JP2002060743A - Fluorescent complex and ink composition having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-viscosity fluorescent complex high in preservation stability and weatherability so as to be usable in ink compositions, especially water-based ink compositions. SOLUTION: This fluorescent complex consists of a rare earth element and a macromolecular compound with a weight-average molecular weight of >=300 but <5,000 having a pyrrolidone moiety of general formula (1) (n is an integer).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a fluorescent complex comprising a rare earth element and a polymer compound. For more information,
Uses are paints, plastics, inks, etc., and especially to water-based ink compositions.

[0002]

2. Description of the Related Art In recent years, various kinds of cards, such as security cards utilizing the properties of fluorescent materials, factory automation, and various kinds of cards used for managing substances, have been actively developed. There is also an example in which a barcode is printed with ink using a fluorescent material, and a system for distributing articles by code management is used for mail or the like.

[0003] As a luminescent material to be used for these, a fluorescent complex in which a low molecular ligand is coordinated to a rare earth element as a luminescent center has been conventionally used to form an ink. For example,
This is shown in JP-B-54-22336, JP-A-9-188835, JP-T-11-510213 and the like. These fluorescent complexes are uniformly dissolved as a dye in a liquid such as water or a solvent, or uniformly dispersed as a pigment to form an ink. In particular, an ink using polyvinylpyrrolidone as a binder resin has high emission intensity and good characteristics. Further, it has a feature that a higher emission intensity can be obtained as compared with an inorganic phosphor.

Further, among the fluorescent complexes, a fluorescent complex using a polymer compound as a ligand has been proposed. For example, Journal of Polymer Science, Vol. 20, 1271-1278
(1982). If these are applied to the ink composition, an ink composition that does not require a binder resin or a dispersant is considered to be possible.

[0005]

However, the above-mentioned fluorescent complexes and fluorescent complexes are usually insoluble in highly polar solvents such as water because they use highly hydrophobic organic substances as ligands. Only soluble in Further, since the affinity for other substances such as water and an organic solvent is weaker than the cohesive force between particles, it is extremely difficult to uniformly mix and disperse them under ordinary mixing and dispersing conditions. In addition, an ink using polyvinylpyrrolidone as a binder resin has sufficient solubility in water and the like. However, the storage stability of the ink and the weather resistance of the printed matter are insufficient.

When the above-mentioned fluorescent complex and the fluorescent complex are to be used for an ink composition of, for example, an ink jet printer, a method of dissolving a specific organic solvent as a main solvent is usually employed. However, there is a problem that the vapor of the organic solvent is harmful to the human body and is severely restricted in the use environment. It is also conceivable to disperse the fluorescent complex and the fluorescent complex as a pigment in an aqueous solvent,
In such a case, the dispersion stability of the fluorescent complex is poor as described above, which causes poor protrusion and clogged nozzles, and is not suitable as an inkjet ink composition.

[0007] In view of the above circumstances, the present invention provides a low-viscosity ink composition, particularly an aqueous ink composition,
It is an object of the present invention to provide a fluorescent complex having excellent storage stability and weather resistance.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that a fluorescent complex comprising a high molecular compound having a weight average molecular weight of 300 or more and less than 5,000 having a rare earth element and a pyrrolidone moiety. And completed the invention.

[0009] The polymer compound in the fluorescent complex of the present invention has a pyrrolidone moiety. The pyrrolidone moiety can form a stable complex because the nitrogen or oxygen element in the skeleton is coordinated with the rare earth element, so that high emission intensity can be obtained. Furthermore, the pyrrolidone moiety has a high affinity for water because of its hydrophilicity, whereby the fluorescent complex composed of the high molecular weight copolymer is dissolved in the aqueous solvent or is stable in the aqueous solvent due to the steric repulsion by the pyrrolidone moiety. Can be dispersed. The pyrrolidone moiety is preferably represented by the chemical formula shown in (Chemical Formula 1).

[0010] The molecular weight of the polymer compound is essential to be 300 or more and less than 5000, and more preferably 1000 or more and less than 4000. Since the rare earth element serving as the luminescent center is protected by the polymer compound, the weather resistance is better than that of a normal fluorescent complex using only a low molecular weight ligand. This is because the high molecular copolymer in the structure blocks oxygen and prevents autoxidation, which is a cause of photodeterioration. If it is less than 300, oxygen cannot be blocked in this way, and weather resistance is insufficient, which is not preferable. In addition, if it is 5000 or more, the viscosity of the ink becomes too high, so when printing with an inkjet printer or the like,
It is not preferable because head clogging easily occurs.

Since the fluorescent complex of the present invention contains a high molecular compound in its structure, when used in an ink composition, it does not need to add a resin such as a binder again in order to improve fixability and weather resistance. May be. Also, when the pigment is dispersed in an aqueous solvent, the resin and the surfactant need not be added again as a dispersant because the pigment is stably dispersed by the steric repulsion by the pyrrolidone portion in the structure.

It is considered that the polymer copolymer of the present invention is coordinated with the rare earth element which is the luminescent center via the nitrogen or oxygen element of the pyrrolidone moiety. The polymer copolymer may be one having a polydentate coordination such as a chelating agent or one having a coordination as a neutral ligand. Further, a high molecular compound having another ligand may form a mixed complex, or the weather resistance does not deteriorate even if a mixed complex is formed with a low molecular weight ligand which is usually used.

The polymerization methods include bulk polymerization, solution polymerization,
General methods such as suspension polymerization, emulsion polymerization, and redox polymerization can be mentioned. Among them, solution polymerization is preferable because the reaction method is simple. The reaction conditions vary depending on the polymerization initiator and the solvent, but the reaction temperature is 180 ° C. or lower, preferably 30 to 150 ° C., and the reaction time is 30 minutes to 40 hours, preferably 2 hours to 30 hours.

Examples of the catalyst include peroxides such as t-butylperoxybenzoate, di-t-butyl peroxide, cumene hydroxide, acetyl peroxide, benzoyl peroxide and lauroyl peroxide; azobisisobutylnitrile , Azobis-2,4-
Known polymerization initiators such as azo compounds such as dimethylvaleronitrile and azobiscyclohexanecarbonitrile can be used.

As the non-reactive solvent, water or a water-soluble organic solvent is preferable. Examples of the water-soluble organic solvent include alcohols such as methyl alcohol, ethyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-propyl alcohol, and isopropyl alcohol; dimethylformaldehyde;
Amides such as dimethylacetamide; ketones such as acetone and methyl ethyl ketone; tetrahydrofuran, dioxane, ethylene glycol methyl ether, ethylene glycol ethyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, triethylene glycol monomethyl ether, triethylene ethylene glycol monoethyl ether Ethers such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6
Polyhydric alcohols such as hexanetriol, thiodiglycol, diethylene glycol, polyethylene glycol, polypropylene glycol, and glycerin; N-methyl-pyrrolidone and 1,3-dimethyl-2-imidazolidinone; Further, these solvents may be used in combination.

The fluorescent complex of the present invention may use a general low molecular weight ligand in addition to the above-mentioned high molecular compound as a ligand. The combined use of low molecular weight ligands is preferred because higher fluorescence emission intensity can be obtained. As low-molecular ligands, nitrogen-containing, oxygen, sulfur and phosphorus compounds are generally used.
For example, thenoyltrifluoroacetone, naphthoyltrifluoroacetone, benzoyltrifluoroacetone, methylbenzoyltrifluoroacetone, furoyltrifluoroacetone, pivaloyltrifluoroacetone, hexafluoroacetylacetone, trifluoroacetylacetone, fluoroacetylacetone, heptafluorobutanoyl Pivaloylmethane, 8-hydroquinoline, 8-mercaptoquinoline, tri-n-butyl phosphate, tri-n-butylphosphine oxide, tri-n-octylphosphine oxide, di-n-butylsulfoxide, pyridine, α -Picolin, β-picoline, γ-picoline, piperidine, quinoline and the like. Among these, tenoyl trifluoroacetone and naphthoyl trifluoroacetone are particularly preferred. The amount of the low molecular ligand is 3 with respect to the rare earth element.
The molar ratio is preferably from 8 to 8 times, more preferably from 4 to 6 times.
If it is less than 3, sufficient fluorescence emission intensity cannot be obtained.
If it is more than 8, concentration quenching will occur. The low molecular ligand may or may not be coordinated with the rare earth element, but it is preferable that a low molecular ligand not coordinated exists. The storage stability is further improved by the presence of a non-coordinated low molecular weight ligand.

The rare earth element which is the emission center of the fluorescent complex of the present invention is europium, dysprosium, terbium,
Neodymium, Pseodymium, Samarium, Sadmium,
It is preferably made of at least one of holmium, erbium and thulium. These elements can stably form the fluorescent complex of the present invention and can obtain a sufficient emission intensity. In addition, when considering the application of the fluorescent complex of the present invention to security, FA, various cards, barcode systems, etc., europium is the most preferable among the above rare earths. When europium is used as the emission center, the emission is red at 615 ± 20 nm. Therefore, the printed mark emits the visible light on the longer wavelength side when excited by ultraviolet light, so that it is less affected by the color of the base, and can be detected with high sensitivity by a silicon photodiode or the like. . Blue or green emission may be poor in detectability. When a mark that emits blue light is formed on white paper impregnated with a fluorescent whitening agent, the base also emits light, so that the difference in the amount of emitted light is substantially small, and detection may not be possible. In addition, when detecting visible light to be emitted, if a silicon photo diode, which is generally inexpensive and easily available, is used as a photoelectric conversion element, the light receiving sensitivity of visible light is lower on the short wavelength side than on the long wavelength side, Visible light of a relatively short wavelength of blue or green is less than half the sensitivity of visible light on the long wavelength side near 600 nm, and it may be difficult to obtain sufficient detection sensitivity.

The fluorescent complex of the present invention can be prepared by an appropriate method known to those skilled in the art. Only the ligand is replaced by a high molecular compound from a normal low molecular compound. Therefore, J. Am. Chem. Soc. Volume 186, Section 5117, 1
It can be synthesized by the method described in 964 or JP-B-6-15269. For example, the above-described polymer compound is synthesized, and the polymer compound and a ligand such as acetylacetone are reacted with a rare-earth metal halide such as europium chloride under appropriate conditions to generate the fluorescent complex of the present invention.

Further, the use of the fluorescent complex of the present invention includes:
Ink, paint, plastic, toner writing implement, organic EL
And the like. When a rare-earth element such as europium that emits light in the visible region is used as a light-emitting center, it can be dispersed in resin, and vivid colors of light emission can be used for toys, stage equipment, interior decoration, show windows, and the like. On the other hand, from the viewpoint of security and the like, it is preferable to apply the ink composition as an ink composition, and among them, an inkjet ink composition capable of inkjet printing is most preferred.

Various solvents such as ethanol, methanol, isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, and ethyl acetate can be used as the solvent for the ink composition containing the fluorescent complex of the present invention.

The viscosity of the ink composition containing the fluorescent complex of the present invention is preferably from 1.5 cp to 8 cp, more preferably from 2 cp to 5 cp. If the viscosity is less than 1.5 cp, the printing stability becomes poor. If the viscosity is more than 8 cp, head clogging occurs and printing becomes impossible.

The ink composition preferably contains 15 to 99 parts by weight of water with respect to the ink composition. This is because the fluorescent complex of the present invention exhibits hydrophilicity because a water-soluble polymer is used for the ligand, and can be more dissolved or stably dispersed in an aqueous solvent. Further, it is possible to provide a water-based ink composition that is harmless to the human body, and it is possible to avoid the use environment from being restricted by using an organic solvent, such as making it difficult to use it in an office. The water content of the ink composition is more preferably 30 to 90 parts by weight.

For the production of the ink composition, a container driving medium mill such as a ball mill, a centrifugal mill, and a planetary ball mill, a high-speed rotation mill such as a sand mill, a medium stirring mill such as a stirring tank mill, and a simple method such as a disperser are used. It can also be manufactured using a disperser.

The above-mentioned ink composition is usually composed of a binder, a charge-imparting agent, a pH adjuster, a fluorescent sensitizer, a rust inhibitor, a surfactant, a leveling agent, a dot adjuster, and an ink defoamer which are usually contained in the ink composition. , A bactericide, an antioxidant and the like. Examples of the binder include vinyl resins such as polyvinyl alcohol, polyvinyl butyral, and polyvinyl acetate, urethane resins, phenol resins, polyester resins, acrylic resins, cellulose resins, and polyamides. , A maleic resin, and a copolymer thereof. Examples of the charge control agent include Li salts such as LiNO ₃ , K salts such as KCN and KSCN, and cationic compounds such as tetraphenylphosphonium bromide. Examples of the pH adjuster include amine compounds such as diethanolamine, triethanolamine, and triethylenetetramine, and amide compounds, hydroxides and carbonates such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. . Examples of the fluorescent sensitizer include phosphorus-based organic compounds such as phosphine oxide compounds, phosphine sulfide compounds and phosphine compounds, and nitrogen-based organic compounds such as benzotriazole.

In the above ink composition, the content of the fluorescent complex of the present invention is preferably from 0.1 to 10% by weight, and more preferably from 0.5 to 5% by weight. When the content is 0.1% by weight or more, the light emission intensity can be maintained without reduction. When the content is 10% by weight or less, concentration quenching can be prevented and the light emission intensity can be prevented from being reduced again.

When the fluorescent complex of the present invention is used, since the high molecular compound of the ligand also has the function of the binder as described above, the ligand may not be contained at all. The content of other additives is 10% by weight or less, preferably 5% by weight or less, and the remainder is a solvent.

The printed matter of the above ink composition is completely or substantially invisible to the naked eye and cannot be confirmed.
Printed material using rare earth europium etc. as the luminescent center,
When irradiated with ultraviolet light, it is possible to confirm printing only after emitting red light in the visible light region. When neodymium is used as the rare earth element at the emission center, it is excited by infrared light and emits light in the infrared light region, and can be detected only by a dedicated detector. These printed matter of the present invention, which emit visible light and infrared light, are usually invisible.
A, can be applied to various things such as various cards.

When a bar code is printed using the above ink composition, it can be used as an improvement in a black and white bar code.
Conventional black-and-white barcodes have drawbacks such as impairing the appearance of articles, but they can be avoided. Barcode printing using the above ink composition can also be used for postal items to which a system for distributing articles by code management is applied.

The method of producing the printed matter may be any ordinary printing method. For example, inkjet printing, offset printing, gravure printing, thermal transfer printing, and the like. In particular, the ink composition of the present invention is suitable for inkjet printing. Since the ink composition of the present invention is dissolved or stably dispersed in an aqueous solvent, it can be stably ejected without causing nozzle clogging of an ink jet printer.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION

EXAMPLES Examples of the present invention will be described below in more detail. In the following, “parts” means “parts by weight”.

(Synthesis Example 1) N-vinyl-2-pyrrolidone 100.0 parts 2,2′-azobis (isobutylnitrile) 1.8 parts 2-propanol 100.0 parts These components are mixed to prepare a solution. did.

Next, a reaction vessel equipped with a nitrogen inlet
100 parts of 2-propanol was measured, and the temperature was raised to 70 ° C. while sealing with nitrogen. The above solution was added dropwise over 2 hours, and reacted for 14 hours while maintaining the same temperature after completion of the addition,
The solvent after the reaction was distilled off with an evaporator to obtain a polymer compound A.

(Synthesis Example 2) N-vinyl-2-pyrrolidone 100.0 parts 2,2′-azobis (isobutylnitrile) 3.6 parts isopropyl alcohol 100.0 parts These components were mixed to prepare a solution. .

Next, a polymer compound B was obtained in the same manner as in Synthesis Example 1.

(Synthesis Example 3) N-vinyl-2-pyrrolidone 100.0 parts 2,2′-azobis (isobutylnitrile) 7.2 parts isopropyl alcohol 100.0 parts These components were mixed to prepare a solution. .

Next, a polymer compound C was obtained in the same manner as in Synthesis Example 1.

Table 1 shows the measurement results of the weight average molecular weights of the synthesized high molecular compounds (all values are in terms of polyethylene glycol). The measurement was carried out by gel permission chromatography (manufactured by HP, model 1050).

[0038]

[Table 1]

(Example 1) (Preparation of ink composition) Tenoyl trifluoroacetone 10.6 parts Ethanol 274.0 parts Europium (III) chloride hexahydrate 3.0 parts Ion-exchanged water 274.0 parts While stirring with a magnetic stirrer.
40.0 parts of an OH aqueous solution (1N) was added dropwise to adjust the pH to 6.
Thereafter, 18.6 parts of polymer compound A was added, and the mixture was stirred at 60 ° C. for 3 hours and filtered to obtain fluorescent complex solution A.

Further, 0.2 part of a surface conditioner (BYK-348, manufactured by BYK-Chemie) and 17.0 parts of a sensitizer (1,3-Dimethyl-2-imidazolidinone) were added to the obtained fluorescent complex solution A, After stirring at 25 ° C. for 1 hour, the mixture was filtered to obtain ink composition A.

Example 2 The same procedure was carried out as in Example 1 except that “polymer compound A” was changed to “polymer compound B”.
Ink composition B was obtained.

Example 3 The same procedure was carried out as in Example 1 except that “polymer compound A” was changed to “polymer compound C”.
Ink composition C was obtained.

Example 4 "Europime chloride" of Example 2
Ink composition D was obtained in the same manner as above, except that “hexahydrate” was changed to “neodymium chloride hexahydrate”.

(Comparative Example 1) (Preparation of ink composition) Tenoyltrifluoroacetone 10.6 parts Ethanol 274.0 parts Na while stirring the above components with a magnetic stirrer
40.0 parts of an OH aqueous solution (1N) is added dropwise to adjust the pH to 6.
Thereafter, 3.0 parts of europium (III) chloride hexahydrate and 274.0 parts of ion-exchanged water were added, and the mixture was stirred at 60 ° C. for 3 hours, followed by filtration to obtain a fluorescent complex solution E.

Further, 0.2 part of a surface conditioner (BYK-348, manufactured by BYK-Chemie) and 17.0 parts of a sensitizer (1,3-Dimethyl-2-imidazolidinone) were added to the obtained fluorescent complex solution E, After stirring at 25 ° C. for 1 hour, the mixture was filtered to obtain an ink composition E.

(Comparative Example 2) {Preparation of Ink Composition} 12.6 parts of Lumix CD331 manufactured by Rieder de Haan 274.0 parts of ethanol 274.0 parts of ion-exchanged water The above substances were adjusted while being mixed with a disper. After filtration, a fluorescent complex solution F was obtained.

Further, 0.2 part of a surface conditioner (BYK-348, manufactured by BYK-Chemie) and 17.0 parts of a sensitizer (1,3-Dimethyl-2-imidazolidinone) were added to the obtained fluorescent complex solution F, After stirring at 25 ° C. for 1 hour, the mixture was filtered to obtain ink composition F.

Comparative Example 3 {Preparation of Ink Composition} Tenoyltrifluoroacetone 10.6 parts Ethanol 274.0 parts Europium (III) chloride hexahydrate 3.0 parts Ion-exchanged water 274.0 parts While stirring with a magnetic stirrer.
40.0 parts of an OH aqueous solution (1N) was added dropwise to adjust the pH to 6.
Thereafter, 37.2 parts of polyvinylpyrrolidone K25 (average molecular weight: 25,000) manufactured by Wako Pure Chemical Industries, Ltd. was added, and the mixture was further stirred for 1 hour to obtain a fluorescent complex liquid G.

Further, 0.2 part of a surface conditioner (BYK-348, manufactured by BYK-Chemie) and 17.0 parts of a sensitizer (1,3-Dimethyl-2-imidazolidinone) were added to the obtained fluorescent complex solution G, After stirring at 25 ° C. for 1 hour, the mixture was filtered to obtain ink composition G.

(Evaluation of Examples 1 to 4 and Comparative Examples 1 to 3) The viscosity, solubility and dispersion stability of the ink compositions prepared in the present invention were evaluated by the following methods. Table 2 shows the evaluation results. Further, the fluorescence intensity of the ink and the printed matter was evaluated by the following method. Table 3 shows the evaluation results.

(Viscosity of Ink Composition) Toki Sangyo Co., Ltd.
The viscosity at 25 ° C. was measured using an E-type viscometer (R100 type).

(Ink Solubility or Dispersion Stability) The ink solubility was evaluated by the presence or absence of sediment after storage at 60 ° C. for one week. Those with sediment were evaluated as x, and those without sediment were evaluated as ○.

(Emission intensity of ink and printed matter) The emission intensity of the ink and printed matter was measured by a fluorescence spectrophotometer (FP750, manufactured by JASCO Corporation). The ink emission intensity was measured before and after storage at 60 ° C. for one week. The luminous intensity of the printed matter was measured by applying the ink composition to an inkjet printer (manufactured by EPSON: J-510
C) was evaluated by printing on plain paper (XEROX). The weather resistance of the printed matter was evaluated after the printed sample was tested in a weather resistance test (Shimadzu Corporation: Shimadzu Santesta XF-180CPS) for 3 hours. The luminescence intensity was measured using a commercially available dye (Liedel DeHahn, Lumix CD33) as a reference.
1) An ink composition was prepared by dissolving 12.6 parts in 568 parts of ethanol, and the luminescence intensity was set to 100 for relative comparison. In addition, except for the printed matter by the ink composition L, the excitation light of 365 nm was irradiated, and the emission peak intensity of 615 nm was irradiated. The printed matter of the ink composition L was irradiated with the excitation light of 810 nm, and the emission peak intensity of 1065 nm was compared. used.

[0054]

[Table 2]

[0055]

[Table 3]

From the results in Tables 2 and 3, it was found that the ink compositions A to D using the fluorescent complex of the present invention were soluble in aqueous solvents or were stable. In addition, the luminescence intensity of the ink composition and printed matter using the fluorescent complex of the present invention has a luminescence intensity equal to or higher than that of an ethanol-based ink using a commercially available dye, and also has better storage stability and weather resistance. It was confirmed that it showed.

[0057]

According to the present invention, the fluorescent complex comprising a high molecular compound having a weight average molecular weight of 300 or more and less than 5000 and having a rare earth element as a luminescent center and a pyrrolidone moiety is soluble in an aqueous solvent and is stable. all right. Therefore, even when used in a jet printer ink composition, since the viscosity is low, good printing is possible without causing ejection failure such as clogging. Since an aqueous ink composition does not use an organic solvent, it is safe for the human body and has no problem of restricting the use environment. Further, compared with the solvent-based ink, the luminescence intensity of the printed matter is equal to or higher than that of the solvent-based ink.
A, various cards, barcode systems, etc.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C08K 5/07 C08L 39/06 C08L 39/06 C09D 11/00 C09D 11/00 B41J 3/04 101Y F term (reference) 2C056 EA13 FC01 2H086 BA01 BA53 BA59 BA60 BA62 4J002 BJ001 DA116 EE047 FD200 GC00 GH00 GH01 GL00 GQ05 GT00 4J039 AD12 BA39 BC07 BC08 BC18 BC22 BE12 CA03 EA28 EA41 EA44 EA45 EA46 GA24

Claims (7)

[Claims] 1. A fluorescent complex comprising a high molecular compound having a rare earth element and a pyrrolidone moiety and having a weight average molecular weight of 300 or more and less than 5,000. 2. The method according to claim 1, wherein the pyrrolidone moiety in the polymer compound is
The fluorescent complex according to claim 1, wherein the complex is represented by the following formula (1). 3. A rare earth element, a dye comprising a β-diketone compound in an amount of 3 to 8 moles relative to the rare earth element, and a high molecular compound having a pyrrolidone moiety and having a weight average molecular weight of 300 or more and less than 5,000. Item 7. The fluorescent complex according to Item 1. 4. The fluorescent complex according to claim 1, wherein the rare earth element comprises at least one of europium, dysprosium, terbium, neodymium, pseodymium, samarium, saddle, holmium, erbium, and thulium. 5. The ink composition according to claim 1, further comprising a fluorescent complex. 6. The ink composition has a viscosity of 1.5 c at 25 ° C.
6. The ink composition according to claim 5, wherein the value is not less than p and not more than 8 cp. 7. The ink composition according to claim 5, wherein water is contained in the ink composition, and the content of water in the ink composition is 30 to 90% by weight.