JP2006342201A - Inkjet ink, inkjet ink set, inkjet ink tank, inkjet recording method, inkjet recorder and method for examining inkjet ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain inkjet ink having excellent ink storage stability. to provide an inkjet ink set and an inkjet ink tank each using the inkjet ink, an inkjet recording method and an inkjet recorder and a method for examining inkjet ink, which judges whether or not inkjet ink has excellent ink storage stability. <P>SOLUTION: The inkjet ink comprises water, a water-soluble organic solvent, pigment, a polymer dispersant used for dispersing the pigment and having ≥800 weight-average molecular weight and has a specific value represented by formula (1) (the ratio of the polymer dispersant to the pigment in the ink from which a precipitate after centrifugal treatment (centrifugal treatment condition: centrifugal acceleration of 9,000g×30min) is removed)/(the ratio of the polymer dispersant to the pigment in the ink before the centrifugal treatment) of 1.0-1.5. The method for examining inkjet ink comprises an ink examination process for obtaining a characteristic value represented by formula (1). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet ink, an inkjet ink set, an inkjet ink tank, an inkjet recording method, an inkjet recording apparatus, and an inkjet ink inspection method.

  An ink jet system that discharges ink from an ink discharge port formed by a nozzle, a slit, a porous film, or the like is used in many printers because it is small and inexpensive. Among these ink jet systems, the piezoelectric ink jet system that ejects ink using deformation of piezoelectric elements and the thermal ink jet system that ejects ink using the boiling phenomenon of ink due to thermal energy are excellent in high resolution and high speed printability. Has characteristics.

  Among the inks used in this ink jet method, in the case of ink jet inks mainly using pigment as a color material, when stored for a long period of time, ink changes such as color material settling and further aggregation are likely to occur, and ink storage stability is poor. There is a problem.

  In order to improve such problems, Japanese Patent Application Laid-Open No. 10-237368 discloses that for the purpose of pigment dispersion stability, carbon black and resin are dispersed or dissolved in an aqueous liquid to prepare a dispersion. After the resin is adsorbed on the surface, the ink is centrifuged at 25,000 to 80000 g, and the carbon black on which the resin is adsorbed is settled to remove the resin not adsorbed on the carbon black. A method has been proposed.

  JP-A-11-302586 discloses a pigment dispersion obtained by dispersing a pigment with a styrene- (meth) acrylic acid-based water-soluble resin for the purpose of improving the dispersion stability of the pigment and improving ejection failure. In the contained inkjet ink, the pigment dispersion contains 0.3 part or more of a water-soluble resin with respect to the pigment 1, and the amount of the released water-soluble resin is 4% or less in the pigment dispersion. Ink jet recording inks have been proposed.

However, the current situation is that it is not sufficient and improvement is desired.
JP-A-10-237368 JP-A-11-302586

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, an object of the present invention is to provide an ink jet ink excellent in ink storage stability. Another object of the present invention is to provide an ink jet ink set, an ink jet ink tank, an ink jet recording method, and an ink jet recording apparatus using the ink jet ink.

  Another object of the present invention is to provide an ink-jet ink inspection method capable of determining whether ink storage stability is excellent.

The above problem is solved by the following means.
That is, the inkjet ink of the present invention includes water, a water-soluble organic solvent, a pigment, and a polymer dispersant having a weight average molecular weight of 800 or more for dispersing the pigment.
And, the formula (1): (ratio of the polymer dispersant to the pigment in the ink excluding sediment after centrifugation (centrifugation condition: centrifugal acceleration 9000 g × 30 min)) / (ink before the centrifugation) The characteristic value indicated by the ratio of the polymer dispersant to the pigment in the inside is 1.0 to 1.5.

  In the inkjet ink of the present invention, formula (2): (solid content ratio in ink excluding sediment after centrifugal treatment (centrifugal treatment condition: centrifugal acceleration 9000 g × 30 min)) / (in the ink before the centrifugal treatment) It is preferable that the characteristic value represented by (solid content ratio) is 0.8 to 1.

  In the inkjet ink of the present invention, it is preferable that the average volume dispersion particle diameter of the pigment is 10 to 300 nm.

  In the inkjet ink of the present invention, it is preferable that the pigment is at least one selected from carbon black, phthalocyanine, and quinacridone pigment.

  In the inkjet ink of the present invention, it is preferable that the polymer dispersant includes a hydrophobic group and a hydrophilic group. The hydrophilic group preferably includes a nonionic functional group.

  In the inkjet ink of the present invention, it is preferable that the viscosity of the ink is 5 mPa · s or more and the characteristic value represented by the formula (1) is 1.0 to 1.4.

In addition, the ink set for inkjet of the present invention is
The inkjet ink of the present invention;
A treatment liquid containing an aggregating agent having an action of aggregating or insolubilizing the components of the ink, a water-soluble organic solvent, and water;
It is characterized by having.

  The ink-jet ink tank of the present invention is characterized by containing the ink-jet ink of the present invention or the ink-jet ink set of the present invention.

  The ink jet recording method of the present invention is characterized in that an image is formed by ejecting each liquid onto a recording medium using the ink jet ink of the present invention or the ink jet ink set of the present invention.

  In the inkjet recording method of the present invention, each liquid supplied from the inkjet ink or an inkjet ink tank containing the inkjet ink set may be ejected onto a recording medium.

  Further, an ink jet recording apparatus of the present invention is characterized by comprising a recording head for discharging each liquid onto a recording medium using the ink jet ink of the present invention or the ink jet ink set of the present invention. .

  The ink jet recording apparatus of the present invention may further include an ink jet ink tank for storing the ink jet ink or the ink jet ink set and supplying each liquid to the recording head.

  Further, the ink-jet ink inspection method of the present invention comprises the polymer dispersant for the pigment in the ink excluding the precipitate after the formula (1): (centrifugation treatment (centrifugal treatment condition: centrifugal acceleration 9000 g × 30 min)) Ink inspection step for obtaining a characteristic value represented by: (ratio of the polymer dispersant to the pigment in the ink before the centrifugal treatment).

  According to the present invention, it is possible to provide an ink jet ink excellent in ink storage stability. An ink jet ink set, an ink jet ink tank, an ink jet recording method, and an ink jet recording apparatus using the ink jet ink can also be provided.

  In addition, according to the present invention, it is also possible to provide an ink-jet ink inspection method capable of determining whether ink storage stability is excellent.

Hereinafter, the present invention will be described in detail.

(Inkjet ink)
The inkjet ink of the present invention contains water, a water-soluble organic solvent, a pigment, and a polymer dispersant having a weight average molecular weight of 800 or more for dispersing the pigment. In addition, other additives may be included as necessary.

  Formula (1): (Ratio of polymer dispersant to pigment in ink excluding sediment after centrifugal treatment (centrifugal treatment condition: centrifugal acceleration 9000 g × 30 min)) / (pigment in ink before centrifugal treatment) The ratio of the polymer dispersant to the ratio of the polymer dispersant is 1.0 to 1.5.

  The characteristic value represented by the formula (1) indicates the change in the ratio of the polymer dispersant to the dispersed pigment (polymer dispersant / pigment) before and after the centrifugal treatment, and the pigment dispersion particle size in the ink This is a comprehensive characteristic value combining a variation (a variation in the dispersion state of pigment particles), a variation in the amount of adsorption of the polymer dispersant, and an adsorption force between the pigment and the polymer dispersant. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) is a mass ratio.

  Ideally, the ratio of the polymeric dispersant to the dispersed pigment does not change before and after the centrifugal treatment, that is, the characteristic value represented by the formula (1) is 1, but as described above, the pigment dispersed particles Due to the dispersion of the diameter, the dispersion of the polymer dispersant, the adsorption power between the pigment and the polymer dispersant, etc., the pigment actually settles more than the polymer dispersant, and the polymer in the liquid after the centrifugal treatment The dispersant ratio increases.

  In other words, the difference in the ratio of the polymer dispersant to the pigment before and after the ink centrifugal treatment is large. 1) The distribution of the amount of the polymer dispersant adhering to the pigment particles is wide, and the adhesion rate of the polymer dispersant is The lower the pigment particle, the larger the particle size, and the more easily settled. 2) Even if the particle size is the same, the amount of the polymer dispersant is small and the specific gravity is heavy or the dispersibility is poor, and the pigment particle tends to settle. It is shown that the adsorbing force is weak, and the pigment and the polymer dispersant are separated by centrifugal force, so that the pigment is not dispersed and settles.

  In the case of the present invention, when the characteristic value represented by the formula (1) is 1.5 or less, it is considered that the dispersion of the pigment dispersion diameter and the dispersion amount of the polymer dispersant are small and the adsorption power between the pigment and the resin is also high. The ink storage stability is excellent. On the other hand, when the characteristic value represented by the formula (1) exceeds 1.5, the dispersion of the pigment dispersion particle diameter in the ink, the dispersion of the polymer dispersant adsorption amount, the adsorption power between the pigment and the polymer dispersant are It is considered weak, and the pigment dispersion state is easily changed with respect to external factors (for example, temperature change), and the storage stability of the ink is lowered.

  From the above viewpoint, the characteristic value represented by the formula (1) is 1 to 1.5, but is preferably as low as possible, preferably 1 to 1.3, and more preferably 1 to 1.2. In particular, when the viscosity of the ink is as high as 5 mPa · s or more (preferably 5 to 15 mPa · s), the characteristic value represented by the formula (1) is preferably 1.0 to 1.4. This is because the higher the ink viscosity (that is, the higher the solvent viscosity), the more difficult the particles settle due to the viscosity factor, and when the same characteristic value is shown in the formula (1), the ink with higher ink viscosity is It is assumed that the dispersion of the pigment dispersion particle size in the ink, the dispersion of the polymer dispersant adsorption amount is large, or the adsorption power between the pigment and the polymer dispersant is weak, which makes the dispersion of the ink essentially unstable. This is because it is assumed that there is.

  Here, how to obtain the characteristic value represented by the equation (1) is as follows. A predetermined amount (1 g) of sample ink is collected, and the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) is determined. The ratio of the polymer dispersant to the pigment is determined by volatilization (or decomposition) corresponding to the dispersant by performing thermogravimetric analysis on the obtained solid content after the ink is heated and dried (250 ° C.) to remove the liquid component. It is calculated from the weight loss at temperature and the weight corresponding to the residual pigment (or the weight decrease at the temperature corresponding to the pigment decomposition temperature).

  Next, a predetermined amount (250 g) is collected from the same ink, and subjected to a centrifugal treatment condition: centrifugal acceleration of 9000 g × 30 min, and then a predetermined amount (230 g) of the supernatant liquid is collected to obtain a polymer dispersant for the pigment. The ratio (polymer dispersant / pigment) is calculated as above.

  And the said characteristic value is calculated | required by substituting the ratio of the polymer dispersing agent with respect to the pigment before and behind the centrifugation process to Formula (1). These operations were performed in an environment of normal temperature and normal humidity (20 ° C., 40% RH).

In order to set the characteristic value represented by the above formula (1) within the above range, for example, the following forms may be mentioned. i) Narrow the molecular weight distribution of the polymeric dispersant. ii) Hydrophobic group unit of polymer dispersant /
The variation in the arrangement of the hydrophilic group units is made as small as possible (that is, an alternating copolymer / block copolymer / graft copolymer is preferable to a random copolymer). iii) For the primary particles of the pigment, by improving the classification accuracy or suppressing the raw materials and intermediates remaining in the pigment synthesis as much as possible and controlling the structural isomer ratio, purifying the pigment and reducing the amount of impurities, Reduces particle size variation. iv) During the preparation of the dispersion, a preparation aid is used so that the pigment and the polymer dispersant are well blended (the adjustment aid is removed after the dispersion is adjusted). v) At the stage of preparing the pigment dispersion, a centrifugal separation operation is performed to remove in advance the dispersed particles having a large particle size.

  In addition, in order to improve the storage stability of the ink, the characteristic value represented by the above formula (1) is set within the above range, and the formula (2): (centrifugal processing (centrifugal processing condition: centrifugal acceleration 9000 g × 30 min) The characteristic value indicated by the ratio of the solid content in the ink excluding the subsequent sediment) / (the ratio of the solid content in the ink before the centrifugal treatment) is 0.8 to 1 (preferably 0.9 to 1). Is good.

  The characteristic value represented by the above formula (2) indicates that the particle size distribution of the pigment dispersed in the ink is small, and there are few coarse particles generated due to pigment aggregation. Ink storage stability can be improved.

  Here, how to obtain the characteristic value represented by the equation (2) is as follows. A predetermined amount (10 g) of ink as a sample is collected, and the solid content ratio is obtained. The solid content ratio is calculated by [weight after drying / ink weight (10 g)] * 100 after drying the ink at 250 ° C. and measuring the weight.

  Next, a predetermined amount (250 g) is collected from the same ink, and subjected to a centrifugal treatment condition: centrifugal acceleration of 9000 g × 30 min. Then, a predetermined amount (230 g) of the supernatant liquid is collected, and the solid content ratio is the same as above. To calculate.

  And the said characteristic value is calculated | required by substituting the solid content ratio before and behind the centrifugation process to Formula (2). These operations were performed in an environment of normal temperature and normal humidity (20 ° C., 40% RH).

  In order to set the characteristic value represented by the above formula (2) within the above range, for example, the following forms can be cited. i) Narrow the molecular weight distribution of the polymeric dispersant. ii) The variation in the arrangement of the hydrophobic group unit / hydrophilic group unit of the polymer dispersant is made as small as possible (that is, an alternating copolymer / block copolymer / graft copolymer is more preferable than a random copolymer). ii) In preparing the dispersion, a preparation aid is used in order to make the pigment and polymer dispersant blend well (the adjustment aid is removed after the dispersion is adjusted). iv) At the stage of preparing the pigment dispersion, a centrifugal separation operation is performed to remove in advance the dispersed particles having a large particle size.

  Hereinafter, each component of the ink will be described in detail. First, the pigment will be described.

  The pigment is non-self-dispersible and is dispersed in the ink by a polymer dispersant. As the pigment, either an organic pigment or an inorganic pigment can be used. Examples of the black pigment include carbon black pigments such as Nesblack, lamp black, acetylene black, and channel black. In addition to black, cyan, magenta, and yellow primary pigments, specific color pigments such as red, green, blue, brown, and white, metallic luster pigments such as gold and silver, colorless or light color extender pigments, plastic pigments, etc. May be used. In addition, a newly synthesized pigment may be used for the present invention. Further, particles having silica, alumina, polymer beads or the like as a core and having a dye or pigment fixed on the surface thereof, insoluble lakes of dyes, colored emulsions, colored latex or the like can be used as pigments.

  Examples of pigments include zinc white, titanium white, chromium oxide, iron oxide, alumina white, cadmium yellow, zinc sulfide, zinc chromate, yellow lead, barium sulfate, basic lead sulfate, calcium carbonate, lead white, ultramarine, and silicic acid. Inorganic pigments such as calcium, manganese violet, cobalt violet, bitumen, carbon black, madele lake, cochineal lake, naphthol green B, naphthol green Y, naphthol yellow S, permanent red 4R, Hansa Elue, benzidine yellow, resol red, lake red C, Lake Red D, Brilliant Carmine 6B, Bordeaux 10B, Phthalocyanine Blue, Phthalocyanine Green, Sky Blue, Rhodamine Lake, Methyl Violet Lake, Quinoline Yellow Lake, Peacock Blue Lake, Thioindigo Maroo , Alizarin lake, quinacridone red, berylene red, aniline black, dioxazine violet, organic fluorescent pigment, organic pigments such as isoindolinone yellow, cobalt oxide, γ-iron oxide, metallic iron powder, barium ferrite magnetite, ferrite, etc. Examples include magnetic materials, superparamagnetic materials, other plastic pigments, and metallic luster pigments.

Pigments are trade names and C.I. An example of the I pigment number is as follows.
Specific examples of black pigments include Raven7000, Raven5750, Raven5250, Raven5000 ULTRAII, Raven3500, Raven2000, Raven1500, Raven1250, Raven1200, Raven1125, Raven10, Raven10, Raven10 Regal 330R, Regal 660R, Mogul L, Black Pearls L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400 (and above Manufactured by Cabotte), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black 18, Color Black FW200, Color Black S150, Color Black S160, Color Black S160, Color Black S160, Color Black S160, Color Black S160, Color Black S160, Color Black FW Black 6, Special Black 5, Special Black 4A, Special Black 4 (manufactured by Degussa), no. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical Co., Ltd.), and the like, but are not limited thereto.

  Specific examples of the cyan pigment include C.I. I. Pigment Blue-1, -2, -3, -15, -15: 1, -15: 2, -15: 3, -15: 4, -16, -22, -60, and the like. It is not limited.

  Specific examples of the magenta color pigment include C.I. I. Pigment Red-5, -7, -12, -48, -48: 1, -57, -112, -122, -123, -146, -168, -177, -184, -202, C.I. I. Pigment Violet-19 etc. are mentioned, However, It is not limited to these.

  Specific examples of yellow pigments include C.I. I. Pigment Yellow-1, -2, -3, -12, -13, -14, -16, -17, -73, -74, -75, -83, -93, -95, -97, -98, -114, -128, -129, -138, -151, -154, -180, and the like, but are not limited thereto.

  Among these pigments, carbon black, phthalocyanine, and quinacridone pigments are preferable. This is because these pigments have a small particle size and small variations and are easy to control.

  The content of the pigment is preferably 0.1% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 10% by mass or less. When the pigment content is less than 0.1% by mass, a sufficient optical density may not be obtained, and when the content is more than 20% by mass, the liquid ejection characteristics are unstable. There was a case.

  In addition, you may make a process liquid mentioned later contain a pigment as needed. In this case, the content of the pigment contained in the treatment liquid is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 10% by mass or less. When the processing liquid contains a pigment, an effect of improving the image density can be obtained. Further, by using the treatment liquid containing the pigment as the color ink of the ink jet printer, the number of print heads can be reduced, and the manufacturing cost of the recording apparatus and the running cost during printing can be reduced.

  The average volume dispersed particle diameter of the pigment is preferably 10 to 300 nm, more preferably 20 to 250 nm, and still more preferably 30 to 200 nm. When the average volume dispersion particle size of the pigment is less than 10 nm, the optical density may be low, whereas when it exceeds 300 nm, the storage stability may not be ensured.

  Here, the average volume dispersion particle size of the pigment refers to the particle size of the pigment itself or the particle size to which the additive has adhered when an additive such as a dispersant is adhered to the pigment. A Microtrac UPA particle size analyzer 9340 (Leeds & Northrup) was used for the measurement of the average volume dispersion particle size. The measurement was performed according to a predetermined measurement method by putting 4 ml of ink jet ink into a measurement cell. As parameters to be input at the time of measurement, the viscosity of the inkjet ink was input as the viscosity, and the density of the pigment was input as the density of the dispersed particles.

  Next, the polymer dispersant will be described. The polymer dispersant is for dispersing the pigment in the ink. As the pigment dispersant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, and the like may be used in combination with the polymer dispersant.

  The polymer dispersant has a weight average molecular weight of 800 or more, and preferably has a weight average molecular weight of 2000 to 50000, more preferably 3000 to 40000, and more preferably 4000 from the viewpoint of achieving both dispersibility of the pigment and ink dischargeability. What is -30000 is more preferable.

  The polymer dispersant preferably contains a hydrophobic group and a hydrophilic group, and in particular, the hydrophilic group preferably contains a nonionic functional group (for example, poly (oxyethylene) alkyl ether, polyhydric alcohol, etc.). . This is because it is difficult to control the delicate hydrophobic / hydrophilic balance if the hydrophilic group is only a polar group such as carboxylic acid / sulfonic acid, and it contains a non-polar hydrophilic group that is nonpolar in terms of matching with the pigment. This makes it possible to perform a more appropriate distribution function.

  As such a polymer dispersant containing a hydrophobic group and a hydrophilic group, a polymer having a hydrophilic group and a hydrophobic group is preferably used. As the polymer having a hydrophilic group and a hydrophobic group, a condensation polymer and an addition polymer can be used. Examples of the condensation polymer include known polyester dispersants. Examples of the addition polymer include addition polymers of monomers having an α, β-ethylenically unsaturated group. The desired polymer dispersant is obtained by copolymerizing a monomer having an α, β-ethylenically unsaturated group having a hydrophilic group and a monomer having an α, β-ethylenically unsaturated group having a hydrophobic group as appropriate. It is done. In addition, a homopolymer of a monomer having an α, β-ethylenically unsaturated group having a hydrophilic group can also be used.

  As the monomer having an α, β-ethylenically unsaturated group having a hydrophilic group, a monomer having a carboxyl group, a sulfonic acid group, a hydroxyl group, a phosphoric acid group, for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, Itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid monoester, vinyl sulfonic acid, styrene sulfonic acid, sulfonated vinyl naphthalene, vinyl alcohol, acrylamide, methacryloxyethyl phosphate, bismethacryloxyethyl phosphate, Examples include methacryloxyethyl phenyl acid phosphate, ethylene glycol dimethacrylate, and diethylene glycol dimethacrylate.

  Examples of monomers having an α, β-ethylenically unsaturated group having a hydrophobic group include styrene derivatives such as styrene, α-methylstyrene, vinyltoluene, vinylcyclohexane, vinylnaphthalene, vinylnaphthalene derivatives, alkyl acrylates, and methacrylic acid. Examples include alkyl esters, methacrylic acid phenyl esters, methacrylic acid cycloalkyl esters, crotonic acid alkyl esters, itaconic acid dialkyl esters, and maleic acid dialkyl esters.

  Examples of preferred copolymers used as the polymer dispersant include styrene-styrene sulfonic acid copolymers, styrene-maleic acid copolymers, styrene-methacrylic acid copolymers, styrene-acrylic acid copolymers, Vinyl naphthalene-maleic acid copolymer, vinyl naphthalene-methacrylic acid copolymer, vinyl naphthalene-acrylic acid copolymer, alkyl acrylate ester-acrylic acid copolymer, alkyl methacrylate ester-methacrylic acid copolymer, styrene -Methacrylic acid alkyl ester-Methacrylic acid copolymer, Styrene-Acrylic acid alkyl ester-Acrylic acid copolymer, Styrene-Methacrylic acid phenyl ester-Methacrylic acid copolymer, Styrene-Methacrylic acid cyclohexyl ester-Methacrylic acid copolymer Etc. . Moreover, you may copolymerize suitably the monomer which has a polyoxyethylene group and a hydroxyl group with these polymers.

  These polymer dispersants may be used alone or in combination of two or more. The amount of the polymeric dispersant added varies greatly depending on the pigment, so it cannot be said unconditionally, but generally 0.1 to 100% by mass, preferably 1 to 70% by mass, and more preferably 3 to 50%, based on the pigment. It is preferable to add in the ratio of the mass%.

  Next, the water-soluble organic solvent will be described. As the water-soluble organic solvent, polyhydric alcohols, polyhydric alcohol derivatives, nitrogen-containing solvents, alcohols, sulfur-containing solvents and the like are used.

  Specific examples of water-soluble organic solvents include polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, and glycerin. Can be mentioned.

  Polyhydric alcohol derivatives include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diglycerin. And ethylene oxide adducts.

Examples of the nitrogen-containing solvent include pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, and triethanolamine. Examples of the alcohol include alcohols such as ethanol, isopropyl alcohol, butyl alcohol, and benzyl alcohol.
Examples of the sulfur-containing solvent include thiodiethanol, thioglycerol, sulfolane, dimethyl sulfoxide and the like.

  In addition, as the water-soluble organic solvent, propylene carbonate, ethylene carbonate, or the like can be used.

  It is preferable to use at least one water-soluble organic solvent. The content of the water-soluble organic solvent is 1 to 60% by mass, preferably 5 to 40% by mass. When the amount of the water-soluble organic solvent in the ink is less than 1% by mass, a sufficient optical density may not be obtained. Conversely, when the amount is more than 60% by mass, the viscosity of the liquid is large. As a result, there are cases where the liquid ejection characteristics become unstable.

  Next, water will be described. As water, it is preferable to use ion-exchanged water, ultrapure water, distilled water, or ultrafiltered water in order to prevent impurities from being mixed.

  Next, other additives will be described. A surfactant can be added to the ink of the present invention.

  Examples of these surfactants include various anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, and the like. Preferably, anionic surfactants and nonionic surfactants are used. An activator is used.

Specific examples of the surfactant are listed below.
Examples of anionic surfactants include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, sulfuric acid of higher alcohol ether. Ester salts and sulfonates, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, etc. can be used, preferably , Dodecylbenzenesulfonate, isopropylnaphthalenesulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenylsulfonate, monobutylbiphenylsulfonate, dibutylphenylsulfonate Nord disulfonic acid salts and the like are used.

  Nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, poly Oxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, alkyl alkanolamide, polyethylene glycol polypropylene glycol block copolymer, acetylene glycol, polyoxyethylene adduct of acetylene glycol Preferably, polyoxyethylene nonyl pheny Ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid alkylolamide, polyethylene glycol polypropylene glycol block copolymer Acetylene glycol and polyoxyethylene adducts of acetylene glycol are used.

  In addition, silicone surfactants such as polysiloxane oxyethylene adducts, fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers, spicrispolic acid and rhamnolipids Biosurfactants such as lysolecithin can also be used.

  These surfactants may be used alone or in combination. Further, the HLB of the surfactant is preferably in the range of 3 to 20 in view of dissolution stability and the like.

  0.001-5 mass% is preferable and, as for the addition amount of these surfactant, 0.01-3 mass% is especially preferable.

  In addition, the ink of the present invention includes a polyethyleneimine, polyamines, polyvinylpyrrolidone, polyethylene glycol, ethylcellulose, carboxymethylcellulose, and the like for the purpose of controlling properties such as a penetrating agent for improving penetrability and ink dischargeability. In order to adjust the rate and pH, compounds of alkali metals such as potassium hydroxide, sodium hydroxide, lithium hydroxide, etc., pH buffer, antioxidant, antifungal agent, viscosity modifier, conductivity, etc. as necessary Agents, ultraviolet absorbers, chelating agents, and the like can also be added.

  Next, preferred characteristics of the ink-jet ink of the present invention will be described. First, the surface tension of the ink of the present invention is preferably 20 to 60 mN / m, more preferably 20 to 50 mN / m, and still more preferably 20 to 45 mN / m. If the surface tension is less than 20 mN / m, ink may overflow on the nozzle surface, and printing may not be performed normally. On the other hand, if it exceeds 60 mN / m, the permeability may be slow and the drying time may be slow.

  Here, as the surface tension, a value measured in an environment of 23 ° C. and 55% RH using a Wilhelmy type surface tension meter (manufactured by Kyowa Interface Science Co., Ltd.) was adopted.

  The viscosity of the ink of the present invention is preferably 1.0 to 30 mPa · s, more preferably 1.2 to 20 mPa · s, and still more preferably 1.5 to 15 mPa · s. When the viscosity of the ink was larger than 30.0 mPa · s, there was a case where the dischargeability was lowered. On the other hand, when it is smaller than 1.0 mPa · s, there is a case where the jetting property is deteriorated.

Here, as the viscosity, a value measured using a rheomat 115 (manufactured by Contraves) as a measuring device, a measurement temperature of 23 ° C., and a shear rate of 1400 s ⁻¹ was adopted.

Further, in the ink of the present invention, the number of particles of 0.5 μm or more in 2 μl of ink is preferably less than 2 × 10 ⁶ , more preferably less than 1.5 × 10 ⁶ , and more preferably 1.0. × 10 ⁶ or less. If the value of the number of particles of 0.5 μm or more is too large, nozzle clogging or pigment sedimentation during ink storage occurs.

  Here, the number of particles of 0.5 μm or more in 2 μl of ink was measured using Accusizer ™ 770 Optical Particle Sizer (manufactured by Particle Sizing Systems). Further, as a parameter input at the time of measurement, the density of the dispersed particles was input as the density of the color material.

  Further, the ζ potential of the ink of the present invention is preferably 10 to 100 mV in absolute value, more preferably 10 to 90 mV, and further preferably 15 to 80 mV. When the ζ potential was less than 10 mV in absolute value, the ink storage stability sometimes deteriorated. On the other hand, when the ζ potential exceeds 100 mV in absolute value, there are cases in which pigment aggregation does not proceed sufficiently when used in combination with a treatment liquid.

Here, the zeta potential was measured by ESA (Electrokinetic Sonic Amplitude method) using ESA-8000 (manufactured by Matec Applied Science) as a measuring device, and the zeta potential was calculated using the following calculation formula.
Formula: ζ potential = [ESA × η × G (α) ⁻¹ ] / [ε × c × Δρ × V]
In the formula, ESA indicates a pressure per unit electric field, which is a value obtained by measurement. η is the viscosity of the solvent, G (α) ⁻¹ is the correction term due to inertial force, ε is the dielectric constant, c is the speed of sound in the solvent, Δρ is the density difference between the solvent and particles, and V is the volume fraction of the particles. Show. In the present invention, the measurement was performed at a temperature of 22.0 ° C. according to a predetermined measurement method. Further, as parameters used when calculating the zeta potential, η is the viscosity of the ink, ε is the dielectric constant of water, c is the speed of sound in water, Δρ is the density difference between the pigment and water, and V is the volume fraction of the pigment. It was.

(Inkjet ink set)
The inkjet ink set of the present invention has the inkjet ink of the present invention and a treatment liquid.

  The treatment liquid will be described. The treatment liquid contains at least an aggregating agent having a function of aggregating or insolubilizing ink components, a water-soluble organic solvent, and water.

  Examples of the aggregating agent include a substance having an action of increasing at least the particle diameter of the coloring material at the time of mixing with the ink, or a substance having an action of separating the coloring material component of the ink from the solvent. Examples of the flocculant include inorganic electrolytes, organic acids, inorganic acids, organic amines, and the like.

  Inorganic electrolytes include alkali metal ions such as lithium ion, sodium ion, potassium ion, aluminum ion, barium ion, calcium ion, copper ion, iron ion, magnesium ion, manganese ion, nickel ion, tin ion, titanium ion, zinc Polyvalent metal ions such as ions, hydrochloric acid, odorous acid, hydroiodic acid, sulfuric acid, nitric acid, phosphoric acid, thiocyanic acid, and acetic acid, succinic acid, lactic acid, fumaric acid, fumaric acid, citric acid, salicylic acid, benzoic acid And the like, and organic carboxylic acids such as salts of organic sulfonic acids.

  Specific examples include lithium chloride, sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide, potassium iodide, sodium sulfate, potassium nitrate, sodium acetate, potassium oxalate, sodium citrate, potassium benzoate and the like. Alkali metal salts and aluminum chloride, aluminum bromide, aluminum sulfate, aluminum nitrate, sodium aluminum sulfate, potassium aluminum sulfate, aluminum acetate, barium chloride, barium bromide, barium iodide, barium oxide, barium nitrate, thiocyanate Barium acid, calcium chloride, calcium bromide, calcium iodide, calcium nitrite, calcium nitrate, calcium dihydrogen phosphate, calcium thiocyanate, calcium benzoate, calcium acetate, salicylic acid Lucium, calcium tartrate, calcium lactate, calcium fumarate, calcium citrate, copper chloride, copper bromide, copper sulfate, copper nitrate, copper acetate, iron chloride, iron bromide, iron iodide, iron sulfate, iron nitrate, oxalic acid Iron, iron lactate, iron fumarate, iron citrate, magnesium chloride, magnesium bromide, magnesium iodide, magnesium sulfate, magnesium nitrate, magnesium acetate, magnesium lactate, manganese chloride, manganese sulfate, manganese nitrate, manganese dihydrogen phosphate , Manganese acetate, manganese salicylate, manganese benzoate, manganese lactate, nickel chloride, nickel bromide, nickel sulfate, nickel nitrate, nickel acetate, tin sulfate, titanium chloride, zinc chloride, zinc bromide, zinc sulfate, zinc nitrate, thiocyanate Examples thereof include salts of polyvalent metals such as zinc acid and zinc acetate.

  Specific examples of organic acids include arginic acid, citric acid, glycine, glutamic acid, succinic acid, tartaric acid, cysteine, oxalic acid, fumaric acid, phthalic acid, maleic acid, malonic acid, lysine, malic acid, and general formula Examples thereof include compounds represented by (1) and derivatives of these compounds.

Here, in the formula, X represents O, CO, NH, NR ₁ , S, or SO ₂ . R ₁ represents an alkyl group, and R ₁ is preferably CH ₂ , C ₂ H ₅ , or C ₂ H ₄ OH. R represents an alkyl group, and R is preferably CH ₂ , C ₂ H ₅ , or C ₂ H ₄ OH. In addition, R may be included in the formula or may not be included. X is preferably CO, NH, NR, or O, and more preferably CO, NH, or O. M represents a hydrogen atom, an alkali metal or an amine. M is preferably H, Li, Na, K, monoethanolamine, diethanolamine, triethanolamine or the like, more preferably H, Na, or K, and still more preferably a hydrogen atom. n is an integer of 3-7. n is preferably a case where the heterocyclic ring is a 6-membered ring or a 5-membered ring, and more preferably a 5-membered ring. m is 1 or 2. The compound represented by the general formula (1) may be a saturated ring or an unsaturated ring as long as it is a heterocyclic ring. l is an integer of 1-5.

  Specifically, the compound represented by the general formula (1) has a furan, pyrrole, pyrroline, pyrrolidone, pyrone, pyrrole, thiophene, indole, pyridine, quinoline structure, and further has a carboxyl group as a functional group. Compounds. Specifically, 2-pyrrolidone-5-carboxylic acid, 4-methyl-4-pentanolide-3-carboxylic acid, furan carboxylic acid, 2-benzofuran carboxylic acid, 5-methyl-2-furan carboxylic acid, 2,5 -Dimethyl-3-furancarboxylic acid, 2,5-furandicarboxylic acid, 4-butanolide-3-carboxylic acid, 3-hydroxy-4-pyrone-2,6-dicarboxylic acid, 2-pyrone-6-carboxylic acid, 4-pyrone-2-carboxylic acid, 5-hydroxy-4-pyrone-5-carboxylic acid, 4-pyrone-2,6-dicarboxylic acid, 3-hydroxy-4-pyrone-2,6-dicarboxylic acid, thiophenecarboxylic Acid, 2-pyrrolecarboxylic acid, 2,3-dimethylpyrrole-4-carboxylic acid, 2,4,5-trimethylpyrrole-3-propionic acid, 3-hydroxy-2-yne Carboxylic acid, 2,5-dioxo-4-methyl-3-pyrroline-3-propionic acid, 2-pyrrolidinecarboxylic acid, 4-hydroxyproline, 1-methylpyrrolidine-2-carboxylic acid, 5-carboxy-1-methyl Pyrrolidine-2-acetic acid, 2-pyridinecarboxylic acid, 3-pyridinecarboxylic acid, 4-pyridinecarboxylic acid, pyridinedicarboxylic acid, pyridinetricarboxylic acid, pyridinepentacarboxylic acid, 1,2,5,6-tetrahydro-1-methyl Examples include nicotinic acid, 2-quinolinecarboxylic acid, 4-quinolinecarboxylic acid, 2-phenyl-4-quinolinecarboxylic acid, 4-hydroxy-2-quinolinecarboxylic acid, and 6-methoxy-4-quinolinecarboxylic acid. .

  The organic acid is preferably citric acid, glycine, glutamic acid, succinic acid, tartaric acid, phthalic acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid Nicotinic acid, derivatives of these compounds, or salts thereof. More preferred are pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, nicotinic acid, or derivatives of these compounds, or salts thereof. More preferred are pyrrolidone carboxylic acid, pyrone carboxylic acid, furan carboxylic acid, coumaric acid, or a compound derivative thereof, or a salt thereof.

The organic amine compound may be any of primary, secondary, tertiary and quaternary amines and salts thereof. Specific examples include tetraalkylammonium, alkylamine, benzalkonium, alkylpyridium, imidazolium, polyamine, and derivatives or salts thereof. Specifically, amylamine, butylamine, propanolamine, propylamine, ethanolamine, ethylethanolamine, 2-ethylhexylamine, ethylmethylamine, ethylbenzylamine, ethylenediamine, octylamine, oleylamine, cyclooctylamine, cyclobutylamine, cyclohexane Propylamine, cyclohexylamine, diisopropanolamine, diethanolamine, diethylamine, di-2-ethylhexylamine, diethylenetriamine, diphenylamine, dibutylamine, dipropylamine, dihexylamine, dipentylamine, 3- (dimethylamino) propylamine, dimethylethylamine, dimethyl Ethylenediamine, dimethyloctylamine, 1,3-dimethylbutylamine, dimethyl 1,3-propanediamine, dimethylhexylamine, amino-butanol, amino-propanol, amino-propanediol, N-acetylaminoethanol, 2- (2-aminoethylamino) -ethanol, 2-amino-2- Ethyl-1,3-propanediol, 2- (2-aminoethoxy) ethanol, 2- (3,4-dimethoxyphenyl) ethylamine, cetylamine, triisopropanolamine, triisopentylamine, triethanolamine, trioctylamine, Tritylamine, bis (2-aminoethyl) 1,3-propanediamine, bis (3-aminopropyl) ethylenediamine, bis (3-aminopropyl) 1,3-propanediamine, bis (3-aminopropyl) methylamine, Bis (2-ethylhexyl ) Amine, bis (trimethylsilyl) amine, butylamine, butylisopropylamine, propanediamine, propyldiamine, hexylamine, pentylamine, 2-methyl-cyclohexylamine, methyl-propylamine, methylbenzylamine, monoethanolamine, laurylamine, Nonylamine, trimethylamine, triethylamine, dimethylpropylamine, propylenediamine, hexamethylediamine, tetraethylenepentamine, diethylethanolamine, tetramethylammonium chloride, tetraethylammonium bromide, dihydroxyethylstearylamine, 2-heptadecenyl-hydroxyethylimidazoline, lauryl Dimethylbenzylammonium chloride, cetylpyridinium mouth Ride, stearamide methylbiridium chloride, diallyldimethylammonium chloride polymer, diallylamine polymer, monoallylamine polymer and the like can be mentioned.
More preferably, triethanolamine, triisopropanolamine, 2-amino-2-ethyl-1,3-propanediol, ethanolamine, propanediamine, propylamine and the like are used.

  The flocculant may be used alone or in combination of two or more. The content of the flocculant is preferably 0.01% by mass or more and 30% by mass or less. More preferably, they are 0.1 mass% or more and 15 mass% or less, More preferably, they are 1 mass% or more and 15 mass% or less. When the addition amount of the flocculant is less than 0.01% by mass, the color material is insufficiently aggregated when contacting the ink, and the optical density, bleeding, and intercolor bleeding may be deteriorated. When the amount exceeds 30% by mass, the jetting characteristics are degraded, and the liquid may not be jetted normally.

As the treatment liquid, a water-soluble organic solvent similar to the ink can be used. The content of the water-soluble organic solvent is 1 to 60% by mass, preferably 5 to 40% by mass. When the amount of the water-soluble organic solvent is less than 1% by mass, a sufficient optical density may not be obtained. Conversely, when the amount is more than 60% by mass, the viscosity of the liquid increases and the liquid In some cases, the injection characteristics of the engine became unstable.
In addition, the polymer dispersant used in the ink can be added to the treatment liquid.

  The surface tension and viscosity of the treatment liquid should have the same characteristics as ink.

  Here, the number of coarse particles of 5 μm or more in the mixed liquid of the ink and the treatment liquid is preferably 1,000 / μL or more. More preferably, it is 2,500 / μL or more, and further preferably 5,000 / μL or more. When the number of coarse particles of 5 μm or more in the mixed liquid of the ink and the treatment liquid is less than 1,000 / μL, the optical density sometimes decreases.

  For the coarse particle number of 5 μm or more in the mixed liquid of ink and processing liquid, two liquids are mixed at a mass ratio of 1: 1, and 2 μL is collected while stirring, and Accumizer TM770 Optical Particle Sizer (Particle Sizing). Measured using a system). In addition, the density of the color material was input to the density of the dispersed particles as a parameter at the time of measurement. The density of the colored fine particles can be determined by measuring the powder obtained by heating and drying the ink using a hydrometer or a specific gravity bottle.

(Inkjet ink tank)
The ink-jet ink tank (including the treatment liquid tank) of the present invention stores each liquid of the ink-jet ink of the present invention or the ink-jet ink set of the present invention. For example, JP-A-2001-138541 It can be applied to the ink tank described in 1. In this case, even when ink is filled in the ink tank and ink is ejected from the recording head, the change in ink characteristics during long-term storage in the ink tank is suppressed, and in particular, the ejection properties from the recording head during long-term storage are sufficiently satisfactory. It will be a thing.

(Inkjet recording method, inkjet recording apparatus)
The inkjet recording method of the present invention is a method of forming an image by ejecting each liquid onto a recording medium using the inkjet ink of the present invention or the inkjet ink set of the present invention. In addition, when the inkjet ink set of the present invention is used, printing is performed so that the inkjet ink and the treatment liquid are brought into contact with each other.

  On the other hand, an ink jet recording apparatus of the present invention comprises a recording head for discharging each liquid onto a recording medium using the ink jet ink of the present invention or the ink jet ink set of the present invention. These are not only ordinary inkjet recording apparatuses, but also recording apparatuses equipped with heaters for controlling the drying of ink, or intermediate transfer mechanisms, and after printing a recording material on the intermediate, A recording apparatus or the like that transfers to a recording medium can be applied.

  In the inkjet recording method (apparatus) of the present invention, the liquid mass per drop is preferably 0.01 ng or more and 25 ng or less for both the inkjet ink and the treatment liquid. More preferably, they are 0.5 ng or more and 20 ng or less, More preferably, they are 0.5 ng or more and 8 ng or less. When the liquid mass per drop exceeded 25 ng, there was a case where bleeding deteriorated. This is because the contact angles of the ink and the treatment liquid with respect to the recording medium change depending on the drop amount, and the drop tends to spread toward the paper surface as the drop amount increases. When the liquid mass per drop was less than 0.01 ng, there was a case where the jetting stability deteriorated.

  However, in an ink jet apparatus capable of ejecting a plurality of drops from a single nozzle, the drop amount refers to the minimum drop amount that can be printed.

  In the case of using an ink jet ink set, the ink jet ink and the treatment liquid are applied onto the recording medium so that they come into contact with each other. This is because the ink aggregates due to the action, and the recording method is excellent in color developability, solid portion unevenness, optical density, bleeding, intercolor bleeding, and drying time. As long as they are in contact with each other, they may be given so as to be adjacent to each other or may be given so as to cover them.

  The order of application to the recording medium is to apply the inkjet ink after applying the treatment liquid. This is because the constituent components of the inkjet ink can be effectively aggregated by applying the treatment liquid first. Any ink jet ink may be applied at any time after the treatment liquid is applied. Preferably, it is 0.5 seconds or less after the treatment liquid is applied.

  In the ink jet recording method (apparatus) of the present invention, the mass ratio between the ink application amount and the treatment liquid application amount required for forming one pixel is preferably 1:20 to 20: 1. More preferably, it is 1: 10-10: 1, More preferably, it is 1: 5-5: 1. When the amount of ink applied for inkjet was too small or too large with respect to the amount of treatment liquid applied, there was a case where aggregation was insufficient, resulting in a decrease in optical density, deterioration in bleeding, and deterioration in intercolor bleeding. . Here, the pixel is a grid point formed when a desired image is divided by the minimum distance that can be applied with ink in the main scanning direction and the sub-scanning direction, and is appropriate for each pixel. By applying an appropriate ink set, the color and image density are adjusted, and an image is formed.

  The ink jet recording method (apparatus) of the present invention preferably adopts a thermal ink jet recording method or a piezo ink jet recording method from the viewpoint of the effect of improving bleeding and intercolor bleeding. The cause of this is not clear, but in the case of the thermal ink jet recording method, the ink is heated at the time of ejection and has a low viscosity, but since the temperature of the ink is lowered on the recording medium, the viscosity rapidly increases. Become. For this reason, it is considered that bleeding and intercolor bleeding have an improving effect. On the other hand, in the case of the piezo ink jet method, it is possible to discharge a high-viscosity liquid, and the high-viscosity liquid can suppress spreading in the paper surface direction on the recording medium. It is estimated that there is an improvement effect on intercolor bleeding.

  In the ink jet recording method (apparatus) of the present invention, replenishment (supply) of ink and processing liquid to the recording head is performed from an ink tank (including a processing liquid tank) filled with each liquid of ink and processing liquid. Is good. The ink tank is preferably a cartridge system that can be attached to and detached from the apparatus, and ink and processing liquid can be easily replenished by replacing the ink tank of this cartridge system.

  Hereinafter, preferred embodiments of the ink jet recording apparatus of the present invention will be described in detail with reference to the drawings. In the drawings, members having substantially the same functions are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a perspective view showing an external configuration of a preferred embodiment of an ink jet recording apparatus of the present invention. FIG. 2 is a perspective view showing an internal basic configuration of the ink jet recording apparatus (hereinafter referred to as an image forming apparatus) of FIG.

  The image forming apparatus 100 of this embodiment has a configuration that operates based on the above-described inkjet recording method of the present invention to form an image. That is, as shown in FIGS. 1 and 2, an image forming apparatus 100 mainly includes an external cover 6, a tray 7 on which a predetermined amount of recording medium 1 such as plain paper can be placed, and the recording medium 1 as an image forming apparatus. An image forming unit 8 (image forming unit) for forming an image by ejecting ink and processing liquid onto the surface of the recording medium 1; The main ink tank 4 is configured to supply ink and processing liquid to the sub ink tanks 5 of the forming unit 8.

  The conveyance roller 2 is a paper feed mechanism constituted by a pair of rollers rotatably disposed in the image forming apparatus 100, sandwiches the recording medium 1 set on the tray 7, and has a predetermined amount of recording medium 1. Are conveyed one by one into the image forming apparatus 100 at a predetermined timing.

  The image forming unit 8 forms an image with ink on the surface of the recording medium 1. The image forming unit 8 mainly includes a recording head 3, a sub ink tank 5, a power supply signal cable 9, a carriage 10, a guide rod 11, a timing belt 12, a driving pulley 13, and a maintenance unit 14. ing.

  The sub ink tank 5 has sub ink tanks 51, 52, 53, 54, and 55 in which different colors of ink and processing liquid are stored so as to be ejected from the recording head. These include, for example, black ink (K), yellow ink (Y), magenta ink (M), and cyan ink (C) as the first liquid, and processing liquid from the main ink tank 4 as the second liquid. Replenished and paid.

  The sub ink tank 5 is provided with an exhaust hole 56 and a supply hole 57, respectively. When the recording head 3 moves to the standby position (or replenishment position), the exhaust pin 151 and the replenishment pin 152 of the replenishing device 15 are inserted into the exhaust hole 56 and the replenishment hole 57, respectively. 5 and the replenishing device 15 can be connected. The replenishing device 15 is connected to the main ink tank 4 via the replenishing pipe 16, and the replenishing device 15 replenishes ink or processing liquid from the main ink tank 4 to the sub ink tank 5 through the replenishing hole 57.

  Here, the main ink tank 4 also has main ink tanks 41, 42, 43, 44, 45 in which different colors of ink and processing liquid are stored. These are filled with, for example, black ink (K), yellow ink (Y), magenta ink (M), and cyan ink (C) as the first liquid, and the processing liquid as the second liquid, Each is stored in the image forming apparatus 100 in a detachable manner.

  Furthermore, the power supply signal cable 9 and the sub ink tank 5 are connected to the recording head 3, and when external image recording information is input from the power supply signal cable 9 to the recording head 3, the recording head 3 detects the image recording information. Based on the above, a predetermined amount of ink is sucked from each ink tank and discharged onto the surface of the recording medium. The power supply signal cable 9 also has a role of supplying power necessary for driving the recording head 3 to the recording head 3 in addition to the image recording information.

  The recording head 3 is arranged and held on a carriage 10, and the carriage 10 is connected to a guide rod 11 and a timing belt 12 connected to a driving pulley 13. With such a configuration, the recording head 3 extends along the guide rod 11 and is parallel to the surface of the recording medium 1 and perpendicular to the conveyance direction X (sub-scanning direction) of the recording medium 1 (main scanning direction). It can also be moved in the scanning direction.

  The image forming apparatus 100 includes control means (not shown) that adjusts the drive timing of the recording head 3 and the drive timing of the carriage 10 based on the image recording information. Thereby, an image based on the image recording information can be continuously formed in a predetermined region of the surface of the recording medium 1 that is transported at a predetermined speed along the transport direction X.

  The maintenance unit 14 is connected to a decompression device (not shown) via a tube. Further, the maintenance unit 14 is connected to the nozzle portion of the recording head 3 and has a function of sucking ink from the nozzles of the recording head 3 by reducing the pressure in the nozzles of the recording head 3. By providing the maintenance unit 14, if necessary, excess ink adhering to the nozzles during operation of the image forming apparatus 100 is removed, or evaporation of ink from the nozzles is suppressed when the operation is stopped. be able to.

  FIG. 3 is a perspective view showing the external configuration of another preferred embodiment of the ink jet recording apparatus of the present invention. FIG. 4 is a perspective view showing an internal basic configuration of the ink jet recording apparatus (hereinafter referred to as an image forming apparatus) of FIG. The image forming apparatus 101 of the present embodiment has a configuration that operates based on the above-described inkjet recording method of the present invention to form an image.

  In the image forming apparatus 101 shown in FIGS. 3 and 4, the width of the recording head 3 is equal to or larger than the width of the recording medium 1 and does not have a carriage mechanism, and the sub-scanning direction (conveying direction of the recording medium 1: arrow X). Direction) paper feed mechanism (the transport roller 2 is shown in the present embodiment, but a belt-type paper feed mechanism may be used, for example).

  Although not shown, the nozzle group for discharging each color (including the treatment liquid) is also provided in the same manner as the sub ink tanks 51 to 55 are sequentially arranged in the sub scanning direction (conveyance direction of the recording medium 1: arrow X direction). They are arranged in the sub-scanning direction. Other configurations are the same as those of the image forming apparatus 100 shown in FIGS. In the drawing, since the recording head 3 does not move, the sub ink tank 5 is always connected to the replenishing device 15. However, the sub ink tank 5 may be connected to the replenishing device 15 at the time of ink replenishment.

  In the image forming apparatus 101 shown in FIGS. 3 and 4, since the printing in the width direction (main scanning direction) of the recording medium 1 is performed collectively by the recording head 3, the configuration of the apparatus is simpler than the system having the carriage mechanism. Yes, the printing speed is also increased.

(Inkjet ink inspection method)
The ink-jet ink inspection method of the present invention has the formula (1): (Ratio of the polymer dispersant to the pigment in the ink excluding sediment after centrifugation (centrifugation condition: centrifugal acceleration 9000 g × 30 min)) ) / (Ratio of the polymer dispersant to the pigment in the ink before the centrifugal treatment), an ink inspection step for obtaining a characteristic value.

  The meaning of the characteristic value represented by the above formula (1), the measurement method, and the range of the characteristic value are as described in the description of the inkjet ink of the present invention. Then, in the ink inspection process, the characteristic value represented by the expression (1) is obtained, and for example, by determining whether or not the characteristic value range is satisfied, the ink to be inspected has improved ink storage stability. Whether it is excellent or not can be inspected.

  In the ink jet ink inspection method of the present invention, the formula (2): (solid content ratio in ink excluding sediment after centrifugal treatment (centrifugal treatment condition: centrifugal acceleration 9000 g × 30 min)) / (centrifugal treatment) You may perform the 2nd test process which calculates | requires the characteristic value shown by the solid content ratio in the previous ink.

  The meaning of the characteristic value represented by the above formula (2), the measurement method, and the range of the characteristic value are as described in the description of the ink-jet ink of the present invention. Then, in the ink inspection process, the characteristic value represented by the equation (2) is obtained, and for example, by determining whether or not the characteristic value range is satisfied, the ink to be inspected has improved ink storage stability. Whether it is excellent or not can be inspected more precisely.

  These ink inspection processes may be carried out as a single process, but by incorporating them into the ink jet ink manufacturing process, they can be inspected appropriately during the manufacturing process, and ink having excellent ink storage stability can be obtained with a high yield. It can be manufactured.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, these examples do not limit the present invention.

Example 1
The following ink components were mixed, stirred, and then filtered using a membrane filter having a pore size of 5 μm to prepare an ink.

-Ink component-
Pigment dispersion (carbon black concentration: 15% by mass, polymer dispersant (methyl methacrylate-ethyl acrylate 2-ethylhexyl methacrylate-polyethylene glycol-acrylic acid polymer, weight average molecular weight 20000) concentration: 5% by mass): 30 mass %
・ Glycerin: 10% by mass
・ Ethylene glycol: 5% by mass
・ 2-Pyrrolidone: 5% by mass
・ Orphine E1010: 0.5% by mass
・ Water: Remaining amount

  However, the pigment dispersion was prepared as follows. First, the polymer dispersant was precisely synthesized to have a molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) = 1.15. Carbon black as a pigment was refined to a volatile content of 0.3% by mass and an inorganic metal impurity of 15 ppm. After the polymer dispersant was dissolved in methyl ethyl ketone, the pigment was added and kneaded, and after adding pure water, methyl ethyl ketone was removed to obtain a base pigment dispersion. Further, this base pigment dispersion was diluted with pure water to obtain an 8% by mass pigment dispersion, and then centrifuged at 12,000 g × 20 min to collect the supernatant. The supernatant was concentrated and filtered through a 2 μm filter to obtain a pigment dispersion.

  The obtained ink was dried under reduced pressure to obtain a solid content ratio of 0.0598. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.334.

  Subsequently, the obtained ink was subjected to a centrifugal treatment (centrifugal acceleration 9000 g × 30 min), and then the supernatant was collected and dried under reduced pressure to obtain a solid content ratio of 0.0539. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.370.

  As a result, the characteristic value represented by the above formula (1) was 1.11. The characteristic value shown by the above formula (2) was 0.95.

The obtained ink has a viscosity of 3.2 mPa · s, a surface tension of 33.5 mN / m, a particle number of 0.5 μm or more in 2 μl of ink of 4.8 × 10 ⁴ particles, and an absolute value of ζ potential. Of 44.6 mV, and the average volume dispersion particle size of the pigment was 69 nm.

(Example 2)
The following ink components were mixed, stirred, and then filtered using a membrane filter having a pore size of 5 μm to prepare an ink.

-Ink component-
Pigment dispersion (Pigment. Red. 122 concentration: 10% by mass, polymer dispersant (styrene-methyl acrylate-acrylic acid tetraethylene glycol-methacrylic acid polymer, weight average molecular weight 30000) concentration: 7.5% by mass) : 50% by mass
・ Diethylene glycol: 15% by mass
Propylene glycol: 5% by mass
・ Butyl carbitol: 4% by mass
・ Oxyethylene oleyl ether: 1.0% by mass
・ Water: Remaining amount

  However, the pigment dispersion was prepared as follows. First, the polymer dispersant is subjected to precise synthesis, and the methyl acrylate / tetraethylene glycol acrylate portion is subjected to block polymerization, and the overall molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)). ) = 1.12. After the polymer dispersant was dissolved in methyl ethyl ketone, the pigment was added and kneaded, and after adding pure water, methyl ethyl ketone was removed to obtain a base pigment dispersion. Further, this base pigment dispersion was diluted with pure water to obtain a 7% by mass pigment dispersion, and then centrifuged at 12,000 g × 20 min to collect the supernatant. The supernatant was concentrated and filtered through a 2 μm filter to obtain a pigment dispersion.

  The obtained ink was dried under reduced pressure and the solid content ratio was determined to be 0.0876. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.749.

  Subsequently, the obtained ink was subjected to centrifugal treatment (centrifugal acceleration 9000 g × 30 min), and then the supernatant was collected and dried under reduced pressure to obtain a solid content ratio of 0.0815. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.938.

  As a result, the characteristic value represented by the above formula (1) was 1.25. The characteristic value shown by the above formula (2) was 0.93.

Further, the obtained ink has a viscosity of 4.4 mPa · s, a surface tension of 36.5 mN / m, a number of particles of 0.5 μm or more in 2 μl of ink of 1.5 × 10 ⁵ particles, and an absolute value of ζ potential. 35.7 mV, and the average volume dispersion particle size of the pigment was 93 nm.

(Example 3)
The following ink components were mixed, stirred, and then filtered using a membrane filter having a pore size of 5 μm to prepare an ink.

-Ink component-
Pigment dispersion (Pigment. Blue. 15: 3 concentration: 12% by mass, polymer dispersant (butyl methacrylate-oleyl acrylate-diethylene glycol methacrylate-methacrylic acid polymer, weight average molecular weight 10,000) concentration: 6% by mass) : 50% by mass
・ Diethylene glycol: 7% by mass
・ Dipropylene glycol: 4% by mass
・ Surfinol 440: 1.0% by mass
・ Surfinol 485: 1.0% by mass
・ Water: Remaining amount

  However, the pigment dispersion was prepared as follows. First, the polymer dispersant was subjected to precise synthesis to obtain a total molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) = 1.08. After the polymer dispersant was dissolved in methyl ethyl ketone, the pigment was added and kneaded, and after adding pure water, methyl ethyl ketone was removed to obtain a base pigment dispersion. Further, this base pigment dispersion was diluted with pure water to obtain a 6% by mass pigment dispersion, and then centrifuged at 12,000 g × 20 min to collect the supernatant. The supernatant was concentrated and filtered through a 2 μm filter to obtain a pigment dispersion.

  The obtained ink was dried under reduced pressure to obtain a solid content ratio of 0.0900. Further, the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.501.

  Subsequently, the obtained ink was subjected to a centrifugal treatment (centrifugal acceleration 9000 G × 30 min), and then the supernatant was collected and dried under reduced pressure to obtain a solid content ratio of 0.0753. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.725.

  As a result, the characteristic value represented by the above formula (1) was 1.45. Moreover, the characteristic value shown by the said Formula (2) was 0.84.

Further, the obtained ink has a viscosity of 2.9 mPa · s, a surface tension of 28.7 mN / m, a number of particles of 0.5 μm or more in 2 μl of ink of 1.2 × 10 ⁵ particles, and an absolute value of ζ potential. 33.7 mV, and the average volume dispersion particle size of the pigment was 61 nm.

Example 4
The following ink components were mixed, stirred, and then filtered using a membrane filter having a pore size of 5 μm to prepare an ink.

-Ink component-
Pigment dispersion (carbon black concentration: 11.5% by mass, polymer dispersant (styrene-hexyl methacrylate-propyl acrylate-methacrylic acid polyethylene glycol-methacrylic acid polymer, weight average molecular weight 8000)) concentration: 7.2 mass %): 35% by mass
・ Glycerin: 10% by mass
・ N-methyl-2-pyrrolidone: 5% by mass
・ 1,2-hexanediol: 2% by mass
・ Water: Remaining amount

  However, the pigment dispersion was prepared as follows. 10 parts by mass of carbon black was added to 50 parts by mass of a polymer dispersant (styrene-hexyl methacrylate-propyl acrylate-polyethylene glycol-methacrylic acid polymer) aqueous solution (dispersant concentration 10 mass%), and after stirring, Dispersion treatment was performed with a microfluidizer, and then the coarse portion was cut by centrifugation (conditions 10,000 g × 20 min) to obtain a pigment dispersion.

  The obtained ink was dried under reduced pressure to obtain a solid content ratio of 0.0650. Further, the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.870.

  Subsequently, the obtained ink was subjected to centrifugal treatment (centrifugal acceleration 9000 g × 30 min), and then the supernatant was collected and dried under reduced pressure to obtain a solid content ratio of 0.0605. Further, the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.738.

  As a result, the characteristic value represented by the above formula (1) was 1.18. The characteristic value shown by the above formula (2) was 0.93.

The obtained ink has a viscosity of 2.7 mPa · s, a surface tension of 42.5 mN / m, a particle number of 0.5 μm or more in 2 μl of ink of 7.8 × 10 ⁴ particles, and an absolute value of ζ potential. Of 25.8 mV, and the average volume dispersion particle size of the pigment was 85 nm.

(Example 5)
The following ink components were mixed, stirred, and then filtered using a membrane filter having a pore size of 5 μm to prepare an ink.

-Ink component-
Pigment dispersion (carbon black concentration: 20% by mass, polymer dispersant (methyl acrylate-polyethylene glycol acrylate-acrylic acid polymer, weight average molecular weight 15000) concentration: 8% by mass): 25% by mass
・ Glycerin: 20% by mass
・ Diethylene glycol: 10% by mass
・ Orphine E1010: 1.5% by mass
・ Butyl carbitol: 5% by mass
・ Water: Remaining amount

  However, the pigment dispersion was prepared as follows. First, the polymer dispersant was subjected to precise synthesis to obtain a molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) = 1.14. Carbon black as a pigment was refined to a volatile content of 0.5% by mass and an inorganic metal impurity of 12 ppm. A 10 mass% pigment dispersion composed of the pigment, polymer dispersant, and pure water was centrifuged at 15000 g × 20 min, and the supernatant was recovered. The supernatant was concentrated and filtered through a 2 μm filter to obtain a pigment dispersion.

  The obtained ink was dried under reduced pressure to obtain a solid content ratio of 0.0697. Further, the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.404.

  Subsequently, the obtained ink was subjected to centrifugal treatment (centrifugal acceleration 9000 g × 30 min), and then the supernatant was collected and dried under reduced pressure to obtain a solid content ratio of 0.0662. Further, the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.432.

  As a result, the characteristic value represented by the above formula (1) was 1.07. The characteristic value shown by the above formula (2) was 0.95.

Further, the obtained ink has a viscosity of 5.4 mPa · s, a surface tension of 30.4 mN / m, a particle number of 0.5 μm or more in 2 μl of ink of 2.7 × 10 ⁵ particles, and an absolute value of ζ potential. 34.3 mV, and the average volume dispersion particle size of the pigment was 76 nm.

(Example 6)
The following ink components were mixed, stirred, and then filtered using a membrane filter having a pore size of 5 μm to prepare an ink.

-Ink component-
Pigment dispersion (carbon black concentration: 20% by mass, polymer dispersant (butyl acrylate-methacrylic acid triethylene glycol-acrylic acid polymer, weight average molecular weight 50000) concentration: 2% by mass): 35% by mass
・ Triethylene glycol: 13% by mass
・ N-methylpyrrolidone: 4% by mass
・ Diethylene glycol monohexyl ether: 1% by mass
・ Oxyethylene lauryl ether: 1.5% by mass
・ Water: Remaining amount

  However, the pigment dispersion was prepared as follows. First, molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) = 1.35 was set for the polymer dispersant. After the polymer dispersant was dissolved in methyl ethyl ketone, the pigment was added and kneaded, and after adding pure water, methyl ethyl ketone was removed to obtain a base pigment dispersion. Further, this base pigment dispersion was diluted with pure water and then filtered through a 2 μm filter to obtain a 20 mass% pigment dispersion.

  The obtained ink was dried under reduced pressure and the solid content ratio was determined to be 0.0771. Further, the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.099.

  Subsequently, the obtained ink was subjected to a centrifugal treatment (centrifugal acceleration 9000 g × 30 min), and then the supernatant was collected and dried under reduced pressure to obtain a solid content ratio of 0.0600. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.145.

  As a result, the characteristic value represented by the above formula (1) was 1.46. Moreover, the characteristic value shown by the said Formula (2) was 0.78.

The obtained ink had a viscosity of 2.8 mPa · s, a surface tension of 34.6 mN / m, a particle number of 0.5 μm or more in 2 μl of ink of 1.7 × 10 ⁵ particles, and an absolute value of ζ potential. The average volume dispersion particle size of the pigment was 105 nm.

(Comparative Example 1)
The following ink components were mixed, stirred, and then filtered using a membrane filter having a pore size of 5 μm to prepare an ink.

-Ink component-
Pigment dispersion (carbon black concentration: 15% by mass, polymer dispersant (ethyl acrylate-lauryl methacrylate-acrylic acid polymer, weight average molecular weight 15000) concentration: 1.5% by mass): 40% by mass
・ Ethylene glycol: 5% by mass
Propylene glycol: 3% by mass
Polyethylene glycol (weight average molecular weight 300): 5% by mass
・ Butyl carbitol: 10% by mass
・ Water: Remaining amount

  However, the pigment dispersion was prepared as follows. First, about the said polymer dispersing agent, the thing of molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) = 1.42 was used. Carbon black, which is a pigment, has a volatile content of 1.8% by mass and an inorganic metal impurity of 450 ppm. The above pigment, polymer dispersant, and pure water were kneaded and ground, then dispersed and filtered through a 5 μm filter to obtain a 15% by mass pigment dispersion.

  The obtained ink was dried under reduced pressure and the solid content ratio was determined to be 0.0662. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.100.

  Subsequently, the obtained ink was subjected to centrifugal treatment (centrifugal acceleration 9000 g × 30 min), and then the supernatant was collected and dried under reduced pressure to obtain a solid content ratio of 0.0497. Further, the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.172.

  As a result, the characteristic value represented by the above formula (1) was 1.72. The characteristic value shown by the above formula (2) was 0.75.

The obtained ink has a viscosity of 3.5 mPa · s, a surface tension of 34.5 mN / m, a particle number of 0.5 μm or more in 2 μl of ink of 1.7 × 10 ⁶ particles, and an absolute value of ζ potential. 21.0 mV, and the average volume dispersion particle size of the pigment was 95 nm.

(Comparative Example 2)
Other than using 28% by mass of pigment dispersion (carbon black concentration: 14.2% by mass, polymer dispersant (hexyl methacrylate-ethyl acrylate-acrylic acid polymer, weight average molecular weight 55000) concentration: 7.8% by mass)) Prepared an ink in the same manner as in Example 4.

  However, the pigment dispersion was prepared as follows. 10 parts by mass of carbon black is added to 50 parts by mass of a polymer dispersing agent (hexyl methacrylate-ethyl acrylate-acrylic acid polymer) aqueous solution (dispersing agent concentration: 10% by mass), followed by dispersion treatment with a nanomizer. Thereafter, coarse portions were cut by centrifugation (condition 4000 g × 10 min) to obtain a pigment dispersion.

  The obtained ink was dried under reduced pressure to obtain a solid content ratio of 0.0620. Further, the ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.548.

  Subsequently, the obtained ink was subjected to centrifugal treatment (centrifugal acceleration 9000 g × 30 min), and then the supernatant was collected and dried under reduced pressure to obtain a solid content ratio of 0.0446. The ratio of the polymer dispersant to the pigment (polymer dispersant / pigment) was determined to be 0.882.

  As a result, the characteristic value represented by the above formula (1) was 1.61. Further, the characteristic value represented by the above formula (2) was 0.72.

Further, the obtained ink has a viscosity of 2.8 mPa · s, a surface tension of 42.3 mN / m, the number of particles of 0.5 μm or more in 2 μl of ink is 4.5 × 10 ⁵ particles, and the ζ potential is an absolute value. 35.6 mV, and the average volume dispersion particle size of the pigment was 87 nm.

(Evaluation)
The following evaluation was performed about the ink of the said Example and the comparative example. The obtained ink was stored at room temperature (25 ° C.) for 6 months, and the viscosity after storage, the average volume dispersion particle size of the pigment, and the number of particles of 0.5 μm or more in 2 μl of ink (denoted as coarse amount) were examined. Compared to before storage (ink storage stability test A).

  The obtained ink was repeatedly stored at a temperature of 70 ° C./−30° C. every 2 days and stored for a total of 3 weeks. The viscosity after storage, the average volume dispersion particle diameter of the pigment, the surface tension, and 2 μl of ink. The number of particles having a particle size of 0.5 μm or more (denoted as coarse amount) was examined and compared with that before storage (ink storage stability test B).

  The evaluation criteria are “◎”: viscosity and particle size change <5%, coarse portion increase rate <20%, and “◯”: viscosity and particle size change <5%, coarse portion increase rate 20-50%. , “Δ” is: viscosity and particle size change 5 to 10%, coarse portion increase rate 50 to 100%, “x” is: viscosity and particle size change> 10%, coarse portion increase rate> 100%.

  The results are shown in Table 1.

  From the results in Table 1, it can be seen that the ink of this example satisfying the characteristic value represented by the formula (1) and further the characteristic value represented by the formula (2) is very excellent in ink storage stability. Further, it can be seen that the ink having high viscosity is particularly excellent in storage stability (showing the effect of claim 7).

  Further, it can be seen that the ink storage stability can be determined by obtaining the characteristic value represented by the expression (1) and further the characteristic value represented by the expression (2).

1 is a perspective view showing an external configuration of a preferred embodiment of an ink jet recording apparatus of the present invention. FIG. 2 is a perspective view showing an internal basic configuration of the ink jet recording apparatus of FIG. 1. It is a perspective view which shows the external appearance structure of other suitable one Embodiment of the inkjet recording device of this invention. FIG. 4 is a perspective view showing an internal basic configuration of the ink jet recording apparatus of FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100, 101 Image forming apparatus 1 Recording medium 2 Conveying roller 3 Recording head 4 Main ink tank 5 Sub ink tank 6 External cover 7 Tray 8 Image forming part 9 Power supply signal cable 10 Carriage 11 Guide rod 12 Timing belt 13 Drive pulley 14 Maintenance unit 15 Replenisher

Claims (14)

Water, a water-soluble organic solvent, a pigment, and a polymer dispersant having a weight average molecular weight of 800 or more for dispersing the pigment,
And, the formula (1): (ratio of the polymer dispersant to the pigment in the ink excluding sediment after centrifugation (centrifugation condition: centrifugal acceleration 9000 g × 30 min)) / (ink before the centrifugation) A characteristic value indicated by a ratio of the polymer dispersant to the pigment in the ink is 1.0 to 1.5.   Formula (2): (solid content ratio in ink excluding sediment after centrifugal treatment (centrifugal processing condition: centrifugal acceleration 9000 g × 30 min)) / (solid content ratio in ink before centrifugal treatment) 2. The ink-jet ink according to claim 1, wherein the characteristic value is 0.8 to 1.   The inkjet ink according to claim 1, wherein the pigment has an average volume dispersion particle diameter of 10 to 300 nm.   The inkjet ink according to claim 1, wherein the pigment is at least one selected from carbon black, phthalocyanine, and quinacridone pigment.   The inkjet ink according to claim 1, wherein the polymer dispersant includes a hydrophobic group and a hydrophilic group.   The inkjet ink according to claim 5, wherein the hydrophilic group includes a nonionic functional group.   The water-based inkjet ink according to claim 1, wherein the viscosity of the ink is 5 mPa · s or more, and the characteristic value represented by the formula (1) is 1.0 to 1.4. The ink-jet ink according to any one of claims 1 to 7,
A treatment liquid containing an aggregating agent having an action of aggregating or insolubilizing the components of the ink, a water-soluble organic solvent, and water;
An ink-jet ink set comprising:   An ink-jet ink tank comprising the ink-jet ink according to any one of claims 1 to 7 or the ink-jet ink set according to claim 8.   An ink jet recording using the ink jet ink according to any one of claims 1 to 7 or the ink jet ink set according to claim 8 to form an image by discharging each liquid onto a recording medium. Method.   The inkjet recording method according to claim 10, wherein each liquid supplied from the inkjet ink tank containing the inkjet ink or the inkjet ink set is ejected onto a recording medium.   A recording head for discharging each liquid onto a recording medium using the inkjet ink according to any one of claims 1 to 7 or the inkjet ink set according to claim 8 is provided. Inkjet recording device.   The inkjet recording apparatus according to claim 12, further comprising an inkjet ink tank that stores the inkjet ink or the inkjet ink set and supplies each liquid to the recording head.   Formula (1): (Ratio of the polymer dispersant to the pigment in the ink excluding sediment after centrifugal treatment (centrifugal treatment condition: centrifugal acceleration 9000 g × 30 min)) / (in the ink before the centrifugal treatment) A method for inspecting ink for ink jet, comprising: an ink inspection step for obtaining a characteristic value indicated by a ratio of the polymer dispersant to the pigment).

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