JP2021059654A - Rust-preventive coating composition and method for producing rust-preventive coated film - Google Patents

Abstract

To provide a rust-preventive coating composition capable of forming a coated film which exhibits excellent rust-prevention property over a long period of time and exhibits excellent moisture resistance, and a rust-preventive coating composition which can suppress or greatly reduce blister in a processing part, an end face and a cross-cut part, and can exhibit rust-prevention property and moisture resistance even in such the parts over a long period of time.SOLUTION: A rust-preventive coating composition contains a coated film formation resin (A), a crosslinking agent (B) and a magnesium oxide (C). The magnesium oxide (C) has a lattice constant of less than 0.4214 nm, and a BET specific surface area of 2.0 or less.SELECTED DRAWING: None

Description

The present invention relates to a rust-preventive coating composition and a method for producing a rust-preventive coating film using the coating composition.

Painted steel sheets coated with cold-rolled steel sheets and plated steel sheets as the base material are also called pre-coated metal, and are used for various purposes such as outdoor units of air conditioners, exterior parts of home appliances for water heaters, and exterior building materials such as roofs and walls. It is used. For example, a coated steel sheet including a galvanized steel sheet is usually coated with a rust preventive paint in order to improve rust prevention and prevent rusting.

Conventionally, a chromium-containing paint is generally used as the rust-preventive paint, and the occurrence of rust can be suppressed by forming the chromium-containing coating film. However, the use of chromium is being restricted due to concerns about its adverse effects on the environment.
Therefore, as a rust preventive agent other than the chromium compound, a coating composition containing a vanadium compound has been proposed.

Japanese Patent Application Laid-Open No. 2008-222834 (Patent Document 1) describes 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 derived from (1) vanadium pentoxide, at least one vanadium compound among calcium vanadate and ammonium metavanadate, (2) metal silicate and (3) phosphate-based calcium salt. The coating composition is disclosed.

Japanese Unexamined Patent Publication No. 2009-227748 (Patent Document 2) describes (A) a hydroxyl group-containing film-forming resin of at least one of a specific acrylic resin and a specific polyester resin, and (B) a bisphenol type epoxy resin. C) A curing agent, (D) an epoxy resin having a secondary or tertiary amino group, an acrylic resin having a secondary or tertiary amino group, a resole-type phenol resin, and at least one type of adhesion-imparting 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 vanadium compound among vanadium pentoxide, calcium vanadate and ammonium metavanadate, and (2) at least one of metal silicate and silica fine particles. It is disclosed that it contains a silicon-containing compound and (3) a phosphoric acid-based metal salt.

Japanese Unexamined Patent Publication No. 2008-222834 Japanese Unexamined Patent Publication No. 2009-227748

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 the coating film of a coated steel sheet. Here, "acid rain" means _{that acid rain-causing substances originating from sulfur dioxide (SO 2} ), nitrogen oxides (NOx), etc. dissolve in rain, snow, fog, etc., and the atmosphere becomes more acidic than usual. It refers to the phenomenon of becoming more acidic or the environment becoming more acidic than usual. In addition, from the release of acid rain-causing substances to the time when acid rain falls, hundreds to thousands of kilometers may be transported across national borders, causing corrosion damage to coated steel sheets over a wide area. It is expected to increase in the future.
Furthermore, when the acid rain-causing substance is present in a dew condensation and damp environment, at least one of the sulfides and nitrides contained in the acid rain-causing substance is exposed to a damp state, and the corrosion reaction proceeds. There is.

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

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

The present invention has an object of solving the above-mentioned problems, and more specifically, provides a rust-preventive coating composition which can exhibit excellent rust-preventive properties over a long period of time and also exhibits excellent moisture resistance. That is the 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 has a lattice constant of less than 0.4214 nm.
A rust preventive coating composition having a BET specific surface area of 2.0 or less.
[2] 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 prepared by adding 1 g of the magnesium oxide (C) to 100 g of an artificial acidic sea aqueous solution. Contains magnesium oxide (C).
[3] In one embodiment, the magnesium oxide (C) in the rust preventive coating composition of the present disclosure has a 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. Contains compounds of cm or less.
[4] In one embodiment, the magnesium oxide (C) in the rust preventive coating composition of the present disclosure includes a magnesium fired product fired 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 a 1% by mass aqueous solution in 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 size 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 rust preventive coating composition of the present disclosure is magnesium oxide.
[7] In one embodiment, the coating film-forming resin (A) in the rust-preventive coating composition of the present disclosure is selected from at least a group consisting of an epoxy resin, a polyester resin, an acrylic resin, a urethane resin, and a modified product thereof. Includes one.
[8] In one embodiment, the coating film-forming resin (A) in the rust-preventive 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 resins include urethane resins. 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 rust-preventive 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 resins are It contains at least one selected from the group consisting of ester-based urethane resins, ether-based urethane resins, and carbonate-based urethane resins.
[10] In one embodiment, the coating film-forming resin (A) in the rust-preventive 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 rust-preventive 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 rust-preventive coating composition of the present disclosure is
At least one of the ester-based urethane resin, epoxy resin and polyester resin has a solid acid value of 30 mgKOH / g or less.
[13] In one embodiment, the rust preventive coating composition of the present disclosure contains magnesium with respect to a total of 100 parts by mass of the solid content of the coating film-forming resin (A) and the solid content of the cross-linking agent (B). The oxide (C) is contained 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 applying the rust preventive coating composition to an object to be coated, and curing the coating composition at a temperature of 150 ° C. or higher and 270 ° C. or lower. Provided is a method for producing a rust coating film.

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

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

The background to the present invention will be described.
For example, in the conventional evaluation of rust prevention, the test time is short, and the evaluation site has been judged only by the molded portion (flat surface of the object to be coated).
On the other hand, in recent years, objects to be coated with various shapes have been manufactured. In the object to be coated which can have such various shapes, for example, the protective effect of the coating film may not be sufficient in the processed portion, the end face, the cross-cut portion, etc., and corrosion occurs from these portions. There is a risk of
For this reason, for example, a coating composition that exhibits excellent rust prevention properties over a long period of time even in a processed portion, an end face, and a cross-cut portion, and further exhibits long-term and even ultra-long-term rust prevention properties. Is required.

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

For example, vanadium compounds such as vanadate metal salts are used for the purpose of reducing chromium-based compounds. Further, as a means for improving the rust preventive property of the rust preventive coating composition containing a vanadium compound, it is effective to increase the amount of the vanadium compound contained in the coating composition.
However, since vanadium compounds, particularly vanadate, are highly water-soluble, if the coating composition contains a large amount of vanadium compounds, the coating film tends to absorb moisture. As a result, there is a problem that the moisture resistance of the coating film is lowered and blisters are generated in the coating film. Such blister of the coating film also causes a decrease in rust prevention property and also causes 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 resistance and moisture resistance.

Therefore, the present inventors have diligently studied and completed the present invention.
The rust-preventive coating composition of the present invention can exhibit excellent rust-preventive properties over a long period of time, and can further form a coating film exhibiting excellent moisture resistance. Moreover, even under acidic environmental conditions, it is possible to form a coating film showing excellent rust prevention properties for a long period of time. Therefore, for example, the generation of rust that may be caused by "acid rain" or the like can be suppressed.
Although it should not be construed as limited to a specific theory, in the case of the anticorrosive coating composition of the present disclosure, for example, acid rain-causing substances are absorbed by a water film in a dew condensation and humid environment. , It is thought that it is possible to prevent problems such as the environment being oxidized and corrosion progressing.

Further, even when the object to be coated is exposed to a high temperature and high humidity environment such as when used outdoors, the rust preventive coating composition of the present disclosure can exhibit excellent moisture resistance. The present inventors have stated that the rust preventive coating composition of the present disclosure can significantly reduce the moisture absorption of the coating film as compared with, for example, a vanadium compound by containing the specific magnesium oxide (C) according to the present disclosure. I found it.
Therefore, the decrease in the moisture resistance of the coating film can be suppressed or greatly reduced, and the occurrence of blisters on the coating film can also be suppressed or greatly reduced.

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

Further, in the case of the rust-preventive coating composition of the present disclosure, in the object to be coated which can have various shapes, not only the surface of the object to be coated on a flat surface but also, for example, a processed portion, an end face, a cross-cut portion and the like. , The protective effect of the coating film can be sufficiently exhibited.
In addition, the rust-preventive coating composition of the present disclosure can suppress or significantly reduce blister in the processed portion, end face, and cross-cut portion, and even in such a portion, excellent rust prevention and moisture resistance over a long period of time. 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-preventive properties over a long period of time, it also has excellent processability and adhesion, for example, an object to be coated. It is possible to form a coating film which is excellent in adhesion to a coating material and a topcoat coating composition, and is also excellent in chemical resistance, weather resistance, scratch resistance, design property, and abrasion resistance.
Hereinafter, the rust preventive 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 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 has a lattice constant of less than 0.4214 nm.
The BET specific surface area is 2.0 or less.
By containing the specific magnesium oxide (C), the rust-preventive coating composition of the present disclosure can exhibit excellent rust-preventive properties over a long period of time, and can further 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 has a lattice constant of less than 0.4214 nm.
The BET specific surface area is 2.0 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, for example, various usage environments, for example, in addition to the effects of the coating composition described above. Even under conditions where the air temperature is high and the environment is humid, there is a tendency for stable rust prevention to be exhibited.
In addition, although it should not be construed as being limited to a specific theory, the inclusion of the magnesium oxide (C) according to the present disclosure can suppress a significant increase in the amount of alkaline ions dissolved even in an acidic environment. It is presumed to be. As a result, the magnesium oxide (C) according to the present disclosure stably supplies the corrosion suppressing factor, and corrosion can be suppressed for a long period of time. Further, the coating composition according to the present disclosure can exhibit sufficient rust preventive properties 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 present inventor has found that 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.
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, the occurrence of blisters on the coating film can be suppressed or greatly reduced.
Further, 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 blister 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 exhibit excellent rust resistance for a long period of time, and further, for a long period of time. Furthermore, it can exhibit rust prevention properties over an ultra-long term.

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 or less. It contains at least one selected from the group consisting of substances (SnMgO), indium magnesium oxide (InMgO) and magnesium oxide (MgO).
In one embodiment, the magnesium oxide (C) may be magnesium oxide, which is an oxide whose composition is represented by MgO. Since the magnesium oxide (C) is an oxide represented by magnesium oxide (MgO), a coating film exhibiting 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) or the like.

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 prevention properties for a longer period of time. More specifically, it is possible to form a coating film exhibiting rust prevention properties for a long period of time, and it is possible to suppress or significantly reduce corrosion in an acidic environment for a long period of time.
Such effects should not be construed in a specific theory, but the corrosion of the object to be coated is more effective when the lattice constant of magnesium oxide (C) is within such a range. It is considered that this is because it is possible to suppress the depletion of the corrosion suppressing factor derived from the magnesium oxide (C) with respect to the portion where the above can occur, and the 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. There 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 or less. By having the BET specific surface area, it is possible to form a coating film having excellent rust prevention properties for a longer period of time.
In one embodiment, the BET specific surface area of the magnesium oxide (C) according to the present disclosure is 1.8 or less, for example 1.6 or less, and may be 1.5 or less.
In one embodiment, the BET specific surface area of the magnesium oxide (C) is 1.4 or less, for example 1.3 or less, and may be 1.1 or less.
By having such a BET specific surface area, it is possible to form a coating film having excellent rust prevention properties for a longer period of time. More specifically, it is possible to form a coating film exhibiting rust prevention properties for a long period of time, and it is possible to suppress or significantly reduce corrosion in an acidic environment for a long period of time.
In the present specification, the BET specific surface area can be measured using, for example, an automatic specific surface area measuring device Gemini VII 23900 (manufactured by Shimadzu Corporation).
Such an effect should not be construed in a specific theory, but it is more effective that the BET specific surface area of the magnesium oxide (C) is within such a range. It is considered that this is because it is possible to suppress the depletion of the corrosion suppressing factor derived from the magnesium oxide (C) with respect to the portion where corrosion can occur, and it is possible to continuously supply this suppressing factor.

In one embodiment, the BET specific surface area of the magnesium oxide (C) according to the present disclosure is 0.1 or more, for example, 0.2 or more, and may be 0.3 or more.
By having such a BET specific surface area, it is possible to form a coating film having excellent rust prevention properties for a longer period of time. More specifically, it is possible to form a coating film exhibiting rust prevention properties for a long period of time, and it is possible to suppress or significantly reduce corrosion in an acidic environment for a long period of time.

In one embodiment, the BET specific surface area of the magnesium oxide (C) is 0.1 or more and 2.0 or less, for example, 0.3 or more and 1.5 or less.
In the present disclosure, the BET specific surface area of the magnesium oxide (C) can be appropriately combined within the above range.
When the BET specific surface area is within the above range, a coating film having excellent rust prevention properties can be formed for a longer period of time. More specifically, it is possible to form a coating film exhibiting rust prevention properties for a long period of time, and it is possible to suppress or significantly reduce corrosion in an acidic environment for a long period of time.

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 prepared by adding 1 g of the magnesium oxide (C) according to the present disclosure to 100 g of an artificial acidic sea aqueous solution. Contains oxide (C).
Although it should not be construed as limited to a specific theory, the rust preventive coating composition of the present disclosure contains magnesium oxide satisfying such a condition, so that the steel sheet can be oxidized for a long time without being depleted. A corrosion inhibitor from magnesium is supplied, and 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, it is possible to suppress or greatly reduce the occurrence of blisters on the coating film.
For example, by satisfying the above conditions, blistering and peeling of the coating film can be satisfactorily suppressed for a long time in a high temperature and high humidity environment.
Moreover, with the rust-preventive coating composition of the present disclosure, blister in the processed portion, the end face, and the cross-cut portion can be suppressed or greatly reduced.
Here, in the present disclosure, "exhibiting rust prevention under high temperature conditions" means that even if the atmospheric temperature is high (for example, 40 ° C. or higher) and the temperature is as high as 80 ° C., it is good. 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 prepared by adding 1 g of the magnesium oxide (C) according to the present disclosure to 100 g of an artificial acidic sea aqueous solution. For example, it contains magnesium oxide which is 66 ppm or less and may be 65 ppm or less.
By satisfying such a condition, the corrosion suppressing factor from magnesium oxide is more stably supplied to the steel sheet without being depleted for a longer period of time, and 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, it is possible to suppress or greatly reduce the occurrence of blisters on the coating film.
Further, with the rust preventive coating composition of the present disclosure, blister in the processed portion, the end face, and the cross-cut portion can be suppressed or greatly reduced.

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

In one embodiment, the rust preventive coating composition of the present disclosure may contain other metal compounds as long as the effects of the magnesium oxide (C) are not impaired.

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 in which 1 g of the magnesium oxide (C) is added with respect to 100 g of an artificial acidic sea aqueous 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 in which 1 g of the magnesium oxide (C) according to the present disclosure is added to 100 g of an artificial acidic sea aqueous solution. For example, it is a compound of 66 ppm or less and 65 ppm or less.

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

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

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 added, and the mixture is stirred at room temperature (23 ° C.) for 4 hours.
Then, after leaving it at room temperature for 24 hours, the supernatant is collected with a syringe equipped with a syringe filter, and the element concentration is measured by using, for example, an ICP emission spectrometer (ICPS-7510, manufactured by Shimadzu Corporation). , Magnesium metal ion concentration can be measured.

In one embodiment, the magnesium oxide (C) contains a compound having a conductivity of 320 μS / cm or less in an aqueous solution containing 1 g of magnesium oxide (C) with respect to 100 g of pure water, for example, 310 μS / cm or less. Contains the compounds of. Further, the magnesium oxide (C) may contain a compound having a conductivity of 305 μS / cm or less, and may include, for example, a compound having a conductivity of less than 301 μS / cm.

By satisfying such a condition, the corrosion suppressing factor from magnesium oxide is supplied to the steel sheet without being exhausted for a long time, 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, it is possible to suppress or greatly reduce the occurrence of blisters on the coating film.
Further, with the rust preventive coating composition of the present disclosure, blister in the processed portion, the end face, and the cross-cut portion can be suppressed or greatly reduced.
In one embodiment, the rust preventive coating composition of the present disclosure may contain other metal compounds as long as the above effects of the magnesium oxide (C) are not impaired.

In one embodiment, the magnesium oxide (C) may contain a compound having a conductivity of 10 μS / cm or more in an aqueous solution prepared by adding 1 g of magnesium oxide (C) to 100 g of pure water, for example, 20 μS /. It may contain a compound of cm or more and a compound of 50 μS / cm or more.

In another embodiment, the magnesium oxide (C) is a compound having a conductivity of 320 μS / cm or less in an aqueous solution prepared by adding 1 g of magnesium oxide (C) 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 suppressing factor from magnesium oxide can be more stably supplied to the steel sheet without being depleted for a long time, 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, it is possible to suppress or greatly reduce the occurrence of blisters on the coating film.
Further, with the rust preventive coating composition of the present disclosure, blister in the processed portion, the end face, and the cross-cut portion can be suppressed or greatly reduced.

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

In the present disclosure, for the measurement of conductivity in an aqueous solution in which 1 g of magnesium oxide (C) is added to 100 g of pure water, 100 g of ion-exchanged water and 1 g of magnesium oxide (C) are mixed and a stirrer chip is added. Then, the mixture is stirred at room temperature (23 ° C.) for 4 hours.
After that, the conductivity can be measured using, for example, an electric conductivity meter (CM-42X, manufactured by DKK-TOA CORPORATION).

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 to which 1 g of the magnesium oxide (C) is added with respect to 100 g of an artificial acidic sea aqueous solution. Moreover, the magnesium oxide (C) is a compound having a 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 also exhibits a specific conductivity, for example, corrosion in an acidic environment. Can be suppressed for a longer period of time.
Further, in addition to suppressing corrosion in an acidic environment, it is possible to stably suppress blister and peeling of a coating film in a high temperature and high humidity environment for a long period of time.
In the present disclosure, such a combination of magnesium metal ion concentration and conductivity can be appropriately selected within the range described in the present specification.

In one embodiment, the magnesium oxide (C) comprises a magnesium calcined product calcined at a temperature of 1,000 ° C. or higher. When the rust-preventive coating composition according to the present disclosure contains magnesium oxide fired under such temperature conditions, it is possible to exhibit excellent rust-preventive properties for a longer period of time, and further to provide excellent moisture resistance. The coating film shown can be formed.
In one embodiment, the magnesium oxide (C) comprises a magnesium calcined product fired at a temperature of 1,100 ° C. or higher, and may include, for example, a magnesium calcined product fired at a temperature of 1,200 ° C. or higher. ..
In one embodiment, the magnesium oxide (C) comprises a magnesium calcined product fired at a temperature of 2,200 ° C. or lower, and may include, for example, a magnesium calcined product fired at a temperature of 2,000 ° C. or lower. ..
For example, the magnesium oxide (C) contains a magnesium calcined product fired at a temperature of 1,000 ° C. or higher and 2,200 ° C. or lower, and is fired at a temperature of 1,100 ° C. or higher and 2,000 ° C. or lower. It may contain an object.
Further, the magnesium oxide (C) may contain a plurality of types of fired products fired in such a temperature range in combination.

Although it should not be construed as limited to a specific theory, the rust preventive coating composition of the present disclosure contains magnesium oxide satisfying such a condition, so that the steel sheet can be oxidized for a long time without being depleted. A corrosion inhibitor from magnesium is supplied, and 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, it is possible to suppress or greatly reduce the occurrence of blisters on the coating film.
For example, by satisfying the above conditions, blistering and peeling of the coating film can be satisfactorily suppressed for a long time in a high temperature and high humidity environment.
Moreover, with the rust-preventive coating composition of the present disclosure, blister in the processed portion, the end face, and the cross-cut portion can be suppressed or greatly reduced.

In another embodiment, the magnesium oxide (C) is a fired magnesium product fired at a temperature of 1,000 ° C. or higher. In one embodiment, the magnesium oxide (C) is a magnesium calcined product fired at a temperature of 1,100 ° C. or higher, for example, a magnesium calcined product fired at a temperature of 1,200 ° C. or higher.
When the rust-preventive coating composition according to the present disclosure contains magnesium oxide (C) fired under such temperature conditions, excellent rust-preventive properties can be exhibited for a longer period of time, and further 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 fired at a temperature of 2,200 ° C. or lower, for example, a magnesium calcined product fired at a temperature of 2,000 ° C. or lower.
For example, magnesium oxide (C) is a magnesium calcined product fired in a temperature range of 1,000 ° C. or higher and 2,200 ° C. or lower, and fired in a temperature range of 1,100 ° C. or higher and 2,000 ° C. or lower. It is a fired magnesium product.
Since the magnesium oxide (C) in the rust-preventive coating composition according to the present disclosure is a magnesium oxide fired under such temperature conditions, excellent rust-preventive properties can be exhibited for a longer period of time. Moreover, a coating film showing excellent moisture resistance can be formed.

Although it should not be construed as limited to a specific theory, the rust preventive coating composition of the present disclosure contains magnesium oxide satisfying such a condition, so that the steel sheet can be oxidized for a long time without being depleted. A corrosion inhibitor from magnesium is supplied, and 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, it is possible to suppress or greatly reduce the occurrence of blisters on the coating film.
For example, by satisfying the above conditions, blistering and peeling of the coating film can be satisfactorily suppressed for a long time in a high temperature and high humidity environment.
Moreover, with the rust-preventive coating composition of the present disclosure, blister in the processed portion, the end face, and the cross-cut portion can be suppressed or greatly reduced.

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 containing 1 g of magnesium oxide (C) with respect 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, an increase in the corrosion rate of the object to be coated can be suppressed more effectively, and a coating film having good corrosion resistance can be formed.
In the present disclosure, the pH value in an aqueous solution in which 1 g of magnesium oxide (C) is added 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 added, and the mixture is stirred at room temperature (23 ° C.) for 4 hours.
Then, for example, the pH can be measured using a pH meter (desktop pH meter F-74, manufactured by HORIBA, Ltd.) or the like.

In one embodiment, the average particle size 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 limited to a specific theory, the apparent volume concentration (PVC) of magnesium oxide (C) is due to the fact that the average particle size of magnesium oxide (C) is within such a range. It is considered that the excessive increase can be suppressed, and higher corrosion resistance can be exhibited. In addition, it can have excellent coating film blocking properties and can exhibit higher corrosion resistance.
In the present specification, the average particle size can be measured using, for example, a laser diffraction type particle size distribution measuring device SALD-2300 (manufactured by Shimadzu Corporation) or the like.
Here, the corrosion of the object to be coated according to the present disclosure is caused by the corrosion factors such as water, salt water, acidic water and the like permeating to 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 block such corrosive factors from penetrating into the object to be coated. In the present disclosure, such a blocking property is also referred to as a coating film blocking property.

In one embodiment, the coating composition of the present disclosure comprises magnesium oxide (C) with respect to a total of 100 parts by mass of the solid content of the coating film-forming resin (A) and the solid content of the cross-linking agent (B). It can be contained in 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 containing magnesium oxide (C) in such a relationship, the rust-preventive coating composition of the present invention can exhibit excellent rust-preventive properties over a long period of time, and further, a coating film exhibiting excellent moisture resistance. Can be formed.

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

For example, the coating film-forming resin (A) is an epoxy resin and its modified product (acrylic modified epoxy resin, etc.); a polyester resin and its modified product (urethane modified polyester resin, epoxy modified polyester resin, silicone modified polyester resin, etc.); acrylic. Resin and its modified product (silicone modified acrylic resin, etc.); Urethane resin and its modified product (ester-based urethane resin, ether-based urethane resin, carbonate-based urethane resin, epoxy-based urethane resin, etc.); Modified phenol resin, epoxy-modified phenol resin, etc.); phenoxy resin; alkyd resin and its modified products (urethane-modified alkyd resin, acrylic-modified alkyd resin, etc.); resins such as fluorine resin can be mentioned. Only one of these resins may be used alone, or two or more of these resins may be used in combination.

In one embodiment, the coating film-forming resin (A) comprises 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 balance between the bending processability of the obtained coating film and the moisture resistance, corrosion resistance, and weather resistance of the obtained coating film. Includes at least one selected from the group consisting of objects.

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 showing excellent corrosion resistance can be formed, and further, a coating film having excellent adhesion to an object to be coated and a topcoat coating composition (topcoat coating) can be formed. ..

(Epoxy resin)
The number average molecular weight (Mn) of the epoxy resin, for example, the modified product thereof, the hydroxyl group-containing epoxy resin, is preferably 1,400 or more and 20,000 or less, and preferably 2,000 or more and 10,000 or less. More preferably, it is 2,000 or more and 4,000 or less.
Unless otherwise specified, in the present disclosure, when simply referring to an epoxy resin, it means that it contains at least one selected from the group consisting of an epoxy resin and a modified product of the epoxy resin.
In the present specification, the number average molecular weight (Mn) is a polystyrene-equivalent value obtained by gel permeation chromatography (GPC).

When the epoxy resin has such a number average molecular weight, the cross-linking reaction with the cross-linking agent (B) described later sufficiently proceeds, and a coating film having high moisture resistance can be formed. Further, excellent corrosion resistance can be ensured. For example, although it should not be interpreted only in a specific theory, the elution of magnesium oxide (C) contained in the coating film becomes appropriate, and the corrosion resistance under acidic environmental conditions becomes good.
Further, it is possible to prevent the crosslink density of the coating film from becoming too high, and it is possible to form a coating film having a sufficient elongation rate, for example, 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, and may be 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.) or the like.

When the glass transition temperature (Tg) of the epoxy resin is within the above range, the moisture permeability of the coating film does not become excessively high, the moisture resistance of the coating film becomes sufficient, and the corrosion resistance also 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 solid acid value can be measured in accordance with the provisions of JIS K 0070.

The epoxy resin may be a hydroxyl group-containing epoxy resin (including a modified product of the hydroxyl group-containing epoxy resin).
As the epoxy resin, a resin obtained by condensing epichlorohydrin and bisphenol to a high molecular weight in the presence of a catalyst such as an alkaline catalyst as necessary; bisphenol type epoxy resin such as bisphenol A type and bisphenol F type; and novolak type epoxy resin, etc. Can be mentioned.
Examples of the modified epoxy resin 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, this 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.
Taking a urethane-modified epoxy resin as an example, it can be prepared by reacting the bisphenol type epoxy resin or the novolak 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, the modified product thereof, the 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 the term "polyester resin" is simply used, it means that the polyester resin and at least one selected from the group consisting of modified products of the polyester resin are included.

When the polyester resin has such a number average molecular weight, the cross-linking reaction with the cross-linking agent (B) proceeds sufficiently, and a coating film having high moisture resistance can be formed. Further, excellent corrosion resistance can be ensured. For example, although it should not be interpreted only in a specific theory, the elution of magnesium oxide (C) contained in the coating film becomes appropriate, and the corrosion resistance under acidic environmental conditions becomes good.
Further, it is possible to prevent the crosslink density of the coating film from becoming too high, and it is possible to form a coating film having a sufficient elongation rate, for example, 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 −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 permeability of the coating film does not become excessively high, the moisture resistance of the coating film becomes sufficient, and the corrosion resistance also 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 in such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed. Further, excellent corrosion resistance can be ensured.

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. -Butandiol 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, annitol, trimethylolethane, Examples thereof include trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol, tris- (hydroxyethyl) isocyanate and the like. Only one type of polyhydric alcohol may be used alone, or two or more types may be used in combination.

Specific examples of polybasic acids include, for example, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic acid, methyltetraphthalic acid, methyltetrahydrophthalic acid, and 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, endoacid anhydride and the like. Only one type of polybasic acid may be used alone, or two or more types may be used in combination.

Examples of the modified polyester resin 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 having polyester in the main chain and having its ends modified with isocyanate to be urethane-modified.
For example, taking a silicone-modified polyester resin as an example, this is a polyester resin and an organic silicone (for example, an organic silicone having a number average molecular weight of about 300 to 1,000 having _{3 -SiOCH groups and / or SiOH groups as functional groups).} 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, this can be prepared by reacting the polyester resin with a polyisocyanate compound.

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

(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 more preferably 2,000 to 30,000. Is particularly preferable.
Unless otherwise specified in the present disclosure, the term "acrylic resin" simply means that it contains at least one selected from the group consisting of acrylic resin and modified products of acrylic resin.

When the acrylic resin has such a number average molecular weight, the cross-linking reaction with the cross-linking agent (B) proceeds sufficiently, and a coating film having high moisture resistance can be formed. Further, excellent corrosion resistance can be ensured. For example, although it should not be interpreted only in a specific theory, the elution of magnesium oxide (C) contained in the coating film becomes appropriate, and the corrosion resistance under acidic environmental conditions becomes good.
Further, it is possible to prevent the crosslink density of the coating film from becoming too high, and it is possible to form a coating film having a sufficient elongation rate, for example, 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 −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 permeability of the coating film does not become excessively high, the moisture resistance of the coating film becomes sufficient, and the corrosion resistance also 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 in such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed. Further, excellent corrosion resistance can be ensured.

The acrylic resin has, for example, a hydroxyl group such as hydroxymethyl (meth) acrylate, hydroxylethyl (meth) acrylate, hydroxylpropyl (meth) acrylate, hydroxybutyl (meth) acrylate, N-methylolacrylamide, etc. ( Meta) acrylic monomer and lactone adduct thereof; (meth) acrylic acid; (meth) acrylic acid ester such as alkyl (meth) acrylic acid; from one or more monomers selected from (meth) acrylonitrile and the like. Acrylic acid can be mentioned. In addition to the structural units derived from the above-mentioned monomers, the acrylic resin can be used for other monomers (for example, carboxyl group-containing ethylenic monomers such as crotonic acid, itaconic acid, fumaric acid, and maleic acid, vinyl-based monomers such as styrene, etc.). It may contain the building blocks from which it is derived. In the present disclosure, (meth) acrylic acid represents acrylic acid or methacrylic acid.
Examples of the modified acrylic resin include modified acrylic resins such as silicone-modified acrylic resins. For example, taking a silicone-modified acrylic resin as an example, this can be prepared by reacting the acrylic resin with the 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 number average molecular weight (Mn) of the urethane resin and the modified urethane resin is 6,000 or more and 15,000 or less.
In the present disclosure, unless otherwise specified, when simply referring to urethane resin, it means that it contains at least one selected from the group consisting of urethane resin and modified products of urethane resin.

When the urethane resin has such a number average molecular weight, the cross-linking reaction with the cross-linking agent (B) proceeds sufficiently, and a coating film having high moisture resistance can be formed. Further, excellent corrosion resistance can be ensured. For example, although it should not be interpreted only in a specific theory, the elution of magnesium oxide (C) contained in the coating film becomes appropriate, and the corrosion resistance under acidic environmental conditions becomes good.
Further, it is possible to prevent the crosslink density of the coating film from becoming too high, and it is possible to form a coating film having a sufficient elongation rate, for example, 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 can be −30 ° C. or higher and 80 ° C. or lower, for example, −30 ° C. or higher and 60 ° C. or lower, and −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 permeability of the coating film does not become excessively high, the moisture resistance of the coating film becomes sufficient, and the corrosion resistance also 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 in such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed. Further, excellent corrosion resistance can be ensured.

In one embodiment, the urethane group concentration (% by mass) in the resin of the urethane resin in the present disclosure is 2% by mass or more and 20% by mass or less, for example, 5% by mass or more and 17% by 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 ensured.

Examples of the urethane resin include those obtained by reacting a polyol compound with 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 containing two or more hydroxyl groups per molecule, and for example, ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, and triethylene glycol. , Polyether polyols such as glycerin, trimethylolethane, trimethylolpropane, polycarbonate polyols, polyester polyols, bisphenol hydroxypropyl ethers, polyesteramide polyols, acrylic polyols, polyurethane polyols, or mixtures thereof. The polyisocyanate compound is not particularly limited as long as it is a compound containing two or more isocyanate groups per molecule, and for example, an aliphatic isocyanate such as hexamethylene diisocyanate (HDI) and a fat such as isophorone diisocyanate (IPDI). Examples thereof include aromatic diisocyanates such as cyclic diisocyanate and tolylene diisocyanate (TDI), aromatic aliphatic diisocyanates such as diphenylmethane diisocyanate (MDI), and mixtures thereof. The chain extender is not particularly limited as long as it is a compound containing one or more active hydrogens in the molecule, and water or an amine compound can be applied. Examples of the amine compound include aliphatic polyamines such as ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine and tetraethylenepentamine, and aromatic polyamines such as tolylene diamine, xylylene diamine and diaminodiphenylmethane. Aliphatic polyamines such as diaminocyclohexylmethane, piperazin, 2,5-dimethylpiperazin, isophoronediamine, hydrazine, etc.
Examples thereof include hydrazines such as dihydrazide succinate, adipic acid dihydrazide and dihydrazide phthalate, 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, the ester-based urethane resin means a resin having both a urethane group and an ester group in the main chain. Further, a resin in which the number of urethane groups is 5% or more larger than the number of ester groups by comparing the number of urethane groups and the number of ester groups in the main chain is referred to as an ester-based urethane resin.
Examples of the urethane polymer include those obtained by reacting the above-mentioned 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 with a polyhydric alcohol.

In one embodiment, the urethane resin is an ether-based 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. Further, when the number of urethane groups in the main chain is compared with the number of ester groups and the number of urethane groups is 5% or more larger than the number of ether groups, it is called an ether urethane resin.

In one embodiment, the urethane resin is a carbonate-based urethane resin. In the present disclosure, the carbonate-based urethane resin means a resin having both a urethane group and a carbonate group in the main chain. Further, when the number of urethane groups in the main chain is compared with the number of carbonate groups and the number of urethane groups is 5% or more larger than the number of carbonate groups, it is called a 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 may be 0.3 mgKOH / g or more and 40 mgKOH / g or less.
When the solid content acid value is in such a range, for example, hydrolysis resistance can be improved and a coating film having moisture resistance can be formed. Further, excellent corrosion resistance can be ensured.

Examples of the polycarboxylic acid constituting 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 acids, as polyol components, ethylene glycol, propylene glycol, trimethylene glycol, 1,3-butadiol, 1.4-butadiol, 1.5-bentandiol, 1.6- Examples thereof include hexanediol, neopentyl glycol, trimethylolpropane, trimethylolethane, and pentaerythritol.
The copolymerized polyester of the present invention contains an excess of hydroxyl groups in the range of 1.0 / 1.001 to 1.0 / 2.0, which is the equivalent ratio of the carbonyl group in the polycarboxylic acid to the hydroxyl group of the polyol component. Preferably, it is obtained by a usual transesterification method or a direct esterification reaction. A particularly preferable equivalent ratio is in the range of 1.0 / 1.01 to 1.0 / 1.5.

The acid anhydride that can be contained in the acid component is not particularly limited, and is, for example, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, succinic anhydride, trimellitic anhydride. Examples thereof include acid, phthalic anhydride, 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 specifically, for example, monoepoxyside compounds such as Cardura E (manufactured by Shell Chemical Co., Ltd.) and lactones can be mentioned. The above lactones can be ring-opened and added to polyesters of polyhydric carboxylic acid and polyhydric alcohol to form a graft chain. For example, β-propiolaclone, dimethylpropiolactone, butyllactone, γ- Examples thereof include valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotolactone, δ-valerolactone, and δ-caprolactone. Of these, ε-caprolactone is the most preferable.

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

In the coating composition of the present disclosure, in addition to the coating film-forming resin (A), a thermoplastic resin can also be used.
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 and the like as monomer components; cellulose resins; acetal resins. Alexandre resin; Rubber chloride resin; Modified polypropylene resin (acid anhydride-modified polypropylene resin, etc.); Fluororesin (for example, vinylidene fluoride resin, vinyl fluoride resin, copolymer of fluorinated olefin and vinyl ether, fluorination (Copolymer of olefin and vinyl ester) and the like can be mentioned.
Only one type of thermoplastic resin may be used alone, or two or more types may be used in combination. By using the thermoplastic resin in combination, better coating film physical characteristics such as coating film strength and elongation can be obtained.

[Crosslinking agent (B)]
The cross-linking 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 the isocyanate group of the polyisocyanate compound is blocked with an active hydrogen-containing compound (sometimes referred to as “BI”); an amino resin; a phenol resin, and the like. Can be done.
Of these, it is preferable to contain one or more selected from the blocked polyisocyanate compound and the amino resin. By including such a cross-linking agent (B), it is possible to exhibit excellent rust prevention properties for a long period of time, and further, it is possible to form a coating film exhibiting excellent moisture resistance.

The polyisocyanate compound and the polyisocyanate compound constituting the blocked polyisocyanate compound are not particularly limited, and conventionally known ones can be used. Specific examples include, for example, 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'-Tetramethylxylylene diisocyanate, 2,4- or 2,6-diisocyanatotoluene, 2,2'-, 2,4'-or 4,4'-diisocyanatodiphenylmethane (MDI) , 1,5-naphthalenediocyanate, p- or m-phenylenediocyanate, 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. Only one type of polyisocyanate compound may be used alone, or two or more types may be used in combination. The isocyanurate-type polyisocyanate compound is one of those preferably used in the present invention.

For example, as the polyisocyanate compound, it is preferable to use an aromatic polyisocyanate compound containing one or more aromatic functional groups in the molecule. By using the aromatic polyisocyanate compound, the moisture resistance of the coating film can be improved and the strength of the coating film can be improved. Preferred aromatic polyisocyanate compounds include 2,4- or 2,6-diisocyanatotoluene (TDI), 2,2'-, 2,4'-or 4,4'-diisocyanatodiphenylmethane ( MDI), xylene diisocyanate (XDI), naphthalene diisocyanate (NDI) and the like can be mentioned.

The isocyanate group content of the polyisocyanate compound constituting the blocked polyisocyanate compound as measured in accordance with JIS K 7301-1995 is usually 3 to 20%, preferably 5 to 5% of the solid content of the polyisocyanate compound. It is 15%. When the isocyanate group content is within the above range, the curability of the coating film is further improved. In addition, it is possible to suppress an excessively high crosslink density of the obtained coating film, and the corrosion resistance can be improved.

The active hydrogen-containing compound (blocking agent) used in the blocked polyisocyanate compound is not particularly limited, and is: -OH group (alcohols, phenols, etc.), = N-OH group (oximes, etc.), = NH. group (amines, amides, imides, lactams and the like) or a compound having, -CH 2 _- compound having a group (an active methylene group), can be mentioned 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, acetoaldoxime, acetoxime, methyl ethyl kedoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime, dimethyl malonate, ethyl acetoacetate, acetyl acetone , Pyrazole, etc. As the active hydrogen-containing compound, only one kind may be used alone, or two or more kinds may be used in combination.

The thermal dissociation temperature of the blocked polyisocyanate compound depends on the type of the polyisocyanate compound and the active hydrogen-containing compound constituting the blocked polyisocyanate compound, the presence or absence of a catalyst, and the amount thereof. ) Is 120 to 180 ° C., a blocked polyisocyanate compound is preferably used. By using a block polyisocyanate compound showing a dissociation temperature within this range, the stability of the coating material can be improved, and since it is excellent in the cross-linking reactivity with the coating film-forming resin (A), it has moisture resistance. Can obtain a good coating film. Examples of the blocked polyisocyanate compound (e) having a dissociation temperature of 120 to 180 ° C. include Death Module BL3175 manufactured by Sumika Covestro Urethane Co., Ltd. and Coronate 2554 manufactured by Tosoh Co., Ltd.
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. "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 is a _{fully alkyl type containing -N- (CH 2} OR) ₂ [R is an alkyl group, the same applies hereinafter] as a reactive functional group; -N- (CH ₂ OR) (CH _{2) as a reactive functional group.} Methylol group containing OH); _{imino group containing -N- (CH 2} OR) (H) as reactive functional group; -N- (CH ₂ OR) (CH ₂ OH) as reactive functional group Four types of methylol / imino group types containing -N- (CH ₂ OR) (H) or containing -N- (CH _{2 OH) (H) can be exemplified.}
In the present invention, among the above melamine resins, a melamine resin having at least one methylol group or imino group on average in one molecule (hereinafter referred to as amino resin (f)), that is, a methylol group type or an imino group. It is preferable to use a mold or methylol / imino-based melamine resin or a mixture thereof.
As the melamine resin, for example, the trade name Mycoat 715 manufactured by Ornex Japan Co., Ltd. can be mentioned.
Amino resins such as melamine resins have excellent cross-linking reactivity with the coating film-forming resin (A) even under no 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 in terms of solid content with respect to 100 parts by mass of solid content of the coating film forming resin (A), for example, 2 parts by mass or more. It is 150 parts by mass or less. By containing the cross-linking agent (B) under such conditions, it is possible to exhibit excellent rust prevention properties for a long period of time, and further, it is possible to form a coating film exhibiting 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 in terms of solid content with respect to 100 parts by mass of the solid content of the coating film forming resin (A).
By containing the cross-linking agent (B) under such conditions, the cross-linking reaction with the coating film-forming resin (A) proceeds more satisfactorily, the moisture permeability of the coating film becomes better, and the moisture resistance of the coating film becomes further improved. It will be good. Moreover, the corrosion resistance is further improved.
Further, the magnesium oxide (C) contained in the coating film can be stably eluted for a long period of time, and further excellent corrosion resistance can be obtained.

[Constitution 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 strength of the coating film can be further improved, and unevenness may occur on the surface of the coating film without impairing the physical characteristics of the coating film formed from the coating composition according to the present disclosure. Thereby, the adhesion with the topcoat coating film can be further improved. Moreover, 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 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), for example, 10 parts by mass. More than 30 parts by mass or less.
When the amount of the extender pigment is within such a range, the moisture resistance can be improved. Further, it is possible to suppress the excessively high moisture permeability of the coating film, for example, it is possible to suppress the 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 contain at least one coupling agent selected from the group consisting of silane-based coupling agents, titanium-based coupling agents and zirconium-based coupling agents.
By adding the coupling agent, the adhesion between the base material (object to be coated) and the coating film formed from the coating composition according to the present disclosure can be further improved, and the moisture resistance of the coating film can be further improved. Can be done.

The coupling agent is not particularly limited, and conventionally known ones can be used. Specific examples of the coupling agents preferably used are silane coupling agents such as Z-6011 and Z-6040 manufactured by Dow Corning Toray Co., Ltd .; titanium such as Organix TC-401 and Organix TC-750 manufactured by Matsumoto Fine Chemicals. Coupling agents: Examples thereof include zirconium-based coupling agents such as Organix ZC-580 and Organix ZC-700 manufactured by Matsumoto Fine Chemicals. Of these, silane-based coupling agents are preferably used.
The amount of the coupling agent may be 0.1 part by mass or more and 20 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), for example, 0. It may be 0.5 parts by mass or more and 10 parts by mass or less.
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 well maintained.

[Curing catalyst]
When a blocked polyisocyanate compound and / or a polyisocyanate compound is used as the cross-linking agent (B), the coating composition of the present invention may contain a curing catalyst.
Examples of the curing catalyst include tin catalysts, amine catalysts, lead catalysts and the like, and among them, organotin compounds are preferably used. As the organic tin compound, for example, dibutyltin dilaurate (DBTL), dibutyltin oxide, tetra-n-butyl-1,3-diacetoxystanoxane and the like can be used. The amount of the curing catalyst may be 0.1 part 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 well maintained.

Further, even when an amino resin is used as the cross-linking 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, dodecylbenzenesulfonic acid, paratoluenesulfonic acid and the like 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 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 well maintained.

[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 above-mentioned extender pigments; colorants such as color pigments and dyes; bright pigments; solvents; ultraviolet absorption. Agents (benzophenone-based UV absorbers, etc.); Antioxidants (phenol-based, sulfoid-based, hindered amine-based antioxidants, etc.); Plastic agents; Surface conditioners (silicone, organic polymers, etc.); Anti-sagging agents; Thickeners Lubricant such as wax; Pigment dispersant; Pigment wetting agent; Leveling agent; Color-coding inhibitor; Anti-precipitation agent; Antifoaming agent; Antiseptic agent; Antifreeze agent; Emulsifier; Antifungal agent; Antibacterial agent; Stabilizer, 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 can be used in combination as long as the effects produced by the present disclosure are not impaired.
For example, molybdate pigments (zinc molybdate, strontium molybdate, etc.), molybdate pigments (aluminum molybdate pigments, etc.), calcium silica-based pigments, phosphate-based rust preventive pigments, silicate-based anticorrosives. Examples thereof include rust pigments, havanazinate-based rust preventive pigments, calcium hydroxide, magnesium hydroxide, and non-chromium-based rust preventive pigments such as hydroxides or oxides of the second element such as magnesium oxide other than this claim.
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 magnesium oxide (C) as described above is further added. Can include.

As other pigments other than the above-mentioned extender pigments in detail, alumina, bentonite and the like may be added as long as the moisture resistance, rust prevention, bending processability and the like of the obtained coating film are not impaired. These may be used alone or in combination of two or more.

Colored pigments include, for example, colored inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, and cold dust; phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azoorange, and flavanthron yellow. , Isoindoline Yellow, Azo Yellow, Induslon Blue, Dibrom Anzaslon Red, Perylene Red, Azo Red, Anthraquinone Red, etc. Colored Organic Pigments; Aluminum Powder, Alumina Powder, Bronze Powder, Copper Powder, Tin Powder, Zinc Powder, Phosphorus Examples thereof include iron oxide and atomized titanium. These may be used alone or in combination of two or more.

Examples of the glitter pigment include aluminum foil, bronze foil, tin foil, gold leaf, silver foil, titanium metal foil, stainless steel foil, alloy foil such as nickel and copper, and foil pigment such as foil-like 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, and the like. 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 and ethyl acetate , Ester-based organic solvents such as isopropyl acetate and butyl acetate; ketone-based organic solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone and isophorone; and N-methyl-2-pyrrolidone, toluene, pentane, iso-pentane and hexane. , Iso-hexane, cyclohexane, solvent naphtha, mineral spirit, Solbesso 100, Solbesso 150 (all are aromatic hydrocarbon solvents, manufactured by Shell Chemical Co., Ltd.) and the like. 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 material or an organic solvent-based coating material.

[Preparation method of paint 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 coating film-forming resin (A), a cross-linking agent (B) and a magnesium oxide (C), and optionally used thermoplastic resins, extender pigments, coupling agents, and the like. The curing catalyst and other additives can be prepared by mixing 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, or a disper.
Alternatively, the coating composition of the present disclosure is a two-component coating material comprising a main agent component containing a coating film-forming resin (A) and a magnesium oxide (C) and a cross-linking agent component containing a cross-linking agent (B). You may.

The coating composition of the present invention may be applied as an undercoat coating, which is also called a primer. Further, it may be used as a top coat paint to be overlaid on the base coat paint. Further, it may be used as an intermediate coating paint formed in an intermediate layer between the undercoat coating and the topcoat coating.
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 multi-layer coating film.
The coating composition of the present invention can exhibit excellent corrosion resistance and moisture resistance when used on any portion of the multi-layer coating film. Above all, the coating composition of the present invention is preferably used as an undercoat coating material. Undercoat paints, topcoat paints and intermediate coat paints other than the coating composition of the present invention may be conventionally known, and examples of the undercoat paint include conventionally known non-chromium-based rust preventive paints and the like. Examples of the intermediate coating paint include polyester resin-based paints and fluororesin-based paints.

[Object to be coated]
The object to be coated on which the coating film is formed by the rust preventive coating composition of the present invention is not particularly limited as long as corrosion resistance is required. For example, a steel plate as a base material such as a precoated metal (painted steel plate) can be mentioned.
Examples of the steel sheet include galvanized steel sheets, cold-rolled steel sheets, stainless steel sheets, aluminum sheets and the like. Examples of galvanized steel sheets include zinc-containing galvanized steel sheets that utilize the sacrificial anticorrosion of zinc, specifically, hot-dip galvanized steel sheets, electrogalvanized steel sheets, alloyed hot-dip galvanized steel sheets, aluminum-galvanized steel sheets, and nickel-zinc plated steel sheets. Examples thereof include steel sheets, magnesium-aluminum-galvanized steel sheets, and magnesium-aluminum-silica-galvanized steel sheets. The steel sheet is preferably surface-treated with a chemical conversion treatment agent before painting. The surface treatment may be carried out by a known method, and examples thereof include non-chromate treatment such as chromate treatment and zinc phosphate treatment. The surface treatment can be appropriately selected depending on the steel sheet to be used, but a treatment that does not contain heavy metals is preferable.

[Manufacturing method of rust preventive coating film]
In another embodiment, the present disclosure comprises a coating step of applying the rust-preventive coating composition according to the present disclosure to an object to be coated, and curing the coating composition at a temperature of 150 ° C. or higher and 270 ° C. or lower. Provided is a method for producing a rust coating film.
As a method for coating the coating composition of the present invention on an object to be coated, conventionally known methods such as a roll coater, an airless spray, an electrostatic spray, and a curtain flow coater can be adopted.
The coating film composed of 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, sufficient strength is obtained. A coating film can be formed. By forming a coating film having sufficient strength, it is possible to further exhibit excellent rust resistance for a long period of time, and further, it is possible to form a coating film exhibiting excellent moisture resistance.
The baking time (curing time) is, for example, 10 to 200 seconds. For example, in the case of forming a multi-layer coating film consisting of two layers of an undercoat coating film and a topcoat coating film, the undercoat coating composition is applied and then baked, and then the topcoat coating composition is applied and the topcoat coating film is baked. After applying the undercoat coating composition, the topcoat coating composition may be applied wet-on-wet without baking, and then baked 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. It is preferably 10 to 30 μm.

[Corrosion resistance]
The coating film formed from the coating composition of the present disclosure can show good results in both "immersion in acidic salt water-drying cycle test 15 cycles" and "CCHC test 2,000 hours", for example.
Since good results can be shown in these tests, it is possible to achieve both long-term stable rust prevention and moisture resistance.
Here, the "immersion-drying cycle test with acidic salt water" can be measured based on the method shown in Japanese Patent No. 5857156. It is considered that a coating film having rust preventive properties and stable rust preventive properties for a long period of time can be obtained, for example, by giving good test results.
In addition, the "CCHC test 2,000 hours" is performed by exposing the coating film to a high temperature and high humidity environment called CCHC (Cleveland Condensing Humidity Cabinet: ASTM D-2247-87-Type A2) for 2,000 hours. This 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 period of time even if the coating film is exposed to a harsher 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 long-term stable rust prevention and moisture resistance.
In addition, good rust resistance and moisture resistance can be achieved at both the processed portion, the end face, 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 prevention property under acidic environmental conditions can be evaluated based on a test using "acidic salt water". Further, in the present disclosure, a coating film having excellent rust prevention properties under acidic environmental conditions can be obtained, and for example, excellent rust prevention properties against acid rain can be exhibited.

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 for 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 the comparative example are shown below.
-Nickel oxide; Nickel oxide powder II Large particle size (manufactured by Kusaka Rare Metal Research Institute) Lattice constant: 0419 nm, BET specific surface area: 20, average particle size: 1.8 μm
・ Tricalcium phosphate (manufactured by Taihei Kagaku Sangyo Co., Ltd.)
-Condensed phosphate: K-WHITE # 82 (manufactured by TAYCA)
・ Calcium vanadate
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 urethane resin 1)]
55 parts by mass of adipic acid, 6.1 parts by mass of phthalic anhydride, 27 parts by mass of neopentyl glycol and 26.1 parts by mass of propylene glycol were mixed in a reaction vessel equipped with a thermometer, a condenser and a stirrer, and in a nitrogen stream. The temperature was gradually raised to 230 ° C., and the esterification reaction was carried out for about 10 hours until the acid value became 1 or less while distilling off the produced water (dehydrated 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 were mixed and held at 80 ° C. for 8 hours to react, and the ester-based urethane resin 1 (solid). Concentration: 50% by mass) was obtained.

Coating film-forming resins (A2) to (A8) (ester-based urethane resins 2 to 8, respectively) 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 special values such as monomer composition and molecular weight of each resin.

[Preparation of coating film forming resin (A9) (ether-based urethane resin 1)]
100 parts by mass of PTMG650 (polytetramethylene glycol manufactured by Mitsubishi Chemical Co., Ltd.), 135 parts by mass of cyclohexanone and 35 parts by mass of 4,4'-diphenylmethane diisocyanate are mixed in a reaction vessel equipped with a thermometer, a condenser and a stirrer, and 80 ° C. The mixture was kept for 8 hours and reacted to obtain ether-based urethane resin 1 (solid content concentration: 50% by mass).

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

[Coating film forming resin (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 Co., Ltd., hydroxyl group-containing epoxy resin) Number average molecular weight: 10,000, solid acid value: 1.0 mgKOH / g, glass transition temperature: 85 ℃, solid content concentration: 30% by mass
-Coating resin (A12) (polyester resin 1); Byron UR4410 (manufactured by Toyobo Co., Ltd.) Number average molecular weight: 10,000, solid acid value: 0.5 mgKOH / g, glass transition temperature: 56 ° C, solid content concentration : 40% by mass
-Coating resin (A13) (acrylic resin 1); Acrydic A452 (manufactured by DIC, acrylic resin); number average molecular weight: 17,000, solid acid value: 2.7 mgKOH / g, glass transition temperature: 70 ℃, solid content concentration: 40% by mass

[Crosslinking agents (B1), (B2)]
The details of the cross-linking agent (B) are as follows.
Cross-linking agent (B1) (polyisocyanate compound 1); Death module BL3575 (blocked polyisocyanate manufactured by Sumika Cobestrourethane) 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 (manufactured by Ornex Japan, imino-based melamine resin) Solid content concentration: 80% by mass

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

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

[Method of manufacturing evaluation coated plate]
After alkali degreasing of a 0.4 mm thick aluminum galvanized steel sheet, a phosphoric acid treatment agent, Surfcoat EC2310 (manufactured by Nippon Paint Surf Chemicals), is applied to the front and back surfaces of the steel sheet to perform non-chromium chemical conversion treatment. Alkaline 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 reaching 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 is applied to the surface of the steel sheet so that the dry coating film has a thickness of 5 μm, and baked at a maximum temperature of 200 ° C. for 30 seconds. Was carried out to form a surface undercoat coating film. Further, Nippe Super Coat 300HQ (manufactured by Nippon Paint Industrial Coatings Co., Ltd.), which is a polyester-based topcoat coating, is applied onto the surface undercoat coating film so that the dry coating film has a maximum temperature of 210 ° C. Baking was performed for 40 seconds to form a surface topcoat film, and a coated steel sheet for evaluation was obtained.

(Examples 2-33, Comparative Examples 1-7)
Hereinafter, unless otherwise specified, various physical property evaluations were carried out using the coated steel sheet thus formed. A coating film was formed in the same manner in the 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. Comparative examples are shown in Tables 5A and 5B.
A coating composition was prepared in the same manner as in Example 1 except that the type and amount of each component 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), NRC300 (manufactured by Nippon Paint Surf Chemicals Co., Ltd.), which is a chromate treatment agent, is applied to the front and back surfaces of the steel plate, chromate treatment is applied, and chromium is applied. Nippe Super Coat 667 Primer (manufactured by Nippon Paint Industrial Coatings), which is the corresponding undercoat paint containing strontium acid acid, and Nippe Super Coat 300HQ (manufactured by Nippon Paint Industrial Coatings), which is the top coat paint, under the same conditions. It was applied, baked and dried. Various conditions and evaluation results are shown in Tables 5A and 5B, respectively.

(Procedure for measuring solubility in artificially acidic seawater)
As an acidic solution containing sulfate roots, the acid salt aqueous solution used in Method B defined by the 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 similar to the artificial seawater specified in JIS G 0594, and using a mixed solution of nitric acid and sulfuric acid specified in Section 4.2.2. The pH was adjusted to 2.5 to prepare artificially acidic seawater.
Next, 100 g of the artificial acidic seawater and 1 g of the pigment were added to a polyethylene narrow-mouthed bottle, a stirrer chip was added, and the mixture was stirred at room temperature for 4 hours. Then, after leaving it 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).

(Procedure for measuring conductivity in pure water)
To a polyethylene narrow-mouthed bottle, 100 g of ion-exchanged water and 1 g of pigment were added, a stirrer chip was added, and the mixture was stirred at room temperature for 4 hours. Then, the conductivity was measured using an electric conductivity meter CM-42X (manufactured by DKK-TOA CORPORATION).

(3) Evaluation items
1) Boiling water resistance test The coated steel sheet obtained above is cut into 5 cm x 10 cm, and the obtained test piece is immersed in boiling water at about 100 ° C. for 2 hours and then pulled up to give the appearance of the coating film on the surface side. , ATM D714-56 (evaluation of flat surface blisters).
Here, ASTM D714-56 evaluates the size (mean diameter) and density of each blister in comparison with a standard photo finish, and indicates 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 this 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.
Further, the coated steel sheet test piece after being immersed in boiling water at about 100 ° C. for 2 hours was evaluated by performing a grid tape adhesion test (grid adhesion test). In the grid tape adhesion test, according to the JIS K 5400 8.5.2 (1990) grid tape method, the gap between the cuts is set to 1 mm, 100 grids are made, and cellophane adhesive tape is adhered to the surface. , The number of grids remaining on the coated surface when peeled off suddenly was investigated.

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

3) Corrosion resistance test The obtained coated steel sheet was cut to a size of 5 cm × 15 cm. At this time, cutting was performed alternately from the front surface and the back surface, and the test pieces were prepared so that the cross section of each test piece had both upper burrs (cut from the back surface) and lower burrs (cut from the front surface).
Next, make a cross cut with a narrow angle of 30 degrees and a cut width of 0.5 mm with a cutter knife so that it reaches the base material in the center of the surface side, seal the upper edge of the painted steel sheet with rust preventive paint, and at the lower end. A 4T bending part (4 plates are removed after processing) is provided.
The 4T bending process is a process in which the surface of the coated plate is turned to the outside, four plates of the same thickness as the coated plate are sandwiched inside, and the coated plate is bent 180 degrees by a vise. After processing, the four plates were removed and used for the test.

A schematic diagram of the coated steel sheet 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 sheet test piece 10. Further, the coated steel sheet test piece 10 has a coating film front surface 11 and a coating film back surface 12.
FIG. 1B is a schematic view showing a cross-cut portion 40 and a 4T bent portion 50 provided on the coated steel sheet test piece 10 used in the corrosion resistance test. Further, the coated steel sheet test piece 10 has an upper burr 21 and a lower burr 31.

Each of the obtained coated steel sheet test pieces was subjected to a composite cycle corrosion test (CCT) according to JIS K 5600-7-9A JASO M609. 120 cycle test (total 960) with (2 hours of 5% saline spray at 35 ° C)-(4 hours of drying at 60 ° C)-(2 hours of standing in a moisture resistance tester with RH of 95% or more at 50 ° C) as one cycle. Time) was done. The state of the edge portion, the cross-cut portion, and the 4T bent portion of the coated steel sheet test piece after this test was evaluated based on the following evaluation method and evaluation criteria. In each case, a score of 4 or higher was evaluated as good.
Equipment used: Composite cycle tester CYP-90 (manufactured by Suga Test Instruments Co., Ltd.)

(Corrosion resistance test: 4T bending part)
The total length of the rusted portion in the 4T bent portion was determined and evaluated according to the following criteria.
5: No rust is observed.
4: White rust is observed, 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 red rust is observed.

(Corrosion resistance test: edge part)
The average value of the edge creep width (blister width) 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 obtained and evaluated according to the following criteria.
5: Blister width is less than 5 mm.
4: Fukure 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: Fukure width is 15 mm or more and less than 20 mm.
1: Fukure width is 20 mm or more.

(Corrosion resistance test: cross cut part)
The corrosion state of the cross-cut part was evaluated by the following criteria based on the ratio of the length of white rust generated in the exposed part of the substrate with a cut width of 0.5 mm and the average value of the left and right blisters width (sum of both sides) of the cross-cut part. ..
5: The ratio of the length of white rust generated in the exposed portion of the substrate is less than 25%, and the blistering width is less than 3 mm.
4: White rust generation length ratio of 25% or more and less than 50% in the exposed part of the substrate and blistering width of 3 m
Less than m.
3: White rust generation length ratio of 50% or more and blister width less than 3 mm in the exposed part of the substrate.
2: White rust generation length ratio of 50% or more and blistering width of 3 mm or more and less than 5 mm in the exposed part of the substrate.
1: White rust generation length ratio of 50% or more and blistering width of 5 mm or more in the exposed part of the substrate.

4) Alkali resistance test
Each of the obtained coated steel sheets was cut into 5 cm × 10 cm, and each test piece was immersed in a 5% aqueous sodium hydroxide solution at 23 ° C. for 48 hours, taken out, washed with water, and dried at room temperature. The painted steel sheet test piece was evaluated for blister on a flat surface 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 sheet 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. The painted steel sheet test piece was evaluated for blister on a flat surface 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 with acidic salt water-drying 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 portion of the obtained test piece in the same manner as in the case of the corrosion resistance test.

(Adjustment of acidic salt water)
As an acidic solution containing sulfate roots, the acid salt aqueous solution used in Method B defined by the 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 similar to the artificial seawater specified in JIS G 0594, and using a mixed solution of nitric acid and sulfuric acid specified in Section 4.2.2. The pH was adjusted to 2.5 to obtain acidic salt water.

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

(Test with acidic salt water: 4T bending part)
The total length of the rusted portion in the 4T bent portion was determined and evaluated according to the following criteria.
5: No rust is observed.
4: White rust is observed, 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 red rust is observed.

(Test with acidic salt water: edge part)
The average value of the edge creep width (blister width) 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 obtained and evaluated according to the following criteria.
5: Blister width is less than 5 mm.
4: Fukure 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: Fukure width is 15 mm or more and less than 20 mm.
1: Fukure width is 20 mm or more.

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

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-preventive properties over a long period of time, and can further form a coating film exhibiting excellent moisture resistance. Moreover, even under acidic environmental conditions, it is possible to form a coating film showing excellent rust prevention properties for a long period of time. Therefore, for example, the generation of rust that may 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, it is possible to suppress or greatly reduce the occurrence of blisters on the coating film.
Further, in the case of the rust-preventive coating composition of the present disclosure, in the object to be coated which can have various shapes, not only the surface of the object to be coated on a flat surface but also, for example, a processed portion, an end face, a cross-cut portion and the like. , The protective effect of the coating film can be sufficiently exhibited.
Here, comparing the chromate-treated test piece shown in Reference Example 1 with the surface-treated steel material of the present invention, the rust-preventive coating composition according to the present invention is equal to or higher than the coating composition containing chromium. Was able 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. Therefore, the formed coating film could not exhibit sufficient rust prevention and moisture resistance.
Comparative Examples 4 to 7 do not contain the magnesium oxide (C) according to the present invention. Therefore, the formed coating film could not exhibit sufficient rust prevention and moisture resistance.

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

10 Painted steel plate test piece 11 Painted surface surface 12 Painted film back surface 20 Upper burr cross section 21 Upper burr 30 Lower burr cross section 31 Lower burr 40 Cross cut part 50 4T Bending part

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 has a lattice constant of less than 0.4214 nm.
A rust preventive 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 of the present disclosure has a magnesium metal ion concentration of 70 ppm or less in an aqueous solution prepared by adding 1 g of the magnesium oxide (C) to 100 g of an artificial acidic sea aqueous solution. Contains magnesium oxide (C).
[3] In one embodiment, the magnesium oxide (C) in the rust preventive coating composition of the present disclosure has a 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. Contains compounds of cm or less.
[4] In one embodiment, the magnesium oxide (C) in the rust preventive coating composition of the present disclosure includes a magnesium fired product fired 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 a 1% by mass aqueous solution in 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 size 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 rust preventive coating composition of the present disclosure is magnesium oxide.
[7] In one embodiment, the coating film-forming resin (A) in the rust-preventive coating composition of the present disclosure is selected from at least a group consisting of an epoxy resin, a polyester resin, an acrylic resin, a urethane resin, and a modified product thereof. Includes one.
[8] In one embodiment, the coating film-forming resin (A) in the rust-preventive 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 resins include urethane resins. 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 rust-preventive 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 resins are It contains at least one selected from the group consisting of ester-based urethane resins, ether-based urethane resins, and carbonate-based urethane resins.
[10] In one embodiment, the coating film-forming resin (A) in the rust-preventive 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 rust-preventive 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 rust-preventive coating composition of the present disclosure is
At least one of the ester-based urethane resin, epoxy resin and polyester resin has a solid acid value of 30 mgKOH / g or less.
[13] In one embodiment, the rust preventive coating composition of the present disclosure contains magnesium with respect to a total of 100 parts by mass of the solid content of the coating film-forming resin (A) and the solid content of the cross-linking agent (B). The oxide (C) is contained 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 applying the rust preventive coating composition to an object to be coated, and curing the coating composition at a temperature of 150 ° C. or higher and 270 ° C. or lower. Provided is a method for producing a rust coating film.

The rust-preventive coating composition of the present disclosure is 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 has a lattice constant of less than 0.4214 nm.
The BET specific surface area is 2.0 m ² / g or less.
By containing the specific magnesium oxide (C), the rust-preventive coating composition of the present disclosure can exhibit excellent rust-preventive properties over a long period of time, and can further 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 has a lattice constant of less than 0.4214 nm.
The BET specific surface area is 2.0 m ² / g or less.

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, and is, for example, zinc magnesium oxide (ZnMgO). , At least one selected from the group consisting of 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 whose composition is represented by MgO. Since the magnesium oxide (C) is an oxide represented by magnesium oxide (MgO), a coating film exhibiting excellent corrosion resistance can be formed.

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, it is possible to form a coating film having excellent rust prevention properties for a longer period of time.
In one embodiment, the BET specific surface area of the magnesium oxide (C) according to the present disclosure is 1.8 m ² / g or less, for example 1.6 m ² / g or less, 1.5 m ^{2 or less.} It may be less than / g.
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, and 1.1 m ² / g or less. It may be there.
By having such a BET specific surface area, it is possible to form a coating film having excellent rust prevention properties for a longer period of time. More specifically, it is possible to form a coating film exhibiting rust prevention properties for a long period of time, and it is possible to suppress or significantly reduce corrosion in an acidic environment for a long period of time.
In the present specification, the BET specific surface area can be measured using, for example, an automatic specific surface area measuring device Gemini VII 23900 (manufactured by Shimadzu Corporation).
Such an effect should not be construed in a specific theory, but it is more effective that the BET specific surface area of the magnesium oxide (C) is within such a range. It is considered that this is because it is possible to suppress the depletion of the corrosion suppressing factor derived from the magnesium oxide (C) with respect to the portion where corrosion can occur, and it is possible to continuously supply this suppressing factor.

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 or more.} It may be / g or more.
By having such a BET specific surface area, it is possible to form a coating film having excellent rust prevention properties for a longer period of time. More specifically, it is possible to form a coating film exhibiting rust prevention properties for a long period of time, and it is possible to suppress or significantly reduce corrosion in an acidic environment for a long period of 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 or more. ^{It is 2} / g or less.
In the present disclosure, the BET specific surface area of the magnesium oxide (C) can be appropriately combined within the above range.

The materials different from the magnesium oxide (C) according to the present disclosure used in the comparative example are shown below.
-Nickel oxide; Nickel oxide powder II Large particle size (manufactured by Kusaka Rare Metal 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 Kagaku Sangyo Co., Ltd.)
-Condensed phosphate: K-WHITE # 82 (manufactured by TAYCA)
・ Calcium vanadate
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.

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 has a lattice constant of less than 0.4214 nm.
A rust preventive coating composition having a BET specific surface area of 2.0 or less. The rust preventive coating composition comprises 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 sea aqueous solution. Item 3. The rust preventive coating composition according to Item 1. The protection according to claim 1 or 2, wherein the magnesium oxide (C) contains a compound having a conductivity of 320 μS / cm or less in an aqueous solution prepared by adding 1 g of the magnesium oxide (C) 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 calcined product calcined at a temperature of 1,000 ° C. or higher. The pH of the magnesium oxide (C) in an aqueous solution prepared by adding 1 g of the magnesium oxide (C) to 100 g of pure water is 8 or more and 12 or less, and the average particle size is 0.5 μm or more and 20 μm or less. The rust preventive coating composition according to any one of claims 1 to 4. The rust preventive coating composition according to any one of claims 1 to 5, wherein the magnesium oxide (C) is magnesium oxide. The coating film-forming resin (A) comprises at least one selected from the group consisting of epoxy resin, polyester resin, acrylic resin, urethane resin and modified products thereof, according to any one of claims 1 to 6. The rust preventive coating composition according to the above. 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) contains at least one selected from the group consisting of urethane resins and modified products thereof, and the urethane resins are selected from ester-based urethane resins, ether-based urethane resins, and carbonate-based urethane resins. The rust preventive coating composition according to any one of claims 1 to 8, which comprises at least one selected from the group. 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. The coating film-forming resin (A) according to any one of claims 1 to 10, which comprises at least one selected from the group consisting of an ester-based urethane resin, an epoxy resin, a polyester resin, and a modified product thereof. Epoxy paint composition. The rust-preventive coating composition according to claim 11, wherein the solid content acid value of at least one of the ester-based urethane resin, the epoxy resin, and the polyester resin is 30 mgKOH / g or less. 1 part by mass or more and 150 parts by mass or less of the magnesium oxide (C) with respect to a total of 100 parts by mass of the solid content of the coating film forming resin (A) and the solid content of the cross-linking agent (B). The rust-preventive coating composition according to any one of claims 1 to 12, which is included in the 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. , How to manufacture rust preventive coating.

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