JPH0431083A - Thermal recording medium - Google Patents

Abstract

PURPOSE:To obtain high recording sensitivity and heat resistance without generation of a whitening phenomenon and deterioration of whiteness by adding p- methoxyphenylester cinnamonate to a thermal coloring layer. CONSTITUTION:p-methoxyphenylester cinnamonate is a compound shown by formula I or II and is used with leuco dye and developer. The preferable dosage of the compound is 10 to 1000 wt. % for a developer. The blend which is composed of properly mixed various materials and colors due to heating is applied to the surface of paper or mainly plastic film to obtain a thermal recording medium. The thermal recording medium thus obtained has an excellent high speed recording properties, high whiteness and does not indicate an undesirable trend such as whitening.

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]

A heat-sensitive recording material utilizing a heated coloring reaction between a normally colorless or light-colored leuco dye and a phenol or an organic acid was published in Japanese Patent Publication No. 43-41. (No. 30, Japanese Patent Publication No. 4514039, Japanese Patent Publication No. 48-2773 (No. 3'', 9) and has been widely put into practical use. Because of the advantages such as being able to make the recording device relatively compact,
It is widely used as a material for recording various information. In particular, a thermal facsimile using such a thermal recording medium,
Thermal printers and other devices have improved and are now capable of high-speed printing and high-speed image formation, which was difficult to do in the past. As the speeds of equipment and hardware become faster, the thermal recording media used are required to have significantly higher recording sensitivity than before. Many proposals have been made to meet this requirement, many of which involve the combination of a leuco dye and a color developer in combination with a thermofusible substance.

These thermofusible substances are called sensitizers, such as 1-hydroxy-2-naphthoic acid phenyl ester (Japanese Patent Application Laid-open No.
1.91089), p-benzylbiphenyl (JP 60-82382), pencil naphthyl ether (JP 58-87094), dibenzyl terephthalate (JP 5898285), p-benzyloxybenzoic acid Benzyl (JP 57-201691), diphenyl carbonate, ditolyl carbonate (JP 58-136489), m-terphenyl (JP 57-89994),
1.2-bis(m-tolyloxy)ethane (Unexamined Japanese Patent Publication No. 1983
-56588), 1.5 his(p-methoxyphenoxy)-3-oxapentane (JP-A-62-1.81.1
83), benzyl oxalate, p-methylbenzyl oxalate, and 0-chloropenzyl oxalate (Japanese Patent Application Laid-open No. 641583).

[Problems to be solved by the invention] When a heat-sensitive recording material containing such a thermofusible substance is heated,
First, the thermofusible substance melts and dissolves the dye and color developer, thereby mixing the two at the molecular level and inducing a color reaction.

Therefore, these thermofusible substances must have an appropriate melting point (preferably 80 to 120 DEG C.) and have excellent compatibility with dyes and color developers. In addition, in order not to reduce the whiteness of the heat-sensitive recording material, it is desirable that these thermofusible substances are extremely poorly soluble in water and do not color the heat-sensitive coloring layer; It is desirable to have characteristics such as floridity or less. The latter is thought to be particularly 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 heat-sensitive recording materials. becomes. Furthermore, such heat-sensitive recording materials are often temporarily placed at relatively high temperatures of 60° C. to 70° C. during use, and it is desired that color development be suppressed to a low level at these temperatures. Another important feature is that it is relatively inexpensive when used industrially. As mentioned above, many thermofusible materials have been proposed in the past, but there are very few materials that do not meet all of the above requirements.Therefore, new materials that do not meet these requirements have been sought. The present invention solves the problems of conventional sensitizers by providing a new thermofusible substance to be used together with the above-mentioned leuco dye and color developer, thereby achieving high recording sensitivity and high quality recorded images. The present invention aims to provide a heat-sensitive recording material that can be formed at high speed.

[Means to solve the problem]

In order to achieve the above object, the present inventors have conducted research and found that a sheet-like substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet-like substrate,
In a heat-sensitive recording material having a heat-sensitive color-forming layer including a color developer that develops color by reacting under heating, the heat-sensitive color-forming layer is a silica formed by the following structural formula [I] % formula %11] When containing acid p-methoxyphenyl ester, stearic acid amide, palmitic acid amide F, etc., which have been proposed as typical thermofusible substances (Japanese Patent Publication No. 14531/1982) and have been put into practical use. It has been discovered that, compared to higher fatty acid amides, extremely high recording sensitivity and heat resistance can be obtained without causing a decrease in whiteness and without experiencing the phenomenon of whitening that deteriorates the quality of colored images over time. , the present invention has been achieved.

The reason why a specific thermofusible substance (hereinafter referred to as a sensitizer) as mentioned above improves the color development sensitivity of a thermosensitive recording medium containing it is not fully clear, but if this compound is It is presumed that this is because it has a melting point and has appropriate compatibility with color developers and dye precursors.

In addition, in order not to reduce whiteness, the compound of the present invention has low solubility in water, and the reason why phenomena such as whitening that deteriorate recorded image quality are extremely low is due to low gastric irritability and heat resistance. The reason for this is thought to be that it has an appropriate melting point.

Although the compounds shown in the present invention can be synthesized by various synthetic methods, a typical synthetic reaction for cinnamic acid p-methoxyphenyl ester is shown below.

The compound of the present invention is used together with a leuco dye and a color developer.

Further, it can be used in combination with other sensitizers within a range that does not inhibit the desired effects of the present invention. The amount of the compound of the present invention used is preferably 10 to 1000% by weight, more preferably 50 to 300% by weight, based on the color developer.

The heat-sensitive coloring layer using the compound of the present invention mainly consists of leuco dyes,
It consists of a color developer made of phenols or organic acids, and the compound of the present invention. Further, the coloring layer preferably contains an inorganic pigment, and may further contain waxes if necessary. In addition, a binder for fixing these components to the support is included as an essential component.

The content of the leuco dye in the heat-sensitive coloring layer is generally 5 to 20% by weight, and the content of the color developer is generally 10 to 40% by weight.
It is. The binder content is generally 5 to 20% by weight, and when white pigments and waxes are included, the f content is generally 10 to 50% by weight and 5 to 30% by weight, respectively.

The leuco dye spot may be any conventionally known one, such as the following.

Crystal violet lactone, 3-(N-ethyl-N
-isopentylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6methyl-7-(0
, 1)-dimethylanilino)fluorane, 3-(N-ethyl-1]-toluidino)-6-methyl-7-anilinofluorane, 3-pyrrolisino6-methyl-7-anilinofluorane, 3- Dibutylamino-6-methyl-7-
Anilinofluorane, 3-(N-cyclohexyl-N-
methylamino)-6-methyl-7anilinofluorane,
3-diethylamino-7-(0-chloroanilino)fluoran, 3-diethylamino-7-(m-)lifluoromethylanilino)wallaoran 3-diethylamino-6-
Methyl-7-chlorofluorane, 3-diethylamino 6
-Methylfluorane, 3-cyclohexylamino-6-
Chlorofluorane. Two or more of these may be used in combination.

As the color developer made of phenols or organic acids, any conventionally known developer may be used, and examples thereof include the following.

Bisphenol A, benzyl p-hydroxybenzoate (
JP-A-52-1.40483), hisphenol S,
4-Hydroxy-4°-isopropyloxydiphenylsulfone (JP 6013852), ], 1-di(
These include 4-hydroxyphenyl)cyclohexane, 1,7-(hyroxyphenylthio)-3,5-thioxahebutane (Japanese Patent Application Laid-Open No. 59-52694), and the like.

Here, the compound of the present invention and the so-called sensitizer that can be used as a sensitizer have a melting point of 80 to 12 (heat of BiC iiJ
Melt↑! 1.Whether organic compounds are used or not has been explained using typical examples.

In addition, organic or inorganic pigments used in the coloring layer include calcium carbonate, silica, 1111 lead oxide, titanium oxide, alumina j1 hydroxide, rrrr lead hydroxide, barium sulfate, clay, fired clay, and talc. In addition to surface-treated inorganic fine powders such as carbonic acid and silica, fine powders such as urea-formalin resin, styrene/methacrylic acid copolymer, polystyrene resin, etc. can.

Furthermore, the coloring layer of the present invention may contain various waxes as required. They may be known ones such as paraffin, amide wax, bisimide wax, and metal salts of high-quality fatty acids. Also, regarding the adhesive,
Borihinyl alcohol of various molecular weights, starch and its derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide/acrylic acid ester copolymer, acrylamide /acrylic acid ester/methacrylic acid terpolymer, styrene/maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate,
In addition to water-soluble polymers such as gelatin and casein, polyvinyl acetate, polyurethane, styrene/butadiene copolymers,
Polyacrylic acid, polyacrylic ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, ethylene/onyl acetate copolymer, styrene/butadiene/
Latex such as acrylic copolymer can be used.

A mixture that develops color when heated by appropriately mixing these materials is applied to paper, coated paper whose surface is coated with clay plastic, synthetic paper made mainly from plastic, or even plastic film. Made with heat-sensitive recording material. The coating amount is preferably 1 to 1.0 g/nf, and 2 to 7 g/nf when the coating layer is dry.
Particularly preferred is n.

In this way, the heat-sensitive recording material obtained by the present invention has excellent high-speed recording suitability, high whiteness, and does not exhibit undesirable properties such as whitening in the recorded image area.

In addition, as related to the present invention, the following general formula [II
I] Sensitizer represented by (JP-A-62-53876)
It has been known.

(In the above general formula, n is an integer of 0.1.2) However, among the compounds represented by the general formula [TIT], compounds in which at least one R is coordinated at the ortho position or the meta position has a lower effect of y1 on sensitivity than the sensitizer of the present invention (a compound that coordinates only at the R or para positions). The reason for this is not fully clear, or it may be related to the fact that the presence of substituents at the ortho or meta positions limits the linearity of the molecule, resulting in a decrease in crystallinity. Examples of compounds having a substituent at the ortho or meta position include the following.

Furthermore, among those having a substituent at the para position, compounds having an alkoxy group, which is a particularly strong electron-donating group, have a high ability to increase the sensitivity by ten shifts, and in particular, in the case of meI, xy, and ethoxy, the sensitivity increases significantly. This discovery led to the completion of the present invention.

EXAMPLES The present invention will be explained in detail with reference to Examples below. Please note that there are no special provisions.++1. ．． ! The numbers are 1i-i.

〔Example〕

"Synthesis Example 1" Synthesis of cinnamic acid p-methquin phenyl ester 4. 4 g (0°03 mol) of cinnamic acid and 3. 6g (0.03mo
Add thionyl chloride from I) and slowly heat this mixture to 80°C using a bath. It was warm. Gas generation is observed as the reaction progresses. This gas was absorbed into an alkaline aqueous solution. Once gas evolution has stopped, cool the mixture to room temperature; 3. 7 g (0.03 mo I) of p-methoxyphenol was added.

It reacts violently and generates gas. Leave it for a while until the gas generation stops, remove the hot water bath, and heat it in an oil bath at 200℃.
It was heated for 2 hours. When the mixture was cooled to room temperature again, it became a solid, which was recrystallized from ethanol.5.
5 g of white crystals were obtained. The melting point was 99.0°C. This solid product was confirmed to be cinnamic acid p-methoxyphenyl ester by measurements of nuclear magnetic resonance spectrum and mass spectrometry.

"Synthesis Example 2" Synthesis of cinnamic acid p-ethoxyphenyl ester The same procedure as Synthesis Example 1 was carried out. However, instead of p-methoxyphenol, p-ethoxyphenol 4゜1 g (0
, 03mo I) was used. 5.7 g (7) of white crystals were obtained. The melting point was 110°C. This solid product was confirmed to be cinnamic acid p-ethoxyphenyl ester by measurements of nuclear magnetic resonance spectrum and mass spectrometry.

Example 1 ■ Preparation of dispersion A 3-(N-isopentyl-N-ethylamino)6-methyl-7-anilite fluoran polyvinyl alcohol 10% solution 10 water
70 This composition was ground to an average particle size of 1 μm using a sand grinder.

■ Preparation of dispersion B 4.4゛ -isopropylidene biphenyl cinnamic acid p
-Methoxyphenyl ester polyvinyl alcohol 1
0% liquid 10 water
70 This composition was ground to an average particle size of 1 μm using a sand grinder.

(2) Preparation of coloring layer 40 parts of the above liquid A, 160 parts of liquid 13, 40 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. 50g/rr of this coating liquid? A heat-sensitive recording paper was obtained by applying and drying the mixture to a base paper so that the coating amount after drying was 7°0 g/rd.

Example 2 ■ Adjustment of pigment undercoated paper: 85 parts of fired lay (trade name: Ansilex) and 320 parts of water.
40 parts of styrene-butanene copolymer emulsion (solid content 50%) was added to 10
The coating liquid obtained by mixing 50 parts of 7% starch oxide aqueous solution was 4
8 g/n (base paper) Second, the coating amount after drying is 7.0 g/n.
A pigment-primed paper was obtained by coating to obtain rrf.

■ To form a coloring layer: 50 parts of dispersion, 200 parts of B dispersion, Cal carbonate 9915
25 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 coated liquid was applied to the above-mentioned pigment undercoated paper at a coating weight of 5.0 g/i after drying and dried to obtain a heat-sensitive recording paper.

Example 3 A thermosensitive recording paper was obtained in the same manner as in Example 2, except that in the preparation of liquid B, p-methoxyphenyl cinnamate ester was used instead of p-methoxyphenyl cinnamate ester.

Comparative Example 1 The same operation as in Example 1 was performed. However, in Preparation Solution 13, stearic acid amide was used instead of cinnamic acid l)-methoxyphenyl ester.

Comparative Example 2 The same operation f+ as in Example 2 was performed. However, due to the odor of the I3 preparation, stearamide was used instead of p-methoxyphenylnisder cinnamate.

Comparative Example 3 The same operation as in Example 2 was performed. However, in Preparation B, 1-hydroxy-2-naphthoic acid phenyl ester was used instead of cinnamic acid 1)-methoxyphenyl ester.

Comparative Example 4 Example 2 The operation was repeated seven times. However, in the mouth preparation liquid, cinnamic acid 0-methylphenyl ester was used instead of cinnamic acid l)-methoxyphenyl ester.

Comparative Example 5 The same operation as in Example 2 was performed. However, in the mouth preparation liquid, instead of cinnamic acid p-methoxyphenyl ester,
Cinnamic acid 2,4-dichlorophenyl ester was used.

Comparative Example 6 The same operation as in Example 2 was performed. However, in the I3 preparation solution, cinnamic acid 0-acetylphenyl ester was used instead of cinnamic acid p-methoxyphenyl ester.

Comparative Example 7 The same operation as in Example 2 was performed. However, in Preparation Solution 13, cinnamic acid 2-acetyl-5-methoxyphenyl ester was used instead of cinnamic acid p-methoxyphenyl ester.

The ten types of thermal papers obtained as described above were treated with a supercalender so that the surface smoothness measured at a smoothness of 31 was 600 to 1000 seconds. Measurement of recording sensitivity for the sample obtained in this way,
The color density of the uncolored area of the recording layer surface was measured and a comparative test of whitening was conducted, and the results are summarized in Table 1.

Table 1 Recording sensitivity and measurement of blank area density Recording sensitivity was measured using a Toyo Seiki thermal gradient tester at a temperature of 120
°C pressure 2, 5 kg / 100m5 in ClIr
The ec sample was heated 7, and the color density at that time was measured using a Maches density (formerly R1)-914, which was taken as a value representative of the recording sensitivity of thermal paper. The density of the uncolored area (blank area) on the surface of the recording layer was measured using the same densitometer, and was taken as a representative value of whiteness.

Evaluation of whitening For whitening, use the above test machine to develop a sample at a temperature of 150°C, and leave the printed area in an environment of 40"C and 90% for 24 hours.
Changes in the surface were sensually evaluated.

In the table, "Good" indicates that no change in the colored printed area was observed, and "Poor" indicates that the printed surface became powdery, so-called whitening.

As shown in Table 1, the compound of the present invention has a recording sensitivity comparable to that of conventionally used stearic acid amide, and
It can be seen that it has excellent whitening resistance compared to 1-hydroxy-2-naphthoic acid phenyl ester. Also, comparative example 4
7 shows that the recording sensitivity is superior to that of the compound exemplified in JP-A No. 625387G.

According to the claims of JP-A No. 62-53876,
If the substituent is applicable, the substituent is ortho, meta,
It should be a highly sensitive sensitizer for the para and position, but as shown in Table 1, specific high sensitivity can be achieved by placing a specific substituent at a specific position. has been done.

〔Effect of the invention〕

Since the present invention uses a new thermofusible material, it has excellent high-speed recording suitability, high whiteness, little static coloring, and does not induce undesirable phenomena such as whitening, so it has excellent quality. The present invention provides a heat-sensitive recording material having extremely well-balanced properties.

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;
It has a heat-sensitive coloring layer including a coloring agent that develops color by reacting under heating, and the heat-sensitive coloring layer has the following structural formula [I
] ▲There are mathematical formulas, chemical formulas, tables, etc.▼...[I] or [II] ▲There are mathematical formulas, chemical formulas, tables, etc.▼...[II] Contains cinnamic acid p-alkoxyphenyl esters A heat-sensitive recording medium characterized by the following.