JP2001348518A - Ink for ink jet, ink set using the same and method for ink jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ink for ink jets capable of surely suppressing the occurrence of color bleed and cogation, improving even the shelf life and further avoiding the complication of the constitution of an ink head and suitably usable in a thermal jet type image forming device. SOLUTION: This ink for the ink jets is obtained by using a color ink comprising a water-soluble dye having a betaine structure and a cationic surfactant in an aqueous solvent and a black ink comprising a black pigment in an aqueous solvent and assuming alkalinity. Since the color ink has especially the betaine structure, the color ink becomes an extremely stable state even under acidic conditions and the shelf life can be improved without causing the cogation. An acid-alkali reaction is caused between the color ink and the black ink to thereby rapidly fix the black ink. As a result, the color bleed can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink used in an image forming apparatus of an ink jet system, and more particularly, it suppresses not only the occurrence of color bleed but also the occurrence of so-called kogation and further improves the storage stability. The present invention relates to an ink-jet ink capable of forming a high-quality image.

[0002]

2. Description of the Related Art Various types of image forming apparatuses for hard copy have been proposed and put into practical use. Above all, an image forming apparatus (ink jet printer) of an ink jet system (droplet ejection recording system) can form a high-quality image and can keep the cost of the entire apparatus low. It is preferably used for forming a color image.

Here, in the above-mentioned ink jet system, it has been known that a problem called color bleeding or bleeding occurs.

That is, in the ink jet system, in order to obtain a color image, a plurality of color inks each containing water as a main solvent are usually superimposed and recorded on a recording material such as paper. At this time, before a certain color ink previously ejected on the recording material is fixed, another color ink is ejected one after another and overlapped. Therefore, in a portion that is a boundary between different colors, a phenomenon that inks of different colors are diffused or moved to make the boundary line of each color unclear, that is, color bleed or bleeding (hereinafter referred to as “color bleed”). appear.

When the color bleed occurs, bleeding occurs between different colors or the colors are mixed unevenly, thereby deteriorating the image quality. In particular, in image formation, black is the most important color, but when color bleed occurs between this black and other colors,
The boundaries of the black image are blurred or blurred, greatly degrading the image quality.

Therefore, various techniques for suppressing the occurrence of the color bleed have been conventionally proposed. For example,
JP-A-5-202328 and JP-A-6-106
No. 375 discloses a technique for suppressing color bleed by using a polyvalent metal salt for coagulation of ink.

Specifically, Japanese Patent Application Laid-Open No. Hei 5-202328 discloses that an ink containing a dye having at least one carboxyl group and a polyvalent metal salt are used, and a polyvalent metal salt solution is first applied to a recording material. After supplying the ink, the ink is supplied.
Accordingly, it is possible to suppress the occurrence of color bleed due to the rapid drying of the ink on the recording material, and to improve the water resistance of the dried ink.

In Japanese Patent Application Laid-Open No. 6-106735, each of yellow, magenta, and cyan inks contains a surfactant or a penetrating solvent that imparts permeability and a salt, and the black ink contains Contains a component that causes thickening or aggregation due to the action of the salt. As a result, the occurrence of color bleed can be suppressed, the uniformity of the image density can be improved, and the quality of black can be further improved.

Further, Japanese Patent Application Laid-Open No. Hei 8-209049 discloses a second composition containing a first composition containing a gel-forming species and a gel-initiating species that reacts with the first composition to form a gel.
Techniques using compositions are disclosed. With this technology,
Each composition is discharged to adjacent regions to form a gel between the regions, thereby suppressing the occurrence of color bleed.

Japanese Patent Application Laid-Open No. 9-207424 discloses a technique in which a pigment and a resin emulsion are contained in an ink in addition to the use of the polyvalent metal salt. The above-mentioned resin emulsion suppresses penetration of the coloring component by interaction with polyvalent metal ions, and promotes fixation to a recording material. The resin emulsion can also form a coating on the recording material to improve the abrasion resistance of the printed matter. Further, if a pigment is used, it is possible to further suppress the penetration of the coloring component in the ink. By such an action, color bleed is further suppressed.

[0011] In addition, Japanese Patent Application Laid-Open No. H11-34978 discloses a technique in which ion interaction occurs between black ink and color ink to suppress color bleeding. In this technique, a black ink contains an anionic pigment and a component (for example, a cationic surfactant or a cation salt) for supplying a cation to a color ink. As a result, interaction of ions occurs between the black ink and the color ink, and the occurrence of color bleed is suppressed.

By the way, among the above-mentioned ink jet systems, in a thermal jet system in which ink is instantly heated by a heater in a nozzle and the ink is ejected from the nozzle by the pressure of generated bubbles, in addition to the above-described color bleed,
It is also known that a problem called kogation occurs.

[0013] Kogation generally means that substances generated by thermal decomposition of coloring components in ink, trace inorganic impurities and agglomerates contained in ink adhere and deposit on the heater, and as a result, the heater Is a phenomenon in which the ink cannot be sufficiently heated, and stable ink ejection cannot be maintained. The occurrence of this kogation, in particular,
It is known that inorganic ions (especially metal ions) in ink have a great effect.

For example, when a cationic salt is contained in the composition of the ink, inorganic ions and the like forming the cationic salt are heated on a heater to react with other components of the ink to form insolubles. May be formed. When such insoluble matter adheres and accumulates on the heater, the kogation occurs.

[0015]

In the above-described conventional technique, although the color bleeding can be suppressed to some extent, it is difficult to avoid the occurrence of the kogation. I have.

First, in the technique using a polyvalent metal salt for coagulation of ink, ions of the polyvalent metal salt cause kogation, and the ink cannot be normally ejected from the head. Therefore, Japanese Patent Application Laid-Open Nos. Hei 5-202328, Hei 6-106375, and Hei 9-106375 describe above.
In each of the techniques disclosed in Japanese Patent Application Publication No. 207424, a reaction liquid containing a polyvalent metal salt and an ink are separately discharged onto a recording material (paper), and the reaction liquid and the ink are mixed on the recording material. ing. However, such a technique of separately ejecting two types of components complicates the structure of the ink head, increases the manufacturing cost, and complicates the control and maintenance of image formation. Invite you.

On the other hand, in JP-A-8-209049, the combination of the gel-forming species and the gel-initiating species contained in the first and second compositions causes kogation. However, this method has a problem that the method is not practical.

Furthermore, Japanese Patent Application Laid-Open No. H11-34978 contains almost no substances that cause kogation such as the above-mentioned polyvalent metal salts, gel-forming species and gel-initiating species. Therefore, it is theoretically possible to suppress both the occurrence of kogation and the occurrence of color bleed. However, in this technique, it is essential to use a cationic salt or a cationic surfactant. These substances are stable under acidic conditions. However, when an alkali or the like is added, unnecessary substances are generated in water and the efficiency is lost, so that the ink must be acidic.

When the ink is acidic, the dyes and pigments usually contained as color components are liable to coagulate and precipitate, and as a result, a serious problem occurs in the storage stability and stability of the ink. When the storage stability and stability of the ink are reduced in this manner, there is a high possibility that solidification or precipitation occurs in the thermal jet head during image formation, and as a result, the occurrence of kogation cannot be reliably suppressed.

Further, according to the technique disclosed in Japanese Patent Application Laid-Open No. H11-34978, p is used to optimize various characteristics of the ink.
Although reference is made to the adjustment of H, there is no mention of a specific pH range or the like. Therefore, in the above-mentioned technology, no specific measures have been taken with respect to a decrease in storage stability due to coagulation or precipitation of the dye or pigment.

Generally, most dyes and pigments contain a sulfo group or a carboxyl group. Therefore, when a cationic surfactant or a cation salt is added to the ink containing these dyes or pigments, the sulfo group or carboxyl group and the cationic surfactant or the cation salt easily cause an acid-alkali reaction, and the ink contains Agglomerates form. Therefore, the ink containing the above-mentioned cationic surfactant or cationic salt has a composition in which an aggregate is easily generated by an acid-alkali reaction.

In such an ink, not only the aggregates are easily generated in the ink, but also the number of aggregates and the size thereof increase with time. for that reason,
Even if left alone for a long period of time, agglomerates are generated and easily clog in the ink flow path in the ink cartridge, hindering the ejection of ink. In addition, the agglomerates adhere to the heater.
Since the deposits cause kogation, stable heating of the ink by the heater is hindered, and the ejection of the ink becomes unstable.

That is, an ink having a composition containing a cationic surfactant or a cationic salt not only tends to cause kogation but also causes agglomerates to be generated over time, thereby deteriorating the storage stability of the ink. Become. As a result, eventually, there is a problem that the ink ejection ability is irreversibly reduced and the life of the ink cartridge is shortened.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to surely suppress the occurrence of color bleeding and kogation, to improve the storability, and to further improve the structure of the ink head. An object of the present invention is to provide an inkjet ink which can be suitably used in a thermal jet type image forming apparatus while avoiding complication.

[0025]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above problems, and as a result, have found that ions interact between the color ink and the black ink and that the ink used as the color ink contains By using a dye having a betaine structure at the end as the dye to be used, it was found that not only the occurrence of color bleeding but also the occurrence of kogation could be suppressed and the storage stability could be improved. The invention has been completed.

That is, the ink-jet ink according to the present invention is characterized in that the aqueous solvent contains a water-soluble dye having a betaine structure and a cationic surfactant in an aqueous solvent. I have.

Usually, under the condition that a cationic surfactant is present, the ink becomes acidic and a problem occurs in that the water-soluble dye solidifies. However, according to the above configuration, the water-soluble dye has a betaine structure. Therefore, the ink becomes very stable even under acidic conditions, and the storage stability of the ink is improved. In addition, the ink contains almost no metal salts or components related to gelation. Therefore, kogation hardly occurs even when heated by the nozzle. Further, in the above configuration, when used in combination with an alkaline ink, color bleeding can also be suppressed.

In the ink jet ink,
Preferably, the cationic surfactant is an amine acetate.

According to the above configuration, by using an acetate of an amine, a sufficient effect of adjusting the surface tension of the ink can be obtained, and the occurrence of kogation can be more reliably avoided.

In the above ink for ink jet,
It is preferable that the pH is adjusted within a range of 4 or more and less than 7.

According to the above configuration, when the pH of the ink is adjusted to be within the above range, that is, in a weakly acidic state, the effect of suppressing color bleed is further improved by combining the ink with an alkaline ink. be able to.

Further, in order to solve the above-mentioned problems, an ink-jet ink set according to the present invention comprises a color ink comprising a water-soluble dye having a betaine structure and a cationic surfactant in an aqueous solvent; It is characterized in that the solvent contains a black pigment and a black ink showing alkalinity.

According to the above arrangement, first, the black ink is in a state in which the black pigment is stably dispersed (suspended) under alkaline conditions, while the color ink is in an aqueous solution having a betaine structure under acidic conditions. Sex dye is in a stable state. In addition, each of these inks hardly contains metal salts and components related to gelation. for that reason,
Even if these inks are heated by the nozzles, the occurrence of kogation is suppressed.

When the black ink and other color inks associate on the recording material, an alkaline-black ink and an acidic color ink cause an acid-alkali reaction. Settles easily and quickly on the recording material. As a result, the black pigment is fixed without causing color bleed.

Further, since the black ink and the color ink are in a very stable state, even if the frequency of image formation is low and the time between image forming operations is long, the black pigment and the water There is no coagulation or precipitation of the dye. Therefore, excellent preservability can be exhibited.

The pH of the color ink is in the range of 4 to less than 7, and the pH of the black ink is 7
It is preferable to be within the range of more than 10 and less than 10.

According to the above configuration, since the pH of both the black ink and the color ink is adjusted to a preferable range, the acid-alkali reaction can be more effectively generated.

In the above ink set for ink jet, the black pigment contained in the black ink is preferably an anionic pigment.

According to the above configuration, since the black pigment is an anionic pigment, the dispersibility of the black pigment in the black ink is further improved. As a result, the storability of the black ink can be further improved. In addition, since the dispersion state of the anionic pigment largely depends on the balance of the ionic charges in the black ink, if the balance of the ionic charges is lost due to the acid-alkali reaction of the black ink-color ink, the anionic pigment can easily be formed. Aggregation and sedimentation will occur. Therefore, color bleed of black ink in color image formation can be effectively suppressed.

In the above ink set for ink jet, the black ink contains at least one of a dispersant for dispersing the black pigment and a binder for fixing the black pigment on the recording material during image formation. Is preferred.

According to the above configuration, the dispersibility of the black pigment is further improved by the presence of the dispersant. As a result, the storage stability of the black ink can be improved, and the occurrence of kogation can be further suppressed. In addition, since the fixing of the black pigment becomes faster and more reliable due to the presence of the binder, the occurrence of color bleed can be further suppressed. In particular, when both the dispersant and the binder are contained, the effect of suppressing kogation and color bleed can be further improved, and the storage stability can be further improved.

The ink jet recording method according to the present invention uses the ink set for ink jet described above,
It is characterized in that an image is formed on a recording material.

According to the above method, when a black ink stable under alkaline conditions and a color ink stable under acidic conditions associate on a recording material, the black ink and the color ink undergo an acid-alkali reaction. As a result, the balance of the ionic charges of the black ink is reduced. Therefore, the uniformly dispersed black pigment precipitates (or solidifies) very easily, and the black pigment precipitates easily and quickly on the recording material. As a result, the black pigment is fixed without causing color bleed, and color bleed can be suppressed.

In addition, since it does not contain a polyvalent metal salt or a component for gelation as in the prior art, the occurrence of kogation can be suppressed, and the black ink and the color ink can be kept in a very stable state. As a result, preservability is also improved. Furthermore, since it is not necessary to adopt a configuration in which the polyvalent metal salt and the ink are ejected separately, it is possible to avoid the complexity of the configuration of the ink head, reduce the cost, and simplify the maintenance. can do.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Note that the present invention is not limited to this.

The ink-jet ink according to the present invention is particularly preferably used as a color ink for forming a color image, and comprises a water-soluble dye having a betaine structure and a cationic surfactant in an aqueous solvent. . Therefore, occurrence of color bleeding and kogation can be suppressed, and high-quality images can be favorably formed while exhibiting high storage stability.

Further, the ink set according to the present invention comprises at least one kind of color ink and one kind of black ink, and the black ink must have a composition containing a black pigment in an aqueous solvent. On the other hand, the above-mentioned color ink is an ink which has a composition containing a water-soluble dye having a betaine structure in an aqueous solvent and a cationic surfactant and is acidic.

That is, in the ink jet recording method according to the present invention, a color image is formed using a color ink and a black ink, and the color ink and the black ink have different compositions.

The color ink according to the present invention contains a water-soluble dye as an essential component, and the water-soluble dye has a betaine structure.

The betaine structure in the present invention refers to a structure possessed by betaine in a broad sense, that is, a structure possessed by a compound which forms a zwitterion with an internal salt and exists as a zwitterion in a solution. In other words, betaine in the present invention refers to a cation (cation) structure (referred to as an intramolecular basic group) such as a quaternary ammonium base and a carboxyl group or a sulfo group in one molecule. Is defined as an intramolecular salt type compound having an anion (anion) structure (referred to as an intramolecular acidic group).

Therefore, since the water-soluble dye of the present invention has the above-mentioned betaine structure, it forms an amphoteric ion with an internal salt, and is stable regardless of whether the aqueous solvent is acidic or alkaline. To dissolve in the aqueous solvent.
As a result, it is possible to avoid problems such as coagulation and precipitation of the water-soluble dye.

The water-soluble dye is not particularly limited as long as it has the above-mentioned betaine structure. Specifically, for example, in various water-soluble dyes, the basic structure of the water-soluble dye is represented by X In this case, there can be mentioned those having the following two types of structures including a quaternary ammonium structure as an intramolecular basic group.

I) Chain compound A quaternary ammonium structure of a chain formula (which may have a side chain) as shown by the following structural formula (1): among the atomic groups containing a water-soluble dye of the basic structure X, intramolecular acidic group B ^- structure and atomic group containing it is contained one each.

[0054]

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However, in the above structural formula (1), R
¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms, and Q ¹ may be omitted or
It represents an oxygen atom, an alkylene structure having 1 or 2 carbon atoms or an oxyalkylene structure, and Q ² represents an alkylene structure or an oxyalkylene structure having 1 to 4 carbon atoms.

Ii) Cyclic compound An atomic group containing a water-soluble dye having a basic structure X at the nitrogen atom in the quaternary ammonium structure of the nitrogen-containing monocyclic heterocyclic compound as shown in the following structural formula (2) intramolecular acidic group B ^-
And a single atomic group.

[0057]

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However, in the above structural formula (2), n
And m are each independently an integer of 1 or 2, Q ¹ may be absent, or represents an oxygen atom, an alkylene structure or an oxyalkylene structure having 1.2 carbon atoms, and Q ² is It shows a C1-C4 alkylene structure or an oxyalkylene structure, and D shows an oxygen atom and a C1-C2 alkylene structure.

Preferable examples of the water-soluble dye represented by the above-mentioned basic structure X include, for example,
Acid Yellow 23, Direct Yellow 86 and the like, and magenta dyes such as Reactive Red 5
8, Reactive Red 120, Reactive Red 1
80, Acid Red 52, Acid Red 214, etc., and cyan dyes include Acid Blue 7, Acid Blue 9, Direct Blue 86, Direct Blue 199, etc. Conventionally known water-soluble dyes can be appropriately selected according to the color to be developed.

[0060] The intramolecular acidic group B ^- is not particularly limited as long as it is an atom group that exhibits acidity, for example, a sulfo group (-SO ₃ ^-) or a carboxyl group (-COO ^-)
Are preferred.

The above-mentioned R ¹ or R ² has 1 to 1 carbon atoms.
Examples of the alkyl group 4 include a methyl group (CH ₃
−), An ethyl group (C ₂ H ₅ −), a propyl group (C ₃ H _7).
-), butyl (C ₄ H ₉ -), isopropyl ((C
H _{3) 2} CH-) and the like.

The above Q¹C1 and C2 alkyl represented by
The methylene (-CH_Two−), Ethylene
(-C_TwoH_Four-), And an oxyalkylene structure and
Is oxymethylene (-OCH_Two−), Oxyethyl
Ren (-OC_TwoH_Four-). In addition, the above Q^Two
The alkylene structure having 1 to 4 carbon atoms represented by
Tylene (-CH_Two-), Ethylene (-C_TwoH_Four−), To
Limethylene (-C_ThreeH ₆-), Tetramethylene (-C_Four
H₈-), And as the oxyalkylene structure,
Oxymethylene (-OCH_Two-), Oxyethylene (-
OC_TwoH_Four-), Oxytrimethylene (-OC_ThreeH
₆-), Oxytetramethylene (-OC_FourH ₈-)
I can do it.

Examples of the alkylene structure having 1.2 carbon atoms represented by D include the structures of methylene and ethylene. Since D may be an oxygen atom, specific examples of the nitrogen-containing monocyclic heterocyclic compound in the structural formula (2) include pyrrolidine, piperidine, hexamethyleneimine, and morpholine.

In the above example, the most common quaternary ammonium structure is given as an example of an intramolecular basic group. However, in the present invention, as long as the above betaine structure can be formed, the intramolecular basic group may be used. It goes without saying that the basic group may have another basic structure.

As a method for producing a water-soluble dye having a betaine structure having the structural formula (1) or (2), a water-soluble dye represented by the above-mentioned basic structure X may be prepared by a conventionally known method. For example, in the 86th edition of "Full Edition New Introduction to Surfactants" (author: Takehiko Fujimoto, Sanyo Chemical Industries, Ltd.)
And a method of introducing a betaine structure by the method described on page 88.

[0066] Specifically, for example, the quaternary ammonium structure as intramolecular basic group, intramolecular acidic group B ^-
When a sulfo group (—SO ₃ ⁻ ) is selected as the above, the method described below is suitably used.

First, a tertiary amine (tertiary amine) structure is introduced into the water-soluble dye having the above-mentioned basic structure X by a conventionally known method, and a chain water-soluble dye represented by the following structural formula (3) is obtained. A heterocyclic water-soluble dye amine as shown in the structural formula (4) is obtained. If the water-soluble dye originally contains an amine structure, it can be used as it is.

[0068]

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[0069]

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Next, any of the water-soluble dye amines described above,
Sodium chloroalkyl sulfonate having 1 to 4 carbon atoms,
Next or chloro alkyloxy sodium sulfonate (both compounds represented by Cl-Q ² -SO ₃ Na) and is added and mixed in a suitable solvent, if necessary, with stirring for several hours at 60-80 ° C. Of the reaction formula (5-1) or (5-
The reaction of 2) is advanced to introduce a sulfo group into the tertiary amine structure to obtain a betaine structure.

[0071]

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[0072]

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In the present embodiment, introducing a betaine structure to the water-soluble dye represented by the basic structure X is sometimes referred to as "betaine formation".
In addition, a water-soluble dye having a betaine structure introduced therein is referred to as “(name of water-soluble dye) betaine derivative” or “(name of water-soluble dye) derivative” (for example, “acid yellow 23 betaine derivative”). Or simply referred to as “acid yellow 23 derivative”).

The above-mentioned betaine which forms an internal salt usually exists as one zwitterion in an aqueous solution like the betaine structure used in the present invention. In some cases, betaine contains what separates it. Here, when an ink is prepared using an ink that separates into cations and anions in an aqueous solution as in the latter case, cations are present in the composition of the ink, as in the case of conventional inks. This is not preferred because it leads to a decrease in storage stability and the occurrence of kogation.

The cationic surfactant contained as an essential component in the color ink according to the present invention may be any material as long as the portion that dissociates into ions in an aqueous solvent and becomes a cation (cation) exhibits surface activity. There is no particular limitation. Accordingly, any cationic surfactant known to be usable in ink jet inks can be applied to the present invention.

Specifically, for example, amine salts, quaternary ammonium salts, sulfonium salts, phosphonium salts, carboxybetaine type, aminocarboxylates, lecithin,
Sapamin A (manufactured by Ciba Geigy), Arcover G (manufactured by Arnold Hoffman) and the like can be mentioned. Among the above, amine salts and quaternary ammonium salts are preferable, and particularly, acetates of amines (amine acetates) and acetate or chloride salts of quaternary ammonium are more preferable.

As specific examples of amine acetates, for example, the longest hydrophobic group is an alkyl group having 12 to 18 carbon atoms, and is a primary amine, a secondary amine, or a tertiary amine. Preference is given to acetates of amines selected from the group consisting of amines and mixtures thereof. Examples of such amine acetates include laurylamine acetate.

When the number of carbon atoms of the hydrophobic group is 11 or less,
Hydrophobicity tends to decrease and become hydrophilic. On the other hand, when the number of carbon atoms is 19 or more, the hydrophobicity is excessively improved. That is,
When the number of carbon atoms of the hydrophobic group is out of the range of 12 to 18, the balance between the hydrophilic group and the hydrophobic group as the cationic surfactant is lost, and a good surface active effect (that is, adjustment of surface tension described later) Effect) cannot be exhibited.

As specific examples of the quaternary ammonium salt, for example, polypropoxy quaternary ammonium salts such as polypropoxy quaternary ammonium acetates and polypropoxy quaternary ammonium chlorides are preferably used. All of these polypropoxy quaternary ammonium salts are commercially available, such as the Emcol series of WITCO Corporation.

Examples of the counter ion capable of binding to the above-mentioned cationic surfactant include acetate ion, formate ion, chloride ion, gluconate ion, succinate ion, tartrate ion, glutarate ion, malonate ion, Examples include carboxylate ion, fumarate ion, malate ion, sebacate ion, adipate ion, stearate ion, oleate ion, laurate ion, benzoate ion, and citrate ion.
Among them, as described above, acetate ions and chloride ions are preferred, and acetate ions are even more preferred.

The above cationic surfactant is added to adjust the surface tension of the color ink. As a specific content, it is present in the color ink at a concentration in the range of about 0.5 to 5% by weight,
It is more preferable that the concentration is in the range of weight%. When the cationic surfactant is contained within this range, it is possible to satisfactorily adjust the wettability of the thermal jet on the orifice and the recording material (paper) in the head.

The content of the cationic surfactant is about 0.5.
If it is less than 5% by weight, a sufficient effect of adjusting the surface tension cannot be obtained, which is not preferable. On the other hand, if it exceeds about 5% by weight, the effect of adjusting the surface tension in proportion to the added amount cannot be obtained, and the viscosity or the like becomes high, and the function as a color ink is undesirably reduced.

The color ink according to the present invention comprising the above-mentioned water-soluble dye having a betaine structure and a cationic surfactant exhibits acidic properties.
Is within the range of 4 or more and less than 7 (the pH of the color ink is adjusted to pH _Cl
In this case, 4 ≦ pH _Cl <7) is preferable, and the pH is more preferably in the range of 6 or more and less than 7 (6 ≦ pH _Cl <7). That is, the color ink more preferably exhibits a weak acidity. By the addition of the cationic surfactant, the color ink according to the present invention shows a weak acidity,
In particular, when an acetate or quaternary ammonium salt of an amine is used as the cationic surfactant, the pH can be adjusted to a more preferable range of 6 to less than 7.

In order to adjust the ink to be acidic, the pH is adjusted.
A modifier (buffer / buffer) may be added. However, in the color ink according to the present invention, since it is necessary to avoid occurrence of kogation, a pH-adjusting agent containing a metal salt cannot be used.

The aqueous solvent contained in the color ink according to the present invention contains at least water and further contains another water-soluble solvent. As the above water,
There is no particular limitation as long as it does not contain inorganic ions that cause kogation and has a degree of purity that is generally used for inks. Deionized water) is used.

The water content in the color ink is 10% when the total weight of the color ink is 100% by weight.
It is in the range of 90 to 90% by weight, preferably in the range of 30 to 80% by weight, and more preferably in the range of 50 to 95% by weight.

The other solvent soluble in water is one that inhibits various functions in the color ink, that is, the functions of drying the ink, developing the color, or suppressing the occurrence of kogation and color bleed in the present invention. If not, there is no particular limitation.

As the other solvent, specifically, for example, methanol, ethanol, n-propanol, is
C1-C5 alkyl alcohols such as o-propanol (2-propanol), n-butanol, sec-butanol, tert-butanol, iso-butanol and n-pentanol; amides such as dimethylformamide and dimethylacetamide Ketone or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; oxypropylene copolymers (polyalkylene glycols) such as polyethylene glycol and polypropylene glycol; polyethylene imine; ethylene glycol, propylene glycol; Butylene glycol, trimethylene glycol, triethylene glycol, 1,2,6-hexanetriol, thioglycol, hexylene glycol, diethylene glycol, Tiger ethylene glycol, dipropylene glycol, tripropylene glycol, 1,
Polyhydric alcohols such as 5-pentanediol and glycerin; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, etc. Lower monoalkyl ethers of polyhydric alcohols; lower dialkyl ethers of polyhydric alcohols such as triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether; trimethylolpropane; monoethanolamine , Diethanolamine, trie Noruamin, 2-pyrrolidone,
N-methyl-2-pyrrolidone, 1,3-dimethyl-2-
Various water-soluble organic solvents such as organic amines such as imidazolidinone and sulfolane; urea; The water-soluble organic solvents may be used alone or as a mixture of two or more.

Among the above water-soluble organic solvents, in particular, iso
Monohydric alcohols such as propanol (2-propanol), polyhydric alcohols such as diethylene glycol and 1,5-pentanediol, and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether and diethylene glycol monobutyl ether And trimethylolpropane. Since the monohydric alcohol has a low boiling point, the effect of shortening the drying time of the color ink during image formation can be obtained. Further, polyhydric alcohols and lower alkyl ethers of polyhydric alcohols have a high boiling point, and thus function as wetting agents for suppressing undesirable drying of color inks.

The content of the water-soluble organic solvent contained in the color ink according to the present invention is not particularly limited.
When the total weight of the color ink is 100% by weight, 3 to
It is preferably within a range of 50% by weight, and more preferably within a range of 3 to 40% by weight.

When the water-soluble organic solvent is separately added to a low-boiling organic solvent and a high-boiling organic solvent, the low-boiling organic solvent is added in an amount of 0.1% when the color ink is 100% by weight. It is preferably in the range of 5 to 10% by weight, and 1.5 to 10% by weight.
More preferably, it is in the range of 6% by weight. In the case of a high-boiling organic solvent, the content is preferably in the range of 0.5 to 40% by weight, based on 100% by weight of the color ink.
More preferably, it is within the range of% by weight.

The preferred range of the content of the water-soluble organic solvent described above includes the case where each water-soluble organic solvent is used alone and the case where two or more water-soluble organic solvents are used as a mixture. That is, the above preferable range is a preferable range as the total content of the water-soluble organic solvent.

Further, in order to obtain desired physical properties, the color ink according to the present invention may be provided with an antifoaming agent, a preservative, a fungicide, etc., as necessary, in addition to the above-mentioned components. Further, other commercially available water-soluble dyes and the like can be added. Specific examples and addition amounts of these antifoaming agents, preservatives, antifungal agents, and the like are not particularly limited as long as they do not adversely affect various characteristics of the color ink, and conventionally known techniques can be suitably used. it can.

The ink set for inkjet according to the present invention contains, in addition to the color ink containing each of the above-mentioned components, a composition containing a black pigment in an aqueous solvent, and a black ink showing alkalinity.

Examples of the black pigment contained in the black ink include carbon black generally used for black ink, and are not particularly limited. Among them, a carboxyl group is modified on the surface of the black pigment. The anionic pigment which is charged anionic in an aqueous solution is particularly preferred.

Specific examples of the anionic pigment include:
A method of introducing -COONa (sodium salt of a carboxyl group) into the surface of carbon black to obtain anionic charged carbon black. In particular,
For example, after commercially available acidic carbon black is thoroughly mixed and dispersed in water, sodium hypochlorite is added dropwise thereto and heated. Thereafter, the obtained slurry is filtered and washed with water to obtain a pigment wet cake. Further, there is a method of redispersing the pigment in water, desalting with a reverse osmosis membrane, and concentrating the pigment dispersion, but is not particularly limited.

Further, a commercially available self-dispersible carbon black can be used as the anionic pigment. For example, self-dispersible carbon black “Cabjet” (trade name, manufactured by Cabot), which is anionically charged with a carboxyl group (—COO ⁻ ) directly bonded thereto, may be mentioned.

It is very preferable that the black ink contains a dispersant for dispersing the black pigment. In particular, when a carbon black that is not a self-dispersion type is used, it is very preferable to add a dispersant from the viewpoint of avoiding precipitation of the carbon black and improving storage stability.

Specific examples of the dispersant include various resins having a carboxyl group. When such a resin having a carboxyl group is added as a dispersant, the black ink shows alkalinity, and the black pigment, particularly an anionic pigment, becomes a stable solution (dispersion / suspension) under this condition. Become. As a result, precipitation and coagulation of the pigment are suppressed even after being left for a long period of time, and excellent preservability can be obtained.

Examples of the various resins having a carboxyl group include styrene-acrylic acid copolymer, styrene-acrylic acid-alkyl acrylate copolymer, styrene-maleic acid copolymer, and styrene-maleic acid-acrylic acid. Acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinylnaphthalene-acrylic acid copolymer, vinylnaphthalene- Maleic acid copolymers or salts thereof are exemplified. Among them, a styrene-acrylic resin is preferable, and a styrene-acrylic acid copolymer is particularly preferable.

The above various resins are preferably contained in the range of 0.1 to 5% by weight, and more preferably in the range of 0.3 to 2% by weight, based on 100% by weight of the whole black ink. More preferably, it is contained.

The above various resins include those which can also be used as a binder described later. In that case,
As the number of components added to the black ink decreases,
Preparation of black ink can be simplified.

[0103] As the dispersant, a resin emulsion may be used. The resin emulsion mentioned here means an emulsion in which the continuous phase is water and the dispersed phase is the following resin component.

As the resin component of the dispersed phase in the above resin emulsion, acrylic resin, vinyl acetate resin,
Styrene-butadiene resin, vinyl chloride resin, acryl-styrene resin, butadiene resin, styrene resin, crosslinked acrylic resin, crosslinked styrene resin, benzoguanamine resin, phenol resin, silicone resin, epoxy resin, and the like.

The above resin emulsion can be obtained by dispersion polymerization (emulsion polymerization) of a resin monomer in water together with a surfactant depending on the situation. For example, an emulsion of an acrylic resin or a styrene-acrylic resin is obtained by dispersing and polymerizing a (meth) acrylate or a (meth) acrylate and styrene together with a surfactant in water.

The ratio of the resin as the disperse phase component to water is 60 to 400 parts by weight of water with respect to 100 parts by weight of the resin.
Preferably within the range of 100 to 200 parts by weight.

It is also possible to use a commercially available resin emulsion. As a commercially available resin emulsion,
For example, Microgel E-1002, E-5002
(Styrene-acrylic resin emulsion, manufactured by Nippon Paint Co., Ltd.), Boncoat 4001 (acrylic resin emulsion, manufactured by Dainippon Ink and Chemicals, Inc.), Boncoat 5454 (styrene-acrylic resin emulsion, Dainippon Ink and Chemicals, Inc.) Manufactured), SAE-1
014 (styrene-acrylic resin emulsion, manufactured by Zeon Corporation), Sibinol SK-200 (acrylic resin emulsion, manufactured by Seiden Chemical Co., Ltd.),
And the like.

In the present invention, the above resin emulsion is preferably contained in the range of 0.1 to 40% by weight, assuming that the black ink is 100% by weight, and 1 to 25% by weight.
More preferably, it is contained within the range of weight%.

Further, the dispersant in the present invention may include both the resin having a carboxyl group and the resin emulsion. Further, when the black pigment is an anionic pigment having high dispersibility, the dispersant does not necessarily need to be contained.

Further, the black ink may contain a binder for fixing a black pigment on a recording material during image formation. Examples of the binder include water-soluble polymers such as polyurethane resin, starch, gelatin, latex, casein, gum arabic, sodium alginate, and polyacrylamide; cellulose derivatives such as methylcellulose, carboxycellulose, and hydroxymethylcellulose; polyacrylic acid Salts, vinylnaphthalene-acrylic acid copolymers, styrene-maleic acid copolymers and salts thereof, sodium salts of β-naphthalenesulfonic acid formalin condensate, anionic (anionic) polymers such as phosphates; polyvinyl Nonionic (nonionic) polymers such as alcohol, polyvinylpyrrolidone, and polyethylene glycol are exemplified.

The content of the binder is preferably in the range of 0.5 to 30% by weight, based on 100% by weight of the black ink. If it is less than 0.5% by weight, the effect obtained by adding the binder cannot be obtained. On the other hand, if it exceeds 30% by weight, the effect corresponding to the added amount cannot be obtained, and the viscosity or the like becomes high, so that the function as a black ink is undesirably reduced.

The aqueous solvent contained in the black ink contains at least water, and further contains another water-soluble solvent, similarly to the above-described color ink. Since both the water and the other solvent are the same as the water-soluble organic solvents exemplified in the description of the color ink, the detailed description is omitted.

The above-mentioned black ink shows alkalinity as described above, and specifically, has a pH in the range of more than 7 and 10 or less (the pH of the black ink is adjusted to pH
_{If Bk} , 7 <pH _Bk ≦ 10) is preferable, and the pH is 7
More preferably, it is more than 9 and not more than 9 (7 <pH _Bk ≦ 9). That is, the black ink more preferably exhibits weak alkalinity.

Here, it is very preferable that the black ink contains an organic amine such as 2-pyrrolidone among the above-mentioned water-soluble organic solvents. These organic amines are preferably used because they function as a pH adjuster (buffer / buffer) for adjusting the black ink to be slightly alkaline and do not cause kogation. The content is 0.001 to 1 when the black ink is 100% by weight.
It is preferably contained in the range of 0% by weight.

Further, the black ink according to the present invention comprises:
In order to obtain desired physical property values, in addition to the above-described components, if necessary, an antifoaming agent, a preservative, an antifungal agent, and the like can be attached, and further, other commercially available water-soluble dyes and the like Can also be added. Specific examples and addition amounts of these antifoaming agents, preservatives, antifungal agents, and the like are not particularly limited as long as they do not adversely affect various characteristics of the black ink, and conventionally known techniques can be suitably used. it can.

The color ink as the ink for inkjet according to the present invention, and the ink set according to the present invention including the color ink and the black ink can be widely applied to conventionally known various inkjet printers.

As a typical method of the ink jet printer, a piezo jet method in which ink in a nozzle is ejected by physical deformation of a piezo element or a thermal jet method in which ink is ejected by applying heat to the ink in the nozzle is used. System. The ink set according to the present invention can be suitably used in any of the above-mentioned methods, and among them, it is particularly preferably used in a thermal jet method in which kogation is easily generated by heating the ink.

In the above ink jet recording system,
The black ink and the color ink are separately discharged from the nozzles of the head, and come into contact with each other by forming an image on a recording material, for example, paper.

Here, heretofore, in the related art, especially in a portion which is a boundary between black and another color, each ink is diffused or moved to make the boundary line of each color unclear, that is, color bleeding. Occurs. As a result, particularly, the boundary of the black image is blurred or blurred, and the image quality is greatly reduced.

Also, due to the problem of the ink composition, kogation occurs due to the ink component adhering to the heater portion of the nozzle, or the frequency of image formation is low and the time between image forming operations is long. In this case, the dyes and pigments of the ink are coagulated or settled, so that the nozzles are clogged, resulting in a problem that storage stability is reduced.

On the other hand, in the present invention, first, in the head, the black ink is in a state where the black pigment is stably dispersed (suspended) under alkaline conditions, while the color ink is in the acidic conditions. Thus, the water-soluble dye having a betaine structure is in a stable state. In addition, each of these inks hardly contains metal salts and components related to gelation. For this reason, kogation does not occur even when heated by the nozzle, and even when the frequency of image formation is small and the time between image forming operations is long, the black pigment or water-soluble dye may be coagulated. No precipitation.

Further, when the black ink and the other color inks associate on the recording material, the alkaline black ink and the acidic color ink cause an acid-alkali reaction, and the ionic charge balance of the black ink is reduced. descend. In the black ink, when the charge balance of the ions is good, the black pigment is uniformly dispersed. However, when the balance is reduced, the black pigment is easily precipitated (or solidified). Settles easily and quickly on the material. As a result, the black pigment is fixed without causing color bleed, and color bleed can be suppressed.

The mechanism for suppressing color bleed will be described more specifically. For example, suppose that a black ink contains an anionic pigment as a black pigment and a styrene-acrylic resin as a dispersant, and a color ink contains a water-soluble dye having a betaine structure and a cationic surfactant.

When these are separately ejected from the nozzles and associated on the recording material, the styrene-acrylic resin, which is a dispersant in which the anionic pigment is well dispersed, and the cationic surfactant of the color ink are acidified. Causing an alkaline reaction; That is, the carboxyl group at the end of the styrene-acrylic resin reacts with a cation exhibiting a surfactant effect in the cationic surfactant, and this reaction is used as a driving force to make the ionic charge balance in the black ink unstable. . As a result, the anionic pigment is easily precipitated, while the styrene-acrylic resin dispersed in the black ink is also easily solidified.

As a result, the precipitated anionic pigment is fixed by the styrene-acrylic resin, the black ink does not penetrate into the recording material, and no color bleed occurs with the color ink. Solidified
Aggregate.

As described above, in the ink jet recording method according to the present invention, by using an alkaline black ink and an acidic color ink, a black fixing reaction using an acid-alkali reaction as a driving force on a recording material is performed. Cause. As a result, color bleed is reliably suppressed.

In addition, since each of the above inks does not contain a metal salt or a component relating to a gelling reaction, kogation does not occur even in a thermal jet type ink jet printer. Further, each of the above-mentioned inks shows acidity or alkalinity which is an unstable state as an ink in order to suppress color bleeding. However, since the water-soluble dye is converted to betaine and the pigment is well dispersed by anionizing and dispersing agents, the ink components do not coagulate or precipitate even after being left for a long period of time, and the nozzle is clogged to form an image. The problem of not being able to do so can also be avoided. As a result, the preservability of the ink has been greatly improved.

[0128]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the following description, parts by weight are simply abbreviated as “parts”, and weight% is also simply abbreviated as “%”.

Further, color bleeding, kogation, and storage stability were evaluated by the following methods.

[Color Bleed] Using a commercially available thermal head type color ink jet printer, a PPC
It was visually confirmed whether or not bleeding between different colors occurred when an image was formed on the paper, and the boundaries between the colors became unclear. At this time, if no bleeding etc. occurs and the boundary of each color is clear,
A case where bleeding or the like occurred and the boundary of each color was unclear was evaluated as x.

[Kogation] As in the evaluation of color bleed, using a thermal jet type color ink jet printer, the operation of filling each color ink up to a specified amount in an ink cartridge and using up all the color inks completely in image formation is performed. Repeated times. At the time of this image formation,
It was visually confirmed whether or not the image was blurred. Thereafter, the cartridge was disassembled and the heater portion of the thermal head was visually checked.

At this time, if no abnormality such as blurring is confirmed during image formation and the heater portion is almost the same as before the image formation and no abnormal condition is observed, the symbol "O" indicates When an abnormality such as blurring was observed, or when any attached matter was observed, the evaluation was evaluated as x.

[Storability] As in the evaluation of color bleed and kogation, each color ink was filled up to a specified amount in an ink cartridge using a thermal jet type color ink jet printer, and left at room temperature for 3 months. Saved. Thereafter, the same ordinary image formation as before storage was performed using the ink cartridge.
Then, the following three points were evaluated.

1. Image forming operation The image forming operation was compared before and after storing the color ink. At this time, x indicates that the color ink could not be ejected from the head and the image could not be formed, x indicates that the image could be formed temporarily, but the image formed after forming the image to a certain degree was blurred, and was as good as before storage. A case where a good image was formed was evaluated as ○.

[0135] 2. After completing the image forming operation after storing the heater in the thermal head, the cartridge was disassembled and the heater portion of the thermal head was visually checked similarly to the evaluation of kogation. At this time, the case where the heater portion was almost the same as before the image formation and no abnormal state was observed was evaluated as ○, and the case where any attached matter was observed was evaluated as ×.

[0136] 3. State of Ink After the image forming operation after storage was completed, the state of the color ink itself was visually checked. At this time, the case where no coagulation or precipitation occurred as before storage was evaluated as ○, and the case where any aggregate was generated was evaluated as x.

By summing up the above three evaluations,
The storage stability of the color ink was evaluated. That is, when all the three evaluations were ○, the evaluation was ○, when there was even one of the three evaluations, the evaluation was △, and when there was even one of the three evaluations, the evaluation was x. .

Example 1 In this example, as an ink set according to the present invention, a black ink having the composition shown in Table 1 and cyan, magenta and yellow color inks were prepared, and these ink sets were used. To form an image.

That is, carbon black MA7 (manufactured by Mitsubishi Chemical) is used as a black pigment, styrene-acrylic acid copolymer is used as a dispersant, polyurethane emulsion is used as a binder, and pure water (ion-exchanged water) is used as a solvent. Using 2-pyrrolidone, diethylene glycol monobutyl ether, trimethylolpropane, and 2-propanol as other water-soluble organic solvents, these were blended to have the contents shown in Table 1, and the black ink according to the present invention was obtained. (1) was prepared. The pH of this black ink (1) was about 8, indicating weak alkaline.

Next, the preparation of the color ink will be described. First, in preparing the cyan color ink,
Direct Blue 199 (manufactured by Daiwa Kasei) and Acid Blue 9 (manufactured by Daiwa Kasei) were used as the water-soluble dyes, and a betaine structure was introduced into each of these dyes by a conventionally known method (see the above-described embodiment). As a water-soluble dye having a betaine structure used in the present invention, Direct Blue 199 betaine derivative and Acid Blue 9 betaine derivative were obtained.

Similarly, in preparing a magenta color ink, Acid Red 52 (manufactured by Daiwa Kasei) and Reactive Red 180 (manufactured by Clariant) were used as water-soluble dyes, and each of these dyes was subjected to a conventionally known method. Acid Red 52 betaine derivative and Reactivelet 1 as a water-soluble dye having a betaine structure used in the present invention by introducing a betaine structure
An 80 betaine derivative was obtained.

Similarly, in preparing a yellow color ink, Acid Yellow 23 was used as a water-soluble dye.
A betaine structure was introduced by a conventionally known method using (manufactured by Daiwa Kasei) to obtain an acid yellow 23 betaine derivative as a water-soluble dye having a betaine structure used in the present invention.

In addition to the above betaine derivatives, laurylamine acetate is used as a cationic surfactant, pure water (ion-exchanged water) is used as a solvent, and 2-pyrrolidone and trimethylolpropane are used as other water-soluble organic solvents. ,
And 1,5-pentanediol or diethylene glycol were blended so as to have the contents shown in Table 2 to prepare cyan, magenta, and yellow color inks (1). The pH of each of these color inks (1) was about 5 to 6, and all showed weak acidity.

[0144]

[Table 1]

[0145]

[Table 2]

In Table 2 and Tables 4 and 5 below, the betaine derivative of the water-soluble dye is simply abbreviated as “(water-soluble dye name) derivative”.
Further, the water-soluble dyes described in Tables 6 and 7 below do not have a description of “derivative”, but this indicates that the water-soluble dye is an intact water-soluble dye that does not introduce a betaine structure. And is different from the above betaine derivative.

The black ink (1) was filled in a head-integrated ink cartridge in the above-described thermal head type color ink jet printer. Each of the cyan, magenta, and yellow color inks (1) was filled in a three-color integrated head / integrated head ink cartridge of the color inkjet printer until a specified amount was reached.

By using the above-mentioned ink cartridge and using a generally used PPC paper as a recording material,
Image formation was performed until the above color inks (1) were completely consumed. Further thereafter, each of the above color inks (1)
Was filled into the ink cartridge until the specified amount was reached, and image formation was performed again until the respective color inks (1) were completely consumed.

Thereafter, the image formed on the paper was visually checked to evaluate the color bleed. After completion of image formation, the ink cartridge was disassembled, and the heater portion of the ink head was visually observed to evaluate kogation. The evaluation results are shown in Table 8 below.

Further, after storing each of the color inks (1) in the ink cartridges for 3 months in a state of being filled, an image was formed in the same manner as described above. The storage performance was evaluated by comparing the image forming operation after storage and the formed image before storage. The evaluation results are shown in Table 8 below.

Example 2 In this example, as an ink set according to the present invention, a black ink having the composition shown in Table 3 and each color ink of cyan, magenta, and yellow were prepared, and these ink sets were used. To form an image.

A commercially available self-dispersible carbon black “Cabjet” (trade name, manufactured by Cabot) is used as a black pigment, a polyurethane emulsion is used as a binder, pure water (ion-exchanged water) and another water Using 2-pyrrolidone, diethylene glycol monobutyl ether, polyethyleneimine, and 2-propanol as the reactive organic solvent, these were blended so as to have the contents shown in Table 3, to prepare the black ink (2) according to the present invention. did. PH of this black ink (2)
Was about 8, indicating weak alkalinity.

Next, the preparation of the color ink will be described. First, in preparing the cyan color ink,
Acid Blue 7 (manufactured by Daiwa Kasei) as a water-soluble dye
Using a conventionally known method to introduce a betaine structure,
An acid blue 7 betaine derivative was obtained as a water-soluble dye having a betaine structure used in the present invention.

Similarly, in preparing a magenta color ink, Acid Red 52 (manufactured by Daiwa Kasei) and Reactive Red 58 (manufactured by Daiwa Kasei) are used as water-soluble dyes, and each of these dyes is conventionally known. A betaine structure was introduced by the method to obtain a betaine derivative of Acid Red 52 and a betaine derivative of Reactivelet 58 as a water-soluble dye having a betaine structure used in the present invention.

Similarly, in preparing a yellow color ink, Acid Yellow 23 was used as a water-soluble dye.
A betaine structure was introduced by a conventionally known method using (manufactured by Daiwa Kasei) to obtain an acid yellow 23 betaine derivative as a water-soluble dye having a betaine structure used in the present invention.

In addition to the above betaine derivatives, laurylamine acetate was used as a cationic surfactant, pure water (ion-exchanged water) was used as a solvent, and polyethyleneimine and 2-pyrrolidone were used as other water-soluble organic solvents. And 1,5-pentanediol or diethylene glycol were blended so as to have the contents shown in Table 4 to prepare cyan, magenta, and yellow color inks (2). The pH of each of these color inks (2) was about 5 to 6, and all showed weak acidity.

[0157]

[Table 3]

[0158]

[Table 4]

The black ink (2) and each of the cyan, magenta, and yellow color inks (2) were filled in the ink cartridge of the above-described thermal head type color ink jet printer in the same manner as in Example 1. Then, image formation was performed in the same manner as in Example 1, and color bleeding, kogation, and storage stability were evaluated. The evaluation results are shown in Table 8 below.

Comparative Example 1 A black ink (1) was prepared in the same manner as in Example 1 (see Table 1). Further, in the same manner as in Example 1 except that sodium lauryl sulfate was used as an anionic surfactant without using a cationic surfactant which is an essential component of the color ink according to the present invention, cyan and magenta were used. , And yellow comparative color inks (1) were prepared. The pH of each of these comparative color inks (1) was about 8 to 9, and all showed weak alkalinity. Table 5 shows the content of each component in each comparative color ink (1).

[0161]

[Table 5]

Using the black ink (1) and the comparative color ink (1), an image was formed in the same manner as in Example 1, and color bleed, kogation, and storability were evaluated. The evaluation results are shown in Table 8 below.

Comparative Example 2 A black ink (1) was prepared in the same manner as in Example 1 (see Table 1). Further, in the same manner as in Example 1 except that the water-soluble dye having a betaine structure, which is an essential component of the color ink according to the present invention, is not used, each of the comparative color inks of cyan, magenta, and yellow (2 ) Was prepared. The pH of each of these comparative color inks (2) was about 5 to 6, and all showed weak acidity. Table 6 shows the content of each component in each comparative color ink (2). Table 6 and Table 7 below.
Are the same as the water-soluble dyes before the introduction of the betaine structure in Example 1 as described above.

[0164]

[Table 6]

Using the above black ink (1) and comparative color ink (2), an image was formed in the same manner as in Example 1, and color bleeding, kogation, and storability were evaluated. The evaluation results are shown in Table 8 below.

Comparative Example 3 A black ink (1) was prepared in the same manner as in Example 1 (see Table 1). Further, in the same manner as in Example 1 except that magnesium nitrate or calcium nitrate as a polyvalent metal salt (cation salt), which is a component not added to the color ink of the present invention to induce kogation, was used. , Cyan, magenta, and yellow comparative color inks (3) were prepared.
The pH of each of these comparative color inks (3) was about 6 to 7, and all showed weak acidity. Each comparative color ink (3)
Is shown in Table 7.

[0167]

[Table 7]

Using the above black ink (1) and comparative color ink (3), an image was formed in the same manner as in Example 1, and color bleeding, kogation, and storage stability were evaluated. The evaluation results are shown in Table 8 below.

[0169]

[Table 8]

As is evident from the results in Table 8, when the ink set for inkjet according to the present invention is used, it is possible to prevent color bleeding, prevent kogation, and improve storage stability. (Examples 1 and 2). However, unless a betaine structure was introduced into the water-soluble dye, the storage stability was lowered and the occurrence of kogation could not be prevented (Comparative Examples 2.3). In particular, when a cation salt was used, the storage stability was significantly deteriorated (Comparative Example 2).

On the other hand, if a betaine structure is introduced into the water-soluble dye, the prevention of kogation and the improvement of the storage stability can be sufficiently achieved (Examples 1, 2 and Comparative Example 1), but the cationic surface activity is improved. Without the use of the agent, the occurrence of color bleed could not be prevented, and the image quality was significantly deteriorated (Comparative Example 1).

As described above, in the ink-jet ink according to the present invention, since the aqueous solvent contains the water-soluble dye having a betaine structure and the cationic surfactant, color bleed prevention and kogation are prevented. Prevention,
An excellent ink that can achieve all of the improvement in storage stability can be obtained.

[0173]

As described above, the ink-jet ink according to the present invention has a constitution comprising a water-soluble dye having a betaine structure and a cationic surfactant in an aqueous solvent.

According to the above configuration, since the water-soluble dye has a betaine structure, the ink is in a very stable state even under acidic conditions, the storage stability is improved, and in addition, the ink is not susceptible to metal salts or gelation. Since almost no related components are contained, it is possible to prevent the occurrence of kogation due to heating at the nozzle. Further, in the above configuration, when used in combination with an alkaline ink, there is an effect that color bleeding can also be suppressed.

In the ink-jet ink described above,
Preferably, the cationic surfactant is an amine acetate.

According to the above configuration, by using the acetate of amines, a sufficient effect of adjusting the surface tension of the ink can be obtained, and the occurrence of kogation can be more reliably avoided. To play.

In the ink-jet ink described above,
It is preferable that the pH is adjusted within a range of 4 or more and less than 7.

According to the above configuration, if the pH of the ink is in the weakly acidic state, the effect of suppressing the color bleed can be further improved by combining it with an alkaline ink.

In order to solve the above-mentioned problems, an ink-jet ink set according to the present invention comprises a color ink comprising a water-soluble dye having a betaine structure and a cationic surfactant in an aqueous solvent; The solvent contains a black pigment and a black ink showing alkalinity.

According to the above configuration, first, the black ink is in a state where the black pigment is stably dispersed (suspended) under the alkaline condition, while the color ink is the aqueous solution having the betaine structure under the acidic condition. Sex dye is in a stable state. In addition, each of these inks hardly contains metal salts and components related to gelation. for that reason,
Even when these inks are heated by the nozzles, the effect of suppressing the occurrence of kogation is exhibited.

When the black ink and other color inks are associated on the recording material, the alkaline black ink and the acidic color ink cause an acid-alkali reaction, which triggers the black pigment Settles easily and quickly on the recording material. As a result, the effect of suppressing the occurrence of color bleed in the black pigment is also exerted.

Further, since the black ink and the color ink are in a very stable state, even if the frequency of image formation is low and the time between image forming operations is long, the black pigment and the water There is no coagulation or precipitation of the dye. Therefore, an effect that excellent preservability can be exhibited is also exhibited.

The pH of the color ink is in the range of 4 to less than 7, and the pH of the black ink is 7
It is preferable to be within the range of more than 10 and less than 10.

According to the above configuration, since the pH of both the black ink and the color ink is adjusted to a preferable range, there is an effect that the acid-alkali reaction can be more effectively generated. .

In the above ink set for inkjet, the black pigment contained in the black ink is preferably an anionic pigment.

According to the above arrangement, since the black pigment is an anionic pigment, the dispersibility of the black pigment in the black ink is further improved, and the storage stability of the black ink can be further improved. In addition, since the anionic pigment easily aggregates and precipitates due to the collapse of the ionic charge balance due to the acid-alkali reaction of the black ink-color ink, the color bleeding of the black ink in color image formation is effectively suppressed. It also has the effect of being able to do so.

In the above ink set for ink jet, the black ink contains at least one of a dispersant for dispersing the black pigment and a binder for fixing the black pigment on the recording material during image formation. Is preferred.

According to the above configuration, the dispersibility of the black pigment is further improved by the presence of the dispersant. As a result, it is possible to improve the storability of the black ink and to further suppress the occurrence of kogation. In addition, since the fixing of the black pigment becomes quicker and more reliable due to the presence of the binder, there is an effect that generation of color bleed can be further suppressed. In particular, when both the dispersant and the binder are contained, the effects of suppressing kogation and color bleed can be further improved, and the effect of further improving the storage stability can be obtained.

The ink jet recording method according to the present invention uses the above ink set for ink jet,
This is a method of forming an image on a recording material.

According to the above method, when a black ink stable under alkaline conditions and a color ink stable under acidic conditions associate on a recording material, the black ink and the color ink undergo an acid-alkali reaction. As a result, the balance of the ionic charges of the black ink is reduced. Therefore, the uniformly dispersed black pigment precipitates (or solidifies) very easily, and the black pigment precipitates easily and quickly on the recording material. As a result, the black pigment is fixed without causing color bleed, and the effect of suppressing color bleed is achieved.

Further, unlike the conventional case, since it does not contain a polyvalent metal salt or a component for gelling, the occurrence of kogation can be suppressed, and the black ink and the color ink can be kept in a very stable state. As a result, there is an effect that storage stability can be improved.

Further, since it is not necessary to employ a configuration in which the polyvalent metal salt and the ink are ejected separately, it is possible to avoid the complexity of the configuration of the ink head, reduce the cost, and maintain the ink head. Is also simplified.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaru Nakamura 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroaki Nakaya 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) in CAP Co., Ltd. (reference)

Claims (8)

[Claims] 1. An ink-jet ink comprising a water-soluble dye having a betaine structure and a cationic surfactant in an aqueous solvent. 2. The ink according to claim 1, wherein the cationic surfactant is an acetate of an amine. 3. The ink-jet ink according to claim 1, wherein the pH is adjusted within a range of 4 or more and less than 7. 4. A color ink comprising a water-soluble dye having a betaine structure and a cationic surfactant in an aqueous solvent, and a black ink containing a black pigment and being alkaline in an aqueous solvent. Ink set for inkjet. 5. The pH of the color ink is in the range of 4 to less than 7, and the pH of the black ink is 7
The ink set for inkjet according to claim 4, wherein the value is within a range of more than 10 and less than 10. 6. The ink set according to claim 4, wherein the black pigment contained in the black ink is an anionic pigment. 7. The black ink contains at least one of a dispersant for dispersing a black pigment and a binder for fixing the black pigment on a recording material during image formation. Item 7. An ink-jet ink set according to Item 4, 5, or 6. 8. An ink jet recording method comprising forming an image on a recording material by using the ink set for ink jet according to any one of claims 4 to 7.