JP4324095B2 - Pre-coated metal plate - Google Patents

Description

  The present invention relates to a precoated steel sheet excellent in processing characteristics (for example, press formability). The present invention relates to a pre-coated steel sheet that is less likely to break the coating even in a processing method that involves compressive strain in the steel sheet, particularly in drawing or the like.

  In recent years, from the viewpoint of environmental protection, pre-coated steel sheets coated with colored organic coatings are sometimes used instead of post-painted products that have been painted after conventional processing for home appliances, building materials, automobiles, etc. It is getting more. This pre-coated steel sheet is usually a rust-proof steel sheet and a plated steel sheet coated with an organic coating, and has the characteristics of having good workability and good corrosion resistance while having an aesthetic appearance. Yes.

  The pre-coated steel sheet can be processed in the same manner as cold-rolled or plated steel sheets that are not coated with a coating film. However, due to the problem of coating film destruction (cracking and peeling of the coating film) during molding, Mainly focused on bending with tensile strain (Patent Document 1 and Patent Document 2). On the other hand, in recent years, there is an increasing demand for applying a pre-coated steel sheet to a portion subjected to drawing forming in which compression and tensile strain act.

  However, when the precoated steel sheet is drawn, there is a problem that the tensile strain acts on the coating film at the drawing portion to cause cracks, or the compression strain acts to cause the coating film to buckle and peel. . In particular, in the pre-coated steel sheet, the blocking resistance of the coating film and the workability as the pre-coated steel sheet are in a so-called trade-off relationship, and it has been difficult to achieve both these characteristics. That is, for example, when emphasizing the workability as a pre-coated steel sheet, the blocking resistance of the coating film is reduced. On the other hand, when the emphasis is placed on the blocking resistance of the coating film, the workability as a pre-coated steel sheet is reduced. .

JP-A-8-257492 JP-A-7-912

  The object of the present invention is to provide a pre-coated steel sheet that is excellent in workability (for example, press formability) that can be formed without substantially destroying or peeling off the coating film even when drawn. There is to do.

  Another object of the present invention is to provide a precoated steel sheet having a good balance between workability and blocking resistance and excellent workability.

  As a result of diligent research, the present inventor not only has a specific value for a coating layer containing at least an undercoat coating layer and a top coating layer, but that the Ra value at the interface between these two layers is within a specific range. Has been found to be extremely effective in achieving the above objective.

The pre-coated metal plate of the present invention is based on the above knowledge, and more specifically, a pre-coated metal plate having a metal plate and a thermosetting organic resin coating film disposed on at least one surface thereof; Type organic resin coating film includes at least two layers of an undercoat coating film layer and a top coating film layer; and both coating films of the undercoat coating film layer and the top coating film layer are in a rubber-like elastic region. The minimum value of the dynamic storage elastic modulus is 2.3 × 10 ⁷ Pa or less, and the Ra (centerline average roughness) at the interface between the undercoat layer and the topcoat layer is from 0.3 to It is characterized by being 0.6 μm.

  According to the knowledge of the present inventor, in the pre-coated metal sheet of the present invention having the above-described configuration, for example, in a deformed portion that undergoes compression deformation (drawing processing, etc.) Pre-coated metal sheet with excellent workability (for example, press formability) based on the combination of the effect of reducing the distortion energy and the effect of improving the adhesion based on the specific Ra described above (undercoat layer and topcoat layer) Is estimated to be obtained.

  As described above, according to the present invention, a precoated metal sheet excellent in workability is provided. The precoated metal sheet of the present invention can withstand more severe processing than in the prior art.

  Furthermore, since the precoated metal sheet of the present invention can expand the range of usable resins than in the past, not only can the moldability and other performances be improved, but also the same. It is possible to reduce the manufacturing cost while substantially maintaining the performance.

Hereinafter, the present invention will be described more specifically with reference to the drawings as necessary.
(Pre-coated metal plate)
The pre-coated steel sheet of the present invention is a pre-coated metal plate having a metal plate and a thermosetting organic resin coating film disposed on at least one side of the metal plate, and the thermosetting organic resin coating film is an undercoat coating film layer. It contains at least two layers with the top coat layer. In the present invention, both the undercoat layer and the topcoat layer have a value of 2.3 × 10 ⁷ Pa or less as the minimum value of the dynamic storage elastic modulus in the rubber-like elastic region. Not only that, Ra at the interface between the undercoat film layer and the topcoat film layer is 0.3 to 0.6 μm.

(Dynamic storage modulus)
In the precoated metal sheet of the present invention, both the undercoat film layer and the topcoat film layer have a minimum value of 2.3 × 10 ⁷ Pa or less as the minimum value of the dynamic storage elastic modulus in the rubber-like elastic region. Has a value. The minimum value of the dynamic storage elastic modulus in this rubber-like elastic region is further preferably 1.95 × 10 ⁷ Pa or less.

  In the research group of the present inventors, as a result of various studies on the coating film breakage when the precoated steel sheet is drawn, in the deformed part that undergoes compression deformation like drawing, it accumulates inside the paint film after deformation. It has been found that a coating film having a small accumulated strain energy, which is influenced by the elastic strain energy applied, is unlikely to buckle, and is further difficult to break and peel (Coating Engineering, 10 (33), 399-406). ).

  From this point, in the present invention, by limiting the specific dynamic storage elastic modulus of the coating layer of the undercoat coating layer and the top coating layer, the elastic strain energy accumulated in the coating after being deformed is reduced. It is estimated that it can be reduced. In the present invention, the elastic strain energy accumulated in the coating film after deformation depends on the molecular weight between the crosslinking points of the main resin constituting the coating film, and the molecular weight between crosslinking points of the resin is the rubber-like elasticity of the resin. It has been confirmed that there is a correlation with the equilibrium elastic modulus of the region.

Here, details of the rubber-like elastic modulus of the resin will be described below. That is, the elastic modulus of a resin that is a viscoelastic body changes depending on temperature and time (frequency in the case of a dynamic elastic modulus). In the case of a cross-linked thermosetting resin, a high elastic modulus (generally this region is called a glassy elastic region) at a low temperature or a short time (high frequency in the case of dynamic storage elastic modulus) is 10 ⁹ to 10 ¹⁰ Pa. A region where the elastic modulus decreases rapidly as the temperature becomes higher or the time becomes longer (in the case of dynamic storage elastic modulus, the frequency becomes lower) appears (generally a transition region). The equilibrium elastic modulus becomes constant at higher temperatures or longer time (low frequency in the case of dynamic elastic modulus), and this equilibrium elastic region is called a rubber-like elastic region (generally around 10 ⁶ to 10 ⁸ Pa). Value).

In the present invention, a high temperature rubber-like elastic region among dynamic elastic modulus measured in a region of a constant frequency (each frequency of 6.28 rad / sec) and a temperature of −50 to 200 ° C. with a dynamic viscoelasticity measuring device. It is defined by the minimum value of the dynamic elastic modulus that appears in The dynamic storage elastic modulus is generally represented by E ′ and is defined by E ′ = (σ ⁰ / γ ⁰ ) cos δ. Where σ ⁰ is the maximum stress amplitude, γ ⁰ is the maximum strain amplitude, and δ is the phase angle between the stress and strain.

(Ra of interface)
In the precoat metal plate of this invention, Ra of the interface of a base coat film layer and a top coat film layer is 0.3-0.6 micrometer. This Ra is further preferably 0.4 to 0.6 μm (in the present invention, Ra can be measured by the same method for the interface between layers other than this interface).

  In the present invention, Ra of this interface can be suitably measured by the following method (that is, a method basically according to JIS B 0601-1982).

  That is, the interface where the surface roughness Ra is to be measured is photographed and used as a micrograph, the unevenness (roughness curve) of the interface is traced by a tracing device, and the weight of the paper cut out along the unevenness is measured. Thus, the center line average roughness Ra of the interface is obtained according to a predetermined formula of JIS B 0601.

  That is, the reference length L (el) = 35 μm is extracted from the roughness curve in the direction of the average line, and the absolute value of the deviation from the average line of the extracted part to the measurement curve is calculated according to the following equation (1). The sum is averaged to obtain the value of Ra.

  In the present invention, in order for the coating film covering the metal plate to satisfy the above-mentioned dynamic storage elastic modulus, for example, there are the following methods. In the present invention, any method (or a combination of two or more thereof) can be used.

  (A) The molecular chain of the resin constituting the coating film has a structure with fewer branches (by making the structure less branched, the minimum value of the dynamic storage modulus decreases),

  (B) To reduce the number of cross-linking points of the resin (by decreasing the cross-linking point of the resin, the minimum value of the dynamic storage modulus decreases),

  (C) Decreasing the strength of the cross-linking points (reducing the strength of the cross-linking points lowers the minimum value of the dynamic storage modulus).

  In the present invention, the viscoelastic properties of the resin can be obtained not only from the dynamic viscoelasticity test of the resin but also from the stress relaxation test. In this case, the relaxation elastic modulus (E (t)) obtained by the stress relaxation test is defined as the storage elastic modulus (E ′).

  The conditions of the present invention can also be obtained by calculation using the respective conversion rules from generally known viscoelasticity test methods in addition to the test methods described above. For example, for viscoelastic materials, it is known that the time-temperature conversion rule is established, so the frequency dependence curve of the storage elastic modulus of the dynamic viscoelasticity test and the time dependence curve of the stress relaxation test are The conditions in the flow region can be obtained by calculation, and the conditions in the flow region of the paint film are converted from the creep compliance obtained from the creep test (the creep compliance is proportional to the inverse of the elastic modulus) to the elastic modulus. (Regarding the details of the measurement of the two types of storage elastic modulus described above, JP-A-2003-103697 can be referred to if necessary).

  For general knowledge on viscoelasticity or rheology, please refer to well-known literatures such as “Viscoelastic Properties” (published by John Wiley and Sons) by JDFerry and “Courses / Rheology” edited by the Japanese Society of Rheology (published by Polymer). Publishing society) etc. can be referred to.

(Metal plate)
The metal plate which comprises the precoat metal plate of this invention is not restrict | limited especially as long as the coating film which has the said characteristic can be formed on this metal plate. From the viewpoint of satisfactorily exhibiting the characteristics of the coating film of the present invention, the metal plate material is preferably a metal material that can be drawn. In the present invention, the “metal” may be an alloy. Examples of the metal plate include a steel plate, an aluminum plate, and a titanium plate, but these are not limited.

  The surface of these metal materials may be plated as necessary. Examples of the type of plating include zinc plating, aluminum plating, copper plating, nickel plating and the like. Alloy plating may be used.

  When the above-mentioned metal plate is a steel plate, cold-rolled steel plate, hot-rolled steel plate, hot-dip galvanized steel plate, electrogalvanized steel plate, hot-dip galvanized steel plate, aluminized steel plate, aluminum-zinc alloyed steel plate, stainless steel plate Such as steel plates and plated steel plates can be applied. These metal plates can be subjected to ordinary treatments such as washing with hot water and alkaline degreasing before the pretreatment for coating.

  In the present invention, the thickness of the metal plate is not particularly limited. For example, when the precoated metal plate of the present invention is used for drawing, the thickness of the metal plate is usually preferably about 0.05 to 5 mm.

(Pretreatment for painting)
The above-described metal plate may be subjected to pre-painting treatment as necessary. As such coating pretreatment, known ones such as coating chromate treatment, electrolytic chromate treatment, phosphoric acid treatment, zirconia pretreatment, and the like can be used. In recent years, a non-chromate pretreatment has been developed based on a resin. However, using this non-chromate pretreatment is more preferable because it reduces the burden on the environment.

(Thermosetting organic resin)
In the present invention, the thermosetting organic resin to be used for the coating film is not particularly limited as long as the coating film can be formed on the metal plate. As such a thermosetting organic resin, generally known thermosetting resins for precoated steel sheets such as polyester resins, urethane resins, acrylic resins, epoxy resins, melamine resins, etc. Can be used. In addition, these resins can be appropriately blended and applied.

  Among these thermosetting resins, in the present invention, from the viewpoint of molding processability, a polyester resin is the main resin, and a polyester / melamine resin using melamine resin as a curing agent, or isocyanate is a curing agent. Particularly preferred is a polyester / isocyanate resin.

(Curing agent)
In this invention, you may add hardening | curing agents other than the above to the above-mentioned resin as needed. As such a curing agent, known materials such as epoxy resins and aminoplast resins other than melamine can be used.

  The addition amount of the curing agent can be appropriately selected depending on the type of the main resin and the type of the curing agent. In general, it is preferable that the addition amount of the curing agent is (more preferably 5 to 45 parts by mass) with respect to 100 parts by mass of the main resin. Moreover, the polymer chain constituting the main resin is preferably one having as few branches as possible, and a straight chain type is more preferred. This is because if the polymer chain constituting the main resin has many branches, the polymer chains are entangled with each other and flow is difficult to occur.

(Contains a curing agent in the coating film)
In the present invention, when a curing agent (for example, a melamine resin) is contained in all or part of the two-layer coating film of the undercoat coating film layer and the top coating film layer, It is possible to contain a curing agent for the resin constituting the coating film. In addition, in the present invention, in addition to or in place of such a curing agent for the same coating film, a curing agent for another coating film may be contained. That is, in the present invention, for example, a curable resin and a curing agent can be combined as described below (in the following table, a curing agent for resin A is a, and a curing agent for resin B is b. And c is a curing agent common to the resins A and B).

<Lower layer><Hardener contained in lower layer><Upperlayer><Hardener contained in upper layer>
(1) Resin A curing agent a Resin B curing agent b
(2) Resin A Hardener c Resin B None (3) Resin A None Resin B Hardener c

  Thus, when a curing agent that also reacts with other layers is added to the upper layer and / or the lower layer, these layers are based on mutual diffusion at the upper layer / lower layer interface of the curing agent (for example, melamine resin). The adhesiveness in can be further improved.

(Physical properties of resin, etc.)

  The number average molecular weight of the resin constituting the coating film of the precoated metal sheet of the present invention is preferably 10,000 or more. When the number average molecular weight of the resin constituting the coating film is less than 10,000, the coating film is poorly stretched when it is pulled and subjected to strain by press working, and the coating film is easily cracked at the processed site. A higher number average molecular weight is preferable because the elongation at break of the coating film is higher.

  If the number average molecular weight is too high, it may not be possible to make a paint, or the viscosity at the time of making a paint may become too high and the application workability may be deteriorated. Is preferably selected according to the working conditions and working environment.

(Pigments etc.)
In these coating films, coloring pigments and rust preventive pigments can be used in combination as required. Examples of the color pigment include titanium oxide (TiO ₂ ), zinc oxide (ZnO), zirconium oxide (ZrO ₂ ), calcium carbonate (CaCO ₃ ), barium sulfate (BaSO ₄ ), alumina (Al ₂ O ₃ ), kaolin clay, Examples thereof include inorganic pigments such as carbon black and iron oxide (Fe ₂ O ₃ , Fe ₃ O ₄ ), and colored pigments such as organic pigments.

  In addition, for rust preventive pigments, chromium-based rust preventive pigments such as strontium chromate and calcium chromate, zinc phosphate, zinc phosphite, aluminum phosphate, aluminum phosphite, molybdic acid, vanadic acid / phosphoric acid mixed pigment And non-chromium rust preventive pigments such as Ca ion exchange silica. In the case of a non-chromate rust preventive pigment, the environmental load is reduced, which is more preferable.

(Application)
When applying each coating film constituting the precoated metal plate of the present invention, the resin can be applied in the form of a paint. For example, a solvent-based paint in which a resin is dissolved in a solvent, a water-based paint in which an emulsified resin is dispersed in water or the like, and a form in which the resin is melted and applied are included.

  In addition, in order to improve coating-film adhesiveness before coat | covering a coating-film layer, you may perform a pre-coating process on a metal plate or the metal plate which gave plating to the precoat metal plate. Also in the precoat metal plate of the present invention, it is preferable to perform a pre-coating treatment. Even if the coating pretreatment is not performed, if the coating film adheres, the coating pretreatment process can be omitted, which is more preferable.

(Layer structure)
In the precoated metal sheet of the present invention, the thermosetting organic resin coating film has at least two layers of an undercoat coating film layer and an overcoating coating film layer, and has the above-mentioned predetermined dynamic storage elastic modulus and interface. As long as the condition of Ra is satisfied, the coating film may have three or more layers.

(Film thickness)
The film thickness of the precoated metal sheet of the present invention is not particularly limited. That is, since an appropriate film thickness may vary depending on the coating film performance, the coating method, and the application, it is preferable to select appropriately as necessary.

(Preferable coating method)
In the present invention, both the above-described undercoat coating layer and topcoat coating layer can be simultaneously applied by a slide curtain method and dried by heating .

In the present invention, from the viewpoint of the efficiency of the manufacturing process, that using a multilayered code data form both an undercoating film layer and the top coating layer, and baking both these coating layers simultaneously preferable.

(Method using multilayer coater)
In the present invention, it is preferable to use a multilayer coater from the viewpoint of productivity. As such a multilayer coater, for example, a coater or a coating method described in JP-A-6-190335 can be suitably used.

  A schematic perspective view of an embodiment of such a coater (slide hopper type curtain coating apparatus) is shown in FIG.

  Referring to FIG. 1, the slide hopper 1 is provided with a paint supply hole 8 and a slit 6 through which three layers of paint are quantitatively sent out by a gear pump or the like. A chain-like curtain guide 3 is provided so as to be in contact with both end portions of the lip portion 7A of the slide surface 7. A paint pan 5 is installed below the lip 7 </ b> A, and the curtain guide 3 hangs down to the bottom of the paint pan 5. The paint P is uniformly supplied to the slide surface 7 through the slit 6 from each paint supply hole 8 of the slide hopper 1, and is laminated on the slide surface 7. Since the laminated paint is spread by the curtain guide 3 when falling to the paint pan 5 at the tip end (lip part 7A) of the slide surface 7, it flows as a uniform liquid film in the width direction as the curtain 4 of paint. By passing a strip-shaped metal plate such as the steel strip 2 through this liquid film, a plurality of layers of paint can be applied simultaneously on the surface of the steel strip 2.

  Since multiple layers are simultaneously coated by the slide hopper type coating device without contacting the metal plate surface, roping that cannot be avoided by the roll coater does not occur. Further, since the paint film is a multi-layer curtain 4, if the total film thickness of the curtain 4 is equal to or greater than the stable film thickness, that is, about 20 μm in dry film thickness, one paint film thickness is applied with several μm. It is possible. Therefore, by painting the primer and the top coat at the same time, it is possible to obtain a coated metal plate having a beautiful appearance without causing roping.

  Further, when simultaneously applying a plurality of coating films, it is possible to make the surface of the coating film smoother than the surface of the original plate by controlling the surface tension of each coating as necessary. For example, by making the surface tension of the upper paint A lower than the surface tension of the lower paint B, the upper paint film becomes smooth. This is because when the surface tension of the upper layer paint is lower than that of the lower layer paint, the lower layer paint is restrained by the metal plate surface, so that it is more stable hydrodynamically the outermost surface paint. is there.

  Hereinafter, the present invention will be described in more detail with reference to examples.

The measuring methods of various physical properties used in the examples are as follows.
(Dynamic storage modulus)
A paint to be used for the pre-coated steel sheet (a paint whose film characteristics are to be measured, for example, a polyester resin such as “Byron” described later) is applied on the tin plate so that the dry film thickness is 10 μm, and the ultimate plate temperature is After curing and drying at 230 ° C., the coating film was released from the tin plate by the mercury amalgam method to prepare a free film of the coating film. The dynamic storage elastic modulus in a temperature range of −50 to 200 ° C. was measured on the prepared free film with a dynamic viscoelasticity test apparatus (RSA-II, manufactured by Rheometrics). The measurement conditions were a strain of 0.01% and an angular frequency of 6.28 rad / sec. FIG. 2 shows a representative example of the relationship between the temperature obtained by this experiment and the dynamic storage elastic modulus (logarithm display). As can be seen from this graph, a glassy elastic region having a high dynamic storage elastic modulus appears in a low temperature region (a temperature region of about 20 ° C. or lower in FIG. 2), and a region having a higher temperature (about 20 to about 2 in FIG. 2). A transitional region in which the value of the dynamic storage elastic modulus suddenly decreases in the region of 50 ° C. appears, and in a higher region (approximately 50 ° C. or higher in FIG. 2), a rubber-like state in which the dynamic storage elastic modulus is balanced at a low value. An elastic region appears. In the present invention, the minimum value of the storage elastic modulus appearing in the rubber-like elastic region is compared.

Example 1
(Simultaneous application with slide coater + simultaneous baking)
<Paint>
Coating materials for the undercoat coating layer and the top coating layer were prepared in a quantitative ratio as shown in Table 1 described below.

  That is, each polyester resin shown in Table 1 (for example, Byron 103 Mn 23000, Tg 47 ° C., Byron GK140 Mn 13000, Tg 20 ° C., Byron GK590 Mn 7000, Tg 17 ° C. (manufactured by Toyobo Co., Ltd.), microhexanone / Solbec 150) is used as an organic solvent (= 1/1 wt). Next, 20 parts by mass of a melamine resin (methylated melamine (trade name: Cymel 303, manufactured by Mitsui Cytec Co., Ltd.)) is added to these paints as required, based on 100 parts by mass of the solid content of the polyester resin. Furthermore, a catalyst (trade name: Catalyst 6000, manufactured by Mitsui Cytec Co., Ltd.) was added and stirred to obtain a paint.

  The following pigments were added to the paint for the undercoat film layer and the topcoat film layer used in this example.

  Pigment for undercoat layer coating: Calcium ion exchanged silica (Sealdex, manufactured by Grace) 15% by mass, titanium oxide 10% by mass

  Pigment for topcoat layer paint: White: 50% by mass of titanium oxide, Black: 4% by mass of carbon black

<Production of steel plate>
Degreasing is performed by immersing a hot-dip galvanized steel sheet with a thickness of 0.8 mm, coated on both sides with an adhesion amount of 60 g / m ² in a degreasing agent (trade name: FC-4336, manufactured by Nihon Parkerizing Co., Ltd.). , Washed with water and dried. Next, a chromate-free pretreatment agent (E300N, manufactured by Nippon Parkerizing Co., Ltd.) was applied onto the degreased hot-dip galvanized steel sheet using a roll coater, and dried with hot air under conditions such that the ultimate plate temperature was 60 ° C.

  After the non-chromate treatment described above, the resin coating for forming the lower layer and the upper layer is simultaneously applied to the hot-dip galvanized steel plate after the chromate-free pretreatment with the paint shown in Table 1 using the slide coater shown in FIG. After forming by coating, these layers are simultaneously baked (PMT (maximum ultimate plate temperature) 235 ° C., 1 minute), and on this hot-dip galvanized steel sheet, an undercoat layer (thickness 5 μm) and an overcoat layer Layers (thickness 15 μm).

Example 2 (Lower layer coating with a roll coater + baking + Upper layer coating with a roll coater + baking; 2C2B)

  On the hot dip galvanized steel sheet after the same chromate-free pretreatment as that used in Example 1, a resin layer for forming an undercoat coating film layer was formed using a roll coater. Next, this coating layer was baked (PMT 215 ° C., 1 minute) to form an undercoat coating layer (thickness 5 μm) on the hot-dip galvanized steel sheet.

  Thereafter, an undercoat film layer is formed on the hot-dip galvanized steel sheet on which the undercoat film layer has been formed using a roll coater, and then this paint film layer is baked (PMT 235 ° C., 1 minute). A top coat layer (thickness 15 μm) was formed on the coat layer (thickness 5 μm).

Example 3 (Cylindrical drawing test)
The cylindrical drawing test was performed under the conditions of a punch diameter of 50 mm, a punch shoulder R3 mm, a die shoulder R3 mm, a drawing ratio of 2.3, and BHF1t, and processing was performed until the steel plate was drawn out of the mold. Furthermore, after making a cross-cut flaw with a cutter knife in the body of the material that has undergone these drawing processes (the part where the drawing has been applied), the drawn material with this cut is immersed in boiling water for 1 hour. It was. And the tape peeling test of the coating-film surface of the cut part after immersion in boiling water was carried out.
No paint film peeling ○
The paint film is △
The paint film has been peeled off before the tape is peeled off. ×

  The results obtained as described above are shown in Table 1 below.

It is a model perspective view which shows an example of the slide coater which can be used conveniently in this invention. It is a typical graph for demonstrating the measuring method of the dynamic storage elastic modulus in this invention.

Claims (7)

A pre-coated metal plate having a metal plate and a thermosetting organic resin coating film disposed on at least one surface thereof,
The thermosetting organic resin coating includes at least two layers of an undercoat coating layer and an overcoat coating layer; and
Both the undercoat layer and the topcoat layer have a value of 2.3 × 10 ⁷ Pa or less as the minimum value of the dynamic storage elastic modulus in the rubber-like elastic region, and the undercoat A precoated metal sheet, wherein Ra (centerline average roughness) at the interface between the film layer and the top coat layer is 0.3 to 0.6 μm.   The resin constituting the both undercoat film layer and the topcoat film layer has a common curing agent that cures both of these resins, and at least one of both the undercoat film layer and the topcoat film layer The precoated metal sheet according to claim 1, wherein the common curing agent is contained.   The precoated metal sheet according to claim 1 or 2, which has a gradient of curing agent concentration at the interface between both coating layers. The precoat metal plate in any one of Claims 1-3 in which the said undercoat coating-film layer contains a rust preventive pigment . The precoat metal plate according to any one of claims 1 to 4, wherein the top coat layer contains a color pigment . The pre-coated metal sheet according to any one of claims 1 to 5 , wherein the curing agent is a melamine resin. It produced using the multilayer co data, and, precoated metal sheet according to any one of claims 1 to 6, both the coating layer is baked at the same time.

Images