TWI612181B - Surface treated galvanized steel sheet and manufacturing method thereof - Google Patents

Abstract

The surface-treated galvanized steel sheet provided by the present invention can exhibit excellent dark spot resistance and excellent oil repellency even under severe press processing such as continuous high-speed press forming.

The surface-treated galvanized steel sheet according to the present invention includes a galvanized steel sheet and a surface-treated film; and the surface-treated film is formed on the surface of the galvanized steel sheet and contains fluororesin particles; On the surface, the area of the molten fluororesin formed by melting the fluororesin particles is more than 40% in terms of the area ratio with respect to the surface of the surface-treated film; the number density of unmelted fluororesin particles inside the area of the fused resin It is 50 pieces / 10 μm ² or less.

Description

Surface treatment galvanized steel sheet and manufacturing method thereof

The present invention relates to a surface-treated galvanized steel sheet, and more particularly to a surface-treated galvanized steel sheet that has both excellent dark spot resistance and oil repellency, and is not coated. The present invention relates to a method for producing the surface-treated galvanized steel sheet.

Surface-treated galvanized steel sheets (hereinafter also referred to as "steel sheets"), which are surface-treated to improve the corrosion resistance of the surface of galvanized steel sheets, are used in various fields. For example, in recent years, a chromate-free surface-treated galvanized steel sheet having a surface-treated film that does not contain hexavalent chromium has been widely used in parts of home appliances and OA equipment, and in electronic equipment parts of automobiles.

When parts such as motor housings are manufactured using surface-treated galvanized steel sheets, they are stamped without coating and deep drawing. For example, there may be cases where continuous high-speed press forming is performed by applying a lubricant on the surface of a steel sheet and using a progressive press to produce more than 100 formed products in one minute. In such a severe stamping environment of continuous high-speed stamping, there is a problem that part of the surface treatment film (hereinafter also referred to as "film") and the galvanized layer are peeled due to the sliding of the steel plate and the mold. If the surface treatment film and galvanized layer are peeled off, the appearance of the molded product will be impaired, and the corrosion resistance will be reduced.

Furthermore, peeling caused by peeling of the surface-treated film or the galvanized layer In the separation sheet (film shavings), those who are extremely fine are accumulated in the lubricating oil and adhere to the subsequent press-formed product. The release sheet adhered to the surface of the molded product is discolored and becomes dark spots, and thus causes the appearance of the molded product to be damaged. Here, in order to prevent dark spots, washing is performed using an organic solvent in the final step after press forming to remove the attached peeling sheet, but the peeling sheet may be left incompletely washed, posing a problem.

In addition, in recent years, due to the increasing concern for reducing environmental load, there has been a replacement of the conventional high-viscosity stamping oils, and the use of quick-drying oils as lubricants. It is also required to omit washing steps using organic solvents. However, because the lubricity of the quick-drying oil is lower than that of the conventional stamping oil, black spots are more likely to occur when the press-drying oil is used for press forming than in the case of the conventional stamping oil.

From the background described above, the development of surface-treated galvanized steel sheets with excellent characteristics such as dark spots resistance has evolved.

For example, Patent Document 1 proposes a technique for forming a film mainly composed of an inorganic substance by using a surface treatment liquid mainly composed of a water-soluble zirconium compound. The aforementioned film is finely pulverized during press forming, so that it is not as adhesive as a film mainly composed of an organic polymer. Therefore, it is difficult for the film swarf to adhere to the surface of the molded product or the mold, and the occurrence of dark spots can be prevented.

Furthermore, Patent Document 2 proposes a surface treatment film mainly composed of lithium silicate. Patent Document 2 suppresses the occurrence of dark spots by adjusting the ratio of SiO ₂ and LiO ₂ contained in the lithium silicate.

However, in most cases, the bearing portion of a motor is a plain bearing. The sliding bearing is used in a state where the lubricating oil of the working fluid is present in the bearing portion. When the shaft rotates, the above-mentioned lubricating oil generates oil pressure to prevent the rotary shaft from contacting with the bearing and sticking. In addition, the use of the lubricating oil can prevent vibration and noise from occurring in the motor. In the motor using the sliding bearing, the temperature of the bearing portion rises during use of the motor, which causes the viscosity of the lubricating oil to decrease. Therefore, the lubricant easily leaks from the bearing portion to the inner surface of the motor housing. If the lubricant in the bearing part is insufficient due to the leakage of the lubricant, it will be the cause of noise and vibration of the motor. In the worst case, the motor will fail.

The surface treatment films mainly composed of inorganic components described in Patent Documents 1 and 2 have a property that the lubricant oil can easily spread on the surface of the steel plate compared to the organic film, which poses a problem when applied to a motor case. Therefore, there are proposals to improve the technology as follows.

Patent Document 3 proposes to contain a small amount of sodium silicate for the purpose of imparting a plunging lubricating oil property (oil repellency) to a film of a lithium silicate main body. In addition, Patent Document 4 proposes to improve the oil retention property in a high-temperature and high-humidity environment by adding an organic polysiloxane compound to a surface treatment liquid mainly composed of a water-soluble zirconium compound.

In addition, Patent Document 5 proposes a surface treatment liquid containing a zirconium carbonate compound but not using an acrylic resin latex. By adding a hydroxycarboxylic acid to the surface treatment liquid, the adhesion of the obtained surface treatment film is improved. In addition, Patent Document 5 also describes that the surface of the surface treatment liquid contains a fluororesin emulsion in a trace amount, thereby improving the oil repellency of the surface of the steel sheet.

[Prior technical literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2008-169470

Patent Document 2: Japanese Patent Laid-Open No. 2010-037584

Patent Document 3: Japanese Patent Laid-Open No. 2010-215973

Patent Document 4: Japanese Patent Laid-Open No. 2012-026033

Patent Document 5: International Publication No. 2014/122900

However, in the technologies proposed in Patent Documents 1 and 4, since the surface treatment liquid contains acrylic resin latex as an essential component, it is easy for re-adhesion of film crumbs to occur during pressing. Therefore, the dark spot resistance of a surface-treated steel sheet obtained by using this surface-treatment liquid is hardly a sufficient level for stamping using quick-drying oil.

Furthermore, although the technologies proposed in Patent Documents 2 and 3 use a silicate-based surface treatment film, the adhesion between the silicate-based film and the galvanized layer is not high. Membrane crumbs can occur with high surface pressure. Therefore, dark spots cannot be completely prevented.

Although the technology proposed in Patent Document 5 shows a certain improvement in dark spot resistance, it is difficult to sufficiently obtain the oil-repellent effect by using a fluororesin latex. The reason is that if the amount of fluororesin latex is increased in order to improve oil repellency, the film will soften and easily peel off during press forming, resulting in a decrease in dark spot resistance.

As mentioned above, for surface-treated galvanized steel sheets that are used without coating in motor housings and other applications, in addition to the requirements for dark spot resistance during press forming, there is also a need to reduce the occurrence of lubricant wetting and diffusion from the bearing section. Oily, but no technology exists that meets these characteristics at the same time.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a surface-treated galvanized steel sheet that exhibits excellent dark spot resistance and has excellent oil repellency even in severe press processing such as continuous high-speed press forming. Another object of the present invention is to provide a method for producing the surface-treated galvanized steel sheet.

The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and found that even when a surface-treated film is formed using a surface-treatment liquid containing the same amount of fluororesin latex, the oil-repellency of the film may be caused according to the state of the fluororesin on the surface of the film difference. This point will be described below.

The surface of a surface-treated film formed using the surface-treating solution described in Patent Document 5 is observed with an electron microscope shown in FIG. 1. The surface treatment liquid is an aqueous solution containing: sodium zirconium carbonate: 25% by mass, phosphoric acid: 40% by mass, and fluororesin particles. As the fluororesin particle system, AG-E081 (softening point: 40 ° C) manufactured by Asahi Glass Co., Ltd. was used.

The electron microscope is a scanning low energy electron microscope (SLEEM, Scanning Low Energy Electron Microscope) (manufactured by FEI, Helios Nanolab 600i). Because the energy of the electron beam irradiated by the SLEEM on the sample can be lower than that of an ordinary SEM, a secondary electron image (SLEEM image) can be obtained only by acquiring the surface information of the sample pole. The lower the energy of the electrons incident on the surface of the sample, the higher the sensitivity of the surface, but if it is too low, the surface of the sample will be charged, which will cause charge up which is the cause of image noise, so the original sample surface information cannot be obtained. Taking the above into consideration, the incident electron energy (Landing Energy) during observation is set to 500 eV.

(A) is a SLEEM image of a steel plate with good oil repellency, and (b) is a SLEEM image of a steel plate with poor oil repellency. All the steel plates are in the SLEEM image, and black particles are observed in black contrast. The particulate matter was analyzed by an energy dispersive characteristic X-ray analyzer (EDX) attached to SLEEM. As a result, from the detection of fluorine (F), it was found that particles of a substance-based fluororesin having a black contrast were observed in the SLEEM image. However, if the SLEEM images of (a) a steel plate with good oil repellency and (b) a steel plate with poor oil repellency are compared, (a) The above-mentioned fluororesin particles are in a sparse state, and in (b), a difference in the distribution of the fluororesin particles in the fluororesin particle aggregation region can be seen everywhere.

Furthermore, in (a), a slightly dark gray area was observed from the matrix portion of the film so that a plurality of fluororesin particles were contained therein. The area was analyzed by using an Ogilvy electronic spectroscopic analysis device capable of analyzing polar surface elements, and as a result, a slight F was detected. From this phenomenon, it is known that the size of the above-mentioned area is significantly larger than the size of the fluororesin particles added in the surface treatment liquid, so it is presumed that this area is caused by the fluororesin latex melting and expanding on the surface of the film when the film is dry. On the other hand, in (b), such a gray region formed by melting the fluororesin particles was not observed.

Based on the above observation results, the surface state of the film formed by the surface treatment liquid of the fluorine-containing resin latex was further examined. As a result, the present inventors have obtained the following findings (1) to (4).

(1) Even when a surface treatment liquid of the same composition is used, the existence state of the fluororesin on the surface of the film varies depending on the manufacturing conditions.

(2) When the fluororesin particles are present on the surface of the film in an unmelted state, the oil-repellency improvement effect of the film is low, and if the number of the particles is increased, the dark spot resistance may be reduced.

(3) When the fluororesin particles are melted and spread on the surface of the film, the oil-repellency of the film can be effectively improved.

(4) If the area ratio of the molten fluororesin region is increased and the number density of the unmelted fluororesin particles is reduced, excellent oil repellency and dark spot resistance can be achieved at the same time.

The present invention is based on the above findings, and the gist constitution is as follows.

A surface-treated galvanized steel sheet comprising: a galvanized steel sheet; and a surface-treated film formed on the surface of the galvanized steel sheet and containing fluororesin particles; on the surface of the surface-treated film The area of the molten fluororesin formed by melting the fluororesin particles is more than 40% based on the area ratio with respect to the surface of the surface-treated film; the number density of the unmelted fluororesin particles in the area of the fused fluorine resin is 50 / 10 μm ² or less.

2. The surface-treated galvanized steel sheet according to the above 1, wherein (a) the area ratio is 80% or more, or (b) the area ratio is 40% or more and less than 80%, and the molten fluororesin is The average diameter of the region is 5 μm or less.

3. A method for producing a surface-treated galvanized steel sheet, which is the method for producing a surface-treated galvanized steel sheet according to claim 1 or 2, characterized in that it contains a softening point for latex relative to the total solid content. SP (° C) fluororesin 0.3 ~ 3.0% by mass surface treatment liquid, coated on the surface of galvanized steel sheet below plate temperature (SP + 10) ° C; galvanized steel sheet coated with the surface treatment liquid According to the average heating rate: 5 ~ 30 ℃ / s, heating to the highest reaching temperature: (SP + 30) ℃ or more.

According to the present invention, a surface-treated galvanized steel sheet having both excellent oil repellency and dark spot resistance can be obtained. This surface-treated galvanized steel sheet is suitable for applications such as motor housings that are used without coating.

Fig. 1 is a SLEEM image of (a) a steel plate having good oil repellency and (b) a steel plate having poor oil repellency obtained by using the same surface treatment liquid of a fluororesin latex.

Next, the method for implementing the present invention will be specifically described. In addition, the following description is an example of a preferred embodiment of the present invention, and the present invention is not limited in any way by the following description.

<Surface-treated galvanized steel sheet>

The surface-treated galvanized steel sheet of the present invention includes a galvanized steel sheet and a surface-treated film. The surface treatment film is formed on the surface of the galvanized steel sheet and contains fluororesin particles.

[Galvanized steel sheet]

In the present invention, the galvanized steel sheet serving as the base is not particularly limited, and a steel sheet having an arbitrary galvanized layer can be used. Here, the galvanized layer includes any one of a galvanized layer and a galvanized alloy layer. Examples of the galvanized steel sheet that can be preferably used include galvanized steel sheets such as hot-dip galvanized steel sheet (GI), alloyed hot-dip galvanized steel sheet (GA), and electro-galvanized steel sheet (EG); Zn-Ni plated steel sheet, Zn-Al-Mg plated steel plate, Zn-Al plated steel plate, etc. The Zn-Al-Mg plated steel sheet is preferably, for example, a Zn-6 mass% Al-3 mass% Mg alloy plated steel sheet, or a Zn-11 mass% Al-3 mass% Mg alloy plated steel sheet. The Zn-Al-plated steel sheet is preferably, for example, a Zn-5 mass% Al alloy plated steel sheet, Zn-1.6 mass% Si-55 mass% Al alloy plated steel sheet, or the like.

The galvanized layer may contain, for example, one or two of nickel, cobalt, manganese, iron, molybdenum, tungsten, titanium, chromium, aluminum, silicon, magnesium, lead, antimony, strontium, tin, and copper. More than that. These elements can also be contained in the plating layer as an additive component, and can also be contained as impurities. The galvanized steel sheet of the present invention may be provided with two or more layers of the same or different types of galvanized steel.

[Surface treatment film]

The present invention is to form a surface-treated film containing fluororesin particles on the surface of the galvanized steel sheet. The surface treatment film may be any material provided that it contains fluororesin particles. However, from the viewpoint of reducing environmental load, it is preferable to use a chromate-free surface treatment film (that is, a surface treatment not containing hexavalent chromium). Film), and more preferably a surface-treated film that does not contain chromium containing hexavalent chromium and trivalent chromium. From the viewpoint of improving the dark spot resistance, it is preferable to use a surface-treated film containing an organic resin other than the fluorine-containing resin. In other words, it is preferable to use a surface-treated film containing an organic resin containing only fluororesin particles. Furthermore, it is more preferable to use a chromate-free surface-treated film containing an organic resin containing only fluororesin particles. The chromate-free surface treatment film is preferably a phosphate-based surface treatment film.

The present invention focuses on: on the surface of the surface-treated film, a molten fluororesin region formed by melting the fluororesin particles exists in an area ratio of 40% or more relative to the surface of the surface-treated film, and the molten fluororesin region The number density of the internal unmelted fluororesin particles is 50 particles / 10 μm ² or less. The reasons for limiting the form of the surface-treated film will be described below.

[[Melted fluororesin area]]

In the present invention, the surface of the surface-treated film must have a molten fluororesin region formed by melting the fluororesin particles. With the presence of this molten fluororesin region, In the absence of a molten fluororesin region (that is, all fluororesin particles are not melted and maintained in a particulate state), both oil repellency and dark spot resistance can be improved.

In the present invention, the area ratio of the molten fluororesin region to the surface of the surface-treated film is set to 40% or more. The oil-repellency of the surface-treated film is that the higher the proportion of the molten fluororesin area occupied by the surface of the surface-treated film, the higher the oil-repellency. If the area ratio is above 40%, good oil-repellency can be obtained. The area ratio is preferably 50% or more. On the other hand, the upper limit of the area ratio is not particularly limited, and may be 100%.

The presence of the above-mentioned molten fluororesin region is shown in FIG. 1, for example, and it can be confirmed by observing the surface of the surface-treated film by SLEEM. The area ratio of the molten fluororesin region can be measured in accordance with a method described later.

[[Unmelted fluororesin particles]]

The present invention focuses on controlling the number density of unmelted fluororesin particles in the molten fluororesin region in addition to forming the fused fluororesin region. If the number density is more than 50 pieces per 10 μm ² , the amount of film swarf generated during press forming will increase, resulting in a decrease in dark spot resistance. When the fluororesin content of the surface treatment liquid is the same, the higher the number density is, the smaller the molten fluororesin area is and the lower the oil repellency is. Therefore, in the present invention, the number density of the unmelted fluororesin particles inside the fused fluororesin region is set to 50/10 μm ² or less. In addition, the number density is preferably set to 30/10 μm ² or less.

The above-mentioned unmelted fluororesin particle system is shown in FIG. 1 and can be confirmed by observing the surface of the surface-treated film by SLEEM. The number density of the unmelted fluororesin particles can be measured in accordance with the method described later.

The average diameter of unmelted fluororesin particles present on the surface of the surface-treated film is preferably 200 nm or less. By setting the average diameter of the unmelted fluororesin particles to 200 nm or less, the dark spot resistance can be further improved.

Furthermore, the present invention preferably satisfies any one of the following conditions (a) and (b).

(a) The area ratio of the molten fluororesin region is 80% or more.

(b) The area ratio is 40% or more and less than 80%, and the average diameter of the molten fluororesin region is 5 μm or less.

If the area ratio of the molten fluororesin area is more than 80%, most of the surface of the film will be occupied by the molten fluororesin area, so the oil repellency and dark spot resistance will be extremely good.

Furthermore, even when the area ratio of the molten fluororesin region is 40% or more and less than 80%, if the average diameter of the molten fluororesin region is 5 μm or less, excellent oil repellency and dark spot resistance can be obtained. This phenomenon can be considered as a case where the area ratio is the same. If each molten fluororesin region is large, the oil-repellent region becomes dense, and as a result, the oil-repellency of the entire surface is reduced. By reducing each molten fluororesin region so that the entire surface of the molten fluororesin region is dispersed, the oil repellency can be effectively improved even at a low area ratio. The measurement of the average diameter of the molten fluororesin region can be performed in accordance with the method described in Examples described later.

<Measurement method>

In one embodiment of the present invention, the above-mentioned SLEEM can be used in the measurement of the fluororesin present on the surface of the surface-treated film. When using SLEEM to observe the surface of the film, it is best to adjust the bias voltage applied to the sample platform and set the energy of the incident electrons to a range of 75eV or more and less than 1000eV. If the energy of the incident electron is lower than 75eV, it will cause the charge accumulation of the film, and the original surface information cannot be obtained. Case. On the other hand, if the energy of the incident electrons is more than 1000 eV, the information inside the film is overlapped and detected, so it is impossible to selectively observe only the surface of the film. In the SLEEM image, the unfused fluororesin particles and the fused fluororesin area are observed with different contrasts and are darker than other areas, which can be further identified. The contrast can also be emphasized by performing appropriate image processing on the obtained SLEEM image.

When measuring the presence of fluororesin on the surface of the surface-treated film, observation means other than SLEEM can also be used. For example, by using a field emission scanning OU-ELECTRON electron spectrometry (FE ~ AES) to measure the constituent atoms (carbon, fluorine, etc.) of a fluororesin, the fluororesin distribution on the outermost layer of the film can be measured.

[Area ratio of molten fluororesin area]

The area ratio of the molten fluororesin area to the surface of the surface-treated film can be obtained by analyzing, for example, a SLEEM image obtained by using image analysis software. In the above analysis, for example, if the image is binarized and divided into a molten fluororesin region and the remaining regions, the area ratio of the molten fluorine tree finger region to the entire area can be calculated.

[Average diameter of molten fluororesin region]

The average diameter of the molten fluororesin region is obtained by arbitrarily capturing at least 40 molten fluororesin regions from the surface of the film surface, such as a SLEEM image, and measuring the diameter of each region. At this time, when the molten fluororesin region is oval, the long diameter is set to the diameter.

[Number density of unmelted fluororesin particles]

The number density of unmelted fluororesin particles inside the fused fluororesin area is based on images of surface-treated film surfaces such as SLEEM images, and at least 40 fused fluororesin areas are arbitrarily captured. The average number of particles per unit area can be calculated by the number of particles present inside. When measuring the number of particles, software for image analysis can be used. Any of the above 40 regions of the molten fluororesin may be used for the measurement of the average diameter, and other regions may be used.

<Manufacturing method>

Next, a method for manufacturing a surface-treated galvanized steel sheet according to the present invention will be described. The surface-treated galvanized steel sheet according to an embodiment of the present invention can be manufactured by sequentially performing the following steps.

i) A fluororesin with a softening point SP (° C) as a latex and a surface treatment liquid containing 0.3 to 3.0% by mass relative to the total solid content is applied to a galvanized steel sheet having a plate temperature (SP + 10) ° C or lower Surface steps.

ii) the step of heating the galvanized steel sheet coated with the surface treatment liquid to a maximum reaching temperature: (SP + 30) ° C or more according to an average temperature increase rate: 5 to 30 ° C / s.

Hereinafter, examples of usable surface treatment liquids and details of each of the above steps will be described.

[Surface treatment liquid]

The present invention uses the oil-repellent property of the fluororesin to control the fluororesin form on the surface of the surface-treated film. Therefore, the effect does not depend on the film components other than the fluororesin, and any surface can be used to form a film on the premise that the surface treatment liquid contains a fluororesin latex.

In addition, from the viewpoint of reducing environmental load substances, it is preferable to use a chromate-free surface treatment liquid (that is, a surface treatment liquid not containing hexavalent chromium), and more preferably to use chromium not containing hexavalent chromium and trivalent chromium. Surface treatment fluid. From the viewpoint of improving the dark spot resistance, it is preferable to use a surface treatment liquid of an organic resin other than the fluorine-free resin. In other words, it is preferable to use a surface treatment liquid of an organic resin-based fluororesin emulsion only. Furthermore, it is more preferable to use a chromate-free surface treatment liquid of an organic resin containing only a fluororesin latex. The above-mentioned chromate-free surface treatment liquid is particularly preferably a phosphate-based surface treatment liquid.

The above-mentioned fluororesin can be extracted before it can exist as a latex in the surface treatment liquid, and any substance can be used. Examples of usable fluororesins include: monopolymers of fluorinated acrylate monomers; fluorinated acrylate monomers; and ethylene-based monomers such as ethylene, styrene, acrylic, methacrylic, and methacrylic esters. Copolymers and so on.

The fluororesin content of the surface treatment liquid is 0.3 to 3.0% by mass based on the total solid content of the surface treatment liquid. In other words, the ratio of the solid content of the fluororesin latex to the total solid content of the surface treatment liquid is set to 0.3 to 3.0% by mass. If the content of the fluororesin in the surface treatment liquid is less than 0.3% by mass, sufficient oil repellency cannot be obtained. On the other hand, if the content of the fluororesin exceeds 3.0% by mass, although the oil repellency is improved, the number of fluororesin particles remaining on the surface of the surface-treated film will increase, resulting in a decrease in dark spot resistance.

The fluororesin has a particle form and is used by being dispersed in a surface treatment liquid. The particle diameter of the fluororesin particles is not particularly limited, and it can be extracted before the surface treatment liquid can exist in the form of latex. Any value can be used, but it is preferable to use a particle diameter of 10 to 200 nm.

As described above, the present invention can be used in which the above-mentioned fluororesin particle latex is added to a surface treatment liquid having an arbitrary composition, and it is particularly preferable to use a composition containing the following examples (A) ~ (G), Chromate-free surface treatment liquid with solvent water. The above-mentioned chromate-free surface treatment liquid system may optionally further contain the component (I).

(A) zirconium carbonate compound, (B) phosphoric acid compound, (C) hydroxycarboxylic acid, (D) tetraalkoxysilane, (E) epoxy-based silane coupling agent, (F) vanadium compound, (G) Nickel compound, (I) wax.

(A) Zirconium carbonate compound

These zirconium carbonate compounds can be used alone or in combination of two or more of them. Among these, it is preferable to use a zirconium carbonate salt, and it is more preferable to use one or more types selected from the group consisting of an alkali metal salt and an ammonium salt of zirconium carbonate. Examples of the alkali metal salt system include a lithium salt, a sodium salt, and a potassium salt.

(B) phosphate compound

The above-mentioned phosphoric acid compound is extracted before being soluble in the surface treatment liquid, and the rest is not particularly limited, and any one of them may be used alone or in combination of two or more. The phosphoric acid compound can be selected from 1 or 2 or more selected from the group consisting of oxyacids of phosphorus, condensed phosphoric acid, and salts thereof.

The phosphoric acid compound may be at least one selected from the group consisting of an inorganic phosphoric acid compound and an organic phosphoric acid compound. The inorganic phosphate compound may be For example, oxyacids such as phosphoric acid, phosphorous acid, and diphosphoric acid; condensed phosphoric acid such as pyrophosphate (diphosphate) and tripolyphosphoric acid (triphosphate); and salts thereof. As the organic phosphoric acid compound, nitrogen trimethylene phosphonic acid, phosphonobutane tricarboxylic acid, ethylene diamine tetramethylene phosphonic acid, methyl diphosphonic acid, and methylene phosphonic acid can be used. And organic phosphonic acids such as ethylene diphosphonic acid; and such salts. As said salt system, an ammonium salt, an alkali metal salt, etc. can be used. Examples of the alkali metal salt system include a lithium salt, a sodium salt, and a potassium salt.

The ratio (B / A) of the P-converted solid content mass of the phosphoric acid compound (B) to the Zr-converted solid content mass of the zirconium carbonate compound (A) is preferably 0.3 to 2.2.

(C) hydroxycarboxylic acid

The said hydroxycarboxylic acid system can be used individually by 1 type or in combination of 2 or more types. Examples of the hydroxycarboxylic acid include lactic acid, tartaric acid, malic acid, and citric acid. The ratio (C / A) of the solid content mass of the hydroxycarboxylic acid (C) to the Zr-equivalent solid content mass of the zirconium carbonate compound (A) is preferably 0.05 to 0.87.

(D) Tetraalkoxysilane

The said tetraalkoxysilane type can be used individually by 1 type or in combination of 2 or more types. Examples of the tetraalkoxysilanes include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane. The ratio (D / A) of the solid content of the tetraalkoxysilane (D) to the Zr-equivalent solid content of the zirconium carbonate compound (A) is preferably 0.11 to 1.80.

(E) Epoxy-containing silane coupling agent

The said epoxy-group-containing silane coupling agent is a silane coupling agent which has an epoxy group and an alkoxy group in 1 molecule, and can be used individually by 1 type or in combination of 2 or more types. The alkoxy group is preferably an alkoxy group having 1 to 4 carbon atoms, and more preferably an alkoxy group having 1 to 3 carbon atoms. Examples of the epoxy group-containing silane coupling agent include: 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxy Propylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane, and the like. The ratio (E / A) of the solid content mass of the epoxy group-containing silane coupling agent (E) to the Zr-equivalent solid content mass of the zirconium carbonate compound (A) is preferably 0.06 to 0.50.

(F) Vanadium compounds

These vanadium compounds can be used alone or in combination of two or more of them. Examples of the vanadium compound include compounds containing oxoanion of vanadium such as ammonium metavanadate and sodium metavanadate; and acetoacetone vanadium. The ratio (F / A) of the V-converted solid content mass of the vanadium compound (F) to the Zr-converted solid content mass of the zirconium carbonate compound (A) is preferably 0.02 to 0.30.

(G) Nickel compounds

The said nickel compound can be used individually by 1 type or in combination of 2 or more types. Examples of the nickel compound include nickel salts such as nickel nitrate, nickel sulfate, nickel carbonate, nickel chloride, and nickel phosphate. The ratio (G / A) of the Ni-based solid content mass of the nickel compound (G) to the Zr-based solid content mass of the zirconium carbonate compound (A) is preferably 0.02 to 0.16.

(I) Wax

The wax system is extracted before being compatible with the surface treatment liquid, and may be used alone or in combination of two or more of them. Examples of the wax system include polyolefin wax, montan wax, paraffin wax, microcrystalline wax, palm wax, lanolin wax, and silicon wax. For example, the polyolefin wax may be polyethylene wax, oxidized polyethylene wax, polypropylene wax, or the like, and one or more of them may be used. When using a wax, the ratio (I / X) of the solid content of the wax (I) to the total solid content (X) of the surface treatment liquid is preferably set to 0.01 to 0.05.

The surface treatment liquid containing the above-mentioned components in this embodiment is further water containing a solvent. This surface treatment liquid is obtained by mixing the above components in water such as deionized water and distilled water, for example. The surface treatment liquid system may optionally contain one or more additives. Examples of the additives include water-soluble solvents such as alcohols, ketones, cyperidine, and amines; defoamers, antibacterial and antifungal agents, colorants, wettability enhancers and surfactants that can be uniformly applied Wait. The above-mentioned additives are added within a range that does not impair the characteristics of the surface-treated film, and can be added in any amount.

When a surface treatment liquid containing the above components is used, the pH of the surface treatment liquid is preferably 8 to 10, and more preferably 8.2 to 9.6. If the pH is 8 or more, the storage stability of the surface treatment liquid, the adhesion and appearance of the surface treatment film will not be impaired. In addition, if the pH is 10 or less, etching of the galvanized layer will not be excessively intense, and the corrosion resistance of the flat portion and the appearance of the surface-treated film will not be impaired. The additives used in the pH adjustment are not particularly limited, and any acid or base can be used. The base is preferably a compound selected from ammonium, an amine, an amine derivative, and an amine polycarboxylic acid, and the acid is preferably a compound selected from the hydroxycarboxylic acid (C) and the phosphoric acid compound (B). Selected acid.

The surface-treated galvanized steel sheet of the present invention is obtained by applying a surface treatment solution containing the above-mentioned fluororesin latex to at least one side of a galvanized steel sheet, and then heating it.

[Pre-processing]

For the purpose of rust prevention, galvanized steel sheets are often coated with rust preventive oil, and even if the rust preventive oil is not applied, oil, dirt, etc. may still adhere during operation. Therefore, before the surface treatment liquid is applied to the galvanized steel sheet, it is preferable to perform a pretreatment for the purpose of removing oil and dirt adhered to the surface of the galvanized steel sheet. With the above pretreatment, the surface of the galvanized layer is cleaned, and the treatment liquid can be easily wetted uniformly. When there is no oil, dirt, etc. on the surface of the galvanized steel sheet, and the surface treatment liquid is uniformly wetted, there is no need for a pretreatment step in particular. The method of the pretreatment is not particularly limited, and examples thereof include methods such as hot water washing, solvent washing, and alkali degreasing.

[Coating step]

After the pretreatment is performed as necessary, a surface treatment liquid is applied to the surface of the galvanized steel sheet. The method of applying the surface treatment liquid may be selected by selecting an appropriate optimum method according to the shape of the galvanized steel sheet to be treated. For example, a roller coating method, a bar coating method, a dipping method, or a spray method may be used. method. In addition, after the coating, the coating amount can be adjusted by an air knife method, a roll extrusion method, or the like, and the appearance can be made uniform and the film thickness can be made uniform.

In the present invention, when the softening point of the fluororesin contained as a latex in the surface treatment liquid is set to SP (° C), it is important to set the temperature (plate temperature) of the galvanized steel sheet when the surface treatment liquid is applied to ( SP + 10) ° C or lower. If the plate temperature is higher than (SP + 10) ° C, the surface treatment liquid is dried before the fluororesin particles are melted and spread on the film surface, so the area ratio of the molten fluororesin area on the film surface cannot be increased, resulting in oil repellency reduce.

In addition, the fluororesin added to the surface treatment liquid as a latex is softened The point is not particularly limited, but is preferably set to 35 to 50 ° C. When there are two or more kinds of fluororesins with different softening points in the treatment liquid, when the softening point of at least one fluororesin contained in the treatment liquid is set to SP (° C), the plate temperature during coating is preferably When the lowest of the softening points of the fluororesin contained in the treatment solution is set to SP (° C) at (SP + 10) ° C or lower, the plate temperature during coating is more preferably (SP + 10) ° C or lower.

[Heating step]

Next, a galvanized steel sheet coated with a surface treatment liquid is heated to dry the surface treatment liquid to form a film. Any heating means can be used, such as a dryer, a hot blast stove, a high-frequency induction heating furnace, and an infrared furnace. The heating is preferably started within 5 seconds after the surface treatment liquid is applied.

The above-mentioned heating is performed until the steel sheet reaches a temperature (highest reaching temperature) of (SP + 30) ° C or higher. If the maximum temperature reached is less than (SP + 30) ° C, the heating will be completed before the formation of the molten fluororesin region, which will not only cause oil repellency but also reduce dark spot resistance. In addition, it is more preferable that the maximum reaching temperature is set to (SP + 50) ° C or higher. On the other hand, there is no particular limitation on the upper limit of the maximum reachable temperature. If the temperature is excessively high, the fluororesin may undergo oxidation and decomposition. Therefore, it is preferable to set it at 150 ° C or lower.

In the heating step, it is important that the average temperature rise rate from the time when heating is started to the above-mentioned maximum temperature reached 5 to 30 ° C / s. If the average temperature rise rate is less than 5 ° C / s, the agglomeration of the fluororesin particles is more advantageous, and the number density of the unmelted fluororesin particles will increase, which will result in a decrease in dark spot resistance. On the other hand, if the average temperature rise rate is higher than 30 ° C / s, the drying of the fluororesin latex is completed before the fluororesin latex melts and spreads on the surface of the film, so that a sufficient area ratio of the molten fluororesin cannot be obtained, resulting in a reduction in oil repellency. In addition, the average heating rate is more preferably set to 10 to 20 ° C / s.

In addition, after reaching the maximum reaching temperature, the heating and drying may be stopped before the temperature can be maintained at that temperature or the film can be confirmed to be dried. The cooling process is not particularly limited.

<Example>

Next, the present invention will be described more specifically based on examples. The following embodiment is merely an example of the preferred embodiment of the present invention, and the present invention is not limited in any way by this embodiment.

On the surface of the galvanized steel sheet, a surface-treated film containing fluororesin particles was formed under various conditions, and the state of the fluororesin on the surface of the obtained film was observed, and the black spot resistance and oil repellency of the surface-treated galvanized steel sheet were evaluated.

The galvanized steel sheet is an electro-galvanized steel sheet (plate thickness: 0.5 mm, plating adhesion amount: 15 g / m ² per one side). The surface treatment liquid was applied using a bar coater, and the surface treatment liquid was applied so that the adhesion amount became 0.7 g / m ² . The heating system after coating was performed using an IH heater. The surface treatment liquid used is shown below. Table 1 shows the fluororesin content in the treatment liquid, the plate temperature during coating, the average temperature rise rate during heating, and the maximum temperature reached. In addition, after reaching the maximum reaching temperature, it was held at this temperature for 5 seconds, and then air-cooled to room temperature.

The composition of the surface treatment liquid used is as follows. The content of the fluororesin relative to the total solid content of the surface treatment liquid is set as shown in Table 1. In addition, when adjusting pH, ammonia is used as needed.

[Surface treatment liquid A]

‧Fluorine resin (AG-E081 manufactured by Asahi Glass Co., Ltd., softening point: 40 ° C)

‧Sodium zirconium carbonate: 25% by mass

‧ Phosphoric acid: 40% by mass

‧Malic acid: 5% by mass

‧Alkoxysilane, silane coupling agent: 15% by mass

‧Water (the rest)

[Surface treatment liquid B]

‧Fluorine resin (AG-E081 manufactured by Asahi Glass Co., Ltd., softening point: 40 ° C)

‧Sodium zirconium carbonate: 15% by mass

‧ Phosphoric acid: 40% by mass

‧Malic acid: 5% by mass

‧Alkoxysilane, silane coupling agent: 30% by mass

‧Water (the rest)

[Surface treatment liquid C]

‧Fluorine resin (AG-E081 manufactured by Asahi Glass Co., Ltd., softening point: 40 ° C)

‧Sodium zirconium carbonate: 25% by mass

‧Phosphoric acid: 55% by mass

‧Alkoxysilane, silane coupling agent: 5 mass%

‧Water (the rest)

<Fluorine resin state on film surface>

The state of the fluororesin on the surface of the film of the obtained surface-treated galvanized steel sheet was observed using SLEEM (FEI Corporation, Helios Nanolab 600i). The incident electron energy at the time of observation takes into account the difference in conductivity caused by the sample, which is between 75 ~ 1000eV Adjustment. The observation magnification was set to 5000 times, and a 10 μm square SLEEM image in any 10 fields of view was obtained.

Image processing was performed on the obtained SLEEM image, and three regions, such as a fluororesin particle (black), a molten fluororesin region (gray), and the rest, were identified based on the comparison. Based on this result, the area ratio of the molten fluororesin region, the average diameter of the region, and the number density of the unmelted fluororesin particles inside the region were calculated as the average values in the above 10 fields of view. In the case where the molten fluororesin region is oval, the major axis is set to the diameter. In addition, when the area ratio of the molten fluororesin region is 80% or more, it is difficult to measure the diameter because the regions overlap each other, and the average diameter is not calculated.

<Dark Spot Resistance>

The obtained surface-treated galvanized steel sheet was subjected to continuous high-speed press forming, and the dark spot resistance was evaluated based on the appearance after press forming. The evaluation method will be described below.

Each steel sheet was coated with a quick-drying stamping oil (manufactured by Japan Working Oil Co., Ltd .: non-washing stamping cutting oil G-6231F), and multi-stage deep drawing was performed under the following stamping conditions. In the case where the dirt adhered to the mold was not wiped, after 10 samples were continuously formed, the degree of dark spots adhered to the surface of the 10th sample was visually observed to evaluate the dark spot resistance.

(Stamping conditions)

90mm Forming speed 450mm / s, blank diameter

90mm

49mm、衝頭與模具之間隙1.0mm Paragraph 1: punch diameter

49mm, 1.0mm clearance between punch and die

39mm、衝頭與模具之間隙0.8mm Paragraph 2: punch diameter

39mm, 0.8mm clearance between punch and die

32mm、衝頭與模具之間隙0.8mm Paragraph 3: punch diameter

32mm, 0.8mm clearance between punch and die

27.5mm、衝頭與模具之間隙0.8mm Paragraph 4: punch diameter

27.5mm, 0.8mm clearance between punch and die

24.4mm、衝頭與模具之間隙0.8mm Paragraph 5: punch diameter

24.4mm, 0.8mm clearance between punch and die

(Evaluation criteria)

：: No dark spots were adhered to the surface of the sample even after pressing.

○: Although the dark spots were adhered to the surface of the sample at an area ratio of 5% or less immediately after the stamping, the black spots disappeared from the surface of the steel plate with the passage of time and were hardly found.

○-: Dark spots were adhered to the surface of the sample at an area ratio of 5% or less immediately after stamping. Even if time passed, black spots remained on the surface of the steel plate.

△: Dark spots adhered to the surface of the sample in an area ratio of more than 5% to 15%. Even if time passed, black spots remained on the surface of the steel sheet.

×: Dark spots adhered to the surface of the sample by more than 15% by area ratio. Even if time passed, black spots remained on the surface of the steel sheet.

<Oil repellency>

The oil repellency of the obtained surface-treated galvanized steel sheet was evaluated according to the following method.

With each steel sheet heated to 85 ° C, bearing oil ("ALL TIME J 1652" manufactured by NOK Klüber Co., Ltd.) was dropped on the surface of the steel sheet, and after being dropped, it was left to stand at 85 ° C for 3 days. Dynamic viscosity of the bearing oil system at 40 ℃ of 51 ~ 69mm ² / s, at 100 deg.] C is 11.1 ~ 14.9mm ² / s. Then, the contact angle between the surface of each steel plate and the bearing oil was measured using a solid-liquid interface analyzer ("Drop Master 500" manufactured by Kyowa Interface Science Co., Ltd.). The evaluation criteria are as follows:

<Evaluation Criteria>

◎: Contact angle above 40 °

○: Contact angle is 30 ° or more and less than 40 °

△: Contact angle 15 ° or more and less than 30 °

×: The contact angle is less than 15 °

From the results shown in Table 1, it was found that the surface-treated galvanized steel sheet that satisfies the conditions of the present invention can balance the opposite properties of dark spot resistance and oil repellency at a high level. In contrast, a steel sheet having a molten fluororesin area ratio that does not meet the conditions of the present invention has poor oil repellency. In addition, the number density of unmelted fluororesin particles inside the molten fluororesin region did not satisfy the conditions of the present invention, and the dark spot resistance was poor.

(Industrial availability)

According to the present invention, a surface-treated galvanized steel sheet having both excellent oil repellency and dark spot resistance can be obtained. This surface-treated galvanized steel sheet is suitable for applications such as motor housings that are used without coating.

Claims (2)

A surface-treated galvanized steel sheet includes: a galvanized steel sheet; and a surface-treated film formed on the surface of the galvanized steel sheet and containing fluororesin particles; and on the surface of the surface-treated film, The area of the molten fluororesin formed by melting the fluororesin particles is 40% or more and less than 80% based on the area ratio of the surface of the surface-treated film. It is 50 pieces per 10 μm ² or less; the average diameter of the molten fluororesin region is 5 μm or less. A method for manufacturing a surface-treated galvanized steel sheet, which is the method for manufacturing a surface-treated galvanized steel sheet according to claim 1, characterized in that the softening point of the latex is SP (° C) relative to the total solid content. The surface treatment liquid of fluororesin 0.3 ~ 3.0% by mass is applied on the surface of galvanized steel sheet below the plate temperature (SP + 10) ° C; the galvanized steel sheet coated with the surface treatment liquid is subjected to the average heating rate: 5 ~ 30 ℃ / s heating to the highest reached temperature: (SP + 30) above.