JP7634037B2 - One-liquid coating composition, coating method, coated body, and coating film - Google Patents

Description

The present invention relates to a one-component coating composition, a coating method, a coated body, and a coating film.

Undercoat paints for metal substrates used in automotive production machinery and the like have traditionally been required to have excellent water resistance and corrosion resistance, and one-component paints with the above properties are in demand, particularly from the viewpoint of eliminating the need to consider the labor of mixing during painting and the usable time. In addition, in order to efficiently paint large objects, paints with high paint solids content and excellent paint workability, which allows for easy buildup of film thickness, are in demand.

As a conventional one-liquid paint, for example, Patent Document 1 discloses a paint composition that contains a modified epoxy resin solution (F) consisting of a modified epoxy resin (D) obtained by reacting a bisphenol-type epoxy resin (a), amines (b) containing an aliphatic secondary amine having a specific structure, and a (semi) drying oil fatty acid (c), and a solvent (E) containing an aliphatic hydrocarbon solvent, and the ratio of the aliphatic hydrocarbon solvent in the solvent (E) is 30 to 70% by weight, and an example is an example of a one-liquid epoxy resin paint with an organic solvent content of about 50% by mass. Patent Document 2 discloses, as paint resins, an epoxy resin containing a bisphenol-type epoxy resin, an amine-modified epoxy resin consisting of amines, and a urethane-modified epoxy resin that is a reaction product of polyisocyanates. Furthermore, Patent Document 3 discloses a paint composition that contains at least one modified epoxy resin selected from an amine-modified epoxy resin, an isocyanate-modified epoxy resin, and an acrylic-modified epoxy resin, an epoxy ester resin, a pigment, and a solvent, and the content of the solvent in the paint composition is 40% by mass or less.

JP 2004-231853 A JP 2018-030997 A JP 2020-152877 A

Patent documents 1 to 3 all disclose one-component paints, but the paintability, particularly in airless spray painting, water resistance, corrosion resistance, and adhesion are insufficient. Therefore, there is a demand for one-component paints that have even better paintability, water resistance, and corrosion resistance than the conventional techniques.

The object of the present invention is to provide a one-component paint composition that has a high paint solids content, good paint workability, and is capable of forming an undercoat layer that has excellent water resistance, corrosion resistance, and adhesion, as well as a painting method, coated body, and coating film that use the same.

The features of the present invention are listed below.
(1) A one-component coating composition comprising a modified epoxy resin (A), an epoxy resin (B) other than the modified epoxy resin (A) and containing multiple epoxy groups in one molecule, a pigment (C), and an organic solvent (D), wherein the weight-average molecular weight of the epoxy resin (B) is 300 to 1,500, the mass ratio ((A)/(B)) of the modified epoxy resin (A) to the epoxy resin (B) is 20/80 to 65/35, and the content of the pigment (C) in the solid content is 50 to 80 mass%.
(2) The one-component coating composition according to (1), wherein the one-component coating composition has a viscosity of 10 to 40 seconds at 23° C. as measured using a Ford Cup No. 4.
(3) The one-component coating composition according to (1), wherein the epoxy resin (B) contains a plurality of epoxy resins having different weight average molecular weights.
(4) The one-component coating composition according to (1), wherein the mass ratio (pigment/resin solids) of the pigment (C) to the resin solids (the total amount of all resin solids contained in the one-component coating composition) in the solids of the one-component coating composition is 2.5 to 3.8.

(5) A coating method comprising coating a one-component coating composition according to any one of (1) to (4) on a metal substrate to form an undercoat layer, and then coating a topcoat layer on the undercoat layer to form a topcoat layer.
(6) A primer layer formed by applying a one-component coating composition according to any one of (1) to (4) on a metal substrate;
A coated body comprising a coating film having a topcoat layer formed by applying a topcoat paint on the undercoat layer.
(7) A coating film constituting the coated body described in (6).

The present invention provides a one-component paint composition that has a high paint solids content, good paint workability, and is capable of forming an undercoat layer that is excellent in water resistance, corrosion resistance, and adhesion, as well as a painting method, coated body, and coating film that use the same.

The one-component coating composition of the present invention, the coating method using the same, the coated body, and the coating film are described in detail below.

<One-component paint composition>
The one-component coating composition of the present invention is a one-component coating composition comprising a modified epoxy resin (A), an epoxy resin (B) other than the modified epoxy resin (A) and containing a plurality of epoxy groups in one molecule, a pigment (C), and an organic solvent (D), wherein the weight average molecular weight of the epoxy resin (B) is 300 to 1500, the mass ratio ((A)/(B)) of the modified epoxy resin (A) to the epoxy resin (B) is 20/80 to 65/35, and the content of the pigment (C) in the solid content is 50 to 80 mass%.

<Modified Epoxy Resin (A)>
The one-liquid coating composition of the present invention uses an epoxy resin. In particular, the modified epoxy resin (A) is used in the one-liquid coating composition because it is an epoxy resin that can form a film by itself without using a curing agent. The modified epoxy resin (A) in the one-liquid coating composition of the present invention includes alkyd-modified epoxy resin, fatty acid-modified epoxy resin, urethane-modified epoxy resin, amine-modified epoxy resin, acrylic-modified epoxy resin, polyester-modified epoxy resin, dimer acid-modified epoxy resin, etc. In particular, it is preferable that the modified epoxy resin is selected from alkyd-modified epoxy resin, fatty acid-modified epoxy resin, amine-modified epoxy resin, isocyanate-modified epoxy resin, and acrylic-modified epoxy resin, and further, it is preferable that the modified epoxy resin contains an alkyd-modified epoxy resin and a fatty acid-modified epoxy resin. In the one-liquid coating composition of the present invention, the modified epoxy resin (A) may contain one type of modified epoxy resin, or may contain two or more types.

The weight-average molecular weight of the modified epoxy resin (A) is preferably in the range of 10,000 to 70,000. When the weight-average molecular weight is in the above range, a resin solution having a relatively low viscosity can be obtained, and the amount of organic solvent (D) added can be reduced when adjusting the viscosity to a level suitable for a coating material.
The solid content of the modified epoxy resin (A) is 4 to 30 mass %, preferably 5 to 15 mass %, relative to 100 mass % of the solid content of the one-component coating composition, from the viewpoint that a coating film having excellent corrosion resistance can be easily obtained.
The weight average molecular weight was measured by size exclusion chromatography using polystyrene as a standard substance.

The modified epoxy resin (A) preferably has a Gardner viscosity of G to Z1 at 25°C measured in accordance with JIS-K-5600-2-2:1999 in the resin solution state, and more preferably has a Gardner viscosity of P to Y. If the viscosity of the modified epoxy resin (A) solution is within the above range, the amount of organic solvent (D) added can be reduced when adjusting the viscosity to a level suitable for use as a coating material.

The modified epoxy resin (A) of the present invention may be one obtained by synthesis using a conventional method, or it may be available as a commercially available product. Examples of commercially available products include the Epiclon series and Alkidia series manufactured by DIC Corporation, the Arakawa Chemical Industries Co., Ltd. Araquid series and Modepics series, the Mitsui Chemicals Co., Ltd. Epoch series, and the Phthalkid series manufactured by Resonac Corporation.

<Epoxy resin (B)>
The one-liquid coating composition of the present invention also contains an epoxy resin (B) containing a plurality of epoxy groups in one molecule. Examples of the epoxy resin (B) include glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, bisphenol type epoxy resins, phenol novolac type epoxy resins, cresol type epoxy resins, dicyclopentadiene type epoxy resins, aliphatic type epoxy resins, alicyclic type epoxy resins, and fatty acid modified epoxy resins.
Among these, bisphenol type epoxy resins are preferred because they can easily form a coating film having excellent adhesion to the substrate, and one or more types selected from bisphenol A type, bisphenol AD type and bisphenol F type epoxy resins are more preferred, with bisphenol A type epoxy resins being particularly preferred.
The epoxy resin (B) may be used alone or in combination of two or more kinds.

The weight average molecular weight of the epoxy resin (B) is preferably in the range of 300 to 1,500, and the epoxy equivalent is preferably in the range of 150 to 1,000. When two or more kinds of epoxy resins (B) are used, at least one kind of epoxy resin (B1) preferably has a weight average molecular weight of 500 to 1,500, and the epoxy resin (B2) different from (B1) preferably has a weight average molecular weight of 300 to 500. In this case, the mass ratio ((B1)/(B2)) of the epoxy resin (B1) to the epoxy resin (B2) in the solid content is preferably 50/50 to 90/10, more preferably 55/45 to 80/20.
The content of the epoxy resin (B) is 7 to 40% by mass, preferably 8 to 20% by mass, relative to 100% by mass of the solid content of the one-component coating composition, from the viewpoint of being able to obtain a coating film having excellent adhesion to the substrate.
The epoxy equivalent was measured in accordance with JIS K 7336:2001.

The epoxy resin (B) of the present invention may be one obtained by synthesis using a conventional method, or may be available as a commercially available product. Examples of commercially available products include "E-028" (manufactured by Ohtake Meishin Chemical Co., Ltd., epoxy equivalent 180-190, solid content 100%), "jER807" (manufactured by Mitsubishi Chemical Co., Ltd., bisphenol F type epoxy resin, epoxy equivalent 160-175, solid content 100%), "E-028-90X" (manufactured by Ohtake Meishin Chemical Co., Ltd., xylene solution of bisphenol A type epoxy resin, weight average molecular weight 370, epoxy equivalent 200-210, solid content 90%), "HP-820" (manufactured by DIC Corporation, alkylphenol type epoxy resin, epoxy equivalent 150-200, solid content 100%), "jER828" (manufactured by Mitsubishi Chemical Co., Ltd., bisphenol A type epoxy resin, weight average molecular weight 370, epoxy equivalent 184-194, solid content 100%), "jER834" (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, weight average molecular weight 470, epoxy equivalent 230-270, solid content 100%), "E-834-85X" (manufactured by Ohtake Meishin Chemical Co., Ltd., xylene solution of bisphenol A type epoxy resin, weight average molecular weight 470, epoxy equivalent 270-320, solid content 85%), "jER1001" (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, weight average molecular weight 900, epoxy equivalent 450-500, solid content 100%), "E-001-75" (manufactured by Ohtake Meishin Chemical Co., Ltd., xylene solution of bisphenol A type epoxy resin, weight average molecular weight 900, epoxy equivalent 600-660, solid content 75%), etc.

Here, the mass ratio ((A)/(B)) of the solid content of the modified epoxy resin (A) and the epoxy resin (B) is preferably in the range of 20/80 to 65/35. In the above ratio, if the modified epoxy resin (A) is less than 20 mass% and the epoxy resin (B) is more than 80 mass%, the crosslink density of the coating film formed may decrease, and the water resistance and corrosion resistance may decrease. In addition, if the modified epoxy resin (A) is more than 65 mass% and the epoxy resin (B) is less than 35 mass%, the paint viscosity may increase, resulting in a decrease in paintability, and the flexibility may decrease, resulting in a decrease in adhesion to the substrate. Furthermore, it is more preferable that the mass ratio ((A)/(B)) is in the range of 30/70 to 55/45.

<Other resins>
Furthermore, for the purpose of improving the performance within a range that does not affect the effects of the present invention, the one-component coating composition of the present invention can also be used in combination with other resins that can be normally blended into coatings, such as acrylic copolymers, cellulose compounds, acrylated alkyd resins, alkyd resins, silicone resins, fluororesins, or epoxy resins other than the modified epoxy resin (A) and the epoxy resin (B).

<Pigment (C)>
The one-liquid coating composition of the present invention contains a pigment (C). In order to form a coating film having excellent water resistance, corrosion resistance, and rust prevention properties, the pigment (C) may contain a coloring pigment (C2), an anti-rust pigment (C3), etc. in addition to the extender pigment (C1).

In the one-component coating composition of the present invention, the content of pigment (C) in the solid content of the coating film-forming components is preferably in the range of 50 to 80 mass %, and more preferably in the range of 60 to 80 mass %. If the content of pigment (C) is less than 50 mass %, corrosion resistance in particular decreases, and if it exceeds 80 mass %, adhesion and water resistance decrease, and it becomes difficult to form a coating film.

<<Extender pigment (C1)>>
The extender pigment (C1) is a white or colorless pigment. Because of its low refractive index, it has almost no effect on hiding power even when mixed with a vehicle, and is therefore used as an extender to adjust coloring power, gloss, strength, usability, etc. Known materials can be used as the extender pigment (C1), such as precipitated barium sulfate, silica, cristobalite, calcium carbonate, talc, kaolin, alumina, alum, white clay, magnesium hydroxide, and magnesium oxide.

<<Coloring pigment (C2)>>
The color pigment (C2) is broadly classified into inorganic pigments and organic pigments based on its composition, and in consideration of corrosion resistance, it is particularly preferable to include an inorganic pigment. As the inorganic pigment, known materials can be used, such as titanium oxide, red iron oxide, yellow iron oxide, carbon black, etc.

<<Anti-rust pigment (C3)>>
As the rust-preventive pigment, known materials can be used, such as zinc powder, zinc oxide, barium metaborate, calcium silicate, aluminum phosphate, condensed aluminum phosphate, aluminum tripolyphosphate, zinc phosphate, zinc phosphite, potassium phosphite, calcium phosphite, aluminum phosphite, calcium zinc phosphate, zinc aluminum phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, magnesium phosphate, vanadate/phosphoric acid mixed pigment, etc. In particular, zinc phosphomolybdate, aluminum phosphomolybdate, etc. are preferred. In the one-liquid coating composition of the present invention, the content of the rust-preventive pigment in the solid content is preferably 1 to 15 mass%.

Furthermore, the pigment (C) contained in the one-component coating composition of the present invention preferably contains an extender pigment (C1) having an oil absorption in the range of 5 to 20 ml/100 g, and more preferably an oil absorption in the range of 8 to 16 ml/100 g.
Here, the oil absorption is measured by the refined linseed oil method using linseed oil according to the JIS standard (JIS K 5101-13-1).
When the pigment (C) having an oil absorption of more than 20 ml/100 g is contained in a large amount, a larger amount of organic solvent or resin is required to reduce the viscosity of the one-component coating composition, which may result in a decrease in coating film strength and a large burden on the environment.

Furthermore, the mass ratio (pigment/resin solids) of the pigment (C) in the solids in the one-component coating composition of the present invention to the resin solids (the sum of all the resin solids contained in the one-component coating composition) is preferably 2.5 to 3.8. In order to make the (pigment/resin solids) range from 2.5 to 3.8, for example, as described above, a pigment with low oil absorption is selected. If the (pigment/resin solids) is less than 2.5, the paint viscosity increases significantly, resulting in poor paint workability and reduced corrosion resistance. If the (pigment/resin solids) is more than 3.8, the coating film strength may decrease, and adhesion and water resistance may decrease, and further, poor film formation may result in reduced water resistance, corrosion resistance, and adhesion.

<Organic Solvent (D)>
The organic solvent (D) used in the one-liquid coating composition of the present invention is not particularly limited, and examples thereof include aromatic solvents such as xylene and toluene, ester solvents such as ethyl acetate, butyl acetate, isobutyl acetate, and 2-methoxypropyl acetate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, 2-methoxyethyl acetate, 2-ethoxyethyl acetate, 3-methoxy-3-methylbutanol, 3-methoxy-3-methylbutyl acetate, 1-methoxy-2-propanol, 1-methoxypropyl-2-propanol, and the like. Examples of the solvent include glycol ester solvents such as acetate and 3-methoxy-1-butyl acetate, alcohol solvents such as isopropyl alcohol, butyl alcohol, and 1-methoxy-2-propanol, ether solvents such as dioxane, diethyl ether, and dibutyl ether, ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, diethyl ketone, butyl methyl ketone, methyl pentyl ketone, methyl isopentyl ketone, dipropyl ketone, diisobutyl ketone, isophorone, cyclohexanone _, methylcyclohexanone, acetonylacetone, and acetylacetone, paraffinic hydrocarbon solvents such as octane, nonane, decane, dodecane, and tetradecane, which are saturated chain compounds represented by the molecular formula C n H _2n+2 and have linear and branched structures, and naphthenic hydrocarbon solvents such as cyclohexane and methylcyclohexane. Among these, glycol ester solvents and ketone solvents are preferable. These solvents can be used alone or in combination of two or more.

<<Ketone-based organic solvent (D1)>>
The organic solvent (D) in the one-liquid coating composition of the present invention preferably contains a ketone-based organic solvent (D1), and the content of the ketone-based organic solvent (D1) in the total amount of the organic solvent (D) is preferably in the range of 20 to 40 mass%. Furthermore, among the ketone-based organic solvents (D1), those having an SP value (solubility parameter) in the range of 9.0 to 10.0 are particularly preferred, and since they have a high ability to dissolve resins, even when the content of the organic solvent (D) in the coating composition is low, good coating workability can be achieved. Specific examples include methyl isobutyl ketone (SP value: 9.0), methyl ethyl ketone (SP value: 9.5), etc.

Here, the SP value is a guideline for determining compatibility, and there are various calculation and measurement methods. The SP value of the one-component coating composition of the present invention is indicated by the solubility parameter calculated by the Hoy method based on the structure. The SP value of the organic solvent is a value calculated using the vapor pressure method proposed by Hoy, in accordance with the method described in the literature [K. L. Hoy, J. Paint Technology, 42, (541), 76 (1970)].

<<Glycol ester organic solvent (D2)>>
The organic solvent (D) in the one-liquid coating composition of the present invention preferably contains a glycol ester organic solvent (D2). The glycol ether solvent (D2) has many hydrogen bonds via hydroxyl groups and strong intermolecular forces, so it has a high melting point and viscosity compared to its molecular weight, and is easy to dissolve epoxy resins as a solvent. In addition, since it dries relatively slowly, the appearance of the coating film after application is good.

The content of the organic solvent (D) in the one-component coating composition of the present invention is preferably in the range of 25 to 45 mass %, particularly preferably in the range of 30 to 40 mass %. By making the content of the organic solvent (D) relatively small, the amount of volatile organic compounds (VOCs) during and after coating can be reduced, thereby reducing the burden on the environment.
In the one-component coating composition of the present invention, examples of the method for adjusting the content of the organic solvent (D) to the above range include using a relatively low-viscosity modified epoxy resin (A) and a low-molecular-weight epoxy resin (B), including an extender pigment (C1) having a relatively low oil absorption of 5 to 20 ml/100 g, setting the ratio of the pigment (C) to the resin component (pigment/resin solids) to a range of 2.5 to 3.8, using a solvent that is highly soluble in the modified epoxy resin (A) and the epoxy resin (B), etc. By selectively combining these, it is possible to obtain a one-component coating composition having a low viscosity of 10 to 40 seconds at 23°C when measured with Ford Cup No. 4, even if the content of the organic solvent (D) is relatively small.

<Other Additives (E)>
The one-liquid coating composition of the present invention may further contain a matting agent, a flexibility imparting agent, a surface conditioner, a wetting agent, a dispersing agent, an emulsifier, a viscosity adjuster, a settling inhibitor, an anti-skinning agent, an anti-sagging agent, an antifoaming agent, a color separation inhibitor, a leveling agent, a drying agent, a plasticizer, a film-forming assistant, an antifungal agent, an antibacterial agent, an antiviral agent, an insecticide, a light stabilizer, an ultraviolet absorber, an electrostatically charged lubricant, an antistatic agent, and an electroconductive agent, etc., as appropriate, depending on the purpose. Commercially available products may be suitably used as these components. The content of the additive (E) in the one-liquid coating composition of the present invention is preferably 0.1 to 10% by mass.

<<Pigment dispersant (E1)>>
The one-liquid coating composition of the present invention can be used as a pigment dispersant to reduce the viscosity of the coating composition, prevent the pigment from settling, and form a smooth surface. The dispersant is not particularly limited, but a high molecular weight one is preferable. Examples of commercially available polymer dispersants include Disperbyk111, 160, 161, 162, 163, 164, 166, 168, 170, 171, 182, 2000, 2001, 2070, 2150, and 2163 (all manufactured by BYK Japan KK); EFKA PX4300, PX4310, PX4320, PX4330, PX4340, PX4350, PA4400, PA4401, PA4402, PA4403, PA4450, PX4700, PX4701, PX4731, and PX4732 (all manufactured by EFKA); Dispex Examples of such a surfactant include Ultra 4585 (manufactured by BASF), Solsperse 24000 and 32550 (both manufactured by Lubrizol Nippon), and Ajisper PB821, PB-822 and PB-823 (all manufactured by Ajinomoto Fine-Techno Co., Ltd.).

<Viscosity>
The one-component coating composition of the present invention preferably has a viscosity of 10 to 40 seconds, more preferably 15 to 30 seconds, at 23°C when measured using Ford Cup No. 4. By setting the viscosity of the one-component coating composition in the range of 10 to 40 seconds, coating workability, particularly dischargeability when coating using an airless spray, and finished appearance after coating are improved. In addition, the method of measuring the viscosity using Ford Cup No. 4 is as follows: first, the coating composition is thoroughly stirred, and then the orifice of Ford Cup No. 4 fixed horizontally is held down with a finger, and the composition is poured into the orifice until it is full. Then, the finger is released and time measurement is started at the same time, and the time (seconds) until the coating composition stops flowing out of Ford Cup No. 4 is measured, and the measured time is regarded as the viscosity.

<Method of manufacturing one-liquid type coating composition>
The one-liquid coating composition of the present invention is not particularly limited, and a known manufacturing method can be used. For example, the one-liquid coating composition can be manufactured by mixing the modified epoxy resin (A), the epoxy resin (B) having a weight average molecular weight of 300 to 1500, the pigment (C), the organic solvent (D), and various additives (E) appropriately selected as necessary, in a disperser, and dispersing them uniformly.

<Method of forming coating film>
The one-liquid coating composition of the present invention can be applied onto a metal substrate to form an undercoat layer. The undercoat layer preferably has a dry film thickness of 20 to 150 μm, more preferably 25 to 60 μm. The one-liquid coating composition of the present invention is prepared by blending the modified epoxy resin (A) and the low molecular weight bisphenol A type epoxy resin (B) in a solid content mass ratio ((A)/(B)) in the range of 20/80 to 65/35, thereby forming a coating film having good coating workability, excellent adhesion to the substrate, water resistance, and corrosion resistance. In particular, by setting the mass ratio (pigment/resin solid content) of the pigment (C) to the resin solid content of 2.5 to 3.8, by containing a pigment having a relatively low oil absorption of 5 to 20 ml/100 g, and by selecting an organic solvent (D) having high solubility in the modified epoxy resin (A) and the low molecular weight bisphenol A type epoxy resin (B), the coating composition can be applied with a Ford Cup No. 1000 even if it is a high solid content coating. The viscosity at 23° C., as measured by the method of claim 4, is 10 to 40 seconds, preferably 15 to 30 seconds, and thus a one-pack type coating composition having excellent coating workability is obtained, and a coating film suitable for use as an undercoat coating can be formed.
In addition, a topcoat layer can be provided by applying a one-component or two-component paint onto an undercoat layer of the one-component paint composition of the present invention. In order to impart weather resistance, the topcoat layer is preferably a coating film made of a two-component urethane resin paint.

<Painting method>
The method for applying the one-component coating composition of the present invention is not particularly limited, and examples thereof include known coating methods, such as dipping, spin coating, flow coating, roll coating, spray coating including air spray and airless spray, blade coating, and air knife coating.
The one-liquid coating composition of the present invention has a relatively high solid content but a low viscosity, making it possible to apply it by airless spraying. The airless spraying method is a method in which the coating material is sprayed into the atmosphere by applying high pressure to the tip of a fine nozzle, and atomized by collision with the air. Since there is little scattering of the coating material, the coating efficiency is high and a coating film with good adhesion can be obtained.

<Painted body>
The one-liquid coating composition of the present invention can be applied to, for example, structures such as buildings and structures, vehicles (automobiles, etc.), furniture, fittings, electronic devices (home appliances, etc.), and parts thereof that have a coating film on the surface of the metal substrate. The metal substrate is not particularly limited, but its shape can be, for example, plate-like, sheet-like, foil-like, etc. In addition, examples of the metal constituting the substrate include steel, galvanized steel, stainless steel, magnesium alloy, aluminum, aluminum alloy, etc., and among these, steel is preferred. Furthermore, the metal substrate may be subjected to various surface treatments, such as oxidation treatment. As an example, a substrate obtained by subjecting steel or aluminum to oxidation treatment by a method such as anodizing, phosphate treatment, chromate treatment, or non-chromate treatment can be used. In addition, the metal substrate also includes various plastic substrates having a metal thin film on the surface. For forming a metal film, deposition, sputtering, plating, etc. can be used. Examples of the metal thin film include thin metal films of aluminum, tin, zinc, gold, silver, platinum, nickel, etc.
The amount of the one-pack coating composition of the present invention to be applied can be varied depending on the type of substrate to be coated and the intended use.

Preparation of Examples 1 to 12 and Comparative Examples 1 to 5
The modified epoxy resin (A), epoxy resin (B), pigment (C), organic solvent (D), and other raw materials were mixed using a disperser so as to be uniformly dispersed according to the formulations (values are in mass %) shown in Tables 1 and 2, to obtain one-component coating compositions (Examples 1 to 12, Comparative Examples 1 to 5).
NV indicates the non-volatile content (%) in the resin. The non-volatile content refers to the components remaining when the coating composition is dried under the measurement conditions of 130° C. and 40 minutes.

Details of the raw materials used and an example of the composition are shown in Table 1.
(A-1) Alkyd-modified epoxy resin solution (product name: Arakido 9212, manufactured by Arakawa Chemical Industries, Ltd., NV: 40%, solvent components: xylene, cyclohexanone, 1-methoxy-2-propyl acetate, n-butanol)
(A-2) Alkyd-modified epoxy resin solution (product name: Phthalkid E9500, manufactured by Resonac, NV: 40%, solvent components: butyl alcohol, xylene, toluene)
(A-3) Fatty acid modified epoxy resin solution (NV: 60%)

<Preparation of fatty acid modified epoxy resin solution>
(A-3) The fatty acid-modified epoxy resin solution was prepared as follows.
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a dehydrator and a nitrogen gas inlet tube, 36 parts by mass of epoxy resin (jER1001, manufactured by Mitsubishi Chemical Corporation), 24 parts by mass of soybean oil, 15 parts by mass of butyl acetate and 12 parts by mass of propylene glycol monomethyl ether were charged, and the mixture was heated and stirred under a nitrogen atmosphere, reacted at 250°C until the acid value reached 3 mgKOH/g or less, and then cooled. Next, 13 parts by mass of Ipzol 100 (hydrocarbon solvent mixture, manufactured by Idemitsu Kosan Co., Ltd.) was charged to obtain the desired fatty acid modified epoxy resin solution (A-3) (non-volatile content 60% by mass).

(B1-1) Bisphenol A type epoxy resin solution (product name: jER1001, manufactured by Mitsubishi Chemical Corporation, NV: 70%, solvent component: xylene, epoxy equivalent: 450 to 500, weight average molecular weight: 900)
(B2-1) Bisphenol A type epoxy resin solution (product name: jER828, manufactured by Mitsubishi Chemical Corporation, NV: 100%, epoxy equivalent: 184 to 194, weight average molecular weight: 370)
(B2-2) Bisphenol A type epoxy resin solution (product name: jER834X90, manufactured by Mitsubishi Chemical Corporation, NV: 90%, epoxy equivalent: 230 to 270, weight average molecular weight: 470)

(C1-1) Extender pigment: heavy calcium carbonate (product name: DURCAL5, manufactured by OMYA-SAS, NV: 100%, oil absorption: 16 mL/100 g)
(C1-2) Extender pigment: barium sulfate (product name: Sparwite W-20HB, manufactured by Shino-can-mivronized Co., Ltd., NV: 100%, oil absorption: 9 mL/100 g)
(C1-3) Extender pigment: Precipitated barium sulfate (product name: Precipitated barium sulfate, manufactured by Kawazu Sangyo Co., Ltd., NV: 100%, oil absorption: 20 mL/100 g)
(C2-1) Color pigment: titanium oxide (product name: TITONE-R-5N, manufactured by Sakai Chemical Industry Co., Ltd., NV: 100%, oil absorption: 20 mL/100 g)
(C3-1) Rust-preventive pigment; aluminum phosphomolybdate (product name: LF Bousei PM-300, manufactured by Kikuchi Color Industries Co., Ltd., NV: 100%, oil absorption: 31 mL/100 g)
(C3-2) Anti-rust pigment: zinc oxide (product name: zinc oxide type 2, manufactured by Sakai Chemical Industry Co., Ltd., NV: 100%, oil absorption: 13 mL/100 g)

(D1-1) Ketone-based solvent (methyl ethyl ketone)
(D2-1) Glycol ester solvent (3-methoxy-1-butyl acetate)
(D-1) Aromatic compound-containing solvent (xylene)
(D-2) Alcohol-based solvent (butyl alcohol)

(E1-1) Pigment dispersant (product name: DISPER-BYK2155, manufactured by BYK Japan, block copolymer, NV: 99%)
(E1-2) Pigment dispersant (product name: DISPER-BYK2163, manufactured by BYK Japan, block copolymer, NV: 45%)
(E-1) Silane coupling agent (product name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd., epoxy group-containing silane coupling agent, NV: 100%)
(E-2) Suspension inhibitor (product name: Disparlon 4200-200, manufactured by Kusumoto Chemical Industries, Ltd., oxidized polyolefin suspension inhibitor, NV: 20%)
(E-3) Anti-sagging agent (product name: Penton 34, manufactured by Tanabe Chemical Industry Co., Ltd., reaction product of quaternary amine and bentonite clay, NV: 20%)
(E-4) Defoamer (product name: FLOWLEN AC300F, manufactured by Kyoeisha Chemical Co., Ltd., acrylic defoamer, NV: 77%)
(E-5) Surface conditioner (product name: KF-69, manufactured by Shin-Etsu Silicones, silicone oil-based surface conditioner, NV: 1%)

Tables 1 and 2 show Examples 1 to 12 and Comparative Examples 1 to 5 prepared according to the formulations.
Also shown are the solid concentration (mass%) of the paint, such as the modified epoxy resin (A) in the solid content, the epoxy resin (B) in the solid content, and the pigment (C) in the solid content, the content (mass%) of the organic solvent (D) in the paint composition, the mass ratio of the modified epoxy resin (A) to the epoxy resin (B) ((A)/(B)), and the mass ratio of the pigment/resin solid content (pigment/resin solid content) in the solid content.

<Method of forming coating film>
The coating compositions obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were applied to a cold-rolled steel plate that had been subjected to an iron phosphate treatment using an airless spray so that the dry film thickness was 35 to 45 μm, and the plate was dried at 80° C. for 30 minutes to form a test coated plate.

<Evaluation of paint and coating performance>
The paint viscosity, painting workability, water resistance, corrosion resistance, and adhesion of the paint compositions and test panels obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were evaluated by the following methods. The results are shown in Table 3.

<<Paint viscosity>>
The coating compositions obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were thoroughly stirred, and then poured into a horizontally fixed Ford Cup No. 4 until the orifice was pressed with a finger until the composition was filled to the brim. The finger was then released and time measurement was started at the same time. The time (seconds) until the outflow of the coating composition from Ford Cup No. 4 stopped was measured, and the measured time was recorded as the viscosity.

<<Painting workability>>
The resin compositions obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were applied using an airless sprayer so that the dry film thickness was 35 to 45 μm without dilution, and the coating workability was evaluated from the results of observing the finished appearance.
⊚: The paint is spread evenly, no irregularities are visible to the naked eye, and the finish of the coated surface is good.
Good: Some of the paint did not spread evenly, slight unevenness was visible on the coated surface, and the finish of the coated surface was somewhat poor, but there was no problem with painting workability.
×: The paint does not spread evenly over the entire surface, and the finish of the applied surface is poor.

<<Adhesion>>
The surfaces of the test coated plates obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were cut with a cutter to create 100 grids of 1 mm squares, and adhesive tape (cellophane tape) was attached on the grids, followed by a forced peel-off test, which was evaluated according to the following criteria.
⊚: No peeling of the coating was observed.
◯: Peeling was observed on the edges of the grid, but there was no problem with adhesion.
×: Peeling of the coating film from the substrate was observed.

＜＜Water resistance＞＞
The test coated plates obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were immersed in deionized water at 23° C. for 360 hours, and then the appearance and adhesion of the coating film were evaluated immediately after wiping off the water droplets on the surface.
⊚: The coating film is not blistered, and no peeling of the coating film is observed in the adhesion evaluation.
◯: The coating film is not blistered, and peeling is observed at the edges of the grid, but there is no problem with adhesion.
×: Blisters were observed in the coating film, or peeling of the coating film from the substrate was observed.

<<Corrosion resistance>>
Salt spray resistance test: Cross cuts were made with a cutter knife on the surfaces of the test coated plates obtained in Examples 1 to 12 and Comparative Examples 1 to 5. The test coated plates were subjected to a salt spray test at 35° C. for 144 hours, and the occurrence of rust was observed, and the abnormal width from the cut was evaluated according to the following criteria.
⊚: No rust or blister was observed except at the crosscut area, and the rust was less than 1 mm from the cut area.
◯: No rust or blister was observed except at the crosscut area, and the rust was within 1 to 3 mm from the cut area.
×: Rust and swelling were observed over the entire coating film.

From the results shown in Table 3, the one-component coating compositions of Examples 1 to 12 had a viscosity at 23°C measured using Ford Cup No. 4 within the range of 10 to 40 seconds. In addition, the coating workability, water resistance, corrosion resistance, and adhesion were all evaluated as "◎" or "〇", indicating that there are no practical problems and that the compositions have excellent performance.

The one-component coating composition of Comparative Example 1 did not contain modified epoxy resin (A), and therefore the crosslink density of the coating film was reduced, and the evaluation results for water resistance and corrosion resistance were poor, with an "X" rating.

The one-component coating composition of Comparative Example 2 had a low content of modified epoxy resin (A) in the mass ratio ((A)/(B)) of modified epoxy resin (A) to epoxy resin (B), so the crosslink density of the coating film was low and the evaluation results for water resistance and corrosion resistance were poor, with an "X" rating.

The one-component coating composition of Comparative Example 3 had a low content of epoxy resin (B) in the mass ratio ((A)/(B)) of modified epoxy resin (A) and epoxy resin (B), and therefore had a high coating viscosity and was evaluated as poor in terms of coating workability, earning a grade of "x".

The one-component coating composition of Comparative Example 4 did not contain epoxy resin (B), and therefore the coating viscosity was very high and the flexibility of the coating film formed was reduced, resulting in poor evaluation results of coating workability and adhesion, with a grade of "x."

The one-component coating composition of Comparative Example 5 had a low content of pigment (C) in the solids, which reduced the coating strength and resulted in an evaluation result of "x" for corrosion resistance, making it poor.

From the results of Examples 1 to 12 and Comparative Examples 1 to 5, it was found that the one-component coating composition of the present invention is excellent and has no practical problems in terms of coating viscosity, coating workability, water resistance, corrosion resistance, and adhesion.

Claims (7)

A modified epoxy resin (A);
an epoxy resin (B) other than the modified epoxy resin (A) and containing a plurality of epoxy groups in one molecule;
A pigment (C),
A one-component coating composition comprising an organic solvent (D),
The weight average molecular weight of the epoxy resin (B) is 300 to 1,500,
a mass ratio ((A)/(B)) of the modified epoxy resin (A) to the epoxy resin (B) is 20/80 to 65/35;
The content of the pigment (C) in the solid content is 50 to 80 mass %,
A one-component coating composition that does not contain a curing agent for curing epoxy resins . The one-component coating composition according to claim 1, wherein the viscosity of the one-component coating composition at 23°C is 10 to 40 seconds when measured using a Ford Cup No. 4. The one-component coating composition according to claim 1, wherein the epoxy resin (B) contains multiple epoxy resins having different molecular weights. The one-component coating composition according to claim 1, wherein the mass ratio (pigment/resin solids) of the pigment (C) to the resin solids (the total of all the resin solids contained in the one-component coating composition) in the solids of the one-component coating composition is 2.5 to 3.8. A coating method in which a one-component coating composition according to any one of claims 1 to 4 is applied onto a metal substrate to form an undercoat layer, and then a topcoat layer is formed by applying a topcoat paint onto the undercoat layer. An undercoat layer formed by applying the one-component coating composition according to any one of claims 1 to 4 on a metal substrate;
A coated body comprising a coating film having a topcoat layer formed by applying a topcoat paint on the undercoat layer. A coating film constituting the coated body according to claim 6.