JPH01150539A - Steel coating material - Google Patents

Abstract

PURPOSE:To obtain a steel coating material having superior resistance against the boiling water, by sequentially laminating a chromate processing agent layer, a mixed processing agent layer and an organic resin application film onto the surface of a steel material. CONSTITUTION:A mixed solution of phosphoric acid and anhydrous chromic acid is partially reduced by partially-saponified polyvinyl acetate or dextrin, and then added with silica fine particles, whereby a chromate processing agent is obtained. The chromate processing agent is applied onto the surface of a steel material, heated and backed to be a chromate processing agent layer 2. On the chromate processing agent layer 2, a mixed processing agent layer 3 of chelate agent and amino silane coupling agent and, an organic resin application film 4 are sequentially laminated. Thus, a steel coating material having superior resistance to the boiling water can be obtained. It is proper that the baking temperature of the chromate processing agent is 120-300 deg.C at the surface temperature of the steel material. If the baking temperature is below 120 deg.C, it takes a long time to make the coating film of chromate insoluble. If the baking temperature exceeds 300 deg.C, the chromate coating film is thermally decomposed, with lowering the resistance against the boiling water. A favorable result can be obtained when the adhering amount of the chromate processing agent layer 2 is 100-900mg/m<2> by the total weight of chrome, that of the mixed processing agent layer 3 is 10-900mg/m<2> by the dry weight, and the thickness of the organic resin coating layer 4 is 0.3-10mm.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a coated steel material, and more particularly to a coated steel material having excellent boiling water resistance.

[Prior art] Coated steel products have been manufactured by coating the surfaces of steel products such as steel pipes, steel plates, steel structures, and preformed bodies with organic resins such as epoxy resins to improve the corrosion resistance of the above-mentioned steel products. .

In recent years, steel products coated with the above-mentioned organic resin on the inner and outer surfaces of steel pipes have come into widespread use, and demands on quality have become stricter.
It is desired to develop painted steel materials that have both hot water resistance and boiling water resistance.

Conventionally, for example, for powder resin-coated steel pipes, a method has been proposed in which the surface of the steel pipe is subjected to a base treatment in advance in order to improve cathodic peeling resistance.

For example, in JP-A-52-14392, as shown in FIG. 3, a compound of hexavalent chromium and an amino acid,
Chromate treatment agent layer 12 coated with chromate treatment agent C mixed with organic components such as acid amide, lactam, saturated or unsaturated polycarboxylic acid and baked, powder coating of thermoplastic or thermosetting resin composition. There is a proposal for a coated steel pipe with a layered membrane 4.

In addition, as shown in Figure 4, instead of the above chromate treatment agent C, chromic acid (Cr03) is used as an organic reducing agent such as sugar, polyhydric alcohol, -hydric alcohol, alkylolamine, aromatic polyhydric alcohol, etc. C,64/total chromium=
A painted steel pipe laminated with a chromate treatment agent layer 13 partially reduced to a ratio of 0.35 to 0.65 (weight ratio) and heat-baked using a chromate treatment agent prepared by adding silica fine particles to the reduced product; As shown in Figure 5, instead of chromate treatment agent C, a nonionic water-soluble resin such as polyvinyl alcohol, methylcellulose, polyethylene oxide, hexamethylmethoxymethylmelamine-modified polyhydroxyethyl acrylate is added to chromate treatment agent C. There is a painted steel pipe on which a chromate treatment agent layer 14 is laminated, which is heated and baked using treatment agent E.

Furthermore, as shown in FIG. 6 in Japanese Patent Application Laid-Open No. 60-23038, a silane coupling agent layer 14 such as an epoxy-based silane coupling agent and a powder epoxy resin coating 4 are sequentially laminated on the surface of the steel pipe 1. There is painted steel pipe.

(Problems to be Solved by the Invention) However, the coated steel materials shown in FIGS. 3, 4, 5, and 6 all have the problem that the organic resin coating peels off when immersed in boiling water for a long time. There is a point.

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

[Means for solving problems]

The present inventors conducted intensive studies to solve the above-mentioned problems, and found that a mixed aqueous solution of phosphoric acid and chromic anhydride was partially reduced with partially saponified polyvinyl acetate or dextrin on the surface of the steel material to create a silica-based material. Coated steel with excellent boiling water resistance by applying a chromate treatment agent containing fine particles and baking, then applying a mixed treatment agent of a chelating agent and an amino-based silane coupling agent, baking, and applying an organic resin coating. It was discovered that the following could be obtained, leading to the present invention.

That is, as shown in FIG. 1, the present invention is a chromate treatment in which the surface of a steel material 1 is partially reduced with a mixed aqueous solution of phosphoric acid and chromic anhydride with partially saponified polyvinyl acetate or dextrin, and silica-based fine particles are added. A boiling water resistant product characterized by sequentially laminating a chromate treatment agent layer 2 obtained by applying a chromate agent and baking with heat, a mixed treatment agent layer 3 of a chelating agent and an amino-based silane coupling agent, and an organic resin coating 4. It concerns superior painted steel materials.

Hereinafter, the present invention will be explained in detail.

The steel materials used in the present invention are steel materials such as steel plates, steel pipes, shaped steels, and steel molded products made of alloy steels such as carbon steel and stainless steel. In addition, the above-mentioned steel materials are plated with zinc, aluminum, chromium, nickel, etc., alloy plated with zinc-iron, zinc-aluminum, zinc-nickel, zinc-nickel-cohalt, etc., or the above-mentioned platings are used. The alloy plating layer is coated with a dispersion plating in which fine inorganic particles such as silica, alumina, titanium oxide, boron oxide, silica-alumina, silica titanium, silicon carbide, silicon oxynitride, and boron nitride are dispersed. There is no problem.

Next, the chromate treatment agent used for forming the chromate treatment agent layer of the present invention will be explained.

The chromate treatment agent used in the present invention is produced by partially reducing an aqueous solution of phosphoric acid and chromic anhydride (Cr03) dissolved in distilled water with a polymer reducing agent to produce phosphate ions and hexavalent chromium ions. Although trivalent chromium ions and silica-based fine particles are mixed therein, part of the phosphoric acid can be replaced with condensed phosphoric acid such as pyrophosphoric acid or tripolyphosphoric acid, if necessary.

As the polymeric reducing agent used for partial reduction of chromium from hexavalent to trivalent, starch containing a large amount of amylopectin,
For example, it has a molecular structure of dextrin (average molecular weight 50,000 to 250,000) that is made by partially hydrolyzing corn starch etc. with a hydrolytic enzyme such as amyloglucosidase and making it easier to form a coordination bond with chromium ions. Partially saponified polyvinyl acetate having a saponification degree of □XX100=80+n to 90% and a molecular weight of 60,000 to 140,000 is used.

The above polymer reducing agent has an extremely large molecular weight, so 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 completely dissolve.

The polymer reducing agent added to the mixed aqueous solution of phosphoric acid and chromic acid by the above method causes the chromate treatment agent and the group to be baked by heating, as estimated from the analysis results of the film and the measurement results of the amount of chromium ions eluted in hot water. At the same time, a portion of the polymeric reducing agent decomposes and reduces 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 bonded to this chromium ion. It has a remarkable effect on making the coating insoluble in hot water. Furthermore, polymeric reducing agents other than those mentioned above, such as corn starch,
When using a polysaccharide that is not partially hydrolyzed by enzymes, such as wheat starch, compared to using the above-mentioned dextrin or partially saponified polyvinyl acetate, it is necessary to add mochrome ions to a mixed aqueous solution of phosphoric acid and chromic acid. Since the coordination of is insufficient, the effect of making the chromate film insoluble in hot water is small.

In addition, as a polymer reducing agent, a water-soluble resin other than the above partially saponified polyvinyl acetate, for example, →C)1. -CHh
.

■ When using polyvinyl alcohol with a molecular structure of H, all substituents are active hydroxyl groups, so
When added to a mixed aqueous solution of phosphoric acid and chromic acid, it is susceptible to oxidative decomposition by the chromic acid, and the effect of making the chromate film insoluble in hot water is reduced.

In addition, when using a low-molecular reducing agent such as methyl alcohol, succinic acid, or sorbitol instead of a polymeric reducing agent, most of it will be decomposed when added to a mixed aqueous solution of phosphoric acid and chromic acid, so the chromate film should not be coated. It has almost no effect of making it insoluble in hot water.

Among the above polymer reducing agents, dextrin having an average molecular weight in the range of 50,000 to 250,000 is used. If the average molecular weight of dextrin is less than 50,000, it will have little effect on making the chromate film insoluble in hot water.
If it exceeds 250,000, it is not desirable because it is difficult to dissolve in a mixed aqueous solution of phosphoric acid and chromic acid and the smoothness of the coating obtained by coating is impaired.

Further, the above partially saponified polyvinyl acetate has a molecular weight of 60
000 to 140,000 and a saponification degree of 80 to 90%. If the molecular weight of the partially saponified polyvinyl acetate is less than 60,000, the effect of making the chromate film insoluble in hot water is small,
o, 1! This is not desirable because it is difficult to dissolve in a mixed aqueous solution of phosphoric acid and chromic acid and the smoothness of the coating obtained by coating is impaired. In addition, the degree of saponification of partially saponified polyvinyl acetate is 80
If the amount is less than 90% or more than 90%, the effect of making the chromate film insoluble in hot water decreases.

The above dextrin and partially saponified polyvinyl acetate are used in amounts necessary to maintain the ratio of hexavalent chromium to total chromium at a desired ratio. The desired ratio is a weight ratio of hexavalent chromium to total chromium in the range of 0.35 to 0.65. When this ratio is less than 0.35, the adhesion between the steel surface and the chromate coating decreases, and when it exceeds 0.65, the effect of making the chromate coating insoluble in hot water decreases significantly.

The weight ratio of hexavalent chromium to the total chromium above is 0.35.
The amount of dextrin required to achieve a range of ~0.65 is:
0.0 as a weight ratio to the total solid content in the chromate treatment solution
The amount of partially saponified polyvinyl acetate is in the range of 0.009 to 0.052 as a weight ratio to the total solid content in the chromate treatment liquid.

In addition, the phosphoric acid added to the chromate treatment agent mentioned above is estimated from the analysis results of the film and the measurement results of the elution amount of chromium ions in hot water. It binds to a coordination compound in which chromium ions are coordinated to polyvinyl acetate.

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

In addition to integrating the chromate film with the effects of
Free phosphoric acid and a portion of the phosphoric acid group bonded to the above-mentioned chromium ion-coordinated dextrin or partially saponified polyvinyl acetate react with the surface of the steel material to generate an iron chromium phosphate compound, thereby forming a chromate coating on the steel material. For strong adhesion to
Even when immersed in boiling water, there is almost no elution of chromium ions or phosphate ions, and it is thought that the adhesiveness between the steel material and the organic resin coating film is less likely to deteriorate.

The amount of phosphoric acid added is such that the weight ratio of PO43- to total chromium is 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 the amount is 2.0, free soluble phosphoric acid remains in the chromate film, which has the effect of making the chromate film insoluble in hot water. decreases.

As the silica-based fine particles added to the chromate treatment agent, for example, Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.
．． Aerosil 300. Aerosil 380. Aerosil 0
X50 and Nip Seal L300 manufactured by Nippon Sirikani Gyogyo Co., Ltd.
．． Nip Seal N300A, Nip Seal E200. Silica fine particles such as Nip Seal E200A, Aerosil Cok84. manufactured by Nippon Aerosil Co., Ltd. Aerosil MOX
80. Silica-alumina fine particles such as Aerosil Mox 170, Snowtex 0. Snowtex OL, Snowtex O3, Snowtex OM
L, Cataloid SN manufactured by Catalysts & Chemicals Co., Ltd.
Cataloid SA.

Colloidal silica such as Cataloid 20L, Alumina Sol 100, Alumina Sol 20 manufactured by Shirataki Chemical Industry Co., Ltd.
1 or 2 of 0 grade silica alumina sol etc.
Use a mixture of more than one species.

Inferred from the analysis results of the chromate treatment agent and its heated coating and the measurement results of the elution amount of phosphate ions and chromium ions in hot water, the silica-based fine particles mentioned above have surface hydroxyl groups that correspond to the phosphate ions and chromium ions in the chromate treatment agent. The amino-based chromate film is combined with chromium ion-coordinated dextrin or partially saponified polyvinyl acetate to integrate the chromate film, and the amino-based silane coupling agent in the mixed treatment agent of the chelating agent and amino-based silane coupling agent is applied onto the chromate film. The silane coupling agent forms a siloxane bond to firmly adhere the chromate coating and the mixed treatment agent layer of the chelating agent and silane coupling agent, so the adhesion between the organic resin coating and the steel material is strong even when immersed in boiling water. It has a remarkable effect on preventing deterioration. The amount of silica-based fine particles added is such that the weight ratio to the total chromium in the chromate treatment solution is in the range of 0.5 to 2.5. If the amount added is less than 0.5, the above effect will hardly be achieved, and if it exceeds 2.5, the fluidity of the chromate treatment agent will be significantly deteriorated, impairing the smoothness of the coating obtained by applying it to the surface of steel materials, which is not desirable.

In addition, if the adhesion between the chromate coating and the steel material or the adhesion between the chromate coating and the mixed treatment agent layer of a chelating agent and an amino-based silane coupling agent is insufficient, phosphovanadate or phosphomolybdenum may be added to the chromate treatment agent. Phosphorous and oxygen acid compounds such as acids, ammonium metavanadate,
Oxyacid ammonium salts such as ammonium molybdate,
After appropriately selecting from metal salts such as manganese carbonate, cobalt carbonate, dialuminum hydrogen phosphate, or boric acid,
Added.

Before applying the above-mentioned chromate treatment agent to the surface of the steel material, scale, oil, etc. on the surface of the steel material are removed by pickling, sandblasting, grid blasting, shot blasting, or the like. When a chromate treatment agent is applied to the steel surface from which scale, oil, etc. have been removed, hexavalent chromium is reduced due to the oxidation effect on the steel surface and heating of the steel material after application, and the hydroxyl groups on the surface of the silica particles and phosphoric acid are reduced. The dehydration condensation reaction between the phosphoric acid groups of the dehydrated condensate and chromium ions and the chromium ion-coordinated dextrin or partially saponified polyvinyl acetate is promoted, making the product poorly soluble and strong in hot water. A lomate film is formed. The appropriate temperature for baking the chromate treatment agent is the steel surface temperature of 120 to 300°C. If the steel plate surface temperature is less than 120°C, it will take a long time to make the chromate film insoluble, making it unsuitable for practical use.
If the temperature exceeds 00°C, thermal decomposition of the chromate film occurs and boiling resistance decreases.

Further, good boiling water resistance can be obtained when the amount of the chromate treatment agent deposited is in the range of 100 to 900 mg/rr1 m as the total chromium weight.

Next, a mixed treatment agent of a chelating agent and an amino-based silane coupling agent used in the present invention will be explained.

The mixed treatment agent of a chelating agent and an amino-based silane coupling agent used in the present invention is preferably prepared by mixing an aqueous solution of a chelating agent and an aqueous solution of an amino-based silane coupling agent. Regarding the preparation method of the above mixed treatment agent,
The optimum pH value for dissolving the chelating agent in water to make a uniform aqueous solution, the dissolving of the amino-based silane coupling agent in water to make a uniform aqueous solution, and the sufficient hydrolysis of the amino-based silane coupling agent. The optimum pH value for converting into highly reactive silanol compounds is different.
Both need to be made into separate aqueous solutions and then mixed together to form a homogeneous aqueous solution. If the above-mentioned mixed treatment agent is uneven, it will be difficult to smooth the film obtained by applying it to the surface of the steel material coated with the above-mentioned chromate treatment agent, and the adhesion will become uneven, resulting in a decrease in boiling water resistance. .

Chelating agents include ethylenediaminetetraacetic acid, nitrilotriacetic acid, 1,2-diaminocyclohexanetetraacetic acid, N
-Aminocarboxylic acids such as oxyethylenediaminetriacetic acid, ethylene glycol bis(β-aminoethyl ether)tetraacetic acid, and ethylenediaminetetrapropionic acid, and alkylolamines such as jetanolamine and triethanolamine are suitable; Cr, Mn, and Go contained in the above-mentioned chromate treatment agent.

Any water-soluble chelating agent that causes a chelate-forming reaction with metal ions such as 8λ, Mo, and V may be used. A chelating agent may not be dissolved simply by adding it to water, but a homogeneous solution can be obtained by dissolving it in water whose pH has been adjusted using an alkali such as ammonia and a weak acid such as acetic acid or phosphoric acid. The pH value may be pi (a value that allows the above-mentioned chelating agent to be dissolved as a stable aqueous solution).

Examples of amino-based silane coupling agents include silane coupling agents that have a silicon atom to which three alkoxy groups are bonded in the molecule and one or more amino groups or amino residues, such as γ-anilinopropyltritri Methoxysilane, n-butylaminopropyltrimethoxysilane,
γ-(2-aminoethyl)aminopropyltrimethoxysilane, trimethoxysilylpropyldiethylenetriamine, bis[3-(rothymethoxysilyl)propyl]ethylenediamine, p-aminophenyltrimethoxysilane, m.

p-(aminoethylaminomethyl)phenethyltrimethoxysilane, etc. are used.

Some amino-based silane coupling agents are poorly soluble in water, and can be completely dissolved by adding them to water whose pH has been adjusted in advance with a weak acid such as acetic acid or phosphoric acid. In addition, suitable hydrolysis occurs with a weak acid, and it can be converted into a highly reactive silanol compound for use. Regarding the pH value of the water in which the above-mentioned amino-based silane coupling agent is dissolved, there is no problem as long as the pH value can sufficiently hydrolyze the amino-based silane coupling agent and form a uniform aqueous solution.

When the aqueous solution of the above-mentioned amino-based silane coupling agent is applied alone, the adhesive force between the steel material and the organic resin coating decreases due to immersion in boiling water.

On the other hand, when applying a mixed treatment agent made by mixing an aqueous solution of the above-mentioned chelating agent and an aqueous solution of the above-mentioned amino-based silane coupling agent, surprisingly, the steel material remains intact even when immersed in boiling water for a long time. There is almost no decrease in adhesive strength between the film and the organic resin coating. Regarding this effect, we have analyzed the results of analysis of chromate coating, baked coating of mixed treatment agent of chelating agent and amino-based silane coupling agent, hardened coating of epoxy primer, and laminated coatings of these, and the elution of chromium ions and phosphate ions in hot water. Judging from the amount measurement results, ■ The surface of the steel material coated with the above-mentioned chromate treatment agent,
If an aqueous solution of an amino-based silane coupling agent is applied alone without adding a chelating agent, the silanol compounds in the aqueous solution are too reactive, so the silanol compounds in the film obtained by applying the aqueous solution are Excessive condensation reaction occurs between the compounds, producing non-adhesive inert molecules such as siloxane oligomers, which are deactivated.

However, by using a chelating agent in combination, the condensation reaction between the silanol groups and the hydroxyl groups on the surface of the silica particles in the chromate coating is promoted in order to suppress the excessive condensation reaction between silanol compounds and prevent deactivation. Siloxane bonds are generated, and the mixed treatment agent layer of the amino-based silane coupling agent and chelating agent and the chromate coating are strongly adhered and integrated.

■ Furthermore, part of the chelating agent is Cr in the chromate film,
It coordinates with soluble ions of metals such as Mn, Go, A, ff, Mo, and V, and suppresses their elution into hot water.

(2) In particular, when an organic resin containing an epoxy group such as an epoxy resin is used to form an organic resin coating, a crosslinking reaction occurs between the epoxy group and the amino group of the amino-based silane coupling agent.

It is thought that these effects significantly improve boiling water resistance.

When preparing the above-mentioned mixed treatment agent, the concentration of the chelating agent in the aqueous solution of the chelating agent and the concentration of the amino-based silane coupling agent in the aqueous solution of the amino-based silane coupling agent prepared in advance are arbitrary, but both Regarding the mixed treatment agent obtained by mixing aqueous solutions of , the final mole number of the amino-based silane coupling agent contained in the mixed treatment agent IL is set to 0. O is 1 to 2.0 mol, and the ratio of the number of moles of the chelating agent to 1 mol of the amino-based silane coupling agent is 0.
．． Good boiling water resistance can be obtained by mixing in an amount of O1 to 0.5.

Good boiling resistance can be obtained by applying the above-mentioned chromate treatment agent to the surface of the steel material in a dry weight range of 10 to 900 mg/rd.

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

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

The organic resin referred to in the present invention refers to epoxy resin, epoxy resin,
Silicone resin, polyimide/epoxy resin, polyphenylene sulfide resin, polyether sulfone resin, polyurethane.

resin, modified polyethylene resin, modified ethylene-10 pyrene copolymer, modified polyamide/pro1 pyrene copolymer,
Powder coatings mainly composed of 11 resins such as modified polypropylene resins, solvent-based coatings diluted with solvents, and internal resin-based coatings such as liquid solvent-free coatings, but pigments, It is also possible to add filler reinforcing materials and the like.

Pigments include silica, alumina, titanium oxide, silica/alumina, talc (hydrated magnesium silicate), mica (phlogopite, biotite, muscovite, sugilite), kaolin clay, boron nitride, fine powders such as silicon carbide, and phosphorus. General commercially available extender pigments that are flaky powders, Mapico (synthetic iron oxide yellow, synthetic iron oxide red), red iron oxide, acetylene black, Ketchien black EC, cadmium red, cadmium yellow, cadmium orange, cobalt blue, cobalt green, cobalt General commercially available coloring pigments that are fine powders such as purple, strontium yellow, manganese purple, chromium oxide, Turkish green, zirconium silicate, silicomolybdic acid, tungstic silicoic acid, aluminum phosphate, zirconium phosphate, aluminum hydrogen tripolyphosphate, phosphorus Ammonium molybdate, zinc phosphate, dichromic phosphate, magnesium phosphate, male phosphate, zinc chromate, strontium chromate, basic lead chromate, lead zinc oxide, lead cyanamide, basic lead silicate, zinc molybdate , zinc oxide, red lead, barium sulfate, barium chromate, and other commercially available antirust pigments can be appropriately selected and used alone or in combination of two or more.

In addition, examples of filling reinforcing materials include inorganic fibrous fillers such as glass, slag, carbon, alumina, silicon carbide, boron, and boron nitride, and organic fibrous fillers such as nylon, polyester, vinylon, aramid, and Kevlar. They can be appropriately selected from commercially available fibrous fillers and used alone or in combination of two or more.

The coated steel material based on 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, a chromate treatment agent is applied to the surface of the steel pipe 1 from which oil, scale, etc. have been removed using a chromate treatment agent coating device 5, and is baked by a heating device 6, after which a mixed treatment agent of a chelating agent and an amino-based silane coupling agent is applied. The mixed treatment agent is applied by the coating device 7 and baked by the heating device 8. Next, an organic resin is applied by an organic resin coating device 9, heated and cured or melted by a post-heating device 1o to form a film, and then cooled by a water cooling device 11 to produce a coated steel pipe.

In the case of the above manufacturing method, after applying a chromate treatment agent to the surface of the steel pipe 1 and baking it with 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 pipe and sufficiently cured before the steel pipe reaches the organic resin coating device 9. The method for applying the mixed treatment agent of the silane coupling agent can be appropriately selected from conventionally known methods such as atomized application using an atomizer nozzle, spray application using a spray coating machine, roll application, and brush application.

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

In addition, in Figure 2, an electrostatic powder coating machine is used to apply the organic resin, but spray coating, roll coating, ironing coating, etc.
An appropriate method can be selected from conventionally known methods such as brush coating.

[Function] 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. The removed steel material, 2 is a chromate treatment agent layer made by heating and baking a chromate treatment agent made by partially reducing a mixed aqueous solution of phosphoric acid and chromic anhydride with dextrin or partially saponified polyvinyl acetate and adding silica-based fine particles, and 3 is a layer of a chromate treatment agent that is heated and baked. A mixed treatment agent layer of a chelating agent and an amino-based silane coupling agent, and 4 represent an organic resin coating layer.

In addition, the chromate treatment layer 2 in the figure has an adhesion amount of 100 to 900 m37 m' as a total chromium weight, the mixed treatment agent layer 3 has an adhesion amount of 10 to 900 mg/rn' as a dry weight, and the organic resin coating layer 4 has an adhesion amount of 0. Good results can be obtained with a thickness of .3 to 10 mm.

〔Example〕

In order to specifically explain the present invention, a preparation example of a chromate treatment agent in the wood invention and a comparative example are given below.
A comparative preparation example of a chromate treatment agent corresponding to Japanese Patent Application Laid-open No. 143934, a preparation example of a mixed treatment agent of a chelating agent and an amino-based silane coupling agent in the present invention, and an epoxy treatment agent corresponding to JP-A No. 60-23038 as a comparative example. Examples of formulations of treatment agents for silane coupling agents and examples and comparative examples of coated steel materials are given below.

◎Preparation example of chromate treatment agent-1 First, the following solutions ①, ② and ② were prepared.

■ Mixed aqueous solution of phosphoric acid and chromic anhydride in distilled water 247.
49.2 g of phosphoric acid and 78.8 g of chromic anhydride were dissolved in 6 g.

■ 5% by weight partially saponified polyvinyl acetate aqueous solution, molecular weight 8
Partially saponified polyvinyl acetate having a molecular weight of 8000 and a degree of saponification of 87% was added to distilled water and allowed to stand for 2 hours to swell.

Next, this aqueous solution was heated to 98°C to completely dissolve it,
An aqueous solution containing 5% by weight of partially saponified polyvinyl acetate was prepared.

(2) 10% by weight Aerosil 200 aqueous solution Aerosil 200 manufactured by Nippon Aerosil Co., Ltd. was used as the silica-based fine particles. Add Aerosil 200 to distilled water and use a high speed mixer (
The mixture was stirred and dispersed at a rotational speed of 3000 rpm to prepare an aqueous solution containing 10% by weight of Aerosil 200.

Next, mix aqueous solution 3 of phosphoric acid and chromic anhydride from above
To 73.6 g, 106 g of the 5% by weight partially saponified polyvinyl acetate aqueous solution of (1) was added and heated to 90° C. to reduce some of the hexavalent chromium ions to trivalent chromium ions. The weight ratio of hexavalent chromium to total chromium in the reduced aqueous solution is 0.
．． 60. The weight ratio of PO43- to total chromium is 1.1
It was 6. Next, add 10 of the above (①) to the above reduced aqueous solution.
A chromate treatment agent A according to the present invention was prepared by adding and dispersing 515.6 g of an aqueous solution of Aerosil 200 (wt%). 5i0 relative to the total chromium in the chromate treatment agent A
The weight ratio of 2 (Aerosil 200) was 1.29.

◎ Comparative Preparation Example of Chromate Treatment Agent-1 As comparative materials, Chromate treatment agents C, D, and E corresponding to Japanese Patent Application Laid-Open No. 52-143934 were prepared.

・Chromate treatment agent C 76.8 g of chromic anhydride and 28 amber in 700 g of distilled water
．． 8g of barbylic acid and 19.2g of barbylic acid in the aqueous solution.
was added and dispersed, and then distilled water was added to prepare No. 11 Chromate Treatment Agent C.

Chromate treatment agent: 76.8 g of chromic anhydride was dissolved in 823 g of distilled water, 8.4 g of wheat starch was added thereto, and the mixture was heated and boiled for 1 hour to partially reduce the hexavalent chromium ions. The weight ratio of trivalent chromium to total chromium in the reduced aqueous solution is 0.
It was 38. Add the above Aerosil #20 to the reduced aqueous solution.
0 was added and stirred and dispersed to prepare a chromate treatment agent.

- Chromate treatment agent E 76.8 g of chromic anhydride was dissolved in 800 g of distilled water, and 3.4 g of corn starch was added thereto and boiled for 1 hour to partially reduce the hexavalent chromium ions.

The weight ratio of trivalent chromium to total chromium in the reduced aqueous solution was 0.22. Add 23g of the above Aerosil #200 and 22g of talcum powder (magnesium silicate) to the reduced aqueous solution.
After stirring and dispersing 3 g, 5% of polyvinyl alcohol (Gohsenol NM-11, manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.)
A chromate treatment agent E was prepared by adding and dispersing 46 g of an aqueous solution.

◎ Preparation example of a mixed treatment agent of a chelating agent and an amino-based silane coupling agent Ethylenediaminetetraacetic acid was used as a chelating agent, and an aqueous solution was prepared by dissolving it in distilled water whose pH was adjusted to 6 with aqueous ammonia. Separately from the above aqueous solution, γ-anilinopropyltrimethoxysilane (Toray, Silicone Co., Ltd. 526083) was used as an amino-based silane coupling agent and dissolved in distilled water with p)I adjusted to 2.5 with acetic acid. An aqueous solution was prepared. Next, the aqueous solution of ethylenediaminetetraacetic acid and the aqueous solution of γ-anilinopyrtrimethoxysilane were mixed together and the γ-
The number of moles of anilinopropyltrimethoxysilane is 0.0
4 mol of ethylenediaminetetraacetic acid and 0.1 mol of ethylenediaminetetraacetic acid per 1 mol of the γ-anilinopropyltrimethoxysilane. B was created.

◎Comparative formulation example of treatment agent for epoxy silane coupling 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/1. Processing agent F corresponding to the publication was prepared.

Example-1 Steel plate (5541, 200mm width x 200mm length x
9mm thick) was subjected to grid blasting treatment, and the above-mentioned chromate treatment agent A was applied on the large surface to 380m in terms of total chromium adhesion.
g/m' and heated to 190°C and baked.

Next, on the surface, 2 ml of the above-mentioned mixed treatment agent B of the chelating agent and amino-based silane coupling agent was applied in terms of dry weight of the coating film.
Apply an amount of 90 mg/rn' in a mist form with a spray nozzle,
It was heated and cured at 30°C.

Next, powder epoxy resin paint is applied to the surface to a film thickness of 45 mm.
A powder epoxy coated steel sheet (I) according to the present invention was prepared by electrostatically coating the steel plate to a thickness of 0μ and curing by heating.

In addition, as a comparative example, a powder epoxy coated steel sheet corresponding to JP-A-52-143934 was used, omitting the application of the mixed treatment agent B, and replacing the chromate treatment agent A with the chromate treatment agent C. Powder epoxy coated steel plate (11) corresponding to Figure 3 coated with chromate treatment agent (Ill), powder epoxy coated steel plate corresponding to Figure 4 coated with chromate treatment agent (Ill), and No. 5 coated with chromate treatment agent E.
Powder epoxy coated steel sheet corresponding to the figure (V eyelet was created and compared.

Furthermore, as a powder epoxy coated steel sheet corresponding to JP-A-60-23038, the application of chromate treatment agent A was omitted and the treatment agent F described above was applied in place of mixed treatment agent B, using the same method as above. A powder epoxy coated steel plate (V) corresponding to that shown in Fig. 6 was prepared and compared.

The above powder epoxy coated steel plates (1), (11),
(III).

Regarding (IV) and (V), an adhesion test (substrate test: according to JISK 5400, the adhesion of the coating film to the steel material is expressed on a scale of 0 to 10 (out of 10)) and a boiling water immersion test (immersion test) Table 1 shows the results of a post-immersion adhesion test conducted at a temperature of 98°C and a immersion time of 8000 hours.

Table 1 As shown in Table 1, a remarkable difference was observed in the boiling water immersion test, especially when a mixed aqueous solution of phosphoric acid and chromic anhydride was partially reduced with partially saponified polyvinyl acetate as a surface treatment agent. When using the chromate treatment agent A according to the present invention to which fine particles have been added in combination with the mixed treatment agent B of a chelating agent and an amino-based silane coupling agent (I), a chromate treatment corresponding to JP-A-52-143934 is used. When using agents C, D or E, i.e. (II
), (Ill) or (IV) and when using treatment agent F, an epoxy-based silane coupling agent corresponding to JP-A No. 60-23038, results are much better than in (V). can get.

Example-2 Using the same method as in Example 1, when preparing chromate treatment agent A, (1) Added phosphoric acid and silica (Aerosil 200) as described in the above chromate treatment formulation example (2) Omitted the addition of phosphoric acid. (Comparative example) ■ Omitting the addition of silica (Comparative example) The powder epoxy coated steel pipe (1) described above was prepared, and the results of the adhesion test and boiling water immersion test are shown in Table 2. .

Table 2 As shown in Table 2, a remarkable difference was observed in the boiling water immersion test, especially when the chromate treatment agent of the present invention containing both phosphoric acid and silica-based fine particles as a surface treatment agent was used as a chelating agent and in a silane cup. Good results were obtained when the ring agent was used in combination with a mixed treatment agent.

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

Example 3 In the same manner as in Example 1, the type of reducing agent used in preparing chromate treatment agent A was changed as follows. Partially saponified polyvinyl acetate (molecular weight 811,000
.

Saponification degree 87%) ■ Dextrin (average molecular weight 120,000) ■ Corn starch ■ Wheat starch ■ Polyvinyl alcohol (molecular weight 10,000) The above powder epoxy coated steel plate (1) was prepared, and an adhesive force test and a boiling water immersion test were conducted. The results are shown in Table 3.

Table 3 As shown in Table 3, a remarkable difference was observed in the boiling water immersion test, and the chromate treatment agent according to the present invention using partially saponified polyvinyl acetate or dextrin as a reducing agent as a surface treatment agent. Good results were obtained when using a combination of a chelating agent and an amino-based silane coupling agent.

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

Example-4 In the same manner as in Example 1, the types of chelating agent and amino-based silane coupling agent used in preparing a mixed treatment agent of chelating agent and amino-based silane coupling agent were changed as follows, and the chelating agent was prepared. 20 Ethylenediaminetetraacetic acid ◎ Nitrilotriacetic acid ◎ 1,2-diaminocyclohexanetetraacetic acid ■ None (Comparative example) Amino-based silane coupling agent: ■ γ-anilinopropyltrimethoxysilane ■ Trimethoxysilylpropyldiethylenetriamine ■ Bis(3 -()-rimethoxysilyl)propyl]ethylenediamine ■ None (Comparative example) The above powder epoxy coated steel plate (I) was prepared and subjected to an adhesion test and a boiling water immersion test. The results are shown in Table 4. .

Table 4 As shown in Table 4, a remarkable difference was observed in the adhesion test and the boiling water immersion test, and the chromate treatment agent according to the present invention was used as a base treatment agent with the chelating agent ■~◎ and amino-based silane coupling. Good results were obtained when used in combination with the mixed treatment agents (1) to (2).

Example-5 A steel pipe (200A x 5500mm length x 5.8mm thickness) was subjected to grid blasting treatment, and the above-mentioned chromate treatment agent A was applied to the surface of the pipe at a rate of 620mg/rn in terms of total chromium adhesion amount.
After coating and baking by heating at 160°C, the mixed treatment agent B of the above-mentioned chelating agent and amino-based silane coupling agent was applied in dew form with a spray nozzle in an amount of 280 mg/rn' in terms of coating film weight. , heat-cured at 190°C.

Next, the following organic resin was applied to the surface with a film thickness of 2.5 mm.
A coated steel pipe according to the present invention was manufactured by coating and curing the steel pipe so as to give the following properties.

Organic resin: I Powder epoxy resin paint II Solvent type epoxy resin paint II + Non-soluble epoxy resin paint! ■Epoxy/silicone resin paint ■Polyimide/epoxy resin paint Vl Polyphenylene sulfide resin paint ■Polyether sulfone resin paint ■Powder polyethylene resin paint The above coated steel pipes were subjected to adhesion tests and boiling water immersion tests. It is shown in Table 5.

Table 5 As shown in Table 5, when the chromate treatment agent of the present invention is combined with a mixed treatment agent of a chelating agent and an amino-based silane coupling agent as a surface treatment agent for steel pipes, depending on the type of organic resin, Regardless, very good results are obtained in adhesion tests, boiling tests, and water immersion tests.

(Effect of the invention) As is clear from the examples, the coated steel material according to the present invention has the following properties:
It has much better boiling water resistance than conventional coated steel, so it has the remarkable effect of providing coated steel with unprecedented high-temperature durability.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a painted steel material according to the present invention, FIG. 2 is a schematic diagram showing an example of manufacturing the coated steel material of the present invention, and FIGS.
5 and 6 are partial cross-sectional views of painted steel materials by conventional methods. 1...Steel 2...Chromate obtained by partially reducing a mixed aqueous solution of phosphoric acid and chromic anhydride with partially saponified polyvinyl acetate or dextrin, and heating and baking a chromate treatment agent to which silica-based fine particles are added. Processing agent layer. 3...Mixed treatment agent layer of chelating agent and amino-based silane coupling agent 4...Organic resin coating film 5...Chromate treatment agent coating device 6...Heating device 7...Chelating agent and amino-based silane coupling agent Mixed treatment agent coating device for silane coupling agent, 8...Heating device 9...Organic resin coating device 1
0... Post-heating device 11... Cooling device 12...
Hexavalent chromium compounds, amino acids, acid amides, lactams,
A chromate treatment agent layer obtained by heating and baking a chromate treatment agent mixed with organic components such as saturated or unsaturated polycarboxylic acids. 13... Chromic acid (Cr03) is partially reduced with an organic reducing agent such as sugar, polyhydric alcohol, -hydric alcohol, alkylolamine, aromatic polyhydric alcohol, etc., and the chromate treatment agent to which silica fine particles are added is heated. Chromate treatment agent layer obtained by baking. 14...Chromic acid (Cr03) is partially reduced with an organic reducing agent such as sugar, polyhydric alcohol, -hydric alcohol, alkylolamine, aromatic polyhydric alcohol, etc., silica fine particles are added, and polyvinyl alcohol is added. A chromate treatment agent layer obtained by heating and baking a chromate treatment agent to which a nonionic water-soluble resin such as methylcellulose, polyethylene oxide, hexamethylmethoxymethylmethamine-modified polyhydroxyethyl acrylate, etc. is added. 15... Silane coupling agent layer such as epoxy silane coupling agent Figure 1 Mixed treatment agent layer 4: Organic resin coating Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] A chromate treatment agent prepared by partially reducing a mixed aqueous solution of phosphoric acid and chromic acid anhydride with partially saponified polyvinyl acetate or dextrin and adding silica-based fine particles to the surface of the steel material is heated and baked. A coated steel material characterized by sequentially laminating a chromate treatment agent layer, a mixed treatment agent layer of a chelating agent and an amino-based silane coupling agent, and an organic resin coating film.