Method for evaluating aqueous pigment dispersions and method for producing aqueous pigment dispersions

Abstract

To provide a method for evaluating water-based pigment dispersion liquid that is useful for producing water-based pigment dispersion liquid with superior dispersibility, storage stability, and redispersibility for organic pigments, enabling the prediction and evaluation of a suitable combination of a polymer dispersant and a water-soluble organic solvent to achieve better dispersion of organic pigments.SOLUTION: For a mixture a containing a polymer dispersant, a water-soluble organic solvent, and water, a mixture b containing a water-soluble organic solvent and water, a mixture o containing a polymer dispersant and water, and the T2 relaxation durations of water (T2a, T2b, T2o, and T2w) are measured by pulse NMR, and a Rsp value and a Rspo value are determined by formulae (1) and (2). From a reduction rate (%) of the Rsp value based on the Rspo value, the dispersibility of an organic pigment in an aqueous pigment dispersion is evaluated. Rsp=(Ra / Rb)-1 (1) (Ra: a reciprocal of T2a, Rb: a reciprocal of T2b). Rspo=(Ro / Rw)-1 (2) (Ro: a reciprocal of T2o, Rw: a reciprocal of T2w).SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for evaluating aqueous pigment dispersions and a method for producing aqueous pigment dispersions. [Background technology]

[0002] Inkjet printing methods have become highly functional and are widely used for personal, office, and business purposes. In recent years, the application range of inkjet printing has expanded from consumer inkjet printers and large-format inkjet printers to industrial inkjet printing presses. Inkjet printing speeds are improving in line with productivity. Furthermore, high-speed printing capabilities are required for recording devices, such as maintenance-free print heads. In addition, water-based inkjet printing methods are primarily adopted due to environmental considerations.

[0003] Unlike water-based inks containing dyes (water-based dye inks), water-based inks containing pigments (water-based pigment inks) are prone to aggregation and sedimentation of pigments in particulate form over time. Therefore, when dispensing water-based pigment inks using an inkjet method, it is important to prevent clogging of the dispensing nozzles in order to ensure dispensing stability. As dispersions with good pigment dispersibility, various inkjet dispersions have been proposed, for example, using amphiphilic polymers having hydrophobic and hydrophilic segments as polymer dispersants for dispersing pigments (Patent Documents 1-7). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2002-053628 [Patent Document 2] Patent No. 4157868 [Patent Document 3] Patent No. 6979142 [Patent Document 4] Patent No. 6967168 [Patent Document 5] International Publication No. 2011 / 136000 [Patent Document 6] Japanese Patent Publication No. 2017-214469 [Patent Document 7] Japanese Patent Publication No. 2012-021120 [Overview of the project] [Problems that the invention aims to solve]

[0005] The polymeric dispersants used in dispersions proposed in Patent Documents 1 to 7 suppress pigment aggregation and sedimentation by having hydrophobic segments adsorbed onto the pigment surface and hydrophilic segments dissolved in the aqueous medium. Therefore, the dispersion effect of pigments in the aqueous medium varies depending on the monomer composition of the polymeric dispersant and the ratio of hydrophilic to hydrophobic segments. Furthermore, the hydrophobic segments of the polymeric dispersant may shrink or form micelles in the aqueous medium and not be exposed. Therefore, depending on the composition of the aqueous medium, the hydrophobic segments may not adsorb easily onto the pigment surface, making it difficult to improve the dispersibility of the pigment.

[0006] Prior to manufacturing aqueous pigment dispersions with excellent dispersibility and suppressed pigment aggregation and sedimentation, it is difficult to directly observe and quantify the behavior of polymer dispersants in aqueous media. Therefore, evaluating the performance of polymer dispersants requires a series of tests and verifications, from pigment dispersion to print evaluation. However, conducting a series of tests and verifications for all of the numerous polymer dispersants manufactured experimentally is extremely time-consuming and has been a factor in reducing development efficiency.

[0007] The present invention has been made in view of the problems of the prior art, and its objective is to provide an evaluation method for aqueous pigment dispersions that is useful when producing aqueous pigment dispersions with excellent dispersibility, storage stability, and redispersibility of organic pigments, and that can predict and evaluate suitable combinations of polymer dispersants and water-soluble organic solvents that result in good dispersibility of organic pigments. Furthermore, the objective of the present invention is to provide a method for producing aqueous pigment dispersions that are capable of producing aqueous pigment dispersions with excellent dispersibility, storage stability, and redispersibility of organic pigments. [Means for solving the problem]

[0008] In other words, the present invention provides a method for evaluating aqueous pigment dispersions as shown below. [1] A method for evaluating an aqueous pigment dispersion containing an organic pigment, a polymer dispersant, a water-soluble organic solvent, and water, comprising: a step of obtaining a mixture a containing the polymer dispersant, the water-soluble organic solvent, and water, but not containing the organic pigment; a step of obtaining a mixture b containing the water-soluble organic solvent and water, but not containing the organic pigment and the polymer dispersant; and a step of determining the T2 relaxation time (T2) of mixture a by pulsed NMR. a ) and the T2 relaxation time of the mixture b (T2 b The steps include measuring the Rsp value using the following formula (1), obtaining a mixture o containing the polymer dispersant and water, wherein the concentration of the polymer dispersant is the same as the concentration of the polymer dispersant in mixture a, and determining the T2 relaxation time (T2) of mixture o by pulsed NMR. o ) and the T2 relaxation time of the water (T2 w ) is measured, and Rsp is calculated using the following formula (2) o The process of obtaining a value, and the Rsp o A method for evaluating an aqueous pigment dispersion, comprising the steps of: calculating the rate of decrease (%) of the Rsp value based on a value; and evaluating the dispersibility of the organic pigment in the aqueous pigment dispersion based on the magnitude of the calculated rate of decrease. Rsp=(R a / R b )-1 ···(1) (In formula (1) above, Ra is T2 a represents the reciprocal of, and R b is T2 b represents the reciprocal of) Rsp o =(R o / R w ) - 1 ···(2) (In the above formula (2), R o represents the reciprocal of T2 o and R w represents the reciprocal of T2 w ) [2] The method for evaluating an aqueous pigment dispersion according to [1], wherein the composition of the mixture a is equivalent to the raw material mixture used for the dispersion treatment of the organic pigment except that it does not contain the organic pigment, and the composition of the mixture b is equivalent to the raw material mixture except that it does not contain the organic pigment component and the polymer dispersant. [3] The method for evaluating an aqueous pigment dispersion according to [1] or [2], wherein the polymer dispersant after acid precipitation, the water, and a neutralizing agent are mixed to dissolve the polymer dispersant, and then diluted with water to obtain the mixture o. [4] The method for evaluating an aqueous pigment dispersion according to any one of [1] to [3], wherein the polymer dispersant is a block copolymer having a hydrophobic segment and a hydrophilic segment derived from a methacrylate monomer containing methacrylic acid. [5] The method for evaluating an aqueous pigment dispersion according to any one of [1] to [3], wherein the content of the polymer dispersant in the aqueous pigment dispersion is 5 to 50 parts by mass with respect to 100 parts by mass of the organic pigment. [6] The method for evaluating an aqueous pigment dispersion according to [4], wherein the content of the polymer dispersant in the aqueous pigment dispersion is 5 to 50 parts by mass with respect to 100 parts by mass of the organic pigment.

[0009] Further, according to the present invention, there is provided a method for producing an aqueous pigment dispersion shown below. [7] A method for producing an aqueous pigment dispersion containing an organic pigment, a polymer dispersant, a water-soluble organic solvent, and water, comprising the steps of: obtaining a plurality of mixtures a containing the polymer dispersant, the water-soluble organic solvent, and water, but not containing the organic pigment, wherein at least one of the polymer dispersant and the water-soluble organic solvent is different; obtaining a plurality of mixtures b containing the water-soluble organic solvent and water, but not containing the organic pigment and the polymer dispersant, wherein the water-soluble organic solvent is different in type; and determining the T2 relaxation time (T2) of the plurality of mixtures a by pulsed NMR. a ) and the T2 relaxation time of the multiple mixtures b (T2 b The steps include measuring the Rsp value using the following formula (1), obtaining a plurality of mixtures o containing the polymer dispersant and water, wherein the concentration of the polymer dispersant is the same as the concentration of the polymer dispersant in the plurality of mixtures a, and the different types of polymer dispersants, and determining the T2 relaxation time (T2) of the plurality of mixtures o by pulsed NMR. o ) and the T2 relaxation time of the water (T2 w ) is measured, and Rsp is calculated using the following formula (2) o The process of obtaining a value, and the Rsp o A method for producing an aqueous pigment dispersion, comprising the steps of: calculating the rate of decrease (%) of the Rsp value based on a value, and selecting the mixture a such that the calculated rate of decrease is 20% or more; and dispersing the organic pigment in a raw material mixture obtained by mixing the polymer dispersant and the water-soluble organic solvent contained in the selected mixture a, the organic pigment and the water. Rsp=(R a / R b )-1 ···(1) (In formula (1) above, R a is T2 a It represents the reciprocal of R b is T2 b (Represents the reciprocal of) Rsp o =(R o / R w )-1 ···(2) (In the above formula (2), R o is T2 o It represents the reciprocal of R w is T2w (Represents the reciprocal of) [8] A method for producing an aqueous pigment dispersion according to [7], wherein the composition of mixture a is the same as that of the raw material mixture except that it does not contain the organic pigment, and the composition of mixture b is the same as that of the raw material mixture except that it does not contain the organic pigment component and the polymer dispersant. [9] A method for producing an aqueous pigment dispersion according to [7] or [8], comprising mixing the acid-deposited polymer dispersant, water, and neutralizing agent to dissolve the polymer dispersant, and then diluting it with water to obtain the mixture o.

[10] A method for producing an aqueous pigment dispersion according to any one of [7] to [9], wherein the polymer dispersant is a block copolymer having a hydrophobic segment and a hydrophilic segment derived from a metacrate monomer containing methacrylic acid.

[11] A method for producing an aqueous pigment dispersion according to any one of [7] to [9], wherein the content of the polymer dispersant in the aqueous pigment dispersion is 5 to 50 parts by mass per 100 parts by mass of the organic pigment.

[12] The method for producing the aqueous pigment dispersion according to

[10] , wherein the content of the polymer dispersant in the aqueous pigment dispersion is 5 to 50 parts by mass per 100 parts by mass of the organic pigment. [Effects of the Invention]

[0010] According to the present invention, it is possible to predict and evaluate suitable combinations of polymer dispersants and water-soluble organic solvents that result in good dispersibility of organic pigments, and to provide a method for evaluating aqueous pigment dispersions that are useful when producing aqueous pigment dispersions with excellent dispersibility, storage stability, and redispersibility of organic pigments. Furthermore, according to the present invention, it is possible to provide a method for producing aqueous pigment dispersions that are capable of producing aqueous pigment dispersions with excellent dispersibility, storage stability, and redispersibility of organic pigments. [Brief explanation of the drawing]

[0011] [Figure 1] This graph plots the "average particle size (nm)" against the "percentage decrease in Rsp value (%)" for the aqueous pigment dispersions prepared in Examples 1 and 2, and Comparative Examples 1 to 3. [Figure 2] This graph plots the "average particle size (nm)" against the "percentage decrease in Rsp value (%)" for the aqueous pigment dispersions prepared in Examples 3-7 and Comparative Example 2. [Modes for carrying out the invention]

[0012] <Evaluation Method and Manufacturing Method of Aqueous Pigment Dispersion> The embodiments of the present invention will be described below, but the present invention is not limited to the embodiments described below. One embodiment of the method for evaluating an aqueous pigment dispersion of the present invention is a method for evaluating an aqueous pigment dispersion containing an organic pigment, a polymer dispersant, a water-soluble organic solvent, and water. The evaluation method of this embodiment is a step of obtaining a mixture a containing a polymer dispersant, a water-soluble organic solvent, and water, but not containing an organic pigment; a step of obtaining a mixture b containing a water-soluble organic solvent and water, but not containing an organic pigment or a polymer dispersant; and a step of determining the T2 relaxation time (T2) of mixture a by pulsed NMR. a ) and the T2 relaxation time of mixture b (T2 b The steps include measuring the Rsp value using the following formula (1), obtaining a mixture o containing a polymer dispersant and water, wherein the concentration of the polymer dispersant is the same as the concentration of the polymer dispersant in mixture a, and determining the T2 relaxation time (T2) of mixture o by pulsed NMR. o ) and the T2 relaxation time of water (T2 w ) is measured, and Rsp is calculated using the following formula (2) o The process of obtaining the value, and Rsp o The process includes a step of calculating the percentage decrease in the Rsp value based on a given value, and evaluating the dispersibility of the organic pigment in the aqueous pigment dispersion based on the magnitude of the calculated percentage decrease.

[0013] Rsp=(R a / R b )-1 ···(1) (In formula (1) above, R a is T2 a It represents the reciprocal of R b is T2 b (Represents the reciprocal of) Rsp o =(Ro / R w )-1 ···(2) (In the above formula (2), R o is T2 o It represents the reciprocal of R w is T2 w (Represents the reciprocal of)

[0014] Furthermore, one embodiment of the method for producing an aqueous pigment dispersion of the present invention is a method for producing an aqueous pigment dispersion containing an organic pigment, a polymeric dispersant, a water-soluble organic solvent, and water. The production method of this embodiment is a step of obtaining a plurality of mixtures a that contain a polymeric dispersant, a water-soluble organic solvent, and water, but do not contain an organic pigment, and in which at least one of the polymeric dispersant and the water-soluble organic solvent is different; a step of obtaining a plurality of mixtures b that contain a water-soluble organic solvent and water, but do not contain an organic pigment and a polymeric dispersant, and in which the type of water-soluble organic solvent is different; and a pulse NMR is used to determine the T2 relaxation time (T2 a ) and the T2 relaxation time of multiple mixtures b (T2 b The steps include measuring the Rsp value using the following formula (1), obtaining multiple mixtures o containing a polymer dispersant and water, wherein the concentration of the polymer dispersant is the same as the concentration of the polymer dispersant in multiple mixtures a, and the different types of polymer dispersants, and determining the T2 relaxation time (T2) of the multiple mixtures o by pulsed NMR. o ) and the T2 relaxation time of water (T2 w ) is measured, and Rsp is calculated using the following formula (2) o The process of obtaining the value, and Rsp o The process includes the steps of: calculating the percentage decrease in the Rsp value based on a given value and selecting a mixture a such that the calculated decrease is 20% or more; and dispersing the organic pigment in a raw material mixture obtained by mixing the polymer dispersant and water-soluble organic solvent contained in the selected mixture a, along with the organic pigment and water.

[0015] Rsp=(R a / R b )-1 ···(1) (In formula (1) above, R a is T2 a It represents the reciprocal of R b is T2 b(Represents the reciprocal of) Rsp o =(R o / R w )-1 ···(2) (In the above formula (2), R o is T2 o It represents the reciprocal of R w is T2 w (Represents the reciprocal of)

[0016] Pulse NMR (Pulse Nuclear Magnetic Resonance) measurement allows for the evaluation of molecular mobility by measuring the relaxation time of nuclear magnetic resonance. In aqueous pigment dispersions containing a polymeric dispersant and an aqueous medium (a mixed solvent of water-soluble organic solvent and water), the relaxation time of protons constrained by the polymeric dispersant is shorter than the relaxation time of protons freely present in the aqueous medium. This is thought to be because the molecules of the aqueous medium are constrained by the hydrophilic segment constituting the polymeric dispersant, reducing the mobility of the protons. On the other hand, the hydrophobic segment constituting the polymeric dispersant has a weaker ability to constrain protons compared to the hydrophilic segment. In other words, the amount of protons constrained by the polymeric dispersant differs depending on the monomer composition of the polymeric dispersant, the ratio of hydrophilic to hydrophobic segments, and the solubility in the aqueous medium.

[0017] In the evaluation and manufacturing methods of this embodiment, the degree of water affinity of the polymer dispersant in an aqueous medium, which is a mixed solvent of water and a water-soluble organic solvent, is quantified by the T2 relaxation time measured by pulsed NMR, and the properties of the polymer dispersant in the aqueous medium, such as solubility and molecular mobility, are understood. This makes it possible to predict and evaluate suitable combinations of polymer dispersants and water-soluble organic solvents that result in good dispersibility of organic pigments, and to produce aqueous pigment dispersions with excellent dispersibility, storage stability, and redispersibility of organic pigments.

[0018] In this embodiment, a mixture a containing a polymer dispersant, a water-soluble organic solvent, and water and not containing an organic pigment, and a mixture b containing a water-soluble organic solvent and water and not containing an organic pigment and a polymer dispersant are prepared. Then, the T2 relaxation time (T2 a ) of the mixture a and the T2 relaxation time (T2 b ) of the mixture b are measured by pulsed NMR, and the Rsp value is obtained by the following formula (1).

[0019] Rsp = (R a / R b ) - 1 ···(1) (In the above formula (1), R a represents the reciprocal of T2 a , and R b represents the reciprocal of T2 b )

[0020] The Rsp value calculated by the formula (1) is a physical property value that serves as an index of the degree of hydrophilicity of the polymer dispersant. It is preferable to prepare a plurality of mixtures a in which at least one of the types of the polymer dispersant and the water-soluble organic solvent is different, and a plurality of mixtures b in which the types of the water-soluble organic solvent are different, and obtain the Rsp value for a plurality of combinations of the mixture a and the mixture b.

[0021] Also, in this embodiment, a mixture o containing a polymer dispersant and water and having a concentration of the polymer dispersant substantially the same as the concentration of the polymer dispersant in the mixture a is prepared. Then, the T2 relaxation time (T2 o ) of the mixture o and the T2 relaxation time (T2 w ) of water are measured by pulsed NMR, and the Rsp o value is obtained by the following formula (2). The mixture o is preferably prepared by mixing an acid-precipitated polymer dispersant, water, and a neutralizing agent to dissolve the polymer dispersant and then diluting with water.

[0022] Rsp o = (R o / R w ) - 1 ···(2) (In the above formula (2), R o is T2 orepresents the reciprocal of, and R w is T2 w represents the reciprocal of)

[0023] The Rsp calculated by Equation (2) o value is a physical property value that serves as an indicator of the degree of hydrophilicity of the polymer dispersant, similar to the Rsp value calculated by Equation (1). Note that a plurality of mixtures o of different types of polymer dispersants are prepared, and it is preferable to obtain the Rsp o value for a plurality of combinations of mixture o and water.

[0024] Examples of the pulse sequence for measuring pulsed NMR include the Hahn echo method, the solid echo method, the CPMG method, and the saturation recovery method. Since an aqueous sample containing a plurality of components is the measurement target, it is preferable to apply the CPMG method. An example of the measurement conditions for pulsed NMR is shown below. · Measuring device: Product name "TD-NMR Spectrometer Spin Track", manufactured by Resonance Systems, Observation nucleus = 1 H · Pulse sequence: CPMG (Carr-Purcell-Meiboom-Gill) method · Measurement temperature: 30 °C · Amount of sample: ≤ 2.0 mL

[0025] From the obtained Rsp value and Rsp o value, Rsp oThe percentage decrease in the Rsp value is calculated based on the value. Based on the magnitude of the Rsp value decrease percentage calculated in this way, the dispersibility of the organic pigment in the aqueous pigment dispersion can be evaluated. In the manufacturing method of this embodiment, a mixture a is selected in which the Rsp value decrease percentage is 20% or more, preferably 30% or more, and more preferably 40% or more. The polymer dispersant and water-soluble organic solvent contained in the selected mixture a, along with the organic pigment and water, are mixed to prepare a raw material mixture such as a mill base. The prepared raw material mixture such as a mill base is subjected to a dispersion treatment, and the organic pigment is dispersed in the raw material mixture to obtain the desired aqueous pigment dispersion. The raw material mixture after dispersion treatment may be used as is as the aqueous pigment dispersion, or it may be diluted with a liquid medium such as water as needed, or coarse particles may be filtered out to remove them before being used as the aqueous pigment dispersion.

[0026] The composition of mixture a is preferably equivalent to that of a raw material mixture such as mill base, except that it does not contain organic pigments, and more preferably substantially identical. Similarly, the composition of mixture b is preferably equivalent to that of a raw material mixture such as mill base, except that it does not contain organic pigment components and polymer dispersants, and more preferably substantially identical. When the composition of mixture a is "equivalent" to that of the raw material mixture except that it does not contain organic pigments, it means that the composition of mixture a is the same as that of the raw material mixture in which the organic pigment is replaced with the same amount of water. Likewise, when the composition of mixture b is "equivalent" to that of the raw material mixture except that it does not contain organic pigments and polymer dispersants, it means that the composition of mixture b is the same as that of the raw material mixture in which the organic pigment and polymer dispersant are replaced with the same amount of water.

[0027] Mixtures a, b, and o may each further contain other additives. Examples of other additives include alkalis used for neutralizing polymer dispersants or adjusting pH. Examples of alkalis include ammonia, dimethylaminoethanol, sodium hydroxide, lithium hydroxide, and potassium hydroxide. The alkali content in the mixture is preferably 0.5 to 5% by mass.

[0028] As organic pigments, you can use organic pigments commonly used in inkjet inks, such as CI Pigment Blue 15:3, 15:4, 15:6; CI Pigment Red 122, 176, 254, 269, 291; CI Pigment Violet 19, 23; CI Pigment Yellow 74, 155, 180; CI Pigment Green 36, 58; CI Pigment Orange 43, 71; CI Pigment Black 7; and CI Pigment White 6.

[0029] The average particle size (primary particle size) of the organic pigment is preferably 250 nm or less, and more preferably 150 nm or less. By using an organic pigment with an average particle size within the above range, the optical density, saturation, and color development characteristics of the recorded image can be improved, as can the ink ejection stability and print quality, and the sedimentation of the organic pigment in the ink can be appropriately suppressed. The average particle size of the organic pigment is measured using an electron microscope or a particle size analyzer with a dynamic light scattering method, etc., as the median diameter (D 50 )

[0030] The pigment content in the aqueous pigment dispersion is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass. If the pigment content is less than 5% by mass, it may be difficult to add additives during ink preparation. On the other hand, if the pigment content exceeds 30% by mass, the free movement of pigment particles may be hindered, and aggregation may occur.

[0031] As a polymer molecular dispersant, it is preferable to use a block copolymer having a hydrophobic segment and a hydrophilic segment derived from a methcrate monomer containing methacrylic acid. The hydrophobic segment is a polymer block insoluble in aqueous media. Examples of components (monomers) constituting the hydrophobic segment include vinyl monomers; aliphatic, alicyclic, and aromatic alkyl (meth)acrylates; monomers having hydroxyl groups or amino groups; and the like.

[0032] The hydrophilic segment is a hydrophilic polymer block containing constituent units derived from monomers having acidic groups. Examples of monomers having acidic groups include monomers having carboxyl groups, sulfonic acid groups, and phosphate groups. Examples of monomers having carboxyl groups include acrylic acid, acrylic acid dimers, methacrylic acid, maleic acid, itaconic acid, fumaric acid, and crotonic acid. Furthermore, monomers obtained by reacting hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate with maleic anhydride, succinic anhydride, and phthalic anhydride can also be used.

[0033] Examples of monomers having a sulfonic acid group include styrene sulfonic acid, dimethylpropyl sulfonic acid (meth)acrylamide, sulfonic acid ether (meth)acrylate, sulfonic acid ether (meth)acrylamide, and vinyl sulfonic acid. Examples of monomers having a phosphate group include methacryloyloxyethyl phosphate ester.

[0034] If the amount of polymeric dispersant is too small, it may not be able to coat and encapsulate the organic pigment, making it difficult to improve dispersibility. On the other hand, if the amount of polymeric dispersant is too large, the viscosity of the raw material mixture to be dispersed may become too high, which can easily reduce the efficiency of the dispersion process. For this reason, the amount of polymeric dispersant in the aqueous pigment dispersion is preferably 5 to 50 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of organic pigment.

[0035] Water-soluble organic solvents include alcoholic solvents such as methanol, ethanol, isopropanol, propyl alcohol, butanol, and isobutanol; glycol solvents such as ethylene glycol, propylene glycol, and glycerin; diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, and tripropylene Examples include glycol ethers such as ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol butyl methyl ether, dipropylene glycol dimethyl ether, and 3-methoxy-3-methyl-1-butanol; amide solvents such as dimethylformamide, dimethylacetamide, pyrrolidone, N-methylpyrrolidone, 3-methoxy-N,N-dimethylpropanamide, and 3-butoxy-N,N-dimethylpropanamide; carbonate solvents such as ethylene carbonate, propylene carbonate, and dimethyl carbonate; dimethyl sulfoxide; tetramethylurea; dimethylimidazolidinone; and the like.

[0036] Water-soluble organic solvents play a role in accelerating the dispersion process by wetting the surface of the dry organic pigment, replacing the air layer on the surface with an aqueous medium, and dissolving the polymer dispersant. However, if the amount of water-soluble organic solvent is too large, the viscosity of the aqueous pigment dispersion may become excessively high, which can reduce the drying properties of the resulting ink. For this reason, the content of water-soluble organic solvents in the aqueous pigment dispersion is preferably 5 to 80 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of organic pigment.

[0037] Conventional methods can be used to disperse raw material mixtures such as mill base. For example, organic pigments can be dispersed by processing the raw material mixture using a disperser. Examples of dispersers include kneaders such as kneaders, two-roll kneaders, three-roll kneaders, SS5 (product name, manufactured by M-Technique Co., Ltd.), and Miracle KCK (product name, manufactured by Asada Steel Co., Ltd.); high-speed stirrers; ultrasonic dispersers; high-pressure homogenizers; etc. Examples of high-speed stirrers include TK Homomix, TK Robomix, TK Filmix (all manufactured by Primix Co., Ltd.); Clearmix (manufactured by M-Technique Co., Ltd.); Ultra Disper (manufactured by Asada Steel Co., Ltd.); etc. Examples of high-pressure homogenizers include Microfluidizer (manufactured by Mizuho Industries Co., Ltd.), Nanomizer (manufactured by Yoshida Machinery Industry Co., Ltd.), Starburst (manufactured by Sugino Machine Co., Ltd.), G-Smasher (manufactured by Rix Co., Ltd.); etc. Furthermore, ball mills, sand mills, horizontal media mill dispersers, and colloid mills using bead media such as glass or zircon can be used. For the media used in the bead mill, bead media with a diameter of 1 mm or less are preferred, and bead media with a diameter of 0.5 mm or less are even more preferred.

[0038] The mixture of raw materials such as mill base obtained by dispersion treatment may be used as is as an aqueous pigment dispersion, or coarse particles may be removed as necessary. To remove coarse particles, a centrifuge, ultracentrifuge, and filter can be used.

[0039] The aqueous pigment dispersion may further contain, as needed, additives other than the aforementioned water-soluble organic solvents, such as leveling agents, surface tension modifiers, pH adjusters, UV absorbers, light stabilizers, antioxidants, dyes, fillers, waxes, thickeners, defoamers, fungicides, preservatives, and antistatic agents.

[0040] Examples of preservatives include sodium benzoate, benzimidazole, thiabendazole, potassium sorbitanate, sodium sorbitanate, sodium dehydroacetate, thiazosulfamide, and pyridinethiol oxide. The preservative content in the aqueous pigment dispersant is preferably 0.05 to 2.0% by mass, and more preferably 0.1 to 1.0% by mass. [Examples]

[0041] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0042] <Synthesis of polymer dispersants> (Polymer dispersant D-1) 300 parts of diethylene glycol monobutyl ether (DEGMBE), 3 parts of 2-iod-2-cyanopropane (CP-1), 52 parts of benzyl methacrylate (BzMA), 60 parts of methacrylic acid (MAA), 2.5 parts of azobisisobutyronitrile (AIBN), and 0.1 part of iodosuccinimide (NIS) were placed in a reaction vessel and stirred while flowing nitrogen. Polymerization was carried out at 40°C for 3 hours to form hydrophilic segments, namely BzMA / MAA polymer blocks. The number-average molecular weight (Mn) of a sample of the polymerization solution, measured by gel permeation chromatography (GPC), was 3,500, indicating a polymerization rate of approximately 100%.

[0043] A mixture of 35 parts cyclohexyl methacrylate (CHMA), 70 parts BzMA, 20 parts methyl methacrylate (MMA), and 0.2 parts AIBN was added to the polymerization solution. Polymerization was carried out at 40°C for 3 hours to form a hydrophobic segment, the CHMA / BzMA / MMA polymer block, and obtained the polymeric dispersant D-1, which is an AB block copolymer. The obtained polymeric dispersant D-1 had a manganese content of 7,500 and an acid value of 146 mg KOH / g. After adding an amount of lithium hydroxide aqueous solution to neutralize the carboxyl groups, acetic acid was added dropwise while stirring. After washing the precipitate with pure water, pure water and lithium hydroxide aqueous solution were added to obtain a light brown, transparent aqueous solution of polymeric dispersant D-1. The obtained aqueous solution had a solid content of 40% and a pH of 9.3.

[0044] (Polymer dispersants D-2~5) Aqueous solutions of polymer dispersants D-2 to D-5 were obtained in the same manner as described above for polymer dispersant D-1, except that the types and amounts of materials (monomers) shown in Table 1 were used. The solid content of all obtained aqueous solutions was 40%.

[0045] TIFF0007857893000001.tif70170

[0046] <Method for measuring pulsed NMR> According to the conditions shown below, pulsed NMR was used to determine the T2 relaxation time (T2) of mixture a, mixture b, mixture o, and water. a , T2 b , T2 o , and T2 w The following parameters were measured. The T2 relaxation time was measured three times, and the average value was used. The Rsp value was calculated using the following formula (1), and the Rsp value was calculated using the following formula (2). o Each value is calculated, and Rsp o Percentage decrease in Rsp value relative to the value (%) (={(Rsp o -Rsp) / Rsp o The result of (} × 100) was calculated. [Measurement conditions for pulsed NMR] • Measurement device: Product name "TD-NMR Spectrometer Spin Track", manufactured by Resonance Systems, observed nuclei = 1 H • Pulse sequence: CPMG (Carr-Purcell-Meiboom-Gill) method ·Measurement temperature: 30℃ • Sample volume: ≤2.0mL

[0047] Rsp=(R a / R b )-1 ···(1) (In formula (1) above, R a is T2 a It represents the reciprocal of R b is T2 b (Represents the reciprocal of) Rsp o =(R o / R w )-1 ···(2) (In the above formula (2), R o is T2 o It represents the reciprocal of R w is T2 w (Represents the reciprocal of)

[0048] <Manufacturing of aqueous pigment dispersion (1)> (Example 1) 212.5 parts of an aqueous solution of polymer dispersant D-1, 52.5 parts of triethylene glycol monobutyl ether (TEGMBE), and 140 parts of pure water were mixed. 150 parts of pure water were added and mixed to obtain mixture a. 2 mL of the obtained mixture a was sampled, and the pulsed NMR was measured to determine the T2 relaxation time (T2 a The value of ) was obtained. In addition, 52.5 parts of TEGMBE and 502.5 parts of pure water were mixed to obtain mixture b. 2 mL of the obtained mixture b was sampled and pulsed NMR was measured to obtain the T2 relaxation time (T2 b The value of ) was obtained. Then, the Rsp value was calculated from equation (1). Furthermore, 212.5 parts of an aqueous solution of polymer dispersant D-1 and 342.5 parts of pure water were mixed to obtain mixture o. 2 mL of the obtained mixture o and 2 mL of pure water were sampled, and pulsed NMR was measured for each to obtain the T2 relaxation time (T2 o and Tw The value of ) was obtained from equation (2). Then, from equation (2), Rsp o The value is calculated, and the calculated Rsp value and Rsp o The "percentage decrease in Rsp value (%)" was calculated from the values. The results are shown in Table 2.

[0049] 212.5 parts of an aqueous solution of polymer dispersant D-1, 52.5 parts of TEGMBE, and 140 parts of pure water were mixed. 150 parts of copper phthalocyanine pigment (PB-15:3, trade name "Cyanine Blue A220JC", manufactured by Dainichi Seika Kogyo Co., Ltd.) were added, and the mixture was stirred for 30 minutes using a disperser to prepare a mill base. The pigment was thoroughly dispersed in the mill base using a horizontal media disperser (trade name "Dinomill 0.6 liter ECM type", manufactured by Shinmaru Enterprises, zirconia bead diameter: 0.3 mm). After diluting with pure water until the pigment concentration reached 14%, the mixture was filtered through a pore size 5 μm membrane filter to obtain an aqueous pigment dispersion S1 (cyan) for inkjet printing. The average particle size (median diameter; D) of the pigment in the dispersion was measured using a particle size analyzer (trade name "NICOMP 380ZLS-S", manufactured by International Business Co., Ltd.) 50 Table 2 shows the values ​​(nm).

[0050] (Example 2, Comparative Examples 1-3) Aqueous pigment dispersions S2-5 (cyan) for inkjet printing were obtained in the same manner as in Example 1 described above, except that the types of polymer dispersants (aqueous solutions thereof) shown in Table 2 were used. o Table 2 shows the percentage decrease in Rsp value and the average particle size (nm) of the pigment in the dispersion. Figure 1 shows a graph plotting the "average particle size (nm)" against the "percentage decrease in Rsp value (%)".

[0051] <Rating (1)> (Storage stability) The prepared aqueous pigment dispersion was stored at 70°C for one week. The average particle size, pH value, and viscosity of the pigment in the aqueous pigment dispersion were measured before and after storage, and the percentage change (%) of these values ​​was calculated. The storage stability of the aqueous pigment dispersion was evaluated according to the evaluation criteria shown below. The results are shown in Table 2. ○: The average particle size, pH value, and viscosity change rate were all 5.0% or less. ×: The rate of change of at least one of the average particle size, pH value, and viscosity was 5.0% or higher.

[0052] (Redispersibility) A 3.5% pigment concentration sample was prepared by diluting an aqueous pigment dispersion with pure water. One drop of the prepared sample was placed on a concave microscope slide using a pipette. The slide containing the sample was placed in a constant temperature and humidity chamber (product name "Low Temperature Constant Temperature and Humidity Chamber PL-3J", manufactured by ESPEC Corporation) and heated at 60°C for 10 hours to dry the sample. After adding pure water to the dried residue on the slide, the dispersion was observed under a microscope, and the redispersibility of the aqueous pigment dispersion was evaluated according to the evaluation criteria shown below. The results are shown in Table 2. ○: Visually confirmed to be completely redistributed. △: Some redispersion occurred, but visible residue remained. If there was little residue and it was almost completely dispersed, it was rated "○△". On the other hand, if there was a lot of residue and it was closer to a loosened state than dispersed, it was rated "△×". ×: Did not redistribute.

[0053] TIFF0007857893000002.tif61170

[0054] <Manufacturing of aqueous pigment dispersion (2)> (Example 3) 212.5 parts of an aqueous solution of polymer dispersant D-4, 52.5 parts of DEGMBE, and 140 parts of pure water were mixed. 150 parts of pure water were added and mixed to obtain mixture a. 2 mL of the obtained mixture a was sampled, and the pulsed NMR was measured to determine the T2 relaxation time (T2 a The value of ) was obtained. In addition, 52.5 parts of DEGMBE and 502.5 parts of pure water were mixed to obtain mixture b. 2 mL of the obtained mixture b was sampled and pulsed NMR was measured to obtain the T2 relaxation time (T2 bThe value of ) was obtained. Then, the Rsp value was calculated from equation (1). Furthermore, 212.5 parts of an aqueous solution of polymer dispersant D-4 and 342.5 parts of pure water were mixed to obtain mixture o. 2 mL of the obtained mixture o and 2 mL of pure water were sampled, and pulsed NMR was measured for each to obtain the T2 relaxation time (T2 o and T w The value of ) was obtained from equation (2). Then, from equation (2), Rsp o The value is calculated, and the calculated Rsp value and Rsp o The "percentage decrease in Rsp value (%)" was calculated from the values. The results are shown in Table 3.

[0055] 212.5 parts of an aqueous solution of polymer dispersant D-4, 52.5 parts of DEGMBE, and 140 parts of pure water were mixed. 150 parts of copper phthalocyanine pigment (PB-15:3, trade name "Cyanine Blue A220JC", manufactured by Dainichi Seika Kogyo Co., Ltd.) were added, and the mixture was stirred for 30 minutes using a disperser to prepare a mill base. The pigment was thoroughly dispersed in the mill base using a horizontal media disperser (trade name "Dinomill 0.6 liter ECM type", manufactured by Shinmaru Enterprises, zirconia bead diameter: 0.3 mm). After diluting with pure water until the pigment concentration reached 14%, the mixture was filtered through a pore size 5 μm membrane filter to obtain an aqueous pigment dispersion S6 (cyan) for inkjet printing. The average particle size (median diameter; D) of the pigment in the dispersion was measured using a particle size analyzer (trade name "NICOMP 380ZLS-S", manufactured by International Business Co., Ltd.) 50 Table 3 shows the values ​​(nm).

[0056] (Examples 4-7) Aqueous pigment dispersions S7-10 (cyan) for inkjet printing were obtained in the same manner as in Example 3 described above, except that the types and amounts of water-soluble organic solvents shown in Table 3 were used. The percentage decrease in Rsp value and the average particle size of the pigment in the dispersion (nm) are shown in Table 3. Figure 2 shows a graph plotting the "average particle size (nm)" against the "percentage decrease in Rsp value (%)". The meanings of the abbreviations in Table 3 are as follows. BEG: Ethylene glycol monobutyl ether • PFG: Propylene glycol monopropyl ether BDM: Diethylene glycol butyl methyl ether IPA: Isopropylene glycol • MFG: Propylene glycol monomethyl ether

[0057] (Comparative Examples 4 and 5) We attempted to prepare aqueous pigment dispersions S11 and S12 for inkjet printing in the same manner as in Example 3 described above, except that we used the types and amounts of water-soluble organic solvents shown in Table 3. However, due to poor dispersion, we were unable to obtain the desired dispersions.

[0058] (Comparative Example 6) An attempt was made to prepare an aqueous pigment dispersion S13 for inkjet printing in the same manner as in Example 3 described above, except that a water-soluble organic solvent was not used. However, due to poor dispersion, the desired dispersion could not be obtained.

[0059] <Rating (2)> The storage stability and redispersibility of the prepared aqueous pigment dispersion were evaluated using the same method as described in "Evaluation (1)" above. The results are shown in Table 3.

[0060] TIFF0007857893000003.tif86170 [Industrial applicability]

[0061] The evaluation method of the present invention is useful as a method for predicting and evaluating suitable combinations of polymer dispersants and water-soluble organic solvents that result in good dispersibility of organic pigments when producing aqueous pigment dispersions with excellent dispersibility, storage stability, and redispersibility of organic pigments.

Claims

1. A method for evaluating an aqueous pigment dispersion containing an organic pigment, a polymer dispersant, a water-soluble organic solvent, and water, A step of obtaining a mixture a containing the polymer dispersant, the water-soluble organic solvent, and the water, but not containing the organic pigment, A step of obtaining a mixture b containing the water-soluble organic solvent and the water, and not containing the organic pigment and the polymer dispersant, Pulse NMR determines the T2 relaxation time (T2) of the mixture a. ａ ) and the T2 relaxation time of the mixture b (T2 ｂ The process involves measuring ) and obtaining the Rsp value using the following formula (1), A step of obtaining a mixture o containing the polymer dispersant and water, wherein the concentration of the polymer dispersant is the same as the concentration of the polymer dispersant in the mixture a, Pulse NMR determines the T2 relaxation time (T2) of the mixture o. ｏ ) and the T2 relaxation time of the water (T2 ｗ ) is measured, and Rsp is calculated using the following formula (2) ｏ The process of obtaining a value, The Rsp ｏ A step of calculating the percentage decrease of the Rsp value based on the value, and evaluating the dispersibility of the organic pigment in the aqueous pigment dispersion based on the magnitude of the calculated percentage decrease, A method for evaluating an aqueous pigment dispersion containing [specific properties]. Rsp=(R ａ / R ｂ )-1 ・・・(1) (In the above formula (1), R ａ represents the reciprocal of T2 ａ and R ｂ represents the reciprocal of T2 ｂ ) Rsp ｏ =(R ｏ / R ｗ )-1 ・・・(2) (In formula (2) above, R ｏ is T2 ｏ It represents the reciprocal of R ｗ is T2 ｗ (Represents the reciprocal of)

2. The composition of mixture a is equivalent to that of the raw material mixture used for the dispersion treatment of the organic pigment, except that it does not contain the organic pigment. The method for evaluating an aqueous pigment dispersion according to claim 1, wherein the composition of mixture b is the same as that of the raw material mixture except that it does not contain the organic pigment component and the polymer dispersant.

3. A method for evaluating an aqueous pigment dispersion according to claim 1, wherein the acid-deposited polymer dispersant, water, and neutralizing agent are mixed to dissolve the polymer dispersant, and then diluted with water to obtain the mixture o.

4. A method for evaluating an aqueous pigment dispersion according to any one of claims 1 to 3, wherein the polymer dispersant is a block copolymer having a hydrophobic segment and a hydrophilic segment derived from a metacrate monomer containing methacrylic acid.

5. A method for evaluating an aqueous pigment dispersion according to any one of claims 1 to 3, wherein the content of the polymer dispersant in the aqueous pigment dispersion is 5 to 50 parts by mass per 100 parts by mass of the organic pigment.

6. The method for evaluating an aqueous pigment dispersion according to claim 4, wherein the content of the polymer dispersant in the aqueous pigment dispersion is 5 to 50 parts by mass per 100 parts by mass of the organic pigment.

7. A method for producing an aqueous pigment dispersion containing an organic pigment, a polymer dispersant, a water-soluble organic solvent, and water, A step of obtaining a plurality of mixtures a that contain the polymer dispersant, the water-soluble organic solvent, and water, but do not contain the organic pigment, wherein at least one of the polymer dispersant and the water-soluble organic solvent is different in type. A step of obtaining a plurality of mixtures b containing the water-soluble organic solvent and water, but not containing the organic pigment and the polymer dispersant, wherein the water-soluble organic solvents are of different types. Pulse NMR determines the T2 relaxation time (T2) of multiple mixtures a. ａ ) and the T2 relaxation time of the plurality of the mixture b (T2 ｂ The process involves measuring ) and obtaining the Rsp value using the following formula (1), A step of obtaining a plurality of mixtures o containing the polymer dispersant and water, wherein the concentration of the polymer dispersant is the same as the concentration of the polymer dispersant in a plurality of mixtures a, and the polymer dispersant is of a different type. Pulse NMR determines the T2 relaxation time (T2) of multiple mixtures o. ｏ ) and the T2 relaxation time of the water (T2 ｗ ) is measured, and Rsp is calculated using the following formula (2) ｏ The process of obtaining a value, The Rsp ｏ A step of calculating the percentage decrease of the Rsp value based on the value, and selecting the mixture a such that the calculated percentage decrease is 20% or more. A step of dispersing the organic pigment in a raw material mixture obtained by mixing the polymer dispersant and the water-soluble organic solvent contained in the selected mixture a, and the organic pigment and water, A method for producing an aqueous pigment dispersion having [the specified properties]. Rsp=(R ａ / R ｂ )-1 ・・・(1) (In formula (1) above, R ａ is T2 ａ It represents the reciprocal of R ｂ is T2 ｂ (Represents the reciprocal of) Rsp ｏ =(R ｏ / R ｗ )-1 ・・・(2) (In formula (2) above, R ｏ is T2 ｏ It represents the reciprocal of R ｗ is T2 ｗ (Represents the reciprocal of)

8. The composition of mixture a is the same as that of the raw material mixture, except that it does not contain the organic pigment. A method for producing an aqueous pigment dispersion according to claim 7, wherein the composition of mixture b is the same as that of the raw material mixture except that it does not contain the organic pigment component and the polymer dispersant.

9. A method for producing an aqueous pigment dispersion according to claim 7, wherein the acid-deposited polymer dispersant, water, and neutralizing agent are mixed to dissolve the polymer dispersant, and then diluted with water to obtain the mixture o.

10. A method for producing an aqueous pigment dispersion according to any one of claims 7 to 9, wherein the polymer dispersant is a block copolymer having a hydrophobic segment and a hydrophilic segment derived from a metacrate monomer containing methacrylic acid.

11. A method for producing an aqueous pigment dispersion according to any one of claims 7 to 9, wherein the amount of the polymer dispersant in the aqueous pigment dispersion is 5 to 50 parts by mass per 100 parts by mass of the organic pigment.

12. The method for producing an aqueous pigment dispersion according to claim 10, wherein the amount of the polymer dispersant in the aqueous pigment dispersion is 5 to 50 parts by mass per 100 parts by mass of the organic pigment.

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