JPH07119086B2 - Painted steel - Google Patents

Description

The present invention relates to a coated steel material, and more particularly to a coated steel material having excellent boiling water resistance.

[Conventional technology]

BACKGROUND ART Conventionally, a coated steel material in which an organic resin such as an epoxy resin is coated on the surface of a steel product such as a steel pipe, a steel plate, a steel structure, and a steel formed product to improve the corrosion resistance of the steel product is manufactured.

In recent years, steel products coated with the above organic resin on the inner and outer surfaces of steel pipes have become widely used, and demands on quality have become strict, especially in high-temperature environments, that is, high-temperature cathode peeling resistance,
It is desired to develop a coated steel material that has both hot water resistance and boiling water resistance.

Conventionally, for a powder resin coated steel pipe, for example, a method of preliminarily subjecting the surface of the steel pipe to a base treatment has been proposed in order to improve the cathode peel resistance.

For example, in Japanese Unexamined Patent Publication No. 52-14392, as shown in FIG.
Chromate treatment agent layer 12 obtained by applying a chromate treatment agent C in which a compound of hexavalent chromium and an organic component such as an amino acid, an acid amide, a lactam, a saturated or unsaturated polycarboxylic acid are applied to the surface of the steel pipe 1 and baked, and heated. There is a proposal for a coated steel pipe in which a powder coating film 4 of a plastic or thermosetting resin composition is laminated.

Further, as shown in FIG. 4, instead of the above chromate treating agent C, chromic acid (CrO ₃ ) is used as an organic reducing agent such as sugar, polyhydric alcohol, monohydric alcohol, alkylolamine, aromatic polyhydric alcohol and the like. Cr ⁶⁺ / total chrome = 0.35 to 0.65
A coated steel pipe in which a chromate treating agent layer 13 which is partially reduced to a ratio of (weight ratio) and which is heated and baked using a chromate treating agent D in which silica fine particles are added to the reduced product is further laminated, and as shown in FIG. Instead of the chromate treating agent C, a chromate treating agent E obtained by adding a nonionic water-soluble resin such as polyvinyl alcohol, methyl cellulose, polyethylene oxide, hexamethylmethoxymethylmelamine modified polyhydroxyethyl acrylate to the chromate treating agent C
There is a coated steel pipe in which a chromate treatment agent layer 14 which is heated and baked by using is laminated.

Further, as shown in FIG. 6 in JP-A-60-23038,
A silane coupling agent layer 14 such as an epoxy silane coupling agent and a powdered epoxy resin coating film 4 on the surface of the steel pipe 1.
There is a coated steel pipe that is sequentially laminated.

[Problems to be solved by the invention]

However, all of the coated steel materials shown in FIGS. 3, 4, 5, and 6 have a problem that the organic resin coating film peels off when immersed in boiling water for a long time.

The present invention provides a coated steel material having excellent boiling water resistance.

[Means for solving problems]

As a result of intensive studies to solve the above-mentioned problems, the present inventors partially reduced a mixed aqueous solution of phosphoric acid and chromic anhydride on the surface of a steel material with partially saponified polyvinyl acetate or dextrin to obtain a silica system. A coated steel material with excellent boiling water resistance by applying a chromate treatment agent containing fine particles and heating and baking it, then applying a mixture treatment agent of a chelating agent and an amino-based silane coupling agent and baking and applying an organic resin coating. It was found that the following was obtained, and the present invention was achieved.

That is, according to the present invention, as shown in FIG. 1, the surface of steel material 1 is subjected to a chromate treatment in which a mixed aqueous solution of phosphoric acid and chromic anhydride is partially reduced with partially saponified polyvinyl acetate or dextrin and silica fine particles are added. A chromate treatment agent layer 2 obtained by applying an agent and heating and baking, a mixture treatment agent layer 3 of a chelating agent and an amino-based silane coupling agent, and an organic resin coating film 4 are sequentially laminated. It relates to excellent coated steel materials.

Hereinafter, the present invention will be described in detail.

The steel material used in the present invention is a steel material such as a steel plate made of an alloy steel such as carbon steel or stainless steel, a steel pipe, a shaped steel and a steel molded product. Further, the above steel material plated with zinc, aluminum, chromium, nickel, etc., the alloy plated zinc-iron, zinc-aluminum, zinc-nickel, zinc-nickel-cobalt, etc., or the above plating Layer, alloy plated layer, dispersion plated with dispersed inorganic fine particles such as silica, alumina, titanium oxide, boron oxide, silica-alumina, silica titanium, silicon carbide, silicon oxynitride, boron nitride, etc. It doesn't matter.

Next, the chromate treating agent used for forming the chromate treating agent layer of the present invention will be described.

The chromate treating agent used in the present invention is a phosphate ion or hexavalent chromium ion obtained by partially reducing an aqueous solution of phosphoric acid and chromic anhydride (CrO ₃ ) dissolved in distilled water with a polymer reducing agent. And trivalent chromium ions are mixed together and silica-based fine particles are mixed together. If necessary, part of phosphoric acid can be replaced with condensed phosphoric acid such as pyrophosphoric acid or tripolyphosphoric acid.

As the polymer reducing agent used for the partial reduction of chromium from hexavalent to trivalent, starch containing a large amount of amylopectin,
For example, dextrin (average molecular weight of 50,000 to 250,000) that partially hydrolyzes corn starch and the like with a hydrolase such as amyloglucosidase and facilitates formation of coordination bond with chromium ion, or Has a molecular structure of And partially saponified polyvinyl acetate having a molecular weight of 60,000 to 140,000 is used.

Since the above-mentioned polymer reducing agent has an extremely large molecular weight, it is difficult to dissolve in a mixed aqueous solution of phosphoric acid and chromic acid at room temperature,
The mixed aqueous solution is heated to 80 to 100 ° C. and added to dissolve completely.

The polymeric reducing agent added to the mixed aqueous solution of phosphoric acid and chromic acid by the above method is highly inferred from the analysis result of the chromate treatment agent and the heat-baked coating of the group and the elution amount measurement result of chromium ion to hot water. A part of the molecular reducing agent is decomposed to reduce hexavalent chromium to trivalent chromium, and at the same time, chromium ions are coordinated to the remaining polymeric reducing agent, and phosphoric acid is further bound to the chromium ions. Has a remarkable effect on making water insoluble. Furthermore, polymer reducing agents other than the above, such as corn starch,
When a polysaccharide that is not partially hydrolyzed by an enzyme such as wheat starch is used, it may be added to a mixed aqueous solution of phosphoric acid and chromic acid as compared with the case of using the above-mentioned dextrin or partially saponified polyvinyl acetate. Since the coordination of chromium ions becomes insufficient, the effect of making the chromate film insoluble in hot water is small.

Further, as the polymer reducing agent, a water-soluble resin other than the partially saponified polyvinyl acetate, for example, When using polyvinyl alcohol having a molecular structure of, because all the substituents are active hydroxyl groups,
When it is added to a mixed aqueous solution of phosphoric acid and chromic acid, it is susceptible to oxidative decomposition by chromic acid, and the effect of making the chromate film insoluble in hot water becomes small.

If a low molecular weight reducing agent such as methyl alcohol, succinic acid or sorbitol is used instead of the polymeric reducing agent, it will be almost decomposed when added to a mixed aqueous solution of phosphoric acid and chromic acid. It has almost no effect of making it insoluble in hot water.

Among the above-mentioned polymer reducing agents, dextrin has an average molecular weight of
Use the one in the range of 50000 to 250,000. If the average molecular weight of dextrin is less than 50,000, there is almost no effect of insolubilizing the chromate film in hot water, and if it exceeds 250,000, it is difficult to dissolve in a mixed aqueous solution of phosphoric acid and chromic acid, and the smoothness of the film obtained by application is improved. It is not desirable because it damages.

The partially saponified polyvinyl acetate has a molecular weight of 6000.
Those having a saponification degree of 0 to 140,000 and a saponification degree of 80 to 90% are used. When the molecular weight of partially saponified polyvinyl acetate is less than 60,000, the effect of insolubilizing the chromate film in hot water is small, and when it exceeds 140,000, it is difficult to dissolve in a mixed aqueous solution of phosphoric acid and chromic acid, and thus the coating obtained It is not desirable because it impairs smoothness. If the saponification degree of the partially saponified polyvinyl acetate is less than 80% or more than 90%, the effect of making the chromate film insoluble in hot water is lowered.

The above-mentioned dextrin and partially saponified polyvinyl acetate are used in the amounts necessary to maintain the desired ratio of hexavalent chromium to total chromium. The desired ratio is a weight ratio of hexavalent chromium to total chromium in the range of 0.35 to 0.65. If this ratio is less than 0.35, the adhesion between the surface of the steel material and the chromate coating will be reduced, and if it exceeds 0.65, the effect of making the chromate coating insoluble in hot water will be significantly reduced.

The weight ratio of hexavalent chromium to total chromium is 0.35 to 0.
The amount of dextrin required for the range of 65 is 0.008 to 0.058 by weight ratio to the total solid content in the chromate treatment liquid, and the amount of partially saponified polyvinyl acetate is based on the total solid content in the chromate treatment liquid. The weight ratio is in the range of 0.009 to 0.062.

Further, the phosphoric acid added to the chromate treating agent is inferred from the analysis results of the chromate treating agent and its heat-baked coating and the measurement results of the amount of chromium ions eluted into hot water. It binds to a coordination compound in which chromium ions are coordinated to vinyl acetate.

It binds to a hydroxyl group on the surface of the silica-based fine particles, and the phosphate group bound to this hydroxyl group further binds to free chromium ions and to dextrin or partially saponified polyvinyl acetate to which the above chromium ions are coordinated.

In addition to integrating the chromate film by the effect of
A part of the phosphate group bound to the free phosphoric acid and the dextrin in which the above-mentioned chromium ions are coordinated or partially saponified polyvinyl acetate reacts with the surface of the steel material to form a chromium iron phosphate compound to form a chromate coating on the steel material. To firmly adhere to
It is considered that there is almost no elution of chromium ions and phosphate ions even when immersed in boiling water, and that the adhesiveness between the steel material and the organic resin coating film is less likely to decrease.

The amount of phosphoric acid added is such that the weight ratio of PO ₄ ^3-to total chromium is
Add in the range of 0.5 to 2.0. If the amount of phosphoric acid added is less than 0.5, the above effect is almost absent, and if it exceeds 2.0, free soluble phosphoric acid remains in the chromate film, so that the effect of insolubilizing the chromate film in hot water decreases.

Examples of silica-based fine particles added to the chromate treatment agent include, for example, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil 0X50 manufactured by Nippon Aerosil Co., Ltd., Nipseal L300, Nipseal N300A manufactured by Nihon Silica Industry Co., Ltd.,
Nipseal E200, Nipseal E200A silica fine particles, Aerosil Cok84 and Aerosil manufactured by Nippon Aerosil Co., Ltd.
Silica-alumina fine particles such as Mox80, Aerosil Mox170,
Nissan Chemical Industries Snowtex O, Snowtex O
L, Sunotex OS, Snowtex OML and colloidal silica such as Cataloid SN, Cataloid SA, Cataloid 20L made by Catalysts & Chemicals Industries, Alumina sol 100 made by Nissan Chemical Industries,
Among silica-alumina sol such as alumina sol 200, one kind or a mixture of two or more kinds is used.

The above silica-based fine particles are inferred from the analysis results of the chromate treating agent and its heated coating and the elution amount measurement results of phosphate ions and chromium ions with respect to hot water, and the surface hydroxyl groups are phosphate ions in the chromate treating agent and Chromium ion-coordinated dextrin or partially saponified poly (vinyl acetate) binds the chromate film together, and the chelating agent applied on the chromate film and the amino-based silane coupling agent in the mixed treatment agent Adhesion between the organic resin coating and the steel material against immersion in boiling water because the chromate coating and the mixed treatment agent layer of the chelating agent and the silane coupling agent are firmly adhered by forming a siloxane bond with the silane coupling agent. It is extremely effective in preventing the deterioration. The amount of silica fine particles added is such that the weight ratio to the total chromium in the chromate treatment liquid is in the range of 0.5 to 2.5. If the addition amount is less than 0.5, the above effect is hardly obtained, and if it exceeds 2.5, the fluidity of the chromate treatment agent is remarkably deteriorated and the smoothness of the coating film obtained by coating the surface of the steel material is impaired.

When the adhesion between the chromate film and the steel material or the adhesion between the chromate film and the mixed treatment agent layer of the chelating agent and the amino-based silane coupling agent is insufficient, the chromate treatment agent may be phosphovanadic acid or phosphomolybdenum. Phosphorus / oxygen acid compounds such as acids, ammonium metavanadate,
Oxygen ammonium salts such as ammonium molybdate,
After appropriately selecting from metal salts such as manganese carbonate, cobalt carbonate, and dialuminum hydrogen phosphate or boric acid,
Added.

Before the chromate treatment agent is applied to the surface of the steel material, the scale, oil and the like on the surface of the steel material are removed by pickling, sand blasting, grit blasting, shot blasting and the like. When a chromate treatment agent is applied to the steel material surface from which scales, oils, etc. have been removed, hexavalent chromium is reduced by the oxidation effect of the steel material surface and the heating of the steel material after application, and dehydration between the hydroxyl groups and phosphoric acid on the surface of the silica-based fine particles. The condensation reaction, the dehydration condensation reaction between the phosphate group of the dehydration condensate and the chromium ion and the dextrin or partially saponified polyvinyl acetate in which the chromium ion is coordinated is promoted, and a chromate film which is hardly soluble in hot water and is strong is formed. To generate. The appropriate baking temperature for the chromate treatment agent is 120 to 300 ° C at the steel surface temperature. If the surface temperature of the steel sheet is less than 120 ° C, it takes a long time to insolubilize the chromate film, which is not suitable for practical use, and if it exceeds 300 ° C, the chromate film is thermally decomposed and boiling resistance decreases.

In addition, the amount of chromate treatment agent attached is the total chromium weight.
Good boiling water resistance is obtained in the range of 100 to 900 mg / m ² .

Next, the mixed treatment agent of the chelating agent and the amino silane coupling agent used in the present invention will be described.

The chelating agent and the amino-based silane coupling agent mixed treatment agent used in the present invention is preferably prepared by mixing an aqueous solution of the chelating agent and an amino-based silane coupling agent. Regarding the mixing method of the above-mentioned mixed treatment agent,
The optimum pH value for dissolving the chelating agent in water to form a uniform aqueous solution, and dissolving the amino silane coupling agent in water to form a uniform aqueous solution, and hydrolyzing the amino silane coupling agent sufficiently. Since the optimum pH value for converting into highly reactive silanol compound is different, it is necessary to make both aqueous solutions separately and then mix them to obtain a uniform aqueous solution. If the above-mentioned mixed treatment agent is non-uniform,
The coating obtained by coating the surface of the steel material coated with the above-mentioned chromate treatment is difficult to smooth, and the adhesiveness becomes non-uniform, so that the boiling water resistance decreases.

As the chelating agent, ethylenediaminetetraacetic acid, nitrilotriacetic acid, 1,2-diaminocyclohexanetetraacetic acid, N-
Aminocarboxylic acids such as oxyethylenediaminetriacetic acid, ethyleneglycolbis (β-aminoethylether) tetraacetic acid and ethylenediaminetetrapropionic acid, and alkylolamines such as diethanolamine and triethanolamine are suitable. Any water-soluble chelating agent that causes a chelate-forming reaction with ions of metals such as Cr, Mn, Co, Al, Mo, and V contained in the treating agent may be used. The chelating agent may not be dissolved simply by adding it to water, and alkali such as ammonia and acetic acid,
A uniform solution can be obtained by dissolving it in water whose pH is adjusted with a weak acid such as phosphoric acid. The pH value may be a pH value at which the above chelating agent can be dissolved as a stable aqueous solution.

As the amino-based silane coupling agent, a silane coupling agent having a silicon atom to which three alkoxy groups are bonded in the molecule and having one or more amino groups or amino residues, for example, γ-anilinopropyltriene Methoxysilane, n-butylaminopropyltrimethoxysilane,
γ- (2-aminoethyl) aminopropyltrimethoxysilane, trimethoxysilylpropyldiethylenetriamine, bis [3- (rotimethoxysilyl) propyl] ethylenediamine, p-aminophenyltrimethoxysilane, m, p- (aminoethylaminomethyl) ) Phenethyltrimethoxysilane is used.

Some amino silane coupling agents are also sparingly soluble in water, and can be completely dissolved by adding them to water whose pH has been adjusted beforehand with a weak acid such as acetic acid or phosphoric acid. Also,
Appropriate hydrolysis is caused by a weak acid, and the silanol compound can be converted into a highly reactive silanol compound for use. Regarding the pH value of the water in which the amino-based silane coupling agent is dissolved, there is no problem as long as the pH value is sufficient to hydrolyze the amino-based silane coupling agent and form a uniform aqueous solution.

When the above aqueous solution of the amino-based silane coupling agent is applied alone, the adhesive force between the steel material and the organic resin coating film is lowered by immersion in boiling water. On the other hand, in the case of applying a mixed treatment agent in which the above aqueous solution of the chelating agent and the above aqueous solution of the amino silane coupling agent are mixed, surprisingly, even if the steel material is immersed in boiling water for a long time, The adhesive force with the organic resin coating film is hardly reduced. Regarding this effect, analysis results of chromate film, baking film of mixed treatment agent of chelating agent and amino-based silane coupling agent, cured film of epoxy primer and laminated film of these and elution of chromium ion and phosphate ion to hot water As can be inferred from the amount measurement result, on the surface of the steel material coated with the above chromate treatment agent,
When an aqueous solution of an amino-based silane coupling agent is applied alone without adding a chelating agent, the silanol compound in the aqueous solution is too reactive, so the silanol compound in the coating film obtained by applying the aqueous solution is Excessive condensation reaction occurs between the compounds, and inactive molecules with no adhesive property such as siloxane oligomer are generated and deactivated.

However, by using the chelating agent together, the condensation reaction between the silanol group and the hydroxyl group on the surface of the silica-based fine particles in the chromate coating is promoted in order to suppress the excessive condensation reaction of the silanol compounds and prevent deactivation. A siloxane bond is generated, and the mixed treatment agent layer of the amino-based silane coupling agent and the chelating agent and the chromate film are firmly adhered and integrated.

Furthermore, part of the chelating agent is Cr, Mn,
Coordinates with soluble ions of metals such as Co, Al, Mo and V, and suppresses elution into hot water.

In particular, when an organic resin containing an epoxy group such as an epoxy resin is used for forming the organic resin coating film, a crosslinking reaction occurs between the epoxy group and the amino group of the amino silane coupling agent.

It is considered that boiling water resistance is remarkably improved by such effects.

In the preparation of the above-mentioned mixed treatment agent, the concentration of the chelating agent in the aqueous solution of the aforementioned chelating agent and the concentration of the amino silane coupling agent in the aqueous solution of the amino silane coupling agent, which are preliminarily prepared, are arbitrary, Regarding the mixed treating agent obtained by mixing the aqueous solution of 1., the final number of moles of the amino silane coupling agent contained in the mixed treating agent 1 is 0.01 to 2.0 moles, and 1 mole of the amino silane coupling agent is used. The ratio of the number of moles of the chelating agent is 0.01 to 0.
Good boiling water resistance can be obtained by mixing so as to be 5.

Good boiling resistance can be obtained by applying to the surface of the steel material coated with the above chromate treating agent in the range of 10 to 900 mg / m ² as the dry weight of the mixed treating agent.

The condensation reaction between the silanol compound in the mixed treatment agent layer and the hydroxyl group on the surface of the silica-based fine particles in the chromate treatment agent layer is promoted by heating the mixed treatment agent layer, and preferably the above chromate. The surface temperature of the steel material coated with the treatment agent is heated to 120 to 250 ° C., but the mixed treatment agent may be applied after heating the steel material, or after the above-mentioned application on the surface of the steel material. You may heat.

Next, the organic resin used for forming the organic resin coating film of the present invention will be described.

The organic resin referred to in the present invention means epoxy resin, epoxy resin,
Organic resin such as silicone resin, polyimide / epoxy resin, polyphenylene sulfide resin, polyether sulfone resin, polyurethane resin, modified polyethylene resin, modified ethylene / propylene copolymer, modified polyamide / propylene copolymer, modified polypropylene resin, etc. as the main component It is an organic resin paint such as a powder paint, a solvent-type paint diluted with a solvent, and a liquid solvent-free paint, but it is also possible to add a pigment, a filling reinforcing agent and the like as necessary.

Pigments include silica, alumina, titanium oxide, silica-alumina, talc (hydrous magnesium silicate), mica (phlogopite, biotite, muscovite, suzolite), kaolin clay, boron nitride, silicon carbide, and other fine powders, phosphorus. Ordinary commercially available extender pigments that are flaky powders, Mapico (synthetic iron oxide yellow, synthetic iron oxide red), red iron oxide, acetylene black, Ketjen black EC, cadmium red, cadmium yellow, cadmium orange, cobalt blue, cobalt green, cobalt Purple, strontium yellow, manganese purple, chromium oxide, turquoise, etc.
Silicomolybdic acid, silicotungstic acid, aluminum phosphate, zirconium phosphate, aluminum tripolyphosphate hydrogen phosphate, ammonium phosphomolybdate, zinc phosphate, chromic phosphate, magnesium phosphate, calcium phosphate, zinc chromate, strontium chromate, basic An appropriate selection is made from general commercially available anticorrosion pigments which are fine powders of lead chromate, lead suboxide, lead cyanamide, basic lead silicate, zinc molybdate, zinc oxide, red lead, barium sulfate, barium chromate, etc. Moreover, 1 type (s) or 2 or more types can be mixed and used.

Further, as the filler reinforcing material, inorganic fibrous fillers such as glass, slag, carbon, alumina, silicon carbide, boron, boron nitride, etc., organic fibrous fillers such as nylon, polyester, vinylon, aramid, Kevlar, etc. It is possible to use one kind or a mixture of two or more kinds by appropriately selecting from general commercially available fibrous fillers.

The coated steel material according to the present invention, for example, in the case of a coated steel pipe, can be obtained by the manufacturing method shown in FIG.

That is, the chromate treatment agent coating device 5 applies a chromate treatment agent to the surface of the steel pipe 1 from which oil and scale have been removed, and the heating device 6 bake it, and then a mixed treatment agent of a chelating agent and an amino silane coupling agent. The mixed treatment agent is applied by the application device 7 and baked by the heating device 8. Then, an organic resin is applied by the organic resin applying device 9, and is heated and hardened or melted by the post-heating device 10 to form a film, and then cooled by the water cooling device 11 to manufacture a coated steel pipe.

In the case of the manufacturing method as described above, after the chromate treatment agent is applied to the surface of the steel pipe 1 and baked by the heating device 6,
It is sufficient that a mixed treatment agent layer of a chelating agent and an amino-based silane coupling agent is formed on the surface of the steel tube until the steel tube reaches the organic resin coating device 9, and the mixture is sufficiently cured. The method for applying the silane coupling agent-mixing treatment agent can be appropriately selected and used from conventionally known methods such as atomized coating with a spray nozzle, spray coating with a spray coating machine, roll coating, and brush coating.

The method of heating the steel pipe by the post-heating device 10 can be appropriately selected and used from conventionally known methods such as high frequency induction heating, far infrared heating, gas heating, and laser irradiation heating.

In FIG. 2, the electrostatic powder coating machine is used for coating the organic resin, but spray coating, roll coating, ironing coating,
It can be appropriately selected and used from conventionally known methods such as brush application.

[Operation] A partial cross section of the organic resin-coated steel material according to the present invention obtained as described above is as shown in FIG. 1. In the figure, 1 indicates that oil and scale are removed by pickling, blasting, etc. The removed steel material, 2 is a chromate treating agent layer obtained by heating and baking a chromate treating agent to which silica-based fine particles are added by partially reducing a mixed aqueous solution of phosphoric acid and chromic anhydride with dextrin or partially saponified polyvinyl acetate, and 3 is A mixed treatment agent of a chelating agent and an amino-based silane coupling agent, 4 indicates an organic resin coating layer.

In addition, the chromate treatment layer 2 in the figure represents the total chromium weight.
Adhesion amount of 100~900mg / m ^2, mixed treatment agent layer deposition amount of 10~900mg / m ² as a dry weight of 3, 4 of the organic resin coating layer is 0.
Good results can be obtained when each has a thickness of 3 to 10 mm.

〔Example〕

In order to specifically explain the present invention, the following is a formulation example of the chromate treating agent in the present invention and a comparative example.
Japanese Patent Application Laid-Open No. Sho 60-163, as a comparative formulation example of a chromate treating agent corresponding to Japanese Patent No. 143934, a formulation example of a mixed treating agent of a chelating agent and an amino silane coupling agent in the present invention.
Preparation examples of a treatment agent for an epoxy silane coupling agent corresponding to JP-A-23038 and Examples and comparative examples of coated steel materials will be given.

◎ Preparation example-1 of chromate treatment agent First, the following solutions and were prepared.

Phosphoric acid / chromic anhydride mixed aqueous solution Phosphoric acid 49.2 g and chromic anhydride 76.8 g were dissolved in distilled water 247.6 g.

5% by weight partially saponified polyvinyl acetate aqueous solution Partially saponified polyvinyl acetate having a molecular weight of 88,000 and a saponification degree of 87% was added to distilled water and left to swell for 2 hours. Next, this aqueous solution was heated to 98 ° C. and completely dissolved to prepare an aqueous solution containing 5% by weight of partially saponified polyvinyl acetate.

10 wt% Aerosil 200 aqueous solution As a silica-based fine particle, Aerosil manufactured by Nippon Aerosil Co., Ltd.
200 was used. Aerosil 200 was added to distilled water and dispersed by stirring with a high speed mixer (rotation speed 3000 rpm) to prepare an aqueous solution containing 10 wt% of Aerosil 200.

Next, the above mixed aqueous solution of phosphoric acid and chromic anhydride 37
3.6g of 5wt% partially saponified polyvinyl acetate aqueous solution
106 g was added and heated to 90 ° C. to reduce a part of hexavalent chromium ions to trivalent chromium ions. The weight ratio of hexavalent chromium against said reducing total chromium in the original aqueous solution is 0.60, PO ₄ ^3- weight ratio of to total chromium was 1.16. Then, to the above-mentioned reduced aqueous solution, the above 10 wt% Aerosil 200 aqueous solution 5
15.6 g was added and dispersed to prepare a chromate treating agent A according to the present invention. The weight ratio of SiO ₂ (Aerosil 200) to the total chromium in the chromate treating agent A was 1.29.

◎ Comparative Preparation Example-1 of Chromate Treatment Agents-1 As comparison materials, chromate treatment agents C, D and E corresponding to JP-A-52-143934 were prepared.

Chromate treatment agent C Chromic anhydride (76.8 g) and amber (28.8 g) were dissolved in distilled water (700 g), and parbituric acid (19.2 g) was added to the aqueous solution to disperse, and distilled water was further added to prepare chromate treatment agent (1).

Chromate treatment agent D 76.8 g of chromic anhydride was dissolved in 823 g of distilled water, and 8.4 g of wheat starch was added thereto, followed by heating and boiling for 1 hour to partially reduce hexavalent chromium ions. The weight ratio of trivalent chromium to the total chromium in the reduced aqueous solution was 0.38. 92 g of the above Aerosil # 200 was added to the reduced aqueous solution and stirred.
A chromate treatment agent D was prepared by dispersing.

Chromating agent E Chromic anhydride 76.8 g was dissolved in distilled water 800 g, corn starch 3.4 g was added, and the mixture was heated and boiled for 1 hour.
Valence chromium ions were partially reduced. The weight ratio of trivalent chromium to the total chromium in the reduced aqueous solution was 0.22. After stirring and dispersing 23 g of Aerosil # 200 and 23 g of talc powder (magnesium silicate) in the reduced aqueous solution, 46 g of a 5% aqueous solution of polyvinyl alcohol (Nippon Gosei Kagaku NM-11) was added. By dispersing, a chromate treating agent E was prepared.

Preparation Example of Mixed Treatment Agent of Chelating Agent and Amino Silane Coupling Agent Ethylenediaminetetraacetic acid was used as a chelating agent and dissolved in distilled water whose pH was adjusted to 6 with ammonia water to prepare an aqueous solution. Separately from the above aqueous solution, γ-anilinopropyltrimethoxysilane (Toray, SZ6083 manufactured by Silicone) was used as an amino-based silane coupling agent, and acetic acid was used.
The solution was dissolved in distilled water having a pH adjusted to 2.5 to prepare an aqueous solution. Then, an aqueous solution of the above ethylenediaminetetraacetic acid and an aqueous solution of γ-anilinopropyltrimethoxysilane,
The mole number of γ-anilinopropyltrimethoxysilane contained in the treating agent 1 after mixing both is 0.04 moles, and ethylenediaminetetraacetic acid is contained in 0.1 moles relative to 1 mole of the γ-anilinopropyltrimethoxysilane. The mixture was mixed as described above to prepare a mixed treatment agent B of the chelating agent and the amino silane coupling agent according to the present invention.

◎ Comparative Preparation Example of Epoxy Silane Coupling Agent Treatment Agent As an epoxy silane coupling agent, γ-glycidoxypropyltrimethoxysilane (manufactured by Nippon Unicar Co., Ltd.
A-187) was added and dissolved in distilled water so that the concentration of β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane was 0.04 mol /, corresponding to JP-A-60-23038. A treating agent F was prepared.

Example-1 A steel plate (SS41, 200 mm width × 200 mm length × 9 mm thickness) is grit blasted, and the surface of the chromate treatment agent A is applied at 380 mg / m ^{2 in} terms of the total chromium deposition amount and heated to 190 ° C. And baked it. Next, the chelating agent and the amino-based silane coupling agent mixed treatment agent B was sprayed onto the surface thereof in an amount of 290 mg / m ^{2 in} terms of the dry weight of the coating film by means of a spraying nozzle.
It was heat-cured at 0 ° C.

Then, coat the surface with powdered epoxy resin paint to a film thickness of 450
The powder epoxy coated steel sheet (I) according to the present invention was prepared by electrostatically coating to a thickness of μ and heating and curing.

Further, as a comparative example, the powdered epoxy coated steel sheet corresponding to JP-A-52-143934 omits the application of the mixed treatment agent B and replaces the chromate treatment agent A with the chromate treatment agent C. 3 coated with powdered epoxy coated steel sheet (II), chromate treatment agent D coated with powdered epoxy coated steel sheet (III) corresponding to FIG. 4 and chromate treatment agent E coated with FIG. 5 Powder epoxy coated steel sheet (IV) corresponding to the above was prepared and compared.

Further, as a powder-epoxy coated steel sheet corresponding to JP-A-60-23038, in the same manner as above, the application of the chromate treating agent A was omitted, and the treating agent F was used in place of the mixed treating agent B. A powder epoxy coated steel plate (V) corresponding to the applied FIG. 6 was prepared and compared.

Powder epoxy coated steel sheets (I), (II), (II
Regarding I), (IV) and (V), adhesive strength test (cross-cut test: JIS K5400, the adhesion of the coating film to the steel material is indicated by a score of 0 to 10 (maximum 10 points)) and boiling water immersion test Table 1 shows the results of carrying out (adhesion strength test after immersion, immersion temperature 98 ° C, immersion time 8000 hours).

As shown in Table 1, a significant difference was observed in the boiling water immersion test. Particularly, a mixed aqueous solution of phosphoric acid and chromic anhydride was partially reduced with partially saponified polyvinyl acetate as a pretreatment agent, and silica fine particles were added. When the chromate treating agent A according to the present invention is used in combination with the chelating agent and the mixed treating agent B of the amino silane coupling agent (I), the chromate treating agent C corresponding to JP-A-52-143934 is used. In the case of using D or E, that is, in the case of (II), (III) or (IV) and in the case of using the treating agent F of the epoxy-based silane coupling agent corresponding to JP-A-60-23038 (V). By comparison, much better results are obtained.

Example-2 In the same manner as in Example 1, when the chromate-treating agent A was prepared, phosphoric acid and silica (Aerosil 200) were added as described in the chromate-treating preparation example, and addition of phosphoric acid was omitted. Example) The addition of silica was omitted (comparative example), the powder epoxy coated steel pipe (I) was prepared, and the results of adhesive strength test and boiling water immersion test are shown in Table 2.

As shown in Table 2, a remarkable difference was observed in the boiling water immersion test, and in particular, the chromate treating agent of the present invention containing both phosphoric acid and silica-based fine particles as a base treating agent was used as a chelating agent and a silane coupling agent. Good results have been obtained when used in combination with mixed treating agents.

Therefore, it is necessary to add both phosphoric acid and silica fine particles to the chromate treating agent of the present invention.

Example-3 In the same manner as in Example 1, the type of the reducing agent used in the preparation of the chromate treating agent A was changed as follows, and partially saponified polyvinyl acetate (molecular weight 88000, saponification degree) was used.
87%) Dextrin (average molecular weight 120,000) Corn starch Wheat starch Polyvinyl alcohol (molecular weight 10000) The above-mentioned powder epoxy coated steel sheet (I) was prepared, and the results of adhesion test and boiling water immersion test are shown in Table 3. Indicated.

As shown in Table 3, a significant difference was observed in the boiling water immersion test, and the chromate treating agent according to the present invention using partially saponified polyvinyl acetate or dextrin as the reducing agent was used as the base treating agent. Good results were obtained when the mixed treatment agent of the silane coupling agent was used in combination.

Therefore, it is necessary to use partially saponified polyvinyl acetate or dextrin as a reducing agent in the chromate treating agent of the present invention.

Example-4 In the same manner as in Example 1, the chelating agent and the amino type silane coupling agent used in the preparation of the mixed treatment agent of the chelating agent and the amino type silane coupling agent were changed as follows, and the chelating agent was used. A: Ethylenediaminetetraacetic acid Ronitrilotriacetate Ha 1,2-diaminocyclohexanetetraacetic acid N None (Comparative example) Amino-based silane coupling agent: γ-anilinopropyltrimethoxysilane trimethoxysilylpropyldiethylenetriamine bis [3- (tri (Methoxysilyl) propyl] ethylenediamine None (Comparative Example) The above-mentioned powder epoxy coated steel sheet (I) was prepared and subjected to an adhesion test and a boiling water immersion test.

As shown in Table 4, a significant difference was observed in the adhesive strength test and the boiling water immersion test, and the chromate treatment agent according to the present invention was used as the base treatment agent for the chelating agent I-C and the amino silane coupling agent-. Good results have been obtained when used in combination with mixed treating agents.

Example-5 A steel pipe (200 A x 5500 mm length x 5.8 mm thickness) was grit blasted, and the chromate treatment agent A was applied to the surface thereof in an amount of 620 mg / m ^{2 in} terms of total chromium deposition amount and heated at 160 ° C. After baking, the above-mentioned chelating agent and amino silane coupling agent mixed treatment agent B was atomized and applied at an amount of 280 mg / m ^{2 in} terms of coating film weight by means of a spray nozzle, and heated and cured at 190 ° C.

Then, the surface thereof was coated with the following organic resin so as to have a film thickness of 2.5 mm and cured to manufacture a coated steel pipe according to the present invention.

Organic resin: I Powder epoxy resin paint II Solvent type epoxy resin paint III Insoluble epoxy resin paint IV Epoxy / silicone resin paint V Polyimide / epoxy resin paint VI Polyphenylene sulfide resin paint VII Polyether sulfone resin paint VIII Powder polyethylene resin Paints Table 5 shows the results of the adhesive strength test and boiling water immersion test performed on the above coated steel pipes.

As shown in Table 5, when the chromate treating agent according to the present invention is used as a base treating agent for a steel pipe in combination with a mixed treating agent of a chelating agent and an amino silane coupling agent, regardless of the type of organic resin, Very good results are obtained in the adhesion test and the boiling and water immersion tests.

〔The invention's effect〕

As is clear from the examples, the coated steel material according to the present invention is
Compared with the conventional coated steel materials, the boiling water resistance is remarkably excellent, so that there is a remarkable effect that a coated steel material having unprecedented high temperature durability can be provided.

[Brief description of drawings]

FIG. 1 is a partial sectional view of a coated steel material according to the present invention, FIG. 2 is a schematic view showing an example of manufacturing the coated steel material of the present invention, FIG. 3, FIG.
FIG. 5, FIG. 5 and FIG. 6 are partial cross-sectional views of a coated steel material according to a conventional example. 1 ... Steel material 2 ... Chromate treating agent obtained by heating and baking a chromate treating agent to which silica-based fine particles are added after partially reducing an aqueous mixed solution of phosphoric acid and chromic anhydride with partially saponified polyvinyl acetate or dextrin layer. 3 ... Chelating agent and amino-based silane coupling agent mixed treatment agent layer 4 ... Organic resin coating film 5 ... Chromate treatment agent coating device 6 ... Heating device 7 ... Chelating agent and amino silane coupling agent Mixing agent coating device, 8 ... Heating device, 9 ... Organic resin coating device, 10 ... Post heating device, 11 ... Cooling device, 12 ... Hexavalent chromium compound and amino acid, acid amide, lactam, saturated or unsaturated A chromate treating agent layer obtained by heating and baking a chromate treating agent mixed with an organic component such as saturated polycarboxylic acid. 13 …… Chromic acid (CrO ₃ ) is partially reduced with organic reducing agents such as sugars, polyhydric alcohols, monohydric alcohols, alkylolamines and aromatic polyhydric alcohols, and the chromate treatment agent containing silica fine particles is heated. Chromate treatment layer obtained by baking. 14 …… Chromic acid (CrO ₃ ) is partially reduced with organic reducing agents such as sugars, polyhydric alcohols, monohydric alcohols, alkylolamines, aromatic polyhydric alcohols, silica fine particles are added, and polyvinyl alcohol is further added. A chromate treatment agent layer obtained by heating and baking a chromate treatment agent to which a nonionic water-soluble resin such as methyl cellulose, polyethylene oxide, and hexamethylmethoxymethylmelamine-modified polyhydroxyethyl acrylate is added. 15 …… Silane coupling agent layer such as epoxy silane coupling agent

Claims (1)

[Claims] 1. A chromate treatment agent obtained by partially reducing an aqueous mixed solution of phosphoric acid and chromic anhydride with partially saponified polyvinyl acetate or dextrin and heating and baking it on the surface of a steel material. A coated steel material comprising a chromate treatment agent layer, a chelating agent and an amino silane coupling agent mixed treatment agent layer, and an organic resin coating film, which are sequentially laminated.