Patent Description:
Thermal recording materials in each of which a thermal recording layer is provided on a support are used in various industrial fields. A thermal recording layer that includes a basic dye which is colorless or light-colored at normal temperature and an organic color developer and that allows color developing recording by applying thermal energy (Joule heat) such as a thermal head, a thermal pen, and the like, and a thermal recording material including such a thermal recording layer have been widely put into practical use.

The required performance of the printed part formed by the thermal recording layer in the thermal recording material is influenced by, for example, a basic dye, a color developer, a sensitizer, and the like, which are components of the thermal recording layer, and in particular, the influence of the color developer is large. As color developers, synthetic compounds derived from petrochemicals such as phenolic compounds, sulfonylurea compounds, and the like have been proposed. Among them, many phenolic compounds have been developed and put into practical use.

However, since some phenolic compounds are suspected of being endocrine disrupting substances, their use tends to be suppressed in recent years. For this reason, various non-phenolic color developers have been proposed as color developers in place of phenolic compounds.

For example, as the non-phenol color developer, there have been proposed an N-(phenylureidophenyl)benzenesulfonamide compound (Patent Literature <NUM>), a phenylureidophenyl-benzenesulfonate compound such as <NUM>-(<NUM>-phenylureido)phenyl-<NUM>-methylbenzenesulfonate (Patent Literature <NUM>), and the like.

However, the N-(phenylureidophenyl)benzenesulfonamide compound described in Patent Literature <NUM> and the phenylureidophenyl-benzenesulfonate compound such as <NUM>-(<NUM>-phenylureido)phenyl-<NUM>-methylbenzenesulfonate described in Patent Literature <NUM> have good printing properties and the like, but have low plasticizer resistance, and there is a possibility that the printed part fads away when a plasticizer coexists.

Hence, an object of the present invention is to provide a color developer, a thermal recording material, and a thermal recording layer coating material, which are excellent in plasticizer resistance.

In order to achieve the above object, the present invention provides a color developer for a thermal recording layer, including:.

The present invention also provides a thermal recording material, including:.

The present invention also provides a thermal recording layer coating material for use in forming a thermal recording layer, including:.

According to the present invention, it is possible to provide a color developer, a thermal recording material, and a thermal recording layer coating material, which are excellent in plasticizer resistance.

As described above, in the color developer, the thermal recording material, and the thermal recording layer coating material, a compound of formula (I-<NUM>) or formula (I-<NUM>) is used in combination with N-(m-tolylaminocarbonyl)-phenylalanine or N-(phenylaminocarbonyl)-phenylalanine as the color developer. According to this, for example, it is possible to further improve the plasticizer resistance without deteriorating various good storage characteristics such as color development density of the compound of formula (I-<NUM>) or formula (I-<NUM>), whiteness, and the like.

The performance required for the thermal recording material includes, for example, the whiteness of a non-printed part, the color development density of a printed part, and the storage stability of the printed part under various environmental conditions.

The storage stability of the printed part refers to the performance of the remaining properties of the printed part concerning external factors such as the stability when the printed part is placed in an environment of heat or high humidity, the stability when the printed part is attached to water, the stability when the printed part is attached to oil or alcohol, or the stability when the printed part is attached to a plasticizer which is used to produce the plasticity of tanning or synthetic leather used in leather products such as wallets or the plasticity of film products.

In particular, thermal recording materials are often used in POS register paper. There is a possibility that the POS register paper is stored in leather or synthetic leather purse for a long time, and the printed part of the POS register paper fades away by the plasticizer. On the other hand, when thermal recording materials are used as food labels, a film product such as a wrap used may come into direct contact with food label paper, and a plasticizer of the film product may cause a printed part of the food label paper to fade away. As described above, the plasticizer resistance of the printed part is one of the most important factors in the storage stability of the thermal recording material.

As described above, since the color developer, the thermal recording material, and the thermal recording layer coating material of the present invention are excellent in plasticizer resistance, they are suitable for use in the POS register paper, the food label, and the like, but not limited thereto and can be used in a wide range of applications.

The compound of formula (I-<NUM>) or formula (I-<NUM>)is excellent in, for example, printing properties, heat resistance, moist heat resistance, water resistance, and the like. In the color developer, the thermal recording material, and the thermal recording layer coating material of the present invention, by using the compound of formula (I-<NUM>) or formula (I-<NUM>)in combination with N-(m-tolylaminocarbonyl)-phenylalanine or N-(phenylaminocarbonyl)-phenylalanine, the plasticizer resistance can be further improved while maintaining excellent printing properties, heat resistance, moist heat resistance, water resistance, and the like of the compound of formula (I-<NUM>) or formula (I-<NUM>), for example.

In the color developer, the thermal recording material, and the thermal recording layer coating material of the present invention, when a compound of formula (I) is a phenylureidophenyl-benzenesulfonate compound of formula (I-<NUM>), by using N-(m-tolylaminocarbonyl)-phenylalanine or N-(phenylaminocarbonyl)-phenylalanine in combination, for example, moist heat resistance and heat resistance can further be improved. Thereby, for example, it is possible to suppress or prevent a phenomenon in which the printed part fades away due to problems of moist heat resistance and heat resistance.

In the present invention, when a compound (e. g, the compound of formula (I-<NUM>) or formula (I-<NUM>), the N-(m-tolylaminocarbonyl)-phenylalanine or N-(phenylaminocarbonyl)-phenylalanine, etc.) has isomers such as tautomers and stereoisomers (e.g., a geometric isomer, a conformer, and an optical isomer), any isomer can be used in the present invention, unless otherwise stated. Furthermore, when a compound can form a salt, the salt can be used in the present invention, unless otherwise stated. The salt may be an acid addition salt, or may be a base addition salt. Moreover, an acid that forms the acid addition salt may be either an inorganic acid or an organic acid, and a base that forms the base addition salt may be either an inorganic base or an organic base. The inorganic acid is not particularly limited, and examples thereof include sulfuric acid, phosphoric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypofluorous acid, hypochlorous acid, hypobromous acid, hypoiodous acid, fluorous acid, chlorous acid, bromous acid, iodous acid, fluorine acid, chloric acid, bromic acid, iodic acid, perfluoric acid, perchloric acid, perbromic acid, and periodic acid. The organic acid also is not particularly limited, and examples thereof include p-toluenesulfonic acid, methanesulfonic acid, oxalic acid, p-bromobenzenesulfonic acid, carbonic acid, succinic acid, citric acid, benzoic acid, and acetic acid. The inorganic base is not particularly limited, and examples thereof include ammonium hydroxides, alkali metal hydroxides, alkaline-earth metal hydroxides, carbonates, and hydrogencarbonates. More specifically, examples of the inorganic base include sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, calcium hydroxide, and calcium carbonate. The organic base also is not particularly limited, and examples thereof include ethanolamine, triethylamine, and tris(hydroxymethyl)aminomethane. The method for producing these salts also is not particularly limited. For example, they can be produced by adding an acid or a base such as described above to the compound as appropriate by a known method.

Moreover, in the present invention, a chain substituent (e.g., an alkyl group, hydrocarbon groups such as an unsaturated aliphatic hydrocarbon group, etc.) may be straight-chain or branched, unless otherwise stated, and the number of carbons thereof is not particularly limited, and may be, for example, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM> (at least <NUM> in the case of an unsaturated hydrocarbon group). Furthermore, in the present invention, as to a cyclic group (e.g., an aryl group, a heteroaryl group, etc.), the number of ring members (the number of carbons that compose a ring) is not particularly limited and may be, for example, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>. When a substituent or the like has isomers, any isomer can be used, unless otherwise stated. For example, in the case of simply describing as a "naphthyl group", it may be a <NUM>-naphthyl group or a <NUM>-naphthyl group.

In the color developer, the thermal recording material, and the thermal recording layer coating material of the present invention, the compound of formula (I) may be an N-(phenylureidophenyl)benzenesulfonamide compound of formula (I-<NUM>).

In the formula (I-<NUM>), the halogen atom is not particularly limited, and examples thereof include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

In the formula (I-<NUM>), the alkyl group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include linear or branched alkyl groups such as methyl, ethyl, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a hexyl group, and an isohexyl group.

In the formula (I-<NUM>), the cycloalkyl group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include cyclic cycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, a <NUM>-methylcyclopropyl group, a cyclopropylmethyl group, a cyclopentyl group, and a cyclohexyl group.

In the formula (I-<NUM>), the alkoxy group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include linear or branched alkoxyl groups such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a sec-butoxy group, a t-butoxy group, a pentyloxy group, an isopentyloxy group, a neopentyloxy group, a hexyloxy group, and an isohexyloxy group.

In the formula (I-<NUM>), the cycloalkoxy group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include cyclic alkoxyl groups such as a cyclopropyloxy group, a cyclobutyloxy group, a <NUM>-methylcyclopropyloxy group, a cyclopropylmethyloxy group, a cyclopentyloxy group, and a cyclohexyloxy group.

In the formula (I-<NUM>), the alkenyl group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include a vinyl group, an allyl group, an isopropenyl group, a <NUM>-propenyl group, a <NUM>-propenyl group, a <NUM>-butenyl group, a <NUM>-butenyl group, a <NUM>-butenyl group, <NUM>,<NUM>-butanedienyl group, and a <NUM>-methyl-<NUM>-propenyl group.

In the formula (I-<NUM>), the fluoroalkyl group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluorohexyl group, and a perfluorocyclohexyl group.

In the formula (I-<NUM>), the N (R<NUM>)<NUM> group is not particularly limited, and examples thereof include amino groups in which R<NUM> is a hydrogen atom, a phenyl group, a benzyl group, or an alkyl group having <NUM> to <NUM> carbon atoms.

In the formula (I-<NUM>), the NHCOR<NUM> group is not particularly limited, and examples thereof include a methylcarbonylamino group, an ethylcarbonylamino group, a propylcarbonylamino group, an isopropylcarbonylaminocarbonylamino group, a butylcarbonylaminocarbonylamino group, an isobutylcarbonylaminocarbonylamino group, a sec-butylcarbonylamino group, a t-butylcarbonylamino group, a pentylcarbonylamino group, an isopentylcarbonylamino group, a neopentylcarbonylamino group, a hexylcarbonylamino group, an isohexylcarbonylamino group, a cyclopropylcarbonylamino group, a cyclobutylcarbonylamino group, a <NUM>-methylcyclopropylcarbonylamino group, a cyclopropylmethylcarbonylamino group, a cyclopentylcarbonylamino group, and a cyclohexylcarbonylamino group.

In the formula (I-<NUM>), examples of the substituent of the optionally substituted phenyl group and the optionally substituted benzyl group include the alkyl group having <NUM> to <NUM> carbon atoms, the alkoxy group having <NUM> to <NUM> carbon atoms, the cycloalkyloxy group having <NUM> to <NUM> carbon atoms, the alkenyl group having <NUM> to <NUM> carbon atoms, the fluoroalkyl group having <NUM> to <NUM> carbon atoms, an N(R<NUM>)<NUM> group (wherein R<NUM> represents a hydrogen atom, a phenyl group, a benzyl group, or an alkyl group having <NUM> to <NUM> carbon atoms), and an NHCOR<NUM> group.

The N-(phenylureidophenyl)benzenesulfonamide compound of formula (I-<NUM>) is not particularly limited, and examples thereof include <NUM>-methyl-N-[<NUM>-(<NUM>-phenylureido)phenyl]benzenesulfonamide and N-[<NUM>-(<NUM>-phenylureido)phenyl]benzenesulfonamide.

In the color developer, the thermal recording material, and the thermal recording layer coating material of the present invention, the compound of formula (I) may be a phenylureidophenyl-benzenesulfonate compound of formula (I-<NUM>).

In the formula (I-<NUM>), the alkyl group of R<NUM> and R<NUM> is preferably an alkyl group having <NUM> to <NUM> carbon atoms. The alkyl group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include linear or branched alkyl groups such as methyl, ethyl, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a hexyl group, and an isohexyl group. Among them, a methyl group is particularly preferable.

In the formula (I-<NUM>), the cycloalkyl group of R<NUM> and R<NUM> is preferably a cycloalkyl group having <NUM> to <NUM> carbon atoms. The cycloalkyl group having <NUM> to <NUM> carbon atoms is not pacrticulaly limited and examples thereof include a cyclopropyl group, a cyclobutyl group, a <NUM>-methylcyclopropyl group, a cyclopropylmethyl group, a cyclopentyl group, and a cyclohexyl group.

In the formula (I-<NUM>), the alkoxy group of R<NUM> and R<NUM> is preferably an alkoxy group having <NUM> to <NUM> carbon atoms. The alkoxy group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include linear or branched alkoxyl groups such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a sec-butoxy group, a t-butoxy group, a pentyloxy group, an isopentyloxy group, a neopentyloxy group, a hexyloxy group, and an isohexyloxy group.

In the formula (I-<NUM>), the cycloalkyloxy group of R<NUM> and R<NUM> is preferably a cycloalkyloxy group having <NUM> to <NUM> carbon atoms. The cycloalkyloxy group having <NUM> to <NUM> carbon atoms is not particularly limited, and examples thereof include cyclic cycloalkyloxy groups such as a cyclopropyloxy group, a cyclobutyloxy group, a <NUM>-methylcyclopropyloxy group, a cyclopropylmethyloxy group, a cyclopentyloxy group, and a cyclohexyloxy group.

In the formula (I-<NUM>), the aryl group of the aryloxy group, the arylcarbonyloxy group, the arylcarbonylamino group, or the arylsulfonylamino group of R<NUM> and R<NUM> is not particularly limited, and examples thereof include a phenyl group and a naphthyl group. Examples of the naphthyl group include a <NUM>-naphthyl group and a <NUM>-naphthyl group.

In the formula (I-<NUM>), the alkyl group of the alkylcarbonyloxy group, the alkylcarbonylamino group, or the alkylsulfonylamino group is not particularly limited, and is preferably, for example, the alkyl group having <NUM> to <NUM> carbon atoms, and particularly preferably a methyl group.

In the formula (I-<NUM>), n1 is preferably <NUM> or <NUM>, and more preferably <NUM>. n3 is preferably <NUM> or <NUM>, and more preferably <NUM>. When n1 is <NUM>, the substituent position of R<NUM> is preferably the ortho position or the para position, and more preferably the para position. When n3 is <NUM>, the substituent position of R<NUM> is preferably the ortho position or the para position, and more preferably the para position.

The phenylureidophenyl-benzenesulfonate compound of formula (I-<NUM>) is not particularly limited, and examples thereof include the following compounds.

Hereinafter, in the present specification, the compound of formula (I) may be referred to as a "color developer (B)". The color developer (B) of formula (I) is the N-(phenylureidophenyl)benzenesulfonamide compound of formula (I-<NUM>) or the phenylureidophenyl-benzenesulfonate compound of formula (I-<NUM>).

In the thermal recording layer coating material of the present invention or the thermal recording layer in the thermal recording material of the present invention, the content of the color developer (B) is not particularly limited, and from the viewpoint of the color development density, the color developer (B) is preferably present in an amount from <NUM> to <NUM> parts by mass, more preferably from <NUM> to <NUM> parts by mass, and still more preferably from <NUM> to <NUM> parts by mass per <NUM> parts of the basic dye of the thermal recording layer.

In the color developer, the thermal recording material, and the thermal recording layer coating material of the present invention, the color developer includes an N-substituted amino acid derivative of formula (II) as described above.

wherein in the N-substituted amino acid derivative of formula (II) is N-(m-tolylaminocarbonyl)-phenylalanine or N-(phenylaminocarbonyl)-phenylalanine.

The N-substituted amino acid derivatives N-(m-tolylaminocarbonyl)-phenylalanine or N-(phenylaminocarbonyl)-phenylalanine of formula (II) used in the present invention have been found to be usable as a color developer by the inventors of the present invention as a result of the studies from the viewpoint of whether an amino acid which is also a food can be used as a thermal recording material. Since the basic amino group and the acidic carboxyl group coexist in the same molecule and are intramolecularly neutralized in an amino acid, the amino acid does not develop colors even when it comes into contact with the basic dye.

The inventors of the present invention have proposed the invention relating to a thermal recording material using an N-substituent amino acid derivative made especially from natural amino acids as a color developer, wherein a functional group that contributes to the required performance and color development ability of the color developer of the thermal recording material is introduced as a protecting group for an amino group of an amino acid, thereby canceling intramolecular neutralization and further strongly expressing the color development ability of an amino acid (<CIT>).

Hereinafter, in the present specification, the N-substituted amino acid derivative of formula (II) may be referred to as a color developer (C).

In the thermal recording layer coating material of the present invention or the thermal recording layer in the thermal recording material of the present invention, the color developer (C) is preferably present in an amount from <NUM> to <NUM> parts by mass, more preferably from <NUM> to <NUM> parts by mass, and still more preferably from <NUM> to <NUM> parts by mass per <NUM> parts of the basic dye of the thermal recording layer, from the viewpoint of color development density and plasticizer resistance.

In the color developer of the present invention, the thermal recording layer coating material of the present invention, or the thermal recording layer in the thermal recording material of the present invention, the content of the color developer (C) is not particularly limited, and from the viewpoint of plasticizer resistance, the color developer (C) may be present in an amount of, for example, <NUM> or more parts by mass, preferably <NUM> or more parts by mass, more preferably <NUM> or more parts by mass, still more preferably <NUM> or more parts by mass, still more preferably <NUM> or more parts by mass, preferably <NUM> or more parts by mass, preferably <NUM> or more parts by mass, preferably <NUM> or more parts by mass, preferably <NUM> or more parts by mass, preferably <NUM> or more or more, and preferably <NUM> or more parts by mass. The same applies to the case where the color developer (B) is represented by formula (I-<NUM>) and the case where the color developer (B) is represented by formula (I-<NUM>).

In the color developer of the present invention, the thermal recording layer coating material of the present invention, or the thermal recording layer in the thermal recording material of the present invention, the upper limit of the content of the color developer (C) per <NUM> parts of the color developer (B) is not particularly limited, and is preferably set to an appropriate amount within a range in which the effect of the plasticizer resistance can be obtained. Specifically, for example, the upper limit of the content of the color developer (C) may be <NUM> or less parts by mass, may be <NUM> or less parts by mass, may be <NUM> or less parts by mass, may be <NUM> or less parts by mass, and may be <NUM> or less parts by mass. The same applies to the case where the color developer (B) is represented by formula (I-<NUM>) and the case where the color developer (B) is represented by formula (I-<NUM>).

In the thermal recording layer coating material of the present invention or the thermal recording layer in the thermal recording material of the present invention, the total content of the color developer (B) and the color developer (C) is not particularly limited, and from the viewpoint of color development density, the color developer (B) and the color developer (C) are present in an amount, for example, from <NUM> to <NUM> parts by mass, <NUM> to <NUM> parts by mass, <NUM> to <NUM> parts by mass, <NUM> to <NUM> parts by mass, <NUM> to <NUM> parts by mass, or <NUM> to <NUM> parts by mass, and preferably from <NUM> to <NUM> parts by mass, more preferably <NUM> to <NUM> parts by mass, and still more preferably from <NUM> to <NUM> parts by mass per <NUM> parts of the basic dye of the thermal recording layer, for example. The same applies to the case where the color developer (B) is represented by formula (I-<NUM>) and the case where the color developer (B) is represented by formula (I-<NUM>).

In the color developer, the thermal recording material, and the thermal recording layer coating material of the present invention, the color developer (B) and the color developer (C) may be used in combination with a color developer other than the color developer (B) and the color developer (C) as long as the effect of the present invention is not hindered. The other color developer is not particularly limited, and may be, for example, a known or existing color developer. When the other color developer is used, one of the other color developers may be used alone or two or more of them may be used in combination.

In the thermal recording material and the thermal recording layer coating material of the present invention, the basic dye which is colorless or light-colored at normal temperature is not particularly limited, and examples thereof include triphenylmethane-based, fluorane-based, diphenylmethane-based, spiro-based, fluorene-based, and thiazine-based compounds. The basic dye which is colorless or light-colored at normal temperature may be selected from, for example, conventionally known leuko dyes. The basic dye which is colorless or light-colored at normal temperature is preferably a colorless or light-colored basic dye which is solid at normal temperature, and more preferably a colorless or light-colored basic dye having a melting point of <NUM> or higher.

In the present invention, "normal temperature" may be, for example, room temperature. In the present invention, "normal temperature" or "room temperature" may be, for example,-<NUM> or higher, -<NUM> or higher, <NUM> or higher, <NUM> or higher, or <NUM> or higher, and may be, for example, <NUM> or lower, <NUM> or lower, <NUM> or lower, <NUM> or lower, <NUM> or lower, <NUM> or lower, or <NUM> or lower. That is, in the present invention, the "basic dye which is colorless or light-colored at normal temperature" may be, for example, a basic dye which is colorless or light-colored in a temperature range of the "normal temperature" or "room temperature" (for example, a temperature range from -<NUM> to <NUM> or <NUM> to <NUM>). In addition, in the present invention, the "colorless or light-colored basic dye which is solid at normal temperature" may be, for example, a colorless or light-colored basic dye which is solid in a temperature range of the "normal temperature" or "room temperature" (for example, a temperature range from-<NUM> to <NUM> or <NUM> to <NUM> or the like).

In addition, in the present invention, the "basic dye which is colorless or light-colored at normal temperature" may be any basic dye that can be used for a thermal recording layer of a thermal recording material by developing color by heating. Such a basic dye is not particularly limited, and may be, for example, a basic dye generally used in a thermal recording layer of a thermal recording material, or may be, for example, a conventionally known basic dye as described above. Specific examples thereof are not particularly limited, and are as described above, for example. In the present invention, "light-colored" is not particularly limited, and may be, for example, light yellow, light blue, or the like.

In the thermal recording material and the thermal recording layer coating material of the present invention, specific examples of the basic dye which is colorless or light-colored at normal temperature are as follows, for example. However, in the thermal recording material and the thermal recording layer coating material of the present invention, the basic dye which is colorless or light-colored at normal temperature is not limited to the following specific examples. Further, in the thermal recording material and the thermal recording layer coating material of the present invention, one of the basic dyes which are colorless or light-colored at normal temperature may be used alone or two or more of them may be used in combination.

<NUM>,<NUM>-bis(p-dimethylaminophenyl)-<NUM>-dimethylaminophthalide, <NUM>,<NUM>-bis(p-dimethylaminophenyl) phthalide, <NUM>-(<NUM>-diethylamino-<NUM>-ethoxyphenyl)-<NUM>-(<NUM>-ethyl-<NUM>-methylindole-<NUM>-yl)-<NUM>-azaphthalide, <NUM>,<NUM>-bis(P-methylaminophenyl) -<NUM>-dimethylaminophthalide , <NUM>-diethylamino-<NUM>-dibenzylaminobenzo[α]fluorane, <NUM>-(<NUM>-ethyl-<NUM>-methylindole-<NUM>-yl)-<NUM>-(<NUM>-diethylamino-<NUM>-n-hexyloxyphenyl)-<NUM>-azaphthalide, <NUM>-(<NUM>-ethyl-<NUM>-methylindole-<NUM>-yl)-<NUM>-(<NUM>-diethylamino)-<NUM>-methylphenyl-<NUM>-azaphthalide, <NUM>-(<NUM>-diethylaminophenyl)-<NUM>-(<NUM>-ethyl-<NUM>-methylindole-<NUM>-yl)phthalide, <NUM>-(<NUM>-methyl-<NUM>-n-octylindol-<NUM>-yl)-<NUM>-(<NUM>-diethylamino-<NUM>-ethoxyphenyl)-<NUM>-azaphthalide, <NUM>-(N-ethyl-N-isopentylamino)-<NUM>-methyl-<NUM>-anilinofluoran, <NUM>-diethylamino-<NUM>-methyl-<NUM>-anilinofluoran, <NUM>-diethylamino-<NUM>-methyl-<NUM>-(o,p-dimethylanilino)fluorane.

<NUM>-(N-ethyl-N-p-toluidino)-<NUM>-methyl-<NUM>-anilinofluoran, <NUM>-pyrrolidino-<NUM>-methyl-<NUM>-anilinofluoran, <NUM>-(N,N-dibutylamino)-<NUM>-methyl-<NUM>-anilinofluoran, <NUM>-(N-cyclohexyl-N-methylamino)-<NUM>-methyl-<NUM>-anilinofluoran, <NUM>-diethylamino-<NUM>-(o-chloroanilino)fluoran, <NUM>-diethylamino-<NUM>-(m-trifluoromethylanilino)fluoran, <NUM>-di(n-pentyl)amino-<NUM>-methyl-<NUM>-anilinofluoran, <NUM>-[N-(<NUM>-etoxypropyl)-N-ethylamino]<NUM>-methyl-<NUM>-anilinofluoran, <NUM>-(N-n-hexyl-N-ethylamino)-<NUM>-(o-chloroanilino)fluoran, <NUM>-(N-ethyl-N-<NUM>-tetrahydrofurfurylamino)-<NUM>-methyl-<NUM>-anilinofluorane, <NUM>,<NUM>-bis{<NUM>-[<NUM>'-(N-cyclohexyl-N-methylamino)-<NUM>'-methylspiro[phthalido-<NUM>,<NUM>'-xanthene]-<NUM>'-ylamino]phenyl}propane, and <NUM>-dibutylamino-<NUM>-(o-chloroanilino)fluorane.

<NUM>,<NUM>-dimethoxyfluorane, <NUM>-pyrrolidino-<NUM>-chlorofluorane, <NUM>-diethylamino-<NUM>-methyl-<NUM>-chlorofluorane, <NUM>-diethylamino-<NUM>-chlorofluorane, <NUM>-diethylamino-<NUM>,<NUM>-dibenzofluorane, <NUM>-diethylamino-<NUM>,<NUM>-dimethylfluorane, <NUM>-(N-methyl-p-toluidino)-<NUM>-methylfluorane, <NUM>-(N-methyl-N-isoamylamino)-<NUM>,<NUM>-benzofluorane, <NUM>,<NUM>'-bis(<NUM>-n-amyl-<NUM>-methylindole-<NUM>-yl)phthalide, <NUM>-(N-methyl-N-isoamylamino)-<NUM>-phenoxyfluorane, <NUM>,<NUM>'-bis(<NUM>-n-butyl-<NUM>-methylindole-<NUM>-yl)phthalide, <NUM>,<NUM>'-bis(<NUM>-ethyl-<NUM>-methylindole-<NUM>-yl)phthalide, <NUM>,<NUM>'-bis(p-dimethylaminophenyl)phthalide, <NUM>-(N-ethyl-N-p-tolylamino)-<NUM>-(N-phenyl-N-methylamino) fluorane, <NUM>-diethylamino-<NUM>-anilinofluorane, <NUM>-diethylamino-<NUM>-benzylaminofluorane, <NUM>-pyrrolidino-<NUM>-dibenzylaminofluorane.

As described above, the thermal recording layer in the thermal recording material of the present invention and the thermal recording layer coating material of the present invention include a basic dye which is colorless or light-colored at normal temperature; and a color developer for developing color upon contact with the basic dye by heating, and may or may not include any other optional components.

The optional component may be, for example, a sensitizer. The sensitizer is not particularly limited, and for example, a conventionally known sensitizer can be used in combination. Specific examples of the sensitizer include fatty acid amides such as stearic acid amide, bisstearic acid amide, and palmitic acid amide, and the like; calcium such as p-toluene sulfonamide, stearic acid, behenic acid, palmitic acid, and the like; fatty acid metal salts such as zinc, aluminum, and the like; p-benzylbiphenyl; diphenylsulfone; benzyloxybenzoic acid benzyl; <NUM>-benzyloxynaphthalene; <NUM>,<NUM>-bis(p-tolyloxy)ethane; <NUM>,<NUM>-bis(phenoxy)ethane; <NUM>,<NUM>-bis(<NUM>-methylphenoxy)ethane, <NUM>,<NUM>-bis(phenoxy)propane; dibenzyl oxalate; p-methylbenzyl oxalate; m-terphenyl; and <NUM>-hydroxy-<NUM>-naphthoic acid.

The optional component maybe, for example, a storage stabilizer. The storage stabilizer is not particularly limited, and for example, a conventionally known storage stabilizer can be used in combination. Specific examples of the storage stabilizer include hindered phenol compounds such as <NUM>,<NUM>'-methylenebis(<NUM>-methyl-<NUM>-tert-butylphenol), <NUM>,<NUM>'-methylenebis(<NUM>-ethyl-<NUM>-tert-butylphenol), <NUM>,<NUM>'-ethylidenebis(<NUM>,<NUM>-di-tert-butylphenol), <NUM>,<NUM>'-thiobis(<NUM>-methyl-<NUM>-tertbutylphenol), <NUM>,<NUM>'-butylidenebis(<NUM>-tert-butyl m-cresol), <NUM>,<NUM>,<NUM>-tris(<NUM>-methyl-<NUM>-hydroxy-<NUM>-tert-butylphenyl)butane, <NUM>,<NUM>,<NUM>-tris(<NUM>-methyl-<NUM>-hydroxy-<NUM>-cyclohexylphenyl)butane, <NUM>,<NUM>'-bis[(<NUM>-methyl-<NUM>-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, tris(<NUM>,<NUM>-dimethyl-<NUM>-tert-butyl-<NUM>-hydroxybenzyl)isocyanurate, <NUM>,<NUM>'-thiobis(<NUM>-methylphenol), <NUM>,<NUM>'-dihydroxy-<NUM>,<NUM>',<NUM>,<NUM>'-tetrabromodiphenylsulfone, <NUM>,<NUM>'-dihydroxy <NUM>,<NUM>',<NUM>,<NUM>'-tetramethyldiphenylsulfone, <NUM>,<NUM>-bis(<NUM>-hydroxy-<NUM>,<NUM>-dibromophenyl) propane, <NUM>,<NUM>-bis(<NUM>-hydroxy-<NUM>,<NUM>-dichlorophenyl) propane, <NUM>,<NUM>-bis(<NUM>-hydroxy-<NUM>,<NUM>-dimethylphenyl) propane, and the like; epoxy compounds such as <NUM>,<NUM>-diglycidyloxybenzene, <NUM>,<NUM>'-diglycidyloxydiphenylsulfone, <NUM>-benzyloxy-<NUM>'-(<NUM>-methylglycyloxy)diphenylsulfone, terephthalic glycidyl, bisphenol A type epoxy resin, cresol novolac type epoxy resin, phenol novolac type epoxy resin, and the like; N,N'-di-<NUM>-naphthyl-p-phenylenediamine, sodium salt or polyvalent metal salt of <NUM>,<NUM>'-methylenebis(<NUM>,<NUM>-di-tert-butylphenyl)phosphate; bis(<NUM>-ethyleneiminecarbonylaminophenyl)methane; <NUM>,<NUM>'-bis[(<NUM>-methyl-<NUM>-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, and a diphenylsulfone-crosslinked compound of formula (<NUM>). These storage stabilizers contribute to the storage stability of the printed part of the thermal recording material.

In the formula, n represents an integer of <NUM> to <NUM>.

When a storage stabilizer is used, the content of the storage stabilizer is not particularly limited, and the storage stabilizer is preferably present in an amount of <NUM> to <NUM> parts by mass, and more preferably <NUM> to <NUM> parts by mass per <NUM> parts of the total content of the color developer (B) and the color developer (C).

The optional component may be, for example, an auxiliary agent. The auxiliary agent is not particularly limited, and examples thereof include dispersants such as sodium dioctylosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate, a fatty acid metal salt, and the like; waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, and the like; hydrazide compounds such as adipic acid dihydrazide, and the like; water-resistant agents such as glyoxal, boric acid, dialdehyde starch, methylol urea, glyoxylate, an epoxy compound, and the like; defoaming agents; coloring dyes; fluorescent dyes; and pigments.

The optional components used in the thermal recording layer in the thermal recording material of the present invention and the thermal recording layer coating material of the present invention may be, for example, a binder. The binder is not particularly limited, and examples thereof include completely saponified polyvinyl alcohol with a degree of polymerization of <NUM> to <NUM>, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, cellulose derivatives such as ethyl cellulose and acetyl cellulose, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyral polystyrene, and copolymers thereof, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, and chroman resins. One of these binders may be used alone or two or more of them may be used in combination. The binders may be used in a state of being dissolved in a solvent, or dispersed in water or other medium in an emulsified or pasty form.

The optional components used in the thermal recording layer in the thermal recording material of the present invention and the thermal recording layer coating material of the present invention may be, for example, a pigment. The pigment is not particularly limited, and may be an inorganic pigment or an organic pigment. Examples of the pigment include silica, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, zinc oxide, aluminum hydroxide, polystyrene resins, urea-formalin resins, styrene-methacrylic acid copolymers, styrene-butadiene copolymers, and hollow plastic pigments.

The type and amount of the basic dye, the color developer, the sensitizer, the binder, the pigment, and other additives used in thermal recording layer in the thermal recording material of the present invention and the thermal recording layer coating material of the present invention are not particularly limited, and can be appropriately determined according to, for example, the quality performance required for the thermal recording layer.

The method for producing the thermal recording layer coating material of the present invention is not particularly limited, and can be produced in the same manner as a general thermal recording layer coating material except that the color developer (B) (the compound of formula (I)) and the color developer (C) (N-substituted amino acid derivative of formula (II)) are used in combination as a color developer, for example. Specifically, for example, the thermal recording layer coating material of the present invention can be produced by adding a binder, a sensitizer, a filler, a lubricant, other additives, and the like in addition to a basic dye which is colorless or light-colored at normal temperature and a color developer for developing color upon contact with the basic dye by heating. The thermal recording layer coating material of the present invention can also be produced, for example, by the production method described in the following Examples.

In the thermal recording material of the present invention, the method for forming the thermal recording layer and the method for producing the thermal recording material are not particularly limited, and may be the same as the general method for forming the thermal recording layer and the general method for producing the thermal recording material except that the thermal recording layer coating material of the present invention is used as the thermal recording layer coating material, for example. Specifically, for example, the thermal recording material of the present invention can be produced by applying the thermal recording layer coating material (coating liquid) of the present invention produced as described above on a support to form a thermal recording layer. In the thermal recording material of the present invention, the support is not particularly limited, and may be, for example, at least one of paper and a film. That is, the thermal recording material of the present invention may be, for example, thermal recording paper in which the support is paper. The thermal recording material of the present invention may be, for example, a thermal recording film in which the support is a film. The paper is not particularly limited, and examples thereof include paper, recycled paper, and synthetic paper. The film is not particularly limited, and examples thereof include a plastic film, a nonwoven fabric, and a metal foil. The support of the present invention may be formed of, for example, a single material, or may be a composite sheet obtained by combining a plurality of materials.

The thermal recording layer in the thermal recording material of the present invention and the thermal recording layer coating material of the present invention preferably contain, for example, <NUM> to <NUM> parts by mass of a sensitizer per <NUM> parts of the basic dye, and preferably contain <NUM> to <NUM>% by mass of a binder in the total solid content.

The thermal recording material of the present invention may or may not include any optional components other than the support and the thermal recording layer. For example, as the optional component, an overcoat layer made of a polymer material containing an organic pigment may be provided for the purpose of enhancing the storage stability of the thermal recording layer. In addition, for example, an undercoat layer containing an organic pigment, an inorganic pigment, hollow fine particles, or the like may be provided as the optional components for the purpose of preventing the adhesion of grains to the thermal head, improving the print quality, improving the sensitivity, and the like.

In the present invention, the basic dye, the color developer, the sensitizer, and as needed the storage stabilizer and the like used in the thermal recording layer or the thermal recording layer coating material may be used, for example, by pulverizing with water as a dispersion medium using a stirring/grinding machine such as a ball mill, an attritor, a sand mill, or the like so as to achieve the average particle size of <NUM> or less.

By mixing and stirring a pigment, a binder, an auxiliary agent, and the like, as needed, in the dispersed liquid finely dispersed in this manner, it is possible to produce a thermal recording layer coating material as described above.

Further, by applying the thermal recording layer coating material thus obtained on the support and then drying to form a thermal recording layer on the support, the thermal recording material of the present invention can be produced. The application amount of the thermal recording layer coating material on the support is not particularly limited, and the application amount after drying of the thermal recording layer coating material is preferably <NUM> to <NUM>/m<NUM>, and more preferably <NUM> to <NUM>/m<NUM>, for example.

As the support in the thermal recording material of the present invention, for example, paper, recycled paper, synthetic paper, a plastic film, a nonwoven fabric, metal foil, or the like can be used as described above. A composite sheet obtained by combining these materials can also be used as a support. The thickness of the support is not particularly limited, and can be adjusted appropriately according to the application of the thermal recording material of the present invention, for example.

According to the present invention, it is possible to provide a thermal recording material that satisfies the required performance as a thermal recording material, such as color development density, whiteness, and heat resistance, heat resistance, water resistance, and plasticizer resistance of a printed part.

Hereinafter, Examples of the present invention will be described together with Comparative Examples. However, the present invention is not limited to the following Examples. In the following examples, the term "parts" represents "parts by mass" unless otherwise specified, and "%" represents "% by mass" unless otherwise specified.

In the following Examples, the thermal recording layer coating material and the thermal recording material were produced as follows.

An undercoat layer coating material was prepared by mixing <NUM> parts of plastic hollow particles (trade name: ROPAQU™ SN-<NUM>: hollow ratio: <NUM>%, solid content: <NUM>%), <NUM> parts of a <NUM>% dispersion of calcined kaolin, <NUM> parts of a styrene-butadiene latex (trade name: L-<NUM>, solid content: <NUM>%), <NUM> parts of a <NUM>% aqueous solution of oxidized starch, and <NUM> parts of water. This undercoat layer coating material was used for the production of the thermal recording materials in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> below.

Each of the dispersed liquids (liquid A, liquid B, liquid C, and liquid D) was pulverized by a sand grinder until the average particle size became <NUM> or less, and the dispersed liquids were mixed at the following ratios to obtain a coating liquid.

A thermal recording layer coating material of the present Example was prepared by mixing the coating liquid with <NUM> parts of aluminum hydroxide (trade name: Heidilite® H-<NUM>), <NUM> parts of amorphous silica (trade name: Mizukasil® P-<NUM>), <NUM> parts of <NUM>% lysate of oxidized starch, <NUM> parts of zinc stearate dispersed liquid (trade name: Hidorin® Z-<NUM>-<NUM>), and <NUM> parts of water.

As a support, high-quality paper (acid paper) having a basis weight of <NUM> gm<NUM> was prepared. An undercoat layer was formed on the support by applying and drying the undercoat layer coating material so as to achieve the mass per area after drying of <NUM>/m<NUM>. A thermal recording layer was formed on the undercoat layer by applying and drying the thermal recording layer coating material of the present Example so as to achieve the mass per area after drying of <NUM>/m<NUM>, thereby obtaining a sheet including high-quality paper, an undercoat layer, and a thermal recording layer. The resulting sheet was treated with a super calender so as to have the smoothness of <NUM> to <NUM>, thereby producing (preparing) the thermal recording material of the present Example. The smoothness was measured by a method according to JIS P8155:<NUM> "Paper and board-Determination of smoothness-Oken method".

The following tests <NUM> to <NUM> were performed on the thermal recording material produced (prepared) in the present Example.

An energy of <NUM> mJ/dot was applied to the produced thermal recording material using a thermal recording paper printing tester (TH-PMD manufactured by Ohkura Electric Co. The print density of the recorded part was measured by a Macbeth reflection densitometer (trade name: RD-<NUM>, manufactured by Gretag-Macbeth). The resultant was used as a sample (blank).

The thermal recording material recorded in the thermal recording performance test was left for <NUM> hours under an environment of an <NUM>% RH at a test temperature of <NUM>, and then the image density of the printed part and the density of the non-printed part of the test piece were measured by the Macbeth reflection densitometer.

The thermal recording material recorded in the thermal recording performance test was left for <NUM> hours under a constant temperature environment at a test temperature of <NUM>, and then the image density of the printed part and the density of the non-printed part of the test piece were measured by the Macbeth reflection densitometer.

The thermal recording material recorded in the thermal recording performance test was immersed in water for <NUM> hours, and then the test piece was air-dried, and the image density and the non-printed part were measured by the Macbeth reflection densitometer.

A lap film (trade name: Hi-Wrap® KMA, manufactured by Mitsui Chemicals, Inc. ) was wound in triplicate on a polycarbonate pipe (<NUM> mmφ), thermal recording paper recorded in the thermal recording performance test was placed thereon, and the lap film was again wound in triplicate thereon and left for <NUM> hours under an environment of <NUM>% RH at <NUM>, after which the image density and the non-printed part were measured by the Macbeth reflection densitometer.

The results of the tests <NUM> to <NUM> for the thermal recording material of the present Example were as summarized in Table <NUM> below.

A thermal recording layer coating material of Example <NUM> and a thermal recording material of Example <NUM> were prepared in the same manner as in Example <NUM> except that <NUM> parts of the liquid B and <NUM> parts of the liquid C of Example <NUM> were changed to <NUM> parts of the liquid B and <NUM> parts of the liquid C. The results of the tests for the thermal recording material according to Example <NUM> are summarized in Table <NUM>.

A thermal recording layer coating material of Example <NUM> and a thermal recording material of Example <NUM> were prepared in the same manner as in Example <NUM> except that N-(m-tolylaminocarbonyl)-phenylalanine of the liquid C of Example <NUM> was changed to N-(phenylaminocarbonyl)-phenylalanine. The results of the tests for the thermal recording material according to Example <NUM> are summarized in Table <NUM>.

A thermal recording layer coating material of Comparative Example <NUM> and a thermal recording material of Comparative Example <NUM> were prepared in the same manner as in Example <NUM> except that <NUM> parts of the liquid B and <NUM> parts of the liquid C of Example <NUM> were changed to <NUM> parts of the liquid B and no liquid C. The results of the tests for the thermal recording material according to Comparative Example <NUM> are summarized in Table <NUM>.

A thermal recording layer coating material of Comparative Example <NUM> and a thermal recording material of Comparative Example <NUM> were prepared in the same manner as in Example <NUM> except that <NUM> parts of the liquid B and <NUM> parts of the liquid C of Example <NUM> were changed to no liquid B and <NUM> parts of the liquid C. The results of the tests for the thermal recording material according to Comparative Example <NUM> are summarized in Table <NUM>.

A thermal recording layer coating material of Comparative Example <NUM> and a thermal recording material of Comparative Example <NUM> were prepared in the same manner as in Comparative Example <NUM> except that N-(m-tolylaminocarbonyl)-phenylalanine of the liquid C of Comparative Example <NUM> was changed to N-(phenylaminocarbonyl)-phenylalanine. The results of the tests for the thermal recording material according to Comparative Example <NUM> are summarized in Table <NUM>.

A thermal recording layer coating material of Comparative Example <NUM> and a thermal recording material of Comparative Example <NUM> were prepared in the same manner as in Comparative Example <NUM> except that N-[<NUM>-(<NUM>-phenylureido)phenyl]benzenesulfonamide of the liquid B of Comparative Example <NUM> was changed to bisphenol A. The results of the tests for the thermal recording material according to Comparative Example <NUM> are summarized in Table <NUM>.

A thermal recording layer coating material of Comparative Example <NUM> and a thermal recording material of Comparative Example <NUM> were prepared in the same manner as in Comparative Example <NUM> except that N-[<NUM>-(<NUM>-phenylureido)phenyl]benzenesulfonamide of the liquid B of Comparative Example <NUM> was changed to bisphenol S. The results of the tests for the thermal recording material according to Comparative Example <NUM> are summarized in Table <NUM>.

The thermal recording materials of Examples <NUM> to <NUM> were thermal recording materials in which a thermal recording layer that includes an N-(phenylureidophenyl)benzenesulfonamide compound of formula (I) or the formula (I-<NUM>) as a color developer (B) and an N-substituted amino acid derivative of formula (II) as a color developer (C) was provided on a support. As is apparent from Table <NUM>, the thermal recording materials of Examples <NUM> to <NUM> were superior in plasticizer resistance to the thermal recording material (Comparative Example <NUM>) in which the thermal recording layer including the color developer (B) alone was provided on the support, while maintaining the characteristics of the thermal recording material in which the thermal recording layer including the color developer (B) was provided on the support. Furthermore, the thermal recording materials of Examples <NUM> to <NUM> were superior in plasticizer resistance to the thermal recording materials (Comparative Examples <NUM> to <NUM>) in which the thermal recording layer including the color developer (C) alone was provided on the support.

A thermal recording layer coating material was produced (prepared) by mixing the coating liquid with <NUM> parts of aluminum hydroxide (trade name: Heidilite® H-<NUM>), <NUM> parts of amorphous silica (trade name: Mizukasil® P-<NUM>), <NUM> parts of <NUM>% lysate of oxidized starch, <NUM> parts of zinc stearate dispersed liquid (trade name: Hidorin® Z-<NUM>-<NUM>), and <NUM> parts of water.

The following tests <NUM> to <NUM> were performed on the thermal recording material of the present Example. The results of the tests were as summarized in Table <NUM> below.

A thermal recording layer coating material of Comparative Example <NUM> and a thermal recording material of Comparative Example <NUM> were prepared in the same manner as in Comparative Example <NUM> except that <NUM>-(<NUM>-phenylureido)phenyl-<NUM>-methylbenzenesulfonate of the liquid B of Comparative Example <NUM> was changed to bisphenol A. The results of the tests for the thermal recording material according to Comparative Example <NUM> are summarized in Table <NUM>.

A thermal recording layer coating material of Comparative Example <NUM> and a thermal recording material of Comparative Example <NUM> were prepared in the same manner as in Comparative Example <NUM> except that <NUM>-(<NUM>-phenylureido)phenyl-<NUM>-methylbenzenesulfonate of the liquid B of Comparative Example <NUM> was changed to bisphenol S. The results of the tests for the thermal recording material according to Comparative Example <NUM> are summarized in Table <NUM>.

The thermal recording materials of Examples <NUM> to <NUM> were thermal recording materials in which a thermal recording layer that includes <NUM>-(<NUM>-phenylureido)phenyl-<NUM>-methylbenzenesulfonate, which is one of the compounds of formula (I) or the formula (I-<NUM>), as a color developer (B) and an N-substituted amino acid derivative of formula (II) as a color developer (C) was provided on a support. As is apparent from Table <NUM>, the thermal recording materials of Examples <NUM> to <NUM> were superior in plasticizer resistance to the thermal recording material (Comparative Example <NUM>) in which the thermal recording layer including the color developer (B) alone was provided on the support, while maintaining the characteristics of the thermal recording material in which the thermal recording layer including the color developer (B) was provided on the support. Furthermore, the thermal recording materials of Examples <NUM> to <NUM> were superior in plasticizer resistance to the thermal recording materials (Comparative Examples <NUM> to <NUM>) in which the thermal recording layer including the color developer (C) alone was provided on the support.

Claim 1:
A color developer for a thermal recording layer, comprising:
a compound of formula (I); and
an N-substituted amino acid derivative of formula (II),
<CHM>

        (R<NUM>-X)-Y-(Z)     (II),

wherein the compound of formula (I) is an N-(phenylureidophenyl)benzenesulfonamide compound of formula (I-<NUM>) or a phenylureidophenyl-benzenesulfonate compound of formula (I-<NUM>),
<CHM>
<CHM>
wherein in the formula (I-<NUM>),
R<NUM>, R<NUM> and R<NUM> each represent a hydrogen atom, a halogen atom, a nitro group, an alkyl group having <NUM> to <NUM> carbon atoms, a cycloalkyl group having <NUM> to <NUM> carbon atoms, an alkoxy group having <NUM> to <NUM> carbon atoms, a cycloalkyloxy group having <NUM> to <NUM> carbon atoms, an alkenyl group having <NUM> to <NUM> carbon atoms, a fluoroalkyl group having <NUM> to <NUM> carbon atoms, an N(R<NUM>)<NUM> group (wherein R<NUM> represents a hydrogen atom, a phenyl group, a benzyl group, or an alkyl group having <NUM> to <NUM> carbon atoms), an NHCOR<NUM> group (wherein R<NUM> represents an alkyl group having <NUM> to <NUM> carbon atoms), an optionally substituted phenyl group, or an optionally substituted benzyl group;
n1 and n3 each independently represent an integer of <NUM> to <NUM>;
n2 represents an integer of <NUM> to <NUM>;
R<NUM>, R<NUM> and R<NUM> are identical to or different from one another;
when two or more R<NUM>s are present, R<NUM>s are identical to or different from each other;
when two or more R<NUM>s are present, R<NUM>s are identical to or different from each other; and
when two or more R<NUM>s are present, R<NUM>s are identical to or different from each other,
wherein in the formula (I-<NUM>),
R<NUM> and R<NUM> each represent an alkyl group, a cycloalkyl group, an alkoxy group, a cycloalkyloxy group, an aryloxy group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an alkylcarbonylamino group, an arylcarbonylamino group, an alkylsulfonylamino group, or an arylsulfonylamino group;
n1 and n3 each independently represent an integer of <NUM> to <NUM>;
R<NUM> and R<NUM> are identical to or different from each other;
when two or more R<NUM>s are present, R<NUM>s are identical to or different from each other; and
when two or more R<NUM>s are present, R<NUM>s are identical to or different from each other,
and
wherein the N-substituted amino acid derivative of formula (II) is N-(m-tolylaminocarbonyl)-phenylalanine or N-(phenylaminocarbonyl)-phenylalanine.