JPH03180385A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance recording sensitivity remarkably without lowering various recording capacities by adding a specific thermoplastic substance to a thermal coloring layer along with a dye precursor and a developer. CONSTITUTION:A thermal recording material comprises a thermal color developing layer consisting of a sheet like substrate, a colorless or light-colored dye precursor formed on at least one face of the substrate, and a coloring agent thermally reacting with the dye precursor to develop a color, and at least one kind of a sensitizer composed of an aromatic compound represented by formula (wherein R1 is a hydrogen atom or a lower alkyl group and R2, R3 and R4 are respectively and independently a hydrogen atom, a lower alkyl group, an alkoxy group, an aryl group, an aryloxy group, an aralkyloxy group, a halogen atom or an aralkyl group) is further added into the thermal color developing layer. The use amount of the sensitizer is pref. 10-1000%, more pref. 50-300% by wt. of the coupler.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a heat-sensitive recording medium, and more specifically, it relates to a heat-sensitive recording medium that has high whiteness and excellent suitability for high-speed recording.

[Conventional technology]

A heat-sensitive recording material that records a colored image by utilizing a heated color-developing reaction between a dye precursor made of a colorless or light-colored leuco dye and a color developer made of phenols or an organic acid is disclosed in Japanese Patent Publication No. 43-4160, for example. Special Publication No. 45-14039,
and Japanese Patent Publication No. 48-27736.

In recent years, such heat-sensitive recording materials have been widely used as various information recording materials due to their advantages such as the ability to form colored images simply by heating and the ability to make recording devices relatively compact. has been done. especially,
Thermal facsimiles, thermal printers, and the like that use such thermal recording materials have been improved and are now capable of high-speed printing and high-speed image formation, which were previously considered difficult. As the speed of such equipment and hardware increases, the heat-sensitive recording media used are required to have significantly improved recording sensitivity than before.

Many proposals have been made to meet this requirement, but most of these proposals have characteristics in the combination of a dye precursor and a color developer, or the use of a thermofusible substance in addition to these. It is characterized by The above-mentioned thermofusible substances are also called sensitizers, and examples include l-hydroxy-2-naphthoic acid phenyl ester (Japanese Patent Application Laid-open No. 191089-1989), p-benzylbiphenyl (Japanese Patent Application Laid-open No. 82382-1982)
No.), benzyl naphthyl ether (JP-A-58-870
No. 94), dibenzyl terephthalate (JP-A No. 58-9
No. 8285 Lp-benzyloxybenzoate benzyl (JP 57-201691), diphenyl carbonate, ditolyl carbonate (JP 58-136489), m-terphenyl (JP 57-89994), and 1 , 2-bis(m-tolyloxy)ethane (JP-A-60-5658
No. 8) are known.

[Problem to be solved by the invention]

When a heat-sensitive recording medium containing a thermofusible substance as described above is heated, the thermofusible substance first melts, and the dye precursor and color developer are dissolved in this melt, so that both of them are dissolved. are mixed at the molecular level and a color reaction is induced. Therefore, these thermofusible substances have a suitable melting point (preferably 60-
140°C) and must have excellent compatibility with the dye precursor and color developer. It is also important that the thermofusible substance does not reduce the whiteness of the thermosensitive recording medium, and for this purpose, it is necessary to
It is desirable that it be extremely poorly soluble. Furthermore, it is desirable that the thermofusible substance has properties such as low sublimation properties. This is because it is thought to be deeply related to the phenomenon of so-called whitening, which causes a wispy appearance, and is an extremely important property for the practical use of thermosensitive recording materials. As mentioned above, many thermofusible materials have been proposed in the past, but there are few that satisfy all of the above conditions, and therefore there has been a demand for new materials.

The present invention provides a heat-sensitive recording material having a heat-sensitive coloring layer containing a novel thermofusible substance together with the dye precursor and color developer described above, and which has significantly improved recording sensitivity without deteriorating recording performance. This is what we are trying to provide.

[Means to solve the problem]

The heat-sensitive recording material of the present invention includes a sheet strip substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet strip substrate, and a dye precursor that reacts with the dye precursor under heating to develop color. and a thermosensitive coloring layer containing a color developer, and the thermosensitive coloring layer has the following general formula (I): (wherein R represents a hydrogen atom or a lower alkyl group, RZ, R3 and R4 each independently represents a hydrogen atom, a lower alkyl group, an alkoxy group, an aryl group, an aryloxy group, an aralkyloxy group, a halogen, or an aralkyl group. It is characterized by further containing a sensitizing agent.

The present inventors discovered that the use of the thermofusible substance of formula (1) above as a sensitizer has been proposed as a typical thermofusible substance (Japanese Patent Publication No. 14531/1983), and Compared to the use of stearic acid amide or higher fatty acid amide such as palmitic acid amide, which has been put into practical use,
It has been discovered that it is possible to obtain a heat-sensitive recording paper that exhibits extremely high recording sensitivity without causing a decrease in the whiteness of the heat-sensitive coloring layer and without exhibiting a phenomenon such as whitening that deteriorates the quality of colored images over time. , we have completed the present invention.

The present invention provides a heat-sensitive recording material that utilizes a color reaction between a colorless or monochromatic dye precursor (basic leuco dye) and a color developer that can develop a color by contacting this dye precursor with heating. The thermosensitive color forming layer is characterized in that a sensitizer consisting of the compound of the above formula (I) is contained. The reason why a specific thermofusible substance (hereinafter referred to as a sensitizer) as mentioned above improves the coloring sensitivity of a thermosensitive coloring layer is not fully clear, but it is because this compound has a low viscosity in the molten state and is a dye precursor. It is assumed that part of the reason for this is that it has appropriate compatibility with the body and color developer. Furthermore, the reason why the compound of formula (I) does not reduce the whiteness of the heat-sensitive coloring layer is because it is poorly soluble in water, and the reason why the compound of formula (I) does not reduce the whiteness of the heat-sensitive coloring layer is that it rarely causes phenomena such as whitening that deteriorate the recorded image quality. This is thought to be due to its low sublimation. However, the inventor does not adhere to this interpretation. Specific examples of the compound of formula (1) used in the present invention include the following.

(1) CH3+co, -C)lz4toCH□ (melting point 8
3°C) (melting point 110°C) (melting point 115°C) (melting point 108'C) (melting point 89°C) (melting point 83°C) (melting point 119°C) Sensitization consisting of a compound of formula (1) The agent is used in conjunction with a dye precursor and a developer. Further, it can be used in combination with other sensitizing compounds within a range that does not inhibit the desired effects of the present invention. The amount of the sensitizer used in the present invention is preferably 10 to 1000% by weight, and 50 to 1000% by weight based on the weight of the developer.
It is more preferable that it is 300% by weight.

The thermosensitive coloring layer containing the sensitizer of the present invention comprises a dye precursor, a color developer made of phenols or an organic acid, and a coloring agent for binding these and bonding the thermosensitive coloring layer to the sheet-like substrate. It preferably contains a binder and further contains an inorganic pigment, and may further contain waxes if necessary.

The leuco dye used as the dye precursor can be selected from conventionally known ones, such as crystal violet lactone, 3-(N-ethyl N-isopentylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-
Diethylamino-6-methyl-7-(o,p-dimethylanilino)fluorane, 3-(N-ethyl-p-)binder)-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl -7-anilinofluorane, 3-
Dibutylamino-6-methyl-7-anilinofluorane, 3-(N-cyclohexine-N-methylamino)-6
-Methyl-7-anilinofluorane, 3-diethylamino-7-(Ochloroanilino)fluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-diethylamino-6-methyl-7-chloro One or more selected from fluoran, 3-diethylamino-6-methylfluoran, 3-cyclohexylamino-6-chlorofluoran, etc. can be used.

As the color developer made of phenols or organic acids, conventionally known color developers can be used.
140483), bisphenol S, 4-hydroxy-4'-isopropyloxydiphenyl sulfone (JP-A-60-13852), 1.1-di(4-hydroxyphenyl)cyclohexane, 1.7-di(4-hydroxy phenylthio)-35-dioxahebutane
9-52694) and the like can be used.

Here, as other sensitizing compounds that can be used in combination with the sensitizer of the present invention, thermofusible organic compounds with a melting point of 50-150°C are used, but these have already been described [
This is as explained in the ``Prior Art'' column using typical examples.

In addition, examples of organic or inorganic pigments used in the heat-sensitive coloring layer include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate,
Clay, calcined clay, talc, and surface-treated inorganic fine powders such as calcium carbonate and silica, as well as urea-formalin resin, styrene/methacrylic acid copolymer,
and organic fine powder such as polystyrene resin.

Furthermore, the heat-sensitive coloring layer of the present invention may contain various waxes as required. As for those waxes,
Known waxes such as paraffin, amide wax, bisimide wax, and metal salts of highly absorbent fatty acids can be used.

The binder may include polyvinyl alcohol of 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. water-soluble polymeric materials such as acrylamide/acrylic ester/methacrylic acid terpolymer, styrene/maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein; Vinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, ethylene/vinyl acetate copolymer, and styrene/butadiene/acrylic copolymer. Various latexes such as polymers can be used.

The sheet-like substrate used in the thermal recording medium of the present invention is paper,
Coated paper whose surface is coated with clay plastic, etc.
You can choose from synthetic paper, which is mainly made from plastic, or plastic film. A coating liquid containing a mixture of the above-mentioned necessary components is applied onto at least one surface of such a sheet-like substrate and dried to produce a heat-sensitive recording material.

The coating amount is 1-15g/1 when the coating liquid layer is dry.
nT is preferable, and 2 to 10 g/rrf is more preferable. The heat-sensitive recording material of the present invention thus obtained has excellent high-speed recording suitability, high whiteness,
It has the advantage of not causing undesirable phenomena such as whitening in the recorded image area.

〔Example〕

The present invention will be specifically explained below with reference to Examples.

In addition, unless otherwise specified, "1 part" and "%" refer to "part by weight" and "11%", respectively.

Husband's house A thermosensitive recording paper was prepared by the following procedure.

10% polyvinyl alcohol water N solution 10 water
7. The above composition was ground in a sand grinder until the average particle size was 1.

10% polyvinyl alcohol aqueous solution 10% water
7
゜The above composition was subjected to a sand grinder and ground until the average particle size became 1-.

Q-varnish' JLv mineral 1 1.2-bis(4-methylphenyl) 20 polyvinyl alcohol 10% Ht.

water
70 The above composition was subjected to a sand grinder and ground until the average particle size was 1 Ha.

- Amount of color developed: 40 parts of liquid A, 80 parts of liquid rB, liquid J of C.
80 parts of calcium carbonate pigment, 20 parts of 30% paraffin dispersion, and 180 parts of 10% polyvinyl alcohol aqueous solution were mixed and stirred to prepare a coating liquid. This coating liquid was applied and dried on one side of a base paper having a basis weight of 50 g/rrf so that the coating amount after drying was 7.0 g/nf to form a heat-sensitive coloring layer. Furthermore, the surface smoothness of the surface is 600.
A heat-sensitive recording paper was prepared by processing with a super calender for a time of 1,000 seconds.

The heat-sensitive recording paper obtained as described above was subjected to the following tests to measure the recording sensitivity, measure the color density of the uncolored area on the surface of the heat-sensitive coloring layer, and compare whitening.

(a) Using a five-degree Toyo Seiki tilt tester, heat the sample for 100 milliseconds at a temperature of 120°C and a pressure of 2.5 kg/cJ, and measure the color density using a Macbeth densitometer RD. -9
14 (manufactured by Macbeth). This measured value represents the recording sensitivity of the thermal recording paper. Further, the density of the uncolored area (white area) on the surface of the recording layer was measured using the above densitometer, and the measured value was expressed as the degree of whiteness of the white area of the thermosensitive coloring layer.

(b) Using the thermal gradient tester described above, the sample was developed at a temperature of 150°C, and then the printed part was left in an environment of 40°C and 90% for 24 hours, and changes in the surface were observed. It was evaluated sensually. In Table 1, "Good" indicates that no change was observed in the colored printed area, and "Poor" indicates that so-called whitening, in which the printed surface becomes powdery, has occurred.

The test results are shown in Table 1.

1 lid group 1 The same operation as in Example 1 was performed. However, "Liquid D" having the following composition was used instead of "Liquid C".

2-bis(3-methoxyphenyl) 0 10% polyvinyl alcohol aqueous solution 10 water
70 test results are shown in Table 1.

The same operations as in Example 1 were carried out by Mr. Kojo. However, instead of "liquid C", "rE liquid" having the following composition was used.

1"" Formal dress 3 4-bis(2-methoxyphenyl) 0 10% polyvinyl alcohol water? g liquid 10 water
70 test results are shown in Table 1.

The same operation as in Example 1 was carried out. However, instead of "Liquid C", "Liquid F" having the following composition was used.

"ヱ"口"1 4-bis(4-n butoxyphene) 10% polyvinyl alcohol aqueous solution 1゜water
The results of the 7° test are shown in Table 1.

A thermosensitive recording paper was prepared in the same manner as in Example 1, except that the following "Liquid G" was used instead of "Liquid C" in Fumasu Ikaku Example 1.

``SAshi'' formal dress screw (2-phenoxyphenylene 0 10% polyvinyl alcohol water 1llWt 1
0 water
70 test results are shown in Table 1.

The same operation as in Comparative Flaming Example 1 was performed. However, instead of "Liquid C", "Liquid H" having the following composition was used.

Stearic acid adduct 20]O%
Polyvinyl alcohol water soluble Kl 10 water
70 test results are shown in Table 1.

And m The same operation as in Example 1 was performed.

however, "Liquid C" Instead, use “Liquid I” with the following composition. It was used.

10% polyvinyl alcohol aqueous solution 0 Water 0 As is clear from Table 1, Examples 1 to 5 according to the present invention
The thermal recording paper of Comparative Example 1 was satisfactory in terms of recording sensitivity, white background density, and whitening resistance, but the thermal recording paper of Comparative Example 1 had low recording density, white background density, and unsatisfactory V. The thermal recording paper of Comparative Example 2 had poor whitening resistance;
Moreover, the density haze in the white background area was unsatisfactory.

〔Effect of the invention〕

Since the heat-sensitive recording material of the present invention has a heat-sensitive coloring layer containing a sensitizer made of a new thermofusible compound, it has excellent high-speed recording suitability, high whiteness, and undesirable problems such as whitening. It does not induce any phenomena, has extremely well-balanced properties in terms of quality, and has extremely high practical value.

Claims (1)

[Claims] 1. A sheet-like substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet-like substrate, and reacting with the dye precursor under heating to develop color. It has a heat-sensitive coloring layer containing a color developer, and the heat-sensitive coloring layer has the following general formula (I): ▲There are mathematical formulas, chemical formulas, tables, etc.▼・・・・・・(I
) (However, in the formula, R_1 represents a hydrogen atom or a lower alkyl group, and R_2, R_3 and R_4 each independently represent a hydrogen atom, a lower alkyl group, an alkoxy group,
Aryl group, aryloxy group, aralkyloxy group,
1. A heat-sensitive recording material, further comprising a sensitizer consisting of at least one aromatic compound represented by a halogen or an aralkyl group.