JP7502152B2 - Water-based anti-rust paint, laminated structure and application method thereof - Google Patents

Description

This disclosure relates to a water-based anti-rust paint for preventing rust from occurring on metal components such as steel materials used in buildings and civil engineering structures, and also to a layered structure formed by a coating film using the water-based anti-rust paint and a method for applying the same.

Conventionally, steel materials have been widely used in buildings, civil engineering structures, etc. However, rust may occur in such steel materials under normal conditions, which not only impairs their aesthetic appearance but may also cause a decrease in the strength of the steel materials. Therefore, it is common to apply rust prevention treatment to the steel materials and then apply a top coat of paint or other finishing agent.
Anti-rust treatments include painting with anti-rust paint, plating, etc. Anti-rust treatments can protect steel materials by blocking substances that cause rust, such as oxygen, water, and salt.

However, some of the anti-rust paint compositions used in the anti-rust treatment contain phosphorus components and transition metals, and may cause eutrophication and heavy metal pollution in rivers and lakes.
Thus, there is an anti-rust paint described in Patent Document 1. This anti-rust paint contains (a) at least one selected from calcium hydroxide, magnesium hydroxide, magnesium oxide, and calcium oxide, and (b) a synthetic resin emulsion, in which the mass of the component (a) is 50 to 150 parts by mass per 100 parts by mass of the non-volatile content of the component (b), and this anti-rust paint has excellent anti-rust properties and is highly safe.

JP 2011-068868 A

However, although the anti-rust paint of Patent Document 1 is highly safe and has anti-rust effects, the finish of the coating film produced by the anti-rust paint may be insufficient, and therefore, when an upper layer such as a topcoat is formed, the finish may be affected, and the adhesion may also be affected.
Furthermore, if the anti-rust paint coating is left for a long period of time, an overlayer material may form on the surface, which may reduce the adhesion and the anti-rust effect.

The water-based anti-rust paint disclosed herein provides a coating film that has a good finish after application, and even if exposed to long periods of time, the coating film is alkaline, dense, and soft, so that the water-based anti-rust paint has good anti-rust effect and adhesion to the upper layer material.

The aqueous anti-rust paint contains a synthetic resin emulsion having a glass transition point of 0°C or less and three components, namely calcium hydroxide, magnesium hydroxide and magnesium oxide, the aqueous anti-rust paint having a solid content of 60 to 80%, a pH of 8 or more and a specific gravity of 1.0 to 1.8, a ratio of the solid content of the synthetic resin emulsion to the three components of 1:1 to 1:5, and an average particle size of the three components of 80 μm or less.
As a result, the finish of the coating film formed after applying the water-based rust-preventive paint is good, and even if the coating film is exposed to light for a long period of time, the coating film is alkaline, dense, and soft, so it has good rust-preventive effect and adhesion to the upper layer material.

The coating film formed by the water-based anti-rust paint is flexible, and the water absorption rate of a 2 mm thick coating film is in the range of 5-20%, so it conforms well to moving substrates such as metals, has few cracks in the coating film, and has a high anti-rust effect. It also has good adhesion to the upper layer material.

By laminating a metal substrate, a coating film formed from a water-based anti-rust paint, and a layer of an upper layer material with a pH range of 7 to 13 and a specific gravity range of 1.0 to 2.1, the coating film formed on the metal substrate has good anti-rust properties even when exposed to long periods of time, and the adhesion between each layer is also sufficient.

By applying a water-based anti-rust paint to a metal substrate and then forming an upper layer of an upper layer material with a pH range of 7 to 13 and a specific gravity range of 1.0 to 2.1, the coating film formed on the metal substrate has good anti-rust effects even when exposed to long periods of time, and the adhesion between each layer is also sufficient.

An embodiment of the present disclosure will be described.
The aqueous anti-rust paint contains a synthetic resin emulsion having a glass transition point of 0°C or less and three components, namely calcium hydroxide, magnesium hydroxide and magnesium oxide, the aqueous anti-rust paint having a solid content of 60 to 80%, a pH of 8 or more and a specific gravity of 1.0 to 1.8, a ratio of the solid content of the synthetic resin emulsion to the three components of 1:1 to 1:5, and an average particle size of the three components of 80 μm or less.

The synthetic resin emulsion is a dispersion of synthetic resin in water, and may be a general one that can be produced by a general polymerization technique such as emulsion polymerization. The synthetic resin may be an acrylic resin, a styrene resin, a polyurethane resin, a silicone resin, a fluorine resin, an epoxy resin, a melamine resin, an alkyd resin, a vinyl chloride resin, a vinyl acetate resin, a polyester resin, a polyether resin, or the like, either alone or in a mixture of two or more kinds.
These constituent monomers may be copolymerized and used.

Among these, those having good miscibility with the three components calcium hydroxide, magnesium hydroxide, and magnesium oxide described below are used.
For this purpose, it is preferable to reduce the content of -COOH groups in the resin composition of the synthetic resin emulsion, which improves the miscibility with the three components, calcium hydroxide, magnesium hydroxide, and magnesium oxide, by reducing the content of -COOH groups.

As the synthetic resin emulsion, it is preferable to use an acrylic synthetic resin emulsion, a urethane synthetic resin emulsion, a silicone synthetic resin emulsion, a fluorine synthetic resin emulsion, or an acrylic silicone synthetic resin emulsion, which have good weather resistance.
This is because the coating film formed after applying the water-based anti-rust paint may be left for a relatively long period of time, and if the coating film deteriorates quickly, its anti-rust effect and adhesion to the upper layer material may decrease. Also, even if the upper layer material peels off and the anti-rust coating film is exposed, or if no upper layer material is provided, the deterioration of the anti-rust coating film can be suppressed and the anti-rust performance can be maintained.

It is preferable that the synthetic resin emulsion has a good drying property. If the drying property is slow, the water in the water-based anti-rust paint will remain in the coating film for a long time, which may cause rust in rare cases. Also, if it rains after application, the coating may be washed away if it is not cured or dried.
The solid content of the synthetic resin is preferably in the range of 15 to 45% by weight based on the solid content of the aqueous anti-rust paint. If it is less than 15% by weight, the coating film becomes brittle, easily absorbs water, and loses flexibility, which may result in a decrease in the anti-rust effect. If it is more than 45% by weight, the coating film becomes easily soiled and its adhesion to the upper layer material may become poor if it is left for a long period of time.

The synthetic resin emulsion must have a glass transition point (hereinafter, Tg) of not more than 0° C. If the Tg is higher than 0° C., the formed coating film will be hard and will have difficulty following the expansion and other movements of the metal substrate, which may result in peeling or cracking of the coating film.
In addition, in winter when the temperature during application falls below 0°C, the film formation of the water-based anti-rust paint after application may be incomplete, and the film-forming effect may not be sufficient.

Furthermore, since the coating film formed is flexible, even if an external force is applied to the surface of the coating film, the coating film is prevented from being damaged.
Furthermore, this Tg is preferably in the range of 0 to -20°C. If it is lower than -20°C, the formed coating film will be easily soiled if left for a long period of time, and adhesion to the upper layer material may be deteriorated.

The three components, calcium hydroxide, magnesium hydroxide, and magnesium oxide, make the water-based anti-rust paint alkaline, and a coating film with excellent anti-rust properties can be obtained, and the adhesion to metal substrates is also good. The storage stability of the water-based anti-rust paint containing these components is also good. In addition, these are easy to obtain and handle, and are highly safe.
By blending these three components, it is possible to form a paint and coating film that is well-balanced in terms of stability, rust prevention effect, etc.

Calcium hydroxide is a white powder that is slightly soluble in water and its aqueous solution is alkaline. Magnesium hydroxide is a hydroxide of magnesium that is almost insoluble in water but is weakly alkaline. Magnesium oxide is an oxide of magnesium that is a white or gray powder.
By adding calcium hydroxide or magnesium hydroxide to the paint, the pH of the paint can be increased, providing the paint with an anti-rust effect. In addition, by adding calcium hydroxide to the paint, the adhesion to the object to be coated, such as a metal substrate, can be improved.

However, when calcium hydroxide is used alone, the coating film formed tends to be brittle and has low strength. For this reason, magnesium hydroxide is added. This increases the strength of the coating film, allowing it to withstand the weight of the upper layer material described below.
Furthermore, the addition of magnesium oxide has the effect of promoting the hardening of the coating film, allowing the next step to proceed more quickly and efficiently, with less cracking of the coating film.

For this reason, calcium hydroxide, magnesium hydroxide, and magnesium oxide must be mixed in a well-balanced manner in a water-based anti-rust paint.
The average particle size of these three components is preferably 80 μm or less in terms of median diameter, so that the finish of the coating film formed after application of the water-based rust-preventive paint is good, and the rust-preventive coating film becomes dense and provides excellent rust-preventive performance.

Furthermore, when this water-based anti-rust paint is applied by spray gun, the nozzle of the spray gun is less likely to be clogged, improving work efficiency.
The median diameter referred to here is a value calculated from the volume-based particle size distribution measured by a laser diffraction method.

The mixing ratio of these three components, calcium hydroxide, magnesium hydroxide, and magnesium oxide, is preferably in the range of calcium hydroxide:magnesium hydroxide = 4:1 to 8:5 with respect to magnesium oxide 1. If it is within this range, a paint and coating film with a better balance of stability, rust prevention effect, etc. can be formed, and workability will be good.
Water-based anti-rust paints containing these compounds may contain ordinary paint additives as required, provided that the effect of the paint is not impaired.

The additives may include various additives that are generally blended into paints, such as surfactants used as defoamers, dispersants, wetting agents, etc.; high boiling point solvents used as film-forming aids, antifreeze agents, etc.; thickeners and leveling agents for adjusting viscosity and stickiness; preservatives, algae inhibitors, fungicides, pH adjusters, crosslinking agents, silane coupling agents, etc.
Furthermore, it is possible to contain a white pigment such as titanium oxide, which is a coloring component, or an extender pigment such as calcium carbonate. It is also possible to add a coloring pigment.

The color pigment may be inorganic, organic or both, and may be used for coloring general paints, such as titanium oxide, carbon black, oxide yellow, red oxide, cyanine blue, cyanine green, etc.
It is also preferable to add additives capable of improving the weather resistance of the coating film, such as a hindered amine light stabilizer, an ultraviolet absorber, and an antioxidant.

The water-based anti-rust paint of the present disclosure is composed of the constituent materials described above.
The water-based anti-rust paint must have a solids content in the range of 60-80%, a pH of 8 or higher, and a specific gravity adjusted to a range of 1.0-1.8, with the ratio of the solids content of the synthetic resin emulsion to the three components adjusted to a range of 1:1 to 1:5.
As a result, the finish of the coating film formed after application of the water-based rust-preventive paint is good, and even if the coating film is exposed to light for a long period of time, the coating film maintains good rust-preventive effect and adhesion to the upper layer material.

The solid content of water-based anti-rust paint is in the range of 60-80%. If it is lower than 60%, the formed coating film becomes porous and sufficient anti-rust effect cannot be obtained. In addition, the drying time of the paint is slow, and the transition to the next process is delayed. If it is higher than 80%, the painting workability is poor, the finish of the coating film is affected, and it may not be possible to obtain a coating film of a certain thickness, and sufficient anti-rust effect cannot be obtained.
Within this range, the coating film has a good finish and can provide sufficient rust prevention effects.

The pH of the water-based anti-rust paint is 8 or more, and if it is lower than this, sufficient anti-rust effect cannot be expected. It is preferably 9 or more, so that sufficient anti-rust effect can be expected even if the coating film contains water.
Next, the specific gravity is in the range of 1.0 to 1.8. If it is lower than 1.0, it is not possible to form a dense coating film, and the coating film will have high water absorption, and sufficient rust prevention effect cannot be achieved. If it is higher than 1.8, the paint becomes heavy, the painting workability is deteriorated, it affects the finish of the coating film, and it may not be possible to obtain a coating film of a certain thickness, and sufficient rust prevention effect cannot be achieved.

The specific gravity is preferably in the range of 1.1 to 1.5, and within this range, a dense coating film can be formed, sufficient rust prevention effect can be obtained, and the finish can be good.
If the ratio of the solid content of the synthetic resin emulsion to the three components is in the range of 1:1 to 1:5, the coating film will have excellent rust-preventive effect and adhesion to the substrate. If the solid content of the synthetic resin emulsion is higher than this range, adhesion will improve but the rust-preventive effect will be poor. If the solid content is lower, conversely, the rust-preventive effect will increase but adhesion and storage stability will decrease.

It is also preferable that the ratio of the solid content of the synthetic resin emulsion to the three components is in the range of 1:2 to 1:4. Within this range, a coating film with a good balance between adhesion and rust prevention effect can be obtained.
The viscosity of this aqueous anti-rust paint is preferably in the range of 10,000 to 30,000 Pa·s as measured with a B-type viscometer, which improves workability during painting, prevents the applied paint from dripping, and forms a uniform coating, resulting in excellent anti-rust properties.

The method for applying the water-based rust-preventive paint of the present disclosure can be carried out using spray coating, a paint roller, a brush, a trowel, etc., and spray coating is particularly preferred when a large area needs to be painted efficiently and uniformly.
The water-based anti-rust paint disclosed herein does not clog spray guns or other spray painting equipment, can efficiently apply a uniform coating, and provides consistent, even anti-rust effects.

The thickness of the coating film of this aqueous anticorrosive paint (thickness after drying) is not particularly limited, but is preferably 50 μm to 3000 μm, and more preferably 100 μm to 1000 μm.
If the thickness is within this range, a rust-preventive coating film with excellent rust prevention properties can be obtained. If the coating film is too thin, a coating film with sufficient rust prevention properties may not be obtained. On the other hand, if the coating film is too thick, sufficient rust prevention properties can be obtained, but the weight of the coating film becomes large, and the weight of the coated substrate becomes large, so it is not preferable to form a thick coating film.

This water-based anti-rust paint is often applied to areas where anti-rust effects are required for metals such as steel used in buildings and civil engineering structures, and to interfaces with other fluid materials such as concrete.
The coating film made of such an anti-rust paint is flexible, the water absorption rate of the coating film of 2 mm thickness is preferably in the range of 5 to 20%, it has good conformability to moving substrates such as metals, there are few cracks in the coating film, and it has a high anti-rust effect.In addition, it has good adhesion to the upper layer material.

This flexibility enables the coating to follow the movement of the substrate and makes the coating less susceptible to cracking and peeling due to such movement, and thus affects the anti-rust effect of the coating.
One indicator of flexibility is the flexibility test of JIS A6909, in which a coating film is formed on a bendable substrate such as a steel plate, and the coating film is bent 90° around a steel rod with a diameter of 10 mm with the coating film facing outward, after which it is confirmed that there are no cracks on the coating film surface.
It is preferable that no cracks occur in this flexibility test. If the flexibility is within this range, the coating has sufficient flexibility to be able to follow the movement of the substrate and maintain the rust-preventing effect of the coating film.

Another method is to apply paint to a certain thickness on release paper, cure it, peel off the release paper, cut it to a certain size, and wrap the coating around a cylinder.The diameter of the cylinder to be wrapped around can be changed to check whether cracks occur in the coating.
Specifically, a coating film is formed on a rectangle measuring 90 mm in length and 180 mm in width so that the coating film is 2 mm thick, and the coating film is then wrapped around different cylinders with diameters of 5, 10, 14, 20, 25 cm, etc., and the flexibility of the coating film is expressed by the diameter at which the coating film cracks.

With this method, when the diameter is small, the coating film is flexible, but when the diameter is large, the coating film is less flexible. Therefore, when the diameter that the coating film can follow is large, the coating film is less flexible and cracks may occur in the coating film that is formed.

The water absorption rate of this coating film is preferably in the range of 5 to 20% for a coating film 2 mm thick. If it is less than 5%, adhesion to the upper layer material may be poor, and if it is more than 20%, the coating film may easily absorb water and cause rust on the metal substrate.
More preferably, the water absorption rate is in the range of 7 to 15% for a coating film with a thickness of 2 mm. This range provides a good balance between the rust prevention effect and the adhesion to the upper layer material. In addition, the coating absorbs the moisture contained in the upper layer material to an appropriate degree, resulting in better adhesion.

Such a coating film is formed on a metal substrate, and an upper layer material is formed on the surface of the coating film. In this case, the coating film formed on the metal substrate has good rust prevention effect even when exposed to long periods of time, and the adhesion between the layers is also sufficient.
Metal substrates include steel materials such as square steel materials, round steel materials, L-shaped steel materials, steel wire materials, and steel plates, rust-proof steel materials in which an anti-rust layer is formed on the surface of the steel material, other metals such as aluminum, and alloys such as stainless steel and galvanized iron. As long as the substrate is made of metal, its use, shape, and the like are not particularly limited.

The aqueous anti-rust paint may be applied directly to the metal substrate, or may be applied after forming an anti-rust layer by plating such as zinc plating or hot-dip galvanization, or by applying zinc-based anti-rust paint such as zinc-rich primer or zinc-rich paint, or an anti-rust paint based on epoxy resin. The surface of the substrate may be treated by shot blasting, scraping, sanding, etc., before application.
It is more preferable to apply a water-based anticorrosive paint after forming the anticorrosive layer in this manner, which can further enhance the anticorrosive effect of the metal substrate.

Many zinc anti-rust paints use inorganic components such as alkyl silicates as binders, but may also use organic components such as epoxy resins, polystyrene resins, rubbers, etc. As epoxy resins, general anti-rust and anti-corrosion resins are used.
Before the zinc anti-rust paint is applied to the surface of the steel material by coating or the like, the surface of the steel material may be subjected to a surface treatment such as shot blasting, scraping, sanding or the like.

The thickness of this anticorrosive layer is not particularly limited and may be appropriately set depending on the purpose, and is often set to 30 μm to 3000 μm, preferably 70 μm to 300 μm.
The upper layer material is a material that protects the coating film formed by the aqueous anti-rust paint or a bonding material with the metal substrate, and examples of such materials include fluid paint, mortar, concrete, etc. This upper layer material preferably has a pH value in the range of 7 to 13 and a specific gravity in the range of 1.0 to 2.1, and can supplement the anti-rust effect of the coating film formed by the aqueous anti-rust paint and suppress the infiltration of water into the coating film even when the coating film formed on the metal substrate is exposed to the atmosphere for a long period of time.

The pH of the upper layer material is preferably in the range of 8.0 to 13.0, which can better supplement the rust-preventive effect of the coating film and provide a good finish when the upper layer material layer is finished with paint.Moreover, the specific gravity is preferably in the range of 1.2 to 2.1, which is easy to form when forming the upper layer material layer and allows the formation of a denser layer.
According to the above embodiment, the following effects can be obtained.

The aqueous anti-rust paint contains a synthetic resin emulsion having a glass transition point in the range of 0 to -20°C, and three components, namely calcium hydroxide, magnesium hydroxide, and magnesium oxide, the aqueous anti-rust paint having a solid content in the range of 60 to 80%, a pH of 9 or more, and a specific gravity in the range of 1.1 to 1.5, a ratio of the solid content of the synthetic resin emulsion to the three components in the range of 1:2 to 1:4, and an average particle size of the three components being 80 μm or less.
As a result, the coating film formed after application of the water-based rust-preventive paint is dense, has a good finish, and is resistant to dirt even when exposed to long periods of time.Even when the coating film contains water, it is alkaline, dense, and soft, so it has a good balance of sufficient rust-preventive effect and adhesion to the upper layer material.

The coating film formed by the water-based anti-rust paint is flexible, and the water absorption rate of a 2 mm thick coating film is in the range of 7 to 15%.
This allows the coating to conform well to moving substrates such as metals, reduces cracks in the coating, and provides a good balance between anti-rust effect and adhesion to the upper layer material. It also absorbs moisture in the upper layer material to provide better adhesion.

A water-based anti-rust paint is applied to a metal substrate having an anti-rust layer formed on the surface thereof, and then an upper layer material layer is formed thereon, the upper layer material having a pH in the range of 8.0 to 13.0 and a specific gravity in the range of 1.2 to 2.1.
This makes it possible to further enhance the rust-preventive effect of the coating film formed on the metal substrate even when the coating film is exposed to the metal substrate for a long period of time, and also ensures sufficient adhesion between the layers, resulting in a denser layer with a good finish.

The synthetic resin emulsion is any one of an acrylic synthetic resin emulsion, a urethane synthetic resin emulsion, a silicone synthetic resin emulsion, a fluorine synthetic resin emulsion, and an acrylic silicone synthetic resin emulsion.
For this reason, when the coating film formed after application of the water-based anti-rust paint is left for a relatively long period of time, the deterioration of the coating film is relatively slow, and the initial performance of the coating film, such as the anti-rust effect and adhesion to the upper layer material, can be maintained for a relatively long period of time. Furthermore, even if the upper layer material peels off and the anti-rust coating film is exposed, or if no upper layer material is provided, the deterioration of the anti-rust coating film can be suppressed, and the anti-rust performance can be maintained.

The solid content of the synthetic resin is in the range of 15 to 45% by weight of the solid content of the water-based anti-rust paint, so that a coating film that is flexible, does not absorb water easily, is strong, and has an anti-rust effect can be formed. In addition, even if the coating film is left for a long period of time, it is difficult to get dirty, and has good adhesion to the upper layer material.
The mixing ratio of calcium hydroxide, magnesium hydroxide, and magnesium oxide is in the range of 4:1 to 8:5 calcium hydroxide:magnesium hydroxide = 1 magnesium oxide, so that a paint and coating film with a better balance of stability, rust prevention effect, etc. can be formed, and workability is improved.

The viscosity of the water-based anti-rust paint is in the range of 10,000 to 30,000 Pa·s when measured with a B-type viscometer, which improves workability during painting, prevents the applied paint from dripping, and forms a uniform coating, resulting in excellent anti-rust properties.
The thickness of the coating film of this water-based anti-rust paint (thickness after drying) is in the range of 100 to 1000 μm, which is appropriate in terms of weight and makes it possible to obtain an anti-rust coating film with excellent anti-rust properties.

The above embodiment will be described in more detail below. The formulation of the water-based anti-rust paint is exemplified below.
(Formulation Example 1)
Synthetic resin emulsion: Acrylic silicone copolymer resin emulsion, solid content 50% by weight, glass transition point -15°C, 200.0% by weight
Calcium hydroxide 180.0% by weight
Magnesium hydroxide 90.0% by weight
Magnesium oxide 30.0% by weight
Thickener (cellulose-based (methylcellulose)) 3.0% by weight
Defoamer (silicone type) Solid content 10% by weight 2.0% by weight
Blended water 50.0% by weight
Total 555.0% by weight

The solid content of this aqueous anti-rust paint was 72.6% by weight, its pH was 10, and the paint specific gravity was 1.7. The resin content in the solid content of the aqueous anti-rust paint was 24.8% by weight.
The total of the three components (calcium hydroxide, magnesium hydroxide, magnesium oxide) was 300% by weight relative to 100% by weight of the solid content of the synthetic resin emulsion. The ratio of the three components was calcium hydroxide:magnesium hydroxide:magnesium oxide=6:3:1, and the average particle size of these three components was 70 μm.

This water-based anti-rust paint was applied onto a release paper to form a coating film of 2 mm thickness, and a coating film was obtained as a test piece of 50 mm square. The water absorption rate of this coating film after 24 hours was measured and confirmed to be 10% by weight.
The flexibility of a similar 2 mm thick coating film was also confirmed by carrying out a flexibility test according to JIS A 6909:2014 7.25, which confirmed that no cracks were generated on the coating film surface, and confirmed that the coating film had flexibility.

(Mixture Example 2, Mixture Example 3)
Formulation Example 2 was prepared by blending only calcium hydroxide from Formulation Example 1, and Formulation Example 3 was prepared by omitting magnesium oxide from Formulation Example 1.
The solids content of Formulation Example 2 was 65.1% by weight, the pH was 8, the paint specific gravity was 1.6, and the solids content in the paint was 35.3% by weight.
The solids content of Formulation Example 3 was 71.1% by weight, the pH was 10, the paint specific gravity was 1.7, and the solids content in the paint was 26.8% by weight.

(Confirmation of the rust prevention effect, adhesion, and drying properties of Mixture Examples 1 to 3)
The paints of Formulation Examples 1, 2 and 3 were examined for their rust-preventing effect, adhesion to steel plates and drying properties of the coating film.
The paints of Formulation Examples 1 to 3 were applied to three iron plates at a thickness of 2 mm each, and the drying properties were checked. The drying properties were checked by touching the applied paint with a finger.

Compared to Mixture Example 1, Mixture Examples 2 and 3 dried more slowly. This confirmed the difference caused by the presence or absence of magnesium oxide. Next, an adhesion test was conducted to check the adhesion of the paint-coated test specimens that had been left to cure for one week. This adhesion test was conducted in accordance with JIS A 6909:2014 7.10, using a Construction Research Institute tensile tester.

The adhesion of all the test pieces was good, at 0.5 N/ ^mm2 or more. However, the coating film of Blend Example 2 was strong, but felt brittle. This was because magnesium hydroxide was not blended.
In addition, the test specimens after curing were submerged in water and observed for the occurrence of rust on the coating surface, but no rust was observed on any of the test specimens.

From this test, it was found that the coating film made from the water-based anti-rust paint of Formulation Example 1 exhibits an anti-rust effect by raising the pH of the paint due to the presence of calcium hydroxide and magnesium hydroxide in the paint, and that the inclusion of calcium hydroxide in the paint also increases the strength of the coating film and provides sufficient adhesion to the object being coated.
It was also confirmed that the addition of magnesium oxide had the effect of promoting the hardening of the coating film.

(Formulation Example 4)
The calcium hydroxide and magnesium hydroxide of Blend Example 1, which had an average particle size of 100 μm, were used to confirm the finish. The properties of the paint were the same as those of Blend Example 1.
The paints of Formulation Examples 1 and 4 were applied to a thickness of 2 mm on the prepared iron plate and dried to form the upper layer material. A water-based acrylic emulsion paint was applied to this upper layer material, and the finish was confirmed. The application method was a spray gun.
In terms of finish, the coating film of Formulation Example 4 had a rougher surface condition than that of Formulation Example 1, while the coating film of Formulation Example 1 had a better finish.

(Formulation Example 5)
Mixture Example 5 was prepared by changing the amounts of calcium hydroxide, magnesium hydroxide, and magnesium oxide to 90.0% by weight, 45.0% by weight, and 15.0% by weight, respectively, from Mixture Example 1, and adjusting the paint solids content to 62.5% by weight.
The pH of this paint was 8, and the specific gravity of the paint was 1.3. The resin content in the solid content of the water-based anti-rust paint was 39.5% by weight.

The total of the three components (calcium hydroxide, magnesium hydroxide, magnesium oxide) was 150% by weight relative to 100% by weight of the solid content of the synthetic resin emulsion. The ratio of the three components was calcium hydroxide:magnesium hydroxide:magnesium oxide=6:3:1, and the average particle size of these three components was 70 μm.
The water absorption rate was measured and found to be 5% by weight.

(Formulation Example 6)
Mixture Example 6 was prepared by changing the amounts of calcium hydroxide, magnesium hydroxide, and magnesium oxide to 288.0% by weight, 144.0% by weight, and 48.0% by weight, respectively, from Mixture Example 1, and adjusting the paint solids content to 79.3% by weight.
The pH of this paint was 10, and the specific gravity of the paint was 1.8. The resin content in the solid content of the water-based rust-preventive paint was 17.1% by weight.

The total amount of the three components (calcium hydroxide, magnesium hydroxide, magnesium oxide) was 480% by weight based on 100% by weight of the solid content of the synthetic resin emulsion. The ratio of the three components was calcium hydroxide:magnesium hydroxide:magnesium oxide=6:3:1, and the average particle size of these three components was 70 μm.
The water absorption rate was measured and found to be 20% by weight.

The paints of Formulation Examples 1, 5, and 6 were tested in accordance with JIS K 5551:2018 (rust-preventive paint for structures) in accordance with 7.5 (low-temperature stability), 7.7 (painting workability), 7.8 (appearance of coating film), 7.12 (resistance to falling weight), 7.13 (adhesion), and 7.17 (cyclic corrosion resistance).
In addition, the suitability for topcoating was confirmed for water-based acrylic emulsion resin paint and mortar, which are common top layer materials. The confirmation method was to apply the paint of the formulation example to an iron plate, harden and dry it, form the top layer material, and then cure for 7 days to prepare the test specimen.

The water-based acrylic emulsion resin paint had a pH of 8 and a specific gravity of 1.2. The mortar had a pH of 13 and a specific gravity of 2.1.
After the test specimens were cured, the surface layers of the test specimens were visually inspected, and then an adhesion test was carried out using a Construction Research Institute type tensile tester in accordance with JIS A 6909 7.9 as described above.

However, the paints of Formulation Examples 1, 5 and 6 were applied in one coat, and the thickness of the dried coating film was 100 μm.
As a result of the test, all the paints were stable without any deterioration in 7.5 (low temperature stability). As for 7.7 (paintability), all the paints had no problems and were free of any problems.

Regarding 7.8 (appearance of the coating), all the coatings had a smooth finish, and there were no particular problems or impediments.
There were no particular problems with 7.13 (adhesion), and all adhesion was good. Similarly, there were no particular problems with 7.17 (cyclic corrosion), and no rust, blistering, cracking, or peeling was observed on the coating of any of the three test pieces after 120 cycles.

Regarding 7.12 (resistance to falling weight), no cracking or peeling of the coating was observed.
The suitability of the topcoat was examined by visual inspection and adhesion tests. The results were good, with no abnormalities such as cracks in the topcoat being found.

In the adhesion test, it was confirmed that the paint layer of all test specimens underwent cohesive failure, and good test results were obtained.

Claims (4)

An aqueous anti-rust paint containing a synthetic resin emulsion with a glass transition point of 0°C or less and three components, calcium hydroxide, magnesium hydroxide, and magnesium oxide, in which the solid content of the aqueous anti-rust paint is in the range of 60-80%, the pH is 8 or more, the specific gravity is in the range of 1.0-1.8, the ratio of the solid content of the synthetic resin emulsion to the three components is in the range of 1:1-1:5, and the average particle size of the three components is 80μm or less. An aqueous anti-rust paint according to claim 1, in which the coating film formed is flexible and the water absorption rate of a 2 mm thick coating film is in the range of 5 to 20%. A laminated structure in which a metal substrate, a coating film formed by the water-based anti-rust paint according to claim 1 or claim 2, and a layer of an upper layer material having a pH in the range of 7 to 13 and a specific gravity in the range of 1.0 to 2.1 are laminated. A method for applying an aqueous rust-preventive paint, comprising the steps of: applying the aqueous rust-preventive paint according to claim 1 or 2 to a metal substrate; and then forming an upper layer material layer having a pH in the range of 7 to 13 and a specific gravity in the range of 1.0 to 2.1.