JPH0281670A - Thermal recording element - Google Patents

Abstract

PURPOSE:To ensure high sensitivity and degree of whiteness and also that the degree of whiteness does not decrease, if it is exposed to high temperature by adding dibenzylester oxalate as a fusible substance and a specific compound as a coloring agent. CONSTITUTION:A recording layer containing a colorless or light-colored basic dye and a coloring agent which forms a color due to its contact with said dye. At least, one kind of chemical is selected as the coloring agent from among 4-hydroxy-4'-isopropyloxydiphenylsulfon, 4,4'-(1-3-dimethylbutylidene)bisphenol, 4,4'-(1-phenylethylidene)bisphenol, 4,4'-(p-phenylenediisopropylidene)bisphenol and 4,4'-(m-phenylenediisopropylidene)bisphenol. In addition, dibenzylester oxalate is added as a thermally fusible material. If the above-mentioned compounds are used as a coloring agent and dibenzylester oxalate is jointly used as a thermally fusible material, a thermal recording element is obtained which not only has high-speed recording properties but also shows no deterioration of the degree of whiteness in the recording layer, if the element is stored at high temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a heat-sensitive recording medium, which is particularly suitable for high-speed recording,
Moreover, the present invention relates to a heat-sensitive recording material that can stably maintain a recorded image without causing a decrease in whiteness in the blank paper portion.

``Prior Art'' Conventionally, heat-sensitive recording materials utilize a color reaction between a colorless or light-colored basic dye and an organic or inorganic coloring agent to obtain a recorded image by bringing a recoloring substance into contact with heat. well known.

Recently, with remarkable progress in thermal recording methods, thermal faxes and the like have become capable of high-speed printing, and it has become possible to record a standard A4 size original in 10 seconds or less. As described above, with the increase in speed in the hardware field, there is a demand for heat-sensitive recording bodies that are excellent in suitability for high-speed recording.

Conventionally, as a means of improving the color development sensitivity of thermal recording materials, a thermofusible substance with a lower melting point than a basic dye or coloring agent is added to the recording layer, and the dye is first absorbed by the melted thermofusible substance. A widely known method is to lower the temperature at which color development starts by dissolving a coloring agent (JP-A-49-34842, JP-A-53-39139, etc.).

However, it is generally difficult to make one type of thermofusible substance have the property of dissolving both a basic dye and a coloring agent, and a sufficient sensitivity improvement effect is not necessarily obtained. or,
Thermofusible substances with good sensitivity improvement effects include dyes/
The temperature at which color development starts falls excessively due to the melting point drop due to the eutectic phenomenon of the three-way coloring agent/thermofusible substance, and the whiteness of the recording layer is significantly reduced, especially if the thermosensitive recording material is stored under high temperature conditions. The disadvantage is that it decreases.

``Problems to be Solved by the Invention'' In view of the current situation, the present inventors have developed a thermal recording material that has excellent color development sensitivity and does not lose whiteness even when exposed to high temperature conditions, in addition to thermofusible materials. A wide range of coloring agents used in combination were also investigated. As a result, they discovered that the above object could be achieved by using oxalic acid dibenzyl ester as a thermofusible substance and selectively using a specific compound as described below as a coloring agent, and completed the present invention. It's arrived.

``Means for Solving the Problems'' The present invention provides a heat-sensitive recording material in which a recording layer containing a colorless or light-colored basic dye and a coloring agent that develops a color upon contact with the dye is provided on a support. , as a coloring agent, 4-hydroxy-4'-isopropyloxydiphenylsulfone, 4.4'-(1°3-dimethylbutylidene)bisphenol, 4°4'-(1-phenylethylidene)
At least one member selected from bisphenol, 4.4'-(p-)ylene diisopropylidene) bisphenol, and 4.4'-(m-phenylene diisopropylidene) bisphenol is used, and oxalic acid is used as the thermofusible substance. This is a heat-sensitive recording material characterized by containing dibenzyl ester.

"Function" In the present invention, when the above-mentioned specific compound is used as a coloring agent, and oxalic acid dibenzyl ester is used as a heat-fusible substance, not only is the suitability for high-speed recording excellent, but also storage under high-temperature conditions is achieved. Although it is not necessarily clear why a heat-sensitive recording material that does not cause a decrease in the whiteness of the recording layer even if the coloring agent is It is presumed that this is because the melting point drop due to the eutectic phenomenon is small.

In the present invention, 4-hydroxy-4'-isopropyloxydiphenyl sulfone, 4,4'-(1,3-dimethylbutylidene)bisphenol, 4,4'-( 1-phenylethylidene)bisphenol, 4.4'-(p-phenylenediisopropylidene)bisphenol, 4.4'
-(mphenylenediisopropylidene)bisphenol is selectively used, and among these, 4.4'(1,3-dimethylbutylidene)bisphenol, 4.4'- (1-phenylethylidene)bisphenol, 4.4'-(p-
) unilene diisopropylidene) bisphenol or 4,4'-(m-phenylene diisopropylidene) bisphenol is more preferable because a heat-sensitive recording material with particularly little reduction in whiteness can be obtained.

The ratio of the color former to dibenzyl oxalate is not particularly limited, but usually 1 to 100 parts by weight, preferably 10 parts by weight of dibenzyl oxalate per 100 parts by weight of the color former. It is desirable to adjust the content within a range of about 300 parts by weight.

In the heat-sensitive recording material of the present invention, various colorless or light-colored basic dyes are known as the colorless or light-colored basic dyes that constitute the recording layer together with a specific coloring agent and a thermofusible substance. Ru.

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-methylindol-3-yl phthalide, 3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide, 3,3-bis(1
゜2-dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazol-3-yl)-6-dimethylaminophthalide, 3,3
-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophthalide, etc. triallylmethane dye; 4.
4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N-2
, diphenylmethane dyes such as 4,5-trichlorophenylleucoolamine, thiazine dyes such as benzoylleucomethylene blue and p-nitrobenzoylleucomethylene blue, 3-methyl-spiro-dinaphthopyran,
3-ethyl-spiro-dinaphthopyran, 3-phenyl-
Spiro dyes such as spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzobilane, rotamine-B-anilinolactam, rhodamine (p -lactam dyes such as -nitroanilino)lactam, rhodamine (0-chloroanilino)lactam, 3-dimethylamino-7-methoxyfluorane, 3-diethylamino-6-methoxyfluorane, 3-
Diethylamino-7-methoxyfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,7-dimethylfluorane, 3-(N- Ethyl-p-toluidino)-7-methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamino-7-N-methylaminofluorane, 3-diethylamino-7-dibenzyl Aminofluorane, 3-diethylamino-7-(N-methyl-N
-benzylamino)fluoran, 3-diethylamino-
7-(N-chloroethyl-N-methylamino)fluoran, 3-diethylamino-7-N-diethylaminofluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-phenylaminofluoran, 3- (N-ethyl-p-toluidino)-6-methyl-7-(p-toluidino)fluoran, 3-diethylamino-6-methyl-7
-phenylaminofluorane, 3-dibutylamino-6
-Methyl-7-phenylaminofluorane, 3-diethylamino-7-(2-carbomethoxy-phenylamino)fluoran, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-phenylaminofluorane ,3
-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7-phenylaminofluorane, 3-piperidino-6-methyl-7-phenylamino Fluoran, 3-diethylamino-6-methyl-7-xylidinofluorane, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-dibutylamino-7-(
0-chlorophenylamino)fluoran, 3-(N-ethyl-N-tetrahydrofurfuryl)amino-6-methyl-7-phenylaminofluoran, 3-(N-methyl-N-n-propyl)amino-6- Methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7
-P-butylphenylaminofluorane, 3-(N-ethyl-N-n-propyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-N-butyl)amino- 6-Methyl-7-phenylaminofluorane, 3-(N-methyl-Nn-hexyl)amino-6-methyl-7-phenylaminofluorane, 3-
(N-ethyl-N-n-hexyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-
Fluoran dyes such as N-cyclopentyl)amino-6-methyl-7-phenylaminofluorane, etc. Of course, the dyes are not limited to these dyes, and two or more types of dyes can be used in combination.

The proportion of the specific coloring agent and basic dye used in combination is not necessarily limited, but is usually 100 to 700 parts by weight, preferably 150 to 400 parts by weight, per 100 parts by weight of the basic dye. A coloring agent is added.

Preparation of coating liquids containing these generally uses water as a dispersion medium,
It is prepared by dispersing the dye, coloring agent, and dibenzyl oxalate together or separately using a stirring/pulverizing machine such as a ball mill, attritor, or sand mill.

Such coating liquids usually contain starches and binders as binders.
Hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene/maleic anhydride copolymer salt, styrene/acrylic acid copolymer salt, styrene/butadiene copolymer emulsion, etc. have a total solid content. It is blended in an amount of 10 to 40%, preferably 15 to 30%.

Furthermore, various auxiliary agents can be added to the coating liquid.
For example, dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate, fatty acid metal salts, ultraviolet absorbers such as triazoles, oil cleaning agents thereof,
Examples include fluorescent dyes and colored dyes. In addition, dispersions or emulsions of stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, ester wax, etc. are added to prevent sticking of the heat-sensitive recording material due to contact with recording equipment or recording heads. You can also do that.

Further, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, valmitic acid amide, coconut fatty acid amide, 2,2'-methylene bis(4
-methyl-5-tert-butylphenol), 1,1
．． 3-) Lis(2-methyl-4-hydroxy-5ter
Hindered phenols such as t-butylphenyl)butane, 1°2-bis(phenoxy)ethane, 1,2-bis(4-methylphenoxy)ethane, 1.2-bis(3-
Ethers such as methylphenoxy)ethane, 2-naphthol benzyl ether, dibenzyl terephthalate, 1
Various known thermofusible substances such as esters such as -hydroxy-2-naphthoic acid phenyl ester can also be used in combination.

In addition, inorganic pigments such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine particulate anhydrous silica, and activated clay can be added to improve the adhesion of residue to the recording head. .

The thermosensitive recording material of the present invention has an important feature in that it uses the above-mentioned specific compound as a coloring agent, but bisphenol A, 44'-cyclo hexylidene diphenol, p-
Various known coloring agents such as benzyl hydroxybenzoate, dimethyl 4-hydroxyphthalate 1, and antipyrine complex of zinc thiocyanate can also be used in combination.

As the support, paper, plastic film, synthetic paper, etc. can be used, but paper is most preferably used in terms of cost, coatability, etc. Further, the amount of coating liquid forming the recording layer applied to the support is not particularly limited, and is usually 2 to 12
g/rd, preferably in the range of about 3 to 10 g/rrf.

The heat-sensitive recording material of the present invention obtained by (2) selectively uses a specific coloring agent and a thermofusible substance, so it has high sensitivity and high whiteness, and can be stored under high temperature conditions. The whiteness does not easily decrease even when the recording head is coated, and it also exhibits excellent properties in terms of preventing debris from adhering to the recording head (piling).

Note that it is also possible to provide an overcoat layer on the recording layer for the purpose of protecting the recording layer, and it is of course also possible to provide a protective layer on the back side of the support or an undercoat layer on the support. In addition, various known techniques in the field of heat-sensitive recording material production, such as applying an adhesive to the back surface of the support, can be added.

"Example" The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these.

Further, unless otherwise specified, parts and percentages in the examples indicate parts by weight and percentages by weight, respectively.

Example 1 Oki U row 4 Bokiyaki Ray (Product name: Anterex. Appearance is specific gravity:
0.22 g/crl, manufactured by Engelhard) 100
Styrene-butadiene copolymer latex (solid content: 5
0%) 15 parts polyvinyl alcohol 10% 7 [8 liquids 30 parts water
A coating solution for an intermediate layer was prepared by mixing 200 parts of the above composition.

The obtained coating liquid was applied to 50 g/rd of high-quality paper so that the coating amount after drying was 10 g/rd, and dried to form an intermediate layer.

! ■Preparation of A liquid 3-(N-ethyl-N-isopentylamino)-6-methyl-7-phenylaminofluorane
L O
Part oxalic acid dibenzyl ester 20 parts Methylcellulose 5% aqueous solution 15 parts Water
120 parts of this composition was ground in a sand mill until the average particle size was 3 μm.

■ Preparation of B solution 4.4'-(1,3-dimethylbutylidene)bisphenol 30 parts methylcellulose
5% aqueous solution 30 parts water
70 parts of this composition was ground in a sand mill until the average particle size was 3 μm.

■ Formation of recording layer 165 parts of liquid A, 130 parts of liquid B, silicon oxide pigment (oil absorption 1
80 m1/100 g), 150 parts of a 20% oxidized starch aqueous solution, and 55 parts of water were mixed and stirred to prepare a recording layer coating liquid. The resulting coating liquid was applied onto the intermediate layer at a dry weight of 5.0 g/
A thermosensitive recording paper was obtained by coating and drying so as to give r+(.

Examples 2 to 4 In the preparation of Solution B in Example 1, 4.4'-(13-dimethylbutylidene)bisphenol was replaced with 4.4'-(13-dimethylbutylidene)bisphenol.
'-(1-phenylethylidene)bisphenol (Example 2), 4.4'-(p-phenylenediisopropylidene)bisphenol (Example 3), 4.4'-(m
- phenylene diisopropylidene) bisphenol (Example 4) was used in the same manner as in Example 1.
Various types of thermal recording paper were obtained.

Comparative Example 1 In preparing the B solution of Example 1, 4.4'-(1°3-
A thermosensitive recording paper was obtained in the same manner as in Example 1 except that bisphenol A was used instead of dimethylbutylidene) bisphenol.

Comparative Example 2 Stearic acid amide was used instead of dibenzyl oxalate in the preparation of Solution A in Example 1, and 4.4'-(1,3-dimethylbutylidene) was used in the preparation of Solution B.
A thermosensitive recording paper was obtained in the same manner as in Example 1 except that bisphenol A was used instead of bisphenol.

The six types of thermal recording paper thus obtained were tested in a Kyocera simulator (voltage: 16V, pulse cycle: 5a+5
ec), 0.30m5ec and 0,4 during the pulse
The color density was measured using a Macbeth densitometer (model RD-100R, using an amber filter), and the results are shown in Table 1.

In addition, the whiteness of the recording layer before recording was measured using a Hunter whiteness meter, and the heat-sensitive recording paper was placed in an atmosphere of 60°C for 2 hours.
After standing for 4 hours, the whiteness was measured again in the same manner, and the results are shown in Table 1.

Table 1 "Effects" As is clear from the results in Table 1, the heat-sensitive recording material of the present invention has high sensitivity and high whiteness, and has the advantage of not causing a decrease in whiteness even when exposed to high temperature conditions. It was a record body.

Claims (1)

[Claims] In a heat-sensitive recording material in which a recording layer containing a colorless or light-colored basic dye and a coloring agent that develops color upon contact with the dye is provided on a support, the coloring agent is 4-hydroxy-4.
'-Isopropyloxydiphenyl sulfone, 4,4
'-(1,3-dimethylbutylidene)bisphenol,
Using at least one selected from 4,4'-(1-phenylethylidene)bisphenol, 4,4'-(p-phenylenediisopropylidene)bisphenol, and 4,4'-(m-phenylenediisopropylidene)bisphenol. , and contains dibenzyl oxalate as a thermofusible substance.