JP5211829B2 - Super durable organic resin coated steel - Google Patents

Description

  The present invention relates to an anticorrosion technique for steel structures in a severely corrosive environment, for example, near a beach.

  The resin coating for heavy anticorrosion is used for the purpose of anticorrosion to a steel structure in a severe corrosive environment such as marine environment-a temperature difference due to sunshine, a high concentration of salinity, a dry and wet repeated environment or a constantly submerged environment.

  Generally, polyethylene and polyurethane are used for the coating resin for heavy anticorrosion, and the coating thickness is as thick as 2 to 10 mm. Since this thick resin coating layer is mainly responsible for the corrosion protection of steel materials, the primer and chemical conversion treatment of the base are required to maintain adhesion with the coating resin over a long period of time (long-term seawater adhesion resistance) rather than anticorrosion. Combined with this, long-term corrosion protection of steel materials becomes possible. At present, the polyethylene resin coating itself is expected to have a life of about 40 years, but the adhesive strength decreases after about 5 to 20 years, and peeling of the resin coating starts.

  In recent years, due to the demands of the times, a condition has been imposed that the period (life) until the resin coating is peeled off is further extended and hexavalent chromium or the like, which is an environmentally hazardous substance, is not used. This is very strict from the development side.

Under such conditions, aluminum phosphate has attracted attention in terms of non-chromate treatment in the surface treatment field.
Aluminum phosphate has been known for a long time as an inorganic adhesive. For dental cements that require extremely high adhesion and durability, II, III group oxides, hydroxides, etc. It is used by adding a curing agent. Dental cement has a large calorific value and high viscosity, so a small amount of about 1 g may be kneaded by hand and applied with putty, but it is completely unsuitable for use in line production.

  For these reasons, aluminum phosphate has not been used for the production of resin-coated steel materials in the past, but in recent years its use has been studied from the point of non-chromate treatment. Proposed.

In Patent Document 1, Al ₂ O ₃ / P ₂ O ₅ = 0.2 to 0.6, B ₂ O ₃ / P ₂ O ₅ = 0.01 to 0.1, in molar ratio in terms of anhydrous oxide. Disclosed is a technique for producing a non-chromate resin-coated steel material comparable to a chromate material by forming an inorganic oxide layer with MO / P ₂ O ₅ = 0.01 to 0.2 (M is an alkaline earth metal). However, further studies are needed to improve long-term seawater adhesion.

  Patent Document 2 discloses a technique that uses aluminum phosphate as an insulating film forming agent for an electromagnetic steel sheet used for an iron core of a transformer and exhibits good adhesion, weldability, corrosion resistance, and insulation. However, the adhesion mentioned here is the adhesion between the formed insulating film and the substrate, and not the adhesion between the resin layer formed on it and this technology requires the strict required performance of heavy anti-corrosion steel. (Long-term seawater adhesion) cannot be satisfied.

  In Patent Document 3, in the composition of the treatment liquid for forming the insulating film on the magnetic steel sheet, the composition ratio of the phosphate and the organic acid is defined by the ratio of the oxygen atom in the organic acid to the total number of metal ions. Discloses a technique that is excellent in film formability even at low temperature baking without using chromium. Moreover, in patent document 4, the white rust resistance equivalent to the chromate sealing processing material of a galvanized steel plate with the chemical conversion treatment liquid containing water-based epoxy resin, a silane coupling agent, and water-soluble phosphates, such as aluminum phosphate, is provided. A chemical conversion treatment agent having paintability is disclosed. However, as disclosed in Patent Documents 3 and 4, when the organic resin component is present in the chemical conversion treatment layer, since it gradually hydrolyzes in a severe corrosive environment, there is anxiety in terms of long-term seawater resistance.

JP 2007-313885 A JP 2003-147543 A Japanese Patent No. 3935664 Japanese Unexamined Patent Publication No. 2006-9065

  As described above, in the non-chromate chemical conversion treatment used in the field of thin plates (plated steel plates), generally long-term seawater adhesion cannot be expected, and the water resistance and cathode resistance as disclosed in Patent Document 1 are not expected. Even with chemical conversion treatment that achieves both peelability, long-term seawater adhesion needs to be further improved. Therefore, there is a need for a new resin-coated steel material that has improved long-term seawater adhesion using non-chromate chemical conversion treatment.

  The present inventor considered that in order to realize high water resistance like mineral ore, enamel, and earthenware, it is necessary to form a chemical conversion treatment layer only with an inorganic substance without including an organic resin. However, formation of the inorganic layer generally requires firing for several hours at a temperature of several hundred degrees.

Therefore, attention has been paid to a technique disclosed in Patent Document 1 or the like that uses a treatment liquid that is an easy-to-handle liquid and contains boric acid-containing aluminum phosphate whose baking temperature is low. The long-term seawater adhesion when using an inorganic chemical conversion treatment layer mainly composed of aluminum phosphate is not the molar ratio of the constituent elements in the inorganic treatment layer, but the total amount of charges of constituent metal elements and hydrogen. The knowledge determined by the ratio of ions (including those coordinated to PO ₄ ^3- ) was obtained.

FIG. 1 shows the values obtained in the examples described later. Aluminum phosphate in which the total number μ of products of the number of moles of constituent metal elements and their valences and the number of moles of hydrogen ions θ is adjusted. An organic oxide coating layer is formed after forming an inorganic oxide layer on the surface of a steel material using a treatment liquid containing as a main component, coating the sample with an organic resin, and conducting a seawater immersion acceleration test on the sample. It was obtained as a result of investigating the peeling distance, and it can be seen that the peeling distance is greatly reduced when the value of μ / θ is around 1.
Furthermore, it has been found that when the pigment is added to the chemical conversion treatment solution, this ratio changes when the pigment is dissolved in the chemical conversion treatment solution, so that a restriction requirement for the solubility of the pigment is also necessary.

As a result of further investigation based on these findings, the present inventor has reached the present invention as follows. That is,
(1) In an organic resin-coated steel material in which an inorganic oxide layer composed of Al, P, Mg, B, O, and H and an organic resin layer are sequentially laminated on the steel material surface, the element molar composition ratio of the inorganic oxide layer However, the super-durable organic resin-coated steel material satisfies the following condition (Formula 1).
μ / θ = 0.8 to 1.2 (Formula 1)
Here, the sum of products of the number of moles of ions of μ: Al, Mg, B and their valence
θ: Number of moles of hydrogen ions

(2) The inorganic oxide layer contains an inorganic pigment whose pH increase after 5 minutes after addition of 8 mass% to a phosphoric acid solution having a pH of 2 at room temperature is 0.05 or less, and the content thereof is an inorganic oxide. The super-durable organic resin-coated steel material according to (1), which is 10 to 50 mass% with respect to the layer.
(3) The super-durable organic resin-coated steel material according to (1) or (2), wherein a top layer of the organic resin layer is a polyethylene resin layer or a polyurethane resin layer having a thickness of 1.5 mm or more .

  According to the present invention, it is a resin-coated steel material that reduces the use of environmentally hazardous substances, and has an organic resin-coated steel material that has long-term seawater adhesion and corrosion resistance equivalent to or better than that of conventional chromate chemical conversion treatment materials, particularly organic materials for heavy anticorrosion. A resin-coated steel material can be provided.

Hereinafter, embodiments of the present invention will be sequentially described.
The steel material used in the present invention is not particularly limited as long as it is a steel material that is generally used for steel structures, but the steel types constituting the steel material include ordinary steel, low alloy steel, and high alloy steel. It can be illustrated. Moreover, as a kind of steel material, the thick board, steel pipe, steel pipe pile, steel pipe sheet pile, steel sheet pile, H-section steel, wire rod etc. to which heavy anti-corrosion coating is applied can be illustrated.
The steel material used in the present invention needs to be subjected to a ground treatment for removing scale, contaminants and the like on the surface before coating. Examples of the base treatment include alkali degreasing, pickling, sand blasting, grid blasting, and shot blasting.

In the present invention, as described above, long-term seawater-resistant adhesion with the organic resin coating layer is ensured by forming an inorganic oxide layer on the steel surface.
The inorganic oxide layers are all ionic binding materials, and do not include a metal binding material such as a single element having an oxidation number of 0 and a covalent binding material such as an organic compound except for inevitable impurities. However, there may be a covalent bond in the ionic molecule.

  The inorganic chemical conversion treatment layer of the present invention is composed of Al, P, Mg, B, O, and H elements. As disclosed in the above-mentioned Patent Document 1, the aluminum phosphate binder is composed of aluminum, phosphorus, oxygen, and hydrogen. In order to lower the firing temperature, boron, In order to improve adhesiveness, it is comprised by adding magnesium.

Since the inorganic oxide layer is an ionic substance, it exists as ions, and there is a restriction that the sum of the number of moles of each element × the number of oxidations (number of charges) is zero. Furthermore, since this inorganic oxide layer is an indefinite composition, there is no fixed chemical formula, but the main component is primary aluminum phosphate Al (H ₂ PO ₄ ) ₃ , and the composition of each element is in the following range: Is preferred.
Al is a molar ratio with respect to P, and a range of Al / P = 0.23 to 0.43 is preferable, and 0.35 to 0.4 is more preferable. Mg and B are additive elements. Similarly, the molar ratio to P is preferably in the range of 0.01 to 0.2, more preferably 0.01 to 0.05 for Mg and 0.05 to B, respectively. ~ 0.1.

In the inorganic oxide of the present invention, it is sufficient that the cation and oxygen atom of the metal element or typical element are present, and the existence form is not limited. That is, the oxygen atom may be present as oxide ion O ²⁻ , oxo anion X _a O _b ⁿ⁻ , and hydroxide ion OH ⁻ .

The cations constituting the inorganic oxide layer are Al ³⁺ , B ³⁺ , Mg ²⁺ , H ⁺ . P has an oxidation number of +5 and exists as PO ₄ ³⁻ , and when H ⁺ is sequentially coordinated thereto, HPO ₄ ²⁻ and H ₂ PO ₄ ⁻ are sequentially formed. In the present invention, these anions are used. Is counted as consisting of H ⁺ and PO ₄ ³⁻ .

In the present invention, the element molar composition ratio μ / θ of the inorganic oxide layer satisfies the following formula (1).
μ / θ = 0.8 to 1.2 (1)
In the formula (1), μ is the total charge amount of ions of Al, Mg, and B, and is represented by the following formula (2).
μ = ΣXi × ni (2)
Here, Xi is the number of moles of ions of elements i constituting the inorganic oxide layer, ni is the same ionic valence of ions of elements i. Μ can be obtained by summing up the products of the number of moles and the valence of all the ions of Al, Mg, and B constituting the inorganic oxide layer.

Θ is the total charge amount (number of moles) of hydrogen ions. For anion of the inorganic oxide layer is the PO ₄ ^3- only, the total charge quantity of the anion, is three times the molar amount X _p of phosphorus element. According to the law of conservation of charge, the total charge amount of cations is also equal to this, so that the total amount of hydrogen ions can be obtained by subtracting the total charge amount of cations other than hydrogen ions (all metal ions). Since the total charge amount of cations other than hydrogen ions is μ, θ can be expressed by the following equation (3).
θ = 3X _p −μ (3)

  As shown in FIG. 1, the present inventor has found that seawater adhesion is maximized when the value of μ / θ is around 1, but μ / θ = 1 ± 0.2 is the upper and lower limit. Therefore, the practicality is recognized within the range, so that the range of the formula (1) is adopted. However, the closer to 1.0, the better the seawater resistance, and a range of 1 ± 0.1 is recommended. If possible, the range of 1 ± 0.05 is more preferable. This is because even a slight difference in performance opens greatly in the ultra-long term.

The adhesion amount of the inorganic oxide layer is preferably an Al element average adhesion amount of 0.01 to 10 g / m ² . This corresponds to 0.1 to 100 g / m ² when the film composition is Al ₂ O ₃ .3P ₂ O ₅ .2H ₂ O by the oxide notation. A more preferable adhesion amount is an Al element average adhesion amount of 0.1 to 3 g / m ² , and more preferably 0.5 to 1 g / m ² . When converted to a film thickness (μm), it varies slightly depending on the composition of the film, but is 30 times the Al element average adhesion amount (g / m ² ).

If the average Al element deposition amount of the inorganic oxide layer exceeds 10 g / m ² , the adhesion is saturated even in a dense and homogeneous layer, and if it is less than 0.01 g / m ² , sufficient adhesion is difficult to obtain. Become.

In the present invention, in order to further improve the seawater adhesion resistance, an inorganic pigment may be added to the aluminum phosphate solution to contain the inorganic pigment in the inorganic oxide layer.
However, since the aluminum phosphate solution is acidic at about pH 2, it may be slightly dissolved depending on the type when an inorganic pigment is added. In that case, μ may change and deviate from the range of the expression (1). Therefore, the inorganic pigment to be added must be insoluble in the acidic solution.

Therefore, as a simple insolubility test and its acceptance criteria, the amount of increase in pH when 8 mass% of pigment was added to a phosphoric acid solution at pH 2 was used. The pH of the solution and the amount of pigment added mimic the actual chemical conversion solution. When the oxide pigment dissolves in this solution, the pH of the liquid phase increases.
Therefore, the increase in pH is defined as 0.05 or less as an insoluble index. The reading accuracy of the current general pH meter is 0.01, but considering the calibration error, if the width is 0.05, the effect of insolubility or dissolution can be ignored. .

Examples of pigments that satisfy this criterion include titania, silica, and precipitated barium sulfate.
The addition amount of the pigment is defined as 10 to 50 mass% as a preferable amount because the addition effect is small when the amount is small, and when the amount is too large, the seawater peel resistance is adversely affected.

  When the oxide pigment is added, the inorganic oxide layer has a structure in which the inorganic pigment is dispersed in the binder (continuous solid phase), but the above formula (1) is for the binder phase only. This is a condition that applies to

  The inorganic oxide layer can be formed by treating the steel with a chemical conversion treatment solution containing an aqueous aluminum phosphate solution and having a liquid phase composition excluding insoluble dispersed particles such as pigments that satisfies the above formula (1). For example, in an aluminum phosphate binder as disclosed in Patent Document 1, boron is added in an amount of 1 to 2 mass% in order to lower the firing temperature, and magnesium is added in an amount of 0.1 to improve water resistance and adhesion. Add 5-5 mass% each. Usually, oxides and hydroxides of B and Mg are dissolved in an aqueous solution of primary aluminum phosphate (aluminum biphosphate).

Magnesium oxide or magnesium oxide and orthophosphoric acid are added to and mixed with this aqueous solution, and μ and θ are adjusted to values satisfying the expression (1).
Since this aqueous solution is acidic, it can be dissolved by adding basic magnesium oxide, boron oxide or magnesium hydroxide, and the μ value can be increased. Further, when orthophosphoric acid is added, hydrogen ions increase and θ can be increased.
The advantage of using μ and θ is that they are calculated from the components of the dry film, and therefore do not depend on the dilution of the treatment liquid, pH, and the degree of dissociation of hydrogen ions.

  This treatment liquid is applied to the surface of the steel material by using a roller method or a spray method, and then baked to form an inorganic oxide layer. The baking temperature is not limited, but is in the range of 180 ° C. or higher and 500 ° C. or lower on the condition that the steel material does not change or melt. The ratio of μ / θ is the same as the ratio of the aqueous solution after baking and curing.

A heavy anticorrosion coating with an organic resin is formed on the inorganic oxide layer described above.
Since the heavy anticorrosion coating prevents corrosion by blocking corrosion factors (water, oxygen, electrolyte) from the steel material, it is preferable that the coating is thick. In order to achieve long-term durability, the thickness is at least 1.5 mm or more. Is desirable.

The type of organic resin used for the coating is not particularly limited, and any of the commonly used resins such as epoxy resins, fluororesins, acrylic resins, polyester resins, polyurethane resins, polyolefins (including any modified products) I just need it. In particular, polyethylene is excellent in terms of barrier properties, and polyurethane is excellent in that a thick film can be easily formed.
The organic resin layer may be either a single layer or a laminated layer, and examples thereof include a primer layer / adhesive layer / polyethylene layer or a primer layer / polyurethane layer.

  The top layer constituting the outermost steel material of the organic resin layer is important for the durability of the steel material. The top layer is the organic resin layer itself when the organic resin layer is a single layer, or the outermost organic resin layer when the organic resin layer is a laminated structure. The chemical conversion treatment layer used in the present invention is excellent in adhesion to the resin layer for a very long period of time, but if the top layer does not have sufficient durability, it will not have durability as a coated steel material. For this reason, the top layer needs to have a certain thickness or more, and actually, an organic resin layer of 1.5 mm or more is desired. Although 2 to 3 mm is recommended for a polyethylene resin excellent in durability, and 3 to 10 mm is recommended for a polyurethane resin capable of increasing the thickness, it is not particularly limited to these examples.

Hereinafter, the feasibility and effects of the present invention will be further described using examples.
Note that the conditions used in the examples are a condition example for the confirmation, and the present invention is not limited to these examples.

The steel material was plain steel having a thickness of 4 mm, and the surface was blasted to 3a (glossy surface from which rust was completely removed) by grid blasting.
In order to form an inorganic oxide layer on the surface of the steel material, it is mass%, Al ₂ O ₃ : 9%, P ₂ O ₅ : 31% , B ₂ O ₃ : 1.5% containing boric acid An aqueous solution of aluminum monophosphate (Al phosphate) was prepared, and magnesium oxide, or magnesium oxide and orthophosphoric acid were added to and mixed with this to prepare a treatment solution in which μ and θ were adjusted to various values. When the viscosity was high, water was added for adjustment. Moreover, the processing liquid which added the inorganic pigment to each processing liquid was also created.
Tables 1 and 2 show the composition of the treatment liquid, the value of μ / θ, and the type and amount of the added pigment.

This treatment liquid was applied to a steel material, dried, and then baked on the surface of the steel material at a PMT (maximum temperature reached) of 200 ° C. and a holding time of 0 minutes.
The chromate treatment performed for the comparative material was performed by baking a coating type trivalent chromate containing silica at 200 ° C. In this case, the chromium element adhesion amount is 500 mg / m ² .

The test for examining the solubility of the inorganic pigment was carried out by measuring the pH increase ΔpH when 8 mass% was added to the pH 2 phosphoric acid solution. The pH was read after 5 minutes. The results of testing several types of oxide pigments are shown in Table 3. In Table 1, when adding a pigment, a titania pigment (with TiO ₂ ) was used as an invention example, and a zinc oxide pigment (with ZnO) was used as a comparative example, and 30 mass% was added respectively.

Organic resin coating layers were formed in various thicknesses on the resulting inorganic oxide layer of steel as follows.
The polyurethane coating material is spray-coated and cured with a two-component mixed-curing urethane resin coating of polyol and isocyanate curing agent to a thickness of 60 μm as a primer, and a two-component cured urethane elastomer containing kaolin clay powder is sprayed on the surface. A polyurethane resin layer having a thickness of 3 mm or 0.5 mm was formed by coating. The created sample is denoted as PU.

  The polyethylene coating material first formed a primer layer with a one-part curable primer in which dicyandiamide and silica were added to a bisphenol A-based epoxy resin (60 μm). On the primer layer, a 300 μm maleic anhydride-modified polyolefin adhesive layer, a polyethylene resin layer having a thickness of 2 mm or 0.5 mm was sequentially laminated. This sample is referred to as PE.

  The seawater resistance of the samples obtained as described above was evaluated by the following seawater immersion acceleration test. First, a 1 × 7.5 cm coating is stripped along one side of a sample of about 7.5 cm square to expose the steel surface. The back and sides are sealed. It puts in the artificial seawater tank maintained at 50 degreeC, blows air bubbles from the bottom, and immerses the sample so that the bubbles may be applied. Two months later, the sample was taken out, the coating was removed, and the average peel distance from the end face from which the coating was peeled was determined. When all the coating peeled from the substrate, it was marked as 35 mm.

Tables 1 and 2 show the results. From Table 1, the example of the present invention in which the value of μ / θ is adjusted in the range of 0.8 to 1.1 has excellent seawater adhesion resistance compared to the comparative example in which the value of μ / θ is out of the range. It has been shown. In particular, it can be seen that the present invention example having a top layer thickness of 1.5 mm or more exhibits better seawater adhesion than the chromate material.
Tables 1 and 2 show that when an inorganic pigment whose pH increase when added to a phosphoric acid solution is 0.05 or less is added in a suitable range, the seawater adhesion resistance is further improved. ing. Furthermore, even with inorganic pigments having an increase in pH of 0.05 or less, it has been shown that when the amount added exceeds 50 mass%, the seawater resistance is deteriorated.

It is a figure for showing the relation between μ / θ and the peeling distance.

Claims (3)

In an organic resin-coated steel material in which an inorganic oxide layer composed of Al, P, Mg, B, O and H and an organic resin layer are sequentially laminated on the steel material surface, the element molar composition ratio of the inorganic oxide layer is as follows: An ultra-durable organic resin-coated steel material that satisfies the condition of formula (1).
μ / θ = 0.8 to 1.2 (1)
Here, the sum of products of the number of moles of ions of μ: Al, Mg, B and their valence
θ: Number of moles of hydrogen ions   The inorganic oxide layer contains an inorganic pigment whose pH increase after 5 minutes after addition of 8 mass% to a phosphoric acid solution having a pH of 2 at room temperature is 0.05 or less, and the content of the inorganic oxide layer is less than that of the inorganic oxide layer. The super-durable organic resin-coated steel material according to claim 1, which is 10 to 50 mass%.   The super-durable organic resin-coated steel material according to claim 1 or 2, wherein a top layer of the organic resin layer is a polyethylene resin layer or a polyurethane resin layer having a thickness of 1.5 mm or more.

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