JP2016011320A - Aqueous ink and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet aqueous ink capable of suppressing deterioration in color development of an image recorded on a non-water-absorbing recording medium, and an inkjet recording method.SOLUTION: The inkjet aqueous ink is used in the inkjet recording method which records an image on a non-water-absorbing recording medium by ejecting ink from a recording head of an inkjet system. The inkjet aqueous ink contains at least a pigment, resin fine particles, water, and a water-soluble solvent. The absolute value |Δζ| of the difference between the zeta potential ζof the pigment and the zeta potential ζof the resin fine particles is 0 mV or more and 20 mV or less. The glass transition point Tg of a resin constituting the resin fine particles is higher than 30°C and lower than 80°C.

Description

  The present invention relates to an aqueous ink and an ink jet recording method.

  Ink-jet inks are applied and developed not only for recording on water-absorbing recording media such as paper, but also for recording on non-water-absorbing recording media such as polyvinyl chloride and polyethylene terephthalate. In recent years, water-based inks having high environmental safety have been commercialized as inks for non-water-absorbing recording media.

  As a water-based ink for a non-water-absorbing recording medium, an ink containing a pigment as a coloring material and a resin for fixing the pigment on the surface of the non-water-absorbing recording medium has been proposed. According to this water-based ink, after recording an image on a non-water-absorbing recording medium, the non-water-absorbing recording medium provided with the ink is heated to form a resin film on the surface of the non-water-absorbing recording medium (film formation). The pigment can be fixed on the surface of the non-water-absorbing recording medium by solidifying the ink layer.

  As the resin contained in the ink, resin fine particles that can be contained at a high concentration in the ink are widely used in order to increase the fixing power of the pigment. Since the resin fine particles are dispersed in the ink and exist in a particle state, there is an advantage that the viscosity of the ink is hardly increased even if the amount added is increased as compared with the water-soluble resin existing in the dissolved state.

  As an ink containing pigment particles and resin fine particles in an ink, an ink jet pigment ink containing pigment particles, a hydrophilic solvent, water, and latex has been proposed, although it is not an ink for non-water-absorbing recording media (Patent Literature). 1). This pigment ink is intended to improve the glossiness of an image formed on a water-absorbing recording medium, paying attention to the physical properties of the particles, and the absolute value of the zeta potential of latex (resin fine particles) contained in the ink This is smaller than the absolute value of the zeta potential of the particle. Patent Document 1 describes that it is preferable that both the absolute value of the zeta potential of the latex and the pigment particle are large, and further, it is preferable that the difference of the zeta potential of the latex and the pigment particle is large.

  Also, as an ink jet recording method for recording an image on a non-water-absorbing recording medium, a water-based ink containing water, a colorant, thermoplastic resin particles, a solvent, etc. is used, and the ink non-absorbing recording medium is heated to form a water-based ink. A recording method for ejecting liquid droplets has been proposed (Patent Document 2). This recording method focused on the boiling point of the solvent in the ink composition for the purpose of forming an image with low ink bleeding and high image quality and excellent scratch resistance on a non-ink-absorbing recording medium. Is. That is, in this recording method, the ink composition includes a glycol diether having a boiling point of 150 ° C. or higher and 220 ° C. or lower (first solvent), 1,2-hexanediol (second solvent), and 170 ° C. or higher. Glycols (third solvent) of 220 ° C. or lower are contained.

JP 2003-171589 A JP 2011-201228 A

  However, when the pigment ink described in Patent Document 1 is used as an ink for a non-water-absorbing recording medium, depending on the characteristics of the latex (resin fine particles) contained in the ink and the heating temperature of the non-water-absorbing recording medium, There existed a subject that glossiness (color development) might fall.

  Further, even when an ink composition containing a solvent having a predetermined boiling point is used as in the recording method described in Patent Document 2, the characteristics of the thermoplastic resin particles contained in the ink and the ink non-absorbing recording medium Depending on the heating temperature, the color developability of the image sometimes deteriorated.

  Accordingly, an object of the present invention is to provide an inkjet water-based ink and an inkjet recording method capable of suppressing a decrease in color developability of an image recorded on a non-water-absorbing recording medium.

The above object is achieved by the present invention described below. That is, according to the present invention, an inkjet water-based ink used in an inkjet recording method for recording an image on a non-water-absorbing recording medium by ejecting ink from an inkjet recording head, comprising at least a pigment and a resin The resin contains a fine particle, water, and a water-soluble solvent, and an absolute value | Δζ | of a difference between a zeta potential ζ _{pig of the} pigment and a zeta potential ζ _res of the resin fine particle is 0 mV to 20 mV, and the resin A water-based ink is provided in which the glass transition point Tg of the resin constituting the fine particles is more than 30 ° C. and less than 80 ° C.

  ADVANTAGE OF THE INVENTION According to this invention, the water-based ink for inkjets which can suppress the fall of the coloring property of the image recorded on the non-water-absorbing recording medium, and the inkjet recording method can be provided.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments. The present invention is an aqueous inkjet ink used in an inkjet recording method for recording an image on a non-water-absorbing recording medium by discharging ink from an inkjet recording head, and includes at least a pigment, resin fine particles, water, and the like. And a water-soluble solvent. In the present invention, the absolute value | Δζ | of the difference between the zeta potential ζ _{pig of the} pigment and the zeta potential ζ _res of the resin fine particles is 0 mV to 20 mV, and the glass transition of the resin constituting the resin fine particles. The point Tg is more than 30 ° C. and less than 80 ° C.

Prior to the present invention, the present inventors analyzed an ink layer of a recorded matter in which the color developability deteriorated. As a result, it was found that the pigment was unevenly distributed in the ink layer and scattered light was generated, and the color developability of the recorded matter was lowered as the mass of the unevenly distributed pigment was larger. In order to ensure various image characteristics and reliability, the water-based ink contains a water-soluble solvent (in particular, a water-soluble solvent having a vapor pressure lower than that of water) as a solvent. However, in the recording method including the step of heating the recording medium to which ink has been applied as in the present invention, the water having a high vapor pressure evaporates first and the water-soluble solvent evaporates after the heating. The distribution of the solvent composition (and hence the dielectric constant) is generated inside the ink droplets. In addition, in the ink containing the pigment and the resin fine particles as in the present invention, the charge characteristics of the pigment and the resin fine particles are different. When the dielectric constant is distributed inside the ink droplets as described above, the present inventors have found that the layers in which the pigment and the resin fine particles can stably exist in the ink layer are different. It was thought that this was the cause of uneven distribution of pigments. Therefore, the inventors suppress the uneven distribution of the pigment in the ink layer by setting the absolute value | Δζ | of the difference between the zeta potential ζ _{pig of the} pigment and the zeta potential ζ _res of the resin fine particles to 0 mV or more and 20 mV or less, We decided to solve the problems of the prior art.

  Hereinafter, details of the water-based ink and the ink jet recording method of the present invention will be described.

<Water-based ink>
The aqueous ink of the present invention contains at least a pigment, resin fine particles, water, and a water-soluble solvent. Hereinafter, each component constituting the water-based ink of the present invention will be described.

(Pigment)
The water-based ink of the present invention contains a pigment as a color material. Any conventionally known pigment can be used as the pigment. For example, it is preferable to use carbon black or an organic pigment. A pigment can be used individually by 1 type or in combination of 2 or more types.

  Examples of the dispersion method of the pigment include a resin dispersion type pigment using a resin as a dispersant (a resin dispersion type pigment using a resin dispersant; a microcapsule type pigment in which the particle surface of the pigment is coated with a resin). . Examples of the resin dispersion type pigment include a resin-bonded self-dispersion pigment in which an organic group containing a resin is chemically bonded to the surface of the pigment particle. Furthermore, a self-dispersion type pigment (self-dispersion type pigment) in which a hydrophilic group is introduced on the particle surface of the pigment can be mentioned. Of course, in the water-based ink of the present invention, pigments having different dispersion methods can be used in combination.

The charge state of the dispersed pigment can be represented by a zeta potential. The absolute value | ζ _pig | of the zeta potential of the pigment is preferably 0 mV or more and 30 mV or less. If it is higher than 30 mV, in the process in which moisture evaporates from the ink droplets applied to the recording medium, the pigment tends to flow due to the change in the dielectric constant distribution of the solvent, and the pigment tends to be unevenly distributed in the ink layer.

The charge amount of the pigment can be represented by the charge amount per mass of the pigment. The charge amount Q _{pig of the} pigment is preferably 0.07 mmol / g or more and 0.25 mmol / g or less. If it is less than 0.07 mmol / g, the dispersion stability of the pigment in the ink is lowered, and the dispersion state is easily destroyed in the process of evaporating water from the ink droplets applied to the recording medium. And the color developability of the image may be reduced. On the other hand, if it exceeds 0.25 mmol / g, the flow of the pigment accompanying the change of the dielectric constant distribution of the solvent is likely to occur in the process of evaporating the water from the ink droplets applied to the recording medium, and the pigment is likely to be unevenly distributed. There is a case.

  Moreover, it is preferable that the particle diameter of a pigment is 60 nm or more and 300 nm or less. If it is less than 60 nm, it is difficult to ensure the dispersion stability of the pigment in the ink, and the pigment tends to aggregate in the process of evaporating water from the ink droplets applied to the recording medium, so that the color developability of the image is lowered. There is a case. If it is larger than 300 nm, the pigment particles are large, so that the pigment is likely to scatter light, and the color developability of the image may be lowered.

  The pigment content (% by mass) is preferably 0.3% by mass or more and 20.0% by mass or less, and preferably 0.5% by mass or more and 12.0% by mass or less based on the total mass of the ink. Is more preferable.

(Resin fine particles)
In the present invention, the “resin fine particles” mean fine particles made of a resin and having a particle diameter that can be dispersed in an aqueous medium. The resin fine particles have a function of fixing the pigment on the surface of the recording medium by melting by heating and forming a film on the surface of the recording medium (film formation).

  The glass transition point Tg of the resin constituting the resin fine particles is more than 30 ° C. and less than 80 ° C. When the temperature is 30 ° C. or lower, the difference between the Tg of the resin and the room temperature is small, and the resin fine particles are almost in a molten state in the ink. There is a case. When the temperature is 80 ° C. or higher, a large amount of heat is required to melt the resin fine particles, and the resin fine particles cannot be melted before the pigment aggregation occurs due to the evaporation of moisture in the ink. The color developability may be reduced. The Tg of the resin is preferably 31 ° C. or higher and 79 ° C. or lower, and more preferably 40 ° C. or higher and 60 ° C. or lower.

  The resin constituting the resin fine particles is not particularly limited as long as the glass transition point Tg satisfies the above range. Specific examples include acrylic resins; styrene-acrylic resins; polyethylene resins, polypropylene resins, polyurethane resins, styrene-butadiene resins, and fluoroolefin resins. For example, the acrylic resin can be synthesized by emulsion polymerization of monomers such as (meth) acrylic acid alkyl ester and (meth) acrylic acid alkylamide. The styrene-acrylic resin can be synthesized by emulsion polymerization of a styrene monomer with (meth) acrylic acid alkyl ester, (meth) acrylic acid alkylamide, or the like. By emulsion polymerization, an emulsion in which fine particles (resin fine particles) made of the resin are dispersed in a medium can be obtained.

  As a method for adjusting the Tg of the resin, a method of controlling the Tg of the resin by copolymerizing a monomer that increases the Tg of the resin and a monomer that decreases the Tg of the resin is preferable. Monomers that increase the Tg of the resin include styrene, methyl methacrylate, ethyl methacrylate, tert-butyl methacrylate, and the like. Monomers that decrease the Tg of the resin include 2-ethylhexyl acrylate and n-butyl (meth). An acrylate etc. are mentioned.

  Furthermore, in order to improve the dispersion stability of the resin fine particles in the ink, the resin constituting the resin fine particles is preferably a copolymer obtained by copolymerizing a monomer having an anionic functional group. Specifically, the resin constituting the resin fine particles is selected from the group consisting of α, β-unsaturated carboxylic acids, α, β-unsaturated carboxylic acid derivatives, and salts of α, β-unsaturated carboxylic acids. In addition, a copolymer containing a repeating unit derived from at least one monomer is preferable.

  Examples of the α, β-unsaturated carboxylic acid include (meth) acrylic acid, maleic acid, itaconic acid, fumaric acid, etc. Among them, (meth) acrylic acid is preferable. Derivatives of α, β-unsaturated carboxylic acid include monomethyl maleate, monoethyl maleate, monobutyl maleate, monooctyl maleate, monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, etc., among which monomethyl maleate Is preferred. Examples of the salt of the α, β-unsaturated carboxylic acid include alkali metal (lithium, sodium, potassium, etc.) salts, ammonium salts, and organic ammonium salts of unsaturated carboxylic acids. Among them, sodium (meth) acrylic acid Salts or potassium salts are preferred.

  The acid value of the copolymer is preferably 50 mgKOH / g or less. When the acid value exceeds 50 mgKOH / g, it is difficult to control the uneven distribution of the pigment and the resin fine particles in the heating step, and the color developability of the image may be lowered.

  Further, it is possible to impart charge to the resin fine particles by copolymerizing the anionic monomer. By imparting electric charges to the resin fine particles, the dispersion stability of the resin fine particles can be improved, and the difference in cohesiveness with the pigment accompanying evaporation of moisture in the ink can be reduced in the heating step. The charge amount of the resin fine particles is preferably 50 μmol / g or more and 1500 μmol / g or less, and more preferably 80 μmol / g or more and 430 μmol / g or less. If it is less than 50 μmol / g, the dispersion stability of the resin fine particles in the ink may be lowered. If it is greater than 1500 μmol / g, it will be difficult to control the uneven distribution of the pigment and the resin fine particles in the heating step. The color developability may be reduced.

  As described above, as the resin constituting the resin fine particles, monomers for adjusting Tg such as styrene, α, β-unsaturated carboxylic esters (methyl methacrylate, 2-ethylhexyl acrylate, etc.); α, β-unsaturated A copolymer obtained by copolymerizing an anionic monomer of a carboxylic acid (such as (meth) acrylic acid) or a salt of an α, β-unsaturated carboxylic acid (such as an alkali metal salt of (meth) acrylic acid) is preferable. As described above, it is preferable to copolymerize by combining α, β-unsaturated carboxylic acid derivatives, because the polymerization becomes stable and the charge state of the resin fine particles to be produced can be easily adjusted.

  However, the resin fine particles need not be composed of one kind of resin, and may be composed of two or more kinds of resins. For example, different types of monomers are emulsified in core-shell type resin particles with different resin compositions in the core and shell and acrylic particles (seed particles) prepared in advance to control the particle size. Fine particles obtained by polymerization may be used. Furthermore, hybrid resin fine particles obtained by chemically bonding resin fine particles composed of different resins, such as fine particles made of acrylic resin and fine particles made of urethane resin, may be used. In view of storage stability in ink and fixability to various recording media, resin fine particles made of the acrylic resin are preferable.

  The molecular weight of the resin constituting the resin fine particles is such that the polystyrene-reduced number average molecular weight (Mn) obtained by gel permeation chromatography (GPC) is 100,000 or more and 3,000,000 or less, and more preferably 300,000 or more and 2 It is preferable that it is below 1,000,000.

  The volume average particle diameter of the resin fine particles is not particularly limited as long as the dispersion stability in the ink can be maintained, but is preferably 100 nm or more and 300 nm or less.

The absolute value of the zeta potential of the resin fine particles | ζ _res | is preferably 0 mV or more and 20 mV or less. If it is higher than 20 mV, resin fine particles tend to flow due to the change in the dielectric constant distribution of the solvent in the process of evaporating water from the ink droplets applied to the recording medium, and the pigment is unevenly distributed in the ink layer, so that the color development of the image. May decrease.

In the water-based ink of the present invention, the absolute value | Δζ | of the difference between the zeta potential ζ _{pig of the} pigment and the zeta potential ζ _res of the resin fine particles is 0 mV to 20 mV. When the difference becomes larger than 20 mV, in the process of evaporating moisture from the ink droplets applied to the recording medium, the difference in the fluidity of the pigment and the resin fine particles due to the change in the dielectric constant distribution of the solvent tends to occur. It may be unevenly distributed and the color developability of the image may be reduced.

The relationship between the charge amount of the pigment and the charge amount of the resin fine particles is related to the uneven distribution of the pigment in the ink layer. In the aqueous ink of the present invention, the ratio of the charge amount Q _pig of the pigment to the charge amount Q _res of the resin fine particles (Q _pig / Q _res ) is preferably 0.8 or more and 2.5 or less. When the ratio is less than 0.8, the pigment is unevenly distributed on the surface of the ink layer. When the ratio is greater than 2.5, the pigment is unevenly distributed inside the ink layer, and the color developability of the image is reduced. There is a case.

In each of the pigment and the resin fine particle, the value obtained by dividing the charge amount by the volume average particle diameter indicates a value corresponding to the charge density on the particle surface, and the relationship between the charge density of the resin fine particle and the charge density of the pigment is the ink density. Involved in uneven distribution of pigments in the layer. In the water-based ink of the present invention, the charge amount Q _{pig of the} pigment with respect to a value σ _res obtained by dividing the charge amount Q _res of the resin fine particles by the volume average particle size D _res of the resin fine particles is a volume average particle size D of the pigment. it is preferable ratio of a value obtained by dividing sigma _pig is 1 or more and 6 or less in _pig. When the ratio is less than 1, the pigment is unevenly distributed on the surface of the ink layer. When the ratio is larger than 6, the pigment is unevenly distributed inside the ink layer, so that the color developability of the image may be lowered. .

  The resin fine particle content (solid content, mass%) is preferably 2.0 mass% or more and 21.0 mass% or less based on the total mass of the ink. When the content is less than 2.0% by mass, the resin particle surface may not be sufficiently covered with the resin film when the resin fine particles are melted in the heating step to form the resin film. Since the light is scattered by the exposed pigment, the color developability of the image may be lowered. On the other hand, if the amount is more than 21.0% by mass, the resin may not be sufficiently melted in the heating step, and irregularities due to the remaining resin fine particles are formed on the surface of the recorded material, so that light is scattered by the irregularities. In addition, the color developability of the image may be reduced.

In the water-based ink of the present invention, the ratio of the pigment content W _{pig based on} the total mass of the ink to the content W _res of the resin fine particles based on the total mass of the ink is 0.2 or more and 0.7 or less. It is preferable that If it is less than 0.2 times, the required color reproduction range may not be realized due to too little pigment. On the other hand, if the ratio is larger than 0.7 times, the relative amount of the resin fine particles is small with respect to the pigment, the pigments tend to approach (aggregate), and light scattering in the ink layer cannot be suppressed. The color developability may be lowered.

(Water-soluble solvent)
The water-based ink of the present invention contains a water-soluble solvent. The characteristics required for the water-soluble solvent include those described below.
(1) Low dielectric constant (low dielectric constant). That is, the dielectric constant of the ink can be reduced, and the difference in charge state between the pigment and the resin fine particles can be reduced.
(2) Lowering the film forming temperature of the resin fine particles (film forming temperature reducing action). That is, the resin fine particles can be melted and formed into a film at an appropriate timing and temperature for heating.
(3) It is difficult to remain in the ink layer after the heating step (difficult to remain). That is, it can be removed from the ink layer at an appropriate heating temperature and time, and the recording layer can be fixed on the surface of the non-water-absorbing recording medium.
These characteristics may be imparted by one type of water-soluble solvent, or may be imparted by a plurality of water-soluble solvents having different functions.

  From the viewpoint of imparting the above characteristics, the water-based ink of the present invention is at least one selected from the group consisting of a low dielectric constant solvent, a film-forming temperature reducing solvent, and a hardly persistent solvent as the water-soluble solvent. It is preferable to contain these solvents. These three solvents are appropriately selected from, for example, glycols that are glycols or glycol condensates; glycol ethers that are alkyl ethers of glycols; cyclic amides; cyclic esters; Can be used. This will be specifically described below.

[Low dielectric constant solvent]
In the present invention, the “low dielectric constant solvent” means a water-soluble solvent having a dielectric constant at 25 ° C. of 23 or less, preferably 20 or less. If the dielectric constant exceeds 23, the function of reducing the dielectric constant of the ink may be insufficient. Specifically, alkane diols such as 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol; ethylene glycol mono n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono n -Glycol ethers such as butyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol mono n-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono n-butyl ether; And alkylene glycols such as polyethylene glycol which are liquid at room temperature. Among the above solvents, 1,2-alkanediol is preferable in that it is difficult to dissolve the resin fine particles and hardly increase the viscosity of the ink even if it is contained in the ink at a high concentration. In addition, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol (1,4 having 1 to 6 carbon atoms) in that the freezing point is 30 ° C. or less (that is, liquid at room temperature). 2-alkanediol) is more preferred.

  The content (% by mass) of the low dielectric constant solvent is preferably 3.0% by mass or more and 26.0% by mass or less based on the total mass of the ink. When the amount is less than 3.0% by mass, the effect of reducing the dielectric constant of the ink is reduced, and it may be difficult to suppress the uneven distribution of the pigment. If it is greater than 26.0% by mass, the dielectric constant of the ink will be too low, and the dispersion stability of the pigment and resin fine particles in the ink may be reduced. In the present invention, the low dielectric constant solvent may be used alone or in combination of two or more of the above water-soluble solvents. When using 2 or more types together, content (mass%) of the said low dielectric constant solvent means the sum total of content of the low dielectric constant solvent used together.

As described above, the relationship between the charge amount of the pigment and the charge amount of the resin fine particles is related to the uneven distribution of the pigment in the ink layer. When the ratio of the charge amount Q _pig of the pigment to the charge amount Q _res of the resin fine particle (Q _pig / Q _res ) is large, the difference in the dielectric constant between the pigment and the resin fine particle is reduced. It is preferable to increase the content of the dielectric constant solvent. More specifically, the aqueous ink of the present invention, the ratio R _Q amount of charge Q _pig of pigment resin particles to the charge amount Q _res, ink amount W _sol1 low dielectric constant solvent relative to the total weight The divided value is preferably 0.12 or more and 0.30 or less. If the value is less than 0.12, the amount of the low dielectric constant solvent is too large to adjust the difference in charge state between the pigment and the resin fine particles, so that the solvent cannot be sufficiently removed from the ink layer. The color developability of the image may be reduced. If it is larger than 0.30, the difference in the amount of charge between the pigment and the resin fine particles may not be sufficiently reduced, and the uneven distribution of the pigment in the ink layer cannot be suppressed, and the color developability of the image is reduced. May decrease.

[Film-forming temperature reducing solvent]
In the present invention, the term "film-forming temperature reduces solvent" is a water-soluble solvent means a solvent which reduces the minimum film forming temperature T _MF resin particles in the ink. Specifically, 1,2-alkanediols such as 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n -Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono n-butyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol mono n-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, Glycol ethers such as propylene glycol mono n-butyl ether; 2-pyrrolidone, N-methyl Cyclic amides such as 2-pyrrolidone; cyclic esters such as γ- butyrolactone, and the like. Among the above solvents, 1,2-alkanediol having 4 to 6 carbon atoms such as 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol; and cyclic amides such as 2-pyrrolidone Is preferred. Even if these solvents are contained in the ink at a high concentration, it is difficult to increase the viscosity, and the difference in addition amount does not greatly change the minimum film forming temperature. It is possible to easily control the minimum film-forming temperature of the resin fine particles.

  The content (% by mass) of the film-forming temperature reducing solvent is preferably 5.0% by mass or more and 30.0% by mass or less based on the total mass of the ink. When the content is less than 5.0% by mass, it is difficult to lower the minimum film-forming temperature of the resin fine particles, so that the resin fine particles cannot be melted at an appropriate timing, and the pigment is unevenly distributed in the ink layer. It may not be possible to suppress it. If it is greater than 30.0% by mass, the minimum film-forming temperature of the resin fine particles is excessively lowered, so that the viscosity of the ink may increase. Further, since the molten resin fine particles are easily fixed on the surface of the recording head, an appropriate image cannot be formed, and the color developability of the image may be lowered. In the present invention, the film-forming temperature reducing solvent may be used alone or in combination of two or more of the above water-soluble solvents. When using 2 or more types together, content (mass%) of the said film forming temperature reduction solvent means the sum total of content of the film forming temperature reduction solvent used together.

The ratio of the content W _sol2 of the film _forming temperature reducing solvent based on the total mass of the ink to the content W _res of the fine resin particles based on the total mass of the water-based ink of the present invention is 0.2 or more and _0.00 . It is preferable that it is 7 or less. If it is less than 0.2, for a minimum film-forming temperature T _MF is not reduced sufficiently, a suitable temperature, or can not be melted fine resin particles at the time, the pigment is unevenly distributed in the ink layer, the image color development of May decrease. If it is greater than 0.7, the minimum film-forming temperature _TMF may be too low, and the ink viscosity may increase, and the melted resin fine particles are likely to adhere to the surface of the recording head. May not be formed, and the color developability of the image may be reduced.

[Refractory solvent]
In the present invention, “difficult solvent” means a water-soluble solvent having a vapor pressure at 25 ° C. of 0.001 kPa to 0.02 kPa. When the vapor pressure at 25 ° C. is less than 0.001 kPa, the amount of heat necessary for removing the solvent in the heating step may increase. On the other hand, if it exceeds 0.02 kPa, the solvent tends to volatilize and the dielectric constant of the ink may change abruptly, making it difficult to control the physical properties of the ink in the heating process. Specifically, both terminal alkanediols such as ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol; 1,2-alkanediols such as propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol; glycol ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono n-butyl ether A cyclic amide such as 2-pyrrolidone; Among these solvents, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol (both terminal alkanediol having 3 to 5 carbon atoms) are preferable.

  The content (% by mass) of the hardly persistent solvent is preferably 2.0% by mass or more and 20.0% by mass or less based on the total mass of the ink. If the amount is less than 2.0% by mass, the volatilization of the solvent (drying of the ink) proceeds quickly, so it is difficult to control the physical properties of the ink in the heating process, and the uneven distribution of the pigment in the ink layer cannot be suppressed. There is. If it is larger than 20.0% by mass, it takes time to remove the solvent from the recorded matter on which an image is formed by heating the recording medium, and it may take a long time to fix the pigment. In addition, in this invention, only 1 type may be used for a hardly persistent solvent from the said water-soluble solvent, and 2 or more types may be used together. When using 2 or more types together, content (mass%) of said hard-to-remaining solvent means the sum total of content of hard-to-retained solvent to use together.

[Other water-soluble solvents]
The water-based ink of the present invention may contain a water-soluble solvent other than the low dielectric constant solvent, the film-forming temperature reducing solvent, and the hardly persistent solvent as long as the effects of the present invention are obtained. Specifically, alkyl alcohols having 1 to 4 carbon atoms, amides, polyalkylene glycols, glycols, alkylene glycols having 2 to 6 carbon atoms in the alkylene group, polyhydric alcohols, alkyls of polyhydric alcohols. And ethers and nitrogen-containing compounds. Of these, those that do not satisfy the physical properties of the low dielectric constant solvent, the film forming temperature reducing solvent, and the hardly persistent solvent may be appropriately selected and used. At this time, the content of the other water-soluble solvent in the ink is preferably smaller than the respective contents of the low dielectric constant solvent, the film-forming temperature reducing solvent, and the hardly persistent solvent. More specifically, the content (% by mass) of the other water-soluble solvent in the ink is 0% by mass or more and 10.0% by mass or less, further 0% by mass or more and 5.0% by mass based on the total mass of the ink. It is preferable that it is below mass%.

  In incorporating these water-soluble solvents into the ink, the total of the low dielectric constant solvent, the film-forming temperature reducing solvent, the hardly persistent solvent, and other water-soluble solvents is 13% by mass or more and 30% by mass based on the total mass of the ink. It is preferable that it is below mass%. If it is less than 13% by mass, it becomes easy to dry, so the ink may adhere to the recording head. On the other hand, when the amount is more than 30% by mass, it takes time to remove the solvent in the heating step, and the fixing time of the image may become long.

(water)
The water-based ink of the present invention contains water. As water, it is preferable to use ion-exchanged water (deionized water) instead of general water (such as tap water) containing various ions. The water content (% by mass) in the ink is 10.0% by mass or more and 90.0% by mass or less, and further 30.0% by mass or more and 80.0% by mass or less based on the total mass of the ink. Is preferred.

(Other ingredients)
In addition to the above components, the water-based ink of the present invention includes a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, and Various additives such as a chelating agent may be contained. The content (% by mass) of such an additive in the ink is 0.05% by mass or more and 10.0% by mass or less, and further 0.2% by mass or more and 5.0% by mass based on the total mass of the ink. The following is preferable.

  The water-based ink of the present invention preferably contains a fluorine-based or silicone-based surfactant among the surfactants. A fluorine-based or silicone-based surfactant can reduce the surface tension of the ink even with a small amount of the surfactant, so that the wettability of the ink with respect to the recording medium can be improved. As a result, even when recording on a non-water-absorbing recording medium, the phenomenon of ink being repelled on the surface of the recording medium is suppressed, and the image quality can be further improved.

  The fluorine-based or silicone-based surfactants are all trade names below, for example, Zonyl FSO, Zonyl FSO100, Zonyl FSN, Zonyl FSN100, Capstone FS-3100 (above, manufactured by Dupont); MegaFuck F-410 , Megafuck F-493, Megafuck F-443, Megafuck F-444, Megafuck F-445 (above, manufactured by DIC); Novec FC-4430, Novec FC-4432 (above, made by 3M); , Aftergent 150, Aftergent 150CH, Aftergent 250, Aftergent 400SW, Aftergent 501 (more than Neos); KS508, KP360A, KP360A (more than Shinetsu Silicone); FZ-21 1, FZ-2123,8211ADDITIVE (Toray Dow Corning); and the like.

(PH)
The pH of the aqueous ink of the present invention is preferably in the range of 7.0 to 10.0. When the pH of the ink is in the acidic region (less than 7.0), the anionic group (for example, carboxylate ion group) of the pigment or resin fine particles existing in a dissolved or dispersed state in the ink receives protons, The neutral functional group (for example, carboxy group) increases. For this reason, the solubility of the pigment and resin fine particles is lowered, and the repulsive force between these particles is also reduced, so that the pigment and resin fine particles may be unstable and precipitate in the ink. On the other hand, if the pH of the ink is too high, corrosion of members and the like constituting the ink jet recording apparatus may occur. Therefore, the pH of the ink is preferably 10.0 or less. Examples of the pH adjuster include organic amines such as diethanolamine and triethanolamine; alkali metal hydroxides such as sodium hydroxide, lithium hydroxide and potassium hydroxide; acids such as organic acids and inorganic acids. . The pH of the ink is a value at 25 ° C., and can be measured using a general pH meter.

(ink cartridge)
The water-based ink of the present invention can be used by being stored in an ink storage portion of an ink cartridge. The ink cartridge includes an ink storage portion that stores ink, and ink is stored in the ink storage portion. The structure of the ink cartridge is not particularly limited. For example, the ink storage portion stores an ink storage chamber that stores liquid ink, and a negative pressure generation member storage chamber that stores a negative pressure generation member that holds the ink therein by negative pressure. The thing comprised by is mentioned. Alternatively, the ink cartridge may be an ink container that does not have an ink storage chamber for storing liquid ink and is configured to hold the entire storage capacity by a negative pressure generating member. Furthermore, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Inkjet recording method>
The ink jet recording method of the present invention is a method of recording an image on a non-water-absorbing recording medium by ejecting ink from an ink jet recording head.

(ink)
In the recording method of the present invention, the above-described aqueous ink of the present invention is used as the ink.

(Recording head)
In the recording method of the present invention, an ink jet recording head is used. Specifically, an image is recorded on a recording medium by ejecting ink from an ejection port of an inkjet recording head in accordance with a recording signal. In the recording method of the present invention, it is particularly preferable to use a recording head of a method (thermal method) in which thermal energy is applied to ink and ink is discharged from the discharge port of the recording head. When a thermal recording head is used, it is preferable that the diameter of the ejection port is 14 μm or more and 30 μm or less. When the diameter of the ejection port is less than 14 μm, depending on the ejection frequency, moisture evaporates from the ejection port, and the moisture concentration of the ink droplet applied to the surface of the recording medium fluctuates. The uneven distribution of the pigment may not be suppressed. When the diameter of the ejection port is larger than 30 μm, the ejected ink droplets become larger, and depending on the ejection frequency, the drying speed of the ink droplets applied to the surface of the recording medium becomes slower, thereby suppressing the uneven distribution of the pigment in the ink layer. It may not be possible.

(Non-water-absorbing recording medium)
The recording method of the present invention may be a water-absorbing recording medium such as plain paper or an exclusive inkjet paper having an ink-receiving layer formed as a recording medium, but is particularly remarkable when a non-water-absorbing recording medium is used as the recording medium. The effect can be obtained. The “non-water-absorbing recording medium” in the present invention means a recording medium that does not absorb water contained in water-based ink, or a recording medium that hardly absorbs water (also referred to as a non-permeable recording medium).
More quantitatively, the non-permeable recording medium refers to a recording medium having a recording surface in which the amount of water absorption from the start of contact to 30 msec ^1/2 in the Bristow method is 10 mL / m ² or less. This Bristow method is the most popular method for measuring the amount of liquid absorbed in a short time, and is also adopted by the Japan Paper Pulp Technology Association (JAPAN TAPPI). For details of the test method, refer to Standard No. of “JAPAN TAPPI Paper Pulp Test Method 2000”. 51 "Paper and paperboard-Liquid absorbency test method-Bristow method".
For example, an ink receiving layer such as a glass plate, a plastic film, corrugated paper, a cloth, and a synthetic paper made of polypropylene (for example, YUPO <registered trademark>) is not formed and is not produced as a recording medium for water-based inkjet ink. A recording medium may be mentioned. The “non-water-absorbing recording medium” also includes recording media such as printing paper used for offset printing such as art paper and coated paper.

(Heating process)
The recording method of the present invention includes a step of heating at least the surface of a non-water-absorbing recording medium provided with ink to a heating temperature Tx higher than the glass transition point Tg of the resin constituting the resin fine particles. By heating to a heating temperature Tx higher than the glass transition point Tg of the resin, the resin fine particles are melted, the viscosity of the ink is increased, the flowability of the pigment is lowered, and the pigment can be fixed to the recording medium.

  The heating temperature Tx may be any temperature higher than the glass transition point Tg of the resin fine particles, but the difference between Tx and Tg is preferably 5 ° C. or more and 40 ° C. or less, and preferably 5 ° C. or more and 20 ° C. or less. Further preferred. When the difference between Tx and Tg is larger than 40 ° C., the vicinity of the recording head is also exposed to a high temperature, so that the temperature of the ink rises when the ink is ejected and the resin fine particles melt and the viscosity of the ink rises. In some cases, however, ink ejection characteristics may deteriorate. On the other hand, if the difference between Tx and Tg is less than 5 ° C., it takes time for the resin fine particles to melt, and the uneven distribution of the pigment in the ink layer may not be suppressed.

  Moreover, it is preferable that heating temperature Tx shall be 50 degreeC or more and 80 degrees C or less. When Tx is less than 50 ° C., beading may occur between ink droplets applied to the recording medium, the solvent evaporation efficiency may be reduced, and the image fixing time may be increased. On the other hand, when the temperature is higher than 80 ° C., since the vicinity of the recording head is also exposed to a high temperature, the water content of the ink droplets evaporated on the surface of the recording medium is evaporated from the nozzle holes. Are likely to fluctuate and uneven distribution of the pigment may not be suppressed.

Furthermore, the heating temperature Tx is preferably a minimum film forming temperature T _MF or (T _MF +30) ℃ temperature below the resin particles in the ink, ° C. or less (T _MF +10) ℃ or higher (T _MF +20) Preferably there is. Tx is not low, so the resin particles melt than T _MF, it may not be possible to suppress the uneven distribution of pigment in the ink layer. If Tx is higher than (T _MF +30) ° C., the resin fine particles melt in the vicinity of the heated recording head, the ink adheres to the recording head, the ink discharge amount decreases, and the color developability of the image may decrease. is there.

The “minimum film-forming temperature T _MF ” referred to in the present invention means the minimum temperature necessary for the resin fine particles to melt by heating and form a resin film (film formation). _TMF can be easily measured using a minimum film-forming temperature measuring device. In this minimum film-forming temperature measuring device, ink containing resin fine particles (including at least pigment, water, water-soluble solvent, and resin fine particles) is spread on a highly heat conductive metal plate with a temperature gradient and dried. The temperature at the point where the film is formed is measured as the minimum film forming temperature. In the present invention, unless otherwise stated, T _MF means the minimum film-forming temperature of the resin fine particles in the ink forms, it does not include a coloring material and a water-soluble solvent such as a pigment, the minimum film-forming temperature of the water dispersion Does not mean.

  The recording method of the present invention includes a step of heating at least the surface of the non-water-absorbing recording medium to which ink has been applied. You may have the process of heating the part of the subscanning direction downstream. In this case, the heating temperature in the vicinity of the portion to which ink is applied and the portion on the downstream side in the sub-scanning direction may be the same temperature or different temperatures. In the case of different temperatures, it is preferable to increase the heating temperature of the portion on the downstream side in the sub-scanning direction as long as the recording medium is not thermally deformed. Therefore, if such a condition is satisfied, the case where recording is performed while heating from the back surface of the recording medium is also included.

  Specifically, a nickel alloy heater is disposed under a platen made of an aluminum alloy that is not easily deformed by heat, and the platen is heated by the heater, and the recording medium is heated by the platen. The method of recording while doing. In addition to the heating method from the lower part of the platen as described above, the heating method of the portion on the downstream side in the sub-scanning direction is a method of heating the surface of the recording medium using a sheathed heater, a halogen heater and a heat reflecting plate. Etc. Furthermore, if necessary, a step of heating the recording medium can be provided by installing any of the heaters or the like upstream of the vicinity of the recording head. By further providing a heating step for heating upstream of the vicinity of the recording head, the surface of the recording medium can be maintained at a desired temperature before the recording medium comes close to the recording head. According to such a method, the heating in the vicinity of the recording head mainly replenishes the heat deprived by the moisture of the ink and the heat of vaporization of the water-soluble solvent, and the temperature fluctuation in the vicinity of the recording head is reduced. Since it becomes easy to suppress, it is preferable. In the case of using a non-water-absorbing recording medium, it is preferable to heat at a temperature not higher than the temperature at which the recording medium is deformed in any heating step.

Hereinafter, the present invention will be described in more detail using Examples and Comparative Examples. The present invention is not limited in any way by the following examples as long as the gist thereof is not exceeded. In the description of the following examples, “part” is based on mass unless otherwise specified. The meanings of the abbreviations in the specification and the table are as follows.
-KPS: Potassium persulfate-PD-104: Latemul PD-104 (trade name of emulsifier manufactured by Kao. Ammonium polyoxyalkylene alkenyl ether sulfate (solid content 20%))
2Me13PD: 2-methyl-1,3-propanediol 15PenD: 1,5-pentanediol 2-Py: 2-pyrrolidone St: styrene MMA: methyl methacrylate 2EHA: 2-ethylhexyl acrylate nBA: n-butyl acrylate MAA: methacrylic acid AA: acrylic acid BMA: n-butyl methacrylate DEGA: diethylene glycol methacrylate MEK: methyl ethyl ketone 12HD: 1,2-hexanediol 12BD: 1,2-butanediol DEGMmM : Diethylene glycol monomethyl ether • DEGmE: diethylene glycol monoethyl ether • DEGmB: diethylene glycol mono n-butyl ether • EGmB: ethylene glycol mono n Ether · TEG: Triethylene glycol · 12PD: 1,2- propanediol · the DEG: Diethylene glycol · FS3100: Capstone FS3100 (trade name DuPont fluorosurfactants.)
AIBN: Azobisisobutyronitrile (manufactured by Otsuka Chemical)

<Preparation of resin fine particle dispersion>
The resin fine particle dispersion Em. 1 to Em. 22 was prepared.

(Preparation of resin fine particle dispersion Em.1)
A three-necked flask was connected to a stirring rod, a cooling tube, a dropping syringe, and a nitrogen gas introduction tube, and the three-necked flask was placed in a thermostatic bath maintained at 50 ° C.

The following raw material (flask charging raw material) was previously stirred for 15 minutes with a homogenizer (stirring rotation speed: 10,000 rpm) to form an emulsion, and the emulsion was put into the three-necked flask.
[Raw material for flask loading]
Polymerization initiator: KPS 0.5 part Emulsifier: PD-104 3.0 part Monomer 1: St 31.0 part Monomer 2: 2EHA 66.0 parts Monomer 3: AA 3.0 parts Dispersion medium : Ion exchange water 100.0 parts

Further, the following raw material (raw material for dropping) was previously stirred for 15 minutes with a homogenizer (stirring rotation speed: 10,000 rpm) to obtain an emulsion, and the emulsion was put into a dropping syringe.
[Raw material]
Polymerization initiator: KPS 0.5 part Emulsifier: PD-104 3.0 part Monomer 1: St 31.0 part Monomer 2: 2EHA 66.0 parts Monomer 3: AA 3.0 parts Dispersion medium : Ion exchange water 100.0 parts

  And the said raw material for dripping was dripped at the inside of the said 3 necked flask over 1 hour, Then, the temperature of the thermostat was heated up to 80 degreeC, and the resin fine particle was obtained by heat-retaining for 30 minutes. In order to enhance the stability of the obtained resin fine particles, a 10% potassium hydroxide aqueous solution and ion-exchanged water were further dropped into the three-necked flask, and the pH was 8.3 and the content of the resin fine particles (solid content) was The resin fine particle dispersion Em. 1 was obtained.

(Preparation of resin fine particle dispersions Em.2 to Em.17 and Em.20 to Em.22)
Resin fine particle dispersion Em. Except that the raw materials for introducing the flask and the raw materials for dropping were changed as shown in Table 1-1. 1 and the resin fine particle dispersion Em. 2 to Em. 17, and Em. 20 to Em. 22 was obtained.

(Resin fine particle dispersion Em.18)
Resin fine particle dispersion Em. As the No. 18, latex Lx-2 described in JP-A No. 2003-171589 was used. The resin fine particles of Lx-2 are composed of a resin obtained by copolymerizing nBA (50 parts), MMA (50 parts), and AA (5 parts). The solid content concentration of Lx-2 is 45%.

(Resin fine particle dispersion Em.19)
Resin fine particle dispersion Em. As for 19, Jonkrill 775 described in JP 2011-201228 A was used. “Johncrill 775” is a trade name of a styrene / acrylic polymer emulsion manufactured by BASF. Moreover, the solid content concentration of Jonkrill 775 is 45%.

  With respect to the obtained resin fine particle dispersion, the glass transition point Tg of the resin, the zeta potential of the resin fine particles, the charge amount, and the volume average particle diameter were measured. The glass transition point Tg is a differential scanning calorimeter (trade name “Thermo plus EVOII / DSC8230, manufactured by Rigaku”), the zeta potential is an ultrasonic zeta potential measuring device (trade name “DT-1200”, manufactured by Dispersion Technology), electric charge. The amount is a potentiometric automatic titrator (trade name “AT510”, both manufactured by Kyoto Electronics Co., Ltd.) to which a streaming potential detection unit (trade name “PCD-500”) is connected, and the volume average particle size is a dynamic light scattering particle. It measured using the diameter measuring apparatus (Brand name "Nanotrack UPA EX150", the Nikkiso make). The results are shown in Table 1-2.

The symbols in the table have the following meanings.
Tg: Glass transition point of resin fine particle ζ _res : Zeta potential of resin fine particle Q _res : Charge amount of resin fine particle D _res : Volume average particle diameter of resin fine particle

<Preparation of resin aqueous solution for pigment dispersion>
According to the procedure shown below, an aqueous resin solution R.P. 1 to R.I. 8 was prepared.

(Preparation of resin r.1 for pigment dispersion)
A three-necked flask was connected to a stirring rod, a cooling tube, a dropping syringe, and a nitrogen gas introduction tube, and the three-necked flask was placed in a thermostatic bath maintained at 70 ° C.

The three-necked flask was charged with the following raw materials (flask charging raw materials).
[Raw material for flask loading]
Polymerization initiator: AIBN 0.5 part Monomer 1: St 60.0 part Monomer 2: BMA 12.0 parts Monomer 3: AA 28.0 parts Solvent: MEK 300.0 parts

Furthermore, the following raw material (raw material for dripping) was put into the dropping syringe.
[Raw material]
Polymerization initiator: AIBN 0.5 part Monomer 1: St 60.0 part Monomer 2: BMA 12.0 parts Monomer 3: AA 28.0 parts Solvent: MEK 300.0 parts

  And the said raw material for dripping was dripped at the inside of the said 3 necked flask over 1 hour, Then, the temperature of the thermostat was heated up to 70 degreeC, it heat-retained for 30 minutes, and it stirred for 10 minutes at room temperature, and was obtained. The solid material was washed with pure water three times and then dried to obtain a resin for pigment dispersion r. 1 was obtained. Resin aqueous solution for pigment dispersion 1 to produce the resin r. The acid value of 1 was measured. The acid value was determined using a potentiometric titrator (trade name “AT510”, manufactured by Kyoto Electronics Industry Co., Ltd.) and resin r. A solution of 1 in THF was measured by titration with 0.5N KOH ethanol solution. The results are shown in Table 2.

(Adjustment of pigment aqueous resin solution R.1)
The resulting resin r. After dissolving 1 in THF, the resin r. An aqueous solution containing potassium hydroxide in an amount 0.8 times the acid value of 1 and an appropriate amount of ion-exchanged water were added and stirred. Thereafter, THF was removed under reduced pressure, and resin r. 1 (solid content) is added with ion-exchanged water so that the content is 25%, and an aqueous resin solution R.D. 1 was obtained.

(Preparation of aqueous resin solutions R.2 to R.8 for pigment dispersion)
Resin aqueous solution R.P., except that the types and amounts of the raw material for introducing the flask and the raw material for dropping were changed as shown in Table 2. In the same manner as in Example 1, 2 to R.I. 8 was obtained. The results are shown in Table 2.

<Preparation of pigment dispersion>
According to the procedure shown below, the pigment dispersion K.P. 1 to K.I. 14 and pigment dispersions A to F were prepared.

(Preparation of pigment dispersion K.1)
After adding 1.6 parts of 3-aminophthalic acid to 10 parts of a 6N hydrochloric acid aqueous solution, the solution was cooled to 5 ° C., and 1.8 parts of sodium nitrite was added and stirred. Add 5 parts of carbon black (trade name “Printex95”, manufactured by Orion Engineered Carbons), heat up until the liquid temperature reaches 80 ° C. while stirring, and continue heating until nitrogen gas is no longer generated. After that, the reaction solution was cooled. Next, acetone is added to the reaction solution, and the pigment is filtered and washed. Then, ion exchange, ultrafiltration, and centrifugation are performed, and ion exchange water is added to adjust the pigment (solid content) content to 15. % Of the pigment dispersion K. 1 was obtained.

(Preparation of pigment dispersion K.2)
Except for changing 1.6 parts of 3-aminophthalic acid to 1.2 parts of anthranilic acid, the pigment dispersion K.P. 1 and the pigment dispersion K. 2 was obtained.

(Preparation of pigment dispersion K.3)
Resin aqueous solution To 1 and 18.0 parts, 67.0 parts of ion-exchanged water was added, and 15.0 parts of carbon black (trade name “NIPex 160 IQ”, manufactured by Degussa) was added with stirring, and premixing was performed for 30 minutes. Then, using a bead mill (trade name “UAM-015”, manufactured by Kotobuki Kogyo Co., Ltd.), the premixing liquid is dispersed to obtain a pigment dispersion K.K. 3 was obtained. The dispersion conditions were as follows: beads used: 0.05 mm diameter zirconia beads, bead filling rate: 70% (in terms of bulk specific gravity), rotor rotation speed: 42.1 Hz, dispersion time: 2 h. Pigment dispersion K.I. The content of pigment 3 (solid content) was 15.0%.

(Preparation of pigment dispersions K.4 to K.12)
Pigment dispersion K. except that the type and amount of the resin aqueous solution for pigment dispersion, the amount of pigment and ion-exchanged water were changed as shown in Table 3-1. 3 and the pigment dispersion K. 4 to K.I. 12 was obtained.

(Preparation of pigment dispersion K.13)
Pigment dispersion As magenta, magenta pigment dispersion 2 described in JP-A No. 2003-171589 was used. The content of the pigment (solid content) was 15%.

(Preparation of pigment dispersion K.14)
Pigment dispersion As No. 14, a black pigment dispersion described in JP2011-201228A was used. The content of the pigment (solid content) was 12%.

(Preparation of pigment dispersions A to F)
Pigment dispersion K. except that the types and amounts of the pigment and the aqueous resin solution were changed as shown in Table 3-2. In the same manner as in No. 3, pigment dispersions A to F were obtained.

With respect to the obtained pigment dispersion, the zeta potential, the charge amount, and the volume average particle diameter of the pigment were measured by the same method as the resin fine particle dispersion. The results are shown in Table 3-1 and Table 3-2. The symbols in the table have the following meanings.
ζ _pig : Zeta potential of pigment Q _pig : Charge amount of pigment D _pig : Volume average particle diameter of pigment

<Preparation of ink>
(Preparation of ink 1)
Ink 1 was prepared by mixing the following raw materials in the following composition ratio (Comparative Example 1).
Pigment dispersion K. 1 (pigment solid content 15.0%): 13.4% (solid content 2%)
-Resin fine particle dispersion Em. 1 (resin solid content 45.0%): 24.4% (solid content 11%)
・ 2-Py: 7.0%
・ 2Me13PD: 10.0%
・ 15PenD: 3.0%
・ FS3100: 1.0%
・ Ion exchange water: 41.2%

(Preparation of inks 2 to 67)
Inks 2 to 67 were the same as Ink 1 except that the types and amounts of pigment dispersion, resin fine particle dispersion, water-soluble solvent, and ion-exchanged water were changed as shown in Tables 4-1 to 4-6. Were prepared (Examples 1 to 59, Comparative Examples 2 to 8). The inks 31 and 32 have a resin fine particle dispersion, a pigment dispersion, a water-soluble solvent, and ion-exchanged water so that the solid content concentrations of the resin fine particles and the pigment are as shown in Table 4-3. The amount was adjusted accordingly.

Table 5-1 and Table 5-2 show the physical properties of the inks of Examples and Comparative Examples. The symbols in the table have the following meanings.
| Δζ |: absolute value of the difference between the zeta potential ζ _{pig of the} pigment and the zeta potential ζ _res of the fine resin particles Tg: the glass transition point of the fine resin particles W _pig / W _res : the content W of the fine resin particles based on the total mass of the ink W _res for the ink total mass ratio of the content of W _pig of the pigment relative to the Q _pig / Q _res: resin fine particles to the charge amount Q _res, the ratio of the charge amount Q _pig pigment sigma _pig / sigma _res: resin fine particles the ratio R _Q / W of the charge amount Q _res for dividing the value sigma _res volume average particle diameter D _res of the resin fine particles, a charge amount Q _pig pigment values sigma _pig obtained by dividing the volume average particle diameter D _pig pigment _sol1: the ratio R _Q amount of charge Q _pig of pigment to charge amount Q _res of the resin fine particles, the total mass of the ink value obtained by dividing the content W _sol1 low dielectric constant solvent relative to the W _sol2 / W _res: total ink Based on the total mass of the ink relative to the resin fines content W _{res based} on the mass The ratio of solvent content W _sol2

<Example 60>
In Example 60, a recorded matter was produced using the ink of Example 1 (ink 2) shown in Table 5-1 at a heating temperature of 80 ° C.

<Examples 61 to 129 and Comparative Examples 9 to 14>
A recorded matter was produced in the same manner as in Example 60 except that the types of ink and recording medium and the heating temperature Tx were changed as shown in Tables 6-1 to 6-2. The produced recorded matter was evaluated by the following method. In Examples and Comparative Examples, A to E are preferable levels and F is an unacceptable level in the evaluation criteria of the following evaluation items. The evaluation results are shown in Table 6-1 and Table 6-2. The symbols in the table have the following meanings.
Tx: Heating temperature Tg: Glass transition point of resin fine particles Tx-T _MF : Difference between heating temperature and minimum film-forming temperature PVC: Non-water-absorbent recording medium made of vinyl chloride (trade name “LLJET Glossy PVC Starch EX LLSPEX 133”, Made by Sakurai)
PET: Non-water-absorbing recording medium made of PET (trade name “Lumirror E20 # 100”, manufactured by Toray)
Acrylic: Non-water-absorbing recording medium made of acrylic resin (trade name “Technoloy Film S000”, manufactured by Sumika Acrylic Sales)
Printed paper: Coated paper (trade name “OK Top Coat +”, made by Oji Paper)

(Color development of images)
[Method for producing evaluation image]
Each of the inks of Examples and Comparative Examples was filled in an ink cartridge and mounted on an ink jet recording apparatus (trade name: imagePROGRAF iPF9400S, manufactured by Canon Inc.). Then, using a non-water-absorbing recording medium (trade name “LLJET Glossy PVC Gray Paste EX LLSPEX 133”, manufactured by Sakurai), a 100 mm wide solid image (an image having a recording duty of 100%) is recorded with a recording pass of 10 pass. did. The recording pass is related to the feed length in which the print medium is fed in the sub-scan direction after the print head scans once in the main scan direction, and the feed length is the length in the nozzle row direction of the print head. Divided by the number of passes. Therefore, usually, a desired image is recorded on the recording medium while the recording head reciprocates the number of passes on the recording medium.

  In the ink jet recording apparatus, the resolution is 1200 dpi × 1200 dpi, and the recording duty is 100% under the condition that four drops of 4 pL of ink per droplet are applied to a unit area of 1/600 inch × 1/600 inch. Is defined. In the following examples, a nickel alloy heater is disposed under the aluminum alloy platen produced by a die casting method that is not easily deformed by heat, the platen is heated by the heater, and the recording medium is made by the platen. Recording was performed while heating. The surface temperature of the recording medium in the vicinity of the recording head was measured, and the surface temperature of the recording medium was maintained by PID control to suppress temperature fluctuation. The heating temperature Tx at this time was set so that the surface temperature of the recording medium was the temperature described in Table 6-1 and Table 6-2.

[Color development evaluation method]
About the solid image of the recorded matter obtained by the above method, the optical density was measured using a reflection densitometer (trade name “RD-19I”, manufactured by Gretag Macbeth). The measured optical density was taken as OD, and the color developability was evaluated by the value of OD. The evaluation criteria of color developability are as follows. The evaluation results are shown in Table 6-1 and Table 6-2.
(1) Evaluation criteria for Bk recorded matter:
A: The OD was 2.6 or more.
B: The OD was 2.4 or more and less than 2.6.
C: The OD was 2.1 or more and less than 2.4.
D: The OD was 1.8 or more and less than 2.1.
E: OD was 1.6 or more and less than 1.8.
F: OD was less than 1.6.
(2) Evaluation criteria for Y records:
A: OD was 2.2 or more B: OD was 2.0 or more and less than 2.2.
C: The OD was 1.8 or more and less than 2.0.
D: The OD was 1.6 or more and less than 1.8.
E: OD was 1.5 or more and less than 1.6.
F: OD was less than 1.5.
(3) Evaluation criteria for M records:
A: The OD was 2.6 or more.
B: The OD was 2.4 or more and less than 2.6.
C: The OD was 2.1 or more and less than 2.4.
D: The OD was 1.8 or more and less than 2.1.
E: OD was 1.6 or more and less than 1.8.
F: OD was less than 1.6.
(4) Evaluation criteria for C records:
A: The OD was 2.4 or more.
B: The OD was 2.2 or more and less than 2.4.
C: The OD was 2.0 or more and less than 2.2.
D: The OD was 1.8 or more and less than 2.0.
E: OD was 1.6 or more and less than 1.8.
F: OD was less than 1.6.

Claims (12)

An inkjet water-based ink used in an inkjet recording method for ejecting ink from an inkjet recording head and recording an image on a non-water-absorbing recording medium,
Containing at least a pigment, resin fine particles, water, and a water-soluble solvent,
The absolute value | Δζ | of the difference between the zeta potential ζ _{pig of the} pigment and the zeta potential ζ _res of the resin fine particle is 0 mV to 20 mV,
A water-based ink characterized in that the glass transition point Tg of the resin constituting the resin fine particles is more than 30 ° C. and less than 80 ° C.   The water-based ink according to claim 1, wherein a glass transition point Tg of the resin constituting the resin fine particles is 31 ° C or higher and 79 ° C or lower. The absolute value | ζ _pig | of the zeta potential of the pigment is 0 mV to 30 mV,
3. The water-based ink according to claim 1, wherein an absolute value | ζ _res | of the zeta potential of the resin fine particles is 0 mV or more and 20 mV or less. The ratio of the pigment content W _{pig based on} the total mass of the ink to the resin fine particle content W _{res based} on the total mass of the ink is 0.2 to 0.7. The water-based ink according to any one of the above. 5. The water-based ink according to claim 1, wherein a ratio of the charge amount Q _pig of the pigment to the charge amount Q _res of the resin fine particles is 0.8 or more and 2.5 or less. The charge amount Q _res resin fine particles to a value obtained by dividing sigma _res volume average particle diameter D _res of the resin particles, the value of the charge amount Q _pig of the pigment obtained by dividing the volume average particle diameter D _pig of the pigment sigma _pig The water-based ink according to any one of claims 1 to 5, wherein the ratio is from 1 to 6. The resin constituting the resin fine particles is at least one selected from the group consisting of α, β-unsaturated carboxylic acids, derivatives of α, β-unsaturated carboxylic acids, and salts of α, β-unsaturated carboxylic acids. A copolymer containing repeating units derived from the monomer of
The water-based ink according to any one of claims 1 to 6, wherein the acid value of the copolymer is 50 mgKOH / g or less. As the water-soluble solvent, a low dielectric constant solvent having a dielectric constant of 23 or less at 25 ° C., a film forming temperature reducing solvent for reducing the minimum film forming temperature T _MF of the resin fine particles in the ink, and a vapor pressure at 25 ° C. The water-based ink according to any one of claims 1 to 7, comprising at least one solvent selected from the group consisting of hard-to-remain solvents that are 0.001 kPa to 0.02 kPa. Wherein the ratio R _Q amount of charge Q _pig of the pigment to the charge amount Q _res of the resin fine particles, the value obtained by dividing the content W _sol1 of the low dielectric constant solvent relative to the total ink mass, 0.12 or 0 The water-based ink according to claim 8, wherein the water-based ink is 30 or less. The ratio of the content W _sol2 of the film- _forming temperature reducing solvent based on the total mass of the ink to the content W _res of the resin fine particles based on the total mass of the ink is 0.2 or more and 0.7 or less. The water-based ink according to 8 or 9. An ink jet recording method for recording an image on a non-water absorbent recording medium by discharging ink from an ink jet recording head,
As the ink, the water-based ink according to any one of claims 1 to 10,
An ink jet recording method comprising a step of heating at least the surface of the non-water-absorbing recording medium provided with the ink to a heating temperature Tx higher than a glass transition point Tg of a resin constituting the resin fine particles. The heating temperature Tx-jet recording method according to the minimum film forming temperature T _MF or (T _MF +30) ℃ a temperature below claims 11 of the resin particles in the ink.