-dibenzylbenzene

In the present invention, the compound of the formula (I) is, for example, xylylene dichloride and a corresponding benzene derivative, or a corresponding benzene derivative and a benzyl chloride derivative in the presence of a Friedel-Crafts catalyst such as aluminum chloride. It can be synthesized by reacting.

The sensitizer comprising at least one compound of the general formula (I) of the present invention is used together with the dye precursor and the color developer, but within the range not impairing the desired effect of the present invention. You may use together another sensitizer. The amount of the sensitizer used in the present invention is 10 to 1000 based on the weight of the color developer.
It is preferably wt%, and more preferably 50 to 300 wt%.

The heat-sensitive color forming layer containing the sensitizer of the present invention is a color developing agent mainly composed of a dye precursor, a phenol or an organic acid,
Further, it preferably contains a binder for binding these to bond the thermosensitive coloring layer to the sheet-like substrate, and further preferably contains an inorganic pigment, and may further contain waxes, if necessary.

Examples of the dye precursor used as the dye precursor include triphenylmethane-based, fluorane-based, and diphenylmethane-based leuco compounds, which can be selected from conventionally known ones. For example, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, crystal violet lactone, 3- (N-ethyl-N-iso). Pentylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-
7-anilinofluorane, 3-diethylamino-6methyl-7- (o, p-dimethylanilino) fluorane, 3
-(N-ethyl-p-toluidino) -6-methyl-7-
Anilinofluorane, 3-pyrrolidino-6-methyl-7
-Anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3- (N-cyclohexyne-N-methylamino) -6-methyl-7-anilinofluorane, 3-diethylamino -7- (o-chloroanilino) fluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6-methylfluorane , 3- (N-ethyl-N-hexylamino) -6-methyl-7- (p-chloroanilino) fluorane, and 3-cyclohexylamino-6-chlorofluorane. it can.

In the present invention, a conventionally known developer can be used as the color developer comprising phenols or organic acids. For example, bisphenol A, benzyl p-hydroxybenzoate (JP-A-52-140483), bisphenol S, 4-hydroxy-4'-isopropyloxydiphenyl sulfone (JP-A-60-13852).
No.), 1,1-di (4-hydroxyphenyl) cyclohexane, 1,7-di (4-hydroxyphenylthio)-
3,5-Dioxaheptane (JP-A-59-52694)
No.), and 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone (JP-A-60-208286).
No.) etc. can be used.

As the other sensitizer which can be used in combination with the sensitizer of the present invention, a heat-fusible organic compound having a melting point of 60 to 150 ° C. can be selected. As I explained.

The organic or inorganic pigments used in the thermosensitive coloring layer include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcined clay, talc, and Inorganic fine powder such as surface-treated calcium carbonate and silica,
Other examples include urea-formalin resin, styrene / methacrylic acid copolymer, and organic fine powder such as polystyrene resin.

Further, the thermosensitive color developing layer of the present invention may contain various waxes, if necessary. Such waxes include paraffin, amide wax,
Known materials such as bisimide wax and metal salts of superabsorbent fatty acids can be used.

As the binder for the thermosensitive coloring layer, polyvinyl alcohol having various molecular weights, starch and its derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone and acrylic acid. Amide / acrylic acid ester copolymer,
Acrylic amide / acrylic ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, water-soluble polymer materials such as casein, and polyvinyl acetate , Polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, and styrene / butadiene / acrylic copolymer Etc. of each latex can be used.

The sheet-like substrate used in the heat-sensitive recording material of the present invention is made of paper, coated paper having a surface coated with a pigment, latex, etc., laminated paper, synthetic paper made of polyolefin resin, plastic film, etc. You can choose.

In order to form a thermosensitive coloring layer on at least one surface of such a sheet-like substrate, a coating solution containing a mixture of the above-mentioned required components may be applied onto the substrate and dried, whereby thermal recording is carried out. The body is obtained. The coating amount of the thermosensitive coloring layer is 1 to 15 g / m ² when the coating liquid layer is dried.
Is preferable and ² to 10 g / m ² is particularly preferable.

The thermal recording material of the present invention thus obtained is excellent in suitability for high-speed recording, has high whiteness, and does not cause an undesirable phenomenon such as whitening in a recorded image portion. .

[0027]

The present invention will be described in detail with reference to the following examples. Unless otherwise specified, "part" and "%" represent "part by weight" and "% by weight", respectively.

Example 1 A thermal recording paper was prepared by the following operation. (1) dye precursor dispersion A prepared INGREDIENT AMOUNT (parts) 3- (N-isopentyl -N- ethylamino) 20 6-methyl-7-anilinofluoran polyvinyl alcohol 10% solution 10 Water 70 The above composition The material is subjected to a sand grinder and the average particle size is 1
It was pulverized to a size of μm.

[0029] (2) a color developer and a sensitizing agent dispersion B prepared INGREDIENT AMOUNT (parts) 4,4'-isopropylidene-biphenol 10 1,4-bis (p- methylbenzyl) benzene 10 polyvinyl alcohol 10% solution 10 Water 70 The above composition was subjected to a sand grinder and the average particle size was 1
It was pulverized to a size of μm.

(3) Preparation of Thermosensitive Coloring Layer 40 parts of the above liquid A and 160 parts of the above liquid B were mixed with 40 parts of calcium carbonate pigment, 20 parts of 30% paraffin dispersion, and 180 parts of 10% polyvinyl alcohol aqueous solution and stirred. Then, a coating solution was prepared. This coating liquid is used in a basis weight of 50 g /
The coating amount after drying on one side of the m ² base paper is 7.0 g / m ²
Was coated and dried to form a thermosensitive coloring layer to prepare a thermosensitive recording paper.

(4) The thermosensitive recording paper obtained as described above was processed by a super calender, and the surface smoothness was adjusted to 600 to 1000 seconds.

(5) Test The samples thus obtained were subjected to the following tests to measure the recording sensitivity, the color density of the uncolored portion of the recording layer surface, and the whitening comparison test. The results are shown in Table 1. (A) Recording sensitivity Using a thermal gradient tester manufactured by Toyo Seiki Co., Ltd., the sample was heated for 100 milliseconds under the conditions of a temperature of 120 ° C. and a pressure of 2.5 Kg / cm ² , and the color density at that time was measured by a Macbeth densitometer RD- The recording sensitivity of the thermal paper was displayed with this measurement value. Further, the density of the uncolored part (white paper part) on the surface of the thermosensitive coloring layer was measured by the above densitometer, and the whiteness was displayed by the measured value.

(B) Whitening resistance Using the above tester, after the color of the sample was developed at a temperature of 150 ° C., the printed portion was left in an environment of 40 ° C. and 90% for 24 hours,
The change on the surface was visually observed and evaluated. In Table 1, "good" indicates that no change was observed in the color printed portion, and "bad" indicates that the printed surface became dusty, that is, whitening occurred.

Example 2 A thermosensitive recording paper was prepared by the following operation. (1) Preparation of Pigmented Undercoat Paper 85 parts of fired clay (trademark: Ansilex) was added to 320 parts of water.
To 40 parts of styrene-butadiene copolymer emulsion (solid content 50%) and 10%
50 parts of an aqueous solution of oxidized starch is mixed, and the resulting coating solution is applied onto one side of a base paper having a basis weight of 48 g / m ² so that the coating amount after drying is 7.0 g / m ² , and the pigment is added. An undercoat paper was prepared.

(2) Formation of thermosensitive coloring layer 50 parts of A dispersion liquid described in Example 1 and 20 parts of B dispersion liquid 20
To 0 part, 25 parts of calcium carbonate, 20 parts of 30% paraffin dispersion, and 10% aqueous solution of polyvinyl alcohol 1
80 parts were mixed and stirred to prepare a coating liquid. The resulting coating liquid is applied and dried on the pigment-coated surface of the above-mentioned pigment-undercoated paper so that the coating amount after drying will be 5.0 g / m ² to form a thermosensitive coloring layer to prepare a thermosensitive recording paper. did. Using this thermal recording paper, the same test as in Example 1 was conducted. The results are shown in Table 1.

Example 3 A thermal recording paper was prepared and tested in the same manner as in Example 2. However, in the preparation of the solution B used for forming the thermosensitive color developing layer, 4,4'-bis (p-methoxybenzyl) benzene was used instead of 4,4'-bis (p-methylbenzyl) benzene. The test results are shown in Table 1.

Comparative Example 1 A thermal recording paper was prepared and tested in the same manner as in Example 1. However, in the preparation of solution B, stearic acid amide was used instead of 1,4-bis (p-methylbenzyl) benzene. The test results are shown in Table 1.

Comparative Example 2 A thermal recording paper was prepared and tested in the same manner as in Example 2. However, in the preparation of solution B, stearic acid amide was used instead of 1,4-bis (p-methylbenzyl) benzene. The test results are shown in Table 1.

Comparative Example 3 A thermal recording paper was prepared and tested in the same manner as in Example 2. However, in the preparation of solution B, 1-hydroxy- was used instead of 1,4-bis (p-methylbenzyl) benzene.
2-Naphthoic acid phenyl ester was used. The test results are shown in Table 1.

[0040]

[Table 1]

As is clear from Table 1 above, the novel sensitizers used in the present invention have a higher sensitivity than stearic acid amide or 1-hydroxy-2-naphthoic acid phenyl ester, which are typical of conventional sensitizers. The high-speed recording suitability was excellent without giving white coloring to the thermosensitive color-developing layer with high coloring sensitivity and whiteness.

[0042]

The heat-sensitive recording material of the present invention has a heat-sensitive color forming layer containing a sensitizer made of a novel heat-fusible material, and therefore has excellent high-speed recording suitability, high whiteness and whitening. It does not induce such an unfavorable phenomenon as described above, has an extremely well balanced property in terms of quality, and has an extremely high practical value.

Claims (1)

[Claims] 1. A sheet-like substrate, and a colorless or light-colored dye precursor which is formed on at least one surface of the sheet-like substrate, and a developer which reacts with the dye precursor under heating to develop a color. And a thermosensitive coloring layer containing the thermosensitive coloring layer, wherein the thermosensitive coloring layer has the following general formula (I): (However, in the formula, R ¹ , R ² , R ³ , R ⁴ , and R
^5's each independently represent a lower alkyl group, a lower alkoxy group, a halogen atom, or a hydrogen atom.
¹ , ¹ , R ² , R ³ , R ⁴ , and R ⁵ are not all hydrogen atoms at the same time. 7. A heat-sensitive recording material, further comprising a sensitizer containing at least one dibenzylbenzene compound according to 1).