JPH05140504A - Metallic coating composition - Google Patents

Abstract

PURPOSE:To obtain a metallic coating composition capable of providing coated products excellent in resistance to peeling from the cathode and water-resistant adhesion for a long period when used as a primer for coating a heavy-duty rust preventing urethane by adding strontium sulfate to a thermosetting polyurethane resin. CONSTITUTION:The objective metallic coating composition is obtained by mixing (A) 100 pts.wt. thermosetting polyurethane resin prepared by reacting a polyol (a polyol, prepared by adding an alkylene oxide to an epoxy-modified polyol or bisphenols and having 100-500 molecular weight per OH group) with a polyisocyanate compound (preferably diphenylmethane diisocyanate or polymethylene polyphenylene polyisocyanate) with (B) 50-200 pts.wt. powdery strontium sulfate (preferably anhydride) having preferably 0.1-20mum average particle diameter. (A) The polyol is uniformly premixed with the component (B) and preserved. The preserved mixture is then mixed with (A) the polyisocyanate just before coating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal coating composition, and more particularly to a metal coating composition for corrosion protection which is excellent in water-resistant adhesion, cathodic peeling resistance and adhesion.

[0002]

2. Description of the Related Art Since steel, which is the most common metal material, has a drawback of being easily corroded, it is usually subjected to various anticorrosion treatments before or during use. As the anticorrosion treatment of steel materials, for example, a method using anticorrosion coating, a method using a plastic coating material such as polyethylene, or the like is used. The method using anticorrosion coating is widely used because it can be coated relatively easily regardless of the form of the steel material. In particular, polyurethane heavy-duty anticorrosion paints have excellent anticorrosion properties, impact resistance, water resistance, adhesive properties, and long-term durability. It is growing greatly. The polyurethane heavy-duty anticorrosive paint has the above-mentioned excellent features, but if a primer is not used, the water-resistant adhesion and the cathodic peeling resistance may be slightly lowered.

[0003]

[Problems to be Solved by the Invention] However, in the past,
Epoxy resin-based or polyurethane-based primers have been used to improve water-resistant adhesion and cathode peeling resistance. Some epoxy resin-based primers have excellent water-resistant adhesion and cathode peeling resistance. For example, JP-A-57-
159866, JP-A-58-91778, JP-A-5
8-217573, JP-A-59-71374, JP-A-59-222275, JP-A-59-232160.
No. 60-258277 and 60-258.
No. 278 describes an adhesive for laminating a polyolefin with a metal, which has excellent cathode peel resistance and water resistance adhesion. However, careful coating control is necessary to secure the adhesiveness between the epoxy primer, which is a different material, and the polyurethane resin for the top coat. On the other hand, the polyurethane resin-based primer has good adhesion after coating with the overcoat polyurethane resin, but has a problem that the cathode peeling resistance and the water resistance are slightly inferior. In order to solve this problem, the present inventors proposed to include calcium sulfate in the coating composition according to Japanese Patent Application No. 1-86600 to improve cathode peeling resistance and water resistant adhesion. .. In order to further improve this, as a result of extensive studies, a metal coating composition having excellent performance in a long-term accelerated test for fresh water and seawater at a high temperature, and a temperature gradient test capable of short-term evaluation of water-resistant adhesive strength. I came to find something. The present invention relates to a primer for heavy-duty anticorrosion urethane coating, and an object thereof is to improve cathode peel resistance and long-term water-resistant adhesion.

[0004]

To achieve the above object, in the metal coating composition of the present invention, 50 parts of strontium sulfate is added to 100 parts by weight of a thermosetting polyurethane resin.
~ 200 parts by weight are added.

[0005]

Next, the present invention will be described in detail. In the metal coating composition of the present invention, 50 to 200 parts by weight of strontium sulfate is added to 100 parts by weight of the thermosetting polyurethane resin, but the strontium sulfate used in the present invention is in the form of powder and has an average particle size of Diameter is 0.1 to 20 μm
It is preferable to use those of As strontium sulfate, there are generally anhydrous, hemihydrate and dihydrate, but it is preferable to use anhydrous.

The amount of strontium sulfate added is set to 50 to 200 parts by weight with respect to 100 parts by weight of the thermosetting polyurethane resin. If the addition amount is less than 50 parts by weight, the cathode peeling resistance is lowered and the object of the present invention cannot be achieved. If the addition amount is more than 200 parts by weight,
This will reduce the strength of the primer coating and cause a decrease in initial adhesion and water resistance adhesion. When powdered pigments other than strontium sulfate are added for the purpose of coloring, the total amount of the pigments added should not exceed 200 parts by weight.

Next, the thermosetting polyurethane resin used in the present invention is obtained by reacting a compound having two or more hydroxyl groups (hereinafter referred to as polyol) with a compound having two or more isocyanate groups (hereinafter referred to as polyisocyanate compound). is there. As the polyol, epoxy modified polyol, polyether polyol, polyester polyol, polybutadiene polyol, polycarbonate polyol, etc. can be used. Of these polyols,
Polyester polyols are less preferred because they undergo hydrolysis due to ester bonds. Epoxy-modified polyols and polyols obtained by adding alkylene oxides to bisphenols have a phenyl group in the molecular skeleton, and therefore have excellent adhesiveness and water resistance, and the thermosetting polyurethane resin used in the present invention is obtained. Is preferred. The molecular weight of these polyols is preferably 100 to 500 per hydroxyl group. If the molecular weight per hydroxyl group is less than 100, the resin obtained will be too hard, so cracking will tend to occur in the primer layer in the impact test. On the contrary, when the molecular weight per hydroxyl group is larger than 500, the primer layer may be softened and the adhesiveness and the water resistant adhesiveness may be deteriorated. Therefore, the molecular weight per hydroxyl group of the polyol is 1
It is preferably from 00 to 500.

As the polyisocyanate compound,
Tolylene diisocyanate, diphenylmethane diisocyanate (hereinafter referred to as MDI), polymethylene polyphenylene polyisocyanate (hereinafter referred to as crude MDI), liquid MDI, hexamethylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate and these polyisocyanates in the state of excess isocyanate groups. A terminal isocyanate prepolymer obtained by reacting with the polyol may be used. Among these polyisocyanates, MDI and crude MDI are particularly excellent in performance such as curability, adhesion, and water resistance adhesion.

As a method for obtaining a thermosetting polyurethane resin, a method of mixing and applying a polyol and a polyisocyanate compound immediately before coating, a method of applying the isocyanate-terminated prepolymer and curing it with moisture in the air, etc. Yes, any method can be used. It is preferable that strontium sulfate is usually mixed in advance with a polyol and stored, and is mixed with a polyisocyanate compound immediately before coating before use.

When coating the metal coating composition of the present invention, a solvent may be used or a solvent may not be used. If the viscosity of the compounded resin and calcium sulfate is high, a solvent should be added to adjust the viscosity. As the solvent to be used, aromatic solvents such as toluene and xylene, ester solvents such as ethyl acetate and butyl acetate, ketone solvents such as acetone and methyl ethyl ketone, and halogen solvents such as methylene chloride and trichloroethane may be used alone or as a mixture. Can be used. Alcohol-based solvents such as ethanol, methanol and isopropanol react with the polyisocyanate compound and are not preferred. Further, a catalyst for promoting the curing reaction,
The addition of auxiliaries such as antioxidants and stabilizers is optional.

The metal coating composition of the present invention can be applied in the same manner as usual paints, such as a method of applying with a brush or a roller, a method of spraying with an air spray, an airless spray or the like. When the metal coating composition of the present invention is used as a primer for heavy-duty anticorrosion coating, it is usually preferable to coat it so as to have a dry film thickness of 10 to 100 μm, but it is not particularly limited.

The metal to be coated with the metal coating composition of the present invention includes iron, steel, copper, aluminum, etc.
Effective for steel. The form is steel pipe, iron pipe,
It can be applied to steel sheet piles, H-section steels, steel sheets, steel strips, and structures made from these.

[0013]

The present invention will be described in more detail with reference to the following examples. In the examples and comparative examples, "part" and "%" are based on weight. Example 1 Polyether polyol (bisphenol A with propylene oxide added to give a molecular weight of 400) 1
80 parts of strontium sulfate was added to 00 parts and kneaded with a three-roll mill, and then 40 parts of toluene was added. 260 parts of this liquid and 75 parts of liquid MDI were mixed and coated on a steel plate that had been grid-blasted using air spray so that the film thickness when dried was 30 μm. Then, this was dried for one day, and then a polyurethane heavy anticorrosive paint was applied thereon so that the thickness was 2.5 mm. The thus-obtained steel sheet having a coating film thickness of about 2.5 mm was subjected to an initial adhesion strength test, a water resistant adhesion test, and a cathodic peeling resistance test. For the temperature gradient test, a film having a film thickness of 1 mm was used. The test results are shown in Table 1. Example 2 The addition amount of strontium sulfate in Example 1 was set to 140.
The same test was performed by changing the parts. The test results are shown in Table 1.
Shown in. Comparative Examples 1 and 2 Similar tests were conducted using calcium carbonate or calcium sulfate instead of strontium sulfate in Example 1. The test results are shown in Table 1. Calcium carbonate was used as Comparative Example 1 and calcium sulfate was used as Comparative Example 2.

[Table 1] Example 3 100 parts of polypropylene glycol having a molecular weight of 400 and 140 parts of crude-MDI were reacted at 90 ° C. for 2 hours in the presence of 240 parts of toluene to obtain a polyurethane prepolymer solution having a solid content of 50%. To 100 parts of this solution, 60 parts of strontium sulfate and 30 parts of silicon oxide were mixed by a high-speed disperser, and coated on a grid-blasted steel plate so that the film thickness when dried was 30 μm. This was dried at room temperature for 1 day, and then a polyurethane heavy-duty anticorrosive paint was applied thereon so that the applied film thickness was 2.5 mm or 1.0 mm. A steel sheet having a coating film thickness of 2.5 mm was subjected to an initial bond strength test, a water resistant bond test, and a cathodic debonding test. For the temperature gradient test, a paint film having a thickness of 1 mm was used. The test results are shown in Table 2. Comparative Examples 3 and 4 Instead of strontium sulfate in Example 2, aluminum silicate or calcium sulfate was used. The test results are shown in Table 2. The case of aluminum silicate is shown in Comparative Example 3, and the case of calcium sulfate is shown in Comparative Example 4. Comparative Example 5 The addition amount of strontium sulfate in Example 1 was set to 220.
The test was carried out by setting it to a part. The test results are shown in Table 2.

[Table 2] In Tables 1 and 2, (1) is DIN 30671
Adhesion test by (2) ASTM
It is a test by G-8, (3) is the adhesive strength after being immersed in 3% saline solution at 50 ° C, and the adhesive strength evaluation is DIN.
According to 30671. (4) 50 ° C for the coated surface and 2 for the back surface
After immersing in tap water at 5 ° C., the appearance is observed by blister and the adhesive strength is measured. The adhesive strength is evaluated according to DIN 306.
71.

As is apparent from Tables 1 and 2,
By using the metal coating composition of the present invention as a primer, it is possible to obtain both excellent cathodic peeling resistance and long-term water resistant adhesion, and to obtain an excellent urethane heavy-corrosion coated material. On the other hand, as in Comparative Examples 1 and 3, in the case of a primer using an inorganic filler outside the scope of the present invention, the cathode peel resistance is particularly poor. When calcium sulfate is used as in Comparative Examples 2 and 4, long-term water-resistant adhesion tends to be poor,
Blister occurs in the temperature gradient test which is the short-term accelerated test.

[0015]

As is clear from the above description, the metal coating composition of the present invention comprises the thermosetting polyurethane resin 100.
Since 50 to 200 parts by weight of strontium sulfate was added to the parts by weight, by using the metal coating composition as a primer for a heavy anticorrosion paint, it was excellent in cathodic peeling resistance, long-term water resistant adhesion test and room temperature gradient test. Urethane heavy anti-corrosion coating can be obtained.

Claims (1)

[Claims] 1. A metal coating composition comprising 50 to 200 parts by weight of strontium sulfate added to 100 parts by weight of a thermosetting polyurethane resin.