JPH01278A - Surface treatment method for organic coating, surface treatment liquid, and organic coated steel with excellent anticorrosion performance - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention provides a method for treating a base for heavy-duty anti-corrosion organic coating on steel materials for structures such as pipelines, the inner and outer surfaces of steel pipes for piping, steel pipe piles, steel sheet piles, and reinforcing bars. and regarding surface treatment liquids and heavy corrosion-resistant organic coated steel materials.

<Prior art and its problems> Conventional surface treatment technology for organic coating will be explained using a polyethylene coated steel pipe as an example.

To bond polyethylene to a steel surface, a layer of polyethylene that has been modified by introducing maleic anhydride or the like is sandwiched between the outer layer of anticorrosive polyethylene and the steel surface that has been cleaned by blasting or pickling. Although heat and pressure bonding is used, peeling from the coating edges and eaves is likely to occur with only that, and the corroded area will spread deep under the coating layer.

In order to cope with this problem, introduction of chemical conversion treatments such as phosphate treatment and chromate treatment has been considered for the purpose of increasing the adhesion between the adhesive modified polyethylene layer and the steel surface.

Among them, chromate treatment is relatively superior, and along with chromic acid, silica or alumina sol (Special Publication Publication No. 42-14
050, Japanese Patent Publication No. 52-2851, etc.) 9 phosphates (Japanese Patent Publication No. 55-35069, etc.) are used as active ingredients, but these were originally used in galvanized steel sheets etc. This product was developed for rust prevention or as a base treatment for coating decorative steel plates and automotive steel plates.It has excellent performance against peeling (hot water peeling, cathode peeling) when relatively thick coatings such as polyethylene are peeled off in hot water environments or under cathodic protection. is insufficient.

On the other hand, apart from chemical conversion treatment, studies have also been conducted to improve the adhesion between the steel surface and the polyethylene layer by forming an organic brimer layer between the steel surface and the modified polyethylene layer. When polyethylene is bonded without using a chemical conversion treatment, the adhesive strength is improved, but the performance against hot water peeling and cathodic peeling is insufficient, as is the case with chemical conversion treatment.

In addition, organic coating systems other than polyethylene coating (epoxy resin, polyurethane, etc.) alone do not have sufficient adhesion and anticorrosion performance, so surface treatments have been introduced and improvements have been made, but as with polyethylene, 5 Further improvement is required.

<Purpose of the Invention> The present invention is intended for use in applications where long-term corrosion protection performance over several decades is required.
In order to deal with corrosion in splash zones and beach areas, and peeling from the coating edges and eaves of externally organic coated line pipes, heavy corrosion-resistant steel pipe piles, steel sheet piles, etc., we have improved salt spray resistance, and installed them underwater. When buried in wetlands, the cathodic peeling resistance has been improved to prevent peeling from defective parts due to electric current during cathodic protection and stray currents.Furthermore, in line pipes, problems arise due to high-temperature operation to improve transportation efficiency. The aim is to improve the anti-corrosion performance required of these organic coated steel materials, such as improved hot water peeling resistance.

<Structure of the Invention> The present inventors focused on the fact that among chemical conversion treatments, chromate treatment is inexpensive and has relatively excellent anti-corrosion and rust-preventing performance for steel materials by itself, and developed an improvement in chromate treatment. I tried.

The chromate treatment solution is mixed with the Or state (trivalent and hexavalent) and additives, i.e., colloidal metal oxides that have a film-forming effect (
The effects of silica, alumina, iron oxide, tin oxide, antimony oxide, titania, zirconia, etc.) and water-soluble organic substances that exhibit reducing properties (ethanol, ethylene glycol, glycerin, starch, etc.) during chromate film formation were investigated in detail.

As a result, a portion of Cr'+ was reduced to trivalent chromic acid (
Or'°/Cr6+≦1) an aqueous dispersion containing colloidal silica at an atomic ratio of Si/Cr of 0.4 to 0.8,
Alternatively, an aqueous dispersion containing an aqueous organic substance such as ethylene glycol or glycerin in a weight ratio of 2 or less to chromic acid can be applied to the steel surface at a dry weight of 0.1 to 10 g/g and dried. The adhesion between the material and the organic coating layer such as polyethylene has been improved, and the anticorrosion performance of salt spray resistance, hot water peeling resistance, and cathodic peeling resistance has been significantly improved to the extent that peeling of the coating layer is hardly observed. We have discovered that this is the case, and have arrived at the present invention.

That is, the present invention provides chromic acid with a Cr"/Cr" of 1 or less and an atomic ratio of Si/II to Crr in the chromic acid.
The present invention provides a base treatment liquid for organic coating of steel, characterized by containing colloidal silica in an amount of r = 0.4 to 0.8, and water.

Further, the present invention provides a chromic acid having a Cr"/Cr6+ of 1 or less, a colloidal silica having an atomic ratio of Si/Cr of 0.4 to 0.8 with respect to Cr in the chromic acid, and Provided is a base treatment liquid for organic coating of steel, which contains water and 200 parts by weight or less of at least one water-soluble organic substance having a reducing property per 100 parts by weight of chromic acid. .

Then, the present invention applies Cr to the surface of the cleaned steel material.
Chromic acid with "/Cr6" of 1 or less and C in the chromic acid
A base treatment liquid containing colloidal silica with an atomic ratio of 0.4 to 0.8 and water is applied to r, with a dry weight of 0.1 to 10 g/d. 50-30
The present invention provides a method for treating a base for organic coating of steel materials, which is characterized by drying at a temperature of 0°C.

In addition, the present invention provides Cr"
Chromic acid with /Cr6+ of 1 or less and C'' in the chromic acid
In contrast, colloidal silica with an atomic ratio of Si/C:r of 0.4 to 0.8, and 100 parts by weight of the chromic acid, 20 parts of at least one water-soluble organic substance having reducing properties.
A base treatment liquid containing 0 parts by weight or less and water is applied at a dry weight of 0.1 to 10 g/m2, and
The present invention provides a method for treating a base for organic coating of steel materials, which is characterized by drying at a temperature of .degree.

Further, the present invention provides a steel material coated with an organic material through an oxide layer containing chromium between the steel material, the amount of the oxide layer deposited is 0.1 to 10 g/d in terms of dry weight, and the oxidized The present invention provides an organic coated steel material having excellent anticorrosion performance, which is characterized by containing silica having an atomic ratio of Si/Cr of 0.4 to 0.8 in the material layer.

<Specific Structure of the Invention> The present invention aims to improve the adhesion and anti-corrosion performance of organic coating on steel materials by providing a stable and stable coating between the steel surface and the organic coating layer. This was achieved by forming a chromate layer that creates a strong bond between both. The chromate layer is formed on steel materials [regardless of steel type or form (steel plate, steel strip, steel sheet pile, steel pipe, etc.)] that has been cleaned by blasting or pickling with the following chromic acid-based treatment solution. After applying it to the surface,
Obtained by drying at a temperature range of 50 to 300°C.

Furthermore, by coating it with an organic coating material such as polyethylene or epoxy, an organic coated steel material with excellent adhesion and anticorrosion performance can be obtained.

The treatment liquid of the present invention contains chromic acid (OS"/Cr6+≦1
)1, colloidal silica has an atomic ratio of St/II
: Water consisting of r of 0.4 to 0.8 and water, or in addition, a water-soluble and reducing organic substance such as ethanol, ethylene glycol, glycerin, starch, etc. in a weight ratio of 2 or less to chromic acid. It is a dispersion liquid. By applying this aqueous dispersion at a dry weight of 0.1 to 10 g/m2 (preferably 0.3 to 2 g/m2), a very high surface treatment effect is exhibited.

It is believed that the effects of other treatments of the present invention are caused by the following factors.

First, the chromate layer (chromate and silica) has a small oxygen reduction current during cathodic polarization, and in order to suppress the generation of hydrogen and alkali in the chromate layer under cathodic protection or in corroded local cells, it is necessary to prevent peeling and corrosion. slow down progress.

The reason why Cr3+/C'6+ of chromic acid is set to 1 or less is that if Cr'/Cr'+ exceeds 1, sediment will occur and the liquid will become unstable.

Furthermore, there is an optimum amount of silica relative to the amount of chromic acid, which makes the chromate film strong and stable. Therefore, the composition ratio of chromic acid and silica needs to be set within a narrow range of 0.4 to 0.8 in terms of atomic ratio Si/Cr.

The test materials shown in Table 1 below, prepared by varying the ratio of 5i10r in the base treatment solution, were subjected to a cathode peel test and a salt spray test as described in the <Example> section below.

FIG. 1 shows the results of the cathodic peel test. According to this, when the 5i10r ratio was in the range of 0.4 to 0.8, the progress distance of peeling was as small as 1 mm or less, which was extremely good. Furthermore, even if Si/(:r exceeds 0.8, the progress distance of cathode peeling does not immediately increase rapidly;
The salt spray test resulted in increased peeling.

Based on this knowledge, the atomic ratio Si/Cr of Or in the chromic acid and Si in the silica of the base treatment method for organic coating and the base treatment liquid of the present invention was set to 0.4 to 0.8.

Table 1 Composition of test materials On the other hand, ethanol, ethylene glycol, glycerin,
A water-soluble organic substance having a reducing power such as starch has the function of increasing the reduction ratio of chromium in the chromate layer and making the chromate layer strong and hardly soluble in water. As a result, the adhesion with the organic coating layer is improved, and peeling of the organic coating layer is suppressed. However, if these are present in excess in the chromate layer, they are inherently water-soluble, so they may easily dissolve the chromate layer, or the chromate layer after the organic matter itself has eluted may form a mesh shape, making it stronger. becomes weaker.

Therefore, the total amount of water-soluble organic matter added is 10% of chromic acid.
It is necessary to make it 200 parts by weight or less with respect to 0 parts by weight.

Next, a method for treating a base for an organic film according to the present invention will be explained.

The amount of the chromate treatment liquid applied is 0.00% by dry weight. If it is less than 1 g/m2, the effect of improving corrosion protection performance will be small, and if it exceeds 10 g/rn2, the chromate layer will easily receive water intrusion from the end face direction at the eaves of the organic coating, and the steel surface will The anchoring effect of the material is reduced, and when the upper coating layer is subjected to lateral shrinkage stress as in the case of polyethylene, peeling becomes more likely to occur. Therefore, the coating amount of the treatment liquid is 0.1 to 10 g/rn2 in terms of dry weight.

The drying temperature of the treatment liquid is preferably 50 to 300°C.
At temperatures lower than 50°C, the reaction between the treatment solution and the steel surface is insufficient, and moisture within the chromate layer is difficult to release. At temperatures above 300°C, the chromate layer rapidly shrinks and cracks occur on the surface. This is because it causes

After performing the base treatment according to the present invention as described above,
An organic coating can be applied thereon. The coating material includes all kinds of resins such as polyethylene, epoxy resin, polyurethane, polyvinyl chloride, nylon, and polyester.
By coating in a temperature range up to .degree. C., the organic coated steel material of the present invention having excellent adhesion and anticorrosion performance can be obtained.

The amount of silica (atomic ratio Si/Cr) in the oxide layer (chromate layer) in the organic coated steel material of the present invention is the silica amount (atomic ratio Si/Cr) in the base treatment solution of the present invention (f!).
fl, r).

<Example> EXAMPLES The present invention will be explained in detail by way of examples below.

(Example 1) A common steel plate (SS41) with a thickness of 3.2 mm x 150 mm x 150 mm was subjected to blast treatment using alumina #40 to thoroughly clean the steel plate surface, and then treatment solution 1 of the present invention [chromic acid , (Cr”/ (:r”= 0, 3
5) In contrast to 1, colloidal silica (atomic ratio Si/
1 g/rr? After coating and drying for 15 minutes in an electric oven at 160°C,
Polyethylene was immediately pressed using a hot press at 180° C. for 10 minutes. 2mm for outer layer polyethylene
Thick high-density polyethylene, adhesive polyethylene
．． A modified polyethylene having a thickness of 5 mm and containing 0.03 wt % maleic anhydride was used.

(Example 2) Treatment liquid 2 of the present invention [chromic acid, (-Cr3+/Cr6+
=0.35) 1, the atomic ratio of colloidal silica is S
i/Cr of 0.55, glycerin to chromic acid weight ratio of 0.2 and water (weight ratio of chromic acid to 38
．． The surface treatment was carried out in the same manner as in Example 1, except that 3) was used, and polyethylene was crimped in the same manner.

(Example 3) Ordinary steel plate (SS41) in which the surface of the steel plate was cleaned and the surface was treated with the treatment liquid 1 of the present invention in the same manner as in Example 1.
was heated to 180°C and coated with epoxy powder.

The epoxy powder coating used was a resin coating using a phenolic curing agent, and the coating thickness was 360 μm.

(Comparative Example 1) An ordinary steel plate whose surface was cleaned in the same manner as in Example 1 (
SS41) was preheated at 160° C. for 15 minutes without surface treatment, and polyethylene was crimped in the same manner as in Example 1.

(Comparative Example 2) An ordinary steel plate whose surface was cleaned in the same manner as in Example 1 (
Chromate treatment solution A [chromic acid (Gr
"/C"s+=0,54) 1, after applying colloidal silica with an atomic ratio of Si/Cr of 1.5 and water] at a dry weight of 1 g/rrr', 160
After drying at ℃ for 15 minutes, polyethylene was immediately pressed in the same manner as in Example 1.

(Comparative Example 3) As a base treatment, chromate treatment liquid B containing phosphate (
A chromate layer with a dry weight of 1 g/m2 was formed using chromic acid (Cr3"/Cr"=0,37) 1, phosphoric acid at a molar ratio of 1+3P04/Cr of 0.2, and water. Other than that, the same procedure as Comparative Example 2 was carried out.

(Comparative Example 4) An ordinary steel plate whose surface was cleaned in the same manner as in Example 1 (
SS41) was preheated at 160°C for 15 minutes, and a commercially available amine curing type epoxy primer was applied to a thickness of 30 μm.
After curing at 160°C for 10 minutes, polyethylene was immediately pressed in the same manner as in Example 1.

(Comparative Example 5) An ordinary steel plate whose surface was cleaned in the same manner as in Example 1 (
S3.41) was coated with epoxy powder in the same manner as in Example 3 without performing any surface treatment.

(Comparative Example 6) After cleaning the steel plate and performing base treatment with chromate treatment liquid B in the same manner as in Comparative Example 3, epoxy powder coating was performed in the same manner as in Example 3.

The following tests were conducted on the various steel plates obtained as described above in order to investigate their anticorrosion performance. The results are shown in Table 2 below.

1. Salt spray test specimen size 50 x 50 mm coated steel plate with 30
Make an X30 cross cut up to the steel surface and seal the coated end and back surface.

It was exposed for 30 days under JIS 22371 conditions and evaluated based on the peeling distance from the eaves.

2. Warm salt water immersion test A coated steel plate with a sample size of 50 x 100 mm was immersed as it was in a 3% NaCiL aqueous solution at 80°C for 30 days without sealing the edges and back, and then the peel strength was measured and evaluated at room temperature. .

3.Cathode peeling test A hole of 5 mm diameter was drilled in the center of the coated steel plate with specimen size 10100xlOO to the steel surface, and while applying cathodic protection at -1.5V vs SCE, it was heated to 3% CIt aqueous solution at room temperature.
The film was exposed for 0 days, and the peeling distance that progressed during that period was measured and evaluated.

As is clear from Table 2 below, the organic coated steel materials of Examples 1, 2 and 3 obtained by the organic coating base treatment method of the present invention were highly evaluated in all of the salt spray test, warm salt water immersion test, and cathode peeling test. It was confirmed that the material had excellent corrosion protection performance overall.

<Effects of the Invention> According to the base treatment liquid for organic coating, the base treatment method using the same, and the organic coated steel of the present invention, corrosion resistance is significantly improved compared to conventional organic coated steel.

Therefore, steel pipes for externally coated line pipes with excellent corrosion resistance,
We can provide small diameter inner and outer coated steel pipes, steel materials for heavy corrosion protection structures (steel pipe piles, steel sheet piles, reinforcing bars, steel frames, etc.).

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the Si/Cr ratio in the chromate treatment solution and anticorrosion performance (cathode peeling progress distance). FIG.1

Claims (5)

[Claims] (1) Chromic acid with Cr^3^+/Cr^6^+ of 1 or less and a colloid with an amount of Si/Cr in the atomic ratio of 0.4 to 0.8 with respect to Cr in the chromic acid. A base treatment liquid for organic coating of steel, characterized by containing silica and water. (2) Chromic acid with Cr^3^+/Cr^6^+1 or less and an atomic ratio of Si/Cr of 0 to Cr in the chromic acid
．． It is characterized by containing colloidal silica in an amount of 4 to 0.8, 200 parts by weight or less of at least one water-soluble organic substance having reducing properties per 100 parts by weight of the chromic acid, and water. Base treatment liquid for organic coating of steel materials. (3) Cr^3^+/C on the surface of the cleaned steel material
Chromic acid with r^6^+ of 1 or less and Cr in the chromic acid
On the surface, a base treatment liquid containing colloidal silica with an atomic ratio of 0.4 to 0.8 Si/Cr and water is applied at a dry weight of 0.1 to 10 g/m^2, This is 50-3
1. A method for treating a base for organic coating of steel material, the method comprising drying at a temperature of 00°C. (4) Cr^3^+/C on the surface of the cleaned steel material
Chromic acid with r^6^+ of 1 or less and Cr in the chromic acid
In contrast, colloidal silica with an atomic ratio of Si/Cr of 0.4 to 0.8 and 100 parts by weight of the chromic acid,
200% of at least one water-soluble organic substance with reducing properties
An organic coating for steel material characterized by applying a base treatment liquid containing 0.1 to 10 g/m^2 in dry weight and drying it at a temperature of 50 to 300°C. Groundwork treatment method. (5) In a steel material coated with an organic material through an oxide layer containing chromium between the steel material, the amount of the oxide layer deposited is 0.1 to 10 g/m^2 in terms of dry weight, and the oxide layer An organic coated steel material with excellent anti-corrosion performance, characterized in that the layer contains silica with an atomic ratio of Si/Cr of 0.4 to 0.8.