JP3511738B2 - Heavy corrosion protection coated steel with excellent cathodic peel resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy corrosion protection coated steel material,
More specifically, it relates to a heavy corrosion-resistant coated steel material having excellent cathodic peeling resistance.

[0002]

BACKGROUND OF THE INVENTION Protective coatings steel, usually is being used for a long period of time in combination with cathodic protection, alkali water such as by corrosion current is generated by decomposition (OH ^-) generated during transportation and installation by coating A phenomenon called cathodic peeling (see FIG. 4) in which peeling occurs from the damaged portion of the above deteriorates the anticorrosion performance. In recent years, along with the increasing demand and demand for maintenance-free performance, the demand for anticorrosion performance has also become strict, and it is an important issue to improve the cathodic peeling resistance of heavy-corrosion-coated steel materials.

In order to improve the durability performance of the heavy anticorrosion coated steel material, it is necessary to firmly adhere the coating film to the surface of the steel material.
As a method for improving the adhesion of the coating film, treatment with a chromate treatment agent consisting of chromic acid, a reducing agent, vapor phase and liquid phase silica, phosphoric acid, alkali metal ions, etc. has been conventionally used.
A method of applying it as a base treatment has been proposed. For example, as disclosed in Japanese Patent Publication No. 3-66393, a chromate treatment agent obtained by adding a reducing agent, silica fine particles and phosphoric acid to an aqueous chromic acid solution, and silane coupling as disclosed in Japanese Patent Publication No. 6-98731. There is a chromate-treating agent whose addition to the agent improves the high-temperature cathode resistance. Further, a method of applying a resin layer containing an epoxide as a primer layer, which is an upper layer of the chromate treatment agent layer, as disclosed in, for example, JP-A-4-169229, has been widely and generally proposed.

[0004]

However, the heavy-corrosion-coated steel material subjected to such a surface treatment has the following problems. a The treating agent in which the liquid phase silica is added to the chromate has less effect on the cathodic peel resistance when compared with the treating agent in which the liquid phase silica is not added. b In a treating agent in which phosphoric acid is added to chromate, the wettability of phosphoric acid may reduce the cathode peeling resistance. From the above points, it was difficult to obtain desired cathode peeling resistance. Further, the addition of the silane coupling agent was difficult to put into practical use because the stability of chromate was poor.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a heavy corrosion-resistant coated steel material having excellent cathodic delamination resistance and having cathodic delamination resistance according to required performance. is there.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have earnestly studied the case of using a resin containing an epoxide for a chromate treating agent and a primer layer as an upper layer thereof. In an aqueous solution of chromic acid that has been partially reduced so that the weight ratio of trivalent chromium to total chromium is 0.1 to 0.7 times, the weight ratio to total chromium is 0.01 to 0.5 times. Chromate-treating agent and phosphoric acid in which a large amount of formic acid and vapor-phase silica having ^{2 to} 4 hydroxyl groups per 1 nm ^{2 of} specific surface area are added in a weight ratio of 2.0 to 7.0 times the total amount of chromium. 10-200g / k
By using an epoxy primer containing g and further forming an organic resin layer, preferably a modified polyolefin resin and a polyolefin resin, or an organic resin layer composed of a modified polyurethane resin and a polyurethane resin on the epoxy primer, it is possible to obtain a resin having excellent cathode peeling resistance. The inventors have found that a corrosion-resistant coated steel material can be obtained, and have completed the present invention.

That is, according to the present invention, a chromate-treating agent which is partially reduced on the surface of a steel material so that the weight ratio of trivalent chromium to the total chromium content is 0.1 to 0.7 has a specific surface area of 1
The vapor phase silica having ^{2 to} 4 hydroxyl groups per nm ² is 2.0 to 7.0 times by weight with respect to the total chromium amount, and the formic acid is 0.01 to by weight with respect to the total chromium amount. Chromate layer containing 0.5 times in total chromium amount of 50 to 1000 mg / m ²
And an epoxide of 1. 5 to 6.0 mol
/ Kg and phosphoric acid-based rust preventive pigment 10-200g / kg
Provided is a heavy anticorrosion coated steel material having an excellent cathode peeling resistance, characterized by having a primer layer containing it and further having an organic resin layer on it.

The primer layer is preferably at least one epoxy-modified resin selected from epoxy resins, amine-epoxy resins, phenol-epoxy resins, polyimide-epoxy resins and epoxy-silicone resins.

Further, it is preferable that the organic resin layer is formed of a modified polyolefin resin and an upper polyolefin resin, or a modified polyurethane resin and an upper polyurethane resin.

The heavy anticorrosion coated steel material (hereinafter referred to as the heavy anticorrosion coated steel material) of the present invention which is excellent in cathodic peeling resistance will be described in detail below.

FIG. 1 is a conceptual diagram of the heavy corrosion resistant coated steel material of the present invention. As shown in FIG. 1, the heavy anticorrosion coated steel material of the present invention has a predetermined chromate layer formed on the steel material, a predetermined primer layer formed thereon, and an organic resin layer formed thereon. , Composed.

The steel materials used in the present invention include H-shaped steel and I
Shaped steel, shaped steel such as L-shaped steel, steel sheet pile, steel bar, steel wire, cast iron pipe,
It is a steel pipe, a steel plate such as a thick steel plate, a hot rolled steel plate, a cold rolled steel plate or the like, and the heavy anticorrosion coating may be one surface or the other surface may be a plated surface.

Next, the chromate treating agent used for forming the chromate layer of the heavy corrosion resistant coated steel material of the present invention will be explained. The chromate treating agent used in the present invention is obtained by partially reducing an aqueous solution in which chromic acid (CrO ₃ ) is dissolved in pure water to obtain a predetermined trivalent chromium amount, and adding formic acid afterwards, and It is a mixture of gas phase silica fine particles having ^{2 to} 4 hydroxyl groups per surface area of 1 nm ² .

As the reducing agent used for the partial reduction of hexavalent chromium to trivalent chromium, monovalent alcohols such as methanol, ethanol and propanol, and carboxylic acids such as oxalic acid are used.

By partially reducing chromium from hexavalent to trivalent, the alkali dissolution resistance of the chromate layer can be improved. That is, since the chromium reduced to trivalent and the hexavalent chromium combined with the trivalent chromium do not dissolve in alkali, the alkali dissolution resistance performance of the chromate layer (heavy corrosion protection coated steel material) can be improved. However, when the amount of trivalent chromium increases, the reaction between the surface of the steel material and hexavalent chromium hardly occurs, and the adhesiveness between the surface of the steel material and the chromate layer decreases. Therefore, the chromium treatment agent used in the present invention is such that the weight ratio of trivalent chromium to the total chromium amount is 0.1 to 0.7, preferably 0.2 to 0.7. If it is less than 0.1 times, the amount of trivalent chromium is small and the chromate is easily dissolved, which is not preferable. If it exceeds 0.7 times, the amount of hexavalent chromium that reacts with the surface of the steel material is small and the adhesion between the steel surface and the chromate is low. This is because it will decrease.

Before the chromate treatment agent is applied to the surface of the steel material, oil, scale and the like on the surface of the steel material are removed by degreasing, pickling, blasting and the like. When the chromate treatment agent is applied to the steel material surface from which scales and the like have been removed, the hexavalent chromium is partially reduced by the oxidation effect of the steel material surface and the heating after the application, and the dehydration condensation reaction between the hydroxyl groups bonded to chromium proceeds, A chromate film with excellent alkali dissolution resistance is formed.

In the heavy-corrosion-coated steel sheet of the present invention, the chromate-treating agent has a specific surface area of ^{2 to 2} per 1 nm ² .
Gas phase silica with four hydroxyl groups is added. Here, the vapor-phase silica fine particles are a general term for silica particles produced by thermally decomposing an organic silica compound in a vapor phase. An example is extremely fine silicon dioxide produced by hydrolysis of a volatile silane compound in an oxyhydrogen flame.
Specifically, Aerosil 130 manufactured by Nippon Aerosil Co., Ltd.,
Aerosil 380, Aerosil OX50, Aerosil O
One type or a mixture of two or more types of gas phase silica having ^{2 to} 4 hydroxyl groups per 1 nm ² of specific surface area such as X170 is used. Incidentally, the specific surface area of the vapor phase silica in the present invention,
It is measured by the nitrogen adsorption method according to the BET method.

The hydroxyl group concentration per specific surface area is Li
According to the H ₂ O ₄ method and the HD exchange method. Specific surface area 1 nm
^{If the} number of hydroxyl groups per 2 is less than 2, the effect of the hydroxyl groups possessed by the vapor phase silica cannot be exhibited, and if it exceeds 4, the dissolution resistance such as alkali dissolution resistance of the chromate layer deteriorates.

[0019] SiO having a GDS (glow discharge optical emission spectroscopy) depth of the element distribution measurement result of chromate layer by (see FIG. 5) and 2 to 4 hydroxyl groups per ^square specific surface 1nm shown in Table 1 ₂ / As can be inferred from the contact angle measurement results (see FIG. 2) between the chromate layer added with an amount of Cr = 3.2 and the chromate layer without addition, and phenylglycidyl ether (PGE), the gas phase silica is It is considered that the hydroxyl groups on the surface react with the functional groups such as epoxide in the primer of the upper layer to increase the adhesion between the chromate layer and the primer layer of the upper layer.

[0020]

The relationship between the contact angle θ and the adhesiveness shown in FIG. 2 can be expressed by Young's formula as work of adhesion W = γ × (1 + cos θ) γ: surface tension of the resin, and when γ is the same The smaller the contact angle, the greater the work of adhesion and the greater the adhesiveness.

The amount of the vapor phase silica added is 2.0 to 7.0 times by weight the total amount of chromium in the chromate treatment liquid,
It is preferably 3.0 to 5.0 times. If the amount of the vapor phase silica added is less than 2.0 times, the total amount of the hydroxyl groups of the vapor phase silica effective for adhesion is small, and therefore the difference in the cathodic peeling resistance performance depending on the concentration of the epoxide of the primer is large, and the addition amount is 7.0 times. If it is contained in excess of 5, the effect of lowering the alkali dissolution resistance of the chromate layer is large, which is not preferable.

The reason why the formic acid is post-added to the partially reduced chromate treating agent is to enhance the interaction with the epoxy primer layer containing the phosphoric acid type rust preventive pigment as the upper layer. The addition amount of formic acid is preferably 0.01 to 0.5 by weight relative to the total chromium in the chromate treatment liquid,
It is added so as to be in the range of 0.1 to 0.35 times. If the addition amount of formic acid is 0.01 times or less, the effect is not exhibited because the addition amount is small, and if the addition amount is 0.5 times or more, excess formic acid decreases the epoxide of the primer layer effective for adhesion. Not preferable.

The baking temperature of the chromate treatment agent is 60 to 300, preferably 70 to 110 ° C., as the surface temperature of the steel material. If the surface temperature of the steel material is less than 60 ° C., the chromate treatment agent is not suitable because the chromate layer may dissolve when the primer layer is applied to the upper surface of the steel material. If baking is performed at a temperature higher than ° C, the dehydration condensation reaction of the hydroxyl groups will proceed too much, and the hydroxyl groups on the surface of the chromate layer necessary for adhesion to the primer layer, which is the upper layer, will be lost, which is not preferable for improving the cathode peel resistance.

In the heavy-corrosion-coated steel sheet of the present invention, the amount of the chromate layer formed by such a chromate treating agent is 100 to 1000 mg / m 2 in terms of total chromium weight.
² , preferably 300 to 800 mg / m ² . If the adhesion amount is less than 100 mg / m ² , the effect of the chromate treatment cannot be exhibited, and the adhesion amount is 1000 mg / m ²
If it exceeds, the effect of lowering the alkali dissolution resistance of the chromate layer increases, which is not preferable.

In the heavy anticorrosion coated steel sheet of the present invention, a primer layer is formed on the chromate layer. In the present invention, the primer layer comprises 1. An epoxy resin layer containing 5 to 6.0 mol / kg, preferably a modified epoxy resin such as an epoxy resin, an amine / epoxy resin, a phenol / epoxy resin, a polyimide / epoxy resin, an epoxy / silicone resin, or an epoxy-modified resin as a main component A coating film obtained by applying a solventless coating composition, a solvent coating composition, or a powder coating composition and curing the composition is used as a primer layer.

Here, the primer layer is composed of 1.
5 to 5.0 mol / kg, preferably 3.0 to 4.5 m
ol / kg is included.

When the amount of the epoxide is less than 1.5 mol / kg, the adhesive strength with the chromate layer is weak and the desired cathode peeling resistance cannot be obtained. In addition, 5.0 mol / k
If it is contained in excess of g, a problem occurs in the curability of the resin forming the primer layer. In the present invention, containing epoxide in an amount of 1.5 to 5.0 mol / kg means that the epoxide in the resin forming the primer layer before the curing reaction is 1.5 to 5.0 mol / kg.

In addition, a phosphoric acid-based rust preventive pigment is added to the primer layer containing the above organic resin as a main component in an amount of 10 to 200, preferably 30 to 150 g / kg. The phosphoric acid-based rust preventive pigment is a general pigment mainly containing a phosphate such as aluminum phosphate and a polyphosphate such as aluminum polyphosphate. This phosphoric acid-based rust-preventive pigment contains silica, alumina, in addition to the phosphate, polyphosphate, which is the main component.
It is possible to add general extender pigments such as titania, talc, silicate, zinc white, carbon black, red iron oxide, aniline black, azo pigments, phthalocyanine, and coloring pigments.

In the heavy corrosion resistant coated steel sheet of the present invention, an organic resin layer is formed on the primer layer. As the organic resin layer, a layer having a structure of a modified polyolefin resin and an upper layer polyolefin resin, or a modified polyurethane resin and an upper layer polyurethane resin is preferably used. By thus forming the resin layer on the modified resin layer, the adhesion between the primer layer and the organic resin layer can be improved, and more preferable results can be obtained.

In addition to the main component, such an organic resin layer may contain a pigment or the like, if necessary. As the pigment, silica, alumina, titania, talc, silicate,
Examples include general extender pigments such as zinc white, aluminum phosphate, carbon black, red iron oxide, aniline black, azo pigments, and phthalocyanines, and coloring pigments. In addition,
The thickness of this layer is usually about 0.5 to 20 mm.
FIG. 1 shows a cross section of the heavy anticorrosion coated steel material according to the present invention obtained as described above. In the figure, when the chromate layer has a chromium deposition amount of 100 mg / m ² or more and the organic resin layer has a thickness of 10 μm or more, good cathode peeling resistance can be obtained.

[0032]

EXAMPLES The present invention will be specifically described below based on examples.

After degreasing JIS G 3141 SPCC steel plate, a chromate treatment agent was added to the chromium coating amount of 30 with a spin coater.
After applying 0 mg / m ² and heating and baking at 80 ° C., an epoxy resin as a primer was applied so that the film thickness was 30 to 100 μm, and baking was performed at 120 ° C. As the upper layer, modified polyethylene (manufactured by Mitsubishi Kasei) and polyethylene (manufactured by Mitsubishi Kasei) are pressure-bonded so that the film thickness after coating is 2 mm, and various heavy-corrosion-coated steel sheets having the configuration shown in FIG. 1 are produced. did.

At that time, the components of the chromate treatment solution, the epoxide concentration of the primer and the pigment concentration were prepared as follows. In the chromate treatment liquid, as a silica, Aerosil 130 (specific surface area 1 nm ² manufactured by Nippon Aerosil Co., Ltd.) is used.
Gas phase silica with 2 to 4 hydroxyl groups per) was added.

[ Invention Example 1] Chromate treatment liquid: Weight ratio of trivalent chromium to total chromium amount = 0.4 times Formic acid is added to the total chromium amount 0.05 times by weight Gas phase silica to total chromium amount Ratio by weight = 4.0 times Epoxy resin: Epoxide concentration = 4.5 mol / kg Concentration of rust preventive pigment whose main component is aluminum phosphate = 30 g / kg

[ Invention Example 2] Chromate treatment liquid: weight ratio of trivalent chromium to total chromium amount = 0.4 times Formic acid was added to the total chromium amount 0.15 times by weight ratio Gas phase silica to total chromium amount Of epoxy resin = 3.0 times Epoxy resin: Epoxide concentration = 3.8 mol / kg Concentration of rust preventive pigment containing aluminum phosphate as the main component = 60 g / kg

[ Invention Example 3] Chromate treatment liquid: Weight ratio of trivalent chromium to total chromium amount = 0.2 times Formic acid was added to the total chromium amount 0.15 times by weight Gas phase silica to total chromium amount Ratio of epoxy resin = 4.5 times Epoxy resin: Epoxide concentration = 5.5 mol / kg Concentration of rust preventive pigment whose main component is aluminum phosphate 120 g / kg

[ Invention Example 4] Chromate treatment liquid: weight ratio of trivalent chromium to total chromium amount = 0.3 times Formic acid was added 0.2 times to total chromium amount Gas phase silica to total chromium amount Epoxy resin: Epoxide concentration = 4.0 mol / kg Concentration of rust preventive pigment containing aluminum phosphate as the main component = 80 g / kg

[ Invention Example 5] Chromate treatment liquid: Weight ratio of trivalent chromium to total chromium amount = 0.2 times Formic acid was added at 0.45 weight ratio to total chromium amount Gas phase silica to total chromium amount Of epoxy resin = 6.0 times Epoxy resin: Epoxide concentration = 5.0 mol / kg Concentration of rust preventive pigment whose main component is aluminum phosphate = 170 g / kg

Further, a comparative example was prepared as follows in comparison with the example. [Comparative Example 1] Chromate treatment liquid: weight ratio of trivalent chromium to total chromium amount = 0 Formic acid was added 0.1 times by weight ratio to total chromium amount Weight ratio of vapor phase silica to total chromium amount = 4. 0 times Epoxy resin: Epoxide concentration = 4.5 mol / kg Concentration of rust preventive pigment whose main component is aluminum phosphate = 100 g / kg

[Comparative Example 2]   Chromate treatment solution: Weight ratio of trivalent chromium to total chromium amount = 0.2 times                     Add 0.7 times the weight of formic acid to the total chromium.                     Weight ratio of vapor phase silica to total chromium amount = 4.0 times   Epoxy resin: Epoxide concentration = 4.3 mol / kg                     Concentration of anti-corrosion pigment mainly composed of aluminum phosphate                                         = 40g / kg

[Comparative Example 3]   Chromate treatment liquid: Weight ratio of trivalent chromium to total chromium amount = 0.4 times                     Add 0.3 times the weight of formic acid to the total chromium                     Weight ratio of vapor phase silica to total chromium amount = 1.0 times   Epoxy resin: Epoxide concentration = 4.0 mol / kg                     Concentration of anti-corrosion pigment mainly composed of aluminum phosphate                                       = 120 g / kg

[Comparative Example 4]   Chromate treatment liquid: Weight ratio of trivalent chromium to total chromium amount = 0.3 times                     Add formic acid 0.05 times weight ratio to total chromium                     Weight ratio of vapor phase silica to total chromium amount = 6.0 times   Epoxy resin: Epoxide concentration = 1.0 mol / kg                     Concentration of anti-corrosion pigment mainly composed of aluminum phosphate                                         = 70 g / kg

[Comparative Example 5]   Chromate treatment liquid: Weight ratio of trivalent chromium to total chromium amount = 0.4 times                     Add 0.40 times the weight ratio of formic acid to the total amount of chromium.                     Weight ratio of vapor phase silica to total chromium amount = 3.5 times   Epoxy resin: Epoxide concentration = 4.5 mol / kg                     Concentration of anti-corrosion pigment mainly composed of aluminum phosphate                                           = 0 g / kg

A 6 mmφ defect was formed from the resin layer side at the center of each of the heavy-duty anticorrosion coated steel sheets thus prepared, and a cathode peeling test was conducted using the apparatus shown in FIG. The test was conducted under two conditions of 80 ° C. for 14 days and 25 ° C. for 30 days. After the test was completed, the coating film near the peeled portion of the sample was peeled off, and the peeling distance (distance indicated by arrow a in FIG. 3) was measured.
The results are shown in Table 2 below.

[0046] In addition, the non-coating ^* of Comparative Example 1 is because the chromate was dissolved when the primer layer was applied.

As shown in Table 2 above, the heavy-corrosion-coated steel sheet of the present invention has very good resistance to cathodic peeling. From the above results, the effect of the present invention is clear.

[0048]

As described above in detail, the heavy-corrosion-coated steel sheet of the present invention is remarkably excellent in high-temperature cathodic peeling resistance as compared with the conventional heavy-corrosion coated steel, and therefore is excellent in cathodic peeling resistance. It is a heavy-duty anticorrosion coated steel material and is suitably used for various purposes.

[Brief description of drawings]

FIG. 1 is a view conceptually showing a configuration example of a heavy corrosion-resistant coated steel sheet.

FIG. 2 is a conceptual diagram for explaining contact angle measurement.

FIG. 3 is a conceptual diagram of a cathode peeling test device.

FIG. 4 is a conceptual diagram for explaining cathode peeling resistance.

FIG. 5 is a diagram showing measurement results of element distribution in the depth direction of a chromate layer by glow discharge emission spectroscopy.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-169229 (JP, A) JP-B 3-66393 (JP, B2) JP-B 6-98731 (JP, B2) (58) Field (Int.Cl. ⁷ , DB name) B32B 1/00-35/00 B05D 1/00-7/26 C23C 22/30

Claims (3)

(57) [Claims] 1. A on the surface of the steel, the chromate treatment agent weight ratio of trivalent chromium of the total amount of chromium is partially reduced to become 0.1 to 0.7, a specific surface area of 1 nm ² per 2-4
Chromate containing vapor phase silica having one hydroxyl group in a weight ratio of 2.0 to 7.0 times, and formic acid in a weight ratio of 0.01 to 0.5 times, relative to the total chromium amount. Layer having a total chromium content of 50 to 1000 mg / m ² , with an epoxide of 1. 5 to 6.0 mol / kg
And a heavy corrosion-resistant coated steel material having excellent cathode peeling resistance, which has a primer layer containing 10 to 200 g / kg of a phosphoric acid-based rust preventive pigment, and an organic resin layer on the primer layer. 2. The primer layer is at least one epoxy-modified resin selected from an epoxy resin, an amine-epoxy resin, a phenol-epoxy resin, a polyimide-epoxy resin, and an epoxy-silicone resin. Heavy anticorrosion coated steel with excellent cathodic peeling resistance. 3. The excellent cathode peeling resistance according to claim 1 or 2, wherein the organic resin layer is formed of a modified polyolefin resin and an upper polyolefin resin, or a modified polyurethane resin and an upper polyurethane resin. Heavy anticorrosion coated steel.