JPH04318077A - Ink for ink jet recording, method for ink jet recording and color development of recorded image - Google Patents

Abstract

PURPOSE:To provide the subject new recording method for making a secret document, capable of protecting visual observation of recorded images and capable of color development by heat treatment. CONSTITUTION:An ink for ink jet recording, characterized by ink components composed of an electron-donating chromogenic compound and an electron- accepting compound respectively contained in an unreacted state and an ink jet recording method using the same ink. Images recorded by the ink are latent and development thereof can be carried out by heating them to react the ink components.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet recording ink containing an electron-donating color-forming compound and an electron-accepting compound as ink components, an inkjet recording method, and a method for coloring a recorded image.

0002

BACKGROUND OF THE INVENTION Conventionally, various methods have been proposed for creating confidential documents in order to prevent them from being copied or to make the recorded contents impossible to read. Examples of document creation methods for preventing copying include the following. (1) Those using colored paper (Japanese Unexamined Patent Publication No. 62-296
No. 154, USP No. 4632429) (2) Using paper with a camouflage pattern printed on it (Japanese Unexamined Patent Publication No. 6
No. 3-256980, Japanese Unexamined Patent Publication No. 63-314583) (
3) Using metallized film (Japanese Unexamined Patent Publication No. 1983-1971)
875, JP-A-64-42678) (4) Paper coated with a material that absorbs or reflects light (JP-A-63-254482, JP-A-63-311374,
JP-A No. 64-73376, JP-A No. 64-90480) (5) A copying machine that uses a sensor to detect specially treated paper and stops the copying operation (JP-A No. 60-8880)
62-188782) (6) Those using inks or toners that emit light or disappear when exposed to heat or light (JP-A No. 62-14163, JP-A-63-3)
No. 11265)

In method (1), paper is colored with dye or pigment to reduce the difference in absorption of irradiated light between non-image areas and image areas, thereby eliminating image exposure to the photoreceptor and eliminating re-copying. However, in order to do so, it is necessary to increase the coloring density of the paper, which poses a problem in that it becomes difficult to read the original, and it becomes possible to copy by changing the copying conditions. Method (2) involves printing a background pattern on paper, and when it is copied, the background pattern is clearly copied, making it difficult to read, or special characters or marks appear, indicating that it is a counterfeit, but it is also expensive. However, it has the disadvantage that copy protection is not sufficient. Method (3) uses metal vapor deposition to form a mirror surface.
The light from the copying machine's light source is prevented from being reflected onto the photoreceptor by specular reflection of the incident light from the copying machine's light source.
If you copy again, the entire surface of the copy becomes black and becomes unreadable, but the cost is high, and if you insert a sheet that causes diffused reflection between the contact glass and the original, such as translucent paper or film, the copy will not work properly. It has the disadvantage of being copied. In order to eliminate this drawback, some products are available that are combined with coloring, but the manuscript becomes even more difficult to read. In method (4), the paper is treated with a fluorescent material or other light-emitting or absorbing material.The former emits light when exposed to light, eliminating the contrast between image and non-image areas and making the paper unreadable. However, there are no materials that emit light so strongly that they cannot be copied, and their effectiveness in preventing copying is small. The latter also eliminates contrast by absorbing irradiated light, but it is different from dyes and pigments and has no color, so no material that exhibits this effect has been found. In method (5), the paper is treated with a magnetic material, metal material, infrared absorbing material, etc., and when making copies again, a specially installed sensor in the copying machine detects this and stops the copying operation. However, there are drawbacks such as modification of the copying machine, limited range of use for specific copying machines, and high cost. The method (6) prevents re-copying by using an original with ink or toner that emits or erases color when exposed to heat or light from a copying machine, and requires special ink or toner.

As described above, conventional anti-copying techniques are still not perfect. According to JP-A-1-259374, an uncolored toner image is created by copying a transparent toner containing an ultraviolet absorber onto a transparent sheet using an electrophotographic copying machine, and if necessary, this transparent sheet A method has been proposed in which a document is used as a manuscript, copied onto diazo photosensitive paper, and visualized. However, this method cannot be said to be an advantageous method because it requires copying onto diazo photosensitive paper using a diazo copying machine, which is not very popular at present. On the other hand, the inkjet recording method forms an image by ejecting liquid ink as droplets from a micro-diameter nozzle onto a recording medium.(a) High-speed recording is possible;(b) Since images can be formed without contact, it is possible to use a variety of recording materials including plain paper, (c) color recording is easy, (d) high image quality can be obtained, (e) recording It is used in computers, word processors, facsimile machines, etc. because it has many advantages such as no noise, and (f) the ability to make devices smaller and lighter. However, no inkjet recording method is known that uses ink containing an unreacted electron-donating color-forming compound and an electron-accepting compound for creating confidential documents.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a new method for creating secret documents.

[0006]

[Means for Solving the Problems] As a result of extensive research to solve the above problems, the present inventors have developed an electron-donating color-forming compound and an electron-accepting compound that are commonly used as components of heat-sensitive recording materials. The present inventors have discovered that the above-mentioned problems can be solved by performing inkjet recording using an ink containing in an unreacted state, and have completed the present invention.

That is, according to the present invention, there is provided an inkjet recording ink characterized by containing an ink component consisting of an electron-donating color-forming compound and an electron-accepting compound in an unreacted state. Further, there is provided an inkjet recording method, characterized in that inkjet recording is performed on a sheet-like material using the ink under conditions where the electron-donating color-forming compound and the electron-accepting compound do not react. . Furthermore, using the ink containing one of the ink components consisting of an electron-donating color-forming compound and an electron-accepting compound, and using a sheet-like article whose surface is coated with the other of the ink components, An inkjet recording method is provided, which comprises performing inkjet recording with the ink on the sheet material under conditions where the electron-donating color-forming compound and the electron-accepting compound do not react. Furthermore, a method for coloring a recorded image, which comprises heating the recorded matter obtained by the inkjet recording method to cause the electron-donating color-forming compound and the electron-accepting compound to react to form a coloring body. is provided.

Electron-donating color-forming compound (
The color forming agent (hereinafter also referred to as a color former) is itself a colorless or light-colored dye precursor, and is not particularly limited, and may include conventionally known ones such as triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, and leuco Examples include auramine compounds, rhodamine lactam compounds, spiropyran compounds, and indolinophthalide compounds. In the present invention, a halogen-containing electron-donating color-forming compound and/or a compound represented by the following general formula [Formula 1] is particularly preferably used.

[0009]

[Formula 1] (However, R1 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R2 is a hydrogen atom or an optionally substituted amino group, and X is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or phenyl Amino group, m is an integer of 1 or 2, Y is 1 carbon number
-4 alkyl group or alkoxy group having 1 to 2 carbon atoms, n
represents an integer of 1 or 2)

[0010] Examples of coloring agents containing halogen as a substituent used in the present invention include the following. 3,3-bis(p-dimethylaminophenyl)
-6-chlorphthalide, 3-cyclohexylamino-6
-Chlorfluorane, 3-cyclohexylamino-6-
Bromofluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-bromofluorane, 3-dipropylamino-7-chlorofluorane,

0
3-Diethylamino-6-chloro-7-phenylamino-fluorane, 3-pyrrolidino-6-chloro-
7-phenylamino-fluorane, 3-diethylamino-6-chloro-7-(m-trifluoromethylphenyl)
Amino-fluorane, 3-cyclohexylamino-6-
Chlor-7-(o-chlorophenyl)amino-fluorane, 3-diethylamino-6-chloro-7-(2',3
'dichlorophenyl)amino-fluorane,

0012
]3-diethylamino-6-methyl-7-chlorofluoran, 3-dibutylamino-6-chloro-7-ethoxyethylamino-fluoran, 3-diethylamino-7-
(o-chlorophenyl)amino-fluorane, 3-diethylamino-7-(o-bromophenyl)amino-fluorane, 3-diethylamino-7-(o-chlorphenyl)amino-fluorane, 3-dibutylamino-7-(
o-fluorophenyl)amino-fluorane, 6'-bromo-3'-methoxybenzoindolino-pyrylospirane, 3-(2'-methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chlor-5'
-chlorphenyl) phthalide, 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorphenyl) phthalide, 2-{3,6
-bis(diethylamino)}-9-(o-chlorophenyl)amino-xantylbenzoic acid lactam, etc.

[0013] As the coloring agent represented by the above general formula [Formula 1] used in the present invention, the following are exemplified.

3-(N-methyl-N-phenylamino)
-7-amino-fluorane, 3-(N-ethyl-N-phenylamino)-7-amino-fluorane, 3-(N-
Propyl-N-phenylamino)-7-amino-fluorane, 3-{N-methyl-N-(p-methylphenyl)
amino}-7-amino-fluorane, 3-{N-ethyl-N-(p-methylphenyl)amino}-7-amino-
Fluoran, 3-{N-propyl-N-(p-methylphenyl)amino}-7-amino-fluoran, 3-{N
-Methyl-N-(p-ethylphenyl)amino}-7-
Amino-fluoran, 3-{N-ethyl-N-(p-ethylphenyl)amino}-7-amino-fluoran, 3
-{N-propyl-N-(p-ethylphenyl)amino}-7-amino-fluorane,

3-{N-methyl-N-(2',4'-dimethylphenyl)amino}-7-amino-fluorane,
3-{N-ethyl-N-(2',4'-dimethylphenyl)amino}-7-amino-fluorane, 3-{N-propyl-N-(2',4'-dimethylphenyl)amino}- 7-amino-fluorane, 3-{N-methyl-N-
(p-chlorophenyl)amino}-7-amino-fluorane, 3-{N-ethyl-N-(p-chlorophenyl)
amino}-7-amino-fluorane, 3-{N-propyl-N-(p-chlorophenyl)amino}-7-amino-fluorane,

3-(N-methyl-N-phenylamino)
-7-methylamino-fluorane, 3-(N-ethyl-
N-phenylamino)-7-methylamino-fluorane, 3-(N-propyl-N-phenylamino)-7-methylamino-fluorane, 3-{N-methyl-N-(p
-methylphenyl)amino}-7-ethylamino-fluoran, 3-{N-ethyl-N-(p-methylphenyl)amino}-7-benzylamino-fluoran, 3-{
N-Methyl-N-(2',4'-dimethylphenyl)amino}-7-methylamino-fluorane, 3-{N-ethyl-N-(2',4'-dimethylphenyl)amino}
-7-ethylamino-fluoran, 3-{N-methyl-
N-(2',4'-dimethylphenyl)amino}-7-
benzylamino-fluorane,

3-{N-ethyl-N-(2',4'-dimethylphenyl)amino}-7-benzylamino-fluorane, 3-(N-methyl-N-phenylamino)-7
-dimethylamino-fluorane, 3-(N-ethyl-N
-phenylamino)-7-dimethylamino-fluorane, 3-{N-methyl-N-(p-methylphenyl)amino}-7-diethylamino-fluorane, 3-{N-ethyl-N-(p-methylphenyl) ) amino}-7-diethylamino-fluorane, 3-(N-methyl-N-phenylamino)-7-dipropylaminofluorane, 3-
(N-ethyl-N-phenylamino)-7-dipropylaminofluorane, 3-{N-methyl-N-(p-methylphenyl)amino}-7-dibenzylamino-fluorane,

3-{N-ethyl-N-(p-methylphenyl)amino}-7-dibenzylamino-fluorane, 3-{N-ethyl-N-(p-methylphenyl)
amino}-7-di(p-methylbenzyl)amino-fluorane, 3-{N-methyl-N-(p-methylphenyl)amino}-7-acetylamino-fluorane, 3-{
N-ethyl-N-(p-methylphenyl)amino}-7
-benzoylamino-fluorane, 3-{N-methyl-
N-(p-methylphenyl)amino}-7-(o-methoxybenzoyl)amino-fluorane, 3-{N-ethyl-N-(p-methylphenyl)amino}-6-methyl-7-phenylamino- Fluoran, 3-{N-methyl-N-(p-methylphenyl)amino}-6-methyl-
7-phenylamino-fluorane,

3-{N-methyl-N-(p-methylphenyl)amino}-6-tert-butyl-7-(p-methylphenyl)amino-fluorane, 3-(N-ethyl-N-phenylamino) )-6-methyl-7-(N-ethyl-N-(p-methylphenyl)amino-fluorane,
3-{N-propyl-N-(p-methylphenyl)amino}-6-methyl-7-{N-methyl-N-(p-methylphenyl)amino}-fluorane, 3-{N-ethyl-N -(p-methylphenyl)amino}-5-methyl-
7-benzylamino-fluorane, 3-{N-ethyl-
N-(p-methylphenyl)amino}-5-chloro-7
-dibenzylamino-fluorane, 3-{N-methyl-
N-(p-methylphenyl)amino}-5-methoxy-
7-dibenzylamino-fluorane, 3-{N-ethyl-N-(p-methylphenyl)amino}-6-methyl-
fluoran, 3-{N-ethyl-N-(p-methylphenyl)amino}-5-methoxy-fluoran, and the like.

Electron-accepting compound in the present invention (hereinafter referred to as
(also referred to as color developer), conventionally known ones, for example,
Organic acids, phenolic compounds, etc. can be used. In the present invention, it is particularly preferable to use the organic phosphoric acid compounds and/or organic acids shown below. (1) Organic phosphoric acid compound represented by the following general formula (1)
R1-PO(OH)2
(
1) However, R1 is a linear or branched higher alkyl group or higher alkenyl group, and usually has 8 to 30 carbon atoms.
It is. Specific examples of this organic phosphoric acid compound include the following. Octylphosphonic acid, nonylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid,
Octadecylphosphonic acid, eicosylphosphonic acid, docosylphosphonic acid, tetracosylphosphonic acid.

(2) Organic acid having a hydroxyl group at the α-position carbon represented by the following general formula (2) R2-CH(OH)COOH
(2) However, R2 is a linear or branched higher alkyl group or higher alkenyl group, and usually has 6 to 28 carbon atoms. Specific examples of the organic acid having a hydroxyl group at the α-position carbon include the following. α-hydroxyoctanoic acid, α-hydroxydodecanoic acid,
α-hydroxytetradecanoic acid, α-hydroxyhexadecanoic acid, α-hydroxyoctadecanoic acid, α-hydroxypentadecanoic acid, α-hydroxyeicosanoic acid, α-hydroxydocosanoic acid acids etc.

[0022] As the combination of color former and color developer in the present invention, it is advantageous to use a combination that can cause a reversible reaction, that is, a combination that can once again decolorize the color former formed by the reaction between the two. It is. When such a combination of a color former and a color developer is used, a colored image can be decolored again, which is very advantageous in terms of preserving confidential documents. Combinations of a color former and a color developer that perform a reversible reaction include conventionally known combinations, such as a salt of bis(hydroxyphenyl)acetic acid or butyric acid with a higher aliphatic amine as a color developer. (Japanese Unexamined Patent Publication No. 2-188293), or a combination of a salt of gallic acid and a higher aliphatic amine as a coloring agent (Unexamined Japanese Patent Publication No. 2-18).
No. 8294) etc. can be used, but the organic phosphoric acid compound represented by the above general formula (1) developed by the present inventors and/or the hydroxyl group at the α-position carbon represented by the general formula (2) can be used. It is preferable to use an organic acid containing a color developer in combination with a color forming agent. The colored body formed using the combination of color former and color developer can be decolored again by heating it to a temperature lower than the heating temperature used for the coloring reaction, and The colored body can be turned into a colored body again by heating it.

[0023] The inkjet recording ink of the present invention includes:
It contains ink components consisting of a color former and a color developer in an unreacted state, and is in an uncolored state. The color forming agent and color developer can be used as they are or in a microencapsulated state. As a medium for dispersing or dissolving the ink components, an aqueous medium or an organic solvent is used. As the aqueous medium, water or a mixed solvent of water and a water-soluble organic solvent is used. Examples of water-soluble organic solvents include:
Ethyl alcohol, isopropyl alcohol, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol,
Examples include polyethylene glycol, glycerin, N-methyl-pyrrolidone, ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, and the like. Further, for microcapsulation, known techniques such as coacervation method, interfacial polymerization method, in situ polymerization method, etc. can be adopted, and it is preferable to obtain microcapsules with a particle size of about 0.5 to 10 μm. . The ink of the present invention further includes a surface tension adjuster, if necessary.
Customary auxiliary ingredients such as viscosity modifiers, preservatives, etc. are added.

[0024] In the ink of the present invention, the ratio of the color former and the color developer used is 1 to 10 parts by weight of the color former to 1 part by weight of the color former.
The ratio of parts by weight is appropriate. In inks containing microencapsulated color formers and color developers, the content of these microencapsulated substances is 5 to 40% by weight, preferably 10 to 30% by weight. It is usually preferable that the ink contains a water-soluble organic solvent in an amount of 10 to 50% by weight. When obtaining an ink containing a non-microencapsulated color former and color developer, the color former and color developer are dispersed in the form of fine particles in an aqueous medium or dissolved in an organic solvent.

The inkjet recording method of the present invention uses an ink containing the above-described ink components consisting of a color forming agent and a color developer in an unreacted state, and is applied to paper or plastic film as a recording medium. This is a method in which liquid droplets are sprayed onto the surface of a sheet-like object such as through a micro-diameter nozzle. By performing inkjet recording in this manner, an image is obtained in which an ink component consisting of an undeveloped color forming agent and a color developer is attached to the surface of a sheet-like object, but this ink component is unreacted. Therefore, the image is a latent image and cannot be read visually. Also, this latent image cannot be copied,
Copying does not produce a copy with a visible image. On the other hand, the recording medium having this latent image can be turned into a visually visible colored image by heating it and causing the color forming agent and color developer forming the latent image to react. . When performing inkjet recording using the ink of the present invention, it is necessary to perform the recording under conditions that do not cause a reaction between the color former and the color developer, which are ink components, and the recording temperature or ink temperature is It is carried out at a temperature lower than the color development reaction temperature with the agent. In the present invention, as the ink,
Similarly, by performing inkjet recording using an ink component that contains one of the ink components consisting of a color forming agent and a color developer, and using a sheet-like material coated with the other in advance as the recording medium, the sheet can be A latent image can be formed on the surface of a shaped object. By heating this latent image, it can be similarly converted into a visually visible colored image.

[0026]

According to the present invention, confidential documents can be easily created using a normal inkjet recording device. In other words, the image obtained using the ink of the present invention is a latent image that cannot be visually read or visualized by copying, and there is no fear that the confidential information will be read by a third party, and that confidential information will not be leaked by copying. There is no need to worry. The latent image recorded in this manner can be converted into a clear visible image by applying thermal energy necessary for causing a color reaction between the color former and the color developer to occur. In the present invention, when a combination of a color forming agent and a color developer having reversible reactivity is used, the visible image can be decolorized again, so the document can be stored as a latent image again. There is an advantage that it can be done.

[0027]

EXAMPLES Next, the present invention will be explained in more detail with reference to examples. Note that all parts and percentages shown below are based on weight.

Example 1 3-dibutylamino-7-(o-chlorophenyl)
Amino-fluorane 7 parts Hexadecylphosphonic acid
The material consisting of 21 parts is uniformly melted at about 100°C. The above melt was added dropwise into 80 parts of a 3% aqueous solution of styrene-maleic anhydride copolymer whose pH was adjusted to 4.5 and heated to 80°C.
Using a mixer, the mixture is emulsified and dispersed into fine droplets with an average particle size of 3 μm. Next, 7.0 parts of melamine-formalin prepolymer (manufactured by Sanwa Chemical Co., Ltd., Nikalac MX-54) was added to the obtained emulsion while stirring, and the mixture was stirred at 80°C.
The reaction was carried out for a period of time to obtain a microcapsule dispersion having an average particle diameter of 3.2 μm. Next, microcapsule particles were separated from this dispersion by centrifugation, and an inkjet recording ink for producing confidential documents was prepared using the microcapsule particles with the following ink composition. microcapsule particles

Part 15 Glycerin

20 parts polyethylene glycol type nonionic dispersant
Part 2 Water


Remaining amount
total
1
This ink was then used to print on recording paper using an on-demand inkjet printer. The recorded image obtained is colorless and cannot be read with the naked eye, and this image is used as a manuscript in an electronic copying machine (Recopy FT69).
50), but the recorded image could not be copied. On the other hand, this recording paper was used for 100
When passed through a heating roll machine set at ℃, the color density is 1.25.
A clear black print appeared. When this visualized recorded image was passed through a heated roll machine whose temperature was changed to 75°C, it was erased again and returned to its original colorless state. This repeated test was performed 10 times, but no decline in function was observed.

Example 2 3-{N-ethyl-N-(p-methylphenyl)amino} 7 parts -6-methyl-7-phenylamino-fluorane α-hydroxyoctadecanoic acid
The material consisting of 21 parts is uniformly melted at about 100°C. 100 parts of a 5% aqueous gelatin solution adjusted to pH 7.0 was heated to 80°C, 30 parts of the dissolved material was added dropwise, and the average particle size was 3μ using a mixer.
Emulsify and disperse to form microdroplets of m. Next, 120 parts of a 5% gum arabic aqueous solution heated to 80°C was added to this emulsified dispersion, diluted with 210 parts of 80°C warm water, and 10% acetic acid was gradually added with stirring to adjust the pH to 4.3.
to cause coacervation, then 10
After cooling to a temperature of 0.degree. C. to form a gel, 2 parts of 25% glutaraldehyde was added to adjust the pH to 9, and stirring was continued for 1 hour to obtain a microcapsule dispersion having an average particle size of 3.3 .mu.m. Microcapsule particles were separated from this dispersion, and an ink was prepared using the same in the same manner as in Example 1, and printing was performed by inkjet recording. The recorded images obtained were impossible to read and could not be copied. 10 of this
When placed in a constant temperature bath at 0° C. for 2 seconds, a clear black print with a color density of 1.23 appeared. This visualized recorded image was erased again when it was placed in a constant temperature bath with a temperature setting of 75° C. for 10 seconds. This repeat function showed the same characteristics as in Example 1.

Example 3 3-diethylamino-7-(o-chlorophenyl)
Amino 1 part Fluorane α-hydroxydocosanoic acid

Part 3 Polyvinylpyrrolidone

1 part ethyl alcohol

40 copies
xylene

Total amount remaining

1
00 parts or more of the mixed melt was filtered through a 1 micron filter to prepare an ink. Printing was carried out on synthetic paper in the same manner as in Example 1 except that this ink was used, and when a recorded image reproduction test was conducted, a clear black print with a color density of 1.85 appeared. This image also showed good erasability and good repeatability.

Example 4 3-{N-ethyl-N-(p-methylphenyl)amino} 3 parts -7-phenylamino-fluoran glycerin

20 copies
Isopropyl alcohol

Part 3 Polyethylene glycol type nonionic dispersant
Part 2 Water

Remaining amount
total

More than 100 parts of the ingredients were placed in a stirring mill together with glass beads, subjected to atomization and dispersion treatment, and filtered through a 5 micron filter to prepare an ink. On the other hand, a coating solution obtained by dispersing fine particles of 5 parts of octadecylphosphonic acid and 15 parts of a 10% polyvinyl alcohol aqueous solution on 48 g/m2 high-quality paper had a dry adhesion weight of 5 g/m2.
2, and after drying, calendering was performed to prepare recording paper. Printing was performed on this paper in the same manner as in Example 1, but the recorded image was unreadable.
I couldn't even make copies. In addition, when this paper was placed in a constant temperature bath at 100°C for 2 seconds to develop color as in Example 2,
A clear black print with a density of 1.28 was obtained. This visualized recorded image was erased again when it was placed in a constant temperature bath set at 75° C. for 10 seconds. This reversible test of color development and erasure was repeated 10 times, but no decline in function was observed.

Claims (7)

[Claims] 1. An inkjet recording ink comprising an ink component consisting of an electron-donating color-forming compound and an electron-accepting compound in an unreacted state. 2. The ink according to claim 1, wherein the electron-donating color-forming compound and the electron-accepting compound cause a reversible reaction. 3. As an electron-accepting compound, the general formula R1
-PO(OH)2 (wherein R1 represents a higher alkyl group or higher alkenyl group) and/or the general formula R2-CH(OH)COOH (wherein R2 represents a higher alkyl group or higher alkenyl group) The ink according to claim 1 or 2, wherein an organic acid having a hydroxyl group at the α-position carbon represented by the following formula is used. 4. Claims 1 to 3 in which a halogen-containing electron-donating color-forming compound and/or a compound represented by the following general formula [Formula 1] is used as the electron-donating color-forming compound.
Any ink. [Formula 1] (However, R1 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R2 is a hydrogen atom or an optionally substituted amino group,
X is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenylamino group, m is an integer of 1 or 2, Y is an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 2 carbon atoms, n is 1 or (represents an integer of 2) 5. Performing inkjet recording using the ink according to any one of claims 1 to 4 on a sheet material under conditions where the electron-donating color-forming compound and the electron-accepting compound do not react. An inkjet recording method characterized by: 6. Using the ink according to any one of claims 1 to 4, which contains one of the ink components consisting of an electron-donating color-forming compound and an electron-accepting compound, and the other of the ink components. A sheet-like material coated on the surface thereof is used, and inkjet recording is performed with the ink on the sheet-like material under conditions that the electron-donating color-forming compound and the electron-accepting compound do not react. Inkjet recording method. 7. A recorded image characterized in that the recorded matter obtained according to claim 5 or 6 is heated to cause the electron-donating color-forming compound and the electron-accepting compound to react to form a coloring body. Color development method.