JPH10249997A - Corrosion-proof covered steel material with excellent anti-cathdic releasability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion-proof steel material having excellent anti- cathodic releasability by improving adhesive properties of a chromate layer with a primer layer. SOLUTION: This covered steel material is formed on the surface with a composite corrosion-proof layer having a chromate layer, epoxy primer layer and organic resin layer sequentially laminated. In this case, the chromate layer in the composite layer contains 2.0 to 7.0 of vapor phase silica having two to four hydroxyl groups per BET specific surface area 1nm<2> by weight and 0.1 to 0.7 of trivalent chromium to entire chrome amount. The epoxy primer layer contains 10 to 200g of pigment containing 1.5 to 5.0mol of epoxy group of epoxy resin containing titania as a main component per epoxy primer of 1kg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anticorrosion-coated steel material having excellent cathodic peeling resistance, and more particularly to an anticorrosion coated steel material having improved cathodic peeling resistance by improving adhesion between a chromate layer and a primer layer. .

[0002]

2. Description of the Related Art It is common for corrosion-resistant coated steel materials to suppress a corrosion reaction by also using an electrolytic protection. However, when this corrosion-resistant coated steel is used in combination with cathodic protection, the alkali generated by the corrosion protection current enters the damaged portion of the coating generated during transportation and laying, causing a phenomenon called so-called cathodic peeling, which causes a phenomenon called so-called cathodic peeling. There is a disadvantage that performance is reduced.

[0003] In addition, with the recent increase in demand for corrosion-resistant coated steel materials and the demand for maintenance-free products, the requirements for the corrosion-resistant performance have also become more stringent. Has become.

[0004] On the other hand, conventionally, there has been an attempt to firmly adhere a coating film to the surface of a steel material in order to improve the corrosion protection performance of the coated steel material. As a means for improving the adhesion of the coating film, there is proposed a method of applying a chromate treatment agent containing chromic acid, a reducing agent, gas phase or liquid phase silica, phosphoric acid, alkali metal ions, etc. as a base treatment of the coated steel material. Have been. For example,
A method using a chromate treating agent obtained by adding a reducing agent, silica fine particles, and phosphoric acid to a chromic acid aqueous solution (Japanese Patent Publication No. 3-6639)
No. 3) and a method using a chromate treating agent to which a silane coupling agent is added (see Japanese Patent Application Laid-Open No. 3-234527).

Further, there has been proposed a method of forming a resin layer containing an epoxide as a primer layer on the chromate treating agent layer, for example, as disclosed in JP-A-4-169229.

[0006]

However, when such an undercoating agent is applied to an anticorrosion-coated steel material, there are the following problems. (1) The treating agent in which the liquid phase silica is added to the chromate has less effect on the cathodic peeling resistance than the treating agent in which the liquid phase silica is not added. (2) A treating agent obtained by adding phosphoric acid to chromate may deteriorate the cathodic peeling resistance of the coated steel material due to the wettability of the phosphoric acid. (3) A treating agent obtained by adding a silane coupling agent to chromate is not practical because chromate has poor stability. For these reasons, it has been difficult with the above-mentioned conventional technology to obtain a corrosion-resistant coated steel having desired cathodic peeling resistance.

[0007] In particular, the conventional anticorrosion-coated steel material has insufficient adhesion between the chromate layer and the primer layer, so that peeling occurs between the chromate layer and the primer layer in a cathode peel test. Therefore, an object of the present invention is to provide an anticorrosion-coated steel material having improved adhesion between a chromate layer and a primer layer and having excellent cathodic peeling resistance.

[0008]

Means for Solving the Problems The inventors of the present invention have intensively studied for realizing the above-mentioned object, and as a result, have arrived at an invention having the following content as a gist configuration. That is, the present invention relates to a coated steel material in which a composite corrosion protection layer in which a chromate layer, an epoxy primer layer, and an organic resin layer are sequentially laminated on the surface of a steel material, wherein the chromate layer in the composite corrosion protection layer is
By weight ratio to total chromium amount, gaseous silica having 2 to 4 hydroxyl groups per 1 nm ^{2 of} BET specific surface area is 2.0 to 7.0,
The epoxy primer layer contains 0.1 to 0.7 of trivalent chromium, and the epoxy primer layer contains 1.5 to 5.0 mol of an epoxy group of an epoxy resin and 10 to 200 g of a pigment mainly composed of titania per 1 kg of an epoxy primer. Provided is an anticorrosion-coated steel material having excellent cathodic peeling resistance.

The present invention also relates to a coated steel material comprising a steel material and a composite corrosion protection layer formed by sequentially laminating a chromate layer, an epoxy primer layer, a modified organic resin layer and an organic resin layer on the surface of the steel material. The above chromate layer of
By weight ratio to the total chromium content, gaseous silica having 2 to 4 hydroxyl groups per 1 nm ^{2 of} BET specific surface area is 2.0 to 7.0,
The epoxy primer layer contains 0.1 to 0.7 of trivalent chromium, and the epoxy primer layer contains 1.5 to 5.0 mol of an epoxy group of an epoxy resin and 10 to 200 g of a pigment mainly composed of titania per 1 kg of an epoxy primer. Provided is a corrosion-resistant coated steel material having excellent cathodic peeling resistance.

In the anticorrosion-coated steel material of the present invention, the resin constituting the modified organic resin layer is a modified polyolefin resin, and the resin constituting the organic resin layer is preferably a polyolefin resin. It is desirable that the resin forming the resin layer is a modified polyurethane resin and the resin forming the organic resin layer is a polyurethane resin. In the anticorrosion-coated steel material of the present invention, the epoxy resin constituting the epoxy primer is at least one selected from an amine resin-modified epoxy resin, a phenol resin-modified epoxy resin, a polyimide resin-modified epoxy resin, and a silicone resin-modified epoxy resin.
It is desirable to be made of the following resin.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of a corrosion-resistant coated steel material according to the present invention will be specifically described below. . Regarding steel materials: As an example of steel materials used in the present invention, H
Shaped steel such as shaped steel, I-shaped steel, L-shaped steel, steel sheet pile, steel bar, steel wire,
There are steel materials such as cast iron pipe, steel pipe or thick steel plate, hot rolled steel plate, cold rolled steel plate and the like. It is preferable that these steel materials are subjected to pretreatment such as degreasing, pickling, and blasting treatment to remove oil, scale, and the like on the surface of the steel materials. When a chromate treatment agent is applied to the surface of the steel material from which scale has been removed, hexavalent chromium is partially reduced by the oxidizing action of the steel surface and heating after the application, and the dehydration condensation reaction of the hydroxyl groups bonded to the chromium proceeds. This is because a chromate film having excellent alkali dissolution resistance is formed. The baking temperature of the chromate treatment agent at this time is suitably from 60 to 300 ° C. at the steel material surface temperature. That is, if the steel material surface temperature is lower than 60 ° C, the drying becomes insufficient, while if the steel material surface temperature exceeds 300 ° C, the dehydration-condensation reaction of the hydroxyl group of the gas-phase silica described later proceeds too much, and The reason for this is that the hydroxyl groups on the surface of the chromate treatment layer necessary for adhesion to a certain primer layer are lost, so that the cathode peeling resistance is not improved.

[0012] Regarding the chromate layer in the composite anticorrosion layer; the chromate layer constituting the coated steel material of the present invention comprises a chromium compound and gas-phase silica. The ratio of trivalent chromium contained in the chromate layer is 0.1 to 0.7 by weight ratio to the total amount of chromium (weight of trivalent chromium / weight of total chromium).
And The reason is that when the amount of trivalent chromium is within this range, the chromate layer has good alkali dissolution resistance. That is, since chromium reduced to trivalent and hexavalent chromium combined with trivalent chromium do not dissolve in alkali, if the amount of trivalent chromium is less than 0.1 times the total amount of chromium, the amount of trivalent chromium is reduced. Less chromate is easily dissolved. On the other hand, the amount of trivalent chromium is 0.7% of the total amount of chromium.
If it exceeds twice, the amount of hexavalent chromium that reacts with the steel material surface decreases, and the adhesion between the steel material surface and the chromate layer decreases.

[0013] The chromate layer in which the content of trivalent chromium is adjusted is formed by dissolving an aqueous solution in which chromic anhydride (CrO ₃ ) is dissolved in pure water, a monohydric alcohol such as methanol, ethanol or propanol, or a carboxylic acid such as oxalic acid. It is obtained by applying a treatment liquid partially reduced with an acid or the like to the surface of a steel material and then baking it.

The ratio of the gas phase silica contained in the chromate layer is 2.0 to 7.0 in terms of a weight ratio to the total amount of chromium (weight of gas phase silica / weight of total chromium). The reason for this is that if the blending ratio of the gas-phase silica fine particles is less than 2.0, the total amount of hydroxyl groups of the gas-phase silica effective for bonding to the steel material is small, so that the cathode peeling resistance is deteriorated. On the other hand, when the mixing ratio of the gas phase silica fine particles exceeds 7.0, the alkali-solution resistance of the chromate layer is reduced.

Here, the gas-phase silica added to the chromate treating agent is a general term for silica particles produced by pyrolyzing an organic silica compound in a gas phase. For example, extremely fine silicon dioxide produced by hydrolysis of a volatile silane compound in an oxyhydrogen flame can be exemplified. Specifically, Aerosil 130 and Aerosil manufactured by Nippon Aerosil Co., Ltd.
380, Aerosil OX50 and Aerosil OX170.

In the present invention, the gas-phase silica particles need to have 2 to 4 hydroxyl groups per 1 mm ^{2 of} specific surface area. The reason is that if the number of hydroxyl groups is less than 2, adhesiveness is not sufficient, while if the number of hydroxyl groups exceeds 4, the adhesiveness is saturated and no further effect can be obtained. In addition, a plurality of types of gas-phase silica having different numbers of hydroxyl groups per 1 mm ^{2 of} specific surface area may be mixed. Here, the specific surface area of the gas phase silica in the present invention is measured by a nitrogen adsorption method using a BET method. The hydroxyl group concentration per specific surface area is measured by a LiH ₂ O ₄ method, an HD exchange method, or the like.

This chromate layer has an adhesion amount of 100 to 1000
Desirably, mg / m ² . So-called adhesion amount is 100mg
If it is less than / m ² , the corrosion resistance is poor, while the amount of adhesion is 1000 mg.
This is because if it exceeds / m ² , the alkali-solution resistance of the chromate-treated layer will decrease.

[0018] Regarding the epoxy primer layer in the composite anticorrosion layer; the epoxy primer layer is laminated on the above-mentioned chromate treatment layer. The amount of epoxy groups contained in this epoxy primer layer is 1.5 to 5.0 mol per kg of epoxy primer. The reason for this is that if the amount of the epoxy group is less than 1.5 mol, the adhesion between the chromate-treated layer and the primer-treated layer is weak, and the desired cathodic peeling resistance cannot be obtained. On the other hand, if the amount of epoxy groups is 5.0
If the amount exceeds mol, the primer resin is easily cured, and it is difficult to handle at the time of production.

The epoxy primer layer contains a pigment containing titania as a main component. This pigment has the effect of increasing the adhesion between the gas-phase silica in the chromate layer and the epoxy groups in the epoxy primer layer. The amount of this pigment added is
10 to 200 g per kg of epoxy primer. The reason is that if the added amount of the pigment is less than 10 g, the above-mentioned effect is not sufficiently exhibited, while if the added amount of the pigment exceeds 200 g, the viscosity of the primer resin becomes high, which is not preferable in practical use. . It should be noted that, in addition to titania as a main component, a general extender pigment such as silica, alumina, silicate, carbon black, red iron oxide, aniline black, an azo pigment, and phthalocyanine, and a coloring pigment may be added to the pigment. it can. At this time, the content of titania is desirably 50 to 90% by weight (in the pigment).

The epoxy resin constituting such an epoxy primer layer is at least one resin selected from an amine resin-modified epoxy resin, a phenol resin-modified epoxy resin, a polyimide resin-modified epoxy resin, and a silicone resin-modified epoxy resin. Desirably, it consists of The epoxy primer layer can be obtained by applying and curing these epoxy resins, and preferably has a thickness of 5 to 200 μm. In addition, these epoxy resins are preferably paints such as solventless paints, solvent paints, and powder paints.

[0021] Regarding the modified organic resin layer and the organic resin layer in the composite anticorrosion layer; the modified organic resin layer and the organic resin layer provided as needed are laminated on the above-mentioned chromate treatment layer. In particular, it is preferable that a modified organic resin layer is present between the epoxy primer layer and the organic resin layer because the adhesion between the layers is further improved. At this time, it is preferable that the resin constituting the modified organic resin layer is a modified polyolefin resin, and the resin constituting the organic resin layer is a polyolefin resin.The resin constituting the modified resin layer is a modified polyurethane resin, and the organic resin is an organic resin. It is desirable that the resin constituting the layer be a polyurethane resin. The total thickness of the modified organic resin layer and the organic resin layer is desirably 0.5 to 20 mm.

In the present invention, as the modified organic resin, a resin modified with maleic anhydride, acrylic acid, an epoxy group, a hydroxyl group, or the like is preferable, and as the polyolefin resin, polyethylene or polypropylene is particularly preferable.
The modified organic resin layer and the organic resin layer include silica,
Phosphates such as alumina, titania, talc, silicate, zinc white, magnesia, aluminum phosphate, polyphosphate, carbon black, red iron oxide, aniline black,
General extenders such as azo pigments and phthalocyanines and coloring pigments can be added.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. (Example 1) After degreasing the SPCC steel sheet, the surface of the steel sheet was
The amount of chromium applied to the chromate treatment agent using a spin coater 3
It was coated at 00 mg / m ² and baked at 80 ° C. to form a chromate layer to obtain a chromate-treated steel sheet. At this time, the amount of trivalent chromium in the chromate layer is 0.1 by weight ratio to the total amount of chromium (= trivalent chromium / total chromium), and the amount of gas phase silica in the chromate layer is the weight ratio to the total amount of chromium (= gas Phase silica / total chromium) and is 4.0
It had three hydroxyl groups per 1 nm ^{2 of} BET specific surface area.

Next, an amine-modified epoxy resin (epoxy group: 4 mol / epoxy primer kg, pigment: 100 g (including titania: 80 g) / epoxy primer kg) was applied as an epoxy primer on the surface of the chromate-treated steel sheet. Baking was performed to form an epoxy primer layer having a thickness of 30 μm.

Further, a 0.5 mm-thick maleic anhydride-modified polyethylene sheet and a 2 mm-thick polyethylene sheet are sequentially laminated on the upper layer of the epoxy primer layer,
The sample was crimped at 180 ° C. and 1 kg / cm ² to prepare a sample of a corrosion-resistant coated steel material.

A 6 mmφ defect was formed at the center of the sample thus prepared from the coating film side, and after setting this sample as shown in FIG. 1, a cathode peeling test was performed. At this time, the test conditions were as follows: a voltage of -1.5 V was applied to the Pt electrode with respect to the saturated calomel electrode;
C. for 30 days. After the test was completed, the coating film near the peeling portion of the sample was peeled off, and the peeling distance (portion a in FIG. 1) was measured. Table 3 shows the results.

(Examples 2 to 14, Comparative Examples 1 to 7) As shown in Tables 1 and 2, the amount of trivalent chromium in the chromate layer
Same as Example 1 except that the amount of the gas-phase silica, the epoxy group concentration in the epoxy primer layer, the titania content, the type of the epoxy primer layer, the type of the modified organic resin layer, and the type of the organic resin layer were changed. A sample of an anticorrosion-coated steel material was prepared by the method, and a cathode peel test was performed. Table 3 shows the results.

Example 15 A sample of an anticorrosion-coated steel material was prepared in the same manner as in Example 1 except that the modified polyethylene sheet was not laminated, and a cathodic peeling test was performed. Table 3 shows the results.

As is evident from the results shown in Table 3, the corrosion-resistant coated steel material according to the present invention is remarkably excellent in the cathodic peeling resistance as compared with the conventional corrosion-resistant coated steel material.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

As described above, according to the anticorrosion-coated steel material of the present invention in which the adhesion between the chromate layer and the primer layer is improved, a desired cathodic peeling resistance can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an implementation state of a cathode peel test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel material 2 Coating 3 Pt electrode 4 Saturated calomel electrode 5 Potentiometer 6 3% NaCl aqueous solution a Peeling distance

Claims (5)

[Claims] 1. A coated steel material in which a chromate layer, an epoxy primer layer and an organic resin layer are sequentially laminated on a surface of a steel material, wherein the chromate layer in the composite anticorrosion layer has a total chromium content. Gaseous silica having 2 to 4 hydroxyl groups per 1 nm ^{2 of} BET specific surface area of 2.0 to 7.0, and trivalent chromium
0.1 to 0.7, the epoxy primer layer is 1kg of epoxy primer
Per, the epoxy group of the epoxy resin is 1.5 to 5.0 mol,
An anticorrosion-coated steel material having excellent cathodic peeling resistance, comprising 10 to 200 g of a pigment mainly composed of titania. 2. A coated steel material in which a chromate layer, an epoxy primer layer, a modified organic resin layer, and an organic resin layer are sequentially laminated on a surface of a steel material, wherein the chromate layer in the composite anticorrosion layer is provided. Is a gaseous silica having 2 to 4 hydroxyl groups per 1 nm ^{2 of} BET specific surface area in a weight ratio to the total amount of chromium.
0.1 to 0.7, the epoxy primer layer is 1kg of epoxy primer
Per, the epoxy group of the epoxy resin is 1.5 to 5.0 mol,
An anticorrosion-coated steel material having excellent cathodic peeling resistance, comprising 10 to 200 g of a pigment mainly composed of titania. 3. The anticorrosion-coated steel material according to claim 2, wherein the resin constituting the modified organic resin layer is a modified polyolefin resin, and the resin constituting the organic resin layer is a polyolefin resin. 4. The anticorrosion-coated steel material according to claim 2, wherein the resin constituting the modified organic resin layer is a modified polyurethane resin, and the resin constituting the organic resin layer is a polyurethane resin. 5. The epoxy resin constituting the epoxy primer comprises at least one resin selected from an amine resin-modified epoxy resin, a phenol resin-modified epoxy resin, a polyimide resin-modified epoxy resin, and a silicone resin-modified epoxy resin. The anticorrosion-coated steel material according to any one of claims 1 to 4, characterized in that: