One-component metal primer coating composition

Abstract

To provide a one-liquid type undercoat coating composition for metal that can be applied to a wide range of substrate, can allow a wide range of topcoat coating composition to be applied, has excellent rust resistance, and can deal with ordinary temperature drying and baking-and-drying.SOLUTION: Provided is a one-liquid type undercoat coating composition for metal that contains an epoxy resin, an isocyanate resin, a rust preventive pigment, and an organic solvent, and in which the equivalent ratio (NCO group / OH group) between the hydroxyl group of the epoxy resin and the isocyanate group of the isocyanate resin is 0.02 to 0.12, and the mass ratio (A / B) of (A) the contained amount of the rust preventive pigment and (B) the contained amount of the epoxy resin is 0.05 to 0.3.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a one-component undercoat paint composition for metals. More specifically, the present invention relates to a one-component undercoat paint composition for metals that can be applied to a wide range of substrates, can be applied to a wide range of topcoat paint compositions, has excellent rust prevention properties, and can be used for room temperature drying and baking drying. [Background technology]

[0002] Undercoat paints for use on metal materials have been developed (Patent Documents 1 to 3). These paint compositions are applied to metals and dried to form a coating film. These paint compositions also contain a large amount of rust inhibitors to obtain corrosion resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-179261 A [Patent Document 2] JP 2012-12497 A [Patent Document 3] Japanese Patent Application Publication No. 3-66766 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the undercoat paint compositions described in Patent Document 1 and Patent Document 2 require baking drying in the coating film drying process, which results in poor productivity of the coated product. The undercoat paint described in Patent Document 1 also requires a large amount of anti-rust pigment to achieve high rust prevention. The anti-rust paint described in Patent Document 3 is limited to a topcoat paint composition of powder paint. Therefore, the anti-rust paint described in Patent Document 3 requires equipment suitable for powder paint during painting.

[0005] The present invention has been made in consideration of such conventional problems, and aims to provide a one-component undercoat paint composition for metals that can be applied to a wide range of substrates, can be used with a wide range of topcoat paint compositions, has excellent rust prevention properties, and can be used for both room temperature drying and baking drying. [Means for solving the problem]

[0006] The one-liquid type metal undercoat paint composition of the present invention, which solves the above problems, mainly comprises the following components.

[0007] (1) A one-component undercoat paint composition for metals comprising an epoxy resin, an isocyanate resin, an anti-rust pigment, and an organic solvent, wherein an equivalent ratio (NCO group / OH group) of a hydroxyl group of the epoxy resin to an isocyanate group of the isocyanate resin is 0.02 to 0.12, and a mass ratio (A / B) of a content (A) of the anti-rust pigment to a content (B) of the epoxy resin is 0.05 to 0.3.

[0008] According to this configuration, the one-liquid metal undercoat paint composition has excellent adhesion to various metal substrates. In addition, the one-liquid metal undercoat paint composition has excellent adhesion not only to powder paints but also to various topcoat paint compositions. Furthermore, the coating film can be dried at drying temperatures including room temperature such as 0 to 40°C, and baking drying is also possible. The obtained coated product has excellent rust resistance and durability.

[0009] (2) The one-component undercoat paint composition for metals according to (1), wherein the anti-rust pigment comprises a phosphate or phosphite containing at least one metallic element selected from the group consisting of zinc and calcium.

[0010] According to such a configuration, the one-liquid type metal undercoat paint composition can provide a coated article with superior rust prevention properties and improved durability.

[0011] (3) A one-component undercoat paint for metal according to (1) or (2), wherein the organic solvent contains an oxygen-containing organic solvent, the oxygen-containing organic solvent has a relative evaporation rate of 0.5 or more when the evaporation rate of butyl acetate as a reference is taken as 1, and the content of the oxygen-containing organic solvent in the organic solvent is 10 mass% or more.

[0012] According to this configuration, the one-liquid metal undercoat coating composition easily dissolves the resin component. In addition, when the one-liquid metal undercoat coating composition is applied to a metal substrate and dried, it is easy to dry at drying temperatures including room temperature such as 0 to 40°C, and baking temperatures such as 120 to 200°C, and is therefore highly versatile.

[0013] (4) A one-component undercoat paint composition for metal according to any one of (1) to (3), having a pigment volume concentration (PVC) of 25 to 35%.

[0014] According to this configuration, the one-component metal undercoat coating composition is unlikely to impair the gloss of the topcoat coating composition, even when the one-component metal undercoat coating composition is applied to a metal substrate and dried, and then a topcoat coating composition is applied thereto.

[0015] (5) A method for producing a coated product, comprising: a primer coating step of coating a metal substrate with the one-component primer coating composition for metal according to any one of (1) to (4); and a primer drying step of drying the applied one-component primer coating composition for metal at 0 to 40°C.

[0016] According to this configuration, the method for producing a coated article uses the one-liquid metal undercoat paint composition described above, and thus can form a coating film with excellent adhesion when applied to a metal substrate and dried, even at drying temperatures including room temperature, such as 0 to 40° C. Therefore, the method for producing a coated article does not require equipment such as a drying oven in the drying step, and the productivity of the coated article is improved.

[0017] (6) The method for producing a coated product according to (5), further comprising a topcoat step of applying a topcoat paint composition after the undercoat drying step, and a topcoat drying step of drying the applied topcoat paint composition at 0 to 40°C.

[0018] According to this configuration, the method for producing a coated product employs drying temperatures including room temperature, such as 0 to 40° C., not only when providing the undercoat layer but also when providing the topcoat layer. Therefore, the method for producing a coated product does not require equipment such as a drying oven not only in the drying step of the undercoat layer but also in the drying step of the topcoat layer, improving the productivity of the coated product.

[0019] (7) A method for producing a coated product according to (5), comprising the steps of: applying a topcoat coating composition after the undercoat drying step; and baking and drying the applied topcoat coating composition at 120 to 200°C for 5 to 60 minutes.

[0020] According to this configuration, the method for producing a coated article forms a topcoat layer by drying the topcoat paint composition at a baking temperature of 120 to 200° C. Therefore, the reaction of the resin in the coating film of the obtained coated article is further promoted by the baking and drying process, and the coating film performance is further improved. Effect of the Invention

[0021] According to the present invention, it is possible to provide a one-component undercoat paint composition for metal that can be applied to a wide range of substrates, can be used with a wide range of topcoat paint compositions, has excellent rust prevention properties, and can be used for both room temperature drying and baking drying. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] <One-liquid metal undercoat paint composition> A one-liquid type undercoat paint composition for metals (hereinafter, simply referred to as undercoat paint composition) according to one embodiment of the present invention contains an epoxy resin, an isocyanate resin, an anti-rust pigment, and an organic solvent. The equivalent ratio (NCO group / OH group) of the hydroxyl group of the epoxy resin to the isocyanate group of the isocyanate resin is 0.02 to 0.12. The mass ratio (A / B) of the content (A) of the anti-rust pigment to the content (B) of the epoxy resin is 0.05 to 0.3. Each of these will be described below.

[0023] (Epoxy resin) Epoxy resins harden when dried under various conditions, becoming a component that forms a coating film.

[0024] The epoxy resin is not particularly limited. The epoxy resin may be any epoxy resin that dissolves in an organic solvent. For example, the epoxy resin may be a bisphenol type epoxy resin, a novolac type epoxy resin, an aromatic epoxy resin, an alicyclic epoxy resin, an aliphatic epoxy resin, a glycidyl ester type epoxy resin, a glycidyl amine type epoxy resin, or the like. Note that "dissolving in an organic solvent" refers to dissolving 1 g or more in 100 g of toluene, which is a typical organic solvent, at 25°C. In addition, epoxy resins may be used in combination.

[0025] Examples of bisphenol type epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol AD ​​type epoxy resins, bisphenol S type epoxy resins, and their brominated products and water additives. Examples of novolac type epoxy resins include phenol novolac type epoxy resins and cresol novolac type epoxy resins. Examples of aromatic epoxy resins include trisphenolmethane triglycidyl ether.

[0026] Alicyclic epoxy resins include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, bis(3,4-epoxycyclohexyl)adipate, bis(3,4-epoxycyclohexylmethyl adipate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxycyclohexa Examples include non-meta-dioxane, bis(2,3-epoxycyclopentyl) ether, and the like.

[0027] Examples of aliphatic epoxy resins include diglycidyl ether of 1,4-butanediol, diglycidyl ether of 1,6-hexanediol, triglycidyl ether of glycerin, triglycidyl ether of trimethylolpropane, diglycidyl ether of polyethylene glycol, diglycidyl ether of polypropylene glycol, and polyglycidyl ethers of long-chain polyols including polyoxyalkylene glycols containing an alkylene group having 2 to 9 carbon atoms and polytetramethylene ether glycol.

[0028] Examples of the glycidyl ester type epoxy resin include diglycidyl phthalate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, diglycidyl-p-oxybenzoate, glycidyl ether-glycidyl ester of salicylic acid, and glycidyl dimer acid ester.

[0029] Examples of the glycidylamine type epoxy resin include triglycidyl isocyanurate, N,N'-diglycidyl derivatives of cyclic alkylene urea, N,N,O-triglycidyl derivatives of p-aminophenol, and N,N,O-triglycidyl derivatives of m-aminophenol.

[0030] Among these, the epoxy resin is preferably a bisphenol type epoxy resin, and more preferably a bisphenol A type epoxy resin, because the coating film has excellent weather resistance and flexibility and has excellent adhesion to the base.

[0031] The content of the epoxy resin is not particularly limited. For example, the content of the epoxy resin in the undercoat paint composition is preferably 10% by mass or more, more preferably 15% by mass or more. The content of the epoxy resin in the undercoat paint composition is preferably 30% by mass or less, more preferably 25% by mass or less. By having the epoxy resin content within the above range, the undercoat paint composition has excellent barrier properties of the coating film and excellent workability during painting.

[0032] The weight average molecular weight (Mw) of the epoxy resin is not particularly limited. For example, Mw is preferably 10,000 or more, more preferably 30,000 or more. Moreover, Mw is preferably 100,000 or less, more preferably 50,000 or less. When Mw of the epoxy resin is within the above range, the obtained coating film is likely to have excellent coating film strength, processability, and smoothness. In this embodiment, Mw can be measured by gel permeation chromatography (GPC) method or the like. More specifically, Mw can be calculated by measuring the difference in refractive index using a GPC device (HLC-8220; manufactured by Tosoh Corporation) equipped with a differential refractometer (RI) detector, and converting it into polystyrene.

[0033] The acid value of the epoxy resin is not particularly limited. For example, the acid value of the epoxy resin is preferably 5 mgKOH / g or less, more preferably 1 mgKOH / g or less. When the acid value of the epoxy resin is within the above range, the chemical resistance of the resulting coating film is likely to be improved. In this embodiment, the acid value can be measured by a potentiometric method in accordance with JIS K 0070-1992.

[0034] The hydroxyl value of the epoxy resin is not particularly limited. For example, the epoxy resin is preferably 50 mgKOH / g or more, more preferably 100 mgKOH / g or more. The hydroxyl value of the epoxy resin is preferably 1000 mgKOH / g or less, more preferably 500 mgKOH / g or less. When the hydroxyl value of the epoxy resin is within the above range, the coating composition has excellent scratch resistance and coating strength of the resulting coating film. In this embodiment, the hydroxyl value can be calculated by acetylating the hydroxyl groups in the resin and expressing the amount of potassium hydroxide required to neutralize the acetic acid required for the acetylation in mg per 1 g of resin.

[0035] (Isocyanate resin) The isocyanate resin hardens when dried under various conditions, and becomes a component that forms a coating film.

[0036] The isocyanate resin (polyisocyanate compound) is not particularly limited. Examples of the polyisocyanate compound include aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate, and trimethylhexane diisocyanate; and alicyclic diisocyanate compounds such as hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6-diisocyanate, 4,4'-methylenebis(cyclohexylisocyanate), and 1,3-(isocyanatomethyl)cyclohexane. Examples of blocking agents include ketoxime-based blocking agents such as ε-caprolactam, methyl ethyl ketoxime, methyl isoamyl ketoxime, methyl isobutyl ketoxime, etc.; phenol-based blocking agents such as phenol, cresol, catechol, nitrophenol, etc.; alcohol-based blocking agents such as isopropanol, trimethylolpropane, etc.; active methylene-based blocking agents such as malonic acid esters, acetoacetate esters, etc.; and heterocyclic pyrazole compounds. The polyisocyanate compounds may be used in combination.

[0037] Among these, the isocyanate resin is preferably an aliphatic blocked isocyanate resin, more preferably a blocked hexamethylene diisocyanate polyisocyanate, from the viewpoints of preventing yellowing of the coating film and excellent storage stability.

[0038] (Anti-rust pigment) The anti-rust pigment is not particularly limited. For example, the anti-rust pigment is a metal oxide and / or a metal nitrate, a metal carbonate, a metal phosphate, a fluorine-containing metal compound, an ammonium complex salt, or zinc powder of one or more metal elements selected from zinc, calcium, aluminum, magnesium, titanium, manganese, strontium, barium, iron, zirconium, cerium, etc. Anti-rust pigments may be used in combination.

[0039] Among these, the anti-rust pigment preferably contains a metal phosphate, metal phosphite or metal tripolyphosphate containing one of the metal elements zinc, calcium or aluminum, from the viewpoint of providing the resulting painted article with better anti-rust properties and improved durability, and more preferably contains a phosphate or metal phosphite containing at least one of the metal elements zinc or calcium.

[0040] The content of the rust-preventive pigment is not particularly limited as long as the mass ratio (A / B) of the content (A) of the rust-preventive pigment to the content (B) of the epoxy resin is 0.05 to 0.3. As an example, the content of the rust-preventive pigment in the undercoat paint composition is preferably 1.0 mass% or more, more preferably 2.0 mass% or more. The content of the rust-preventive pigment in the undercoat paint composition is preferably 10.0 mass% or less, more preferably 5.5 mass% or less. Thus, the undercoat paint composition of the present embodiment exhibits excellent rust prevention properties despite the low content of the rust-preventive pigment.

[0041] The undercoat paint composition of the present embodiment may contain other pigments other than the above-mentioned anti-rust pigment. The other pigments are not particularly limited. For example, the other pigments are various color pigments, extender pigments, etc. The other pigments may be used in combination.

[0042] The color pigment is not particularly limited, and examples of the color pigment include titanium oxide, carbon black, and ferric oxide.

[0043] The extender pigment is not particularly limited, and examples of the extender pigment include talc, barium sulfate, mica, and calcium carbonate.

[0044] The content of the other pigments is not particularly limited. For example, the content of the other pigments may be determined in consideration of the desired color and the pigment volume concentration (PVC) described later.

[0045] (Organic solvent) The organic solvent is blended to dissolve or disperse the epoxy resin and isocyanate resin. The organic solvent is not particularly limited. For example, the organic solvent may be a hydrocarbon-based solvent such as hexane, benzene, cyclohexane, heptane, toluene, xylene, or mineral spirits; an alcohol-based solvent such as methyl alcohol, ethyl alcohol, isopropyl alcohol, butyl alcohol, cyclohexanol, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, or ethylene glycol monobutyl ether; an ester-based solvent such as methyl acetate, ethyl acetate, or butyl acetate; an ether-based solvent such as 1,4-dioxane, diethyl ether, or tetrahydrofuran; or a ketone-based solvent such as acetone, methyl ethyl ketone, or cyclohexanone. The organic solvents may be used in combination.

[0046] Among these, the organic solvent preferably contains an oxygen-containing organic solvent, and contains an oxygen-containing organic solvent having a relative evaporation rate of 0.5 or more when the evaporation rate of butyl acetate as a reference is taken as 1, and more preferably contains an oxygen-containing organic solvent having a relative evaporation rate of 1.0 or more. Furthermore, the content of the oxygen-containing organic solvent having a relative evaporation rate of 0.5 or more when the evaporation rate of butyl acetate as a reference is taken as 1 is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more in the organic solvent. By containing the oxygen-containing organic solvent within the above range, the undercoat paint composition is easy to dissolve the resin component. In addition, when the undercoat paint composition is applied to a metal substrate and dried, it is easy to dry at a drying temperature including room temperature such as 0 to 40 ° C. and a baking temperature such as 120 to 200 ° C., and is highly versatile. The oxygen-containing organic solvent may be an organic solvent containing an oxygen element, such as an alcohol-based, ester-based, ether-based, or ketone-based solvent. Specifically, the evaporation rates of oxygen-containing organic solvents are ethylene glycol monobutyl ether (evaporation rate: 0.09), cyclohexanone (evaporation rate: 0.32), n-butanol (evaporation rate: 0.37), butyl acetate (evaporation rate: 1.00), propylene glycol monomethyl ether (evaporation rate: 0.70), methyl ethyl ketone (evaporation rate: 6.00), and the like. In this embodiment, the evaporation rate is expressed as a ratio of the evaporation rate of each organic solvent to the evaporation rate of butyl acetate, which is 1.00 at a temperature of 23°C and a relative humidity of 50%. The evaporation rate is measured as a relative rate to the weight loss per unit time of butyl acetate at a temperature of 25°C and a relative humidity of 55%RH, as specified in the ASTM D 3539-87 standard test method. The higher the evaporation rate of an organic solvent, the easier it is to evaporate.

[0047] The flash point of the undercoat paint composition is not particularly limited. For example, the flash point of the undercoat paint composition is preferably 21° C. or higher, and more preferably adjusted to 23° C. or higher with an organic solvent. When the flash point of the undercoat paint composition is within the above range, the undercoat paint composition is easy to handle in terms of storage method, etc. In this embodiment, the method of adjusting the flash point of the undercoat paint composition is not particularly limited. For example, the flash point of the undercoat paint composition can be adjusted by using multiple organic solvents with different flash points in combination. In this embodiment, the flash point is a flash point measured in accordance with JIS K 2265-1:2007.

[0048] The content of the organic solvent is not particularly limited. For example, the content of the organic solvent in the undercoat paint composition is preferably 40% by mass or more, more preferably 50% by mass or more. The content of the organic solvent in the undercoat paint composition is preferably 70% by mass or less, more preferably 60% by mass or less. By having the content of the organic solvent within the above range, the undercoat paint composition has excellent smoothness of the coating film, and excellent workability and coating efficiency during coating.

[0049] The undercoat paint composition of this embodiment contains the above-mentioned epoxy resin, isocyanate resin, amount of rust inhibitor, and organic solvent, and is characterized in the equivalent ratio (NCO group / OH group) of the hydroxyl group of the epoxy resin to the isocyanate group of the isocyanate resin, and in the mass ratio (A / B) of the content of the rust inhibitor (A) to the content of the epoxy resin (B).

[0050] (Regarding the equivalent ratio (NCO group / OH group) of the hydroxyl group of the epoxy resin and the isocyanate group of the isocyanate resin) In the undercoat coating composition of this embodiment, the equivalent ratio (NCO group / OH group) of the hydroxyl group of the epoxy resin and the isocyanate group of the isocyanate resin is 0.02 or more, preferably 0.03 or more. In addition, the equivalent ratio (NCO group / OH group) is 0.12 or less, preferably 0.10 or less. When the equivalent ratio (NCO group / OH group) is less than 0.02, the undercoat coating composition is likely to cause shrinkage on the coating film surface when the undercoat coating composition is applied to a metal substrate to provide a coating film of an undercoat layer, and when a topcoat layer is further provided. On the other hand, when the equivalent ratio (NCO group / OH group) is more than 0.12, the undercoat coating composition is likely to cause poor adhesion between the metal substrate and the undercoat layer, and peeling between the metal substrate and the undercoat layer occurs easily when the undercoat coating composition is applied to a metal substrate to provide a coating film of an undercoat layer. Furthermore, even when a topcoat layer is provided, the adhesion between the undercoat layer and the topcoat layer is poor, and peeling is likely to occur between the undercoat layer and the topcoat layer.

[0051] (The mass ratio (A / B) of the content of anti-rust pigment (A) and the content of epoxy resin (B)) In the undercoat paint composition of this embodiment, the mass ratio (A / B) of the content (A) of the rust-preventive pigment to the content (B) of the epoxy resin is 0.05 or more, and preferably 0.1 or more. The mass ratio (A / B) is 0.3 or less, and preferably 0.2 or less. By having the mass ratio (A / B) within the above range, the undercoat paint composition has good rust prevention properties, can protect metal substrates from corrosion, and has excellent durability.

[0052] The undercoat paint composition of this embodiment has a suitable pigment volume concentration (PVC) of 25 to 35%.

[0053] (About pigment volume concentration (PVC)) The pigment volume concentration (PVC) is the volume percentage (%) of the pigment in the total solid content of the total resin content and the total pigment content in the coating composition. In this embodiment, the pigment volume concentration (PVC) is preferably 25% or more, and more preferably 26% or more. The pigment volume concentration (PVC) is preferably 35% or less, and more preferably 32% or less. By having the pigment volume concentration (PVC) within the above range, even when the undercoat coating composition is applied to a metal substrate and dried, and then a topcoat coating composition is further applied, the gloss of the topcoat coating composition is unlikely to be impaired.

[0054] (Additives) The undercoat coating composition of the present embodiment may contain a thickener, a dispersant, a matting agent, an antifoaming agent, a leveling agent, an anti-sagging agent, a surface conditioner, a viscosity adjuster, an ultraviolet absorber, a wax, etc. Additives may be used in combination.

[0055] As described above, according to this embodiment, the undercoat paint composition has excellent adhesion to various metal substrates. In addition, the undercoat paint composition has excellent adhesion not only to powder paints but also to various topcoat paint compositions. Furthermore, the coating film can be dried at drying temperatures including room temperature such as 0 to 40°C, and baking drying is also possible. The resulting coated product has excellent rust prevention and durability. Therefore, the undercoat paint composition of this embodiment is suitable for use in products using various metal substrates such as automobiles, home appliances, and office automation equipment, which are used indoors and outdoors, in environments exposed to sea breezes and rain, and in environments exposed to factory exhaust gases.

[0056] The method for preparing the one-liquid metal undercoat paint composition of this embodiment is not particularly limited. As an example, the undercoat paint composition can be prepared by mixing and stirring the above-mentioned epoxy resin, isocyanate resin, rust-preventive pigment, organic solvent, and appropriate color pigment, extender pigment, additives, etc.

[0057] <Manufacturing method for painted products> The method for producing a coated article according to one embodiment of the present invention includes an undercoat step of applying the above-mentioned one-liquid undercoat coating composition for metals to a metal substrate, and an undercoat drying step of drying the applied one-liquid undercoat coating composition for metals at 0 to 40° C. The undercoat drying step of the one-liquid undercoat coating composition for metals may be a step of baking and drying for 5 to 60 minutes at 120 to 200° C. depending on suitability with the topcoat coating composition, when there is equipment capable of baking and drying, etc. In addition, the method for producing a coated article may further include applying a topcoat coating composition to form a coating film of a topcoat layer. Each of these steps will be described below.

[0058] (Undercoat process) The undercoating step is a step of applying the above-mentioned undercoating paint composition to a metal substrate.

[0059] The metal substrate is not particularly limited. For example, the metal substrate is a carbon steel plate, an alloy steel plate, a plated steel plate, etc., more specifically, a cold-rolled steel plate, a hot-dip galvanized steel plate, an aluminum-containing galvanized steel plate, an electrolytic galvanized steel plate, an alloyed galvanized steel plate, a zinc-nickel plated steel plate, a zinc-cobalt plated steel plate, a vapor-deposition galvanized steel plate, a nickel plated steel plate, a tin plated steel plate (tin plate), a stainless steel plate, etc.; a metal plate other than a steel plate, such as an aluminum plate, a copper plate, a titanium plate, a magnesium plate, or a brass plate.

[0060] The method of applying the undercoat coating composition to the metal substrate is not particularly limited. For example, the undercoat coating composition can be applied to the surface of the metal substrate by a roll coater method, a spray method, a dipping method, a brush coating method, a curtain coater method, a flow coater method, an immersion method, or the like. In addition, the surface of the metal substrate may be solvent degreased before the undercoat coating composition is applied. Solvent degreasing is a process of removing dirt from the substrate surface using various degreasers. In addition, when applying the undercoat coating composition, the viscosity of the undercoat coating composition may be appropriately adjusted with a thinner so that it can be easily applied.

[0061] (Undercoat drying process) The undercoat drying step is a step in which the applied undercoat paint composition is dried at 0 to 40°C.

[0062] Thus, the undercoat drying step employs drying temperatures including room temperature, such as 0 to 40° C. As described above, the undercoat paint composition can be sufficiently dried even at a relatively low temperature compared to the baking temperature (e.g., 120 to 200° C.) in baking drying. Therefore, equipment such as a drying oven is not necessary, and the productivity of coated products is improved.

[0063] The drying temperature may be 0° C. or higher, and preferably 10° C. or higher. The drying temperature may be 40° C. or lower, and preferably 30° C. or lower. Within the above range, the evaporation rate of the organic solvent is appropriate, so that the undercoat coating composition has excellent workability during application and the appearance of the coating film is also excellent.

[0064] The drying time is not particularly limited. For example, the drying time may be 10 minutes or more, preferably 30 minutes or more, and more preferably 60 minutes or more. By keeping the drying time within the above range, the applied undercoat paint composition is sufficiently dried to form a coating film (undercoat layer).

[0065] The thickness of the undercoat layer is not particularly limited. For example, the thickness of the undercoat layer is preferably 10 μm or more, more preferably 20 μm or more. The thickness of the undercoat layer is preferably 50 μm or less, more preferably 40 μm or less. When the thickness of the undercoat layer is equal to or more than the lower limit, the undercoat layer can protect the metal substrate and has excellent corrosion resistance such as water resistance and acid resistance. On the other hand, when the thickness is equal to or less than the upper limit, the undercoat layer has a good coating appearance and is also excellent in workability during painting.

[0066] In the method for producing a coated article of this embodiment, since the undercoat paint composition described above is used, when the coating is applied to a metal substrate and dried, a coating film with excellent adhesion can be formed even if a low drying temperature, including room temperature, such as 0 to 40° C. is adopted. Therefore, the method for producing a coated article does not require equipment such as a drying oven in the drying step, and the productivity of the coated article is improved.

[0067] In the method for producing a coated article of this embodiment, after the undercoat layer is provided, a topcoat layer may be provided as appropriate to impart design or further improve corrosion resistance. In this case, the topcoat coating composition constituting the topcoat layer may be dried at 0 to 40°C or may be baked.

[0068] When drying the topcoat paint composition at 0 to 40°C The method for producing a coated article of this embodiment may include, after the undercoat drying step, a topcoat step of applying a topcoat paint composition, and a topcoat drying step of drying the applied topcoat paint composition at 0 to 40°C.

[0069] (Topcoat process) The topcoat process is a process of applying a topcoat paint composition after the undercoat drying process. The type of the topcoat paint composition is not particularly limited. For example, the topcoat paint composition is a one-liquid solvent paint, two-liquid solvent paint or powder paint such as phthalic acid resin paint, urethane resin paint, acrylic urethane resin paint, silicon resin paint, melamine alkyd resin paint, acrylic melamine resin paint, polyester resin paint, epoxy resin paint, and fluororesin paint.

[0070] The method of applying the topcoat coating composition to the undercoat layer is not particularly limited. For example, the topcoat coating composition can be applied to the surface of the undercoat layer by a roll coater method, a spray method, a dipping method, a brush coating method, a curtain coater method, a flow coater method, a dipping method, or the like.

[0071] (Top coat drying process) The topcoat drying step is a step in which the applied topcoat paint composition is dried at 0 to 40°C.

[0072] The drying temperature may be 0° C. or higher, and preferably 10° C. or higher. The drying temperature may be 40° C. or lower, and preferably 30° C. or lower. Within the above range, the organic solvent volatilization rate is appropriate, and the topcoat coating composition has good drying efficiency and excellent appearance of the coating film.

[0073] The drying time is not particularly limited, and may be any drying time suitable for the topcoat paint composition. For example, the drying time is preferably 10 minutes or more, more preferably 30 minutes or more, and even more preferably 60 minutes or more. By the drying time being within the above range, the applied topcoat paint composition is sufficiently dried to form a coating film (topcoat layer).

[0074] The thickness of the topcoat layer is not particularly limited, and may be any thickness suitable for the topcoat coating composition. For example, the thickness of the topcoat layer is preferably 10 μm or more, more preferably 20 μm or more. The thickness of the topcoat layer is preferably 50 μm or less, more preferably 40 μm or less. By having the thickness of the topcoat layer within the above range, and being equal to or greater than the lower limit, the topcoat layer is more likely to protect the metal substrate, and has excellent corrosion resistance such as water resistance and acid resistance. On the other hand, by having the thickness equal to or less than the upper limit, the topcoat layer has a good coating appearance and is also excellent in workability during painting.

[0075] Thus, when a step of drying the applied topcoat paint composition at 0 to 40° C. is adopted as the topcoat drying step when providing the topcoat layer, the method for producing a coated product of this embodiment employs drying temperatures including room temperature, such as 0 to 40° C., not only when providing the undercoat layer but also when providing the topcoat layer. Therefore, the method for producing a coated product does not require equipment such as a drying oven not only for the undercoat layer but also for the drying step of the topcoat layer, improving the productivity of the coated product.

[0076] When drying the topcoat paint composition by baking The method for producing a coated article of this embodiment may include, after the undercoat drying step, a topcoat step of applying a topcoat paint composition, and a bake-drying step of baking and drying the applied topcoat paint composition at 120 to 200°C for 5 to 60 minutes.

[0077] (Topcoat process) The topcoating step is the same as the topcoating step described above in relation to "when the topcoat paint composition is dried at 0 to 40°C".

[0078] (Baking and drying process) The baking and drying step is a step in which the applied topcoat paint composition is baked and dried at 120 to 200° C. for 5 to 60 minutes.

[0079] The baking and drying temperature may be 120° C. or higher, and preferably 130° C. or higher. The baking and drying temperature may be 200° C. or lower, and preferably 180° C. or lower. By keeping the baking and drying temperature within the above range, the resin curing reaction in the topcoat layer is likely to proceed easily, drying efficiency is good, and the appearance of the coating film is also excellent.

[0080] The baking and drying time is not particularly limited, and may be any drying time suitable for the topcoat paint composition. For example, the baking and drying time may be 5 minutes or more, preferably 10 minutes or more, and more preferably 20 minutes or more. The baking and drying time may be 60 minutes or less, and preferably 40 minutes or less. If it is within the above range, the curing reaction of the resin proceeds, the drying efficiency is good, and the appearance of the coating film is also excellent.

[0081] The thickness of the topcoat layer is not particularly limited and is the same as that described above in relation to "When the topcoat coating composition is dried at 0 to 40°C".

[0082] When the topcoat layer is provided by baking and drying in this manner, the reaction of the resin in the coating film of the resulting coated article is further promoted by the baking and drying process, and the coating film performance is further improved.

[0083] In this embodiment, the undercoat drying step is exemplified by a step of drying the applied undercoat paint composition at 0 to 40° C. Alternatively, in the method for producing a coated product of this embodiment, the undercoat paint composition can also be baked and dried. EXAMPLES

[0084] The present invention will be described in more detail below with reference to the following examples. The present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass".

[0085] The raw materials used are shown below. <Epoxy resin> Epoxy resin: Bisphenol A type epoxy resin, Weight average molecular weight (Mw): 35000, Hydroxyl value: 210mgKOH / g <Isocyanate resin> Isocyanate resin: Asahi Kasei Chemicals Corporation, Duranate K6000, NCO: 7.3% <Anti-rust pigment> Anti-rust pigment 1: Zinc phosphate / calcium phosphite-based anti-rust pigment Anti-rust pigment 2: Aluminum tripolyphosphate-based anti-rust pigment <Organic solvent> Xylene: Evaporation rate: 0.76 Cyclohexanone: Evaporation rate: 0.32 Butyl acetate: evaporation rate 1.00 n-Butanol: Evaporation rate 0.37 Ethylene glycol monobutyl ether: evaporation rate 0.09 Propylene glycol monomethyl ether: Evaporation rate: 0.70 Methyl ethyl ketone: Evaporation rate: 6.00 *The evaporation rate is the relative evaporation rate when the evaporation rate of the standard butyl acetate is set to 1 (measurement conditions: in accordance with the ASTM D 3539-87 standard test method). <Other> Titanium oxide: Furukawa Chemicals Co., Ltd., titanium oxide FR-48 Carbon black: Mitsubishi Carbon Black, manufactured by Mitsubishi Chemical Corporation Calcium carbonate: Maruo Calcium Co., Ltd., MC-SII Precipitated barium sulfate: SOLVAY BARIO E DERIVATI SpA, precipitated barium sulfate Surface conditioner: Toray Dow Corning Co., Ltd., FZ-2122, 10% dilution

[0086] (Examples 1 to 11, Comparative Examples 1 to 4) According to the formulation shown in Table 1 below, each component was placed in a tank and stirred with a disperser to prepare a one-liquid type metal undercoat paint composition.

[0087] [Table 1]

[0088] The one-component metal undercoat paint compositions of Examples 1 to 11 and Comparative Examples 1 to 4 were evaluated for drying property, adhesion (lifting property), rust prevention property (neutral salt spray resistance), adhesion (recoatability), 20 degree specular gloss retention, and 60 degree specular gloss retention by the following evaluation methods. The results are shown in Table 1.

[0089] (dryness) In an environment of 23°C, the one-liquid metal primer paint composition was applied to the following test panels, and the drying properties of the coating were confirmed. Test plate creation conditions Test piece: 0.8mm x 75mm x 150mm, dull steel plate Surface treatment: Solvent degreasing Coating thickness: 20~25μm Evaluation method Touch dryness: According to JIS K 5600-1-1, after applying the undercoat paint composition, the center of the coating surface was lightly touched with a fingertip at a certain time (10, 20, 30 minutes) and the time until the fingertip was no longer dirty was measured.

[0090] <Evaluation of single undercoat layer (adhesion (lifting property), rust prevention (neutral salt spray resistance))> The one-liquid metal primer paint composition was applied to the following test panels, and the performance of the coating film was confirmed. Test plate creation conditions Test piece: 0.8mm x 75mm x 150mm, dull steel plate Surface treatment: Solvent degreasing Coating system: The undercoat coating compositions of Examples 1 to 8 and Comparative Examples 1 to 4 were dried at 23° C. for 10 minutes, and the resulting coating film was evaluated. The undercoat coating composition of Example 9 was dried at 23° C. for 30 minutes, and the resulting coating film was evaluated. Coating thickness: 20~25μm Test conditions and evaluation methods Lifting property: The obtained coating film was visually observed to confirm the presence or absence of shrinkage on the coating film surface. Neutral salt spray resistance: According to JIS K 5400;1990 8.5.3 X-cut tape method, test pieces with X-cut scratches were prepared, and the test pieces were tested at 35℃ for 120 hours using a neutral salt spray resistance tester (Suga Test Instruments Co., Ltd., STP-160) in accordance with JIS K 5600 7-1, using a 5% NaCl aqueous solution. After that, the test pieces that had peeled off within 3mm in either direction from the intersection of the X-cut part of the scratch were considered to have passed the test.

[0091] <Evaluation when undercoat layer and topcoat layer are applied (adhesion (recoatability), 20 degree specular gloss retention, 60 degree specular gloss retention)> The one-liquid metal undercoat paint composition was applied to the following test plate, and the topcoat paint composition was further applied on the resulting undercoat layer to provide a topcoat layer, and the performance was confirmed. Test plate creation conditions Test piece: 0.8 x 75 x 150 mm, dull steel plate Surface treatment: Solvent degreasing Coating system: In Examples 1 to 10 and Comparative Examples 1 to 4, an undercoat paint composition was applied (undercoat step) and dried at 23°C for 10 minutes (undercoat drying step). Next, a topcoat paint composition was applied to the undercoat layer (topcoat step) and baked and dried at 120°C for 20 minutes (baking and drying step). In Example 11, a coated product was produced in the same manner as in Example 1, except that the drying time in the undercoat drying step was 30 minutes. The topcoat paint composition used was a baked melamine alkyd resin paint (Tohpe Corporation, Toamelataite #300). Coating thickness: undercoat layer 20-25 μm, topcoat layer 25-30 μm. Test conditions and evaluation methods Recoatability: The resulting coating film was visually inspected to confirm whether the topcoat layer had peeled off. 20 degree specular gloss retention: In accordance with JIS K 5600 4-7, the gloss value of a single film of the topcoat paint composition was used as the standard. After applying the undercoat paint composition, the 20 degree specular gloss of the coating film to which the topcoat paint composition was applied was measured, and the retention was calculated (VG7000 gloss meter, manufactured by Nippon Denshoku Industries Co., Ltd.). 60 degree specular gloss retention: In accordance with JIS K 5600 4-7, the gloss value of a single film of the topcoat paint composition was used as the standard. After applying the undercoat paint composition, the 60 degree specular gloss of the coating film to which the topcoat paint composition was applied was measured, and the retention was calculated (VG7000 gloss meter, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0092] As shown in Table 1, the undercoat coating compositions of Examples 1 to 11 had excellent drying properties at 23°C, and excellent adhesion and rust prevention properties. On the other hand, the undercoat coating composition of Comparative Example 1, in which the equivalent ratio (NCO group / OH group) between the hydroxyl group of the epoxy resin and the isocyanate group of the isocyanate resin was less than 0.05, caused shrinkage in the coating film. The undercoat coating composition of Comparative Example 2, in which the equivalent ratio (NCO group / OH group) between the hydroxyl group of the epoxy resin and the isocyanate group of the isocyanate resin was more than 0.12, had poor adhesion to the substrate. The undercoat coating composition of Comparative Example 3, in which the mass ratio (A / B) between the content (A) of the rust-preventive pigment and the content (B) of the epoxy resin was less than 0.05, had poor rust prevention properties. The undercoat coating composition of Comparative Example 4, in which the mass ratio (A / B) between the content (A) of the rust-preventive pigment and the content (B) of the epoxy resin was more than 0.3, had poor rust prevention properties.

[0093] <Base material suitability evaluation> The one-liquid metal undercoat paint compositions of Examples 1 and 2 were applied to each of the substrates shown in Table 2 according to the following test conditions, and the adhesion of the coating film was confirmed.

[0094] Test plate creation conditions Test piece: 0.8 x 75 x 150 mm Surface treatment: Solvent degreasing Coating system: Under normal drying conditions, the coating was dried at 23°C for 10 minutes to form a primer layer. Under baking drying conditions, the coating was dried at 140°C for 20 minutes to form a primer layer. Coating thickness: 20~25μm Test conditions and evaluation methods Adhesion: In accordance with JIS K 5600 5-6, tape was applied to a test plate with 1 mm grid cross cuts, the tape was removed, and the result was evaluated on a scale of 0 to 5 according to JIS K 5600 5-6 Table 1. Evaluation results of 0 to 1 were considered to be acceptable. Moisture resistance: A test plate with 1 mm grid cross cuts was prepared in accordance with JIS K 5600 5-6, and tested at 50°C and RH 95% or higher for 240 hours in accordance with JIS K 5600 7-2. Tape was attached to the test plate, which was then peeled off and rated on a scale of 0 to 5 in accordance with JIS K 5600 5-6 Table 1. A rating of 0 to 1 was considered a pass. Neutral salt spray resistance: According to JIS K 5400;1990 8.5.3 X-cut tape method, test pieces with X-cut scratches were prepared, and the test pieces were tested at 35℃ for 120 hours using a neutral salt spray resistance tester (Suga Test Instruments Co., Ltd., STP-160) in accordance with JIS K 5600 7-1, using a 5% NaCl aqueous solution. After that, the test pieces that had peeled off within 3mm in either direction from the intersection of the X-cut part of the scratch were considered to have passed the test.

[0095] [Table 2]

[0096] As shown in Table 2, the one-component metal primer coating composition of the present invention can form a primer layer on various metal substrates not only by baking drying but also under normal drying conditions at room temperature, and exhibits excellent adhesion, moisture resistance and rust prevention properties.

[0097] <Appropriate evaluation of topcoat paint composition> The one-component metal undercoat paint composition of Example 1 was applied to a test plate (metal substrate) according to the following test conditions to form an undercoat layer, and then each topcoat paint composition listed in Table 3 was applied, and the performance of the resulting coating film was confirmed.

[0098] Topcoat paint composition Two-component acrylic urethane resin paint: Tohpe Corporation, Neo Urethane Baking melamine alkyd resin paint: Tohpe Corporation, Toamelatito #300 One-component baked urethane resin paint: Tohpe Corporation, Toametal Urethane CW Polyester resin powder coating: Tohpe Corporation, Toa Powder #4000P Test plate creation conditions Test piece: 0.8mm x 75mm x 150mm, dull steel plate Surface treatment: Solvent degreasing Coating system: Under normal drying conditions, the undercoat coating composition of Example 1 was dried at 23°C for 10 minutes to form an undercoat layer. When the topcoat coating was a powder coating, the undercoat coating composition was baked and dried at 140°C for 20 minutes to form an undercoat layer. After that, various topcoat coating compositions were applied under the drying conditions in Table 3 to form topcoat layers. Coating thickness: The undercoat layer was 20 to 25 μm thick, and the various topcoat layers were 25 to 30 μm thick (when powder paint (polyester resin powder paint) was used, the topcoat layer thickness was 60 to 80 μm). Test conditions and evaluation methods Finished appearance: In accordance with JIS K 5600 4-7, the 60-degree specular gloss was measured and a gloss value of 40 to 80 was considered acceptable (VG7000 gloss meter, manufactured by Nippon Denshoku Industries Co., Ltd.). Adhesion: In accordance with JIS K 5600 5-6, tape was applied to a test plate with 1 mm grid cross cuts, the tape was removed, and the result was evaluated on a scale of 0 to 5 according to JIS K 5600 5-6 Table 1. Evaluation results of 0 to 1 were considered to be acceptable. Neutral salt spray resistance: According to JIS K 5400;1990 8.5.3 X-cut tape method, test pieces with X-cut scratches were prepared, and the test pieces were tested at 35℃ for 120 hours using a neutral salt spray resistance tester (Suga Test Instruments Co., Ltd., STP-160) in accordance with JIS K 5600 7-1, using a 5% NaCl aqueous solution. After that, the test pieces that had peeled off within 3mm in either direction from the intersection of the X-cut part of the scratch were considered to have passed the test.

[0099] [Table 3]

[0100] As shown in Table 3, the one-component metal primer coating composition of the present invention was less likely to affect gloss and exhibited excellent adhesion and rust prevention properties, even when a topcoat layer was formed using various topcoat coating compositions.

Claims

1. A coating composition comprising an epoxy resin having a hydroxyl group, an isocyanate resin, an anti-rust pigment, and an organic solvent, an equivalent ratio (NCO group / OH group) of a hydroxyl group of the epoxy resin to an isocyanate group of the isocyanate resin is 0.02 to 0.12; A one-component undercoat paint composition for metal, wherein the mass ratio (A / B) of the content (A) of the anti-rust pigment to the content (B) of the epoxy resin is 0.05 to 0.

2.

2. 2. The one-component metal primer coating composition of claim 1, wherein the anti-rust pigment comprises a phosphate or phosphite containing at least one metallic element selected from the group consisting of zinc and calcium.

3. The organic solvent includes an oxygen-containing organic solvent, The oxygen-containing organic solvent has a relative evaporation rate of 0.5 or more when the evaporation rate of butyl acetate serving as a reference is taken as 1; 3. The one-component undercoat paint composition for metal according to claim 1, wherein the content of the oxygen-containing organic solvent in the organic solvent is 10 mass % or more.

4. The one-component metal undercoat paint composition according to any one of claims 1 to 3, wherein the pigment volume concentration (PVC) is 25 to 35%.

5. A primer coating step of applying the one-liquid metal primer coating composition according to any one of claims 1 to 4 to a metal substrate; and drying the applied one-component metal undercoat paint composition at 0 to 40°C.

6. A topcoat step of applying a topcoat paint composition after the undercoat drying step; The method for producing a coated article according to claim 5, further comprising a topcoat drying step of drying the applied topcoat paint composition at 0 to 40°C.

7. A topcoat step of applying a topcoat paint composition after the undercoat drying step; The method for producing a coated article according to claim 5, further comprising a baking and drying step of baking and drying the applied topcoat coating composition at 120 to 200° C. for 5 to 60 minutes.

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