JP6690046B1 - Antirust coating composition and method for producing antirust coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rust preventive coating composition capable of exhibiting excellent rust preventive property for a long period of time and further capable of forming a coating film exhibiting excellent moisture resistance. Further, a rust preventive coating composition capable of suppressing or greatly reducing blisters in a processed part, an end face, and a cross cut part and exhibiting excellent rust preventive property and moisture resistance for a long period even in such a part is provided. thing. A rust preventive coating composition comprising a coating film forming resin (A), a cross-linking agent (B) and a magnesium oxide (C), wherein the magnesium oxide (C) has a lattice constant of A rust-preventive coating composition having a BET specific surface area of less than 0.4214 nm and 2.0 or less. [Selection diagram] None

Description

  The present invention relates to an anticorrosion coating composition and a method for producing an anticorrosion coating film using the coating composition.

Cold-rolled steel sheets and coated steel sheets coated with plated steel sheets as base materials are also called pre-coated metal, and are used for various applications such as outdoor units for air conditioners, home electric appliances for water heaters, roofs, exterior building materials such as walls, etc. It is used. For example, a coated steel sheet including a galvanized steel sheet is usually coated with a rust preventive paint on its surface in order to improve rust prevention and prevent rusting.

Conventionally, a chrome-containing paint is generally used as the rust preventive paint, and the formation of the chrome-containing coating film can suppress the generation of rust. However, chromium is feared to have a bad effect on the environment, and its use is being restricted.
Therefore, a coating composition containing a vanadium compound as a rust preventive other than the chromium compound has been proposed.

  Japanese Patent Application Laid-Open No. 2008-222834 (Patent Document 1) discloses a coating composition containing (A) a hydroxyl group-containing coating film-forming resin, (B) a cross-linking agent, and (C) a rust-preventive pigment mixture. The rust preventive pigment mixture (C) is composed of (1) at least one vanadium compound selected from vanadium pentoxide, calcium vanadate and ammonium metavanadate, (2) metal silicate and (3) phosphate-based calcium salt. A coating composition is disclosed.

  JP 2009-227748 A (Patent Document 2) discloses that (A) at least one hydroxyl group-containing film-forming resin of a specific acrylic resin and a specific polyester resin, (B) a bisphenol type epoxy resin, C) at least one adhesion-imparting resin selected from a curing agent, (D) an epoxy resin having a secondary or tertiary amino group, an acrylic resin having a secondary or tertiary amino group, and a resol-type phenol resin, and ( E) A rust-preventive coating composition containing a rust-preventive pigment is disclosed. Further, the rust preventive pigment (E) is (1) at least one kind of vanadium compound selected from vanadium pentoxide, calcium vanadate and ammonium metavanadate, (2) at least one kind selected from metal silicate and silica fine particles. It is disclosed that the compound contains a silicon-containing compound and (3) a phosphoric acid-based metal salt.

JP, 2008-222834, A JP, 2009-227748, A

In recent years, durability of coated steel sheets under various environmental conditions has been required.
For example, it has been recognized that "acid rain" causes corrosion of a coating film on a coated steel sheet. Here, "acid rain" means that the substances caused by acid rain, which originate from sulfur dioxide (SO ₂ ) and nitrogen oxides (NOx), dissolve into rain, snow, fog, etc., and the atmosphere is more acidic than usual. The phenomenon of becoming acidic or the environment becoming more acidic than usual. In addition, from the release of the acid rain-causing substance until it falls as acid rain, it may be transported hundreds to thousands of kilometers across the border, and the corrosion damage to the coated steel sheet spreads over a wide area. It is expected to increase in the future.
Further, when the acid rain-derived substance is present in an environment with dew condensation and humidity, at least one of sulfide and nitride contained in the acid rain-derived substance is exposed to the moisture state to promote a corrosion reaction. There is.

However, the coating compositions described in Patent Documents 1 and 2 have insufficient rust preventive properties, for example, the rust preventive properties are not sufficient for application to outdoor applications, and there is room for improvement. In addition, there is room for improvement in rust prevention under acidic environmental conditions.
As described above, there is a demand for a coating composition that has rust preventive properties under acidic environmental conditions and, in addition, has rust preventive properties for a longer period of time.

Further, when used outdoors, the article to be coated may be exposed to a high humidity environment, and therefore a coating composition exhibiting excellent moisture resistance is required.

  The present invention aims to solve the above problems, and more specifically, provides a rust preventive coating composition that can exhibit excellent rust preventive properties over a long period of time and, in addition, exhibit excellent moisture resistance. This is an issue.

In order to solve the above problems, the present invention provides the following aspects.
[1] A rust preventive coating composition containing a coating film forming resin (A), a cross-linking agent (B), and a magnesium oxide (C),
Magnesium oxide (C) has a lattice constant of less than 0.4214 nm, and
An anticorrosion coating composition having a BET specific surface area of 2.0 m ² / g or less.
[2] In one embodiment, the rust-preventive coating composition according to the present disclosure has a magnesium metal ion concentration of 70 ppm or less in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of the artificial acidic seawater solution. It contains magnesium oxide (C).
[3] In one embodiment, the magnesium oxide (C) in the anticorrosive coating composition of the present disclosure has an electric conductivity of 320 μS / in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water. cm or less of the compound is included.
[4] In one embodiment, the magnesium oxide (C) in the rust preventive coating composition of the present disclosure includes a magnesium calcined product calcined at a temperature of 1,000 ° C or higher.
[5] In one embodiment, the magnesium oxide (C) in the rust-preventive coating composition of the present disclosure is 1% by mass of an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water. The pH is 8 or more and 12 or less, and the average particle diameter of the magnesium oxide (C) is 0.5 μm or more and 20 μm or less.
[6] In one embodiment, the magnesium oxide (C) in the anticorrosive coating composition of the present disclosure is magnesium oxide.
[7] In one embodiment, the coating film-forming resin (A) in the anticorrosive coating composition of the present disclosure is at least selected from the group consisting of epoxy resins, polyester resins, acrylic resins, urethane resins and modified products thereof. Including one.
[8] In one embodiment, the coating film-forming resin (A) in the anticorrosive coating composition of the present disclosure contains at least one selected from the group consisting of urethane resins and modified products thereof, and the urethane resin is It has a glass transition temperature of -50 ° C or higher and 70 ° C or lower.
[9] In one embodiment, the coating film-forming resin (A) in the anticorrosive coating composition of the present disclosure contains at least one selected from the group consisting of urethane resins and modified products thereof, and the urethane resin is At least one selected from the group consisting of ester-based urethane resins, ether-based urethane resins and carbonate-based urethane resins is included.
[10] In one embodiment, the coating film-forming resin (A) in the anticorrosive coating composition of the present disclosure has a number average molecular weight of 1,000 or more and 40,000 or less.
[11] In one embodiment, the coating film-forming resin (A) in the anticorrosive coating composition of the present disclosure is at least one selected from the group consisting of ester-based urethane resins, epoxy resins, polyester resins and modified products thereof. Including seeds.
[12] In one embodiment, the coating film-forming resin (A) in the anticorrosion coating composition of the present disclosure is
At least one of the ester urethane resin, the epoxy resin, and the polyester resin has a solid content acid value of 30 mgKOH / g or less.
[13] In one embodiment, the rust-preventive coating composition of the present disclosure contains magnesium based on 100 parts by mass of the total solid content of the film-forming resin (A) and the solid content of the crosslinking agent (B). The oxide (C) is included in the range of 1 part by mass or more and 150 parts by mass or less.
[14] In another embodiment, the present disclosure includes a coating step of coating the above anticorrosion coating composition on an object to be coated, and curing the coating composition at a temperature of 150 ° C. or higher and 270 ° C. or lower. A method for producing a rust coating film is provided.

The rust-preventive coating composition of the present invention can exhibit excellent rust-preventive properties for a long period of time and can form a coating film exhibiting excellent moisture resistance.
Further, with the method for producing a coating film according to the present invention, it is possible to form a coating film that exhibits excellent rust-preventing properties for a long period of time and that also exhibits excellent moisture resistance.

It is a schematic diagram which shows the outline of the cross section of the coated steel plate test piece used for the corrosion resistance test. It is a schematic diagram which shows the cross cut part and 4T bending process part which were provided in the coated steel plate test piece used for the corrosion resistance test.

The background of the present invention will be described.
For example, the conventional evaluation of anticorrosion property has been performed only for a short test time, and the evaluation site has been determined only at the molding part (flat surface of the article to be coated).
On the other hand, in recent years, objects to be coated in various shapes have been manufactured. In objects to be coated that can have such various shapes, for example, in the processed portion, the end surface, the cross cut portion, etc., the protective effect of the coating film may not be sufficient, and corrosion may occur from these portions. May occur.
Therefore, for example, the processed portion, the end surface, even in the cross-cut portion, showing a superior rust preventive property over a long period of time, further, a coating composition showing a rust preventive property over a long period of time, and further over a very long period of time. Is required.

Further, a coating composition containing a chromium-based compound is used in order to impart rust prevention properties to the anticorrosion coating composition. For example, a coating composition containing a chromium compound can satisfactorily suppress the occurrence of rust on the article to be coated.
On the other hand, also in the technical field of anticorrosion coating compositions, reduction in environmental load is required, and it is necessary to reduce the compounding amount of chromium-based compounds in anticorrosion coating compositions in the future. Conceivable.

For example, vanadium compounds such as metal vanadates are used for the purpose of reducing chromium compounds. Further, increasing the amount of the vanadium compound contained in the coating composition is said to be effective as a means for improving the rust prevention property of the rust preventing coating composition containing the vanadium compound.
However, since vanadium compounds, especially vanadate, have high water solubility, when the coating composition contains a large amount of vanadium compound, the coating film is likely to absorb moisture. As a result, there has been a problem that the moisture resistance of the coating film is lowered and blistering occurs in the coating film. Such blistering of the coating film causes a decrease in rust resistance and also a decrease in moisture resistance of the coating film. Therefore, when the coating composition contains a large amount of vanadium compound, it may be difficult to provide both long-term rust prevention and moisture resistance.

Therefore, the inventors of the present invention have made earnest studies and completed the present invention.
The rust-preventive coating composition of the present invention can exhibit excellent rust-preventing properties for a long period of time and can form a coating film having excellent moisture resistance. In addition, it is possible to form a coating film that exhibits excellent rust resistance over a long period of time even under acidic environmental conditions. Therefore, for example, the generation of rust that can be caused by "acid rain" or the like can be suppressed.
Although it should not be construed as being limited to a particular theory, in the case of the anticorrosion coating composition of the present disclosure, for example, an acid rain-induced substance may be absorbed into a water film under a dew and humid environment. It is considered that it is possible to prevent the problem that the environment is oxidized and the corrosion progresses.

Further, even in the aspect in which the article to be coated is exposed to a high temperature and high humidity environment such as when it is used outdoors, the anticorrosive coating composition of the present disclosure can exhibit excellent moisture resistance. The present inventors have found that the anticorrosive coating composition of the present disclosure can greatly reduce the moisture absorption of a coating film by containing the specific magnesium oxide (C) according to the present disclosure, compared with, for example, a vanadium compound. I found it.
Therefore, it is possible to suppress or greatly reduce the deterioration of the moisture resistance of the coating film, and further suppress or significantly reduce the occurrence of blisters in the coating film.

  As described above, the rust-preventive coating composition of the present disclosure can exhibit excellent rust-preventing properties for a long period of time and can form a coating film having excellent moisture resistance.

Furthermore, if the rust-preventive coating composition of the present disclosure, in an object to be coated that can have various shapes, not only in the flat surface of the object to be coated, but also in, for example, a processed portion, an end surface, a cross-cut portion, etc. The protective effect of the coating film can be sufficiently exhibited.
Moreover, the rust-preventive coating composition of the present disclosure can suppress or significantly reduce blisters in the processed portion, the end surface, and the cross-cut portion, and even in such a portion, excellent rust-preventing property and moisture resistance Can be shown.

With the rust-preventive coating composition of the present disclosure, in addition to being able to form a coating film having such excellent rust-preventing properties over a long period of time, it has excellent processability and adhesion, for example, an article to be coated. It is possible to form a coating film which is excellent in adhesiveness with respect to the above, an adhesiveness with respect to the top coating composition, and is also excellent in chemical resistance, weather resistance, scratch resistance, designability, and abrasion resistance.
Hereinafter, the anticorrosion coating composition of the present disclosure will be described.

The rust-preventive coating composition of the present disclosure is a rust-preventive coating composition containing a film-forming resin (A), a crosslinking agent (B), and a magnesium oxide (C),
Magnesium oxide (C) has a lattice constant of less than 0.4214 nm, and
The BET specific surface area is 2.0 m ² / g or less.
The rust preventive coating composition of the present disclosure can exhibit excellent rust preventive properties over a long period of time by containing a specific magnesium oxide (C), and can form a coating film exhibiting excellent moisture resistance. ..
Hereinafter, the magnesium oxide (C) according to the present disclosure will be described, and then each component and the like will be described.

[Magnesium oxide (C)]
Magnesium oxide (C) has a lattice constant of less than 0.4214 nm, and
The BET specific surface area is 2.0 m ² / g or less.

Since the magnesium oxide (C) has a specific relationship according to the present invention, the coating composition according to the present disclosure has, in addition to the effects of the above-described coating composition, for example, an object to be coated in various usage environments, for example, Even under conditions of high atmospheric temperature and high humidity, stable rust prevention tends to be exhibited.
In addition, although it should not be interpreted as being limited to a particular theory, the inclusion of the magnesium oxide (C) according to the present disclosure can suppress a significant increase in the amount of alkali ion dissolved even in an acidic environment. It is supposed to be. As a result, the magnesium oxide (C) according to the present disclosure stably supplies the corrosion inhibiting factor, which makes it possible to inhibit corrosion for a long period of time. Furthermore, the coating composition according to the present disclosure can exhibit sufficient rust preventive property even in an acidic environment.
For example, the specific magnesium oxide (C) according to the present disclosure can exhibit a function as a rust preventive pigment in the coating composition according to the present disclosure. In one embodiment, the magnesium oxide (C) is a rust preventive pigment.

Furthermore, the coating composition of the present disclosure containing the magnesium oxide (C) according to the present disclosure can significantly reduce water absorption and moisture absorption of the coating film as compared with the coating composition containing a vanadium compound. Found out.
Therefore, the coating film formed from the rust-preventive coating composition containing the magnesium oxide (C) according to the present disclosure can suppress or greatly reduce the decrease in moisture resistance. In addition, it is possible to suppress the occurrence of blistering in the coating film, or to significantly reduce it.
Furthermore, the rust-preventive coating composition according to the present disclosure containing the magnesium oxide (C) according to the present disclosure can suppress or significantly reduce blisters in the processed portion, the end face, and the cross cut portion.

  Since the magnesium oxide (C) has a specific relationship according to the present invention, for example, the processed portion, the end face, and the cross-cut portion also show excellent rust preventive properties for a long period of time, and further, for a long period of time, Furthermore, it can exhibit rust-preventing properties for an extremely long period of time.

The magnesium oxide (C) in the present disclosure is an oxide having a lattice constant of less than 0.4214 nm and a BET specific surface area of 2.0 m ² / g or less, for example, zinc magnesium oxide (ZnMgO). , Tin magnesium oxide (SnMgO), indium magnesium oxide (InMgO), and magnesium oxide (MgO).
In one embodiment, the magnesium oxide (C) may be magnesium oxide, which is an oxide having the composition MgO. Since the magnesium oxide (C) is an oxide represented by magnesium oxide (MgO), a coating film having excellent corrosion resistance can be formed.

The magnesium oxide (C) according to the present disclosure has a lattice constant of less than 0.4214 nm, for example, a lattice constant of 0.4213 nm or less. In one embodiment, the magnesium oxide (C) has a lattice constant of less than 0.4212 nm.
By having such a lattice constant, it is possible to form a coating film having good rust prevention properties.
Further, the magnesium oxide (C) according to the present disclosure may be a cubic crystal.
In the present specification, the lattice constant can be measured using, for example, an X-ray diffractometer MAXima_X XRD-7000 (manufactured by Shimadzu Corporation).

In one embodiment, the magnesium oxide (C) according to the present disclosure has a lattice constant of 0.4211 nm or less. By having such a lattice constant, it is possible to form a coating film having excellent rust-preventive properties for a longer period of time. More specifically, it is possible to form a coating film exhibiting antirust property for a long period of time, and it is possible to suppress or greatly reduce corrosion in an acidic environment for a long time.
Such an effect should not be construed as being limited to a particular theory, but the fact that the lattice constant of magnesium oxide (C) is within such a range makes it more effective to corrode the object to be coated. It is considered that depletion of the corrosion inhibitor derived from the magnesium oxide (C) can be suppressed to the portion where the corrosion can occur, and this suppressing factor can be continuously supplied.

In one embodiment, the magnesium oxide (C) according to the present disclosure has a lattice constant of 0.4200 nm or more, for example, a lattice constant of 0.4205 nm or more, and a lattice constant of 0.4208 nm or more. It may be.
In one embodiment, the magnesium oxide (C) according to the present disclosure has a lattice constant of 0.4209 nm or more, for example, a lattice constant of 0.4210 nm or more.

The magnesium oxide (C) according to the present disclosure has a BET specific surface area of 2.0 m ² / g or less. By having the BET specific surface area described above, a coating film having excellent rust preventive properties can be formed for a longer period of time.
In one embodiment, the magnesium oxide (C) according to the present disclosure has a BET specific surface area of 1.8 m ² / g or less, such as 1.6 m ² / g or less and 1.5 m ² / G or less.
In one embodiment, the BET specific surface area of the magnesium oxide (C) is 1.4 m ² / g or less, for example, 1.3 m ² / g or less, 1.1 m ² / g or less. You can
By having such a BET specific surface area, it is possible to form a coating film having excellent rust preventive properties for a long period of time. More specifically, it is possible to form a coating film exhibiting antirust property for a long period of time, and it is possible to suppress or greatly reduce corrosion in an acidic environment for a long time.
In the present specification, the BET specific surface area can be measured using, for example, an automatic specific surface area measuring device Gemini VII23900 (manufactured by Shimadzu Corporation).
Such an effect should not be construed as being limited to a particular theory, but the BET specific surface area of the magnesium oxide (C) is within such a range, so that it is more effective. It is considered that this is because depletion of the corrosion inhibitor derived from the magnesium oxide (C) can be suppressed and the inhibitor can be continuously supplied to the portion where corrosion can occur.

In one embodiment, the BET specific surface area of the magnesium oxide (C) according to the present disclosure is 0.1 m ² / g or more, for example, 0.2 m ² / g or more, 0.3 m ² / G or more.
By having such a BET specific surface area, it is possible to form a coating film having excellent rust preventive properties for a long period of time. More specifically, it is possible to form a coating film exhibiting antirust property for a long period of time, and it is possible to suppress or greatly reduce corrosion in an acidic environment for a long time.

In one embodiment, the BET specific surface area of the magnesium oxide (C) is 0.1 m ² / g or more and 2.0 m ² / g or less, for example, 0.3 m ² / g or more and 1.5 m. ^{It is 2} / g or less.
In the present disclosure, the BET specific surface area of magnesium oxide (C) can be appropriately combined within the above range.

In one embodiment, the rust preventive coating composition of the present disclosure has a magnesium metal ion concentration of 70 ppm or less in an aqueous solution obtained by adding 1 g of the magnesium oxide (C) according to the present disclosure to 100 g of an artificial acidic seawater solution. Includes oxide (C).
Although it should not be construed as being limited to a particular theory, the anticorrosive coating composition of the present disclosure contains magnesium oxide that satisfies such conditions, so that the steel sheet can be oxidized without depletion for a long time. Corrosion can be suppressed by supplying the corrosion suppression factor from magnesium.
Further, it is possible to suppress or greatly reduce the deterioration of the moisture resistance of the coating film, and further suppress or significantly reduce the occurrence of blistering in the coating film.
For example, by satisfying the above conditions, blistering and peeling of the coating film can be favorably suppressed in a high temperature and high humidity environment for a long time.
Moreover, the anticorrosive coating composition of the present disclosure can suppress or greatly reduce blisters in the processed portion, the end surface, and the cross cut portion.
Here, in the present disclosure, “showing anticorrosiveness under high temperature conditions” means that even if the temperature is a condition where the atmospheric temperature is high (for example, 40 ° C. or higher) and a high temperature of about 80 ° C. It means to show rust prevention.

In one embodiment, the magnesium oxide (C) according to the present disclosure has a magnesium metal ion concentration of 69 ppm or less in an aqueous solution obtained by adding 1 g of the magnesium oxide (C) according to the present disclosure to 100 g of an artificial acidic seawater solution. And, for example, includes magnesium oxide that can be 66 ppm or less and can be 65 ppm or less.
By satisfying such a condition, the corrosion inhibiting factor from magnesium oxide can be more stably supplied to the steel sheet for a longer time without depletion, and the corrosion can be suppressed.
Further, it is possible to suppress or greatly reduce the deterioration of the moisture resistance of the coating film, and further suppress or significantly reduce the occurrence of blistering in the coating film.
Furthermore, with the rust-preventive coating composition of the present disclosure, blisters in the processed portion, the end surface, and the cross cut portion can be suppressed or greatly reduced.

On the other hand, the magnesium oxide (C) according to the present disclosure has a magnesium metal ion concentration of 10 ppm or more, for example, in an aqueous solution obtained by adding 1 g of the magnesium oxide (C) according to the present disclosure to 100 g of the artificial acidic seawater solution. It is 20 ppm or more.
By satisfying such a condition, the corrosion inhibiting factor from magnesium oxide is supplied to the steel sheet without exhaustion for a long time, and the corrosion can be inhibited.

  In one embodiment, the rust-preventive coating composition of the present disclosure can contain other metal compounds within a range that does not impair the effects of the magnesium oxide (C).

  In another embodiment, the magnesium oxide (C) is a compound having a magnesium metal ion concentration of 70 ppm or less in an aqueous solution obtained by adding 1 g of the magnesium oxide (C) to 100 g of the artificial acidic seawater solution. For example, the magnesium oxide (C) according to the present disclosure has a magnesium metal ion concentration of 69 ppm or less in an aqueous solution obtained by adding 1 g of the magnesium oxide (C) according to the present disclosure to 100 g of the artificial acidic seawater solution. For example, it is a compound of 66 ppm or less and 65 ppm or less.

On the other hand, the magnesium oxide (C) according to the present disclosure has a magnesium metal ion concentration of 10 ppm or more, for example, in an aqueous solution obtained by adding 1 g of the magnesium oxide (C) according to the present disclosure to 100 g of the artificial acidic seawater solution. It is 20 ppm or more.
By satisfying such a condition, the corrosion inhibiting factor from magnesium oxide can be more stably supplied to the steel sheet for a long time without depletion, and the corrosion can be suppressed.

In the present disclosure, the measurement of the magnesium metal ion concentration in an aqueous solution in which 1 g of magnesium oxide (C) is added to 100 g of the artificial acidic seawater solution can be measured based on the JIS G 0594 cycle corrosion test method.
More specifically, an aqueous solution based on the acidic salt aqueous solution used in the method B defined in JIS G 0594 cycle corrosion test method can be used as the artificial acidic seawater solution.
That is, as a composition close to the composition of artificial seawater specified in JIS G 0594, a mixed solution of nitric acid and sulfuric acid specified in 4.2.2 of JIS G 0594 is used to adjust pH = 2.5, Artificial acidic seawater can be prepared. For example, as a reagent, Marine Art series (manufactured by Tomita Pharmaceutical Co., Ltd.) or the like can be used.

Next, 100 g of artificial acidic seawater and 1 g of magnesium oxide (C) according to the present disclosure are added to the container, a stirrer chip is put therein, and the mixture is stirred at room temperature (23 ° C.) for 4 hours.
Then, after leaving at room temperature for 24 hours, the supernatant is collected with a syringe equipped with a syringe filter, and the element concentration is measured using, for example, an ICP emission spectrometer (ICPS-7510, manufactured by Shimadzu Corporation). The concentration of magnesium metal ions can be measured.

  In one embodiment, the magnesium oxide (C) contains a compound having an electric conductivity of 320 μS / cm or less in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water, for example, 310 μS / cm or less. Including compounds of In addition, the magnesium oxide (C) may include a compound having an electric conductivity of 305 μS / cm or less, for example, a compound having an electric conductivity of less than 301 μS / cm.

By satisfying such a condition, the corrosion inhibiting factor from magnesium oxide is supplied to the steel sheet without exhaustion for a long time, and the corrosion can be inhibited.
Further, it is possible to suppress or greatly reduce the deterioration of the moisture resistance of the coating film, and further suppress or significantly reduce the occurrence of blistering in the coating film.
Furthermore, with the rust-preventive coating composition of the present disclosure, blisters in the processed portion, the end surface, and the cross cut portion can be suppressed or greatly reduced.
In one embodiment, the rust-preventive coating composition of the present disclosure can contain other metal compounds within a range that does not impair the above-described effects of the magnesium oxide (C).

  In one embodiment, the magnesium oxide (C) may include a compound having an electric conductivity of 10 μS / cm or more in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water, for example, 20 μS / cm. cm or more of the compound, and 50 μS / cm or more of the compound may be included.

In another embodiment, the magnesium oxide (C) is a compound having an electric conductivity of 320 μS / cm or less in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water. For example, the magnesium oxide (C) is, for example, a compound having a conductivity of 310 μS / cm or less, a compound having a conductivity of 305 μS / cm or less, and a compound having a conductivity of less than 301 μS / cm.
By satisfying these conditions, the corrosion inhibiting factor from magnesium oxide is more stably supplied to the steel sheet for a long time without depletion, and the corrosion can be suppressed.
Further, it is possible to suppress or greatly reduce the deterioration of the moisture resistance of the coating film, and further suppress or significantly reduce the occurrence of blistering in the coating film.
Furthermore, with the rust-preventive coating composition of the present disclosure, blisters in the processed portion, the end surface, and the cross cut portion can be suppressed or greatly reduced.

  In one embodiment, the magnesium oxide (C) may be a compound having an electric conductivity of 10 μS / cm or more in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water, for example, 20 μS. / Cm 2 or more and may be a compound of 50 μS / cm or more.

In the present disclosure, the conductivity of an aqueous solution obtained by adding 1 g of magnesium oxide (C) to 100 g of pure water is measured by mixing 100 g of ion-exchanged water and 1 g of magnesium oxide (C) and adding a stirrer chip. Then, the mixture is stirred at room temperature (23 ° C.) for 4 hours.
After that, the electrical conductivity can be measured using, for example, an electrical conductivity meter (CM-42X, manufactured by Toa DKK Co., Ltd.).

In one embodiment, the magnesium oxide (C) is a compound having a magnesium metal ion concentration of 70 ppm or less in an aqueous solution obtained by adding 1 g of the magnesium oxide (C) to 100 g of the artificial acidic seawater solution. Furthermore, magnesium oxide (C) is a compound having an electric conductivity of 320 μS / cm or less in an aqueous solution in which 1 g of magnesium oxide (C) is added to 100 g of pure water.
As described above, since the magnesium oxide (C) is a compound that exhibits a specific metal ion concentration under the measurement conditions according to the present disclosure and further exhibits a specific conductivity, for example, corrosion in an acidic environment Can be suppressed for a longer time.
Further, in addition to suppressing corrosion in an acidic environment, it is possible to stably suppress blistering and peeling of the coating film in a high temperature and high humidity environment for a long time.
In the present disclosure, such a combination of the magnesium metal ion concentration and the electric conductivity can be appropriately selected within the range described in the present specification.

In one embodiment, the magnesium oxide (C) includes a magnesium calcined product calcined at a temperature of 1,000 ° C. or higher. The rust-preventive coating composition according to the present disclosure contains the magnesium oxide that has been baked under such temperature conditions, and thus can exhibit excellent rust-preventing properties for a long period of time, and further has excellent moisture resistance. The coating film shown can be formed.
In one embodiment, the magnesium oxide (C) includes a magnesium calcined product calcined at a temperature of 1,100 ° C. or higher, and may include, for example, a magnesium calcined product calcined at a temperature of 1,200 ° C. or higher. .
In one embodiment, the magnesium oxide (C) includes a magnesium calcined product calcined at a temperature of 2,200 ° C. or less, and may include, for example, a magnesium calcined product calcined at a temperature of 2,000 ° C. or less. .
For example, the magnesium oxide (C) includes a magnesium calcined product calcined at a temperature of 1,000 ° C. or more and 2,200 ° C. or less, and a magnesium calcined at a temperature of 1,100 ° C. or more and 2,000 ° C. or less. You may include things.
Further, the magnesium oxide (C) may include a plurality of kinds of fired products fired in such a temperature range in combination.

Although it should not be construed as being limited to a particular theory, the anticorrosive coating composition of the present disclosure contains magnesium oxide that satisfies such conditions, so that the steel sheet can be oxidized without depletion for a long time. Corrosion can be suppressed by supplying the corrosion suppression factor from magnesium.
Further, it is possible to suppress or greatly reduce the deterioration of the moisture resistance of the coating film, and further suppress or significantly reduce the occurrence of blistering in the coating film.
For example, by satisfying the above conditions, blistering and peeling of the coating film can be favorably suppressed in a high temperature and high humidity environment for a long time.
Moreover, the anticorrosive coating composition of the present disclosure can suppress or greatly reduce blisters in the processed portion, the end surface, and the cross cut portion.

In another embodiment, the magnesium oxide (C) is a calcined magnesium product calcined at a temperature of 1,000 ° C. or higher. In one embodiment, the magnesium oxide (C) is a magnesium calcined product calcined at a temperature of 1,100 ° C. or higher, for example, a magnesium calcined product calcined at a temperature of 1,200 ° C. or higher.
When the rust-preventive coating composition according to the present disclosure contains the magnesium oxide (C) that has been baked under such temperature conditions, it can exhibit excellent rust-preventing properties for a longer period of time, and further, it is excellent. A coating film showing moisture resistance can be formed.
The magnesium oxide (C) can also be produced by a method of oxidizing metallic magnesium.

In one embodiment, the magnesium oxide (C) is a magnesium calcined product calcined at a temperature of 2,200 ° C. or lower, for example, a magnesium calcined product calcined at a temperature of 2,000 ° C. or lower.
For example, magnesium oxide (C) is a magnesium calcined product that is calcined within a temperature range of 1,000 ° C. or higher and 2,200 ° C. or lower, and is calcined within a temperature range of 1,100 ° C. or higher and 2,000 ° C. or lower. It is a burned magnesium product.
When the magnesium oxide (C) in the rust-preventive coating composition according to the present disclosure is a magnesium oxide that has been baked under such temperature conditions, it is possible to exhibit excellent rust-preventing properties for a longer period, Furthermore, a coating film having excellent moisture resistance can be formed.

Although it should not be construed as being limited to a particular theory, the anticorrosive coating composition of the present disclosure contains magnesium oxide that satisfies such conditions, so that the steel sheet can be oxidized without depletion for a long time. Corrosion can be suppressed by supplying the corrosion suppression factor from magnesium.
Further, it is possible to suppress or greatly reduce the deterioration of the moisture resistance of the coating film, and further suppress or significantly reduce the occurrence of blistering in the coating film.
For example, by satisfying the above conditions, blistering and peeling of the coating film can be favorably suppressed in a high temperature and high humidity environment for a long time.
Moreover, the anticorrosive coating composition of the present disclosure can suppress or greatly reduce blisters in the processed portion, the end surface, and the cross cut portion.

In one embodiment, the magnesium oxide (C) contains a compound having a pH of 8 or more and 13 or less in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water, for example, 9 or more and 13 or less. Yes, it may be 10 or more and 13 or less. By satisfying such conditions, it is possible to more effectively suppress an increase in the corrosion rate of the object to be coated and to form a coating film having good corrosion resistance.
In the present disclosure, the pH value of an aqueous solution obtained by adding 1 g of magnesium oxide (C) to 100 g of pure water can be measured by a known method.
For example, 100 g of ion-exchanged water and 1 g of magnesium oxide (C) are mixed, a stirrer chip is put thereinto, and the mixture is stirred at room temperature (23 ° C.) for 4 hours.
After that, the pH can be measured using, for example, a pH meter (tabletop pH meter F-74, manufactured by Horiba Ltd.).

In one embodiment, the average particle diameter of the magnesium oxide (C) is 0.5 μm or more and 20 μm or less, for example, 1 μm or more and 15 μm or less, and 1 μm or more and 10 μm or less. Although it should not be construed as being limited to a particular theory, the apparent volume concentration (PVC) of the magnesium oxide (C) is controlled by the average particle diameter of the magnesium oxide (C) being within such a range. It is considered that an excessive increase can be suppressed, and higher corrosion resistance can be exhibited. In addition, it can have an excellent coating film barrier property and can exhibit higher corrosion resistance.
In the present specification, the average particle size can be measured using, for example, a laser diffraction particle size distribution measuring device SALD-2300 (manufactured by Shimadzu Corporation).
Here, the corrosion of the article to be coated according to the present disclosure occurs due to a corrosion factor such as water, salt water, and acidic water penetrating into the metal side through the coating film. On the other hand, the coating film formed from the coating composition according to the present disclosure can prevent such a corrosion factor from penetrating into the object side. In the present disclosure, such barrier properties are also referred to as coating barrier properties.

In one embodiment, the coating composition of the present disclosure contains magnesium oxide (C) in a total amount of 100 parts by mass of the solid content of the film-forming resin (A) and the solid content of the crosslinking agent (B). The amount may be 1 part by mass or more and 150 parts by mass or less, for example, 10 parts by mass or more and 100 parts by mass or less.
By including the magnesium oxide (C) in such a relationship, the rust-preventing coating composition of the present invention can exhibit excellent rust-preventing properties for a long period of time, and further exhibits excellent moisture resistance. Can be formed.

[Coating film forming resin (A)]
The coating film-forming resin (A) in the anticorrosion coating composition of the present disclosure is not particularly limited as long as it is a resin having a functional group capable of reacting with the crosslinking agent (B) and having a coating film forming ability.

For example, the coating film forming resin (A) is an epoxy resin and its modified products (acrylic modified epoxy resin or the like); polyester resin and its modified products (urethane modified polyester resin, epoxy modified polyester resin, silicone modified polyester resin, etc.); Resin and its modified products (silicone modified acrylic resin, etc.); Urethane resin and its modified products (ester urethane resin, ether urethane resin, carbonate urethane resin, epoxy urethane resin, etc.); Phenolic resin and its modified products (acrylic Examples thereof include modified phenol resins, epoxy modified phenol resins and the like); phenoxy resins; alkyd resins and their modified products (urethane modified alkyd resins, acryl modified alkyd resins, etc.); These resins may be used alone or in combination of two or more.

In one embodiment, the film forming resin (A) contains at least one selected from the group consisting of epoxy resins, polyester resins, acrylic resins, urethane resins and modified products thereof.
For example, the coating film-forming resin (A) is an epoxy resin, a polyester resin, a urethane resin, or a modification thereof, from the viewpoint of the bending processability of the obtained coating film and the balance of the moisture resistance, corrosion resistance and weather resistance of the obtained coating film. At least one selected from the group consisting of things is included.

  The coating film forming resin (A) can have a number average molecular weight of 1,000 or more and 40,000 or less. When the number average molecular weight is within such a range, a coating film having excellent corrosion resistance can be formed, and further a coating film having excellent adhesion to an object to be coated and a top coating composition (top coating) can be formed. .

(Epoxy resin)
The number average molecular weight (Mn) of the epoxy resin, for example, the modified hydroxyl group-containing epoxy resin, is preferably 1,400 or more and 20,000 or less, and 2,000 or more and 10,000 or less. More preferably, it is 2,000 or more and 4,000 or less.
In the present disclosure, unless otherwise specified, when simply described as an epoxy resin, it means that at least one selected from the group consisting of epoxy resins and modified epoxy resins is included.
In the present specification, the number average molecular weight (Mn) is a value converted into polystyrene by gel permeation chromatography (GPC).

When the epoxy resin has such a number average molecular weight, the crosslinking reaction with the crosslinking agent (B) described below sufficiently progresses, and a coating film having high moisture resistance can be formed. Furthermore, excellent corrosion resistance can be secured. For example, although not limited to a particular theory, the elution of the magnesium oxide (C) contained in the coating film is appropriate and the corrosion resistance under acidic environmental conditions is good.
Further, it is possible to prevent the cross-linking density of the coating film from becoming too high, and to form a coating film having a sufficient elongation, for example, to form a coating film having a sufficient bending workability.
Further, the rust-preventive coating composition of the present disclosure has an appropriate viscosity and is easy to handle.

The glass transition temperature (Tg) of the epoxy resin may be 120 ° C. or lower, or 115 ° C. or lower. For example, the glass transition temperature (Tg) of the epoxy resin may be 110 ° C. or lower.
In one embodiment, the glass transition temperature (Tg) of the epoxy resin is 50 ° C or higher, and may be 55 ° C or higher.
For example, the glass transition temperature (Tg) of the epoxy resin can be in the range of 50 ° C or higher and 120 ° C or lower.
In the present specification, the glass transition temperature (Tg) can be measured using, for example, a thermal analyzer TMA7100 (manufactured by Hitachi High-Tech Science Co., Ltd.).

  When the glass transition temperature (Tg) of the epoxy resin is within the above range, the moisture resistance of the coating film does not become excessively high, the moisture resistance of the coating film becomes sufficient, and the corrosion resistance becomes good.

The solid acid value of the epoxy resin (including its modified product) can be 0 mgKOH / g or more and 30 mgKOH / g or less.
In the present disclosure, the acid value of solid content can be measured in accordance with JIS K 0070.

The epoxy resin may be a hydroxyl group-containing epoxy resin (including a hydroxyl group-containing epoxy resin modified product).
As the epoxy resin, a resin obtained by condensing epichlorohydrin and bisphenol up to a high molecular weight in the presence of a catalyst such as an alkali catalyst, if necessary; a bisphenol type epoxy resin such as bisphenol A type and bisphenol F type; and a novolak type epoxy resin, etc. Can be mentioned.
Examples of modified epoxy resins include modified epoxy resins such as acrylic modified epoxy resin, urethane modified epoxy resin, and amine modified epoxy resin. For example, taking an acrylic modified epoxy resin as an example, it can be prepared by reacting the bisphenol type epoxy resin or the novolac type epoxy resin with a polymerizable unsaturated monomer component containing acrylic acid, methacrylic acid or the like. it can.
Further, taking a urethane-modified epoxy resin as an example, it can be prepared by reacting the bisphenol type epoxy resin or the novolac type epoxy resin with a polyisocyanate compound.

  Examples of the epoxy resin include jER1004, jER1007, 1255HX30 (bisphenol A skeleton) and YX8100BH30 manufactured by Mitsubishi Chemical Corporation.

(Polyester resin)
The number average molecular weight (Mn) of the polyester resin, for example, a modified hydroxyl group-containing polyester resin, is preferably 1,400 to 40,000, more preferably 2,000 to 40,000. , 2,000 to 30,000 is particularly preferable.
In the present disclosure, unless otherwise specified, when simply described as a polyester resin, it means that at least one selected from the group consisting of polyester resins and modified polyester resins is included.

When the polyester resin has such a number average molecular weight, the crosslinking reaction with the crosslinking agent (B) sufficiently proceeds, and a coating film having high moisture resistance can be formed. Furthermore, excellent corrosion resistance can be secured. For example, although not limited to a particular theory, the elution of the magnesium oxide (C) contained in the coating film is appropriate and the corrosion resistance under acidic environmental conditions is good.
Further, it is possible to prevent the cross-linking density of the coating film from becoming too high, and to form a coating film having a sufficient elongation, for example, to form a coating film having a sufficient bending workability.
Further, the rust-preventive coating composition of the present disclosure has an appropriate viscosity and is easy to handle.

  The glass transition temperature (Tg) of the polyester resin is preferably −35 ° C. or higher and 110 ° C. or lower, for example, −30 ° C. or higher and 80 ° C. or lower, and can be −30 ° C. or higher and 60 ° C. or lower.

  When the glass transition temperature (Tg) of the polyester resin is within the above range, the moisture resistance of the coating film does not become excessively high, the moisture resistance of the coating film becomes sufficient, and the corrosion resistance becomes good.

The solid acid value of the polyester resin (including its modified product) is 0.1 mgKOH / g or more and 30 mgKOH / g or less, for example, 0.1 mgKOH / g or more and 30 mgKOH / g or less, and 0.3 mgKOH / g or more. It may be 30 mgKOH / g or less.
When the solid content acid value is within such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed. Furthermore, excellent corrosion resistance can be secured.

  The polyester resin can be obtained by polycondensation of a polyhydric alcohol and a polybasic acid. Specific examples of the polyhydric alcohol include, for example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,3. -Butanediol or 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, hydrogenated bisphenol A, hydroxyalkylated bisphenol A, 1,4-cyclohexanedimethanol, 2,2-dimethyl- 3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate (BASHPN), N, N-bis- (2-hydroxyethyl) dimethylhydantoin, polycaprolactone polyol, glycerin, sorbitol , An'nitoru, trimethylol ethane, trimethylol propane, trimethylol butane, hexanetriol, pentaerythritol, dipentaerythritol, tris - can be mentioned (hydroxyethyl) isocyanate. The polyhydric alcohols may be used alone or in combination of two or more.

  Specific examples of the polybasic acid include, for example, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetraphthalic acid, methyltetrahydrophthalic anhydride, hymic anhydride. Acid, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid , Succinic anhydride, lactic acid, dodecenyl succinic acid, dodecenyl succinic anhydride, cyclohexane-1,4-dicarboxylic acid, and endo acid anhydride. The polybasic acids may be used alone or in combination of two or more.

Examples of modified polyester resins include modified polyester resins such as urethane modified polyester resin, epoxy modified polyester resin, acrylic modified polyester resin, and silicone modified polyester resin.
For example, a urethane-modified polyester resin is a resin that has polyester in its main chain and has its ends modified with isocyanate to make it urethane-modified.
For example, taking a silicone-modified polyester resin as an example, it is a polyester resin and an organic silicone (for example, an organic silicone having a -SiOCH ₃ group and / or a SiOH group as a functional group and having a number average molecular weight of about 300 to 1,000). It can be prepared by reacting with. The amount of the organic silicone used is usually about 5 to 50 parts by mass with respect to 100 parts by mass of the polyester resin. Further, taking a urethane-modified polyester resin as an example, it can be prepared by reacting the above polyester resin with a polyisocyanate compound.

  For example, as an example of a modified polyester resin and a hydroxyl group-containing polyester resin, Beckolite 46-118, Beckolite M-6205-50, Beckolite M-6401-52, Beckolite M-6402-50, Toyobo manufactured by DIC Corporation are used. Examples thereof include Byron 220, Byron UR3500, Byron UR5537, Byron UR8300, Byron UR4410 and the like.

(acrylic resin)
The number average molecular weight (Mn) of the acrylic resin and its modified product is preferably 1,400 to 40,000, more preferably 2,000 to 40,000, and 2,000 to 30,000. Is particularly preferable.
In the present disclosure, unless otherwise specified, when simply described as an acrylic resin, it means that at least one selected from the group consisting of acrylic resins and modified acrylic resins is included.

When the acrylic resin has such a number average molecular weight, the crosslinking reaction with the crosslinking agent (B) proceeds sufficiently and a coating film having high moisture resistance can be formed. Furthermore, excellent corrosion resistance can be secured. For example, although not limited to a particular theory, the elution of the magnesium oxide (C) contained in the coating film is appropriate and the corrosion resistance under acidic environmental conditions is good.
Further, it is possible to prevent the cross-linking density of the coating film from becoming too high, and to form a coating film having a sufficient elongation, for example, to form a coating film having a sufficient bending workability.
Further, the rust-preventive coating composition of the present disclosure has an appropriate viscosity and is easy to handle.

  The glass transition temperature (Tg) of the acrylic resin is preferably −35 ° C. or higher and 110 ° C. or lower, for example, −30 ° C. or higher and 80 ° C. or lower, and can be −30 ° C. or higher and 60 ° C. or lower.

  When the glass transition temperature (Tg) of the acrylic resin is within the above range, the moisture resistance of the coating film does not become excessively high, the moisture resistance of the coating film becomes sufficient, and the corrosion resistance becomes good.

The solid acid value of the acrylic resin (including its modified product) is 0.1 mgKOH / g or more and 30 mgKOH / g or less, for example, 0.1 mgKOH / g or more and 30 mgKOH / g or less, and 0.3 mgKOH / g or more. It may be 30 mgKOH / g or less.
When the solid content acid value is within such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed. Furthermore, excellent corrosion resistance can be secured.

The acrylic resin has a hydroxyl group such as hydroxymethyl (meth) acrylate, hydroxylethyl (meth) acrylate, hydroxylpropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and N-methylolacrylamide ( (Meth) acrylic monomers and lactone adducts thereof; (meth) acrylic acid; (meth) acrylic acid esters such as alkyl (meth) acrylate; one or more monomers selected from (meth) acrylonitrile and the like The following acrylic resin can be mentioned. Acrylic resin, in addition to the structural units derived from the above monomers, other monomers (for example, carboxyl group-containing ethylenic monomers such as crotonic acid, itaconic acid, fumaric acid, maleic acid, vinyl-based monomers such as styrene) It may contain a structural unit derived from it. In addition, in this indication, (meth) acrylic acid represents acrylic acid or methacrylic acid.
Examples of the modified acrylic resin include modified acrylic resins such as silicone modified acrylic resin. For example, taking a silicone-modified acrylic resin as an example, it can be prepared by reacting an acrylic resin with an organic silicone as described above. The amount of the organic silicone used is usually about 5 to 50 parts by mass with respect to 100 parts by mass of the acrylic resin.

(Urethane resin)
In one embodiment, the number average molecular weight (Mn) of the urethane resin and the modified urethane resin is 1,000 or more and 30,000 or less, for example, 2,000 or more and 28,000 or less, and 2,500 or more and 25, It may be 000 or less.
In one embodiment, the urethane resin and the modified urethane resin have a number average molecular weight (Mn) of 6,000 or more and 15,000 or less.
In the present disclosure, unless otherwise specified, when simply described as a urethane resin, it means that at least one selected from the group consisting of urethane resins and modified urethane resins is included.

When the urethane resin has such a number average molecular weight, the crosslinking reaction with the crosslinking agent (B) sufficiently proceeds, and a coating film having high moisture resistance can be formed. Furthermore, excellent corrosion resistance can be secured. For example, although not limited to a particular theory, the elution of the magnesium oxide (C) contained in the coating film is appropriate and the corrosion resistance under acidic environmental conditions is good.
Further, it is possible to prevent the cross-linking density of the coating film from becoming too high, and to form a coating film having a sufficient elongation, for example, to form a coating film having a sufficient bending workability.
Further, the rust-preventive coating composition of the present disclosure has an appropriate viscosity and is easy to handle.

  In one embodiment, the glass transition temperature (Tg) of the urethane resin is -30 ° C or higher and 80 ° C or lower, for example, -30 ° C or higher and 60 ° C or lower, and can be -30 ° C or higher and 50 ° C or lower. .

  When the glass transition temperature (Tg) of the urethane resin is within the above range, the moisture resistance of the coating film does not become excessively high, the moisture resistance of the coating film becomes sufficient, and the corrosion resistance becomes good.

The solid acid value of the urethane resin (including its modified product) is 0.1 mgKOH / g or more and 30 mgKOH / g or less, for example, 0.1 mgKOH / g or more and 30 mgKOH / g or less, and 0.3 mgKOH / g or more. It may be 30 mgKOH / g or less.
When the solid content acid value is within such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed. Furthermore, excellent corrosion resistance can be secured.

  In one embodiment, in the present disclosure, the urethane group concentration (mass%) in the resin of the urethane resin is 2 mass% or more and 20 mass% or less, for example, 5 mass% or more and 17 mass% or less. When the urethane group concentration in the urethane resin is within such a range, excellent moisture resistance and corrosion resistance can be secured.

Examples of the urethane resin include those obtained by reacting a polyol compound and a polyisocyanate compound and then further chain-extending with a chain extender. The polyol compound is not particularly limited as long as it is a compound having two or more hydroxyl groups per molecule, and examples thereof include ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol and triethylene glycol. , Glycerin, trimethylolethane, trimethylolpropane, polycarbonate polyol, polyester polyol, polyether polyol such as bisphenol hydroxypropyl ether, polyester amide polyol, acrylic polyol, polyurethane polyol, or a mixture thereof. The polyisocyanate compound is not particularly limited as long as it is a compound containing two or more isocyanate groups per molecule, and examples thereof include aliphatic isocyanates such as hexamethylene diisocyanate (HDI) and fats such as isophorone diisocyanate (IPDI). Examples thereof include aromatic diisocyanates such as cyclic diisocyanates and tolylene diisocyanates (TDI), araliphatic diisocyanates such as diphenylmethane diisocyanate (MDI), or a mixture thereof. The chain extender is not particularly limited as long as it is a compound containing at least one active hydrogen in the molecule, and water or an amine compound can be applied. As the amine compound, aliphatic polyamines such as ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine and tetraethylenepentamine, and aromatic polyamines such as tolylenediamine, xylylenediamine and diaminodiphenylmethane. Alicyclic polyamines such as diaminocyclohexylmethane, piperazine, 2,5-dimethylpiperazine, isophoronediamine, hydrazine,
Examples thereof include hydrazines such as succinic acid dihydrazide, adipic acid dihydrazide and phthalic acid dihydrazide, and alkanolamines such as hydroxyethyldiethylenetriamine, 2-[(2-aminoethyl) amino] ethanol and 3-aminopropanediol.

In one embodiment, the urethane resin is an ester-based urethane resin.
In the present disclosure, an ester-based urethane resin means a resin having both a urethane group and an ester group in the main chain. Moreover, what compares the number of urethane groups in the main chain with the number of ester groups, and the number of urethane groups contains more than 5% of the number of ester groups is called ester urethane resin.
Examples of the urethane polymer include those obtained by reacting the above-described polyol compound with a polyisocyanate compound, and then further chain-extending with a chain extender.
For example, it can be obtained by polycondensation of a copolymerized polyester resin having a hydroxyl group and a polyisocyanate compound.
In one embodiment, the hydroxyl group-containing polyester resin can be prepared by polycondensing an acid component such as a polycarboxylic acid and / or an acid anhydride and a polyhydric alcohol.

  In one embodiment, the urethane resin is an ether type urethane resin. In the present disclosure, the ether-based urethane resin means a resin having both a urethane group and an ether group in the main chain. Moreover, what compares the number of urethane groups and the number of ester groups in the main chain, and the number of urethane groups is larger than the number of ether groups by 5% or more is called an ether urethane resin.

  In one embodiment, the urethane resin is a carbonate-based urethane resin. In the present disclosure, a carbonate-based urethane resin means a resin having both a urethane group and a carbonate group in the main chain. Moreover, what compares the number of urethane groups and the number of carbonate groups in the main chain, and the number of urethane groups contained by 5% or more than the number of carbonate groups is called carbonate-based urethane resin.

In one embodiment, the solid acid value of the ester-based urethane resin, the ether-based urethane resin, and the carbonate-based urethane resin is 0.1 mgKOH / g or more and 50 mgKOH / g or less, for example, 0.1 mgKOH / g or more and 40 mgKOH / g. It is less than or equal to 0.3 mgKOH / g and less than or equal to 40 mgKOH / g.
When the solid content acid value is within such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed. Furthermore, excellent corrosion resistance can be secured.

Examples of the polycarboxylic acid which constitutes the copolymerized polyester resin having a hydroxyl group include aliphatic polycarboxylic acids such as oxalic acid, succinic acid, adipic acid and azelaic acid, terephthalic acid, isophthalic acid, orthophthalic acid and 4,4'-diphenyldicarboxylic acid. Aromatic polycarboxylic acids such as acids and trimellitic acid, and as the polyol component, ethylene glycol, propylene glycol, trimethylene glycol, 1,3-butadiol, 1.4-butadiol, 1.5-bentanediol, 1.6- Examples include hexanediol, neopentyl glycol, trimethylolpropane, trimethylolethane, pentaerythritol and the like.
The copolyester of the present invention is one in which the hydroxyl group is excessively blended in the equivalent ratio of the carbonyl group in the polycarboxylic acid and the hydroxyl group of the polyol component in the range of 1.0 / 1.001 to 1.0 / 2.0. It is preferably obtained by an ordinary transesterification method or direct esterification reaction. A particularly preferred equivalent ratio is in the range of 1.0 / 1.01 to 1.0 / 1.5.

  The acid anhydride that may be contained in the acid component is not particularly limited, and examples thereof include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hymic acid anhydride, and trimellitic anhydride. Examples thereof include acids, pyromellitic dianhydride, maleic anhydride, succinic anhydride, dodecenyl succinic anhydride and the like.

  In the preparation of the hydroxyl group-containing polyester resin, other reaction components may be used in addition to the acid component and the polyol component. Examples of other reaction components include monocarboxylic acids, hydroxycarboxylic acids, lactones, drying oils, semi-drying oils and fatty acids thereof. More specific examples include monoepoxide compounds such as Cardura E (manufactured by Shell Chemical Co.) and lactones. The lactones are those capable of ring-opening addition to polyesters of polyvalent carboxylic acids and polyhydric alcohols to form graft chains, and include, for example, β-propiolacurone, dimethylpropiolactone, butyl lactone, γ- Examples thereof include valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotolactone, δ-valerolactone, δ-caprolactone. Of these, ε-caprolactone is most preferable.

  An ester urethane resin can be prepared by reacting a hydroxyl group-containing polyester resin with an aliphatic diisocyanate compound by, for example, a known method.

The coating composition of the present disclosure may further use a thermoplastic resin in addition to the coating film forming resin (A).
Examples of the thermoplastic resin include chlorinated olefin resins such as chlorinated polyethylene and chlorinated polypropylene; homopolymers or copolymers containing vinyl chloride, vinyl acetate, vinylidene chloride, etc. as monomer components; cellulose resins; acetal resins. Alkyd resin; chlorinated rubber resin; modified polypropylene resin (acid anhydride modified polypropylene resin etc.); fluororesin (eg vinylidene fluoride resin, vinyl fluoride resin, copolymer of fluorinated olefin and vinyl ether, fluorinated) Copolymers of olefin and vinyl ester) and the like.
The thermoplastic resins may be used alone or in combination of two or more. By using a thermoplastic resin in combination, better coating film physical properties such as coating film strength and elongation can be obtained.

[Crosslinking agent (B)]
The crosslinking agent (B) reacts with the coating film forming resin (A) to form a cured coating film.
Examples of the cross-linking agent (B) include a polyisocyanate compound; a blocked polyisocyanate compound in which an isocyanate group of the polyisocyanate compound is blocked with an active hydrogen-containing compound (may be referred to as "BI"); an amino resin; a phenol resin and the like. You can
Of these, it is preferable to include at least one selected from a blocked polyisocyanate compound and an amino resin. By including such a cross-linking agent (B), excellent rust-preventing property can be exhibited for a long period of time, and a coating film having excellent moisture resistance can be formed.

  The polyisocyanate compound and the polyisocyanate compound constituting the blocked polyisocyanate compound are not particularly limited, and conventionally known compounds can be used. Specific examples 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'- Isocyanatocyclohexylmethane, 1,3- or 1,4-bis- (isocyanatomethyl) -cyclohexane, bis- (4-isocyanato-3-methylcyclohexyl) methane, 1,3- or 1,4-α, α , Α'α'-Tetramethylxylylenediene Cyanate, 2,4- or 2,6-diisocyanatotoluene, 2,2'-, 2,4'- or 4,4'-diisocyanatodiphenylmethane (MDI), 1,5-naphthalene diisocyanate, p- Alternatively, m-phenylene diisocyanate, xylene diisocyanate, diphenyl-4,4′-diisocyanate and the like. Further, a cyclized polymer of each diisocyanate (isocyanurate type), an isocyanate biuret type (biuret type), or an adduct type may be used. The polyisocyanate compounds may be used alone or in combination of two or more. The isocyanurate type polyisocyanate compound is one of those preferably used in the present invention.

  For example, the polyisocyanate compound is preferably an aromatic polyisocyanate compound containing one or more aromatic functional groups in the molecule. By using the aromatic polyisocyanate compound, not only the moisture resistance of the coating film can be improved but also the coating film strength can be improved. As the aromatic polyisocyanate compound preferably used, 2,4- or 2,6-diisocyanatotoluene (TDI), 2,2′-, 2,4′- or 4,4′-diisocyanatodiphenylmethane ( MDI), xylene diisocyanate (XDI), naphthalene diisocyanate (NDI), etc. can be mentioned.

  The isocyanate group content of the polyisocyanate compound constituting the blocked polyisocyanate compound, which is measured according to JIS K 7301-1995, is usually 3 to 20% in the solid content of the polyisocyanate compound, and preferably 5 to 5. 15%. When the isocyanate group content is within the above range, the curability of the coating film is further improved. Further, it is possible to suppress the crosslinking density of the obtained coating film from becoming excessively high, and the corrosion resistance may be improved.

The active hydrogen-containing compound (blocking agent) used in the blocked polyisocyanate compound is not particularly limited, and -OH group (alcohols, phenols, etc.), = N-OH group (oximes, etc.), = NH Examples thereof include compounds having a group (amines, amides, imides, lactams, etc.), compounds having a —CH ₂ — group (active methylene group), and azoles. Specific examples include, for example, 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, methyl ethyl kedoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime, dimethyl malonate, ethyl acetoacetate, acetylacetone. , Pyrazole and the like. The active hydrogen-containing compounds may be used alone or in combination of two or more.

The dissociation temperature of the blocked polyisocyanate compound due to heat depends on the types of the polyisocyanate compound and the active hydrogen-containing compound constituting the block polyisocyanate compound, the presence or absence of a catalyst, and the amount thereof. A blocked polyisocyanate compound having a) of 120 to 180 ° C. is preferably used. By using a blocked polyisocyanate compound having a dissociation temperature within this range, it is possible to improve the stability of the coating material, and because it is excellent in cross-linking reactivity with the coating film forming resin (A), moisture resistance A good coating film can be obtained. Examples of the block polyisocyanate compound (e) having a dissociation temperature of 120 to 180 ° C. include Desmodur BL3175 manufactured by Sumika Covestrourethane Co., and Coronate 2554 manufactured by Tosoh Corporation.
In the present specification, the blocked polyisocyanate compound may be referred to as (BI).

Examples of the amino resin include melamine resin and urea resin, and among them, melamine resin is preferably used. The “melamine resin” generally means a thermosetting resin synthesized from melamine and aldehyde, and has three reactive functional groups —NX ¹ X ² in one molecule of triazine nucleus. The melamine _resin,-N-as the reactive functional group (CH _{2 OR)} 2 wherein R is an alkyl group, hereinafter the same] complete alkyl type including; as a reactive functional group _{-N- (CH 2 OR) (CH} 2 methylol group type including OH); imino group type including _-N- as a reactive functional group (CH 2 OR) (H) ; as a reactive functional _group, -N- and _{(CH 2 OR) (CH 2} OH) _{-N- (CH 2 oR) (H} ) and a, or _-N- (CH 2 OH) can be exemplified four methylol / imino group type containing (H).
In the present invention, among the above melamine resins, a melamine resin having an average of one or more methylol groups or imino groups in one molecule (hereinafter referred to as an amino resin (f)), that is, a methylol group type, an imino group Type or methylol / imino group type melamine resin or a mixture thereof is preferably used.
Examples of the melamine resin include Mycoat 715 manufactured by Ornex Japan Co., Ltd.
An amino resin such as a melamine resin has excellent cross-linking reactivity with the coating film forming resin (A) even without a catalyst, and a coating film having good moisture resistance can be obtained.
In the present specification, the melamine resin may be referred to as (MF).

The amount of the cross-linking agent (B) according to the present invention is 1 part by mass or more and 150 parts by mass or less, based on 100 parts by mass of the solid content of the coating film forming resin (A), and for example, 2 parts by mass or more. It is 150 parts by mass or less. By including the cross-linking agent (B) under such conditions, it is possible to form an excellent rust preventive property for a long period of time and to form a coating film which exhibits excellent moisture resistance.
In one embodiment, the amount of the cross-linking agent (B) is 5 parts by mass or more and 95 parts by mass or less based on 100 parts by mass of the solid content of the coating film forming resin (A).
By including the cross-linking agent (B) under such conditions, the cross-linking reaction with the coating film-forming resin (A) proceeds more favorably, the moisture permeability of the coating film becomes better, and the moisture resistance of the coating film further increases. It will be good. Moreover, the corrosion resistance is further improved.
Moreover, the magnesium oxide (C) contained in the coating film can be stably eluted over a long period of time, and further excellent corrosion resistance can be obtained.

[Extended pigment]
The coating composition of the present invention may further contain at least one extender pigment selected from the group consisting of calcium carbonate, barium sulfate, clay, talc, mica and silica.
By including the extender pigment, the coating film strength can be further improved, and unevenness can occur on the coating film surface without impairing the physical properties of the coating film formed from the coating composition according to the present disclosure. This makes it possible to further improve the adhesion to the top coat film. Also, the moisture resistance can be improved.
In one embodiment, the amount of the extender pigment is 1 part by mass or more and 40 parts by mass or less, for example, 10 parts by mass with respect to 100 parts by mass of the total solid content of the coating film-forming resin (A) and the crosslinking agent (B). It is from 30 parts by mass to 30 parts by mass.
When the amount of extender pigment is within such a range, the moisture resistance can be improved. Further, it is possible to prevent the moisture permeability of the coating film from becoming excessively high, for example, it is possible to prevent excessive infiltration of water into the coating film, and it is possible to improve the moisture resistance of the coating film.

[Coupling agent]
The coating composition of the present disclosure may further include at least one coupling agent selected from the group consisting of a silane coupling agent, a titanium coupling agent, and a zirconium coupling agent.
By adding a coupling agent, it is possible to further improve the adhesiveness between the undercoat (object to be coated) and the coating film formed from the coating composition according to the present disclosure, and further improve the moisture resistance of the coating film. You can

The coupling agent is not particularly limited, and conventionally known ones can be used. Specific examples of the coupling agent preferably used include silane coupling agents such as Z-6011 and Z-6040 manufactured by Dow Toray Co .; titanium such as Organix TC-401 and Organix TC-750 manufactured by Matsumoto Fine Chemical Co., Ltd. Examples of coupling agents include zirconium coupling agents such as Organix ZC-580 and Organix ZC-700 manufactured by Matsumoto Fine Chemical Co., Ltd. Of these, a silane coupling agent is preferably used.
The amount of the coupling agent may be 0.1 parts by mass or more and 20 parts by mass or less based on 100 parts by mass of the total solid content of the coating film-forming resin (A) and the cross-linking agent (B), for example, 0. It may be not less than 0.5 parts by mass and not more than 10 parts by mass.
When the amount of the coupling agent is within such a range, the moisture resistance can be improved and the storage stability of the coating composition can be kept good.

[Curing catalyst]
When a blocked polyisocyanate compound and / or a polyisocyanate compound is used as the crosslinking agent (B), the coating composition of the present invention may contain a curing catalyst.
Examples of the curing catalyst include a tin catalyst, an amine catalyst, a lead catalyst, and the like. Among them, an organic tin compound is preferably used. As the organic tin compound, for example, dibutyltin dilaurate (DBTL), dibutyltin oxide, tetra-n-butyl-1,3-diacetoxystannoxane, or the like can be used. The amount of the curing catalyst may be 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the total solid content of the coating film-forming resin (A) and the cross-linking agent (B). It may be 1 part by mass or more and 1.0 part by mass or less. When the amount of the curing catalyst is within such a range, for example, the storage stability of the coating composition can be kept good.

Further, even when an amino resin is used as the crosslinking agent (B), the coating composition of the present invention may contain a curing catalyst.
Examples of the curing catalyst in this case include acid catalysts such as carboxylic acid and sulfonic acid, and among them, dodecylbenzene sulfonic acid and paratoluene sulfonic acid are preferably used. The content of the curing catalyst is, for example, 0.1 part by mass or more and 10 parts by mass or less based on 100 parts by mass of the total solid content of the film-forming resin (A) and the cross-linking agent (B). It may be 1 part by mass or more and 1.0 part by mass or less.
When the amount of the curing catalyst is within such a range, for example, the storage stability of the coating composition can be kept good.

[Other additives]
The coating composition of the present disclosure may contain other additives other than the above, if necessary.
Examples of other additives include rust preventive pigments other than the magnesium oxide (C) according to the present disclosure; extender pigments other than the extender pigments; coloring agents such as coloring pigments and dyes; bright pigments; solvents; ultraviolet absorption. Agents (benzophenone-based UV absorbers, etc.); Antioxidants (phenolic, sulfoid-based, hindered amine-based antioxidants, etc.); Plasticizers; Surface modifiers (silicone, organic polymers, etc.); Anti-sagging agents; Thickeners Lubricants such as waxes; Pigment dispersants; Pigment wetting agents; Leveling agents; Color separation inhibitors; Precipitation inhibitors; Defoamers; Antiseptics; Antifreeze agents; Emulsifiers; Antifungal agents; Antibacterial agents; Stabilizers, etc. is there.
These additives may be used alone or in combination of two or more.

In addition to the magnesium oxide (C) according to the present disclosure, a non-chromium-based rust preventive pigment may be used in combination, as long as the effects of the present disclosure are not impaired.
For example, molybdate pigments (zinc molybdate, strontium molybdate, etc.), phosphomolybdate pigments (aluminum phosphomolybdate pigments, etc.), calcium silica pigments, phosphate anticorrosion pigments, silicate anticorrosion pigments. Examples thereof include rust pigments, havanadate-based rust preventive pigments, calcium hydroxide, magnesium hydroxide, and non-chromium rust preventive pigments such as hydroxides or oxides of the second element such as magnesium oxide other than the present claims.
These may be used alone or in combination of two or more. Since the coating composition of the present invention contains a predetermined magnesium oxide (C), it exhibits sufficiently high corrosion resistance, but if necessary, a rust preventive pigment other than the above magnesium oxide (C) is further added. May be included.

  As pigments other than the extender pigments described in detail above, alumina, bentonite, etc. may be added as long as the moisture resistance, rust resistance, bending workability, etc. of the resulting coating film are not impaired. These may be used alone or in combination of two or more.

Examples of coloring pigments include coloring inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, and coal dust; phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azo orange, flavanthron yellow. , Isoindoline yellow, azo yellow, induslon blue, dibromo anzasulon red, perylene red, azo red, anthraquinone red and other colored organic pigments; aluminum powder, alumina powder, bronze powder, copper powder, tin powder, zinc powder, phosphorus Examples include iron oxide and atomized titanium. These may be used alone or in combination of two or more.

  Examples of the bright pigment include aluminum foil, bronze foil, tin foil, gold foil, silver foil, titanium metal foil, stainless steel foil, alloy foil such as nickel and copper, and foil pigments such as foil phthalocyanine blue. . These may be used alone or in combination of two or more.

Examples of the solvent include water; ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, Glycol-based organic solvents such as dipropylene glycol monoethyl ether and propylene glycol monomethyl ether acetate; alcohol-based organic solvents such as methanol, ethanol and isopropyl alcohol; ether-based organic solvents such as dioxane and tetrahydrofuran; 3-methoxybutyl acetate, ethyl acetate , Ester-based organic solvents such as isopropyl acetate and butyl acetate; Ketyl-based organic solvents such as tyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, and isophorone; and N-methyl-2-pyrrolidone, toluene, pentane, iso-pentane, hexane, iso-hexane, cyclohexane, solvent naphtha, minerals. Examples thereof include Spirit, Solvesso 100, Solvesso 150 (all of which are aromatic hydrocarbon solvents, manufactured by Shell Chemical Co.). These may be used alone or in combination of two or more.
The coating composition of the present invention may be a water-based coating or an organic solvent-based coating.

[Method for preparing coating composition]
The method for preparing the coating composition according to the present disclosure is not particularly limited. The coating composition according to the present disclosure includes, for example, a film-forming resin (A), a cross-linking agent (B) and a magnesium oxide (C), and optionally a thermoplastic resin, an extender pigment, a coupling agent, The curing catalyst and other additives can be prepared by mixing them using a mixer such as a roller mill, a ball mill, a bead mill, a pebble mill, a sand grind mill, a pot mill, a paint shaker and a disper.
Alternatively, the coating composition of the present disclosure is a two-pack type coating composition comprising a main component containing a film-forming resin (A) and magnesium oxide (C), and a crosslinking agent containing a crosslinking agent (B). May be.

The coating composition of the present invention may be applied as an undercoat paint which is also called a primer. Further, it may be an overcoating material that is overlaid on the undercoating material. Further, it may be an intermediate coating composition formed in an intermediate layer between the undercoat coating composition and the top coating composition.
Alternatively, the coating composition of the present invention may be used as a coating composition for forming a single-layer coating film, not for forming a multilayer coating film.
The coating composition of the present invention can exhibit excellent corrosion resistance and moisture resistance regardless of where it is used in a multilayer coating film. Above all, the coating composition of the present invention is preferably used as an undercoating paint. The undercoat paint other than the coating composition of the present invention, the top coat paint and the intermediate coat paint may be conventionally known ones, and examples of the undercoat paint include conventionally known non-chrome anticorrosive paints and the like. Examples of the intermediate coating material include polyester resin-based coating material and fluororesin-based coating material.

[Subject]
The article to be coated with the rust-preventive coating composition of the present invention is not particularly limited as long as it is required to have corrosion resistance. For example, a steel plate serving as a base material such as a pre-coated metal (painted steel plate) can be mentioned.
Examples of the steel plate include a galvanized steel plate, a cold rolled steel plate, a stainless steel plate, and an aluminum plate. As a galvanized steel sheet, a zinc-containing galvanized steel sheet that utilizes sacrificial corrosion of zinc, specifically, a galvanized steel sheet, an electrogalvanized steel sheet, a galvannealed steel sheet, an aluminum-galvanized steel sheet, a nickel-galvanized steel sheet. A steel plate, a magnesium-aluminum-zinc plated steel plate, a magnesium-aluminum-silica-zinc plated steel plate and the like are exemplified. The steel sheet is preferably surface-treated with a chemical conversion treatment agent before coating. The surface treatment may be performed by a known method, and examples thereof include chromate treatment, non-chromate treatment such as zinc phosphate treatment, and the like. Further, the surface treatment can be appropriately selected according to the steel sheet used, but a treatment containing no heavy metal is preferable.

[Production method of anti-corrosion coating]
In another embodiment, the present disclosure includes a coating step of coating an anticorrosive coating composition according to the present disclosure on an object to be coated, and curing the coating composition at a temperature of 150 ° C. or higher and 270 ° C. or lower. A method for producing a rust coating film is provided.
As a method for applying the coating composition of the present invention to an object to be coated, a conventionally known method such as a roll coater, airless spray, electrostatic spray, or curtain flow coater can be adopted.
The coating film comprising the coating composition of the present invention can be formed by applying the coating composition to an object to be coated such as a steel plate and then performing a baking treatment for heating the object to be coated. The baking temperature (the maximum temperature reached by an object to be coated such as a steel plate) is, for example, 150 ° C. or higher and 270 ° C. or lower, and by curing the coating composition according to the present disclosure at such a temperature, it has sufficient strength A coating film can be formed. By being able to form a coating film having sufficient strength, it is possible to further exhibit excellent rust-preventing property for a long period of time, and further it is possible to form a coating film having excellent moisture resistance.
The baking time (curing time) is, for example, 10 to 200 seconds. For example, in the case of forming a multilayer coating film consisting of two layers of an undercoat coating film and an overcoat coating film, baking is performed after applying the undercoat coating composition, then applying the overcoat coating composition and baking the overcoat coating film. Alternatively, the undercoating coating composition may be applied, and then the topcoating coating composition may be applied wet-on-wet without baking, and baking may be performed at the same time.
The film thickness (dry film thickness) of the coating film (hereinafter referred to as the coating film of the present invention) obtained by using the coating composition of the present invention is usually 1 to 30 μm, and for example, in the case of a top coating film, It is preferably 10 to 30 μm.

[About corrosion resistance]
A coating film formed from the coating composition of the present disclosure can show good results in, for example, both “immersion-drying cycle test with acidic salt water: 15 cycles” and “CCHC test: 2,000 hours”.
Since good results can be shown in these tests, both long-term stable rust prevention and moisture resistance can be achieved.
Here, the “immersion-dry cycle test with acidic salt water” can be measured based on the method disclosed in Japanese Patent No. 5857156. It is considered that the good result of this test makes it possible to obtain, for example, a coating film having a rust preventive property under acidic environmental conditions and a stable rust preventive property for a long period of time.
In addition, "CCHC test 2,000 hours" is called CCHC (Cleveland Condensing Humidity Cabinet: ASTM D-2247-87-Type A2), and the coating film is exposed to a high temperature and high humidity environment for 2,000 hours. It is an evaluation test for coating film blisters to be evaluated.
Further, by setting the test time to 2,000 hours, it is considered that the coating film according to the present disclosure can maintain excellent moisture resistance for a long time even when the coating film is exposed to a more severe environment.
The coating composition according to the present disclosure can show excellent results in such a plurality of tests, and can form a coating film having both stable rust resistance for a long period of time and moisture resistance.
In addition, good rust prevention and moisture resistance can be achieved at the processed portion, the end surface, the cross cut portion, and the like.
Further, it is possible to suppress the generation of rust that may be caused by acid rain or the like.
In the present disclosure, the rust preventive property under acidic environmental conditions can be evaluated based on a test using "acidic salt water". Further, in the present disclosure, it is possible to obtain a coating film having excellent rust prevention properties under acidic environmental conditions, and for example, it is possible to exhibit excellent rust prevention properties against acid rain.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[Magnesium oxide (C1)]
Table 1 shows various conditions and characteristic values regarding the magnesium oxides (C1) to (C6) used in the examples.

The materials different from the magnesium oxide (C) according to the present disclosure used in Comparative Examples are shown below.
Nickel oxide; Nickel oxide powder II large particle size (made by Kusaka Rare Metals Research Institute) Lattice constant: 0419 nm, BET specific surface area: 20 m ² / g , average particle size: 1.8 μm
・ Tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.)
Condensed phosphate: K-WHITE # 82 (manufactured by Teika)
・ Calcium vanadate
The calcium vanadate was prepared by the following method.
[Preparation of calcium vanadate]
46 g of calcium carbonate (CaCO ₃ ) and 954 g of vanadium pentoxide (V ₂ O ₅ ) were added to 10 L of water, the temperature was raised to 60 ° C., and the mixture was stirred at the same temperature for 2 hours. The obtained reaction product (white solid) was washed with water, dried at 100 ° C., and then pulverized to obtain calcium vanadate.

[Preparation of coating film-forming resin (A1) (ester-based urethane resin 1)]
In a reaction vessel equipped with a thermometer, a condenser and a stirrer, 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, and the mixture was mixed in a nitrogen stream. The temperature was gradually raised to 230 ° C., and the produced water was distilled off, and the esterification reaction was carried out for about 10 hours until the acid value became 1 or less (dehydration amount: 14.2 parts by mass). Then, after lowering the temperature of the reaction vessel to 50 ° C., 135 parts by mass of cyclohexanone and 35 parts by mass of 4,4′-diphenylmethane diisocyanate are mixed and held at 80 ° C. for 8 hours to cause reaction, and ester urethane resin 1 (solid Partial concentration: 50% by mass) was obtained.

  Coating film forming resins (A2) to (A8) (respectively, ester-based urethane resins 2 to 8) were prepared in the same manner as above except that the monomer type and amount were changed as shown in Table 2. Table 2 shows various characteristic values such as the monomer composition and the molecular weight of each resin.

[Preparation of Coating Film Forming Resin (A9) (Ether Urethane Resin 1)]
In a reaction vessel equipped with a thermometer, a condenser and a stirrer, 100 parts by mass of PTMG650 (manufactured by Mitsubishi Chemical Corporation, polytetramethylene glycol), 135 parts by mass of cyclohexanone and 35 parts by mass of 4,4′-diphenylmethane diisocyanate were mixed, and 80 ° C. The mixture was held for 8 hours for reaction to obtain an ether type urethane resin 1 (solid content concentration: 50% by mass).

[Preparation of coating film forming resin (A10) (carbonate-based urethane resin 1)]
A reaction vessel equipped with a thermometer, a condenser and a stirrer was mixed with 100 parts by mass of Duranol T5650E (polycarbonate diol manufactured by Asahi Kasei Corporation), 135 parts by mass of cyclohexanone and 35 parts by mass of 4,4′-diphenylmethane diisocyanate, and the mixture was mixed at 8 ° C. at 80 ° C. The reaction was carried out by holding for a time to obtain a carbonate-based urethane resin 1 (solid content concentration: 50% by mass).

[Coating film forming resins (A11) to (A13)]
In addition to the above, the details of the coating film-forming resin (A) used in Examples and Comparative Examples are as follows.
-Coating film forming resin (A11) (epoxy resin 1); E1255HX30 (manufactured by Mitsubishi Chemical Corporation, hydroxyl group-containing epoxy resin) number average molecular weight: 10,000, solid acid value: 1.0 mgKOH / g, glass transition temperature: 85 ° C, solid content concentration: 30 mass%
-Coating film forming resin (A12) (polyester resin 1); Byron UR4410 (manufactured by Toyobo Co., Ltd.) Number average molecular weight: 10,000, solid content acid value: 0.5 mg KOH / g, glass transition temperature: 56 ° C, solid content concentration : 40 mass%
-Coating film forming resin (A13) (acrylic resin 1); Acridic A452 (manufactured by DIC, acrylic resin); number average molecular weight: 17,000, solid content acid value: 2.7 mgKOH / g, glass transition temperature: 70 ℃, solid content concentration: 40 mass%

[Crosslinking agent (B1), (B2)]
Details of the cross-linking agent (B) are as follows.
-Crosslinking agent (B1) (polyisocyanate compound 1); Desmodur BL3575 (manufactured by Sumika Covestrourethane Co., block polyisocyanate) hexamethylene diisocyanate (HDI) block (isocyanurate type, blocking agent: dimethylpyrazole), Isocyanate group content: 10.5% by mass, solid content concentration: 75% by mass
-Crosslinking agent (B2) (amino resin); Mycoat 715 (Ornex Japan, imino group-type melamine resin) Solid content concentration: 80 mass%

Details of other components are as follows.
・ Solvent 1: Cyclohexanone (manufactured by Shoei Chemical Industry Co., Ltd.)
-Solvent 2: Solvesso 150 (Shell Chemical Co., Ltd.)
-Curing catalyst; TVS KS-1260 (manufactured by Kyodo Chemical Co., Ltd., dibutyltin dilaurate) Nonvolatile content: 100% by mass

(Example 1)
142.9 parts by mass of the coating film-forming resin (A1), 45.0 parts by mass of cyclohexanone, 45.0 parts by mass of Solvesso 150 and 60 parts by mass of magnesium oxide (C1) were mixed, and a sand mill (dispersion medium: glass beads) was mixed. ) Was used to disperse the coarse pigment particles until the maximum particle diameter was 10 μm or less, to prepare Dispersion Composition 1. In the obtained dispersion composition 1, 38.1 parts by mass of a crosslinking agent (B1) (Desmodur BL-3575, manufactured by Sumika Covestro Urethane Co., Ltd.) and 0.5 parts by mass of KS1260 (manufactured by Kyodo Chemical Co., Ltd.) as a curing catalyst. Parts were added and mixed uniformly with a disper to prepare coating composition 1.
Details of the composition according to Example 1 are shown in Table 3A.

[Method for producing coated plate for evaluation]
After degreasing a 0.4 mm thick aluminum-galvanized steel sheet with alkali, a phosphoric acid treatment agent, Surfcoat EC2310 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.), is applied to the front and back surfaces of the steel sheet to perform a non-chromium chemical conversion treatment. Applied and dried.
Next, the coating composition 1 obtained above was applied to the back surface of the obtained steel sheet so that the dry coating film had a thickness of 7 μm, and baked at a maximum reached temperature of 180 ° C. for 30 seconds to obtain a back surface coating film. Was formed.
On the other hand, the coating composition of any of Examples 1 to 33 and Comparative Examples 1 to 7 was applied to the surface of the above steel sheet so that the dry coating film had a thickness of 5 μm, and baked at the maximum temperature of 200 ° C. for 30 seconds. Was carried out to form a surface undercoat coating film. Furthermore, Nippe Supercoat 300HQ (manufactured by Nippon Paint Industrial Coatings Co., Ltd.), which is a polyester-based topcoat paint, was applied on the surface undercoat paint film so that the dry paint film had a thickness of 10 μm, and the maximum temperature reached 210 ° C. After baking for 40 seconds, a surface top coating film was formed to obtain a coated steel sheet for evaluation.

(Examples 2-33, Comparative Examples 1-7)
Hereinafter, unless otherwise stated, various physical properties were evaluated using the coated steel sheet thus formed. Coating films were formed in the same manner in other examples and comparative examples.
Various conditions are shown in Tables 3A to 3G for Examples, and evaluation results and the like are shown in Tables 4A to 4G. Further, Comparative Examples are shown in Table 5A and Table 5B.
A coating composition was prepared in the same manner as in Example 1 except that the types and amounts of the components were changed as shown in Table 3A and the like.

(Reference example 1)
Regarding Reference Example 1, instead of the phosphoric acid treatment agent (Surfcoat EC2310), a chromate treatment agent NRC300 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.) was applied to the front and back surfaces of the steel sheet, chromate treatment was performed, and chromium was applied. Under the same conditions, Nippe Super Coat 667 Primer (manufactured by Nippon Paint Industrial Coatings Co., Ltd.), which is a corresponding undercoat containing strontium acid salt, and Nippe Super Coat 300HQ (manufactured by Nippon Paint Industrial Co., Ltd.), which is an overcoat paint. It was applied, baked and dried. Various conditions and evaluation results are shown in Table 5A and Table 5B, respectively.

(Procedure for measuring solubility in artificial acidic seawater)
As an acidic solution containing sulfate, an aqueous solution of an acidic salt used in Method B defined in JIS G 0594 cycle corrosion test method was referred to. That is, using a marine art SF-1 (manufactured by Tomita Pharmaceutical Co., Ltd.) as a composition close to the composition of artificial seawater specified in JIS G 0594, with a mixed solution of nitric acid and sulfuric acid specified in Section 4.2.2, The pH was adjusted to 2.5 to obtain artificial acidic seawater.
Next, 100 g of the artificial acidic seawater and 1 g of the pigment were added to a polyethylene narrow-mouth bottle, a stirrer chip was put therein, and the mixture was stirred at room temperature for 4 hours. Then, after standing at room temperature for 24 hours, the supernatant was collected with a syringe equipped with a syringe filter, and the element concentration was measured using an ICP emission spectrometer ICPS-7510 (manufactured by Shimadzu Corporation).

(Conductivity measurement procedure in pure water)
To a polyethylene narrow-mouth bottle, 100 g of ion-exchanged water and 1 g of pigment were added, a stirrer chip was put thereinto, and the mixture was stirred at room temperature for 4 hours. Then, the electric conductivity was measured using an electric conductivity meter CM-42X (manufactured by Toa DKK Co., Ltd.).

(3) Evaluation items
1) Boiling Water Resistance Test The coated steel sheet obtained above was cut into 5 cm × 10 cm, and the obtained test piece was immersed in boiling water at about 100 ° C. for 2 hours and then pulled up to give a surface side coating film appearance. , ASTM D714-56 (flat part blister evaluation).
Here, ASTM D714-56 is to evaluate the size (average diameter) and density of each blister in comparison with a standard judgment photograph, and show a grade symbol. The size is 8 (diameter about 1 mm), 6 (diameter about 2 mm), 4 (diameter about 3 mm), 2 (diameter about 5 mm) in four stages in order, and the density is F, FM, M, MD from the smallest. , D is classified into 5 stages, and if there is no blistering, it is set to 10. A score of 8 FM or higher was evaluated as good.
In addition, a cross-cut tape adhesion test (cross-cut adhesion test) was performed and evaluated for the coated steel plate test piece after being immersed in boiling water at about 100 ° C. for 2 hours. The cross-cut tape adhesion test is based on the JIS K 5400 8.5.2 (1990) cross-cut tape method, with a gap between cuts of 1 mm, 100 cross-cuts are made, and cellophane adhesive tape is adhered to the surface. The number of grids remaining on the coated surface when rapidly peeled off was examined.

2) Moisture resistance test (CCHC test)
The coated steel plate was cut into 5 cm × 10 cm, and the obtained test piece was left under the condition of 50 ° C. × 98 RH% with pure water for 500 hours, and then subjected to the boiling water resistance test in accordance with ASTM D714-56. The blister of the flat portion was evaluated. A score of 8 FM or higher was evaluated as good. In this test, a large wetness tester (manufactured by Suga Test Instruments Co., Ltd.) was used.

3) Corrosion resistance test The obtained coated steel sheet was cut into pieces each having a size of 5 cm x 15 cm. At this time, cutting was alternately performed from the front surface and the back surface, and a test piece was produced so that each test piece had both an upper burr (cut from the back surface) and a lower burr (cut from the surface).
Next, a cross knife with a narrow angle of 30 degrees and a cut width of 0.5 mm is inserted with a cutter knife so as to reach the substrate in the center of the front surface side, the top edge of the coated steel plate is sealed with rust preventive paint, and the bottom end is A 4T bent portion (four plates are removed after processing) was provided.
The 4T bending process is a process in which the surface of the coated plate is bent outward, four plates having the same thickness as the coated plate are sandwiched inside, and the coated plate is bent 180 degrees with a vise. After processing, the four plates were removed and subjected to the test.

A schematic view of the coated steel plate test piece obtained as described above is shown in FIG. FIG. 1A is a diagram schematically showing a cross section 20 of an upper burr and a cross section 30 of a lower burr in the obtained coated steel plate test piece 10. The coated steel plate test piece 10 has a coating film front surface 11 and a coating film back surface 12.
FIG. 1 (B) is a schematic diagram showing the cross-cut portion 40 and the 4T bent portion 50 provided on the coated steel plate test piece 10 used for the corrosion resistance test. Further, the coated steel plate test piece 10 has an upper burr 21 and a lower burr 31.

Each of the obtained coated steel plate test pieces was subjected to a combined cycle corrosion test (CCT) according to JIS K 5600-7-9A JASO M609. 120 cycles of a total of 960 (total 960) Time). The state of the edge portion, the cross cut portion and the 4T bent portion of the coated steel plate test piece after this test were evaluated based on the following evaluation method and evaluation criteria. In each case, 4 points or more were evaluated as good.
Device used: Combined cycle tester CYP-90 (manufactured by Suga Test Instruments Co., Ltd.)

(Corrosion resistance test: 4T bent part)
The total length of the rust portion in the 4T bent portion was obtained and evaluated according to the following criteria.
5: No rust is observed.
4: White rust is recognized, but less than 10 mm.
3: White rust is 10 mm or more and less than 25 mm.
2: White rust is 25 mm or more and less than 40 mm.
1: White rust is 40 mm or more, or generation of red rust is recognized.

(Corrosion resistance test: Edge part)
The average value of the edge creep widths (blister widths) of the left and right long sides (that is, the long side having the upper burr and the long side having the lower burr) of the coated steel plate test piece was determined and evaluated according to the following criteria.
5: The blistering width is less than 5 mm.
4: The blistering width is 5 mm or more and less than 10 mm.
3: The blistering width is 10 mm or more and less than 15 mm.
2: The blistering width is 15 mm or more and less than 20 mm.
1: The blistering width is 20 mm or more.

(Corrosion resistance test: Cross-cut part)
The corrosion state of the cross-cut portion was evaluated according to the following criteria by the white rust generation length ratio in the exposed portion of the substrate having a cut width of 0.5 mm and the average value of the left and right blistering widths (sum of both sides) of the cross-cut portion. .
5: White rust generation length ratio in the exposed portion of the base material is less than 25% and blistering width is less than 3 mm.
4: White rust generation length ratio in exposed base material is 25% or more and less than 50% and blistering width is 3 m
less than m.
3: White rust generation length ratio in the exposed portion of the base material was 50% or more and the blistering width was less than 3 mm.
2: White rust generation length ratio in the exposed portion of the base material is 50% or more and the blistering width is 3 mm or more and less than 5 mm.
1: Proportion of white rust generation length in exposed area of the substrate is 50% or more and blistering width is 5 mm or more.

4) Alkali resistance test
Each of the coated steel sheets obtained was cut into 5 cm × 10 cm, and each test piece was immersed in a 5% sodium hydroxide aqueous solution at 23 ° C. for 48 hours, taken out, washed with water, and then dried at room temperature. With respect to this coated steel plate test piece, blistering evaluation of the flat surface portion was performed according to ASTM D714-56 in the same manner as in the boiling water resistance test. A score of 8 FM or higher was evaluated as good.

5) Acid resistance test Each coated steel plate obtained above was cut into 5 cm x 10 cm, and the obtained test piece was immersed in a 5% sulfuric acid aqueous solution at 23 ° C for 48 hours, taken out, washed, and dried at room temperature. did. With respect to this coated steel plate test piece, blistering evaluation of the flat surface portion was performed according to ASTM D714-56 in the same manner as in the boiling water resistance test. A score of 8 FM or higher was evaluated as good.

6) Immersion in acid salt water-dry cycle test (adjustment of test plate)
Each of the coated steel sheets obtained above was cut into 5 cm × 10 cm, and a 4T bent portion was provided at the lower end of the obtained test piece in the same manner as in the corrosion resistance test.

(Adjustment of acidic salt water)
As an acidic solution containing sulfate, an aqueous solution of an acidic salt used in Method B defined in JIS G 0594 cycle corrosion test method was referred to. That is, using Marine Art SF-1 (manufactured by Tomita Pharmaceutical Co., Ltd.) as a composition close to the composition of artificial seawater specified in JIS G 0594, with a mixed solution of nitric acid and sulfuric acid specified in Section 4.2.2, The pH was adjusted to 2.5 and used as acidic salt water.

(Test condition)
Each of the obtained coated steel plate test pieces was subjected to a 15-cycle test (total 360 hours) under the condition of 23 ° C., with immersion of 6 hours → drying of 18 hours as one cycle. The state of the edge portion, the cross cut portion, and the 4T bent portion of the coated steel plate test piece after the test was evaluated based on the following evaluation method and evaluation criteria. In each case, 4 points or more were evaluated as good.

(Test with acidic salt water: 4T bent part)
The total length of the rust portion in the 4T bent portion was obtained and evaluated according to the following criteria.
5: No rust is observed.
4: White rust is recognized, but less than 10 mm.
3: White rust is 10 mm or more and less than 25 mm.
2: White rust is 25 mm or more and less than 40 mm.
1: White rust is 40 mm or more, or generation of red rust is recognized.

(Test with acidic salt water: edge part)
The average value of the edge creep widths (blister widths) of the left and right long sides (that is, the long side having the upper burr and the long side having the lower burr) of the coated steel plate test piece was determined and evaluated according to the following criteria.
5: The blistering width is less than 5 mm.
4: The blistering width is 5 mm or more and less than 10 mm.
3: The blistering width is 10 mm or more and less than 15 mm.
2: The blistering width is 15 mm or more and less than 20 mm.
1: The blistering width is 20 mm or more.

(Test with acidic salt water: cross-cut part)
The corrosion state of the cross-cut portion was evaluated according to the following criteria by the white rust generation length ratio in the exposed portion of the substrate having a cut width of 0.5 mm and the average value of the left and right blistering widths (sum of both sides) of the cross-cut portion. .
5: White rust generation length ratio in the exposed portion of the base material is less than 25% and blistering width is less than 3 mm.
4: White rust generation length ratio in the exposed portion of the base material is 25% or more and less than 50% and the blistering width is less than 3 mm.
3: White rust generation length ratio in the exposed portion of the base material was 50% or more and the blistering width was less than 3 mm.
2: White rust generation length ratio in the exposed portion of the base material is 50% or more and the blistering width is 3 mm or more and less than 5 mm.
1: Proportion of white rust generation length in exposed area of the substrate is 50% or more and blistering width is 5 mm or more.

  Details of the evaluation results in each Example and Comparative Example are shown in Tables 4A to 4G and Table 5B.

According to the results of Examples, the rust-preventive coating composition of the present invention can exhibit excellent rust-preventing property for a long period of time, and can form a coating film having excellent moisture resistance. In addition, it is possible to form a coating film that exhibits excellent rust resistance over a long period of time even under acidic environmental conditions. Therefore, for example, the generation of rust that can be caused by "acid rain" or the like can be suppressed.
Further, it is possible to suppress or greatly reduce the deterioration of the moisture resistance of the coating film, and further suppress or significantly reduce the occurrence of blistering in the coating film.
Furthermore, if the rust-preventive coating composition of the present disclosure, in an object to be coated that can have various shapes, not only in the flat surface of the object to be coated, but also in, for example, a processed portion, an end surface, a cross-cut portion, etc. The protective effect of the coating film can be sufficiently exhibited.
Here, when the chromate-treated test piece shown in Reference Example 1 is compared with the surface-treated steel material of the present invention, the rust-preventive coating composition according to the present invention is equal to or more than the coating composition containing chromium. It was possible to show the rust prevention property of.

On the other hand, in Comparative Examples 1 to 3, the BET specific surface area and the lattice constant of magnesium oxide are outside the range of the magnesium oxide (C) according to the present invention. For this reason, the formed coating film could not exhibit sufficient rust resistance and moisture resistance.
Comparative Examples 4 to 7 do not contain the magnesium oxide (C) according to the present invention. For this reason, the formed coating film could not exhibit sufficient rust resistance and moisture resistance.

The rust-preventive coating composition of the present invention can exhibit excellent rust-preventive properties for a long period of time and can form a coating film exhibiting excellent moisture resistance.
Further, with the method for producing a coating film according to the present invention, it is possible to form a coating film that exhibits excellent rust-preventing properties for a long period of time and that also exhibits excellent moisture resistance.

10 Painted Steel Plate Specimen 11 Coating Surface 12 Coating Back Surface 20 Top Burr Section 21 Top Burr 30 Bottom Burr Section 31 Bottom Burr 40 Cross Cut Section 50 4T Bending Section

Claims (14)

A rust preventive coating composition containing a coating film forming resin (A), a cross-linking agent (B), and a magnesium oxide (C),
The magnesium oxide (C) has a lattice constant of less than 0.4214 nm, and
An anticorrosion coating composition having a BET specific surface area of 2.0 m ² / g or less.   The rust-preventive coating composition contains the magnesium oxide (C) having a magnesium metal ion concentration of 70 ppm or less in an aqueous solution obtained by adding 1 g of the magnesium oxide (C) to 100 g of the artificial acidic seawater solution. Item 1. The anticorrosion coating composition according to item 1.   The protection according to claim 1 or 2, wherein the magnesium oxide (C) contains a compound having an electric conductivity of 320 µS / cm or less in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water. Rust paint composition.   The rust preventive coating composition according to any one of claims 1 to 3, wherein the magnesium oxide (C) contains a magnesium fired product fired at a temperature of 1,000 ° C or higher. The magnesium oxide (C) has a pH of 8 or more and 12 or less in an aqueous solution in which 1 g of the magnesium oxide (C) is added to 100 g of pure water, and has an average particle size of 0.5 μm or more and 20 μm or less. The anticorrosive coating composition according to any one of claims 1 to 4, which is   The rust-preventive coating composition according to any one of claims 1 to 5, wherein the magnesium oxide (C) is magnesium oxide.   7. The coating film-forming resin (A) contains at least one selected from the group consisting of epoxy resins, polyester resins, acrylic resins, urethane resins and modified products thereof, according to any one of claims 1 to 6. The rust-preventive coating composition described. The coating film-forming resin (A) contains at least one selected from the group consisting of urethane resins and modified products thereof,
The rust preventive coating composition according to any one of claims 1 to 7, wherein the urethane resin has a glass transition temperature of -50 ° C or higher and 70 ° C or lower.   The coating film-forming resin (A) includes at least one selected from the group consisting of urethane resins and modified products thereof, and the urethane resin includes ester urethane resin, ether urethane resin and carbonate urethane resin. The anticorrosion coating composition according to any one of claims 1 to 8, comprising at least one selected from the group consisting of:   The rust preventive coating composition according to any one of claims 1 to 9, wherein the coating film forming resin (A) has a number average molecular weight of 1,000 or more and 40,000 or less.   11. The coating film forming resin (A) according to claim 1, wherein the coating film forming resin (A) contains at least one selected from the group consisting of ester urethane resins, epoxy resins, polyester resins and modified products thereof. Anticorrosion paint composition.   The rust preventive coating composition according to claim 11, wherein at least one of the ester-based urethane resin, the epoxy resin, and the polyester resin has a solid content acid value of 30 mgKOH / g or less.   1 part by mass or more and 150 parts by mass or less of the magnesium oxide (C) based on 100 parts by mass in total of the solid content of the coating film forming resin (A) and the solid content of the cross-linking agent (B). The anticorrosion coating composition according to any one of claims 1 to 12, which is contained in a range.   A coating step of applying the rust-preventive coating composition according to any one of claims 1 to 13 to an object to be coated, and curing the rust-preventive coating composition at a temperature of 150 ° C or higher and 270 ° C or lower. , A method for producing an anticorrosion coating film.

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