JPH0372714B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a method for producing a metal surface-treated steel sheet with excellent corrosion resistance and coating performance, in which a two-layer chromate coating is applied to a metal surface-treated steel sheet. The metal surface-treated steel sheets mentioned here include zinc and zinc alloy plated steel sheets, lead and lead alloy plated steel sheets,
It is a steel plate plated with metal, such as aluminum and aluminum alloy plated steel plate. Specifically, galvanized steel sheets and zinc alloy-plated steel sheets include: (a) galvanized steel sheets that contain elements that are unavoidably mixed in as impurities by electroplating or vacuum evaporation plating; and (b) galvanized steel sheets with an Al content of 0.1 to 0.3. %, other substances include Pb, Cd, Fe,
Hot-dip galvanized steel sheet containing one or more elements such as Sb and unavoidable impurity elements (c) Fe-Zn alloy-plated steel sheet containing 5 to 90% Fe and unavoidable impurity elements (d ) Zn-Ni alloy plated steel sheet containing 5 to 20% Ni and unavoidable impurity elements (e) Zn containing 3 to 60% Al or containing Si, Mg, Mitsushi metal, or unavoidable impurities
-Al alloy plated steel sheets, etc.; lead plated and lead alloy plated steel sheets include (a) lead plated steel sheets containing unavoidable impurities during the manufacturing process; (b) containing 30% or less of Sn; and in some cases Sb,
Examples include Pb-Sn alloy plated steel sheets that contain Zn or other unavoidable impurity elements; furthermore, aluminum and aluminum alloy plated steel sheets include (a) unavoidable amounts of Fe and other elements during plating; , aluminized steel sheet (b) Contains one or more of Si and Mg, and Si is 12
% or less, or an aluminum alloy plated steel plate with Mg content of 5% or less. (Prior art) Recently, users have asked us about the appearance, uniform coverage, corrosion resistance, and painting performance (paint adhesion, corrosion resistance after painting, etc.) of metal surface-treated steel sheets such as galvanized steel sheets and zinc alloy-plated steel sheets. Since there is a strong desire for an excellent treatment method, various chromate treatments are being carried out. For example, (1) a method of forming a film on the surface of a surface-treated steel sheet by applying an aqueous solution containing a chromium compound in an organic resin and then drying it (for example, JP-A-59-200768). (2) On the surface of the surface-treated steel sheet, a first layer coating is formed by applying an aqueous solution containing a chromium compound in an organic resin and then drying, and then coating the first layer coating on the surface of the first layer coating. A method of forming a second layer film by further applying a water-soluble organic resin (for example, Japanese Patent Application Laid-Open No. 14552/1983). (3) A first layer film is formed by applying an aqueous solution consisting of a chromium compound and an inorganic acid on the surface of the surface-treated steel sheet and then drying it, and then further applying an aqueous solution on the surface of the first layer film. A method of forming a second layer film by applying a synthetic organic resin (for example, JP-A-59-166678, JP-A-59-162278, JP-A-59-162279). (4) Surface-treated galvanized or alloyed galvanized steel sheet is coated with a chromium compound aqueous solution containing phosphoric acid, zinc ions, and fluorine ions to form a first layer of chromate film, and silicon dioxide is applied on top of the first layer of chromate film. A method of forming a second layer of chromate film by applying an aqueous solution of a chromium compound to which each of the above-mentioned contained ions is added (for example, Japanese Patent Application Laid-Open No. 1983-1999)
4880). etc. (Problems to be Solved by the Invention) Although the surface-treated steel sheet manufactured by the method (1) above has excellent paint film adhesion and corrosion resistance after painting, it has a problem that it is inferior in bare corrosion resistance without painting. have. In other words, since the coating formed by method (1) above contains many organic substances, when exposed to a corrosive environment for a long time without coating, the functional groups of the organic substances absorb moisture, and further tends to penetrate into the coating and deteriorate bare corrosion resistance. The surface-treated steel sheets produced by the methods (2) and (3) above are unpainted and have excellent bare corrosion resistance and paint film adhesion. However, if the drying or insolubilization reaction of the first layer chromate film is insufficient when applying the water-soluble organic resin of the second layer film onto the surface of the first layer film, this film may The components are eluted into the water-soluble organic resin of the second layer, gelling the water-soluble organic resin, resulting in deterioration of the bath life of the water-soluble organic resin bath and deterioration of the coating performance of the second layer. Therefore, in order to sufficiently dry or insolubilize the first layer coating, a drying device such as an induction heater or an infrared heater is required. There were also issues that required time. Furthermore, over time, the organic resin in the second layer organic coating reacts with the Cr ⁶⁺ in the first layer coating, resulting in deterioration of coating performance. In addition, when applying these organic resins or aqueous solutions of organic resins containing chromium compounds to the surface of surface-treated steel sheets, a coating method using a roll coater is mainly used to ensure good appearance performance and uniform coverage of the film. are doing. This method is advantageous for uniform coating when a thick coating layer with a thickness of 1μ or more, preferably 3μ or more is applied, but it is advantageous for uniform coating when a thin coating layer of less than 1μ is applied, improving appearance performance and spreading properties. Therefore, it is difficult to form a coating with excellent corrosion resistance. Further, in the method (4) above, the chromate film of the first layer is eluted into the second layer forming treatment bath due to long-term operation. Therefore, in order to form a chromate film with good performance in the second layer, it is necessary to control the ions eluted from the first layer film, and it is necessary to perform complicated bath composition adjustment and management of the second layer treatment bath. There were some problems. Furthermore, Japanese Patent Application Laid-Open No. 52-10834 discloses a chromate treatment method in which an aqueous solution containing a chromium compound, colloidal silica, etc. is applied to a metal surface using an electrostatic atomizer. However, in this method, an aqueous solution containing a chromium compound is applied in an atomized state under electrostatic charge, so the atomized particles are efficiently attached to the metal surface, but the distance between the attached particles is small. There was a problem that the uniform coverage of the chromate film deteriorated and the corrosion resistance deteriorated. The present invention solves the performance problems and processing problems of the various chromate treatment methods described above, and provides an industrially stable chromate treatment method with excellent appearance, uniform coverage, corrosion resistance, and coating performance. It is intended to be formed on the surface of a steel plate. (Means for solving the problem) Excellent appearance, coating uniformity, corrosion resistance, and painting performance of metal surface-treated steel sheets such as zinc or zinc alloy plated steel sheets, aluminum or aluminum alloy plated steel sheets, and lead or lead alloy plated steel sheets. As a result of various studies on manufacturing methods for metal surface-treated steel sheets with a two-layer chromate coating, we found that the composition and properties of the second layer chromate bath were adapted to the uniform formation of electrostatically atomized particles, and that this chromate bath was used in the first layer. A second layer of chromate film is deposited and formed on a metal surface-treated steel sheet with a chromate film by electrostatic atomization, and a second layer of film is formed by mixing a chromate bath that forms a chromate film on the first layer. The chromate bath for formation is not contaminated, and the second layer of chromate film can be provided at a predetermined amount regardless of the amount (thickness) of the second layer, and the superimposed effect with the first layer of chromate film can be avoided. It was thus discovered that a film with excellent uniformity could be obtained. The present invention was constructed based on this knowledge,
The gist of this is that by applying an electrolytic treatment method or a coating treatment method using an aqueous solution containing Cr ⁶⁺ as the main component to a steel sheet that has been subjected to metal surface treatment, 5 to 150 mg/m ² of metal Cr can be added per side to the steel plate in terms of metal Cr.
An inorganic first chromate treatment layer with a chromium adhesion amount of When mixed, the viscosity at room temperature is 3 to 50 centipoise, and the electrical conductivity is 2.
~30ms/cm of chromium component-containing resin aqueous solution at -80
20,000 to 45,000 per minute by applying a voltage of ~-100KV
A resin-containing chromate treatment layer is applied using an electrostatic atomization method in which negatively charged atomized particles are produced by colliding with a rotary body that rotates 1,000 times to form a chromium coating of 3 to 180 mg/ ^m2 per side. , heating temperature 50-350
This is a method for producing a two-layer chromate-coated metal surface-treated steel sheet that is heat-treated at ℃. (Function) The present invention will be explained in detail below. In the present invention, first, a predetermined amount of chromate coating layer is applied to the surface of a metal surface-treated steel sheet as a first layer by electrolytic treatment or coating treatment using an aqueous solution containing Cr ⁶⁺ as the main component. . Next, a chromium component-containing resin aqueous solution having the above-described composition and properties is applied to the surface of the chromate film, either as it is or dried, at a voltage of -80 to -100 KV and rotated at a speed of 20,000 to 45,000 times per minute. The atomized particles are negatively charged by colliding with a rotating body, and then become positively charged through the electrostatic field formed between the discharge port of this atomized solution and the grounded metal surface-treated steel plate to be treated. It is attached to a metal surface-treated steel plate. During electrostatic atomization, the applied voltage is -
If the voltage is lower than 80 KV, the amount of charge in the particles that are atomized by colliding with the rotating body is small, so the repulsive force between the particles is weak, and it is also difficult to make the particles finer, so they do not adhere uniformly to the metal surface-treated steel sheet. On the other hand, at a voltage higher than -100KV, the atomized particles moving in the electrostatic field become too fine and are affected by the exhaust flow, causing them to adhere unevenly.
For this reason, the charging voltage of the atomized particles is set to −80~
-100KV. In addition, when the chromium-containing resin aqueous solution is collided with a rotating body and atomized at a low rotation speed of 20,000 times per minute or less, the atomized particles are too large and form an uneven adhesion layer on the spots. On the contrary, 4
When it rotates at high speeds exceeding 5,000 times, it becomes ultrafine particles and forms an uneven adhesion layer due to the influence of the exhaust flow. Therefore, the number of rotations of the rotating body during electrostatic atomization was set to 20,000 to 45,000 times per minute. Metal surface treated steel sheet By supplying a predetermined amount of chromium-containing resin aqueous solution, the negatively charged atomized particles repel each other and do not aggregate when sprayed from the discharge port, and are evenly distributed to form a metal surface treated steel sheet. The metal surface treated steel sheet is uniformly coated.
In particular, by controlling the supply amount of the chromium-containing resin aqueous solution and the moving speed (passing speed) of the steel sheet to be surface-treated, the coating amount (coating thickness) can be adjusted to an arbitrary value. According to this method, the eluted substances of the chromate bath forming the first layer and the chromate coating of the first layer do not mix into the chromate bath of the second layer, causing a change in the composition or deterioration of the properties. Facilitates the adhesion of the chromate coating of the layer. At the same time, the resin-containing chromate bath forming the second layer is spray coated on the chromate coating of the first layer by the method described above, and is then widely coated due to the wettability of the resin component, followed by subsequent heating. Through the treatment, a polymerization reaction between the Cr-containing component in the chromate bath and the resin, and the Cr-containing component on the surface of the first layer chromate coating and the resin results in a uniform coating effect and improved adhesion between the first and second layers. effect and the accompanying performance improvement can be obtained at the same time. That is, the present invention has excellent uniform coverage regardless of the amount of coating due to the mutual effect of the two-layer chromate coating on the metal surface-treated steel sheet and the treatment bath.
Forms a high-performance, chromium-containing resin coating with excellent appearance, corrosion resistance, and coating performance. In the present invention, the surface of a metal surface-treated steel sheet such as a zinc or zinc alloy plated steel plate, an aluminum or aluminum alloy plated steel plate, or a lead or alloy plated steel plate is applied immediately after plating or after activation treatment with an alkaline bath or the like. , a first chromate coating layer is provided using an aqueous solution of an inorganic chromium compound containing Cr ⁶⁺ as a main component. For this chromate treatment, a conventional roll coater coating method using an aqueous solution of an organic chromium compound containing a resin is employed, but if the amount of coating is particularly small, it is difficult to uniformly adhere the film. In addition, in the present invention, when the first and second layers are formed with a chromate film containing an organic resin, as described above, the functional groups of these organic substances absorb moisture, and moisture enters the film, resulting in the formation of bare metal. There is a tendency for corrosion resistance to deteriorate. Therefore, in the present invention, it is easy to control the amount of chromate coating in the first layer, and even if moisture enters the organic coating in the second layer, the chromate coating made of the inorganic chromium compound in the first layer protects the metal surface. It has the effect of preventing moisture from reaching the. In this case, the treatment bath and treatment method for the chromate film are not particularly limited ^; make use of,
It is preferable to use the method exemplified below. That is, (a) CrO ₃ −SiO ₂ (silicate sol) bath, (b) CrO ₃ −SO ₄ ^2- bath, (c) CrO ₃ −SiO ₂ −PO ₄ ³ -bath (d) CrO ₃ -SiO ₂ -NH ₄ F-H ₂ ZrF _6- based bath or the like or a chromate bath containing Cr ³⁺ ions is used for electrolytic treatment at a bath temperature of room temperature to 80°C and a current density of 10 to 80°C. A cathodic electrolytic treatment is carried out at 100 A/dm ² for an electrolytic treatment time of 0.3 to 15 seconds, or an anodic electrolytic treatment is carried out under similar conditions for a period of 0.1 to 1 second after the cathodic electrolytic treatment. In addition, the coating treatment method is to perform immersion treatment, spray treatment, roll coater treatment, etc. at a treatment bath temperature of room temperature to 80°C for a treatment time of 1 to 15 seconds to remove excess chromate bath. The desired amount of chromate coating is controlled by wiping with a wiping roll or high-pressure gas. In order to form this first layer of chromate film, an inorganic chromate bath is used to reduce the amount of chromate film to 5 to 150 mg per side in terms of the amount of metallic chromium.
Limited to a coating weight of m ² . If the amount of Cr deposited is less than 5 mg/ ^m2 , it is difficult to uniformly cover the surface of the metal surface-treated steel sheet with the chromate film, and the chromate film containing the organic resin of the second layer is coated on the surface of the first layer. Even if it is applied, when exposed to a corrosive environment for a long period of time, the corrosive aqueous solution that has entered the second layer easily reaches the metal surface of the first layer coating, degrading the corrosion resistance or the corrosion resistance after painting. Furthermore, when the amount of Cr attached exceeds 150 mg/m ² , the performance improvement effect of the first layer is saturated, and cracks are generated in the chromate film due to processing, which become starting points and propagate to the second layer. Deteriorates corrosion resistance and corrosion resistance after painting. Therefore, the amount of Cr deposited in the first layer is 5 to 150 per side.
mg/m ² , preferably 10-100 mg/m ² . Next, after the first layer chromate coating treatment, the second layer resin chromate coating treatment is applied as it is or after washing with water, or after drying and heat treatment. The aqueous resin solution containing the chromium component is coated using an electrostatic atomization coating device as shown in Figs. Spray on metal surface treated steel plate with chromate coating to ensure uniform adhesion. That is, a predetermined amount of the solution is electrostatically atomized by the pump 3 from a solution tank 2 to a resin solution 1 containing a chromium component, in accordance with the desired coating amount and the speed of passing the metal surface-treated steel sheet 6. This atomizing device 4 is connected to an air turbine 5, and as shown in an enlarged schematic diagram in FIG.
A is atomized. The solution 1 supplied to the electrostatic atomizer 4 is supplied from the solution supply pipe B to the rotating body part A in FIG. , passes through a small diameter (usually 1 to 5 mm in diameter) D provided between the rotating bodies A and A', flows through the surface F of the tip end of the rotating body A, and reaches the tip end E. In the process of solution 1 flowing on this F plane,
It is atomized very uniformly by the centrifugal force based on high-speed rotation, and is ejected from the leading edge portion E with a uniform particle size. On the other hand, this electrostatic atomizer 4 is applied with a high voltage (usually -
80KV to -100KV), the solution supplied to the atomizer 4 is negatively charged, and the atomized particles G that have flowed out of the atomizer are negatively charged. Therefore, these negatively charged atomized particles G
The particles do not repel each other and aggregate, but rather uniformly fly out and adhere to the nearby ground, that is, the positively charged metallic surface-treated steel plate 6. As a result, the particles adhere uniformly to the surface of the metal-surface-treated steel sheet. In addition, the amount of coating on the material to be treated is determined by the solution supply pump 3.
It is easy to arbitrarily change the threading speed of the steel sheet 6 to be processed by adjusting the speed of the steel sheet 6. In order to increase the threading speed, it is easy to arrange the electrostatic atomizers 4 in multiple stages. Of course, depending on the width of the board, they can be arranged in multiple stages in the board width direction, making it easy to deal with wide-width post-processed materials. Next, in this coating method, the coating of uniform atomized particles on the surface of the metal surface-treated steel sheet is adhered in an extremely uniform layered state, but even if the particles are extremely fine, the heat treatment after the coating treatment is necessary. It is also important that the coating spreads well and has excellent uniform coverage. For this purpose, the composition of the chromate treatment bath,
Properties and heat treatment temperature are important. Therefore, in order to obtain a film with excellent uniform coverage, appearance performance, painting performance, and coating performance, regardless of the film amount, the composition of the treatment bath,
Regulate properties and heating temperature. That is, the resin concentration of the resin treatment bath containing the chromium component is 50 to 400 g/2, the chromium component content is contained at a ratio of 1/50 to 1/1 to the resin content, and the viscosity is 3 to 50 centipoise. , a chromium-containing resin solution having an electrical conductivity of 2 to 30 milliSequences/cm (ms/cm) is used. A chromium-containing resin aqueous solution with a resin concentration of less than 50g/1 and a chromium component content of 1/50 to 1/1 of the resin concentration should be used after the first layer of chromate treatment after electrostatic atomization painting. The wetting and spreading properties of the treatment solution on the surface of the metal surface-treated steel sheet are poor, and even if heat treatment is applied, a sufficient uniform coating effect cannot be obtained.
Uniform coverage, treated appearance, corrosion resistance, and coating performance are poor. In addition, chromium-containing resin aqueous solutions in which the resin concentration exceeds 400g and the chromium component content is 1/50 to 1/1 of the resin concentration will have a high viscosity, resulting in electrostatic atomization. After painting and in the heat treatment process, it takes time for the treatment bath to wet and spread on the surface of the metal surface-treated steel sheet, which is disadvantageous in forming a chromium-containing resin film uniformly in high-speed processing, and reduces the uniform appearance performance and the film's performance. Deterioration of performance etc. Therefore, in the present invention, the resin concentration is 50~
400g/, preferably 15g/-300g/. Although the resin used in the present invention is not particularly limited, for example, acrylic resin, epoxy resin, phenokylene resin, fluorine resin, or phenol resin may be used alone or in combination of two or more. These resins each have a concentration of 50 to 400 in aqueous solution.
g/Used as a contained solution. Furthermore, the chromium-containing resin aqueous solution used in the present invention undergoes heat polymerization of the chromium component in the chromate bath and the resin, or the chromate coating of the first layer and the resin of the second layer, during the heat treatment performed after coating. Therefore, it is important to form a film at high speed and in a short time. In order to accelerate this thermal polymerization, 0.5 g/hardening accelerator (for example,
Phosphoric acid) may be added. Furthermore, in the present invention, the chromium component is contained in a ratio of 1/50 to 1/1 to the resin. In other words, the chromium component has a Cr content of 1g/~250g/
It is added to the solution used in the present invention in a range of 1/50 to 1/1 of the resin content. This chromium component uses Cr6 ⁺ as its main component, but the corrosion resistance of the coating formed by heat treatment,
This is important for ensuring coating performance. During heat treatment, the resin and chromium components polymerize, resulting in corrosion resistance and
A chromate film with excellent coating performance is formed, but if the chromium content is less than 1/50 of the resin content, it is difficult to ensure sufficient corrosion resistance. In other words, since a film mainly composed of a resin component is formed, it is difficult to obtain the desired performance of the present invention. On the other hand, the chromium content is 1/1/1 of the resin content.
If it is contained in a ratio exceeding 1, it will be difficult to achieve sufficient uniform mixing in the treatment bath itself, and there will also be a lack of uniform coverage due to the wetting and spreading effect of the resin after electrostatic coating, and heat polymerization with the first chromate layer. Deterioration causes drawbacks such as deterioration of corrosion resistance and deterioration of adhesion between the first and second chromate coatings. Therefore, in the present invention, it is necessary that the treatment bath contain the chromium component in a ratio of 1/50 to 1/1 of the resin concentration, preferably 1/30 to 1/5. be. In addition, this chromium component contains Cr ⁶⁺ as a main component, and reacts with the resin in the heat treatment process to form a film mainly composed ^of Cr ³⁺ . Cr ³⁺ may be mixed as ⁺ in a proportion of 40% or less of the total chromium. As the chromium component contained together with the resin as an essential component in the treatment bath used in the present invention, one or more of chromic acid, dichromate, and chromate can be used. Then, corresponding to the resin content, chromic acid, chromate, etc. are mixed in the form of chromic acid, chromate, etc. within the range specified above in terms of Cr amount. In preparing a chromate treatment bath containing a chromium component and a resin component, it is preferable to use a chromium component that corresponds to the stable PH range of the resin component used. For example, when using an acrylic resin that is stable in an acidic region, chromic acid is used as the main chromium component, and when using an epoxy resin that is stable in a neutral region, ammonium chromate is used as the main chromium component. The ingredients and method of use are taken. That is, from the viewpoint of stability over time of a chromate solution in which a resin component and a chromium component are mixed, it is preferable to mix and use them in a range where both are stable. Next, the properties of the treatment solution mainly consisting of chromium and resin components are defined as follows in order to obtain the desired effects of the present invention using an electrostatic atomization coating method. First, the viscosity of the treatment bath must be within the range of 3 to 50 centipoise at room temperature. That is, if the viscosity is less than 3 centipoise,
Immediately after application, the treatment bath spreads quickly on the metal surface-treated steel sheet, and while the treatment bath has the effect of uniformly covering particles between particles in a short time, it also has the effect of coating the coating between particles by heat treatment. During this time, the deposits are fluidized and impede uniform coverage. On the other hand, if the viscosity exceeds 50 centipoise, a considerable holding time is required in order for the electrostatically applied particles to be uniformly coated by the wetting and spreading effect of the treatment bath. Therefore, in high-speed processing,
This is disadvantageous for obtaining good appearance performance with excellent uniform coverage. In the present invention, the viscosity of the treatment bath is 3 to 3 at room temperature.
50 centipoise, preferably 4 to 30 centipoise. Furthermore, in the present invention, it is necessary to apply the processing bath as atomized particles having a uniform particle size and which are negatively charged. Gender is an important factor. That is, the electrical conductivity of the treatment bath used in the present invention is regulated to 2 to 30 millisequences/cm (ms/cm) at room temperature. If the electrical conductivity of the treatment bath is less than 2ms/cm, the resistance value of the treatment bath is large, so a very large high voltage is required to charge the treatment bath, which may pose a safety problem during operation. At the same time, it is difficult to create negatively charged atomized particles of uniform particle size. On the other hand, if the electrical conductivity of the treatment bath exceeds 30 ms/cm, a large current will flow through the solution under the voltage range used in the present invention, making it extremely difficult to work safely. Therefore, the electrical conductivity of the treatment bath used in the present invention is 2 to 30 m at room temperature.
Used in s/cm. As mentioned above, by using a resin-based treatment bath with a composition and properties that contain chromium components, it is possible to uniformly apply the first layer of chromate treatment to the metal surface treated steel plate. However, in order to form a film with excellent appearance and film performance, heat treatment is performed at a heating temperature in the range of 50 to 300°C.
It is necessary to bond the material to be coated and the deposits, and at the same time to form the deposits themselves into a stable film. In this case, if the heating temperature is less than 50℃, a strong bonding effect between the deposit and the treated material cannot be obtained, and the hardening polymerization reaction between the deposit itself and the chromium and resin components is not sufficient, resulting in poor performance. It is difficult to form a good film. On the other hand, if the heating temperature exceeds 350°C, there is a risk that the resin component used in the treatment bath of the present invention will be decomposed, and the corrosion resistance and coating performance of the formed film will deteriorate. Therefore, the heating temperature is 50 to 350°C, preferably 100 to 250°C. Furthermore, the coating formed in this manner has excellent uniform coverage and good appearance, but from the viewpoint of corrosion resistance, it is necessary to ensure a sufficient amount of chromium in the coating. That is, the amount of Cr deposited per one side is regulated to 3 to 180 mg/m ² in terms of the amount of metallic chromium. If the amount of Cr deposited is less than 3 mg/ ^m2 , it is difficult to secure performance characteristics such as corrosion resistance due to the action of Cr in the coating or corrosion resistance after painting.
If the amount of adhesion exceeds 180 mg/m ² , the effect of improving corrosion resistance is saturated, and the corrosion resistance after processing deteriorates, perhaps because partial peeling of the coating, a so-called galling phenomenon, becomes more likely to occur during processing. . Therefore, in the present invention, the amount of Cr deposited is 3 to 180
mg/m ² , preferably 10-120 mg/m ² . The treatment bath used in the present invention is composed of a chromium component and a resin component as main components, but to the extent that the properties of the treatment bath are not impaired, additives may be added to improve the reactivity with the material to be treated. Anions such as SO ₄ ^2- and PO ₄ ^3- , which are effective, or cations, such as Co ²⁺ and Ni ²⁺ , which are effective in improving the paint adhesion of the coating, are added individually or in combination. Good too. Alternatively, for the purpose of further improving the coating performance of the present invention, oxides such as silica sol, alumina sol, silicate, etc. or chromate coatings may be used as long as the composition and properties of the chromate bath used in the present invention are not impaired. A chromate treatment bath may be used in which a coloring pigment such as fine carbon black powder is added for the purpose of coloring the chromate film, and a conductive pigment such as phosphorus iron powder is added for the purpose of improving the weldability of the chromate film. On the other hand, in order to make the chromate film formed by the method of the present invention white and transparent in appearance, the chromate film of the present invention may be subjected to a method of reducing Cr ⁶⁺ present in the chromate film. That is, for example, a method in which a heat-treated chromate film is subjected to cathodic electrolysis treatment in an aqueous solution containing a conductive salt (ammonium chloride, ammonium carbonate, etc.), or an aqueous solution containing a reducing agent such as hydrazine hydrate or hydroquinone. The Cr ⁶⁺ in each coating can be removed by immersion, spray treatment, etc.
Reduction to Cr ³⁺ , dissolution and removal, etc. are carried out, and the coating becomes white and transparent, and further insolubilization of the coating, etc. is promoted. Even if these methods are applied to the chromate coating of the method of the present invention, they do not have any adverse effect on the performance characteristics, but rather may improve the performance in some cases, and do not impair the present invention. As described above, according to the method of the present invention, the multilayer effect of the first inorganic chromate coating layer and the second organic resin-containing chromate coating layer and the formation of the second resin-containing chromate coating layer are achieved. The following excellent effects can be obtained by combining the appropriate treatment bath composition, properties, and film formation method. (1) Due to the superimposed effect of forming a multi-layer coating, the formation of pinholes in the chromate coating is reduced compared to the formation of a single-layer chromate coating, resulting in excellent uniform coverage and improved appearance performance and corrosion resistance. 2) Formation of the second layer of resin-containing chromate film prevents damage to the chromate film due to the effect of the resin-containing components and the moistening effect when this product is processed, improving processability and post-processing properties. The effect of improving corrosion resistance can be obtained. (3) For the same reason as in (2) above, when used after being painted, the effect of improving paint adhesion is remarkable. (4) When the organic resin-containing chromate coating layer of the second layer is exposed to a corrosive environment for a long period of time, the functional groups of the organic resin tend to absorb moisture, and therefore moisture is absorbed into the resin-containing chromate coating layer. However, in the structure of the two-layer coating of the present invention, the presence of the first layer of inorganic chromate coating prevents moisture or aqueous corrosive solution from reaching the surface of the metal surface-treated steel sheet. As a result, it has excellent corrosion resistance when used naked, and also has the same effect on painted materials as against aqueous solution that has entered through paint defects or the paint film, and improves paint adhesion and paint quality after aging. The subsequent corrosion resistance improvement effect is extremely excellent. (5) As the method for forming the second layer film, the chromate bath uses an electrostatic atomization deposition method, so the chromate bath for forming the first layer and the treatment bath for the second layer are not in contact with each other. The second positively charged
The atomized particles of the chromate bath of the layer adhere to and coat the material to be treated, which is coated with the negatively charged chromate coating of the first layer. As a result, there is an advantage that the chromate treatment bath of the first layer and the chromate treatment bath of the second layer do not mix, causing gelation over time or performance deterioration of the chromate coating of the second layer. At the same time, since the coating method relies on the adhesion of positively charged particles to the negatively charged material to be treated, the chromate bath for forming the second layer can be efficiently supplied, and the atomization treatment bath can be supplied quantitatively. By doing so, it is possible to arbitrarily adjust the amount (thickness) of the chromate film. Therefore, it is possible to arbitrarily control the thickness of the coating from thin to thick, and to obtain a coating with excellent uniformity, compared to other treatment methods, it is better to use a chromate treatment bath containing an organic resin. It is excellent despite its use. (6) In the heat treatment process after adhering the second layer chromate film, the chromium component and resin component in the second layer film, the chromium component in the first layer chromate film and the second layer resin component, respectively. By the heating polymerization reaction, it is possible to form a multilayer coating with excellent adhesion to the first layer coating simultaneously with the formation of the second layer coating. The following effects can be obtained. (Examples) In order to clarify the effects of the present invention, several examples and comparative examples will be given and specifically explained. Example 1 Electrolytic galvanized steel sheets with a plating amount of 20 g/m ² per side were used as the material to be treated, and the plate width was
The two-layer treatment of the present invention was carried out under the conditions of 900 mm and a sheet passing speed of 90 m/min, that is, for the first layer, a chromate coating layer was provided using the chromate bath and treatment method shown in Table 1, and then the chromate coating layer was applied as shown in Table 1. The treatment of the present invention was carried out by heat treatment using the electrostatic coating apparatus shown in Table 1 and a treatment bath having the composition and properties shown in Table 1. In addition, the treatment conditions and chromate film properties of comparative examples in which the same treated materials were subjected to chromate treatment by various methods shown in Table 1 are shown. In carrying out the present invention, (1) Basic composition of the treatment bath for forming the second layer of chromate film An emulsion type acrylic resin having an average molecular weight of about 150,000 is used, and CrO ₃ and Cr ⁶ are used as chromium components. Cr ³⁺ is partially reduced with alcohol, and a chromium component-containing resin solution with aluminum sulfate added as a hardening agent is used.( ² ) Electrostatic coating method: The electrostatic coating device shown in Figure 1 is used. In addition to supplying a chromate treatment bath corresponding to the target coating amount using a metering pump and adjusting the plate threading speed and plate width,
Rotate 25,000 times at 2.0Kg/ ^cm2 , set the material to be treated as a positive pole and the air turbine as a negative pole, apply a voltage of 100KV during this period to negatively charge the atomized particles, and electrostatically atomized particles are charged at a constant speed. It was supplied and attached to a galvanized steel sheet. (3) Heat treatment: Heat treatment was performed at a plate temperature of 180°C for 10 seconds in a hot air oven. Using the above method, we also investigated the film performance, focusing on the effects of the treatment bath and the amount of chromate film. Table 1 shows the processing conditions according to the method of the present invention, and Table 2 shows the evaluation results of the performance characteristics of the chromate film according to the method of the present invention. The evaluation method and evaluation criteria were as follows, and the performance was compared and compared with those coated with chromate films with approximately the same amount of chromium deposited. Γ Evaluation method and evaluation criteria Treatment status and appearance After treatment and after the chromate film was formed, visual observations were made and evaluations were made using the following evaluation criteria. ◎...The chromate bath is applied uniformly to both sides during the treatment, and the chromate film formed after the heat treatment is uniformly formed without color unevenness or spot patterns.○...The chromate bath is partially applied during the treatment. The chromate film is adhered with uneven adhesion, but after heat treatment, a relatively uniform chromate film is formed. Although unevenness in the amount (thickness) of the coating is clearly observed, a chromate coating is formed on the entire surface ×...There are areas where the chromate bath is not attached due to phenomena such as running out of the processing bath or poor wetting during processing. In addition, if there are areas where no film is formed even after the chromate film is formed by heat treatment Uniform coverage of the chromate film The evaluation material is subjected to 1000 Cr characteristic Irradiate ×1000 squares, and apply Cr to each square.
Line counts (CPS) were measured. On the other hand, for the standard sample, we measured the chemical analysis value and the corresponding X-ray count number (CPS),
The microscopic chromate coverage was evaluated by determining the amount of Cr attached to each square of the evaluation material in comparison with the above measurement count number. The evaluation criteria were based on the following method, namely, the average chemical analysis value (mg/m ² ) shown in Table 1.
◎… (within ±10%) Cr adhesion amount on the evaluation surface
If the area ratio is 85% or more of the Cr coating amount on the entire surface, ○… (within ±10%) of the Cr coating amount on the evaluation surface.
Less than 85% to 65% of the amount of Cr deposited on the entire surface
When occupying an area ratio of △... (within ±10%),
If the amount of Cr deposited on the entire surface occupies an area ratio of 65% or more, but the amount of Cr deposited (±30% or more) is present in an area ratio of 20% or more ×...The part where the amount of Cr deposit is not detected is on the evaluation surface
Corrosion resistance When present at an area ratio of 2.5% or more, (a)
Cut out a blank size of 200 x 200 mm from the flat plate (b) and the plate thickness of 0.8 mm, and cut this into a height
For each 30 mm square cylinder processed, an evaluation test was conducted for a predetermined period of time, and the evaluation was performed based on the following evaluation criteria. (a) Corrosion resistance of flat plate ◎... White rust occurrence rate less than 1% ○... White rust occurrence rate 1% or more to less than 5% △... White rust occurrence rate 5% or more to less than 20% ×... White rust occurrence rate 20% or more (b) Corrosion resistance after processing◎...White rust incidence less than 5%○...White rust occurrence rate 5% or more to less than 15%△...White rust occurrence rate 15% or more to less than 30%×...White rust occurrence rate 30% Paint adhesion After baking melamine-alkyd resin to a thickness of 25 μm, using a 0.8 mm thick evaluation material, 7 mm
Erichsen processing of height was performed. -1 Evaluation method (A) After Erichsen processing, adhere cellophane tape to the surface and peel it off, and evaluate the peeling status of the paint film using the following evaluation criteria ◎…Almost no peeling of the paint film is observed○…Approximately 1 mm diameter or less 5 points or less for paint film peeling △...More than 5 points for paint film peeling with a diameter of about 1 mm or less, or paint film peeling over a fairly large area of 10% or less of the evaluated surface ×...Large area that is clearly observed More than 10% of paint peeling occurs -2 Evaluation method (B) After immersing the painted material in boiling water for 30 minutes, drying
After being left for 24 hours, Erichsen processing was performed, and the same peeling test as above was carried out, and evaluation was made using the same criteria as above. Corrosion resistance after painting: A 25 μ thick coat of melamine-alkyd paint was applied to the evaluation material of 100 x 150 mm size. - After baking, scratches reaching the surface of the plating layer were made, and a salt spray test was conducted for a predetermined period of time to evaluate the post-painting corrosion resistance performance according to the following evaluation criteria. ◎…The maximum width of blisters from the scratch area is less than 3 mm, and no more than 3 blisters occur from other flat areas. ○...Blister width from the scratch part is less than 6 mm at most, or blisters from other flat surfaces occur in 7 points or less △...Blister width from the scratch part at maximum is less than 10 mm, or blisters occur from other flat surfaces in 10 points or less × ...If the maximum width of blisters from the scratch area is 10 mm or more, or if blisters occur from other flat areas in 11 or more cases.

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[Table] Example 2 For zinc alloy plated steel plates, lead and lead alloy plated steel plates, aluminum and aluminum alloy plated steel plates,
A chromate film according to the method of the present invention was formed under the conditions shown in Table 3, and the film performance was evaluated. The results are shown in Table 4. As a comparative example, chromate coatings having approximately the same amount of chromium deposited were formed by each method, and the performance was compared for each method. Note that performance evaluation was performed using the method shown below, and a relative evaluation was performed according to the evaluation criteria. Processing status and appearance: The same evaluation was carried out as in Example 1-, and the same criteria were used. Uniform coverage of the chromate film: The same evaluation was carried out as in Example 1-, and the evaluation was made using the same standards. Corrosion resistance: The same evaluation was carried out as in Example 1-. The same evaluation was carried out, and the evaluation was made based on the incidence of white rust or red rust depending on the type of each evaluation material. The evaluation criteria for the occurrence rate of each evaluation material were based on Example 1-, and were indicated by white rust or red rust in Table 4. Paint adhesion...Performed the same evaluation as Example 1- and evaluated using the same standards Corrosion resistance after painting...Performed the same evaluation as Example 1- and evaluated using the same standards

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[Table] (Effects of the invention) In other words, the present invention has excellent uniform coverage regardless of the amount of coating due to the mutual effect of the two-layer chromate coating on the metal surface-treated steel sheet and the treatment bath.
Forms a high-performance, chromium-containing resin coating with excellent appearance, corrosion resistance, and coating performance.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an electrostatic atomization coating device, and FIG. 2 is an enlarged explanatory diagram of the electrostatic atomization device. DESCRIPTION OF SYMBOLS 1... Coating solution, 2... Solution tank, 3... Supply pump, 4... Atomization device, 5... Air turbine, 6... Surface treated steel plate, 7... Operation panel, 8...
Electrical control panel, 9...High voltage transformer.

Claims (1)

[Claims] 1. Inorganic chromate with a chromium deposition amount of 5 to 150 mg/m ² per side in terms of metal Cr is applied to a steel plate that has been subjected to metal surface treatment by electrolytic treatment or coating treatment using an aqueous solution containing Cr ⁶⁺ as the main component. A treatment layer is provided, and the resin content is 50 to 400 on the upper layer of the chromate coating.
g/ and chromium component is 1/50 to 1/50 of the resin content
Mix at a ratio of 1/1 and have a viscosity of 3 to 50 at room temperature.
Centipores: Apply a voltage of -80 to -100 KV to a chromium-containing resin aqueous solution with an electrical conductivity of 2 to 30 ms/cm, and collide it with a rotating body that rotates at 20,000 to 45,000 times per minute to make it negative. A resin-containing chromate treatment layer is applied using an electrostatic atomization method using charged atomized particles to achieve a chromium deposition amount of 3 to 180 mg/ ^m2 per side, and is characterized by heat treatment at a heating temperature of 50 to 350°C. A method for producing a metal surface-treated steel sheet with a two-layer chromate coating.