JP7346803B2 - Aqueous pigment dispersion and method for producing an aqueous pigment dispersion - Google Patents

Description

The present invention is based on C. I. The present invention relates to an aqueous pigment dispersion containing Pigment Orange 43 and a method for producing the same.

Inks containing pigments are widely used in printing situations such as offset printing, gravure printing, flexographic printing, silk screen printing, and inkjet printing.

Among them, aqueous pigment inks that use water as a solvent are being considered for use in a variety of applications because they have a lower risk of ignition than conventional organic solvent-based inks.

As the aqueous pigment dispersion used for manufacturing the aqueous pigment ink, those containing a pigment, a pigment dispersion resin, and an aqueous medium are known. Therefore, it is required to be stably dispersed in an aqueous medium.

However, the dispersibility of the pigment contained in the aqueous pigment dispersion differs depending on the type of pigment and the formulation, so in order to improve the dispersibility of the aqueous pigment dispersion, it is necessary to It is necessary to take appropriate measures.

On the other hand, when printing with aqueous pigment ink using the inkjet printing method, in addition to the basic colors of yellow, magenta, cyan, and black, the special colors of green, red, blue, and orange are used. A combination of inks such as these may be used.

Examples of the water-based ink using the orange pigment include C.I. An ink containing Pigment Orange 43 is known (see, for example, Patent Document 1).

However, because these inks have a large volume average particle diameter and a large amount of coarse particles, they cannot achieve a level of dispersibility comparable to that of basic color inks or pigment dispersions, or a level that can suppress changes in physical properties over time. In some cases, storage stability could not be achieved.

Further, as described above, dispersibility and storage stability are often caused by the interaction between the type of pigment and the dispersion resin. Therefore, even if the pigment dispersion resin used in the pigment dispersion for the basic color is used in combination with the pigment for the special color, it is not always possible to immediately achieve good dispersibility. In order to improve the dispersibility of the body, considerable trial and error was sometimes required by those skilled in the art.

International publication 1999/05230 pamphlet

The problem to be solved by the present invention is to manufacture an ink with reduced coarse particles, excellent pigment dispersibility in an aqueous pigment dispersion, and storage stability at a level that does not easily cause changes in physical properties over time. The object of the present invention is to provide a possible aqueous pigment dispersion.

The present invention provides C.I. I. A pigment (A) containing Pigment Orange 43 (a), a pigment dispersion resin (B) containing a radical polymer with an acid value of 80 to 150 mgKOH/g, water (C), and a kneading aid (D). The present invention relates to an aqueous pigment dispersion characterized by containing:

The aqueous pigment dispersion of the present invention and the ink containing the same have a level of dispersibility comparable to basic color inks and aqueous pigment dispersions.

The aqueous pigment dispersion of the present invention has a primary particle size of 150 nm or less. I. A pigment (A) containing Pigment Orange 43 (a), a pigment dispersion resin (B) containing a radical polymer with an acid value of 80 to 150 mgKOH/g, water (C), and a kneading aid (D). It is characterized by containing. The aqueous pigment dispersion refers to a state in which a pigment is dispersed in a solvent such as water. The aqueous pigment dispersion refers to the material used when manufacturing the aqueous pigment ink, or the aqueous pigment ink itself.

In the present invention, C. I. Pigment (A) containing Pigment Orange 43(a) is used.

Said C. I. Pigment Orange 43 used has a primary particle size of 150 nm or less. This makes it possible to achieve a level of dispersibility comparable to that of basic color inks and aqueous pigment dispersions, and a level of storage stability that can suppress changes in physical properties over time. In addition, the above C. I. Pigment Orange 43 having a primary particle size of 50 to 130 nm is preferably used, and it is more preferable to use one having a primary particle size of 65 to 120 nm in order to further improve storage stability. The above primary particle diameter values were measured using the following equipment and conditions.

First, the above C. I. A measurement sample was obtained by dropping a mixture of 1 part by mass of pigment (A) containing Pigment Orange 43(a) and 99 parts by mass of ethanol onto a collodion film-coated mesh and drying it.

Next, any 1000 measurement samples were observed using a scanning transmission electron microscope (STEM, JSM-7500FA, manufactured by JEOL Ltd., accelerating voltage: 30 kv), and the average value of the long axis was calculated as the primary particle diameter. And so.

C.I. with a primary particle diameter of 150 nm or less I. Pigment Orange 43(a) is a C.I. pigment with a primary particle size exceeding 150 nm. I. Pigment Orange 43 can be produced, for example, by dry grinding, wet grinding, solvent salt milling, or the like. However, since dry pulverization and wet pulverization use metal beads, there is a high possibility that metals will be mixed in as impurities. Therefore, it is preferable to use solvent salt milling, which has a low level of metal contamination.

Solvent salt milling is a method of kneading and grinding a mixture containing at least a crude pigment, an inorganic salt, and an organic solvent using a kneader such as a kneader, two-roll mill, three-roll mill, or attritor. In addition, in the present invention, C.I. I. Pigment Orange 43 is used as a crude pigment.

As the inorganic salt that can be used in the solvent salt milling, it is preferable to use a water-soluble inorganic salt, such as sodium chloride, potassium chloride, sodium sulfate, etc. As the inorganic salt, it is more preferable to use an inorganic salt having a primary particle size of 0.5 to 50 μm. The amount of the inorganic salt used is preferably 3 to 20 parts by weight, more preferably 5 to 15 parts by weight, per 1 part by weight of the crude pigment.

As the organic solvent that can be used in the solvent salt milling, it is preferable to use an organic solvent that can suppress crystal growth, and as such an organic solvent, a water-soluble organic solvent can be suitably used, such as diethylene glycol, glycerin, Ethylene glycol, propylene glycol, liquid polyethylene glycol, liquid polypropylene glycol, 2-(methoxymethoxy)ethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy)ethanol, diethylene glycol monomethyl ether, diethylene Glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monomethyl Ether, dipropylene glycol, etc. can be used.

The organic solvent is preferably 0.01 to 5 parts by weight per 1 part by weight of the crude pigment.

The temperature during kneading and grinding in the solvent salt milling is preferably 30 to 150°C. The kneading and grinding time is preferably from 2 hours to 20 hours.

By the above method, C.I. I. A mixture of Pigment Orange 43(a), the inorganic salt and the organic solvent can be obtained. When producing the aqueous pigment dispersion and ink of the present invention using the mixture, if necessary, the inorganic salt and the organic solvent may be washed and filtered, then dried and pulverized. .

In the washing and filtering step, either washing with water or washing with hot water can be employed. In addition, the above C. I. Pigment Orange 43(a) may be washed with acid, alkali, or a solvent so as not to change its crystalline state. The washing may be repeated 1 to 5 times. If a water-soluble inorganic salt and a water-soluble organic solvent are used as the inorganic salt and organic solvent, the water-soluble inorganic salt and the water-soluble organic solvent can be easily removed by the washing.

In the drying step, a batch or continuous drying method may be used in which the pigment is dehydrated and/or the solvent is removed by, for example, heating at 80 to 120° C. using a heat source installed in a dryer. As the dryer, a box dryer, a band dryer, a spray dryer, etc. can be used.

The pulverizing step includes the C. I. Rather than increasing the specific surface area of Pigment Orange 43(a) or further reducing the primary particle size, for example, when a box dryer or band dryer is used, the C. I. This step may be carried out in order to decompose Pigment Orange 43(a) into a lamp shape or the like and turn it into powder.

In the grinding step, for example, a mortar, a juicer, a hammer mill, a disk mill, a pin mill, a jet mill, etc. can be used.

C.I. having a primary particle diameter of 150 nm or less obtained by the solvent salt milling. I. Pigment Orange 43(a) is preferably contained in an amount of 70 to 100 parts by mass based on the entire pigment (A) in order to achieve a storage stability effect, and the closer it is to 100 parts by mass, the more preferred it is.

As the pigment dispersion resin (B), a radical polymer having an acid value of 80 to 150 mgKOH/g is used. By using a radical polymer having an acid value within the above range as the pigment dispersion resin (B), it is possible to obtain an inkjet recording ink in which the pigment (A) has good dispersibility in the aqueous pigment dispersion. . As the dispersion resin (B), it is preferable to use a radical polymer having an acid value of 90 to 150 mgKOH/g, and it is preferable to use a radical polymer having an acid value of 100 to 130 mgKOH/g. ) is particularly preferable in order to further improve the dispersibility of pigment (A).

The above acid value was determined by the neutralization titration method described in the Japanese Industrial Standards "K0070:1992, Test methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiables of chemical products". Refers to the measured value.

As the radical polymer, one having an aromatic ring structure or a heterocyclic structure can be used, and it is more preferable to use one having a benzene ring structure, and one having a styrene-derived structure is used. It is more preferable to do so.

The mass ratio of the styrene-derived structural unit to the total amount of the radical polymer is preferably 50 parts by mass or more. It is more preferable that the mass ratio is in the range of 60 parts by mass to 95 parts by mass in order to achieve a dispersibility effect.

As the radical polymer, a polymer obtained by radical polymerizing various monomers can be used.

As the monomer, if an aromatic cyclic structure is to be introduced into the radical polymer, a monomer having an aromatic cyclic structure can be used, and if a heterocyclic structure is to be introduced, a monomer having an aromatic cyclic structure can be used. Monomers having heterocyclic structures, if available, can be used.

Examples of the monomer having an aromatic ring structure include styrene, p-tert-butyldimethylsiloxystyrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, p-tert-butoxystyrene, m-tert-butoxystyrene, p-tert-(1-ethoxymethyl)styrene, m-chlorostyrene, p-chlorostyrene, p-fluorostyrene, α-methylstyrene, p-methyl-α-methylstyrene, vinylnaphthalene , vinylanthracene, etc. can be used.

As the monomer having the heterocyclic structure, for example, vinylpyridine monomers such as 2-vinylpyridine and 4-vinylpyridine can be used.

When using a radical polymer having both an aromatic cyclic structure and a heterocyclic structure, the monomers include a monomer having an aromatic cyclic structure and a monomer having a heterocyclic structure. The bodies can be used in combination.

As the radical polymer, it is preferable to use a radical polymer having a structural unit derived from styrene as described above, and therefore, styrene, α-methylstyrene, or tert-butylstyrene may also be used as the monomer. is more preferable.

Moreover, as monomers that can be used for producing the radical polymer, other monomers can be used in addition to those described above, if necessary.

Examples of the other monomers include methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl ( meth)acrylate, 2-ethylbutyl(meth)acrylate, 1,3-dimethylbutyl(meth)acrylate, hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, ethyl(meth)acrylate, n -Butyl (meth)acrylate, 2-methylbutyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, nonyl (meth)acrylate, 3-ethoxypropyl (meth)acrylate, 3-ethoxybutyl (meth)acrylate , dimethylaminoethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, ethyl-α-(hydroxymethyl)(meth)acrylate, dimethylaminoethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, phenylethyl (meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate Acrylate, glycerin (meth)acrylate, bisphenol A (meth)acrylate, dimethyl maleate, diethyl maleate, vinyl acetate, and the like can be used alone or in combination of two or more. Note that the above-mentioned "(meth)acrylate" refers to acrylate or methacrylate.

As the radical polymer, a polymer having a linear structure formed by radical polymerization of the monomer, a polymer having a branched (grafted) structure, and a polymer having a crosslinked structure are used. can do. In each polymer, the monomer arrangement is not particularly limited, and polymers with random or block arrangement can be used.

As the radical polymer, it is preferable to use one whose weight average molecular weight is within the range of 2,000 to 20,000, more preferably within the range of 5,000 to 20,000, and further preferably within the range of 7,000 to 15,000. It is particularly preferable because the aggregation and sedimentation of the pigment (A) are less likely to occur, the storage stability of the aqueous pigment dispersion is improved, and the ejection stability of the ink is further improved.

The weight average molecular weight is a value measured by GPC (gel permeation chromatography), and is a value converted to the molecular weight of polystyrene used as a standard substance.

As the radical polymer, it is preferable to use one in which some or all of the acid groups of the radical polymer have been neutralized with a basic compound (neutralized product) in order to achieve excellent storage stability. preferable.

Examples of the basic compound include hydroxides of alkali metals such as potassium and sodium; carbonates of alkali metals such as potassium and sodium; carbonates of alkaline earth metals such as calcium and barium; ammonium hydroxide, etc. Inorganic basic compounds, amino alcohols such as triethanolamine, N,N-dimethanolamine, N-aminoethylethanolamine, dimethylethanolamine, N-N-butyldiethanolamine, morpholine, N-methylmorpholine, N- - Organic basic compounds such as morpholines such as ethylmorpholine, piperazine such as N-(2-hydroxyethyl)piperazine, and piperazine hexahydrate can be used. Among these, the use of alkali metal hydroxides, such as potassium hydroxide, sodium hydroxide, and lithium hydroxide, as the basic compound contributes to lowering the viscosity of the aqueous pigment dispersion, making it suitable for inkjet recording. It is preferable to further improve the storage stability and ejection stability of the ink, and it is particularly preferable to use potassium hydroxide.

The neutralization rate of the radical polymer is not particularly limited, but is preferably in the range of 80 to 120% in order to suppress aggregation of the radical polymer. In the present invention, the neutralization rate refers to a value calculated using the following formula.

Neutralization rate (%) = [{Mass of basic compound (g) x 56.11 x 1000}/{Acid value of radical polymer (mgKOH/g) x Equivalent of basic compound x Mass of radical polymer ( g)}]×100

When the basic compound is mixed with the pigment (A), etc., it is possible to use a compound that has been previously dissolved or dispersed in a solvent such as water.

The aqueous pigment dispersion of the present invention has a mass ratio of the pigment (A) and the pigment dispersion resin (B) [the pigment dispersion resin (B)/the pigment (A)] of 0.1 to 0.7. However, in order to have better dispersibility and storage stability, it is preferably used within the range of 0.1 to 0.4.

As water (C), pure water or ultrapure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, distilled water, etc. can be used. In addition, as for the water (C), it is recommended to use water that has been sterilized by ultraviolet irradiation or addition of hydrogen peroxide, etc., to prevent mold or bacteria from forming when storing aqueous pigment dispersions or inks using them for a long period of time. This is preferable because it can prevent the occurrence.

The water (C) is preferably contained in a range of 40% by mass to 80% by mass based on the total amount of the aqueous pigment dispersion of the present invention.

Moreover, as the aqueous pigment dispersion of the present invention, one containing a kneading aid (D) is used.

In the production of an aqueous pigment dispersion, which is a raw material for ink, a pigment dispersion resin is adsorbed onto the surface of the pigment, thereby achieving good dispersibility of the pigment in water.

However, since the ease of adsorption varies depending on the type of pigment, etc., it is sometimes necessary to select a pigment dispersion resin depending on the pigment used. Particularly when using the Pigment Orange 43 pigment, if the selection is not appropriate, the adsorption of the pigment dispersion resin to the pigment will not be sufficient, and the unadsorbed pigment dispersion resin will remain in the aqueous pigment dispersion. There was a concern that the pigment and the pigment dispersion resin would coexist in large amounts, and that the pigment dispersion resin would cause crosslinking of two or more pigment particles over time, resulting in aggregation of the pigments, etc.

In the present invention, the kneading aid (D) is mixed with the pigment (A) and the pigment dispersion resin (B) in advance in the production of the aqueous pigment dispersion that is the raw material of the ink, so that the kneading aid (D) can be mixed with the pigment (A) and the pigment dispersion resin (B) in advance. Contact with the pigment dispersion resin (B) is promoted, and as a result, aggregation and sedimentation of the pigment (A) can be effectively suppressed.

As the kneading aid (D), for example, one containing one or more selected from the group consisting of acetylene glycol compounds, acetylene glycol compounds, and ether compounds can be used. Among these, the kneading aid (D) is useful in obtaining an aqueous pigment dispersion that has a small number of coarse particles, can further improve the dispersibility of the dispersion, and has excellent long-term storage stability. It is preferable to use a mixture containing an acetylene glycol compound and an ether compound.

Examples of the acetylene glycol compounds include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4,7-diol. Ethylene oxide adducts, etc. can be used, and among them, 2,4,7,9-tetramethyl-5-decyne-4,7-diol can be used to obtain pigment dispersibility and storage stabilization effects. Yes, it is preferable.

As the ether compound, for example, poly(oxyethylene) secondary alkyl ether can be used, and it is preferable to use one having an alkyl ether structure having 12 to 14 carbon atoms, since pigment dispersibility and storage stability are improved. This is preferable in terms of providing a protective effect.

The kneading aid (D) has, for example, a mass ratio of the pigment (A) and the kneading aid (D) [the kneading aid (D)/the pigment (A)] of 0.5/100 to 7. It is preferable to use it in the range of /100, and use in the range of 1/100 to 6/100 can reduce the number of coarse particles, further improve the dispersibility of the dispersion, and provide long-term This is more preferable for obtaining an aqueous pigment dispersion with excellent storage stability.

The aqueous pigment dispersion of the present invention may contain a water-soluble organic solvent in addition to the pigment (A), pigment dispersion resin (B), water (C), and kneading aid (D) described above. However, it increases the wettability of the surface of the pigment (A) and improves the adsorption of the pigment dispersion resin (B) onto the surface of the pigment (A), thereby further improving the dispersibility of the pigment. It is preferable to improve the performance.

Examples of the water-soluble organic solvent include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; butanediol, pentanediol, hexanediol, and diols similar to these, and the like. diols; glycol esters such as propylene glycol laurate; glycol ethers such as diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl ethers, propylene glycol ether, dipropylene glycol ether, and cellosolve including triethylene glycol ether; ; Alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, pentyl alcohol, and alcohols of the same family; or sulfolane; lactones such as γ-butyrolactone; Lactams such as N-(2-hydroxyethyl)pyrrolidone; glycerin, glycerin derivatives such as glycerin added with polyoxyalkylene, etc.; and one or two types of other various solvents known as water-soluble organic solvents. The above can be mixed and used.

Among the above-mentioned water-soluble organic solvents, it is recommended to use polyhydric alcohols such as glycols and diols, which have a high boiling point, low volatility, and high surface tension, and are effective as wetting agents and drying inhibitors. It is preferable to use it because it also plays a role, and it is more preferable to use glycols such as diethylene glycol and triethylene glycol.

The aqueous pigment dispersion of the present invention can be prepared as appropriate within a range where the mass ratio of the pigment (A) to the water-soluble organic solvent [the water-soluble organic solvent/the pigment (A)] is from 0.3 to 2.0. Although it can be selected, it is preferably used in the range of 0.4 to 1.5 in order to provide better dispersibility and storage stability.

The method for producing the aqueous pigment dispersion of the present invention uses C.I. I. A step of producing a kneaded product containing a pigment (A) containing Pigment Orange 43(a), a pigment dispersion resin (B), and the kneading aid (D), and the kneaded product obtained in the step; It is characterized by having a step of mixing water (C).

First, the C.I. I. Pigment (A) containing Pigment Orange 43(a), pigment dispersion resin (B), and, if necessary, the basic compound and water-soluble organic solvent are supplied to a container and kneaded. The step of obtaining the kneaded material is not particularly limited and can be performed by a known dispersion method. For example, media mill dispersion method using media such as paint shaker, bead mill, sand mill, ball mill, etc.; medialess dispersion method using ultrasonic homogenizer, high pressure homogenizer, nanomizer, ultimateizer, etc.; roll mill, Henschel mixer, pressure kneader, Examples include kneading and dispersion methods such as intensive mixers, Banbury mixers, and planetary mixers. Among these, the kneading and dispersion method is a method in which the pigment (A) is made fine by applying strong shearing force to a mixture containing the pigment (A) with a high solid content concentration using a kneader. This method is preferable because it can be obtained and is effective in reducing coarse particles. In the kneading and dispersion method, water is preferably contained in an amount of 50% by mass or less based on the total solid content of the mixture, or preferably water is not contained.

In the kneading and dispersion method, there is no particular limitation on the order in which the mixtures are added, and the entire amount may be added at the same time and kneading may be started, each may be added in small amounts, or the order of addition may be changed depending on the raw materials. The amount of each raw material charged can be within the ranges mentioned above. When blending a basic compound, when using a basic compound aqueous solution dissolved in water in advance, the amount of water in the mixture is determined by taking into account the amount of water contained in the basic compound aqueous solution. It is preferable to do so.

In order to impart a strong shearing force to the mixture, which is an advantage of the kneading and dispersion method, it is preferable to knead the mixture in a state where the solid content ratio is high, so that a higher shearing force can be applied to the mixture. The solid content ratio is preferably in the range of 20 to 100% by mass, more preferably in the range of 30 to 90% by mass, and preferably in the range of 40 to 80% by mass of the mixture during kneading. Since the viscosity can be kept appropriately high, the load applied to the mixture by the kneader can be increased, and as a result, the pigment in the mixture can be sufficiently crushed and the pigment (A) can be coated with the pigment dispersion resin (B). This is particularly preferred since it can be carried out more efficiently.

The temperature during kneading can be appropriately adjusted in consideration of the temperature characteristics such as the glass transition point of the radical polymer contained in the pigment dispersion resin (B) so that sufficient shearing force is applied to the kneaded material. For example, when the radical polymer is a styrene-acrylic acid copolymer, it is preferable to carry out the reaction in a range that is lower than the glass transition point and the temperature difference from the glass transition point is less than 50°C. By performing kneading in such a temperature range, there is no shortage of shear force due to a decrease in the viscosity of the kneaded product due to melting of the radical polymer due to an increase in the kneading temperature.

The kneading device used in the kneading process may be any device that can generate a high shearing force for a mixture with a high solid content ratio, and can be selected from among the known kneading devices described above. Although this is possible, it is preferable to use a kneading device that has a stirring tank and stirring blades and can seal the stirring tank, rather than using an open-type kneader such as a two-roll kneader that does not have a stirring tank.

Examples of such devices include Henschel mixers, pressure kneaders, Banbury mixers, and planetary mixers, with planetary mixers being particularly suitable.

In the kneading step, the viscosity of the mixture to be kneaded may change significantly over time. If the planetary mixer is used, the shearing force applied to the mixture can be adjusted appropriately, so even if the viscosity of the mixture changes significantly, it is possible to mix the mixture sufficiently for practical purposes. Furthermore, when the planetary mixer is used, by supplying water to the planetary mixer after the kneading step is completed, it is possible to quickly proceed to the step of dispersing the kneaded material in water (C).

In the step of dispersing the kneaded product obtained by kneading the mixture into water (C), for example, when using a kneading device that has a stirring tank and stirring blades and can seal the stirring tank, after the completion of the kneading, It is possible to supply water (C). When supplying the water (C), a water-soluble organic solvent can be supplied as necessary.

The aqueous pigment dispersion obtained by the above method is preferably adjusted to have a pigment concentration of 10 to 50% by mass, although it depends on the use, since it can be easily diluted to form an ink. When making an ink using this, a water-soluble solvent and/or water, or additives may be added as appropriate to adjust the pigment concentration to 0.1 to 20% by mass, depending on the desired ink use and physical properties. Ink can be obtained by simply diluting it so that it becomes the same.

Regarding mixing of water (C), the required amount may be mixed into the pigment kneaded material all at once, but it is better to add the required amount continuously or intermittently to advance the mixing. Dilution is performed efficiently and an aqueous pigment dispersion can be prepared in a shorter time.

Further, the obtained aqueous pigment dispersion may be further subjected to a dispersion treatment using a dispersion machine. Dispersing machines include paint shaker, bead mill, roll mill, sand mill, ball mill, attritor, basket mill, sand mill, sand grinder, Dyno mill, Dispermat, SC mill, spike mill, agitator mill, juice mixer, high pressure homogenizer, ultrasonic homogenizer. , nanomizer, resolver, disperser, high-speed impeller disperser, kneader, planetary mixer, etc.

The volume average particle diameter of the particles contained in the aqueous pigment dispersion obtained by the above method is preferably from 50 nm to 300 nm, and preferably from 80 nm to 180 nm in order to provide excellent dispersibility and storage stability. Most preferred.

(Water-based ink for inkjet recording)
The aqueous pigment dispersion is diluted to a desired concentration and used in various applications such as coatings for automobiles and building materials, printing inks such as offset inks, gravure inks, flexographic inks, and silk screen inks, and inkjet recording inks. It can be used for various purposes.

When applying the aqueous pigment dispersion of the present invention to an inkjet recording ink, a water-soluble solvent and/or water, and a resin such as an acrylic resin or a polyurethane resin as a binder may be added as necessary to obtain the desired physical properties. It is prepared by adding drying inhibitors, penetrants or other additives.

A centrifugation or filtration treatment step may be added during or after the preparation of the ink.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Preparation of pigment by solvent salt milling)
In a kneader, 100 parts by mass of pigment Orange A-76 (C.I. Pigment Orange 43, manufactured by Arimoto Chemical Co., Ltd., primary particle size 190 nm), 1000 parts by mass of sodium chloride (water-soluble inorganic salt), diethylene glycol (water-soluble organic solvent) ) 200 parts by mass were charged.

After adjusting the kneader jacket temperature to 40°C, kneading (solvent salt milling) was performed for 6 hours.

Next, the kneaded product obtained above was taken out into an anticorrosive container, and then 10 L of 0.5% by mass HCl aqueous solution was added and stirred to obtain a composition in which the sodium chloride and diethylene glycol were dissolved.

Next, the composition was filtered and the residue (pigment content) was collected. At this time, the residue was washed with warm water and ion-exchanged water so that the sodium chloride and diethylene glycol did not remain in the residue. The collected residue was dried at 90° C. for 32 hours or more to completely remove water and obtain a dried product. Pigment X having a primary particle size of 80 nm was obtained by pulverizing the dried material using a juicer.

PV FAST ORANGE GRL (C.I. Pigment Orange 43, manufactured by Clariant, primary particle size 200 nm) instead of pigment Orange A-76 (C.I. Pigment Orange 43, manufactured by Arimoto Chemical Co., Ltd., primary particle size 190 nm) Pigment Y having a primary particle size of 90 nm was obtained in the same manner as the above method except that the method was changed to .

The primary particle diameters of the pigments X and Y were measured and calculated using the following method.

First, the above C. I. A measurement sample was obtained by dropping a mixture of 1 part by mass of pigment (A) containing Pigment Orange 43(a) and 99 parts by mass of ethanol onto a collodion film-coated mesh and drying it.

Next, any 1000 measurement samples were observed using a scanning transmission electron microscope (STEM, JSM-7500FA, manufactured by JEOL Ltd., accelerating voltage: 30kv), and the average value of the major axis was calculated as the primary particle size. The diameter was taken as the diameter.

Radical polymers A to E, which will be described later, were used as pigment dispersion resins.
(Radical polymer A)
Radical polymer A is a powder (diameter 1 mm or less) produced by solution polymerization, and the monomer composition ratio is styrene/acrylic acid/methacrylic acid/butyl acrylate = 83.00/7.35/9. .55/0.10 (mass ratio), weight average molecular weight 11000, acid value 120 mgKOH/g, and glass transition temperature 120°C.

(Radical polymer B)
Radical polymer B is in the form of powder (diameter 1 mm or less) produced by solution polymerization, and the monomer composition ratio is styrene/acrylic acid = 87.70/12.30 (mass ratio), and the weight The average molecular weight is 8000, the acid value is 90 mgKOH/g, and the glass transition temperature is 103°C.

(Radical polymer C)
Radical polymer C is a powder (diameter 1 mm or less) produced by solution polymerization, and the monomer composition ratio is styrene/acrylic acid/methacrylic acid/butyl acrylate = 76.92/9.99/12. .99/0.10 (mass ratio), weight average molecular weight 8000, acid value 150 mgKOH/g, and glass transition temperature 121°C.

(Radical polymer D)
Radical polymer D is a powder (diameter 1 mm or less) produced by solution polymerization, and the monomer composition ratio is styrene/acrylic acid/methacrylic acid/butyl acrylate = 72.00/12.13/15. .77/0.10 (mass ratio), weight average molecular weight 8000, acid value 180 mgKOH/g, and glass transition temperature 113°C.

(Radical polymer E)
Radical polymer E is in the form of powder (diameter 1 mm or less) produced by solution polymerization, and the monomer composition ratio is styrene/acrylic acid/butyl acrylate = 90.40/9.50/0.10 ( It has a weight average molecular weight of 8000, an acid value of 70 mgKOH/g, and a glass transition temperature of 98°C.

Note that the weight average molecular weight in the present invention is a value measured by GPC (gel permeation chromatography) method, and is a value converted to the molecular weight of polystyrene used as a standard substance. Note that the measurements were carried out using the following equipment and conditions.

Liquid pump: LC-9A
System controller: SLC-6B
Auto injector: S1L-6B
Detector: RID-6A
The above is data processing software manufactured by Shimadzu Corporation: Sic480II Data Station (manufactured by System Instruments).
Column: GL-R400 (guard column) + GL-R440 + GL-R450 + GL-R400M (manufactured by Hitachi Chemical Co., Ltd.)
Elution solvent: Tetrahydrofuran (THF)
Elution flow rate: 2ml/min
Column temperature: 35℃

(Example 1 Method for producing an aqueous pigment dispersion)
3.75 parts by mass of radical polymer A and 15 parts by mass of pigment After reaching 80° C., kneading was performed at an autorotation speed of 80 revolutions/minute and a revolution speed of 25 revolutions/minute. After 5 minutes, 40% by mass of Karbowet GA-211 (manufactured by Evonik Japan, 2,4,7,9-tetramethyl-5-decyne-4,7-diol) and poly(oxyethylene) were added as a kneading aid (D). )=composition containing 42.5% by mass of secondary alkyl ether (alkyl ether having 12 to 14 carbon atoms) and 17.5% by mass of water) and 0.3 parts by mass of triethylene glycol as a solvent. 12 parts by mass of and 1.32 parts by mass of 34% by mass aqueous potassium hydroxide solution were added.

Kneading was continued until 60 minutes had passed since the current value of the planetary mixer showed the maximum current value to obtain a kneaded product. The ratio of the radical polymer A to the pigment X (R/P) was 0.25, and the ratio of the solvent to the pigment X (S/P) was 0.80.

15 parts by mass of ion-exchanged water was added to the obtained kneaded product, mixed, diluted, and dispersed in ion-exchanged water. Further, ion-exchanged water was added and mixed to obtain an aqueous pigment dispersion having a concentration of Pigment Orange 43 of 15% by mass.

(Example 2)
3.75 parts by mass of radical polymer B was used instead of 3.75 parts by mass of radical polymer A, and the amount of 34 mass% potassium hydroxide aqueous solution was changed from 1.32 parts by mass to 0.99 parts by mass. Except for this, an aqueous pigment dispersion was obtained in the same manner as in Example 1. The ratio of the mass of the radical polymer B to the mass of pigment X (R/P) was 0.25, and the ratio of the mass of the solvent to the mass of pigment X (S/P) was 0.80.

(Example 3)
3.75 parts by mass of radical polymer C was used instead of 3.75 parts by mass of radical polymer A, and the amount of the 34 mass% potassium hydroxide aqueous solution was changed from 1.32 parts by mass to 1.65 parts by mass. Except for this, an aqueous pigment dispersion was obtained in the same manner as in Example 1. The ratio of the mass of the radical polymer C to the mass of pigment X (R/P) was 0.25, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 0.80.

(Example 4)
An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that 12 parts by mass of 2-pyrrole was used instead of 12 parts by mass of triethylene glycol. The ratio of the mass of the radical polymer A to the mass of pigment X (R/P) was 0.25, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 0.80.

An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that 15 parts by mass of pigment Y was used instead of 15 parts by mass of pigment X. The ratio of the mass of the radical polymer A to the mass of pigment Y (R/P) was 0.25, and the ratio of the mass of the solvent to the mass of pigment Y (S/P) was 0.80.

(Example 6)
An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that 12 parts by mass of LEG-1 (manufactured by LIPO CHEMICALS INC, polyoxyethylene glycerin) was used instead of 12 parts by mass of triethylene glycol. The ratio of the mass of the radical polymer A to the mass of pigment X (S/P) was 0.25, and the ratio of the mass of solvent to the mass of pigment X (R/S) was 0.80.

(Example 7)
Other than changing the usage amount of radical polymer A from 3.75 parts by mass to 1.50 parts by mass, and changing the usage amount of 34 mass% potassium hydroxide aqueous solution from 1.32 parts by mass to 0.53 parts by mass. An aqueous pigment dispersion was obtained in the same manner as in Example 1. The ratio of the mass of the radical polymer A to the mass of pigment X (R/P) was 0.10, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 0.80.

(Example 8)
Other than changing the amount of radical polymer A used from 3.75 parts by mass to 10.5 parts by mass, and changing the amount of 34 mass% potassium hydroxide aqueous solution from 1.32 parts by mass to 3.76 parts by mass. An aqueous pigment dispersion was obtained in the same manner as in Example 1. The ratio of the mass of the radical polymer A to the mass of pigment X (R/P) was 0.70, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 0.80.

(Example 9)
An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that the amount of triethylene glycol used was changed from 12 parts by mass to 6 parts by mass. The ratio of the mass of the radical polymer A to the mass of pigment X (R/P) was 0.25, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 0.40.

(Example 10)
An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that the amount of triethylene glycol used was changed from 12 parts by mass to 18 parts by mass. The ratio of the mass of the radical polymer A to the mass of pigment X (R/P) was 0.25, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 1.20.

(Example 11)
An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that the amount of Karbowet GA-211 (manufactured by Evonik Japan) was changed from 0.3 parts by mass to 0.75 parts by mass. The ratio of the mass of the radical polymer A to the mass of pigment X (R/P) was 0.25, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 0.80.

(Comparative example 1)
Instead of 15 parts by mass of the pigment Except for this, an aqueous pigment dispersion was obtained in the same manner as in Example 1. The ratio of the mass of the radical polymer A to the mass of "A-76" (R/P) is 0.25, and the ratio of the mass of the solvent to the mass of "A-76" (S/P) is 0.25. It was 80.

(Comparative example 2)
Instead of 15 parts by mass of the pigment X, 15 parts by mass of "A-76" (manufactured by Arimoto Chemical Co., Ltd., C.I. Pigment Orange 43, primary particle diameter 300 nm) which was not subjected to the solvent milling treatment was used, Except that 3.75 parts by mass of radical polymer A was replaced by 3.75 parts by mass of radical polymer D, and the amount of 34 mass% potassium hydroxide aqueous solution used was changed from 1.32 parts by mass to 1.99 parts by mass. An aqueous pigment dispersion was obtained in the same manner as in Example 1. The ratio of the mass of the radical polymer D to the mass of "A-76" (R/P) is 0.25, and the ratio of the mass of the solvent to the mass of "A-76" (S/P) is 0.25. It was 80.

(Comparative example 3)
Except that 3.75 parts by mass of radical polymer D was used instead of 3.75 parts by mass of radical polymer A, and the amount of 34 mass% potassium hydroxide aqueous solution used was changed from 1.32 parts by mass to 1.99 parts by mass. An aqueous pigment dispersion was obtained in the same manner as in Example 1. The ratio of the mass of the radical polymer D to the mass of pigment X (R/P) was 0.25, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 0.80.

(Comparative example 4)
Except that 3.75 parts by mass of radical polymer E was used instead of 3.75 parts by mass of radical polymer A, and the amount of 34 mass% potassium hydroxide aqueous solution used was changed from 1.32 parts by mass to 0.77 parts by mass. An aqueous pigment dispersion was obtained in the same manner as in Example 1. The ratio of the mass of the radical polymer E to the mass of pigment X (R/P) was 0.25, and the ratio of the mass of solvent to the mass of pigment X (S/P) was 0.80.

(Comparative example 5)
An aqueous pigment dispersion was obtained in the same manner as in Example 1, except that 0.30 parts by mass of Karbowet GA-211 (manufactured by Evonik Japan) as a surfactant was not used.

(Evaluation of aqueous pigment dispersion)
[Method for measuring volume average particle diameter]
First, the aqueous pigment dispersions prepared in Examples and Comparative Examples were diluted 2000 times with ion-exchanged water.

Next, approximately 4 ml of the diluted aqueous pigment dispersion was put into a cell, and the scattered light of the laser light was measured in a 25°C environment using a Nanotrac particle size analyzer "UPA150" manufactured by Microtrac Bell Co., Ltd. The volume average particle diameter (MV) was measured by detection.

The volume average particle diameter was measured three times, and the value calculated using the upper two digits of the average value as significant figures was defined as the value of the volume average particle diameter (unit: nm). A volume average particle diameter of 190 or less was judged to be good.

[Method for measuring the number of coarse particles]
First, the aqueous pigment dispersions prepared in Examples and Comparative Examples were diluted 50 times with ion-exchanged water.

Next, the number of particles with a diameter of 0.5 μm or more contained in the diluted aqueous pigment dispersion was measured three times using a particle size distribution analyzer (Accusizer 780 APS) manufactured by Particle Sizing Systems.

Next, the number of coarse particles was calculated by multiplying each of the measured values by the dilution concentration. Next, the average value of the three coarse particle counts calculated by the above method was taken as the coarse particle count of the aqueous pigment dispersions prepared in Examples and Comparative Examples.

(Test method for storage stability of aqueous pigment dispersion)
First, the number of coarse particles in the aqueous pigment dispersions immediately after being produced in Examples and Comparative Examples was measured in the same manner as described in the above [Method for Measuring Number of Coarse Particles].

Next, the aqueous pigment dispersions obtained in Examples and Comparative Examples were sealed in polypropylene containers and stored at 60°C for 4 weeks, after which the number of coarse particles was measured in the same manner as [Method for measuring the number of coarse particles]. .

Next, the number of coarse particles in the aqueous pigment dispersion immediately after the production, the number of coarse particles in the aqueous pigment dispersion after the storage, and the rate of change (%) = [(the coarse particles in the aqueous pigment dispersion after the storage) The rate of change in the number of coarse particles was calculated based on the formula: number−number of coarse particles in the aqueous pigment dispersion immediately after production)/number of coarse particles in the aqueous pigment dispersion immediately after production]×100. If the rate of change was within 10%, the storage stability was judged to be good.

(Test method for dispersibility of aqueous pigment dispersion)
Pour 30 ml of the aqueous pigment dispersion immediately produced in Examples and Comparative Examples into a glass test tube, leave it in a stable place at room temperature, and observe the upper part of the solution after two weeks.
○: The upper part of the dispersion is discolored and not separated. ×: The upper part of the dispersion is discolored and separated into two layers.

Claims (5)

C.I. having a primary particle diameter of 150 nm or less. I. Pigment (A) containing Pigment Orange 43(a);
A pigment dispersion resin (B) containing a radical polymer with an acid value of 80 to 150 mgKOH/g,
Water (C) and
Contains a kneading aid (D),
An aqueous pigment dispersion characterized in that the kneading aid (D) contains one or more selected from the group consisting of acetylene glycol compounds and ether compounds. 1. The pigment dispersion resin (B) is a radical polymer having a styrene-derived structural unit, and the mass ratio of the styrene-derived structural unit to the total amount of the radical polymer is 50% by mass or more. The aqueous pigment dispersion described in . Claim 1 or 2, wherein the mass ratio of the pigment (A) and the pigment dispersion resin (B) [the pigment dispersion resin (B)/the pigment (A)] is in the range of 0.1 to 0.7. The aqueous pigment dispersion described. It further contains a water-soluble organic solvent, wherein the mass ratio of the pigment (A) to the water-soluble organic solvent [the water-soluble organic solvent/the pigment (A)] is from 0.3 to 2.0. The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the aqueous pigment dispersion is within the range. The mass ratio of the pigment (A) and the kneading aid (D) [the kneading aid (D)/the pigment (A)] is in the range of 0.5/100 to 7/100. 4. The aqueous pigment dispersion according to any one of 4.