JPH06330340A - High temp. substrate-treated polyolefin coated steel - Google Patents

Abstract

PURPOSE:To prevent the deterioration of adhesibility between a coating film and a steel in the case of high temp. drying and the deterioration of peeling ability to cathode in the case of using together with electrical protection by further laminating an organic coating film on a steel substrate-treated with a chromate treating agent. CONSTITUTION:A chromate coating film layer 2 is formed by substrate-treating the surface of the steel 1 with a chromate treating agent. The chromate treating agent is obtained by adding 0.8-4 (weight ratio to chromium) silica fine particle into a solution made by partially reducing a mixed solution of phosphoric acid with chromic anhydrate by an organic reducing agent. The silica fine particle is obtained by mixing 20-50% hydrous colloidal silica fine particle with 50-80% silica fine particle synthesized by dry system. The organic coating layers of an epoxy primer 3, a modified polyolefin adhesive 4 and a polyolefin coating film 5 are successively laminated on the coating film 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin-coated steel material, which prevents deterioration of the adhesion between the organic coating and the steel material when high-temperature drying is performed after the chromate treatment as a base treatment of the steel material, and further The present invention relates to a high-temperature base-treated polyolefin-coated steel material that significantly suppresses cathode peeling property.

[0002]

2. Description of the Related Art Polyolefin-coated steel, which is a heavy-corrosion-coated steel, has excellent long-term corrosion resistance, so
It is used for corrosion protection of steel sheet piles. Heavy anticorrosion coated steel is
Since a service life of up to several decades is expected in a water contact environment, it is important to suppress a decrease in the adhesive strength between the steel material and the organic coating and to prevent cathodic peeling when combined with cathodic protection. Further, in pipelines for petroleum, natural gas, etc., polyolefin-coated steel pipes are often used because of their anticorrosive properties. In order to improve the transportation of heavy oil, when the steel material becomes hot due to measures such as heating the heavy oil to reduce its viscosity and then transporting it, in a severe environment exceeding 80 ° C, the adhesion of the coated steel material tends to decrease. Since it is placed, it is an important issue to improve the adhesion between the steel and the coating and the resistance to cathodic peeling by the surface treatment. Conventionally, Japanese Patent Laid-Open No. 1-263 has been used as a base treatment for steel materials.
Although a chromate treatment agent for thin steel sheets, which is represented by Japanese Patent No. 279, has been proposed, in this case, there is a problem in the adhesion between the organic film and the steel material. On the other hand, JP-A-3-2345
As disclosed in Japanese Patent No. 27, a method has been proposed in which phosphoric acid and silica fine particles are treated with a chromate treatment agent in which a silane coupling agent is added to strengthen the film. On the other hand, in the case of a polyolefin-coated steel material, the steel material after chromate treatment is treated with 60% in order to bond the steel material and the coating.
After drying at an ambient temperature of 300 ° C. to 300 ° C., it is heated to a polyolefin melting temperature (120 to 200 ° C.) to manufacture. In particular, when heat-resistant polyolefin coating is applied to thick steel, it is necessary to dry and heat the chromate-treated steel in a higher temperature atmosphere (400 ° C or higher). However, when the high temperature drying is performed, the chromate film layer is decomposed and the performance is deteriorated.

[0003]

When a chromate-treated steel material is dried at a high temperature, deterioration of the chromate treatment agent and oxidation of the steel material occur, resulting in a decrease in performance as compared with the case of performing ordinary drying. Also in the chromate treatment agent for polyolefin coated steel materials disclosed in JP-A-3-234527, it is difficult to maintain the adhesiveness of the coating because the silane coupling agent is decomposed by high temperature drying. For this reason, a polyolefin-coated steel material that is excellent in both the coating-steel material adhesion and the high-temperature cathode peeling resistance is required even when high-temperature drying at 400 ° C. or higher is performed.

[0004]

In order to solve the above-mentioned problems, the present invention has a good water dispersibility as a silica component to be added to a chromate treatment agent in the surface treatment of heavy-corrosion-coated steel materials, and thus, a dry film is suspected. Aqueous colloidal silica with high power of collection,
By mixing and using silica, which has a secondary suspicious component and is synthesized by a dry method with good adhesion to the coating film, at a specific ratio, the strength of the film during high temperature drying is improved and the oxidation of steel materials is prevented by organic. This is a result of intensive studies on improving the adhesion of the coating.
That is, the entire surface or a part of the surface of the steel material 1 is treated with a treatment solution obtained by partially reducing a mixed solution of phosphoric acid and chromic anhydride with an organic reducing agent, and 20 to 5 parts of aqueous colloidal silica particles are added.
0% by weight and 5% silica fine particles produced by the dry method
Chromate treatment agent 2 in which silica fine particles mixed in a proportion of 0 to 80% by weight are added at a weight ratio of 0.8 to 4.0 with respect to total chromium is used to dry the steel material surface-treated at a high temperature, By laminating the coating, a polyolefin-coated steel material is provided which is excellent in the adhesion between the coating and the steel material after being immersed in warm water and is also excellent in high-temperature cathode peeling resistance. The amount of phosphoric acid added in the chromate treatment agent is 0.2 to 3.0 by weight ratio to the total chromium. As the organic coating layer, an epoxy primer layer, a modified polyolefin adhesive layer, and a polyolefin coating layer are laminated in this order. A polyolefin coated steel material according to the present invention is shown in FIG. In FIG. 1, on a surface of a steel material 1, a chromate treatment agent layer 2 containing phosphoric acid containing the above components and dry silica-based fine particles, a primer layer 3 made of a thermosetting epoxy resin or the like, and a modified polyolefin adhesive layer 4 and a polyolefin coating or a cross-linked polyolefin coating 5 are sequentially laminated, which is a polyolefin-coated steel material excellent in both high-temperature cathode peeling resistance in addition to coating-steel material adhesion after hot water immersion.

The present invention will be described in detail below.
The steel material 1 used in the present invention is carbon steel or alloy steel such as stainless steel or titanium alloy steel. Also, on the surface of carbon steel, stainless steel, copper, aluminum, titanium,
Aluminum-magnesium alloy, nickel-chromium-
It may be a steel material obtained by laminating metals such as iron-based alloys, nickel-molybdenum-based alloys, nickel-molybdenum-chromium-tungsten-based alloys, titanium-palladium-based alloys, titanium-aluminum-vanadium-based alloys. Furthermore, the surface of carbon steel is plated with zinc, aluminum, nickel, copper, etc., alloy plated with zinc-iron, zinc-aluminum, zinc-nickel, zinc-nickel-cobalt, etc. Alternatively, it may be a steel material that has been subjected to dispersion plating in which fine particles of an inorganic substance such as titanium oxide are dispersed.

Next, the chromate treating agent used in the present invention will be explained. The chromate treatment agent 2 used in the present invention is phosphoric acid and chromic anhydride (CrO) in distilled water.
₃ ) is partially reduced with an organic reducing agent, phosphoric acid, hexavalent chromium ions and trivalent chromium ions are mixed therein, and dry silica-based fine particles are mixed. If necessary, part of phosphoric acid can be replaced with condensed phosphoric acid such as pyrophosphoric acid or tripolyphosphoric acid. Examples of organic reducing agents used for the partial reduction of chromium from hexavalent to trivalent include alcohols such as methyl alcohol and ethyl alcohol, alkylolamines such as diethanolamine and triethanolamine, saturation of formic acid, acetic acid and oxalic acid. Carboxylic acid, aromatic polyhydric alcohols such as pyrogallol, succinic acid, monomolecular reducing agents such as unsaturated carboxylic acids such as adipic acid, or starches such as wheat starch and corn starch, polymeric reducing agents such as polyvinyl alcohol Can be used. Coating after hot water immersion-To improve adhesion between steel materials and high-temperature cathode peeling resistance, a polymer reducing agent, in particular, starch containing a large amount of amylopectin, for example, corn starch is partially hydrolyzed with a hydrolase such as amyloglucosidase. Obtained by hydrolytic hydrolysis (average molecular weight 50,000-25,000
0), or With a molecular structure of 60,000-140,000
Partially saponified polyvinyl acetate is preferable.

The above-mentioned dextrin and partially saponified vinyl acetate are used in the amounts necessary to maintain the desired ratio of hexavalent chromium to total chromium. What is the desired ratio?
The weight ratio of hexavalent chromium to total chromium is 0.35 to
The range of 0.75 is desirable. Regarding this ratio, when the weight ratio of hexavalent chromium to the total chromium is less than 0.35 and 0.75 or more, the adhesive force after immersion in hot water tends to decrease. The amount of dextrin required for adjusting the weight ratio of hexavalent chromium to the total chromium in the range of 0.25 to 0.65 is 0.06 to 0 in terms of the weight ratio to the total chromium in the chromate treatment liquid. The amount of the partially saponified vinyl acetate is in the range of 0.07 to 0.47 as a weight ratio to the total chromium in the chromate treatment liquid.

Phosphoric acid added to the chromate treating agent 2 lowers the pH of the chromate treating solution, so that the reactivity between the steel material and the chromate treating agent is enhanced, and at the same time, hexavalent chromium is converted to trivalent chromium by heating and baking. It results in an increase in the reducibility of and produces a highly insoluble chromate film. Also, phosphoric acid is a hydroxyl group on the surface of silica-based fine particles,
By bonding with the free or coordinated chromium ion, the chromate film is integrated, the chromate film is made insoluble in hot water, and the physical strength of the film during drying is improved, resulting in adhesion. Therefore, it is considered that the water resistance is improved, and the coating is less likely to be peeled off even when an alkali is generated during the cathode peeling test. The amount of phosphoric acid added is
The weight ratio of phosphate ions to total chromium is 0.2 to 3.
It is desirable to add in the range of 0. The appropriate amount of phosphoric acid added is adjusted by the drying temperature of the chromate film. However, when the coating film is less than 0.2 and more than 3.0, the adhesion after immersion in hot water tends to decrease.

Next, as the aqueous colloidal silica fine particles added to the chromate treating agent 2, for example, Snowtex-20 and Snowtex-3 manufactured by Nissan Chemical Co., Ltd.
0, Snowtex-40, Snowtex-C, Snowtex-O, Snowtex-S, Snowtex-50, Snowtex-20L, Snowtex-X
S, Snowtex-SS, Snowtex-XL, Snowtex-YL, Snowtex-ZL, Snowtex-OUP, Snowtex-N, Snowtex-OL and other ultrafine silica particles having a particle diameter of 4 to 100 nm. Use a colloidal solution. Examples of the silica-based fine particles synthesized by the dry method include AEROSIL 130 and AEROSIL 200 manufactured by Nippon Aerosil Co., Ltd.
AEROSIL 200V, AEROSIL 200C
F, AEROSIL 200FAD, AEROSIL
300, AEROSIL 300CF, AEROSIL
380, AEROSIL OX50, AEROSIL
Silica fine particles such as TT600 and AEROSIL MOX are used.

The aqueous colloidal silica fine particles are in a state where the silica fine particles are individually dispersed in the solution, and have a large surface area and a high adsorptivity. However, when it is added to the chromate treatment agent, a dense glass-like film is formed, so that the film is brittle and there is a problem in the adhesion strength with the steel material. On the other hand, the dry silica fine particles are produced, for example, by chlorinating ferrosilicon to obtain silicon tetrachloride, then refining and hydrolyzing at high temperature in a flame of oxygen and hydrogen. Unlike the aqueous colloidal silica, the dry silica fine particles have a strong tendency to form secondary aggregates in an aqueous solution. Further, when added to the chromate treatment agent, the film has a small shrinkage during drying and forms a porous film, which is excellent in adhesion to a steel material. Also,
Since a porous surface is formed, the organic film flows into the porous surface, which has the effect of improving the adhesiveness with the upper organic film, and has excellent adhesion at a normal drying temperature of 60 to 300 ° C. . However, when dried at a temperature higher than 400 ° C, the coating is apt to decompose due to weak bonding of the coating, and the coating density is rough and cracks reaching the steel surface cause the steel surface to be easily oxidized. There is a problem. Therefore, 20 to 50% by weight of aqueous colloidal silica fine particles and 50 to 8 dry silica fine particles are used.
By adding silica fine particles mixed in a proportion of 0% by weight in a weight ratio of 0.8 to 4.0 with respect to the total chromium, the bond strength of the film during high temperature drying and the adhesion to the steel material and the film are secured. . Addition amount of silica-based fine particles is less than 0.8 and 4.0
In Yue, the adhesion after immersion in hot water tends to decrease.

Before the coating, the chromate treatment agent 2 is subjected to alkali degreasing, pickling, sand blasting, grid blasting, shot blasting, etc., if scales, oils, etc. are present on the surface of the steel material, and the surface treatment is performed. Kimono needs to be removed. When the baking temperature exceeds 400 ° C., the above chromate treating agent is used. In addition, as the amount of chromate treatment agent attached, the total chromium weight,
30 to 800 mg / m ² is desirable. If it is less than 30 mg / m ² , the effect of chromate treatment will not be exerted, and 800 mg / m 2
^If it exceeds ² , a strong coating will not be formed and adhesion will be reduced.

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

The modified polyolefin adhesive used in the polyolefin coating of the present invention includes known polyolefins such as polyethylene, polypropylene and nylon, and known polyolefin copolymer resins such as maleic acid, acrylic acid and methacrylic acid. It is a conventionally known modified polyolefin such as one modified with an unsaturated carboxylic acid or its acid anhydride, or one obtained by appropriately diluting the modified product with a polyolefin resin.

The polyolefin coating used in the polyolefin-coated steel material of the present invention means a conventionally known polyolefin such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene or nylon as a main component, and It is a resin containing a known polyolefin copolymer such as an ethylene-propylene block or a random copolymer, a polyamide-propylene block or a random copolymer. The cross-linked polyolefin coating is mainly composed of cross-linked polyolefin obtained by subjecting the above-mentioned polyolefin to electron beam irradiation or the like to perform cross-linking. As other components, a pigment, a filling reinforcing agent, etc. can be added. As the pigment, silica, silica-alumina, rutile titanium oxide, glass, mica, iron oxide red,
Zirconium silicate, magnesium silicate, talc, barium sulfate, alumina, zinc chromate, strontium chromate, cinnamide lead, lead suboxide, aluminum phosphate, calcium phosphate, silicomolybdic acid, silicotungstic acid, zinc phosphomolybdate, etc. If you need aesthetics with Cadmium Yellow,
Polyazo Yellow, Quinophthalone Yellow, Isoindolinone Yellow, Quinacridone Yellow, Bengala Red, Polyazo Brown, Azo Lake Yellow, Perylene Red, Phthalocyanine Blue, Phthalocyanine Green, Bengala Yellow, Cobalt Aluminate, Aniline Black, Carbon Black, Ultramarine blue,
A coloring pigment such as aluminum fine powder, an ultraviolet absorber, and a hindered amine-based weathering agent can also be added. Filling reinforcer is glass, slag, silicon carbide,
Inorganic fiber fillers such as carbon, boron, boron nitride, alumina, nylon, polyester, vinylon,
Organic fillers such as aramid and Kepler.

[0015]

EXAMPLES In order to specifically explain the present invention, the following chromate treating agents A to J according to the present invention were prepared. Similarly, comparative chromate treating agents K to P and Japanese Patent Application No.
Chromate treating agents Q and R corresponding to JP-30320 and JP-A-1-263279 were prepared (see Tables 1 and 2).

[Table 1]

[Table 2] <Preparation Example of Chromate Treatment Liquids A to J and Comparative Examples K to P> As the chromate treatment liquid of the embodiment, for example, as a chromate stock solution, 38.46 g of chromic anhydride and 30.95 g of phosphoric acid are distilled water 428. 2.56 g of dextrin was added to what was dissolved in 0.03 g, and the mixture was heated and stirred to reduce chromic acid. After cooling, distilled water was added to adjust the total weight to 500 g. To this solution, 400 g of an aqueous solution containing 10% by weight of silica-based fine particles was added and stirred. As the aqueous solution containing silica-based fine particles, an aqueous colloidal silica fine particle, a Snowtex O solution manufactured by Nissan Chemical Co., Ltd., and a dry silica fine particle, Aerosil 200 manufactured by Nippon Aerosil Co., Ltd., dispersed and dissolved in water were used. At this time, the weight ratio of hexavalent chromium to total chromium in the solution was 0.60, the weight ratio of phosphoric acid to total chromium was 1.5,
The weight ratio of silica-based fine particles to all chromium was 2.0. Using the same method, the chromate treating agents A to J of the examples and the chromate treating agent K of the comparative examples were changed by changing the concentrations and mixing ratios of phosphoric acid, the dextrin reducing agent, and the silica solution.
~ P was compounded.

<Formulation Example of Chromate Treatment Liquid Q of Comparative Example>
As a chromate treatment liquid Q of Comparative Example corresponding to JP-A-3-234527, as a chromate stock solution, 38.46 g of chromic anhydride and 30.95 g of phosphoric acid were added to distilled water 4
Dextrin 2.56 dissolved in 28.03 g
Chromic acid was reduced by adding g and heating with stirring. After cooling this, 400 g of an aqueous solution containing 10% by weight of silica-based fine particles was added to a liquid adjusted to a total weight of 500 g by adding distilled water and stirred. As silica-based fine particles, Aerosil 300 (primary particle diameter: 5) manufactured by Nippon Aerosil Co., Ltd.
.About.13 nm) was used. Separately from this solution, an aqueous solution containing 40% by weight of γ-glycidoxypropyltrimethoxysilane was prepared and mixed with the above chromate stock solution at a weight ratio of 9: 1 for use. At this time, the weight ratio of hexavalent chromium to the total chromium in the solution was 0.60, the weight ratio of phosphoric acid to the total chromium was 1.5, the weight ratio of silica-based fine particles to the total chromium was 2.0, and the weight ratio to the total chromium was 2.0. The weight ratio of the silane coupling agent was 2.0.

<Preparation Example of Chromate Treatment Liquid R of Comparative Example>
As a chromate treatment liquid R of a comparative example corresponding to JP-A-1-263279, chromic anhydride 38.46 g,
Distilled water was added to 44.06 g of a partially saponified polyvinyl acetate aqueous solution (saponification degree: 87%) of 10.32 g of phosphoric acid and 5% by weight, and the mixture was heated and stirred to partially reduce chromic acid. Distilled water was added to adjust the total weight to 600 g. After cooling this, add this solution to Nissan Chemical Snowtex Z.
L (particle diameter: 70-100 nm) and Nissan Chemical's Snowtex S (particle diameter: 7-9 nm) were mixed at a ratio of 1: 1 with 400 g of an aqueous solution containing 10% by weight of a silica component and stirred,
A treatment liquid was prepared. At this time, the ratio of hexavalent chromium to the total chromium after reduction was 0.50, the weight ratio of phosphoric acid to the total chromium was 0.5, and the weight ratio of silica fine particles to the total chromium was 2.0.

(Evaluation of Adhesion and Cathodic Peeling Property) As a manufacturing method of Examples 1 to 10 of the high temperature undertreated polyolefin-coated steel material of the present invention, the steel material (35 × 150 × 300 mm) was subjected to grid blasting treatment, and its surface Chromate treatment agents A to J of the present invention prepared as
50-400 mg / m ² was roll coated and dried. Next, after heating and baking to a steel material temperature of 220 ° C. in an atmosphere temperature of 600 ° C., an epoxy-based primer having a film thickness of 5
It was applied by a spray coating machine so as to have a thickness of 0 μm.
Furthermore, a modified polyolefin adhesive (thickness 300 μm) molded with a two-layer T-die and a polyolefin coating (3 mm)
After laminating the laminated sheet of 1) under pressure, it was cooled to manufacture a polyolefin-coated steel material. Further, as a comparative example of the polyolefin-coated steel material, the comparative polyolefin-coated steel materials 11 to 18 were prepared by using the comparative chromate treatment agents K to R by the same procedure. About the above coated steel material, after the hot water immersion test (test temperature: 80 ° C., immersion time: 6000 hours), the adhesion was measured (measurement temperature: room temperature, peeling angle: 90).
The peel strength at the time of peeling the coating was measured at a peeling speed of 50 mm / min. However, when the adhesive strength is sufficient, the polyethylene breaks and the adhesive strength becomes a value equal to or higher than the polyethylene strength. Also, as the cathode peeling test,
The sample after the immersion test was tested under the following test conditions.

(Conditions for Cathode Peeling Test) Test Temperature: 80 ° C. Electrolyte: 3% -NaCl Voltage: 1.5 V [Cu / CuSO ₄ , standard electrode] Initial holographic diameter: 9.0 mmφ Test days: 120 days Test end After that, the peeling diameter of the coating film (X mm) was measured and converted into the converted peeling radius (R = ((X / 2) ² − (3.2 / 2) ² ) ^1/2 mm) of the coating film. The results are shown in Table 1. From the results of Table 1, Examples 1 to 10 of the present invention containing phosphoric acid, aqueous colloidal silica fine particles and dry silica fine particles in the chromate treatment liquid,
It can be seen that, as compared with Comparative Examples 11 to 18, remarkably excellent results are obtained.

[0020]

As is clear from the examples, the base treatment of the steel material 1 with the chromate treatment agent during high temperature drying according to the present invention has excellent performance with little deterioration in adhesion and cathode peeling resistance after immersion in warm water. It is possible to provide a high-temperature base-treated polyolefin-coated steel material having

[Brief description of drawings]

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel material 2 Chromate treating agent layer or chromate treating agent 3 Primer layer consisting of thermosetting epoxy resin 4 Modified polyolefin adhesive layer 5 Polyolefin coating or crosslinked polyolefin coating layer

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

Claims (3)

[Claims] 1. An aqueous colloidal silica fine particle is added to a treatment liquid obtained by partially reducing a mixed liquid of phosphoric acid and chromic anhydride on an entire surface or a part of the surface of a steel material 1 with an organic reducing agent.
Chromate-treating agent 2 containing silica fine particles obtained by mixing 50 wt% to 50 wt% of silica fine particles synthesized by the dry method at a ratio of 50 to 80 wt% at a ratio of 0.8 to 4.0 in terms of weight ratio to total chromium. A high-temperature surface-treated polyolefin-coated steel material, which is obtained by laminating an organic coating on a surface-surface-treated steel material that has been surface-treated by. 2. The high-temperature pretreated polyolefin-coated steel material according to claim 1, wherein the amount of phosphoric acid added to the chromate treating agent is 0.2 to 3.0 in terms of weight ratio to the total chromium. 3. The organic coating layer is an epoxy primer layer,
The modified polyolefin adhesive layer 4 and a polyolefin coating layer are laminated in this order to form a coating layer.
High temperature base treated polyolefin coated steel.