Viscosity modifier for water-based paint, water-based paint composition, coating film, coated article, method for forming multilayer coating film, and method for producing coated article

Abstract

To provide a viscosity modifier for water-based paint that is capable of imparting sufficient viscosity to the paint while inhibiting phase separation in the water-based paint having a polycarboxylic acid-type viscosity modifier added thereto, as well as a water-based paint containing the viscosity modifier, and a multilayer coating film and a coated article formed using the water-based paint.SOLUTION: Provided is a viscosity modifier for water-based paint, comprising a neutralized product of a polycarboxylic acid, in which a polycarboxylic acid having an acid value of 45 or more is neutralized with an amine compound, wherein the amine compound includes at least a hydrophobic amine having an HLB of 1 to 15 inclusive.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a viscosity modifier for aqueous paints, an aqueous paint composition containing the viscosity modifier, a coating film and a coated article formed using the aqueous paint composition, a method for forming a multilayer coating film, and a method for producing a coated article. [Background technology]

[0002] In the field of water-based paints, viscosity modifiers for water-based paints are widely used for reasons such as improving paint workability, preventing sagging, preventing sedimentation, and improving appearance (see, for example, Patent Document 1). In automotive coatings and paints, the above-mentioned viscosity modifiers are also often used to improve the orientation of glittering pigments (see, for example, Patent Document 2).

[0003] Patent Document 1 discloses a viscosity improver capable of imparting excellent finish properties (smoothness, vividness, and resistance to sagging) to aqueous paints for automobiles, which contains a copolymer having, as essential constituent monomers, (a) (meth)acrylic acid (salt), (b) a polyether ester monomer having a specific structure, (c) an alkyl (meth)acrylate having an alkyl group with 1 to 4 carbon atoms, and (d) a polyfunctional monomer.

[0004] Patent Document 2 discloses a glittering pigment dispersion containing water, a viscosity modifier (A) and a scaly glittering pigment (B), the scaly glittering pigment (B) being an optical interference pigment in which a transparent or semi-transparent base material is coated with a metal oxide, and the solid content is 0.1 to 15 mass %. It is said that this glittering pigment dispersion can form a coating film that exhibits a pearlescent appearance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2008-13778 A

[0006] [Patent Document 2] International Publication No. 2018 / 012014 Brochure Summary of the Invention [Problem to be solved by the invention]

[0007] However, the use of these viscosity modifiers for aqueous paints may cause some problems. For example, one problem that the present inventors have found is that when a polycarboxylic acid type viscosity modifier containing a large number of carboxyl groups in its chemical structure is added to an aqueous paint, separation of the paint to which the viscosity modifier has been added occurs. In addition, paints in which this separation phenomenon occurs are non-uniform, and may cause further problems such as the generation of poorly dispersed matter in the paint. If poorly dispersed matter is present in the paint, further problems such as the inability to form a coating film, the coating film thickness becoming non-uniform, and the generation of bumps may occur.

[0008] On the other hand, if the acid value of the polycarboxylic acid is reduced or the amount of the viscosity modifier added is reduced in an attempt to suppress the separation phenomenon, the paint cannot be sufficiently thickened. Thus, in water-based paints to which a polycarboxylic acid type viscosity modifier has been added, there is a trade-off between suppressing the separation phenomenon and imparting viscosity to the paint. Therefore, a polycarboxylic acid type viscosity modifier that can suppress the separation phenomenon of the paint while exerting a sufficient viscosity imparting effect is desired.

[0009] Therefore, the present invention has been made in consideration of the above circumstances, and has an object to provide a viscosity modifier for aqueous paints that can impart sufficient viscosity to the paint while suppressing the separation phenomenon of aqueous paints to which a polycarboxylic acid type viscosity modifier has been added, an aqueous paint composition containing the viscosity modifier, a coating film and a coated article formed using the aqueous paint composition, a method for forming a multilayer coating film, and a method for manufacturing a coated article. [Means for solving the problem]

[0010] As a result of extensive research to solve the above problems, the inventors have discovered that by using a neutralized product obtained by neutralizing a polycarboxylic acid, which has a relatively large acid value, with a hydrophobic amine, which has a low HLB value, as a viscosity adjuster, it is possible to impart sufficient viscosity to the paint while suppressing the separation phenomenon of an aqueous paint to which a polycarboxylic acid type viscosity adjuster has been added, and have completed the present invention based on this finding.

[0011] That is, the present invention relates to a viscosity modifier for aqueous paints, which comprises a neutralized product of polycarboxylic acid obtained by neutralizing a polycarboxylic acid having an acid value of 45 or more with an amine compound, and which comprises at least a hydrophobic amine having an HLB value of 1 or more and 15 or less as the amine compound.

[0012] In one embodiment of the viscosity modifier for aqueous paint of the present invention, the HLB of the hydrophobic amine is preferably 1 or more and 11 or less. In this case, it is more preferable that the distribution rate of the neutralized product of the polycarboxylic acid to water when the neutralized product of the polycarboxylic acid is added to a mixed solvent of water and 2-ethylhexanol in a 1:1 (volume ratio) is 74.0% or less.

[0013] In one embodiment of the viscosity modifier for aqueous paints of the present invention, the polycarboxylic acid may be at least one selected from the group consisting of polymers and copolymers of (meth)acrylic acid, polymers and copolymers of (anhydride) maleic acid, polymers and copolymers of itaconic acid, and thickening polysaccharides. In this case, at least one of the copolymers of (meth)acrylic acid, the copolymers of (anhydride) maleic acid, and the copolymers of itaconic acid may contain (meth)acrylate as a constituent monomer.

[0014] In one embodiment of the viscosity modifier for aqueous paint of the present invention, the hydrophobic amine may be at least one amine compound selected from the group consisting of alkylamines, alkanolamines and polyetheramines.

[0015] In one embodiment of the viscosity modifier for aqueous paint of the present invention, the amine compound may contain the hydrophobic amine in an amount of 25 mol % or more based on the total number of moles of the amine compound.

[0016] The present invention also provides an aqueous coating composition comprising an aqueous resin and the above-mentioned viscosity modifier.

[0017] The present invention also relates to a coating film that is provided on the surface of a substrate, or a coating film that is laminated on another coating film that is provided on the surface of the substrate, characterized in that the coating film is obtained by applying the above-mentioned aqueous paint composition to the surface of the substrate or the other coating film.

[0018] The present invention also relates to a coated article having one or more coating layers on the surface of a substrate, characterized in that at least one of the coating layers is obtained by applying the above-mentioned aqueous paint composition to the surface of the substrate or another coating layer.

[0019] The present invention also relates to a method for forming a multi-layer coating film by forming two or more coating layers on a surface of a substrate, comprising using the above-mentioned aqueous coating composition as at least one of the coating materials for forming the two or more coating layers, The method for forming a multi-layer coating film is characterized by including a step of successively applying the paint for forming the two or more coating layers in a wet-on-wet manner.

[0020] The present invention also relates to a method for producing a coated article, comprising a coating film forming step of forming a multi-layer coating film consisting of two or more coating layers on the surface of a substrate, the method comprising the steps of: using the above-mentioned aqueous coating composition as at least one of the coating films for forming the two or more coating layers; The coating film forming step is a method for producing a coated article, characterized in that it includes a step of successively coating the paint for forming the two or more coating films in a wet-on-wet manner. Effect of the Invention

[0021] According to the present invention, by using a neutralized product of polycarboxylic acid neutralized with a hydrophobic amine as a viscosity adjuster, it is possible to impart sufficient viscosity to the paint while suppressing the separation phenomenon of an aqueous paint to which a polycarboxylic acid type viscosity adjuster has been added. [Brief description of the drawings]

[0022] [Figure 1] 1 is a photograph showing an example of the appearance of an aqueous coating composition when separation was determined to have occurred in an example. [Diagram 2] 1 is a photograph showing an example of the appearance of an aqueous coating composition when it is determined that no separation has occurred in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Preferred embodiments of the present invention will now be described in detail.

[0024] [Viscosity adjuster] The viscosity modifier according to the present invention is an additive used together with an aqueous resin in an aqueous coating composition, and contains as an essential component a neutralized product of polycarboxylic acid in which a polycarboxylic acid having an acid value of 45 or more is neutralized with an amine compound. Here, in the present invention, the amine compound that neutralizes the polycarboxylic acid must contain at least a hydrophobic amine having an HLB of 1 or more and 15 or less. As a result, according to the present invention, it is possible to suppress the separation phenomenon of an aqueous coating to which a polycarboxylic acid type viscosity modifier has been added (separation suppression effect) and to impart sufficient viscosity to the coating (viscosity imparting effect).

[0025] Here, the separation of the aqueous paint in the present invention refers to the state in which crosslinking aggregation caused by the adsorption of the water-soluble polymer containing the neutralized product of polycarboxylic acid to the dispersion of resin, pigment, etc. becomes excessive, and the crosslinked aggregate of resin particles or pigment particles separates from other components in the aqueous paint. The separation suppression effect of the aqueous paint in the present invention refers to the effect of suppressing the occurrence of separation of the crosslinked aggregate of resin particles or pigment particles in the above-mentioned aqueous paint. Furthermore, the viscosity imparting effect in the present invention refers to the effect of increasing (thickening) the viscosity of the aqueous paint to which the viscosity modifier has been added. Below, these essential components and the optional components contained in the viscosity modifier of the present invention will be described in detail.

[0026] (Polycarboxylic acid) The polycarboxylic acid used in the viscosity modifier of the present invention is not particularly limited as long as it has a large number of carboxyl groups and has a sufficient viscosity imparting effect on the water-based paint. The condition for having a sufficient viscosity imparting effect on the water-based paint is that the acid value of the polycarboxylic acid is 45 or more. On the other hand, the upper limit of the acid value of the polycarboxylic acid is not particularly limited. From the viewpoint of the viscosity imparting effect on the water-based paint, a higher acid value is preferable, and even if the acid value is high, the effect of suppressing separation of the water-based paint can be obtained without problems. However, since there is an upper limit to the acid value of the polycarboxylic acid that can be synthesized, the acid value is preferably 750 or less.

[0027] The acid value in the present invention refers to the number of milligrams of potassium hydroxide required to neutralize the free fatty acids, resin acids, etc. contained in 1 g of a sample, and can be measured in accordance with JIS K0070:1992.

[0028] Specific examples of polycarboxylic acids that satisfy the above conditions include polymers and copolymers of (meth)acrylic acid, polymers and copolymers of (maleic anhydride), and polymers and copolymers of itaconic acid, and the constituent monomers of these copolymers may include (meth)acrylates such as any alkyl (meth)acrylate. The polycarboxylic acid of the present invention may also be a thickening polysaccharide. Note that "(meth)acrylic acid" means acrylic acid or methacrylic acid, and "(meth)acrylate" means acrylate or methacrylate. These polycarboxylic acids may be used alone or in combination of two or more.

[0029] The above-mentioned polycarboxylic acids may be synthesized by a known method, or may be purchased as commercial products. Examples of commercially available products include Disparlon (registered trademark) AQ-021 (acrylic copolymer) and AQ-001 (acrylic copolymer) manufactured by Kusumoto Chemicals Co., Ltd., Aron (registered trademark) NW-7060, NW-400, A-3611, A-104, A-106, NS-1200 (1) (all acrylic polymers or copolymers), AS-2000, AS-1100, and AS-1800 (all acrylic acid polymers or copolymers) manufactured by Toagosei Co., Ltd., ZX-CL-AP-200 (acrylic acid copolymer) manufactured by Nippon Shokubai Co., Ltd., ACULYN (registered trademark) 22 (acrylic polymer or copolymer) manufactured by Dow Chemical Co., Ltd., RHEOVIS (registered trademark) AS 1130 (acrylic polymer or copolymer) manufactured by BASF, and AQUATIX (registered trademark) manufactured by BYK. Examples of such polysaccharide thickeners include 8421 ((meth)acrylic polymer or copolymer), Monart Gum DA and Labol Gum GS-C (both thickening polysaccharides) manufactured by MP Gokyo Food & Chemical Co., Ltd., and Leocrysta (registered trademark) I-2SX (polycarboxylic acid-containing cellulose nanofiber) manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

[0030] (Amine compounds) The amine compound used in the viscosity modifier of the present invention is used as a neutralizing agent for neutralizing the above-mentioned polycarboxylic acid. In the present invention, such an amine compound includes at least an amine compound having an HLB of 1 to 15 (hereinafter, sometimes referred to as "hydrophobic amine"). According to the viscosity modifier of the present invention, by using a hydrophobic amine as a neutralizing agent for polycarboxylic acid, separation of resin particles and pigment particles in the water-based paint can be suppressed. The basis for this is described below.

[0031] Polycarboxylic acid type viscosity modifiers are usually used in the form of water-soluble polymers neutralized with amines. It is known that water-soluble polymers containing neutralized polycarboxylic acids are adsorbed to dispersions of aqueous resins and pigments, which are the main components of coating films, in water, and form bridge structures between resin particles and pigment particles, resulting in cross-linking and aggregation of resin particles and pigment particles. Polycarboxylic acid type viscosity modifiers utilize or partially utilize this cross-linking and aggregation effect. Here, the present inventors believe that the adsorption of the polymer chains of the water-soluble polymers containing neutralized polycarboxylic acids to the resins and pigments takes a gently aggregated form immediately after the paint is made, and takes a temporarily stable form. In this form, the paint does not separate.

[0032] However, as time passes, the water-soluble polymer gradually tries to take a thermally stable form, so the adsorption form of the water-soluble polymer changes, and more specifically, the amount of the water-soluble polymer adsorbed to the resin particles or pigment particles increases. The present inventors believe that the water-soluble polymer is more thermally stable when adsorbed to the resin particles or the like than when it is free (in the form of a free polymer) in water. As a result, the present inventors believe that excessive aggregation of the resin particles or pigment particles occurs, causing separation of the resin particles or pigment particles. It is believed that the above-mentioned change in the adsorption form progresses due to the molecular motion of the polymer chain of the water-soluble polymer in water. This molecular motion of the polymer chain is influenced by the solubility in water of the water-soluble polymer containing the neutralized product of polycarboxylic acid. That is, when the polycarboxylic acid is neutralized with a highly hydrophilic amine (in the present invention, an amine compound with an HLB of more than 15), the solubility in water of the neutralized product of the polycarboxylic acid increases, and the molecular motion of the polymer chain described above becomes active. More specifically, when the solubility of a water-soluble polymer in water is high, the water-soluble polymer can spread stably in water, and as a result, the area available for interaction with resin particles etc. increases, and the probability of interaction increases. As a result, the amount of the water-soluble polymer adsorbed to the resin particles etc. increases (the change in the adsorption form progresses), and crosslinking and aggregation of the resin particles and pigment particles progresses, causing excessive aggregation.

[0033] Therefore, in the viscosity modifier according to the present invention, the solubility of the neutralized polycarboxylic acid in water is reduced and the molecular motion of the polymer chain is suppressed by neutralizing the polycarboxylic acid with a hydrophobic amine having an HLB value of 1 to 15. As a result, it is believed that the adsorption form of the water-soluble polymer is less likely to change, and the excessive progress of aggregation and the occurrence of separation of the water-based paint caused by this change in the adsorption form are suppressed.

[0034] From the above viewpoints, the HLB value of the amine compound used in the viscosity modifier of the present invention must be within the range of 1 to 15. In order to suppress the molecular motion of the polymer chain, to suppress the progress of excessive aggregation caused by changes in the adsorption form of the water-soluble polymer, and to further enhance the effect of suppressing separation of the water-based paint, the HLB value is preferably 1 to 14, more preferably 1 to 11.

[0035] The HLB (Hydrophile Lipophile Balance) value in the present invention is determined by using an organic conceptual diagram. The organic conceptual diagram is a conceptual diagram showing the relationship between the organic value (OV) and the inorganic value. In the organic conceptual diagram, the degree of physical properties mainly due to Van Der Waals forces is called "organicity", and the degree of physical properties mainly due to electrical affinity is called "inorganicity", and the physical properties of a compound are captured by a combination of these. This "organicity" and "inorganicity" are given unique characteristic values ​​called the organic value (OV) and inorganic value (IV) for each compound, and by arranging a large number of compounds on a two-dimensional graph, various trends can be confirmed for each region of the graph.

[0036] The concepts of OV and IV in the organic conceptual diagram are highly correlated with the concepts of hydrophilicity and hydrophobicity in HLB, and when the value calculated from the ratio of OV and IV [IV / OV=IOB (Inorganic Organic Balance)] is compared with the HLB value, the relationship shown in the following formula (F1) approximately holds. That is, the HLB value of the present invention is a value calculated by the following formula (F1) using the organic conceptual diagram. HLB value = IOB value × 10 (F1)

[0037] The hydrophobic amine of the present invention is not particularly limited as long as its HLB value is within the range of 1 to 15, and may be any of primary amines, secondary amines, and tertiary amines, and the number of carbon atoms of the functional group of the amine compound is not particularly limited. Specific examples of the hydrophobic amine of the present invention include at least one amine compound selected from the group consisting of alkylamines, alkanolamines, and polyetheramines. The alkyl group of these hydrophobic amines may be linear or branched. Specific examples of the alkylamines include butylamine, hexylamine, stearylamine, octylamine, diethylamine, dibutylamine, dioctylamine, 2-ethylhexylamine, triethylamine, tripropylamine, tributylamine, isobutylamine, oleylamine, laurylamine, dimethyllaurylamine, and dimethyloctylamine. Specific examples of the alkanolamines include dibutylethanolamine. Specific examples of the polyetheramines include polyoxyethylene alkylamines such as polyoxyethylene laurylamine and polyoxyethylene stearylamine, and polyoxyethylene oleylamine. The hydrophobic amine of the present invention may be a diamine such as octamethylenediamine, or a cyclic amine such as N,N-bis(2-hydroxyethyl)-N-cyclohexylamine. These hydrophobic amines may be used alone or in combination of two or more. Among these hydrophobic amines, in order to further enhance the effect of suppressing separation of the water-based paint, it is preferable that the hydrophobic amine is an amine that does not contain a hydrophilic group other than an amino group, such as an alkylamine.

[0038] As the amine compound of the present invention, an amine compound (hydrophilic amine) having an HLB of more than 15 may be used in combination with a hydrophobic amine. Examples of such hydrophilic amines include polyether amines such as polyoxyethylene laurylamine (EO addition mole number: 5 moles, 7 moles, 10 moles, etc.), polyoxyethylene stearylamine (EO addition mole number: 7 moles, 10 moles, 15 moles, etc.), alcohol amines such as ethanolamine, dimethylethanolamine, 2-amino-2-methyl-1-propanol, alkyl amines such as ethylamine, propylamine, and aqueous ammonia. However, when a hydrophilic amine is used in combination with a hydrophobic amine as an amine compound, in order to reduce the solubility of the neutralized product of polycarboxylic acid in water and obtain a sufficient effect of suppressing separation of the aqueous paint, it is preferable that the amine compound contains 25 mol% or more of hydrophobic amine relative to the total mole number of the amine compound. In other words, it is preferable that the molar ratio of hydrophobic amine to hydrophilic amine (amount of hydrophobic amine / amount of hydrophilic amine) is 25 / 75 or more. In order to further enhance the effect of suppressing separation of the aqueous paint, the molar ratio of the hydrophobic amine to the hydrophilic amine is more preferably 50 / 50 or more, even more preferably 75 / 25 or more, and most preferably 80 / 20 or more.

[0039] The above-mentioned amine compounds may be synthesized by known methods, or may be commercially available products.

[0040] (Neutralized polycarboxylic acid) The neutralized product of the polycarboxylic acid obtained by neutralizing the above-mentioned polycarboxylic acid with the above-mentioned amine compound may be a completely neutralized product or a partially neutralized product. The completely neutralized product refers to a neutralized product in which all carboxyl groups of the polycarboxylic acid are neutralized with an amine compound, and the partially neutralized product refers to a neutralized product in which some carboxyl groups of the polycarboxylic acid are neutralized with an amine compound. The neutralization rate of the polycarboxylic acid is not particularly limited, but since a lower neutralization rate may reduce the viscosity-imparting effect of the viscosity adjuster of the present invention, in order to ensure a sufficient viscosity-imparting effect on the aqueous coating composition, the neutralization rate is preferably 30% or more, and more preferably 50% or more. The neutralization rate of the polycarboxylic acid is preferably as close to 100% (complete neutralization). The "neutralization rate" in the present invention refers to the ratio of the number of carboxyl groups neutralized by an amine compound among all carboxyl groups of the polycarboxylic acid, and is calculated by the following formula (F2). Neutralization rate = (number of carboxyl groups neutralized by amine compound / total number of carboxyl groups in polycarboxylic acid) × 100 (%) (F2)

[0041] (Partition ratio of neutralized polycarboxylic acid into water) As described above, the separation suppression effect of the water-based paint according to the present invention increases as the solubility in water of the water-soluble polymer containing the neutralized product of polycarboxylic acid is lower. From this viewpoint, as described above, it is particularly preferable that the HLB of the hydrophobic amine used as the amine compound is 1 or more and 11 or less. In this way, when a hydrophobic amine with an HLB of 11 or less is used, the separation suppression effect can be more reliably increased by using a neutralized product of polycarboxylic acid with a small partition rate in water as the viscosity adjuster of the present invention. Here, the "partition rate in water" in the present invention means the ratio (%) of the pre-neutralized product of polycarboxylic acid that dissolves in water when the pre-neutralized product of polycarboxylic acid is added to a mixed solvent in which water and liquid A that is almost insoluble in water (the neutralized product of polycarboxylic acid dissolves in liquid A) are mixed. The partition rate of the neutralized product of polycarboxylic acid in water is an index of the hydrophobicity of the neutralized product. That is, the partition rate of the neutralized product of polycarboxylic acid in water is calculated by the following formula (F3). Distribution rate to water (%) = (amount of neutralized polycarboxylic acid dissolved in the aqueous phase (g) / amount of neutralized polycarboxylic acid added to the mixed solvent (g)) × 100 (F3)

[0042] Specifically, when a neutralized product of a polycarboxylic acid is added to a 1:1 (weight ratio) mixed solvent of water and 2-ethylhexanol (an example of liquid A), the distribution rate of the neutralized product of the polycarboxylic acid to water is preferably 0.0% or more and 74.0% or less, and more preferably 0.0% or more and 72.0% or less.

[0043] (solvent) The solvent of the viscosity modifier of the present invention is a medium mainly composed of water and a solvent.The solvent is not particularly limited, but from the viewpoint of the solubility of the polycarboxylic acid neutralization product, a highly polar solvent is preferred.The highly polar solvent is preferably, for example, water, an alcohol-based solvent, a glycol-based solvent, etc.

[0044] (Use in combination with other viscosity modifiers) The viscosity modifier of the present invention may be used in combination with the neutralized polycarboxylic acid described above. Examples of the viscosity modifier include polyamide type viscosity modifier, acrylic polymer type viscosity modifier, urethane association type viscosity modifier, urea type viscosity modifier, wax type viscosity modifier, cellulose type viscosity modifier such as cellulose nanofiber and carboxymethylcellulose, inorganic type viscosity modifier such as bentonite and synthetic hectorite.

[0045] (auxiliary agent) The viscosity modifier for aqueous coatings of the present invention may contain auxiliaries for the purpose of imparting other functions, such as surfactants, dispersants, defoamers, leveling agents, anti-cracking agents, and interlayer control agents, for the purpose of improving the gloss retention of the coating film, the dispersibility of the pigment, and the defoaming property of the aqueous coating composition.

[0046] (Method of manufacturing viscosity modifier) The viscosity modifier for aqueous paint of the present invention described above can be obtained by neutralizing the above-mentioned polycarboxylic acid with the above-mentioned amine compound so as to obtain a desired neutralization rate. As the viscosity modifier for aqueous paint of the present invention, a neutralized product of polycarboxylic acid may be prepared in advance, and the pre-neutralized product may be added to the aqueous paint as a viscosity modifier. Alternatively, the polycarboxylic acid and the amine compound may be added separately to the aqueous paint so that the neutralization reaction of the polycarboxylic acid occurs in the aqueous paint. The pre-neutralized product can be obtained, for example, by adding a polycarboxylic acid in an amount necessary to obtain a desired ratio of the solid content of the viscosity modifier and an amine necessary to partially (partially) or completely neutralize the polycarboxylic acid to the above-mentioned solvent, and then diluting and mixing with water and / or a solvent so as to obtain a desired ratio of the solid content of the viscosity modifier.

[0047] (Viscosity adjuster applications) The applications for which the viscosity modifier according to the present invention is suitable are not particularly limited as long as it is added to an aqueous paint together with an aqueous resin. For example, the viscosity modifier according to the present invention can be suitably used in aqueous paints for automobiles that contain a resin containing a hydroxyl group, such as an isocyanate-cured resin or a melamine-cured resin, and in aqueous paints that contain an acrylic / urethane emulsion or dispersion.

[0048] [Water-based paint composition] The aqueous coating composition of the present invention contains an aqueous resin and the viscosity modifier for aqueous coating as essential components. The aqueous coating composition of the present invention may further contain other additives as optional components, such as colorants such as pigments, antifoaming agents, film-forming assistants, and pH adjusters.

[0049] (Viscosity modifier content) The viscosity modifier for aqueous paint of the present invention may be added in an amount that provides the desired viscosity for the aqueous paint, depending on the type of aqueous resin, which is a coating film-forming component in the aqueous paint composition, the blending composition of pigments, etc. For example, the content of the viscosity modifier may be 0.1% by mass or more and 5% by mass or less based on the total solid content of the aqueous paint composition. By setting the content of the viscosity modifier within the above range, the effect of adding the viscosity modifier (the effect of imparting viscosity to the aqueous paint composition) can be further enhanced.

[0050] (Water-based resin) The aqueous resin contained in the aqueous coating composition according to the present invention as a coating film-forming component is a resin component dispersed in a medium mainly composed of water, and examples of the resin component include acrylic resins, acrylic silicone resins, alkyd resins, polyester resins, urethane resins, epoxy resins, silicone resins, and fluororesins. The form of the aqueous resin can be divided into water-soluble, colloidal dispersion, and emulsion depending on the dispersion form, and any form can be applied. These resins may be, for example, heat-curable, ultraviolet-curable, electron beam-curable, oxidation-curable, photocation-curable, peroxide-curable, and curable with a chemical reaction in the presence or absence of a catalyst, or may be a resin with a high glass transition point that does not involve a chemical reaction and becomes a coating only by volatilizing the dilution medium. In addition, examples of the curing agent include amino resins, melamine resins, isocyanate compounds, blocked isocyanate compounds, and epoxy compounds. Among these aqueous resins, anionic aqueous resins are preferable, and resins in the form of emulsion or dispersion are particularly preferable. When an amine compound is added to a cationic resin, the balance (dispersion state of oil droplets) of the emulsion resin or dispersion resin that maintains the oil droplet shape in water is lost, the oil droplet-shaped resin breaks, and the resin solids may aggregate, so an anionic resin is preferable. Also, when the resin is in the form of an emulsion or dispersion, the aqueous resin can become a scaffold (crosslinking point) for the polycarboxylic acid type viscosity modifier, so that the viscosity imparting effect tends to be high, which is preferable.

[0051] (Pigments) Examples of pigments include extender pigments such as calcium carbonate (heavy calcium carbonate (GCC), precipitated calcium carbonate (PCC), etc.), barium sulfate, silicon dioxide, aluminum hydroxide, talc, mica, organic fibers, and glass powder; coloring pigments such as titanium dioxide, carbon black, yellow lead, cadmium yellow, ochre, titanium yellow, zinc chromate, red iron oxide, aluminosilicate, quinacridone, phthalocyanine, anthroquinone, diketopyrrolopyrrole, benzimidazolone, and isoindolinone; and metallic pigments such as aluminum flakes, copper flakes, micaceous iron oxide, mica, and scaly powder of mica coated with a metal oxide.

[0052] (Other additives) The aqueous coating composition of the present invention may contain other substances, such as dehydrating agents (e.g., silane coupling agents), adhesion improvers, surfactants, curing catalysts, film-forming aids, driers, anti-staining agents, sensitizers, antioxidants, light stabilizers, UV absorbers, water resistance agents, preservatives and mildew inhibitors, defoamers, leveling agents, dispersants, flame retardants, antistatic agents, release agents, deodorizers, pH adjusters, fragrances and other additives, provided that the properties of the aqueous coating composition and the objects of the present invention are not impaired.

[0053] (Method of producing aqueous coating composition) The aqueous coating composition of the present invention can be manufactured according to the known method for manufacturing aqueous coatings.For example, the components other than the viscosity modifier described above are mixed with a medium mainly composed of water such as ion-exchanged water while stirring, and then pH is adjusted as necessary to prepare a clear coating.The aqueous coating composition can be manufactured by adding a viscosity modifier to this clear coating and dispersing it.

[0054] The viscosity modifier according to the present invention may be added to the aqueous paint during the process of preparing the clear paint as described above, or after the aqueous paint is produced. It is also possible to prepare a master batch and add the viscosity modifier. The equipment used to disperse the viscosity modifier may be one generally used in the production of aqueous paint. The stirring speed and stirring time conditions during dispersion of the viscosity modifier are not particularly limited, and may be appropriately set while checking the dispersion state of the viscosity modifier.

[0055] (Uses of water-based paint compositions) The aqueous coating composition of the present invention can be used for any application in which an aqueous coating is generally used, and can be suitably used, for example, in aqueous coatings for automobiles containing hydroxyl-containing resins such as isocyanate-cured resins and melamine-cured resins, and aqueous coatings containing acrylic / urethane emulsions or dispersions. Specific examples of such aqueous coatings include intermediate coatings and basecoat coatings for automobile body painting, heavy-duty anticorrosive coatings for ships, heavy-duty anticorrosive coatings for steel structures (e.g., bridges), and coatings for plastic substrates.

[0056] [Paint film] The coating film of the present invention can be formed by applying the above-mentioned aqueous coating composition of the present invention to the surface of the substrate and then drying or baking. The coating film of the present invention may be a single-layer coating film consisting of only one coating film, or a multi-layer coating film consisting of two or more coating films. In the case of a single-layer coating film, one coating film is formed by applying the aqueous coating composition of the present invention to the surface of the substrate. In addition, in the case of a multi-layer coating film, at least one of the two or more coating films constituting the multi-layer coating film may be a coating film formed by applying the aqueous coating composition of the present invention to the surface of the substrate or another coating film provided on the surface of the substrate. That is, the coating film of the present invention is a coating film provided on the surface of the substrate, or a coating film laminated on another coating film provided on the surface of the substrate, and the coating film is obtained by applying the above-mentioned aqueous coating composition of the present invention to the surface of the substrate or another coating film.

[0057] The aqueous paint used in forming other coating films may be the aqueous paint composition of the present invention, or may be other paints. To give a specific example, in the case of painting an automobile body, an electrodeposition paint is applied as an undercoat paint to the surface of a metal such as a steel plate for an automobile body, which is a substrate, and then an intermediate paint is applied for the purpose of improving the color development of the body, and further, a base coat paint containing a colorant for the body (hereinafter referred to as "base paint") is applied, and finally, a clear paint is applied as a top coat. In this case, the paint containing the aqueous paint composition of the present invention may be used as an intermediate paint or as a base paint. Alternatively, the aqueous paint composition of the present invention may be used for both the intermediate paint and the base paint.

[0058] The substrate is not particularly limited, but examples thereof include metal plates such as steel plates, iron plates, and tin plates, electrocoated plates obtained by electrocoating these metal plates, and plastics such as polypropylene, urethane, polycarbonate, polyester, and polyethylene terephthalate (PET).

[0059] The method of forming the multi-layer coating film is not particularly limited, and may include a step of sequentially applying the paint for forming the two or more layers of the multi-layer coating film wet-on-wet (wet-on-wet coating step), or may be applied and baked one by one. When the wet-on-wet coating step is included, all of the paint for forming the two or more layers of the multi-layer coating film may be applied wet-on-wet, or only the paint for forming a part of the layers (at least two layers) may be applied wet-on-wet. In addition, in the wet-on-wet coating step, preheating (preheating) or the like may be performed between the application of the paint for the lower layer and the application of the paint for the upper layer. In addition, as the aqueous coating composition of the present invention, a one-liquid type (i.e., not including a curing agent) aqueous coating may be used, and after applying it as an undercoat paint, it may be dried and cured at room temperature, and then a topcoat paint may be applied. The coating method of the aqueous coating composition of the present invention is not particularly limited, and examples thereof include bell-type electrostatic coating, air spray coating, paint jet coating, roller coating, and airless coating. In addition, the baking conditions are not particularly limited, and may be appropriately adjusted according to the coating method.

[0060] The thickness of the coating is not particularly limited, and may be set within an appropriate range depending on the application.

[0061] [Painted items] The coated article of the present invention is a coating material having the above-mentioned coating film on the surface of the above-mentioned substrate. The coating film of the coated article of the present invention may be a single-layer coating film having only one layer, or may be a multi-layer coating film having two or more layers laminated. That is, the coated article of the present invention has one or more coating films on the surface of the substrate, and at least one of the coating films is obtained by applying the above-mentioned aqueous coating composition of the present invention to the surface of the substrate or other coating film. The coated article of the present invention can be suitably used for applications such as automobile bodies, automobile plutic parts, ship hulls, steel structures such as bridges, plastic home appliances, game consoles, plastic toys, and other plastic products. The manufacturing method of such a coated article of the present invention includes a coating film forming step of forming a coating film on the surface of a substrate or other coating film as described above.

[0062] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment. In other words, it is understood that other embodiments or various modifications that can be conceived by a person skilled in the art within the scope of the invention described in the claims also belong to the technical scope of the present invention.

[0063] For example, the present invention may be the following invention. (1) A viscosity modifier for aqueous paints, comprising a neutralized product of polycarboxylic acid obtained by neutralizing a polycarboxylic acid having an acid value of 45 or more with an amine compound, the amine compound comprising at least a hydrophobic amine having an HLB value of 1 or more and 15 or less. (2) The viscosity modifier for aqueous paints according to (1), characterized in that the HLB of the hydrophobic amine is 1 or more and 11 or less. (3) The viscosity modifier for aqueous paints according to (2), characterized in that when the neutralized product of the polycarboxylic acid is added to a 1:1 (volume ratio) mixed solvent of water and 2-ethylhexanol, the distribution rate of the neutralized product of the polycarboxylic acid into water is 74.0% or less. (4) The viscosity modifier for aqueous paints according to any one of (1) to (3), characterized in that the polycarboxylic acid is at least one selected from the group consisting of polymers and copolymers of (meth)acrylic acid, polymers and copolymers of (anhydride) maleic acid, polymers and copolymers of itaconic acid, and thickening polysaccharides. (5) The viscosity modifier for aqueous paints according to (4), characterized in that at least one of the copolymer of (meth)acrylic acid, the copolymer of (maleic anhydride) and the copolymer of itaconic acid contains (meth)acrylate as a constituent monomer. (6) The viscosity modifier for aqueous paint according to any one of (1) to (5), characterized in that the hydrophobic amine is at least one amine compound selected from the group consisting of alkylamines, alkanolamines and polyetheramines. (7) The viscosity modifier for an aqueous paint according to any one of (1) to (6), characterized in that the amine compound contains the hydrophobic amine in an amount of 25 mol % or more based on the total number of moles of the amine compounds. (8) An aqueous coating composition comprising an aqueous resin and a viscosity modifier, the viscosity modifier including a neutralized product of a polycarboxylic acid having an acid value of 45 or more neutralized with an amine compound, the amine compound including at least a hydrophobic amine having an HLB value of 1 or more and 15 or less. (9) The aqueous coating composition according to (8), wherein the HLB value of the hydrophobic amine is 1 or more and 11 or less. (10) The aqueous coating composition according to (9), characterized in that when the neutralized product of the polycarboxylic acid is added to a 1:1 (volume ratio) mixed solvent of water and 2-ethylhexanol, the distribution rate of the neutralized product of the polycarboxylic acid into water is 74.0% or less. (11) The aqueous coating composition according to any one of (8) to (10), characterized in that the polycarboxylic acid is at least one member selected from the group consisting of polymers and copolymers of (meth)acrylic acid, polymers and copolymers of maleic (anhydride) acid, polymers and copolymers of itaconic acid, and thickening polysaccharides. (12) The aqueous coating composition according to (11), characterized in that at least one of the copolymer of (meth)acrylic acid, the copolymer of (maleic anhydride) and the copolymer of itaconic acid contains (meth)acrylate as a constituent monomer. (13) The aqueous coating composition according to any one of (8) to (12), wherein the hydrophobic amine is at least one amine compound selected from the group consisting of alkylamines, alkanolamines and polyetheramines. (14) The aqueous coating composition according to any one of (8) to (13), wherein the amine compound contains the hydrophobic amine in an amount of 25 mol % or more based on the total number of moles of the amine compound. (15) A coating film provided on the surface of a substrate, or a coating film laminated on another coating film provided on the surface of the substrate, characterized in that the coating film is obtained by applying an aqueous paint composition according to any one of (8) to (14) onto the surface of the substrate or the other coating film. (16) A coated article having one or more coating layers on the surface of a substrate, characterized in that at least one of the coating layers is obtained by applying the aqueous coating composition according to any one of (8) to (14) onto the surface of the substrate or another coating layer. (17) A method for forming a multilayer coating film by forming two or more coating layers on a surface of a substrate, comprising using the aqueous coating composition according to any one of (8) to (14) as at least one of the coating materials for forming the two or more coating layers; A method for forming a multi-layer coating film, comprising the step of successively applying the paint for forming the two or more coating layers in a wet-on-wet manner. (18) A method for producing a coated article, comprising a coating film forming step of forming a multi-layer coating film consisting of two or more coating layers on the surface of a substrate, the method comprising the steps of: using the aqueous coating composition according to any one of (8) to (14) as at least one of the coating films for forming the two or more coating layers; A method for producing a coated article, wherein the coating film forming step includes a step of successively coating the two or more layers of coating film-forming paints in a wet-on-wet manner. EXAMPLES

[0064] The present invention will be specifically described below with reference to examples. Note that the present invention is not limited to these examples. In the examples, "%" and "parts" refer to "% by mass" and "parts by mass" unless otherwise specified.

[0065] [Preparation of viscosity adjuster] First, A1 to A4 listed in Table 1 were prepared as polycarboxylic acids, and B1 to B11 listed in Table 2 were prepared as amine compounds. Disparlon AQ-021 manufactured by Kusumoto Chemical Industries, Ltd. was used as A1, and Disparlon AQ-001 manufactured by Kusumoto Chemical Industries, Ltd. was used as A2. A3 and A4 were synthesized by using a monomer mixture consisting of methacrylic acid, ethyl acrylate, methacrylate of 30 moles of octadecyl alcohol ethylene oxide adduct, and trimethacrylate of 60 moles of glycerin ethylene oxide adduct as monomers and polymerizing this monomer mixture in accordance with the method described in the examples of Patent Document 1. In addition, in the synthesis of A3 and A4, the amount of methacrylic acid was adjusted to obtain the acid value listed in Table 1. Specifically, the acid value of the polycarboxylic acid can be increased by increasing the amount of methacrylic acid, and the acid value of the polycarboxylic acid can be decreased by decreasing the amount of methacrylic acid. In addition, BROWNON (registered trademark) CHA-2P manufactured by Aoki Oil & Fat Industries, Ltd. was used as B8. In Table 2, "EO: 2 moles" and the like represent the number of moles of ethylene oxide (EO) added to the polyoxyethylene alkylamine.

[0066] [Table 1]

[0067] [Table 2]

[0068] Next, viscosity modifiers S1 to S18 were prepared using the polycarboxylic acid in Table 1 and the amine compound in Table 2 in the formulations shown in Tables 3 to 6. More specifically, for S1 to S8 and S10 to S18, viscosity modifiers consisting of pre-neutralized polycarboxylic acids were prepared as follows. After adding a polycarboxylic acid in an amount necessary to make the solid content of the viscosity modifier 5% and an amine compound necessary to completely neutralize this polycarboxylic acid to distilled water, the viscosity modifier was diluted with distilled water so that the solid content of the viscosity modifier was 5%, and mixed to obtain viscosity modifiers S1 to S8 and S10 to S18. For S9, the same amounts of polycarboxylic acid A1 and amine compound B1 as those used to prepare the pre-neutralized product of S1 were added (separately added) to the aqueous paint composition, respectively, and polycarboxylic acid A1 was neutralized in the aqueous paint composition to obtain viscosity modifier S9.

[0069] Further, using the polycarboxylic acids in Table 1 and the amine compounds in Table 2 in the formulations shown in Table 7, viscosity modifiers H1 to H7 were prepared in the same manner as viscosity modifiers S1 to S8 and S10 to S18.

[0070] [Table 3]

[0071] [Table 4]

[0072] [Table 5]

[0073] [Table 6]

[0074] [Table 7]

[0075] [Evaluation of the distribution ratio of neutralized polycarboxylic acids into water] The distribution ratios into water of the pre-neutralized polycarboxylic acids used as the viscosity modifiers S1 to S8, S11, S12, H1, H2, and H4 to H7 prepared as described above were evaluated.

[0076] First, 2.0 g of each pre-neutralized polycarboxylic acid was added to a mixed solvent of water / 2-ethylhexanol (30 ml / 30 ml), stirred for 1 minute, and then allowed to stand for 2 hours. Next, 2.0 g of the aqueous phase of the mixed solution in which the pre-neutralized polycarboxylic acid was dissolved was weighed out into an evaporating dish, and the weight (g) of the heating residue (solid content remaining in the evaporating dish) after heating for 1 hour in a thermostatic bath at 120°C was measured. The heating residue (solid content remaining in the evaporating dish) was the pre-neutralized polycarboxylic acid.

[0077] Next, the proportion of the heating residue in the aqueous phase Rh (%) was calculated from the proportion of the weight Ws of the solids remaining in the evaporating dish to the weight Rw of the aqueous phase weighed out in the evaporating dish, as shown in the following formula (F4). Rh(%)=(Ws(g) / Rw(g))×100 ···(F4)

[0078] Furthermore, as shown in the following formula (F5), the weight Wn (g) of the pre-neutralized polycarboxylic acid dissolved in the aqueous phase in the entire mixed solution was calculated from the ratio Rh (%) of the heating residue in the aqueous phase calculated as described above, and the distribution ratio Rd (%) to water was calculated from this weight Wn using the following formula (F6). Note that "Ww (g)" in formula (F5) indicates the weight (g) of water in the mixed solvent, that is, the total amount of the weight of water in the mixed solvent (30 g) and the weight of water contained in the pre-neutralized polycarboxylic acid. Also, "Wa (g)" in formula (F6) indicates the weight (2.0 g in this embodiment) of the pre-neutralized polycarboxylic acid added to the mixed solvent. Wn(g) = Ww(g) × Rh(%) (F5) Rd(%)=(Wn(g) / Wa(g))×100 ···(F6)

[0079] The distribution ratios to water Rd (%) calculated as above are shown in Tables 3, 4 and 7.

[0080] [Preparation of water-based paint composition] A water-based paint was prepared according to the paint formulation shown in Table 8. Specifically, 36.6 parts of distilled water, 5.6 parts of 2-ethylhexanol, and 1.9 parts of butyl propylene glycol were added to 41.7 parts of Burnock (registered trademark) WE-300 (acrylic emulsion resin manufactured by DIC Corporation) and 14.2 parts of Burnock WD-551 (acrylic dispersion resin manufactured by DIC Corporation), and then mixed to obtain a water-based paint. The viscosity adjusters S1 to S18 and H1 to H7 prepared as described above were added to the water-based paint thus obtained so that the viscosity was 300±50 mPa·s at 60 revolutions using a B-type viscometer, and the mixture was mixed and dispersed to obtain the water-based paint compositions of Examples 1 to 18 and Comparative Examples 1 to 7.

[0081] [Table 8]

[0082] [Evaluation of viscosity imparting effect] Regarding whether or not a viscosity-imparting effect was achieved, when a viscosity modifier was added to the water-based paint to adjust its viscosity, those that could be adjusted to a range of 300 ± 50 mPa s at 60 revolutions were marked as "OK," and those that could not be adjusted to a range of 300 ± 50 mPa s at 60 revolutions were marked as "NG."

[0083] [Evaluation of the effect of inhibiting separation] The separation-inhibiting effect was evaluated by placing the aqueous coating compositions of the Examples and Comparative Examples obtained as described above in a reagent bottle and leaving them in a thermostatic chamber at 25°C, and using the following criteria depending on the number of days until separation of the coating occurred. It was checked every day whether separation of the coating occurred or not. No separation occurred even after 7 days in the thermostatic chamber. A Separation occurs within 5 to 7 days after being placed in the thermostatic chamber. B Separation occurs within 3 to 5 days after placing in the thermostatic chamber. C Separation occurs within 3 days after being placed in the thermostatic chamber, or the viscosity imparting effect is not evaluated as NG.

[0084] The occurrence of separation was confirmed visually by shining a light on the reagent bottle containing the aqueous coating composition. When a light was shone on the back of the sample, it was determined that separation had occurred if a clear boundary line between separated phases could be confirmed (see Figure 1), and it was determined that separation had not occurred if a clear boundary line between separated phases could not be confirmed (see Figure 2).

[0085] [Evaluation Results] As shown in Tables 3 to 6, the aqueous coating compositions of Examples 1 to 18 all had sufficient viscosity imparting effect (OK rating) and separation suppression effect (A rating to C rating). In particular, as can be seen from the comparison of Examples 1 to 8, when the HLB of the amine compound was 11 or more, the separation suppression effect was particularly excellent (A rating). Also, as can be seen from the comparison of Example 1, Examples 12 to 16, and Comparative Example 1, when a hydrophobic amine and a hydrophilic amine were used in combination as the amine compound, when the ratio of hydrophobic amine / hydrophilic amine was 50 / 50 or more, the separation suppression effect was excellent (A rating or B rating), and when the ratio was 80 / 20 or more, the separation suppression effect was particularly excellent (A rating). Furthermore, as can be seen from the comparison of Example 1 and Example 9, even when the polycarboxylic acid and the amine compound were added separately to the aqueous coating, the separation suppression effect was equivalent to that when a pre-neutralized product of the polycarboxylic acid was prepared and added to the aqueous coating.

[0086] On the other hand, as shown in Table 7, the aqueous coating compositions of Comparative Examples 1 to 5, which used only hydrophilic amines with an HLB value of more than 15 as the amine compound, were inferior in the separation suppression effect (rating D). Also, the aqueous coating compositions of Comparative Examples 6 and 7, which used polycarboxylic acids with an acid value of less than 50 as the polycarboxylic acid, were inferior in the viscosity imparting effect (rating NG).

[0087] [Formation of multi-layer coating film and preparation of coated articles] Furthermore, a multi-layer coating film was formed by wet-on-wet coating as described below using either the isocyanate-cured water-based coating composition having the formulation shown in Table 9 or the melamine-cured water-based coating composition having the formulation shown in Table 10 as an undercoat coating, and a clear coating having the formulation shown in Table 11 as a topcoat coating, to produce a coated article. In addition, a coated article was also produced using the same coating material, in which a multi-layer coating film was formed by baking the undercoat coating and the topcoat coating one layer at a time.

[0088] First, as shown in Table 9, 6.1 parts of distilled water, 4.8 parts of 2-ethylhexanol (EHA) and 1.6 parts of butyl propylene glycol (BFG) were added to 35.4 parts of Burnock WE-300, 12.1 parts of Burnock WD-551 and 25.0 parts of aluminum slurry of the formulation shown in Table 12, and then mixed to prepare Part A of an isocyanate-curing water-based paint. The aluminum slurry was obtained by adding 34.0 parts of Emeral (registered trademark) EMR-D6340 (silica-coated aluminum paste pigment manufactured by Toyo Aluminum Co., Ltd.) and 1.7 parts of Disparlon AQ-330 (polyether phosphate ester compound dispersant manufactured by Kusumoto Chemical Co., Ltd.) as a lustrous agent to 64.3 parts of distilled water, mixing and dispersing, as shown in Table 12.

[0089] Next, 2.0 parts of viscosity modifier S1 were added to Part A obtained as described above. Furthermore, 15.0 parts of BURNOCK (registered trademark) DNW-5500 (water-dispersible polyisocyanate manufactured by DIC Corporation) as Part B of the isocyanate-curing water-based paint was added to Part A containing the viscosity modifier S1, and the viscosity was adjusted to 15 seconds with a Ford cup, and then the paint was air-sprayed on one side of the tin plate as an undercoat paint. After the undercoat paint was applied, the paint was preheated at 80 ° C for 5 minutes, and then the clear paint having the composition described in Table 11 was air-sprayed on the undercoat paint as a topcoat paint. After the clear paint was applied, the paint was left to stand (set) at room temperature for 5 minutes, and then baked at 140 ° C for 30 minutes to obtain a coated article 1-1 in which a multi-layer coating film 1A (wet-on-wet coating) was formed on the surface of the tin plate.

[0090] The clear coating was prepared as follows so that the equivalent ratio (NCO / OH) of isocyanate and polyol was 1.2. As shown in Table 11, 41.2 parts of butyl acetate and 12.9 parts of Sumidur (registered trademark) N-3300 (polyisocyanate manufactured by Sumika Covestro Urethane Co., Ltd.) were added and mixed into 45.9 parts of Desmophen (registered trademark) A-870 BA (acrylic polyol manufactured by Covestro), and 1.7 parts of Disparlon NSF-8363 (leveling agent manufactured by Kusumoto Chemical Co., Ltd.) and 2.1 parts of Disparlon OX-883HF (defoaming agent manufactured by Kusumoto Chemical Co., Ltd.) were added and mixed to obtain a clear coating.

[0091] In addition to the wet-on-wet coating, a multi-layer coating film 1B was formed by applying a primer and a top coat one by one and baking them. Specifically, an isocyanate-curing water-based paint was prepared in the same manner as in the wet-on-wet coating, and this water-based paint was used as a primer paint and air-sprayed on one side of a tin plate. After the primer paint was applied, it was preheated at 80°C for 5 minutes and then baked at 140°C for 30 minutes. Next, as a top coat paint, a clear paint having the composition shown in Table 11 was air-sprayed on the surface of the primer coating film. After the clear paint was applied, it was left to stand (set) at room temperature for 5 minutes and baked at 140°C for 30 minutes to obtain a coated article 1-2 in which a multi-layer coating film 1B (a primer coat and a top coat baked one by one) was formed on the surface of the tin plate.

[0092] Secondly, as shown in Table 10, 32.3 parts of distilled water, 4.9 parts of 2-ethylhexanol (EHA) and 1.7 parts of butyl propylene glycol (BFG) were added to 36.8 parts of Burnock WE-300, 12.5 parts of Burnock WD-551, 4.4 parts of Water-Based Concentrate White (colorant for water-based paints manufactured by Yokohama Chemical Industry Co., Ltd.), 7.4 parts of CYMEL (registered trademark) 327 (melamine resin manufactured by Allnex) and 0.2 parts of viscosity modifier S1, and then mixed to adjust the viscosity to 300 mPa s to prepare a melamine-curing water-based paint.

[0093] Next, the melamine-curing water-based paint obtained as described above was applied as an undercoat paint to one side of a tin plate using a 4 mil applicator. After the undercoat paint was applied, it was preheated at 80°C for 5 minutes and then baked at 140°C for 30 minutes. Next, as a topcoat paint, a clear paint having the composition shown in Table 11 was applied to the surface of the undercoat paint film using a 4 mil applicator. After the clear paint was applied, it was left to stand (set) at room temperature for 5 minutes and baked at 140°C for 30 minutes to obtain a coated article 2 in which a multi-layer coating film 2B (undercoat and topcoat baked one layer at a time) was formed on the surface of the tin plate.

[0094] [Table 9]

[0095] [Table 10]

[0096] [Table 11]

[0097] [Table 12]

[0098] In all of the multi-layer coating films 1A, 1B and 2B, the coating film had a uniform thickness and was formed without any bumps.

Claims

1. The present invention includes a neutralized product of polycarboxylic acid obtained by neutralizing a polycarboxylic acid having an acid value of 45 or more with an amine compound, A viscosity modifier for aqueous paints, comprising at least a hydrophobic amine having an HLB of 1 or more and 15 or less as the amine compound.

2. 2. The viscosity modifier for aqueous paints according to claim 1, wherein the HLB of the hydrophobic amine is 1 or more and 11 or less.

3. 3. The viscosity modifier for aqueous paints according to claim 2, characterized in that when the neutralized product of the polycarboxylic acid is added to a mixed solvent of water and 2-ethylhexanol in a 1:1 (volume ratio), the distribution rate of the neutralized product of the polycarboxylic acid to water is 74.0% or less.

4. The viscosity modifier for aqueous paints according to any one of claims 1 to 3, characterized in that the polycarboxylic acid is at least one selected from the group consisting of polymers and copolymers of (meth)acrylic acid, polymers and copolymers of (anhydride) maleic acid, polymers and copolymers of itaconic acid, and thickening polysaccharides.

5. 5. The viscosity modifier for aqueous paints according to claim 4, wherein at least one of the copolymer of (meth)acrylic acid, the copolymer of (maleic anhydride) acid and the copolymer of itaconic acid contains (meth)acrylate as a constituent monomer.

6. The viscosity modifier for aqueous paint according to any one of claims 1 to 3, characterized in that the hydrophobic amine is at least one amine compound selected from the group consisting of alkylamines, alkanolamines and polyetheramines.

7. The viscosity modifier for aqueous paint according to any one of claims 1 to 3, characterized in that the amine compound contains the hydrophobic amine in an amount of 25 mol % or more based on the total number of moles of the amine compound.

8. Contains an aqueous resin and a viscosity modifier, The viscosity modifier includes a neutralized product of polycarboxylic acid obtained by neutralizing a polycarboxylic acid having an acid value of 45 or more with an amine compound, The aqueous coating composition comprises at least a hydrophobic amine having an HLB of 1 or more and 15 or less as the amine compound.

9. A coating film provided on a surface of a substrate, or a coating film laminated on another coating film provided on the surface of the substrate, The coating film is a coating film obtained by applying an aqueous coating composition containing an aqueous resin and a viscosity modifier to the surface of the substrate or the other coating film, The viscosity modifier includes a neutralized product of polycarboxylic acid obtained by neutralizing a polycarboxylic acid having an acid value of 45 or more with an amine compound, A coating film comprising at least a hydrophobic amine having an HLB of 1 or more and 15 or less as the amine compound.

10. A coated article having one or more coating layers on the surface of a substrate, At least one layer of the coating film is obtained by applying an aqueous coating composition containing an aqueous resin and a viscosity modifier to the surface of the substrate or another coating film, The viscosity modifier includes a neutralized product of polycarboxylic acid obtained by neutralizing a polycarboxylic acid having an acid value of 45 or more with an amine compound, A coated article comprising at least a hydrophobic amine having an HLB of 1 or more and 15 or less as the amine compound.

11. A method for forming a multilayer coating film by forming two or more coating films on a surface of a substrate, comprising the steps of: As at least one of the paints for forming the two or more coating layers, an aqueous paint composition containing an aqueous resin and a viscosity modifier is used, The viscosity modifier includes a neutralized product of polycarboxylic acid obtained by neutralizing a polycarboxylic acid having an acid value of 45 or more with an amine compound, The amine compound contains at least a hydrophobic amine having an HLB of 1 or more and 15 or less, A method for forming a multi-layer coating film, comprising the step of successively applying the paint for forming the two or more coating layers in a wet-on-wet manner.

12. A method for producing a coated article, comprising a coating film forming step of forming a multilayer coating film consisting of two or more coating films on a surface of a substrate, As at least one of the paints for forming the two or more coating layers, an aqueous paint composition containing an aqueous resin and a viscosity modifier is used, The viscosity modifier includes a neutralized product of polycarboxylic acid obtained by neutralizing a polycarboxylic acid having an acid value of 45 or more with an amine compound, The amine compound contains at least a hydrophobic amine having an HLB of 1 or more and 15 or less, A method for producing a coated article, wherein the coating film forming step includes a step of successively coating the two or more layers of coating film-forming paints in a wet-on-wet manner.

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