CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese patent Application No. 2005-72061, the disclosure of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat-sensitive recording material, more particularly, a heat-sensitive recording material having a heat-sensitive recording layer using a vegetable oil.

2. Description of Related Art

Heat-sensitive recording materials are used extensively since they are generally relatively inexpensive, and recording instruments therefor are compact and maintenance-free. In recent years, improvements of the functions of the layers of heat-sensitive recording materials which differ from conventional functions have been requested in particular.

Heat-sensitive recording materials should have favorable imaging performances (e.g., developed color density, image storability, and head matching at recording). Moreover, there are needs for improvement in pre-use storage stability (hereinafter, referred to as â€œraw storabilityâ€ ), for prevention of staining developed by exposure to light which is a cause for background coloring, for prevention of unpleasant smell, or for achievement of multicolor recording.

Considering the aforementioned requirements, a variety of heat-sensitive recording materials have been proposed (e.g. see Japanese Patent Application Laid-Open (JP-A) No. 2003-127550). In an example, an isocyanate as a capsule-wall forming agent is used for the formation of a microcapsule.

In the constructions described above, various performances such as multicolor recording can be improved to some extent, and the occurrence of offensive smell can be prevented by using a vegetable oil. However, pre-recording storage stability (raw storability) and prevention of stains developed by exposure to light are still insufficient; thus there are demands for further improvements thereof. Since the improvement in raw storability and the prevention of staining caused by exposure to light have an influence on the finally-obtained recorded image, they are essential elements for the formation of a high-quality image other than the improvement in color developing property and the weather resistance of an image.

In addition, prevention of the color mixing is important in the formation of a multicolor image by coloring of a plurality of laminated layers in different hues. In order to prevent the color mixing, it is necessary to adjust the heat sensitivity of each layer adequately while avoiding the energy amount required for coloring the layer that needs the highest heat for coloring being excessively large.

SUMMARY OF THE INVENTION

The invention has been made in consideration of the problems of the conventional techniques.

The present inventors have found that the use of triglycerides is effective for the improvement of the raw storability of a heat-sensitive recording material that uses a microcapsule containing an electron-donating colorless dye-precursor, and for the prevention of staining upon exposure to light. Based on this finding, the inventors have made the present invention.

The present invention provides a heat-sensitive recording material having one or more heat-sensitive recording layers on a support. At least one of the heat-sensitive recording layer(s) is a leuco color-developing layer that contains a microcapsule containing an electron-donating colorless dye-precursor and a mixture of triglycerides. The particle diameter of the microcapsule is 0.7 to 2.0 Î¼m.

The capsule wall of the microcapsule may contain at least two compounds selected from the group consisting of compound (1), compound (2), and compound (3). [Image Omitted]

In compound (1), n represents an integer of 0 to 2.

In compound (2), X represents â€”CH₂â€”NCO or â€”NCO, and two Xs may be the same as or different from each other. R¹represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R², R³, and R⁴each independently represent an alkylene group having 1 to 3 carbon atoms.

In compound (3), X represents â€”CH₂â€”NCO or â€”NCO, and two Xs may be the same as or different from each other; R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, and R¹²each independently represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, an aryl group, or an aryloxy group; R¹³represents a hydrogen atom, an alkyl group, or an aryl group; R¹⁴represents a hydrogen atom, an alkyl group, or an alkoxy group; and m represents an integer of 1 or2.

The mixture of triglycerides may be a mixture of less than 20% by mass of at least one saturated fatty acid having 14 or more carbon atoms, and 20 to 60% by mass of at least one unsaturated fatty acid having 14 or more carbon atoms.

The mixture of triglycerides may be at least one selected from rapeseed oil, sunflower oil, sesame oil, and peanut oil.

The electron-donating colorless dye-precursor may be at least one selected from a dye represented by formula (A) and a dye represented by formula (B). [Image Omitted]

In formula (A), R²¹represents an alkyl group having 1 to 12 carbon atoms; R²²represents an alkyl group having 1 or 2 carbon atoms; R²³represents a hydrogen atom, an alkyl group having 1 or 2 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, an amido group having 2 to 12 carbon atoms, an alkylsulfonamido group having 1 to 6 carbon atoms, an arylsulfonamido group having 6 to 10 carbon atoms, an anilinocarbonamido group having 7 to 13 carbon atoms, or a halogen atom; R²⁴and R²⁵each independently represent an alkyl group having 1 to 8 carbon atoms; and A represents a group which, together with the lactone portion, forms an aromatic ring. [Image Omitted]

In formula (B), R²⁶represents an alkyl group having 1 to 4 carbon atoms, R²⁷represents an alkyl group having 3 to 12 carbon atoms, and R²⁸and R²⁹each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 3 carbon atoms.

In addition to the leuco color-developing layer, the heat-sensitive recording material may further have a diazo color-developing layer containing a diazo compound and a coupler that reacts with the diazo compound under heat to develop color,.

The heat-sensitive recording material may have a plurality of heat-sensitive recording layers which develop colors of respectively different hues selected from yellow, magenta, and cyan, wherein at least one layer of the plurality of heat-sensitive recording layers may be the leuco color-developing layer.

According to the invention, a heat-sensitive recording material which is excellent in raw storability and, at the same time, prevents coloring of a non-image part (background part) caused by staining upon exposure to light can be provided.

DESCRIPTION OF THE PRESENT INVENTION

The heat-sensitive recording material of the invention will be explained in detail below.

The heat-sensitive recording material of the invention has at least one heat-sensitive recording layer provided on a support. The heat-sensitive recording material may have other layers such as a protecting layer and an intermediate layer as necessary. In a preferable embodiment, the heat-sensitive recording material is a multicolor heat-sensitive recording material having a lamination of a plurality of heat-sensitive recording layers.

At least one heat-sensitive recording layer (hereinafter, also referred to as â€œleuco color-developing layer according to the inventionâ€ ) in the heat-sensitive recording material of the invention contains at least a microcapsule containing an electron-donating colorless dye-precursor and a mixture of triglycerides. In general, an electron-receiving compound that color the electron-donating colorless dye-precursor can be present outside the microcapsule. If necessary, other components may also be contained.

-Mixture of Triglycerides-

The leuco color-developing layer according to the invention contains at least one mixture of triglycerides. The mixture of triglycerides contains a vegetable oil, and is used as a solvent for the electron-donating colorless dye-precursor described later. By using the triglycerides, the raw storability can be effectively improved and, at the same time, the background coloring caused by staining upon exposure to light exposure can also be prevented effectively.

In the invention, triglycerides are used, particularly, in the form of a mixture of a plurality of triglycerides. As is already described above, it is generally useful to use a mixture of triglycerides from the viewpoint of the compatibility with the dye, the wall-material monomer, the substance that reduces coloring of an unprinted part after fixing thus improving the fastness of the colored image to light and heat, and the solvent to dissolve them. By the use of the mixture of plural triglycerides, the effects of the invention can be more effectively exerted while the compatibility is secured. The mixture of triglycerides according to the invention is a mixture having a composition in which the proportions of fatty acid components in the total sum of all the molecules (each containing three fatty acid components) is not excessively uneven. Specifically, the mixture preferably satisfies one or more of the following conditions: (i) the three fatty acid components in a compound molecule have two or more different molecular structures, (ii) the structures of the fatty acid components include both a saturated fatty acid and an unsaturated fatty acid, and (iii) there are 3 or more fatty acid species in the whole fatty acid components.

The triglyceride compounds are preferably selected from glyceride compounds of oleic acid, linoleic acid, palmitic acid, myristic acid, linolenic acid, eicosenoic acid, and erucinic acid. Examples of such a mixture of triglycerides include vegetable oils such as sesame oil, safflower oil, soybean oil, sunflower oil, corn oil, cottonseed oil, rapeseed oil, peanut oil, and palm oil.

Among them, the mixture of triglycerides is preferably a mixture containing at least one saturated fatty acid residue having 14 or more carbon atoms (the content of each residue is preferably less than 20% by mass of the total mixture) and at least one unsaturated fatty acid residue having 14 or more carbon atoms (whose amount is preferably 20 to 60% by mass, more preferably 25 to 55% by mass of the total mixture).

Specifically, rapeseed oil, sunflower oil, sesame oil, or peanut oil is preferable. These are preferable in view of production suitability at the formation of a microcapsule comprising a polyurethane polyurea resin obtained by polymerization of a polyvalent isocyanate and a compound having a hydroxy group. They are also preferable in that they are easily available and eco-friendly.

The content of the mixture of triglycerides in the heat-sensitive recording layer is preferably 20 to 130% by mass, more preferably 30 to 120% by mass relative to the electron-donating colorless dye-precursor. When the content is within the aforementioned range, the raw storability can be effectively improved and an image having a high contrast can be formed effectively while suppressing the background coloring.

-Electron-Donating Colorless Dye-Precursor-

The leuco color-developing layer according to the invention contains at least one electron-donating colorless dye-precursor. This electron-donating colorless dye-precursor is a compound that reacts with an electron-receiving compound described later under heat to develop color. When the electron-donating colorless dye-precursor is heated imagewise, color develops to form an image.

The electron-donating colorless dye-precursor can be appropriately selected among known electron-donating colorless dye-precursors which can dissolve in the aforementioned mixture (vegetable oil) of triglycerides used as a solvent. Inter alia, an indolylphthalide compound and an indolylazaphthalide compound are preferable.

In addition, other known dye-precursors can be used together with an indolylphthalide compound or an indolylazaphthalide compound for the purpose of adjusting the hue. Examples thereof include a triarylmethane-based compound, a fluoran-based compound, a phenothiazine-based compound, a rhodaminelactam-based compound, a leucoauramine-based compound, a triazene-based compound, a diphenylmethane-based compound, a xanthene-based compound, and a spiropyran-based compound.

Only one electron-donating colorless dye-precursor may be used, or two or more electron-donating colorless dye-precursors may be used in combination.

Examples of these compounds include 3,3-bis(p-dimethylaminophenyl)-6-dimethylamino phthalide (namely crystal violet lactone), 3,3-bis(p-dimethylamino) phthalide, 3-(p-dimethylaminophenyl)-3-(1,3-dimethylindol-3-yl) phthalide, 3-(p-dimethylaminophenyl)-3-(2-methylindol-3-yl) phthalide, 3-(o-methyl-p-diethylaminophenyl)-3-(2-methylindol-3-yl) phthalide, 4,4â€²-bis(dimethylamino)benzhydrin benzyl ether, N-halophenyl leucoauramin, N-2,4,5-trichlorophenyl leucoauramin, rhodamin-B-anilinolactam, rhodamin(p-nitroanilino) lactam, rhodamin-B-(p-chloroanilino) lactam, 2-benzylamino-6-diethylaminofluoran, 2-anilino-6-diethylaminofluoran, 2-anilino-3 -methyl-6-diethylaminofluoran, 2-anilino-3 -methyl-6-cyclohexylmethylaminofluoran, 2-anilino-3-methyl-6-isoamylethylaminofluoran, 2-(o-chloroanilino)-6-diethylaminofluoran, 2-octylamino-6-diethylaminofluoran, 2-ethoxyethylamino-3-chloro-2-diethylaminofluoran, 2-anilino-3-chloro-6-diethylaminofluoran, benzoyl leuco methylene blue, p-nitrobenzyl leuco methylene blue, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3â€²-dichloro-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, and 3-propyl-spiro-dibenzopyran.

In the invention, an electron-donating colorless dye-precursor represented by the following formula (A), and an electron-donating colorless dye-precursor represented by the following formula (B) are preferable. These dye-precursors are preferable in compatibility with triglycerides.

The electron-donating colorless dye-precursor represented by formula (A) or formula (B) will be described in detail below, focusing on explanation of each group.
(Electron-Donating Colorless Dye-precursor Represented by Formula (A)) [Image Omitted]

In formula (A), R²¹represents an alkyl group having 1 to 12 carbon atoms or an aryl group having 6 to 10 carbon atoms.

Examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, a t-butyl group, a n-pentyl group, a cyclohexyl group, an octyl group, a 2-ethylhexyl group, an isononyl group, and a dodecyl group. Inter alia, a methyl group, an ethyl group, a n-propyl group, a cyclohexyl group, an octyl group, a 2-ethylhexyl group, and an isononyl group are preferable.

Examples of the aryl group having 6 to 10 carbon atoms include a phenyl group, a p-toluyl group, a m-toluyl group, a 2,6-dimethylphenyl group, a 4-t-butylphenyl group, a 4-methoxyphenyl group, a 4-butoxyphenyl group, a 4-methylthiophenyl group, a 3-ethoxy-4-dimethylaminophenyl group, a 2-chlorophenyl group, and a naphthyl group. Inter alia, a phenyl group and a p-toluyl group are preferable.

R²²represents an alkyl group having 1 or 2 carbon atoms, or a phenyl group. Examples of the alkyl group having 1 or 2 carbon atoms represented by R²²include a methyl group and an ethyl group. As R²², a methyl group or a phenyl group is preferable.

R²³represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an alkylthio group having 1 to 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, an amido group having 2 to 12 carbon atoms, an alkylsulfonamido group having 1 to 6 carbon atoms, an arylsulfonamido group having 6 to 10 carbon atoms, an anilinocarbonamido group having 7 to 13 carbon atoms, or a halogen atom.

Herein, the definition and preferable range of the alkyl group having 1 to 12 carbon atoms represented by R²³are the same as those of the alkyl group having 1 to 12 carbon atoms represented by R²¹.

Examples of the alkoxy group having 1 to 20 carbon atoms represented by R²³include a methoxy group, an ethoxy group, an isopropyloxy group, a sec-butyloxy group, a 3-pentyloxy group, a hexyl group, a cyclohexyl group, an octyloxy group, a 2-ethylhexyloxy group, an isononyloxy group, a dodecyloxy group, a tetradecyloxy group, an octadecyloxy group, and an isooctadecyloxy group. Inter alia, an ethoxy group, an octyloxy group, an isononyloxy group, and an octadecyl group are preferable.

Examples of the alkylthio group having 1 to 6 carbon atoms represented by R²³include a methylthio group, an ethylthio group, an isopropylthio group, a butylthio group, and a hexylthio group. Inter alia, a methylthio group and an ethylthio group are preferable.

The definition and preferable range of the aryl group having 6 to 10 carbon atoms represented by R²³are the same as those of the aryl group having 6 to 10 carbon atoms represented by R²¹.

Examples of the amido group having 2 to 12 carbon atoms represented by R²³include an acetylamido group, a propanoylamido group, an isobutanoylamido group, a pivaloylamido group, a phenylacetylamido group, a diphenylacetylamido group, a benzoylamido group, a cyclohexylcarbonylamido group, a trifluoromethylamido group, a hexanoylamido group, an octanoylamido group, a tetradecyloylamido group, an octadecyloylamido group, a methoxyacetyl group, a phenoxyacetyl group, a 2-(2,4-di-t-butylphenoxy)butanoyl group, a methoxycarbonylamido group, an ethoxycarbonylamido group, a n-propyloxycarbonylamido group, a dimethylaminocarbonylamido group, a n-butylaminocarbonylamido group, an acetylacetylamido group, a benzoylamido group, furoylamido group, and a theoylamido group. Inter alia, an amido group having 2 to 8 carbon atoms is preferable, and an acetylamido group, an isobutanoylamido group, a trifluoromethylamido group, a n-propyloxycarbonylamido group, a dimethylaminocarbonylamido group, a n-butylaminocarbonylamido group, and a theoylamido group are preferable.

Examples of the alkylsulfonamido group having 1 to 6 carbon atoms represented by R²³include a methylsulfonamido group, an ethylsulfonamido group, and a propylsulfonamido group. Inter alia, a methylsulfonamido group is preferable.

Examples of the arylsulfonamido group having 6 to 10 carbon atoms represented by R²³include a phenylsulfonamrido group and a toluylsulfonamido group. Inter alia, a phenylsulfonamido group is preferable.

Examples of the anilinocarbonamido group having 7 to 13 carbon atoms represented by R²³include an anilinocarbonamido group, a 4-methylanilinocarbonamido group, a 4-dimethylaminoanilinocarbonamido group, a N-methyl-anilinocarbonamido group, and a N,N-diphenylaminocarbonamido group. Inter alia, an anilinocarbonamido group is preferable.

Examples of the halogen atom represented by R²³include a fluorine atom and a chlorine atom.

In formula (A), R²⁴and R²⁵each independently represent an alkyl group having 1 to 8 carbon atoms. Examples thereof include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, a t-butyl group, a cyclohexyl group, an octyl group, and a 2-ethylhexyl group. Inter alia, a methyl group, an ethyl group, a n-propyl group, a n-butyl group, a cyclohexyl group, and a 2-ethylhexyl group are preferable.

In formula (A), A represents a group which, together with the lactone portion, forms an aromatic ring. Examples thereof include an aryl group and a heterocyclic group. The aryl group may be substituted by an alkoxy group having 1 to 12 carbon atoms or an alkyl-substituted amino group having 2 to 8 carbon atoms. Examples of the heterocyclic residue include a pyridine ring, a pyrimidine ring, and a pyrazine ring. Inter alia, a benzene ring and a pyridine ring are preferable.

Among the foregoing, a particularly preferable electron-donating colorless dye-precursor represented by formula (A) is a compound in which R²¹is an alkyl group having 1 to 10 carbon atoms, R²²is a methyl group, R²³is an amido group having 2 to 8 carbon atoms, R²⁴is an alkyl group having 1 to 5 carbon atoms, R²⁵is an alkyl group having 1 to 5 carbon atoms, and A is a benzene ring, a benzene ring substituted by an electron-donating group, or a pyridine ring.

Examples of the electron-donating colorless dye-precursor represented by formula (A) are shown below. However, the invention is not limited thereto.

R¹R²R³i-1â€”CH₃â€”CH₃â€”C₂H₅i-2â€”C₂H₅â€”CH₃â€”C₂H₅i-3â€”CH(CH₃)₂â€”CH₃â€”C₂H₅i-4â€”C(CH₃)₃â€”CH₃â€”C₂H₅ i-5 [Image Omitted]

â€”CH₃â€”C₂H₅ i-6 [Image Omitted]

â€”CH₃â€”C₂H₅ i-7â€”CH₂OCH₃â€”CH₃â€”C₂H₅i-8â€”CH₂Clâ€”CH₃â€”C₂H₅i-9â€”CCl₃â€”CH₃â€”C₂H₅i-10â€”CF₃â€”CH₃â€”C₂H₅ i-11 [Image Omitted]

â€”CH₃â€”C₂H₅ i-12 [Image Omitted]

â€”CH₃â€”C₂H₅ i-13â€”C₃H₇(n)â€”CH₃â€”C₂H₅i-14â€”CH₃â€”CH₃â€”C₄H₉(n)i-15â€”CH₃â€”CH₃â€”C₈H₁₇(n)i-16â€”CH(CH₃)₂â€”CH₃â€”C₄H₉(n) i-17 [Image Omitted]

â€”CH₃â€”C₅H₁₁(n) i-18â€”CH₂OCH₃â€”CH₃â€”C₈H₁₇(n) i-19â€”CH₃â€”CH₃ [Image Omitted]

i-20

â€”CH₃â€”C₆H₁₃(n) i-21â€”CH₃ [Image Omitted]

â€”C₂H₅ i-22â€”CH₃ [Image Omitted]

â€”C₈H₁₇(n) ia-1â€”C₅H₁₁(n)â€”CH₃â€”C₂H₅ia-2â€”C₇H₁₅(n)â€”CH₃â€”C₂H₅ia-3â€”C₁₇H₃₅(n)â€”CH₃â€”C₂H₅ ia-4 [Image Omitted]

â€”CH₃â€”C₂H₅ ia-5 [Image Omitted]

â€”CH₃â€”C₂H₅ ia-6 [Image Omitted]

â€”CH₃â€”C₂H₅ ia-7â€”CH₃â€”CH₃â€”C₅H₁₁(n)ia-8â€”CH₃â€”CH₃â€”CH(CH₃)₂ia-9â€”C₃H₇(n)â€”CH₃â€”C₈H₁₇(n)ia-10â€”C₄H₉(n)â€”CH₃â€”C₈H₁₇(n)ia-11â€”CH(CH₃)₂â€”CH₃â€”C₈H₁₇(n)ia-12â€”C₃H₇(t)â€”CH₃â€”C₈H₁₇(n)ia-13â€”C₄H₉(t)â€”CH₃â€”C₈H₁₇(n) ia-14 [Image Omitted]

â€”CH₃â€”C₈H₁₇(n) ia-15 [Image Omitted]

â€”CH₃â€”C₈H₁₇(n) ia-16 [Image Omitted]

â€”CH₃â€”C₈H₁₇(n) ia-17â€”C₃H₇(n)â€”CH₃ [Image Omitted]

ia-18â€”CH₃â€”CH₃ [Image Omitted]

<Electron-Donating Colorless Dye-Precursor Represented by Formula (B)>

R²⁴R²⁵R²³R²²R²¹A1-32â€”C₂H₅â€”C₂H₅â€”Hâ€”CH₃â€”C₄H₉(n) [Image Omitted]

1-33â€”C₂H₅â€”C₂H₅â€”CH₃â€”CH₃â€”C₂H₅ [Image Omitted]

1-34â€”C₂H₅â€”C₂H₅â€”CH₃â€”CH₃â€”C₈H₁₇(n) [Image Omitted]

1-35â€”C₂H₅â€”C₂H₅â€”OC₂H₅â€”CH₃â€”C₂H₅ [Image Omitted]

1-36â€”C₂H₅â€”C₂H₅â€”SC₂H₅â€”CH₃â€”C₂H₅ [Image Omitted]

1-37â€”C₂H₅â€”C₂H₅â€”Fâ€”CH₃â€”C₂H₅ [Image Omitted]

1-38â€”C₂H₅â€”C₂H₅â€”Clâ€”CH₃â€”C₂H₅ [Image Omitted]

1-39â€”C₂H₅â€”C₂H₅ [Image Omitted]

â€”CH₃â€”C₂H₅ [Image Omitted]

1-40â€”C₃H₇(n)â€”C₃H₇(n)â€”NHSO₂CH₃â€”CH₃â€”C₈H₁₇(n) [Image Omitted]

1-41â€”C₃H₇(n)â€”C₃H₇(n) [Image Omitted]

â€”CH₃â€”C₈H₁₇(n) [Image Omitted]

1-42â€”C₃H₇(n)â€”C₃H₇(n)â€”NHCO₂C₃H₇(n)â€”CH₃â€”C₂H₅ [Image Omitted]

1-43â€”C₃H₇(n)â€”C₃H₇(n)â€”NHCO₂CH₃â€”CH₃â€”C₈H₁₇(n) [Image Omitted]

1-44â€”C₃H₇(n)â€”C₃H₇(n)â€”NHCONHC₄H₉(n)â€”CH₃â€”C₈H₁₇(n) [Image Omitted]

1-45â€”C₃H₇(n)â€”C₃H₇(n) [Image Omitted]

â€”CH₃â€”C₈H₁₇(n) [Image Omitted]

[Image Omitted]

In formula (B), R²⁶represents an alkyl group having 1 to 8 carbon atoms whose definition and preferable range are the same as those of the alkyl group having 1 to 8 carbon atoms represented by R²⁴or R²⁵in formula (A).

R²represents an alkyl group having 3 to 12 carbon atoms, or a tetrahydrofurfuryl group. Examples of the alkyl group having 3 to 12 carbon atoms represented by R²⁷include a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a hexyl group, an octyl group, a 2-ethylhexyl group, an isononyl group, and a n-dodecyl group. Inter alia, a n-propyl group, an isopropyl group, an isobutyl group, and a n-butyl group are preferable.

R²⁸and R²⁹each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 8 carbon atoms. Preferable examples of the halogen atom represented by R²⁸or R²⁹include a fluorine atom and a chlorine atom. The alkyl group having 1 to 8 carbon atoms represented by R²⁸or R²⁹has the same definition and preferable range as those of the alkyl group having 1 to 8 carbon atoms represented by R²⁴or R²⁵in formula (A).

Among the foregoing, a particularly preferable electron-donating colorless dye-precursor represented by formula (B) is a compound in which R²⁶is an alkyl group having 1 to 6 carbon atoms, R²⁷is a tetrahydrofurfuryl group or an alkyl group having 3 to 6 carbon atoms, R²⁸is an alkyl group having 1 or 2 carbon atoms, R²⁹is a hydrogen atom or an alkyl group having 1 or 2 carbon atoms.

Examples of the electron-donating colorless dye-precursor represented by formula (B) are shown below. However, the invention is not limited thereto.

R²⁶R²⁷R²⁸R²⁹â€”C₂H₅â€”C₂H₅â€”Hâ€”Hâ€”C₂H₅â€”C₂H₅â€”CH₃â€”Hâ€”CH₃â€”C₃H₇â€”CH₃â€”H â€”CH₃ [Image Omitted]