JP7090507B2 - Painted steel material with chemical conversion coating, and its manufacturing method - Google Patents

Description

The present invention relates to a coated steel material having a specific chemical conversion coating film on its surface in an organic resin coated steel material and a method for producing the same. In particular, the present invention relates to a coated steel material having a chemical conversion coating having an excellent peeling resistance effect in combination with a resin having high heat resistance for the high temperature performance required in recent years for the organic resin coating of line pipes.

Conventionally, in marine structures, line pipes, etc., measures have been taken to improve the heat resistance and thickness of the covering material in order to improve the anticorrosion performance. However, since the corrosion resistance of the organic resin usually decreases at high temperatures, it is difficult to completely suppress the electrochemical reaction caused by the macrocorrosion current between the exposed steel material and the coating film. Further, if a thick organic resin is used to improve the corrosion resistance, the internal stress becomes large, and as a result, it becomes difficult to secure the adhesion between the steel material and the thick organic resin coating film, and some measures are required. To meet these demands, a method of providing a chemical conversion treatment on the surface of a steel material is effective, and conventionally, scale is removed by blasting or pickling, and then, it is shown in Japanese Patent Application Laid-Open No. 07-195612 (Patent Document 1). As described above, a chromate chemical conversion treatment containing chromic acid was performed. This chromate treatment provides good adhesion between the steel material and the anticorrosion coating film, etc. on it only by drying after application, and can greatly improve the peeling resistance, so the thickness is several mm. It is also common as a base treatment for a steel pipe coated with a polyolefin resin. However, since the chromate chemical conversion treatment film contains hexavalent chromium, which is an environmentally hazardous substance, an alternative chemical conversion treatment is desired.

Zinc phosphate treatment is a typical chemical conversion treatment that does not contain hexavalent chromium. In the zinc phosphate treatment, the steel material is immersed in a phosphate treatment bath containing heated zinc to precipitate zinc phosphate crystals on the surface of the steel material to form a film, and then the excess components are washed with water. However, the dipping treatment of the large-diameter steel pipe used for the line pipe is difficult in terms of equipment and time, and the precipitated zinc phosphate crystal coating is brittle, so that there is a problem in adhesion.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 2009-209393 (Patent Document 2) as a method for producing an anticorrosion coated steel material, zircon hydrofluoric acid, titanium hydrofluoric acid, hexafluorophosphate, phosphoric acid, condensed phosphoric acid. Wash with an aqueous solution containing one or more of oxalic acid and one or more of V-based compound, Mo-based compound, W-based compound, Y-based compound, Zr-based compound, and Bi-based compound. Processing is proposed. However, since the chemical conversion treatment film is not formed in the cleaning treatment, the peeling of the coating film due to the electrochemical reaction cannot be suppressed. Therefore, there is still a demand for a chemical conversion treatment method for the surface of steel materials, which does not contain hexavalent chromium and has no restrictions on the process such as washing with water.

A chemical conversion treatment for a steel material that does not use hexavalent chromic acid is described in JP-A-2006-249459 (Patent Document 3). In this chemical conversion treatment, an aqueous solution prepared by adding fine particles of water-dispersible silica at a mass ratio of 0.3 to 4.0 to a metal phosphate compound is applied to the surface of a steel material, and a step such as washing with water is not required. The treatment can be performed only by coating and drying, and provides a steel material surface treatment having water adhesion resistance and cathode peeling resistance of a resin coating film equivalent to chromate treatment.

Further, Japanese Patent Application Laid-Open No. 2009-209394 (Patent Document 4) describes a method for producing a resin-coated steel material that does not use a chemical conversion-treated layer containing chromium, and describes Al-based phosphate, Ca-based phosphate, and Mg. At least one of the phosphates and Zn phosphates and at least one of the V-based compounds, Mo-based compounds, W-based compounds, Y-based compounds, Zr-based compounds, and Bi-based compounds. An aqueous solution for chemical treatment containing a compound contained and silica is disclosed.

However, in the chemical conversion coated film made of phosphate described in the above publications (Patent Documents 3 and 4), it is difficult to form an insoluble film in which excess phosphoric acid components tend to remain. Therefore, there is a problem in suppressing the peeling of the coating film in a high temperature region where the elution of the film due to an electrochemical reaction increases.

Further, as a method for obtaining an insoluble zirconium oxide-based chemical conversion treatment film, Japanese Patent No. 5946358 (Patent Document 5) describes a method using zirconium carbonate, ammonium metavanadate, ammonium phosphate, and a silane coupling agent. It has been disclosed. This method is effective for forming an insulating coating film of a thick film, but since the pH of the chemical conversion treatment liquid is an alkali precipitation type of 8 to 12, there is a problem in the adhesion between the precipitated oxide film and the steel material.

Japanese Unexamined Patent Publication No. 07-195612 JP-A-2009-209393 Japanese Unexamined Patent Publication No. 2006-249459 Japanese Unexamined Patent Publication No. 2009-209394 Japanese Patent No. 5946358

An object of the present invention is excellent adhesion to organic resin coating such as powder epoxy resin coating used for outer surface corrosion protection of line pipes or three-layer polyolefin resin coating having a primer using powder epoxy resin coating, and high temperature. It provides a coated steel material having a chemical conversion coating on the surface of a steel material having good corrosion resistance such as cathode peeling resistance even in use, and a method for producing the same.

As a method of suppressing an electrochemical reaction under a coating film on the surface of a steel material and improving the adhesion to the coating film, the present inventors mainly use a stable metal oxide having high electrical insulation and a steel material. The first layer, which is a dense treatment layer that reacted with the above, was provided. Furthermore, since the weak layer formed by the iron oxide eluted by the reaction reduces the adhesive strength, fine particle silica (SiO ₂ ) forming a porous porous layer, for example, linear silica fine particles is added to form a weak oxide layer. The reinforced second layer was provided to solve the conflicting problems of reaction with iron and adhesion with the coating film.
The coating film that suppresses cathode peeling, which is important as an anticorrosion property, requires adhesion to steel materials and chemical and electrical stability. For this purpose, it is effective to form a stable metal oxide layer that reacts with the iron surface. Therefore, looking at the interaction parameter, which is the affinity with iron, Sc, Ti, Zr, Nb, Al, Si, and As are examples of metals that show a large negative value. Of these, Ti, Zr, Al, and Si are selected as the metals that form stable oxides. Above all, Ti tends to form a stable metal oxide even at room temperature, and it is considered that dissolution is unlikely to occur even if an alkali is generated by an electrochemical reaction on the surface of the steel material of the cathode due to cathode peeling. Zirconium, which is the same titanium group element, also has excellent acid resistance and alkali resistance. From the above viewpoint, an oxide film mainly composed of titanium and zirconium was provided on the surface of the steel material. Among them, zirconium is also used as a chemical conversion treatment for aluminum, and is used for a thin film having a Zr amount of 5 to 30 mg / m ² (0.005 to 0.03 μm) mainly composed of Zr ₃ (PO ₄ ) and nH ₂ O. However, it is easily affected by the surface to be treated, and the management of treatment conditions including cleaning greatly affects the performance. In particular, if the film is thin, the corrosion resistance is inferior, and if the film is thick, the adhesion to the coating film, which is the upper layer thereof, is inferior. Therefore, control of the film thickness is an important control item. In the chemical conversion treatment of the steel material of the present invention, firstly, it is a rough rough surface that has been blasted, and secondly, because the material to be chemical conversion treatment is iron, its reactivity is lower than that of aluminum or zinc. Thirdly, when the coating film to be coated on the chemical conversion treatment film is a line pipe, the stress is large because it is a thick film, and as a result, high adhesion is required, which is different from the chemical conversion treatment of aluminum and zinc. Therefore, a new chemical conversion treatment technology was required.

Even if the surface of the steel material is rust-removed by blasting, it will be covered with a thin oxide in a short time after blasting in the air. Need to be removed. On the other hand, in the case of coating-type chemical conversion treatment, if an attempt is made to increase the reactivity with a strong acid, an unreacted soluble acid component remains, and the amount of precipitates due to the dissolved iron increases, which hinders adhesion. Therefore, studies have been conducted focusing on phosphoric acid, which is a weak acid that combines with iron, or a compound thereof. However, phosphoric acid has a problem that the liquid concentration must be increased in order to react with iron, excess phosphoric acid component tends to remain, the film is dissolved, and the cathode peeling performance is deteriorated. On the other hand, in the present invention, zircon hydrofluoric acid or titanium hydrofluoric acid containing a highly reactive hydrofluoric acid component is used, and the steel plate temperature at the time of coating is raised to 40 to 80 ° C. for coating on the surface of the steel material. It forms a uniformly thin insulating insoluble film containing 7% or more of zirconium or titanium element with respect to iron element. If the concentration of zirconium hydrofluoric acid or titanium hydrofluoric acid is insufficient or the reaction with iron is insufficient, the ratio of zirconium or titanium becomes less than 7% and the corrosion resistance is lowered.
Further, the first layer may contain at least one metal selected from magnesium, zinc and aluminum as a third component in order to fill the defective portion of the zirconium oxide film or the titanium oxide film.

When the hydrofluoric acid component dissolves the surface of the steel material, a dense insulating oxide film mainly composed of zirconium or titanium is formed, while the iron eluted by the reaction is the above-mentioned dense insulating oxide film layer when the liquid dries. A fragile iron oxide layer is formed by depositing on top of it. In order to increase the thickness of the reaction layer that is effective for anticorrosion, it is necessary to increase the concentration of the dilyconium hydrofluoric acid or titanium hydrofluoric acid to be applied, but inevitably the amount of iron dissolved increases and the fragile iron oxide layer Increases and the adhesion to the upper coating film decreases. To solve this contradictory problem, a method of taking in the eluted iron and forming a porous film in order to secure the adhesion with the upper coating film was investigated. As a result, it was found that fine particle silica is effective, and in particular, addition of linear (including pearl necklace-like) fine particle silica that forms a strong adhesive film is effective. Since the linear (including pearl necklace-like) fine particle silica has a secondary structure in which silica particles are strongly bonded to each other, the inside of the fragile iron oxide is reinforced by a silica skeleton. Further, since the porous film can be formed, the effect that the upper layer epoxy resin permeates into the porous voids and becomes one with each other to improve the adhesion can be obtained. That is, the problem of adhesion was solved by forming a porous layer in which granules containing iron, silicon, and oxygen were connected as a second layer film on the above-mentioned insulating oxide film of the first layer. The area ratio of the cross section occupied by the granules at this time is 30 to 80% when observed with a transmission electron microscope (TEM).
As the treatment liquid for forming the second layer film, the concentration B of the linear (or pearl necklace-like) silica fine particles forming a porous shape with respect to the mass concentration A of zircon hydrofluoric acid or titanium hydrofluoric acid is B. The mass ratio of / A is preferably in the range of 0.2 to 2.5. The film thickness at this time is preferably 0.2 to 2 μm in order to bond the iron oxide layer and the coating (epoxy resin) on the iron oxide layer in a well-balanced manner. If it is 0.2 μm or less, iron oxide may not be completely absorbed. On the other hand, if it exceeds 2 μm, the film strength may decrease and the adhesion may also decrease. These film thicknesses can be directly measured by the cross-sectional TEM, and can also be controlled by the amount of silica adhered. The amount of silica adhered is preferably in the range of 100 to 500 mg / m ² .

The gist of the present invention is as follows.
A three-layer polyolefin resin coating composed of a chemical conversion coating, an epoxy resin coating, or a chemical conversion coating, an epoxy resin coating, a modified polyolefin adhesive, and a polyolefin resin in order on a blasted steel material, wherein the chemical conversion treatment is performed. The coating film has a two-layer structure consisting of a first layer oxide coating containing iron, fluorine, zirconium or titanium, and oxygen, and a second layer of a porous layer in which granules containing iron, silicon, and oxygen are connected. A coating having a chemical conversion coating film, characterized in that the epoxy resin forming the coating layer laminated on the second layer has a structure in which the epoxy resin permeates and solidifies into the porous gaps of the second layer and is filled. It is a steel material. Further, it is preferable that the first layer contains at least one metal selected from the group consisting of magnesium, zinc and aluminum. The first layer of this chemical conversion treatment layer has a ratio of zirconium or titanium element of 7% or more to iron element as a value obtained from energy dispersive X-ray analysis (EDS analysis), and the second layer is granular. The cross-sectional area occupied by the porous material formed of the material is 30 to 80%.
When the first layer contains iron, fluorine, zirconium or titanium, and oxygen, and the second layer is connected with granules containing iron, silicon, and oxygen, the other components are not included. It can be selected arbitrarily.
As a chemical conversion treatment method for obtaining the chemical conversion coating structure, it is preferable to heat the steel material to 40 to 80 ° C., apply the treatment liquid, and dry it. The treatment liquid to be applied has a mass concentration A of zircon hydrofluoric acid or titanium hydrofluoric acid and a mass concentration B of linear (including pearl necklace-shaped) silica fine particles in a mass ratio of B / A of 0.2 to 2.5. The chemical conversion treatment liquid is used. Further, it is further preferable that the above-mentioned magnesium, zinc or aluminum metal is contained in the range of the total mass concentration C in terms of oxide in the range of 0.03 to 0.5 in terms of mass ratio of C / A.

As described above, according to the present invention, it is not necessary to use chromic acid as a chemical conversion treatment liquid for steel materials to be subjected to anticorrosion coating, and no water washing is required after the chemical conversion treatment, and a film can be formed only by coating and drying. Therefore, it is possible to provide a coated steel material that prevents peeling due to electric corrosion protection in a high temperature environment.

FIG. 1 is a structural cross-sectional view of a steel material using a powder epoxy resin showing one embodiment of the present invention as a coating layer. FIG. 2 is a structural cross-sectional view of a steel material using a three-layer polyolefin resin as a coating layer, which shows one embodiment of the present invention. FIG. 3 is a transmission electron microscope (TEM) photograph showing a cross section of a chemical conversion-treated membrane under the treatment conditions of Example 1. FIG. 4 is a photograph showing the element distribution of the two-layer structure of the cross section of the chemical conversion-treated membrane under the treatment conditions of Example 1 by energy dispersive X-ray analysis (EDS analysis).

Hereinafter, the present invention will be described in detail.
1 and 2 are structural cross-sectional views of a coated steel material showing one embodiment of the present invention. As the steel material 1 used in the present invention, any steel type such as ordinary steel or high alloy steel can be applied. Any steel grade may be used, but steel pipes for line pipes are required to have long-term corrosion resistance.

When performing a chemical conversion treatment for forming an oxide coating layer 2 made of iron, zirconium or titanium, fluorine, and oxygen and a porous coating layer 3 in which granules made of iron, silicon, and oxygen are connected according to the present invention. Before that, since it is necessary to remove scale, contaminants, etc. on the surface of the steel material 1, blast treatment using sand, alumina, grid, or shot is performed. After the chemical conversion coating film is formed, painting is performed. For painting, the powder epoxy resin layer 4 coated with the powder epoxy resin paint is formed. In order to improve corrosion resistance such as scratch resistance, a powder epoxy resin layer 4 coated with a powder epoxy resin paint relatively thinly, a modified polyolefin adhesive layer 5, and a polyolefin resin layer 6 are sequentially laminated to form three layers. Apply a polyolefin resin coating.

To form a chemical conversion coating film, a chemical conversion treatment liquid is applied to a steel material and dried. In that case, washing with water after application of the chemical conversion treatment liquid is not required. In particular, since a drying step is required to form a film in this chemical conversion treatment, a chemical conversion coating structure is not formed by washing with water. The treatment conditions for forming the chemical conversion treatment film having the two-layer structure of the present invention and the chemical conversion treatment liquid will be described in detail.

The powder epoxy resin-coated steel pipe or the polyolefin resin-coated steel pipe of the present invention is blasted not only to remove rust and dirt on the surface of the steel pipe but also to secure the surface roughness required for adhesion before chemical conversion treatment is performed. Perform processing. As the polishing material used for the blasting treatment, a steel grid or shot grains are generally used. If a cleaner surface is required, a ceramic material such as alumina may be used. You can also use sandwiches. If dirt such as iron powder adheres to the surface after the blasting treatment, treatments such as brushing, suctioning, and cleaning with a liquid can be performed.

An insoluble chemical conversion treatment film is formed on the surface of the steel material after the blast treatment. This insoluble film needs to be a uniform thin film, but in the coating type, there is a limit to the amount of liquid that can be applied to the surface of the steel material and the time until drying, and it is necessary to increase the acid component for the reaction in a short time. However, if the acid component is too large, hydrogen is generated and it is difficult to form a uniform film. Further, there is a problem that the soluble acid component remains in the chemical conversion coating film and the performance is deteriorated. On the other hand, in the present invention, zircon hydrofluoric acid or titanium hydrofluoric acid is used to supply the acid and the precipitated zirconium or titanium. Zirconium or titanium precipitates on the surface of the steel due to the increase in pH caused by the hydrofluoric acid component dissolving on the surface of the steel, forming a uniform insoluble film in close contact. Further, when a metal such as magnesium, aluminum, or zinc is added to the treatment liquid, the defect portion of the coating film is complemented by precipitating at the same time as zirconium or titanium and covering the surface. Since it is safer to add these metal components as oxides, the amount added is calculated using metal oxides. If the mass concentration C of the metal oxide is too small, the effect is insufficient, and if it is too large, the effect of the insulating coating of zirconium or titanium is reduced. Add in the range of 0.03 to 0.5 by mass ratio of A.

A dissolution reaction of iron is indispensable for the formation of an insoluble oxide film having good adhesion in the first layer, but the dissolved iron component forms an oxide having a small film strength when the liquid is dried. In particular, when the treatment liquid is applied in a state where the temperature of the steel material is low, rust (iron oxide layer) having a small film strength increases and the adhesion is lowered, so that the treatment temperature needs to be 40 ° C. or higher. Further, even if the temperature of the steel material is too high, a uniform reaction cannot be obtained, so the temperature is set to 80 ° C. or lower. However, even when the treatment liquid is applied at a temperature of 40 to 80 ° C., it is difficult to completely suppress the iron oxide layer having a small film strength that inhibits the adhesion of the coating film on the reactive oxide layer. Therefore, in the present invention, silica fine particles forming a porous layer are added to the chemical conversion treatment liquid in order to form a second layer for improving adhesion.

As the silica fine particles for forming the porous layer, linear silica (secondary particle diameter: 40 to 150 nm) in which primary particles having a diameter of 5 to 50 nm synthesized by the liquid phase method are linearly arranged to form an aggregate (secondary particle diameter: 40 to 150 nm). (Including pearl necklace) is recommended. By using silica having a linear structure strongly bonded in advance, the cohesive force is increased, and at the same time, a porous mixed film is formed together with the iron oxide, and the adhesion with the epoxy resin layer which is the paint on the silica is improved. Let me. Examples of silica fine particles include Nissan Chemical's Snowtex (registered trademark) -OUP, Snowtex (registered trademark) PS-SO, Snowtex (registered trademark) PS-MO, and Snowtex (registered trademark) AK-PS-S. Catalog S-20L of JGC Catalysts and Chemicals, etc. can be used.
The ratio of the cross-sectional area of the porous material to the porous layer is preferably 30 to 80%. If it deviates from this range, the penetration and filling of the epoxy resin to be coated on it will be insufficient, and the adhesion to the coating layer will decrease.
A porous film is also formed in the vapor phase silica fine particles, but in the vapor phase silica, primary particles having a diameter of several tens of nm are bonded to form an agglomerate having many voids and a light specific density, which is very bulky and coagulated. Sufficient film strength cannot be obtained because the bonding force between the aggregates is weak. Therefore, the adhesion is inferior to the above-mentioned linear (including pearl necklace-like) silica.
On the other hand, for example, in the liquid phase single particle silica that does not form aggregates, the porous layer required for adhesion to the coating film, which is a necessary condition of the present invention, is not formed.

When the mass concentration A of zircon hydrofluoric acid or titanium hydrofluoric acid in the chemical conversion treatment liquid and the mass concentration B of the linear silica fine particles are set, the addition amount ratio of B / A is 0.2 to 2.5. When the addition amount ratio is less than 0.2 or more than 2.5, a fragile iron oxide layer generated by zircon hydrofluoric acid or titanium hydrofluoric acid and a mesh-like reinforcement inside the iron oxide. If the amount of silica fine particles entering as a skeleton is too small, it will not be effective reinforcement, and if it is too large, the upper part will have a structure of only silica fine particles, so that the film will be weak and the adhesion will be reduced.

Further, there is no problem even if a silane coupling agent is added to the chemical conversion treatment liquid. However, if the molecular structure of the silane coupling agent has an amino group or an isocyanate group, the structure of the chemical conversion coating film changes. Therefore, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane and 3-glycidoxypropyl It is preferable to use a silane coupling agent having an epoxy group such as methyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane.

As for the method of applying the chemical conversion treatment liquid to the steel material, any method such as spraying, brushing, rolling, ironing after casting, etc., which can adjust the coating amount may be used. At this time, the film thickness is controlled by the amount of silica adhered, which has a large effect on the adhesiveness, so that the film thickness of 0.2 to 2 μm observed by the cross-sectional TEM having good adhesion to the second layer can be obtained. It is preferable to apply the mixture in an adhesion range of 100 to 500 mg / m ² . If the adhesion amount is less than 100 mg / m ² , the effect of the treatment may not be sufficiently obtained, and if it greatly exceeds 500 mg / m ² , the strength of the second layer mainly composed of silica fine particles of the chemical conversion treatment coating decreases. May reduce the adhesion. The amount of silica adhered can be easily measured by using a fluorescent X-ray analyzer. The performance of fluorescent X-ray analyzers has improved in recent years, and it has become possible to analyze even light elements even in the atmosphere. Therefore, the surface of the steel sheet is melted in advance and chemical analysis is performed to prepare a calibration curve for use.

Next, a coating layer applied on the chemical conversion coating film formed by applying the chemical conversion treatment liquid will be described. A paint using an epoxy resin having excellent corrosion resistance and adhesiveness can be used to form the coating layer. At this time, since it is necessary to secure a film thickness of 100 μm or more in order to obtain high corrosion resistance, coating is performed using a powder-type epoxy resin paint that makes it easy to secure a thick film. A phenol-based curing agent is added to a mixture of bisphenol A-type epoxy resin and bisphenol F-type epoxy resin, which are the main components of powdered epoxy resin paint, alone or in combination, and further combined with polyfunctional phenol novolac and halogenated epoxy resin. A combination is common. The curing rate is adjusted by adding an amine-based compound, an imidazole compound, dicyandiamide, or the like. Further, the inorganic pigment may be added in the range of 3 to 30 vol% with respect to the total volume. As inorganic pigments, pigments such as silica, titanium oxide, wollastonite, mica, talc, kaolin, chromium oxide, zinc borate, zinc phosphate, metal powders such as zinc and Al, ceramic powders, etc., and vanadium phosphorus. A rust-preventive pigment such as a system compound can be appropriately used. The powder epoxy resin paint can be obtained from Nippon Paint Co., Ltd. or Kansai Paint Co., Ltd. in Japan. Overseas, JOUTAN, KCC, Arsonnissi, 3M Co., Ltd. Brands sold for steel pipe coating by manufacturers such as, etc. can be appropriately used.

In the coated steel material of the present invention, the powder epoxy resin paint can be applied to a steel material heated to 160 to 270 ° C. after chemical conversion treatment using an electrostatic powder coating machine. The thickness is usually 100 μm to 500 μm. A thickness of less than 100 μm is not preferable because an unpainted portion (pinhole) is formed, which is an anticorrosion defect portion. Further, if the thickness exceeds 500 μm, it is not preferable from the viewpoint of an increase in internal stress of the coating film and cost. Once the powder epoxy resin paint is in a molten state, it permeates into the porous silica coating of the second layer of the chemical conversion treatment coating having a two-layer structure and is integrated with the chemical conversion treatment coating. As a result, high adhesion between the coating film and the steel material can be obtained.

When a three-layer polyolefin resin coating is performed as an organic resin coating, a powder epoxy resin paint is applied, and then the polyolefin resin is further laminated via a modified polyolefin adhesive. The modified polyolefin adhesive is obtained by modifying known polyolefins such as polyethylene and polypropylene with maleic anhydride, a copolymer of olefins and maleic anhydride, olefins and acrylic acid ester, and maleic anhydride. A copolymer is used. If a polyolefin resin to be coated thereafter and a polyolefin resin of a different type are used (for example, polyethylene and polypropylene), a problem occurs in adhesion, so that a modified polyolefin of the same type is preferable.

When supplied as pellets, the thermoplastic modified polyolefin adhesive is coated in a film form using an adhesive resin die that has been heated and melted using an extruder. In addition, there is also a method of crushing the modified polyolefin adhesive into powder and applying it. By these methods, an adhesive layer having a film thickness of 0.1 to 0.4 mm is formed.

Examples of the polyolefin resin laminated on the modified polyolefin adhesive layer include conventionally known polyolefin resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and polypropylene, and ethylene-propylene blocks. Alternatively, a resin containing a known polyolefin copolymer such as a random copolymer, a polyamide-propylene block or a random copolymer can be mentioned.

In the polyolefin resin layer, carbon black or other coloring pigments, filling enhancers, antioxidants, ultraviolet absorbers, hindered amine-based weather resistant agents, etc. can be optionally added as components other than the polyolefin resin as heat resistance and weather resistance measures. It can be added in combination.

The polyolefin resin is coated by the same extrusion coating method as the modified polyolefin adhesive so as to have a minimum total film thickness of 1.2 mm or more specified in JIS G3469-1. The thicker the polyolefin resin layer, the better the flaw resistance and corrosion resistance, but the thicker the film, the larger the internal stress, so 5 mm or less is desirable.

Hereinafter, the present invention will be specifically described with reference to Tables 1 and 2.
[Preparation of chemical conversion treatment liquid]
The raw materials for the chemical conversion treatment liquids of Examples 1 to 12 and 17 of the present invention, Comparative Examples 1 to 8 having different treatment components or treatment conditions, and Comparative Examples 10 and 14 corresponding to Patent Document 2 are manufactured by Morita Chemical Industries, Ltd. A titanium hydrofluoric acid solution (40%) was used. On the other hand, a zircon hydrofluoric acid solution (40%) also manufactured by Morita Chemical Industries, Ltd. was used as a raw material for the chemical conversion treatment liquids of Examples 13 to 16 and 18 of the present invention. Next, Snowtex (registered trademark) PS-MO manufactured by Nissan Chemical Industries, Ltd. was used as the linear silica of the liquid phase method used in Examples 1 to 18 and Comparative Examples 1 to 6. As the liquid phase method single particle silica fine particles of Comparative Example 7, Snowtex (registered trademark) O manufactured by Nissan Chemical Co., Ltd. synthesized by the liquid phase method, and as the dry method silica fine particles of Comparative Examples 8, 11 and 15, the vapor phase method was used. Synthesized AEROSIL® 200 manufactured by Aerosil Japan was used. Oxide was used as the added metal, and powders of aluminum oxide, zinc oxide, and magnesium oxide were added and dissolved. Commercially available reagents were used for zirconium nitrate of Comparative Examples 10 and 14 and magnesium heavy phosphate of Comparative Examples 11 and 15.
As Comparative Examples 10 and 14, treatment liquids corresponding to Example 17 in Table 1 of Patent Document 2 were produced. This is a 4N solution of titanium hydrofluoride, and since titanium hydrofluoride has a molecular weight of 163.9, the gram equivalent is calculated as 82, and it is added to 1 liter of a 40% solution of hydrogen fluoride (specific gravity 1.38) manufactured by Morita Chemical Industry. On the other hand, 0.68 liters of water was added to make a 1.68-fold diluted solution, and 5% by weight of zirconium nitrate was added thereto to prepare the solution.
Further, as Comparative Examples 11 and 15, AEROSIL (registered trademark) 200 manufactured by Aerosil Japan, which was synthesized by the vapor phase method, was mixed with a magnesium dibasic phosphate solution as a coating type chemical conversion treatment solution. It was adjusted to be 1. )
As the chemical conversion treatment liquid corresponding to Example 6 of Patent Document 5 as Comparative Examples 12 and 16, zirconium carbonate ammonium carbonate was used at a zirconium concentration of 7%, ammonium metavanadate was used at a vanadium concentration of 0.0022%, and second ammonium phosphate was used. The PO4 concentration was adjusted to 0.74%, and ₃ -glycidoxypropyltrimethoxysilane was adjusted to 1.5%. The coating temperature was set to 60 ° C. as in the examples, and the zirconium was applied so as to have an adhesion amount of 800 mg / m ² .

[Methods for producing Examples and Comparative Examples]
As the steel material, a 200A JISG3452 carbon steel pipe for piping with a length of 5.5 m was used. The outer surface of the steel pipe was blasted to remove rust. After heating the steel pipe, the chemical conversion treatment liquids of Examples and Comparative Examples of the present invention were applied with a brush and dried. For the comparative example including a part of the washing steps, after rough washing with sufficient tap water, washing with pure water, and then hot air drying were performed.

When performing 3-layer polyolefin resin coating as organic resin coating, heat the steel tube after chemical conversion treatment to 200 ° C, and then apply powder epoxy resin paint (226N 8G manufactured by 3M) to electrostatic powder coating with a target thickness of 200 μm. Was carried out. After that, pellets of modified polyethylene adhesive (ADMER ^TM NE065, manufactured by Mitsui Chemicals) and polyethylene (NOVATEC ^TM ER002S, manufactured by Japan Polyethylene) were formed into a sheet-like semi-molten state using an extruder and a T-die, and wrapped and coated. rice field. The adhesive film thickness was adjusted to 200 μm, and the polyethylene film thickness was adjusted to 3 mm. Then, the outer surface was water-cooled to produce the three-layer polyolefin resin-coated steel pipes of Examples 1 to 16 and Comparative Examples 1 to 12 of the present invention.
When coating only powder epoxy resin as organic resin coating, heat the steel pipe after chemical conversion treatment to 220 ° C, and then apply powder epoxy resin paint (226N 8G made by 3M) to electrostatic powder with a target thickness of 350 μm. After coating, water cooling was performed to produce powder epoxy resin-coated steel pipes of Examples 17 and 18 and Comparative Examples 13 to 16 of the present invention.

[Measurement of silica adhesion]
As a guideline for the film thickness of the chemical conversion treatment, masking was performed after the chemical conversion treatment to prepare a portion not coated with the resin, and a 5 × 5 cm coupon was cut to prepare a test piece for film thickness measurement. The test pieces were averaged by measuring 9 points per sample with a fluorescent X-ray apparatus (XGT-7200V: manufactured by HORIBA, Ltd.) in which a calibration curve with the amount of silica adhered was prepared in advance.
[Analysis of coating]
A part of the coated steel material of Examples and Comparative Examples was cut out, and the cross-sectional structure of the chemical conversion coating film was observed using JEM-2100F manufactured by JEOL as a transmission electron microscope (TEM). The obtained image was quantified and the cross-sectional occupancy of the porous second layer was obtained by image analysis. Further, using JED-2300T manufactured by JEOL as an energy dispersive X-ray analysis (EDS analysis) apparatus, elemental analysis was performed on the first layer and the second layer of the chemical conversion treatment with a probe diameter of about 2 nm. Five points were measured, and the median value of the measurement was used as the representative value of the element ratio.
[Evaluation test method]
As a cathode peeling test, the manufactured three-layer polyolefin resin-coated steel tube and powder epoxy resin-coated steel tube were divided into eight parts in the length direction and the circumferential direction to prepare test pieces. After drilling holes in the coating film in the center of the test piece by the method shown in Annex H of ISO 21809, set up a test cell for 3 test pieces for the prepared level, and electrolyze 3% saline solution inside. After filling the liquid, the whole was placed in an oven at 60 ° C. to control the temperature, and a cathode corrosion protection of −1.45 V was applied to the exposed portion of the steel material with respect to the silver chloride electrode. After performing the test for 30 days, the polyolefin is removed from the 3-layer polyolefin resin coated steel pipe, the primer is cut in 8 directions around the hole with a cutter, and the primer is easily peeled off from the flawed hole. Was exposed. The peeling diameter was measured in four directions and averaged to calculate the peeling distance from the initial hole. The powder epoxy resin coated steel pipe was also evaluated by the same procedure. A peeling distance of less than 13 mm was regarded as acceptable.
Further, as a method for confirming the adhesion and the anticorrosion performance, the above-mentioned eight-divided 150 mm long test sample was immersed in warm water at 80 ° C. for 50 days, and the peeling distance (mm) from the cut end face of the coating film was measured. Those with a peeling distance of less than 5 mm were considered acceptable.
The test results of the above Examples and Comparative Examples are shown in Tables 1 and 2.

[Contents of Examples and Comparative Examples]
Examples 1 to 4 and Comparative Examples 1 to 3 of the present invention show the silica addition amount ratio range of the treatment liquid component, and the appropriate range of the addition amount ratio (B / A) is 0.2 to 2.5. .. In Examples 2 and 5 to 7 of the present invention, the range of the silica adhesion amount in the chemical conversion treatment is shown. In Example 7, if the adhesion amount is large, the cathode peeling performance is deteriorated. Therefore, 100 to 500 mg / mg / m ² is a more appropriate range.
Examples 8 to 9 and Comparative Examples 4 to 5 of the present invention show the temperature range of the steel material at the time of coating the chemical conversion treatment liquid, and in Comparative Examples 4 and 5 outside the appropriate temperature range of 40 to 80 ° C. It is difficult to form the chemical conversion treatment film of the present invention, and the cathode peeling property and the edge peeling property are deteriorated.
Comparative Example 6 shows a treatment step in which water washing is performed after the chemical conversion treatment, which is different from the treatment method of the present invention, and the cathode peeling property and the edge peeling property are poor.
Examples 10 to 12 are examples in which no additive metal component is used or zinc and magnesium are used as the components of the chemical conversion treatment, and all of them have good performance.
Comparative Examples 7 and 8 are examples in which silica fine particles that do not form a porous layer in which the granules required for the present invention are linked to silica fine particles that are treatment components of chemical conversion treatment are used, and have excellent cathode peeling property and edge peeling property. bad.
In Comparative Examples 9 and 13, when there is no chemical conversion treatment, Comparative Examples 10 and 14 are cleaning treatments corresponding to Patent Document 2, and Comparative Examples 11 and 15 are phosphoric acid-based coating type chemical conversion treatments corresponding to Patent Document 3, Comparative Examples. 12 and 16 are examples of Patent Document 5, and both have poor cathode peeling property and edge peeling property.
Examples 13 to 16 and 18 are examples in which the chemical conversion treatment of the present invention using zircon hydrofluoric acid was used instead of titanium hydrofluoric acid, and all of them have good performance.
Example 17 is the same chemical conversion treatment as in Example 2, and the coating is a powder epoxy resin with respect to a three-layer polyolefin resin.

[Results of evaluation of Examples and Comparative Examples]
As is clear from the results in Tables 1 and 2, the two-layer chemical conversion coating film of the present invention is formed on the steel material by the chemical conversion treatment liquid component of the present invention and the example in which the treatment step is performed, and the cathode is peeled off or immersed at a high temperature. The peeling resistance performance in the above is superior to that of the comparative example in which no treatment is performed or other treatments are used. In the comparative example corresponding to Patent Document 2 having a cleaning treatment step which is a conventional technique, an effective treatment film is not formed, so that the cathode peeling performance and the peeling resistance in immersion are not sufficient. On the other hand, in the phosphoric acid-based chemical conversion treatment of the comparative example corresponding to Patent Document 3, the peeling after immersion is small, but the performance is not sufficient because the film is dissolved by the alkali generated in the cathode peeling test. On the other hand, it can be seen that the method of forming an insoluble oxide film mainly composed of zirconium, which corresponds to Patent Document 5, is effective for cathode peeling, but has a problem in peeling resistance in immersion.

As the coating film structure of the present invention, a TEM photograph of a cross section of the chemical conversion-treated film under the treatment conditions of Example 2 is shown in FIG. 3, and an element distribution analysis photograph thereof is shown in FIG. In the TEM image of FIG. 3, the oxide coating layer 2 and the coating layer 3 of the chemical conversion treatment coating are formed on the surface of the steel material 1, and the resin layer 4 can be seen on the upper layer thereof. By the elemental analysis of FIG. 4, iron, fluorine, titanium, and oxygen are detected in the first layer on the surface of the steel material 1, and it can be seen that a dense metal oxide is formed. The second layer above it has different components, and iron, silicon, and oxygen are detected. Since silicon is granular and oxygen is strongly detected at the same position, it indicates added silica fine particles, and a porous film is formed. Since carbon is detected in the gaps of the second layer, it can be seen that the resin layer 4 of the powder epoxy resin paint and the porous coating layer 3 of the second layer are integrated.
As is clear from the above results, a two-layer chemical conversion coating structure is formed by the chemical conversion treatment of the present invention. This makes it possible to achieve both the high-temperature cathode peeling property required for the anticorrosion coating of the line pipe and the peeling resistance after immersion.

1 Steel material 2 Oxide coating layer composed of iron, zirconium or titanium, fluorine and oxygen 3 Porous coating layer composed of iron, silicon and oxygen 4 Powder epoxy resin layer 5 Modified polyolefin adhesive layer 6 Polyolefin resin layer

Claims (5)

A first layer composed of an oxide film layer containing iron, zirconium or titanium, fluorine and oxygen on the surface of the steel material and having a ratio of the zirconium element or the titanium element to 7% or more with respect to the iron element, and the first layer. On top of the second layer, which is formed by connecting granules containing iron, silicon, and oxygen, and the porous material occupies 30 to 80% of the cross-sectional area, and further on the second layer. A coated steel material having a chemical conversion treatment film, characterized in that the laminated coating layer has a structure in which the porous gaps of the second layer are filled. A coated steel material having a chemical conversion treatment coating, wherein the first layer of the chemical conversion treatment coating layer on the surface of the coated steel material according to claim 1 contains at least one metal selected from the group consisting of magnesium, zinc and aluminum. The method for producing a coated steel material according to claim 1, which comprises zircon hydrofluoric acid or titanium hydrofluoric acid and linear silica fine particles as components, and the mass concentration of zircon hydrofluoric acid or titanium hydrofluoric acid is A. When the mass concentration of linear silica is B, a treatment solution containing a B / A addition amount ratio in the range of 0.2 to 2.5 is applied to the surface of a steel material heated to 40 ° C to 80 ° C, and then applied. A method for producing a coated steel material, which comprises forming a chemical-treated coating by drying and then coating on the chemical-treated coating. The treatment liquid according to claim 3 contains at least one metal selected from the group consisting of magnesium, zinc, and aluminum, and has a mass concentration of zircon hydrofluoric acid or titanium hydrofluoric acid A, an oxide of the metal. The coating having a chemical conversion coating according to claim 3, wherein the total mass concentration in terms of conversion is in the range of 0.03 to 0.5 in terms of the addition amount ratio of C / A, respectively. Manufacturing method of steel materials. The method for producing a coated steel material according to claim 3 or 4, wherein the coated steel material has a chemical conversion coating film in which the adhesion amount of the silica component analysis in the second layer is in the range of 100 to 500 mg / m ² .

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