KR101797116B1 - Moisture curing protective coating composition with zinc flake - Google Patents

Abstract

The present invention relates to a moisture curing type coating composition which comprises a flake shaped zinc powder, diphenyl methane diisocyanate based prepolymer, zinc phosphate (Zn_3(PO_4)_2), p- toluenesulfonyl isocyanate, triethyl orthoformate, solvents, and other additives. The moisture curing type coating composition of the present invention has excellent adhering force, abrasion resistance, solvent resistance, and weather resistance. The moisture curing type coating composition of the present invention can be applied in an environment of Celsius below zero (-5C), high temperature (50C) and high humidity (RH 30 to 90%). The present invention is a moisture curing type coating composition comprising: 10 to 30 wt% of a flake shaped zinc power; 30 to 60 wt% of diphenyl methane diisocyanate based prepolymer; 1 to 10 wt% of zinc phosphate (Zn_3(PO_4)_2); 1 to 5 wt% of p-toluenesulfonyl isocyanate; 1 to 5 wt% of triethyl orthoformate; and 10 to 40 wt% of solvents.

Description

[0001] MOISTURE CURING PROTECTIVE COATING COMPOSITION WITH ZINC FLAKE [0002]

The present invention relates to a conventional coating composition for preventing metal from corrosion. More specifically, the present invention uses zinc, which is more ionized than iron, as a metal pigment for cathodic protection of iron on a locally generated bleaching site to serve as a sacrificial anode to prevent corrosion of iron But it is also possible to use a moisture-curing polyurethane resin to react with water in the rust to react with water in the rust to form a coating on the surface through dehydration and amine-forming reaction, thereby obtaining a coating film having excellent durability ≪ / RTI > Zinc has better anticorrosive properties because it has a larger surface area when zinc flake is used than spherical zinc dust.

Iron is used in many structures such as steel structures, steel bridge, ships and tanks. Since iron is rusted when it comes into contact with water, it is the most common and easy way to prevent water from coming into contact with iron by painting or plating. Therefore, in order to improve durability, a high performance heavy-duty paint is widely used in many structures such as steel structures, steel bridge, ship, tank and the like. However, in various corrosive environments, the paint has to be peeled off due to external impact or aging, and the iron exposed to moisture is locally corroded. In order to prevent further corrosion of corroded steel, proper repair coating should be applied. In order to perform the repair coating, firstly, the rust removal should be performed to remove the rust on the locally generated bleached parts. However, it is time-consuming to do so, and sometimes the person doing the picking operation may be exposed to danger (eg, falling). In addition, when the rust is removed by sand paper or the like in order to perform the degreasing work, the paint may peel off in the process.

Therefore, there is a need for a conventional coating agent which can be applied without peeling off the locally generated bleaching site and coating on the old film. The present invention provides an anticorrosive paint excellent in adhesion and durability even when coated on a bare area without degreasing. The present invention is to provide an anticorrosive paint for effectively preventing corrosion of iron by using a cathode-type principle and a moisture-curing polyurethane resin.

In order to solve the above problems, the moisture curing anticorrosive coating composition of the present invention is characterized in that it contains zinc oxide, diphenylmethane diisocyanate based prepolymer, zinc phosphate (Zn ₃ (PO ₄ ) ₂ ), p P-toluenesulfonyl isocyanate, triethylorthoformiate, a solvent, and other additives. The present invention may further include magnesium powder.

The moisture curing anticorrosive coating composition of the present invention is cured by moisture in the rust to form a coating film having excellent adhesion and crosslinking density at the bleaching site. The moisture curable anticorrosive coating composition of the present invention prevents corrosion and yellowing of iron by using zinc and zinc phosphate together. The water-curing anticorrosive coating composition of the present invention is a coating composition for a moisture-curing type, which prevents p-toluenesulfonyl isocyanate and triethylorthoformiate from self-curing by removing water contained in raw materials, To prevent hardening, so that the storage stability is excellent. The moisture curing anticorrosive coating composition of the present invention can contain magnesium, which is a strong reducing agent, so that iron oxide can be reduced to iron to more effectively prevent corrosion of iron.

The water-curing anticorrosion coating composition of the present invention is excellent in adhesion and can also be applied to an old film. The moisture curing type coating composition of the present invention is excellent in abrasion resistance, solvent resistance and weather resistance. The moisture curing anticorrosive coating composition of the present invention can be applied even in an environment of minus (-5 캜), high temperature (50 캜), and high humidity (RH 30 to 90%). The water-curing anticorrosive coating composition of the present invention is one-part type, which is easy to apply.

FIG. 1 is a photograph showing the comparison of the results of outdoor exposure corrosion resistance test when a flake-shaped aluminum powder and a flaked zinc powder were used in a composition to which zinc phosphate was not added.
FIG. 2 is a photograph comparing the results of outdoor exposure corrosion resistance test when zinc phosphate is added to a composition using a pigmented zinc oxide as a pigment and when zinc phosphate is not added. FIG.
Fig. 3 is a photograph showing the comparison of the results of the outdoor exposure corrosion resistance test of a composition to which zinc phosphate was added while using a flake-like aluminum powder and a composition to which zinc phosphate was added while using a flaky zinc oxide as a pigment.
FIG. 4 is a photograph showing a comparison of the results of the salt spray corrosion resistance test of a composition to which zinc phosphate was added while using a flake-like aluminum powder and a composition to which zinc phosphate was added while using a flake-like zinc oxide as a pigment.
FIG. 5 is a photograph comparing the results of the outdoor exposure corrosion resistance test of a composition using a flaky pinhole and a composition using a flaky pinhole and a magnesium powder together.

The first embodiment of the present invention is a method for producing a polyisocyanate composition comprising a flaky zinc oxide, a diphenylmethane diisocyanate based prepolymer, zinc phosphate (Zn ₃ (PO ₄ ) ₂ ), p-toluenesulfonyl isocyanate (p- toluenesulfonyl isocyanate), triethylorthoformiate, and a solvent.

In a second embodiment of the present invention, there is provided a resin composition comprising 10 to 30% by weight of a flake retardant, 30 to 60% by weight of a diphenylmethane diisocyanate based prepolymer, zinc phosphate (Zn ₃ (PO ₄ ) ₂ ) 1 to 10% by weight, 1 to 5% by weight of p-toluenesulfonyl isocyanate, 1 to 5% by weight of triethylorthoformiate, and 10 to 40% Based coating composition.

The third embodiment of the present invention is a moisture curing type coating composition wherein the NCO content of the diphenylmethane diisocyanate based prepolymer is 10 to 20% by weight in the first and second embodiments.

The fourth embodiment of the present invention is a moisture curable anticorrosion coating composition according to any one of the first to third embodiments, wherein the particle size of the flaked zinc oxide is 9 to 15 탆.

A fifth embodiment of the present invention is the moisture curable anticorrosion coating composition according to any one of the first to fourth embodiments, wherein the solvent is an aromatic hydrocarbon, an ester, or a combination thereof.

The sixth embodiment of the present invention is a moisture curing anticorrosive coating composition further comprising magnesium powder in the first to fifth embodiments.

The seventh embodiment of the present invention is a moisture curing anticorrosive coating composition further comprising 1 to 10% by weight of magnesium powder in the first to fifth embodiments.

The corrosion of iron (rust) occurs through the following reaction.

1. Oxidation of Iron

Fe - > Fe < ^{2 +} & ^{gt ;} + 2e ^-

Fe ^{2 + -} > Fe ^{3 +} + e ^-

2. Reduction of oxygen

O ₂ + 2H ₂ O + 4e ^- ? 4OH ^-

3. Generation of rust

^{2Fe 3 + + 6OH - → Fe} 2 O 3 · 3H 2 O

Therefore, water and oxygen are necessary for the corrosion of iron.

Connecting metals that are more ionized than iron to iron can help prevent iron from being oxidized. When a metal that has a tendency to ionize more than iron is supplied with iron, the oxidation of iron is prevented. It is called cathodic protection to prevent corrosion of iron by connecting a metal having a tendency to ionization more than iron to iron.

The moisture curing anticorrosion coating composition of the present invention comprises a flaky pigment as a rust-preventive pigment. Zinc has a lower ionization tendency than aluminum. Surprisingly, however, the moisture-curing anticorrosive coating compositions of the present invention have a better cathodic effect when zinc is used as the pigment than aluminum.

Magnesium has a tendency to ionize more than zinc and is easy to bond with oxygen and has strong reducing action. Therefore, it can be combined with oxygen in the rust to reduce the rust, and the sacrificial anode can prevent corrosion of the iron, which is the cathode. The moisture-curing anticorrosion coating composition having the composition of the present invention is more excellent in the effect of iron in combination with zinc and magnesium as pigments.

Coating of the inventive moisture curable antistatic coating composition with zinc halide coatings results in zinc contact with iron. Then, zinc tends to ionize more than iron, so zinc is oxidized and releases electrons. This electron can prevent the oxidation of iron by supplying electrons to the iron.

Since the zinc flakes contained in the moisture curing type coating composition of the present invention have a surface area larger than spherical zinc dust, the contact area with iron can be increased. Thus, the cathode method effect can be enhanced. If the size of the particles is too small, the unit price of the raw material becomes high. If the particle size is too large, the appearance becomes rough and the rustproofing property becomes poor.

The water-curing anticorrosive coating composition of the present invention may contain 10 to 30 wt%, preferably 15 to 25 wt%, more preferably 15 to 20 wt% of zinc oxide powder.

The moisture curing anticorrosive coating composition of the present invention comprises a diphenylmethane diisocyanate based prepolymer. The diisocyanate prepolymer may serve as a binder. The diphenylmethane diisocyanate prepolymer reacts with moisture in the rust to form a coating film having high crosslinking density through the dehydration reaction, excellent adhesion to the surface and the old film, good hardness and excellent durability. The coating film formed on the bleaching site prevents the corrosion of iron by blocking the supply of water and oxygen to the iron.

The reason why the anticorrosive coating composition of the present invention is a moisture curing anticorrosion coating composition is that the diphenylmethane diisocyanate prepolymer reacts with moisture in the rust to cause a curing reaction. The process in which the diphenylmethane diisocyanate prepolymer reacts with moisture in the rust to form a coating film is as follows.

(5) The reaction of (1) to (4) actually contributes to the hardening reaction of the coating film. Since carbamic acid decarboxylase decomposition reaction of (2) is much faster than carbamic acid producing reaction of (1), carbamic acid produced by the reaction of water and isocyanate does not exist and proceeds to an amine generating reaction accompanied by generation of carbon dioxide gas . Therefore, the first step of the moisture curing reaction of the diphenylmethane diisocyanate prepolymer can be regarded as an amine-forming reaction in appearance. The curing of the actual coating film takes place by the generation of urea bonds of ③ or the generation of biuret bonds of ④ (two urea bonds).

When the NCO content of the diphenylmethane diisocyanate prepolymer is increased, the flexibility and abrasion resistance of the coating film are improved, but the hardness and solvent resistance are poor. In the present invention, the NCO content of the diphenylmethane diisocyanate prepolymer is preferably 10 to 20% by weight, more preferably 15 to 20% by weight.

The water-curing anticorrosive coating composition of the present invention may contain 30 to 60 wt%, preferably 40 to 60 wt%, more preferably 40 to 50 wt% of the diphenylmethane diisocyanate prepolymer.

The diphenylmethane diisocyanate prepolymer also reacts with water contained in the air or moisture contained in the raw material, and the curing reaction can proceed. In order to prevent the undesired curing reaction from proceeding, the moisture curing type coating composition of the present invention includes a moisture removing agent. The inventors of the present invention have found that when p-toluenesulfonyl isocyanate and triethylorthoformate are used together in various water-removing agents, the storage stability can be improved remarkably.

The p-toluenesulfonyl isocyanate reacts with water in the raw material or air to form p-toluenesulfonamide and releases carbon dioxide gas. Triethyl orthoformiate reacts with raw materials or moisture in the air to form formic acid ethyl ester and produce ethanol. The moisture curable anticorrosive coating composition of the present invention may comprise 1 to 5% by weight of p-toluenesulfonyl isocyanate. The moisture curing type coating composition of the present invention may contain 1 to 5 wt% of triethyl orthoformiate.

The moisture curing type coating composition of the present invention comprises zinc phosphate (Zn ₃ (PO ₄ ) ₂ ). Zinc phosphate can act as a corrosion inhibitor. Zinc phosphate can inhibit the occurrence of pin point rust and white rust. The moisture curing anticorrosive coating composition of the present invention may contain 1 to 10 wt%, preferably 1 to 7 wt%, more preferably 2 to 5 wt% of zinc phosphate.

The moisture curing type coating composition of the present invention may comprise a solvent. The solvent may be selected from aromatic hydrocarbons, esters, or combinations thereof. As aromatic hydrocarbons, for example, solvent naphtha can be used. As the ester, for example, isobutyl acetate can be used.

The water-curing anticorrosive coating composition of the present invention may contain 10 to 40 wt%, preferably 10 to 30 wt%, more preferably 20 to 30 wt% of the solvent. When the moisture curing type coating composition of the present invention comprises a combination of an aromatic hydrocarbon and an ester, the aromatic hydrocarbon may be contained in an amount of 5 to 25% by weight, preferably 10 to 20% by weight, the ester may be contained in an amount of 5 to 15% 5 to 10% by weight.

The moisture curing type coating composition of the present invention may comprise magnesium powder. Magnesium is a powerful reducing agent with a very high ionization tendency. Magnesium can prevent corrosion of iron by supplying electrons to iron oxide. The moisture curing anticorrosive coating composition of the present invention may contain 1 to 10 wt%, preferably 3 to 10 wt%, and more preferably 5 to 10 wt% of magnesium powder. If the magnesium powder is too small, there is a danger of explosion, and if it is too large, the appearance will deteriorate. Therefore, it is preferable to use particles of 325 mesh to 600 mesh.

The moisture curable antifouling compositions of the present invention may include other components commonly used in moisture cure antifouling coating compositions. Other ingredients include thickeners, dispersants, anti-settling agents, antifoaming agents, and ultraviolet absorbers. As the thickening agent, for example, ethyl celluloses can be used. As the dispersing agent, for example, soyabean lecithin can be used. As the precipitation preventing agent, for example, bentonite clay may be used. As the antifoaming agent, for example, a poly siloxane solution can be used. As the ultraviolet absorber, for example, HALS (Hindered Amine Light Stabilizer) may be used.

Example

1. Evaluation of corrosion resistance

46 parts by weight of a diphenylmethane diisocyanate prepolymer, 15 parts by weight of a zinc oxide powder, 3 parts by weight of zinc phosphate, 2 parts by weight of p-toluenesulfonyl isocyanate, 1 part by weight of triethyl orthoformate, 10 parts by weight of solvent naphtha, 10 parts by weight of an antifoaming agent, and 10 parts by weight of a precipitation inhibitor bentonite clay (Example 1 composition). 10 parts by weight of the precipitation inhibitor was obtained by swelling the bentonite clay solid in a solvent, and the actual amount of the bentonite clay solids was 1 part by weight.

The composition of Comparative Example 1 was prepared in the same manner as in Example 1 except that flaky aluminum powder was used instead of zinc oxide and zinc phosphate was not used.

The composition of Comparative Example 2 was prepared in the same manner as in Example 1 except that zinc phosphate was not used.

The composition of Comparative Example 3 was prepared in the same manner as in Example 1 except that the flaky aluminum powder was used instead of the flake-like termination.

The compositions of the above compositions are shown in Table 1 below.

Composition Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Diphenylmethane diisocyanate prepolymer 46 46 46 46 The end of the year - 15 - 15 Flake aluminum powder 15 - 15 - Zinc phosphate - - 3 3 p-toluenesulfonyl isocyanate 2 2 2 2 Triethyl orthoformate One One One One Solvent naphtha 10 10 10 10 acetate 10 10 10 10 Precipitation inhibitor 10 (1) 10 (1) 10 (1) 10 (1)

The above compositions were used for outdoor weathering corrosion test and salt spray corrosion resistance test.

1) Outdoor exposure corrosion resistance test

- Material and Thickness of Specimen: Steel drum, 2T (2T is 2mm in thickness)

- Coating method: 1 coat of roller with dry film thickness of 40-50 ㎛

- Test method and period: Outdoor exposure, 24 months

The test results are shown in Table 2 below.

Comparative Example  1 and Comparative Example  2 comparison ( Zinc Phosphate  In the composition not added, the flaky aluminum powder and Single phase Yeah  Corrosion resistance comparison)

Composition Comparative Example 1 Comparative Example 2 result Cutting pericarp Cutting around fine chitosan

As shown in Fig. 1, the composition of Comparative Example 1 in which zinc phosphate was not added while using a flake-shaped aluminum powder was found to be frayed around the cutting area. The composition of Comparative Example 2, in which zinc oxide was used as a pigment and zinc phosphate was not added, also produced considerable microfibrillation around the cut.

Comparative Example  2 and Example  1 comparison ( Zinc Phosphate  Comparison of Corrosion Resistance According to Addition and Absence)

Composition Comparative Example 2 Example 1 result Pinpoint Speech Pinpoints Almost none

As shown in Fig. 2, the composition of Comparative Example 2 in which zinc oxide was used as a pigment but zinc phosphate was not added showed a lot of pin point firing toward the lower side of the specimen. However, the composition of Example 1 in which zinc oxide was used as a pigment and zinc phosphate was added showed little pin point fogging as shown in Fig.

Comparison between Comparative Example 3 and Example 1 (in the composition to which zinc phosphate was added, the flaky aluminum powder and Single phase Yeah  Corrosion resistance comparison)

Composition Comparative Example 3 Example 1 result Yellowing Good condition

As shown in FIG. 3, the composition of Comparative Example 3 in which zinc phosphate was added while using a flake-shaped aluminum powder was better than Comparative Examples 1 and 2, but yellowing occurred. However, the yellowing phenomenon did not occur in the composition of Example 1 in which zinc phosphate was added while using a pinhole zinc oxide as a pigment.

2) Salt spray corrosion resistance test

Example 1 Composition and Comparative Example 3 The composition was applied to the pretreated test piece in a thickness of 50 占 퐉 on the dried coating film, and the urethane top coat was painted thereon with a thickness of 50 占 퐉 on the dried coating film.

- Specimen material and thickness: Cold rolled steel plate, 2T

- Pretreatment: St3 (St3 means pretreatment to remove rust using power tool)

- Test method and duration: Salt spray (ASTM D-3359), 1,200 hours

Comparative Example  3 and Example  1 comparison ( Single phase  Aluminum powder and Single phase Yeah  Corrosion resistance comparison)

Composition Comparative Example 3 Example 1 result Cutting pericarp Almost none

As shown in FIG. 4, the composition of Comparative Example 3 in which zinc phosphate was added while using a flake-like aluminum powder as a pigment had a large amount of flaking around the cutting portion. However, the composition of Example 1, in which zinc phosphate was added while using a pinhole-type zinc oxide as a pigment, hardly peeled around the cutting as shown in FIG.

2. Physical property evaluation

The physical properties of the compositions of Comparative Examples 1 to 3 and of the composition of Example 1 were evaluated. The adhesion was measured by a cross-cut method according to the test standard ASTM D 3359, and the evaluation method was as follows.

Impact resistance was measured using a DuPont impact tester (500 grams of weight, 1/4 inch rod, drop height 50 cm). The results are shown in Table 6 below.

Composition Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Adhesiveness 5 4 4 5 Pencil hardness 2H 1H 1H 2H Impact resistance Good Good Good Good

As shown in Table 6 above, the moisture curing type coating composition of the present invention has excellent physical properties.

3. Storage stability evaluation

46 parts by weight of a diphenylmethane diisocyanate prepolymer, 15 parts by weight of a zinc oxide powder, 3 parts by weight of zinc phosphate, 2 parts by weight of p-toluenesulfonyl isocyanate, 1 part by weight of triethyl orthoformate, 10 parts by weight of solvent naphtha, 10 parts by weight of an antifoaming agent, and 10 parts by weight of a precipitation inhibitor bentonite clay (Example 1 composition). 10 parts by weight of the precipitation inhibitor was obtained by swelling the bentonite clay solid in a solvent, and the actual amount of the bentonite clay solids was 1 part by weight.

46 parts by weight of a diphenylmethane diisocyanate prepolymer, 15 parts by weight of a zinc oxide powder, 3 parts by weight of zinc phosphate, 2 parts by weight of p-toluenesulfonyl isocyanate, 1 part by weight of triethyl orthoformate, 10 parts by weight of solvent naphtha, 10 parts by weight of an antistatic agent bentonite clay, and 2 parts by weight of zeolite (3 ANGSTROM) (Example 2 composition). 10 parts by weight of the precipitation inhibitor was obtained by swelling the bentonite clay solid in a solvent, and the actual amount of the bentonite clay solids was 1 part by weight.

, 46 parts by weight of diphenylmethane diisocyanate prepolymer, 15 parts by weight of zinc oxide powder, 3 parts by weight of zinc phosphate, 10 parts by weight of solvent naphtha, 10 parts by weight of acetate, 10 parts by weight of a precipitation inhibitor bentonite clay and 3 parts by weight of zeolite (Comparative Example 4 composition). ≪ tb > < TABLE > 10 parts by weight of the precipitation inhibitor was obtained by swelling the bentonite clay solid in a solvent, and the actual amount of the bentonite clay solids was 1 part by weight.

46 parts by weight of a diphenylmethane diisocyanate prepolymer, 15 parts by weight of zinc oxide as a flake, 3 parts by weight of zinc phosphate, 2 parts by weight of p-toluenesulfonyl isocyanate, 10 parts by weight of solvent naphtha, 10 parts by weight of acetate, (Comparative Example 5 composition). ≪ tb > < TABLE > 10 parts by weight of the precipitation inhibitor was obtained by swelling the bentonite clay solid in a solvent, and the actual amount of the bentonite clay solids was 1 part by weight.

 The compositions of the above compositions are shown in Table 7 below.

Composition Comparative Example 4 Comparative Example 5 Example 1 Example 2 Diphenylmethane diisocyanate prepolymer 46 46 46 46 The end of the year 15 15 15 15 Zinc phosphate 3 3 3 3 p-toluenesulfonyl isocyanate - 2 2 2 Triethyl orthoformate - - One One Solvent naphtha 10 10 10 10 acetate 10 10 10 10 Precipitation inhibitor 10 (1) 10 (1) 10 (1) 10 (1) 3 A molecular sieve 3 - - 2

The in-vessel state and viscosity were evaluated from immediately after manufacture to 1 year after the preparation of the compositions. The results are shown in Table 8 below.

Composition Comparative Example 4 Comparative Example 5 Example 1 Example 2 In container
condition



Immediately after manufacture Good Good Good Good A week later swelling Good Good Good After 1 month Gelling swelling Good Good 6 months later swelling Good Good 1 year later swelling Good Good Viscosity
(KU, 25 DEG C)



Immediately after manufacture 78 76 75 78 A week later 120 85 76 77 After 1 month Not measurable 90 78 76 6 months later Not measurable 92 80 78 1 year later Not measurable 92 82 77

The composition of Comparative Example 4 in which p-toluenesulfonyl isocyanate and triethyl orthoformate were not added began to swell after one week from the preparation, and gelatinized after one month. Therefore, it was impossible to measure the viscosity after one month. The composition of Comparative Example 5 in which only p-toluenesulfonyl isocyanate was added began swelling after one month from the production. After one month, the viscosity measured at 25 ° C was higher than 90 KU. However, the composition of Example 1 in which both p-toluenesulfonyl isocyanate and triethyl orthoformate were added did not swell after one year, and the viscosity was good at 82 KU after one year. The composition of Example 2, in which p-toluenesulfonyl isocyanate and triethyl orthoformate were added in addition to zeolite (3 Å), also did not swell after one year, and the viscosity was good at 77 KU after one year.

4. Evaluation of corrosion resistance according to addition of magnesium powder

The composition of Example 3 was prepared in the same manner as in Example 1 except that 10 parts by weight of 15 parts by weight of zinc oxide powder was used and 5 parts by weight of magnesium powder was further added.

The compositions of the above compositions are shown in Table 9 below.

Composition Example 1 Example 3 Diphenylmethane diisocyanate prepolymer 46 46 The end of the year 15 10 Flake aluminum powder - - Zinc phosphate 3 3 p-toluenesulfonyl isocyanate 2 2 Triethyl orthoformate One One Solvent naphtha 10 10 acetate 10 10 Precipitation inhibitor 10 (1) 10 (1) magnesium - 5

Corrosion resistance was evaluated for each of the above compositions.

Comparison of Outdoor Exposure Corrosion Performance between Example 1 and Example 3 ( Comparing Outdoor Corrosion Resistance of Composition Using Pigmented Pigmented Pigment and Pigmented Pigmented Pigment and Magnesium Powder)

The above experimental conditions are as follows.

- Material and thickness of specimen: Cold rolled steel plate with rust, 2T

- Pretreatment: St2 (St2 means pretreatment to remove rust using abrasive paper)

- Coating method and film thickness: Using a roller, dry film 50 ㎛ paint

- Test method and period: After immersing in calcium chloride solution (5% by weight) for 1 day, outdoor exposure, 3 months

Three months after the experiment, the appearance of the composition of Example 1 and that of the composition of Example 3 were compared. The comparison results are shown in Fig. As can be seen from FIG. 5, the composition of Example 1 had very little bleaching on the cutting area, but the blister was slightly generated. The composition of Example 3 in which magnesium was further added had almost no occurrence of blistering, and was superior in appearance to the composition of Example 1.

Claims (7)

delete 10 to 30% by weight of zinc stearate, 30 to 60% by weight of a diphenylmethane diisocyanate based prepolymer, 1 to 10% by weight of zinc phosphate, Zn ₃ (PO ₄ ) ₂ , 1 to 5% by weight of p-toluenesulfonyl isocyanate, 1 to 5% by weight of triethylorthoformiate, and 10 to 40% by weight of a solvent. The moisture curing type coating composition according to claim 2, wherein the NCO content of the diphenylmethane diisocyanate based prepolymer is 10 to 20% by weight. The moisture curing type coating composition according to claim 2, wherein the particle size of the flaky zinc oxide is 9 to 15 탆. The moisture curing type coating composition according to claim 2, wherein the solvent is an aromatic hydrocarbon, an ester, or a combination thereof. delete The moisture curing type coating composition according to claim 2, further comprising 1 to 10% by weight of magnesium powder.

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