JP5355141B2 - Chromate-free coating-coated hot-dip galvanized steel sheet with excellent adhesion between the plating surface and chromate-free coating and method for producing the same - Google Patents

Description

  The present invention relates to a chromate-free film-coated hot-dip galvanized steel sheet in which a chromium-free chromate-free film is formed on the surface of a hot-dip galvanized layer, and a method for producing the same, and in particular, is excellent in corrosion resistance such as white rust resistance. The present invention relates to a chromate-free film-coated hot-dip galvanized steel sheet having excellent adhesion to a chromate-free film, and a useful method for producing such a chromate-free film-coated hot-dip galvanized steel sheet.

  Steel sheets used in various applications such as building equipment, electrical products, and automobiles are often hot dip galvanized on the steel sheet surface from the viewpoint of ensuring corrosion resistance. However, even in hot-dip galvanized steel sheets, corrosion resistance (white rust resistance) may be insufficient, and when used as a coating base, it is difficult to ensure adhesion with paints. A chromate treatment has also been performed on the surface of a hot dip galvanized steel sheet.

  However, when the chromate treatment is performed, the white rust suppressing effect is excellent, but there is a problem that a large amount of harmful hexavalent chromium is contained. In particular, in recent years, as the awareness of environmental issues has increased, chromate treatment has tended to be avoided, and in most applications, the chromate-free surface is coated with a chromate-free coating that does not contain chromium. It is shifting to a film-coated hot-dip galvanized steel sheet.

  Chromate-free coating-coated hot-dip galvanized steel sheet requires advanced barrier properties comparable to chromate coating, and it is easy to add other added values such as lubricity and fingerprint resistance. Has been developed. The inventor of the present invention also has, as such an organic chromate-free film, silica particles: 1 to 30% by mass and a cross-linking agent: 1 in terms of solids with respect to a polyolefin copolymer resin emulsion intermolecularly associated with ion clusters. In addition to ˜8% by mass, it has been proposed that one containing tannic acid and / or ammonium vanadate at a rate of 1 to 8% by mass is useful (Patent Document 1). In this technology, the organic chromate-free film as described above is formed on the surface of the hot-dip galvanized steel sheet, so that not only the corrosion resistance but also the adhesion between the chromate-free film and the hot-dip galvanized layer surface is improved. To do.

  However, as the user's usage environment diversifies, a higher balance is required for the adhesion and corrosion resistance between the hot dip galvanized layer surface and the chromate-free coating. In particular, organic chromate-free coatings tend to have poor adhesion to the plating layer surface compared to inorganic chromate coatings that can be expected to have an anchor effect due to unevenness of the plating surface generated by reaction with the plating layer.

  As a technique for improving the adhesion to the plating surface as described above, Patent Document 2 discloses that an anticorrosion film is formed from a treatment solution containing fluoride so that the plating surface is fluoride ion before the film formation. Etching is used to increase the adhesion between the anticorrosive film and the plating layer, thereby improving the corrosion resistance. However, since the etching component is water-soluble, there is a problem that sufficient corrosion resistance cannot be secured if it remains in the film.

  By the way, the hot dip galvanized steel sheet is usually manufactured by immersing the base steel sheet in a hot dip galvanizing bath containing a small amount of Al. At this time, when Al is contained in the plating bath, the formation of the Fe—Zn alloy layer at the interface between the hot dip galvanized layer and the base steel sheet can be suppressed, and the adhesiveness of the hot dip galvanized layer can be increased. Are known.

  Various techniques for improving the properties of the plated steel sheet focusing on the Al concentration in the plating layer or the plating bath have been proposed so far. For example, in Patent Document 3, after removing Al in the plating layer by the activation treatment, an oxidation treatment is performed to form a Zn-based oxide on the plating surface, and thereby hot dip galvanization excellent in press formability. Techniques for obtaining steel sheets have been proposed. In this technique, it is shown that the Al oxide on the surface portion of the plating layer is removed by temper rolling (skin pass rolling: hereinafter referred to as “SKP rolling”) to the surface of the plating layer. However, according to an experiment confirmed by the present inventors, although the Al content in the surface layer portion of the plating layer is reduced, it is not completely removed but only the concentration distribution in the plating layer is changed. When the total amount of Al from the surface of the plating layer where the Al amount is stable to a depth of about 200 nm is measured, it has been confirmed that there is almost no change in the Al amount before and after SKP rolling. In other words, the fact is that such a technique has not been able to demonstrate the effect of adjusting the Al amount as expected.

Patent Document 4 proposes a technique for manufacturing a hot-dip galvanized steel sheet having excellent spot weldability and sliding property by defining the Al amount in the plating layer and the ratio of the Al concentration in the plating surface layer and the η phase. Has been. In this technique, Al on the plating surface layer is positively removed by immersing it in an alkaline solution, and adjusting the amount of Al does not improve the adhesion between the organic chromate-free film and the plating layer. .

JP 2004-176092 A JP 2001-192851 A JP 2005-120447 A JP 2002-105614 A

  The present invention has been made under such circumstances, and the object thereof is excellent in corrosion resistance such as white rust resistance even when an organic chromate-free coating is coated, and a chromate-free coating. It is to provide a useful method for producing a chromate-free film-coated hot-dip galvanized steel sheet having excellent adhesion and a chromate-free film-coated hot-dip galvanized steel sheet.

  The chromate-free film-coated hot-dip galvanized steel sheet of the present invention that can achieve the above-mentioned object is a hot-dip galvanized steel sheet having a hot-dip galvanized layer and an organic chromate-free film. In the surface layer part from the plating outermost surface to a depth of 10 nm, the gist is that the Al amount is 1 to 5.0% by mass when measured by high-frequency glow discharge optical emission spectrometry.

  As an organic chromate-free film used in the chromate-free film-coated hot-dip galvanized steel sheet of the present invention, silica particles: 1 to 30 in terms of solids with respect to a polyolefin copolymer resin emulsion intermolecularly associated with ion clusters. What contains a mass% and a crosslinking agent: 1-8 mass% is mentioned as a preferable thing.

  In producing the chromate-free coating-coated hot-dip galvanized steel sheet as described above, the base steel sheet is immersed in a hot-dip galvanizing bath in which the Al concentration is adjusted to 0.2 to 0.3% by mass, and hot dip galvanized on the steel sheet surface. After forming the plating layer, hold it in the temperature range of more than 400 to 440 ° C. for 10 to 30 seconds in the cooling process, and then subject the hot dip galvanized layer surface to temper rolling at an elongation of 0.5 to 2%. Then, an organic chromate-free film may be formed on the surface of the hot dip galvanized layer.

  In the chromate-free film-coated hot-dip galvanized steel sheet according to the present invention, in the chromate-free film-coated hot-dip galvanized steel sheet having the hot-dip galvanized layer and the organic chromate-free film, the hot-dip galvanized layer has a depth of 10 nm from the outermost surface of the plating. In the surface layer portion, the Al amount when measured by high-frequency glow discharge optical emission spectrometry is 1 to 5.0% by mass, so that the corrosion resistance such as white rust resistance is excellent, and the galvanized layer The chromate-free film-coated hot-dip galvanized steel sheet is useful as a material for automobile body steel sheets and the like.

  In many cases, a chromate-free film-coated hot-dip galvanized steel sheet is used as it is without being painted after being subjected to processing such as press forming or roll forming. When used in such a situation, it is important that the chromate-free film remains on the processed part. During the processing, the chromate-free film is somewhat damaged, but if the film remains on the plating layer, the corrosion resistance can be exhibited by the barrier effect. However, if the chromate-free film is completely removed, the barrier effect is lost.

  The present inventor was concerned about such a situation and studied from various angles in order to improve the adhesion between the chromate-free film and the surface of the hot dip galvanized layer. As a result, in the surface layer portion from the plating outermost surface to a depth of 10 nm, the above object can be achieved if the Al amount is 1 to 5.0% by mass when measured by high frequency glow discharge optical emission spectrometry. As a result, the present invention has been completed.

  When the amount of Al exceeds 5.0% by mass, the adhesion between the chromate-free film and the surface of the hot dip galvanized layer starts to deteriorate. The amount of Al is preferably 4% by mass or less. The reason why the adhesion between the chromate-free film and the surface of the hot dip galvanized layer is improved by setting the Al content in the surface layer portion of the plating to 5.0% by mass or less has not been clarified. It was considered that Al and an oxide of Al acted to inhibit the bond between the chromate-free film and the Zn of the outermost plating layer.

  When the amount of Al is 5.0% by mass or less, as the content decreases, the adhesion of the chromate-free coating is improved, and it becomes difficult to peel off. However, if the Al content in the plating surface layer is less than 1% by mass, the corrosion resistance of the chromate-free film-coated hot-dip galvanized steel sheet deteriorates, so this Al content needs to be 1% by mass or more. The amount of Al is preferably 2% by mass or more.

  In order to control the amount of Al in the plating surface layer so as to be in the above range, the base steel sheet is immersed in a hot dip galvanizing bath in which the Al concentration is adjusted to 0.2 to 0.3% by mass on the surface of the steel sheet. After forming the hot dip galvanized layer, hold it in the temperature range of over 400 to 440 ° C. for 10 to 30 seconds during the cooling process, and continue temper rolling at a stretch rate of 0.5 to 2% on the surface of the hot dip galvanized layer Should be applied. The reasons for specifying each requirement in this method are as follows.

  As described above, when Al is contained in the plating bath, the formation of the Fe—Zn alloy layer at the interface between the hot dip galvanized layer and the base steel sheet is suppressed and the adhesiveness of the hot dip galvanized layer is increased. However, in order to exert such an effect, the Al concentration in the plating bath needs to be 0.2% by mass or more. However, if the Al concentration in the plating bath becomes excessive, the erosion of the equipment in the bath becomes intense and the life becomes extremely short, so the Al concentration needs to be 0.3% by mass or less.

  The remaining components of the plating bath (hot galvanizing bath) used in the present invention are Zn and inevitable impurities. Examples of the inevitable impurities include Ti, Mn, Mg, Pb, Ni, Co, Sb, As, In, Cu, and Fe as elements inevitably mixed from a base steel plate. These inevitable impurity elements may be generally contained in a total range of about 0.02% or less (may be included in the plating layer). The present inventors have confirmed that the effects of the present invention are not impaired even if such elements are contained.

  In the hot dip galvanized steel sheet using the plating bath having the Al concentration prepared as described above, the amount of Al in the plating surface layer portion is relatively large (about 7 to 10% by mass). The amount of Al in the plating surface layer is affected by the plating bath temperature, line speed, etc., and the amount of Al will show variation. Therefore, in the present invention, in order to diffuse Al in the plating surface layer portion, in the cooling step after plating, the temperature range from 400 ° C. to 440 ° C. at which the hot-dip galvanized layer solidifies is cooled for at least 10 seconds. Specifically, the above temperature range may be cooled (slow cooling) over 10 seconds or may be kept isothermal at a predetermined temperature within the above temperature range.

  The melting point of zinc is about 420 ° C. Even if it is kept for a long time in a temperature range of 400 ° C. or less, Al does not diffuse, and the amount of Al in the vicinity of the outermost surface layer (surface layer portion) of the hot dip galvanized layer can be secured. Can not. On the other hand, when the temperature exceeds 440 ° C., the alloying reaction of Zn and Fe is promoted, and the adhesion between the base steel sheet and the hot dip galvanized layer is lowered. A preferable temperature range is 405 ° C. or higher and 435 ° C. or lower, and more preferably 410 ° C. or higher and 430 ° C. or lower.

  In the present invention, the time until the hot dip galvanized layer is solidified is set to at least 10 seconds, and the time until solidification is extended, whereby Al in the hot dip galvanized layer diffuses to at least the vicinity of the outermost layer. Time can be secured. If the time (hereinafter referred to as “holding time”) at this time is less than 10 seconds, the diffusion of Al becomes insufficient. Preferably it is 13 seconds or more, more preferably 15 seconds or more. The upper limit of the holding time is preferably 30 seconds or less, more preferably 25 seconds or less, considering the adjustment of the surface layer Al amount by the subsequent SKP rolling.

  After Al is diffused in the surface layer portion of the plating as described above, SKP rolling is performed in the range of elongation: 0.5 to 2%. By performing such SKP rolling, the amount of Al in the plating surface layer portion can be adjusted to a range of 1 to 5.0% by mass. Performing such SKP rolling does not destroy or scrape the Al in the plating surface layer portion, but as a result of the SKP rolling pushing the Al in the plating surface layer portion into the plating layer, A change occurs in the amount of Al. In such a situation, when the total amount of Al in the outermost layer (depth from the plating outermost surface to a depth of approximately 200 nm) is measured, the amount of Al in the plating layer is stable, and there is almost no quantitative change before and after SKP rolling. It was confirmed by

  In order to exert the above effects, it is necessary to set the elongation at the time of SKP rolling to about 0.5 to 2%. However, if the elongation at this time is less than 0.5%, This causes a problem in appearance because spangles remain. On the other hand, if the elongation exceeds 2%, pick-up of the SKP work roll Zn is likely to occur, and problems in both quality and operability may occur.

  The remaining components of the hot dip galvanized layer are Zn and inevitable impurities. Examples of the inevitable impurities include Ti, Mn, Mg, Pb, Ni, Co, Sb, As, In, Cu, and Fe as elements inevitably mixed from a base steel plate. These inevitable impurity elements may be contained in a range of approximately 0.02% or less in total. The inventor has confirmed that the effects of the present invention are not impaired even if such elements are contained.

  Other than the above plating conditions, conventionally used methods can be employed. For example, the temperature of the plating bath is generally controlled to about 470 to 450 ° C., and the immersion time in the plating bath is preferably about 2 to 10 seconds.

  The chromate-free film-coated hot-dip galvanized steel sheet of the present invention forms an organic chromate-free film on the surface of the hot-dip galvanized steel sheet obtained as described above. As the chromate-free film, an inorganic film is also known, but the inorganic film is not affected by the Al concentrated layer on the plating surface and originally has a good reactivity. In other words, the inorganic chromate-free film cannot effectively exhibit the effect of controlling the Al content of the plating surface layer as in the present invention. For these reasons, in the present invention, the chromate-free film formed on the surface of the hot dipped layer is limited to an organic type.

  As such an organic chromate-free film, those conventionally known can be used, but those proposed in Patent Document 1 are preferable. In the previously proposed technique, the polyolefin copolymer resin emulsion intermolecularly associated with the ion clusters contains silica particles: 1 to 30% by mass and crosslinking agent: 1 to 8% by mass in terms of solids. However, by forming such an organic chromate-free coating on the surface of a hot-dip galvanized steel sheet, the adhesion between the chromate-free coating and the surface of the plating layer can be further improved and corrosion resistance can be improved. It will be improved.

  The organic chromate-free film as described above is a polyolefin copolymer resin emulsion that is intermolecularly associated with ion clusters, in terms of solids, silica particles: 1 to 30% by mass, cross-linking agent: 1 to 8% by mass. In addition, if necessary, a water-based resin paint containing tannic acid and / or ammonium vanadate at a ratio of 1 to 8% by mass is applied to the surface of the hot dip galvanized steel sheet, and the steel sheet is heated to dry the paint. Can be formed.

  As the resin component in the water-based resin coating, a polyolefin copolymer resin emulsion intermolecularly associated with ion clusters is used. This polyolefin-based copolymer resin emulsion contains an ethylenically unsaturated carboxylic acid component in the range of 1 to 40% by mass and may contain a (meth) acrylic acid ester component. It is preferably a polyolefin copolymer resin obtained by ionizing a polymer resin and further polymerizing by crosslinking with a crosslinking agent.

  The polyolefin copolymer resin emulsion intermolecularly associated with the ion cluster includes a first step of producing a polyolefin copolymer having a carboxyl group and a second step of ionizing the polyolefin copolymer thus obtained. And the third step of polymerizing the obtained ionomer resin.

  In the production of a polyolefin copolymer emulsion intermolecularly associated with ion clusters, the production process of the copolymer, which is the first step, is as follows. First, an olefin as a first monomer and 1 to 40% by mass of an ethylenically unsaturated carboxylic acid as a second monomer, if necessary, other copolymerizable third A monomer mixture comprising monomer components is copolymerized in an aqueous dispersion medium at a temperature of 200 to 300 ° C. and a pressure of 1000 to 2000 atmospheres to prepare a polyolefin copolymer resin emulsion having a carboxyl group. .

  Examples of the ethylenically unsaturated carboxylic acid used above include (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, and the like. Among these, (meth) acrylic acid is particularly preferable. In addition, as the olefin as the first monomer, an aliphatic α-olefin such as ethylene or propylene or an aromatic vinyl compound such as styrene is usually preferably used. Therefore, examples of polyolefin copolymer resins preferably used in the present invention include ethylene- (meth) acrylic acid copolymer resins, styrene- (meth) acrylic acid copolymer resins, and ethylene-styrene- (meth). Examples thereof include acrylic acid copolymer resins.

  In addition to the first and second monomers, if necessary, the third monomer may be, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, or the like. (Meth) acrylic acid esters, styrene monomers such as styrene, vinyltoluene and chloroethylene, hydroxyethyl (meth) acrylate, hydroxyalkyl (meth) acrylate such as hydroxypropyl (meth) acrylate, N-methylol 1 type (s) or 2 or more types, such as N-substituted (meth) acrylamide, such as (meth) acrylamide, epoxy-group-containing (meth) acrylic acid ester, such as glycidyl (meth) acrylate, and (meth) acrylonitrile can be used.

  In the polyolefin copolymer resin as described above, when the ethylenically unsaturated carboxylic acid component exceeds 40% by mass, the polyolefin is intermolecularly associated by an ion cluster obtained through the subsequent emulsion ionomer process and high molecular weight process. Even if the copolymer resin emulsion is used as a film forming material, the resulting resin-coated hot-dip galvanized steel sheet cannot exhibit sufficient corrosion resistance. Further, when the ethylenically unsaturated carboxylic acid component is less than 1% by mass, it is difficult to make the resulting polyolefin copolymer resin water-soluble or water-dispersible, and an emulsion used in the present invention can be obtained. Can not.

  As the aqueous dispersion medium, water or a mixture of water and a hydrophilic organic solvent is used. Examples of the hydrophilic organic solvent include lower fatty acid alcohols such as methanol, ethanol and n-propanol, glycol ethers such as ethylene glycol methyl ether, glycol esters such as ethylene glycol acetate, ethers such as tetrahydrofuran and dioxane, dimethylformamide, and diacetyl. Alcohol or the like is used.

  The polyolefin copolymer resin obtained in the first step is then converted into an emulsion ionomer. This ionomerization is usually performed using an appropriate cation under conditions of a temperature of 80 to 300 ° C. and a pressure of 1 to 20 atmospheres. The cation used at this time is preferably a metal ion, and examples thereof include metal ions such as lithium, potassium, magnesium, zinc, sodium, calcium, iron, and aluminum.

  The polyolefin copolymer resin emulsion molecularly associated with ion clusters is preferably neutralized with an amine. By neutralizing with such an amine addition, the particle size of the emulsion particles is reduced, the film forming property is improved, and the effect of suppressing water permeability is exhibited, thereby improving the corrosion resistance of the coating. The neutralization is generally carried out with ammonia so far, but since the melting point of amine is higher than that of neutralizing agents such as ammonia, the film-forming speed during coating and drying becomes gentle, and the emulsion The fusion and leveling properties of the particles are improved, and a dense film is formed. Examples of the amine used at this time include isopropanolamine, N, N-diethylethanolamine, N, N-dimethylethanolamine, monoethanolamine, N, n-butyldiethanolamine and the like.

  By adding a crosslinking agent to the ionomerized resin and crosslinking it, a polyolefin-based copolymer that is molecularly associated with an ion cluster can be obtained. The cross-linking agent used at this time is not limited as long as it can cross-link the carboxyl group of a polyolefin-based copolymer resin molecularly associated with an ion cluster. For example, an epoxy group, an isocyanate group, a carboxy group can be used. An organic compound having an imide group, an aziridinyl group, or the like can be used, but an epoxy-based crosslinking agent is particularly preferable in terms of not only corrosion resistance but also stability and crosslinking efficiency.

  The content of the crosslinking agent in the film is preferably about 1 to 8% by mass (in terms of solids). When the content of the cross-linking agent is less than 1% by mass, the cross-linking reaction in the polyolefin-based copolymer resin intermolecularly associated with the ion clusters becomes insufficient, resulting in a film having poor corrosion resistance. Moreover, when content of a crosslinking agent exceeds 8 mass%, a water-system coating material gelatinizes and it becomes impossible to apply | coat to a plated steel plate. The crosslinking reaction is usually preferably performed under conditions of a temperature of about 30 to 200 ° C. and a pressure of about normal pressure to 20 atm.

  The above-mentioned organic chromate-free film contains silica particles at a ratio of 1 to 30% by mass in terms of solid matter. The silica particles are effective for imparting excellent corrosion resistance and paintability to the resulting film, and for suppressing the occurrence of wrinkling of the film during processing, the occurrence of blackening, and the like. In order to exhibit such an effect, it is necessary to contain 1 mass% or more of silica particles in terms of solid matter. However, when the content of the silica particles exceeds 30% by mass, the silica particles are deposited on the welded electrode tip and cause sparks, thereby damaging the electrode tip and extremely shortening the electrode life.

  In order to maximize the effect of the silica particles as described above, the average particle diameter of the silica particles is preferably about 1 to 9 nm. The smaller the average particle size of the silica particles, the better the corrosion resistance of the coating. However, even if silica particles having an extremely small particle size are used, the effect of improving the corrosion resistance does not increase correspondingly, and the stability in the coating is deteriorated and gelation tends to occur. From such a viewpoint, the silica particles preferably have an average particle diameter of 1 nm or more. On the other hand, if the silica particles become too large, the film forming property of the film deteriorates and the corrosion resistance decreases, so the average particle size is preferably 9 nm or less.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples as a matter of course, and appropriate modifications are made within a range that can meet the purpose described above and below. Of course, it is also possible to implement them, and they are all included in the technical scope of the present invention.

[Example 1]
Using an experimental machine, Al killed steel (cold rolled steel sheet, plate thickness: 0.8 mm) was hot dip galvanized under the following conditions, and then the chromate free film was coated to obtain a chromate free film coated hot dip galvanized steel sheet. At this time, Al killed steel (base steel plate) is C: 0.05%, Si: 0.02%, Mn: 0.19%, Al: 0.047%, P: 0.015%, S: 0.00. A steel plate containing 012%, the balance being iron and inevitable impurities.

  A K thermocouple was attached to one side of the Al killed steel by spot welding, and the plate temperature during the experiment was measured.

In hot dip galvanizing, the above Al killed steel sheet is annealed at 850 ° C. for 1 minute in an N ₂ gas atmosphere containing 5% by volume of H _2, and then the intrusion plate temperature is set to 460 ° C. in a hot dip galvanizing bath at 460 ° C. It was immersed and adjusted by gas wiping so that the plating adhesion amount was 70 g / m ² . The composition of the hot dip galvanizing bath contains the amount of Al shown in Table 1 below, with the balance being Zn and inevitable impurities.

After hot dip galvanization as described above, the steel was cooled to the holding temperature shown in Table 1 below at a cooling rate of 3 ° C./second in a pure N ₂ gas atmosphere. Subsequently, it was kept isothermally at the above temperature for 10 seconds using an infrared heater in an N ₂ gas atmosphere. Thereafter, it was cooled to room temperature in a pure N ₂ gas atmosphere at a cooling rate of 20 ° C./second. In this example, since the steel plate taken out from the hot dip galvanizing bath is held in the furnace using an experimental machine, the time for passing through the temperature range of 440 ° C. or lower and higher than 400 ° C. is the above holding temperature. It is almost equal to the holding time (10 seconds).

  Next, the hot-dip galvanized steel sheet cooled to room temperature was rolled by lab skin pass rolling (lab SKP rolling) with an aim of elongation: 0.1 to 2.0%. Thereafter, the flatness was corrected using a leveler.

  The amount of Al at the position (surface layer) 10 nm from the outermost surface of the hot-dip galvanized layer was measured by high-frequency glow discharge optical emission spectrometry (GD-OES) for the hot-dip galvanized layer whose surface was flattened in this way. did. The measurement apparatus and measurement conditions used for the measurement are as follows. In this measurement, the measurement results are shown in Table 1 below.

[GD-OES measurement conditions]
Measurement area: An area of φ4 mm was measured at an arbitrary position on the surface of the hot dip galvanized sample.
Measuring device: “GDA750 (device name)” manufactured by SPECTRUM ANALYTIK GmbH
Measurement conditions: Glow discharge power source (anhydrous GDS) -Spectrum Analytical-Grimm type was used in an argon gas of power 50 W, 2.5 hectopascals, and the measurement pulse was 50%.

  The hot dip galvanized steel sheet obtained above was coated with a chromate-free film by the following method.

[Chromate-free coating method]
The emulsion composition was prepared by the following procedure. Add 626 parts of water and 160 parts of ethylene-acrylic acid copolymer to the autoclave, add triethylamine and NaOH, and stir at high speed in an atmosphere of 150 ° C. and 5 Pa to obtain an emulsion of ethylene-acrylic acid copolymer. It was. The ethylene-acrylic acid copolymer contains 20% by mass of acrylic acid and has a melt index (MI) of 300. The triethylamine was added at 40 mol% with respect to 1 mol of the carboxyl group in the ethylene-acrylic acid copolymer, and the NaOH was added at 15 mol% with respect to 1 mol of the carboxyl group in the ethylene-acrylic acid copolymer.

  In the above emulsion, a glycidyl group-containing crosslinking agent (Dainippon Ink and Chemicals, "Epicron CR5L (trade name)") and an aziridinyl group-containing crosslinking agent (Nippon Shokubai, "Chemite DZ-22E (trade name)" , 4,4′-bis (ethyleneiminocarbonylamide) diphenylmethane), silica particles having a particle diameter of 4 to 6 nm (manufactured by Nissan Chemical Industries, “Snowtex XS (trade name)”), and vanadic acid Ammonium was added to obtain an emulsion composition. When the solid content (nonvolatile content) of the finally obtained emulsion composition is 100%, the glycidyl group-containing cross-linking agent and the aziridinyl group-containing cross-linking agent each have a solid content of 5% by mass. The silica particles were added so that the solid content was 25% by mass. The ammonium vanadate was added so that the solid content was 5% by mass.

  The chromate-free film was formed by heating and drying at an ultimate temperature (PMT) of 100 ° C. for 60 seconds.

  About each obtained chromate-free film-coated hot-dip galvanized steel sheet, an acrylic paint (manufactured by Kansai Paint, “Magicron 1000 (trade name)”) was applied with a bar coder and baked (film thickness: 20 μm, baking conditions: 160 ° C., 20 seconds). Two 50 mm × 120 mm test pieces were prepared for each test condition.

  About the said test piece, the primary adhesion test of the coating film was implemented. Using a cutter knife, cut in a grid pattern at intervals of 1 mm (pressing force: 300 g), apply two grids per sample, leave one grid as a grid, and process one for Eriksen (Extrusion amount: 6 mm) was carried out. After sticking the tape on each part, peeling it off and sticking it on the mount, visually judge the attached coating film, and (100-attachment%) is the coating film residual amount (acrylic coating film residual amount) and did. Adhesiveness was evaluated using the average value of n = 2 as the coating film residual ratio of the grid part and elixir part of each condition. A coating film remaining rate of 80% or more was accepted and less than 80% was rejected.

  Moreover, about the coating film peeling part, the qualitative analysis of Si was performed about each of the steel plate side and the tape side using SEM-EDX.

  The reason for adopting the above evaluation method is as follows. The chromate-free film used above is colorless and transparent. Therefore, it is difficult to judge the peeling state of the film as it is. Therefore, after coating the chromate-free film, an acrylic paint is applied, a primary adhesion test (cross-cut, Erichsen) is performed, and the adhesion is evaluated by the presence or absence of adhesion of the coating film to the tape. If the coating film does not adhere to the tape, it can be judged that the adhesion of (plating surface / chromate-free coating) is good. On the other hand, when a coating film adheres to the tape, EDX measurement is performed on the sample surface and the back side of the tape, and the presence or absence of Si, which is one of the components of the chromate-free coating, is investigated. If Si is not detected on the steel plate side, it can be determined that there is peeling of the chromate-free film on the surface of the plating layer. If Si is detected, the film breaks in the chromate-free film (in the above examples, both are in-film breaks) No occurrence).

  On the other hand, for each of the chromate-free film-coated hot-dip galvanized steel sheets obtained above, a salt spray test specified in JIS Z2371 was performed using a flat plate whose back and edge portions were sealed, and after 35 hours at 35 ° C. The area ratio of white rust occurrence was determined according to the following criteria, and corrosion resistance (white rust resistance) was evaluated. A 5% NaCl aqueous solution was used for the salt spray test. The area ratio of white rust was determined visually. The evaluation criteria for corrosion resistance are as follows.

[Evaluation criteria for corrosion resistance]
◎ (Pass): White rust generation area ratio is 1% or less.
○ (Pass): The area ratio of white rust is over 1% and 10% or less.
Δ (failed): White rust generation area ratio exceeds 10% and 30% or less.
X (failed): White rust generation area ratio exceeded 30%.

  These results are shown in Table 2 below, and can be considered as follows from these results. Steel plate No. Nos. 1 to 20 are examples of the present invention in which the Al content in the surface layer portion of the hot dip galvanized layer satisfies the requirements of the present invention, and it can be seen that all are excellent in corrosion resistance as well as adhesion. On the other hand, the steel plate No. 21 to 26 are examples that do not satisfy the requirements defined in the present invention, and it can be seen that the characteristics are deteriorated at least in terms of adhesion.

Claims (3)

In the chromate-free film-coated galvanized steel sheet, by immersing the base steel sheet and the Al concentration in the molten zinc plating bath was adjusted to 0.2 to 0.3 wt% green body having a galvanized layer and an organic-based chromate-free coating After forming the hot dip galvanized layer on the steel sheet surface, it is kept in the temperature range of more than 400 to 440 ° C. for 10 to 30 seconds in the cooling process, and subsequently, the elongation on the hot dip galvanized layer surface is 0.5-2%. Temper rolling was performed, and then an organic chromate-free film was formed on the surface of the hot dip galvanized layer. The hot dip galvanized layer was formed on the surface layer portion from the outermost surface of the plating to a depth of 10 nm at high frequency glow discharge emission spectroscopy. A chromate film with excellent adhesion between the plating surface and the chromate-free film, characterized in that the amount of Al measured by analysis is 1 to 5.0% by mass. Lee coating coated galvanized steel sheet.   The organic chromate-free film contains silica particles: 1 to 30% by mass and cross-linking agent: 1 to 8% by mass in terms of solid matter with respect to the polyolefin copolymer resin emulsion intermolecularly associated with the ion clusters. The chromate-free coating-coated hot-dip galvanized steel sheet according to claim 1.   In manufacturing the chromate-free film-coated hot-dip galvanized steel sheet according to claim 1 or 2, the base steel sheet is immersed in a hot-dip galvanized bath in which the Al concentration is adjusted to 0.2 to 0.3% by mass. After forming the hot dip galvanized layer on the steel sheet surface, it is kept in the temperature range of more than 400 to 440 ° C. for 10 to 30 seconds in the cooling process, and subsequently, the elongation on the hot dip galvanized layer surface is 0.5-2%. A method for producing a chromate-free film-coated hot-dip galvanized steel sheet having excellent adhesion to a chromate-free film, characterized by subjecting the product to temper rolling and then forming an organic chromate-free film on the surface of the hot-dip galvanized layer.