JPH0242076B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermosensitive recording medium. More specifically,
Colorless or light-colored coloring substances (hereinafter referred to as dyes)
In a heat-sensitive recording material having a heat-sensitive functional layer whose main components are a color-forming substance (hereinafter referred to as a color-forming agent) that develops color of a dye, the general formula () {In formula (), R ₁ , R ₂ and R ₃ represent a hydrogen atom, a hydroxyl group, an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, and R ₄ represents an alkyl group having 23 or less carbon atoms. However, at least one of R ₁ , R ₂ and R ₃ is an alkyl group, a cycloalkyl group,
It is an aryl group or an aralkyl group. } The present invention relates to a heat-sensitive recording material containing at least one type of phenolic compound represented by the following as a coloring agent. Special Publication No. 43-4160, No. 45-14039 or Japanese Patent Publication No. 45-14039
As is clear from No. 57-129787, some phenolic compounds have already been used as coloring agents for thermosensitive recording materials. However, in recent years, heat-sensitive recording devices have rapidly developed, and the fields of application of heat-sensitive recording bodies have been expanding accordingly, and various new characteristics have come to be demanded of the recording bodies. Particularly important characteristics that are being questioned are the thermal responsiveness of the recording medium and the archivability of the recording. Here, the thermal responsiveness of a recording medium refers to how much time or energy a recording medium can record, and is a characteristic that is becoming increasingly important as various recording devices become faster. I can say that there is. In addition, the preservation quality of records refers to how well records maintain their clarity over a long period of time in the environment in which they are normally handled or stored, and is a characteristic that has become particularly sought after as the field of application expands. It can be said that The characteristics of such a recording medium are most dependent on the properties of the phenolic compound used as the coloring agent, and for this reason, various phenolic compounds have recently been proposed as the coloring agent. Ta. An object of the present invention is to provide a recording medium particularly excellent in thermal responsiveness and storage stability by using at least one phenolic compound represented by the general formula () as a coloring agent. That's a thing. As is well known, the principle of recording on a record body is as follows.
An originally colorless basic coloring substance (dye) and a coloring agent consisting of a phenolic compound, which are placed close to each other on a support, are melted and fused by heating to form a colored colored phase. obtained by things. In reality, a third substance (sensitizer) that quickly melts upon heating and dissolves the dye and coloring agent is often added, but when emphasis is placed on thermal responsiveness as in the present invention, However, it is not necessarily preferable because it reduces thermal efficiency. Both the dye and the coloring agent are solids with no fluidity at room temperature, preferably crystalline solids, and when heated, at least one of them melts and fuses to form a colored phase. Generally, it is desirable for the coloring agent to melt and flow more quickly to dissolve and fuse the dye. Therefore, the melting point of a color former is one of the most important and fundamental physical properties of a color former, as will be explained below. Thermal responsiveness, which is the characteristic in question in the present invention, is based on the principle of color phase formation described earlier, and includes the specific heat of the coloring agent,
Thermal conductivity, melting point, latent heat of fusion, flow characteristics of the molten liquid, dye solubility of the molten liquid, etc. seem to be closely related. Detailed experiments have confirmed that it is most sensitively influenced by the melting point of the coloring agent and the flow characteristics of the molten liquid. That is, the lower the melting point of the coloring agent and the easier the flow of the melted liquid, the better the thermal responsiveness of the thermosensitive recording material. Furthermore, it is easy to understand that the ease of fluidity of a molten liquid increases as the viscosity and surface tension of the molten liquid decrease in a fine system such as a thermosensitive recording medium. It has also been found that it depends extremely on how fluid the coloring agent is for a long period of time, or in other words, how long the coloring agent, once melted, can exist as a supercooled liquid. In this way, it has been found that the lower the melting point of the coloring agent, the better the thermal responsiveness. However, if the melting point is too low, the heat-sensitive recording material will be affected by the heat and environment it is exposed to during manufacturing, transportation, or storage. The melting point of the coloring agent should preferably be 80°C or higher, since coloring occurs naturally due to the action of the substance, impairing the appearance and reducing the clarity of the record. In addition, it is common practice to use two or more compounds as coloring agents, and in this case, the tendency to form a eutectic mixture and develop color naturally increases further, so the lower limit of the melting point should be raised a little more. It should be done. The melting point range of the coloring agent is from 80℃ to 160℃
This is probably the reason why temperatures up to ℃ are said to be preferable. Next, the preservation of records can be considered to be impaired by two reasons. One of them is that at least one of the essential components that form the colored phase disappears from the colored phase or loses coloring or coloring ability due to volatilization, photochemical deterioration, or the action of environmental substances. The density of the colored phase decreases or disappears, and the density cannot be restored even if the part of the colored phase that has lost its density is reheated, so these can be said to be irreversible changes. The other is that when the colored phase consists of a thermodynamically unstable amorphous phase, at least one of its essential components will undergo phase separation as a more stable independent crystalline phase, resulting in the colored phase becoming This can be said to be a reversible change because the density of the recording decreases or disappears, and the color phase that disappeared temporarily develops color when reheated. Such reversible changes are often promoted by high temperature, high humidity, or the adhesion of environmental substances such as finger oil. In order to prevent irreversible changes in recording, it is necessary to (1) make each component forming the hue nonvolatile, (2) increase the photochemical stability of the hue, and (3) increase the initial Possible countermeasures include increasing the coloring density to make the recording density permanent.
Therefore, increasing the molecular weight of the color former makes it more non-volatile. When the molecular weight of the coloring agent is 170 or more, preferably 200 or more, more preferably 220 or more, its volatility will not be a problem in practice. Generally, coloring agents made of phenolic compounds tend to lose their coloring properties due to photochemical oxidation, but when the phenol nucleus is directly substituted with an electronegative group such as a carbonyl group, such oxidation can occur. It is known that it becomes difficult to receive. In particular, unless the coloring agent has a photochemical sensitizing effect, if the phenol nucleus of the phenolic compound is substituted with a carbonyl group, the photostability of the coloring phase thereby improved. In order to increase the color density of the coloring phase, it is effective to increase the acid strength of the coloring agent, not reducing the dielectric constant of the coloring phase, or optimizing the composition of the dye and coloring agent. It is said that In addition, in order to prevent reversible changes in the hue, 1
2. Decreasing the rate of crystal precipitation from the coloring phase by increasing the viscosity of the coloring phase, that is, the glass transition temperature;
Possible countermeasures include increasing the thermodynamic stability of the coloring phase to reduce the driving force for crystal precipitation. For these countermeasures, multiple color formers have already been used together, and some results have been seen, but there is no strong physicochemical interaction between color formers or between color formers and dyes. The effect of the combined use of coloring agent and coloring agent will not increase. It is already known that when one of the coloring agents contains an electron-donating group or atom such as a carbonyl group, the interaction between them is significant. As mentioned above, it must be said that it is extremely difficult to select or create a phenolic compound that satisfies the requirements as an excellent coloring agent, even if only by recognizing some of the technical problems regarding recording media. In order to provide an understanding of the present invention, the characteristics of the phenolic compound according to the present invention as a coloring agent for a recording medium will be explained below in accordance with the above recognition. In the general formula (), the carbonyl group at the para position of the phenolic hydroxyl group is an essential condition for the compound of the present invention, and as already partially explained, there are several compounds that can be used as coloring agents in the compound of the present invention. brings benefits. 1 It increases the melting point of phenolic compounds, 2 has the effect of sustaining the supercooled state of the compound in relation to R ₁ , R ₂ and R ₃ , and increases the photochemical stability of 3 phenolic compounds. , increases the acid strength of the 4-phenolic compound, has a strong interaction with the 5-hydroxyl group and increases the effect of the color former in combination with other phenolic compounds, etc. It may be necessary to explain this section a little more. As mentioned above, the persistence of the supercooled state of the coloring agent is extremely important for improving the thermal responsiveness of the recording medium, but normally the supercooled state of the liquid is often observed when the liquid has high viscosity. Therefore, when the ease of fluidity of the liquid is a problem as in the present invention, a supercooled state with high viscosity is meaningless. However, in the general formula (), R ₁ is an alkyl group, cycloalkyl group, aryl group, or aralkyl group that inhibits the free rotation of the hydroxyl group, and R ₂ and R ₃
is a hydrogen atom that does not inhibit the free rotation of the carbonyl group, even though the compound has a low viscosity compared to other similar compounds,
A significant extension of the supercooled state is observed. This can be understood theoretically and is one of the important discoveries of the present invention. A recording material using such a compound as one of the coloring agents exhibits particularly high thermal responsiveness. Although the carbonyl group has many advantages as described above, the electron-donating property of the carbonyl group has a desensitizing effect on color development, so unless R ₂ or R ₃ is a hydroxyl group, its color development effect is weakened. When such a compound is used in combination with other phenolic compounds, the carbonyl group hydrogen bonds with the hydroxyl group of the other compound and exhibits the original deep coloring effect, resulting in good effects of combined use. . In the general formula (), R ₄ is an alkyl group having 23 or less carbon atoms. When R ₄ is an alkyl group, the surface tension and viscosity of the molten liquid are the lowest for the same number of carbon atoms, and the most desirable result in thermal response is obtained, compared to when R 4 is a cycloalkyl, aryl, or aralkyl group. give. Also, if R ₄
When is an alkoxy group, cycloalkoxy group, allyloxy group, or aralkoxy group, some of the characteristic effects of the carbonyl group connected to it are ruined by the electron-withdrawing oxygen, so it is used as a coloring agent. The characteristics of will also change. In addition, it was mentioned earlier that the lower limit of the molecular weight of the coloring agent is determined based on volatility, but furthermore, if the molecular weight of the compound of general formula () becomes too small, its water solubility will increase and it will be difficult to It tends to develop color naturally during storage due to high humidity. Therefore, for this reason as well, we should find a lower limit of molecular weight, which also coincides with the lower limit of molecular weight mentioned above. On the other hand, as the molecular weight of the coloring agent increases, the viscosity of the molten liquid increases and the thermal responsiveness of the recording medium decreases. Furthermore, as the molecular weight of the compound of formula () increases, the dielectric constant generally decreases, and the coloring effect decreases accordingly. The upper limit of the molecular weight of the coloring agent is determined for these two reasons, and empirically it is appropriate to set the upper limit to about 500. The upper limit of the number of carbon atoms in R ₄ can be determined to be 23 based on the upper limit of the molecular weight of the coloring agent. Within the preferred molecular weight range of such a coloring agent, in the general formula (), when R ₄ is an alkyl group, it may be a cycloalkyl group, an aryl group, an aralkyl group, a cycloalkoxy group,
The melting point is the lowest when it is an allyloxy group or an aralkoxy group, and if none of R ₁ , R ₂ and R ₃ are an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, the melting point is In many cases, the melting point is so low that it falls outside the range of the melting point that can be used as a coloring agent. However, in general formula (), at least one of R ₁ , R ₂ and R ₃ (especially R ₁ ) is an alkyl group,
When a cycloalkyl group, an aryl group, or an aralkyl group is used, the melting point of the compound is significantly increased, and the compound exhibits a preferable melting point as a color former. Also, the structure that can most effectively increase these melting points is R ₁
is an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, R ₂ is a hydrogen atom, and R ₃ is a hydrogen atom, a hydroxyl group, or an alkyl group, and this will be understood from the following specific examples. Next, we will compare compounds with similar molecular weights. (However, in the formula, i-Pr is an isopropyl group, t-
Bu represents a tertiary butyl group and t-Am represents a tertiary amyl group. ) Finally, in the general formula (), one of the ortho positions of the hydroxyl group is not substituted because if both ortho positions are substituted with an atom or atomic group larger than a hydrogen atom, the coloring ability of the phenolic compound will be almost negligible. This is because it would be lost and would no longer meet the purpose of the present invention. As described above, the phenol compound represented by the general formula () is characteristic as a coloring agent for heat-sensitive recording materials. Now, in the general formula (), R ₁ , R ₂ and R ₃ are a hydrogen atom, a hydroxyl group, an aralkyl group, a cycloalkyl group, an aryl group, or an aralkyl group; Preferred specific examples of the group include a methyl group, an ethyl group, an isopropyl group, a tertiary butyl group, a tertiary amyl group, a cyclohexyl group,
Examples include phenyl group, benzyl group, and α,α-dimethylbenzyl group. Similarly, R ₄ has 23 carbon atoms.
The following alkyl groups include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, an amyl group,
Examples include hexyl group, heptyl group, octyl group, nonyl group, undecyl group, tridecyl group, pentadecyl group, heptadecyl group, heneicosyl group and tricosyl group. Specific examples of the general formula () preferred for the purposes of the present invention include (the numbers in brackets indicate the melting point of the compound in degrees Centigrade): 3-cyclohexyl-4-hydroxyphenylmethylketone (152); 3-Benzyl-4-hydroxyphenylmethylketone (148), 3-(α,α-dimethylbenzyl)-4-hydroxyphenylmethylketone (159), 2-methyl-4-hydroxy-5-isopropylphenyl Methyl ketone (127), 3-isopropyl-4-hydroxyphenylethyl ketone (126.5), 3-cyclohexyl-4-hydroxyphenylethyl ketone (151), 3-phenyl-4
-Hydroxyphenylethyl ketone (152), 2,
4-dihydroxy-5-tertiarybutyl phenylethyl ketone (159), 2,4-dihydroxy-
5-tertiaryamyl phenyl ethyl ketone (121), 3-methyl-4-hydroxyphenyl-
Propyl ketone (132), 3-isopropyl-4-
Hydroxyphenylpropyl ketone (92), 3-
Cyclohexyl-4-hydroxyphenylpropyl ketone (88), 3-phenyl-4-hydroxyphenylpropyl ketone (122), 2-methyl-4
-Hydroxy-5-isopropylphenylpropyl ketone (92), 2,4-dihydroxy-5-tertiarybutylphenylpropyl ketone (158),
2,4-dihydroxy-5-tertiaryamylphenylpropyl ketone (117), 3-methyl-4-
Hydroxyphenylbutylketone (104.5), 3-
Isopropyl-4-hydroxyphenylbutylketone (105), 3-tertiarybutyl-4-hydroxyphenylbutylketone (122.5), 3-cyclohexyl-4-hydroxyphenylbutylketone (100.5), 3-phenyl-4 -Hydroxyphenylbutylketone (109), 2-methyl-4-hydroxy-5-isopropylphenylbutylketone (84), 3-isopropyl-4-hydroxyphenylisobutylketone (93), 2,4-dihydroxy- 5-tertiarybutylphenyl isobutyl ketone (156), 2,4-dihydroxy-5-tertiaryamyl phenyl isobutyl ketone (110), 3
-Methyl-4-hydroxyphenyl amyl ketone (78), 3-isopropyl-4-hydroxy phenyl amyl ketone (97.5), 3-tertiarybutyl-4-hydroxy phenyl amyl ketone (114),
3-phenyl-4-hydroxyphenyl amyl ketone (90), 2,5-dimethyl-4-hydroxy phenyl amyl ketone (105), 2-methyl-4-
Hydroxy-5-isopropylphenyl amyl ketone (101), 2,4-dihydroxy-5-ethyl phenyl amyl ketone (94), 2,4-dihydroxy-5-tertiarybutyl phenyl amyl ketone (148), 3 -Methyl-4-hydroxyphenylhexylketone (113.5), 3-isopropyl-4
-Hydroxyphenylhexylketone (85), 3
-Tarsiabutyl-4-hydroxyphenylhexylketone (136.5), 3-phenyl-4-hydroxyphenylhexylketone (99.5), 2,5
-dimethyl-4-hydroxyphenylheptylketone (92), 3-methyl-4-hydroxyphenylheptylketone (91), 3-tertiarybutyl-4-hydroxyphenylheptylketone (106), 3-phenyl- 4-Hydroxyphenylheptylketone (86), 2,3-dimethyl-4-
Hydroxyphenylheptylketone (80), 2,
5-dimethyl-4-hydroxyphenylheptylketone (100), 2-methyl-4-hydroxy-5
-isopropylphenylheptylketone (81),
2,4-dihydroxy-3-methylphenylheptylketone (81), 2,4-dihydroxy-5-
Methyl phenyl heptyl ketone (93.5), 2,5
-dimethyl-4-hydroxyphenyl octyl ketone (91), 2,5-dimethyl-4-hydroxyphenyl nonyl ketone (82), 2,4-dihydroxy-5-methyl phenyl undecyl ketone (88), 2 , 4-dihydroxy-5-methylphenyl tridecyl ketone (85), 2,5-dimethyl-
4-Hydroxyphenylpentadecyl ketone (95), 2,4-dihydroxy-5-methylphenylheptadecyl ketone (86), 2,5-dimethyl-4-hydroxyphenylheptadecyl ketone (97), 3- Methyl-4-hydroxyphenylheneicosylketone (81), 2,5-dimethyl-4
-Hydroxyphenylheneicosylketone (103) and 3-methyl-4-hydroxyphenyltricosylketone (85). If the present invention is further understood, by changing the combination of R ₁ , R ₂ , R ₃ and R ₄ within the range of general formula (), more compounds preferable as color formers can be created. Things will be easy. Although many of the phenolic compounds of the present invention are new, they can be produced from industrially available raw materials by several already known methods as shown below. 1 Acylation of phenols or Fries rearrangement of phenol esters: {However, R ₁ , R ₂ , R ₃ and R ₄ are the same as defined in general formula (), and X represents a halogen atom or a hydroxyl group. } The above two reaction formulas represent the acylation of phenols and the Fries rearrangement of phenol esters, and as is already known,
Lewis acids such as aluminum chloride and zinc chloride are used as catalysts for these reactions. 2 Hetsushi’s reaction: {However, R ₁ , R ₂ , R ₃ and R ₄ are the same as defined in general formula (). } As shown in the two reaction formulas above, the target compound can be obtained through a two-step chemical process by using Hetsch's reaction. This reaction is
It is said that this reaction will not occur unless at least one of R ₂ or R ₃ is a hydroxyl group, and ether is used as the reaction solvent and zinc chloride is used as the catalyst. The reaction is mild and suitable for acylating phenols that have substituents that are easily eliminated, such as tertiary butyl and tertiary amyl groups. 3 Alkylation of phenyl ketones: {However, R ₁ , R ₂ , R ₃ and R ₄ are the same as defined in the general formula (), and (R ₁ -H) represents an olefin in which one hydrogen atom is removed from R ₁ . } Phenyl ketones can be alkylated as shown in the two reaction formulas above. especially
The reaction is easy when at least one of R ₂ or R ₃ is a hydroxyl group. In addition to Lewis acids, sulfuric acid or sulfonic acids are used as reaction catalysts. Most of the phenolic compounds of the present invention can be used alone as a coloring agent, but some, or more preferably, can be used as a mixture of a plurality of phenolic compounds. Multiple phenolic compounds can be selected only from the general formula (), but at least one from the general formula () can be selected from the general formula ().
Good results can be obtained by selecting at least one of the other phenolic compounds. Examples of other phenolic compounds suitable for this purpose include:
2,2-di(4-hydroxyphenyl)propane (bisphenol A), 2,2-di(3-methyl-
4-hydroxyphenyl)propane (bisphenol C), 2-(4-hydroxyphenyl)-2-
(3-methyl-4-hydroxyphenyl)propane, 2-(4-hydroxyphenyl)-2-(3-
Isopropyl-4-hydroxyphenyl)propane, 2-(4-hydroxyphenyl)-2-(3-
tertiarybutyl-4-hydroxyphenyl)propane, 2-(4-hydroxyphenyl)-2-
(3,5-ditertyabutyl-4-hydroxyphenyl)propane, 2-(4-hydroxyphenyl)-2-(3-tertiaryamyl-4-hydroxyphenyl)propane, 2-(4- Hydroxyphenyl)-2-(3-cyclohexyl-4-hydroxyphenyl)propane, 2,2-di(4-hydroxyphenyl)butane, 2,2-di(3-methyl-4-hydroxyphenyl) Butane, 1,1
-di(2-hydroxy-4-methylphenyl)butane, 1,1-di(2-hydroxy-5-methylphenyl)butane, 1,1-di(4-hydroxyphenyl)isobutane, 1,1-di(2-hydroxyphenyl)butane, -hydroxy-5-methylphenyl)isobutane, 2,2
-di(4-hydroxyphenyl)-4-methylpentane, 1,1-di(4-hydroxyphenyl)
Cyclohexane, 1,1-di(3-methyl-4-
hydroxyphenyl)cyclohexane, 1-(4
-hydroxyphenyl)-1-(3-methyl-4-
hydroxyphenyl)cyclohexane, 1-(4
-hydroxyphenyl)-1-(3-ethyl-4-
hydroxyphenyl)cyclohexane, 1-(4
-hydroxyphenyl)-1-(3-isopropyl-4-hydroxyphenyl)cyclohexane, 1
-(4-hydroxyphenyl)-1-(3-tertiarybutyl-4-hydroxyphenyl)cyclohexane, 1-(4-hydroxyphenyl)-1-
(3-cyclohexyl-4-hydroxyphenyl)
Cyclohexane, 2,2-di(4-hydroxyphenyl)octane, 4,4'-thiobis(3-methyl-6-tertiarybutylphenol), 4,
Examples thereof include 4'-dihydroxydiphenyl sulfone, benzyl parahydroxybenzoate, dimethyl 4-hydroxyphthalate, neopentyl glycol diester of parahydroxybenzoic acid, and hexamethylene glycol diester of parahydroxybenzoic acid. A thermosensitive recording material has a thermosensitive functional layer mainly composed of a dye and a coloring agent on a support, and when heated with a thermal head or a thermal pen, color is developed in the thermosensitive functional layer. A phase is formed and a recorded image is obtained in response to heating. The dye that develops color with the compound of the present invention is an electron-donating, that is, basic dye, and is originally colorless, but when it is mixed with an electron-accepting, that is, acidic substance such as a phenolic compound, it loses electrons. It is said that when the exchange occurs, the light absorption spectrum, especially in the visible region, changes and becomes visible. Specific examples include 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide, 3,3-bis(4-dimethylaminophenyl)phthalide, 3
-(4-dimethylaminophenyl)-3-(1,2
-dimethylindol-3-yl)phthalide,
4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl leuco auramine, benzoyl leucomethylene blue, paranitrobenzoyl leucomethylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3 -propyl-spiro-
Dibenzopyran, 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran, 3-diethylamino-7-methoxyfluoran, 3-diethylamino-7-chlorofluoran, 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-dibenzylaminofluorane, 3-diethylamino-7-N-methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylamino Fluorane, 3,
7-bis(diethylamino)fluorane, 3-
(N-ethyl-P-toluidino)-6-methyl-7
-phenylaminofluorane, 3-(N-ethyl-P-toluidino)-6-methyl-7-(P-toluidino)fluorane, 3-diethylamino-6-
Methyl-7-phenylaminofluoran, 3-diethylamino-7-(2-carbomethoxyphenylamino)fluoran, 3-(N-ethyl-N-
isoamylamino)-6-methyl-7-phenylaminofluorane, 3-(N-cyclohexyl-
N-methylamino)-6-methyl-7-phenylaminofluoran, 3-pyrrolidino-6-methyl-7-phenylaminofluoran, 3-piperidino-6-methyl-7-phenylaminofluoran, 3-diethylamino-6-methyl-7-xylidinofluorane, 3-dimethylamino-7-
(O-chlorophenylamino)fluoran, 3-
Examples include diethylamino-7-(O-chlorophenylamino)fluoran and 3-pyrrolidino-6-methyl-7-(P-butylphenylamino)fluoran. Of course, the dyes are not limited to these dyes, and two or more dyes may be used simultaneously. In a heat-sensitive recording material, the ratio of the dye to the coloring agent in the heat-sensitive functional layer should be selected depending on the type of dye and coloring agent used and is not particularly limited. The coloring agent is used in an amount of 1 to 50 parts by weight, more preferably 2 to 10 parts by weight. The heat-sensitive functional layer is fixed by coating a coating solution containing these as main components onto a support and drying it. Water is generally used as a medium for preparing the coating solution, and the dye and coloring agent are usually ground and dispersed together or separately using a mixing grinder such as a ball mill, attritor, or sand grinder. Such a coating solution contains starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein,
Gum arabic, polyvinyl alcohol, diisobutylene-maleic anhydride copolymer salt, styrene-
Maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt, styrene-acrylic acid copolymer salt, styrene-butadiene copolymer emulsion, etc. are 10 to 70% by weight, preferably 15% by weight of the total solid content. or 50% by weight. Furthermore, various auxiliary agents can be added to the coating liquid. For example, dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate or metal salts of fatty acids, ultraviolet absorbers such as benzophenone or benzotriazole, antifoaming agents, fluorescent dyes, colored dyes, and stearin. Lubricants such as acid zinc, calcium stearate, polyethylene wax, carnauba wax, paraffin wax or ester wax, kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine particulate silicic anhydride or activated earth, etc. Mention may be made of inorganic pigments and sensitizers such as stearamide, methylene bisstearamide, oleic acid amide, palmitic acid amide, matcha oleic acid amide or coconut oil fatty acid amide. As the support, paper, plastic film, synthetic paper, etc. can be used, but paper is most preferably used in terms of cost and coatability. As a method for forming the heat-sensitive functional layer, well-known and commonly used techniques can be used. For example, a coating solution is applied onto a support by air knife coating or blade coating, and dried to form and fix a heat-sensitive functional layer. The heat sensitive functional layer usually has a dry weight in the range of 2 to 12 grams per square meter, preferably 3 to 10 grams per square meter. If smoothness of the surface of the heat-sensitive functional layer is particularly required, smoothing treatment can be carried out using a super calender, a machine calender, or the like. Next, in order to further clarify the present invention, the present invention will be explained by giving examples and comparisons. In addition, parts and % in examples
are parts by weight and weight %, respectively, unless otherwise specified.
represents. Example 1 Preparation of liquid A: 3-(N-cyclohexyl-N-methylamino)
-6-methyl-7-phenylaminofluorane
10 parts Methyl cellulose 5% aqueous solution 5 parts Water 40 parts This composition was milled with a sand grinder to obtain an average particle size of
It was ground to 3 μm. Preparation of Solution B: 3-phenyl-4-hydroxyphenyl amyl ketone 20 parts Methyl cellulose 5% aqueous solution 5 parts Water 55 parts This composition was ground with a sand grinder to determine the average particle size.
It was ground to 3 μm. Formation of recording layer: 55 parts of liquid A, 80 parts of liquid B, silicon oxide pigment (oil absorption
180ml/100g) 15 parts, 50 parts of 20% oxidized starch aqueous solution,
Mix and stir 20 parts of water. 50g/of the obtained coating liquid
A heat-sensitive recording material was obtained by applying and drying the mixture to a dry weight of 7 g/m ² on a m ² base paper. Examples 2 to 9 In the preparation of Solution B, 3-methyl-4-hydroxyphenylheptyl ketone (Example 2) 3-cyclohexyl-4-hydroxyphenyl was used instead of 3-phenyl-4-hydroxyphenyl amyl ketone. Butyl ketone (Example 3) 2,5-dimethyl-4-hydroxyphenylhexyl ketone (Example 4) 2,5-dimethyl-4-hydroxyphenyl octyl ketone (Example 5) 3-isopropyl-4-hydroxy Phenylbutyl ketone (Example 6) 3-isopropyl-4-hydroxyphenyl amyl ketone (Example 7) 3-phenyl-4-hydroxyphenylhexyl ketone (Example 8) 2-methyl-4-hydroxy-5 -Isopropylphenyl amyl ketone (Example 9) Eight types of heat-sensitive recording materials were obtained in exactly the same manner as in Example 1, except that each of the following was used. Examples 10-11 In preparing Solution A, 3-(N-ethyl-N-iso-amylamino) was used instead of 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluorane. )-6-methyl-7-
Using phenylaminofluorane, in the preparation of liquid B, 3-phenyl-4-hydroxyphenylbutyl ketone was substituted for 3-phenyl-4-hydroxyphenyl amyl ketone (Example 10) 3-tertiary butyl-4 -Hydroxyphenylheptylketone (Example 11) Two types of heat-sensitive recording materials were obtained in exactly the same manner as in Example 1, except that hydroxyphenylheptylketone (Example 11) was used. Examples 12-13 In the preparation of Solution A, 3-(N-
cyclohexyl-N-N-methylamino)-6-
5 parts of methyl-7-phenylaminofluorane and 6 parts of 3-(N-ethyl-N-iso-amylamino)-
- Using 5 parts of methyl-7-phenylaminofluorane (10 parts in total), in the preparation of Solution B, 2,4-dihydroxy-5-tertiaria was substituted for 3-phenyl-4-hydroxyphenylamyl ketone. Two types of heat-sensitive recording materials were obtained in exactly the same manner as in Example 1, except that milphenylisobutyl ketone (Example 12) and 2,5-dimethyl-4-hydroxyphenylamylketone (Example 13) were used. Ta. Example 14 Preparation of liquid A: 3-(N-cyclohexyl-N-methylamino)
-6-methyl-7-phenylaminofluorane
10 parts Methylcellulose 5% aqueous solution 5 parts Water 40 parts This composition was milled with a sand grinder to obtain an average particle size of
It was ground to 3 μm. Preparation of Solution B: 2,5-dimethyl-4-hydroxyphenylheptylketone 20 parts Methylcellulose 5% aqueous solution 5 parts Water 55 parts This composition was ground with a sand grinder to determine the average particle size.
It was ground to 3 μm. Preparation of liquid C: 3-phenyl-4-hydroxyphenylethyl ketone 20 parts Methyl cellulose 5% aqueous solution 5 parts Water 55 parts This composition was ground with a sand grinder to reduce the average particle size.
It was ground to 3 μm. Formation of recording layer: 55 parts of liquid A, 80 parts of liquid B, 80 parts of liquid C, 15 parts of silicon oxide pigment (oil absorption 180 ml/100 g), 50 parts of 20% oxidized starch aqueous solution, and 10 parts of water are mixed and stirred. The resulting coating liquid was coated on a 50 g/m ² base paper to a dry weight of 7 g/m ² and dried to obtain a heat-sensitive recording material. Examples 15-16 In the preparation of liquid C, 2,4-dihydroxy-5-tertiaryamyl phenylethyl ketone was replaced with 3-phenyl-4-hydroxyphenylethyl ketone (Example 15) 3-methyl-4- Two types of heat-sensitive recording materials were obtained in exactly the same manner as in Example 14, except that hydroxyphenylhexyl ketone (Example 16) was used in each case. Examples 17-22 In preparing Solution A, 3-(N-ethyl-N-iso-amylamino) was used instead of 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluorane. )-6-methyl-7-
Using phenylaminofluorane, in the preparation of Solution C, 2,4-dihydroxy-5-tertiarybutyl phenylethyl ketone was substituted for 3-phenyl-4-hydroxyphenylethyl ketone (Example 17) 3- (α,α-dimethylbenzyl)-4-hydroxyphenylmetalketone (Example 18) 3-benzyl-4-hydroxyphenylmethylketone (Example 19) 2-(4-hydroxyphenyl)-2-( 3-isopropyl-4-hydroxyphenyl)propane (Example 20) 1-(4-hydroxyphenyl)-1-(3-isopropyl-4-hydroxyphenyl)cyclohexane (Example 21) 2,2-di Six types of heat-sensitive recording materials were obtained in exactly the same manner as in Example 14, except that (4-hydroxyphenyl)propane (Example 22) was used in each case. Examples 23-28 In preparing Solution A, 3-(N-ethyl-N-iso-amylamino) was used instead of 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluorane. )-6-methyl-7-
In the preparation of Solution B, phenylaminofluorane was substituted with 2-(4-hydroxyphenyl)-2-(3-cyclohexyl-4-hydroxyphenyl) instead of 2,5-dimethyl-4-hydroxyphenylheptyl ketone. 2,5-dimethyl-4-hydroxyphenylnonyl ketone (Example 23) 3-phenyl-4 instead of 3-phenyl-4-hydroxyphenyl ethyl ketone in the preparation of liquid C. -Hydroxyphenylheptylketone (Example 24) 2-Methyl-4-hydroxy-5-isopropylphenylheptylketone (Example 25) 2-Methyl-4-hydroxy-5-isopropylphenylbutylketone (Example 26) ) 2,3-dimethyl-4-hydroxyphenylheptylketone (Example 27) and 2,4-dihydroxy-3-methylphenylheptylketone (Example 28) were used, respectively. Six types of thermosensitive recording materials were obtained. Examples 29-33 In the preparation of solution B, 2-
(4-Hydroxyphenyl)-2-(3-isopropyl-4-hydroxyphenyl)propane was used to prepare 3-cyclohexyl-4 instead of 3-phenyl-4-hydroxyphenylethyl ketone in the preparation of Solution C. -Hydroxyphenylpropyl ketone (Example 29) 3-isopropyl-4-hydroxyphenylhexyl ketone (Example 30) 2,4-dihydroxy-5-ethyl phenyl amyl ketone (Example 31) 2,4-dihydroxy -5-methylphenyl tridecyl ketone (Example 32) and 3-methyl-4-hydroxyphenyl tricosyl ketone (Example 33) were used in the same manner as in Example 14, except that 5 types of thermosensitive Obtained a record. Examples 34-37 In preparing Solution A, 3-(N-ethyl-N-iso-amylamino) was used instead of 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylaminofluorane. )-6-methyl-7-
Phenylaminofluorane was added to 2-(4-hydroxyphenyl)-2-(3-isopropyl-4-hydroxyphenyl) in place of 2,5-dimethyl-4-hydroxyphenylheptyl ketone in the preparation of Solution B. 2,4-dihydroxy-5-methylphenyl undecyl ketone (Example 34) 2-methyl- Three types were prepared in exactly the same manner as in Example 14, except that 4-hydroxy-5-isopropylphenyl methyl ketone (Example 35) and 3-cyclohexyl-4-hydroxyphenyl methyl ketone (Example 36) were used. A thermosensitive recording medium was obtained. Comparative Example 1: In the preparation of Solution B, the procedure was exactly the same as in Example 1 except that 2,2-di(4-hydroxyphenyl)propane was used instead of 3-phenyl-4-hydroxyphenyl amyl ketone. A thermosensitive recording medium was obtained. Comparative Examples 2 to 6: In the preparation of Solution B, 4-hydroxyphenylheptylketone was used instead of 3-phenyl-4-hydroxyphenyl amyl ketone.
(Comparative Example 2) 2,4-dihydroxyphenylheptylketone
(Comparative Example 3) 2,4-dihydroxyphenyl octyl ketone
(Comparative Example 4) 3,4-dihydroxyphenylbenzyl ketone
(Comparative Example 5) Five types of heat-sensitive recording materials were obtained in exactly the same manner as in Example 1 except that 2,4-dihydroxyphenyl phenoxymethyl ketone (Comparative Example 6) was used. The 42 types of thermal recording bodies obtained in Examples 1 to 36 and Comparative Examples 1 to 6 above were recorded using a high speed thermal facsimile (Hitachi "HIFAX700"). The whiteness of the obtained recording medium, the recording sensitivity of the recorded image, and
The storage properties of recorded images and blank areas were as follows.

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Claims (1)

[Scope of Claims] 1. In a heat-sensitive recording material having a heat-sensitive functional layer mainly composed of a colorless or light-colored color-forming substance and a color-forming substance that develops color from the color-forming substance, the general formula () {In formula (), R ₁ , R ₂ and R ₃ represent a hydrogen atom, a hydroxyl group, an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, and R ₄ represents an alkyl group having 23 or less carbon atoms. However, at least one of R ₁ , R ₂ and R ₃ is an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group. } A heat-sensitive recording material characterized by containing at least one kind of phenolic compound represented by the following as a coloring substance. 2 The above general formula () {In formula (), R ₁ , R ₂ and R ₃ represent a hydrogen atom, a hydroxyl group, an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, and R ₄ represents an alkyl group having 23 or less carbon atoms. However, at least one of R ₁ , R ₂ and R ₃ is an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group. } The heat-sensitive recording material according to claim 1, which contains at least one phenolic compound represented by the following and at least one other phenolic compound as a coloring substance.