JP2010179519A - Inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording method which inhibits curling and interference with dripping of ink drops in high humidity and reduces maintenance burden. <P>SOLUTION: Ink composition containing dye, 25 mass% or less of water-soluble inorganic solvent based on the entire mass, and water, is cooled by a cooling means at the time of injection, thereby increasing its viscosity more than the viscosity at 25°C to record an image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inkjet recording method for recording an image by applying ink to a recording medium by an inkjet method.

  In recent years, various methods have been proposed as image recording methods for recording color images. In any case, there are high demands on the quality of recorded matter, such as image quality, texture, and curl after recording.

  For example, ink jet technology has been applied to the fields of office printers, home printers, and the like, but in recent years, it has been applied in the field of commercial printing. As a recording medium for ink-jet recording and ink used therefor, various techniques for obtaining a high-quality recorded matter such as color density, fixing property, resolution, and curling property after recording have been studied.

  When recording by the ink jet method, there are various recording media for recording, for example, recording on plain paper, and satisfactory image quality may not be obtained, or curling may occur after recording.

  In relation to the above, in order to prevent curling and ensure ejection stability in high-speed printing, an inkjet that ejects droplets of an ink composition having a viscosity of 2 to 5 mPa · s by heating the ink composition A recording method is disclosed (for example, see Patent Document 1). Also, a technique for obtaining a thick high-viscosity liquid by using a water-based ink containing a thermoreversible thickening polymer and an oil film-forming component and heating the thermoreversible thickening polymer to a transition temperature (see, for example, Patent Document 2) ), An ink jet recording apparatus using ink having a predetermined ink viscosity at room temperature or 40 to 100 ° C., and an ink head temperature-controlled from 40 ° C. to 100 ° C. (see, for example, Patent Document 3).

JP 2008-246749 A JP-A-8-259868 JP 2003-145914 A

  However, the above-described conventional technology cannot suppress the occurrence of curling in a high-humidity environment, and if too much heat is applied to the ink, the ink droplets interfere with each other and the image blurs, the head surface after recording, etc. The maintainability tends to deteriorate.

  In addition, in order to achieve a high resolution of, for example, 1200 dpi or more, the nozzles of the ejection head that ejects ink have recently been arranged with a high density such as a two-dimensional arrangement, and the flow path around the nozzles has been increased. Due to the structure such as shortening, it may be desirable in terms of ejection stability that the ink has a certain viscosity during ejection.

  The present invention has been made in view of the above, and an ink jet recording capable of suppressing the occurrence of curling under high humidity and ink droplet ejection interference, as well as improving ejection stability and reducing maintenance load. The object is to provide a method and to achieve the object.

Specific means for achieving the above object are as follows.
<1> The viscosity at the time of discharge of the ink composition containing a pigment, a water-soluble organic solvent of 25% by mass or less with respect to the total mass, and water is cooled by a cooling unit, so that the viscosity at 25 ° C. And an ink jet recording method for recording an image by raising it.
<2> The inkjet recording method according to <1>, wherein the viscosity of the ink composition at the time of ejection is in the range of 4 to 15 mPa · s.
<3> According to <1> or <2>, the viscosity of the ink composition at the time of ejection is increased by 0.5 mPa · s or more with respect to the viscosity at 25 ° C. by the cooling. Inkjet recording method.
<4> The inkjet recording method according to any one of <1> to <3>, wherein the cooling is performed in a temperature range of 15 ° C. to 24 ° C.
<5> In any one of the above items <1> to <4>, the ink composition is discharged using a liquid discharge head having a nozzle surface in which a plurality of nozzles are two-dimensionally arranged. The inkjet recording method described.
<6> The inkjet recording method according to any one of <1> to <5>, wherein the content of the water-soluble organic solvent in the ink composition is 20% by mass or less. is there.

<7> The ink jet recording method according to any one of <1> to <6>, wherein the ink composition further includes polymer particles.
<8> The inkjet recording method according to any one of <1> to <7>, wherein the total solid content of the ink composition is 20% by mass or less.
<9> The ink jet recording method according to <8>, wherein the total solid content of the ink composition is 15% by mass or less.
<10> The water-soluble organic solvent according to any one of <1> to <9>, wherein at least one of the water-soluble organic solvents is a water-soluble organic solvent having an SP value of 27.5 or less. Inkjet recording method.
<11> At least one water-soluble organic solvent having an SP value of 27.5 or less is a water-soluble organic solvent represented by the following general formula (1) and having a molecular weight of 240 to 1400. The inkjet recording method according to <10>.
R-A _n -OH General formula (1)
[Wherein, R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a group derived from a sugar alcohol having 3 to 12 carbon atoms, and A represents at least one selected from an ethyleneoxy group and a propyleneoxy group. N represents an integer of 3 to 24. ]
<12> The inkjet according to any one of <1> to <11>, wherein the pigment is a water-dispersible pigment in which at least a part of a surface thereof is coated with a water-insoluble resin. It is a recording method.

<13> The ink jet recording method according to any one of <7> to <12>, wherein the polymer particles are self-dispersing polymer particles.
<14> The ink jet recording method according to any one of <7> to <13>, wherein the polymer particles have a glass transition temperature (Tg) of 20 to 200 ° C.
<15> A step of applying a treatment liquid containing an aggregating agent that agglomerates components in the ink composition, wherein the image is recorded by bringing the ink composition into contact with the treatment liquid. The inkjet recording method according to any one of <1> to <14>.
<16> The inkjet recording method according to <15>, wherein the ink composition is discharged after the treatment liquid is applied.
<17> The inkjet recording method according to any one of <1> to <16>, further including a step of fixing the image at least by pressing the image using a pressure applying unit.

  According to the present invention, it is possible to provide an ink jet recording method capable of suppressing the occurrence of curling under high humidity and ink droplet ejection interference, as well as improving the ejection stability and reducing the maintenance load. .

Hereinafter, the ink jet recording method of the present invention will be described in detail.
In the inkjet recording method of the present invention, when an ink composition containing a pigment, a water-soluble organic solvent of 25% by mass or less based on the total mass, and water is ejected, the viscosity (ρ ^j ) of the ink composition at the time of ejection is set. The image is recorded by increasing the viscosity (ρ ²⁵ ) at 25 ° C. by cooling with a cooling means (hereinafter, the process of recording an image by discharging ink may be referred to as an “ink application process”). It is set as the structure which performs.

In the present invention, at the time of image recording, the ink composition is cooled in advance before ejection and the viscosity is increased from the viscosity at 25 ° C. (ρ ²⁵ ), so that the amount of solvent is relatively less than 25% by mass. Although it has a small aqueous composition, the effect on curling, dot formation, and ink spread after landing can be optimized, so that curling not only under normal humidity but also under high humidity is further suppressed. Liquid ejection having a nozzle surface in which a plurality of nozzles for ejecting an ink composition are two-dimensionally arranged to further prevent the ink droplets from interfering with each other (droplet ejection interference) after the droplets to cause blurring and blurring in the image. Also in the head, the ejection stability is good, and the removability (maintenance) of ink attached to the nozzle surface can be further improved. As a result, high-quality image recording can be performed stably over a long period of time.

-Ink application process-
In the ink application process of the present invention, the ink composition (hereinafter referred to simply as ink) to be ejected is cooled by a cooling means at the time of image recording, whereby the viscosity (ρ ^j ) of the ink at the time of ejection is 25 ° C. The viscosity is increased with respect to the viscosity (ρ ²⁵ ). Considering the stability of ink during storage and the fluidity of ink in the device, the viscosity does not become too high at 25 ° C, which is close to the room temperature environment, and the viscosity is increased during ejection, and it is high regardless of the humidity environment. It is possible to suppress the occurrence of curling even in a humid environment and to avoid the ink droplet ejection interference to achieve high image quality and a reduction in maintenance load.

In the present invention, the viscosity ρ ^j of the ink at the time of ejection is not decreased by heating or increased by heating, but by providing a cooling means to cool the ink and lower the temperature, Viscosity ρ ^j is increased from viscosity ρ ²⁵ at 25 ° C. There is no particular limitation as long as the relationship between the viscosity ρ ^j at the time of discharge and the viscosity ρ ²⁵ at 25 ° C. satisfies the relationship ρ ^j > ρ ^25. From the viewpoint of reducing droplet interference and maintenance addition, it is preferable to increase the viscosity ρ ^j at the time of discharge by 0.5 mPa · s or more with respect to the viscosity ρ ²⁵ , and the width of the viscosity increase with respect to the viscosity ρ ²⁵ is 1.0 mPa · More than s is more preferable. Furthermore, it is preferable to increase the viscosity ρ ^j at the time of discharge to a range of 4 to 15 mPa · s.
Among them, the viscosity ρ ²⁵ at 25 ° C. is 0.5 to 8 mPa · s in that the effect of preventing the occurrence of curling under high humidity and the effect of reducing the impact of droplet ejection and maintenance are more remarkable, and the viscosity [rho ²⁵ viscosity [rho ^j during discharge after cooling 0.5 mPa · s or more with respect to, and more preferably embodiment discharges increased 1.0 mPa · s or higher, particularly, 0.5~8mPa · s A mode in which the viscosity ρ ^j at the time of discharge is increased by 1.3 mPa · s or more with respect to the viscosity ρ ²⁵ is preferably discharged.

When the viscosity ρ ^j is increased by cooling the ink, it is effective to adjust the viscosity to the above range based on the temperature range of 15 ° C. to 24 ° C., and the viscosity ρ based on the temperature range of 15 ° C. to 24 ° C. It is more effective to adjust the viscosity of the ink in which ²⁵ is 0.5 to 8 mPa · s to the above range.

  The cooling means is not particularly limited as long as the ink before ejection can be cooled. For example, the cooling means may be a means for cooling ink in a storage tank for storing ink or an ink flow path through which ink flows. Examples of the cooling means include a blower fan, a heat radiating fin, a refrigerant circulation cooler, a chiller, and a Peltier element. Examples of the refrigerant circulation cooler include a refrigerant circulation system including a cooling pipe that circulates and circulates the refrigerant and exchanges heat with the refrigerant to cool the ink.

In the present invention, when an ink composition is ejected using a liquid ejection head having a nozzle surface in which a plurality of nozzles are two-dimensionally arranged in high density, the effect of increasing the viscosity ρ ^j relative to the viscosity ρ ²⁵ Is big. For example, in order to achieve a high resolution of 1200 dpi or more, when the nozzles of the ejection head that ejects ink are arranged at a high density such as a two-dimensional arrangement, the ejection is unstable due to the structure such as the flow path around the nozzle being shortened. May be. For example, in a piezo element, when the ink viscosity at the time of ejection becomes low, the vibration is not attenuated, so that ejection is likely to become unstable. When the nozzles of the ejection head are two-dimensionally arranged at high density, etc., the viscosity ρ ^j is increased with respect to the viscosity ρ ²⁵ , so that a certain degree of viscosity is maintained during ejection. Can be maintained.

  Specifically, the image recording using the ink-jet method is performed by supplying energy to obtain a desired recording medium, that is, plain paper, resin-coated paper, for example, JP-A-8-169172 and JP-A-8-27693. Publication No. 2-276670, No. 7-276789, No. 9-323475, No. JP-A-62-238783, JP-A-10-153898, No. 10-217473, No. 10- No. 235995, No. 10-337947, No. 10-217597, etc., by discharging the ink composition onto an inkjet exclusive paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, etc. The As a preferable ink jet recording method for the present invention, the method described in paragraph Nos. 0093 to 0105 of JP-A No. 2003-306623 can be applied.

The inkjet method is not particularly limited, and is a known method, for example, a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses vibration pressure of a piezoelectric element, An acoustic ink jet system that converts an electrical signal into an acoustic beam, irradiates the ink with ink, and ejects the ink using radiation pressure, and a thermal ink jet that forms bubbles by heating the ink and uses the generated pressure (bubble jet (registered) Trademark)) method or the like. As an ink jet method, in particular, the method described in Japanese Patent Application Laid-Open No. Sho 54-59936 causes an abrupt volume change of the ink subjected to the action of thermal energy, and the ink is ejected from the nozzle by the action force due to this state change. Ink jet method can be used effectively.
The ink jet method includes a method of ejecting a large number of low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method using is included.

Further, the ink jet head used in the ink jet method may be an on-demand method or a continuous method. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Specific examples include an ink jet type, a bubble jet (registered trademark) type, an electrostatic attraction type (for example, an electric field control type, a slit jet type, etc.) and a discharge type (for example, a spark jet type). However, any discharge method may be used.
There are no particular restrictions on the ink nozzles used when recording by the ink jet method, and they can be appropriately selected according to the purpose.

  As an inkjet head, a short serial head is used, and a shuttle system that performs recording while scanning the head in the width direction of the recording medium, and a line head in which recording elements are arranged corresponding to the entire area of one side of the recording medium There is a line system using. In the line system, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, and a carriage system such as a carriage for scanning a short head is not necessary. Further, since complicated scanning control of the carriage movement and the recording medium is not required, and only the recording medium is moved, the recording speed can be increased as compared with the shuttle system. The ink jet recording method of the present invention can be applied to any of these, but when applied to a line system in which ink is applied at high speed and generally does not perform dummy jet, curling prevention, ejection accuracy, and droplet ejection interference. The effect of improving the image quality by avoidance is great.

Next, the ink composition will be described in detail.
The ink composition in the present invention comprises at least a pigment, a water-soluble organic solvent, and water, and the content of the water-soluble organic solvent is 25% by mass or less. The ink composition can be constituted by using other components such as resin particles and a surfactant as required.

In the ink composition of the present invention, the viscosity ρ ^j at the time of ejection is increased with respect to the viscosity ρ ²⁵ as described above, particularly by setting the content of the water-soluble organic solvent to 25% by mass or less based on the total mass of the ink. In this case, it is possible to further improve the effect of preventing the occurrence of curling under high humidity, and the effect of reducing ink drop interference and maintenance load. That is, when it exceeds 25% by mass, the occurrence of curling under high humidity cannot be prevented.

  The ink composition used in the inkjet recording method of the present invention preferably has a total solid content of 20% by mass or less. Although the ink viscosity tends to be low in the low solid content region where the total solid content in the ink is 20% by mass or less, the ink jet recording method of the present invention performs recording by increasing the viscosity at the time of ejection, The effect of reducing ink drop interference and maintenance load is more remarkable. Especially, it is preferable that the range of total solid content is 15 mass% or less, and it is especially preferable that it is the range of 6-15 mass%.

<Pigment>
The ink composition in the present invention contains at least one pigment. The pigment can be appropriately selected according to the purpose, and may be either an organic pigment or an inorganic pigment.
Examples of the organic pigment include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. For example, examples of the azo pigment include azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments. Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinofullerone pigments. Examples of the dye chelates include basic dye chelates and acidic dye chelates. Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable. In addition, as carbon black, what was manufactured by well-known methods, such as a contact method, a furnace method, a thermal method, is mentioned, for example. Among these pigments, water-dispersible pigments are preferable.

Specific examples of the water dispersible pigment include the following pigments (1) to (4).
(1) An encapsulated pigment, that is, a polymer dispersion in which a pigment is contained in fine polymer particles. More specifically, the pigment is coated with a hydrophilic water-insoluble resin and is made hydrophilic by a resin layer on the pigment surface. (2) Self-dispersed pigment, that is, having at least one hydrophilic group on the surface and having at least one of water dispersibility and water solubility in the absence of a dispersant. (3) Resin-dispersed pigment, that is, a water-soluble water having a weight average molecular weight of 50,000 or less. (4) Surfactant-dispersed pigment, that is, a pigment dispersed by a surfactant Among these, (1) an encapsulated pigment, (2) a self-dispersed pigment, In particular Preferred is (1) an encapsulated pigment.

Here, (1) the encapsulated pigment will be described in detail.
The encapsulated pigment resin is not limited, but is a polymer compound that has self-dispersibility or solubility in a mixed solvent of water and a water-soluble organic solvent and has an anionic group (acidic). Is preferred. This resin usually has a number average molecular weight of preferably about 1,000 to 100,000, particularly preferably about 3,000 to 50,000. Further, this resin is preferably one that dissolves in an organic solvent to form a solution. When the number average molecular weight of the resin is within this range, it can function as a coating film for the pigment or as a coating film when used as an ink. The resin is preferably used in the form of an alkali metal or organic amine salt.

Specific examples of encapsulated pigment resins include thermoplastic, thermosetting or modified acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenol, silicone, or fluorine. Resins: Polyvinyl resins such as vinyl chloride, vinyl acetate, polyvinyl alcohol or polyvinyl butyral, polyester resins such as alkyd resins and phthalic resins, melamine resins, melamine formaldehyde resins, aminoalkyd cocondensation resins, urea resins, urea Examples thereof include amino materials such as resins, and materials having an anionic group such as copolymers or mixtures thereof.
Among these resins, an anionic acrylic resin is, for example, an acrylic monomer having an anionic group (hereinafter referred to as “anionic group-containing acrylic monomer”) and, if necessary, the anionic group-containing acrylic monomer. It is obtained by polymerizing another polymerizable monomer in a solvent. Examples of the anionic group-containing acrylic monomer include an acrylic monomer having one or more anionic groups selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic group. Among these, an acrylic monomer having a carboxyl group is used. Particularly preferred. Specific examples of the acrylic monomer having a carboxyl group include acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid and the like. Among these, acrylic acid or methacrylic acid is preferable.

  The encapsulated pigment can be produced by the conventional physical and chemical methods using the above components. For example, as described in JP-A-9-151342, JP-A-10-140065, JP-A-11-209672, JP-A-11-172180, JP-A-10-25440, or JP-A-11-43636. It can be manufactured by a method. Specific examples include the phase inversion emulsification method and the acid precipitation method described in JP-A-9-151342 and JP-A-10-140065. Among them, the phase inversion emulsification method is preferable in terms of dispersion stability. preferable. The phase inversion emulsification method will be described later.

The self-dispersing pigment is also a preferred example. The self-dispersing pigment refers to a large number of hydrophilic functional groups and / or salts thereof (hereinafter referred to as “dispersibility-imparting groups”) directly on the pigment surface or indirectly via an alkyl group, an alkyl ether group, an aryl group, or the like. Are pigments that can be dispersed in an aqueous medium without using a dispersant for dispersing the pigment. Here, “dispersed in an aqueous medium without using a dispersant” means that the pigment can be dispersed in an aqueous medium without using a dispersant for dispersing the pigment.
Inks containing self-dispersing pigments as colorants usually do not need to contain dispersants to disperse the pigments, so there is almost no foaming due to defoaming loss due to the dispersants, and ejection stability It is easy to prepare an ink that excels. The dispersibility-imparting groups to be bonded to the surface of the self-dispersing _{pigment, -COOH, -CO, -OH, -SO} 3 H, -PO 3 H 2 and quaternary ammonium and can be exemplified salts thereof, which are By applying physical treatment or chemical treatment to the pigment, the pigment is bonded by bonding (grafting) the active species having the dispersibility-imparting group or the dispersibility-imparting group to the pigment surface. Examples of the physical treatment include vacuum plasma treatment. Examples of the chemical treatment include a wet oxidation method in which the pigment surface is oxidized with an oxidizing agent in water, and a method in which a carboxyl group is bonded via a phenyl group by bonding p-aminobenzoic acid to the pigment surface. Can be exemplified.
In the present invention, for example, a self-dispersing pigment that is surface-treated by oxidation treatment with hypohalous acid and / or hypohalite or oxidation treatment with ozone can be mentioned as a preferred example. Commercially available products may be used as the self-dispersing pigment. Specifically, Microjet CW-1 (trade name; manufactured by Orient Chemical Industry Co., Ltd.), CAB-O-JET200, CAB-O-JET300 (trade name) ; Manufactured by Cabot Corporation).

  As the pigment, a water-insoluble resin among the pigment dispersant is used, and an encapsulated pigment in which at least a part of the surface of the pigment is coated with the water-insoluble resin, for example, a polymer emulsion in which the pigment is contained in water-insoluble resin particles is preferable. More specifically, a water-dispersible pigment that can be dispersed in water by covering at least a part of the pigment with a water-insoluble resin and forming a resin layer on the surface of the pigment is preferable.

Here, the phase inversion emulsification method will be described.
The phase inversion emulsification method is basically a self-dispersion (phase inversion emulsification) method in which a mixed melt of a resin having a self-dispersing ability or a dissolving ability and a pigment is dispersed in water. The mixed melt may contain the above curing agent or polymer compound. Here, the mixed molten material refers to a mixed state that is not dissolved, a state that is dissolved and mixed, or a state that includes both of these states. A more specific production method of the “phase inversion emulsification method” includes the method described in JP-A-10-140065.
For more specific methods of the above phase inversion emulsification method and acid precipitation method, the descriptions in JP-A-9-151342 and JP-A-10-140065 can be referred to.

~ Pigment dispersant ~
The pigment dispersant can facilitate easy dispersion when the pigment is dispersed and stabilize the dispersion after dispersion. Examples of the pigment dispersant include nonionic compounds, anionic compounds, cationic compounds, and amphoteric compounds.

  Examples thereof include a copolymer of monomers having an α, β-ethylenically unsaturated group. Examples of monomers having an α, β-ethylenically unsaturated group include ethylene, propylene, butene, pentene, hexene, vinyl acetate, allyl acetate, acrylic acid, methacrylic acid, crotonic acid, crotonic acid ester, itaconic acid, itacone Acid monoester, maleic acid, maleic acid monoester, maleic acid diester, fumaric acid, fumaric acid monoester, vinyl sulfonic acid, styrene sulfonic acid, sulfonated vinyl naphthalene, vinyl alcohol, acrylamide, methacryloxyethyl phosphate, bismethacryloxy Styrene derivatives such as ethyl phosphate, methacryloxyethyl phenyl acid phosphate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, styrene, α-methylstyrene, vinyltoluene , Vinylcyclohexane, vinylnaphthalene, vinylnaphthalene derivatives, alkyl acrylates that may be substituted with aromatic groups, phenyl esters of acrylate, alkyl methacrylates that may be substituted with aromatic groups, phenyl esters of methacrylic acid, methacryl And acid cycloalkyl esters, crotonic acid alkyl esters, itaconic acid dialkyl esters, maleic acid dialkyl esters, and derivatives of the above compounds.

  A copolymer obtained by copolymerizing a single monomer or a plurality of monomers having an α, β-ethylenically unsaturated group can be used as a polymer dispersant. Specific examples include acrylic acid alkyl ester-acrylic acid copolymer, methacrylic acid alkyl ester-methacrylic acid copolymer, styrene-alkyl alkyl ester-acrylic acid copolymer, styrene-phenyl methacrylate-methacrylic acid, styrene. -Methacrylic acid cyclohexyl ester-methacrylic acid copolymer, styrene-styrene sulfonic acid copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinyl naphthalene-maleic acid Examples thereof include a copolymer, a vinyl naphthalene-methacrylic acid copolymer, a vinyl naphthalene-acrylic acid copolymer, polystyrene, polyester, and polyvinyl alcohol.

The pigment dispersant preferably has a weight average molecular weight of 2,000 to 60,000.
The amount of the pigment dispersant added to the pigment is preferably in the range of 10% to 100% of the pigment on a mass basis, more preferably 20% to 70% of the pigment, and still more preferably 40% to 50% of the pigment. It is.

One type of pigment may be used alone, or a plurality of types may be selected and used in combination within each group described above or between groups.
The content of the pigment in the ink is preferably 0.1 to 15% by mass with respect to the total mass of the ink from the viewpoint of color density, graininess, ink stability, and ejection reliability. The amount of 5 to 12% by mass is more preferable, and the amount of 1 to 10% by mass is particularly preferable.

<Water-soluble organic solvent>
The ink composition in the present invention contains at least one water-soluble organic solvent.
The water-soluble organic solvent can obtain an effect of preventing drying, wetting or promoting penetration. In order to prevent drying, the ink adheres to and drys at the ink discharge port of the ejection nozzle and is used as an anti-drying agent to prevent clogging. For drying prevention and wetting, the vapor pressure is lower than that of water. A water-soluble organic solvent is preferred. Further, for penetration promotion, it can be used as a penetration enhancer that enhances ink permeability to paper.

  Examples of water-soluble organic solvents include alkanediols (polyhydric alcohols) such as glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, and propylene glycol; sugars such as glucose, mannose, and fructose; Alcohols: hyaluronic acids; C1-C4 alkyl alcohols such as ethanol, methanol, butanol, propanol, isopropanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol Monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol Mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl Ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol Monomethyl ether, dipropylene glycol mono-n-propyl ether, di B propylene glycol glycol ethers such as monomethyl -iso- propyl ether. These can be used individually by 1 type or in combination of 2 or more types.

  For the purpose of preventing drying and wetting, polyhydric alcohols are useful. For example, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol, 2 , 3-butanediol and the like. These may be used individually by 1 type and may use 2 or more types together.

  For the purpose of promoting penetration, polyol compounds are preferred, and aliphatic diols are preferred. Examples of the aliphatic diol include 2-ethyl-2-methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2-diethyl-1,3-propanediol, -Ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol and the like. Among these, preferred examples include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.

The water-soluble organic solvent preferably contains a water-soluble organic solvent having an SP value of 27.5 or less from the viewpoint of suppressing curling of the recording medium. When a water-soluble organic solvent having an SP value of 27.5 or less is used, the occurrence of curling under various environmental humidity after recording can be further suppressed.
The SP value (solubility parameter) is a value represented by the square root of the molecular cohesive energy and is calculated by the method described in RFFedors, Polymer Engineering Science, 14, p. 147 (1967).

Among these, a water-soluble organic solvent represented by the following general formula (1) and having a molecular weight of 240 to 1400 is more preferable.
R-A _n -OH General formula (1)
In the general formula (1), R is derived from a hydrogen atom, an alkyl group having 1 to 4 carbon atoms (for example, a methyl group, an ethyl group, a propyl group, a butyl group, or the like), or a sugar alcohol having 3 to 12 carbon atoms. Represents a group. R is preferably a group derived from an alkyl group having 1 to 4 carbon atoms or a sugar alcohol having 3 to 6 carbon atoms from the viewpoint of curling suppression effect.

  Here, the group derived from a sugar alcohol means a group formed by removing at least one hydroxyl group from a sugar alcohol. The position of the hydroxyl group removed from the sugar alcohol is not particularly limited, and may be a divalent or higher valent group from which two or more hydroxyl groups are removed. The water-soluble organic solvent may be a mixture of two or more formed by removing hydroxyl groups from different positions in the sugar alcohol molecule.

  A represents at least one selected from an ethyleneoxy group and a propyleneoxy group. n represents an integer of 3 to 24.

  Specific examples of the water-soluble organic solvent represented by the general formula (1) include GP-250 (manufactured by Sanyo Chemical Industries, Ltd.), GP-400 (manufactured by Sanyo Chemical Industries, Ltd.), 50HB-55 ( Sanyo Chemical Industries Co., Ltd.), 50HB-100 (Sanyo Chemical Industries Co., Ltd.), 50HB-260 (Sanyo Chemical Industries Co., Ltd.), SC-P400 (Sakamoto Pharmaceutical Co., Ltd.), SC- And E2000 (manufactured by Sakamoto Pharmaceutical Co., Ltd.).

  A molecular weight of 240 or more is useful in terms of curling suppression effect, and a molecular weight of 1400 or less is useful in terms of ink ejection stability. Especially, as a molecular weight of the water-soluble organic solvent whose SP value is 27.5 or less, the range of 250-800 is more preferable.

  Among water-soluble organic solvents having an SP value of 27.5 or less, a compound represented by the following structural formula (1) is particularly preferable from the viewpoint of suppressing the occurrence of curling after recording.

In Structural Formula (1), l, m, and n each independently represent an integer of 1 or more and satisfy l + m + n = 3-15. When the value of l + m + n is 3 or more, the curl suppressing effect is good, and when it is 15 or less, good discharge properties can be maintained.
Especially, l + m + n has the preferable range of 3-12, and the range of 3-10 is more preferable.

AO in the structural formula (1) represents ethyleneoxy (sometimes abbreviated as EO) and / or propyleneoxy (sometimes abbreviated as PO), and among them, a propyleneoxy group is preferable. Each AO of (AO) ₁ , (AO) _m , and (AO) _n may be the same or different.

  Examples of the water-soluble organic solvent having an SP value of 27.5 or less and the compound represented by the structural formula (1) are shown below. The values in parentheses are SP values. However, the present invention is not limited to these.

・ Diethylene glycol monoethyl ether (22.4)
・ Diethylene glycol monobutyl ether (21.5)
・ Triethylene glycol monobutyl ether (21.1)
・ Dipropylene glycol monomethyl ether (21.3)
Dipropylene glycol (27.2)

_{· NC 4 H 9 O (AO} ) 4 -H
(AO = EO or PO (EO: PO = 1: 1), SP value = 20.1)
_{· NC 4 H 9 O (AO} ) 10 -H
(AO = EO or PO (EO: PO = 1: 1), SP value = 18.8)
・ HO (A'O) ₄₀ -H
(A′O = EO or PO (EO: PO = 1: 3), SP value = 18.7)
・ HO (A''O) ₅₅ -H
(A ″ O = EO or PO (EO: PO = 5: 6), SP value = 18.8)
・ HO (PO) ₃ −H (SP value = 24.7)
HO (PO) ₇ -H (SP value = 21.2)
1,2-hexanediol (SP value = 27.4)

The content of the water-soluble organic solvent in the ink composition can be suitably contained in the range of 60% by mass or less, but is preferably 20% by mass or less. When the content of the water-soluble organic solvent is 20% by mass or less, the occurrence of curling during recording can be more effectively prevented regardless of changes in the humidity environment. The lower limit of the content of the water-soluble organic solvent is 1% by mass. The water-soluble organic solvent may be used alone or in combination of two or more.
The content of the water-soluble organic solvent having an SP value of 27.5 or less (particularly the compound represented by the structural formula (1)) in the total water-soluble organic solvent is preferably 10% by mass or more, and 30 More preferably, it is more than 50% by mass. When the content of the water-soluble organic solvent having an SP value of 27.5 or less is in the above range, the occurrence of curling can be more effectively suppressed without deteriorating the ink stability and the dischargeability.

<Water>
The ink composition in the present invention contains water, but the amount of water is not particularly limited. Among them, the amount of water is preferably 10% by mass or more and 99% by mass or less, more preferably 30% by mass or more and 80% by mass with respect to the total mass of the ink composition from the viewpoint of ensuring stability and ejection reliability. % Or less, and more preferably 50% by mass or more and 70% by mass or less.

<Polymer particles>
The ink composition in the invention preferably further contains polymer particles. This effectively improves the abrasion resistance of the formed image.

  Examples of polymer particles include thermoplastic, thermosetting or modified acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenol, silicone, or fluorine resins, chlorides, and the like. Amino resins such as polyvinyl resins such as vinyl, vinyl acetate, polyvinyl alcohol or polyvinyl butyral, polyester resins such as alkyd resins and phthalic resins, melamine resins, melamine formaldehyde resins, aminoalkyd cocondensation resins, urea resins, urea resins, etc. Examples thereof include particles of a resin having an anionic group such as a system material, a copolymer or a mixture thereof. Among these, anionic acrylic resins include, for example, an acrylic monomer having an anionic group (anionic group-containing acrylic monomer) and, if necessary, other monomers copolymerizable with the anionic group-containing acrylic monomer. Obtained by polymerization in a solvent. Examples of the anionic group-containing acrylic monomer include an acrylic monomer having one or more selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic group. Among them, an acrylic monomer having a carboxyl group (for example, acrylic acid) Methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid and the like), and acrylic acid or methacrylic acid is particularly preferred.

  As the polymer particles, self-dispersing polymer particles are preferable from the viewpoint of ejection stability and pigment dispersion stability, and self-dispersing polymer particles having a carboxyl group are more preferable. Self-dispersing polymer particles are water-insoluble polymers that can be dispersed in an aqueous medium by the functional groups (particularly acidic groups or salts thereof) of the polymer itself in the absence of other surfactants, By means of water-insoluble polymer particles containing no free emulsifier.

Here, the dispersed state refers to both an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in an aqueous medium in a solid state. It includes the state of.
The water-insoluble polymer in the present invention is preferably a water-insoluble polymer that can be in a dispersed state in which the water-insoluble polymer is dispersed in a solid state from the viewpoint of aggregation speed and fixing property when an ink composition is used.

  The dispersion state of the self-dispersing polymer particles in the present invention refers to a solution obtained by dissolving 30 g of a water-insoluble polymer in 70 g of an organic solvent (for example, methyl ethyl ketone), and a neutralizing agent capable of neutralizing 100% of the salt-forming group of the water-insoluble polymer. After mixing and stirring (apparatus: stirring apparatus with stirring blade, rotation speed 200 rpm, 30 minutes, 25 ° C.) (sodium hydroxide if the salt-forming group is anionic, acetic acid if cationic) and 200 g of water The state in which even after removing the organic solvent from the mixed solution, it can be visually confirmed that the dispersed state exists stably at 25 ° C. for at least one week.

  The water-insoluble polymer means a polymer having a dissolution amount of 10 g or less when the polymer is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., and the dissolution amount is preferable. Is 5 g or less, more preferably 1 g or less. The dissolution amount is the dissolution amount when neutralized with sodium hydroxide or acetic acid according to the kind of the salt-forming group of the water-insoluble polymer.

  The aqueous medium is configured to contain water, and may contain a hydrophilic organic solvent as necessary. In the present invention, it is preferably composed of water and 0.2% by mass or less of a hydrophilic organic solvent with respect to water, and more preferably composed of water.

  The main chain skeleton of the water-insoluble polymer is not particularly limited. For example, a vinyl polymer or a condensation polymer (epoxy resin, polyester, polyurethane, polyamide, cellulose, polyether, polyurea, polyimide, polycarbonate, etc.) is used. it can. Of these, vinyl polymers are particularly preferred.

Preferable examples of the vinyl polymer and the monomer constituting the vinyl polymer include those described in JP-A Nos. 2001-181549 and 2002-88294. In addition, a radical transfer of a vinyl monomer using a chain transfer agent, a polymerization initiator or an iniferter having a dissociable group (or a substituent that can be derived from the dissociable group), or a dissociable group in either the initiator or the terminator. A vinyl polymer in which a dissociable group is introduced at the end of a polymer chain by ionic polymerization using a compound having (or a substituent that can be derived from a dissociable group) can also be used.
Moreover, as a suitable example of the monomer which comprises a condensation type polymer and a condensation type polymer, what is described in Unexamined-Japanese-Patent No. 2001-247787 can be mentioned.

  From the viewpoint of self-dispersibility, the self-dispersing polymer particle is a water-insoluble polymer comprising a hydrophilic structural unit and a structural unit derived from an aromatic group-containing monomer or a structural unit derived from an alicyclic (meth) acrylate. It is preferable to include. In particular, when it has a structure derived from alicyclic (meth) acrylate, an ink having better image fixability and blocking resistance can be obtained. Further, when applied to ink jet recording, better ejection properties can be obtained.

The hydrophilic structural unit is not particularly limited as long as it is derived from a hydrophilic group-containing monomer, and even if it is derived from one kind of hydrophilic group-containing monomer, it contains two or more hydrophilic groups. It may be derived from a monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
In the present invention, the hydrophilic group is preferably a dissociable group and more preferably an anionic dissociable group from the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state. Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among them, a carboxyl group is preferable from the viewpoint of fixability when an ink composition is configured.

The hydrophilic group-containing monomer is preferably a dissociable group-containing monomer from the viewpoint of self-dispersibility and aggregability, and is preferably a dissociable group-containing monomer having a dissociable group and an ethylenically unsaturated bond. .
Examples of the dissociable group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

Specific examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. Specific examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate. It is done. Specific examples of the unsaturated phosphoric acid monomer include vinyl phosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2- Examples include acryloyloxyethyl phosphate.
Among the dissociable group-containing monomers, unsaturated carboxylic acid monomers are preferable and acrylic acid and methacrylic acid are more preferable from the viewpoints of dispersion stability and ejection stability.

The self-dispersing polymer particles preferably contain a polymer having a carboxyl group from the viewpoint of self-dispersibility and the aggregation rate when contacting with the treatment liquid, and have a carboxyl group and an acid value of 25 to 100 mgKOH / g. More preferably, it contains a polymer. Furthermore, the acid value is more preferably from 25 to 80 mgKOH / g, particularly preferably from 30 to 65 mgKOH / g, from the viewpoints of self-dispersibility and aggregation rate when contacting with the treatment liquid.
In particular, when the acid value is 25 or more, the stability of self-dispersibility is good, and when it is 100 mgKOH / g or less, the cohesiveness is improved.

The aromatic group-containing monomer is not particularly limited as long as it is a compound containing an aromatic group and a polymerizable group. The aromatic group may be a group derived from an aromatic hydrocarbon or a group derived from an aromatic heterocycle. In the present invention, an aromatic group derived from an aromatic hydrocarbon is preferable from the viewpoint of particle shape stability in an aqueous medium.
The polymerizable group may be a condensation polymerizable polymerizable group or an addition polymerizable polymerizable group. In the present invention, from the viewpoint of particle shape stability in an aqueous medium, an addition polymerizable group is preferable, and a group containing an ethylenically unsaturated bond is more preferable.

  The aromatic group-containing monomer is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond. The aromatic group-containing monomer may be used alone or in combination of two or more.

Examples of the aromatic group-containing monomer include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and a styrene monomer. Of these, aromatic group-containing (meth) acrylate monomers are preferred from the viewpoint of the balance between the hydrophilicity and hydrophobicity of the polymer chain and the ink fixability, and include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth). At least one selected from acrylates is more preferable, and phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are more preferable.
“(Meth) acrylate” means acrylate or methacrylate.

  The alicyclic (meth) acrylate includes a structural site derived from (meth) acrylic acid and a structural site derived from alcohol, and the structural site derived from alcohol is unsubstituted or substituted with alicyclic carbonization. It has a structure containing at least one hydrogen group. The alicyclic hydrocarbon group may be a structural site derived from alcohol itself or may be bonded to a structural site derived from alcohol via a linking group. The “alicyclic (meth) acrylate” means methacrylate or acrylate having an alicyclic hydrocarbon group.

The alicyclic hydrocarbon group is not particularly limited as long as it includes a cyclic non-aromatic hydrocarbon group, and is a monocyclic hydrocarbon group, a bicyclic hydrocarbon group, a tricyclic or more polycyclic ring. And a formula hydrocarbon group. Examples of the alicyclic hydrocarbon group include a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, a cycloalkenyl group, a bicyclohexyl group, a norbornyl group, an isobornyl group, a dicyclopentanyl group, a dicyclopentenyl group, and an adamantyl group. , Decahydronaphthalenyl group, perhydrofluorenyl group, tricyclo [5.2.1.0 ^2,6 ] decanyl group, and bicyclo [4.3.0] nonane. The alicyclic hydrocarbon group preferably has 5 to 20 carbon atoms in the alicyclic hydrocarbon group portion from the viewpoint of viscosity and solubility.

  Specific examples of the alicyclic (meth) acrylate are shown below. However, the present invention is not limited to these. As monocyclic (meth) acrylate, for example, cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) acrylate, Examples thereof include cycloalkyl (meth) acrylates having 3 to 10 carbon atoms in the cycloalkyl group such as cyclononyl (meth) acrylate and cyclodecyl (meth) acrylate. Examples of the bicyclic (meth) acrylate include isobornyl (meth) acrylate and norbornyl (meth) acrylate. Examples of the tricyclic (meth) acrylate include adamantyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and dicyclopentenyloxyethyl (meth) acrylate. These can be used alone or in admixture of two or more. Among these, bicyclic (meth) acrylate or tricyclic or higher polycyclic (meth) acrylate is preferable from the viewpoint of dispersion stability of self-dispersing polymer particles, fixing property, and blocking resistance, and isobornyl (meth) acrylate, At least one selected from adamantyl (meth) acrylate and dicyclopentanyl (meth) acrylate is more preferable.

  The self-dispersing polymer particles include a structural unit derived from an aromatic group-containing (meth) acrylate monomer or alicyclic (meth) acrylate, and the content is preferably 10% by mass to 95% by mass. When the content of the aromatic group-containing (meth) acrylate monomer or alicyclic (meth) acrylate is 10% by mass to 95% by mass, self-emulsification or dispersion stability is improved, and ink viscosity is further increased. Can be suppressed. In the present invention, from the viewpoints of stability in a self-dispersing state, stabilization of particle shape in an aqueous medium due to hydrophobic interaction between aromatic rings, and reduction in the amount of water-soluble components due to appropriate hydrophobicization of particles. More preferably, the content is from mass% to 90 mass%, more preferably from 15 mass% to 80 mass%, and particularly preferably from 25 mass% to 70 mass%.

  The self-dispersing polymer particles are configured using, for example, a structural unit derived from an aromatic group-containing monomer or a structural unit derived from an alicyclic (meth) acrylate, and a structural unit derived from a dissociable group-containing monomer. be able to. Furthermore, other structural units may be further included as necessary.

  The glass transition temperature (Tg) of the polymer particles (particularly self-dispersing polymer particles) is preferably 20 to 200 ° C., more preferably 20 to 190 ° C., and more preferably 30 to 180 ° C. from the viewpoint of the storage stability of the ink composition. Is more preferable, and 40-170 degreeC is especially preferable.

The Tg of the polymer particles can be appropriately controlled by a commonly used method. For example, the Tg of the polymer particle can be set to a desired value by appropriately selecting the type of polymerizable group of the monomer constituting the polymer, the type and composition ratio of the substituent on the monomer, the molecular weight of the polymer molecule constituting the polymer particle, and the like. The range can be controlled. Note that “measured Tg” obtained by actual measurement is applied as Tg. However, when measurement is difficult due to polymer decomposition or the like, “calculated Tg” calculated by the following calculation formula is applied.
Specifically, the “measurement Tg” is a value measured under normal measurement conditions using a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology. The “calculated Tg” is a value calculated using the Tg value of the monomer homopolymer according to the following formula (1).
1 / Tg = Σ (X _i / Tg _i ) (1)
In the formula (1), the polymer to be calculated is assumed to be copolymerized with n types of monomer components from i = 1 to n. X _i is the weight fraction of the i-th monomer (ΣX _i = 1), and Tg _i is the glass transition temperature (absolute temperature) of the homopolymer of the i-th monomer. However, Σ is the sum of i = 1 to n. The homopolymer glass transition temperature value (Tg _i ) of each monomer is the value of Polymer Handbook (3rd Edition) (by J. Brandrup, EHImmergut (Wiley-Interscience, 1989)).

The monomer forming the other structural unit is not particularly limited as long as it is a monomer copolymerizable with the aromatic group-containing monomer or the alicyclic (meth) acrylate and the dissociable group-containing monomer. Among these, an alkyl group-containing monomer is preferable from the viewpoint of flexibility of the polymer skeleton and ease of control of the glass transition temperature (Tg).
Examples of the alkyl group-containing monomer include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, alkyl (meth) acrylates such as t-butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate; hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) Ethylenically unsaturated monomers having a hydroxyl group such as acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate; Dialkylaminoalkyl (meth) acrylates such as ru (meth) acrylate; N-hydroxyalkyl (meth) such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide Acrylamide; N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meta And (meth) acrylamides such as N-alkoxyalkyl (meth) acrylamides such as acrylamide and N- (n-, iso) butoxyethyl (meth) acrylamide.

  The molecular weight range of the water-insoluble polymer constituting the self-dispersing polymer particles is preferably 3000 to 200,000, more preferably 5000 to 150,000, and more preferably 10,000 to 100,000 in terms of weight average molecular weight. Further preferred. By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less. In addition, a weight average molecular weight is measured by a gel permeation chromatograph (GPC), and is calculated by polystyrene conversion. As GPC, HLC-8020GPC (manufactured by Tosoh Corporation) is used, and TSKgel SuperHZM-H, TSKgel SuperHZ4000, and TSKgel SuperHZ200 (manufactured by Tosoh Corporation) are used as columns, and THF (tetrahydrofuran) is used as an eluent.

The water-insoluble polymer constituting the self-dispersing polymer particles is a structural unit derived from an aromatic group-containing (meth) acrylate monomer (preferably a structure derived from phenoxyethyl (meth) acrylate) from the viewpoint of controlling hydrophilicity / hydrophobicity of the polymer. Units and / or structural units derived from benzyl (meth) acrylate), or structural units derived from alicyclic (meth) acrylate (preferably isobornyl (meth) acrylate, adamantyl (meth) acrylate, and dicyclopentanyl) It is preferable that the structural unit derived from at least one of (meth) acrylates includes 15 to 80% by mass of the total mass of the self-dispersing polymer particles as a copolymerization ratio.
In addition, the water-insoluble polymer has a copolymerization ratio of 15 to 80% by mass of a structural unit derived from an aromatic group-containing (meth) acrylate monomer or alicyclic (meth) acrylate, from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. It preferably contains a structural unit derived from a carboxyl group-containing monomer and a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid), and phenoxyethyl (meth) A structural unit derived from acrylate and / or a structural unit derived from benzyl (meth) acrylate, or a structure derived from at least one of isobornyl (meth) acrylate, adamantyl (meth) acrylate, and dicyclopentanyl (meth) acrylate 15 to 80% by mass as a copolymerization ratio And a structural unit derived from a carboxyl group-containing monomer and a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester having 1 to 4 carbon atoms of (meth) acrylic acid). More preferably, in addition, the acid value is 25 to 100 and the weight average molecular weight is preferably 3000 to 200,000, the acid value is 25 to 95, and the weight average molecular weight is 5000 to 150,000. It is more preferable.

  Hereinafter, exemplary compounds B-01 to B-24 are listed as specific examples of the water-insoluble polymer constituting the self-dispersing polymer particles. However, the present invention is not limited to these. The numerical values other than Tg in parentheses represent the mass ratio of the copolymer component.

B-01: Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5, calculated Tg: 47 ° C.)
B-02: Phenoxyethyl acrylate / benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (30/35/29/6, calculated Tg: 37 ° C.)
B-03: Phenoxyethyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (50/44/6, calculated Tg: 33 ° C.)
B-04: Phenoxyethyl acrylate / methyl methacrylate / ethyl acrylate / acrylic acid copolymer (30/55/10/5, calculated Tg: 44 ° C.)
B-05: benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (35/59/6, calculated Tg: 56 ° C.
B-06: Styrene / phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (10/50/35/5, calculated Tg: 29 ° C.)
B-07: benzyl acrylate / methyl methacrylate / acrylic acid copolymer (55/40/5, calculated Tg: 44 ° C.)
B-08: Phenoxyethyl methacrylate / benzyl acrylate / methacrylic acid copolymer (45/47/8, calculated Tg: 13 ° C.)
B-09: Styrene / phenoxyethyl acrylate / butyl methacrylate / acrylic acid copolymer (5/48/40/7, calculated Tg: 6 ° C.)
B-10: benzyl methacrylate / isobutyl methacrylate / cyclohexyl methacrylate / methacrylic acid copolymer (35/30/30/5, calculated Tg: 67 ° C.)
B-11: Phenoxyethyl acrylate / methyl methacrylate / butyl acrylate / methacrylic acid copolymer (12/50/30/8, calculated Tg: 25 ° C.)
B-12: benzyl acrylate / isobutyl methacrylate / acrylic acid copolymer (93/2/5, calculated Tg: 11 ° C.)
B-13: Styrene / phenoxyethyl methacrylate / butyl acrylate / acrylic acid copolymer (50/5/20/25, calculated Tg: 53 ° C.)
B-14: Styrene / butyl acrylate / acrylic acid copolymer (62/35/3, calculated Tg: 27 ° C.)
B-15: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/51/4, calculated Tg: 28 ° C.)
B-16: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/49/6, calculated Tg: 31 ° C.)
B-17: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/48/7, calculated Tg: 32 ° C.)
B-18: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/47/8, calculated Tg: 34 ° C.)
B-19: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/45/10, calculated Tg: 36 ° C.)
B-20: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (20/72/8, measured Tg: 137 ° C.)
B-21: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (40/52/8, measured Tg: 128 ° C.)
B-22: Methyl methacrylate / isobornyl methacrylate / benzyl methacrylate / methacrylic acid copolymer (30/50/14/6, calculated Tg: 121 ° C.)
B-23: Methyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (40/50/10, calculated Tg: 118 ° C.)
B-24: Methyl methacrylate / adamantyl methacrylate / methoxypolyethylene glycol methacrylate (n = 23) / methacrylic acid copolymer (30/50/15/5, measurement Tg: 102 ° C.)

  “Measured Tg” is a value measured under normal measurement conditions using a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology, Inc., and “calculated Tg” is the formula described above. The values calculated using the Tg values of the homopolymers of the following monomers according to (1) [Tg = methyl methacrylate: 105 ° C., isobornyl methacrylate: 156 ° C., benzyl methacrylate: 54 ° C., methacrylic acid: 130 ° C, adamantyl methacrylate: 140 ° C, dicyclopentanyl methacrylate: 128 ° C].

  The method for producing the water-insoluble polymer constituting the self-dispersing polymer particles in the present invention is not particularly limited. For example, emulsion polymerization is carried out in the presence of a polymerizable surfactant to obtain a surfactant and a water-insoluble polymer. A method of covalently bonding, a method of copolymerizing a monomer mixture containing a hydrophilic group-containing monomer and an aromatic group-containing monomer or an alicyclic (meth) acrylate by a known polymerization method such as a solution polymerization method or a bulk polymerization method. Can be mentioned. Among the polymerization methods, a solution polymerization method is preferable and a solution polymerization method using an organic solvent is more preferable from the viewpoint of aggregation rate and droplet ejection stability when an ink composition is used.

  The self-dispersing polymer particles include a polymer synthesized in an organic solvent from the viewpoint of the aggregation rate, and the polymer has a carboxyl group (preferably having an acid value of 20 to 100 mgKOH / g). It is preferable that some or all of the carboxyl groups are neutralized and prepared as a polymer dispersion having water as a continuous phase. That is, the production of the self-dispersing polymer particles in the present invention includes a step of synthesizing a polymer in an organic solvent and a dispersion step of making an aqueous dispersion in which at least a part of the carboxyl groups of the polymer is neutralized. It is preferable to do so.

The dispersion step preferably includes the following step (1) and step (2).
Step (1): Step of stirring a mixture containing a polymer (water-insoluble polymer), an organic solvent, a neutralizing agent, and an aqueous medium Step (2): Step of removing the organic solvent from the mixture

The step (1) is preferably a treatment in which a polymer (water-insoluble polymer) is first dissolved in an organic solvent, then a neutralizing agent and an aqueous medium are gradually added, mixed and stirred to obtain a dispersion. In this way, by adding a neutralizing agent and an aqueous medium to a water-insoluble polymer solution dissolved in an organic solvent, a self-dispersing polymer having a particle size with higher storage stability without requiring strong shearing force. Particles can be obtained.
There is no restriction | limiting in particular in the stirring method of this mixture, Dispersing machines, such as a generally used mixing stirring apparatus and an ultrasonic disperser, a high-pressure homogenizer, can be used as needed.

  Preferred examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents. Examples of the alcohol solvent include isopropyl alcohol, n-butanol, t-butanol, ethanol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of ether solvents include dibutyl ether and dioxane. Among these solvents, ketone solvents such as methyl ethyl ketone and alcohol solvents such as isopropyl alcohol are preferable. It is also preferable to use isopropyl alcohol and methyl ethyl ketone in combination for the purpose of moderating the polarity change during the phase inversion from oil to water. By using this solvent in combination, it is possible to obtain self-dispersing polymer particles having a fine particle size with high dispersion stability without aggregation and sedimentation and fusion between particles.

  The neutralizing agent is used so that a part or all of the dissociable group is neutralized and the self-dispersing polymer forms a stable emulsified or dispersed state in water. When the self-dispersing polymer of the present invention has an anionic dissociative group (for example, a carboxyl group) as a dissociable group, the neutralizing agent used is basic such as an organic amine compound, ammonia, or an alkali metal hydroxide. Compounds. Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanol Examples include amines and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing polymer particles of the present invention in water.

  These basic compounds are preferably used in an amount of 5 to 120 mol%, more preferably 10 to 110 mol%, still more preferably 15 to 100 mol%, based on 100 mol% of the dissociable group. . By setting it as 15 mol% or more, the effect which stabilizes dispersion | distribution of the particle | grains in water expresses, and there exists an effect which reduces a water-soluble component by setting it as 100 mol% or less.

  In the step (2), the aqueous dispersion of the self-dispersing polymer particles is obtained by distilling off the organic solvent from the dispersion obtained in the step (1) by a conventional method such as distillation under reduced pressure and phase-inversion into an aqueous system. A dispersion can be obtained. The organic solvent in the obtained aqueous dispersion has been substantially removed, and the amount of the organic solvent is preferably 0.2% by mass or less, more preferably 0.1% by mass or less.

The average particle size of the polymer particles (particularly self-dispersing polymer particles) is preferably in the range of 10 to 400 nm, more preferably in the range of 10 to 200 nm, still more preferably in the range of 10 to 100 nm, and particularly preferably in terms of volume average particle size. It is the range of 10-50 nm. Manufacturability is improved by having an average particle diameter of 10 nm or more. Moreover, storage stability improves by setting it as an average particle diameter of 400 nm or less. Moreover, there is no restriction | limiting in particular regarding the particle size distribution of a polymer particle, Any of what has a wide particle size distribution or a monodispersed particle size distribution may be sufficient. Further, two or more water-insoluble particles may be mixed and used.
The average particle size and particle size distribution of the polymer particles are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is what

  The content of the polymer particles (particularly self-dispersing polymer particles) in the ink composition is preferably 1 to 30% by mass with respect to the ink composition from the viewpoint of the glossiness of the image. More preferably, it is 15 mass%. The polymer particles (particularly self-dispersing polymer particles) can be used singly or in combination of two or more.

<Surfactant>
The ink composition in the present invention can contain a surfactant as required. The surfactant can be used as a surface tension adjusting agent. As a surface tension modifier, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactant, cationic surfactant, amphoteric surfactant, nonionic surfactant Either a surfactant or a betaine surfactant can be used. Further, the above dispersant (polymer dispersant) may be used as a surfactant.

When the surfactant is contained in the ink, the surfactant preferably contains an amount in a range in which the surface tension of the ink can be adjusted to 20 to 60 mN / m from the viewpoint of favorably discharging the ink by the ink jet method. More preferably, it is 20-45 mN / m from the point of surface tension, More preferably, it is 25-40 mN / m.
The specific amount of the surfactant in the ink of the surfactant is not particularly limited except that the range of the surface tension is preferable, preferably 1% by mass or more, more preferably 1 to 10% by mass. Yes, more preferably 1 to 3% by mass.

<Other ingredients>
In addition to the above-described components, the ink can further contain various additives as other components, if necessary.
Examples of the various additives include, for example, ultraviolet absorbers, antifading agents, antifungal agents, pH adjusters, rust inhibitors, antioxidants, emulsion stabilizers, preservatives, antifoaming agents, viscosity modifiers, and dispersions. Known additives such as stabilizers and chelating agents can be mentioned.

~ Physical properties of ink ~
The surface tension (25 ° C.) of the ink composition is preferably 20 mN / m or more and 60 mN / m or less. More preferably, it is 20 mN or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 40 mN / m or less. The surface tension is measured using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) at 25 ° C.
Further, the viscosity at 25 ° C. of the ink composition is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s or more and less than 13 mPa · s, and further preferably 2.5 mPa · s. This is less than 10 mPa · s. Viscosity is measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO.LTD) under conditions of 25 ° C. ink.

-Treatment liquid application process-
The ink jet recording method of the present invention includes a treatment liquid application step of applying a treatment liquid containing a flocculant that promotes aggregation of components in the ink composition to the recording medium before or after the ink application step. It is preferable that an image is formed by bringing an object and a processing liquid into contact with each other. In this case, when the treatment liquid comes into contact with the ink composition, components (for example, pigments and polymer particles) in the ink composition are aggregated, and the image is fixed on the recording medium.

<Flocculant>
The treatment liquid contains at least an aggregating agent capable of forming an aggregate upon contact with the ink composition, and can be constituted using other components as necessary. By mixing the ink composition and the treatment liquid on the recording medium, aggregation of pigments and the like stably dispersed in the ink composition is promoted. The flocculant is preferably at least one selected from acidic compounds, cationic polymers, and polyvalent metal salts from the viewpoint of image quality. A flocculant can be used individually by 1 type or in mixture of 2 or more types.

Examples of the treatment liquid containing an acidic compound include a liquid capable of generating an aggregate by lowering the pH of the ink composition. At this time, the pH (25 ° C.) of the treatment liquid is preferably 3.5 or less, more preferably 0.5 to 2.5, from the viewpoint of the aggregation rate of the ink composition. More preferably, it is -1.5. In this case, the pH (25 ° C.) of the ink composition used in the ink application process is preferably 7.5 or more (more preferably 8 or more).
Among them, from the viewpoint of image density, resolution, and speedup of inkjet recording, the pH (25 ° C.) of the ink composition is 8 or more, and the pH (25 ° C.) of the treatment liquid is 3.5 or less (preferably 0.5 to 2.5) is preferred.

  As the acidic compound, a compound having a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxyl group, or a salt thereof (for example, a polyvalent metal salt) is used. Can do. Among these, from the viewpoint of the aggregation rate of the ink composition, a compound having a phosphate group or a carboxyl group is more preferable, and a compound having a carboxyl group is still more preferable.

  The compound having a carboxyl group includes polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, sulfonic acid, orthophosphoric 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 (for example, polyvalent metal salts), etc. It is preferable to be selected from among Of these, divalent carboxylic acids are preferred.

  The content of the acidic compound in the treatment liquid is preferably 5 to 95% by mass and more preferably 10 to 80% by mass with respect to the total mass of the treatment liquid from the viewpoint of the aggregation effect. The treatment liquid can further comprise an aqueous solvent (for example, water) in addition to the acidic compound.

  As the cationic polymer, a polymer having a primary to tertiary amino group or a quaternary ammonium base as a cationic group is preferable. Examples of the cationic polymer include a homopolymer of a monomer having a primary to tertiary amino group and a salt thereof, or a quaternary ammonium base (cationic monomer), and the cationic monomer and other monomers (non-mono). Those obtained as copolymers or condensation polymers with cationic monomers) are preferred. These polymers can be used in any form of water-soluble polymer or water-dispersible latex particles.

Examples of the cationic polymer include polydiallyldimethylammonium chloride, polymethacryloyloxyethyl-β-hydroxyethyldimethylammonium chloride, polyethyleneimine, polyallylamine and derivatives thereof, polyamide-polyamine resin, cationized starch, dicyandiamide formalin condensate, dimethyl- 2-Hydroxypropylammonium salt polymer, polyamidine, polyvinylamine, dicyandiamide-formalin polycondensate dicyan-type chatin resin, dicyanamide-diethylenetriamine polycondensate-type polyamine-type chatin resin, epichlorohydrin-dimethylamine addition polymerization , Dimethyldialin ammonium chloride-SO ₂ copolymer, diallylamine salt-SO ₂ copolymer, A (meth) acrylate-containing polymer having a quaternary ammonium base-substituted alkyl group in the ester portion, a styryl polymer having a quaternary ammonium base-substituted alkyl group, and the like can also be mentioned as preferable examples. As a specific example of the cationic polymer, a diallyldimethylammonium chloride type polymer or a (meth) acrylate-containing polymer having a quaternary ammonium base in the ester portion is preferably exemplified. Examples of the cationic polymer include a copolymer containing an epihalohydrin derivative and an amine derivative (for example, a copolymer of monomethylamine, monoethylamine, dimethylamine, diethylamine and epichlorohydrin, or the like).
The preferred weight average molecular weight of the cationic polymer is about 1000 to 50000.

  The content of the cationic polymer in the treatment liquid is preferably 5 to 95% by mass with respect to the total mass of the treatment liquid from the viewpoint of the aggregation effect. The treatment liquid may further comprise an aqueous solvent (for example, water) in addition to the cationic polymer.

Examples of the polyvalent metal salt include alkaline earth metals belonging to Group 2 of the periodic table (eg, magnesium, calcium), transition metals belonging to Group 3 of the periodic table (eg, lanthanum), and Group 13 of the periodic table. Mention may be made of salts of cations (for example aluminum) and lanthanides (for example neodymium). As the metal salt, carboxylate (formic acid, acetic acid, benzoate, etc.), nitrate, chloride, and thiocyanate are suitable. Among them, preferred are calcium salts or magnesium salts of carboxylic acids (formic acid, acetic acid, benzoates, etc.), calcium salts or magnesium salts of nitric acid, calcium chloride, magnesium chloride, and calcium salts or magnesium salts of thiocyanic acid.
As content in the process liquid of a polyvalent metal salt, 1-10 mass% is preferable, More preferably, it is 1.5-7 mass%, More preferably, it is the range of 2-6 mass%. The treatment liquid can further comprise an aqueous solvent (for example, water) in addition to the polyvalent metal salt.

  The viscosity of the treatment liquid is preferably in the range of 1 to 30 mPa · s, more preferably in the range of 1 to 20 mPa · s, still more preferably in the range of 2 to 15 mPa · s, from the viewpoint of the aggregation rate of the ink composition. The range of 10 mPa · s is particularly preferable. The viscosity is measured under the condition of 20 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO.LTD). The surface tension of the treatment liquid is preferably 20 to 60 mN / m, more preferably 20 to 45 mN / m, and more preferably 24 to 40 mN / m from the viewpoint of the aggregation rate of the ink composition. Is more preferable. The surface tension is measured at 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

  In the present invention, an embodiment in which the ink application step is provided after the treatment liquid is applied in the treatment liquid application step is preferable. That is, before applying the ink composition to the recording medium, a treatment liquid for aggregating components (particularly, dispersed particles such as pigments and polymer particles) in the ink composition is applied in advance, and applied to the recording medium. A mode in which an ink composition is applied so as to come into contact with the treated liquid and an image is recorded is preferable. Thereby, inkjet recording can be speeded up, and an image with high density and resolution can be obtained even at high speed recording.

-Fixing process-
The ink jet recording method of the present invention preferably further comprises a step of fixing (fixing) the image by press-bonding at least the image by a press-applying means (hereinafter, also referred to as “fixing step”). By fixing the image, it is possible to obtain an image having a good texture such as glossiness of the image, scratch resistance (for example, adhesion to paper) and excellent image quality at high speed.

  The fixing of the image part is performed by, for example, using a pressure applying unit that applies pressure to the image at least after the ink application process, and pressing the image part by pressing the pressure applying unit against the image part (fixing). You may carry out by providing the pressurizing process to process. In addition, a heating means for fixing (fixing process) may be provided by combining the pressure applying means with a heating means for heating the image portion and heat-pressing the image portion. Examples of the pressure applying unit include a pair of rolls and a pressure plate that are in pressure contact with each other, and examples of the heating unit include a heating roll and a hot plate.

  Specifically, for example, after the ink application process, the surface of the recording medium can be pressure-bonded with a heated roll or hot plate. In this case, the resin particles contained in the ink can be melted. At this time, the heating temperature is preferably higher than the Tg of the polymer particles in the ink.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.

  The weight average molecular weight was measured by gel permeation chromatography (GPC). GPC uses HLC-8020GPC (manufactured by Tosoh Corp.) and uses three columns of TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (manufactured by Tosoh Corp., 4.6 mm ID × 15 cm) as the column. THF (tetrahydrofuran) was used. The conditions were as follows: the sample concentration was 0.45 mass%, the flow rate was 0.35 ml / min, the sample injection amount was 10 μl, the measurement temperature was 40 ° C., and an IR detector was used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It produced from eight samples of "A-2500", "A-1000", and "n-propylbenzene".

Example 1
<Preparation of ink>
(Synthesis of polymer dispersant P-1)
According to the following scheme, a polymer dispersant P-1 was synthesized as shown below.

To a 1000 ml three-necked flask equipped with a stirrer and a condenser, 88 g of methyl ethyl ketone was added and heated to 72 ° C. in a nitrogen atmosphere. Then, a solution in which 10 g of methacrylic acid and 30 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution of 0.42 g of dimethyl 2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in a large excess amount of hexane, and the precipitated resin was dried to obtain 96 g of a polymer dispersant P-1.
The composition of the obtained resin was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 44,600. Furthermore, when the acid value was calculated | required by the method as described in JIS specification (JISK0070: 1992), it was 65.2 mgKOH / g.

(Dispersion of resin-coated pigment particles)
Pigment Blue 15: 3 (phthalocyaninemble-A220, manufactured by Dainichi Seika Co., Ltd.), 5 parts of the polymer dispersant P-1, 42 parts of methyl ethyl ketone, 5.5 parts of 1 mol / L NaOH aqueous solution, Then, 87.2 parts of ion-exchanged water was mixed and dispersed with a bead mill using 0.1 mmφ zirconia beads for 2 to 6 hours.
Methyl ethyl ketone was removed from the obtained dispersion at 55 ° C. under reduced pressure, and a part of water was further removed to obtain a dispersion of resin-coated pigment particles having a pigment concentration of 10.2% by mass.

(Synthesis and preparation of self-dispersing polymer particles)
-Synthesis of self-dispersing polymer particles B-21-
In a 2 liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 540.0 g of methyl ethyl ketone was charged and heated to 75 ° C. While maintaining the reaction vessel temperature at 75 ° C., 216 g of methyl methacrylate, 280.8 g of isobornyl methacrylate, 43.2 g of methacrylic acid, 108 g of methyl ethyl ketone, and 2.16 g of “V-601” (manufactured by Wako Pure Chemical Industries, Ltd.) The mixed solution consisting of was dropped at a constant speed so that the dropping was completed in 2 hours. After completion of the dropwise addition, a solution consisting of 1.08 g of “V-601” and 15.0 g of methyl ethyl ketone was added, stirred for 2 hours at 75 ° C., and then a solution consisting of 0.54 g of “V-601” and 15.0 g of methyl ethyl ketone was added. After stirring at 75 ° C. for 2 hours, the temperature was raised to 85 ° C., and stirring was further continued for 2 hours to obtain a methyl methacrylate / isobornyl methacrylate / methacrylic acid (= 40/52/8 [mass ratio]) copolymer. A resin solution was obtained.
The weight average molecular weight (Mw) of the obtained copolymer was 61000, and the acid value was 52.1 (mgKOH / g).

  Next, 588.2 g of the resin solution was weighed, 165 g of isopropanol and 120.8 ml of 1 mol / L NaOH aqueous solution were added, and the temperature in the reaction vessel was raised to 80 ° C. Next, 718 g of distilled water was added dropwise at a rate of 20 ml / min to disperse in water. Then, the solvent was distilled off by keeping the reaction vessel internal temperature at 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure. Furthermore, the pressure in the reaction vessel was reduced, and isopropanol, methyl ethyl ketone, and distilled water were distilled off, and an aqueous dispersion (emulsion) of self-dispersing polymer particles B-21 (the exemplified compound) having a solid content concentration of 26.0% by mass. )

Moreover, when the glass transition temperature of self-dispersing polymer particle B-21 was measured with the following method, it was 128 degreeC by measurement Tg.
<Measurement Tg>
A solid dispersion of 0.5 g of an aqueous dispersion of self-dispersing polymer particles B-21 was dried under reduced pressure at 50 ° C. for 4 hours to obtain a polymer solid. Using the obtained polymer solid content, Tg was measured with a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology. Measurement conditions were such that a sample amount of 5 mg was sealed in an aluminum pan, and the peak top value of DDSC of the measurement data at the second temperature increase in the following temperature profile was defined as Tg in a nitrogen atmosphere.
30 ° C to -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 120 ° C. (temperature rising at 20 ° C./min)
120 ° C to -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 120 ° C. (temperature rising at 20 ° C./min)

(Preparation of cyan ink C-1)
Using the above dispersion of resin-coated pigment particles and the aqueous dispersion of self-dispersing polymer particles B-21, further using a hydrophilic organic solvent, a surfactant, and ion-exchanged water so as to have the following composition: Cyan ink C-1 was prepared. At this time, it prepared so that the total mass of the water-soluble organic solvent might be 16 mass% with respect to the total mass of the ink.
<Composition of cyan ink C-1>
・ Cyan pigment (Pigment Blue 15: 3) ... 4% by mass
・ The polymer dispersant P-1 2% by mass
-Aqueous dispersion (solid content) of the self-dispersing polymer particles B-21: 8% by mass
・ Glycerin: 10.7 mass%
・ Diethylene glycol: 5.3% by mass
・ Olfin E1010 ... 1% by mass
(Nissin Chemical Co., Ltd., nonionic surfactant)
・ Ion-exchanged water (added so that the total amount becomes 100% by mass)

(Preparation of magenta ink M-1)
The cyan pigment in the composition of the cyan ink C-1 was prepared as a composition similar to the cyan ink C-1, except that the magenta pigment (Pigment Red 122) was changed so that the amount of the pigment was the same. did.

(Preparation of yellow ink Y-1)
The cyan pigment in the composition of the cyan ink C-1 was prepared as a composition similar to the cyan ink C-1, except that the cyan pigment was changed to a yellow pigment (Pigment Yellow 74) so that the amount of the pigment was the same. did.

(Preparation of black ink K-1)
Cyan ink C, except that the cyan pigment in the composition of cyan ink C-1 was changed to a black pigment (carbon black; # 2600, manufactured by Mitsubishi Chemical Corporation) so that the amount of the pigment was the same. It was prepared as a composition similar to -1.

(Measurement of viscosity)
The viscosity of the obtained cyan ink C-1, magenta ink M-1, yellow ink Y-1 and black ink K-1 was measured at 25 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD). Measured with The measurement results are shown in Table 1 below.

<Preparation of treatment liquid>
The processing liquid was prepared by mixing components having the following composition. When the viscosity, surface tension, and pH (25 ± 1 ° C.) of the treatment liquid were measured, the viscosity was 2.6 mPa · s, the surface tension was 37.3 mN / m, and the pH was 1.6. The viscosity was measured by the same method as described above, and the surface tension was measured at 25 ° C. using Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.). The pH was measured at 25 ± 1 ° C.
<Composition of treatment liquid>
Malonic acid (divalent carboxylic acid, manufactured by Wako Pure Chemical Industries, Ltd.): 15.0% by mass
・ Diethylene glycol monomethyl ether (Wako Pure Chemical Industries, Ltd.): 20.0% by mass
・ N-oleoyl-N-methyltaurine sodium (surfactant): 1.0% by mass
-Ion exchange water: 64.0% by mass

<Image formation and evaluation>
Tokishi Art Double Sided N (84.9 g / m ² , manufactured by Mitsubishi Paper Industries Co., Ltd.) as a recording medium was fixed on a stage movable in a predetermined linear direction at 500 mm / second, and the treatment obtained above The liquid was applied with a wire bar coater to a thickness of about 5 μm, and was dried at 50 ° C. for 2 seconds immediately after the application. Next, as an ink jet recording apparatus, a dimatics material printer DMP-2831 manufactured by FUJIFILM Dimatics Co., Ltd. was used (the cartridge was modified so that liquid for 10 pl discharge (DMC-11610) can be supplied from the outside, nozzle surface A plurality of nozzles are two-dimensionally arranged), and the ink of the four colors obtained above was loaded into the cartridge. Prior to ejection, the ink storage tank for each ink is cooled to 20 ° C. by cooling it with a chiller, and the ink coating amount is 5 g / m ² at a resolution of 1200 dpi. The solid image was recorded. Thereafter, the solvent was removed by heating at 60 ° C. for 3 minutes, and a solid image was subjected to thermocompression bonding by passing the recording medium through a roller pair under the following conditions. In this way, an evaluation sample was obtained.
<Heat-bonding conditions>
・ Silicon rubber roller (hardness 50 °, nip width 5mm)
・ Roller temperature: 70 ℃
・ Pressure: 0.2 MPa

<Evaluation>
The following evaluation was performed about the evaluation sample obtained above. The evaluation results are shown in Table 1 below.

-Curl-
The ink jet recording medium after solid printing with an ink coating amount of 5 g / m ² is cut into a size of 5 × 50 mm with the curl direction as the long side, under conditions of a temperature of 30 ° C. and a humidity of 80% RH. Left for 24 hours. After standing, the behavior of the curl was confirmed, and evaluated according to the following evaluation criteria using the curl value obtained as follows as an index.
~ Measurement of curl value ~
The sample cut to 5 × 50 mm so that the curl direction becomes the long side is applied to the curl measurement plate, and the curl value (curvature C) is read. That is, the curl is regarded as an arc of a circle with a radius R, and R is obtained from the curl measurement plate and expressed as follows.
C = 1 / R (m)
<Evaluation criteria>
A: Curvature C was 5 or less.
○: Curvature C was more than 5 and 10 or less.
(Triangle | delta): The curvature C exceeded 10 and was 15 or less.
X: Curvature C was more than 15 and 20 or less.
XX: Curvature C exceeded 20.

-Abrasion resistance-
Unprinted special diamond art cut to 10 mm x 50 mm is wrapped around a paperweight (weight 470 g, size 15 mm x 30 mm x 120 mm) (the area where the unprinted special diamond art and the evaluation sample contact is 150 mm ² ) The evaluation sample prepared at the time of evaluation was rubbed 3 times (corresponding to a load of 260 kg / m ² ). The printed surface after rubbing was visually observed and the rubbing resistance was evaluated according to the following evaluation criteria.
<Evaluation criteria>
○: Image (coloring material) peeling was not visible.
Δ: Slight peeling of image (coloring material) was visually recognized.
X: The peeling of the image (coloring material) was visually recognized.

−Dischargeability−
The following pass / fail was determined when the cyan ink C-1 was ejected. The image unevenness was visually observed.
(1) The discharge rate after the 60-minute continuous discharge test is 90% or more. (2) The discharge rate is 90% or more after a pause for 30 minutes after discharging for 1 minute. (3) No image unevenness is observed.
<Evaluation criteria>
○: When all three items pass △: When two items pass ×: When one item passes

-Droplet interference (image quality)-
The cyan ink C-1, magenta ink M-1, yellow ink Y-1, and black ink K-1 obtained above were used as an ink set together with the treatment liquid, and the following was performed using a dimatics material printer DMP-2831. Under these conditions, an image was recorded by performing four-color single pass recording. The order of droplet ejection for each color ink was MKCY.
[conditions]
(1) Treatment liquid application step First, the application amount is 1.7 g / m ² on the entire surface of the recording medium by a roll coater in which the application amount is controlled by an anilox roller (number of lines: 100 to 300 / inch). A treatment solution was applied.
(2) Drying and removing step Next, the recording medium coated with the treatment liquid was dried under the following conditions.
・ Wind speed: 15m / s
Temperature: Heated from the opposite side (back side) of the recording surface of the recording medium with a contact type flat heater so that the surface temperature on the recording surface side of the recording medium becomes 60 ° C. Air blowing area: 450 mm (drying time 0.7) Seconds)
(3) Image recording process Then, ink was ejected by the inkjet method on the coated surface of the recording medium coated with the treatment liquid under the following conditions to record a line image and a solid image.
・ Head: 1,200 dpi / 20 inch width piezo full line heads are arranged for four colors ・ Discharged droplet volume: 0 pL, 2.0 pL, 3.5 pL, 4.0 pL four-value recording ・ Drive frequency: 30 kHz (recording medium) (Conveyance speed of 635mm / sec)
(4) Ink Drying and Removing Step Next, the recording medium provided with ink was dried under the following conditions.
・ Drying method: blow drying ・ wind speed: 15m / s
-Temperature: Heated with a contact type flat heater from the opposite side (back side) of the recording surface of the recording medium so that the surface temperature on the recording surface side of the recording medium becomes 60 ° C.-Air blowing area: 640 mm (drying time: 1 second) )
(5) Fixing Step Next, a heat fixing process was performed by passing a roller pair under the following conditions.
・ Silicon rubber roller (hardness 50 °, nip width 5mm)
・ Roller temperature: 75 ℃
・ Pressure: 0.8MPa

When recording an image, the ink droplets of different colors are ejected one by one alternately with a time difference so that the adjacent ink droplets partially overlap each other, and how long the first ink droplets are aggregated is evaluated. did. Specifically, the image was observed with an optical microscope, and it was determined that the first ink droplets were not yet aggregated when the ink droplets deposited later mixed with the ink droplets deposited first. The time when the ink droplets that landed later did not mix was defined as the landing interference time. Using this landing interference time as an index, evaluation was performed according to the following evaluation criteria.
<Evaluation criteria>
A: The first ink droplets solidified in less than 20 ms, and no mixing of the ink droplets superimposed on the ink droplets was observed.
(Triangle | delta): Although the ink droplet first landed solidified in 20 ms or more and less than 100 ms, and the ink droplet piled up on this was slightly mixed, it was the range which does not have trouble in practical use.
×: It took 100 ms or more for solidification of the first ink droplets to be deposited, and there was a lot of color mixing of the ink droplets superimposed on the ink droplets.

−Maintenance−
After ejecting cyan ink, magenta ink M-1, yellow ink Y-1, and black ink K-1 under the conditions (1) to (3) below, the nozzle surface of the inkjet head is wiped with a wiper blade (hydrogenated NBR). Then, from the results of the subsequent re-ejectability evaluation, the following (1) to (3) were judged as pass / fail. Subsequently, the maintainability was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1 below.
(1) Immediately after the end of continuous discharge for 60 minutes, blade wipe is performed once.
(2) Pause for 30 minutes after ejection for 1 minute, perform blade wipe once after the suspension, and pass if the subsequent ink ejection rate is 90% or more.
(3) When blade wiping is performed once immediately after the end of discharge for 10 minutes and no image unevenness is observed in the image formed thereafter, it passes.
~ Measurement of ink discharge rate ~
After confirming that all nozzles were discharging at the start of the experiment, the number of discharge nozzles after the experiment including maintenance was counted, and the discharge rate was calculated as follows.
Discharge rate (%) = [number of discharge nozzles after maintenance] / [total number of nozzles] × 100
<Evaluation criteria>
◎: When all three items are acceptable ○: When two items are acceptable △: When only one item is acceptable ×: When all three items are unacceptable

(Examples 2-4, Comparative Examples 1-2)
In Example 1, the types and contents of the water-soluble organic solvents used in the preparation of the cyan ink C-1, the magenta ink M-1, the yellow ink Y-1, and the black ink K-1 are shown in Table 1 below. Except for the change to, four color inks were prepared in the same manner as in Example 1, and evaluation samples were prepared and evaluated. The evaluation results are shown in Table 1 below.

(Comparative Examples 3 to 8)
In Example 1, the types and contents of the water-soluble organic solvents used in the preparation of the cyan ink C-1, the magenta ink M-1, the yellow ink Y-1, and the black ink K-1 are shown in Table 1 below. The four colors were changed in the same manner as in Example 1 except that the solid images were recorded at room temperature (25 ° C.) without cooling the four color inks performed prior to the ejection. Ink was prepared, an evaluation sample was prepared and evaluated. The evaluation results are shown in Table 1 below.

  As shown in Table 1, in the examples, the occurrence of curling in a high humidity environment was suppressed, and the occurrence of blurring and blurring in the image due to droplet ejection interference was suppressed, and a high quality image was obtained. Moreover, the removability of the ink adhering to the nozzle surface was also good, and the improvement effect of the maintainability was recognized. Even with a head in which nozzles were arranged at high density, ink could be discharged well. On the other hand, in the comparative example, when the solvent content was too high, the curl improvement effect by the cooling operation was lowered. Further, even if curling was suppressed to some extent by reducing the amount of solvent, droplet ejection interference was liable to occur unless the cooling operation was performed, ink ejection properties and image quality were lowered, and maintenance properties were also deteriorated.

Claims (17)

  The viscosity at the time of ejection of the ink composition containing the pigment, a water-soluble organic solvent of 25% by mass or less with respect to the total mass, and water is increased with respect to the viscosity at 25 ° C. by cooling with a cooling means. Inkjet recording method for recording images.   The inkjet recording method according to claim 1, wherein the viscosity of the ink composition at the time of ejection is in the range of 4 to 15 mPa · s.   The inkjet recording method according to claim 1, wherein the viscosity of the ink composition at the time of ejection is increased by 0.5 mPa · s or more with respect to the viscosity at 25 ° C. by the cooling.   The inkjet recording method according to claim 1, wherein the cooling is performed in a temperature range of 15 ° C. to 24 ° C. 5.   The inkjet recording method according to claim 1, wherein the ink composition is ejected using a liquid ejection head having a nozzle surface in which a plurality of nozzles are two-dimensionally arranged. .   6. The ink jet recording method according to claim 1, wherein the content of the water-soluble organic solvent in the ink composition is 20% by mass or less.   The ink jet recording method according to claim 1, wherein the ink composition further contains polymer particles.   The ink-jet recording method according to claim 1, wherein the total solid content of the ink composition is 20% by mass or less.   9. The ink jet recording method according to claim 8, wherein the total solid content of the ink composition is 15% by mass or less.   The ink jet recording method according to claim 1, wherein at least one of the water-soluble organic solvents is a water-soluble organic solvent having an SP value of 27.5 or less. 11. The water-soluble organic solvent having an SP value of 27.5 or less is a water-soluble organic solvent represented by the following general formula (1) and having a molecular weight of 240 to 1400. The ink jet recording method described in 1.
R-A _n -OH General formula (1)
[Wherein, R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a group derived from a sugar alcohol having 3 to 12 carbon atoms, and A represents at least one selected from an ethyleneoxy group and a propyleneoxy group. N represents an integer of 3 to 24. ]   The inkjet recording method according to any one of claims 1 to 11, wherein the pigment is a water-dispersible pigment in which at least a part of the surface thereof is coated with a water-insoluble resin.   The ink jet recording method according to any one of claims 7 to 12, wherein the polymer particles are self-dispersing polymer particles.   14. The ink jet recording method according to claim 7, wherein the polymer particles have a glass transition temperature of 20 to 200 ° C. 15.   2. The method according to claim 1, further comprising the step of applying a treatment liquid containing an aggregating agent for aggregating components in the ink composition, and recording the image by bringing the ink composition into contact with the treatment liquid. The ink jet recording method according to claim 14.   The inkjet recording method according to claim 15, wherein the ink composition is ejected after the treatment liquid is applied.   The ink jet recording method according to any one of claims 1 to 16, further comprising a step of pressing and fixing the image by a pressure applying unit.