Method for producing colloidal dispersion

Abstract

A method for producing a colloidal dispersion, comprising: a step of dropping a monomer mixture containing a carboxy group-containing ethylenically unsaturated monomer (a) into a reactive solvent (x) having one glycidyl group at a temperature of 50°C or higher and 180°C or lower to obtain a varnish containing a first resin (A); and a step of adding a basic compound to the varnish at a temperature of 70°C or higher and 98°C or lower to neutralize the carboxy groups remaining in the first resin (A), and then adding deionized water to perform phase inversion emulsification to obtain a colloidal dispersion containing particles of the neutralized first resin (A), wherein the solids concentration of the varnish is 85 mass% or higher, the weight average molecular weight of the first resin (A) contained in the varnish is 13,000 or higher and 80,000 or lower, and the average particle size of the particles of the neutralized first resin (A) is 20 nm or higher and 200 nm or lower.

Description

[Technical field]

[0001] The present invention relates to a method for producing a colloidal dispersion. [Background technology]

[0002] In recent years, environmental pollution has become serious, and organic solvent emission regulations have been strengthened internationally. In the field of paints, too, there has been a shift from conventional organic solvent-based paints to water-based paints using water as a medium. In particular, the conversion of paints for automobile painting to water-based paints is said to be highly effective in reducing organic solvents. Water-based paints are blended with water-based resins. As a method for converting resins to water-based paints, for example, emulsion polymerization using an emulsifier can be mentioned. Emulsion polymerization is simple and does not require organic solvents, so it is very effective in reducing the use of organic solvents. However, since this method uses water as a solvent, the raw material monomers that can be used are limited, and the degree of freedom in resin design is low. Furthermore, since an emulsifier is used in emulsion polymerization, the water resistance of the coating film using the obtained resin is easily reduced.

[0003] Therefore, a method has been proposed in which a resin is polymerized in an organic solvent and then the resin is made aqueous (indirect emulsification method).For example, in Patent Documents 1 and 2, after a resin is polymerized in an organic solvent (solution polymerization), the organic solvent is removed by distillation under reduced pressure, and then the resin is neutralized to obtain an emulsion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-199114 [Patent Document 2] JP 2018-2900 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, since an organic solvent is used during solution polymerization, there remains a problem in terms of reducing the use of the organic solvent.

[0006] An object of the present invention is to provide a method for producing a colloidal dispersion having excellent dispersion stability while reducing the use of organic solvents. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following aspects. [1] A step of dropping a monomer mixture containing a carboxyl group-containing ethylenically unsaturated monomer (a) into a reactive solvent (x) having one glycidyl group at a temperature of 50° C. or more and 180° C. or less to obtain a varnish containing a first resin (A); adding a basic compound to the varnish at a temperature of 70° C. or higher and 98° C. or lower to neutralize the carboxyl groups remaining in the first resin (A), and then adding deionized water to effect phase inversion emulsification to obtain a colloidal dispersion containing particles of the neutralized first resin (A); The solid content of the varnish is 85% by mass or more, The weight average molecular weight of the first resin (A) contained in the varnish is 13,000 or more and 80,000 or less, The method for producing a colloidal dispersion, wherein the average particle size of the particles of the neutralized first resin (A) is 20 nm or more and 200 nm or less. [2] The method for producing a colloidal dispersion according to [1] above, which does not include a step of removing an organic solvent. [3] The method for producing a colloidal dispersion according to the above [1] or [2], wherein the average particle size of the particles of the neutralized first resin (A) is 20 nm or more and 150 nm or less. [4] The method for producing a colloidal dispersion according to any one of the above [1] to [3], wherein the mass of the reactive solvent (x) used in the step of obtaining the varnish is 20 parts by mass or more and 60 parts by mass or less relative to 100 parts by mass of the varnish. [5] The reactive solvent (x) further has a hydrophobic group, The step of obtaining the varnish comprises: a first step of dropping a first monomer mixture containing a first carboxy group-containing ethylenically unsaturated monomer (a1) into the reactive solvent (x) at a temperature of 130° C. or higher and 180° C. or lower to synthesize a hydrophobic resin (A1) and obtain a liquid material containing the hydrophobic resin (A1); and a second step of dropping a second monomer mixture containing a second carboxy group-containing ethylenically unsaturated monomer (a2) into the liquid at a temperature of 70°C or higher and 180°C or lower to synthesize a carboxy group-containing resin (A2) and obtain the varnish containing the first resin (A) having the hydrophobic resin (A1) and the carboxy group-containing resin (A2). [6] The method for producing a colloidal dispersion according to the above [5], wherein the reactive solvent (x) has, as the hydrophobic group, a linear or branched alkyl group having 5 to 24 carbon atoms. [7] The step of obtaining the varnish comprises: a step of dropping the monomer mixture containing the carboxyl group-containing ethylenically unsaturated monomer (a) into the reactive solvent (x) at a temperature of 50° C. or higher and lower than 130° C. to polymerize the monomer mixture, thereby obtaining a precursor of the first resin (A); and raising the temperature to 130°C or higher and 180°C or lower to react the reactive solvent (x) with the precursor to obtain a varnish containing the first resin (A). [8] The method for producing a colloidal dispersion according to any one of the above [1] to [7], wherein the solubility parameter of the particles of the first resin (A) is 10.0 or more and 11.3 or less. Effect of the Invention

[0008] According to the present invention, there is provided a method for producing a colloidal dispersion having excellent dispersion stability while reducing the use of organic solvents. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The method for producing a colloidal dispersion according to the present disclosure includes the steps of: dropping a monomer mixture containing a carboxy group-containing ethylenically unsaturated monomer (a) into a reactive solvent (x) having one glycidyl group at a temperature of 50°C or higher and 180°C or lower to obtain a varnish containing a first resin (A); and adding a basic compound to the varnish at a temperature of 70°C or higher and 98°C or lower to neutralize the remaining carboxy groups in the first resin (A), and then adding deionized water to perform phase inversion emulsification to obtain a colloidal dispersion containing particles of the neutralized first resin (A).

[0010] In solution polymerization, the raw material monomer is usually dropped into a large amount of organic solvent to control (remove) the heat of polymerization reaction of the raw material monomer. The organic solvent is also an important component for ensuring that the polymerization reaction proceeds uniformly. On the other hand, the organic solvent is an unnecessary component for colloidal dispersions and water-based paints. Usually, a process is carried out to remove most of the organic solvent before preparing water-based paints.

[0011] By using the reactive solvent (x), it is possible to control the reaction heat and perform a uniform reaction while reducing the use of organic solvents, and as a result, it is possible to increase the solids concentration of the varnish.

[0012] Since the solid content of the varnish is 85% by mass or more, that is, the content of the organic solvent is less than 15% by mass, the colloidal dispersion can be produced without removing the organic solvent. That is, the process of removing the organic solvent can be omitted in the production of the colloidal dispersion, and the environmental load can be reduced. Furthermore, since the amount of the organic solvent used is small, the odor of the colloidal dispersion can also be reduced.

[0013] The solids concentration of the varnish is calculated from the residue when the varnish is heated to 150°C.

[0014] The weight average molecular weight of the first resin (A) contained in the varnish is 13,000 or more and 80,000 or less. If the weight average molecular weight of the first resin (A) is less than 13,000, the dispersion stability of the particles of the first resin (A) in the colloidal dispersion decreases, and the coating strength decreases. If the weight average molecular weight of the first resin (A) exceeds 80,000, the viscosity of the varnish increases.

[0015] The neutralized particles of the first resin (A) (hereinafter sometimes simply referred to as "resin particles") have an average particle size of 20 nm or more and 200 nm or less. If the average particle size of the neutralized resin particles exceeds 200 nm, they tend to settle and have poor dispersion stability. It is preferable that the average particle size of the neutralized resin particles is small, but the lower limit may be 20 nm.

[0016] The average particle size of the neutralized resin particles is the 50% average particle size (D50) in the volume-based particle size distribution measured using a particle size distribution measuring device using a laser diffraction / scattering method.

[0017] In this disclosure, the term "colloidal dispersion" refers to an aqueous dispersion containing dispersed neutralized resin particles, and includes the neutralized resin particles as the dispersoid and deionized water as the dispersion medium.

[0018] The step of removing the organic solvent means that the organic solvent is intentionally removed from the reaction system. The step of removing the organic solvent can be omitted, meaning that the operation of intentionally removing the organic solvent from the reaction system can be omitted. Examples of the method of intentionally removing the solvent include normal pressure distillation and reduced pressure distillation. In general, reduced pressure distillation is used from the viewpoint of solvent removability. In the reduced pressure distillation, for example, distillation is performed at a reduced pressure of 0.05 Pa or more and less than 0.1 Pa, at a temperature of 30° C. or more and 200° C. or less, for 10 minutes or more and 200 minutes or less. In the present disclosure, the colloidal dispersion can be obtained without performing, for example, such reduced pressure distillation from the start of the production of the varnish to the time of obtaining the colloidal dispersion.

[0019] Since the resin particles have excellent dispersion stability, a colloidal dispersion can be obtained with a small amount of deionized water. In other words, the obtained colloidal dispersion has a high solid content concentration. When preparing an aqueous coating composition using the colloidal dispersion, it is not necessary to add additional solvent (water) (or the amount of solvent added can be reduced), and an aqueous coating composition with a high solid content concentration can be obtained. Therefore, a coating film without sagging can be obtained.

[0020] Resin particles have relatively high hydrophobicity. Therefore, the colloidal dispersion can disperse hydrophobic resins well. The hydrophobic resin is, for example, a resin having a solubility parameter (SP value) of 9.5 or more (typically 10.0 or more) and 12.0 or less, as measured by the method described below. The type of hydrophobic resin is not particularly limited. Examples of hydrophobic resins include melamine resins, polyester resins, urethane resins, epoxy resins, and acrylic resins, each having an SP value of 9.5 or more and 12.0 or less. Hereinafter, the ability to disperse other resins is referred to as dispersing ability.

[0021] Colloidal dispersions have the ability to maintain a dispersed state over a long period of time in addition to initial dispersion performance (hereinafter referred to as dispersion stability performance).

[0022] The smaller the average particle size of the neutralized resin particles contained in the colloidal dispersion, the higher the dispersion performance and dispersion stability of the colloidal dispersion. From the viewpoint of dispersion performance and dispersion stability performance, the average particle size of the neutralized resin particles may be 20 nm or more and 150 nm or less.

[0023] The SP value of the resin particles may be 10.0 or more and 11.3 or less. A colloidal dispersion containing resin particles with an SP value of 10.0 or more and 11.3 or less shows higher dispersion performance and dispersion stability performance. The SP value of the resin particles may be 10.2 or more, may be 10.4 or more, or may be 10.6 or more. The SP value of the resin particles may be 11.2 or less, or may be 11.0 or less.

[0024] Colloidal dispersions containing resin particles with an SP value of 10.0 to 11.3 and an average particle size of 20 to 150 nm exhibit particularly high dispersion performance and dispersion stability. The SP value corresponds to the resin particles before neutralization.

[0025] Colloidal dispersions contain resin particles after neutralization. In neutralized resin particles, many of the neutralized carboxyl groups are present near the surface of the resin particles due to their high hydrophilicity, and non-neutralized carboxyl groups may exist inside the resin particles. Therefore, the inside of the resin particles is hydrophobic. Colloidal dispersions can disperse hydrophobic resins by incorporating them into the resin particles. That is, the dispersion performance and dispersion stability performance for hydrophobic resins are affected by the resin components inside the resin particles that do not contain neutralized carboxyl groups. Colloidal dispersions contain resin particles that have hydrophobic parts that do not contain neutralized carboxyl groups, so they exhibit dispersion performance and dispersion stability performance for hydrophobic resins.

[0026] The SP value is an abbreviation for solubility parameter, and is a measure of solubility. The larger the SP value, the higher the polarity, and conversely, the smaller the value, the lower the polarity.

[0027] For example, the SP value can be measured by the following method [Reference: SUH, CLARKE, JPSA-1, 5, 1671-1681 (1967)]. Specifically, the colloidal dispersion (solid content mass 0.5 g) is weighed into a 100 ml glass beaker and heated at 150°C for 1 hour to remove the organic solvent and water. Then, 10 ml of acetone is added using a volumetric pipette, and the resin particles are completely dissolved using a magnetic stirrer to obtain a sample. A poor solvent is dropped into this sample using a 50 ml burette at a measurement temperature of 20°C, and the point at which turbidity occurs is regarded as the amount dropped. Ion-exchanged water is used as a high SP poor solvent, and n-hexane is used as a low SP poor solvent, and the turbidity point is measured for each poor solvent. The SP value δ of an organic solvent is given by the following formula:

[0028] δ = (V ml 1 / 2 δ ml +V mh 1 / 2 δ mh ) / (V ml 1 / 2 +V mh 1 / 2 ) V m = V1V2 / (φ1V2+φ2V1) δ m =φ1δ1+φ2δ2 V i : Molar volume of the solvent (ml / mol) φ i : Volume fraction of each solvent at the clouding point δ i : SP value of the solvent ml: Low SP poor solvent mixed system mh: High SP poor solvent mixed system

[0029] The sample used for calculating the SP value is a colloidal dispersion heated at 150°C for 1 hour. This heating removes the basic compound that neutralized the carboxyl groups on the resin particle surface, and the resin particles become unneutralized. That is, according to the above method, the SP value corresponding to the SP value of the resin particles before neutralization is calculated. The SP value may be measured directly using the resin particles before neutralization by other methods.

[0030] Dispersion performance is affected by the amount of resin to be dispersed. A colloidal dispersion with a solid content concentration of 10% by mass or more and 20% by mass or less can disperse, for example, a hydrophobic resin with a solid content concentration of 40% by mass or less.

[0031] (1) Process for obtaining varnish At a temperature of 50° C. or higher and 180° C. or lower, a monomer mixture containing a carboxy group-containing ethylenically unsaturated monomer (a) is added dropwise to a reactive solvent (x) having one glycidyl group.

[0032] In this step, so-called solution polymerization is carried out. Since the reactive solvent (x) also functions as a solvent for the polymerization reaction, the solid content of the resulting varnish can be 85% by mass or more, in other words, the amount of organic solvent can be less than 15% by mass of the varnish. The solid content of the varnish can be 87% by mass or more, and can be 90% by mass or more.

[0033] In this process, radical polymerization of the monomer mixture and ring-opening addition reaction between the glycidyl group of the reactive solvent (x) and the carboxy group of the carboxy group-containing monomer (a) proceed. This results in the synthesis of the first resin (A). Since this synthesis is carried out under heating, a varnish containing the first resin (A) in a molten state is obtained. The monomer mixture contains the carboxy group-containing ethylenically unsaturated monomer (a) and other ethylenically unsaturated monomers. The first resin (A) is typically an acrylic resin.

[0034] The step of obtaining the varnish (which can also be called the synthesis step of the first resin (A)) may be carried out in two or more stages. Two embodiments of obtaining the varnish in two or more stages are described below. However, the step of obtaining the varnish in the present disclosure is not limited to these embodiments.

[0035] (1-1) First embodiment of the process for obtaining varnish This embodiment is suitable when the reactive solvent (x) has a hydrophobic group. In this embodiment, the process for obtaining a varnish includes a first step of dropping a first monomer mixture containing a first carboxy group-containing ethylenically unsaturated monomer (a1) into a reactive solvent (x) having one glycidyl group and a hydrophobic group at a temperature of 130°C or higher and 180°C or lower to synthesize a hydrophobic resin (A1) and obtain a liquid material containing the hydrophobic resin (A1), and a second step of dropping a second monomer mixture containing a second carboxy group-containing ethylenically unsaturated monomer (a2) into the above liquid at a temperature of 70°C or higher and 180°C or lower to synthesize a carboxy group-containing resin (A2) and obtain a varnish containing a first resin (A) having the hydrophobic resin (A1) and the carboxy group-containing resin (A2).

[0036] In this embodiment, different raw material monomers can be used for polymerization in each step, which increases the degree of freedom in resin design.

[0037] After the second step, the carboxyl group-containing resin (A2) is hydrophilized by neutralization, and then phase inversion emulsification is performed to obtain core-shell structured resin particles having a hydrophobic resin (A1) as the core portion and a hydrophilic resin (A2') as the shell portion.

[0038] The "core portion" and the "shell portion" may or may not be chemically crosslinked. In the present disclosure, the resin particles having a core-shell structure have a hydrophobic resin (A1) inside and a hydrophilic resin (A2') outside, and at least a part of the hydrophobic resin (A1) is covered with the hydrophilic resin (A2').

[0039] (1-1-1) First step In the first step, a first monomer mixture containing a first carboxy group-containing ethylenically unsaturated monomer (a1) is dropped into a reactive solvent (x) having one glycidyl group and a hydrophobic group at a temperature of 130° C. to 180° C. The first monomer mixture contains the first carboxy group-containing ethylenically unsaturated monomer (a1) and other ethylenically unsaturated monomers.

[0040] In the first step, a ring-opening addition reaction between the glycidyl group of the reactive solvent (x) and the carboxy group of the first carboxy group-containing monomer (a1) occurs, and a polymerization reaction of the first monomer mixture occurs. This results in the synthesis of a hydrophobic resin (A1), and a liquid material containing the hydrophobic resin (A1) is obtained. The hydrophobic resin (A1) becomes the base resin that forms the coating film in the water-based paint.

[0041] (1-1-2) Second process In the second step, a second monomer mixture containing a second carboxyl group-containing ethylenically unsaturated monomer (a2) is dropped into the above liquid at a temperature of 70°C or higher and 180°C or lower. The second monomer mixture contains the second carboxyl group-containing ethylenically unsaturated monomer (a2) and other ethylenically unsaturated monomers. The second step may be carried out at a temperature of 100°C or higher and 180°C or lower.

[0042] In the second step, the polymerization of the second monomer mixture mainly proceeds to synthesize a carboxyl group-containing resin (A2). When a basic compound is added in a subsequent step, the carboxyl group is neutralized, and the carboxyl group-containing resin (A2) is hydrophilized to become a hydrophilic resin (A2'). The hydrophilic resin (A2') acts as a dispersing component for dispersing the first resin (A) in water, reducing the particle size of the resin particles and improving their dispersion stability.

[0043] Following the second step, a polymerization initiator may be added and aging may be performed by stirring and heating. The aging is performed, for example, at the same temperature as in the second step for 0.5 hours to 3 hours.

[0044] The weight average molecular weight of the resulting first resin (A) is 13,000 or more and 80,000 or less. The weight average molecular weight of the first resin (A) may be 15,000 or more, or 16,000 or more. The weight average molecular weight of the first resin (A) may be 60,000 or less, or 45,000 or less.

[0045] The weight average molecular weight of the first resin (A) can be adjusted, for example, by the polymerization conditions in the first and second steps, the type of raw material monomer, the amount and type of polymerization initiator, and the aging conditions. For example, if the time of the second step and / or aging is extended, the weight average molecular weight of the first resin (A) tends to increase, and if the aging time is shortened, the weight average molecular weight of the first resin (A) tends to decrease.

[0046] The glass transition temperature (Tg) of the obtained first resin (A) (which contains a hydrophobic resin (A1) and a hydrophilic resin (A2') in this case) may be, for example, 0°C or higher and 50°C or lower. When the Tg of the first resin (A) is 50°C or lower, an increase in the viscosity of the system during neutralization and phase inversion emulsification is suppressed, and a decrease in productivity is suppressed. When the Tg of the first resin (A) is 0°C or higher, the dispersion stability can be further improved. The Tg of the first resin (A) may be 5°C or higher, or 10°C or higher. The Tg of the first resin (A) may be 40°C or lower, or 30°C or lower.

[0047] The Tg may be calculated from the type and amount of the raw material monomers, or may be measured by a differential scanning calorimeter (DSC). Since the Tg of the first resin (A) is almost the same as that of the resin particles, the Tg of the resin particles may be regarded as that of the first resin (A). The Tg of the resin particles is calculated or measured by the above method using the residue when the colloidal dispersion is heated at 150°C.

[0048] (First and second monomer mixtures) The hydrophobic resin (A1) and the carboxyl group-containing resin (A2) are synthesized using a combination of one or more raw material monomers, each of which has an ethylenically unsaturated group.

[0049] The raw material monomers used in the synthesis of the hydrophobic resin (A1) and the carboxyl group-containing resin (A2) may be the same or different. The combinations of raw material monomers used in the synthesis of the hydrophobic resin (A1) and the carboxyl group-containing resin (A2) may be the same or different. The mixing ratios of the multiple raw material monomers used in the synthesis of the hydrophobic resin (A1) and the carboxyl group-containing resin (A2) may be the same or different.

[0050] First and second carboxy-containing monomers (a1) and (a2) Examples of the first and second carboxyl group-containing monomers (a1) and (a2) include (meth)acrylic acid, crotonic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl succinic acid, ω-carboxy-polycaprolactone mono(meth)acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl)oxy)poly(oxy(1-oxo-1,6-hexanediyl)), maleic acid, fumaric acid, itaconic acid, 3-vinyl salicylic acid, 3-vinyl acetylsalicylic acid, and β-carboxyethyl acrylate. These may be used alone or in combination of two or more. (Meth)acrylic acid refers to acrylic acid and methacrylic acid.

[0051] The first carboxy-containing monomer (a1) and the second carboxy-containing monomer (a2) may be the same or different.

[0052] Other ethylenically unsaturated monomers Each monomer mixture may contain other ethylenically unsaturated monomers along with the carboxy-group-containing monomer.

[0053] Examples of other ethylenically unsaturated monomers include hydroxyl group-containing ethylenically unsaturated monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methallyl alcohol, and adducts of these with ε-caprolactone; esters of the above carboxyl group-containing monomers; styrenes such as styrene and α-methylstyrene; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-, i- and t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ) linear aliphatic acrylic esters such as allyl acrylate and lauryl (meth)acrylate; alicyclic acrylic esters such as cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, and dihydrodicyclopentadienyl (meth)acrylate; polymerizable amide compounds such as acrylamide and methacrylamide; polymerizable aromatic compounds, polymerizable nitriles, polymerizable alkylene oxide compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, and polymerizable alkoxysilyl compounds. These may be used alone or in combination of two or more.

[0054] In particular, each monomer mixture may contain a (meth)acrylic alicyclic ester together with a carboxyl group-containing monomer. This increases the hydrophobicity of the first resin (A), and the water resistance of the resulting coating film may be improved. Each monomer mixture may contain a hydroxyl group-containing ethylenically unsaturated monomer (hereinafter, sometimes referred to as a hydroxyl group-containing monomer) together with a carboxyl group-containing monomer. Since the hydroxyl group can be the starting point of a curing reaction, the hardness of the resulting coating film is likely to be high when a hydroxyl group-containing monomer is used. Each monomer mixture may contain both a (meth)acrylic alicyclic ester and a hydroxyl group-containing monomer together with a carboxyl group-containing monomer.

[0055] In terms of improving the physical properties of the resulting coating film, the mass of the carboxyl group-containing monomer in the first monomer mixture may be 5 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass of the first monomer mixture. The mass of the carboxyl group-containing monomer may be 10 parts by mass or more. The mass of the carboxyl group-containing monomer may be 25 parts by mass or less.

[0056] In the first monomer mixture, the mass of the (meth)acrylic acid alicyclic ester may be 5 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the first monomer mixture. The mass of the (meth)acrylic acid alicyclic ester may be 10 parts by mass or more. The mass of the (meth)acrylic acid alicyclic ester may be 35 parts by mass or less.

[0057] In the first monomer mixture, the mass of the hydroxyl group-containing monomer may be 5 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass of the first monomer mixture. The mass of the hydroxyl group-containing monomer may be 7 parts by mass or more. The mass of the (meth)acrylic acid alicyclic ester may be 25 parts by mass or less.

[0058] In order to improve the dispersibility of the resulting hydrophilic resin (A2'), the mass of the carboxyl group-containing monomer in the second monomer mixture may be 5 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass of the second monomer mixture. The mass of the carboxyl group-containing monomer may be 10 parts by mass or more. The mass of the carboxyl group-containing monomer may be 25 parts by mass or less.

[0059] In the second monomer mixture, the mass of the (meth)acrylic acid alicyclic ester may be 5 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the second monomer mixture. The mass of the (meth)acrylic acid alicyclic ester may be 7 parts by mass or more. The mass of the (meth)acrylic acid alicyclic ester may be 35 parts by mass or less.

[0060] In the second monomer mixture, the mass of the hydroxyl group-containing monomer may be 5 parts by mass or more and 30 parts by mass or less, based on 100 parts by mass of the second monomer mixture. The mass of the hydroxyl group-containing monomer may be 10 parts by mass or more. The mass of the (meth)acrylic acid alicyclic ester may be 25 parts by mass or less.

[0061] The first carboxy group-containing monomer (a1), the second carboxy group-containing monomer (a2), and the reactive solvent (x) are mixed, for example, so that the mass ratio of the hydrophobic resin (A1) to the hydrophilic resin (A2') in the core-shell resin particles (hydrophobic resin (A1):hydrophilic resin (A2'), mass %) is 95:5 to 60:40.

[0062] When the mass ratio of the hydrophilic resin (A2') is 5% or more, the dispersibility of the resin particles in water is further improved, and the storage stability of the aqueous coating composition is improved. When the mass ratio of the hydrophilic resin (A2') is 40% or less, the water resistance of the coating film can be improved. The ratio of the hydrophobic resin (A1):hydrophilic resin (A2') may be 90:10 to 70:30, or 85:15 to 75:25.

[0063] (Reactive Solvent (x)) The reactive solvent (x) chemically reacts with the carboxy group-containing monomer (mainly the first carboxy group-containing monomer (a1)) and has a low viscosity, so that it functions as a solvent for the polymerization reaction.

[0064] The viscosity η of the reactive solvent (x) measured by a Brookfield viscometer under conditions of 23°C and a rotation speed of 60 rpm is, for example, 1 mPa·s or more and 50 mPa·s or less. This allows the reactive solvent (x) to function as an excellent solvent. The viscosity η of the reactive solvent (x) may be 2 mPa·s or more, or may be 5 mPa·s or more. The viscosity η of the reactive solvent (x) may be 35 mPa·s or less, or may be 20 mPa·s or less.

[0065] The reactive solvent (x) has a boiling point higher than the solution polymerization temperature (in the range of 130°C or higher and 180°C or lower). The boiling point of the reactive solvent (x) is, for example, 130°C or higher and 300°C or lower. The boiling point of the reactive solvent (x) may be 140°C or higher, or 180°C or higher. The boiling point of the reactive solvent (x) may be 290°C or lower, or 280°C or lower.

[0066] Since the reactive solvent (x) has only one glycidyl group, the reaction between the reactive solvents (x) and the crosslinking reaction are suppressed, and the desired hydrophobic resin (A1) can be obtained. The desired hydrophobic resin (A1) has a carbon-carbon bond as the main chain and a hydrophobic group as the side chain.

[0067] The reactive solvent (x) has one glycidyl group and a hydrophobic group. The reactive solvent (x) may be a monocarboxylic acid glycidyl ester. The monocarboxylic acid glycidyl ester is, for example, represented by the following general formula (1): [ka] (In the formula, R is a monovalent organic group.) It is expressed as:

[0068] R is a monovalent organic group and contains a hydrophobic group. Examples of the hydrophobic group include a hydrocarbon group. The hydrocarbon group is a group containing carbon and hydrogen, and refers to a group obtained by removing one hydrogen atom from a hydrocarbon. Examples of the hydrocarbon group include an aliphatic hydrocarbon group and an aromatic hydrocarbon having 1 to 28 carbon atoms. The aliphatic hydrocarbon group may be linear, branched, or cyclic, and may be saturated or unsaturated. The hydrogen bonded to the carbon may be substituted with a halogen atom, etc.

[0069] The hydrophobic group may be a linear or branched alkyl group having 5 to 24 carbon atoms. This allows the first resin (A1) to have a long-chain alkyl group as a side chain. This long alkyl group imparts plasticity to the first resin (A1), so that the viscosity of the varnish is reduced and the polymerization reaction can proceed more uniformly. Furthermore, the mixability of the first resin (A) with other hydrophobic materials (e.g., crosslinking agents and pigments) blended in the aqueous coating composition is improved, so that the water resistance of the resulting coating film can be further improved. The number of carbon atoms in the alkyl group may be 7 to 18, or 8 to 15. The alkyl group may be saturated. The alkyl group may be branched. In particular, R may be a hydrophobic group, and may be a branched saturated alkyl group having 5 to 24 carbon atoms.

[0070] The amount of reactive solvent (x) used may be, for example, 20 parts by mass or more and 60 parts by mass or less, relative to 100 parts by mass of the total mass of the first monomer mixture, the second monomer mixture, the reactive solvent, and other solvents (hereinafter, sometimes referred to as the "total charge amount"). This makes it easy to control the reaction heat and allows the polymerization reaction to proceed uniformly. The amount of reactive solvent (x) used may be 25 parts by mass or more. The amount of reactive solvent (x) used may be 40 parts by mass or less. The total charge amount may be considered to be the same as the mass of the resulting varnish.

[0071] (Polymerization initiator) A polymerization initiator may be used in the first step, the second step, and the aging. The total amount of the polymerization initiator used is appropriately set, for example, according to the type and amount of the raw material monomer. The total amount of the polymerization initiator used may be, for example, 0.2 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the total of the first monomer mixture and the second monomer mixture. The amount of the polymerization initiator used may be 0.2 parts by mass or more. The amount of the polymerization initiator used may be 1.5 parts by mass or less.

[0072] Examples of the polymerization initiator include 2,2'-azobisisobutyronitrile, benzoyl peroxide, 2,2-di(t-amylperoxy)butane, di-t-butyl peroxide, di-t-amyl peroxide (DTA), t-butyl peroctoate, and 2,2'-azobis(2-methylbutyronitrile).

[0073] (Organic solvent) The varnish may contain an organic solvent other than the reactive solvent (x) at a mass ratio of less than 15 mass %. Examples of the other organic solvent include high-boiling point solvents having a boiling point higher than the solution polymerization temperature (within the range of 130°C to 180°C).

[0074] Examples of high boiling point solvents include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, 3-butoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, N,N-dimethylformamide, ethylene glycol, propylene glycol, glycerin, dimethylcarbitol, butyl carbitol, butyl dicarbitol, butyl cellosolve, 1,4-butanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, diethylene glycol monomethyl ether, and dipropylene glycol monomethyl ether.

[0075] From the viewpoint of reducing the environmental load, it is also desired that the aqueous coating composition has low-temperature curing properties. From the viewpoint of low-temperature curing properties, it is desirable that the mass ratio of the high-boiling point solvent is small. The mass ratio of the high-boiling point solvent in the varnish may be less than 13 mass%, or may be less than 10 mass%.

[0076] (1-2) Second embodiment of the process for obtaining varnish In this embodiment, the process for obtaining a varnish includes a process of dropping a monomer mixture containing a carboxy group-containing ethylenically unsaturated monomer (a) into a reactive solvent (x) at a temperature of 50°C or higher and lower than 130°C, polymerizing the monomer mixture to obtain a precursor of the first resin (A), and a process of raising the temperature to 130°C or higher and 180°C or lower, reacting the reactive solvent (x) with the precursor to obtain a varnish containing the first resin (A).

[0077] In this embodiment, the polymerization reaction and the ring-opening reaction of the ethylenically unsaturated monomer are carried out stepwise, taking advantage of the fact that the ring-opening reaction of the epoxy ring is difficult to occur at low temperatures. According to this embodiment, even when a highly volatile raw material monomer is used, the polymerization reaction can be reliably carried out, and the first resin (A) can contain a hydrophobic portion.

[0078] The temperature in the step of obtaining the precursor of the first resin (A) may be 50° C. or higher. The temperature in the step of obtaining the precursor of the first resin (A) may be 110° C. or lower.

[0079] The raw material monomer, reactive solvent (x), polymerization initiator, and organic solvent contained in the monomer mixture may be the same as those exemplified in the first embodiment. The amount of each component used may be in the same range as in the first embodiment, with the total mass of the first monomer mixture and the second monomer mixture in the first embodiment being read as the mass of the monomer mixture in this embodiment.

[0080] (2) Neutralization and phase inversion emulsification process First, a basic compound is added to the varnish at a temperature of 70°C to 98°C to neutralize the carboxyl groups remaining in the first resin (A). This makes the first resin (A) water dispersible. Then, deionized water is added to the varnish at a temperature of 70°C to 98°C to cause phase inversion emulsification. This produces a colloidal dispersion containing resin particles.

[0081] When the temperature of the varnish during neutralization and phase inversion emulsification is 70°C or higher and 98°C or lower, the first resin (A) can be sufficiently softened while suppressing the volatilization of the basic compound and deionized water. This makes it easier for the first resin (A) to be finely dispersed in the deionized water. In particular, when the temperature of the varnish is equal to or higher than the Tg of the first resin (A), the first resin (A) can be further easily finely dispersed.

[0082] The average particle size of the resin particles formed by phase inversion emulsification is 20 nm or more and 200 nm or less. The average particle size of the resin particles may be 180 nm or less, 160 nm or less, or 150 nm or less. The average particle size of the resin particles may be 25 nm or more, or 30 nm or more. In one embodiment, the average particle size of the resin particles may be 20 nm or more and 150 nm or less.

[0083] Phase inversion emulsification is carried out, for example, by stirring a mixture of a varnish containing the neutralized first resin (A) and deionized water. By stirring, the average particle size of the resin particles can become smaller.

[0084] The average particle size of the resin particles can be adjusted, for example, by the radical polymerization conditions, the type of raw material monomer, and the stirring conditions during phase inversion emulsification. For example, when the neutralization rate is lowered, the average particle size of the resin particles tends to become larger, and when the neutralization rate is increased, the average particle size of the resin particles tends to become smaller.

[0085] The solid content concentration of the colloidal dispersion is, for example, 30% by mass or more and 45% by mass or less. The solid content concentration of the colloidal dispersion may be 34% by mass or more, or 36% by mass or more. The solid content concentration of the colloidal dispersion may be 42% by mass or less, or 40% by mass or less.

[0086] The solids concentration of the colloidal dispersion is calculated from the residue when the colloidal dispersion is heated at 150°C.

[0087] Viscosity η of colloidal dispersion measured by a Brookfield viscometer at 23°C and 60 rpm 60 is, for example, 50 mPa·s or more and 700 mPa·s or less. This allows the colloidal dispersion to be blended into the aqueous coating composition without diluting it with a solvent. The viscosity η of the colloidal dispersion 60 The viscosity η of the colloidal dispersion may be 80 mPa·s or more, or 100 mPa·s or more. 60 may be 630 mPa·s or less, may be 600 mPa·s or less, may be 500 mPa·s or less, may be 300 mPa·s or less, may be 295 mPa·s or less, or may be 290 mPa·s or less.

[0088] Viscosity η 60 is measured at 23°C and a rotation speed of 60 rpm using a B-type viscometer (for example, product name: Viscometer VT-06, No. 2 rotor, manufactured by Rion Co., Ltd.) in accordance with JIS-Z8803 "Method of measuring viscosity of liquids, 9. Method of measuring viscosity using a single cylindrical rotational viscometer".

[0089] (Basic compounds) Examples of basic compounds include secondary aliphatic amine compounds such as diethylamine, di-n-propylamine, diisopropylamine, diisobutylamine, di-n-butylamine, di-sec-butylamine, diamylamine, N-ethyl-1,2-dimethylpropylamine, N-methylhexylamine, di-n-octylamine, and diallylamine; tertiary aliphatic amine compounds such as triethylamine, tributylamine, triallylamine, N,N-dimethylethanolamine, N-methyldiallylamine, and N,N-dimethylallylamine; secondary cyclic amine compounds such as piperidine, 2-pipecoline, 3-pipecoline, 4-pipecoline, 2,4-lupetidine, 2,6-lupetidine, 3,5-lupetidine, and 3-piperidinemethanol; tertiary cyclic amine compounds such as N-methylpiperidine, N-methylpiperazine, and N-methylmorpholine; and aromatic amine compounds such as pyridine and 4-ethylpyridine.

[0090] The basic compound is added in an amount such that the neutralization rate of the carboxyl groups in the first resin (A) is 70% or more and 100% or less. When the neutralization rate is in this range, the water dispersibility of the first resin (A) is improved and the average particle size can be smaller. The neutralization rate may be 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more.

[0091] The neutralization rate is equivalent to the amount of the basic compound used relative to the carboxyl group, and is calculated according to the following formula: TIFF0007607182000002.tif12150

[0092] The acid value of the first resin (A) may be, for example, 10 mgKOH / g or more and 50 mgKOH / g or less. The acid value of the first resin (A) may be 15 mgKOH / g or more, or 20 mgKOH / g or more. The acid value of the first resin (A) may be 40 mgKOH / g or less, or 35 mgKOH / g or less.

[0093] The acid value of the first resin (A) may be calculated from the composition of the raw material monomers based on the JIS regulations, or may be determined by neutralization titration using an aqueous potassium hydroxide solution in accordance with JIS K 0070. Since the acid value of the first resin (A) is approximately the same as the acid value of the resin particles, the acid value of the resin particles may be regarded as the acid value of the first resin (A). The acid value of the resin particles can be calculated by dividing the acid value determined by the neutralization titration method described above using a colloidal dispersion by the solids concentration of the colloidal dispersion.

[0094] (Water-based paint composition) The colloidal dispersion obtained by the method according to the present disclosure is suitable for use in preparing an aqueous coating composition, which contains water as a solvent in an amount of 50% by mass or more (particularly 80% by mass or more) of the total solvent.

[0095] The colloidal dispersion can be blended into the aqueous coating composition as a coating film-forming resin, and can be blended as a pigment dispersant. When the resin particles have a hydroxyl group (when the monomer mixture contains a hydroxyl group-containing monomer), they can react with the crosslinking agent contained in the aqueous coating composition. Therefore, when the colloidal dispersion obtained by the present disclosure is used, various physical properties of the resulting coating film can be improved.

[0096] The aqueous coating composition contains, for example, the above-mentioned colloidal dispersion, a crosslinking agent, a pigment, and, if necessary, deionized water and various additives. The aqueous coating composition may contain a conventionally known film-forming resin and / or a pigment dispersant, if necessary. Examples of the pigment include color pigments, luster pigments, and extender pigments. Examples of the additives include surface conditioners, viscosity control agents, thickeners, antioxidants, ultraviolet inhibitors, and defoamers. EXAMPLES

[0097] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0098] [Example 1] (1) First Step (Preparation of Hydrophobic Acrylic Resin (A1)) A reaction vessel equipped with a stirrer, a temperature controller, a cooling tube, and a dropping device was charged with 30 parts of a reactive solvent (CAE, glycidyl ester of monocarboxylic acid having a branched alkyl group with 9 carbon atoms, trade name: Cardurer E10P, manufactured by Hexion, viscosity 7 mPa·s, boiling point 251-278°C), and the temperature was raised to 165°C while stirring, and refluxed. Separately, a mixture of 9.47 parts of acrylic acid (AA), 5.8 parts of 2-hydroxyethyl methacrylate (HEMA), 11.6 parts of cyclohexyl methacrylate (CHMA), 7.5 parts of n-butyl acrylate (NBA), 16.9 parts of styrene (ST), 0.28 parts of a polymerization initiator (DTA, trade name: Luperox DTA, manufactured by Arkema Yoshitomi), and 6.5 parts of a high boiling point solvent (dipropylene glycol monomethyl ether (DPM)) was prepared. This mixture was added dropwise to the reaction vessel at 165° C. over 3.5 hours to carry out polymerization and ring-opening addition reactions.

[0099] (2) Second step (preparation of carboxyl group-containing acrylic resin (A2)) and aging Separately, a mixture of 3.43 parts of AA, 3.8 parts of HEMA, 2.7 parts of CHMA, 2.9 parts of NBA, 5.8 parts of ST, 0.11 parts of polymerization initiator (Luperox DTA), and 2.4 parts of high boiling point solvent (DPM) was prepared. This mixture was dropped into the reaction vessel over a period of 1 hour at 165°C while stirring, and polymerized for 1 hour. Furthermore, a mixture of 0.1 parts of polymerization initiator (Luperox DTA) and 0.1 parts of high boiling point solvent (DPM) was added to the reaction vessel, and polymerization reaction was carried out for 1 hour at 165°C while stirring.

[0100] In this way, a varnish containing a hydrophobic resin (A1) and an acrylic resin (A) having a carboxyl group-containing resin (A2) and having a solid content concentration of 91% by mass was obtained. The weight average molecular weight of the obtained acrylic resin (A) was 32,000.

[0101] (Weight average molecular weight) The weight average molecular weight was measured using a GPC apparatus "HLC8220GPC" (trade name, manufactured by Tosoh Corporation) and four columns "Shodex KF-606M" and "Shodex KF-603" (both trade names, manufactured by Showa Denko K.K.), under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 0.6 cc / min, and detector: RI.

[0102] (3) Neutralization and phase inversion emulsification A basic compound (dimethylethanolamine, DMEA) was added to the varnish at a ratio of 5.33 parts per 100 parts of acrylic resin at 80°C, and the mixture was stirred for 15 minutes. The neutralization rate of the carboxyl group was adjusted to 90%. Next, 150 parts of deionized water was added dropwise to the neutralized varnish at 80°C while stirring, to obtain a milky white colloidal dispersion.

[0103] The solid concentration of the colloidal dispersion is 38% by mass, and the viscosity is η 60 The viscosity was 130 mPa s and the pH was 8.2. The acrylic resin particles contained in the colloidal dispersion are expected to have a core-shell structure, with an average particle size of 85 nm, a Tg of 20°C, and an acid value of 34 mgKOH / g. The Tg and acid value of the acrylic resin particles can be regarded as those of the first resin (A).

[0104] (Acid Value (AV)) 1 g of the colloidal dispersion was dissolved in 50 ml of tetrahydrofuran (THF), and the acid value of the colloidal dispersion was determined by neutralization titration using an aqueous potassium hydroxide solution in accordance with JIS K 0070. Next, the acid value was divided by the solid content concentration of the colloidal dispersion to calculate the solid content acid value of the resin particles, which was defined as the acid value of the acrylic resin (A).

[0105] (Glass transition temperature (Tg)) The colloidal dispersion was heated at 150°C for 1 hour to obtain a heating residue. Using a DSC (Differential Scanning Caloriemeter) manufactured by Seiko Denshi Kogyo Co., Ltd., data was obtained at a heating rate of 10°C / min, and the intersection point of the baseline and the tangent line to the inflection point was taken as Tg. This Tg was taken as the Tg of the acrylic resin (A).

[0106] (SP value) The SP value of the neutralized resin particles was calculated as described above.

[0107] [Examples 2-11, Comparative Examples 1 and 2] Colloidal dispersions were obtained in the same manner as in Example 1, except that the types of raw material monomers, neutralization rates, etc. were changed as shown in Tables 1 and 2.

[0108] [Table 1]

[0109] [Table 2]

[0110] [Comparative Example 3] A dispersion containing particles of a core-shell type acrylic resin (B) was obtained without using a reactive solvent as follows.

[0111] (a) Preparation of macromonomer (core part) A reaction vessel equipped with a stirrer, a temperature controller, a cooling tube and a dropping device was charged with 23.7 parts of methyl isobutyl ketone (MIBK) and heated to 110 ° C. Then, the raw material monomers shown in Table 3 and a solution in which 8.3 parts of tert-butylperoxy-2-ethylhexanate were dissolved in 4.8 parts of MIBK were dropped in parallel at a constant speed over 90 minutes. After the reaction vessel was kept at 110 ° C. for 30 minutes, a solution in which 0.3 parts of tert-butylperoxy-2-ethylhexanate were dissolved in 3.2 parts of MIBK was dropped at a constant speed over 30 minutes. Then, the mixture was stirred at 110 ° C. for 60 minutes. While the reaction vessel was kept at 110 ° C., 0.8 parts of methacrylic anhydride was further added and held for 2 hours. Then, the mixture was cooled to 60 ° C. to obtain a macromonomer.

[0112] (b) Preparation of core-shell type acrylic resin (B) Separately, 39.7 parts of MIBK was charged into a reactor equipped with a cooling and heating device and heated to 110° C. Then, the raw material monomers shown in Table 3 and a solution in which 2.1 parts of tert-butylperoxy-2-ethylhexanate were dissolved in 8.6 parts of MIBK were dropped in parallel at a constant rate over 90 minutes.

[0113] After the reaction vessel was kept at 110°C for 30 minutes, a solution of 0.3 parts of tert-butylperoxy-2-ethylhexanate in 2.9 parts of MIBK was added dropwise at a constant rate over 30 minutes. After stirring at 110°C for 60 minutes, the mixture was cooled to 70°C.

[0114] In this way, a varnish v1 containing a core-shell type acrylic resin (B) and having a solid content concentration of 55 mass % was obtained. The weight average molecular weight of the obtained acrylic resin (B) was 15,000.

[0115] (c) Desolvation From varnish v1 (181.8 parts), 81.8 parts of MIBK was distilled off under reduced pressure. Then, 15 parts of DPM was added to obtain varnish v2. The reduced pressure distillation was carried out at about 5 kPa and a temperature of 90° C. for 120 minutes.

[0116] (d) Neutralization and phase inversion emulsification To varnish v2, 2.53 parts of DMEA was added per 100 parts of acrylic resin (B) at 80°C, and the mixture was stirred for 15 minutes (neutralization rate 75%). Then, 155 parts of deionized water was added dropwise to the neutralized varnish at 80°C while stirring, to produce a milky white colloidal dispersion. The resin solid content of the resulting dispersion of acrylic resin (B) was 36% by mass.

[0117] The conditions for (c) desolvation, (d) neutralization and phase inversion emulsification are shown in Table 4.

[0118] [Table 3]

[0119] [Table 4]

[0120] [evaluation] The colloidal dispersion was subjected to the following evaluations, and the results are shown in Table 6.

[0121] (1) Dispersion stability The colloidal dispersion was allowed to stand for one month at a temperature of 40° C. The presence or absence of settling was visually observed and evaluated according to the following criteria.

[0122] A: No settling after one month B: No settling after one week C: Sedimentation was confirmed after 24 hours. D: Subsidence was confirmed after 1 hour.

[0123] (2) Odor The presence or absence of odor of the colloidal dispersion was evaluated by sensory evaluation according to the following criteria. None: There is no irritating smell that stings the nose, and there is almost no smell. Yes: Has a thinner and / or pungent odor

[0124] (3) Dispersion performance of colloidal dispersions for hydrophobic resins Sample preparation A hydrophobic melamine resin (SP value: 10.1, product name: Cymel 250, manufactured by Allnex), a surfactant (acetylene glycol type, product name: Surfynol 465, manufactured by Evonik Industries), and an organic solvent (isoparaffin, product name: Merveille 30, manufactured by Idemitsu Kosan Co., Ltd.) were mixed so that the solid content ratio was as shown in the table below. Next, a colloidal dispersion was added while stirring with a disperser, and the mixture was further stirred for 10 minutes. Next, pure water was added to a total amount of 100 mass% while stirring with a disperser, and the mixture was further stirred for 3 minutes. In this manner, a sample was prepared.

[0125] [Table 5]

[0126] ·Initial dispersion performance The above sample was diluted with water so that the solid content concentration was 0.01% by mass. The particle size of the resin contained in the diluted sample was measured three times using a dynamic light scattering method (instrument name: ELSZ-2000ZS, Otsuka Electronics), and the cumulant diameter was obtained by cumulant analysis. The obtained cumulant diameters were averaged to obtain the dispersion diameter of the melamine resin. If the dispersion diameter is 300 nm or less, it can be said that the colloidal dispersion has excellent initial dispersion performance.

[0127] ·Dispersion stability performance The above sample was placed in a transparent bottle and allowed to stand at room temperature. After one day and after five days, the bottle was tilted and visually observed to see if there was any precipitate at the bottom. If no precipitate was observed after five days, the colloidal dispersion was deemed to have excellent dispersion stability.

[0128] (Evaluation Criteria) A: No settling even after 5 days B: Precipitation can be confirmed after 5 days. C: Precipitation can be confirmed after 1 day. D: The sample has no fluidity during preparation and dispersion cannot be confirmed.

[0129] [Table 6] [Industrial Applicability]

[0130] The production method of the present disclosure can obtain a colloidal dispersion having excellent dispersion stability while reducing the use of organic solvents. The obtained colloidal dispersion is suitable for use in an aqueous coating composition.

[0131] This application claims priority based on Japanese Patent Application No. 2023-074538, filed in Japan on April 28, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. a step of dropping a monomer mixture containing a carboxyl group-containing ethylenically unsaturated monomer (a) into a reactive solvent (x) having one glycidyl group at a temperature of 50° C. or higher and 180° C. or lower to obtain a varnish containing a first resin (A); adding a basic compound to the varnish at a temperature of 70° C. or higher and 98° C. or lower to neutralize the carboxyl groups remaining in the first resin (A), and then adding deionized water to effect phase inversion emulsification to obtain a colloidal dispersion containing particles of the neutralized first resin (A); The solid content of the varnish is 85% by mass or more, The weight average molecular weight of the first resin (A) contained in the varnish is 13,000 or more and 80,000 or less, The method for producing a colloidal dispersion, wherein the neutralized particles of the first resin (A) have an average particle size of 20 nm or more and 200 nm or less.

2. 2. The method for producing a colloidal dispersion according to claim 1, which does not include a step of removing the organic solvent.

3. 3. The method for producing a colloidal dispersion according to claim 1, wherein the neutralized particles of the first resin (A) have an average particle size of 20 nm or more and 150 nm or less.

4. 3. The method for producing a colloidal dispersion according to claim 1, wherein a mass of the reactive solvent (x) used in the step of obtaining the varnish is 20 parts by mass or more and 60 parts by mass or less relative to 100 parts by mass of the varnish.

5. The reactive solvent (x) further has a hydrophobic group, The step of obtaining the varnish comprises: a first step of dropping a first monomer mixture containing a first carboxy group-containing ethylenically unsaturated monomer (a1) into the reactive solvent (x) at a temperature of 130° C. or higher and 180° C. or lower to synthesize a hydrophobic resin (A1) and obtain a liquid material containing the hydrophobic resin (A1); and a second step of dropping a second monomer mixture containing a second carboxy group-containing ethylenically unsaturated monomer (a2) into the liquid at a temperature of 70° C. or higher and 180° C. or lower to synthesize a carboxy group-containing resin (A2) and obtain the varnish containing the first resin (A) having the hydrophobic resin (A1) and the carboxy group-containing resin (A2).

6. 6. The method for producing a colloidal dispersion according to claim 5, wherein the reactive solvent (x) has, as the hydrophobic group, a linear or branched alkyl group having 5 to 24 carbon atoms.

7. The step of obtaining the varnish comprises: a step of dropping the monomer mixture containing the carboxy group-containing ethylenically unsaturated monomer (a) into the reactive solvent (x) at a temperature of 50° C. or higher and lower than 130° C. to polymerize the monomer mixture, thereby obtaining a precursor of the first resin (A); and raising the temperature to 130° C. or more and 180° C. or less to react the reactive solvent (x) with the precursor to obtain a varnish containing the first resin (A).

8. 3. The method for producing a colloidal dispersion according to claim 1, wherein the particles of the first resin (A) have a solubility parameter of 10.0 or more and 11.3 or less.