JP4923431B2 - Surface-treated steel sheet for organic resin-coated steel sheets - Google Patents

Description

  The present invention is a surface-treated steel sheet for an organic resin-coated steel sheet having a zinc-based plated steel sheet as a base steel sheet, the surface-treated film does not contain hexavalent chromium, and excellent adhesion of the organic resin coating is obtained. It relates to a surface-treated steel sheet.

  Conventionally, organic resin-coated steel sheets such as coated steel sheets and laminated steel sheets have been widely used for home appliances and building materials. When high corrosion resistance is required for the organic resin-coated steel plate, a zinc-based plated steel plate is used as the base steel plate, and further, phosphate treatment or chromate treatment is performed as the base pretreatment. However, such conventional organic resin-coated steel sheets have the following problems.

  First, since the treatment process of phosphate treatment is complicated, a long facility is required for efficient production, which is disadvantageous in terms of production cost. Moreover, since the film obtained is a crystalline film, the crystals are destroyed when subjected to severe processing. In particular, in a coated steel sheet or a laminated steel sheet in which the film thickness of the organic resin coating is 100 μm or more, the organic resin coating is easily peeled off due to the cohesive failure of the phosphate film.

  On the other hand, the chromate treatment is a treatment using hexavalent chromium, and is an economical treatment method that is excellent in corrosion resistance and paint adhesion and can be performed relatively easily. Regarding this chromate treatment technique, for example, Patent Documents 1 to 3 show that a treatment liquid in which fumed silica is added to chromic acid is used, and Patent Document 4 discloses Co or Ni as a pretreatment of chromate. It is shown to be processed. However, the methods disclosed in Patent Documents 1 to 3 do not provide excellent adhesion of the organic resin coating. Moreover, although the method of patent document 4 is effective in an adhesive improvement, since a process process increases, it is unpreferable from the point of manufacturing cost.

On the other hand, in Patent Document 5, an oxide sol or the like is added to the chromate film to provide irregularities on the film surface, and high adhesion of the organic resin coating is realized by increasing the anchor effect and interface bonding. Technology is shown.
However, hexavalent chromium used in chromate treatment is a pollution-controlling substance, and in recent years there has been an increasing trend to reduce the use of hexavalent chromium in consideration of environmental conservation, so surface treatment that does not use hexavalent chromium. Development of steel sheets is strongly desired.

JP 52-17340 A JP 60-86282 A JP-A-61-585 Japanese Patent Publication No. 56-36869 Japanese Patent Laid-Open No. 10-306381

  Against this background, a number of technologies (chromate-free technologies) aimed at improving the corrosion resistance and paint adhesion of galvanized steel sheets without using hexavalent chromium have recently been proposed. Many methods for forming a film by applying and drying a treatment solution containing phosphoric acid have been proposed. For example, Patent Documents 6 and 7 propose a surface treatment agent containing Al, a phosphoric acid compound, silica, and a water-based organic resin emulsion, and a metal material coated therewith. Patent Document 8 discloses a zinc-based plated steel sheet in which an amorphous resin film is formed by applying and drying a mixed aqueous solution of a polyvalent metal primary phosphate and a metal oxide sol, and then forming an organic resin coating layer. Has been proposed. Further, in Patent Documents 9 to 11, a composite oxide film layer containing oxide fine particles, phosphoric acid and / or a phosphoric acid compound, and one or more metals selected from Mg, Mn, and Al is used as a lower layer, A surface-treated steel sheet having an organic resin film formed thereon is proposed.

Japanese Patent Laid-Open No. 11-350157 JP 2000-26980 A JP 2000-129460 A JP 2002-53979 A JP 2002-53980 A JP 2002-53999 A

  The method of forming a film by applying and drying a treatment liquid containing phosphoric acid as an inorganic component described above is a corrosion-resistant material by forming a sparingly soluble phosphate by reacting the plating metal on the substrate with the treatment liquid. And paint adhesion. However, when the surface-treated steel sheet obtained by these methods is used for coating an organic resin with a film thickness of 100 μm or more, the adhesiveness when bending is performed, and the corrosion resistance of the end portion and the cross-cut portion is phosphate. It is inferior to the surface-treated steel sheet subjected to the treatment or the chromate treatment, and no steel having properties equivalent to those treatments has been obtained. In particular, when a part of the organic resin coating (particularly a film laminate) is peeled off for some reason, the end user may try to forcibly remove the peeled part, but the film thickness is 100 μm. The above organic resin coating has high film strength, so if the adhesion between the organic resin coating and its base (film) is poor, the large area coating including the part that has not been peeled off will be peeled off. Becomes worse. Therefore, when trying to remove the partially peeled organic resin coating, the other organic resin coating can be firmly adhered to the ground (film) until the organic resin coating is cut (broken). Sex is required.

  Accordingly, an object of the present invention is to form a surface-treated steel sheet for an organic resin-coated steel sheet using a zinc-based plated steel sheet as a base steel sheet, and to form an organic resin coating having a film thickness of 100 μm or more without containing hexavalent chromium in the film. Even in such a case, the object is to provide a surface-treated steel sheet that has excellent adhesion with an organic resin coating and can be easily manufactured.

  The inventors of the present invention have a high degree of adhesiveness that surpasses a phosphate-treated film with respect to an organic resin coating having a film thickness of 100 μm or more, which does not contain hexavalent chromium, regarding the surface-treated film of a zinc-based plated steel sheet. In order to find out, it was examined from the viewpoint of the film structure. As a result, a film mainly composed of an amorphous phase (hereinafter referred to as an amorphous film) is formed, and (1) a reaction layer with a plating film is formed under predetermined conditions under the amorphous film. By improving the adhesion between the plating film and the amorphous film, and (2) increasing the adhesion between the amorphous film and the organic resin coating by providing fine irregularities on the surface of the amorphous film, It was found that a high degree of adhesion can be obtained even with an organic resin coating having a thickness of 100 μm or more. Furthermore, it has been found that by optimizing the area magnification measured by the BET method on the surface of the film, better adhesion to the organic resin coating can be obtained.

The present invention has been made on the basis of the above knowledge, and the gist thereof is to apply an aqueous solution containing phosphoric acid (but not containing hexavalent chromium) to the surface of a zinc-based plated steel sheet and to dry it. A film mainly composed of an amorphous phase and having a film thickness of 0.10 to 0.6 μm, containing Zn and P in the lower part of the film, and a mass of Zn / (Zn + P) the ratio has a thickness of 50nm or more reaction layers of less than 1.0, a difference between the highest and lowest points of the roughness of the surface roughness of the film is 250 to 400 nm, and Ra is 35～50Nm, coating surface The surface-treated steel sheet for an organic resin-coated steel sheet having excellent adhesion, wherein the area magnification measured by the BET method is 10 to 25 .

  The surface-treated steel sheet of the present invention has an effect of improving the adhesion between the plating film and the film by the reaction layer under the film mainly composed of the amorphous phase, and fine unevenness on the film surface mainly composed of the amorphous phase. By combining the effect of improving the adhesion between the coating and the organic resin coating, a high degree of adhesion can be obtained even with an organic resin coating having a thickness of 100 μm or more, and in the coating It is an environment-adaptive surface-treated steel sheet that does not contain hexavalent chromium and can be easily manufactured.

  The surface-treated steel sheet of the present invention is a film mainly composed of an amorphous phase formed by applying an aqueous solution containing phosphoric acid (but not containing hexavalent chromium) to the surface of a zinc-based plated steel sheet and drying it. (Surface treatment film), the film has a film thickness of 0.10 to 0.6 μm, contains Zn and P at the lower part of the film, and the mass ratio of Zn / (Zn + P) is less than 1.0. The reaction layer has a thickness of 50 nm or more, the difference between the highest point and the lowest point of the roughness of the surface roughness of the film is 250 to 400 nm, and Ra is 35 to 50 nm. Here, a film mainly composed of an amorphous phase (hereinafter referred to as “amorphous film” for convenience) is a film whose main phase is amorphous, and therefore contains a crystalline substance as a part thereof. It may be. Thus, by making the film mainly composed of an amorphous phase, it is possible to exhibit a high degree of adhesion as compared with a crystalline-based phosphating film.

The surface-treated steel sheet of the present invention comprises a plating film formed by a reaction layer under the amorphous film, an effect of improving adhesion between the amorphous films, and an amorphous film formed by optimizing the surface roughness of the amorphous film. It is designed so that a high degree of adhesion can be obtained even for an organic resin coating having a film thickness of 100 μm or more by combining the effect of improving the adhesion between the organic resin coatings.
This surface-treated steel sheet is for an organic resin-coated steel sheet that forms an organic resin coating on its surface, and examples of the organic resin-coated steel sheet include painted steel sheets and laminated steel sheets.

  In the present invention, the galvanized steel sheet used as the base steel sheet is a hot dip galvanized steel sheet, an electrogalvanized steel sheet, an alloyed hot dip galvanized steel sheet, a Zn-Al alloy plated steel sheet (for example, a Zn-5% Al alloy plated steel sheet). , Al-Zn alloy-plated steel sheet (for example, 55% Al-Zn alloy-plated steel sheet), zinc-based alloy-plated steel sheet containing one or more of Ni, Fe, Cr, Co, Mg, etc. in the plated film, plated film Examples thereof include, but are not limited to, a zinc-based composite plated steel sheet in which a metal oxide or a polymer is dispersed.

  An amorphous film formed by applying an aqueous solution containing phosphoric acid to the plating film surface (this aqueous solution does not contain hexavalent chromium) and drying the film has a thickness of 0.10 to 0.6 μm. If the film thickness of the amorphous film is less than 0.10 μm, it is difficult to provide surface irregularities sufficient to develop an anchor effect on the organic resin coating, while if the film thickness exceeds 0.6 μm, the effect of improving adhesion is saturated. On the other hand, productivity and economy are impaired.

  In order to improve the adhesion between the plating film and the amorphous film, the amorphous film contains Zn and P at the bottom thereof, and the reaction layer having a Zn / (Zn + P) mass ratio of less than 1.0. Must have a thickness of 50 nm or more. This reaction layer is a layer formed in the lower part of the amorphous film (interface with the plating film) by chemically dissolving the plating metal with an aqueous solution containing phosphoric acid applied to the surface of the galvanized steel sheet. Therefore, a layer in which Zn and P are mixed is formed. When the thickness of the reaction layer where the mass ratio of Zn / (Zn + P) is less than 1.0 is less than 50 nm, sufficient adhesion between the plating film and the amorphous film is not ensured, and thus the film thickness It is difficult to develop a high degree of adhesion to an organic resin coating of 100 μm or more.

  In addition, as a method for measuring the film thickness of the amorphous film and the thickness of the reaction layer, the bright field of the film cross section by a transmission electron microscope (TEM) of the film cross section sample prepared by the focused ion beam (FIB) method is used. Image observation and quantitative analysis by characteristic X-ray analysis (EDX) are preferable because they are quick and simple methods.

  In order to improve the adhesion between the amorphous film and the organic resin coating, the difference between the highest and lowest surface roughness irregularities of the amorphous film is set to 250 to 400 nm, and the surface roughness Ra is set to 35. ˜50 nm. Here, when the difference between the highest point and the lowest point of the unevenness of the film surface roughness is less than 250 nm, or the surface roughness Ra is less than 35 nm, the anchor effect on the organic resin coating (coating film or laminate resin film) In the case where the difference between the highest point and the lowest point of the unevenness is more than 400 nm, or the surface roughness Ra is more than 50 nm, the coating or adhesion for organic resin coating The agent (adhesive for the laminate resin film) does not reach the lowest point of the recess, and a gap is formed between the film and the amorphous film, which causes interface peeling.

In addition, it is preferable to apply an atomic force microscope as a measuring method of the unevenness | corrugation on the film | membrane surface, and the measurement length should just be the range of 5 micrometers-50 micrometers.
Further, the surface roughness Ra is an average value (average roughness) of actually measured roughness curves with respect to the center line, and the area surrounded by the roughness curve and the center line is equal above and below the center line. This is a calculated straight line.

  Furthermore, in order to improve the adhesion between the amorphous film and the organic resin coating, the area magnification measured by the BET method on the surface of the amorphous film is preferably 10-25. Here, the area magnification measured by the BET method is a value obtained by dividing the surface area measured by the BET method by the geometric area. When the area magnification is less than 10, sufficient interfacial bonding is not provided, while when it exceeds 25, the amorphous coating has a porous structure and has fine pores, so that coatings and adhesives for coating organic resins are fine. It cannot penetrate into the pores. For this reason, the adhesion area between the amorphous film and the organic resin coating is reduced, and sufficient interface bonding is not provided.

The method for measuring the area magnification by the BET method is not particularly limited, but it is preferable to use xenon or krypton having a low saturated vapor pressure as the adsorption gas. Moreover, molecular area of adsorbed gas, i.e. the resolution of the surface area measured by a BET method (measurement limit), the xenon is 0.25 nm ^2, krypton is 0.2 nm ^2.

The amorphous film may contain an organic resin from the viewpoint of improving performance such as corrosion resistance. In order to contain an organic resin in the amorphous film, a water-soluble resin and / or a water-dispersible resin is added to the aqueous solution for film formation. There is no special restriction | limiting in the kind of organic resin, For example, 1 or more types, such as an acrylic resin, a urethane resin, an epoxy resin, a phenol resin, can be used. The amorphous film may further contain one or more various additives such as a rust preventive additive, an oxide sol, and a wax, if necessary.
Further, in order to obtain a desired surface roughness of the amorphous film, the outermost surface layer may contain fine particles such as an oxide having an appropriate number of hydroxyl groups or a water-dispersible resin. In order to contain such fine particles in the amorphous film, the fine particles are added to an aqueous solution for film formation.

In addition, in the aqueous solution for film formation, from the viewpoint of reactivity control and adhesion improvement, as additives, inorganic acids such as hydrofluoric acid and salts thereof, organic acids such as carboxylic acid and salts thereof, silane coupling, etc. One or more agents such as an agent can be added.
When forming an amorphous film, there is no particular limitation on the type of phosphoric acid contained in the aqueous solution for film formation, and phosphates may be used in addition to phosphoric acid such as orthophosphoric acid and polyphosphoric acid. One or more selected from these can be used. However, it is preferable to use primary phosphate from the viewpoints of reactivity with the plating film and poor solubility of the film, whereby particularly excellent adhesion can be obtained.

  In order to form an amorphous film (film mainly composed of an amorphous phase) by applying and drying an aqueous solution, (1) suppressing excessive reaction between the plating metal and the applied aqueous solution, (2) It is important to remove foreign matters (contaminants) on the plating film that become the growth point of crystal nuclei before applying the aqueous solution. As a countermeasure of the above (1), it is preferable not to include an acid having an etching effect other than phosphoric acid such as nitric acid, nitrous acid, chloric acid or the like usually contained in a phosphating solution, As a countermeasure for the above (2), it is preferable to sufficiently remove foreign matters such as plating solution remaining on the plating film surface by washing before applying the aqueous solution.

  Further, in order to form a reaction layer as defined in the present invention under the amorphous film, the pH of the aqueous solution containing phosphoric acid applied to the surface of the galvanized steel sheet is 4.0 or less, preferably 3.0. It is preferable to adjust to the following. In addition, since there exists a possibility that Zn may melt | dissolve excessively and the plating film may lose | disappear if the pH of the aqueous solution containing phosphoric acid is less than 1.0, it is preferable to make pH into 1.0 or more.

  Further, the surface roughness of the amorphous film (difference between the highest and lowest points of the surface roughness unevenness, the surface roughness Ra) and the area magnification measured by the BET method are within a predetermined range defined by the present invention. Therefore, for example, the outermost surface layer has an appropriate number of hydroxyl groups (if the number of hydroxyl groups is too small, the desired water dispersibility cannot be obtained, and if it is too large, the surface of the film is smoothed by the repulsive force due to negative charges). It is possible to adopt a method of imparting fine roughness to the surface by incorporating fine particles such as a product or water-dispersible resin in the amorphous film. As described above, in order to include such fine particles in an amorphous film, the fine particles are added to an aqueous solution for film formation and dispersed in the aqueous solution.

  The method of applying the aqueous solution to the surface of the galvanized steel sheet is not particularly limited as long as the aqueous solution can be continuously and uniformly attached to the surface of the plated steel sheet. Alternatively, a method of adjusting the adhesion amount by gas squeezing, a method of applying by a roll coater, or the like can be adopted.

After applying a treatment liquid having the composition shown in Table 1 to an electrogalvanized steel sheet (plating amount per side: 20 g / m ² ) with a roll coater, it is dried in an induction heating furnace under a condition that the ultimate plate temperature is 120 ° C. Was used as a test material. Analysis of the structure of the amorphous film of each of the test materials was performed by the analysis method (1) below.
A general polypropylene film adhesive was applied to each sample material so that the dry film thickness was 3 μm, baked at a furnace temperature of 100 ° C., and then a 150 μm-thick polypropylene film was pressed against the steel sheet surface with a roll. And bonded by thermocompression bonding. Thus, about the test material which gave organic resin coating (resin film lamination), the adhesiveness of organic resin coating was evaluated by the evaluation test of the following (2). The results are shown in Tables 1 and 2 together with the structure of the amorphous film and the composition of the treatment liquid.

(1) Analysis method of amorphous film
(1-1) Measurement of the film thickness of the amorphous film and the thickness of the reaction layer The film cross-section sample prepared by the focused ion beam (FIB) method was accelerated using a transmission electron microscope “CM30” manufactured by Philips. A bright field image is observed under the conditions of voltage: 200 kV and magnification: 120,000 times, and the inside of the film is quantitatively analyzed by EDX, whereby the film thickness of the amorphous film and the mass ratio of the reaction layer (Zn / (Zn + P)) Of the reaction layer having a thickness of less than 1.0).
(1-2) Highest and lowest points of surface roughness irregularities and surface roughness Ra
Atomic force microscope images are observed with the “Nano Scope II” atomic force microscope manufactured by Digital Instrument, and the highest and lowest surface roughness irregularities are determined from the cross-sectional profile at a measurement length of 7.5 μm. Ra was determined.

(1-3) Area magnification Measured Kr adsorption isotherm at liquid nitrogen temperature (77K) after degassing under reduced pressure at 50 ° C using BELSORP 36, a high precision fully automatic gas adsorption device manufactured by Bell Japan did. The BET surface area was obtained by applying the multilayer adsorption theory to this isotherm. The ratio of the BET surface area to the geometric surface area measured and calculated for the measurement material (BET surface area / geometric surface area) was defined as the area magnification of the measurement material.

(2) Adhesion evaluation test
(2-1) Adhesion strength after processing A draw bead test was conducted under the conditions of tip R: 0.5 mm, deformation height: 3 mm, and pressing load: 250 kg, and the film peel strength of the deformed portion was measured according to JIS.
Measured according to K 6845.
(2-2) Adhesion strength after immersion in boiling water After immersion in boiling water for 1 hour, the film peel strength is measured according to JIS.
Measured according to K 6845.

Claims (1)

The surface of the galvanized steel sheet has a film mainly composed of an amorphous phase formed by applying an aqueous solution containing phosphoric acid (but not containing hexavalent chromium) and drying it. A film thickness of 0.10 to 0.6 μm, a reaction layer containing Zn and P at the bottom of the film and having a Zn / (Zn + P) mass ratio of less than 1.0, having a thickness of 50 nm or more, and the surface of the film The difference between the highest and lowest roughness irregularities is 250 to 400 nm, Ra is 35 to 50 nm, and the area magnification measured by the BET method on the coating surface is 10 to 25 Surface-treated steel sheet for organic resin-coated steel sheets with excellent adhesion.