Organic solvent-based paint and method for producing precoated metal sheet

Abstract

An organic solvent-based coating material for use in curtain coating, the coating material comprising: a resin; a surfactant; and an organic solvent, wherein the number-average molecular weight of the resin is more than 1500 but less than 10000, and the dynamic surface tension of the organic solvent-based coating material as measured by the maximum bubble pressure method is 36-50 mN / m at a bubble lifetime of 0.05 seconds and 32-45 mN / m at a bubble lifetime of 0.5 seconds. A method for producing a precoated metal sheet using the organic solvent-based coating material.

Description

[Technical Field]

[0001] The present disclosure relates to an organic solvent-based paint and a method for producing a precoated metal sheet. [Background technology]

[0002] Pre-coated metal sheets are widely used for the housings of home appliances and building materials. Pre-coated metal sheets are generally made by laminating a chemical treatment layer, a primer layer, and a top layer on the surface of a metal sheet. Each layer is painted and baked in order on a continuously passing metal sheet. Roll coaters are often used to paint each layer. The top layer of a pre-coated metal sheet is the layer that ensures the design. If there are any paint defects in this top layer, the design will be impaired, and the product value will be reduced. Uniformity is particularly required for the top layer.

[0003] Pre-coated metal sheets are continuously manufactured and wound into coils in lengths of several kilometers to several tens of kilometers for storage and transportation. To increase the productivity of pre-coated metal sheets, it is necessary to increase the threading speed of the metal sheets. A roll coater applies paint by bringing the roll into contact with the metal sheet with a negative gap. The film thickness depends on the roll peripheral speed / sheet threading speed. The higher the sheet threading speed, the faster the roll must rotate. Increasing the roll rotation speed increases the likelihood of paint scattering and roping, a knot-like coating defect that occurs when the paint is transferred. For this reason, it has been difficult to run sheets at high speeds with a roll coater.

[0004] Curtain coaters are known as a more uniform coating method than roll coaters. Curtain coaters allow paint to fall freely, forming a curtain film. The metal plate is coated as it passes through the curtain film. Because the film thickness is adjusted by the paint flow rate, coating defects such as paint splashing and roping, which are common with roll coaters, are less likely to occur, and a uniform coating appearance is more likely to be achieved. When applying a curtain coater to the painted metal sheet manufacturing process, the paint must be able to form a stable curtain film. Paints with poor curtain film stability can cause issues such as curtain film not forming or the curtain film not forming suddenly, causing discoloration, making them unsuitable for continuous production.

[0005] As a method for stably forming a curtain film, the molecular weight of the resin in the paint has been investigated. For example, Patent Document 1 discloses that a stable curtain film can be formed by adjusting the number average molecular weight of the resin contained in the coating material to 10,000 or more.

[0006] Patent Document 1 Japanese Patent Application Laid-Open No. 11-152448 Summary of the Invention [Problem to be solved by the invention]

[0007] However, as disclosed in Patent Document 1, when curtain coating is performed using a coating material with a resin number-average molecular weight of less than 10,000, the curtain film is prone to breakage and the curtain film stability is poor. Therefore, coating must be performed using a roll coater, which makes it difficult to increase the sheet running speed.

[0008] On the other hand, resins with a small number-average molecular weight of less than 10,000 are more easily dissolved in organic solvents than resins with a large number-average molecular weight. This makes it easier to increase the solids concentration, which reduces the cost of the paint. Furthermore, because the molecular weight between crosslinks is smaller than that of resins with a large number-average molecular weight, it is possible to form a hard coating film with excellent stain resistance.

[0009] Therefore, there is a demand for curtain coating suitability, i.e., curtain film stability, for paints using resins with a number-average molecular weight of less than 10,000. On the other hand, in curtain coating, paint is recycled and reused, so the paint also needs to have defoaming properties.

[0010] Therefore, the object of the present disclosure is to provide an organic solvent-based paint that has excellent curtain film stability and defoaming properties and is capable of curtain coating even when using a resin with a number average molecular weight of less than 10,000, and a method for manufacturing pre-coated metal sheets using the same that is highly productive. [Means for solving the problem]

[0011] The means for solving the above problems include the following aspects. <1> An organic solvent-based paint containing a resin, a surfactant, and an organic solvent, The number average molecular weight of the resin is more than 1500 and less than 10000, The organic solvent-based paint has a dynamic surface tension measured by a maximum bubble pressure method of 36 to 50 mN / m at a bubble lifetime of 0.05 s and 32 to 45 mN / m at a bubble lifetime of 0.5 s, An organic solvent-based paint used for curtain painting. <2> Contains color pigments <1> The organic solvent-based paint according to claim 1. <3> The resin is a resin other than fluororesin. <1> or <2> The organic solvent-based paint according to claim 1. <4> The resin is at least one selected from the group consisting of polyester resin, acrylic resin, and urethane resin. <1> ~ <3> 1. An organic solvent-based paint according to any one of the above. <5> The solid content concentration of the organic solvent-based paint is 20 to 70 mass %. <1> ~ <4> 1. An organic solvent-based paint according to any one of the above. <6> The organic solvent-based paint further contains a curing agent, and the curing agent contains at least one selected from the group consisting of melamine resin and isocyanate. <1> ~ <5> 1. An organic solvent-based paint according to any one of the above. <7> The concentration of the resin is 5 to 50% by mass relative to the organic solvent-based paint. <1> ~ <6> 1. An organic solvent-based paint according to any one of the above. <8> The concentration of the surfactant is 0.05 to 0.80% by mass relative to the organic solvent-based paint. <1> ~ <7> 1. An organic solvent-based paint according to any one of the above. <9> <1> ~ <8> a step of discharging the organic solvent-based paint according to any one of the above items to form a curtain film having a height of 50 to 500 mm, and continuously coating a metal plate with the curtain film to form a coating film; a step of drying and / or curing the coating film to form a precoat layer; A method for producing a precoated metal sheet, comprising: [Effects of the Invention]

[0012] According to the present disclosure, it is possible to provide an organic solvent-based paint that is excellent in curtain film stability and defoaming properties and is capable of curtain coating, even when using a resin with a number average molecular weight of less than 10,000, and a method for manufacturing a pre-coated metal sheet using the same, which is highly productive. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment that is an example of the present disclosure will be described. In this specification, when a numerical range is expressed using "to" without the addition of "greater than" or "less than" before or after the numerical value, it means a range that includes these numerical values ​​as the lower and upper limits. When the numerical value is added with "greater than" or "less than" before or after the numerical value, it means a range that does not include these numerical values ​​as the lower or upper limit. In the present specification, the upper limit of a numerical range may be replaced by the upper limit of another numerical range, or may be replaced by a value shown in an example. The lower limit of a numerical range may be replaced by the lower limit of another numerical range, or may be replaced by a value shown in an example.

[0014] The organic solvent-based paint of the present disclosure contains a resin, a surfactant, and an organic solvent, and is an organic solvent-based paint used for curtain coating. In the organic solvent-based paint of the present disclosure, the number average molecular weight of the resin is more than 1,500 and less than 10,000, and the dynamic surface tension of the organic solvent-based paint measured by the maximum bubble pressure method of the organic solvent-based paint is 36 to 50 mN / m at a bubble lifetime of 0.05 s and 32 to 45 mN / m at a bubble lifetime of 0.5 s.

[0015] Due to the above-described configuration, the organic solvent-based coating material of the present disclosure has excellent curtain film stability and defoaming properties, even when a resin with a number average molecular weight of less than 10,000 is used, making curtain coating possible. The organic solvent-based paint of the present disclosure was discovered based on the following findings.

[0016] The inventors have investigated organic solvent-based paints that are excellent in curtain film stability and defoaming properties even when using resins with a number-average molecular weight of less than 10,000. As a result, they have made the following findings. In order to make the curtain film less likely to break during curtain coating, it is preferable that the surfactant is not oriented at the air-liquid interface of the curtain film and cannot exert its function from the time the curtain film is discharged until it reaches the metal plate surface. On the other hand, in order to improve the defoaming properties of organic solvent-based paints, it is advisable to orient the surfactant at the gas-liquid interface of the organic solvent-based paint so that the surfactant functions can be exerted.

[0017] To achieve this, it is best to slow down the migration speed of the surfactant in the organic solvent-based paint. This slows down the rate at which the curtain film adheres to the gas-liquid interface, preventing uneven surface tension and preventing curtain film breakage. After painting, the organic solvent-based paint adheres to the gas-liquid interface, causing uneven surface tension and defoaming. The migration speed of surfactants in organic solvent-based paints can be reduced by adjusting the difference in Hansen solubility parameter (HSP) between the resin and surfactant, and controlling the dynamic surface tension of the organic solvent-based paint measured by the maximum bubble pressure method, at a bubble lifetime of 0.05 seconds and at a bubble lifetime of 0.5 seconds, within the above range.

[0018] From the above findings, it has been found that the organic solvent-based coating material of the present disclosure has excellent curtain film stability and defoaming properties, and enables curtain coating, even when a resin with a number average molecular weight of less than 10,000 is used.

[0019] The organic solvent-based paint of the present disclosure will be described in detail below.

[0020] The organic solvent-based paint of the present disclosure contains a resin, a surfactant, and an organic solvent. The organic solvent-based paint of the present disclosure may also contain a color pigment, a curing agent, etc.

[0021] [resin] The number average molecular weight of the resin is more than 1,500 and less than 10,000, preferably from 2,000 to less than 10,000, and more preferably from 3,000 to less than 10,000. Resins with a number-average molecular weight within this range can achieve lower paint viscosity than organic solvent-based paints with a resin molecular weight of 10,000 or higher. As a result, the amount of organic solvent added during the paint manufacturing process or to ensure paintability can be reduced, allowing for a higher solids concentration in the organic solvent-based paint. As a result, when applying the same coating thickness at the same paint unit price (yen / kg), coating costs can be reduced. Organic solvent-based paints with a higher solids concentration can cover a larger area for the same coating thickness. This reduces the transportation costs of organic solvent-based paints. Furthermore, during the production of pre-coated metal sheets, the organic solvent volatilizing from organic solvent-based paints must be burned to reduce the concentration of volatile organic solvents (VOCs) released into the atmosphere. Organic solvent-based paints with a higher solids concentration have lower organic solvent combustion costs. Furthermore, resins with a low number-average molecular weight and a high hydroxyl value have a low molecular weight between crosslinks, so optimizing the amount of curing agent facilitates the formation of hard, stain-resistant coatings. When resins having different number average molecular weights are used in combination, the number average molecular weight of the resin is a weighted average number average molecular weight.

[0022] The number average molecular weight of the resin is measured as follows. After centrifuging the organic solvent-based paint, measure out the supernatant paint so that it has 20 mg of resin solid content. The obtained sample is dissolved in 10 ml of tetrahydrofuran (THF) and then measured using gel permeation chromatography (GPC, Tosoh Corporation HLC8220 GPC, Shodex KF type column) at a pump flow rate of 0.6 ml / min and a temperature of 40°C. The number average molecular weight of the resin is then calculated from the chromatogram based on the molecular weight of standard polystyrene.

[0023] The resin is not particularly limited, and examples thereof include well-known resins that are used in organic solvent-based paints, such as polyester resin, polyurethane resin, acrylic resin, fluororesin, epoxy resin, etc. These resins may be used alone or in a blend of two or more. Among these, the resin is preferably at least one selected from the group consisting of polyester resin, acrylic resin, and urethane resin, which can easily achieve both processability and other performance properties, and more preferably at least one selected from the group consisting of polyester resin and urethane resin.

[0024] The resin is preferably a resin other than fluororesin. Fluoroplastics are expensive and have poor adaptability to processing, so when fluoroplastics are used, the applications of organic solvent-based paints tend to be limited.

[0025] The type of resin can be identified by known methods, such as by measuring infrared absorption spectroscopy (IR) or pyrolysis gas chromatography on a sample obtained by drying an organic solvent-based paint that has been centrifuged.

[0026] The concentration of the resin is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, based on the organic solvent-based paint. When the resin concentration is within the above range, the solid content of the organic solvent-based paint can be increased, and the cost of painting can be reduced.

[0027] [Organic solvents] An organic solvent is a solvent other than water that dissolves resin. The organic solvent must remain liquid and not react with hardeners, color pigments, surfactants, etc. The organic solvent is not particularly limited, and examples thereof include known solvents, such as ester-based organic solvents such as 3-methoxybutyl acetate, ethyl acetate, isopropyl acetate, and butyl acetate; ketone-based organic solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, and isophorone; Solvesso 100 (ExxonMobil Corp.); and Solvesso 150 (ExxonMobil Corp.). These organic solvents may be used alone or in combination of two or more in any proportion.

[0028] From the viewpoint of curtain formability, the content of the organic solvent is preferably the remainder other than the solid content. That is, the content of the organic solvent is preferably the value obtained by subtracting the solid content concentration of the paint from the total organic solvent-based paint when the total organic solvent-based paint is taken as 100 mass % (total organic solvent-based paint - solid content concentration of paint).

[0029] [Surfactants] The surfactant has the function of defoaming bubbles generated in organic solvent-based paints and the function of forming a stable curtain film. Examples of the surfactant include acrylic surfactants, silicone surfactants, and fluorine-modified silicone surfactants.

[0030] Acrylic surfactants include copolymers of acrylic monomers. Examples of the acrylic monomer include alkyl acrylates, alkylene oxide acrylates, (meth)acrylic acid alkyl ether esters, amino alkyl acrylates, and acrylic acid amide compounds.

[0031] Examples of silicone surfactants include polydimethylsiloxanes whose side chains or main chain ends are modified with alkylene glycols (ethylene glycol, propylene glycol, etc.). Examples of fluorine-modified silicone surfactants include those obtained by substituting a portion of the above silicone surfactants with a perfluoroalkyl group.

[0032] The concentration of the surfactant is preferably 0.05 to 0.80% by mass, more preferably 0.10 to 0.50% by mass, based on the organic solvent-based coating material. When the concentration of the surfactant is within the above range, the dynamic surface tension of the organic solvent-based paint is controlled, and the curtain film stability and defoaming properties are easily improved.

[0033] [Coloring pigments] The color pigment is not particularly limited, and any known color pigment can be used. Examples of color pigments include titanium oxide, carbon black (furnace black, ketjen black, acetylene black, channel black), iron oxide, aluminum, mica, and the like.

[0034] The type of color pigment can be identified by a known method. For example, the type of color pigment can be identified by elemental analysis using SEM-EDX or X-ray crystal diffraction measurement of the coating film or the precipitate after centrifugation.

[0035] The concentration of the color pigment is preferably 2 to 45% by mass, more preferably 10 to 40% by mass, based on the organic solvent-based paint.

[0036] [Hardening agent] The curing agent hardens the resin. As the curing agent, a known curing agent can be used, and a curing agent that reacts during the baking step of the coating film is preferred because it has excellent storage stability. The curing agent is preferably at least one selected from the group consisting of, for example, melamine resin and isocyanate. Suitable examples of the melamine resin include methylated melamine, imino group-type melamine, and butylated melamine, and the melamine resin has a number average molecular weight of 1,500 or less. A preferred example of the isocyanate is a blocked isocyanate, which is an isocyanate obtained by blocking a base isocyanate with a blocking agent. Base isocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- or 1,4-diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (also known as isophorone diisocyanate; IPDI), dicyclohexylmethane-4,4'-diisocyanate (also known as hydrogenated MDI), 2- or 4-isocyanatocyclohexyl-2'-isocyanatocyclohexylmethan, Examples of diisocyanates include 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane, bis(4-isocyanato-3-methylcyclohexyl)methane, 1,3- or 1,4-α,α,α'α'-tetramethylxylylene diisocyanate, 2,4- or 2,6-diisocyanatotoluene, 2,2'-, 2,4'- or 4,4'-diisocyanatodiphenylmethane (MDI), 1,5-naphthalene diisocyanate, p- or m-phenylene diisocyanate, xylene diisocyanate, and diphenyl-4,4'-diisocyanate. Also listed are cyclized polymers of each diisocyanate (isocyanurate type), as well as isocyanate-biuret products (biuret type), and adduct types. Examples of blocking agents include phenol, cresol, xylenol, ε-caprolactam, σ-valerolactam, γ-butyrolactam, methanol, ethanol, n-, i-, or t-butyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol, formamide oxime, acetaldoxime, acetoxime, methylethylkedoxime, diacetylmonoxime, benzophenone oxime, cyclohexane oxime, dimethyl malonate, ethyl acetoacetate, acetylacetone, and pyrazole.

[0037] The type of curing agent can be identified by known methods. For example, the type of curing agent can be identified by measuring infrared absorption spectroscopy (IR), pyrolysis gas chromatography, etc. on a sample obtained by drying an organic solvent-based paint that has been centrifuged.

[0038] The concentration of the curing agent is preferably 15 to 55% by mass, more preferably 20 to 50% by mass, based on the resin.

[0039] [Other additives] The organic solvent-based coating of the present disclosure may contain other well-known additives such as catalysts, waxes, ultraviolet absorbers, antioxidants, plasticizers, coupling agents, pigment dispersants, suspending agents, antibacterial agents, and the like.

[0040] From the viewpoint of curtain forming properties, the organic solvent-based coating material of the present disclosure preferably does not contain water. However, unintentional water contamination, such as absorption of moisture contained in the air or contamination by water adhering to the packaging of organic solvent-based paint, is permitted. From the viewpoint of curtain formability, the organic solvent-based paint of the present disclosure preferably has a water content of 0% by mass or more and less than 10% by mass, more preferably 0% by mass or more and 5% by mass or less, and even more preferably 0% by mass, based on the total amount of the organic solvent-based paint.

[0041] [Solid content concentration] The solids concentration of the organic solvent-based coating material of the present disclosure is not particularly limited as long as the dynamic surface tension can be appropriately controlled. The solid content concentration of the organic solvent-based coating material of the present disclosure is preferably 20 to 70 mass %, more preferably 30 to 60 mass %. When the solids concentration of organic solvent-based paint is 20% by mass or more, the occurrence of coating defects called "potholes" caused by bumping of the organic solvent is suppressed. When the solid content concentration of the organic solvent-based paint is 70 mass % or less, the deterioration of the storage stability of the organic solvent-based paint is suppressed.

[0042] The solids concentration of organic solvent-based paint can be calculated by placing a sample (approximately 2g) in an aluminum cup, drying the sample in an oven at 105°C for 3 hours, and then calculating the solids concentration from the sample mass before and after drying.

[0043] [Dynamic surface tension] The organic solvent-based paint of the present disclosure is prepared by controlling the dynamic surface tension as measured by the maximum bubble pressure method. Specifically, the dynamic surface tension of the organic solvent-based paint of the present disclosure measured by the maximum bubble pressure method is 36 to 50 mN / m at a bubble lifetime of 0.05 s, and 32 to 45 mN / m at a bubble lifetime of 0.5 s. When the dynamic surface tension is within these ranges, both curtain stability and defoaming properties can be achieved. The dynamic surface tension can be adjusted by the type of resin and surfactant, and the concentration of the surfactant.

[0044] The dynamic surface tension of organic solvent-based paints can be measured by the maximum bubble pressure method, for example, using a DP-51 made by Kyowa Interface Science Co., Ltd. Specifically, the measurement is as follows. In order to stabilize the pressure at the start and end of the measurement, the dynamic surface tension is measured while the bubble lifetime is changed from 0.01 seconds to 5 seconds, and the dynamic surface tension is calculated at bubble lifetimes of 0.05 seconds and 0.5 seconds. A probe with a diameter of 1 mm is used, and measurements are started when the air in the tank built into the device is 100%. If the viscosity of an organic solvent-based paint is so high that the dynamic surface tension cannot be measured, the paint temperature may be increased (the paint viscosity may be decreased) for measurement. Note that increasing the paint temperature and decreasing the viscosity does not change the dynamic surface tension. The paint temperature during dynamic surface tension measurement is preferably in the range of 10 to 60°C. If the temperature is too high, the organic solvent used as the solvent may volatilize, which may change the dynamic surface tension.

[0045] [Applications for organic solvent-based paints] The uses of the organic solvent-based paint of the present disclosure are not particularly limited, and it can be used, for example, to paint metal surfaces. The organic solvent-based paint of the present disclosure is preferably used as a paint for producing a precoated metal sheet by curtain coating. Because the organic solvent-based paint of the present disclosure has excellent curtain film stability and defoaming properties, a precoated metal having a coating film that is hard and has excellent stain resistance can be obtained by curtain coating.

[0046] In particular, the organic solvent-based paint of the present disclosure is preferably used as a paint for forming a top layer of a precoated metal sheet. The organic solvent-based paint of the present disclosure contains a resin having a number-average molecular weight of more than 1,500 but less than 10,000. Therefore, compared with resins having a large number-average molecular weight (for example, resins having a number-average molecular weight of 10,000 or more), the molecular weight between crosslinking points is small, and therefore a coating film that is hard and has excellent stain resistance can be formed. Since the top layer of the precoated metal sheet may be required to have a design, the paint forming the top layer of the precoated metal sheet preferably contains a color pigment. Therefore, when used as the paint forming the top layer of the precoated metal sheet, the organic solvent-based paint of the present disclosure preferably contains a color pigment.

[0047] [Method of manufacturing pre-coated metal sheet] The method for manufacturing a precoated metal sheet of the present disclosure includes a step of discharging the organic solvent-based paint of the present disclosure to form a curtain film 50 to 500 mm high, and continuously applying the curtain film to a metal sheet to form a coating film (hereinafter also referred to as the "first step"), and a step of drying and / or curing the coating film to form a precoat layer (hereinafter also referred to as the "second step").

[0048] -First step- In the first step, the method of coating the metal plate with the organic solvent-based paint is curtain coating, and the height of the curtain film of the organic solvent-based paint in the curtain coating is 50 to 500 mm. By making the curtain film height 50 mm or more, contact between the metal plate and the curtain coater is suppressed, so continuous curtain coating can be carried out even if the metal plate is not very flat. By keeping the height of the curtain film at 500 mm or less, the curtain film is instantaneously divided, which prevents the occurrence of circular color loss called spots. The height of the curtain film of the organic solvent-based paint in curtain coating is preferably 100 to 300 mm.

[0049] The type of curtain coater used for curtain coating is not particularly limited and may be any known type, such as a roller curtain coater, a slide curtain coater, or a slit curtain coater. In curtain coating, there are no particular restrictions on the width of the curtain coater or the speed at which the metal sheet is passed. The paint flow rate may be set appropriately depending on the organic solvent-based paint used, as long as it can stably form a curtain film.

[0050] The metal sheet to be subjected to curtain coating is not particularly limited, and known sheets can be used. Examples of the metal sheet include a steel sheet, an aluminum sheet, and a stainless steel sheet. When the metal sheet is a steel sheet, a zinc-plated steel sheet, an aluminum-plated steel sheet, a tin-plated steel sheet, etc. can be used. As the steel sheet, a zinc-plated steel sheet is preferred from the viewpoint of corrosion resistance.

[0051] -Second process- In the second step, a coating film is formed on the surface of the metal plate using a curtain film of the organic solvent-based coating material of the present disclosure, and then the coating film is dried and / or cured to form a precoat layer, thereby obtaining a precoated metal plate. The drying and curing conditions for the coating film may be appropriately set depending on the organic solvent-based coating material used. Before applying the organic solvent-based paint to the metal plate, the metal plate may be coated with a known chemical conversion coating film or a known primer coating film. [Example]

[0052] The organic solvent-based paint and the coating method thereof according to the present disclosure will be specifically described below with reference to examples and comparative examples. Note that the examples shown below are merely examples of the organic solvent-based paint and coating method according to the present disclosure, and the organic solvent-based paint and coating method according to the present disclosure are not limited to the following examples.

[0053] <Preparation of organic solvent-based paint> ≪Paint 1≫ "DYNAPL LH724", a polyester resin manufactured by Evonik Corporation, was dissolved in an organic solvent (a solvent in which cyclohexanone and Solvesso 150 (trade name) were mixed at a mass ratio of 1:1). Next, titanium oxide "CR-90" manufactured by Ishihara Sangyo Kaisha was added and dispersed, and then a methylated melamine resin "Cymel (registered trademark) 303" manufactured by Allnex Japan Co., Ltd. was added as a curing agent to the base. The mass ratio of the polyester resin to the mixed melamine resin was adjusted to 100:35 in terms of solid content. Furthermore, 0.5% by mass of the acid catalyst "Catalyst 600" manufactured by Allnex Japan Co., Ltd. and 0.15% by mass of the surfactant (surface conditioner) Polyflow No. 50E manufactured by Kyoeisha Chemical Co., Ltd. (active ingredient concentration) were added to this mixed base and stirred. The same organic solvent used to dissolve the resin was then added to adjust the solids concentration, and paint 1 was obtained.

[0054] ≪Paint 2~45≫ According to Table 7, paints 2 to 45 were prepared by changing the raw materials and concentrations of paint 1.

[0055] Tables 2 to 6 show the types of materials used to prepare the organic solvent-based paints. The urethane resins 1 to 3 were prepared by the following method. [Preparation of urethane resin 1 (ester-based urethane resin 1)] 55 parts by mass of adipic acid, 6.1 parts by mass of phthalic anhydride, 27 parts by mass of neopentyl glycol, and 26.1 parts by mass of propylene glycol were mixed in a reaction vessel equipped with a thermometer, a condenser, and a stirrer, and the mixture was gradually heated to 230°C in a nitrogen stream. The water produced was distilled off while the esterification reaction was carried out for approximately 10 hours until the acid value reached 1 or less (amount of water removed: 14.2 parts by mass). The temperature of the reaction vessel was then lowered to 50°C, and 133 parts by mass of cyclohexanone and 33 parts by mass of 4,4'-diphenylmethane diisocyanate were mixed in. The mixture was then maintained at 80°C for 8 hours to react, yielding an ester-based urethane resin 1 (solids concentration: 50% by mass).

[0056] [Preparation of Urethane Resins 2-3 (Ester Urethane Resins 2-3)] Ester-based urethane resins 2 and 3 were prepared in the same manner as above, except that the monomer types and amounts were changed as shown in Table 1. The specific values ​​of the monomer composition and molecular weight of each resin are shown below.

[0057] [Table 1]

[0058] <Dynamic surface tension> The dynamic surface tension of the prepared organic solvent-based paint was measured by the maximum bubble pressure method as described above. The paint temperature was set at 50°C. Dynamic surface tension (mN / m) at bubble lifetime (BLT) of 0.05 seconds Dynamic surface tension (mN / m) at 0.5 seconds of bubble lifetime (referred to as BLT in the table)

[0059] <Defoaming property> The defoaming properties of the prepared organic solvent-based paint were investigated. 180 mL of the organic solvent-based paint was placed in a 200 mL round can and stirred at 2000 rpm for 2 minutes with a stirrer to create foam on the surface of the organic solvent-based paint. After leaving it for 3 minutes, the area of ​​foam on the surface of the organic solvent-based paint was visually observed and evaluated according to the following criteria. A score of 3 or higher was considered a pass. -Evaluation criteria- 5: Foam occupancy area less than 10% 4: Foam area 10% or more, less than 20% 3: Foam area 20% or more but less than 30% 2: Foam area 30% or more but less than 50% 1: Foam occupied area 50% or more

[0060] <Curtain film stability> An organic solvent-based paint was pumped into a slide curtain coater (width 350 mm) to form a curtain film. The paint flow rate was set to a flow rate that would result in a dry film thickness of 15 μm at a plate speed of 80 m / min. For organic solvent-based paints that were able to form a curtain film, curtain film formation was continued for 30 minutes under constant paint flow conditions. The condition of the curtain film was visually observed, and the number of times the curtain was broken was counted. Curtain film stability was evaluated according to the following evaluation criteria. A score of 3 or more was considered a pass. The curtain film height was set to the heights shown in Table 7. -Evaluation criteria- 5: Number of curtain membrane cuts: 0 4: Number of times the curtain membrane is cut: 1 or more, 5 or less 3: Number of times the curtain membrane is cut: 6 or more, 10 or less 2: Number of curtain membrane cuts: 11 or more 1: Curtain film cannot be formed

[0061] [Table 2]

[0062] [Table 3]

[0063] [Table 4]

[0064] [Table 5]

[0065] [Table 6]

[0066] [Table 7-1]

[0067] [Table 7-2]

[0068] From the above results, it can be seen that the organic solvent-based paints of the examples of the present disclosure have excellent curtain film stability and defoaming properties, and are capable of curtain coating, even when using resins with a number average molecular weight of less than 10,000. Reference examples 2, 4, 12, and 13 use resins with a number-average molecular weight of 10,000 or more, and the use of resins with a high number-average molecular weight makes it possible to achieve both curtain film stability and defoaming properties. However, because the solids concentration of the paint can only be increased to about 50%, the coating costs tend to be higher than those of the organic solvent-based paints of the examples of the present disclosure.

[0069] The disclosure of Japanese Patent Application No. 2021-069925, filed on April 16, 2021, is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An organic solvent-based paint containing a resin, a surfactant, and an organic solvent, the resin is at least one selected from the group consisting of polyester resin, acrylic resin, and urethane resin, and has a number average molecular weight of more than 1,500 and less than 10,000; The surfactant contains an acrylic surfactant, and the concentration of the surfactant is 0.05 to 0.9 mass% with respect to the organic solvent-based paint; The organic solvent-based paint has a dynamic surface tension measured by a maximum bubble pressure method of 36 to 50 mN / m at a bubble lifetime of 0.05 s and 32 to 45 mN / m at a bubble lifetime of 0.5 s, An organic solvent-based paint used for curtain painting.

2. 2. The organic solvent-based paint according to claim 1, which contains a color pigment.

3. 3. The organic solvent-based paint according to claim 1, wherein the organic solvent comprises a ketone-based organic solvent.

4. The organic solvent-based paint according to any one of claims 1 to 3, wherein the solids concentration of the organic solvent-based paint is 20 to 70 mass%.

5. The organic solvent-based paint according to any one of claims 1 to 4, further comprising a curing agent, and the curing agent comprises at least one selected from the group consisting of melamine resin and isocyanate.

6. The organic solvent-based paint according to any one of claims 1 to 5, wherein the concentration of the resin is 5 to 50 mass% based on the organic solvent-based paint.

7. 7. The organic solvent-based paint according to claim 1, wherein the concentration of the surfactant is 0.05 to 0.80% by mass based on the organic solvent-based paint.

8. a step of discharging the organic solvent-based paint according to any one of claims 1 to 7 to form a curtain film having a height of 50 to 500 mm, and continuously coating a metal plate with the curtain film to form a coating film; a step of drying and / or curing the coating film to form a precoat layer; A method for producing a precoated metal sheet, comprising:

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