JP2006199744A - Ink jet recording ink, ink set, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink using a monoazo pigment having a high coloring power and a high color development image as a coloring material, sufficient ejection stability when ink is ejected continuously, and further long-term storage stability Provide ink for inkjet recording.
An ink for use in ink jet recording in which ink droplets are ejected from a recording head by the action of thermal energy to form an image on a recording material, the ink comprising at least an aqueous medium, a monoazo pigment, and the above An ink for ink jet recording, wherein the pigment contains a substance that inhibits re-aggregation after being dispersed and broken by the temperature rise of the ink, and the monoazo pigment satisfies a specific condition.
[Selection figure] None

Description

  The present invention relates to ink used in ink jet recording in which ink droplets are ejected from a recording head by the action of thermal energy to record an image on a recording material, an ink set having such ink, and an image forming apparatus using such ink. Furthermore, an ink that achieves both high discharge stability and storage stability of an ink using a pigment having a low thermal stability as a coloring material, and achieves high color development when image recording is performed using the ink, and such an ink. The present invention relates to an ink set and an image forming apparatus using the ink.

  Inkjet recording is a printing method in which droplets of ink are ejected and attached to a recording medium such as paper, but printing can be performed at high speed with a high-resolution and high-quality image using an inexpensive device. In recent years, it has been widely used as a means for easily forming a high-quality color image, and there is an increasing demand for a higher-quality color image.

  On the other hand, various pigments are used as colorants for inkjet inks. In particular, azo pigments are excellent in coloring power and advantageous in terms of cost. For example, two types of yellow monoazo pigments having different structures are produced at the time of pigment synthesis, and a mixed yellow monoazo pigment composition is used as a coloring material to improve weather resistance and heat resistance (for example, Patent Document 1). In addition, a proposal has been made to improve storage stability by using a monoazo pigment having a purity of 90% or more (see, for example, Patent Document 2).

  Also, since pigments are not soluble in water unlike dyes, it is necessary to disperse pigments in water in the form of fine particles, but it is very difficult to keep this dispersed state stable. Therefore, various techniques for stably dispersing the pigment in water have been proposed. Examples that have been studied in the past include a method using a dispersible surfactant (see, for example, Patent Document 3), a microencapsulated dye in which a pigment is dispersed in a water-insoluble solvent and this is emulsified in water with a dispersible surfactant. (For example, see Patent Document 4), and a method for coating and dispersing a pigment by a phase inversion emulsification reaction or an acid precipitation method (for example, see Patent Document 5).

  In addition, various proposals have been made for the purpose of improving the reliability (storage stability, ejection stability, etc.) and image quality (fixing property, marker property, etc.) of ink jet ink using pigment ink as a colorant. Yes. In recent years, many proposals have been made to solve the above-mentioned problems by devising the characteristics and amount of water-soluble organic solvents and additives used together with the colorant contained in the ink.

  For example, a proposal for improving ejection performance and preventing clogging of fine ink ejection ports (orifices) provided in the recording head by including a compound having an alkylene oxide in the ink (for example, Patent Document 6). In addition, for the purpose of improving the permeability, a proposal has been made to contain 1,2-alkanediol or glycol monoether in the ink (see, for example, Patent Document 7).

In addition, the dispersibility-imparting group is chemically bonded to the pigment particle surface to improve the dispersibility of the pigment so that it can be dispersed and / or dissolved in water without a dispersant. Proposals have been made to solve the above problems by including 1,2-alkanediol or glycol ether in an ink using a treated pigment (hereinafter sometimes referred to as a surface-treated pigment) (for example, Patent Documents). 8-10).
JP-A-10-158555 JP 2004-123866 A JP-A-1-301760 JP-A-1-170672 Japanese Patent Laid-Open No. 10-140065 JP-A-9-165538 JP 2001-354888 A JP 2002-201388 A JP 2004-143272 A JP 2004-277449 A

  Conventionally, various dispersion forms of pigments used in ink jet recording inks have been proposed as disclosed in Patent Documents 3, 4, and 5. Among them, resin dispersion (including so-called microcapsule pigments in which a pigment is coated with a resin as disclosed in Patent Document 5) is most practically used. The reason is that even after printing, the resin is coated with pigment on the recording medium, so that the image quality (scratch resistance and marker resistance) is excellent, and printing on glossy media etc. In this case, excellent gloss can be obtained.

  In view of this, inks using a monoazo pigment dispersed in a resin as a coloring material were examined in more detail. As a result, it has been confirmed that heat resistance and storage stability are improved by using an azo pigment as described in Patent Documents 1 and 2 as a coloring material. However, as a result of a detailed examination of the stability of ink droplets ejected from the recording head by the action of thermal energy using these inks as color materials, orifice clogging, a problem that has been recognized conventionally, However, if ink is ejected continuously, deposits adhere to the ink flow path and in the vicinity of the ejection port, and the ink flow path in the nozzle is blocked, so that sufficient ejection stability cannot be obtained. It came to confirm the new subject that there might be a case.

  On the other hand, various additives such as those described in Patent Documents 6 to 10 for the purpose of improving various performances of the pigment ink are used when the pigment is ejected from the recording head by the action of thermal energy. The ink flow path is for the purpose of reducing so-called kogation that burns on the heater or for improving the fixability when ink is applied on the recording medium. The problem unique to a specific pigment, such as deposits adhering to the inside and the vicinity of the discharge port, has not yet been recognized.

  Accordingly, the present inventors have studied in detail the above-described deposit generation mechanism, and as a result, the deposit in the ink flow path and in the vicinity of the discharge port is a colorant in the ink when ink droplets are discharged from the recording head. After the monoazo pigment has caused the dispersion failure due to the temperature rise of the ink, the ink droplets are cooled in the ink flow path in the nozzle, so that the pigment that caused the dispersion failure re-aggregates and accumulates. I found out what it was. Therefore, as a result of further investigations for suppressing the deposits, the present inventors can reduce the deposits by adding a substance 1 that inhibits reaggregation to suppress reaggregation of the pigment in the ink. Newly found.

  However, as a new problem, a new problem has been recognized that long-term storage stability is impaired by the addition of substance 1 that inhibits reaggregation.

  Accordingly, an object of the present invention is to provide good ejection stability and storage stability when used in an image forming method in which ink droplets are ejected from a recording head by the action of thermal energy and an image is recorded on a non-recording medium. Furthermore, it is to provide an ink using a monoazo pigment as a colorant capable of obtaining a high-quality image having high color developability and an image forming apparatus using the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have reached the present invention.

  That is, the ink of the present invention is an ink for ink-jet recording used in ink-jet recording in which ink droplets are ejected from a recording head by the action of thermal energy to record an image on a recording material. An ink jet recording comprising: a monoazo pigment and a substance that inhibits re-aggregation after the pigment is dispersed and destroyed by the temperature rise of the ink, and the monoazo pigment satisfies at least one of the following two conditions: Ink.

(1) The surface is treated so that at least one of the functional group represented by the following formula and a salt thereof is chemically bonded to the pigment surface directly or through another atomic group on the surface, without a dispersant. It can be dispersed and / or dissolved in water. (Hereinafter referred to as surface-treated pigment)
(2) An organic group is chemically bonded to the surface and modified, and the organic group is functionally bonded to the surface directly or via another atomic group; It includes a reaction product of a copolymer of an ionic monomer and a hydrophobic monomer. (Hereafter referred to as surface modified pigment)
_{-OM, -COOM, -CO -, -} SO 3 M, -SO 2 NH 2, -RSO 2 M, -PO 3 HM, -PO 3 M 2, -SO 2 NHCOR, -NH 3, -NR 3
(In the formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium, and R represents an alkyl group having 1 to 12 carbon atoms, a phenyl group or a naphthyl group, an alkylene group having 1 to 12 carbon atoms, a phenylene group, or Represents a naphthylene group.)
Moreover, the following are mentioned as a preferable form of this invention. In the above configuration, the monoazo pigment contained in the ink is preferably a pigment represented by the following formula (1).

  Formula (1)

(R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ in the above formula are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, C1-C3 alkoxyl group, halogen atom, nitro group, sulfo group or alkaline earth metal salt thereof, N-phenylaminosulfonyl group, carboxyl group or alkaline earth metal salt thereof, carboamide group, N-phenylcarbamoyl Group, ureylene group, iminodicarbonyl group or carboxylic acid ester group).

  Further, as a preferable form, the treated or modified monoazo pigment is C.I. I. Pigment Yellow 74 is preferable, and the substance that inhibits reaggregation is at least one selected from nonionic surfactants, anionic surfactants, 1,2-alkanediols, and glycol monoalkyl ethers. Can be mentioned.

  The present invention also relates to an ink jet recording ink comprising an aqueous medium, a monoazo pigment as a coloring material, and a substance that inhibits re-aggregation after the pigment is dispersed and broken by the temperature rise of the ink. Provides an ink set comprising an inkjet recording ink having at least one of a surface-treated pigment and a surface-modified pigment, and at least one inkjet recording ink having a hue different from that of the ink.

  The present invention also relates to an ink jet recording ink comprising an aqueous medium, a monoazo pigment as a coloring material, and a substance that inhibits re-aggregation after the pigment is dispersed and broken by the temperature rise of the ink. Inkjet recording ink, which is at least one of a surface-treated pigment and a surface-modified pigment, and at least one inkjet recording ink having a hue different from that of the ink are ejected from the recording head by the action of thermal energy, and the target is covered. An image forming apparatus including a step of forming an image on a recording medium is provided.

  By using the pigment ink described in the present case, ink droplets are ejected from the recording head by the action of thermal energy, and ink is continuously ejected when used in an image forming method for recording an image on a recording medium. In addition, it is possible to solve a problem inherent to pigments with low thermal stability, typified by azo pigments, in which deposits adhere in the ink flow path and in the vicinity of the discharge port, and block the ink flow path in the nozzle. Furthermore, by using a surface-treated pigment or a surface-modified pigment, it is possible to achieve both storage stability.

  As a result, good ejection stability and storage stability can be obtained, and a high-quality image having higher color development can be obtained.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments.

  First, when a monoazo pigment is used as an ink colorant used in a recording method in which ink droplets are ejected from a recording head by the action of thermal energy, it occurs in the ink flow path and in the vicinity of the ejection port, which degrades ejection stability. The deposit generation mechanism will be described in detail.

(Mechanism of sediment generation)
1A to 1H are cross-sectional views for explaining the operation of an ink ejection head to which the ink ejection method of the present invention is applied. FIG. 3 (a) shows a state where film-like bubbles are generated on the heater 1, (b) after about 1 μsec, (c) after about 2.5 μsec, (d) after about 3 μsec, (E) shows the state after about 4 μs, (f) after about 4.5 μs, (g) after about 6 μs, and (h) after about 9 μs, respectively. In addition, the part which gave the horizontal direction in (a)-(h) has shown the orifice plate or the flow-path wall.

  First, as shown in (a), bubbles 6 are generated in the ink flow path 2 on the heater 1 with energization of the heater 1 based on a recording signal or the like. At this time, the temperature of the ink around the heater 1 is raised to about 200 ° C., and in the portion where the temperature rises, the dispersion of the pigment dispersion occurs, and the functional group from the pigment or the polymer with the functional group is peeled off, Phenomena such as fragmentation of the pigment and further change to a state dissolved in the ink occur. Thereafter, as shown in (b) and (c) in about 2.5 μs, the bubble 6 rapidly expands and grows, and accordingly, the ink whose temperature has risen is cooled.

  The pigment from which the functional group or the polymer with the functional group is peeled, the pigment that has been fragmented, and the pigment dissolved in the ink are adsorbed by the polymer with the functional group or the functional group necessary for maintaining the dispersion stability. Since the part which shows the hydrophobicity which is not exposed is in the state exposed in the ink, the state cannot be maintained. Therefore, these pigments in an unstable state reaggregate as the temperature of the ink that has increased in temperature advances, and some of the pigments that precipitate in the ink also appear. Some of the pigment re-aggregates 4 thus deposited are discharged from the ink outlet 5 in the form of being contained in the ink droplets 5 from the discharge ports 3, but some of them remain in the ink passage 2. , Adheres to the channel wall. By repeating the ink ejection as shown in (a) to (h), it is presumed that the re-aggregate 4 deposited in the ink accumulates on the channel wall.

  Next, the inclusion of a substance that inhibits re-aggregation after the monoazo pigment contained in the ink is dispersed and destroyed by the temperature rise of the ink suppresses the generation of deposits, resulting in improved ejection characteristics. Explain why.

(Effects of substances that inhibit reaggregation)
The substance that inhibits reaggregation of the present invention inhibits the phenomenon that the pigment is reaggregated due to the exposed portion of the pigment surface after the pigment dispersion is dispersed and destroyed by the thermal energy received during ejection. It means the substance to do. The reason why generation of deposits can be suppressed by the above substances is described below.

  FIG. 2 shows changes in the state of the pigment dispersion existing in the vicinity of the heater when ink containing a substance that inhibits reaggregation is ejected by the ink ejection method shown in FIG. 2A shows a state before energization of the heater based on a recording signal or the like, and FIG. 2B shows a state until energization of the heater is started and a film-like bubble is generated on the heater. FIG. 2C shows a state until ink suitability is discharged as the bubble grows.

  First, when the heater temperature rises as the heater is energized, and the temperature of the ink in the ink flow path rises, the pigment dispersion in that portion causes dispersion failure as described above, and the functional group from the pigment 7 Alternatively, phenomena such as peeling of the polymer 8 from the functional group, fragmentation of the pigment 7, and a change to a state dissolved in the ink occur. After that, the substance 9 that inhibits reaggregation coordinates to the part where the functional group or the polymer 8 with the functional group is peeled off or the part where the pigment surface is exposed due to fragmentation (see FIG. 2B).

  Thereafter, as the bubble grows, the temperature of the ink decreases, and re-aggregation of the pigment 7 starts. However, since the substance 9 that inhibits re-aggregation is coordinated at a site that becomes unstable due to the temperature decrease, re-aggregation occurs. It is thought that the precipitation in the ink due to is reduced (see FIG. 2C).

  However, on the other hand, when a substance that inhibits reaggregation is contained in the ink, it is considered that the substance that inhibits reagglomeration tries to coordinate with the pigment to the pigment. As a result, the dispersant is peeled off from the pigment, and a substance that inhibits reaggregation is coordinated instead. However, even if the substance that inhibits reaggregation has a high ability to coordinate with the pigment, it is considered that the ability to maintain a dispersion-stable state for a long time is low, so that long-term storage stability is impaired.

  Therefore, the present inventors have conducted detailed studies on the colorant contained in the ink in order to provide an ink jet recording ink that suppresses the generation of deposits and has excellent long-term storage stability. Even if a substance that inhibits re-aggregation for the purpose of suppressing the generation of deposits is contained in the ink by using a surface-treated pigment or surface-modified pigment that does not cause the removal of the dispersant as the monoazo pigment. In addition, it has become possible to propose an ink having excellent long-term storage stability.

  Next, each component constituting the ink according to the present invention will be described, and the present invention will be described in more detail.

(Substance that inhibits reaggregation)
The substance that inhibits reaggregation is preferably at least one selected from nonionic surfactants, anionic surfactants, 1,2-alkanediols, and glycol monoalkyl ethers. Nonionic surfactants include polyoxyethylene glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbit fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene polyoxy Examples include propylene alkyl ethers, polyoxyethylene alkyl aryl ethers, and acetylene glycol surfactants.

  Examples of the anionic surfactant include alkyl sulfates, alkylaryl sulfates, polyoxyethylene alkyl ether sulfates, alkyl sulfoacetates, fatty acid salts, alkylaryl carboxylates, and polyoxyethylene alkyl ether carboxylates. .

  Examples of the 1,2-alkanediol include 1,2-alkanediols having 5 or more carbon atoms, and examples of the glycol monoalkyl ether include ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and triethylene glycol monobutyl ether. .

  In particular, acetylene glycol surfactants and 1,2-alkanediol are preferably used.

  The content of the substance is not particularly limited as long as the effect of the present invention is expressed, but is preferably 10% by weight or less. If it exceeds 10% by weight, the storage stability of the ink may decrease, or the ejection stability may decrease due to an increase in viscosity.

(Pigment)
As the monoazo pigment used in the present invention, a known one or a new one can be used. Among these, monoazo pigments represented by the following formula (1) are preferable.

  Formula (1)

  Specifically, C.I. I. Pigment Yellow: 1, 2, 3, 5, 6, 49, 65, 73, 74, 75, 97, 98, 111, 116, 130, 61, 62: 1, 133, 168, 169, C.I. I. Pigment Orange 1 and the like. Furthermore, C.I. I. It is preferable to use Pigment Yellow 74. Furthermore, the pigment purity is preferably 90% or more. If the purity is less than 90%, if the pigment contains a large amount of residual diazo component, residual couple component, side reaction products generated during synthesis, decomposition products, etc., these organic impurities may be contained in the inkjet ink over time. This is because crystal precipitation may impair the ink-jet ink properties, such as clogging the nozzles of the ink-jet ink. More preferably, the pigment purity is 90% or more, preferably 93% or more, more preferably 95% or more.

  In the present invention, the amount of pigment added in the ink is preferably in the range of 0.1 to 15%, particularly 1 to 10% on the mass basis with respect to the total amount of the ink. By setting it within this range, the pigment dispersion can maintain a sufficiently dispersed state when it is contained in the ink.

(Surface treatment pigment)
The surface-treated pigment used in the present invention is surface-treated so that at least one of the functional group represented by the following formula and the salt thereof is directly or indirectly bonded to the pigment surface and dispersed in water without a dispersant. And / or those which can be dissolved.
_{-OM, -COOM, -CO -, -} SO 3 M, -SO 2 NH 2, -RSO 2 M, -PO 3 HM, -PO 3 M 2, -SO 2 NHCOR, -NH 3, -NR 3
(In the formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium, and R has an alkyl group having 1 to 12 carbon atoms, a phenyl group which may have a substituent, or a substituent. A naphthyl group which may have a substituent, a alkylene group having 1 to 12 carbon atoms, a phenylene group which may have a substituent or a naphthylene group which may have a substituent.

  The functional group or salt thereof bonded to one pigment particle may be single or plural. The type and degree of the functional group bonded or the salt thereof may be appropriately determined in consideration of the dispersion stability in the water-based ink, the color density, the drying property on the front surface of the inkjet head, and the like. In the surface-treated pigment contained in the water-based ink of the present invention, the functional group or a salt thereof may be present at least on the particle surface, and may be contained inside the particle.

Further, as the surface-treated pigment, -SO ₃ M and / or -RSO ₂ M (M is a counter ion, hydrogen ion, alkali metal ion, ammonium ion, or A solvent in which the pigment is surface-treated so as to chemically bond, that is, the pigment has no active protons, no reactivity with sulfonic acid, and the pigment is insoluble or hardly soluble In which the pigment is dispersed and then surface-treated so that —SO ₃ M and / or —RSO ₂ M are chemically bonded to the particle surface by amidosulfuric acid or a complex of sulfur trioxide and tertiary amine, It is preferable that it can be dispersed and / or dissolved.

  Various known surface treatment means can be applied as the surface treatment means for grafting the functional group or a salt thereof directly on the surface of the pigment particle or via a polyvalent group.

  For example, means for treating a commercially available oxidized carbon black with ozone or a sodium hypochlorite solution to further oxidize the carbon black to make the surface more hydrophilic (for example, JP-A-7-258578, JP-A-H10-238707). 8-3498, JP-A-10-120958, JP-A-10-195331, JP-A-10-237349), means for treating carbon black with 3-amino-N-alkyl-substituted pyridium bromide ( For example, JP-A-10-195360 and JP-A-10-330665), an organic pigment is dispersed in a solvent in which the organic pigment is insoluble or hardly soluble, and a sulfone group is introduced onto the surface of the pigment particles by a sulfonating agent. Means (for example, JP-A-8-283596, JP-A-10-110110, JP-A-10-1101 No. 1), means for dispersing an organic pigment in a basic solvent that forms a complex with sulfur trioxide, treating the surface of the organic pigment by adding sulfur trioxide, and introducing a sulfone group or a sulfonamino group (For example, Unexamined-Japanese-Patent No. 10-110114) etc. are mentioned, However, The preparation means for the surface treatment pigment used with the water-based ink of this invention is not limited to these means.

  The particle diameter of the surface-treated pigment is preferably 5 μm or less from the viewpoint of dispersion stability, more preferably 0.3 μm or less (300 nm or less), and still more preferably 0.01 to 0.15 μm (10 to 150 nm). is there.

  As a dispersion method, a dispersion method such as a method using ultrasonic dispersion, a bead mill, a sand mill, a roll mill, or the like can be used.

  By using the surface-treated pigment having the functional group or salt thereof as described above as a coloring component, a water-based ink suitable for inkjet printing having excellent storage stability can be obtained. Moreover, the above-mentioned coloring component can be used suitably also for ink for writing instruments.

(Surface modification pigment)
Taking carbon black as an example, a method for modifying the pigment by chemically bonding an organic group to the pigment particle surface will be described. In the present invention, first, a functional group on the surface of the pigment particle or a functional group is introduced on the surface of the pigment particle, and a copolymer composed of an ionic monomer and a hydrophobic monomer is bonded to these functional groups, and the above-mentioned copolymer is bonded. Any method can be used as long as it is a method of chemically bonding the polymer to the surface of the pigment particles, and there is no particular limitation. As such a method, the following method etc. can be used, for example.

  A method in which polyethyleneimine or the like is introduced on the surface of pigment particles such as carbon black, and a copolymer composed of an ionic monomer and a hydrophobic monomer having an amino group at its terminal functional group is bonded by a diazonium reaction, carbon Methods such as a method of bonding a copolymer having an amino group and a carboxyl group in the molecule to the surface of pigment particles such as black by a diazonium reaction can be used. As the other example, the most typical example is disclosed in WO01 / 51566A1.

In the above method, for example, when an anionic copolymer is chemically bonded to the surface of the carbon black particles, the following three steps are included.
1st process; The process of adding an aminophenyl (2-sulfoethyl) sulfone group (APSES) to carbon black by a diazonium reaction.
Second step: A step of adding polyethyleneimine or pentaethylenehexamine (PEHA) to carbon black subjected to APSES treatment.
Third step: A step of attaching a copolymer of a hydrophobic monomer and an ionic monomer having a carboxyl group.

  In the second step, a phenyl (2-sulfoethyl) sulfone group chemically bonded to the carbon black surface in the first step is reacted with an amino group such as polyethyleneimine or pentaethylenehexamine (PEHA). By doing so, an amino group as a functional group chemically bonded to the carbon black surface is introduced. In the third step, for example, by reacting a part of the carboxyl group of the ionic monomer portion of the copolymer with an amino group to form an amide bond, the copolymer is formed on the surface of carbon black, APSES. A copolymer can be introduced through an atomic group containing a phenyl (2-sulfoethyl) group that is a residue of the above and a residue of PEHA.

  Further, in the above-described method, for example, when the cationic copolymer is chemically bonded to the surface of the carbon black particles, the following two steps are included.

  First step: A step of adding an aminophenyl (2-sulfoethyl) sulfone group (APSES) to carbon black by a diazonium reaction.

  2nd process; The process of attaching the copolymer of a hydrophobic monomer and a cationic monomer. Through the first step, a sulfone group is introduced as a functional group chemically bonded to the carbon black surface. In the second step, for example, a part of the amino group of the ionic monomer portion of the copolymer is reacted with a sulfone group (nucleophilic substitution), the copolymer is placed on the surface of carbon black, and the APSES A copolymer can be introduced through an atomic group containing a phenyl (2-sulfoethyl) group as a residue.

(Presence of free polymer)
By the way, the surface-modified pigment used in the present invention is a segment containing the copolymer that is not chemically bonded to the pigment surface (hereinafter referred to as a free polymer, and this includes a segment that is physically adsorbed on the pigment surface. Does not exclude the presence in the ink. However, the amount of the free polymer is preferably controlled from the viewpoint of further improving the ink jet characteristics of the aqueous ink according to the present invention. Specifically, based on the total mass of the free polymer and the organic group bonded to the pigment surface, the ratio of the free polymer is less than 2% by mass, particularly less than 1% by mass, more preferably 0.5%. It is preferable to be less than mass%.

  When ink containing a large amount of free polymer is used for ink jet recording, free organic groups adhere to the orifices around the ejection openings of the recording head, resulting in uneven wetting around the ejection openings, resulting in poor ink ejection. There is a problem that the ejection direction bends in a regular manner and the landing point of the ink shifts. In addition, when a large amount of free polymer is present in the ink, the free polymer may be physically adsorbed on the pigment to improve dispersion stability. However, as in the present invention, a reaggregation inhibitor is contained in the ink. In this case, the free polymer is peeled off from the pigment and the dispersion state becomes unstable. As a result, when the ink is stored for a long period of time, the performance may deteriorate. From the above, the effective range of the free polymer for satisfying the ink reliability for long-term storage is the sum of the organic group and the free polymer of the organic group chemically bonded to the pigment particle surface. It is preferable that the ratio to 90% is 90% or more, more preferably 95% or more, and further preferably 98% or more. This value can be obtained by a thermogravimetric analysis method for the sample using a dried solid sample taken out from the ink.

(Aqueous medium)
As an example, ink used in the ink jet recording apparatus according to the present invention will be described.

  Examples of the aqueous medium used in the ink composition according to the present invention include water or a mixed solvent of water and a water-soluble organic solvent. As the water-soluble organic solvent, those having an effect of preventing the reaction solution from drying are particularly preferable. Specifically, for example, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; dimethylformamide Amides such as dimethylacetamide; ketones or ketoalcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene glycol, propylene glycol, butylene glycol, Alkylene groups such as triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol and the like are 2 to 2. Alkylene glycols containing one carbon atom; lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether Lower alkyl ethers of polyhydric alcohols such as; polyhydric alcohols such as trimethylolpropane and trimethylolethane; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, etc. It is done. The above water-soluble organic solvents can be used alone or as a mixture. It is desirable to use deionized water as the water.

  In particular, when 1,2-alkanediol, glycol monoalkyl ether, or acetylene glycol surfactant is used as a substance that inhibits reaggregation, it is stable by using polyethylene glycol having an average molecular weight of 600 or more as a solvent. It is possible to obtain the discharged performance.

  Furthermore, it is preferable to use a solvent exhibiting poor solvent properties for the dispersant. By using this, it is possible to further improve the effect of reducing the phenomenon of deposits adhering in the ink flow path and in the vicinity of the ejection openings. For example, when a styrene / butyl acrylate / acrylic acid copolymer is used as a dispersant, 1,5-pentanediol, 1,6-hexanediol, and 2-pyrrolidone are preferably used.

  Further, in addition to the above components, the ink of the present invention includes a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, a reduction inhibitor, an evaporation accelerator, and a chelating agent as necessary. Various additives such as a water-soluble polymer may be contained.

  For example, as surfactants, fatty acid salts, higher alcohol sulfate esters, liquid fatty oil sulfate esters, alkylallyl sulfonates and other anionic surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, There are nonionic surfactants such as polyoxyethylene sorbitan alkyl esters, acetylene alcohol, and acetylene glycol, and one or more of these can be appropriately selected and used. Among the above-mentioned, acetylene alcohols and acetylene glycols can be preferably used in order to exhibit an effect excellent in permeability to plain paper. The amount used varies depending on the amount of dispersant added, but is preferably 0.01 to 5% by mass relative to the total amount of ink. At this time, the surface tension of the ink at 25 ° C. is preferably 10 mN / m (dyn / cm) or more, more preferably 20 mN / m or more, and the surface tension of 60 mN / m or less. It is preferable to determine the amount to be added. This is because, in the ink jet recording system used in the present invention, it is possible to effectively suppress the occurrence of printing misalignment (deviation of the landing point of ink droplets) due to wetting of the nozzle tip.

  The ink is preferably adjusted to have a desired viscosity and pH in order to obtain good ejection characteristics in the ink jet recording apparatus.

(Ink set)
The color of the ink when the ink set is configured by combining the ink described above with at least one kind of ink having a different color tone from the ink is not particularly limited. I. When the yellow ink using Pigment Yellow 74 is used, the ink having a different hue may be an ink having one color selected from magenta, cyan, red, green, blue, and black. There is no restriction | limiting of the coloring material to be used, A conventionally well-known dye and a pigment can be used.

  Next, an image recording apparatus suitable for recording an image on a recording medium using the ink described above will be described.

(Recording device)
As an apparatus suitable for performing recording using the ink according to the present invention described above, for example, a method in which thermal energy corresponding to a recording signal is applied to ink in a recording head chamber and droplets are generated by the thermal energy. And devices.

  The present invention is used for an ink jet ejection type head, and is also effective as an ink storage container in which the ink is stored or as a filling ink. In particular, the present invention provides an excellent effect in a bubble jet (registered trademark) type recording head and recording apparatus among ink jet recording methods.

  As its typical configuration and principle, for example, those performed using the basic principle disclosed in US Pat. Nos. 4,723,129 and 4,740,796 are preferable. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, the electric circuit arranged corresponding to the sheet or liquid path holding the ink is used. By applying at least one drive signal corresponding to the recording information and giving a rapid temperature rise exceeding the nucleate boiling to the heat conversion body, heat energy is generated in the electrothermal conversion body, and the heat acting surface of the recording head This is effective because the film can be boiled, and as a result, the drive signals can be made to correspond one-to-one and bubbles in the ink can be formed. By the growth and contraction of the bubbles, ink is ejected through the ejection openings to form at least one droplet. It is more preferable that the drive signal has a pulse shape, because the bubble growth and contraction is performed immediately and appropriately, and thus ink discharge with particularly excellent responsiveness can be achieved. As this pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. Further excellent recording can be performed by employing the conditions described in US Pat. No. 4,313,124 of the invention relating to the temperature rise rate of the heat acting surface.

  As the configuration of the recording head, in addition to the combination configuration (linear liquid channel or right-angle liquid channel) of the discharge port, the liquid channel, and the electrothermal transducer as disclosed in each of the above-mentioned specifications, the heat acting part The present invention is also effective for configurations using US Pat. No. 4,558,333 and US Pat. No. 4,459,600, which disclose a configuration in which is disposed in a bending region. In addition, the present invention is also effective for a configuration in which the discharge hole is a discharge portion of the electrothermal transducer when common to a plurality of electrothermal transducers (JP-A No. 123670/93). is there. Furthermore, as a full-line type recording head having a length corresponding to the width of the maximum recording medium that can be recorded by the recording apparatus, the length is set by combining a plurality of recording heads as disclosed in the above specification. Either a satisfying configuration or a single integrated recording head configuration may be used, but the present invention can exhibit the above-described effects more effectively.

  In addition, it is mounted on the main body of the device so that it can be electrically connected to the main body of the device and supplied with ink from the main body of the device. The present invention is also effective when a cartridge type recording head is used. In the present invention, it is preferable to add recovery means for the recording head, preliminary auxiliary means, etc. provided as the configuration of the recording apparatus to be applied, because the effects of the present invention can be further stabilized. . Specific examples thereof include a capping unit for the recording head, a cleaning unit, a pressure or suction unit, an electrothermal converter, a heating element different from this, or a preheating unit using a combination thereof, This is a preliminary ejection mode in which ejection different from recording is performed.

  Hereinafter, although it demonstrates more concretely using an Example, this invention is not limited by the following Example, unless the summary is exceeded.

  In the following description, “%” is based on mass unless otherwise specified.

(Production of surface-treated Yellow pigment)
22 parts of a monoazo pigment (CI Pigment Yellow 74) was mixed with 510 parts of quinoline, and conditions of Eiger Motor Mill M250 type (trade name, manufactured by Eiger Japan Co., Ltd.) with a bead filling rate of 70% and a rotation speed of 5,000 rpm. The mixture of the pigment paste and the solvent, which has been subjected to particle size dispersion for 2 hours, is transferred to an evaporator, heated to 120 ° C. while reducing the pressure to 30 mmHg or less, and the water contained in the system is distilled off as much as possible. The temperature was controlled at 160 ° C. Next, 21 parts of a sulfonated pyridine complex was added as a reactant and reacted for 4 hours. After completion of the reaction, the mixture was washed several times with excess quinoline, poured into water, and filtered to obtain a surface-treated yellow pigment.

  20 parts of the surface-treated yellow pigment obtained by the above operation, 5 parts of a sodium hydroxide aqueous solution (10% by weight) as a neutralizing agent, and 75 parts of ion-exchanged water were mixed to prepare a paint shaker (bead filling rate = 60). %; Media diameter = 1.7 mm) was used until the average particle diameter (secondary particle diameter) of the pigment became 110 nm to obtain a dispersion of a surface-treated yellow pigment.

(Preparation of surface-modified yellow pigment)
A monoazo pigment (CI Pigment Yellow 74) 500 g, aminophenyl (2-sulfoethyl) sulfone (APSES) 45 g, and distilled water 900 g were charged into the reactor, kept at 55 ° C., and stirred at a rotational speed of 300 RPM for 20 minutes. Thereafter, 40 g of 25% sodium nitrite was added dropwise for 15 minutes, and 50 g of distilled water was further added. Then, it was made to react for 2 hours, keeping at 60 degreeC. And the obtained reaction material was taken out, diluting with distilled water, and it adjusted to the density | concentration from which solid content will be 15%. Thereafter, a centrifugal separation treatment and a purification treatment for removing impurities were performed. This prepared dispersion became a dispersion in which the functional group of APSES was bonded to the pigment. This dispersion is designated as A1.

  Next, in order to determine the number of moles of functional groups bonded to the pigment in the dispersion A1, Na ions in the dispersion are measured with a probe-type sodium electrode, and the obtained value is converted per pigment powder. Thus, the number of moles of the functional group bonded to the pigment was determined. Next, the previously prepared dispersion A1 having a solid content of 15% was dropped into a pentaethylenehexamine (PEHA) solution. At this time, the PEHA solution was kept at room temperature with vigorous stirring, and the dispersion A1 was added dropwise over 1 hour. The PEHA concentration at this time was 2 to 3 times the molar number of Na ions measured previously, and the solution amount was the same as that of the dispersion A1. Furthermore, this mixture was stirred for 48 hours, and then a purification treatment for removing impurities was performed. Finally, a dispersion having a solid content of 10% to which pentaethylenehexamine (PEHA) was bound was obtained. This dispersion is designated as B1.

  Next, a styrene-acrylic acid resin as a copolymer was prepared as follows. First, 190 g of a styrene-acrylic acid resin having a weight average molecular weight of 15,000, an acid value of 140, and a polydispersity Mw / Mn (weight average molecular weight Mw, number average molecular weight Mn) of 1.5 was weighed, and 1,800 g was measured. Of distilled water was added, NaOH necessary for neutralizing the resin was added, and the mixture was stirred and dissolved to prepare a styrene-acrylic acid resin aqueous solution.

  Next, 500 g of the previously prepared dispersion B1 having a solid content of 10% was dropped into the styrene-acrylic acid resin aqueous solution while stirring. Next, the mixture of B1 and a styrene-acrylic acid resin aqueous solution was transferred to a Pyrex (registered trademark) evaporating dish, heated at 150 ° C. for 15 hours to evaporate, and then the evaporated and dried product was cooled to room temperature.

  Subsequently, this evaporated and dried product was dispersed in NaOH-added distilled water adjusted to pH = 9.0 using a disperser, and 1.0 M NaOH was further added with stirring to adjust the pH to 10-11. did. Thereafter, desalting, purification to remove impurities, and removal of coarse particles are performed, and further, a dispersion of surface-modified Yellow pigment is obtained by removing excess resin not chemically bonded to the pigment by centrifugation. It was. The obtained physical properties of the surface-modified yellow pigment dispersion were 10% solids, pH = 10.1, and an average particle size of 130 nm.

  Next, a specific method for measuring the ratio of chemically bonded organic groups in the surface-modified pigment will be described. First, the pigment dispersion is salted out or coagulated. Specifically, when the organic group has an anionic group, an acid such as hydrochloric acid or sulfuric acid is added, and when the organic group has a cationic group, By adding an alkali such as sodium hydroxide, the pigment and organic groups in the ink can be precipitated by salting out. In some cases, the pigment in the pigment dispersion can be precipitated by coagulating by adding an excessive amount of alcohol. Can be precipitated.

  In addition, as a method for precipitating the pigment in the pigment dispersion, it is possible to effectively take out the pigment in the pigment dispersion by combining salting out or coagulation or performing centrifugation. The precipitate containing the pigment obtained by the above operation is collected by filtration, the filtered solid content is thoroughly washed with pure water, and the washed pigment-containing solid is dried in an oven at 60 ° C. overnight. I let you. Then, the obtained pigment-containing dried product was washed with tetrahydrofuran (THF), which is a good solvent for the segment containing the copolymer. This pigment-containing dried product was washed with THF three times, and then the residual moisture and solvent were volatilized using a vacuum dryer at 60 ° C. × 3 at a degree of vacuum of several hundred Pa or less. Dried for about an hour. As described above, a dried solid product in which the segment containing the copolymer as a free polymer was composed of only the surface-modified pigment removed as a result of washing the copolymer with a good solvent was obtained.

  Next, the weight loss rate of thermogravimetric analysis was measured by thermogravimetric analysis (Thermogravimetric Analysis) using the dried product obtained above as a measurement sample. The amount of organic group chemically bonded to the pigment was determined from the weight loss rate obtained at that time. For thermogravimetric analysis, a TGA thermogravimetric measuring device, TGA851e / SDTA, manufactured by METTLER TOLEDO was used.

  The measured data of the thermogravimetric analysis weight reduction rate obtained by thermogravimetric analysis on the dried solid sample prepared by the above method was 22.87%. This is the result of thermal analysis for a dried solid sample that has not been washed with THF after coagulation. This thermogravimetric weight loss rate is the total amount of the organic group chemically bonded to the surface-modified pigment in the pigment dispersion and the segment including the polymer portion as a free polymer. It represents the ratio to the surface modified pigment.

  Moreover, the measurement data of the thermogravimetric analysis with respect to the dried solid sample obtained after carrying out the THF washing | cleaning of the said dried solid sample further was 20.89%. That is, the weight loss rate of thermogravimetric analysis is based on the sample after removing the segment as the free polymer with THF, which is a good solvent for the reaction product, and thus the chemical bond in the surface-modified pigment is caused by chemical bonding. It shows the ratio of organic groups.

Furthermore, from the thermogravimetric analysis weight reduction rate, the ratio of the chemically bonded organic groups contained in the ink to the total of the chemically bonded organic groups and the free polymer is obtained by the following equation.
Ratio of chemically bonded organic groups to the total amount of chemically bonded organic groups and free polymer = (thermal gravimetric analysis weight reduction rate after washing with good solvent (%)) / (sample thermogravimetric analysis weight after coagulation) Reduction rate (%)) x 100 (%)
By substituting the weight loss rate of thermogravimetric analysis obtained above into the above formula, it is chemically bonded to the pigment particle surface, accounting for the total amount of organic groups and free polymer chemically bonded to the modified pigment. The proportion of organic groups was determined. As a result, the ratio of the organic group chemically bonded to the total amount of the organic group chemically bonded to the modified pigment and the free polymer is (20.9 / 22.9) × 100 = 91.2. %Met.

(Preparation of Yellow dispersion)
Pigment (CI Pigment Yellow 74 (product name: Hansa Brilliant Yellow 5 GXB (manufactured by Clariant)) 10 parts, anionic polymer P-1 (styrene-acrylic acid copolymer, acid value 200, weight average molecular weight 10,000, A 10% solids aqueous solution, 20 parts of neutralizing agent: potassium hydroxide) and 70 parts of pure water were mixed, charged into a batch type vertical sand mill (manufactured by IMEX), and filled with 150 parts of 0.3 mm diameter zirconia beads. The dispersion was centrifuged for 5 hours, and this dispersion was centrifuged to remove coarse particles, and then the final adjusted product was treated with a yellow dispersion having a solid content of about 12% and a weight average particle size of 125 nm. Obtained.

(Preparation of ink)
The components shown below were mixed, dissolved sufficiently by stirring, and then pressure filtered with a micro filter (manufactured by Fuji Film) having a pore size of 1.0 μm to prepare an ink used in this example.

(Ink of Example 1)
-Surface treatment Yellow pigment (as solids) 4 parts-Glycerol 9 parts-Ethylene glycol 6 parts-1,2-hexanediol 5 parts-Polyethylene glycol (molecular weight 1000) 4 parts-Water balance (ink of Example 2)
・ Surface treatment Yellow pigment (as solids) 4 parts ・ Glycerin 9 parts ・ Ethylene glycol 6 parts ・ Polyoxyethylene-polyoxypropylene condensate 5 parts (trade name: Adeka Pluronic L34; manufactured by Asahi Denka Kogyo)
-Water balance (ink of Example 3)
・ Surface modified yellow pigment (as solid content) 4 parts ・ Glycerin 9 parts ・ Ethylene glycol 6 parts ・ 1,2-hexanediol 5 parts ・ Polyethylene glycol (molecular weight 1000) 4 parts ・ Water balance (ink of Comparative Example 1)
・ Surface treatment Yellow pigment (as solid content) 4 parts ・ Glycerin 9 parts ・ Ethylene glycol 6 parts ・ Polyethylene glycol (molecular weight 1000) 4 parts ・ Water balance (ink of Comparative Example 2)
・ Yellow dispersion (as solid content) 4 parts ・ Glycerin 9 parts ・ Ethylene glycol 6 parts ・ 1,2-hexanediol 5 parts ・ Polyethylene glycol (molecular weight 1000) 4 parts ・ Water balance (ink of Comparative Example 3)
・ Yellow dispersion (as solids) 4 parts ・ Glycerin 9 parts ・ Ethylene glycol 6 parts ・ Polyoxyethylene-polyoxypropylene condensate 5 parts (trade name: Adeka Pluronic L34; manufactured by Asahi Denka Kogyo)
・ Water balance

<Evaluation>
The recording ink prepared as described above was packed in an ink cartridge for Canon BJF-900 and evaluated using a Canon inkjet printer BJF-900.

  The evaluation method is described below.

(1) Continuous ejection stability Solid printing was continuously performed on 200 sheets of A4 paper. After printing, a nozzle check pattern was printed, and the result was evaluated according to the following criteria.
○: The check pattern is not disturbed and can be printed normally.
Δ: Level where the check pattern is slightly disturbed but does not cause non-ejection.
X: Non-ejection or disturbance is clearly confirmed in the check pattern, and printing cannot be performed normally.

(2) Deposit After printing in (1), the print head was removed from the printer, the inside of the nozzle was observed with an optical microscope, and the deposit was evaluated according to the following criteria.
○: Level at which deposits are hardly visible.
Δ: Level at which deposits are slightly seen on the nozzle wall.
X: Level at which deposits are seen in the nozzle as a whole.

(3) Long-term storage stability After placing the ink in a sealed container and leaving it in a constant temperature bath at 60 ° C. for 30 days, the ink is taken out, cooled to room temperature, and then packed in an ink cartridge for a Canon inkjet printer BJF-900. 900 was used to print patches with varying amounts of ink applied between 200% and 0%. At this time, Mitsubishi inkjet paper IJ-RC-UF120 manufactured by Mitsubishi Paper Industries was used as the recording medium. The printed matter is naturally dried for 24 hours, CIE / L ^* a ^* b ^* is measured by Gretag Spectrolino (trade name; manufactured by Gretag), C ^* (saturation) is calculated by the following formula, and C ^* is the highest Judged by the value in the patch.

C ^* = (a ^{* 2} + b ^{* 2} ) ^1/2
○: C ^* (saturation) change amount is 2 or less.
Δ: C ^* (saturation) change amount is 2 or more and 6 or less.
X: The amount of change in C ^* (saturation) is 6 or more.

FIG. 3 is a cross-sectional view of a recording head cartridge showing a mechanism of deposit generation that is a subject of the present invention. It is the schematic diagram which showed the effect of the reaggregation inhibitor used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heater 2 Ink flow path 3 Ejection port 4 Re-aggregate 5 Ink droplet 6 Bubble 7 Pigment 8 Functional group or polymer with functional group 9 Substance which inhibits re-aggregation

Claims (5)

An ink for ink jet recording used in ink jet recording in which ink droplets are ejected from a recording head by the action of thermal energy to form an image on a recording material, the ink comprising at least an aqueous medium, a monoazo pigment, and the pigment An ink for ink jet recording, comprising a substance that inhibits reaggregation after being dispersed and destroyed by the temperature rise of the ink, and the monoazo pigment satisfies at least one of the following two conditions.
(1) The surface is treated so that at least one of the functional group represented by the following formula and a salt thereof is chemically bonded to the pigment surface directly or through another atomic group, and water is added without a dispersant. It can be dispersed and / or dissolved.
(2) An organic group is chemically bonded to the surface and modified, and the organic group is functionally bonded to the surface directly or via another atomic group; It includes a reaction product of a copolymer of an ionic monomer and a hydrophobic monomer.
_{-OM, -COOM, -CO -, -} SO 3 M, -SO 2 NH 2, -RSO 2 M, -PO 3 HM, -PO 3 M 2, -SO 2 NHCOR, -NH 3, -NR 3
(In the formula, M represents a hydrogen atom, an alkali metal, ammonium or organic ammonium, and R represents an alkyl group having 1 to 12 carbon atoms, a phenyl group or a naphthyl group, an alkylene group having 1 to 12 carbon atoms, a phenylene group, or Represents a naphthylene group.) The ink for inkjet recording according to claim 1, wherein the monoazo pigment is a monoazo pigment represented by the following formula (1).
Formula (1)

(In the above formula (1), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are each independently a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, or a fluoro having 1 to 3 carbon atoms. An alkyl group, an alkoxyl group having 1 to 3 carbon atoms, a halogen atom, a nitro group, a sulfo group or an alkaline earth metal salt thereof, an N-phenylaminosulfonyl group, a carboxyl group or an alkaline earth metal salt thereof, a carboamide group, N -A phenylcarbamoyl group, a ureylene group, an iminodicarbonyl group or a carboxylic acid ester group.   The monoazo pigment represented by the formula (1) is C.I. I. The ink for inkjet recording according to claim 1, which is Pigment Yellow 74.   An ink set comprising: the inkjet recording ink according to claim 1; and at least one inkjet recording ink having a hue different from that of the ink. 5. A step of forming an image on a recording medium by ejecting ink droplets from the recording head of the ink jet recording ink constituting the ink set according to any one of claims 1 to 4 by the action of thermal energy. An image forming apparatus comprising:

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