JP3260957B2 - Heavy corrosion protection coated steel with excellent resistance to cathodic peeling at high temperatures - 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-duty corrosion-resistant coated steel.
More specifically, the present invention relates to a heavy-duty corrosion-resistant coated steel material having excellent resistance to cathodic peeling at high temperatures.

[0002]

2. Description of the Related Art Heavy corrosion protection coated steel is usually used for a long period of time in combination with cathodic protection. However, cathodic peeling occurs when the alkali generated by the anticorrosion current peels off from the damaged portion of the coating when transported and laid. Due to the phenomenon referred to as 1), the anticorrosion performance decreases. In recent years, along with an increase in demand and a demand for maintenance-free, a demand for its anticorrosion performance has also become strict, and improvement of high-temperature cathodic peeling performance of heavy anticorrosion coated steel materials has become an important issue.

[0003] In order to improve the anticorrosion performance of coated steel, it is necessary to firmly adhere the coating to the surface of the steel. As a method for improving the adhesion of the coating, chromic acid,
A method has been proposed in which a chromate treatment agent comprising a reducing agent, gas phase or liquid phase silica, phosphoric acid, alkali metal ions or the like is used as a base treatment. For example, JP-A-3-6639
As can be seen in Japanese Patent Publication No. 3, a reducing agent is added to the aqueous solution of chromic acid,
Silica fine particles, chromate treatment agent with phosphoric acid, etc.
Also, as seen in JP-A-3-234527,
There are chromate treatment agents having good high-temperature cathodic peeling performance by adding a silane coupling agent.

[0004]

However, when such a surface treatment agent is applied to a heavy corrosion-resistant coated steel material, a treatment agent in which liquid phase silica is added to chromate is a treatment in which liquid phase silica is not added. As compared with the agent, the effect of its addition on the cathodic peeling resistance is small. (b) In the treating agent obtained by adding phosphoric acid to chromate, the larger the amount is, the lower the cathodic peeling resistance is. For example, the effect of improving the cathodic peeling performance is not seen for the cathodic peeling performance.
Meeting performance demands is difficult. The conventional techniques have the above-mentioned problems.Moreover, in a treating agent in which a large amount of gas-phase silica is added to d-chromate, in a high-temperature environment due to a decrease in alkali-soluble resistance, Cathode peeling resistance may decrease. (e) Increasing the chromium reduction ratio in the chromate improves the alkali dissolution resistance of the chromate layer, but lowers the adhesion to the underlying steel material and lowers the cathodic peeling resistance.

[0005] From the above points, it has been difficult to obtain the desired cathode peeling resistance. In addition , high temperature above normal temperature during chromate
Addition of glucose or the like , which has a reducing action at a temperature, or a silane coupling agent has been difficult to put into practical use due to poor chromate stability. In view of the above, an object of the present invention is to provide a heavy-duty corrosion-resistant coated steel material excellent in high-temperature cathodic peeling performance.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively studied a chromate treatment agent, and as a result, have found that a monohydric alcohol and / or
Or a reducing agent which is a carboxylic acid, and the weight ratio of trivalent chromium to total chromium is 0.1 while leaving unreacted reducing agent.
Partial reduction is performed to 0.7, and the specific surface area is 1 nm.
By using a chromate treating agent containing a large amount of gas-phase silica having ^{2 to} 4 hydroxyl groups per 2 in a weight ratio of 2.0 to 7.0 times relative to the total chromium, a weight excellent in high-temperature cathodic peeling resistance is obtained. The present inventors have found that an anticorrosion coated steel material can be obtained, and have reached the present invention.

That is, according to the present invention, a monovalent alcohol and / or a carboxylic acid is added to an aqueous chromium solution on a steel material surface.
The partial reduction is performed so that the weight ratio of trivalent chromium to total chromium is 0.1 to 0.7 while leaving the unreacted reducing agent, and ^{2 to} 4 chromium per 1 nm ^{2 of} specific surface area is added. Gaseous silica having a hydroxyl group of 2.
A chromate-treating agent added by 0-7.0 times is applied and dried to form a chromate base layer for a heavy-duty anticorrosion coating, and an epoxide formed as a primer on the chromate layer is 3.5-5.0.
An object of the present invention is to provide a heavy-duty corrosion-resistant coated steel excellent in high-temperature cathodic peeling resistance, comprising an organic resin coating film containing mol / kg and an organic resin layer further formed thereon. The drying temperature of the chromate treatment agent is 60-300 ° C., and the amount of the chromate layer deposited is 100-100
It is preferably 00 mg / m ² . The organic resin coating film of the primer is a film of an epoxy-modified resin, and the upper organic resin layer is a layer formed of a modified polyolefin resin and a polyolefin resin of the upper layer, or a modified polyurethane resin and a polyurethane resin of the upper layer. Is preferred. Modification of the modified polyolefin resin and modified polyurethane resin in the present invention is preferably performed with an anhydride such as maleic anhydride. The gas-phase silica in the present invention is silica particles produced by subjecting an organic silica compound or the like to thermal decomposition in a gas phase, and is generally referred to as gas-phase silica. For example, finely divided silicon dioxide produced by hydrolysis of a volatile silane compound in an oxyhydrogen flame, or silicon tetrachloride or the like as a starting material and formed into fine particles by a gas phase method are exemplified.

[0008]

The present invention will be described below in more detail. The steel material used in the present invention is a shaped steel such as an H-shaped steel, an I-shaped steel, or an L-shaped steel, a steel sheet pile, a steel bar, a steel wire, a cast iron pipe, a steel pipe or a thick steel plate, a hot-rolled steel plate, a cold-rolled steel plate or the like. , Etc. are optional.

Next, the chromating agent used in the present invention will be described. The chromate treating agent used in the present invention refers to a chromium aqueous solution obtained by dissolving a chromium source such as chromic anhydride (CrO ₃ ), chromic acid, or dichromic acid in pure water, and having a specific surface area of ² per 1 nm 2. It is a mixture of gas-phase silica fine particles having up to four hydroxyl groups.

As the reducing agent used for the partial reduction of chromium from hexavalent to trivalent, CH ₃ OH, C ₂ H ₅ OH, C ₃
A reducing agent such as a monohydric alcohol such as H ₇ OH or a carboxylic acid such as formic acid, acetic acid or oxalic acid is used. This is reducing action at high temperature
This is because, when a reducing agent is used, the chromate is easily gelled by the unreacted reducing agent.

The reason why the partial reduction of chromium from hexavalent to trivalent is performed in order to increase the alkali dissolution resistance of the chromate layer. Trivalent reduced chromium and hexavalent chromium combined with trivalent chromium do not dissolve in alkali. However, when the amount of trivalent chromium increases, the reaction between the steel material surface and hexavalent chromium hardly occurs, and the adhesion between the steel material surface and the chromate layer decreases. The degree of reduction is such that trivalent chromium is 0.1 to 0.7 with respect to all chromium. This is 0.
If it is less than 1, the amount of trivalent chromium is small and the chromate layer is easily dissolved, which is not preferable. If it is more than 0.7, the amount of hexavalent chromium that reacts with the steel surface is small, and the adhesion between the steel surface and the chromate decreases. To do that.

It is considered that the reducing agent reacts with chromium (hexavalent) as follows when, for example, methanol is used as the reducing agent. 2HCrO ₄ ⁻ + CH ₃ OH + 8H ⁺ → Cr ³⁺ CO ₂ +
6H ₂ O This reaction is an equilibrium reaction and an unreacted reducing agent always exists.
The same applies when a carboxylic acid is used. This unreacted reducing agent further promotes the reduction reaction when the upper layer of chromate is coated and heated. Therefore, a chromate having good reactivity with the steel material surface and good alkali solubility resistance is obtained.

Before applying the chromate treatment agent to the steel material surface, oil, scale, etc. on the steel material surface are removed by degreasing, pickling, blasting or the like. When a chromate treatment agent is applied to the surface of the steel material from which the scale or the like has been removed, hexavalent chromium is partially reduced by the oxidizing action of the steel material and heating after the application, and a dehydration condensation reaction of the hydroxyl groups bonded to the chromium proceeds, A chromate film having excellent alkali dissolution resistance is formed.

The gas-phase silica fine particles to be added to the above-mentioned chromate treating agent include, for example, Aerosil 130, Aerosil 380, Aerosil O, manufactured by Nippon Aerosil Co., Ltd.
Specific surface area of 1 nm, such as X50, Aerosil OX170
Gas-phase silica having ^{2 to} 4 hydroxyl groups per 2 is used alone or in combination of two or more. Incidentally, by N ₂ adsorption method according to the BET method to the specific surface area of the gas phase silica in this invention. If the number of hydroxyl groups per 1 nm ^{2 of} specific surface area is less than 2, the effect of the hydroxyl groups of the gas phase silica is not exhibited, and if it is more than 4, the solubility resistance of the chromate treatment layer is reduced.

Measurement results of elemental distribution in the depth direction of the chromate layer by GDS (glow discharge optical emission spectroscopy) (FIG. 2), a chromate-treated layer in which gas phase silica was added in an amount of SiO ₂ /Cr=3.2, and phenylglycidyl ether (PG
As can be inferred from the contact angle measurement results of E) (Table 1), in the gas phase silica, hydroxyl groups on the surface react with functional groups such as epoxide in the upper coating film, and the chromate-treated layer and the upper coating film It is believed to increase the adhesion of the layer. The relationship between the contact angle θ and the adhesiveness shown in FIG. 3 can be expressed by the Young's formula as follows: work of attachment W = γ · (1 + cos θ) γ: surface tension of resin, and when γ is the same, the contact angle is small. The larger the attachment work, the greater the adhesion.

[0016]

The amount of the gas phase silica fine particles to be added is such that the weight ratio to the total chromium in the chromate treatment liquid is in the range of 2.0 to 7.0 times. When the addition amount of the gas-phase silica fine particles is less than 2.0 times, the total amount of the hydroxyl groups of the gas-phase silica effective for adhesion is small, so that the difference in the cathodic peeling performance due to the epoxide concentration of the primer is large, and when the addition amount is more than 7.0 times. It is not preferable because the effect of lowering the alkali solubility of the chromate treatment layer is large.

The baking temperature of the chromate treatment agent is suitably from 60 to 300 ° C. on the surface of the steel material. Steel surface temperature is 60
If the temperature is lower than 0 ° C, the chromate-treated layer may be dissolved when the organic resin is applied to the upper layer, which is not suitable. If the surface temperature of the steel material is higher than 300 ° C, the dehydration-condensation reaction of hydroxyl groups proceeds too much, and the upper layer is formed. Hydroxyl groups on the surface of the chromate treatment layer required for adhesion to the organic resin layer are lost, which is not preferable for improving the cathode peeling resistance. The amount of the chromate treating agent is preferably 100 to 1000 mg / m ^{2 in} terms of the total chromium weight. If the adhesion amount is less than 100 mg / m ² , the effect of the chromate treatment agent is not exhibited, and the adhesion amount is 1000 m / m ^2.
If it is more than g / m ² , the influence of the decrease in the dissolution resistance of the chromate-treated layer is undesirably large.

Next, the organic resin coating film used for the primer treatment on the above-mentioned chromate treatment layer will be described.
The organic resin coating film used for the primer treatment of the upper layer of the above-mentioned chromate treatment layer is an amine epoxy resin, a phenol
Epoxy resin, polyimide / epoxy resin, epoxy /
It is a coating film obtained by applying and curing a modified epoxy resin such as a silicone resin, a solvent-free paint containing an epoxy-modified resin as a main component, a solvent paint, or a powder paint. Here, the epoxide concentration is 3.5 to 5.0 mol / kg. This is 3.5mol / kg
If the amount is less than the above, the adhesive strength to the chromate layer is weak, and desired performance cannot be obtained. In the present invention,
The epoxide content of 3.5 to 5.0 mol / kg means that the epoxide in the resin forming the primer layer is 3.5 to 5.0 mol / kg.
l / kg. The epoxide in the present invention refers to an oxide forming a three-membered ring, and the epoxide contained per 1 kg of resin solid content forming the primer layer (=
(Epoxy group) of 3.5 to 5.0 mol.

In the paint containing the above-mentioned organic resin as a main component,
Pigments and the like can be added in addition to the organic resin as the main component. Pigments are silica, alumina, titania, talc, silicate, zinc white, aluminum phosphate, carbon black, red iron oxide, aniline black, azo pigments,
It is a general extender pigment such as phthalocyanine and a coloring pigment.
In addition, the primer layer is usually applied to about 10 to 100 μm.

Next, the upper organic resin layer provided on the primer layer will be described. The upper organic resin coating film referred to in the present invention is an organic resin film such as a polyolefin resin via a modified polyolefin resin or a polyurethane resin via a modified polyurethane resin. This layer may be provided in any number of layers. The reason for using the modified resin for the upper organic resin layer is that
This is for improving the adhesion between the primer and the upper organic resin layer. In addition, a pigment or the like can be added to the organic resin as the main component. Pigments are silica, alumina,
General extender pigments such as titania, talc, silicate, zinc white, aluminum phosphate, carbon black, red iron oxide, aniline black, azo pigment, phthalocyanine,
It is a coloring pigment. In addition, the thickness of this layer is usually 0.5 to
It is applied about 20 mm.

FIG. 5 shows a cross section of the heavy corrosion-resistant coated steel material according to the present invention obtained as described above. In the figure, when the chromate treatment layer has a chromium adhesion amount of 100 mg / m ² or more, and the organic resin layer as a primer has a thickness of 10 μm or more, good cathode peeling resistance can be obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments. (Example) JIS G3141, SPCC steel sheet (sheet thickness 1
mm), a chromate treatment agent is applied by a spin coater at 300 mg / m ^2, and baked at 80 ° C., and then, as a primer, an epoxy resin (manufactured by Mitsubishi Kasei Co., Ltd.) is applied to a thickness of about 30 μm. After coating and drying at 120 ° C., modified polyethylene (manufactured by Mitsubishi Kasei Co., Ltd.) and polyethylene (manufactured by Mitsubishi Kasei Co., Ltd.) were pressure-bonded to a total thickness of 2 mm after coating to obtain a sample ( The laminated structure of the coating film is shown in FIG. 5). At that time, the above-mentioned chromate treating agent component and the epoxide concentration of the primer used were those prepared as follows. Silica was manufactured by Nippon Aerosil Co., Ltd., and gas-phase silica having ^{2 to} 4 hydroxyl groups per 1 nm ^{2 of} specific surface area was used.

[Inventive Example 1] Chromate treatment liquid: weight ratio of trivalent chromium to total chromium = 0.4 Methanol as a reducing agent was 0.4 weight ratio to total chromium.
Weight ratio of gas phase silica to total chromium added = 4.0 Epoxy resin: Epoxide concentration = 4.5 mol / kg (amine / epoxy resin)

[Inventive Example 2] Chromate treatment liquid: weight ratio of trivalent chromium to total chromium = 0.4 Oxalic acid was added as a reducing agent at a weight ratio of 0.5 to total chromium Weight of gas phase silica to total chromium Ratio = 3.0 Epoxy resin: Epoxide concentration = 3.8 mol / kg (amine / epoxy resin)

[Inventive Example 3] Chromate treatment solution: weight ratio of trivalent chromium to total chromium = 0.2 Methanol as a reducing agent is 0.1 to weight ratio of total chromium.
5 Weight ratio of gas phase silica to total chromium = 4.5 Epoxy resin: Epoxide concentration = 4.5 mol / kg (phenol-epoxy resin)

[Inventive Example 4] Chromate treatment solution: weight ratio of trivalent chromium to total chromium = 0.3 Methanol as reducing agent is 0.2 to weight ratio to total chromium.
5 Weight ratio of gas phase silica to total chromium = 3.5 Epoxy resin: Epoxide concentration = 4.0 mol / kg (polyimide epoxy resin)

[Inventive Example 5] Chromate treatment solution: weight ratio of trivalent chromium to total chromium = 0.2 Oxalic acid as a reducing agent is 0.20 weight ratio to total chromium.
Weight ratio of gas phase silica to total chromium added = 6.0 Epoxy resin: Epoxide concentration = 5.0 mol / kg (epoxy / silicone resin)

Comparative Example 1 Chromate treatment liquid: weight ratio of trivalent chromium to total chromium = 0 (no reducing agent added) weight ratio of gas phase silica to total chromium = 4.0 Epoxy resin: epoxide concentration = 4 .5mol / kg (amine / epoxy resin)

[Comparative Example 2] Chromate treatment liquid: weight ratio of trivalent chromium to total chromium = 0.2 Methanol as a reducing agent was 0.2 to weight ratio to total chromium.
After the addition of 5, the chromate solution was heated to remove the unreacted reducing agent. The weight ratio of gas phase silica to total chromium = 4.0 Epoxy resin: Epoxide concentration = 4.3 mol / kg (amine / epoxy resin)

Comparative Example 3 Chromate treatment liquid: weight ratio of trivalent chromium to all chromium = 0.4 Methanol as a reducing agent was 0.4 weight ratio to all chromium.
Weight ratio of gas-phase silica to total chromium added = 1.5 Epoxy resin: Epoxide concentration = 4.0 mol / kg (polyimide / epoxy resin)

Comparative Example 4 Chromate treatment liquid: weight ratio of trivalent chromium to total chromium = 0.3 Methanol as a reducing agent was 0.2 to weight ratio of total chromium.
5 Weight ratio of gas-phase silica to total chromium = 6.0 Epoxy resin: Epoxide concentration = 2.5 mol / kg (epoxy / silicone resin)

[Comparative Example 5] Chromate treatment liquid: weight ratio of trivalent chromium to total chromium = 0.4 weight ratio of gas phase silica to total chromium = 3.5 weight of oxalic acid as a reducing agent relative to total chromium After adding 0.5, the chromate solution is heated and the unreacted reducing agent is removed. Epoxy resin: epoxide concentration = 4.5 mol / kg (phenol / epoxy resin)

Test / Evaluation Method The center of the sample prepared by the above-mentioned method was
After a defect of mmφ was created and an apparatus as shown in FIG. 6 was installed, a cathode peeling test was performed. Test conditions: 80 ° C for 14 days, 80 ° C for 30 days. After the test, the coating film near the peeling portion of the sample was peeled off, and the peeling distance (portion a in FIG. 6) was measured. Table 2 shows the results of the above-mentioned cathode peel test.

[0035]

[0036]

As is clear from the examples, the heavy corrosion-resistant coated steel material according to the present invention is much more excellent in the high-temperature cathodic peeling resistance than the conventional heavy corrosion-resistant coated steel material. I got it.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining cathodic peeling of a heavy corrosion-resistant coated steel material.

FIG. 2 is a diagram showing a GDS measurement result.

FIG. 3 is a diagram for explaining adhesiveness with a chromate layer according to a contact angle.

FIG. 4 is a diagram showing the structure of a heavy-corrosion-coated steel material of the present invention.

FIG. 5 is a diagram showing the structure of a heavy-corrosion-coated steel material of an example.

FIG. 6 is a diagram of a cathode peel test apparatus.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-234527 (JP, A) JP-A-62-222841 (JP, A) JP-A-63-157878 (JP, A) JP-A-1- 150539 (JP, A) JP 3-66393 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 15/08 B05D ⁷ /14-7/24 C23C 22/00- 22/86

Claims (5)

(57) [Claims] A chromium aqueous solution is added to a monovalent alcohol on a steel material surface.
And a partial reduction is performed so that the weight ratio of trivalent chromium to total chromium is 0.1 to 0.7 while leaving an unreacted reducing agent. A chromate-treating layer formed by applying and drying a chromate treating agent in which gas-phase silica having ^{2 to} 4 hydroxyl groups per 1 nm ^{2 is} added to the total chromium in a weight ratio of 2.0 to 7.0 times, and An organic resin coating film containing 3.5 to 5.0 mol / kg of an epoxide formed as a primer on the upper layer, and an organic resin layer further formed on the organic resin coating layer. Heavy corrosion protection coated steel. 2. The heavy corrosion-resistant coated steel material according to claim 1, wherein the amount of the chromate layer deposited is 100 to 1000 mg / m ² in terms of chromium weight. 3. The drying temperature of the chromate treating agent is 60 to 3
The heavy corrosion-resistant coated steel material according to claim 1, wherein the temperature is 00 ° C. 4. 4. The heavy-corrosion-coated steel material according to claim 1, wherein the organic resin coating film of the primer is a film of an epoxy-modified resin. 5. The anticorrosion-coated steel material according to claim 1, wherein the organic resin layer is formed of a modified polyolefin resin and a polyolefin resin as an upper layer thereof, or a modified polyurethane resin and a polyurethane resin as an upper layer thereof. .