JP2023138552A - Anticorrosive coating composition, method of corrosion control using the composition, and coated molding - Google Patents

Abstract

To provide an anticorrosive coating composition capable of developing sufficient anticorrosive effect so as not to spread corrosion by securing adhesion between a coated film and a metal even if generating unexpected coated film defects while securing barrier property of a factor inducing rust such as water, and oxygen particularly to a material made of a magnesium alloy, and capable of drying and curing at ambient temperature to a large-sized structural member such as a high-speed transport vehicle to exhibit good coating workability.SOLUTION: The anticorrosive coating composition is an anticorrosive coating composition containing an epoxy resin, and a curing agent including: a bisphenol type epoxy resin (A-1) having an average molecular weight of 470-900, and an epoxy equivalent of 180-1,000 g/eq.; a polymer type epoxy resin (A-2) having a weight average molecular weight of 10,000-100,000; and an amine-based curing agent (B), where the mass ratio of these constituent (A-1) and constituent (A-2) is (A-1):(A-2)=10:90-90:10 in terms of solid content.SELECTED DRAWING: None

Description

The present invention relates to a coating composition for corrosion prevention, and more specifically, it is capable of suitably preventing corrosion of magnesium alloy materials, and has excellent drying properties, painting workability, and resistance to cleaning fluids. In particular, the present invention provides an anticorrosive coating composition that can be applied to large magnesium alloy materials such as high-speed transportation vehicles, construction machinery, and buses.

Magnesium alloy has the lowest density among practical structural metal materials, is lighter than aluminum alloy, has almost the same density as carbon fiber reinforced plastic (CFRP), has excellent strength, is easy to recycle, and is resource-friendly. Since it exists in abundance, it is applied to home appliances, OA equipment, mobile devices, automobile parts, etc. In recent years, flame-retardant magnesium alloys have been developed that have raised the ignition temperature by adding calcium to solve the problem of easy ignition, which was one of the drawbacks of magnesium alloys. Development into components of high-speed transportation vehicles such as the following is being considered (see, for example, Patent Documents 1 to 3 and Non-Patent Document 1).

When deploying such flame-retardant magnesium alloys to transportation vehicles and the like, it is necessary to address the corrosion problem, which has been recognized as another problem with magnesium alloys. Magnesium alloys have high chemical activity and poor corrosion resistance compared to other metals, and it has been shown that the addition of calcium causes further corrosion. Therefore, surface treatment (chemical conversion) is necessary to ensure corrosion resistance. processing film, anodizing treatment, painting, etc.), but based on our experience so far, most of these have been for small products for indoor use, and when processing large parts, it is necessary to perform A chemical conversion treatment method using a complicated treatment tank method is difficult to apply, and a coating method and a paint suitable for the method are required. Since conventional thermal curing operations are difficult due to equipment and process considerations, there is a need for paints that can be dried and cured at relatively low temperatures, preferably at room temperature.

Here, several paints for magnesium alloys and coating methods using them have been proposed, mainly targeting small items such as home appliances and automobile wheels.In particular, epoxy resins such as bisphenol type Methods of using it together with a curing agent and the like have been proposed (Patent Documents 4 to 7). As disclosed in these Patent Documents 4 to 7, the use of bisphenol-type epoxy resin in particular shows good results in salt spray and adhesion tests; According to the inventors' verification, even if the paint film has barrier properties that prevent water and oxygen from entering, defects such as pinholes can occur in the paint film due to some unforeseen circumstances. We confirmed that water, oxygen, etc. can penetrate between the paint film and the metal through such defects, causing rust to spread horizontally. In particular, since magnesium alloys do not have strong oxide films like aluminum alloys, it has been found that the influence of water and oxygen penetration caused by coating film defects is greater. Along with this, the inventors of the present application have also confirmed that simply reducing the water permeability of the paint film will make it easier for the moisture that has entered to stay, which will result in blistering, etc. of the paint film. .

That is, as disclosed in Patent Documents 4 to 7, even if the barrier properties of the coating film against water and oxygen are improved by using a bisphenol type epoxy resin, the corrosion resistance is still not sufficient. In order to improve the corrosion resistance of magnesium alloys that do not have a strong oxide film and are easily corroded, it is necessary to deal with unexpected coating film defects, etc., and to prevent the progression of corrosion from defective areas. It has been found that it is necessary to have good adhesion between the coating film and the metal.

Japanese Patent Application Publication No. 2017-78184 Japanese Patent Application Publication No. 2017-159345 Japanese Patent Application Publication No. 2017-159346 Japanese Patent Application Publication No. 7-204577 Japanese Patent Application Publication No. 2001-11672 Japanese Patent Application Publication No. 2003-82277 Japanese Patent Application Publication No. 2017-105221

ISMA REPORT No. 3, “Taking on the challenge of manufacturing high-speed rail vehicles using a new flame-retardant magnesium alloy,” published by the New Structural Materials Technology Research Association (ISMA), June 2016.

Under these circumstances, magnesium alloy materials can maintain barrier properties against factors that induce rust, such as water and oxygen; It has a sufficient anticorrosion effect to ensure adhesion to metals and prevent the spread of corrosion, and it dries and hardens at room temperature even for large structural members such as high-speed transportation vehicles that will be developed in the future. The inventors of this application have conducted intensive studies on anticorrosion paints that can be used to improve paint workability and have good workability. The present invention was completed based on the new discovery that an anticorrosive paint that can solve these problems can be obtained by blending a polymer-type modified epoxy resin in a specific ratio.

Therefore, it is an object of the present invention to have sufficient barrier properties, especially for magnesium alloy metals that are prone to corrosion, and to prevent corrosion between the coating film and the metal even if an unexpected defect occurs. To provide an anticorrosive coating composition capable of forming an anticorrosive coating film with sufficient adhesion to prevent corrosion, which can be dried even at room temperature, and has excellent coating workability.

That is, the present invention is an anticorrosive coating composition containing an epoxy resin and a curing agent,
A bisphenol type epoxy resin (A-1) having a weight average molecular weight of 470 to 900 and an epoxy equivalent of 180 to 1000 g/eq., and a polymer type epoxy resin having a weight average molecular weight of 10,000 to 100,000. Contains a resin (A-2) and an amine curing agent (B),
Corrosion prevention characterized in that the mass ratio of these components (A-1) and (A-2) is (A-1):(A-2)=10:90 to 90:10 in terms of solid content. It is a paint composition.

Further, the present invention provides a method for preventing corrosion of a magnesium alloy molded product, which comprises coating a molded product containing a magnesium alloy with at least the above-mentioned anticorrosive paint composition to form a coating film on the surface of the molded product. It is.

Furthermore, the present invention is a coated molded product in which the surface of a molded product containing magnesium is coated with at least the above-mentioned anticorrosive paint composition.

According to the present invention, it has sufficient barrier properties even for base materials that are prone to corrosion, especially magnesium alloys, and even if an unexpected defect occurs, corrosion will not progress between the coating film and the metal. It is possible to provide an anticorrosive coating composition that can form an anticorrosive coating film with sufficient adhesion to prevent corrosion, can be dried even at room temperature, and has excellent coating workability. Such an anticorrosive coating composition of the present invention is particularly useful as an undercoat coating for large-sized magnesium alloy materials such as high-speed transportation vehicles, construction machinery, and buses.

The present invention will be described in detail below, but the scope of the present invention is not limited to these descriptions, and modifications other than the following examples may be made as appropriate without departing from the gist of the present invention.

In the present invention, the material (base material) to be coated is not limited as long as it is within the scope of the present invention, that is, a material for the purpose of corrosion prevention, but in particular, magnesium alloy is the target material. do. The composition of the magnesium alloy is not particularly limited, but for reasons of lightness and strength, those containing 85% by mass or more of magnesium may be targeted. Other elements may include aluminum (denoted by "A") from 1% by mass to 10% by mass, and zinc (denoted by "Z") from 1% by mass to 5% by mass. For the purpose of imparting flammability, calcium (indicated by "X") may be blended in an amount of 0.5% by mass or more and 2.5% by mass or less. Other elements may include, for example, zirconium, manganese (indicated by "M"), yttrium, rare earth elements, and the like. Specific examples include AZ61, which contains magnesium as the main component, approximately 6% by mass of aluminum (A), and approximately 1% by mass of zinc (Z); AZ91 containing about 1% by mass, AZX311 containing about 3% by mass of aluminum (A), about 1% by mass of zinc (Z), about 1% by mass of calcium (X), and about 2% of calcium in AZX311. AZX312 with aluminum (A) changed to about 6% by mass, AZX611 with about 1% by mass of zinc (Z) and about 1% by mass of calcium (X), and AZX611 with about 2% by mass of calcium. Modified AZX612, AZX911 containing approximately 9% by mass of aluminum (A), approximately 1% by mass of zinc (Z), and approximately 1% by mass of calcium (X), calcium of AZX911 has been changed to approximately 2% by mass. Examples include AZX912, which has magnesium as its main component, and AMX601, which contains about 6% by mass of aluminum (A) and about 1% by mass of calcium (X), and AMX602, which has the calcium content of AMX601 changed to about 2% by mass. It will be done. As for the form of use, it is possible to use either a cast material of magnesium alloy having the above-mentioned composition or a molded product such as a wrought material obtained by processing the cast material by rolling or forging. It can also be used for small parts such as cars, mobile devices, etc., the bodies of automobiles, high-speed transportation vehicles, and aircraft, and large parts such as industrial machinery and construction machinery. The anticorrosive coating composition of the present invention can be used particularly for fairly large members with a cross-sectional diameter exceeding 3 m, such as high-speed transportation vehicles, which has not been used in the past.

The anticorrosive coating composition of the present invention comprises at least each of the epoxy resins A-1 and A-2 described below and an amine curing agent (B). Each will be specifically explained below.

<Bisphenol type epoxy resin (A-1)>
As the A-1 component used in the anticorrosive paint composition of the present invention, a general bisphenol type epoxy resin can be used, and bisphenol A type or bisphenol F type can be used, and as described below. It is used as a main agent for the amine curing agent (B).

Such a bisphenol type epoxy resin preferably has a weight average molecular weight of 470 to 900 from the viewpoint that the viscosity of the solution is suitable for coating. In addition, from the viewpoint of adhesion to the substrate and corrosion resistance, the epoxy equivalent is preferably 180 to 1,000 g/eq., preferably 230 to 600 g/eq.

Further, the content of the epoxy resin as the A-1 component is preferably 2 to 19% by mass in the composition in terms of solid content from the viewpoint of adhesion to the substrate and physical properties of the dry coating film. The content is preferably 5 to 15% by mass.

Such bisphenol type epoxy resins in the present invention include, for example, jER825, jER827, jER828, jER834, jER834X90 (90% solution product), jER1001, jER1001X70 (70% solution product) manufactured by Mitsubishi Chemical Corporation as bisphenol A type epoxy resins. (solution product), jER1001X75 (75% solution product), jER1001T75 (75% solution product), etc., Adeka Resin EP-4100 made by Adeka Corporation, Epotote YD-128 made by Nippon Steel & Sumikin Chemical Co., Ltd., etc. Examples of bisphenol F-type epoxy resins include jER806, jER806H, and jER807 manufactured by Mitsubishi Chemical Corporation, and EPICLON830 and EPICLON835 manufactured by DIC Corporation. These bisphenol A type epoxy resins and bisphenol F type epoxy resins may be used alone, or two or more types may be used in combination. When using a mixture of two or more types, a plurality of bisphenol A epoxy resins or bisphenol F epoxy resins having different molecular chains (repeat units) may be mixed, or a plurality of bisphenol A epoxy resins may be mixed. The bisphenol F type epoxy resin and a plurality of bisphenol F type epoxy resins can be mixed as desired within the scope of the present invention.

<Polymer type epoxy resin (A-2)>
In addition to the above-mentioned component A-1, the anticorrosive paint composition of the present invention has the following properties: In order to provide adhesion that can suppress the progress of corrosion, a polymeric epoxy resin is further blended. Specifically, this high-molecular type epoxy resin is a bisphenol A-type epoxy resin that has been made to have a high molecular weight using a modifier and is added with a specific functional group resulting from the modifier. This A-2 component, unlike the above A-1 component, can increase the hardness of the coating film with just one liquid by drying the lacquer (volatilization of the solvent) without using a hardening agent, and can develop film properties. It is a type of resin, and its compounding form may be as a main ingredient together with the A-1 component, or as a third compound as a separate compound from the A-1 component and the amine curing agent (B) described below. It is also possible to form the anticorrosive coating composition of the present invention by making it into a component and finally mixing it with component A-1 and the amine curing agent (B). Preferably, for reasons of product management and user convenience, it is preferable to use it as a main ingredient in combination with component A-1.

Here, the weight average molecular weight of the A-2 component needs to be 10,000 to 100,000, preferably 20,000 to 100,000, in order to develop the adhesive property unique to the A-2 component described above. 000 to 60,000.

Here, as the modifier in the A-2 component, alkyl glycidyl ether, glycidyl ester of t-alkane carboxylic acid, ε-caprolactone, acid anhydride, propionyl chloride, acyl chloride, etc. can be used.

As for such A-2 component, it is preferable to use one having a hydroxyl value of 100 to 500 mgKOH/g, more preferably 100 to 350 mgKOH/g. This is preferable because the adhesiveness between the formed coating film and the base material (metal) becomes good.

Further, the content of the epoxy resin as the A-2 component is preferably 3 to 20% by mass in the composition in terms of solid content, from the viewpoint of ensuring sufficient adhesion to the base material. , more preferably 5 to 15% by mass.

Specific examples of such A-2 components include EPICLON H304-40, H-401-45, H403-45, H408-40 (all manufactured by DIC Corporation), Modepics 401, 402, etc. Examples include 9201N, 9203N, 9205, 9208, KA-1439A (all manufactured by Arakawa Chemical Industries, Ltd.), and Epoky 813, 814, 818, and 863 (all manufactured by Mitsui Chemicals, Inc.). Within the scope of the purpose of the present invention, these may be used alone or in combination of two or more.

Here, the blending amount of the epoxy resin of the A-1 component and the epoxy resin of the A-2 component is A-1:A-2 = 10:90 to 90:10 in terms of solid content on a mass basis. If necessary, preferably A-1:A-2=30:70 to 70:30, more preferably A-1:A-2=40:60 to 60:40. If the A-1 component is less than 10 (A-2 component is more than 90), problems such as blistering of the paint film may occur in high temperature and high humidity environments; If it exceeds 90 (component A-2 is less than 10), there is a risk that problems such as poor adhesion to the substrate may occur.
Such A-1 component and A-2 component are preferably blended in a total of 5 to 25% by mass of the epoxy resins A-1 and A-2, more preferably in terms of solid content. is preferably 10 to 20% by mass.

In addition, in the anticorrosive coating composition of the present invention, in addition to the epoxy resin that is the above-mentioned A-1 and A-2 components, within the scope of the present invention, particularly applicable to flame-retardant magnesium alloy materials. It is not excluded that other resin components may be included within the objective range, and resin components that do not have reactivity with the A-1 component and A-2 component of the present invention, such as fluororesin. , acrylic resin, nitrified cotton resin, polyester resin, etc.

<Amine curing agent (B)>
In the anticorrosive coating composition of the present invention, the B component used as a curing agent for the A-1 component is amine-based, that is, it contains at least an amino group, and has a hardening effect on the epoxy group of the A-1 component. The addition reaction is carried out to advance curing. Preferably, an amine curing agent is selected whose ratio to the epoxy equivalent of the component A-1 (active hydrogen equivalent/epoxy equivalent) is preferably 1/0.8 to 1/1.2.

Examples of such amine-based curing agents include polyamine compounds such as aliphatic polyamines, alicyclic polyamines, aromatic polyamines, and polyamidoamines, as well as modified products thereof, but they cannot be used at room temperature. Furthermore, from the viewpoint of curing and drying properties and coating workability, aliphatic polyamines and polyamide amines are preferably used, and one or more of these may be used in combination. Furthermore, it is also possible to use amine-based resins obtained by reacting these aliphatic polyamines or polyamide amines with epoxy resins and modified with epoxy adducts. Aliphatic polyamines have excellent light resistance, and polyamide amines are presumed to have the effect of preventing the spread of rust in the horizontal direction at the interface between the base material and the coating film. These amine resins may be used alone or in combination of two or more.

Examples of aliphatic polyamines include ethylene diamine, propylene diamine, butylene diamine, hexamethylene diamine, diethylene triamine, triethylene tetramine, pentaethylene hexamine, and modified polyamines thereof. Examples of aromatic polyamines include phenylene diamine, xylylene diamine, and modified polyamines thereof. Examples of polyamide amines include products such as polyamide amines obtained by reacting dimer acids (polymerized products of unsaturated fatty acids) or other polycarboxylic acids with polyamines, and modified polyamide amines thereof.

<Rust inhibitor (C)>
The anticorrosive coating composition of the present invention preferably further contains a rust preventive agent (C), mainly for the purpose of effectively suppressing the spread of corrosion. As this rust preventive agent (C), a wide range of known ones can be used as long as it falls within the scope of the purpose of the present invention, particularly within the scope of the purpose of applying it to flame-retardant magnesium alloy materials. For example, magnesium phosphate , aluminum phosphate, zinc phosphate, zirconium phosphate, manganese phosphate, calcium phosphate, aluminum pyrophosphate, calcium pyrophosphate, aluminum dihydrogen tripolyphosphate, aluminum metaphosphate, calcium metaphosphate, strontium silicate, silicon Use silicates such as potassium acid, calcium silicate, barium silicate, titanium silicate, aluminum silicate, magnesium silicate, magnesium ion exchange silica, calcium ion exchange silica, colloidal silica, fumed silica, etc. Can be done. In particular, magnesium phosphate, strontium silicate, aluminum phosphate, and calcium ion exchange silica can be suitably used because they have excellent corrosion resistance. Among them, magnesium phosphate is more suitable, and specific examples include Pigmenthan 465M and Pigmenthan E from Banner Chemicals. The content of the rust preventive agent (C) in the composition is preferably 1 to 10% by mass, more preferably 3 to 5% by mass. As for the blending form, it can be used together with the above A-1, A-2 and the amine curing agent (B), or it can be blended separately from these as a third component, but the reason for shortening the mixing process is Therefore, it is preferable to mix it together with A-1 and A-2 in advance.

In addition, in the anticorrosive coating composition of the present invention, a silane coupling agent (D) is added in order to prevent water from being introduced into the coating film, which causes corrosion, and to maintain the adhesion of the coating film to the material. It is preferable to further include. As such a silane coupling agent (D), any known silane coupling agent can be used as long as it falls within the scope of the purpose of the present invention, particularly within the scope of the purpose of application to flame-retardant magnesium alloy materials. -2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3 -Triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane It is preferable to use a silane coupling agent having an amino group, such as a hydrochloride of , from the viewpoint of improving adhesion to the material. The content of the silane coupling agent (D) in the composition is preferably 0.1 to 5.0% by mass, more preferably 0.3 to 2.0% by mass. As for the blending form, it can be used together with A-1, A-2 and the amine curing agent (B), or it can be blended separately from these as a third component, similar to component C. However, in order to shorten the mixing process, it is preferable to mix it together with the amine curing agent (B) in advance.

Note that each of the components C to D may be added singly, or two or more types may be added, and each is appropriately selected and added within the scope of the purpose of the present invention. It is preferable.

<Additives>
Furthermore, in the anticorrosion composition of the present invention, reactive diluents, non-reactive Diluent, color pigment, extender pigment, thickener, pH adjuster, dispersant, surface conditioner, anti-sag agent, antifoaming agent, anti-settling agent, fungicide, preservative, ultraviolet absorber, light stabilizer The composition may further contain various additives commonly used in paints, such as organic solvents and the like.

<Preparation/painting method>
The anticorrosive coating composition of the present invention is prepared using such ingredients, but preferably, procedures such as rough stirring, pigment dispersion using a medium, and dissolution of the mill base and resin are carried out. Preferably, it is prepared by As mentioned above, the prepared anticorrosive coating composition of the present invention can be used for metal substrates in general, but is particularly intended for use with large molded articles made of flame-retardant magnesium alloys. As a coating method, a known coating method can be selected as appropriate in consideration of the size and shape of the target member, such as spray coating, shower coating, electrostatic coating, electrodeposition coating, powder coating, Dip coating, roll coating, curtain flow coating, spin coating, brush coating, etc. can be used for large components such as the bodies of high-speed transportation vehicles, and methods using drying ovens and treatment tanks have equipment limitations. Therefore, spray coating and brush coating are preferably used for coating such large-sized members. It is preferable to adjust the coating amount as appropriate to form a film so that the film thickness after drying is approximately 50 to 100 μm.

Due to the above-mentioned restrictions on the coating method, the anticorrosive coating composition of the present invention is preferably one that can be cured by low-temperature baking, more preferably 100°C or less, and still more preferably dryable at room temperature. Good. Here, normal temperature refers to 23° C., although it varies depending on the atmospheric temperature of the environment in which painting is performed, and refers to the absence of forced temperature manipulation such as heating or cooling.

The anticorrosive coating composition of the present invention may be applied directly to the target base material (metal) or coated with a chemical conversion film (e.g. A coating of zinc phosphate, calcium zinc phosphate, zirconium, etc.) may be applied. For example, magnesium alloys may be treated by immersion in strong acids such as phosphoric acid or hydrofluoric acid, or by shower coating. . Further, pre-treatments such as degreasing treatment and etching treatment may be performed. Regarding the anticorrosive coating film formed by the anticorrosive coating composition of the present invention, the physical properties of the coating film are preferably zinc phosphate, zinc calcium phosphate, zirconium, and iron phosphate.

On the other hand, it is also possible to use the anticorrosive coating composition of the present invention as an undercoat, and further coat it with intermediate coats, top coats, and the like. When painting over the composition of the present invention, it can be changed as appropriate depending on the purpose and use, but for example, polyester putty or urethane resin paint is used for vehicles, and other coatings are used. Also, a paint containing at least one selected from the group consisting of fluororesin paint, acrylic resin paint, nitrocotton resin paint, and polyester resin paint is preferably applied 1 to 5 times to form a coating film. It is preferable to form. For decoration purposes, conventionally known topcoats such as various enamels or clear paints can also be used. Preferably, the total thickness of the coating film to be formed is 100 to 200 μm or more, although it is not limited and is appropriately selected depending on the purpose and use.

<Preparation of undercoat paint>
Production Examples 1 to 17 were prepared by mixing various raw materials in a disper for undercoat paints, which are anticorrosive paint compositions, based on the formulations shown in Tables 1 and 2.
Of the components used in Tables 1 and 2, the physical properties of the epoxy resin (A-1), epoxy resin (A-2), and amine curing agent (B) are as follows. *1 and *2 indicate analytical values, and the analytical method is shown below. Other values are catalog values.
<Epoxy resin (A-1)>
・jER834X90 [solid content 90% by mass, weight average molecular weight 470, epoxy equivalent 230-270g/eq. , manufactured by Mitsubishi Chemical Corporation]
・jER1001X70 [Solid content 70% by mass, weight average molecular weight 900, epoxy equivalent 450-500g/eq. , manufactured by Mitsubishi Chemical Corporation]
<Epoxy resin (A-2)>
・Epicron H403-45 [solid content 45% by mass, weight average molecular weight 22,000 (*1), hydroxyl value 200mgKOH/g, manufactured by DIC Corporation]
・Epicron H304-45 [solid content 45% by mass, weight average molecular weight 30,000, hydroxyl value 200mgKOH/g, manufactured by DIC Corporation]
・Arakido 9201N [solid content 40% by mass, weight average molecular weight 50,000, hydroxyl value 245mgKOH/g, manufactured by Arakawa Chemical Industry Co., Ltd.]
・Epokey 863 [solid content 45% by mass, weight average molecular weight 14,000 (*1), hydroxyl value 250mgKOH/g (*2), manufactured by Mitsui Chemicals, Inc.]
(Measurement of weight average molecular weight related to *1)
Weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).
(Measurement of hydroxyl value related to *2)
After the free hydroxyl groups in 1 g of the resin were completely acetylated with acetic anhydride, the number of mg of potassium hydroxide required to neutralize it was determined, and the hydroxyl value of the resin solid content was determined.
<Amine curing agent (B)>
- Daitoclar HD-Q [aliphatic polyamine, solid content 60% by mass, theoretical active hydrogen equivalent 415g/eq. , amine value 125mgKOH/g, manufactured by Daito Sangyo Co., Ltd.]
- Tomide TXP-696 [Polyamidoamine, solid content 80% by mass, active hydrogen equivalent 95g/eq. , amine value 330mgKOH/g, manufactured by T&K TOKA Co., Ltd.]

<Preparation of top coat>
Based on the formulation shown in Table 3 below, various raw materials were mixed using a disper to prepare a top coating base. Further, based on the formulation shown in Table 4, various raw materials were mixed using a disper to prepare a top coating curing agent. Thereafter, the hydroxyl groups derived from the varnish in the topcoat base material and the isocyanate groups derived from the isocyanate resin in the topcoat curing agent were mixed in an equivalent ratio of 1:1 to prepare a topcoat paint.

<Creation of test piece>
A base material was prepared by cutting a magnesium alloy (AZX611 manufactured by Sankyo Materials Co., Ltd.) into a size of 150 mm x 70 mm x 3 mm thick. Thereafter, the undercoat paint of each production example prepared above was applied by air spray to a dry film thickness of 50 μm, and dried at 23° C. for 16 hours to form an undercoat film.
Then, on the formed undercoat film, the topcoat paint prepared above is applied with air spray so that the dry film thickness becomes 50 μm, and dried at 23 ° C. for 7 days to form a topcoat film, Each specimen was used as a test piece.
Using each test piece thus obtained, the adhesion and anticorrosion properties of the coating film were evaluated using the methods described below.

<Adhesion>
Initial adhesion immediately after painting according to JIS K 5600-5-6 (adhesive cross-cut method) and after 40°C warm water immersion test conducted under the conditions of JIS K 5600-6-2 (liquid resistance water immersion method) The adhesion was evaluated using the following criteria.
◎: The coating film does not peel off from the cut. and/or the extent of peeling is less than 5%.
○: The coating film is peeled off along the edge of the cut. The range is 5% or more and less than 15%.
Δ: The coating film is peeled off along the edges of the cut. The range is 15% or more and less than 35%.
×: The coating film is peeled off along the edge of the cut. The range is over 35%.

<Salt spray test>
In accordance with JIS K 5600-7-1 (neutral salt spray resistance), the state of the coating film surface was visually confirmed after 480 hours.
◎: Blistering and peeling of the coating film from the cross-cut is within 2 mm, and no thread rust occurs.
○: Blistering and peeling of the coating film from the cross cut is within 2 mm, and no more than 3 threads are rusted.
△: Blistering and peeling of the coating film from the cross cut is within 5 mm, and no more than 6 threads are rusted.
×: Significant blistering, peeling, or thread rust of the coating film from the crosscut.

<Moisture resistance test>
In accordance with JIS K 5600-7-2 (moisture-resistant continuous dew condensation method), the state of the coating film surface was visually confirmed after 480 hours.
◎: No abnormality on the coating film surface.
○: There was no blistering on the surface of the coating film, and some gloss fading occurred.
Δ: Five or more blisters and fading occurred on the surface of the coating film.
×: Blisters occurred on the entire surface of the coating film.

<Painting workability (room temperature curability)>
The coating film was applied to a specified thickness by air spraying and dried at room temperature for 7 days, and then evaluated in accordance with JIS K 5600-3-6 (non-stick drying property).
○: Completely hardens after drying at room temperature and does not soften at the temperature inside the humidity test chamber (50° C.).
Δ: After drying at room temperature, the coating film does not remain sticky, but softens at the temperature inside the humidity test chamber (50° C.).
×: After drying at room temperature, the coating film remains sticky.

<Evaluation results>
The evaluation results are shown in Tables 5 and 6.

Claims (9)

An anticorrosive coating composition containing an epoxy resin and a curing agent,
The weight average molecular weight is 470 to 900, and the epoxy equivalent is 180 to 1,000 g/eq. A bisphenol type epoxy resin (A-1), a polymer type epoxy resin (A-2) having a weight average molecular weight of 10,000 to 100,000, and an amine curing agent (B),
The mass ratio of these components (A-1) and (A-2) is (A-1):(A-2)=10:90 to 49.94:50.06 in terms of solid content,
An anticorrosive coating composition characterized in that the amine curing agent (B) contains an aliphatic polyamine and/or a polyamidoamine. The anticorrosive coating composition according to claim 1, wherein the component (A-2) has a hydroxyl value of 100 to 350 mgKOH/g. Claim 1 or 2 further comprising (C) one or more rust inhibitors selected from the group consisting of magnesium phosphate, strontium silicate, aluminum phosphate, and calcium ion exchange silica. The anticorrosive paint composition described in . The anticorrosive coating composition according to any one of claims 1 to 3, further comprising a silane coupling agent having an amino group. The ratio of the active hydrogen equivalent in the amine curing agent (B) to the epoxy equivalent of the component (A-1) (active hydrogen equivalent/epoxy equivalent) is 1/0.8 to 1/1.2. The anticorrosive coating composition according to any one of claims 1 to 4, characterized by: The anticorrosive coating composition according to any one of claims 1 to 5, which is cured at 100°C or lower. The anticorrosive coating composition according to any one of claims 1 to 6, which is used by applying it to a molded article containing a magnesium alloy. A magnesium alloy molded article, characterized in that a molded article containing a magnesium alloy is coated with at least the anticorrosive coating composition according to any one of claims 1 to 7 to form a coating film on the surface of the molded article. Corrosion prevention method. A coated molded article comprising at least the anticorrosive coating composition according to any one of claims 1 to 7 coated on the surface of a molded article containing a magnesium alloy.