JP6519766B2 - Pigment water dispersion for inkjet recording - Google Patents

Description

  The present invention relates to a pigment water dispersion for inkjet recording, and a method for producing the water dispersion.

The ink jet recording method is a recording method in which ink droplets are directly ejected from a very fine nozzle onto a recording member and adhered to obtain characters and images. This system is widely popular because it has many advantages such as easy full color and inexpensive, usable plain paper as a recording member, and non-contact with printed matter.
Recently, in order to impart weather resistance and water resistance to printed matter, an ink jet recording ink using a pigment as a colorant is widely used in the ink jet recording system.

For example, Patent Document 1 shows a water-based ink including a dispersible colorant in which a chargeable resin pseudo fine particle smaller than the colorant is fixed to a water-insoluble colorant, and at least one water-soluble colorant. With the average value of the surface zeta potential of the dispersible colorant and the distribution thereof in a specific range, the low coloring ability (low image density) can be greatly improved, and it has fast drying properties. It is disclosed that a recorded image with good print area uniformity can be obtained.
In Patent Document 2, after dissolving a water-insoluble polymer in a solvent and dispersing it in a medium, it is heated at 100 to 150 ° C. for about 4 hours, and finally the solvent is removed to increase the particle size even if it receives heat history. There is also disclosed a method of producing a pigment dispersion having a high degree of dispersion stability in which nozzle clogging and ejection failure of a recording liquid do not occur.
Patent Document 3 discloses a method for producing an ink having excellent ejection stability by dissolving a water-insoluble polymer in a solvent, performing high-pressure dispersion, adding water and stirring, and then removing the solvent.

Unexamined-Japanese-Patent No. 2006-8786 JP 2005-15550 A JP 2007-99915 A

In the technology of Patent Document 1, the standard deviation and the like are also defined from the value obtained by measuring the moving speed of the dispersed particles when a constant electric field is applied by the image processing method. However, with regard to the ejection durability performance, it is necessary to consider the influence of the particles themselves on the measurement value by the Brownian motion, and the value of the zeta potential measured in Patent Document 1 is not necessarily an indicator of the image performance of the ink. In the technology of Patent Document 1, it was insufficient to provide a pigment water dispersion for ink jet recording excellent in printing density in ejection durability and long-term use of printer with zeta potential as an index.
It is an object of the present invention to provide a pigment water dispersion for ink jet recording, which is excellent in discharge durability and can suppress a decrease in printing density even when recording over a long period of time, and a method of manufacturing the water dispersion. Do.

In order to solve the above problems, the inventors of the present invention have found that the electric repulsion of pigment particles obtained by adsorbing the polymer on the pigment surface becomes uniform throughout the ink while enhancing the adsorption of the polymer to the pigment. I thought it was desirable. On the other hand, the electric field intensity given to the pigment particle is controlled as an index showing that the electric repulsion of the pigment particle is uniform, and the difference between the two zeta potential distributions different in electric field intensity obtained under the conditions is evaluated We considered that we could measure the zeta potential distribution excluding the influence of Brownian motion by doing it.
As a result, it has been found that the zeta potential distribution can be measured excluding the influence of the Brownian motion by acquiring two zeta potential distributions and performing specific processing to obtain the difference. In addition, it has been found that there is a close relationship between the obtained zeta potential distribution and the ejection durability, and in the zeta potential distribution obtained by the zeta potential measurement step described later, the scattering intensity of the component included in the specific range It has been found that a pigment dispersion for inkjet recording can be obtained by setting conditions under which the area ratio is set to a specific value or less.

That is, the present invention relates to the following [1] to [6].
[1] A pigment water dispersion containing pigment particles and water,
Inkjet having a scattering intensity area ratio of 5% or less of components included in the range of 0 to -55 mV of the standardized zeta potential distribution 4 obtained by the following zeta potential measurement steps (i) to (iv) and (v) Recording pigment water dispersion (first embodiment).
Step (i): a step of measuring zeta potential distribution 1 without applying an electric field to particles in the measurement cell and then normalizing to obtain normalized zeta potential distribution 1.
Step (ii): applying an electric field of 1200 V / m to the particles in the measurement cell to measure the zeta potential distribution 2 and then normalizing to obtain the normalized zeta potential distribution 2.
Step (iii): obtaining a normalized zeta potential distribution 3 obtained by taking the difference between the normalized zeta potential distributions 1 and 2
Step (iv): Step of obtaining the normalized zeta potential distribution 4 by making a histogram of the normalized zeta potential distribution 3 in 1 mV steps and normalizing the histogram.
Step (v): Read the range (area) of 0 to -55 mV and the range (area) between the normalized zeta potential distribution 4 and the line of zero scattering intensity in the normalized zeta potential distribution 4 Step of obtaining the scattering intensity area ratio (%) of the components contained in the range of 55 mV.
[2] A pigment water dispersion containing pigment particles and water,
The scattering intensity area ratio of the components included in the range of 0 to -58 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and the following step (vi) is 10% or less And a pigment water dispersion for ink jet recording (second aspect).
Step (vi): Read the range (area) of 0 to -58 mV and the range (area) between the normalized zeta potential distribution 4 and the line of zero scattering intensity in the normalized zeta potential distribution 4 Step of obtaining the scattering intensity area ratio (%) of the components included in the range of 58 mV.
[3] A pigment water dispersion containing pigment particles and water,
The scattering intensity area ratio of the components included in the range of 0 to -60 mV of the standardized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and the following step (vii) is 40% or less And a pigment water dispersion for ink jet recording (third aspect).
Step (vii): Read the range (area) of 0 to -60 mV and the range (area) between the normalized zeta potential distribution 4 and the line of zero scattering intensity in the normalized zeta potential distribution 4 Step of obtaining the scattering intensity area ratio (%) of the components included in the range of 60 mV.

[4] The scattering intensity area ratio of the components contained in the range of 0 to -55 mV of the standardized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (v) is 5% or less A method for producing a pigment water dispersion for ink jet recording, comprising the steps of
[5] The scattering intensity area ratio of components included in the range of 0 to -58 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (vi) is 10% or less A method for producing a pigment water dispersion for ink jet recording, comprising the steps of
[6] The scattering intensity area ratio of the components included in the range of 0 to -60 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (vii) is 40% or less A method for producing a pigment water dispersion for ink jet recording, comprising the steps of

  According to the present invention, it is possible to provide a pigment water dispersion for ink jet recording, which is excellent in discharge durability and can suppress a decrease in print density even when recording over a long period of time, and a method of manufacturing the water dispersion. it can.

It is a schematic diagram of process (i) which obtains the normalization zeta-potential distribution 1. FIG. It is a schematic diagram of process (ii) of obtaining the normalization zeta-potential distribution 2. FIG. It is a schematic diagram of process (iii) of obtaining the normalization zeta-potential distribution 3. FIG. It is a schematic diagram of process (iv) of obtaining the normalization zeta-potential distribution 4. FIG. It is a schematic diagram of the range which calculates | requires a scattering intensity area ratio.

The pigment water dispersion for ink jet recording (hereinafter, also simply referred to as “pigment water dispersion”) of the present invention includes the first to third aspects described above.
Although the reason why the water-based ink containing the pigment water dispersion of the present invention is excellent in the ejection durability is not clear, it is considered as follows.
Ink jet recording heads are manufactured using microfabrication techniques such as semiconductor manufacturing processes, and it is required that the ink flow smoothly in a minute pipe. In the case of ink in which ink deposition and the like are easily generated in the ink flow path, resistance easily occurs in the ink flow path, so the meniscus shape of the ink droplet in the discharge nozzle tends to be unstable, and discharge instability and eventually discharge failure May be
Further, in particular, water-based ink containing a polymer dispersant tends to cause clogging and ejection bending due to ink thickening at the nozzle opening when dried at the ejection nozzle opening. In this phenomenon, the distance between the pigment particles (that is, the pigment particles to which the water-dispersible polymer is adsorbed or the polymer particles containing the pigment) is narrowed by the drying of water at the nozzle opening, and the solvent component contained in the ink It is considered that, when the overall relative dielectric constant is lowered, the charge repulsion between the pigment particles is lowered and the pigment particles are clogged to cause clogging and ejection bending.
In addition, in such an aggregation phenomenon of pigment particles, it is considered that a phenomenon called hetero aggregation is also related. Hetero aggregation is a phenomenon in which aggregation is caused by the presence of pigment particles having different zeta potentials in the same system, and is generally generated between different particles.
In the present invention, in the normalized zeta potential distribution 4, the pigment surface is made to have the scattering intensity area ratio of a component included in a specific range near 0 where the electric potential with small charge repulsive force between pigment particles is a specific amount or less. It is thought that hetero-aggregation can be suppressed and discharge durability can be improved because the adsorption state of the water-dispersible polymer adsorbed on the pigment particles becomes uniform among the pigment particles and the variation in zeta potential of the pigment particles can be reduced. Be

Further, in an apparatus using an inkjet thermal recording head, film boiling occurs in water in the ink by the heating of the heater, and the ink is discharged by the shock wave generated at that time. At that time, since the surface of the heater is heated to 300 ° C. or higher, a so-called kogation phenomenon in which the ink component is burnt on the surface of the heater is observed, and the discharge durability becomes a problem.
The heater is mainly formed of metal oxide, and in the pH 7-11 environment where the anionic ink stabilizes, the heater surface is slightly negatively charged, and cations in the ink, for example, sodium derived from a neutralizing agent I am attracting ions. On the other hand, since the pigment particles in the ink are also negatively charged, sodium ions are also attracted to the pigment surface.
As the pigment particles approach the heater surface, the concentration of sodium ions present between the heater and the pigment particles increases, so an osmotic pressure is generated from the difference with the sodium concentration in the ink bulk, and the pigment particles move away from the heater It receives repulsive force by osmotic pressure.
For this reason, when the surface potential of the pigment particles is high, the pigment particles themselves do not easily approach the heater, and burning of the pigment particles on the heated heater surface layer is suppressed. In the present invention, by setting the scattering intensity area ratio of the components included in a specific range to a specific amount or less in the standardized zeta potential distribution 4, the variation in zeta potential of the pigment particles is reduced, and the pigment has a low surface potential. Since the particles are reduced, it is considered that the pigment particles can be prevented from burning at the heater surface.

  In addition, since different types of materials such as metal and polymer adhesive are used in combination, the ink jet recording head may cause elution of the metal material or the polymer adhesive if the ink is left filled inside during standby. Swelling or the like may shorten the life of the recording head. On the other hand, in some printers, attempts have been made to recover the ink from the recording head to an ink tank or the like to extend the life of the recording head. In addition, it is also attempted to suppress clogging of the recording head by filtering the ink at the time of ink recovery. On the other hand, when the surface potential of the pigment is high, aggregation of pigment particles when passing through the flow path filter is suppressed, clogging by the filter is reduced, and negative pressure applied to the ink supply at the time of discharge and the meniscus of the recording head nozzle. Is stable even in long-term use. In the present invention, by setting the scattering intensity area ratio of the components included in a specific range to a specific amount or less in the standardized zeta potential distribution 4, the variation in zeta potential of the pigment particles is reduced, and the pigment has a low surface potential. It is thought that clogging of the filter can be prevented because the particles are reduced.

[Pigment water dispersion for inkjet recording]
The pigment water dispersion of the present invention can be suitably obtained by the method for producing a pigment water dispersion described later, wherein the pigment particles to which the water dispersible polymer is adsorbed or the polymer particles (solid content) containing the pigment is water In the main medium. The pigment particles are, for example, in the form of particles in which the pigment is encapsulated in a polymer, in the form of particles in which the pigment is uniformly dispersed in the polymer, in the form of particles in which the pigment is exposed on the surface of the polymer particles, hydrophilic functional groups directly on the surface of the pigment. And particle forms which are covalently bonded via other functional groups.

In the first aspect of the pigment water dispersion of the present invention, the scattering intensity area ratio of the components contained in the range of 0 to −55 mV is, from the viewpoint of improving the discharge durability and obtaining the printed matter with high printing density, The total content is 5% or less, preferably 2% or less, more preferably 1% or less, and still more preferably 0%.
In the second aspect of the pigment water dispersion of the present invention, the scattering intensity area ratio of the components contained in the range of 0 to −58 mV is, from the viewpoint of improving the discharge durability and obtaining a printed matter having a high printing density, The total content is 10% or less, preferably 7% or less, more preferably 4% or less, and still more preferably 2% or less.
In the third aspect of the pigment water dispersion of the present invention, the scattering intensity area ratio of the components included in the range of 0 to −60 mV is, from the viewpoint of improving the discharge durability and obtaining the printed matter with high printing density, The total content is 40% or less, preferably 20% or less, more preferably 10% or less, and still more preferably 5% or less.

The scattering intensity area ratio is obtained by four steps of the following zeta potential measurement steps (i) to (iv) and one step of any one of steps (v) to (vii).
Step (i): a step of measuring zeta potential distribution 1 without applying an electric field to particles in the measurement cell and then normalizing to obtain normalized zeta potential distribution 1.
Step (ii): applying an electric field of 1200 V / m to the particles in the measurement cell to measure the zeta potential distribution 2 and then normalizing to obtain the normalized zeta potential distribution 2.
Step (iii): obtaining a normalized zeta potential distribution 3 obtained by taking the difference between the normalized zeta potential distributions 1 and 2
Step (iv): Step of obtaining the normalized zeta potential distribution 4 by making a histogram of the normalized zeta potential distribution 3 in 1 mV steps and normalizing the histogram.
Step (v): In the normalized zeta potential distribution 4, the range (area) between 0 to -55 mV and the line between the normalized zeta potential distribution 4 and the line of zero scattering intensity is read, and the range of 0 to -55 mV Obtaining the scattering intensity area ratio (%) of the components contained in
Step (vi): Read the range (area) between the range of 0 to -58 mV and the line between the normalized zeta potential distribution 4 and the line of zero scattering intensity in the normalized zeta potential distribution 4 and the range of 0 to -58 mV Obtaining the scattering intensity area ratio (%) of the components contained in
Step (vii): In the normalized zeta potential distribution 4, read the range (area) between 0 to -60 mV and the line between the normalized zeta potential distribution 4 and the line of zero scattering intensity, and the range of 0 to -60 mV Obtaining the scattering intensity area ratio (%) of the components contained in
Note that "do not apply an electric field" means to apply an electric field of 0 V / m. Also, normalization of the zeta potential distribution is performed by dividing each peak intensity at 1 mV by the peak maximum intensity value so that the peak maximum intensity is 1.
The measurement method of the zeta potential distribution is preferably a dynamic light scattering method, and specifically, it can be measured by the method described in the examples.
FIG. 1 shows a schematic view of the step (i) for obtaining the normalized zeta potential distribution 1 and FIG. 2 shows a schematic view of the step (ii) for obtaining the normalized zeta potential distribution 2 and FIG. 3 shows the normalized zeta potential distribution A schematic view of the step (iii) for obtaining 3 is shown, a schematic view of the step (iv) for obtaining the normalized zeta potential distribution 4 is shown in FIG. 4, and a schematic view of a range for obtaining the scattering intensity area ratio is shown in FIG.

Of the first to third aspects, the pigment water dispersion of the present invention preferably satisfies any two aspects, and more preferably all the first to third aspects.
As a method of decreasing the scattering intensity area ratio in the predetermined zeta potential range, for example, a) a method of applying an electric field to a pigment water dispersion to remove particles having a low zeta potential, b) a pigment water dispersion described later C) a method of carrying out the production step (2) (step of holding at a specific temperature), c) a monomer containing a polymerizable surfactant monomer having a hydrophilic functional group and polymerization with respect to a system in which a pigment is dispersed After the polymerization reaction is carried out under the predetermined conditions by adding an initiator and, if necessary, a chain transfer agent, the pigment dispersion is precipitated by acid precipitation and then washed with a hydrophilic organic solvent, and then the total of the pigment dispersion is obtained. A method of adjusting the neutralization degree to about 20 mol% with potassium hydroxide etc. with respect to the amount of acid, redispersing in an aqueous solution, removing particles with a small amount of acid by centrifugation, and d) dispersing a pigment with a resin Add acid or salt to the system to make the resin face After salting out and aciding out on the surface, add about 5% by weight of the non-water-soluble organic solvent to the precipitate, leave the acid or salt as an additional solvent after leaving at rest for 24 hours or more at normal temperature under sealing. Method to remove by ultrafiltration etc. e) After dissolving pigment particles, UV curable resin, UV initiator etc. in good solvent beforehand, add to poor solvent and at the same time expose UV to pigment particles and resin The resulting complex is dropped into an alcohol of low dielectric constant, and after removing particles of low zeta potential which precipitate, the residual alcohol of high dielectric constant is removed as a solvent by ultrafiltration or the like. Method f) After adding a compound having both a hydrophilic functional group and a crosslinkable resin such as an epoxy group to a system in which a pigment is dispersed in a resin, the crosslinking reaction is promoted by heat or the like. Pigment particles and dispersion resin After increasing the amount of hydrophilic functional groups to be carried, it is dropped into alcohol of low dielectric constant, and after removing the particles of low zeta potential which precipitate, unreacted cross-linking agent remaining with alcohol of high dielectric constant as solvent is used. The method of removing by ultrafiltration etc., etc. are mentioned.
The first to third embodiments of the pigment water dispersion of the present invention are water dispersions containing at least pigment particles and water. Pigment particles include self-dispersed pigments and pigments dispersed with water dispersible polymers.
Examples of the device for dispersing the pigment in water include a mixing and stirring device described later, a high-speed stirring and mixing device, a kneader, a high pressure homogenizer, and a media type dispersing device.

The volume average particle diameter of the pigment particles in the pigment water dispersion of the first to third aspects is the viewpoint of improving the dispersion stability of the pigment water dispersion, the storage stability of the water-based ink, and the ejection durability, and the printing density Is preferably 40 nm or more, more preferably 50 nm or more, still more preferably 60 nm or more, and preferably 150 nm or less, more preferably 140 nm or less, still more preferably 130 nm or less.
The volume average particle diameter of the pigment particles can be adjusted by dispersion treatment in the production process (1) described later, removal of the volatile base, classification operation and the like.
The volume average particle size of the pigment particles can be measured by the dynamic light scattering method according to the method described in the examples.

The surface tension (20 ° C.) of the pigment water dispersion of the first to third aspects is preferably 30 mN / m or more, more preferably 35 mN / m or more, and 65 mN / m or less, more preferably 60 mN / m. m or less.
The viscosity (20 ° C.) of 20% by mass (solid content) of the pigment water dispersion of the first to third aspects is preferably 2 mPa · s or more in order to obtain a preferable viscosity when used as an aqueous ink, Preferably it is 6 mPa · s or less, more preferably 5 mPa · s or less.
The viscosity can be measured by the method described in the examples.

[Pigment]
The pigment used in the present invention may be either an inorganic pigment or an organic pigment. In addition, if necessary, they may be used in combination with an extender pigment.
Examples of the inorganic pigment include carbon black, metal oxides, metal sulfides, metal chlorides and the like, and carbon black is preferable particularly in black ink. As carbon black, furnace black, thermal lamp black, acetylene black, channel black etc. are mentioned.
Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments and the like.
Specific examples of preferred organic pigments include C.I. I. Pigment yellow, C.I. I. Pigment red, C.I. I. Pigment violet, C.I. I. Pigment blue, and C.I. I. And one or more product number products selected from the group consisting of pigment green. Examples of extender pigments include silica, calcium carbonate and talc.
As the pigment, a so-called self-dispersible pigment can also be used. The self-dispersion pigment refers to one or more kinds of hydrophilic functional groups (anionic hydrophilic groups such as carboxy group and sulfonic acid group, or cationic hydrophilic groups such as quaternary ammonium group) directly or other atomic groups. By binding to the surface of the pigment via the surface, it means an inorganic pigment or an organic pigment which can be dispersed in an aqueous medium without using a surfactant or a resin. Here, as another atomic group, a C1-C12 alkanediyl group, a phenylene group, or a naphthylene group etc. are mentioned.
The amount of the hydrophilic functional group is not particularly limited, but is preferably 100 μmol or more and 3,000 μmol or less per 1 g of the self-dispersible pigment, and 200 μmol or more and 700 μmol or less per 1 g of the self-dispersible pigment when the hydrophilic functional group is a carboxy group. Is preferred.
Commercially available self-dispersing pigments include CAB-O-JET 200, 300, 352K, 250C, 260M, 270Y, 450C, 465M, 470Y, 480V (manufactured by Cabot Corp.) and BONJET. Examples thereof include CW-1, CW-2 (manufactured by Orient Chemical Industry Co., Ltd.), Aqua-Black 162 (manufactured by Tokai Carbon Co., Ltd.), and the like. The above pigments can be used alone or in combination of two or more.

  The pigment content is the viewpoint of improving the dispersion stability of the pigment water dispersion, and the storage stability and discharge durability of the water-based ink obtained from the pigment water dispersion (hereinafter, also simply referred to as “water-based ink”) From the viewpoint of improving the productivity of the pigment water dispersion, it is preferably 5% by mass or more, more preferably 8% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or more in the pigment dispersion. The content is preferably 25% by mass or less, more preferably 20% by mass or less.

[Water-dispersible polymer]
The water dispersible polymer means a polymer dispersible in water or a medium containing water as a main component at normal temperature, and examples thereof include polyester, polyurethane, vinyl polymer, etc. Dispersion stability of pigment water dispersion And from the viewpoint of improving the storage stability of the aqueous ink, vinyl polymers obtained by addition polymerization of vinyl monomers are preferable.

In addition, as the water-dispersible polymer, one formed by copolymerizing a monomer containing an ionic group (hereinafter, also referred to as "ionic monomer") is preferable. Furthermore, as the water dispersible polymer, from the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the aqueous ink, a hydrophobic monomer (a) (hereinafter also referred to as “component (a)”), A polymer obtained by copolymerizing a monomer mixture containing an ionic monomer (b) (hereinafter also referred to as “component (b)”) (hereinafter also referred to as “monomer mixture”) is preferable. This polymer has a constituent unit derived from the (a) component and a constituent unit derived from the (b) component.
Further, the polymer used in the present invention is also referred to as a nonionic monomer (c) (hereinafter also referred to as “component (c)” from the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the aqueous ink. Is preferably used as the monomer component.
From the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the water-based ink, the vinyl polymer contains (a) component, (b) component and, if necessary, (c) component. Preferred are vinyl polymers obtained by copolymerizing a monomer mixture. The vinyl-based polymer has a constituent unit derived from the component (a) and a constituent unit derived from the component (b), and further optionally has a constituent unit derived from the component (c).

<Hydrophobic Monomer (a)>
Examples of the hydrophobic monomer (a) include aromatic group-containing monomers, alkyl (meth) acrylates and the like.
As an aromatic group containing monomer, the vinyl monomer which has a C6-C22 aromatic group is preferable, and a styrene-type monomer, aromatic group containing (meth) acrylate, etc. are more preferable.
As a styrene-type monomer, styrene and 2-methylstyrene are preferable, and styrene is more preferable.
Further, as the aromatic group-containing (meth) acrylate, benzyl (meth) acrylate and phenoxyethyl (meth) acrylate are preferable, and benzyl (meth) acrylate is more preferable.
From the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the aqueous ink, the aromatic group-containing (meth) acrylate is preferable, and it is also preferable to use the aromatic group-containing (meth) acrylate and the styrene-based monomer in combination .
In addition, "(meth) acrylate" means both a methacrylate and an acrylate.

The alkyl (meth) acrylate is preferably one having an alkyl group having 1 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate and (iso) propyl (meth) ) Acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) Examples include decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (iso) stearyl (meth) acrylate and the like.
In addition, "(iso or tertiary)" and "(iso)" mean both the case where these groups exist, and the case where they do not exist, and when these groups do not exist, they show a normal.

Macromers can also be used as hydrophobic monomers (a).
The macromer is a compound having a number average molecular weight of 500 to 100,000 having a polymerizable functional group at one end, and from the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the water-based ink, the number average of the macromer The molecular weight is preferably 1,000 or more, preferably 10,000 or less.
The number average molecular weight is a value measured by gel permeation chromatography using chloroform containing 1 mmol / L of dodecyldimethylamine as a solvent, using monodispersed polystyrene having a known molecular weight as a standard substance. .
As the polymerizable functional group present at one end, a (meth) acryloyloxy group is preferable, and a methacryloyloxy group is more preferable.
As the macromer, from the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the water-based ink, aromatic group-containing monomer type macromers and silicone type macromers are preferable, and aromatic group-containing monomer type macromers are more preferable.
Examples of the aromatic group-containing monomer constituting the aromatic group-containing monomer-based macromer include the aromatic group-containing monomer described in the hydrophobic monomer (a), styrene and benzyl (meth) acrylate are preferable, and styrene is more preferable. preferable.
Specific examples of commercially available styrenic macromers include AS-6 (S), AN-6 (S), HS-6 (S) (trade names of Toagosei Co., Ltd.), and the like.
Examples of silicone macromers include organopolysiloxanes having a polymerizable functional group at one end.

<Ionic monomer (b)>
The ionic monomer (b) can be used as a monomer component from the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the aqueous ink.
Examples of the ionic monomer include anionic monomers and cationic monomers, and from the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the water-based ink, and the viewpoint of improving the ejection durability, the anionic monomer is preferable.
As an anionic monomer, a carboxylic acid monomer, a sulfonic acid monomer, a phosphoric acid monomer etc. are mentioned.
Examples of carboxylic acid monomers include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethyl succinic acid and the like.
Examples of sulfonic acid monomers include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate and the like.
Examples of phosphoric acid monomers include vinyl phosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate and the like.
Among the above-mentioned anionic monomers, from the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the aqueous ink, carboxylic acid monomers are preferable, and one or more selected from acrylic acid and methacrylic acid are more preferable, Methacrylic acid is more preferred.

<Nonionic monomer (c)>
As the nonionic monomer (c), 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol (n = 2 to 30, n represents an average added mole number of oxyalkylene group. The same) polyalkylene glycol (meth) acrylates such as (meth) acrylates, methoxypolyethylene glycol (n = 1 to 30) (meth) acrylates, and alkoxy such as 2-ethylhexyl polyethylene glycol (n = 1 to 30) (meth) acrylates Aralkoxypolyalkylene glycols such as polyalkylene glycol (meth) acrylate, phenoxy (ethylene glycol / propylene glycol copolymerization) (n = 1 to 30, ethylene glycol contained therein: 1 to 29) (meth) acrylate Data) acrylate and the like. Among them, alkoxypolyalkylene glycol (meth) acrylate is preferable.
Specific examples of the commercially available component (c) include NK esters M-20G, 40G, 90G, EH-4E, etc. manufactured by Shin-Nakamura Chemical Co., Ltd., and Blemmer PE- manufactured by NOF Corporation. 90, 200, 350, PME-100, 200, 400, etc., PP-500, 800, etc., AP-150, 400, 550, 50PEP-300, 50POEP-800B, 43PAPE-600B, etc. Can be mentioned. Among them, NK ester EH-4E (polyethylene glycol [n = 4] methacrylate 2-ethylhexyl ether) manufactured by Shin-Nakamura Chemical Co., Ltd. is particularly preferable from the viewpoint of printing density.

Each component of said (a) component-(c) component can be used individually or in combination of 2 or more types, respectively.
Content of the above components (a) to (c) in the monomer mixture at the time of production of water dispersible polymer (content as unneutralized amount. The same applies hereinafter), ie, component (a) in water dispersible polymer The content of the constituent unit derived from the component (c) is as follows.
The content of the component (a) is preferably 40% by mass or more, more preferably 45% by mass or more, from the viewpoint of improving the dispersion stability of the pigment water dispersion, the storage stability of the aqueous ink, and the discharge durability. The content is preferably 48% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, and still more preferably 75% by mass or less.
The content of the component (b) is preferably 15% by mass or more, and preferably 25% by mass, from the viewpoint of improving the dispersion stability of the pigment water dispersion, the storage stability of the aqueous ink, and the discharge durability. The following content is more preferably 23% by mass or less, still more preferably 21% by mass or less.
The content of the component (c) is preferably 0% by mass or more, more preferably 10% by mass or more, from the viewpoint of improving the dispersion stability of the pigment water dispersion, the storage stability of the water-based ink, and the discharge durability. The content is preferably 20% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, and still more preferably 32% by mass or less.

The water dispersible polymer is prepared by copolymerizing the above-mentioned hydrophobic monomer (a), ionic monomer (b), and, if necessary, a mixture of nonionic monomer (c) and other monomers by a known polymerization method. Manufactured by As a polymerization method, a solution polymerization method is preferable.
There is no limitation on the organic solvent used in the solution polymerization method, but methyl ethyl ketone, toluene, methyl isobutyl ketone and the like are preferable from the viewpoint of monomer copolymerizability.
At the time of polymerization, a polymerization initiator and a polymerization chain transfer agent can be used. As a polymerization initiator, azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), t-butylperoxy octoate, dibenzoyl peroxide Well-known radical polymerization initiators, such as organic peroxides, etc. can be used. Among them, an azo compound is preferable, and 2,2′-azobis (2,4-dimethylvaleronitrile) is more preferable.
As the polymerization chain transfer agent, known polymerization chain transfer agents such as mercaptans such as octyl mercaptan and 2-mercaptoethanol, and thiuram disulfides may be mentioned, but mercaptans are preferable, and 2-mercaptoethanol is more preferable.

The preferred polymerization conditions vary depending on the type of polymerization initiator etc., but the polymerization temperature is preferably 50 ° C. or more, more preferably 60 ° C. or more, still more preferably 70 ° C. or more, and preferably 90 ° C. or less, more Preferably it is 85 degrees C or less. The polymerization time is preferably 1 hour or more, more preferably 4 hours or more, further preferably 6 hours or more, preferably 20 hours or less, more preferably 15 hours or less, further preferably 10 hours or less. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, unreacted monomers and the like can be removed from the reaction solution by reprecipitation, membrane separation, chromatography, extraction and the like.

(Weight-average molecular weight of water-dispersible polymer)
The weight average molecular weight of the water dispersible polymer is preferably 5,000 or more from the viewpoint of improving the dispersion stability of the pigment water dispersion, the storage stability of the water-based ink, the discharge durability, and the printed matter having a high print density. More preferably 10,000 or more, further preferably 30,000 or more, still more preferably 40,000 or more, still more preferably 50,000 or more, and preferably 500,000 or less, more preferably 300,000 or less, further preferably Is less than 200,000, more preferably less than 150,000, and still more preferably less than 100,000.
In addition, a weight average molecular weight can be calculated | required by the method as described in an Example.
When a water dispersible polymer is used in the pigment water dispersion of the first to third aspects, the mass ratio of the pigment amount to the water dispersible polymer amount (pigment / water dispersible polymer) is the dispersion stability of the pigment water dispersion And 80/20 or less, more preferably 75/25 or less, still more preferably 70/30 or less, and preferably 50 or less, from the viewpoint of improving the storage stability and discharge durability of the obtained water-based ink. / 50 or more, more preferably 60/40 or more, still more preferably 65/35 or more.

  The pigment water dispersions of the first to third aspects can be used as they are as water-based inks, but if necessary, wetting agents, penetrants, dispersing agents, viscosity modifiers, antifoaming agents, antifoaming agents, which are usually used. It can be prepared by adding a lubricant, a rust inhibitor and the like.

[Water-based ink for inkjet recording]
The water base ink for ink jet recording contains the pigment water dispersion for ink jet recording of the present invention, and can be produced by adding water and various additives to the pigment water dispersion.
The content of each component in the water-based ink is as follows.
The content of the pigment is preferably 1% by mass or more, more preferably 2% by mass or more, and further preferably 2% by mass or more in the water-based ink from the viewpoint of improving storage stability and ejection durability of the ink and obtaining printed matter with high printing density. The content is preferably 3% by mass or more, more preferably 4% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less, still more preferably 8% by mass It is below.
When a water-dispersible polymer is used, the content of the water-dispersible polymer is preferably 1 mass in the water-based ink from the viewpoint of improving the storage stability and discharge durability of the water-based ink, and from the viewpoint of obtaining printed matter with high printing density. % Or more, more preferably 1.2% by mass or more, still more preferably 1.5% by mass or more, still more preferably 1.8% or more, and preferably 5% by mass or less, more preferably 4% by mass The content is more preferably 3% by mass or less, still more preferably 2.5% by mass or less.
The content of water is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 75% by mass or more, in the water-based ink, from the viewpoint of improving the storage stability and discharge durability of the water-based ink. And And, Preferably it is 95 mass% or less, More preferably, it is 90 mass% or less, More preferably, it is 85 mass% or less.

The static surface tension of the aqueous ink at 20 ° C. is preferably 25 mN / m or more, more preferably 30 mN / m or more, still more preferably 32 mN / m or more, from the viewpoint of improving the ejection durability of the water-based ink. Preferably it is 45 mN / m or less, More preferably, it is 40 mN / m or less, More preferably, it is 38 mN / m or less.
The viscosity of the water-based ink at 35 ° C. is preferably 1 mPa · s or more, more preferably 1.5 mPa · s or more, and still more preferably 2 mPa · s, from the viewpoint of improving the discharge durability of the water-based ink. The above, and preferably 10 mPa · s or less, more preferably 7 mPa · s or less, and still more preferably 4 mPa · s or less.

As additives to be added as necessary to adjust physical properties of the water-based ink, wetting agents commonly used in water-based inks, penetrants, dispersing agents such as surfactants, hydroxypropyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol Etc., antifoaming agents such as silicone oil, mildew proofing agents, rust preventives and the like.
Examples of wetting agents and penetrants include polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, trimethylolpropane, diethylene glycol diethyl ether and the like, ethers thereof, acetates, etc. Triethylene glycol and trimethylolpropane are preferred. Among these, polyethylene glycol from the viewpoint of further improving the discharge durability by imparting steric repulsion without inhibiting charge repulsion between pigment particles and suppressing aggregation of pigment particles in water-based ink. Is preferred. The average molecular weight of polyethylene glycol is preferably 100 or more, more preferably 200 or more, and still more preferably 300 or more from the viewpoint of imparting steric repulsion between pigment particles, and from the viewpoint of suppressing the viscosity increase of the aqueous ink. Preferably it is 5000 or less, More preferably, it is 3000 or less, More preferably, it is 2000 or less, More preferably, it is 1500 or less.
As surfactant, nonionic surfactant, such as ethylene oxide adduct of acetylene diol, etc. are mentioned.
The volume average particle diameter of the pigment particles in the obtained aqueous ink is preferably 40 nm or more, more preferably 50 nm or more, still more preferably 60 nm or more, from the viewpoint of prevention of clogging of the nozzle of the printer and dispersion stability. Preferably it is 150 nm or less, More preferably, it is 140 nm or less, More preferably, it is 130 nm or less.
The volume average particle diameter of the pigment particles can be measured by the method described in the examples.

The ink jet recording method is not particularly limited, and can be used in any discharge method such as an electro-mechanical conversion method such as a piezo method or an electro-thermal conversion method such as a thermal method.
The pigment particles contained in the water-based ink containing the pigment water dispersion for ink jet recording of the present invention are preferably used for thermal ink jet recording in that they have a suppressing effect on the kogation phenomenon.

[Method of producing pigment water dispersion for inkjet recording]
The pigment water dispersion for ink jet recording according to the present invention comprises the components contained in the range of 0 to -55 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (v). It is preferable to have a step of making the scattering intensity area ratio 5% or less (hereinafter, also referred to as step a).
In addition, the pigment water dispersion for ink jet recording of the present invention is included in the range of 0 to -58 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (vi). It is preferable to have a step (hereinafter, also referred to as step b) to make the scattering intensity area ratio of the component 10% or less.
In addition, the pigment water dispersion for ink jet recording of the present invention is included in the range of 0 to -60 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (vii). It is preferable to have a step (hereinafter, also referred to as step c) to make the scattering intensity area ratio of the component 40% or less.
Furthermore, it is preferable to have 2 or more types of process chosen from the group which consists of process a, process b, and process c.

The pigment water dispersion for inkjet recording of the present invention can be produced by a method of dispersing pigment particles in water. The method for producing a pigment water dispersion in the case of using a pigment dispersed with a water dispersible polymer as pigment particles preferably has the following production steps (1), (2) and (3), but this method is not always necessary. Not limited to
Production step (1): a mixture containing water, a pigment, a water-dispersible polymer, and an organic solvent having a solubility in water at 20 ° C. of less than 40% by mass, the volume average particle diameter of pigment particles by dynamic light scattering Process of dispersion treatment preferably to 180 nm or less to obtain a pigment dispersion.
Production step (2): a step of adding water to the pigment dispersion obtained in the production step (1), and preferably maintaining the temperature at 40 ° C. or less, preferably 4 hours or more, preferably 48 hours or less.
Manufacturing process (3): The process of removing the organic solvent of the pigment dispersion obtained at manufacturing process (2), and obtaining a pigment water dispersion.

<Manufacturing process (1)>
Production process (1) is a mixture of water, a pigment, a water-dispersible polymer, and an organic solvent having a solubility in water at 20 ° C. of less than 40% by mass, the volume average particle size of pigment particles by dynamic light scattering method Is a production process to obtain a pigment dispersion by dispersion treatment preferably to 180 nm or less.
(Content of water dispersible polymer)
The content of the water-dispersible polymer in the entire mixture in the production process (1) is preferably 1 from the viewpoint of improving the dispersion stability of the pigment water dispersion, the storage stability of the obtained water-based ink, and the ejection durability. .5% by mass or more, more preferably 2.0% by mass or more, further preferably 2.5% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 7.0 Mass% is the following.

(Organic solvent)
In the present invention, it is desirable that the organic solvent has high affinity to the polymer, while having low solubility in water, which is the main medium in the production process (1). From that point of view, the solubility in water at 20 ° C. needs to be less than 40% by mass, preferably 35% by mass or less, more preferably 30% by mass or less, and preferably 0% by mass or more, more preferably It is 10% by mass or more.
As the organic solvent, aliphatic alcohols having 2 to 8 carbon atoms, ketones, ethers, esters and the like are preferable, and as aliphatic alcohols, n-butanol, tertiary butanol, isobutanol, diacetone alcohol and the like can be mentioned. Examples of the ketone include methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone and the like. Examples of the ether include dibutyl ether, tetrahydrofuran, dioxane and the like. From the viewpoint of improving the wettability to the pigment and the adsorption of the polymer to the pigment, ketone is preferable, and methyl ethyl ketone (the solubility in water: 22% by mass) is more preferable.
The content of the organic solvent in the entire mixture in the production process (1) is preferably 10% by mass or more, more preferably 13% by mass or more, from the viewpoint of improving the wettability of the pigment and the adsorption of the polymer to the pigment. More preferably, it is 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, and still more preferably 22% by mass or less. In addition, when 2 or more types of organic solvents are included, the total amount of those is computed as an amount of organic solvents. The same applies to the following.
The mass ratio of the water-dispersible polymer to the organic solvent (water-dispersible polymer / organic solvent) in the production step (1) is preferably from 0, from the viewpoint of improving the wettability of the pigment and the adsorption of the polymer onto the pigment. It is 10 or more, more preferably 0.20 or more, further preferably 0.25 or more, and preferably 0.60 or less, more preferably 0.50 or less, still more preferably 0.45 or less.

The content of water in the pigment dispersion in the production process (1) is preferably 50% by mass or more, from the viewpoint of improving the dispersion stability of the pigment water dispersion and from the viewpoint of improving the productivity of the pigment water dispersion. More preferably, it is 55% by mass or more, more preferably 60% by mass or more, preferably 80% by mass or less, more preferably 75% by mass or less, and still more preferably 65% by mass or less.
The mass ratio of the organic solvent to water (organic solvent / water) in the production process (1) is preferably 0.27 or more from the viewpoint of dispersion progression due to improvement of the wettability of the pigment and adsorption of the polymer to the pigment. , More preferably 0.29 or more, and preferably 0.50 or less.

(Neutralization of polymer)
In the present invention, from the viewpoint of improving the dispersion stability of the pigment water dispersion, the storage stability of the water-based ink, and the discharge durability, the ionizable group, preferably the anionic group, of the water-dispersible polymer is neutralized. Preferably, a neutralizing agent is used. When using a neutralizing agent, it is preferable to neutralize so that pH of a pigment water dispersion may be 7-11.
As the neutralizing agent to be used, when the ionic group is an anionic group, alkali metal hydroxide, volatile base such as ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, triethanolamine And organic amines such as tributylamine. From the viewpoint of improving the dispersion stability of the pigment water dispersion, the storage stability of the water-based ink, and the discharge durability, alkali metal hydroxides and volatile bases are preferable, and alkali Metal hydroxides are more preferred.
Examples of hydroxides of alkali metals include lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide, with sodium hydroxide being preferred.
The neutralizing agent is preferably used as a neutralizing agent aqueous solution from the viewpoint of sufficiently promoting the neutralization. The concentration of the aqueous neutralizing agent solution is preferably 3% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 30% by mass or less, from the viewpoint of sufficiently promoting the neutralization. And more preferably 25% by mass or less.
The neutralizing agent and the neutralizing agent aqueous solution can be used alone or in combination of two or more.

The degree of neutralization calculated from the amount of neutralizing agent of the polymer is preferably 60 mol% or more, more preferably from the viewpoint of improving the dispersion stability of the pigment water dispersion and the storage stability of the aqueous ink and the ejection durability. It is 80 mol% or more, more preferably 100 mol% or more, and preferably 400 mol% or less, more preferably 200 mol% or less, still more preferably 150 mol% or less.
Here, the degree of neutralization is a value calculated from the amount of the neutralizing agent, that is, the molar equivalent of the neutralizing agent divided by the molar amount of the ionic group of the polymer, and the ionic group is an anionic group In the case, it can be determined by the following equation.
{[Mass of neutralizing agent (g) / equivalent of neutralizing agent] / [acid value of polymer (KOH mg / g) × mass of polymer (g) / (56 × 1000)]} × 100
When a volatile base is used as the neutralizing agent, the degree of neutralization of the pigment dispersion in the production process (1) and the degree of neutralization of the pigment dispersion and the aqueous ink produced through the production process (3) are changed. can do. Specifically, using ammonia or the like, the neutralizing agent is introduced in excess with respect to the molar amount of the anionic group of the polymer in the production process (1), and volatile base such as ammonia is removed in the production process (3) By doing this, it is possible to achieve the desired degree of neutralization as a water-based ink. The degree of neutralization in the case of using a volatile base is preferably 0 mol% or more, and preferably 300 mol% or less, more preferably 100 mol% or less, still more preferably 50 mol% or less. In addition, the neutralization degree of 0 mol% in the case of using a volatile base is a case where no volatile base is used at all.

(Distributed processing)
In the production process (1), the mixture is subjected to dispersion treatment to obtain a pigment dispersion. The volume average particle diameter of the pigment particles after the dispersion treatment is preferably 180 nm or less, more preferably 150 nm or less, still more preferably 125 nm or less, from the viewpoint of preventing the pigment particles from settling in the aqueous ink. Preferably it is 30 nm or more, more preferably 50 nm or more. The volume average particle size of the pigment particles can be measured by the method described in the examples.
Although it is possible to make the volume average particle diameter of the pigment particles into a desired particle diameter by only one main dispersion, it is preferable to perform predispersion and then apply shear stress to perform two-stage dispersion. To control the volume average particle size of the pigment particles to a desired value.
The temperature in the pre-dispersion is preferably -5 ° C or more, more preferably 0 ° C or more, still more preferably 10 ° C or more, and preferably 40 ° C or less, more preferably 20 ° C or less, still more preferably 10 ° C or less It is. The dispersion time in the pre-dispersion is preferably 1 hour or more, more preferably 2 hours or more, further preferably 5 hours or more, and preferably 30 hours or less, more preferably 10 hours or less, still more preferably 5 hours or less It is.
When the mixture is predispersed, a commonly used mixing and stirring apparatus such as an anchor blade or a disper wing can be used. Among the mixing and stirring apparatus, a high-speed stirring and mixing apparatus such as UltraDispers [Asada Steel Co., Ltd., trade name], Ebara Milder [Ebarahara Mfg. Co., trade name], TK homomixer [Primix Co., Ltd., trade name] is preferable. .

Examples of means for giving the shear stress of this dispersion include roll mills, kneaders, kneaders such as extruders, high pressure homogenizers such as Microfluidizer (trade name of Microfluidics), and media type dispersers such as paint shakers and bead mills. It can be mentioned. As a commercially available media type dispersing machine, Ultra Apex Mill (manufactured by Kotobuki Industry Co., Ltd., trade name), Picomill (manufactured by Asada Iron Works, Inc., trade name), etc. may be mentioned. These devices can also be combined. Among these, from the viewpoint of reducing the particle size of the pigment, it is preferable to use a high pressure homogenizer.
When the main dispersion is performed using a high pressure homogenizer, the pigment can be controlled to have a desired particle diameter by controlling the processing pressure and the number of passes of the dispersion processing.
The treatment pressure is preferably 60 MPa or more, more preferably 100 MPa or more, still more preferably 150 MPa or more, and preferably 250 MPa or less, more preferably 200 MPa or less, still more preferably 180 MPa or less.
The number of dispersion processing passes is preferably 3 or more, more preferably 10 or more, still more preferably 15 or more, and preferably 30 or less, more preferably 25 or less, still more preferably 20. It is less than the pass.

<Manufacturing process (2)>
The production step (2) is a step of adding water to the pigment dispersion obtained in the production step (1), and holding it at preferably 40 ° C. or less, preferably 4 hours or more, preferably 48 hours or less.
By adding water to the pigment dispersion and maintaining it at preferably 40 ° C. or less, preferably 4 hours or more, preferably 48 hours or less, the adsorption uniformity of the polymer on the pigment can be enhanced.
The temperature at which the pigment dispersion to which water is added is maintained is preferably 0 ° C. or more, more preferably 10 ° C. or more, still more preferably 15 ° C. or more, from the viewpoint of improving the discharge durability of the water-based ink Is 35 ° C. or less, more preferably 30 ° C. or less, and still more preferably 25 ° C. or less.
The time for holding the pigment dispersion to which water is added is preferably 6 hours or more, preferably 36 hours or less, more preferably 24 hours or less, from the viewpoint of improving the discharge durability.

The mass ratio of the organic solvent to water (organic solvent / water) in the production process (2) is preferably 0.29 or less, more preferably 0.27 or less, and preferably 0.10 or more, More preferably, it is 0.15 or more, further preferably 0.20 or more.
In the production step (2), when holding the pigment dispersion to which water is added, it is preferable to decompress under sealing. This is because it is considered that, by reducing the pressure, the dissolved gas in the pigment dispersion is easily discharged as air bubbles, and the hydrophobic group of the polymer is easily adsorbed on the pigment surface.
Moreover, the non-volatile component concentration (solid content concentration) of the pigment water dispersion after adjusting the mass ratio (organic solvent / water) suppresses the generation of aggregates in the process of removing the organic solvent in the production process (3). From the viewpoint and the viewpoint of improving the productivity of the pigment water dispersion, it is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 30% by mass or less More preferably, it is 20% by mass or less, still more preferably 18% by mass or less.
After water is added to the pigment dispersion in the production step (2), stirring may or may not be performed, but from the viewpoint of making the liquid temperature of the pigment dispersion uniform, foaming can be suppressed It is more preferable to stir.

<Manufacturing process (3)>
A manufacturing process (3) is a process of removing the organic solvent of the pigment dispersion obtained by manufacturing process (2), and obtaining a pigment water dispersion.
There is no restriction | limiting in particular in the method to remove an organic solvent, It can carry out by well-known method. In addition, a part of water contained in the pigment dispersion obtained by a manufacturing process (2) may be removed simultaneously with an organic solvent.
Examples of the apparatus for removing the organic solvent used in this step include a batch single distillation apparatus, a vacuum distillation apparatus, a thin film distillation apparatus such as a flash evaporator, a rotary distillation apparatus, a stirring evaporator and the like. From the viewpoint of efficiently removing the organic solvent, a rotary distillation apparatus and a stirring evaporator are preferable, a rotary distillation apparatus is more preferable, and a rotary evaporator is further preferable.
The temperature of the pigment dispersion at the time of removing the organic solvent can be appropriately selected according to the type of the organic solvent used, but is preferably 40 ° C. or more under reduced pressure, and preferably 80 ° C. or less, more preferably 70 ° C. or less More preferably, it is 65 ° C. or less. The pressure at this time is preferably 5 kPa or more, more preferably 8 kPa or more, still more preferably 10 kPa or more, and preferably 50 kPa or less, more preferably 30 kPa or less, still more preferably 20 kPa or less. The removal time of the organic solvent is preferably 1 hour or more, more preferably 2 hours or more, still more preferably 5 hours or more, and preferably 24 hours or less, more preferably 12 hours or less, still more preferably 10 hours or less It is.

The organic solvent in the obtained pigment water dispersion is preferably substantially removed, but may be left as long as the object of the present invention is not impaired. 0.1 mass% or less is preferable, and, as for the quantity of a residual organic solvent, it is more preferable that it is 0.01 mass% or less.
The concentration of the non-volatile components (solids concentration) of the obtained pigment water dispersion is preferably 10% by mass or more, from the viewpoint of improving the dispersion stability of the pigment water dispersion and facilitating the preparation of the water-based ink. The content is preferably 15% by mass or more, more preferably 18% by mass or more, and 30% by mass or less, more preferably 25% by mass or less, still more preferably 22% by mass or less.

The present invention further discloses the following pigment water dispersion for ink jet recording and the water based ink for ink jet recording containing the water dispersion with respect to the embodiment described above.
<1> A pigment water dispersion containing pigment particles and water, wherein the range of 0 to −55 mV of the normalized zeta potential distribution 4 obtained by the following zeta potential measurement steps (i) to (iv) and (v) The pigment water dispersion for inkjet recording whose scattering intensity area ratio of the component contained in is 5% or less.
Step (i): a step of measuring zeta potential distribution 1 without applying an electric field to particles in the measurement cell and then normalizing to obtain normalized zeta potential distribution 1.
Step (ii): applying an electric field of 1200 V / m to the particles in the measurement cell to measure the zeta potential distribution 2 and then normalizing to obtain the normalized zeta potential distribution 2.
Step (iii): obtaining a normalized zeta potential distribution 3 obtained by taking the difference between the normalized zeta potential distributions 1 and 2
Step (iv): Step of obtaining the normalized zeta potential distribution 4 by making a histogram of the normalized zeta potential distribution 3 in 1 mV steps and normalizing the histogram.
Step (v): In the normalized zeta potential distribution 4, the range (area) between 0 to -55 mV and the line between the normalized zeta potential distribution 4 and the line of zero scattering intensity is read, and the range of 0 to -55 mV Obtaining the scattering intensity area ratio (%) of the components contained in

<2> A pigment water dispersion containing pigment particles and water, wherein 0 to −58 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and the following step (vi) The pigment water dispersion for inkjet recording whose scattering intensity area ratio of the component contained in the range of is 10% or less.
Step (vi): Read the range (area) between the range of 0 to -58 mV and the line between the normalized zeta potential distribution 4 and the line of zero scattering intensity in the normalized zeta potential distribution 4 and the range of 0 to -58 mV Obtaining the scattering intensity area ratio (%) of the components contained in
<3> A pigment water dispersion containing pigment particles and water, wherein 0 to −60 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and the following step (vii) The pigment water dispersion for inkjet recording whose scattering intensity area ratio of the component contained in the range of is 40% or less.
Step (vii): In the normalized zeta potential distribution 4, read the range (area) between 0 to -60 mV and the line between the normalized zeta potential distribution 4 and the line of zero scattering intensity, and the range of 0 to -60 mV Obtaining the scattering intensity area ratio (%) of the components contained in
The pigment water dispersion in any one of said <1>-<3> whose measurement method of <4> zeta-potential distribution is a dynamic light scattering method.

<5> The pigment water dispersion according to any one of <1> to <4>, wherein the water-dispersible polymer is obtained by copolymerizing a monomer mixture containing a monomer (b) containing an ionic group. .
<6> The <1> to <5>, wherein the water-dispersible polymer is obtained by copolymerizing a monomer mixture containing a hydrophobic monomer (a) and a monomer (b) containing an ionic group. The pigment water dispersion according to any one.
<7> The water-dispersible polymer is obtained by copolymerizing a monomer mixture containing a hydrophobic monomer (a), a monomer (b) containing an ionic group, and a nonionic monomer (c). The pigment water dispersion in any one of <1>-<6>.
The content of the constituent unit derived from the hydrophobic monomer (a) in the <8> water dispersible polymer is preferably 40% by mass or more, more preferably 45% by mass or more, and still more preferably 48% by mass or more The pigment water dispersion as described in said <6> or <7> which is preferably 85 mass% or less, more preferably 80 mass% or less, further preferably 75 mass% or less.
<9> The content of the constituent unit derived from the monomer (b) containing an ionic group in the water-dispersible polymer is preferably 15% by mass or more, and preferably 25% by mass or less, more preferably 23% by mass The pigment water dispersion in any one of said <5>-<8> which is% or less, more preferably 21 mass% or less.
The content of the constituent unit derived from the nonionic monomer (c) in the <10> water dispersible polymer is preferably 0% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more, The pigment water dispersion in any one of said <7>-<9> which is preferably 40 mass% or less, more preferably 35 mass% or less, further preferably 32 mass% or less.
<11> The weight average molecular weight of the water dispersible polymer is preferably 5,000 or more, more preferably 10,000 or more, still more preferably 30,000 or more, still more preferably 40,000 or more, still more preferably 50,000 or more. And <5> to <10> which is preferably not more than 500,000, more preferably not more than 300,000, still more preferably not more than 200,000, still more preferably not more than 150,000, still more preferably not more than 100,000. The pigment water dispersion according to any one of the above.

The pigment water dispersion in any one of said <1>-<11> which is a polymer particle containing <12> pigment particle | grains or the pigment particle which the water dispersible polymer adsorb | sucked or a pigment.
<13> The volume average particle diameter of pigment particles by dynamic light scattering method is preferably 40 nm or more, more preferably 50 nm or more, still more preferably 60 nm or more, and preferably 150 nm or less, more preferably 140 nm or less, The pigment water dispersion according to any one of the above <1> to <12>, which is more preferably 130 nm or less.
<14> The mass ratio of the pigment amount to the water-dispersible polymer amount (pigment / water-dispersible polymer) is preferably 80/20 or less, more preferably 75/25 or less, still more preferably 70/30 or less, The pigment water dispersion in any one of said <1>-<13> which is preferably 50/50 or more, more preferably 60/40 or more, still more preferably 65/35 or more.
The surface tension (20 ° C.) of the <15> pigment water dispersion is preferably 30 mN / m or more, more preferably 35 mN / m or more, and 65 mN / m or less, more preferably 60 mN / m or less. The pigment water dispersion in any one of said <1>-<14>.
The viscosity (20 ° C.) of 20% by mass (solid content) of the <16> pigment water dispersion is preferably 2 mPa · s or more, preferably 6 mPa · s or less, more preferably 5 mPa · s or less. The pigment water dispersion in any one of <1>-<15>.
<17> The scattering intensity area ratio of the component contained in the range of 0 to -55 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (v) is 5% or less The manufacturing method of the pigment water dispersion for inkjet recordings which has the process a.
<18> The scattering intensity area ratio of the components included in the range of 0 to −58 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (vi) is 10% or less The manufacturing method of the pigment water dispersion for inkjet recordings which has the process b.
<19> The scattering intensity area ratio of the component included in the range of 0 to −60 mV of the normalized zeta potential distribution 4 obtained by the zeta potential measurement steps (i) to (iv) and (vii) is 40% or less A method for producing a pigment water dispersion for ink jet recording, comprising the step c).
<20> A method for producing a pigment water dispersion for inkjet recording, comprising two or more steps selected from the group consisting of the step a, the step b and the step c according to any one of the above <17> to <19>.

In the following production examples, preparation examples, examples and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified.
The weight average molecular weight of the polymer, the solid content concentration of the polymer solution and the pigment water dispersion, the volume average particle diameter of the pigment particles in the pigment dispersion and the pigment water dispersion, the surface tension of the water based ink, the viscosity of the water based ink, zeta Measurement of potential distribution was performed by the following method.

(1) Measurement of weight average molecular weight of polymer Gel permeation chromatography using a solution of phosphoric acid and lithium bromide dissolved in N, N-dimethylformamide so as to have concentrations of 60 mmol / L and 50 mmol / L, respectively, as an eluent. As a standard substance, the weight average molecular weight is single in advance according to the method [GPC apparatus (HLC-8120GPC, manufactured by Tosoh Corp.), column (TSK-GEL, α-M × 2) manufactured by Tosoh Corp. It measured using the polystyrene specified by dispersion.

(2) Measurement of solid content concentration of polymer solution and pigment water dispersion In a 30 ml polypropylene container (40 mmφ, height 30 mm), 10.0 g of sodium sulfate which has been constantized in a desiccator was weighed, and a sample of about 1. After 0 g was added and mixed, the mixture was accurately weighed and maintained at 105 ° C. for 2 hours to remove volatiles and then left in a desiccator for 15 minutes to measure the mass. The mass of the sample after devolatilization was regarded as solid content, and was divided by the mass of the added sample to obtain solid concentration.

(3) Volume dispersion of pigment particles in pigment dispersion and pigment water dispersion The pigment dispersion obtained in the production step (1) or the pigment water dispersion obtained in the production step (3) is prepared in advance. Dilute using ion-exchanged water filtered with a 0.2 μm filter, and use the laser particle size analysis system “ELS-6100” manufactured by Otsuka Electronics Co., Ltd. at 25 ° C. for pigment particles by dynamic light scattering method Volume average particle size was measured.

(4) Surface tension of water-based ink Using a surface tension meter (trade name: CBVP-Z, manufactured by Kyowa Interface Science Co., Ltd.), a cylindrical polyethylene container (3.6 cm in diameter x containing 5 g of water-based ink) The film was immersed in a depth of 1.2 cm, and the static surface tension of the water-based ink was measured at 20 ° C.
(5) Viscosity of water-based ink Using E-type viscometer RE80 manufactured by Toki Sangyo Co., Ltd., measurement temperature 20 ° C., measurement time 1 minute, rotation speed 100 rpm, rotor standard (1 ° 34 ′ × R24) The viscosity was measured.

(6) Measurement of zeta-potential distribution It measured on condition of the following using zeta-potential measuring machine (Otsuka Electronics Co., Ltd. make, brand name: ELSZ-1000). The measuring cell and unit used the glass cell and unit for dilution measurement. The measurement solution is prepared by using a pigment water dispersion having a solid content concentration of 20% and adjusting the solid solution concentration of the pigment water dispersion with an aqueous sodium hydroxide solution previously adjusted to a concentration of 1 × 10 ⁻² to 1 × 10 ⁻⁴ N The solution was diluted so that the pH of the diluted solution was 0.01 wt% and then filtered, using a Sartorius filter with a filtration pore diameter of 0.45 μm. The measurement was performed under the following conditions.
(I) Device measurement conditions-Light amount adjustment in base measurement: Yes, light amount adjustment by migration direction test: None-Number of measurement repetitions of electrophoresis measurement: 6, light amount adjustment in electrophoresis measurement: Yes-Waiting time before measurement: 0, Wait time after measurement: 0, pinhole: 50 μm
· Light quantity optimum value: 80000, light quantity maximum value: 100,000, light quantity minimum value: 40000
(Ii) Cell condition-Measurement sequence: Type 2
Cell selection: Flow Cell, Cell type: Flow Cell, Cell constant: 70
Center position Z axis: 6, center position X axis: 7.11
・ Correlator: Linear
(Iii) Base measurement conditions-Number of integrations: 100 times, correlation method: TD: time domain method-sampling time: 800 microseconds, number of correlation channels: 512 times-modulator delay: 0.15, modulator time: 1.024 seconds

(Iv) Electrophoretic direction test conditions-Number of integrations: 2 times, correlation method: TD: time domain method-electrophoresis sampling time: 800 microseconds, correlation channel number: 512 times-modulator delay: 0.15, modulator time: 1 .024 seconds · Applied voltage waveform type: Negative
· Applied voltage: 60 V, distance between electrodes: 50 mm
-Voltage delay: 0.2 seconds, Voltage applytime: 1.024 seconds-Migration switching wait ratio: 0.1024, constant current: 51

(V) Conditions of electrophoresis measurement 1-Number of integration: 100 times-Cell measurement position: 0.65 / 0.35 / 0 /-0.35 /-0.65, correlation method: TD: time domain method-Sampling Time: 800 microseconds, correlation channel number: 512 times Modulator delay: 0.15 second, modulator time: 1.024 second Applied voltage: Fixed, applied voltage: 0 V (electric field: 0 V / m, no electric field is applied)
・ Electrode distance: 50 mm, Applied voltage waveform type: Auto, Constant current: 51
-Voltage delay: 0.2 seconds, Voltage applytime: 1.024 seconds-Migration switching wait ratio: 0.1024

(Vi) Conditions for electrophoresis measurement 2-Number of integrations: 100-Cell measurement position: 0.65 / 0.35 / 0 / -0.35 / -0.65, correlation method: TD
Sampling time: 800 microseconds, correlation channel number: 512 times Modulator delay: 0.15 seconds, modulator time: 1.024 seconds Applied voltage: Fixed, Applied voltage: 60 V (electric field: 1200 V / m)
・ Electrode distance: 50 mm, Applied voltage waveform type: Auto, Constant current: 51
-Voltage delay: 0.2 seconds, Voltage applytime: 1.024 seconds-Migration switching wait ratio: 0.1024

(Vii) Solvent conditions-Solvent selection: WATER, refractive index: 1.33, viscosity: 0.89, dielectric constant: 78.3
(Viii) Analysis conditions-FFT filter: BLACKMAN, amount of data: 1024, smoothing: LOW
・ Lorentz fit: 1 peak, zeta potential conversion formula: Smoluchowski
・ FFT filter (base): BLACKMAN, amount of data (base): 1024
・ Smoothing (base): LOW, Lorentz fit (base): 1peak
・ FFT filter (electrophoretic direction): BLACKMAN, amount of data (electrophoretic direction): 1024
Smoothing (electrophoretic direction): LOW, Lorentz fit (electrophoretic direction): 1 peak

(6-1) Zeta Potential Measurement Step (i): Acquisition of Normalized Zeta Potential Distribution 1 Among measurement positions of cells of the measurement result of electrophoresis measurement 1, zeta potential distribution using only data of zero cell measurement position I got one. In the obtained measurement results, the frequency of the peak top of the scattering intensity was set to zero, and the peak intensity was normalized to 1 to obtain a normalized zeta potential distribution 1.
(6-2) Zeta Potential Measurement Step (ii): Acquisition of Standardized Zeta Potential Distribution 2 The normalized zeta potential distribution 2 was obtained from the electrophoresis measurement 2 by the same method as the above step (i).
(6-3) Zeta potential measurement step (iii): Acquisition of normalized zeta potential distribution 3 (a) Normalized zeta potential distributions 1 and 2 in the range of 0.02 to 1.0 of normalized intensity The positive value of the frequency was read in 0.01 steps.
(B) The difference between the positive values of the frequencies of the normalized zeta potential distributions 1 and 2 is determined for each intensity. Next, the correction value obtained by ((applied voltage in electrophoresis measurement 2) / ((applied voltage in electrophoresis measurement 2)-(applied voltage in electrophoresis measurement 1)) and the frequencies of normalized zeta potential distributions 1 and 2 The products of the positive difference values were determined respectively.
(C) Similarly, in the normalized zeta potential distributions 1 and 2, the value on the negative side of the frequency in the range of 0.02 to 1.0 of the normalized intensity was read in steps of 0.01.
(D) The difference between the negative values of the frequencies of the normalized zeta potential distributions 1 and 2 is determined for each intensity. Next, the correction value obtained by ((applied voltage in electrophoresis measurement 2) / ((applied voltage in electrophoresis measurement 2)-(applied voltage in electrophoresis measurement 1)) and the frequencies of normalized zeta potential distributions 1 and 2 The products of the difference values on the negative side were determined respectively.
(E) The difference between the positive side frequency and the negative side frequency obtained is replotted on the X axis and the intensity on the Y axis to obtain a normalized zeta potential distribution 3.

(6-4) Zeta potential measurement step (iv): Histogram formation of the standardized zeta potential distribution 3 (a) Convert the zeta potential average value obtained in the electrophoresis measurement 2 as a peak of the standardized zeta potential distribution 3 The zeta potential distribution 3 was obtained.
(B) The obtained zeta potential distribution 3 is replotted as a zeta potential value on the X axis and a histogram of the appearance frequency normalized on the Y axis, and the appearance frequency for each zeta potential value is integrated and then standardized again. Turned This is taken as the normalized zeta potential distribution 4 of the particles in the pigment water dispersion.
(6-5) Zeta Potential Measurement Step (v): Calculation of Area of Histogram In the standardized zeta potential distribution 4, the zeta potential ranges from 0 to −55 mV from the side where the absolute value of zeta potential is low, and the standard The range (area) between the zeta potential distribution 4 and the line of zero scattering intensity was read, and the scattering intensity area ratio (%) of the components contained in the range of 0 to -55 mV was taken. Similarly, the scattering intensity area ratio (%) of the components contained in the range of 0 to -58 mV and the zeta potential in the range of 0 to -58 mV, 0 to -60 mV of the zeta potential from 0 to -60 mV The scattering intensity area ratio (%) of the components contained in the range was determined. The results are shown in Table 2.

Production Example 1 (Production of Water-Dispersible Polymer)
In a reaction vessel equipped with two dropping funnels 1 and 2, the monomer having the composition shown in the "initially charged monomer solution" column of Table 1 and a polymerization chain transfer agent (2-mercaptoethanol) are mixed and nitrogen gas substitution To obtain an initial charged monomer solution.
On the other hand, a monomer having a composition shown in the "Dropping monomer solution 1" column and the "Dropping monomer solution 2" column in Table 1, an organic solvent (methyl ethyl ketone (MEK)), a polymerization initiator (2,2'-azobis (2,4-) Dimethylvaleronitrile): Wako Pure Chemical Industries, Ltd., trade name: V-65), and a polymerization chain transfer agent are mixed to prepare a dropping monomer solution 1 and a dropping monomer solution 2, and dropping funnels 1 and 2 respectively. The nitrogen gas replacement was performed.
Under a nitrogen atmosphere, the initially charged monomer solution in the reaction vessel is maintained at 75 ° C. with stirring, the dropping monomer solution 1 is gradually dropped into the reaction vessel over 3 hours, and then the dropping monomer solution 2 is over 2 hours It was gradually dropped into the reaction vessel.
After the addition was completed, the mixed solution in the reaction vessel was stirred at 75 ° C. for 2 hours. Then, a polymerization initiator solution is prepared by dissolving 1.5 parts of the above-mentioned polymerization initiator (V-65) in 10 parts of an organic solvent (MEK), added to the mixed solution, and stirred at 75 ° C. for 1 hour for aging Did. The preparation, addition and aging of the polymerization initiator solution were performed twice more. Next, the reaction solution in the reaction vessel was maintained at 85 ° C. for 2 hours to obtain a water dispersible polymer solution. A part of the obtained water-dispersible polymer solution was depressurized to remove the solvent, and the weight average molecular weight was measured. The results are shown in Table 1.

Examples 1 to 8 and Comparative Examples 1 to 8 (Production of pigment water dispersion and water-based ink)
(1) Production process (1): Production of pigment dispersion A disparable container having a container volume of 2 L (T.K. Robomix manufactured by Primix, Inc., stirring unit homodisper 2.5 type, feather diameter 40 mm) was produced in Production Example 1 The water dispersible polymer solution of the amount described in Table 2 (solid content of the water dispersible polymer obtained in Production Example 1 was measured, and the solid content concentration was adjusted to 50% by adding MEK) ), And 93 parts of an organic solvent (MEK: 22% solubility in water at 20 ° C.) described in Table 2 is added while stirring under conditions of 1400 rpm, and ion exchange of the amount described in Table 2 is further performed. Water, 5N (16.9%) aqueous sodium hydroxide solution was added, and stirred at 1400 rpm for 15 minutes while cooling with a 0 ° C. water bath. After stirring, the pigment or pigment dispersion described in Table 2 was added, and the mixture was stirred for 3 hours under the condition of 6000 rpm.
The resulting mixture was subjected to a 20-pass dispersion treatment at a pressure of 180 MPa using a microfluidizer (trade name: Model M-140K, manufactured by Microfluidics) to obtain a pigment dispersion.
Thereafter, the volume average particle size of pigment particles was measured by the dynamic light scattering method, and it was confirmed that the volume average particle size was 180 nm or less.
Details of the pigments listed in Table 2 are shown below.
N-160: Carbon black "Nipex 160" manufactured by Degussa
M717: cabot carbon black "monarch 717"
6111T: Dainichi Seisei Co., Ltd., magenta pigment "CFR 6111T"
· 6338 JC: Dainichi Seisei Co., Ltd., cyan pigment "CFB 6338 JC"
・ FY 840 T: Dainichi Seisei Co., Ltd., yellow pigment “FY 840 T”
SDP 100: SENSIENT Co., Ltd., surface-treated carbon black water dispersion "SENSIJET BLACK SDP 100"
· M 880: cabot carbon black "monarch 880"
・ M800: Carbon black "monarch 800" manufactured by cabot
N-180: Degussa carbon black "Nipex 180"
2BC: manufactured by BASF, magenta pigment "2BC"
· 6337JC: Dainichi Seisei Co., Ltd., cyan pigment "CFB 6337JC"
・ FY7414: Sanyo Dye Co., Ltd., yellow pigment “FY7414”
C-300: surface-treated carbon black aqueous dispersion "Cab-O-Jet 300" manufactured by cabot

(2) Production Step (2): Temperature Holding Step The pigment dispersion obtained in production step (1) is put in a 2 L eggplant flask, and a predetermined amount of ion-exchanged water shown in Table 2 is added. , And maintained at a pressure of 100 kPa for 12 hours.
However, Examples 6 and 7 and Comparative Examples 7 and 8 were shifted to the manufacturing process (3) without providing the holding time in the manufacturing process (2).
(3) Production process (3): Production of pigment water dispersion The pigment obtained in production process (2) using a vacuum distillation apparatus (rotary evaporator, manufactured by Tokyo Rika Kikai Co., Ltd., trade name: N-1000S) The dispersion was held at a pressure of 0.09 MPa for 2 hours in a warm bath adjusted to 40 ° C. to remove the organic solvent. However, in Examples 6 and 7 and Comparative Examples 7 and 8, the organic solvent removal step in the production step (3) was omitted.
Then, the temperature was adjusted to 62 ° C., the pressure was lowered to 10 kPa, and held for 4 hours to remove the organic solvent and part of water, and the total concentration of the pigment and the polymer was 23 to 25%. Next, the total concentration of the pigment and the polymer was measured, and adjusted so that the total concentration of the pigment and the polymer was 20% with ion-exchanged water.
Then, filtration was sequentially performed using 5 μm and 1.2 μm membrane filters (manufactured by Sartorius, trade name: Minisart) to obtain a pigment water dispersion. The volume average particle sizes of these pigment particles are shown in Table 2.

(4) Ink formation process: Production of aqueous ink Pigment aqueous dispersion obtained in production process (2), polyethylene glycol 400 (manufactured by Wako Pure Chemical Industries, Ltd., average molecular weight 400, reagent), surfactant (Nisshin Co., Ltd. Chemical Industry Co., Ltd., Orphin E1010: 0.5 parts of ethylene oxide (10 mol) adduct of acetylene diol, Antifungal agent (Arc Chemicals Japan Co., Ltd., Proxel LV (S): 1,2-benzoisothiazole- 0.1 parts of 3 (2H) -one, active 20%), and ion-exchanged water are added in the amounts shown in Table 2 and mixed, and the obtained mixture is added to a 0.45 μm membrane filter (manufactured by Sartorius, It filtered by brand name: Minisart] and obtained water-based ink. The surface tension at 20 ° C. of the obtained aqueous ink was 36 mN / m.

The following evaluation was performed about the water-based ink obtained in Examples 1-8 and Comparative Examples 1-8.
(1) Evaluation of Discharge Durability A solid image having a width of 200 mm and a length of 254 mm was printed on the plain paper under the same printing conditions using the same printer as the measurement of the printing density of (1). Printing was repeated, and the number of printed sheets was measured until the print density decreased by 10% from the beginning by printing. The above evaluation was performed by replacing the ink with a new recording head for each ink. The results are shown in Table 2.
In addition, when the heater of the recording head in which the printing density decreased by 10% was observed with an optical microscope, black burn was confirmed on the heater.

(2) Measurement of print density and evaluation of printer suitability Refill the yellow intermediate tank ink of the thermal ink jet printer "LPP-6010N" made by LG Electronics, in an environment of temperature 25 ± 1 ° C and relative humidity 30 ± 5% Printing was carried out in the best mode using a regular paper "Xerox 4024" manufactured by Xerox Corporation.
With the recording head loaded into the printer and the ink filled in the recording head as an initial state, the recording head replacement button is pressed, the ink is recovered to the intermediate tank, and the recording head is removed once, and the recording head is immediately The ink was loaded into the recording head. The above recording head replacement operation was repeated 1000 times with this as one cycle.
Subsequently, a solid image having a width of 200 mm and a length of 254 mm was printed on the plain paper under the same printing conditions as described above. Macbeth densitometer (product of Gretag Macbeth, product number: Spectroeye, measurement conditions Observation angle of view: 2 degrees, observation light source: D50, white standard) : Paper standard, Polarizing filter: None, Density standard: ANSI-A) A total of 5 points were measured, and the average value was obtained to obtain an initial print density (a). Further, Table 2 shows the difference (variation range) between the print density obtained by the measurement of the print density of the above (1) and the print density (b) after 1,000 circulations of the head. For each ink to be evaluated, the printer and the head used an unused item.
It is preferable that the fluctuation range of the printing density is 0.1 or less, and when the printing density is 0.2 or more, a clear white stripe is confirmed in the solid image portion, and the printing quality is significantly impaired.

  From Table 2, it can be seen that the water-based inks of Examples 1 to 8 are superior in discharge durability to the water-based inks of Comparative Examples 1 to 8 and can suppress the decrease in print density even if recording is performed over a long period of time.

Claims (7)

A pigment water dispersion comprising pigment particles, a water dispersible polymer and water,
The pigment particles are carbon black dispersed by a water dispersible polymer,
The water dispersible polymer is a structural unit derived from a monomer derived from an aromatic group-containing monomer, a monomer derived from a monomer containing one or more ionic groups selected from acrylic acid and methacrylic acid , and a polyalkylene glycol (meth) acrylate, It is a polymer having a structural unit derived from one or more nonionic monomers selected from alkoxypolyalkylene glycol (meth) acrylate and alkoxypolyalkylene glycol (meth) acrylate ,
The mass ratio of the pigment amount to the water-dispersible polymer amount (pigment / water-dispersible polymer) is 65/35 or more and 80/20 or less ,
The scattering intensity area ratio of the components included in the range of 0 to -55 mV of the standardized zeta potential distribution 4 obtained by the following zeta potential measurement steps (i) to (iv) and (v) is 2% or less,
The scattering intensity area ratio of the components included in the range of 0 to -58 mV of the standardized zeta potential distribution 4 obtained by the following zeta potential measurement steps (i) to (iv) and (vi) is 4% or less,
Inkjet having a scattering intensity area ratio of 10% or less of components included in the range of 0 to -60 mV of the standardized zeta potential distribution 4 obtained by the following zeta potential measurement steps (i) to (iv) and (vii) Pigment water dispersion for recording.
Step (i): a step of measuring zeta potential distribution 1 without applying an electric field to particles in the measurement cell and then normalizing to obtain normalized zeta potential distribution 1.
Step (ii): applying an electric field of 1200 V / m to the particles in the measurement cell to measure the zeta potential distribution 2 and then normalizing to obtain the normalized zeta potential distribution 2.
Step (iii): obtaining a normalized zeta potential distribution 3 obtained by taking the difference between the normalized zeta potential distributions 1 and 2
Step (iv): Step of obtaining the normalized zeta potential distribution 4 by making a histogram of the normalized zeta potential distribution 3 in 1 mV steps and normalizing the histogram.
Step (v): Read the range (area) of 0 to -55 mV and the range (area) between the normalized zeta potential distribution 4 and the line of zero scattering intensity in the normalized zeta potential distribution 4 Step of obtaining the scattering intensity area ratio (%) of the components contained in the range of 55 mV.
Step (vi): Read the range (area) of 0 to -58 mV and the range (area) between the normalized zeta potential distribution 4 and the line of zero scattering intensity in the normalized zeta potential distribution 4 Step of obtaining the scattering intensity area ratio (%) of the components included in the range of 58 mV.
Step (vii): Read the range (area) of 0 to -60 mV and the range (area) between the normalized zeta potential distribution 4 and the line of zero scattering intensity in the normalized zeta potential distribution 4 Step of obtaining the scattering intensity area ratio (%) of the components included in the range of 60 mV.   The pigment water dispersion for ink jet recording according to claim 1, wherein the measurement method of the zeta potential distribution is a dynamic light scattering method.   The pigment water dispersion for inkjet recording according to claim 1 or 2, wherein the volume average particle size of the pigment particles is 40 nm or more and 150 nm or less.   The pigment water dispersion for inkjet recording according to any one of claims 1 to 3, wherein the content of the pigment is 5% by mass or more and 30% by mass or less in the pigment water dispersion. The pigment water dispersion for inkjet recording according to any one of claims 1 to 4 , wherein the weight average molecular weight of the water dispersible polymer is 10,000 or more and 300,000 or less. The pigment water dispersion for inkjet recording according to any one of claims 1 to 5 , which is used for an ink containing polyethylene glycol having an average molecular weight of 200 or more and 1,500 or less . A method for producing a pigment water dispersion for ink jet recording, comprising pigment particles, a water dispersible polymer and water, wherein the pigment particles and the water dispersible polymer are as described in claim 1,
Having the following production steps (1), (2) and (3),
Production step (1): a mixture containing water, a pigment, a water-dispersible polymer, and an organic solvent having a solubility in water at 20 ° C. of less than 40% by mass, the volume average particle diameter of pigment particles by dynamic light scattering method Process of dispersing to 180 nm or less to obtain pigment dispersion
Production step (2): a step of adding water to the pigment dispersion obtained in the production step (1) and holding at 40 ° C. or less for 4 hours or more and 48 hours or less
Production process (3): Zeta potential measurement process (i) to (iv) according to claim 1, wherein the organic solvent of the pigment dispersion obtained in the production process (2) is removed to obtain a pigment water dispersion. And (v) reducing the scattering intensity area ratio of components contained in the range of 0 to -55 mV of the normalized zeta potential distribution 4 to 2% or less, zeta potential measurement steps (i) to (iv) and (I) reducing the scattering intensity area ratio of the component contained in the range of 0 to -58 mV of the normalized zeta potential distribution 4 to 4% or less, and zeta potential measuring step (i) to (iv) and (Vi) A method for producing a pigment water dispersion for ink jet recording, comprising the step of setting the scattering intensity area ratio of the components contained in the range of 0 to -60 mV of the normalized zeta potential distribution 4 obtained by (vii) to 10% or less.