JPH03292186A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain excellent recording sensitivity without lowering various recording capacities by providing a thermal color forming layer formed using a dye precursor, a developer and a specific heat-meltable substance on at least one surface of a sheet like support. CONSTITUTION:A thermal color forming layer containing a colorless or light- colored dye precursor and the developer reacting with the dye precursor under heating to develop a color is provided on at least one surface of a sheet like support. This thermal color forming layer further contains at least one kind of an ether compound represented by formula I (wherein R1 and R2 are a 2 - 4C alkyl group). Since this compound has low viscosity in a molten state and also has a proper affinity for the dye precursor and the developer, the sensitivity of the thermal color forming layer is estimated to be enhanced. The thermal color forming layer is not lowered in whiteness because it is hardly soluble in water and reduced in a phenomenon deteriorating a recording image such as whitening because of its low sublimability.

Description

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

[Conventional technology]

Heat-sensitive recording materials that utilize a color-forming reaction under heating between normally colorless or light-colored leuco dyes and phenols or organic acids are disclosed in, for example, Japanese Patent Publication No. 43-4160 and Japanese Patent Publication No. 45-14039.
It is disclosed in Japanese Patent Publication No. 48-27736, etc., and has been widely put into practical use. In recent years, such heat-sensitive recording materials have been known to form colored images simply by heating;
Due to its advantages such as the fact that the recording device can be made relatively compact, it is widely used as a variety of information recording materials. In particular, the devices of thermal facsimiles, thermal printers, etc. that use such thermal recording materials have been improved, and it has become possible to perform high-speed printing and high-speed image formation, which was 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 many of these proposals have a characteristic in the combination of a dye precursor and a color developer, or in the combination of a thermofusible substance. It is something. The above-mentioned thermofusible substance is also called a sensitizer, and examples include 1-hydroxy-2-naphthoic acid phenyl ester (Japanese Patent Application Laid-open No. 191089/1989), p-benzylbiphenyl (Japanese Patent Application Laid-open No. 82382/1982), Benzyl naphthyl ether (JP 58-87094), dibenzyl terephthalate (JP 58-98285)
, benzyl p-benzyloxybenzoate (Japanese Patent Application Laid-open No. 1983-
No. 201691), diphenyl carbonate, ditolyl carbonate (Japanese Patent Publication No. 136489/1989), m-terphenyl (Japanese Patent Application Publication No. 89994/1989), 1,2-bis(m-tolyloxy)ethane (Japanese Patent Application Publication No. 60/1989) No. 56588) l, 5-bis(p-methoxyphenoxy)-3-oxapentane (
Known examples include JP-A-62-181183) and penzyl oxalate (JP-A-64-1583).

[Problems 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 then the dye precursor and the color developer are melted. By dissolving the two, they mix at the molecular level and a coloring 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 not to reduce the whiteness of the heat-sensitive recording medium, and for this purpose, it is desirable that the thermofusible substance has extremely low solubility in water, and also has properties such as low sublimation. It is desirable to be present. The sublimability of thermofusible substances is
In particular, it is thought to be closely related to the so-called whitening phenomenon in which the heat-colored portion of a heat-sensitive recording material becomes powdery over time, and is an extremely important property for the practical use of a heat-sensitive recording material.

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 has a heat-sensitive coloring layer formed using a novel thermofusible substance together with the dye precursor and color developer described above, and has significantly improved recording sensitivity without deteriorating recording performance. The purpose is to provide a thermosensitive recording medium.

[Means to solve the problem]

The heat-sensitive recording material of the present invention comprises a sheet-like substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet-like substrate, and a developer that reacts with the dye precursor under heating to develop color. and a coloring agent, the thermosensitive coloring layer is represented by the following - Monya (1): (wherein R+ and Rt represent an alkyl group having 2 to 4 carbon atoms.) It is characterized in that it further contains at least one ether compound.

The present inventors discovered that the use of the thermofusible substance of the above formula (I) as a sensitizer has been proposed as a typical thermofusible substance (Japanese Patent Publication No. 14531/1983), and Compared to the use of higher fatty acid amides such as stearic acid amide and balmitic acid amide, which have been put into practical use, there is no reduction in whiteness, and there is a phenomenon called whitening that deteriorates the quality of colored images over time. The present inventors have discovered that extremely high recording sensitivity can be obtained without experiencing the above problems, and have completed the present invention.

The present invention provides a thermosensitive recording material that utilizes a color reaction between a colorless or monochromatic basic leuco dye (dye precursor) and a color developer that can develop a color by contacting the dye precursor. It is characterized in that the coloring layer contains the compound of formula (I) above. 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 the reason is that 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 whiteness of the heat-sensitive coloring layer does not decrease is because it is poorly soluble in water, and the reason why it rarely causes phenomena such as whitening that deteriorate recorded image quality is due to its low sublimability. it is conceivable that. However, the inventor does not adhere to this interpretation. Formula (I) used in the present invention
Specific examples of the sensitizer include the following.

The compound of the present invention can be synthesized by various synthetic methods, but most conveniently, it can be synthesized easily and in high yield using the Wtlliamson reaction shown below. In the reaction formula below, R1 and Rt are the same as defined above.

130-1; mth 180-L, fi The sensitizer of formula (I) is used together with a dye precursor and a color developer. Further, it can be used in combination with other sensitizers within a range without inhibiting the desired effects of the present invention. The amount of the sensitizer used in the present invention is 10 to 1
000% by weight, and more preferably 50 to 300% by weight.

The thermosensitive coloring layer containing the sensitizer of the present invention mainly contains dye precursors,
It preferably contains a color developer made of phenols or organic acids, and a binder for binding these and joining the thermosensitive coloring layer to the sheet-like substrate, and further contains an inorganic pigment,
Furthermore, it may contain waxes if necessary.

The leuco dye used as a dye precursor can be selected from conventionally known ones, such as crystal violet lactone, 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluoran. , 3-diethylamino-6-methyl-7-anilinofluorane, 3
-diethylamino-6methyl-7-(oSp-dimethylanilino)fluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane Linofluorane, 3-
Dibutylamino-6-methyl-7-anilinofluorane, 3-(N-cyclohexine-N-methylamine)-6
-Methyl-7-anilinofluorane, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-(m-trifluoromethylanilino)
One or more selected from fluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 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), SL-di(4-hydroxyphenyl)cyclohexane, 1.7-di(4-hydroxyphenyl) One or more types selected from thio)-3,5-dioxahebutane (Japanese Patent Application Laid-Open No. 59-52694) can be used.

Here, as other sensitizers that can be used in combination with the sensitizer of the present invention, thermofusible organic compounds with a melting point of 60-150°C are used, but these have already been explained with typical examples. That's exactly what I did.

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,
In addition to clay, fired clay, talc, and surface-treated inorganic fine powders such as calcium carbonate and silica, and
Examples include organic fine powders such as urea-formalin resin, styrene/methacrylic acid donor polymer, and polystyrene resin.

Furthermore, the heat-sensitive coloring layer of the present invention may contain various waxes as required. Known waxes such as paraffin, amide wax, bisimide wax, and metal salts of highly absorbent fatty acids can be used. Regarding the adhesive, 11 types of polyvinyl alcohol of various molecular weights, starch and its derivatives,
Cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide/acrylic acid ester copolymer, acrylamide/acrylic acid ester/methacrylic acid ternary copolymer, styrene /Maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin,
and water-soluble polymeric materials such as casein, as well as polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, ethylene/acetic acid vinyl copolymer, and styrene/
Latexes such as butadiene/acrylic copolymers can be used.

The sheet-like substrate used in the heat-sensitive recording medium of the present invention can be selected from paper, coated paper whose surface is coated with clay plastic, synthetic paper made mainly 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/rr when the coating liquid is dry.
r is preferred, and 2 to 10 g/- is particularly preferred.

The heat-sensitive recording material of the present invention thus obtained has excellent high-speed recording suitability, high whiteness, and does not cause undesirable phenomena such as whitening in the recorded image area.

〔Example〕

The present invention will be specifically explained below with reference to Examples. still,
Unless otherwise specified, "part" and "%" respectively refer to "part" and "%".
Parts by weight and % by weight.

35.0 g of α,α′-dichloro-p-xylene and 5
3.7 g of 2,4-dimethylphenol and 60.7 g
Add potassium carbonate to 500 cc of acetone and stir. Heat the bath temperature to 85°C to reflux the acetone. After continuing refluxing for a day and night, acetone was distilled off. Ether was added to this residue to perform ether extraction, and the ether extract was washed with alkali and acid, and the ether was distilled off to obtain a pale yellow solid. This was recrystallized twice from ethyl alcohol to obtain 58.8 g of white solid. Its melting point was 124-126°C. Mass spectrometry and nuclear magnetic resonance spectroscopy revealed that this solid product was α, α
It was confirmed that it was '-bis(2,4-dimethylphenoxy)-p-xylene.

35.0 g of α,α′-dichloro-p-xylene and 5
3.7 g of 2,4-dimethylphenol) and 60,7
g of potassium carbonate is added to 500 cc of acetone and stirred. Heat the bath temperature to 85°C to reflux the acetone.

After continuing refluxing for a day and night, acetone was distilled off. Ether was added to this residue to perform ether extraction, and the ether extract was washed with alkali and acid, and the ether was distilled off to obtain a pale brown solid. This was recrystallized twice from ethyl alcohol to obtain 52.2 g of white solid. Its melting point was 123-125°C. Mass spectrometry and nuclear magnetic resonance spectrometry revealed that this solid product was α
, α'-bis(2,6-dimethylphenoxy)-p-xylene.

35.0 g of α,α′-dichloro-p-xylene and 7
8.3 g of 2,6-di-1so-propylphenol and 60.7 g of potassium carbonate are added to 600 cc of acetone and stirred. Heat the bath temperature to 85°C to reflux the acetone. After continuing reflux for a day and night, the acetone is distilled off. Add ether to this residue and perform ether extraction.
After washing the ether extract with alkali and acid, the ether was distilled off to obtain a pale yellow solid. This was recrystallized twice from ethyl alcohol to obtain 61.0 g of white solid.

Its melting point was 116-117°C. Mass spectrometry and nuclear magnetic resonance spectroscopy revealed that this solid product was α,α′-bis(2,6-diis.

-propylphenoxy)-p-xylene.

43.6 g of α,α′-dichlorop-xylene and 5
9.1 g of p-cresol and 75.5 g of potassium carbonate are added to 600 cc of acetone and stirred.

Heat the bath temperature to 85°C to reflux the acetone.

After continuing refluxing for a day and night, acetone was distilled off. Ether was added to this residue to perform ether extraction, and the ether extract was washed with alkali and acid, and the ether was distilled off to obtain a pale yellow solid.

This was recrystallized twice from ethyl alcohol to yield 59.9 g.
A white solid was obtained. Its melting point was 170-172°C. This solid product was confirmed to be α,α'-bis(4-methylphenoxy)-p-xylene by mass spectrometry and nuclear magnetic resonance spectroscopy.

Example 1 A thermosensitive recording paper was prepared by the following procedure.

■ Ingredients for preparing dispersion A Amount (parts) 3-(N-
Isopentyl-N-ethylamino)-6-methyl-7-anilite fluorane 20 Polyvinyl alcohol 10% liquid 10 Water 7
0 The above-mentioned composite material was subjected to a sand grinder and ground until the average particle size became 1 μm.

■ Dispersion B preparation 11ri and 4,4'-isopropylidene bifernol
10α, α′-bis(2,4-
dimethylphenoxy)-p-xylene
lO polyvinyl alcohol 10% 10
water
70 The above composition was subjected to a sand grinder and ground until the average particle size was 1 μm.

Tsubasa - Tozurinzawaka 40 parts of the above liquid A, 160 parts of liquid B, 4 parts of calcium carbonate pigment
0 parts, 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 coated on one side of base paper with a basis weight of 50 g/nf so that the coated amount after drying was 7.0 g/ffl, and dried to form a thermosensitive coloring layer, thereby producing thermosensitive recording paper. .

The heat-sensitive recording paper obtained as described above is treated with a supercalender, and its surface smoothness is adjusted to 600 to 100.
It was set to 0 seconds. The samples thus obtained were subjected to the following tests to measure the recording sensitivity, measure the color density of the uncolored area on the recording layer surface, and compare whitening, and the results are shown in Table 1.

” Using a Toyo Seiki thermal gradient tester, the temperature was 120°C and the pressure was 2.
．． The sample was heated for 100 milliseconds under the condition of 5 kg/crj, and the color density was measured using a Macbeth densitometer RD-9.
Measured at 14. This measured value represents the recording sensitivity of the thermal paper. The density of the uncolored area (blank 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.

After developing the sample at a temperature of 50°C using the above testing machine, the printed area was left in an environment of 90% at 40°C for 24 hours, and changes in the surface were sensory evaluated. . 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.

Rise Dane A thermosensitive recording paper was prepared by the following procedure.

l Coating: 85 parts of baked clay made of paper (trade name: Ansilex) and 320 parts of water.
40 parts of a styrene-butadiene copolymer emulsion (solid content 50%) and 50 parts of a 10% oxidized starch aqueous solution were mixed into the resulting dispersion, and the resulting coating liquid was
A pigment undercoated paper was prepared by applying the pigment to one side of a base paper having a basis weight of 48 g/rrr so that the coating amount after drying was 7.0 g/rrr.

50 parts of the dispersion A, 200 parts of the dispersion B, 2 parts of calcium carbonate
5 parts of a 30% paraffin dispersion, and 180 parts of a 10% polyvinyl alcohol aqueous solution were mixed and stirred to prepare a coating liquid. The obtained coating liquid was applied and dried on the pigment-coated surface of the pigment undercoated paper so that the coating amount after drying was 5.0 g/rrr to form a thermosensitive coloring layer, thereby producing thermosensitive recording paper. .

The same test as in Example 1 was conducted using this thermosensitive recording paper.

The results are shown in Table 1.

Figure-1 The same operation as in Example 2 was performed. However, in preparing the B solution used for forming the thermosensitive coloring layer, α, α' bis(2,4-
α, instead of dimethylphenoxy)-p-xylene,
α'-bis(2I 6-dimethylphenoxy)-p-xylene was used.

The test results are shown in Table 1.

The same operation as in Example 2 was carried out. However, in preparing the B solution used for forming the thermosensitive coloring layer, α,α'-bis(2,
Instead of 4-dimethylphenoxy)-p-xylene,
α,α′-bis(2,6-di-1so-propylphenoxy)-p-xylene was used.

The test results are shown in Table 1.

The same operation as in Example 1 was carried out. However, in preparing liquid B, α,α'-bis(2,4-dimethylphenoxy)-
Stearin amide was used instead of p-xylene.

The test results are shown in Table 1.

The same operation as in Example 1 was carried out. However, in preparing liquid B, α,α'-bis(2,4-dimethylphenoxy)-
α,α-bis(4-methylphenoxy)-p-xylene was used instead of p-xylene.

The test results are shown in Table 1.

Satoshi 1 The same operation as in Example 2 was performed. However, in preparing liquid B, α,α'-bis(2,4-dimethylphenoxy)-
Stearamide was used instead of p-xylene.

The test results are shown in Table 1.

The same operations as in Example 2 were performed. However, in preparing liquid B, α,α'-bis(2,4-dimethylphenoxy)-
α,α′-bis(4-methylphenoxy)-p-xylene was used instead of p-xylene.

The test results are shown in Table 1.

The same operation as in Example 2 was carried out. However, in preparing liquid B, α,α'-bis(2,4-dimethylphenoxy)-
l-hydroxy-2-naphthoic acid phenyl ester was used instead of p-xylene.

The test results are shown in Table 1.

This is an example using α,α-bis(4-methylphenoxy)-p-xylene shown in Table 1. The chemical structure of α,α-bis(4-methylphenoxy)-p-xylene differs from the compound of the present invention in that the substituent is only one methyl group at the para position, but it has a considerably higher melting point. As is clear from the comparative example, the performance as a sensitizer is much inferior to that of the compound of the present invention.

〔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 material, 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)

[Scope of Claims] A sheet-like substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet-like substrate, and a color developer that reacts with the dye precursor under heating to develop color. The thermosensitive coloring layer has the following general formula (I): ▲There are numerical formulas, chemical formulas, tables, etc.▼(I) (However, in the formula, R_1 and R_2 have 2 to 2 carbon atoms. A thermosensitive recording material further comprising at least one ether compound represented by: