JP2002302750A - Precoated steel sheet with excellent workability and corrosion resistance in worked area, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide excellent workability and corrosion resistance in a worked area to a precoated steel sheet using a hot-dip Al-Zn coated steel sheet having 20-95 mass% Al content in the plating coat. SOLUTION: The plating film is obtained by means of the following thermal histories (a) and (b) at least: (a) a thermal history where the average cooling rate within 10 seconds immediately after the steel sheet leaves a hot-dipping bath is regulated to <11 deg.C/s; (b) a thermal history where, after the solidification of the hot-dipped plating metal, temperature raise and heating are done up to a temperature T( deg.C) between 130 and 300 deg.C and then the average cooling rate from the temperature T( deg.C) down to 100 deg.C is regulated to a value not higher than C( deg.C/h) represented by equation C=(T-100)/2 and/or a thermal history where the average cooling rate from the temperature T( deg.C) between 130 and 300 deg.C after the solidification of the hot-dipped plating metal down to 100 deg.C is regulated to a value not higher than C ( deg.C/h) represented by equation C=(T-100)/2. Further, a chemical conversion coating, an undercoat film and then an overcoat film are coated onto the surface of the plating film, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing A
This is a coated steel sheet using a hot-dip Al-Zn plated steel sheet having a l-content of 20 to 95 mass% as a base steel sheet, and has extremely low occurrence of coating film cracks even in bent parts and is excellent in workability and corrosion resistance in the worked part. To a coated steel sheet and a method of manufacturing the same.

[0002]

2. Description of the Related Art Al in a plating film is 20 to 95 mass%.
The hot-dip Al-Zn plated steel sheet contained is
As shown in No. 7161, since it exhibits superior corrosion resistance as compared with hot-dip galvanized steel sheet, in recent years, demand has been increasing mainly in the field of building materials. The plated steel sheet is produced as follows in a continuous hot-dip plating facility using a hot-rolled steel sheet subjected to pickling descaling or a cold-rolled steel sheet obtained by further cold-rolling the hot-rolled steel sheet as a base steel sheet.

In a continuous hot-dip plating apparatus, a base steel sheet is heated to a predetermined temperature in an annealing furnace maintained in a reducing atmosphere to remove rolling oil and the like adhering to the steel sheet surface simultaneously with annealing.
After the oxide film is reduced and removed, the lower end is immersed in a hot-dip galvanizing bath containing a predetermined concentration of Al through a snout immersed in the plating bath. After the steel sheet immersed in the plating bath is lifted above the plating bath via the sink roll, by injecting pressurized gas toward the surface of the steel plate from the gas wiping nozzle arranged on the plating bath The coating weight was adjusted, and then cooled by a cooling device to form a molten Al-
A Zn-based plated steel sheet is obtained.

The operating conditions such as the heat treatment conditions and atmosphere conditions of the annealing furnace in the continuous hot-dip plating equipment, the plating bath composition, and the cooling rate after plating are controlled within predetermined control ranges in order to ensure desired plating quality and material. Well managed. The plating film of the plated steel sheet manufactured as described above is mainly composed of a portion where Al containing Zn in supersaturation is dendrite solidified and a portion of the remaining dendrite gap, and the dendrites are in the thickness direction of the plating film. Laminated. With such a characteristic film structure, molten Al-
Zn-based plated steel sheets exhibit excellent corrosion resistance.

[0005] In addition, usually about 1.5 mass% of Si is added to the plating bath, and the action of the Si suppresses the growth of the alloy phase at the interface between the plating film and the base steel sheet in the molten Al-Zn-based plated steel sheet. And the alloy phase thickness is about 1 to 2 μm. The thinner the alloy phase, the greater the number of characteristic film structures exhibiting excellent corrosion resistance. Therefore, suppressing the growth of the alloy phase contributes to the improvement of the corrosion resistance. Further, since the alloy phase is harder than the plating film and acts as a starting point of cracks during processing, suppressing the growth of the alloy phase reduces the occurrence of cracks and has an effect of improving workability. In addition, since the cracked portion is inferior in corrosion resistance because the base steel sheet is exposed, reducing the occurrence of cracks also improves the corrosion resistance of the processed portion.

[0006] Usually, the plating bath contains unavoidable impurities, Fe eluted from a steel plate or equipment in the plating bath, and Si for suppressing an alloy phase. These elements are present in the alloy phase or plating film in the form of an alloy or a simple substance.

By the way, since most coated steel sheets are used after being formed after coating, it is very important to prevent the occurrence of cracks (cracks in the coating film) during processing. A coated steel sheet based on a hot-dip A1-Zn-based coated steel sheet containing 20 to 95 mass% of Al has excellent corrosion resistance, but is greatly affected by the workability of the plated film, and is hardly affected by other plated steel sheets, for example, in the plated film. A
cracks occur in the coating film during processing as compared with a coated steel sheet having a base of a hot-dip A1-Zn-based coated steel sheet containing about 5 mass% of l (hereinafter, referred to as "5% Al-Zn plated base coated steel sheet"). The processing strength is often limited.

[0008] Such cracks in the coating film are caused by cracks in the plating film generated from an alloy phase having a thickness of about 1 to 2 µm existing at the interface between the plating film and the base steel sheet. The crack has a larger opening than the 5% Al-Zn base coated steel sheet with the same plating film thickness even under the same processing conditions, so that the crack is visible to the naked eye even under the same processing conditions, because the crack is used as the propagation path in the dendrite gap of the plating film. Such a large crack tends to cause the appearance of the coated steel sheet to be poor. In order to prevent cracking of the coating film and the plating film, improvement of the workability by softening the coating film, and performing a predetermined heat treatment on the plated steel sheet as disclosed in Japanese Patent Publication No. 61-28748, It has been proposed to improve the ductility of the plated steel sheet itself.

[0009]

However, in the former case, other characteristics such as surface flaws are likely to be generated on the coating film, and other characteristics are deteriorated. Is no longer applicable. In addition, it is difficult to sufficiently improve the ductility of the plating film by only the heat treatment such as the latter, and even if the ductility of the plating film is improved to some extent, the workability and cracks of the coated coated steel sheet occur. However, this does not directly improve the corrosion resistance of the processed portion, which is reduced.

[0010] Accordingly, an object of the present invention is to provide a coated steel sheet using a hot-dip Al-Zn-based coated steel sheet having an Al content of 20 to 95 mass% in a plating film as a base steel sheet. It is an object of the present invention to provide a coated steel sheet which has extremely low cracking, has excellent workability superior to that of a 5% Al-Zn-based plated undercoated steel sheet, and also has excellent corrosion resistance in a processed portion, and a method for producing the same.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have set the Al content in the plating film to 20 to 95.
We have conducted intensive studies on means to improve the workability and corrosion resistance of the coated steel sheet using a mass-% hot-dip Al-Zn-coated steel sheet as a base steel sheet. Heat history,
Further, it has been found that by forming a coating film having a specific configuration on the plating film surface, extremely excellent workability and corrosion resistance of a processed portion, which could not be achieved conventionally, can be obtained.

The present invention has been made based on such findings, and the features thereof are as follows. [1] A coated steel sheet using a hot-dip Al-Zn coated steel sheet having an Al content of 20 to 95 mass% in a plating film as a base steel sheet, wherein the plating film has at least the following thermal histories (a) and (b): (A) Thermal history with an average cooling rate of less than 11 ° C / sec for 10 seconds immediately after the steel sheet leaves the hot-dip bath (b) Hot-dip coated metal solidifies After that, 130
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history,
And / or from a temperature T (° C.) in the range of 130 to 300 ° C. after solidification of the hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Thermal history that satisfies the following: C = (T-100) / 2 (1) On the surface of the plating film, a chemical conversion coating film, a coating film thickness of 2 to 15 μm, and a coating film thickness from the lower layer side. Is 5-3
A coated steel sheet having excellent workability and corrosion resistance in a processed portion, which is characterized by having a top coat having a thickness of 0 µm and a glass transition temperature of 30 to 90 ° C.

[2] The coated steel sheet according to the above [1], characterized in that the temperature T (° C.) of the thermal history of (b) is in the range of 130 to 200 ° C., and is excellent in workability and corrosion resistance in the processed part. Painted steel plate. [3] The coated steel sheet according to the above [1] or [2], wherein the plating film contains 0.01 to 10 mass% in total of one or more selected from Mg, V, and Mn. Painted steel sheet with excellent workability and corrosion resistance in the processed part. [4] The coated steel sheet according to any one of the above [1] to [3], wherein the base resin of the undercoat film is made of a polyester resin and / or an epoxy resin, and has excellent workability and corrosion resistance in a processed portion. Painted steel plate. [5] In the coated steel sheet according to any one of the above [1] to [4], the main resin of the overcoat film is a polyester resin or a mixed resin of a polyvinylidene fluoride resin and an acrylic resin, which is characterized by workability. Painted steel sheet with excellent corrosion resistance in the processed part. [6] In the coated steel sheet according to any one of the above [1] to [5], the undercoating film contains chromate in a proportion of 1 to 50 ma in a solid content of the coating film.
A coated steel sheet with excellent workability and corrosion resistance in the processed part characterized by containing ss%.

[7] The Al content in the plating film is 20 to 9
A method for manufacturing a coated steel sheet using a 5 mass% hot-dip Al-Zn-based coated steel sheet as a base steel sheet, comprising the following steps 1) to 4), characterized by excellent workability and corrosion resistance in the processed portion. Manufacturing method. 1) A step of imparting at least the following thermal histories (a) and (b) to the plating film of the steel sheet that has exited the hot dip coating bath. (A) Average cooling for 10 seconds immediately after the steel sheet has left the hot dip coating bath Thermal history at a rate of less than 11 ° C./sec (b)
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history,
And / or from a temperature T (° C.) in the range of 130 to 300 ° C. after solidification of the hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Thermal history that satisfies the following: C = (T-100) / 2 (1) 2) Step of forming a chemical conversion coating by applying a chemical conversion treatment to the plating coating surface 3) Applying an undercoat paint to the chemical conversion coating film surface And baking to form an undercoat film having a film thickness of 2 to 15 μm 4) Applying a top coat to the surface of the undercoat film and baking the film to have a film thickness of 5 to 30 μm and a glass transition temperature of 30 ~ 9
Step of forming a top coat of 0 ° C

[8] In the manufacturing method of the above [7], the heat history temperature T (° C.) of (b) is in the range of 130 to 200 ° C., and the workability and the corrosion resistance of the processed portion are excellent. Manufacturing method of painted steel sheet. [9] The method according to the above [7] or [8], wherein the plating film contains one or more selected from Mg, V and Mn in a total amount of 0.01 to 10 mass. A method for manufacturing painted steel sheets with excellent workability and corrosion resistance in the processed part. [10] The method according to any one of the above [7] to [9], wherein 3)
Forming a base coat by applying a paint containing a polyester-based resin and / or an epoxy-based resin as a main resin in the step of baking and baking at a maximum temperature of 150 to 270 ° C. And method for producing coated steel sheet with excellent corrosion resistance. [11] The method according to any one of the above [7] to [10], wherein 4)
In the step, after applying a paint containing a polyester-based resin or a mixed resin of a polyvinylidene fluoride resin and an acrylic resin as a main resin, a maximum reached plate temperature of 150 to 280 ° C.
A method for producing a coated steel sheet, comprising baking to form an overcoat film.

[12] The process according to any one of the above [7] to [11], wherein the undercoat paint contains chromate in a proportion of 1 to 50 mass% in the paint solid content. For producing coated steel sheets with excellent workability and corrosion resistance. [13] In the manufacturing method according to any one of the above [7] to [12], the imparting of the thermal history of (b) to the plating film is performed by the following (1) to (8)
A method for producing a coated steel sheet having excellent workability and corrosion resistance in a processed portion, wherein the method is performed in at least one of the following steps. (1) Before chemical conversion treatment (2) During chemical conversion drying process (3) After chemical conversion treatment and before undercoat coating (4) During undercoat coating drying process (5) After undercoat coating completion and before topcoat coating (6) Topcoat During the coating drying process (7) After finishing the top coating (8) Cooling process after the hot-dip plated metal solidifies

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The coated steel sheet of the present invention is a hot-dip Al-Zn coated steel sheet containing 20 to 95 mass% of Al in a plating film as a base steel sheet, and a chemical conversion coating film is formed on the plating film surface from the lower side. , An undercoat film and an overcoat film were sequentially formed. Hereinafter, details of these configurations will be described in order.

(1) Hot-dip Al-Zn coated steel sheet Hot-dip A containing 20 to 95 mass% of Al in the plating film
The l-Zn plated steel sheet has excellent corrosion resistance, but from the viewpoint of the corrosion resistance and the like, a more preferable range of the Al content in the plating film is 45 to 65 mass%. Further, a particularly preferable component composition of the plating film is Al: 45 to 65 mass%,
Si: 0.7 to 2.0 mass%, Fe: less than 10 mass%,
The balance is substantially Zn containing unavoidable impurities, and in such a composition, particularly excellent corrosion resistance is exhibited.

Further, one or more kinds selected from Mg, V and Mn in the plating film in a total amount of 0.01 to
By containing 10 mass%, corrosion resistance and workability can be further improved. If the total content of these elements is less than 0.01 mass%, a sufficient effect cannot be obtained, while if it exceeds 10 mass%, the effect of improving corrosion resistance is saturated, and the workability is reduced because the film becomes hard.

However, it is difficult for this hot-dip Al-Zn-based coated steel sheet to obtain high corrosion resistance in the processed portion only by its plating composition. For the first time, excellent corrosion resistance in the processed part can be obtained. Although there is no particular limitation on the coating weight of the hot-dip Al-Zn-based plated steel sheet, it is generally appropriate to set the coating weight to about 30 to 200 g / m ² per one surface.

Further, the plating film of the hot-dip Al-Zn-based steel sheet must be a plating film obtained through at least the following thermal histories (a) and (b). (a) Thermal history in which the average cooling rate during the first 10 seconds immediately after the steel sheet leaves the hot-dip bath is less than 11 ° C./sec. (b) After the hot-dip plated metal solidifies,
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history,
And / or from a temperature T (° C.) in the range of 130 to 300 ° C. after solidification of the hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Thermal history satisfying the following: C = (T-100) / 2 (1) In the thermal history of the above (b), a more preferable range of the temperature T (° C.) is 130 to 200 ° C. Where
Equation (1) is based on experiments conducted by the present inventors to study in detail the effects of the heating condition of the plating film and the subsequent cooling conditions and the cooling conditions after the solidification of the hot-dip plated metal on the plating film, based on experiments, and as a result, It is a derived empirical formula.

By forming the plating film through the thermal histories of (a) and (b) above, the workability (crack resistance and the like) is remarkably improved while being a molten Al-Zn plating film. . It is considered that the workability of the plating film is remarkably improved by passing through the heat histories (a) and (b) for the following reasons. First, immediately after the steel sheet has left the hot-dip plating bath, the heat history of the above (a), that is, a heat history in which the average cooling rate for 10 seconds immediately after leaving the hot-dip bath has been sufficiently slowed down, gives a hot-dip coating film. Solidification is closer to an equilibrium state than solidification by a normal cooling process, and diffusion in a semi-molten state promotes two-phase separation of Al and Zn, and as a result, the plating film is softened. Then, the plating film having undergone such a heat history is further heated to a temperature range of 130 to 300 ° C. (preferably 130 to 200 ° C.) after the heat history of the above (b), and then gradually cooled under specific conditions. Heat history or / and 130 to 300 ° C. after the solidification of the plating film (preferably 130 to 2 ° C.)
Through the thermal history of slow cooling from the temperature range of (00 ° C.) under specific conditions, the strain accumulated in the plating film at the time of solidification is released, and solid diffusion occurs in the plating film. A) in the plating film caused by the thermal history
The two-phase separation of 1 and Zn is further effectively promoted. As a result, it is considered that the plating film is remarkably softened and its workability is remarkably improved.

Therefore, the softening of the plating film and the remarkable improvement of the workability accompanying the softening of the plating film are described in the above (a) and (b).
This is due to the combined action of the heat histories of the two, and it is difficult to achieve only one of them.

The details of the heat histories (a) and (b) will be described below. First, regarding the heat history of the above (a), the average cooling rate of the plating film for the first 10 seconds immediately after the steel sheet exits the hot-dip plating bath is set to less than 11 ° C./sec. Because the solidification of the film is closer to the equilibrium state than the solidification by the normal cooling process,
The two-phase separation of Al and Zn is promoted by diffusion in a semi-molten state, whereby the plating film is softened. If the average cooling rate in the first 10 seconds immediately after the steel sheet leaves the hot-dip plating bath is 11 ° C./sec or more, the solidification rate is too high, so that the solidification of the hot-dip coating proceeds in a non-equilibrium state, Since the certain time is short, the two-phase separation between Al and Zn is not sufficiently promoted, and the softening of the plating film due to the combination with the heat history of (b) cannot be sufficiently achieved.

FIG. 1 shows the effect of the average cooling rate of the plating film on the workability of the coated steel sheet for the first 10 seconds immediately after the steel sheet exits the hot-dip bath. Each of the test materials is a coated steel sheet in which a chemical conversion treatment film, an undercoat film, and an overcoat film that satisfy the conditions of the present invention are formed on a plated steel sheet whose plating film has been manufactured through the thermal history described in (b) above. The evaluation of the workability in this test was performed according to the evaluation of the workability in Examples described later. As shown in FIG. 1, the average cooling rate of the plating film in the first 10 seconds immediately after the steel sheet left the hot-dip plating bath was 11 ° C./sec.
In the above description, the evaluation of workability in the 180 ° bending process is “x”. On the other hand, when the average cooling rate of the plating film was less than 11 ° C./sec, the evaluation of workability was ““ ”or more, indicating that the workability was significantly improved.

In order for the coating film to have undergone the thermal history described in (a) above, the temperature must be set between the hot-dip bath surface of the continuous hot-dip coating equipment and the roll where the steel sheet exiting the hot-dip coating bath first comes into contact. It is necessary to provide an adjusting device and control the cooling rate of the plating film by the temperature adjusting device. It is preferable that the temperature control device be provided with a heating or heat retaining means and, if necessary, a cooling means. The cooling means cools the plated steel sheet, whose cooling rate of the plating film is controlled by the heating or heat retaining means, before it comes into contact with the first roll (such as a top roll), and generates pickup on the roll surface. It is for the purpose of preventing, for example. For example, an induction heater or a gas heating furnace can be used as a heating or heat retaining means of the temperature adjusting device, and a gas blowing device or the like can be used as a cooling means. However, there is no special restriction on the method, shape, scale, etc. of the heating or heat retaining means and cooling means of the temperature control device, and any point that the heat history of (a) can be imparted to the plating film. Good.

Next, regarding the heat history of the above (b),
(a) the heat-treated plating film (plating film after solidification of hot-dip plated metal) is 130 to 300
C, preferably a temperature T (C) in the range of 130 to 200C.
The temperature is then raised and then cooled so that the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less in the above equation (1), or The average cooling rate from the temperature T (° C.) in the range of 130 to 300 ° C., which is the cooling process, to 100 ° C., which is the cooling process of the plated film after the solidified plated metal solidifies, is represented by the above formula (1).
By cooling so as to satisfy (° C./hr) or less, the strain accumulated in the plating film is released as described above, and solid diffusion occurs in the plating film.
Al and Zn in the plating film generated by the thermal history of (a)
Is more effectively promoted. Then, due to the combined action of such heat history and the heat history of the above (a), the plating film is remarkably softened, and its workability is remarkably improved.

Here, if the heating temperature T of the plating film in the thermal history of (b) is lower than 130 ° C., the above-mentioned effect cannot be sufficiently obtained.
If the temperature exceeds ℃, the growth of the alloy phase at the interface between the base steel sheet and the plating film is promoted, which adversely affects workability.
Further, from such a viewpoint, the upper limit of the heating temperature T, which is more preferable for improving the workability, is 200 ° C. Also,
From the temperature T (° C.) in the range of 130 to 300 ° C., which is the cooling process after the hot-dip plated metal solidifies,
Also in the case where the cooling is performed under the condition of imparting the heat history of (b), if the temperature T is lower than 130 ° C., the above-mentioned effect cannot be sufficiently obtained.

FIG. 2 (a) shows the effect of the heating temperature of the plating film on the workability of the coated steel sheet when the coated steel sheet is heat-treated after the hot-dip plated metal has solidified. In each of the test materials from which this result was obtained, the average cooling rate of the plating film from the heating temperature to the heating temperature of 100 ° C. was within the condition of the heat history of the above (b), and the plating film had the above (a). ) Is a coated steel sheet formed by forming a chemical conversion coating, an undercoat, and an overcoat which satisfy the conditions of the present invention, on a plated steel sheet manufactured through the thermal history of (1). The evaluation of the workability in this test was performed according to the evaluation of the workability in Examples described later.

FIG. 2 (b) shows the average cooling rate of the plating film (average cooling rate from the heating temperature to 100 ° C.) when the plated steel sheet after the hot-dip plating metal is solidified is heat-treated. Was examined for the effect on the workability of the coated steel sheet, the test materials obtained this result, the heating temperature of the plating film is within the conditions of the thermal history of the above (b), and This is a coated steel sheet in which a chemical conversion coating, an undercoat, and a topcoat that satisfy the conditions of the present invention are formed on a plated steel sheet whose plating film has been manufactured through the thermal history of the above (a).
The evaluation of the workability in this test was performed according to the evaluation of the workability in Examples described later.

As shown in FIGS. 2A and 2B, when the heating temperature of the plating film is in the range of 130 to 300.degree.
° Evaluation of workability in bending is “○” or more,
Further, in the preferable range of 130 to 200 ° C., the evaluation of the workability is “加工”. On the other hand, when the heating temperature was out of the range of 130 to 300 ° C., the evaluation of the workability was only “Δ”. In addition, 1
When the difference between the average cooling rate up to 00 ° C. and the “C” in the above equation (1) is zero to minus (within the range of the present invention), the evaluation of workability in the 180 ° bending process is based on the temperature rise of the plating film. When the heating temperature is in the range of 130 to 300 ° C., it is “○” or more, and in the range of 130 to 200 ° C., which is a preferable condition, it is “◎”. On the other hand, when the difference was plus (outside the scope of the present invention), only "△" was obtained in the evaluation of workability.

In order to make the plating film have passed the heat history of the above (b), a heating or heat retaining device for heat-treating or keeping the plating film in or out of the continuous hot-dip plating equipment is provided. A predetermined heat treatment or heat retention is performed. For example, a heating mechanism (for example, an induction heater, a gas heating furnace, a hot blast furnace, etc.) may be provided in a continuous hot-dip plating facility to perform continuous heating in-line, or may be performed offline after winding on a coil. It may be performed by batch heating. In addition, a heating mechanism (for example, an induction heater, a gas heating furnace,
The heating may be performed by continuous heating using a hot air oven or the like. Furthermore, after the plated steel sheet continuously heated in the plating line or in the above-described continuous processing equipment is wound around a coil, appropriate heat retention or heat retention may be performed. In addition, a heat retaining device may be provided so that the plating film can be cooled and gradually cooled in a cooling process after the hot-dip plated metal solidifies. However, there is no special restriction on the method, shape, scale, etc. of the heating or heat retaining device, and it is essential that the heat treatment of the above (b) be given to the plating film. (A) and (b) above
By forming a specific coating film on the surface of the plating film that has undergone the thermal history described above, the coated steel sheet exhibits extremely excellent workability and corrosion resistance in the processed portion.

(2) Chemical conversion coating There is no particular limitation on the type of chemical conversion coating serving as a coating base. As the chemical conversion treatment, a chromate treatment, a zinc phosphate treatment, a treatment containing an organic resin as a main component, or the like is performed. Can be. Generally, a treatment mainly containing an organic resin is used when the environment is important, and a chromate treatment is used when the corrosion resistance is important. However, the process of zinc phosphate treatment is complicated, and 20 to 70 mass% of Al is contained in the plating film.
In the case of a hot-dip Al-Zn-based plated steel sheet containing, there may be cases where the reactivity of phosphoric acid is not sufficient, and when using it, it is necessary to consider this point.

(3) Undercoat Film The undercoat film has a thickness of 2 to 15 μm. If the coating thickness is less than 2 μm, sufficient rust prevention cannot be obtained.
If it exceeds 5 μm, the scratch resistance is reduced and the production cost is increased, which is not preferable. It is preferable to use a polyester resin and / or an epoxy resin as the main resin of the undercoating film from the viewpoint of processability and corrosion resistance of the processed portion.

As the polyester resin, bisphenol A-added polyester resin can be used. As the epoxy resin, a resin partially modified with urethane resin, phenol resin, amino resin or the like can be used. Can also. The polyester resin,
Those having a number average molecular weight of 1,000 to 30,000, more preferably 3,000 to 20,000 are desirable. If the number average molecular weight is less than 1,000, sufficient workability cannot be obtained due to insufficient elongation of the coating film, and the coating film performance may be insufficient. On the other hand, when the number average molecular weight exceeds 30,000, the base resin becomes high in viscosity, so that an excess of a diluting solvent is required, and the ratio of the resin in the coating material is reduced, so that an appropriate coating film cannot be obtained, and other components In some cases may also be reduced.

When a bisphenol A-added polyester resin is used as the main resin, the content of bisphenol A in the bisphenol A-added polyester resin is 1 to 70 mass% in terms of the resin solid content, more preferably, 3 to 60 mass%, particularly preferably 5 to 50 mass%
% Is appropriate. The lower limit of this content range is preferable from the viewpoint of ensuring the strength of the coating film, and the upper limit is preferable from the viewpoint of ensuring elongation of the coating film.

The polyhydric alcohol for obtaining the polyester resin includes ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and the like. Further, using 1,4-cyclohexanedimethanol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, pentaerythritol, dipentaerythritol and the like You may. These polyhydric alcohols can be used in combination of two or more.

The polyvalent base for obtaining the polyester resin includes phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, hymic anhydride, trimellitic anhydride And the like. In addition, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, isophthalic acid, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride , 1,4-cyclohexanedicarboxylic acid and the like may be used. Two or more of these polybasic acid components can be used in combination.

Examples of the epoxy resin include an epoxy compound comprising bisphenols such as bisphenol A, bisphenol F and bisphenol S and epihalohydrin or β-methyl epihalohydrin, or a copolymer thereof. Further, monocarboxylic acid or dicarboxylic acid modified products, mono-, di- or polyalcohol-modified products, mono- or diamine-modified products, mono-, di-, or polyphenol-modified products of these epoxy compounds can also be used as the epoxy resin.

As the curing agent for the main resin as described above, a polyisocyanate compound and / or an amino resin can be used. As the polyisocyanate compound, an isocyanate compound obtained by a general production method can be used. In particular, phenol, cresol, aromatic secondary amine, tertiary alcohol, Polyisocyanate compounds blocked with a blocking agent such as lactam and oxime are preferred. By using this blocked polyisocyanate compound, storage with one liquid becomes possible, and use as a paint becomes easy.

More preferred polyisocyanate compounds include non-yellowing hexamethylene diisocyanate (hereinafter, HDI) and its derivatives, and tolylene diisocyanate (hereinafter, TDI) and its derivatives.
'-Diphenylmethane diisocyanate (hereinafter MD)
I) and its derivatives, xylylene diisocyanate (hereinafter, XDI) and its derivatives, isophorone diisocyanate (hereinafter, IPDI) and its derivatives, trimethylhexamethylene diisocyanate (hereinafter, TMDI) and its derivatives, hydrogenated TDI and its derivatives, water MDI and derivatives thereof, hydrogenated XDI and derivatives thereof, and the like can be given.

When a polyisocyanate compound is used as the curing agent, the compounding ratio of the isocyanate group of the polyisocyanate compound to the hydroxyl group in the base resin [NCO / OH]
Is in a molar ratio of 0.8 to 1.2, more preferably 0.90 to
It is desirable to set the range to 1.10. [NCO / O
When the molar ratio [H] is less than 0.8, the coating film is insufficiently cured, and the desired coating film hardness and strength cannot be obtained. On the other hand, [N
When the molar ratio of [CO / OH] exceeds 1.2, a side reaction occurs between excess isocyanate groups or between the isocyanate group and the urethane compound, and the processability of the coating film is reduced.

As the amino resin as a curing agent, a resin obtained by reacting urea, benzoguanamine, melamine or the like with formaldehyde, or a resin obtained by alkyl etherifying these with an alcohol such as methanol or butanol can be used. Specifically, a methylated urea resin, n
-Butylated benzoguanamine resin, methylated melamine resin, n-butylated melamine resin, iso-butylated melamine resin, and the like.

When an amino resin is used as a curing agent, the mixing ratio (weight ratio of solid content) between the amino resin and the base resin is as follows:
Main resin: amino resin = 95: 5 to 60:40, preferably 85:15 to 75:25. The amount of the curing agent is 9 to 50 mass in terms of the resin solid content.
% Is preferable. If the amount of the curing agent is less than 9% by mass, the coating film hardness is not sufficient, while if it exceeds 50% by mass, the processability becomes insufficient.

The resin composition for the undercoat coating film includes a curing catalyst such as p-toluenesulfonic acid, tin octoate, dibutyltin dilaurate, calcium carbonate, kaolin, clay, titanium oxide, Pigments such as red iron oxide, mica, carbon black, and aluminum powder; rust preventive pigments such as chromate and aluminum tripolyphosphate; and other various additives such as antifoaming agents and anti-flow agents can be added.

The rust preventive pigment is most preferably a chromate salt from the viewpoint of corrosion resistance. As this chromate,
Examples include strontium chromate, potassium chromate, zinc chromate, calcium chromate, and barium chromate, with strontium chromate being most preferred. The content of chromate is 1 to 5 as a percentage of the solid content of the coating film.
It is desirably 0 mass%, preferably 10 to 45 mass%. If the content of the chromate is less than 1 mass%, a sufficient rust-preventing effect cannot be obtained, while if it exceeds 50 mass%, the adhesion to the overcoat film decreases.

(4) Top Coating Film The top coating film has a thickness of 5 to 30 μm. If the coating thickness is less than 5 μm, sufficient workability and corrosion resistance in the processed portion cannot be obtained, while if it exceeds 30 μm, the workability decreases and the production cost increases, which is not preferable. The overcoat film has a glass transition temperature of 30 to 90 ° C. If the glass transition temperature of the overcoated film is less than 30 ° C, the scratch resistance is reduced, while if it exceeds 90 ° C, the workability of the coated film is reduced, and as described above, the workability of the plated steel sheet is improved. However, the workability of the coated steel sheet as a whole is low.

As the base resin for the overcoat film, polyester resin, acrylic resin, polyvinylidene fluoride resin (mixed resin of polyvinylidene fluoride resin and acrylic resin) and the like can be used. In addition to the polyester resin, a silicone-modified polyester resin, an acryl-modified polyester resin, and the like can be used. Among these base resins, a polyester resin and a polyvinylidene fluoride resin are particularly preferable from the viewpoint of processability, and a polyester resin is most preferable in consideration of cost.

The polyester resin has at least two hydroxyl groups in one molecule and has a number average molecular weight of 100.
The compound is not particularly limited as long as it is a compound of 0 to 20,000, but a compound having a number average molecular weight of 2000 to 20,000 is particularly preferable. Number average molecular weight of polyester resin is 2
If it is less than 000, workability may be significantly reduced. On the other hand, if the number average molecular weight exceeds 20,000, the weather resistance is reduced, an excessive diluting solvent is required because of high viscosity, and an appropriate coating film cannot be obtained because the ratio of the resin in the coating material is reduced, and The compatibility with other compounding components may also be reduced. Here, the number average molecular weight of the polyester resin is G
It is the molecular weight in terms of polystyrene measured by PC. In addition, the hydroxyl group in the molecule of the polyester resin may be at either the terminal or the side chain in the molecule.

The polyester resin is a copolymer obtained by subjecting a polybasic and a polyhydric alcohol to a heat reaction in a conventional manner. As the polybasic acid component, for example, phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, maleic acid, adipic acid, fumaric acid and the like can be used.

As the polyhydric alcohol, for example,
Ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, glycerin, pentaerythritol, trimethylolpropane, trimethyl glycol Methylolethane or the like can be used.

When the polyvinylidene fluoride resin is blended as an overcoating film component, it is used as a mixed resin in which an acrylic resin is mixed with the polyvinylidene fluoride resin. The weight average molecular weight of the polyvinylidene fluoride resin is 300,000 to 700,000, and the melting point is 150 to 18.
Those at 0 ° C. are preferred. For example, a trade name of “Kyner 500 (weight average molecular weight:
350,000, melting point: 160 to 165 ° C).

The acrylic resin mixed with the polyvinylidene fluoride resin has a number average molecular weight of 1,000 to 2,000.
Are preferred. The acrylic resin can be obtained by polymerizing (or copolymerizing) at least one of the following monomers (including at least one acrylic monomer) by an ordinary method.

Hydroxymethyl (meth) acrylate,
Ethylene monomers having a hydroxyl group such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate and hydroxybutyl (meth) acrylate (meth) acrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, etc. An ethylenic monomer having a carboxyl group of methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl acrylate,
Ethylene monomers copolymerizable with the above monomers, such as n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, alkyl (meth) acrylate Styrene, α-methylstyrene, o-methylstyrene,
Styrene derivatives such as m-methylstyrene and p-methylstyrene

By using a monomer having a functional group such as a hydroxyl group or a carboxyl group among these monomers, a cross-linking reaction with another reactable component is possible. The acrylic resin used in the present invention does not need to be self-crosslinkable, but when it is made to be self-crosslinkable, a so-called crosslinkable monomer having two or more radically polymerizable unsaturated bonds in the molecule is contained. Radical polymerizable monomers include ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate. , 1,4-butanediol diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, glycerol dimethacrylate, glycerol diacrylate, Diallyl terephthalate, diallyl phthalate, glycidyl acrylate, glycidyl Polymerizable unsaturated compounds such as methacrylate and the like. The crosslinkable monomer can be added up to 20% by mass of the acrylic resin.

The compounding ratio (weight ratio of solid resin) of the polyvinylidene fluoride resin and the acrylic resin is [polyvinylidene fluoride resin]: [acrylic resin] = 90: 10 to 50:
It is preferably 50. When the weight ratio of the polyvinylidene fluoride resin to the acrylic resin exceeds 90:10, the thixotropy increases, and coating with a roll coater becomes difficult, resulting in a coating film having a non-uniform finish and poor coating film appearance. On the other hand, when the ratio is less than 50:50, undesirably, the deterioration of the coating film adhesion with time is remarkable, and the weather resistance is greatly reduced. The blending amount of the mixed resin of polyvinylidene fluoride resin and acrylic resin is 40 mass% in the solid content of the coating film.
When the amount is less than 40 mass%, the desired coating film performance cannot be sufficiently obtained.

When a polyester resin or an acrylic resin is used as the main resin, a curing agent can be blended, and a polyisocyanate compound and / or an amino resin can be used as the curing agent. As the polyisocyanate compound, an isocyanate compound obtained by a general production method can be used,
Particularly, a polyisocyanate compound which can be used as a one-pack type coating material and is blocked with a blocking agent such as phenol, cresol, aromatic secondary amine, tertiary alcohol, lactam and oxime is preferable. By using this blocked polyisocyanate compound, storage with one liquid becomes possible, and use as a paint becomes easy.

More preferred polyisocyanate compounds include HDI and its derivatives, TDI and its derivatives, MDI and its derivatives, XDI and its derivatives, IPDI and its derivatives, TMDI and its derivatives, hydrogenated TDI and its derivatives, Examples include hydrogenated MDI and its derivatives, hydrogenated XDI and its derivatives, and the like.

When a polyisocyanate compound is used as a curing agent, the compounding ratio of the isocyanate group of the polyisocyanate compound to the hydroxyl group in the base resin [NCO / OH]
Is in a molar ratio of 0.8 to 1.2, more preferably 0.90 to
It is desirable to set the range to 1.10. [NCO / O
When the molar ratio [H] is less than 0.8, the coating film is insufficiently cured, and the desired coating film hardness and strength cannot be obtained. On the other hand, [N
When the molar ratio of [CO / OH] exceeds 1.2, a side reaction occurs between excess isocyanate groups or between the isocyanate group and the urethane compound, and the processability of the coating film is reduced.

As the amino resin as a curing agent, a resin obtained by reacting urea, benzoguanamine, melamine or the like with formaldehyde, or a resin obtained by alkyl etherifying these with an alcohol such as methanol or butanol can be used. Specifically, a methylated urea resin, n
-Butylated benzoguanamine resin, methylated melamine resin, n-butylated melamine resin, iso-butylated melamine resin, and the like.

When an amino resin is used as a curing agent, the mixing ratio (weight ratio of solid content) between the amino resin and the base resin is as follows:
Main resin: amino resin = 95: 5 to 60:40, preferably 85:15 to 75:25. The amount of the curing agent is 9 to 50 mass in terms of the resin solid content.
% Is preferable. If the amount of the curing agent is less than 9% by mass, the coating film hardness is not sufficient, while if it exceeds 50% by mass, the processability becomes insufficient.

Further, similarly to the resin composition for the undercoat coating film,
Depending on the purpose and use of the resin composition for the top coat,
-Curing catalysts such as toluenesulfonic acid, tin octoate, dibutyltin dilaurate, calcium carbonate, kaolin,
Pigments such as clay, titanium oxide, red iron oxide, mica, carbon black, and aluminum powder, and various additives such as an antifoaming agent and a flow stopper can be added.

Next, a method of manufacturing the coated steel sheet according to the present invention will be described. The production method of the present invention is a method for producing a coated steel sheet using a hot-dip Al-Zn-based coated steel sheet having an Al content of 20 to 95 mass% in a plating film manufactured by a continuous hot-dip plating facility or the like as a base steel sheet, At least the following (a)
And (b) a step of providing a thermal history, and a step of sequentially forming a chemical conversion coating, an undercoat, and an overcoat on the surface of the plated steel sheet. (a) Heat history in which the average cooling rate for 10 seconds immediately after the steel sheet leaves the hot-dip bath is less than 11 ° C./sec. (b) After the hot-dip plated metal solidifies,
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history,
And / or from a temperature T (° C.) in the range of 130 to 300 ° C. after solidification of the hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Heat history that satisfies the following: C = (T-100) / 2 (1)

Of the thermal histories (a) and (b) applied to the plating film, the application of the thermal history (a) is performed by controlling the cooling condition of the plating film immediately after plating. In order to impart the heat history of (a) to the plating film, as described above, the temperature is adjusted from the hot-dip bath surface of the continuous hot-dip plating equipment to the roll where the steel sheet that has exited the hot-dip plating bath first contacts. It is necessary to provide a device and control the cooling rate of the plating film by this temperature adjusting device. As described above, the temperature control device is preferably provided with a heating or heat retaining means, and, if necessary, provided with a cooling means,
There is no special limitation on the method, shape, scale, etc. of the heating or heat retaining means and cooling means, and any material may be used as long as it can impart the heat history of (a) to the plating film. For example, an induction heater or a gas heating furnace can be used as a heating or heat retaining means of the temperature adjusting device, and a gas blowing device or the like can be used as a cooling means.

The heat history of (b) may be applied by subjecting the plated steel sheet after the hot-dip plated metal has solidified to a specific heat treatment, or after the hot-dip plated metal has solidified. The cooling of the plating film is controlled by heat retention or the like. In the manufacturing method of the present invention, a chemical conversion coating, an undercoat and an overcoat are sequentially formed on the plating film surface of the plated steel sheet, and the heat treatment for imparting the heat history of (b) to the plating film is a chemical conversion treatment. Before, during the chemical conversion treatment drying process, after the chemical conversion treatment (after application and drying of the treatment liquid), before undercoating, during the undercoating drying process, after the undercoating application (after coating and drying), and before the overcoating It may be carried out in any of the following steps: during the step of drying the top coat, and after the end of the top coat (after application and drying of the paint). Moreover, you may perform in two or more steps of these.

Therefore, the application of the thermal history of (b) to the plating film can be performed in at least one of the following steps (1) to (8). (1) Before chemical conversion treatment (2) During chemical conversion drying process (3) After chemical conversion treatment and before undercoat coating (4) During undercoat coating drying process (5) After undercoat coating completion and before topcoat coating (6) Topcoat During the coating drying process (7) After finishing the top coat (8) Cooling process after the hot-dip plated metal has solidified Among the above methods of heat treatment, and methods are chemical conversion, undercoat and overcoat Since the heat treatment is performed using the heating in the drying step of the coating, it is particularly economical.

The heat treatment or heat retention for imparting the heat history of the above (b) is performed by a heating or heat retention device provided inside or outside the continuous hot-dip plating equipment. A heating mechanism (e.g., induction heater, hot blast stove, etc.) may be provided in the continuous hot-dip plating equipment to perform continuous heating in-line, or to perform batch heating offline after winding on a coil. Is also good. Further, the heating may be performed by continuous heating using a heating mechanism (for example, an induction heater or a hot blast stove) in a continuous processing facility outside the plating line. Furthermore, after the plated steel sheet continuously heated in the plating line or in the above-described continuous processing equipment is wound around a coil, appropriate heat retention or heat retention may be performed. Also,
In the cooling process after the hot-dip-plated metal is solidified, a heat retaining device may be provided so as to keep the plating film heated and gradually cooled. However, there is no special restriction on the method, shape, scale, etc. of the heating or heat retaining device, and it is essential that the heat treatment of the above (b) be given to the plating film. In addition, the preferable plating composition of the hot-dip Al-Zn-based plated steel sheet, the coating weight, the reasons for limiting the heat history of the above (a) and (b), the obtained effects, and the like are as described above.

As described above, there is no particular limitation on the type of chemical conversion treatment applied to the surface of the plated steel sheet as a coating base, and chromate treatment, zinc phosphate treatment, treatment containing an organic resin as a main component, and the like can be performed. . In general, in the drying step of the chemical conversion treatment, the treated film is heated and dried by a hot air oven, an induction heater, or the like. Therefore, as described above, the heat history of (b) is applied to the plated film by using the heated drying. May be provided.

An undercoat paint, preferably the above-mentioned resin as a main resin, is applied to the upper layer of this chemical conversion treatment film, and if necessary, an undercoat paint containing a curing agent is applied thereto and baked. A top coat, preferably a resin as described above as a main resin, and by applying and baking a top coat containing a curing agent, if necessary, to form an undercoat and an overcoat. . The configurations of the undercoat film and the overcoat film are as described above. Although there is no particular limitation on the method of applying the paint for forming the coating film (undercoat film and topcoat film), roll coater coating, curtain flow coating and the like are preferable. After applying the paint, the coating is baked by hot air heating, infrared heating, induction heating or the like to form a coating.

In the baking treatment for heating and curing the coating film, the baking temperature (maximum reaching plate temperature) is set to 150 to 270 in undercoating.
° C, preferably 180 to 250 ° C. If the baking temperature is lower than 150 ° C., the curing reaction of the coating film becomes insufficient, and the corrosion resistance of the coated steel sheet tends to decrease. Meanwhile, 2
If the temperature exceeds 70 ° C., the reaction becomes excessive, and the adhesion to the overcoat film may decrease.

In the case of top coating, the baking temperature (maximum sheet temperature) is 150 to 280 ° C., preferably 180 to 260 ° C.
C is appropriate. If the baking temperature is lower than 150 ° C., the polymerization reaction of the resin is insufficient, and the corrosion resistance and scratch resistance of the coated steel sheet are likely to be reduced. On the other hand, when the temperature exceeds 280 ° C., the reaction becomes excessive and the processability may be reduced. The baking time for undercoating and topcoating is not particularly limited, but usually about 20 to 120 seconds is appropriate. In addition,
As described above, the heat history of (b) may be imparted to the plating film by utilizing the baking treatment of these coating films.

[0072]

EXAMPLES Example 1 A cold-rolled steel sheet (thickness: 0.35 mm) manufactured by an ordinary method was passed through a continuous hot-dip plating apparatus to obtain 55% Al-1.5% Si-
Zn plating bath (Examples of the present invention No. 1 to No. 6, No. 9)
-No. 18, Comparative Example No. 1 to No. 13), 40%
Al-1.0% Si-Zn plating bath (Example No. 1 of the present invention)
7) and hot-dip plating was performed using a 70% Al-1.8% Si-Zn plating bath (Example No. 8 of the present invention). The line speed was set to 160 m / min, and the amount of coating on one side was adjusted so that the variation between the steel sheets was within the range of 75 to 90 g / m ² . In addition, the comparative example No. 14 as molten 5% Al-
A hot-dip coated steel sheet (single-side plating adhesion amount: 130 g / m ² ) by Zn-based plating was also manufactured. In the production process of these plated steel sheets, the thermal histories (I) and (II) shown in Tables 1, 3 and 5 are imparted to the plating film, and the conditions of the undercoat film and the overcoat film are variously changed. The following coated steel sheets were manufactured. The paint shown in Table 7 was used as the paint for the undercoat, and the paint shown in Table 8 was used as the paint for the overcoat.

[Inventive Example 1] A normal chromate treatment (40 mg / m ^{2 of} chromium equivalent in terms of metallic chromium) was applied to a hot-dip 55% Al-Zn-based plated steel sheet having a plated film having passed through a heat history satisfying the conditions of the present invention. This is a coated steel sheet which has been subjected to the following undercoating and topcoating. The undercoat is
Block urethane-modified epoxy resin which is the main resin in terms of solid content (trade name "EPOKEY 830", Mitsui Chemicals, Inc.)
125 parts by weight), 75 parts by weight of strontium chromate as a rust-preventive pigment, 25 parts by weight of titanium oxide as a pigment, and 25 parts by weight of a clay, and stirred for 1 hour with a sand mill to prepare a coating composition. , Coated with a bar coater so that the dry coating thickness is 4 μm, the reached plate temperature 220 ℃,
The baking process was performed under the conditions of a baking time of 38 seconds.

The top coat is made of a polyester resin (trade name “Almatex P64”) which is a main resin in terms of solid content.
5 ", 100 parts by weight, manufactured by Mitsui Chemicals, Inc .; 25 parts by weight of methylated melamine as a curing agent (trade name: Cymel 303, manufactured by Mitsui Chemicals, Inc.); 0 p-toluenesulfonic acid as a curing catalyst .2 parts by weight, and 100 parts by weight of titanium oxide as a pigment were blended, and the mixture was stirred for 1 hour with a sand mill to prepare a coating composition, and applied with a bar coater so that the dry coating thickness became 13 μm. Sheet temperature 230 ° C, baking time 5
The printing process was performed for 3 seconds. Also, a polyester resin-based backside paint was applied to the backside of the plated steel sheet with a bar coater so that the dry coating thickness became 6 μm.
The baking process was performed under the conditions of a baking time of 38 seconds.

[Inventive Examples 2 to 10] In Inventive Examples 2 to 4, the conditions of the thermal history applied to the plating film were changed from those of Inventive Example 1, and the other conditions were the same as those of Inventive Example 1. And Inventive Examples 5 to 6 are different from the Inventive Example 1 in the stage (time) at which a predetermined thermal history is applied to the plating film, and the other conditions are the same as in Inventive Example 1. Invention Examples 7 to 8
Was obtained by changing the composition of the plating film with respect to Inventive Example 1, and the other conditions were the same as in Inventive Example 1. Inventive Examples 9 and 10 are different from Inventive Example 1 in the thickness of the undercoat film, and other conditions were the same as in Inventive Example 1.

[Inventive Examples 11 and 12] An undercoat paint different from that of Inventive Example 1 was used, and other conditions were the same as those of Inventive Example 1. The undercoat paint of Invention Example 11 is a polyester resin which is a main resin (trade name “Almatex HMP2
7 ", 100 parts by weight, manufactured by Mitsui Chemicals, Inc .; 25 parts by weight of methylated melamine as a curing agent (trade name: Cymel 303, manufactured by Mitsui Chemicals, Inc.); p-toluenesulfonic acid as a curing catalyst 0 .2 parts by weight, and the other components and amounts were the same as in Invention Example 1. The undercoat paint of Invention Example 12 used a urethane-modified epoxy resin (trade name “EPOKEY 802-30CX”, manufactured by Mitsui Chemicals, Inc.) as a main resin.
The other components and amounts were the same as in Invention Example 1.

[Inventive Examples 13 and 14] The thickness of the overcoat film was changed from that of Inventive Example 1, and other conditions were the same as those of Inventive Example 1. [Invention Examples 15 to 17] An overcoat paint different from that of Invention Example 1 was used, and other conditions were the same as those of Invention Example 1.
The overcoat paint of Invention Example 15 used an acrylic resin (trade name “Almatex 745-5M”, manufactured by Mitsui Chemicals, Inc.) as the main resin, and the other components and the compounding amounts were the same as those of Invention Example 1. The overcoating material of Invention Example 16 was a polyvinylidene fluoride resin (trade name “Kyner 50”) as a main resin.
0 ", manufactured by Nippon Penwald Co., Ltd.) and an acrylic resin (trade name" Palolite ", manufactured by Rohm and Haas Co.) at a solid content mass ratio of polyvinylidene fluoride resin: acrylic resin = 70: 30. The other components and compounding amounts were the same as those of Invention Example 1. The overcoat paint of Invention Example 17 used a polyester resin (trade name “Almatex P647BC”, manufactured by Mitsui Chemicals, Inc.) as a main resin, and the other components and the compounding amounts were the same as those of Invention Example 1.

[Invention Example 18] The amount of the curing agent in the top coat was changed from that of Invention Example 1, and the amount of the curing agent was 40 parts by weight with respect to 100 parts by weight of the base resin. Were the same as those of Inventive Example 1. [Comparative Examples 1 to 14] In Comparative Examples 1 to 5, the heat treatment conditions for plating were applied.
9 is a comparative example in which the film thickness of the overcoat film is not satisfied, and Comparative Examples 10 and 11 are comparative examples in which the glass transition temperature of the overcoat film does not satisfy the conditions of the present invention, and other conditions are the same as those of Inventive Example 1. Comparative Example 12 is a comparative example in which the plating film does not have the thermal history defined by the present invention, Comparative Example 13 is a comparative example in which the undercoating is omitted, and Comparative Example 14 is that the undercoated steel sheet has a melting point of 5%. It is a comparative example which is an Al-Zn plated steel sheet (the heat history defined by the present invention is not given),
Other conditions are the same as those of the invention example 1.

For each of the coated steel sheets described above, the workability, adhesion at the processed portion, corrosion resistance at the processed portion, and the hardness of the coating film were evaluated by the following methods, and the glass transition temperature of the overcoated film was measured. Tables 1 to 6 show the results together with the configuration of the coated steel sheet. Workability Perform a 180 ° bending process on the sample in a room at 20 ° C, confirm the presence or absence of cracks with a 30x loupe,
The evaluation was made as follows using the minimum number of sheets with no cracks (T). ◎: No cracks occurred in 6T bending. ：: Cracks occurred in 6T bending, but no cracks occurred in 7T bending. ：: Cracks occurred in 7T bending, but no cracks occurred in 8T bending. X: 8T bending. Crack

Adhesion of Processed Part After subjecting the sample to 5T bending at 180 ° in a room at 20 ° C., the adhesive tape was adhered to and peeled from the bent part, and the peeling rate of the coating film at the bent part ( Area ratio) and evaluated according to the following. ◎: 0% peeling rate of coating film ○: Over 0% peeling rate of film, less than 10%

Corrosion Resistance of Processed Parts The coated steel sheet was cut into a size of 160 mm × 70 mm, and subjected to 180 ° 3T bending in a room at 20 ° C., followed by sealing the four edges with tar epoxy paint. After 300 cycles of an acceleration test (hereinafter referred to as a CCT test) in which dry and wet repetition conditions defined in JIS K5621 were introduced using the test piece, the swelling ratio (area ratio) of the coating film was measured. The swelling ratio was 10 mm at both ends of the test piece.
In the bent portion of 50 mm width except for, the total length in the width direction of the portion where the swelling of the coating film has occurred is expressed in% (for example, when there is two swelling of 5 mm width in 50 mm, The swelling ratio is 20%). JIS K 56
The conditions of the CCT test according to No. 21 are “5% salt spray, 30
0 ° C., 0.5 hour → wet 95% RH, 30 ° C., 1.5 hours → dry 20% RH, 50 ° C., 2 hours → dry 20% RH,
“30 ° C., 2 hours” is one cycle (6 hours), and this is repeated until a predetermined number of times is reached. The measured swelling ratio was evaluated as follows. ：: Swelling ratio of less than 10% ○: Swelling ratio of 10% or more and less than 30% Δ: Swelling ratio of 30% or more and less than 50% ×: Swelling ratio of 50% or more

Coating Film Hardness A pencil having a pencil hardness of H was used in accordance with 8.4 of JIS K 5400 to evaluate whether or not flaws were formed in the overcoating film. ：: flaw generation ×: no flaw generation Measurement of glass transition temperature of coating film TMA (Seiko Instruments “SS610”)
0 ”) to increase the temperature from 0 ° C to 150 ° C at a rate of 10 ° C /
The glass transition temperature of the top coat was measured at a load of 10 g for min.

According to Tables 1 to 6, the coated steel sheet according to the present invention exhibited excellent properties in all of the workability, the adhesion of the processed portion, the corrosion resistance of the processed portion, and the hardness of the coating film. On the other hand, the comparative example is inferior in any of the characteristics as compared with the present invention.

[0084]

[Table 1]

[0085]

[Table 2]

[0086]

[Table 3]

[0087]

[Table 4]

[0088]

[Table 5]

[0089]

[Table 6]

[0090]

[Table 7]

[0091]

[Table 8]

Example 2 A cold-rolled steel sheet (thickness: 0.35 mm) manufactured by an ordinary method was passed through a continuous hot-dip plating apparatus to obtain 55% Al-1.5% Si-
Using a plating bath in which one or more of Mg, V and Mn are added to the Zn plating bath,
g, V, Mn, the content of one or more of the total is 0.1.
Hot-dip plating was performed so as to be 01 to 10 mass%. The line speed was set to 160 m / min, and the amount of coating on one side was adjusted so that the variation between the steel sheets was within the range of 75 to 90 g / m ² . In the manufacturing process of these plated steel sheets, the heat histories (I) and (II) shown in Table 9 were imparted to the plating film, and the chromate-treated film, the undercoat film, and the topcoat film were applied to the plating film surface in the same manner as Invention Example 1. Formed sequentially under the conditions.
For each of the coated steel plates described above, workability, adhesion at the processed portion, corrosion resistance at the processed portion, and hardness of the coating film were evaluated in the same manner as in Example 1. The results are shown in Tables 9 and 10 together with the configuration of the coated steel sheet.

[0093]

[Table 9]

[0094]

[Table 10]

[0095]

As described above, the coated steel sheet of the present invention is
Melt A with Al content of 20-95 mass% in plating film
Although it is a coated steel sheet using an l-Zn-based plated steel sheet as a base steel sheet, it has extremely excellent workability and corrosion resistance in the processed part. Further, according to the manufacturing method of the present invention, such a coated steel sheet can be manufactured stably and with high productivity.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the average cooling rate of a plating film on the workability of a coated steel sheet for the first 10 seconds immediately after the steel sheet leaves a hot-dip bath.

FIG. 2 (a) is a graph showing the effect of increasing the heating temperature of a plating film on the workability of a coated steel sheet when heat-treating a coated steel sheet after solidification of a hot-dip plated metal; FIG. 2 (b) shows the average cooling rate of the plating film (from the heating temperature to the heating temperature of 10%) when the plated steel sheet after the hot-dip plating metal is solidified is heat-treated.
Graph showing the effect of average cooling rate to 0 ° C) on the workability of painted steel sheet

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[Procedure amendment]

[Submission date] March 7, 2002 (2002.3.7)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 2/28 C23C 2/28 2/40 2/40 28/00 28/00 C (72) Inventor's University Toshihiko Ii 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Keiji Yoshida 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Junichi Inagaki 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Yasuhiro Majima Kanagawa Prefecture (72) Inventor: Norio Inoue 6-1 Mizue-cho, Kawasaki-ku, Kawasaki-ku, Kawasaki-ku, Kanagawa Prefecture Person Shinji Hori 6-1 Mizue-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa F-term in KK Steel Sheet Co., Ltd. EB33 EB35 EB38 EB45 EB53 EC01 EC15 EC54 4F100 AA02D AB03B AB10A AB18A AK19E AK25E AK41D AK41E AK53D AL05E BA05 BA07 BA10B BA10E CC00D CC00E EH71A EJ68C GB90 JA05E ABA4 AB02 Y02A02 AB02 YY02A AB02 BA01 BA04 BA10 BA15 BA17 BA21 BB05 BC02 BC05 CA11 CA16 CA53 CA62

Claims (13)

[Claims] An aluminum content in a plating film is 20 to 95.
a coated steel sheet having a mass% hot-dip Al-Zn-based plated steel sheet as a base steel sheet, wherein the plated film is a plated film obtained through at least the following thermal histories (a) and (b); Thermal history in which the average cooling rate for 10 seconds immediately after the steel sheet leaves the hot-dip bath is less than 11 ° C./sec. (B) After the hot-dip plated metal solidifies,
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and thereafter, the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Thermal history and / or temperature T (° C.) in the range of 130 to 300 ° C. after solidification of hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Thermal history that satisfies the following: C = (T-100) / 2 (1) On the surface of the plating film, a chemical conversion coating film, a coating film thickness of 2 to 15 μm, and a coating film thickness from the lower layer side. Is 5-3
A coated steel sheet having excellent workability and corrosion resistance in a processed part, which has an overcoat film having a thickness of 0 µm and a glass transition temperature of 30 to 90 ° C. 2. The heat history temperature T (° C.) of (b) is 130 to
The coated steel sheet according to claim 1, wherein the temperature is in a range of 200 ° C. 3. A plating film comprising one or more selected from Mg, V and Mn in a total amount of 0.01 to 10 mass%.
The coated steel sheet according to claim 1 or 2, wherein the steel sheet has excellent workability and corrosion resistance in a processed portion. 4. The coated steel sheet according to claim 1, wherein the base resin of the undercoat film comprises a polyester resin and / or an epoxy resin. 5. The processability and processed part according to claim 1, wherein the base resin of the overcoat film comprises a polyester resin or a mixed resin of a polyvinylidene fluoride resin and an acrylic resin. Painted steel sheet with excellent corrosion resistance. 6. The processability and processed part according to claim 1, wherein the undercoating film contains chromate in a proportion of 1 to 50 mass% in the solid content of the coating film. Painted steel sheet with excellent corrosion resistance. 7. An aluminum content in a plating film of 20 to 95.
A method for producing a coated steel sheet using a mass-% hot-dip Al-Zn plated steel sheet as a base steel sheet, comprising: Manufacturing method. 1) A step of imparting at least the following thermal histories (a) and (b) to the plating film of the steel sheet that has exited the hot dip coating bath. (A) Average cooling for 10 seconds immediately after the steel sheet has left the hot dip coating bath Thermal history at a rate of less than 11 ° C./sec (b)
The temperature is raised to a temperature T (° C.) in the range of −300 ° C., and then the average cooling rate from the temperature T (° C.) to 100 ° C. satisfies C (° C./hr) or less represented by the following formula (1). Heat history, and / or temperature T (° C.) in the range of 130 to 300 ° C. after solidification of hot-dip plated metal to 100 ° C.
The average cooling rate up to C (° C / hr) shown in the following equation (1)
Thermal history that satisfies the following: C = (T-100) / 2 (1) 2) Step of forming a chemical conversion coating by applying a chemical conversion treatment to the plating coating surface 3) Applying an undercoat paint to the chemical conversion coating film surface And baking to form an undercoat film having a film thickness of 2 to 15 μm 4) Applying a top coat to the surface of the undercoat film and baking the film to have a film thickness of 5 to 30 μm and a glass transition temperature of 30 ~ 9
Step of forming a top coat of 0 ° C 8. The temperature T (° C.) of the heat history of (b) is 130 to
The method for producing a coated steel sheet having excellent workability and corrosion resistance in a processed part according to claim 7, wherein the temperature is in a range of 200 ° C. 9. The processability according to claim 7, wherein the plating film contains one or more selected from Mg, V, and Mn in a total amount of 0.01 to 10 mass. Manufacturing method of painted steel sheet with excellent corrosion resistance in the processed part. 10. In the step of 3), after applying a paint containing a polyester resin and / or an epoxy resin as a main resin, baking is performed at a maximum temperature of 150 to 270 ° C. to form an undercoat film. 9. The method according to claim 7, wherein:
Or a method for producing a coated steel sheet having excellent workability and corrosion resistance in a processed part according to 9. 11. In the step 4), after applying a paint containing a polyester resin or a mixed resin of a polyvinylidene fluoride resin and an acrylic resin as a main resin, baking treatment is performed at a maximum temperature of 150 to 280 ° C. The method for producing a coated steel sheet according to claim 7, wherein a top coat is formed. 12. The processability and processing according to claim 7, wherein the undercoat paint contains chromate in a proportion of 1 to 50 mass% in the solid content of the paint. Method for producing painted steel sheet with excellent corrosion resistance. 13. The method according to claim 7, wherein the application of the thermal history of (b) to the plating film is performed in at least one of the following steps (1) to (8). 13. A method for producing a coated steel sheet excellent in workability and corrosion resistance in a processed part according to 11 or 12. (1) Before chemical conversion treatment (2) During chemical conversion drying process (3) After chemical conversion treatment and before undercoat coating (4) During undercoat coating drying process (5) After undercoat coating completion and before topcoat coating (6) Topcoat During the coating drying process (7) After finishing the top coating (8) Cooling process after the hot-dip plated metal solidifies