JPH0711455A - Surface preparation treated and multilayer corrosion protection coated steel material - Google Patents

Abstract

PURPOSE:To obtain a surface preparation treated and multilayer corrosion protection coated steel material excellent in adhesion and cathodic peeling resistance by forming a chromating undercoat layer of specific composition on the surface of a steel material and then laminating plural specific organic films on it. CONSTITUTION:A chromating undercoat layer 2, prepared by using a chromating agent where phosphoric acid and chromic anhydride are mixed so that the proportion of phosphoric acid to the total chromium of chromic anhydride becomes 0.2-3.0 by weight ratio and fine SiO2 grains, partially reduced by an organic reducing agent such as methyl alcohol and synthesized by a dry method and consisting of 20-70wt.% of SiO2, grains of 5-20nm primary grain size and 30-80% of SiO2 grains of SiO2 grains of 20-120nm primary grain size in the form of mixture, are added by 0.5-4.0 by weight ratio based on the total chromium of chromic anhydride, is formed on the surface of a steel material 1. Subsequently, an epoxy primer layer 3, a modified polyolefin adhesive layer 4, and a polyolefin coating layer or cross-linked polyolefin coating multilayer corrosion protection layer 5 are successively formed on the above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy anticorrosion coated steel material which is required to have adhesiveness because it is excellent in adhesion between an organic coating and a steel material, and particularly in a heavy duty anticorrosion coated steel material such as a polyolefin coated steel material and a polyurethane coated steel material. The present invention relates to a surface-undercoated heavy-corrosion-coated steel material that significantly suppresses deterioration of water-resistant adhesion and cathodic peeling resistance.

[0002]

2. Description of the Related Art Polyolefin, which is a heavy anticorrosion coated steel material,
Polyurethane-coated steel is used for corrosion protection of steel pipes, sheet piles, etc. because of its excellent long-term corrosion resistance. Heavy-duty anticorrosion coated steel is expected to have a service life of up to several decades in a wet environment. Therefore, when the combined use of electrical corrosion protection and suppression of a decrease in the adhesive strength between steel and organic coatings, cathodic peeling resistance is used. Sex is important. Also, in pipelines of petroleum, natural gas, etc., polyolefin-coated steel pipes are often used due to their anticorrosive properties. To improve the transportation of heavy oil, heating heavy oil to reduce its viscosity and transport it, etc. Therefore, it is also an important issue to improve the performance in a severe use environment that significantly reduces the adhesion of the coating such as a high temperature environment. Therefore, in the polyolefin-coated steel material used in such an environment, it is important to prevent the cathode peeling resistance and the decrease in adhesion due to the base treatment. Conventionally, in order to improve the adhesion with an organic coating, a chromate treatment agent is also used for thin steel sheets such as plating. However, paint adhesion is insufficient with the chromate treatment containing only such aqueous colloidal silica. In addition, JP-A-01-2632
As shown in No. 79, a large particle size aqueous colloidal silica is added to improve the fingerprint resistance, paint adhesion and corrosion resistance after processing. Even with a chromate treatment agent, water resistance with an organic coating required for heavy anticorrosion coating. It is difficult to secure adhesion.
In the chromate treatment agent for heavy-corrosion-coated steel, the amount of chromic acid attached is required to be about 10 times the thickness of a chromate film such as a thin plate. Therefore, JP-A-3-23452
As shown in No. 7, a chromate-treating agent whose film is reinforced by adding a silane coupling agent to phosphoric acid and silica fine particles, and in addition to the adhesion between the coating and steel materials after hot water immersion, is also resistant to cathodic peeling. A polyolefin-coated steel material having excellent properties has been proposed.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The chromate treatment agent for polyolefin-coated steel shown in No. 7 contains a silane coupling agent, so the problem that gelation occurs when the treatment liquid is stored for a long period of time and after immersion in hot water which is an ultra-long-term environmental simulation test It is difficult to sufficiently suppress the peeling in the cathodic peel test.
For this reason, coating after immersion in hot water ensuring the stability of the solution
Chromate treatment is required to form a strong chromate film that has excellent cathode peel resistance in addition to adhesion between steel materials.

[0004]

In order to solve the above-mentioned problems, the present invention provides a base treatment for heavy-corrosion-coated steel, as a silica component to be added to a chromate treating agent, as compared with commonly used aqueous colloidal silica. The purpose of this study is to diligently study to improve the strength of a dry film and improve the adhesion to an organic coating by using a silica having a secondary agglomeration component synthesized by a dry method and having a particle size adjusted. That is, a mixed solution of phosphoric acid and chromic anhydride is partially reduced with an organic reducing agent on the entire surface or a part of the surface of a steel material to obtain a treatment solution having a primary particle diameter of 5 to 20 nm synthesized by a dry method. Chromate treatment in which silica fine particles in which silica fine particles are mixed in an amount of 20 to 70% by weight and silica fine particles having a primary particle diameter of 20 to 120 nm in an amount of 30 to 80% by weight are added in an amount of 0.5 to 4.0 by weight ratio with respect to total chromium. Surface-treated steel sheet that has been surface-treated with a chemical agent, by laminating an organic coating on the surface-treated steel material, the surface-treated heavy corrosion-resistant coated steel material has excellent adhesion between the coating and steel material after immersion in warm water, as well as excellent cathodic peeling resistance. Is provided. The amount of phosphoric acid added in the chromate treatment agent is 0.2 to 3.0 by weight ratio to the total chromium. As the above-mentioned heavy anticorrosion coated steel material, as an organic coating layer,
Epoxy primer layer, modified polyolefin adhesive layer,
A polyolefin-coated steel material in which polyolefin coating layers are sequentially laminated. There is a polyurethane-coated steel material having an organic coating layer in which a primer layer and a polyurethane layer are sequentially laminated. A polyolefin coated steel material according to the present invention is shown in FIG. Steel material 1 in Figure 1
On the surface of, a phosphoric acid containing the above components, a chromate treating agent layer 2 containing fine particles of dry silica, a primer layer 3 made of a thermosetting epoxy resin, a modified polyolefin adhesive layer 4, a polyolefin coating or a crosslinked polyolefin coating. It is a polyolefin-coated steel material that is excellent in not only the adhesion between the coating material after immersion in warm water and the steel material, but also the high-temperature cathode peeling resistance, which is characterized in that 5 is sequentially laminated. A polyurethane-coated steel material according to the present invention is shown in FIG. In FIG. 2, after the phosphoric acid containing the above components, the chromate treating agent layer 2 containing the dry silica-based fine particles, the primer layer 6 and the polyurethane layer 7 are sequentially laminated on the surface of the steel material 1 after the immersion in hot water. It is a polyurethane-coated steel material that is excellent in high-temperature cathode peeling resistance in addition to the adhesion between the coating and the steel material.

The present invention will be described in detail below.
The steel material used in the present invention is carbon steel or alloy steel such as stainless steel and titanium alloy steel. Further, on the surface of carbon steel, stainless steel, copper, aluminum, titanium, aluminum-magnesium alloy, nickel-chromium-iron alloy, nickel-molybdenum alloy, nickel-molybdenum-chromium-tungsten alloy, titanium-palladium alloy. It may be a steel material in which metals such as alloys and titanium-aluminum-vanadium alloys are laminated. In addition, plating of zinc, aluminum, nickel, copper, etc. on the surface of carbon steel, alloy plating of zinc-iron, zinc-aluminum, zinc-nickel, zinc-nickel-cobalt, etc., or silica plating on these plating / alloy plating Alternatively, it may be a steel material that has been subjected to dispersion plating in which fine particles of an inorganic substance such as titanium oxide are dispersed.

The chromate treating agent used in the present invention will be described below. The chromate treating agent 2 used in the present invention is obtained by partially reducing an aqueous solution of phosphoric acid and chromic anhydride (CrO ₃ ) in distilled water with an organic reducing agent to form phosphoric acid and hexavalent chromium ions. Although trivalent chromium ions are mixed and dry silica-based fine particles are mixed,
If necessary, a part of phosphoric acid can be replaced with condensed phosphoric acid such as pyrophosphoric acid and tripolyphosphoric acid. Examples of organic reducing agents used for the partial reduction of chromium from hexavalent to trivalent include alcohols such as methyl alcohol and ethyl alcohol, alkylolamines such as diethanolamine and triethanolamine, saturation of formic acid, acetic acid and oxalic acid. Carboxylic acid, aromatic polyhydric alcohols such as pyrogallol, succinic acid, monomolecular reducing agents such as unsaturated carboxylic acids such as adipic acid, or starches such as wheat starch and corn starch, polymeric reducing agents such as polyvinyl alcohol Can be used. Coating after hot water immersion-To improve adhesion between steel materials and high-temperature cathode peeling resistance, a polymer reducing agent, in particular, starch containing a large amount of amylopectin, for example, corn starch is partially hydrolyzed with a hydrolase such as amyloglucosidase. Dextrin (average molecular weight 50,000-250000) obtained by hydrolytic hydrolysis, or

[Chemical 1] With a molecular structure of 60,000-140,000
Partially saponified polyvinyl acetate is preferable. The above dextrin and partially saponified vinyl acetate are used in the amounts necessary to maintain the desired ratio of hexavalent chromium to total chromium. The desired ratio is preferably such that the weight ratio of hexavalent chromium to total chromium is in the range of 0.35 to 0.75.
Regarding this ratio, when the weight ratio of hexavalent chromium to the total chromium is less than 0.35 and 0.75 or more, the adhesive force after immersion in hot water tends to decrease. The amount of dextrin required to set the weight ratio of hexavalent chromium to total chromium in the range of 0.35 to 0.75 is 0.06 to 0. 40, and the amount of partially saponified vinyl acetate is in the range of 0.07 to 0.47 by weight ratio to the total chromium in the chromate treatment liquid.

Phosphoric acid added to the above chromate treating agent lowers the pH of the chromate treating solution, so that the reactivity between the steel material and the chromate treating agent is increased and at the same time, hexavalent chromium is converted to trivalent chromium by heating and baking. It produces a highly insoluble chromate coating that leads to increased reducibility. Phosphoric acid combines with the hydroxyl groups on the surface of the silica-based fine particles and the free or coordinated chromium ions to integrate the chromate coating, making the chromate coating insoluble in hot water and at the same time drying the coating. It is considered that the adhesiveness and water resistance are improved by the effect of improving the physical strength, and the coating is less likely to be peeled off even when an alkali is generated during the cathode peeling test. The phosphoric acid is preferably added in such a manner that the weight ratio of phosphate ions to total chromium is in the range of 0.2 to 3.0. The appropriate amount of phosphoric acid added is adjusted by the drying temperature of the chromate film. However, the film is 0.
If it is less than 2 or more than 3.0, the adhesion after immersion in hot water tends to decrease.

Next, as the silica-based fine particles synthesized by the dry method, which are added to the above chromate-treating agent, for example, AEROSIL 130 and AER manufactured by Nippon Aerosil Co., Ltd.
OSIL 200, AEROSIL 200V, AER
OSIL 200CF, AEROSIL 200FA
D, AEROSIL 300, AEROSIL 300
Silica fine particles with small particle size such as CF and AEROSIL 380 and AEROSIL OX50 and AEROSIL
A silica fine particle having a large particle diameter such as TT600 or AEROSIL MOX is mixed to adjust the particle diameter.

The dry process silica fine particles are produced, for example, by chlorinating ferrosilicon to obtain silicon tetrachloride, then refining and hydrolyzing at high temperature in a flame of oxygen and hydrogen. Unlike dry colloidal silica, dry silica particles are
Since the tendency to form secondary agglomerates is strong, the shrinkage of the film when dried is small and the adhesion to steel is excellent. In addition, since the porous surface is formed, the organic coating applied on the chromate coating flows into the porous surface, so that the adhesiveness with the upper organic coating is improved. This effect is better if the particle size is large, as long as it can be dispersed in an aqueous solution. However, if the particle size is too large, the cohesive force of the film will be insufficient and the adhesion will be reduced.
It is necessary to balance the strength and adhesiveness of the coating by mixing the following) silica with a silica having a large particle size (20 nm or more). As the particle size distribution, silica fine particles having a primary particle diameter of 5 to 20 nm are 20 to 70% by weight and a primary particle diameter is 20 to 120.
The silica fine particles obtained by mixing 30 to 80% by weight of the silica fine particles having a thickness of 0.5 nm are contained in a weight ratio of 0.5 to 4.
0 is added. If the addition amount of the silica-based fine particles is less than 0.5 or more than 4.0, the adhesion after immersion in hot water tends to decrease. Before application of the chromate treatment agent, if there is scale, oil, etc. on the surface of the steel material, alkali degreasing, pickling, sand blasting, grid blasting, shot blasting, etc. must be performed to remove surface deposits. There is. A suitable baking temperature of the chromate treatment agent after coating is 60 to 300 ° C. Steel surface temperature is 60
If the temperature is lower than 0 ° C, dehydration in the chromate treatment agent layer and reduction of chromium are likely to be insufficient. Above 300 ° C, the chromate-treated film decomposes. Further, the amount of the chromate treatment agent deposited is preferably 30 to 800 mg / m ² in terms of total chromium weight. If it is less than 30 mg / m ² , the effect of the chromate treatment is not exhibited, and if it exceeds 800 mg / m ² , a strong coating film is not formed and the adhesion is lowered.

Next, the polyolefin coating which is the heavy anticorrosion coating of the present invention will be explained. The structure of the polyolefin-coated steel material according to the present invention is shown in FIG. FIG. 1 shows that on the surface of a steel material 1, a phosphoric acid containing the above components, a chromate treating agent layer 2 containing dry silica fine particles, a primer layer 3 made of a thermosetting epoxy resin, a modified polyolefin adhesive layer 4, A polyolefin-coated steel material in which a polyolefin coating or a cross-linked polyolefin coating 5 is sequentially laminated.
The primer used for the polyolefin-coated steel material of the present invention contains an epoxy resin, a curing agent and an inorganic pigment as main components. Epoxy resins include bisphenol A, AD,
Diglycidyl ether of F, phenol novolac type glycidyl ether, or the like is used alone or in combination. As the curing agent, an alicyclic modified amine, an aliphatic amine, a dicyandiamide-based curing agent, an imidazole-based curing agent, or the like is used. Further, as the inorganic pigment, silica, titanium oxide, wollastonite, mica, chromium oxide or the like is appropriately used. Furthermore, in order to improve the wettability with the resin, the surface of the above pigment is treated with aluminum-silica,
A chemical treatment such as silane coupling treatment or phosphate treatment may be performed.

The modified polyolefin adhesive used in the polyolefin coating of the present invention includes known polyolefins such as polyethylene, polypropylene and nylon, and known polyolefin copolymer resins such as maleic acid, acrylic acid and methacrylic acid. It is a conventionally known modified polyolefin such as one modified with an unsaturated carboxylic acid or its acid anhydride, or one obtained by appropriately diluting the modified product with a polyolefin resin. The polyolefin coating used in the polyolefin-coated steel material of the present invention means low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, nylon and other conventionally known polyolefins as main components, and ethylene-propylene. It is a resin containing a known polyolefin copolymer such as a block or random copolymer, a polyamide-propylene block or a random copolymer. The cross-linked polyolefin coating is mainly composed of cross-linked polyolefin obtained by subjecting the above-mentioned polyolefin to electron beam irradiation or the like to perform cross-linking. As other components, a pigment, a filling reinforcing agent, etc. can be added. As the pigment, silica, silica-alumina, rutile type titanium oxide, glass, mica, iron oxide red, zirconium silicate, magnesium silicate, talc, barium sulfate, alumina, zinc chromate, strontium chromate, cinnamide lead, lead suboxide , General-purpose pigments such as aluminum phosphate, calcium phosphate, silicomolybdic acid, silicotungstic acid, zinc phosphomolybdate, etc. When aesthetics are required, cadmium yellow, polyazo yellow, quinophthalone yellow, isoindolinone yellow, quinacridone Yellow, red iron oxide, polyazo brown, azo lake yellow, perylene red, phthalocyanine blue, phthalocyanine green, red iron oxide, cobalt aluminate, aniline black, carbon black, cormorant Tiger marine blue, the color pigment and the ultraviolet absorber of aluminum fine powder, etc., may be added hindered amine weathering agents. The filler strengthening agent is an inorganic fiber filler such as glass, slag, silicon carbide, carbon, boron, boron nitride, or alumina, and an organic filler such as nylon, polyester, vinylon, aramid, or kepler.

Next, the polyurethane coating which is the heavy anticorrosion coating of the present invention will be described. A polyurethane-coated steel material according to the present invention is shown in FIG. In FIG. 2, after dipping in hot water, the surface of the steel material 1 is successively laminated with phosphoric acid containing the above components, chromate treatment agent layer 2 containing dry silica type fine particles, primer layer 6 and polyurethane layer 7. In addition to the adhesion between the coating and the steel material, the polyurethane coating steel material is excellent in high-temperature cathode peeling resistance. As the urethane coating primer, for example, an inorganic pigment is added to a polyol and a polyisocyanate compound and used. In this case, polyether polyol, polyolefin polyol, epoxy polyol or the like is used as the polyol. As the polyether polyol, propylene glycol, butanediol, neopentyl glycol, hexanediol, glycerin, trimethyl roll propane, etc. are subjected to addition polymerization with alkylene oxide such as propylene oxide, ethylene oxide or butylene oxide in the presence of an alkali catalyst. A polyalkylene polyol having 2-3 active hydrogen groups (hydroxyl groups) in the obtained molecule is used. As these polyalkylene polyols, for example, a commercially available hydroxyl value is 50 to 50.
About 150 mg-KOH / g polypropylene glycol or the like can be used. Also. As the polyolefin polyol, 2 to the molecule obtained by addition-polymerizing an alkylene oxide such as ethylene oxide or propylene oxide to a diene compound such as butadiene or isoprene
A polydiene polyol having three active hydrogen groups (hydroxyl groups) is used. As these polydiene polyols,
For example, a commercially available hydroxyl value is 50 to 150 mg-KOH
Polybutadiene polyol of about / g can be used. As the polyisocyanate, a polyisocyanate compound containing two or more isocyanate groups in the molecule, such as crude diphenylmethane diisocyanate (crude MDI) and tolylene diisocyanate (TDI), is used.
The above-mentioned polyol and polyisocyanate are subjected to an addition reaction to form an isocyanate-terminated urethane prepolymer,
At this time, the isocyanate group (-N
CO) to the hydroxyl group (OH) of the polyol, ie N
CO / OH should be in the range of 1.6 to 3 by weight. When the NCO / OH weight ratio is less than 1.6 and exceeds 3, the polyurethane coating layer peels off when an immersion test is conducted,
Water resistance is poor. For the urethane primer, an inorganic pigment is added to the above isocyanate-terminated urethane prepolymer. As the inorganic pigment, there are used silicon oxide obtained by crushing minerals such as clay and perlite, aluminum silicate obtained by crushing kaolin, kaolin clay, montmorillonite and the like, talc, alumina, calcium carbonate and the like.
These inorganic pigments are added in the range of 20 to 200 parts by weight based on 100 parts by weight of the isocyanate terminated urethane prepolymer. The addition amount is less than 20 parts by weight and 200
If it exceeds the weight part, the water-resistant adhesiveness becomes poor.

For the polyurethane layer, for example, polyolefin polyol, aromatic amine polyol, polyurethane composed of polyisocyanate and inorganic pigment can be used. In this case, the polyolefin polyol is a polydiene having 2-3 active hydrogen groups (hydroxyl groups) in the molecule obtained by addition-polymerizing an alkylene oxide such as ethylene oxide or propylene oxide to a diene compound such as butadiene or isoprene. A polyol is used. Examples of the polydiene polyol include Poly bd R-45HT and Poly bd R manufactured by Idemitsu Petrochemical Co., Ltd.
General commercially available liquid polybutadiene polyols such as -45, Poly bd CS-15, Nisso PBG-2000 and Nisso PBG-3000 manufactured by Nippon Soda Co., Ltd. can be used. As the aromatic amine polyol, an aromatic amine polyol obtained by adding an alkylene oxide such as propylene oxide to an aniline compound such as bis (2-hydroxypropyl) aniline or methylenebis (-0-chloroaniline) (MOCA) is used. As these aromatic amine polyols, for example, Polyhardener PA400 and Polyhardener PA300 manufactured by Daiichi Kogyo Seiyaku Co., Ltd. can be used. The amount of these aromatic amine polyols is 3 per 100 parts by weight of the above-mentioned polyolefin polyol.
It is added in the range of 0 to 100 parts by weight. As the polyisocyanate, crude diphenylmethane diisocyanate containing two or more isocyanate groups in the molecule (crude MD
I), an isocyanate compound such as tolylene diisocyanate (TDI) is used. These polyisocyanates have an isocyanate group (-NC
O) and the hydroxyl group (OH) ratio of the above-mentioned mixture of polyolefin polyol and aromatic polyol, that is, NCO /
OH is used in a weight ratio range of 0.85 to 1.5. As the inorganic pigment, powders such as silicon oxide obtained by crushing minerals such as clay and perlite, aluminium silicate obtained by crushing kaolin, kaolin clay, montmorillonite and the like, talc, alumina, calcium carbonate are used alone or in combination. The mixing ratio of these inorganic pigments may be arbitrary, but the total content of the inorganic pigments is in the range of 5 to 200 parts by weight with respect to 100 parts by weight of the polyolefin polyol. For black polyurethane, 1 to 30 parts by weight of carbon black is added to the above-mentioned polyolefin polyol. When coloring polyurethane, in order to prevent fading due to ultraviolet rays, especially Co, Al, Cr, F
e, Ti, Zn, Mn, Sb, Ni, Mg, a coloring pigment composed of an oxide or a complex oxide of one or more elements, alone or in a mixture, and bis (1,2,2,6,6)
-Pentamethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, 8-benzyl-7,7,9,9-tetramethyl-3-octyl 1,3,3 8-Triazaspiro [4
5] Add a hindered amine light stabilizer such as undecane-2,4-dione. These hindered amine light stabilizers are added in the range of 0.5 to 10 parts by weight based on 100 parts by weight of the acrylic polyol.

[0014]

EXAMPLES In order to specifically explain the present invention, the following chromate treating agents A to J according to the present invention were prepared. Similarly, comparative chromate treating agents K to P and Japanese Patent Application No.
2-30320 and chromate treating agents Q and R corresponding to JP-A No. 01-263279 were prepared. <Preparation Example of Chromate Treatment Liquids A to J and Comparative Examples K to P> As the chromate treatment liquid of the embodiment, for example, as a chromate stock solution, 38.46 g of chromic anhydride and 30.95 g of phosphoric acid are distilled water 428. 2.56 g of dextrin was added to the solution dissolved in 0.03 g to reduce chromic acid by heating and stirring, and after cooling, distilled water was added to adjust the total weight to 600 g. To this solution, 400 g of an aqueous solution containing 10% by weight of silica-based fine particles was added and stirred. As the silica-based fine particle aqueous solution, Aerosil 200 (primary particle diameter: 5 to 15 nm) and Aerosil OX manufactured by Nippon Aerosil Co., Ltd.
50 (primary particle diameter: 10 to 80 nm) was mixed and dissolved in distilled water before use. The particle size was identified by an electron micrograph. At this time, the weight ratio of hexavalent chromium to total chromium in the solution was 0.60, the weight ratio of phosphoric acid to total chromium was 1.5, and the weight ratio of fine silica particles to total chromium was 2.0. Using the same method, the chromate treating agents A to J of Examples and the chromate treating agents K to P of Comparative Examples were prepared by changing the concentrations and mixing ratios of phosphoric acid, dextrin reducing agent, and silica solution.

<Preparation Example of Chromate Treatment Liquid Q of Comparative Example>
As a chromate treatment liquid Q of Comparative Example corresponding to JP-A-02-30320, as a chromate stock solution, 38.46 g of chromic anhydride and 30.95 g of phosphoric acid were added to distilled water 42.
2.56 g of dextrin was added to the solution dissolved in 8.03 g, and the mixture was heated and stirred to reduce chromic acid. After cooling, add distilled water to adjust the total weight to 500 g,
400 g of an aqueous solution containing 10% by weight of silica-based fine particles was added and stirred. As the silica-based fine particles, Aerosil 300 (primary particle diameter: 5 to 13 nm) manufactured by Nippon Aerosil Co., Ltd. was used. Separately from this solution, an aqueous solution containing 40% by weight of γ-glycidoxypropyltrimethoxysilane was prepared and mixed with the above chromate stock solution at a weight ratio of 9: 1 for use. At this time, the weight ratio of hexavalent chromium to the total chromium in the solution was 0.60, the weight ratio of phosphoric acid to the total chromium was 1.5, the weight ratio of silica-based fine particles to the total chromium was 2.0, and the weight ratio to the total chromium was 2.0. The weight ratio of the silane coupling agent was 2.0.

<Formulation Example of Chromate Treatment Liquid R of Comparative Example>
As the chromate treatment liquid R of Comparative Example corresponding to JP-A No. 01-263279, chromic anhydride 38.46 was used.
g, phosphoric acid 10.32 g, 5% by weight partially saponified polyvinyl acetate aqueous solution (saponification degree: 87%) was added to distilled water 44.06 g, and the mixture was heated and stirred to partially reduce chromic acid. Distilled water was added to adjust the total weight to 600 g. After cooling, add this solution to Nissan Chemical Snowtex ZL (particle size: 70-100 nm) and Nissan Chemical Snowtex S.
Silica component 1 in which (particle size: 7 to 9 nm) was mixed at a ratio of 1: 1
400 g of a 0 wt% aqueous solution was added and stirred to prepare a treatment liquid. At this time, the ratio of hexavalent chromium to the total chromium after reduction was 0.50, the weight ratio of phosphoric acid to the total chromium was 0.5, and the weight ratio of silica fine particles to the total chromium was 2.0.

(Stability Test of Treatment Agent) In order to investigate the stability of the prepared chromate treatment agent, it was stored at 30 ° C. for 90 days and evaluated. The evaluation was made by judging whether redispersion is possible even if there is a sediment due to stirring. The results are shown in Table 1. In the chromate treatment liquid Q of Comparative Example corresponding to Japanese Patent Application No. 02-30320, the treatment liquid thickened and became a complete solid.

[Table 1]

(Evaluation of Adhesiveness and Cathodic Peeling Property) As a method for producing Examples 1 to 10 of the polyolefin-coated steel material which is the surface-undertreated heavy-corrosion-coated steel material of the present invention, a steel plate (9 × 15) is used.
(0 × 300 mm) is subjected to grid blasting, and the chromate treating agents A to J of the present invention prepared on the surface thereof are roll-coated with a chromium adhesion amount of 350 to 400 mg / m ² , dried and then heated to 200 ° C. It was baked. Next, after cooling the steel plate to room temperature, an epoxy-based primer was applied by a spray coating machine to a film thickness of 50 μm, and then heated to a surface temperature of 220 ° C. to be cured, and a modified polyethylene adhesive had a film thickness of 300 μm. Electrostatically applied. After that, extrusion molding was performed with a T die.
After a 0 mm thick polyolefin coating was applied under pressure, it was cooled to produce a polyolefin coated steel material. Also, by the same procedure as a comparative example of polyolefin-coated steel,
Comparative polyolefin coated steel materials 11 to 18 were prepared using comparative chromate treatment agents K to R. Hot water immersion test (test temperature: 80 ° C., immersion time: 6
After 000 hours), the peel strength was measured when the coating was peeled off by measuring the adhesion (measurement temperature: room temperature, peeling angle: 90 degrees, peeling speed: 50 mm / min.). However, when the adhesive strength is sufficient, the polyethylene is broken and the adhesive strength becomes a value equal to or higher than the polyethylene strength. Further, as a cathode peeling test, the sample after the immersion test was tested under the following test conditions. (Cathode peeling test conditions) Test temperature: 80 ° C. Electrolyte: 3% -NaCl voltage: 1.5 V [Cu / CuSO ₄ , standard electrode] Initial holographic diameter: 9.0 mmφ Test days: 120 days After application, coating The film peeling diameter (X mm) was measured, and the converted peeling radius (R = (X / 2) ² − (3.2 / 2) ² ) ^1/2 mm) of the coating film was calculated. The results are shown in Table 2. From the results of Table 2 and Table 3,
It can be seen that Examples 1 to 10 of the present invention in which the chromate treatment liquid contains phosphoric acid and dry-type silica fine particles having a regulated particle diameter can obtain remarkably excellent results as compared with Comparative Examples 11 to 18. .

[Table 2]

[Table 3]

As a manufacturing method of Examples 19 to 28 of the surface-treated heavy-corrosion-coated steel material, polyurethane-coated steel material of the present invention, a steel plate (9 × 150 × 300 mm) was grid-blasted and blended on its surface. Chromate treatment agents A to J of the present invention were used as chromium adhesion amounts of 350 to 400.
mg / m ² was roll-coated, dried, and then heated and baked at 100 ° C. Then, after cooling the steel plate to room temperature,
After spray-coating a urethane primer to a film thickness of 50 μm and curing it at 50 ° C. for 1 hour, coat the surface with a black polyurethane paint containing 1 part by weight of solvent-free carbon black with a two-pack type coating machine. The film thickness after curing is 3.
It was set to 0 mm. In addition, as a comparative example of the polyurethane-coated steel material, the comparative polyurethane-coated steel materials 29 to 36 were prepared using the comparative chromate treatment agents K to R by the same procedure.
It was created. After the hot water immersion test (test temperature: 60 ° C., immersion time: 10,000 hours) for the above coated steel,
Adhesion measurement (measurement temperature: 25 ° C.) A circular (diameter 20 mm) jig for measuring vertical adhesion was adhered to a polyurethane surface via an epoxy adhesive, and the vertical adhesion was measured by a tensile tester. Further, as a cathode peeling test, the sample after the immersion test was tested under the following test conditions.

(Cathode stripping test conditions) Test temperature: 60 ° C. Electrolyte: 3% -NaCl Voltage: 1.5 V [Cu / CuSO ₄ , standard electrode] Initial holographic diameter: 9.0 mmφ Number of test days: 120 days Test end Then, the coating film peeling diameter (X mm) was measured, and the converted peeling radius (R = (X / 2) ² − (3.2 / 2) ² ) ^1/2 mm) of the coating film was calculated. The results are shown in Tables 4 and 5. When the vertical adhesion was more than 100 kg / cm ² , the urethane film was broken and it could not be measured. From the results of Tables 4 and 5, Examples 19 to 28 of the present invention, in which phosphoric acid and dry type silica fine particles having a regulated particle size are contained in the chromate treatment liquid, are Comparative Example 29.
It can be seen that a significantly superior result is obtained as compared with ~ 36.

[Table 4]

[Table 5]

[0021]

As is clear from the examples, the base treatment of the steel material using the chromate treating agent excellent in the long-term stability of the solution according to the present invention is improved by the improved adhesion, so It is possible to provide a surface-undercoated heavy-corrosion-coated steel material which is remarkably excellent in adhesion and cathodic peeling resistance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a polyolefin-coated steel material that is a surface-underground, heavy-corrosion-coated steel material according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a polyolefin-coated steel material that is a surface-underground heavy-corrosion coated steel material according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel material 2 Chromate treating agent or chromate treating agent layer 3 Primer layer 4 Modified polyolefin adhesive layer 5 Polyolefin coating or crosslinked polyolefin coating heavy anticorrosion layer 6 Primer layer 7 Polyurethane heavy anticorrosion layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroyuki Mimura 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Stock of Kimitsu Steel Co., Ltd.

Claims (4)

[Claims] 1. Primary particles synthesized by a dry method on a treatment solution obtained by partially reducing a mixed solution of phosphoric acid and chromic anhydride on the entire surface or a part of the surface of a steel material 1 with an organic reducing agent. 20 to 70% by weight of silica fine particles having a diameter of 5 to 20 nm and 1
Steel material surface-treated with a chromate treatment agent 2 in which silica fine particles having a secondary particle diameter of 20 to 120 nm mixed in a proportion of 30 to 80% by weight are added in a weight ratio of 0.5 to 4.0 with respect to total chromium. A surface-undercoated heavy-corrosion-coated steel material, characterized in that an organic coating is laminated on the surface. 2. The surface-undertreated heavy-corrosion-coated steel material according to claim 1, wherein the amount of phosphoric acid added in the chromate treatment agent is 0.2 to 3.0 in terms of weight ratio to the total chromium. 3. The surface-treated heavy corrosion-resistant coated steel material according to claim 1, wherein the organic coating layer is a coating layer in which an epoxy primer layer, a modified polyolefin adhesive layer and a polyolefin coating layer are laminated in this order. 4. The surface-undertreated heavy-corrosion-coated steel material according to claim 1, wherein the organic coating layer is a coating layer in which a primer layer and a polyurethane layer are sequentially laminated.