JP6323424B2 - Surface-treated hot-dip galvanized steel sheet with excellent corrosion resistance - Google Patents

Description

  The present invention is a surface-treated hot-dip galvanized steel sheet used for automobiles, home appliances, building materials, etc., and does not contain a chromium compound such as hexavalent chromium in the surface-treated film, and is particularly resistant to corrosion and discoloration in a wet environment. The present invention relates to a surface-treated hot-dip galvanized steel sheet having excellent properties.

  Conventionally, for the purpose of improving the corrosion resistance (white rust resistance, red rust resistance) on the surface of galvanized steel sheets used for steel sheets for household appliances, steel sheets for building materials, and steel sheets for automobiles, chromic acid, dichromic acid or Steel sheets subjected to chromate treatment with a surface treatment solution containing salts as main components have been widely used. However, due to recent global environmental problems, there is an increasing demand for adopting non-polluted surface-treated steel sheets that do not depend on chromate treatment, so-called chromium-free treated steel sheets.

  Many technologies related to chromium-free treated steel sheets have already been proposed. Technologies aiming at the passivating action of molybdic acid and tungstic acid belonging to the same group IVA as chromic acid, such as Ti, Zr, V, Mn, Ni, Co, etc. Using technology using metal salts of rare earth elements such as transition metals and La, Ce, technology based on chelating agents such as polyphenolic carboxylic acids such as tannic acid and compounds containing S and N, using silane coupling agents A technique for forming a polysiloxane film or a technique combining these techniques has been proposed.

Specific examples are as follows.
(1) Technology for forming a film from a treatment liquid containing a coating agent obtained by reacting an organic resin such as a polyvinylphenol derivative, an acid component, and an epoxy compound, a silane coupling agent, and a vanadium compound (Patent Document 1) ~ 4)
(2) Technology for forming a film containing an aqueous resin, a thiocarbonyl group, a vanadic acid compound, and phosphoric acid (Patent Document 5)
(3) Technology for forming a film from a treatment liquid containing a metal compound such as Ti and inorganic and organic acids such as fluoride and phosphate compounds (Patent Documents 6 to 12)
(4) Technology to form a composite film of rare earth elements such as Ce, La, Y, etc. and Ti, Zr elements, and to concentrate the oxide layer on the plating interface side and the hydroxide layer on the surface side in the film (patent Document 13) and technology for forming a composite film of Ce and Si oxide (Patent Document 14)

(5) Technology for forming an organic composite coating comprising a phosphoric acid and / or phosphoric acid compound film containing an oxide in the lower layer and a resin film on the upper layer (Patent Documents 15 and 16)
(6) Technology for forming a composite film comprising a specific inhibitor component and a silica / zirconium compound (Patent Document 17)
(7) Technology for forming a composite film comprising a water-soluble zirconium compound, a tetraalkoxysilane, a compound having an epoxy group, a chelating agent, vanadic acid, and a predetermined metal compound (Patent Document 18)
(8) Technology for forming a composite film composed of a specific silane compound, zirconium carbonate compound, vanadic acid compound, and nitric acid compound (Patent Document 19)

JP 2003-13252 A JP 2001-181860 A JP 2004-263252 A Japanese Patent Laid-Open No. 2003-155542 Japanese Patent No. 3549455 Japanese Patent No. 3302677 JP 2002-105658 A JP 2004-183015 A JP 2003-171778 A JP 2001-271175 A JP 2006-213958 A JP 2005-48199 A JP 2001-234358 A Japanese Patent No. 3596665 JP 2002-53980 A JP 2002-53979 A JP 2008-169470 A JP 2010-255105 A JP 2013-60647 A

  Films formed by these technologies aim to suppress the occurrence of zinc white rust by the combined addition of organic or inorganic components. For example, the technologies (1) and (2) above are mainly used. Corrosion resistance is ensured by adding an organic resin. However, such an organic resin film has a problem of discoloration due to resin deterioration in an outdoor environment or a high-temperature and high-humidity environment. Moreover, high temperature baking is essential for film formation, and corrosion resistance cannot be ensured when it is produced by simple dryer drying that can ensure drying conditions of a plate reaching temperature of 30 ° C. or higher.

In the techniques (3) and (4), an inorganic single film that does not contain any organic component has been proposed. However, these metal oxide / metal hydroxide composite films cannot provide sufficient corrosion resistance to the galvanized steel sheet unless the film is thickened. That is, when manufactured by simple dryer drying, drying becomes insufficient, and corrosion resistance cannot be ensured.
The technique (5) has the same problems as the techniques (1) and (2) because a resin film is used as an upper layer in order to ensure corrosion resistance.

  In the technique of (6) above, a passivating action of a vanadate compound and a hardly soluble metal salt by a phosphate compound are used as an inhibitor component, and a composite film of a zirconium compound, fine particle silica, and a silane coupling agent is used as a skeleton film. By forming it, excellent corrosion resistance is expressed. However, with this technique, sufficient corrosion resistance cannot be imparted to the galvanized steel sheet unless the film is thickened. That is, when manufactured by simple dryer drying, drying becomes insufficient, and corrosion resistance cannot be ensured.

With the technologies (7) and (8), it is possible to provide a galvanized steel sheet that is thin and excellent in corrosion resistance. However, it is not possible to obtain discoloration resistance in a wet environment. It was found that the resistance to discoloration in a humid environment cannot be achieved.
As described above, it has been found that the chromium-free treated steel plates proposed so far cannot achieve both the corrosion resistance of the flat plate portion and the discoloration resistance in a wet environment.

  Therefore, the object of the present invention is to solve the problems of the prior art as described above, and to provide a high corrosion resistance and discoloration resistance in a wet environment with a thin film that does not contain a chromium compound such as hexavalent chromium in the surface treatment film. The object is to provide a surface-treated hot-dip galvanized steel sheet that can be made compatible and can be manufactured with simple equipment.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have developed a specific silane compound as a first layer film on the surface of a hot-dip galvanized steel sheet in which an Al oxide layer is formed on the galvanized surface layer. Then, a surface treatment film is formed by a surface treatment liquid in which a zirconium carbonate compound, a vanadic acid compound, and water are blended at a specific ratio, and a specific organic polymer resin is used as a base layer resin as a second layer film on the surface treatment liquid. The present inventors have found that the above problems can be solved by forming an organic film in which an appropriate amount of a specific self-repairing substance is blended in the base resin.

The present invention has been made on the basis of such knowledge and has the following gist.
[1] A silane coupling agent (a1) having a glycidyl group on the surface of a hot dip galvanized steel sheet on which an Al oxide layer having a thickness of 0.5 nm or more and less than 10.0 nm is formed on the surface layer of the galvanized layer, tetra A silane compound (A) having a hydrolyzable group obtained from alkoxysilane (a2) and phosphonic acid (a3), a zirconium carbonate compound (B), a vanadic acid compound (C), and water, A surface treatment film formed by applying a surface treatment solution satisfying the conditions (i) to (iii) and drying, and having a surface treatment film with an adhesion amount per side of 100 to 800 mg / m ² ,
(I) The silane compound (A) is 30 to 70% by mass in the total solid content of the surface treatment liquid.
(Ii) The ratio (B / A) of the mass of the zirconium carbonate compound (B) in terms of ZrO _{2 and the} mass of the silane compound (A) is 0.3 to 2.0.
(Iii) The ratio (C / A) of the V-converted mass of the vanadic acid compound (C) to the mass of the silane compound (A) is from 0.010 to 0.15.
An organic polymer resin (α) having an OH group and / or COOH group is used as a base resin as a second layer film on the upper part thereof, and the following (a) to (e) with respect to 100 parts by mass (solid content) of the base resin: 1) at least one type of rust preventive additive (β) selected from 1 to 100 parts by mass (solid content) and having a film thickness of 0.1 to 5 μm Surface-treated galvanized steel sheet.
(A) Phosphate (b) Ca ion exchange silica (c) Molybdate (d) Silicon oxide (e) One or more kinds selected from triazoles, thiols, thiadiazoles, thiazoles, thiurams Organic compounds

[2] Silane coupling agent (a1) having a glycidyl group on the surface of a hot dip galvanized steel sheet having an Al oxide layer having a thickness of 0.5 nm or more and less than 10.0 nm formed on the surface of the galvanized layer, tetra A silane compound (A) having a hydrolyzable group obtained from alkoxysilane (a2) and phosphonic acid (a3), a zirconium carbonate compound (B), a vanadic acid compound (C), and water, A surface treatment film satisfying the conditions (i) to (iii) is applied and dried to form a surface treatment film having an adhesion amount per side of 100 to 800 mg / m ² .
(I) The silane compound (A) is 30 to 70% by mass in the total solid content of the surface treatment liquid.
(Ii) The ratio (B / A) of the mass of the zirconium carbonate compound (B) in terms of ZrO _{2 and the} mass of the silane compound (A) is 0.3 to 2.0.
(Iii) The ratio (C / A) of the V-converted mass of the vanadic acid compound (C) to the mass of the silane compound (A) is from 0.010 to 0.15.
An organic polymer resin (α) having an OH group and / or COOH group is used as a base resin on the surface of the surface treatment film, and the following (a) to (e) with respect to 100 parts by mass (solid content) of the base resin: By applying a coating composition containing 1 to 100 parts by mass (solid content) of at least one rust-preventing additive component (β) selected from among the above, the film thickness is 0.1 A method for producing a surface-treated hot-dip galvanized steel sheet, comprising forming a 5 μm organic film.
(A) Phosphate (b) Ca ion exchange silica (c) Molybdate (d) Silicon oxide (e) One or more kinds selected from triazoles, thiols, thiadiazoles, thiazoles, thiurams Organic compounds

  The surface-treated hot-dip galvanized steel sheet of the present invention is higher due to the combination of the Al oxide layer of the galvanized surface layer and the surface treatment film containing a specific component, and further the combination of a specific organic film on the upper layer. Barrier properties are obtained, corrosion resistance comparable to that of chromate film and discoloration resistance in a wet environment can be achieved at a high level, and can be manufactured with simple equipment.

The hot dip galvanized steel sheet used in the present invention is not particularly limited as long as it can be obtained by hot dip galvanization, but is usually a hot dip galvanized steel sheet (GI) or an alloyed hot dip galvanized steel sheet obtained by alloying it ( GA) is used.
An Al oxide layer having a thickness of 0.5 nm or more and less than 10.0 nm needs to be formed on the surface layer of the galvanized layer of the hot dip galvanized steel sheet. In hot dip galvanization, since a trace amount of Al is contained in the plating bath, a small amount of Al is contained in the galvanized layer, but Al contained in the galvanized layer has a strong affinity for oxygen. Therefore, an Al oxide layer is formed on the galvanized surface layer.

If the thickness of the Al oxide layer is less than 0.5 nm, sufficient corrosion resistance and discoloration resistance in a wet environment cannot be obtained. On the other hand, if it exceeds 10.0 nm, the adhesion to the film is lowered, so that the corrosion resistance is not. In addition, since the soluble components after the film formation increases as the adhesiveness decreases, the discoloration resistance in a wet environment decreases.
The thickness of the Al oxide layer is not only affected by the Al content of the galvanized layer, but can also be increased by leaving the hot-dip galvanized steel sheet in the air or heating it at several hundred degrees Celsius. By adjusting the above conditions (conditions for leaving in the atmosphere, heating conditions, etc.), the thickness can be adjusted to be thicker. On the other hand, the thickness of the Al oxide layer can be reduced by chemical etching by alkali degreasing or surface grinding. Therefore, for example, in the alkaline degreasing performed as a pretreatment for the surface treatment on the hot-dip galvanized steel sheet, the thickness of the Al oxide layer can be adjusted by adjusting the concentration of the alkaline degreasing solution and the treatment time.
The thickness of the Al oxide layer can be measured by cross-sectional TEM observation. In the present invention, the average value of the measurement values at five randomly selected points is used as the thickness of the Al oxide layer.

The surface-treated hot-dip galvanized steel sheet of the present invention is obtained by applying a surface treatment liquid containing a specific component to the surface of the hot-dip galvanized steel sheet (the surface of the galvanized layer having an Al oxide layer formed on the surface layer). It has a surface treatment film formed by drying, and has an organic film containing a specific base resin and an anticorrosive additive component as a second layer film on the top.
Hereinafter, the surface treatment film formed as the first layer film on the surface of the hot dip galvanized steel sheet will be described.

  The surface treatment liquid for forming a surface treatment film used in the present invention is a silane having a hydrolyzable group obtained from a silane coupling agent (a1) having a glycidyl group, a tetraalkoxysilane (a2) and a phosphonic acid (a3). A compound (A), a zirconium carbonate compound (B), a vanadate compound (C), and water are contained. This surface treatment liquid does not contain a chromium compound such as hexavalent chromium (excluding chromium compounds contained as inevitable impurities).

The silane compound (A) having a hydrolyzable group is obtained by reacting a phosphonic acid (a3) with a low condensate of a silane coupling agent (a1) having a glycidyl group and a tetraalkoxysilane (a2). Compound.
The silane compound (A) is a silane compound having a hydrolyzable group directly bonded to Si element, and the hydrolyzable group forms a silanol group by reacting with moisture. The silane compound (A) may be a group in which all of the groups bonded to the Si element are hydrolyzable groups, or a part of the groups bonded to the Si element may be hydrolyzable groups.

  The silane coupling agent (a1) having a glycidyl group contains a glycidyl group and a lower alkoxyl group having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms, as a hydrolyzable group in one molecule containing Si. If it exists, it will not specifically limit, For example, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-glycidoxypropylmethyl dimethoxysilane, 2- (3,4 epoxy cyclohexyl) ethyl Examples thereof include triethoxysilane, and one or more of these can be used.

The tetraalkoxysilane (a2) contains four lower alkoxyl groups as hydrolyzable groups, and has a general formula Si (OR) ₄ (wherein R is the same or different alkyl group having 1 to 5 carbon atoms). Group) is not particularly limited, and examples thereof include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane, and one or more of these can be used.
Examples of the phosphonic acid (a3) include hydroxyethylene diphosphonic acid, nitrilotris (methylenephosphonic acid), phosphonobutanetricarboxylic acid, and ethylenediaminetetra (methylenephosphonic acid). One or more of these may be used. it can.

  The silane compound (A) having a hydrolyzable group includes a low condensate of the above-described silane coupling agent (a1) having a glycidyl group and tetraalkoxysilane (a2). This low condensate has a polysiloxane bond formed by the condensation reaction of the silane coupling agent (a1) and the tetraalkoxysilane (a2) as the main skeleton, and the terminal group bonded to the Si element is hydrolyzed. It may be a functional group, or a part of the group bonded to the Si element may be hydrolyzable.

As the silane compound (A) having a hydrolyzable group, a compound having a condensation degree of 2 to 30 can be used, and a compound having a condensation degree of 2 to 10 is particularly preferable. This is because if the degree of condensation is 30 or less, no white precipitation occurs and a stable silane compound (A) is obtained.
The silane compound (A) having a hydrolyzable group is prepared by combining a low condensate of a silane coupling agent (a1) and a tetraalkoxysilane (a2) with a phosphonic acid (a3) at a reaction temperature of 1 to 80 ° C. It can be obtained by reacting for about 20 minutes to 20 minutes and performing autoclaving.

In the silane compound (A) having a hydrolyzable group, the specific and condensed state of the hydrolyzable group can be measured using gel permission chromatography (GPC), NMR and IR.
The silane compound (A) having a hydrolyzable group is obtained by reacting a silane coupling agent (a1) having a glycidyl group, a tetraalkoxysilane (a2), and a phosphonic acid (a3). It is considered that (a1) and tetraalkoxysilane (a2) are coordinated by hydrolysis with water and phosphonic acid (a3). This hydrolysis reaction and coordination by phosphonic acid (a3) are obtained at the same time, and a silane compound that has extremely high stability at room temperature and can withstand long-term storage is produced.

  Phosphonic acid (a3) is also an effective component for securing corrosion resistance and storage stability. Although the reason is not necessarily clear, it is considered that the phosphonic acid (a3) coordinates to the silane coupling agent (a1) and the tetraalkoxysilane (a2), and the silane compound (A) is a polymer in the surface treatment liquid. It is thought that it has an action to suppress the formation of the material, and the quality at the time of preparation is maintained without deterioration even when the surface treatment liquid is stored for a long time after preparation due to such action. it is conceivable that. In addition, phosphonic acid (a3) is considered to coordinate with the vanadate compound (C) described later, and it is considered that vanadium dissolves in a corrosive environment to form a polysiloxane bond again.

The blending ratio of the silane coupling agent (a1) having a glycidyl group, the tetraalkoxysilane (a2), and the phosphonic acid (a3) is based on 100 parts by mass of the silane coupling agent (a1) from the viewpoint of corrosion resistance. The tetraalkoxysilane (a2) is preferably 25 to 75 parts by mass and the phosphonic acid (a3) is preferably 5 to 30 parts by mass.
Content of the silane compound (A) in a surface treatment liquid shall be 30-70 mass% in the total solid of a surface treatment liquid. If the content of the silane compound (A) is less than 30% by mass, the corrosion resistance cannot be ensured. On the other hand, if the content exceeds 70% by mass, the corrosion resistance decreases.
By mixing with the zirconium carbonate compound (B), the silane compound (A) has a barrier effect that does not dissolve again in water once dried.

  Examples of the zirconium carbonate compound (B) include salts of zirconium carbonate such as sodium, potassium, lithium, and ammonium (for example, zirconium ammonium carbonate, sodium zirconium carbonate, lithium zirconium carbonate), and one or more of these are used. be able to. Of these, ammonium zirconium carbonate is preferable from the viewpoint of corrosion resistance.

The content of the zirconium carbonate compound (B) is such that the ratio (B / A) of the mass of ZrO ₂ converted to ZrO ₂ (ZrO ₂ converted mass) of the zirconium carbonate compound (B) and the mass of the silane compound (A) is 0. 3 to 2.0, preferably 0.35 to 1.5. If the mass ratio (B / A) is less than 0.3, corrosion resistance cannot be ensured. On the other hand, if the mass ratio (B / A) exceeds 2.0, the corrosion resistance decreases. Moreover, when mass ratio (B / A) exceeds 2.0, the discoloration resistance in a humid environment will also fall.

The vanadic acid compound (C) is present in the film formed on the surface of the zinc-based plated steel sheet, uniformly dispersed in a form that is easily dissolved in water, and exhibits a so-called inhibitor effect during zinc corrosion. In addition, the vanadic acid compound (C) is considered to be coordinated to the phosphonic acid (a3), and the vanadic acid compound (C) is excellent in that it is ionized and passivated in a corrosive environment. Demonstrate corrosion resistance.
Examples of the vanadic acid compound (C) include ammonium metavanadate, sodium metavanadate, vanadyl acetylacetonate, and one or more of these can be used.

  The content of the vanadic acid compound (C) is such that the ratio (C / A) of the V-converted mass of the vanadic acid compound (C) to the mass of the silane compound (A) is 0.010 to 0.15, Preferably it is set to 0.030-0.10. If the mass ratio (C / A) is less than 0.010, corrosion resistance cannot be ensured. On the other hand, if the mass ratio (C / A) exceeds 0.15, discoloration resistance in a wet environment is lowered.

A lubricant can be added to the surface treatment liquid in order to improve the lubricating performance. Examples of the lubricant include polyethylene wax, oxidized polyethylene wax, oxidized polypropylene wax, carnauba wax, paraffin wax, montan wax, rice wax, Teflon (registered trademark) wax, carbon disulfide, and graphite. Can be used.
The content of the lubricant is preferably 1 to 10% by mass, and more preferably 3 to 7% by mass in the total solid content of the surface treatment liquid. When the content of the lubricant is 1% by mass or more, an effect of improving the lubrication performance is obtained, and when it is 10% by mass or less, the corrosion resistance of the galvanized steel sheet is not lowered.

In addition, the surface treatment liquid contains a thickener for improving workability, a conductive substance for improving conductivity, a color pigment for improving design properties, a solvent for improving film forming property, and the like. You may add suitably as needed.
The surface treatment liquid can be obtained by mixing the above-described components in water such as deionized water or distilled water. What is necessary is just to select the solid content concentration of a surface treatment liquid suitably. Moreover, you may add alcohol, a ketone, a cellosolve-type water-soluble solvent, an antifoamer, a fungicidal agent, a coloring agent, etc. to a surface treatment liquid as needed. However, it is important to add these components (that is, components (A) to (C), water, and an additive component other than the lubricant) to the extent that the performance obtained in the present invention is not impaired. The total solid content is preferably less than 5% by mass.

The adhesion amount per one side of the surface treatment film is 100 to 800 mg / m ² , preferably 200 to 500 mg / m ² . If the coating amount per side is less than 100 mg / m ² , there is a concern about insufficient corrosion resistance. On the other hand, if it exceeds 800 mg / m ² , production with simple equipment such as dryer drying becomes difficult.

The surface-treated hot-dip galvanized steel sheet of the present invention is coated on the surface of the hot-dip galvanized steel sheet in which the Al oxide layer is formed on the surface of the galvanized surface, and then dried, so that one side after drying It is manufactured so that the amount of adhesion per unit is 100 to 800 mg / m ² .
As a method for applying the surface treatment liquid to the surface of the hot-dip galvanized steel sheet, any method such as a roll coating method, a bar coating method, a dipping method, a spray coating method, or the like can be employed. What is necessary is just to select an optimal method suitably according to the shape etc. of the hot dip galvanized steel plate to be processed. For example, if the hot dip galvanized steel sheet to be processed is a sheet, then roll coating or bar coating, or spraying a surface treatment solution on the surface of the hot dip galvanized steel sheet, and then spraying with a roll squeezing or gas at a high pressure. It is appropriate to use a spray coating method that adjusts the amount. Moreover, when the hot dip galvanized steel sheet is a molded product, a method of adjusting the coating amount by immersing it in a surface treatment liquid and pulling it up and blowing off excess surface treatment liquid with compressed air as necessary is suitable.

  In addition, before applying the surface treatment liquid to the hot dip galvanized steel sheet, pretreatment for the purpose of removing oil and dirt on the hot dip galvanized steel sheet surface may be performed as necessary. The pretreatment method is not particularly limited, and examples thereof include hot water washing, solvent washing, and alkaline degreasing washing. Hot-dip galvanized steel sheets are often coated with rust-preventive oil for the purpose of rust-prevention, and even when rust-preventive oil is not applied, the surface has oil or dirt attached during work. . By performing the above pretreatment, the surface of the galvanized layer is cleaned and easily wetted uniformly. When the surface treatment liquid gets wet uniformly on the surface of the hot dip galvanized steel sheet, pretreatment is not particularly necessary.

  Although there is no restriction | limiting in particular in the heating temperature at the time of drying after apply | coating a surface treatment liquid (maximum ultimate board temperature), Usually, it is about 30-200 degreeC. If the heating temperature is 30 ° C. or higher, no moisture remains in the film, and if the heating temperature is 200 ° C. or lower, the generation of cracks in the film is suppressed. This is because there is no problem. The heating time is appropriately selected depending on the type of hot-dip galvanized steel sheet used. From the viewpoint of productivity and the like, about 0.1 to 60 seconds is preferable, and about 1 to 30 seconds is more preferable.

  The surface-treated hot-dip galvanized steel sheet of the present invention has the advantage that the surface-treated film does not contain a chromium compound, has excellent corrosion resistance and resistance to discoloration in a wet environment, and can be manufactured with simple equipment. . The reason for such excellent performance is not necessarily clear, but is considered to be due to the following effects.

  In the present invention, it is considered that a high barrier property can be obtained by the effect of combining the Al oxide layer and the surface treatment film existing on the surface layer of the galvanizing. In the conventional chromate film, a film is formed by the reaction of chromic acid with zinc, so that a higher corrosion resistance is obtained when the Al oxide layer is not present on the plating surface layer. On the other hand, in the case of having a chromate-free film, particularly a surface-treated film that does not form many reaction layers with zinc as in the present invention, if the Al oxide layer is present on the plating surface layer with a certain thickness or more, the Al oxide It is considered that the barrier effect possessed by the layer itself and the following effects by the surface treatment film formed by the specific surface treatment liquid are combined to obtain excellent corrosion resistance. Moreover, if the thickness of the Al oxide layer is excessive, the reactivity with the chemical conversion solution decreases, so the soluble components after film formation increase, and the discoloration resistance in a wet environment is considered to decrease. .

  First, among the components of the surface treatment liquid, the skeleton of the coating formed on the surface of the galvanized layer is constituted by the silane compound (A) and the zirconium carbonate compound (B). The hydrolyzable group of the silane compound (A) is considered to fix the coating component by reacting with the surface of the galvanized layer and three-dimensionally crosslink with the zirconium carbonate compound (B). Furthermore, it is considered that the glycidyl group of the silane coupling agent (a1) also reacts with the surface of the galvanized layer, and the bond strength of the film becomes stronger. The surface treatment film formed in this way, once dried, does not dissolve in water again and has a barrier effect, so that excellent corrosion resistance is obtained in combination with the barrier effect of the Al oxide layer. Further, since the film is not formed by a crosslinking reaction that requires a temperature like a resin, the film can be appropriately formed even by a simple drying means such as dryer drying.

  Among the components of the surface treatment liquid, the vanadic acid compound (C) is present in the film in a form that is easily dispersed in a form that is easily soluble in water, and exhibits a so-called inhibitory effect during zinc corrosion. That is, it is considered that the vanadic acid compound (C) is partially ionized and passivated in a corrosive environment, thereby suppressing zinc corrosion itself. Moreover, since it coordinates to phosphonic acid (a3), after ionization, the hydrolyzable group of the silane compound (A) is three-dimensionally cross-linked, thereby repairing a film defect portion and suppressing corrosion of zinc. Conceivable.

  That is, the surface treatment liquid forms a dense film with the silane compound (A) and the zirconium carbonate compound (B) to obtain high corrosion resistance, and contains a vanadate compound (C) as a corrosion inhibitor in the film. Thus, a dense film following the hot dip galvanized steel sheet can be formed.

Next, the organic film formed as the second layer film on the surface treatment film (first layer film) will be described.
The organic film formed on the upper part of the first layer film includes an organic polymer resin (α) having an OH group and / or COOH group as a base resin, and the following (a) to (e) as self-repairing substances. ) And one or more rust preventive additive components (β) selected from (preferably included as a main component). In addition, this organic film does not contain chromium compounds such as hexavalent chromium (however, excluding chromium compounds contained as inevitable impurities).
(A) Phosphate (b) Ca ion exchange silica (c) Molybdate (d) Silicon oxide (e) One or more kinds selected from triazoles, thiols, thiadiazoles, thiazoles, thiurams Organic compounds

  As the base resin for the organic film, an organic polymer resin (α) having an OH group and / or a COOH group is used. Among them, a thermosetting resin is preferable, and an epoxy resin or a modified epoxy resin is particularly preferable. Among them, thermosetting epoxy resins and modified epoxy resins that have excellent barrier properties against corrosion factors such as oxygen are the most suitable, and in particular, the amount of coating to obtain high conductivity and spot weldability. It is particularly advantageous when the level is low. Examples of organic polymer resins having OH groups and / or COOH groups include epoxy resins, polyhydroxy polyether resins, acrylic copolymer resins, ethylene-acrylic acid copolymer resins, alkyd resins, polybutadiene resins, and phenols. Examples thereof include resins, polyurethane resins, polyamine resins, polyphenylene resins, and mixtures or addition polymers of two or more of these resins.

(1) Epoxy resin As an epoxy resin, an epoxy resin obtained by glycidyl etherification of bisphenol A, bisphenol F, novolak, etc., an epoxy resin obtained by adding propylene oxide, ethylene oxide or polyalkylene glycol to bisphenol A, and further, An aliphatic epoxy resin, an alicyclic epoxy resin, a polyether epoxy resin, or the like can be used.
These epoxy resins preferably have a number average molecular weight of 1500 or more, particularly when curing at low temperatures is required. In addition, the said epoxy resin can also be used individually or in mixture of a different kind.

  Examples of the modified epoxy resin include resins obtained by reacting various modifiers with the epoxy group or bidoxyl group in the epoxy resin. For example, an isocyanate compound is reacted with an epoxy ester resin reacted with a carboxyl group in a drying oil fatty acid, an epoxy acrylate resin modified with acrylic acid, methacrylic acid, or the like, a urethane-modified epoxy resin reacted with an isocyanate compound, or an epoxy resin. Examples thereof include amine-added urethane-modified epoxy resins obtained by adding alkanolamines to urethane-modified epoxy resins.

  The polyhydroxy polyether resin is a polycondensation of a mononuclear or binuclear dihydric phenol or a mixed dihydric phenol of mononuclear and binuclear with an approximately equimolar amount of epihalohydrin in the presence of an alkali catalyst. It is a polymer obtained by making it. Representative examples of mononuclear dihydric phenols include resorcin, hydroquinone, and catechol. Representative examples of dinuclear phenols include bisphenol A. These may be used alone or in combination of two or more. May be.

(2) Urethane resin Examples of the urethane resin include an oil-modified polyurethane resin, an alkyd polyurethane resin, a polyester polyurethane resin, a polyether urethane resin, and a polycarbonate polyurethane resin.
(3) Alkyd resin Examples of alkyd resins include oil-modified alkyd resins, rosin-modified alkyd resins, phenol-modified alkyd resins, styrenated alkyd resins, silicon-modified alkyd resins, acrylic-modified alkyd resins, oil-free alkyd resins, and high molecular weight oils. A free alkyd resin etc. can be mentioned.

(4) Acrylic resin Examples of the acrylic resin include polyacrylic acid and copolymers thereof, polyacrylic acid esters and copolymers thereof, polymethacrylic acid esters and copolymers thereof, polymethacrylic acid esters and copolymers thereof. Examples include polymers, urethane-acrylic acid copolymers (or urethane-modified acrylic resins), styrene-acrylic acid copolymers, and these resins were further modified with other alkyd resins, epoxy resins, phenol resins, and the like. A resin may be used.

(5) Ethylene resin (polyolefin resin)
Examples of ethylene resins include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene copolymers such as carboxyl-modified polyolefin resins, ethylene-unsaturated carboxylic acid copolymers, ethylene ionomers, and the like. Furthermore, resins obtained by modifying these resins with other alkyd resins, epoxy resins, phenol resins, or the like may be used.

(6) Acrylic Silicon Resin Examples of the acrylic silicon resin include those containing a hydrolyzable alkoxysilyl group at the side chain or terminal of the acrylic copolymer as a main agent and added with a curing agent. When these acrylic silicon resins are used, excellent weather resistance can be expected.
(7) Fluororesin Fluororesin includes fluoroolefin copolymers, such as alkyl vinyl ether, synchroalkyl vinyl ether, carboxylic acid-modified vinyl ester, hydroxyalkyl allyl ether, tetrafluoropropyl vinyl ether and the like as monomers. And a copolymer obtained by copolymerizing a fluorine monomer (fluoroolefin). When these fluororesins are used, excellent weather resistance and excellent hydrophobicity can be expected.

For the purpose of lowering the drying temperature of the resin, it is possible to use a core / shell type water-dispersible resin made of a resin having different resin types or different glass transition temperatures in the core portion and the shell portion of the resin particles.
In addition, by using a water-dispersible resin having self-crosslinkability, for example, by adding an alkoxysilane group to the resin particles, silanol groups are generated by hydrolysis of the alkoxysilane when the resin is heated and dried, and silanol groups between the resin particles Interparticle cross-linking utilizing the dehydration condensation reaction can be used.
Further, as the resin used for the organic film, an organic composite silicate in which an organic resin is combined with silica through a silane coupling agent is also suitable.

  In the present invention, it is particularly desirable to use a thermosetting resin for the purpose of improving the corrosion resistance and workability of the organic film. In this case, a curing agent such as urea resin (butylated urea resin, etc.), melamine resin (butylated melamine resin), butylated urea / melamine resin, benzoguanamine resin, etc., blocked isocyanate, oxazoline compound, phenol resin, etc. can do.

  Among the organic resins described above, in view of corrosion resistance, workability, and paintability, epoxy resins and ethylene resins are preferable, and thermosetting epoxy having excellent blocking properties against corrosion factors such as enzymes, in particular. Resins and modified epoxy resins are particularly suitable. These thermosetting resins include thermosetting epoxy resins, thermosetting modified epoxy resins, acrylic copolymer resins copolymerized with epoxy group-containing monomers, polybutadiene resins having epoxy groups, and polyurethane resins having epoxy groups. And adducts or condensates of these resins, and one of these epoxy group-containing resins can be used alone or in admixture of two or more.

Next, the antirust additive component (β), which is a self-repairing substance, will be described.
The phosphate which is the said component (a) contains all kinds of salts, such as a single salt and a double salt. Moreover, there is no limitation in the metal cation which comprises it, and any metal cation, such as zinc phosphate, magnesium phosphate, calcium phosphate, and aluminum phosphate, may be used. Further, there is no limitation on the skeleton or the degree of condensation of phosphate ions, and any of normal salt, dihydrogen salt, monohydrogen salt or phosphite may be used. In addition, orthophosphate may be polyphosphate other than orthophosphate. Includes all condensed phosphates such as salts.

  Moreover, corrosion resistance can further be improved by adding a calcium compound together with the phosphate which is the said component (a). The calcium compound may be any of calcium oxide, calcium hydroxide, and calcium salt, and one or more of these can be used. In addition, there are no particular restrictions on the type of calcium salt. In addition to simple salts containing only calcium as a cation such as calcium silicate, calcium carbonate, and calcium phosphate, calcium and calcium such as calcium phosphate / zinc, calcium phosphate / magnesium, etc. Double salts containing other cations may be used.

Moreover, the Ca ion exchange silica which is said component (b) is what fixed the calcium ion on the surface of the porous silica gel powder, Ca ion is discharge | released in a corrosive environment, and forms a precipitation film | membrane.
Any Ca ion-exchanged silica can be used, but those having an average particle size of 6 μm or less, preferably 4 μm or less are preferable, and for example, those having an average particle size of 2 to 4 μm can be used. When the average particle size of the Ca ion exchange silica exceeds 6 μm, the corrosion resistance is lowered and the dispersion stability in the coating composition is lowered.
The Ca concentration in the Ca ion-exchanged silica is 1% by mass or more, preferably 2 to 8% by mass. When the Ca concentration is less than 1% by mass, the rust prevention effect due to Ca release cannot be obtained sufficiently. The surface area, pH, and oil absorption amount of the Ca ion exchange silica are not particularly limited.

  As the Ca ion exchange silica as described above, W.R.Grace & Co. SHIELDEX C303 (average particle size 2.5 to 3.5 μm, Ca concentration 3% by mass), SHIELDEX AC3 (average particle size 2.3 to 3.1 μm, Ca concentration 6% by mass), SHIELDEX AC5 (average particle size) 3.8-5.2 μm, Ca concentration 6% by mass (all are trade names), SHIELDEX (average particle size 3 μm, Ca concentration 6-8% by mass) manufactured by Fuji Silysia Chemical Ltd., SHIELDEX SY710 ( An average particle size of 2.2 to 2.5 μm and a Ca concentration of 6.6 to 7.5% by mass) (all are trade names) can be used.

The molybdate that is the component (c) is not limited in its skeleton and degree of condensation, and examples thereof include orthomolybdate, paramolybdate, and metamolybdate. Moreover, all salts, such as a single salt and a double salt, are included, and phosphoric acid molybdate etc. are mentioned as a double salt.
The silicon oxide as the component (d) may be either colloidal silica or dry silica. When colloidal silica is based on a water-based film-forming resin, for example, Snowtex O, Snowtex N, Snowtex 20, Snowtex 30, Snowtex 40, Snowtex C manufactured by Nissan Chemical Industries, Ltd. , Snowtex S (above, all are trade names), Cataloid S, Cataloid SI-350, Cataloid SI-40, Cataloid SA, Cataloid SN (above, all are trade names) manufactured by Catalytic Kasei Kogyo Co., Ltd., Asahi Denka Adelite AT-20-50 manufactured by Kogyo Co., Ltd., Adelite AT-20N, Adelite AT-300, Adelite AT-300S, Adelite AT20Q (all are trade names) and the like can be used.

  In addition, when the solvent-based film forming resin is used as a base, for example, organosilica sol MA-ST-M, organosilica sol IPA-ST, organosilica sol EG-ST, organosilica sol E-ST manufactured by Nissan Chemical Industries, Ltd. -ZL, organosilica sol NPC-ST, organosilica sol DMAC-ST, organosilica sol DMAC-ST-ZL, organosilica sol XBA-ST, organosilica sol MIBK-ST (all are trade names), manufactured by Catalyst Kasei Kogyo Co., Ltd. OSCAL-1132, OSCAL-1232, OSCAL-1332, OSCAL-1432, OSCAL-1532, OSCAL-1632, OSCAL-1722 (all of which are trade names) can be used.

In particular, the organic solvent-dispersed silica sol is excellent in dispersibility and superior in corrosion resistance than fumed silica.
Examples of the fumed silica include AEROSIL R971, AEROSIL R812, AEROSIL R811, AEROSIL R974, AEROSIL R202, AEROSIL R805, AEROSIL 130, AEROSIL 200, AEROSIL 300, and more from AEROSIL 300CF manufactured by Nippon Aerosil Co., Ltd. Can also be used.

The fine-particle silica contributes to the formation of a dense and stable zinc corrosion product in a corrosive environment, and the corrosion product is considered to be able to suppress the promotion of corrosion by being densely formed on the plating surface. It has been.
From the viewpoint of corrosion resistance, it is preferable to use fine silica particles having a particle diameter of 5 to 50 nm, desirably 5 to 20 nm, more preferably 5 to 15 nm.

  Among the organic compounds of the component (e), triazoles include 1,2,4-triazole, 3-amino-1,2,4-triazole, 3-mercapto-1,2,4-triazole, 5- Amino-3-mercapto-1,2,4-triazole, 1H-benzotriazole, etc., and thiols include 1,3,5-triazine-2,4,6-trithiol, 2-mercaptobenzimidazole, etc. The thiadiazoles include 5-amino-2-mercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole, and the thiazoles include 2-N, N -Diethylthiobenzothiazole, 2-mercaptobenzothiazole, etc., and thiurams include tetraethylthiuramdisulfur Such as soil, and the like, respectively.

  The total amount of the antirust additive component (β) in the organic film (the total amount of one or more self-repairing substances selected from the components (a) to (e)) is: It is 1-100 mass parts (solid content) with respect to 100 mass parts (solid content) of base resin (organic polymer resin ((alpha))), Preferably it is 10-50 mass parts (solid content). If the blending amount of the antirust additive component (β) is less than 1 part by mass, the effect of improving corrosion resistance is small. On the other hand, if the blending amount exceeds 100 parts by mass, the corrosion resistance decreases, which is not preferable.

  In addition to the above rust preventive additives, the organic film contains other oxide fine particles (eg, aluminum oxide, zirconium oxide, titanium oxide, cerium oxide, antimony oxide), phosphomolybdic acid as a corrosion inhibitor. Salts (eg, aluminum phosphomolybdate), organic phosphoric acid and its salts (eg, phytic acid, phytate, phosphonic acid, phosphonate, and metal salts thereof, alkali metal salts, alkaline earth metal salts, etc. ), Organic inhibitors (for example, hydrazine derivatives, thiol compounds, dithiocarbamates, etc.) can be added.

If necessary, a solid lubricant can be blended in the organic film for the purpose of improving the workability of the film.
Examples of the solid lubricant applicable to the present invention include the following, and one or more of these can be used.
(1) Polyolefin wax, paraffin wax: For example, polyethylene wax, synthetic paraffin, natural paraffin, micro wax, chlorinated hydrocarbon, etc. (2) Fluorine resin fine particles: For example, polyfluoroethylene resin (polytetrafluoroethylene resin, etc.) , Polyvinyl fluoride resin, polyvinylidene fluoride resin, etc.

  In addition, fatty acid amide compounds (eg, stearic acid amide, palmitic acid amide, methylene bis stearoamide, ethylene bis stearoamide, oleic acid amide, esylic acid amide, alkylene bis fatty acid amide), metal Soaps (eg, calcium stearate, lead stearate, calcium laurate, calcium palmitate, etc.), metal sulfides (eg, molybdenum disulfide, tungsten disulfide, etc.), graphite, graphite fluoride, boron nitride, polyalkylene glycol, You may use 1 type, or 2 or more types, such as an alkali metal sulfate.

Among the above solid lubricants, polyethylene wax and fluororesin fine particles (in particular, polytetrafluoroethylene resin fine particles) are preferable.
Polyethylene wax includes, for example, Celestus 9615A, Celidust 3715, Celidust 3620, Celidust 3910 (all are trade names) manufactured by Hoechst, Sunwax 131-P, Sanwax 161-P manufactured by Sanyo Chemical Co., Ltd. All of the above are trade names), Chemipearl W-100, Chemipearl W-200, Chemipearl W-500, Chemipearl W-800, Chemipearl W-950 (all are trade names) manufactured by Mitsui Petrochemical Co., Ltd. Can be used.

  Further, as the fluororesin fine particles, tetrafluoroethylene fine particles are most preferable. For example, Lubron L-2, Lubron L-5 (all are trade names) manufactured by Daikin Industries, Ltd., Mitsui DuPont Co., Ltd. MP1100, MP1200 (all are trade names), full-on dispersion AD1, full-on dispersion AD2, full-on L141J, full-on L150J, full-on L155J (all are trade names) manufactured by Asahi IC Fluoropolymers Co., Ltd. Is preferred.

Among these, a particularly excellent lubricating effect can be expected by the combined use of polyolefin wax and tetrafluoroethylene fine particles.
The blending amount of the solid lubricant in the organic film is 1 to 80 parts by mass (solid content), preferably 3 to 40 with respect to 100 parts by mass (solid content) of the base resin (organic polymer resin (α)). It is preferable to set it as a mass part (solid content). When the blending amount of the solid lubricant is less than 1 part by mass, the lubricating effect is poor. On the other hand, when the blending amount exceeds 80 parts by mass, the paintability is lowered, which is not preferable.

In the organic film, as necessary, organic coloring pigments (for example, condensed polycyclic organic pigments, phthalocyanine organic pigments), coloring dyes (for example, organic solvent-soluble azo dyes, water-soluble substances) Azo metal dyes), inorganic pigments (eg, titanium oxide), chelating agents (eg, thiols), conductive pigments (eg, metal powders such as zinc, aluminum, nickel, etc.), iron phosphide, antimony-doped oxidation Tin or the like), a coupling agent (for example, a silane coupling agent, a titanium coupling agent, etc.), or one or more of melamine and cyanuric acid adducts can be added.
The dry film thickness of the organic film is 0.1 to 5 μm, preferably 0.3 to 3 μm, and more preferably 0.5 to 2 μm. When the film thickness of the organic film is less than 0.1 μm, the corrosion resistance is insufficient. On the other hand, when the film thickness exceeds 5 μm, the discoloration resistance in a wet environment is lowered.

The anticorrosion mechanism of the organic film that is the second layer film described above is considered as follows.
That is, an organic polymer resin (α) having an OH group and / or a COOH group (preferably a thermosetting resin, more preferably an epoxy resin and / or a modified epoxy resin) forms a dense barrier film by reaction with a crosslinking agent. Since this barrier film is excellent in permeation suppressing ability of corrosion factors such as oxygen, it is considered that excellent corrosion resistance (barrier property) can be obtained.

  In the present invention, in addition to the excellent corrosion resistance (barrier property) of the organic film itself, strong bonding to the first layer film by OH groups and COOH groups in the organic polymer resin constituting the organic film. It is considered that particularly excellent corrosion resistance (barrier properties) can be obtained because of the strength. Therefore, since these effects and the effect of improving the corrosion resistance by the Al oxide layer and the first layer film on the galvanized surface layer are obtained in combination, it is considered that very excellent corrosion resistance can be obtained.

In the present invention, in the organic film made of the specific organic polymer resin as described above,
(A) Phosphate (b) Ca ion exchange silica (c) Molybdate (d) Silicon oxide (e) One or more kinds selected from triazoles, thiols, thiadiazoles, thiazoles, thiurams A particularly excellent anticorrosion performance (self-healing effect) can be obtained by blending an appropriate amount of at least one rust-preventing additive (β) (self-repairing substance) selected from organic compounds. The anticorrosion mechanism obtained by blending the components (a) to (e) in the specific organic film is considered as follows.

First, the component (a) dissociates into phosphate ions by hydrolysis in a corrosive environment, and forms a protective film by causing a complexing reaction with the eluted metal.
In the case of the component (b), when a cation such as Na ion enters in a corrosive environment, Ca ions on the silica surface are released by an ion exchange action, and further, OH ions are generated by a cathodic reaction in the corrosive environment. When the pH in the vicinity of the plating interface rises, Ca ions released from the Ca ion exchange silica precipitate as Ca (OH) _{2 in the} vicinity of the plating interface, block defects as a dense and poorly soluble product, Inhibits corrosion reactions. Moreover, the eluted zinc ion is exchanged with Ca ion, and the effect fixed to the silica surface is also considered.

The component (c) exhibits self-repairing properties due to a passivating effect. That is, a dense oxide is formed on the surface of the plating film together with dissolved oxygen in a corrosive environment, and this inhibits the corrosion reaction by blocking the corrosion starting point.
In addition, the component (d) contributes to the formation of a dense and stable zinc corrosion product in a corrosive environment, and the corrosion product is formed densely on the plating surface, thereby suppressing the promotion of corrosion. To do.
The component (e) exhibits self-repairing properties due to the adsorption effect. That is, zinc and aluminum eluted by corrosion adsorb to the polar group containing nitrogen and sulfur contained in the component (e) to form an inactive film, which inhibits the corrosion reaction by blocking the corrosion starting point. .

Even when the components (a) to (e) are blended in a general organic film, a certain degree of anticorrosion effect can be obtained, but an organic material having excellent barrier properties made of a specific organic polymer resin as in the present invention. By blending the above self-repairing substances (a) to (e) into the film, both effects (barrier property and self-repairing property) are combined, thereby exhibiting an extremely excellent anticorrosion effect. it is conceivable that.
In addition, when a calcium compound is added together with the component (a) above, the calcium compound elutes preferentially over the plated metal in a corrosive environment, so that the phosphoric acid is not triggered by the elution of the plated metal. It causes a complexing reaction with ions to form a dense and sparingly soluble protective film to suppress the corrosion reaction.
In addition, if two or more of the above-described components (a) to (e) are added in combination, the corrosion inhibiting action by each component is combined, so that more excellent corrosion resistance can be obtained.

  The organic coating (second layer coating) contains the organic polymer resin (α) and the anticorrosive additive (β) as described above, and further treats the coating composition containing other components as necessary. It is formed by applying to the surface of the film and drying by heating. As a method for applying the coating composition for the organic film, any method such as a roll coating method, a bar coating method, a dipping method, and a spray coating method can be adopted. What is necessary is just to select an optimal method suitably according to the shape etc. of the hot dip galvanized steel plate to be processed. For example, if the hot-dip galvanized steel sheet to be treated is a sheet, a roll coating method, a bar coat method, or a surface treatment solution is sprayed on the surface of the hot-dip galvanized steel sheet (surface of the surface treatment film), It is appropriate to use a spray coating method in which the amount of coating is adjusted by blowing gas at a high pressure. Moreover, when the hot dip galvanized steel sheet is a molded product, a method of adjusting the coating amount by immersing it in a surface treatment liquid and pulling it up and blowing off excess surface treatment liquid with compressed air as necessary is suitable.

After application of the coating composition, drying is usually performed without washing with water, but a washing process may be performed after application of the coating composition. For the heat drying treatment, a dryer, a hot air furnace, a high frequency induction heating furnace, an infrared furnace, or the like can be used, but a high frequency induction heating furnace is particularly preferable from the viewpoint of corrosion resistance. The heat treatment is desirably performed in the range of 40 to 350 ° C. at the ultimate plate temperature. If the heating and drying temperature is less than 40 ° C., crosslinking of the film does not proceed and the corrosion resistance may be insufficient. Further, when the heating and drying temperature exceeds 350 ° C., not only is it uneconomical, but there is a risk that defects occur in the film and the corrosion resistance is lowered.
The surface-treated hot-dip galvanized steel sheet of the present invention can be applied to various uses, and is suitably used for materials used in various fields such as architecture, electricity, and automobiles.

(1) Test plate (hot dip galvanized steel plate)
The following commercially available galvanized steel sheets were used as test plates.
(I) Hot-dip galvanized steel sheet (GI): Plate thickness 0.8 mm, plating basis weight 60/60 (g / m ² )
(Ii) Alloyed hot-dip galvanized steel sheet (GA): plate thickness 0.8 mm, plating basis weight 40/40 (g / m ² )
In addition, the plating basis weight is each plating adhesion amount on both surfaces of the steel sheet. For example, the plating basis weight 60/60 (g / m ² ) means that each of both surfaces of the steel sheet has a plating layer of 60 g / m ^2. means.
In addition, the thickness of the Al oxide layer on the plating surface layer was adjusted by adjusting the pretreatment alkaline degreasing solution concentration and the treatment time as described below.

(2) Pretreatment of test plate (cleaning)
Alkali degreasing (treated with “Fine Cleaner E6406” manufactured by Nihon Parkerizing Co., Ltd. according to the instruction manual) is applied to the surface of the above test plate (hot dip galvanized steel plate) to remove oil and dirt on the surface, and Al oxidation The thickness of the material layer was adjusted. Specifically, when alkali degreasing a plated steel sheet having an Al oxide layer formed on the plating surface layer, the higher the alkali degreasing solution concentration and the longer the treatment time, the smaller the thickness of the Al oxide layer. Alkaline degreasing was performed under the conditions shown in Table 5 to adjust the thickness of the Al oxide layer. Next, after rinsing with tap water and confirming that the surface of the test plate is 100% wet with water, pour pure water (deionized water), and then dry the moisture in an oven at 100 ° C., This was used as a test plate.

(3) Surface treatment liquid for surface treatment film (first layer film) (3-1) Compound for surface treatment liquid The following compounds were used as compounds for the surface treatment liquid.
(3-1-1) Production / Production Example 1 of Silane Compound (A) (Silane Compound A1)
3-Glycidoxypropyltrimethoxysilane, tetraethoxysilane, and deionized water were mixed, and ammonia water was added dropwise to precipitate a silane compound. After washing with deionized water, nitrilotris (methylene sulfonic acid) was added as phosphonic acid and stirred to obtain silane compound A1.

Production Example 2 (Silane Compound A2)
A mixture of 3-glycidoxypropyltrimethoxysilane and tetraethoxysilane was added dropwise to a mixture of deionized water and hydroxyethylene diphosphonic acid as phosphonic acid with stirring at 20 ° C. over 1 hour. . Thereafter, aging was carried out at 25 ° C. for 2 hours to obtain a silane compound A2.
Production Example 3 (Silane Compound A3)
Silane compound A2 of Production Example 2 was further aged at 80 ° C. for 1 hour to obtain silane compound A3.

(3-1-2) Zirconium carbonate compound (B)
B1: Ammonium zirconium carbonate B2: Sodium zirconium carbonate (3-1-3) Vanadic acid compound (C)
C1: ammonium metavanadate C2: vanadyl acetylacetonate (V: 19.2% by mass)
(3-2) Preparation of surface treatment liquid The above compounds were mixed in water at the ratio shown in Table 1 to obtain a surface treatment liquid having a solid content of 15% by mass.

(4) Coating composition for organic coating (second layer coating) (4-1) Component for coating composition Organic polymer resin (substrate resin) for coating composition, rust preventive additive component, Things were used.
(4-1-1) Organic polymer resin (α)
α1: Epoxy resin α2: Urethane resin (4-1-2) Antirust additive component (β)
β1: Ca ion exchange silica β2: Zn phosphate
β3: phosphomolybdate Al
β4: Colloidal silica β5: Preparation of coating composition of tetraethylthiuram disulfide (4-2) The above rust preventive additive (β) is blended with the organic polymer resin (α) in the proportions shown in Tables 2 to 4, A composition was obtained.

(5) Surface treatment method The surface treatment solution for the surface treatment film (first layer film) is applied to each test plate by bar coating or spraying, and then dried in a hot air oven without washing, A surface treatment film (first layer film) was formed. The drying conditions were adjusted according to the furnace atmosphere temperature and the time in the furnace.
The bar coat treatment and spray treatment were performed as follows.
Bar coating treatment: The surface treatment solution was dropped onto the test plate and treated with a # 3-5 bar coater. By adjusting the count of the bar coater used and the solid content concentration of the surface treatment liquid, the coating amount was adjusted to be a predetermined amount.
-Spray treatment: The surface treatment solution was sprayed on the test plate, and the amount of the film was adjusted with a roll coater. By adjusting the conditions of the roll coater and the solid content concentration of the surface treatment liquid, adjustment was made so as to obtain a predetermined coating amount.
Next, the coating composition for the organic film (second layer film) was applied by a roll coater and then heat-dried at various temperatures in a hot air drying furnace. The film thickness was adjusted by the solid content (heating residue) of the coating composition or the application conditions (roll rolling force, rotational speed, etc.).

(6) Evaluation Test Method (6-1) Corrosion Resistance A test piece of 70 mm × 150 mm size was cut out from the test plates of the inventive example and the comparative example, and the back and end portions of this test piece were sealed with vinyl tape, and JIS A salt spray test (SST) based on -Z-2371-2000 was performed. The time until the white rust occurrence area ratio in the salt spray test was 5% was measured, and the corrosion resistance was evaluated as follows.
◎: Time until white rust generation area ratio reaches 5% or more 480 hours or more ○: Time until white rust generation area ratio reaches 5% or more 360 hours or less, less than 480 hours Δ: White rust generation area ratio Time until 5% is 240 hours or more and less than 360 hours ×: Time until white rust occurrence area ratio is 5% is less than 240 hours

(6-2) Discoloration resistance in a wet environment Two test pieces having a size of 70 mm × 150 mm were cut out from the test plates of the inventive example and the comparative example, and the target surfaces were overlapped and tightened with a torque strength of 20 kgf. It was kept in a constant temperature bath at 50 ° C. and 98% RH for 4 weeks, and the color tone of the test piece before and after the holding was evaluated. The color tone of the test piece before and after holding was measured with a spectrocolorimeter, the color tone was expressed by the L value of the Lab color system, and the resistance to discoloration was evaluated by the difference ΔL between the L values before and after holding as follows.
A: ΔL ≧ −2
○: −2> ΔL ≧ −5
Δ: −5> ΔL ≧ −10
×: ΔL <−10
(7) Measurement of the thickness of the Al oxide layer The cross section of the test plate is observed with a TEM to measure the thickness of the Al oxide layer, and the average value of the measurement values at five randomly selected points is used as the Al oxide layer. The thickness of the oxide layer.

The results of the above evaluation tests are shown in Tables 1 to 5 together with the type and configuration of the hot-dip galvanized steel sheet, the composition of the surface treatment liquid, the surface treatment conditions, and the formation conditions of the organic film. The drying temperature is the temperature reached on the surface of the test plate.
In the comparative example that does not satisfy the conditions of the present invention, either corrosion resistance or discoloration resistance in a wet environment is insufficient. On the other hand, the examples of the present invention have excellent corrosion resistance and discoloration resistance in a wet environment without containing a chromium compound in the surface treatment film and the organic film.

Claims (2)

A silane coupling agent (a1) having a glycidyl group, tetraalkoxysilane (on the surface of a hot dip galvanized steel sheet on which an Al oxide layer having a thickness of 0.5 nm or more and less than 10.0 nm is formed on the surface layer of the galvanized layer, a hydrolyzable silane compound (A) obtained from a2) and phosphonic acid (a3), a zirconium carbonate compound (B), a vanadic acid compound (C), and water; A surface treatment liquid satisfying the conditions of (iii) ( excluding a surface treatment liquid containing a nitric acid compound) is applied and dried, and the adhesion amount per side is 100 to 800 mg / m ² surface treatment film,
(I) The silane compound (A) is 30 to 70% by mass in the total solid content of the surface treatment liquid.
(Ii) The ratio (B / A) of the mass of the zirconium carbonate compound (B) in terms of ZrO _{2 and the} mass of the silane compound (A) is 0.3 to 2.0.
(Iii) The ratio (C / A) of the V-converted mass of the vanadic acid compound (C) to the mass of the silane compound (A) is from 0.010 to 0.15.
An organic polymer resin (α) having an OH group, COOH group, or OH group and COOH group is used as a base resin as a second layer film on the surface treatment film, and 100 parts by mass (solid content) of the base resin is used. On the other hand, it contains 1 to 100 parts by mass (solid content) of one or more rust preventive additives (β) selected from the following (a) to (e), and the film thickness is 0.1 to 5 μm. A surface-treated hot-dip galvanized steel sheet characterized by having an organic film.
(A) Phosphate (b) Ca ion exchange silica (c) Molybdate (d) Silicon oxide (e) One or more kinds selected from triazoles, thiols, thiadiazoles, thiazoles, thiurams Organic compounds A silane coupling agent (a1) having a glycidyl group, tetraalkoxysilane (on the surface of a hot dip galvanized steel sheet on which an Al oxide layer having a thickness of 0.5 nm or more and less than 10.0 nm is formed on the surface layer of the galvanized layer, a hydrolyzable silane compound (A) obtained from a2) and phosphonic acid (a3), a zirconium carbonate compound (B), a vanadic acid compound (C), and water; A surface having an adhesion amount per side of 100 to 800 mg / m ² by applying and drying a surface treatment liquid satisfying the conditions of (iii) ( excluding a surface treatment liquid containing a nitric acid compound) Forming a treatment film,
(I) The silane compound (A) is 30 to 70% by mass in the total solid content of the surface treatment liquid.
(Ii) The ratio (B / A) of the mass of the zirconium carbonate compound (B) in terms of ZrO _{2 and the} mass of the silane compound (A) is 0.3 to 2.0.
(Iii) The ratio (C / A) of the V-converted mass of the vanadic acid compound (C) to the mass of the silane compound (A) is from 0.010 to 0.15.
An organic polymer resin (α) having an OH group, COOH group, or OH group and COOH group is used as a base resin on the surface of the surface treatment film, and the following (a ) To (e), a coating composition containing a total of 1 to 100 parts by mass (solid content) of one or more rust preventive additives (β) is selected, and then dried by heating. Forms a 0.1-5 micrometer organic membrane | film | coat, The manufacturing method of the surface treatment hot-dip galvanized steel plate characterized by the above-mentioned.
(A) Phosphate (b) Ca ion exchange silica (c) Molybdate (d) Silicon oxide (e) One or more kinds selected from triazoles, thiols, thiadiazoles, thiazoles, thiurams Organic compounds