JPS63243279A - Pretreatment for organic coating and pretreating liquid - Google Patents

Abstract

PURPOSE:To improve adhesivity of an org. film formed on the substrate surface on a steel material by previously applying a treating liq. contg. specified amts. of chromic acid contg. Cr<6+> partially reduced to Cr<3+>, colloidal silica and water to the surface of the steel material and by drying the applied liq. CONSTITUTION:An aq. dispersion liq. contg. chromic acid contg. Cr<6+> partially reduced to Cr<3+> (Cr<3+>/Cr<6+=1) and colloidal silica in 0.4-0.8atom. ratio of Si to Cr or further contg. a water soluble org. reducing substance such as ethylene glycol by <=200pts.wt. per 100pts.wt. chromic acid is prepd. as a pretreating liq. for org. coating. The liq. is applied to the surface of a steel material by 0.1-10g/m<2> on dry basis and dried at 50-300 deg.C. By this pretreatment, the adhesion of an org. coating layer of polyethylene or the like to the surface of the steel material and the corrosion preventiveness of the coated steel material are improved.

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 base treatment liquids.

<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
No. 050, Japanese Patent Publication No. 52-2851, etc.) and phosphates (Japanese Patent Publication No. 55-350695069 containing other effective ingredients) are used, but these were originally used to prevent rust on galvanized steel sheets, etc. It was developed for painting base treatment of decorative steel sheets and automobile steel sheets, and its performance against peeling (hot water peeling, cathodic peeling) with relatively thick coatings such as polyethylene in hot water environments or under cathodic protection is insufficient. be.

On the other hand, apart from chemical conversion treatment, a study was also conducted to improve the adhesion between the steel surface and the polyethylene layer by forming a single layer of organic primer 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, , 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 Cr 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 part of [:r” was reduced to trivalent chromic acid (
Cr”/Cr”≦1) An aqueous dispersion containing colloidal silica with an atomic ratio of Si/Cr of 0.4 to 0.8, or further aqueous organic matter such as ethylene glycol or glycerin with chromium. Applying an aqueous dispersion containing an acid to weight ratio of 2 or less at a dry weight of 0.1 to 10 g/rn'',
Drying improves the adhesion between the steel surface and the organic coating layer such as polyethyline, improving salt spray resistance, hot water peeling resistance,
It was discovered that the anticorrosion performance of cathodic peeling resistance was significantly improved to the extent that peeling of the coating layer was hardly observed, and the present invention was achieved.

That is, the present invention provides chromic acid with a Cr3"/Cr" of 1 or less and an atomic ratio of 5t10r to Cr in the chromic acid.
The present invention provides a base treatment liquid for organic coating of steel material, which contains colloidal silica in an amount of 0.4 to 0.8, and water.

In addition, chromic acid with Cr"/Cr6"" of 1 or less and Si/Cr in the atomic ratio of 0.4 to 0.4 to Cr in the chromic acid.
colloidal silica in an amount of 0.8 and the chromic acid 100
The present invention provides 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.

Then, Cr3+/Cr
A base treatment solution containing chromic acid with 6+ of 1 or less, colloidal silica with an atomic ratio of Si/Cr of 0.4 to 0.8 relative to Or in the chromic acid, and water, 0.1-10g/rr in dry weight? Apply this to 50-300℃
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 .

In addition, Cr3"/Cr" was added to the surface of the cleaned steel material.
is 1 or less, colloidal silica having an atomic ratio of 5t10r of 0.4 to 0.8 with respect to Cr in the chromic acid, and at least one type of colloidal silica with respect to 100 parts by weight of the chromic acid. A base treatment solution containing 200 parts by weight or less of a water-soluble organic substance having reducing properties and water is 0.1 to 0.1 parts by dry weight.
The present invention provides a method for treating a base for organic coating of steel material, which comprises applying 10 g/m' of organic coating and drying it at a temperature of 50 to 300°C.

<Specific Structure of the Invention> The present invention aims to improve the adhesion and anti-corrosion performance of the 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.

The IA treatment solution of the present invention, chromic acid (cr3/cr6+≦1
)1, colloidal silica has an atomic ratio of Si/Cr
is 0.4 to 0.8, and water, or further, an aqueous dispersion consisting of 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. The dry weight of this aqueous dispersion is 0.1 to 10 g/rr? (preferably 0.3 to 2 g/rn''), it exhibits a very high surface treatment effect.

It is believed that the high surface treatment effect of the present invention is 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 corrosion shoulder cells, it is necessary to prevent peeling and corrosion. Suppress the progression of 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 to silica is 0.00% in atomic ratio of Si/Cr to 1% chromic acid.
It is necessary to set it within a narrow range of 4 to 0.8.

The test materials shown in Table 1 below, which were prepared with various Si/Cr ratios in the base treatment solution, were subjected to cathodic peeling tests and salt water spray tests as described in the <Example> section below.

FIG. 1 shows the results of the cathodic peel test. According to this, when the St/(:r 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. However, although 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 St/Cr of Cr in the chromic acid and St 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, since they are inherently water-soluble, the chromate layer may become more easily dissolved, or the chromate layer may form a network after the organic matter itself has eluted, resulting in increased strength. 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/rn2, the effect of improving corrosion protection performance will be small, and if it exceeds 10 g/m2, the chromate layer will easily receive water from the end surface direction due to the extension 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 set to 0.61 to 10 g/rrl 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 the moisture in the chromate layer is difficult to release. At temperatures above 300°C, the chromate layer rapidly shrinks and forms on the surface. This is because cracks occur.

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, polycrethane, polyvinyl chloride, nylon, and polyester.
By coating at temperatures up to ℃, organic coated steel materials with excellent adhesion and anticorrosion performance can be obtained.

<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 blasted using alumina #40 to sufficiently clean the surface of the steel plate, and then treatment solution 1 of the present invention [chromic acid , (CS"/Cr"=0, 3
5) For 'i, colloidal silica atomic ratio St/
(consisting of :, r of 0.55 and water (weight ratio of chromic acid of 38.5)) at a dry weight of 1 g/m
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. 2 for the outer layer polyethylene
The adhesive polyethylene used was 0.5 mm thick modified polyethylene into which maleic anhydride was introduced.

(Example 2) Treatment liquid 2 of the present invention [chromic acid, (Cr 3 N-/Cr
``=0.35)1, colloidal silica has an atomic ratio of St/Cr of 0.55, glycerin has a weight ratio of 0.2 to chromic acid, and water (38.3 has a weight ratio of chromic acid to chromic acid). The base treatment was carried out in the same manner as in Example 1, except that the material [consisting of] was used, and polyethylene was crimped in the same manner.

(Example 3) An ordinary steel plate whose surface was cleaned and surface treated with the treatment liquid 1 of the present invention in the same manner as in Example 1 was heated at 180°C.
The temperature was raised to 100% and epoxy powder coating was applied. The epoxy powder coating used was a resin coating using a phenolic curing agent, and the coating thickness was 360 μm.

(Comparative Example 1) A common steel plate whose surface was cleaned in the same manner as in Example 1 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) Chromate treatment solution A [chromic acid (cr3+/cr8+
= 0, 54) 1, colloidal silica with an atomic ratio of Si/Cr of 1.5 and water] with a dry weight of 1 g/rr? After coating, it was dried at 160° C. for 15 minutes, and polyethylene was immediately pressed in the same manner as in Example 1.

(Comparative Example 3) Phosphate-added chromate treatment solution B [chromic acid (Cr3
Comparative Example 2 was carried out in the same manner as in Comparative Example 2, except that the base treatment was performed using phosphoric acid with a molar ratio of HsPO4/Cr of 0.2, and water].

(Comparative Example 4) An ordinary steel plate whose surface was cleaned in the same manner as in Example 1 was preheated at 160°C for 15 minutes, coated with 30 μm of commercially available amine curing type epoxy primer, and heated at 160°C for 15 minutes.
After curing for 0 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 was coated with epoxy powder in the same manner as in Example 3 without performing any surface treatment.

(Comparative Example 6) As in Comparative Example 3, the steel plate was cleaned and the surface was treated with a chromate treatment solution, and then 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 steel plate to be subjected to nitrogen with a specimen size of 50xlOOmm was immersed in 3% Na (: n
After being immersed in an aqueous solution for 30 days, the peel strength was measured and evaluated at room temperature.

3.Cathode peel test A hole of 5 mm diameter was drilled in the center of the coating of a coated steel plate with a sample size of 10100xlOO to the steel surface, and while applying cathodic protection at -1.5V vs SCE, it was heated to 3% CIL 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> The organic coating surface treatment liquid of the present invention and the surface treatment method using the same can provide an organic liquid with significantly improved corrosion resistance compared to conventional organic coating steel materials. [Wood is obtained.

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.).
εε Dragon Emperor vs. FIG, 1

Claims (4)

[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^+ 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, comprising silica, 200 parts by weight or less of at least one water-soluble organic substance having a reducing property per 100 parts by weight of the chromic acid, and water. (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.