JP2002225177A - Coated steel panel excellent in processability and processed part corrosion resistance and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coated steel panel having excellent processability extremely reducing the generation of a crack in a coating film and also excellent in processed part corrosion resistance. SOLUTION: The coated steel panel has such a structure that a chemical forming treatment film is provided on the surface of the plating film on a steel panel and an undercoating film (a) and a topcoating film (b) are provided on the chemical forming treatment film. The undercoating film (a) is based on a modified polyester resin (C) and a hardening agent (D), and is obtained by reacting a polyester resin (A) and an epoxy resin (B). The k value represented by formula (1): k=[Wb×(Ma+2×Mb)]/[(Wa+Wb)×2×Mb] wherein, Wa is a solid weight ratio of (A) to [(A)+(B)], Wb is a solid weight ratio of (B) to [(A)+(B)], Ma is a number average mol.wt. of (A), and Mb is a number average mol.wt. of (B)] is 0.7-2.5, and a curing agent (P) and the topcoating film (b) is based on a polyester resin (E) and a hardening agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a zinc-based or zinc-based
The present invention relates to a coated steel sheet using an aluminum-based hot-dip coated steel sheet as a base steel sheet and a method for manufacturing the same.

[0002]

2. Description of the Related Art In general, a coated steel sheet on which a plated steel sheet is used as a base is used after being formed, so it is very important that a crack (break of the coating film) does not occur in the coating film during processing. Further, the coated steel sheet has a drawback that it is easily damaged at the time of the forming process, so that the appearance after the processing and the corrosion resistance of the processed portion are inferior to the material coated after the processing.

[0003] Among hot-dip coated steel sheets, a coated steel sheet based on a hot-dip Al-Zn-based coated steel sheet containing 20 to 95 mass% of Al in a plating film is disclosed in JP-B-46-716.
As shown in No. 1, the coated steel sheet as the base has high corrosion resistance as compared with the hot-dip galvanized steel sheet, and thus exhibits excellent corrosion resistance. In particular, the Al content in the plating film is 55 ma.
In recent years, demand has been growing in the field of construction materials, mainly in the case of painted steel sheets obtained by applying a coating to ss% plated steel sheets.

[0004] However, when Al is contained in
The plating film of hot-dip Al-Zn coated steel sheet containing up to 95 mass% is
Is more hard than the plating film of a plated steel sheet containing about 5 mass% of, and cracks (plating cracks) are easily generated during processing, and the opening width of the generated cracks is large. Therefore, even with a coated steel sheet having such a hot-dip Al-Zn-based plated steel sheet as a base, cracking of the coating film due to cracks in the plating film is likely to occur during forming, and the appearance after processing and the corrosion resistance of the processed portion are poor. was there. For this reason, the coated steel sheet based on the hot-dip Al-Zn plated steel sheet cannot be applied to applications in which severe processing is performed.

[0005]

In order to solve such a problem, by increasing the ductility of the coating by softening the coating, it is possible to prevent the occurrence of cracks in the coating caused by cracks in the plating film. A measure to improve workability is conceivable. However, when the coating film is softened, the adhesion between the coating film and the substrate is reduced, and the scratch resistance may be reduced. This scratch resistance is one of the important properties of a coating film in consideration of coating film damage during molding and handling. Therefore, while securing the minimum scratch resistance,
It is necessary to design the coating so as to improve workability,
In this respect, it is difficult to further improve the workability by the conventional technology.

Accordingly, an object of the present invention is to provide a coated steel sheet using a hot-dip galvanized steel sheet or a hot-dip Al-Zn-based steel sheet as a base steel sheet, and in which a coating film crack is extremely unlikely to occur even in a bent part. An object of the present invention is to provide a coated steel sheet which has workability and is excellent in characteristics such as corrosion resistance of a processed portion and a method for manufacturing the same.

[0007]

Means for Solving the Problems To solve the above problems,
The present inventors have determined the viewpoint of the performance as a coated steel plate and have intensively studied the configuration of a coating film optimal for improving workability and corrosion resistance. As a result, in a coated steel sheet using a hot-dip galvanized or hot-dip Al-Zn coated steel sheet as a base steel sheet, a chemical conversion treatment is applied to the surface of the coated steel sheet, and a specific polyester resin and an epoxy resin are reacted on the upper layer to obtain a chemical conversion treatment. An undercoat paint containing a modified polyester resin and a curing agent as a main component resin is applied to form an undercoat paint film, and an overcoat paint containing a specific polyester resin as a main component resin is further applied thereon to form an overcoat paint film. It has been found that by forming, a coated steel sheet having excellent performance which could not be obtained conventionally can be obtained. In addition, such a performance can be achieved by using a hot-dip galvanized steel sheet or a plating film having an A content of about 5 mass%.
1 can be effectively obtained even with a coated steel sheet on the basis of a hot-dip coated steel sheet containing l, but it has been found to be particularly effective in a hot-dip Al-Zn-based coated steel sheet containing 20 to 95% by mass of Al in a plating film. .

[0008] The present invention has been made based on such knowledge, and its characteristic configuration is as follows. [1] A coated steel sheet having a zinc-based or zinc-aluminum-based hot-dip coated steel sheet as a base steel sheet, having a chemical conversion coating film on a plating film surface, and having an undercoat film below (a) above the coating film, Further, a coated steel sheet having excellent workability and corrosion resistance in a processed portion, characterized by having an overcoat film described in (b) above. (A) a number average molecular weight of 14,000 to 26000, a glass transition temperature of 0 to 30 ° C., obtained by a reaction between a polyester resin (A) and an epoxy resin (B), and
A dry coating film formed by applying a coating mainly composed of a modified polyester resin (C) having a k value of 0.7 to 2.5 represented by the formula (1) and a curing agent (D). Undercoat having a thickness of 2 μm or more k = [Wb × (Ma + 2 × Mb)] / [(Wa + Wb) × 2 × Mb] (1) where Wa: [polyester resin (A) + epoxy resin (B)] Weight ratio of solid content of polyester resin (A) to polyester resin (A) Wb: Weight ratio of solid content of epoxy resin (B) to [polyester resin (A) + epoxy resin (B)] Ma: Number average molecular weight of polyester resin (A) Mb: Number average molecular weight of epoxy resin (B) (b) Dry coating film thickness formed by applying a paint containing a polyester resin (E) having a number average molecular weight of 5,000 to 20,000 and a curing agent as a main component resin has a thickness of 5 to 5. 30μm top coat

[2] The coated steel sheet according to [1] above, wherein zinc-
Aluminum-based hot-dip coated steel sheet contains Al
A coated steel sheet having excellent workability and corrosion resistance in a worked portion, characterized by containing 20 to 95 mass%. [3] In the coated steel sheet according to the above [1] or [2], the curing agent (D) contained in the paint for the undercoat coating film contains an amino resin and / or
Or a coated steel sheet having excellent workability and corrosion resistance in a processed part, which is an isocyanate compound.

[4] A method for producing a coated steel sheet using a zinc-based or zinc-aluminum-based hot-dip coated steel sheet as a base steel sheet, in which a chemical conversion treatment is applied to the surface of the plating film, and then an undercoat of the following (a) Apply paint and reach plate temperature 180 ~
By baking at 260 ° C., an undercoating film having a coating thickness of 2 μm or more is formed, and a topcoating material as described in (b) below is further applied on the undercoating film and baked at a reaching plate temperature of 180 to 270 ° C. A method for producing a coated steel sheet having excellent workability and corrosion resistance in a processed part, wherein a topcoat having a thickness of 5 to 30 μm is formed. (A) a number average molecular weight of 14,000 to 26000, a glass transition temperature of 0 to 30 ° C., obtained by a reaction between a polyester resin (A) and an epoxy resin (B), and
An undercoat paint containing a modified polyester resin (C) having a k value of 0.7 to 2.5 represented by the formula (1) and a curing agent (D) as main components k = [Wb × (Ma + 2 × Mb) )] / [(Wa + Wb) × 2 × Mb] (1) where Wa: the solid content weight ratio of polyester resin (A) to [polyester resin (A) + epoxy resin (B)] Wb: [polyester resin ( A) + the weight ratio of the solid content of the epoxy resin (B) to the epoxy resin (B)] Ma: the number average molecular weight of the polyester resin (A) Mb: the number average molecular weight of the epoxy resin (B) (b) the number average molecular weight is 5000 Topcoat paint containing up to 20,000 polyester resin (E) and hardener

[5] The method of the above-mentioned [4], wherein zinc-
Aluminum-based hot-dip coated steel sheet contains Al
A method for producing a coated steel sheet having excellent workability and corrosion resistance in a processed portion, characterized in that the steel sheet contains 20 to 95 mass%. [6] In the production method of the above-mentioned [4] or [5], the curing agent (D) contained in the coating material for the undercoat film is an amino resin and / or
Or a method for producing a coated steel sheet having excellent workability and corrosion resistance in a processed portion, which is an isocyanate compound.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The coated steel sheet of the present invention is a hot-dip galvanized steel sheet or a hot-dip Al-Zn coated steel sheet as a base steel sheet.
An undercoating film and an overcoating film are sequentially formed.
Hereinafter, details of these configurations will be described in order.

(1) Base Coated Steel Sheet The coated steel sheet serving as the base of the coated steel sheet of the present invention is a hot-dip galvanized steel sheet or a hot-dip Al—Zn coated steel sheet. A hot-dip Al-Zn-based plated steel sheet containing up to 95% by mass has excellent corrosion resistance and is preferable as an undercoated steel sheet. Further, from the viewpoint of corrosion resistance and the like, a more preferable range than the amount of Al in the plating film of the hot-dip Al-Zn-based plated steel sheet is 45 to 65 mass.
%. Particularly preferred component compositions of the plating film are Al: 45 to 65 mass%, Si: 0.7 to 2.0 ma.
ss%, Fe: less than 10 mass%, the balance being substantially Zn containing unavoidable impurities, and exhibiting particularly excellent corrosion resistance in such a composition. Further, the coating weight of the hot-dip galvanized steel sheet or hot-dip Al-Zn-coated steel sheet is not particularly limited, but is generally 30 to 120 g / m2 per one side.
It is appropriate to set it to about ² . 30g plating weight
/ M ² , the corrosion resistance tends to be insufficient.
If it exceeds 0 g / m ² , cracks in the processed portion due to the plating film become remarkable, and workability is greatly reduced.

(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 number average molecular weight of 14,000 to 26,000,
Obtained by a reaction between a polyester resin (A) having a glass transition temperature of 0 to 30 ° C and an epoxy resin (B), and
A dry film thickness formed by applying a coating mainly composed of a modified polyester resin (C) having a k value of 0.7 to 2.5 represented by the formula (1) and a curing agent (D). Is a coating film of 2 μm or more. k = [Wb × (Ma + 2 × Mb)] / [(Wa + Wb) × 2 × Mb] (1) where Wa: solid content of polyester resin (A) with respect to [polyester resin (A) + epoxy resin (B)] Weight ratio Wb: Solid component weight ratio of epoxy resin (B) to [polyester resin (A) + epoxy resin (B)] Ma: Number average molecular weight of polyester resin (A) Mb: Number average molecular weight of epoxy resin (B)

The polyester resin (A) for obtaining the modified polyester resin (C) is mainly an ester compound of a polybasic acid and a polyhydric alcohol. Examples of the polybasic acids include dibasic acids such as terephthalic acid, isophthalic acid, succinic acid, adipic acid, sebacic acid, fumaric acid, and maleic anhydride, and trivalent or higher polybasic acids such as trimellitic anhydride and pyromellitic anhydride. An acid or the like is used, and these polybasic acid components can be used in combination of two or more kinds.

The polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol,
Dipropylene glycol, polypropylene glycol,
Neopentyl glycol, 3-methylpentadiol,
Neopentylene glycol, 1,4-butanediol,
Aliphatic or alicyclic dihydric alcohols such as 1,5-pentanediol, 1,4-hexanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol are mainly used. Glycerin, trimethylolethane, trimethylolpropane,
Trihydric or higher polyhydric alcohols such as trimethylolbutane, hexanetriol, pentaerythritol and dipentaerythritol can be used in combination.

The polyester resin (A) has a number average molecular weight of 14,000 to 26000 and a glass transition temperature of 0 to 30.
Must be ° C. Further, the more preferable number average molecular weight of the polyester resin (A) is from 18,000 to 2100.
0, glass transition temperature is 5-25 ° C. When the number average molecular weight of the polyester resin (A) is less than 14,000, the elongation of the coating film becomes insufficient, and the workability is reduced. On the other hand, if the number average molecular weight exceeds 26,000, the adhesion between the coating film and the base becomes insufficient, and the scratch resistance is reduced. Furthermore, since the coating composition has a high viscosity, an excess of a diluting solvent is required, which is not preferable from the viewpoint of coating workability, environmental harmony, and the like. Further, the glass transition temperature of the polyester resin (A) is 30 ° C.
If it exceeds 300, the elongation of the coating film will be insufficient, and the workability will decrease. On the other hand, if the temperature is lower than 0 ° C., the toughness of the coating film is reduced, and sufficient scratch resistance cannot be obtained.

The epoxy resin (B) for reacting with the polyester resin (A) is compounded for improving the adhesion to the substrate, and is an example of an epoxy resin suitable for use in the present invention. Is bisphenol A,
An epoxy compound obtained by reacting a bisphenol such as bisphenol F or bisphenol S with epihalohydrin or β-methyl epihalohydrin, or a bisphenol-type epoxy resin which is a copolymer thereof is exemplified.

The epoxy resin (B) preferably has a number average molecular weight of 500 to 2,000. If the number average molecular weight of the epoxy resin is less than 500, the scratch resistance is not sufficient, while if it is more than 2,000, the compatibility with the polyester resin decreases. Examples of a method for modifying the polyester resin (A) with the epoxy resin (B) include a method of incorporating the epoxy resin in the synthesis of the polyester resin, and a method of reacting the polyester resin with the epoxy resin in the presence of an amine catalyst. From the viewpoint of obtaining the required adhesion without impairing the processability of the coating film, a method of reacting the polyester resin with an epoxy resin in the presence of an amine catalyst after the synthesis is preferred.

Further, the modified epoxy resin (C) is
It is necessary that the k value shown in the expression (1) is 0.7 to 2.5. If the k value is less than 0.7, the amount of epoxy resin is small and the adhesion is poor, so that sufficient scratch resistance cannot be obtained. On the other hand, if the k value exceeds 2.5, the epoxy resin becomes excessive, and the rigid nature of the epoxy resin becomes strong.
Sufficient workability cannot be obtained.

As the curing agent (D), an amino resin and / or a polyisocyanate compound can be used. As an amino resin as a curing agent, urea, benzoguanamine, a part or all of a product obtained by a condensation reaction of formaldehyde with melamine, etc., methanol,
A resin alkyl etherified with alcohols such as ethanol and butanol. Specific examples include a methylated urea resin, an n-butylated benzoguanamine resin, a methylated melamine resin, an n-butylated melamine resin, and an iso-butylated melamine resin.

As the polyisocyanate compound, an isocyanate compound obtained by a general production method can be used. Among them, 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.

Further preferred examples of the polyisocyanate compound include non-yellowing hexamethylene diisocyanate (hereinafter, HDI) and its derivatives, tolylene diisocyanate (hereinafter, abbreviated as TDI) and its derivatives,
4,4'-diphenylmethane diisocyanate (hereinafter, referred to as
MDI) and its derivatives, xylylene diisocyanate (hereinafter abbreviated as XDI) and its derivatives, isophorone diisocyanate and its derivatives, trimethylhexamethylene diisocyanate and its derivatives, hydrogenated TD
I and its derivatives, hydrogenated MDI and its derivatives, hydrogenated X
DI and its derivatives.

The mixing ratio of the modified polyester resin (C) and the curing agent (D) in the undercoating film (coating material for the undercoating film) is expressed as follows: modified polyester resin (C) / curing agent (D) = solids weight ratio. It is preferably 90/10 to 65/35. The ratio of the modified polyester resin (C) is 90/10
If the ratio is too high, sufficient curability will not be obtained, and the scratch resistance and solvent resistance will be reduced. On the other hand, if the ratio of the modified polyester resin (C) is less than 65/35, the excess of the curing agent or the modification with the curing agent will not be obtained. Side reaction with the polyester resin (C) occurs,
Processability and adhesion of the processed part are reduced.

[0026] In addition to the modified polyester resin (C) and the curing agent (D), which are the above-mentioned base resins, a curing catalyst, a pigment, other defoaming agents, a flow stopper, etc. Various additives such as can be added. The curing catalyst is used as needed to accelerate the curing reaction of the resin component (main resin and curing agent), and usable curing catalysts include acids or neutralized products thereof. For example, curing catalysts such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid and neutralized products of these amines, tin octoate, and dibutyltin dilaurate are typical ones. No.

Examples of the pigments include rust preventive pigments such as strontium chromate, potassium chromate, zinc chromate, calcium chromate, barium chromate, and aluminum tripolyphosphate; inorganic pigments such as titanium dioxide, carbon black, and iron oxide; An extender pigment such as talc or silica can be blended according to the purpose. In addition, as the organic solvent used in the paint, xylene, toluene, methyl ethyl ketone, n-butyl acetate, ethyl acetate, methanol, ethanol, cyclohexanone, petroleum solvents, mineral spirits, and other organic solvents are applied. One type or a combination of two or more types can be used depending on the resin type.

The amount of the pigment to be incorporated in the undercoating film is 0.1% in terms of the weight ratio of the solid content to the resin component contained in the coating film [pigment / resin].
6 to 1.0, more preferably 0.65 to 0.8. If the weight ratio is less than 0.6, sufficient scratch resistance cannot be obtained, while if it exceeds 1.0, sufficient workability cannot be obtained. The thickness of the undercoat film is 2 μm or more. If the coating thickness is less than 2 μm, sufficient rust prevention cannot be obtained.

(4) Top Coating Film The top coating film has a dry film thickness of 5 which is formed by applying a paint containing a polyester resin (E) having a number average molecular weight of 5,000 to 20,000 and a curing agent as a main component resin. ~ 30 μm. The polyester resin (E) is mainly an ester compound of a polybasic acid and a polyhydric alcohol, and the polybasic acids and polyhydric alcohols described for the undercoat film can be used.

The polyester resin (E) as the main resin must have a number average molecular weight of 5,000 to 20,000, preferably 5,000 to 15,000. When the number average molecular weight of the polyester resin (E) is less than 5,000, the elongation of the coating film becomes insufficient, and the processability decreases. Meanwhile, 2
If it exceeds 0000, the scratch resistance and the weather resistance are undesirably reduced.

The curing agent for the main resin is not particularly limited, but an amino resin and / or a polyisocyanate compound generally used as a curing agent for a polyester resin can be used. As for the amino resin and the polyisocyanate compound used as the curing agent used in the overcoat, the same compositions as those described for the undercoat can be used.

In addition to the polyester resin (E), which is the main resin, and the curing agent, various additives such as a curing catalyst, a pigment, an antifoaming agent, and a flow-stopping agent may be added to the topcoat paint, if necessary. Can be. The curing catalyst is used as needed to accelerate the curing reaction of the resin component (main resin and curing agent), and usable curing catalysts include acids or neutralized products thereof. , For example, p
-Toluenesulfonic acid, dodecylbenzenesulfonic acid,
Dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid and their neutralized amines, tin octoate,
A typical example is a curing catalyst such as dibutyltin dilaurate.

Examples of the pigment include inorganic pigments such as titanium dioxide, carbon black and iron oxide, cyanine blue,
Organic pigments such as cyanine green, extenders such as talc and silica, and metal powders such as aluminum powder, iron powder and nickel powder can be blended according to the purpose.

The organic solvent used for the coating includes xylene, toluene, methyl ethyl ketone, n-butyl acetate,
From among organic solvents such as ethyl acetate, methanol, ethanol, cyclohexanone, petroleum solvents, and mineral spirits, one or a combination of two or more can be used depending on the type of resin to be applied.

The thickness of the top coat is 5 to 30 μm. If the thickness of the coating film is less than 5 μm, sufficient workability and corrosion resistance at the processed portion cannot be obtained. On the other hand, if it exceeds 30 μm, the processability is lowered and the cost is increased, which is not preferable.

Next, a method for manufacturing the coated steel sheet according to the present invention will be described. The production method of the present invention is directed to a hot-dip galvanized steel sheet or a hot-dip Al-Zn coated steel sheet (preferably hot-dip Al-Zn having an Al content of 20 to 95 mass% in a plating film) manufactured by a continuous hot-dip plating facility or the like. A coated steel sheet is a method of producing a coated steel sheet using a base steel sheet as a base steel sheet. A chemical conversion treatment is performed on the surface of the coated steel sheet, and then a base coat and a top coat are sequentially performed to sequentially form a base coat and a top coat. .

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 blast stove, an induction heater, or the like.

An undercoat is applied to the upper layer of the chemical conversion coating and baked, and an overcoat is applied to the upper layer and baked to form an undercoat and an overcoat. The configurations of the undercoat film and the overcoat film are as described above. Undercoat and topcoat are
It can be prepared using a disperser and a stirrer such as a ball mill, a sand mill and a roll mill.

There are no particular restrictions on the method of applying the coating for forming the coatings (undercoat and topcoat), but it is preferable to apply the coating by a method such as roll coater coating or curtain flow coating. . After applying the paint, the coating is baked by heating means such as hot air heating, infrared heating, induction heating, etc., and the resin is cured to obtain the coating.

In the baking treatment when the coating film is heated and cured, the maximum temperature of the undercoat is 180 ° C. to 270 ° C., and baking is performed in this temperature range for about 30 seconds to 120 seconds. If the ultimate plate temperature is lower than 180 ° C., the curing reaction of the resin is insufficient, and the scratch resistance and the corrosion resistance are reduced. On the other hand, when the ultimate plate temperature exceeds 270 ° C., the adhesion to the top coat may decrease due to excessive reaction.

In the case of the topcoat paint, the maximum attainable plate temperature is 18
0 ° C to 270 ° C, and in this temperature range, about 30 seconds to 120 ° C.
Perform second printing. If the ultimate plate temperature is lower than 180 ° C., the curing reaction of the resin is insufficient, and the solubility in solvents and chemicals and the scratch resistance are reduced. In addition, the ultimate plate temperature is 270 ° C
If it exceeds, the processability may decrease due to excessive reaction.

[0042]

EXAMPLES The following coating materials for undercoating and topcoating were prepared. (1.1) Preparation of resin composition for undercoat paint

Polyester resin synthesis example 1 215.8 parts by weight (1.3 mol) of terephthalic acid, 182.6 parts by weight (1.1 mol) of isophthalic acid, adipic acid 1
89.8 parts by weight (1.3 mol), ethylene glycol 1
24 parts by weight (2.0 mol), neopentyl glycol 1
66.4 parts by weight (1.6 mol), "Epiclon 850"
30.4 parts by weight (trade name, manufactured by Dainippon Ink Co., Ltd.) and 0.1 part by weight of dioctyltin oxide were subjected to an esterification reaction in a nitrogen stream at 240 ° C. for 2 hours. Then 1
The pressure was reduced to 1 mmHg over time, and
The reaction was carried out for a time, dissolved in Solvesso 150, and the nonvolatile content was 35%, the average molecular weight was 20,000, the glass transition temperature was 10
° C polyester resin (A1) was obtained.

Polyester Resin Synthesis Example 21 215.8 parts by weight (1.3 mol) of terephthalic acid, 182.6 parts by weight (1.1 mol) of isophthalic acid, adipic acid 1
89.8 parts by weight (1.3 mol), ethylene glycol 1
24 parts by weight (2.0 mol), neopentyl glycol 1
66.4 parts by weight (1.6 mol), "Epiclon 850"
30.4 parts by weight (trade name, manufactured by Dainippon Ink Co., Ltd.) and 0.1 part by weight of dioctyltin oxide were subjected to an esterification reaction in a nitrogen stream at 240 ° C. for 2 hours. Then 1
The pressure was reduced to 1 mmHg over time,
The reaction was carried out for 0 minutes, dissolved in Solvesso 150, and the nonvolatile content was 35%, the average molecular weight was 16,000, and the glass transition temperature was 15
° C polyester resin (A2) was obtained.

(1.2) Preparation of undercoat paint For undercoat paints corresponding to the undercoat coating components (P1) to (P7) in Table 3, epoxy resin was added to the polyester resin (A1) or (A2) (35% non-volatile content). A resin ("Epiclon 4050" manufactured by Dainippon Ink and Chemicals, Inc.) was blended in the ratio shown in Table 3,
0.5 parts by weight of triethylamine in a nitrogen stream at 140 ° C.
For 2 hours to obtain a resin composition for undercoat paint. For the undercoat paint corresponding to the undercoat coating component (P9) in Table 3, the polyester resin (A1) was replaced with an epoxy resin ("Epiclon 405" manufactured by Dainippon Ink Co., Ltd.).
0 ") at room temperature. As for the undercoat paint corresponding to the undercoat coating component (P8) in Table 3, the polyester resin (A1) was used without being reacted with the epoxy resin.

Each of the above undercoat resin compositions 100
34 parts by weight of strontium chromate with respect to parts by weight,
2.5 parts by weight of aluminum tripolyphosphate dihydrate, 6 parts by weight of titanium oxide, "Dispalon # 1830" (trade name,
0.1 part by weight of Kusumoto Kasei Co., Ltd.) was added, and the pigment was dispersed for 4 hours with a glass bead type high-speed shaker. Further, a curing agent shown in Table 3 and a silane coupling agent 3 parts by weight were added. After stirring, the desired undercoat paints (P1) to (P9) were obtained.

(2.1) Preparation of Resin Composition for Top Coating Resin Synthesis Example 3 332 parts by weight (2.0 mol) of terephthalic acid, 83 parts by weight (0.5 mol) of isophthalic acid, 160.6 parts by weight of adipic acid (1.1 mol), 136.4 parts by weight (2.2 mol) of ethylene glycol, neopentyl glycol 145.
6 parts by weight (1.4 mol) and 0.1 parts by weight of dioctyltin oxide were subjected to an esterification reaction at 230 ° C. for 2 hours in a nitrogen stream. Thereafter, the pressure was reduced to 1 mmHg over 1 hour, and the reaction was further carried out at 260 ° C. for 30 minutes to obtain a mixed solvent of cyclohexanone / solvesso 150 (weight ratio: 50/5).
0), dissolved in non-volatile matter 40%, average molecular weight 1500
A polyester resin (E1) having a glass transition temperature of 18 ° C. was obtained.

Resin Synthesis Example 4 332 parts by weight (2.0 mol) of terephthalic acid, 83 parts by weight (0.5 mol) of isophthalic acid, 160.6 parts by weight (1.1 mol) of adipic acid, ethylene glycol 136. 4 parts by weight (2.2 mol), neopentyl glycol 145.
6 parts by weight (1.4 mol) and 0.1 parts by weight of dioctyltin oxide were subjected to an esterification reaction at 230 ° C. for 2 hours in a nitrogen stream. Thereafter, the pressure was reduced to 1 mmHg over 1 hour, the reaction was further performed at 260 ° C. for 1.5 hours, and a mixed solvent of cyclohexanone / solvesso 150 (weight ratio: 50) was used.
/ 50), and has a nonvolatile content of 35% and an average molecular weight of 22.
Polyester resin (E2) with a glass transition temperature of 10 ° C
I got

(2.2) Preparation of Topcoat Paint 425 parts by weight of polyester resin (E1) for topcoat, 133 parts by weight of inorganic pigment, 0.3 parts by weight of "Dispalon # 2150" (trade name, manufactured by Kusumoto Kasei Co., Ltd.) Was dispersed with a glass bead-type high-speed shaker for 2 hours.
550 "(trade name, manufactured by Dainippon Ink Co., Ltd.) 54.5 parts by weight," Polyflow S "(trade name, manufactured by Kyoeisha Yushi Kagaku Kogyo KK) 0.6 parts by weight, matting agent 5 parts by weight, 0.5 parts by weight of a polyethylene wax was added, and the mixture was stirred to obtain a desired top coat (T1). Similarly, using the polyester resin (E2), the topcoat paint (T2) having the composition shown in Table 4
I got

A coated steel sheet was manufactured using the undercoat paint and the top paint as described above. According to Tables 1 and 2, a molten 55% Al-1.5% Si-Zn having a thickness of 0.35 mm was used.
Plated steel sheet (coating weight per side 75 g / m ² ),
Molten 40% Al-1.0% Si- Zn plated steel sheet (per side coating weight 75g ^{/ m} 2), the melt 70% Al-
After performing a normal chromate treatment on a 1.8% Si-Zn plated steel sheet (plating adhesion amount per side 75 g / m ² ) and a molten 5% Al-Zn plated steel sheet (plating adhesion amount 130 g / m ² per side), The undercoat was applied with a bar coater and baked at a steel plate reaching temperature of 220 ° C. for a baking time of 38 seconds. Then, a top coat was applied with a bar coater and baked at a steel plate reaching temperature of 230 ° C. and a baking time of 53 seconds.

For each of the above coated steel sheets, the workability, the corrosion resistance of the processed portion, and the hardness of the coating film were evaluated by the following methods. Tables 1 and 2 show the results together with the configuration of the coated steel sheet.

(1) Workability In a room at 20 ° C., a steel rod having a different diameter was sandwiched on the back side of the coated steel sheet, and then bent at 180 °, and the coating film at the bent portion was observed with a 30-fold loupe. Was evaluated according to the following criteria. ：: No cracks were formed in the coating film by 180 ° bending with a rod having a diameter of 1.0 mm Δ: No crack was generated in the coating film with 180 ° bending between a rod having a diameter of 1.5 mm ×: 1.5 mm in diameter (2) Film hardness Hardness of JIS K 5400 using Mitsubishi Pencil “UNI”.
The test was performed based on No. 4, and the peeling state of the coating film was observed.
In a test using a pencil having a hardness of 3H, a material that hardly peeled off between the coated steel sheet and the coating film as the base was evaluated as "O",
In the test using a pencil having a hardness of 2H, a sample that hardly peeled off between the coated steel sheet and the coating film, which are the base, was evaluated as “△”.
In a test using a pencil having a hardness of 2H, a sheet where peeling occurred between a plated steel sheet as a base and a coating film was evaluated as “×”.

(3) Corrosion resistance of the processed part The coated steel sheet was cut into 150 mm x 70 mm, and a steel rod having a diameter of 1 mm was bent on the back side of the coated steel sheet in a room at 20 ° C. And the back surface was sealed with a tar epoxy paint to prepare a sample for a corrosion resistance test of a processed portion. The test was performed on the basis of the dry / wet repetition conditions specified in JIS K5621 for a total of 300 cycles with the following cycles, and then the swelling ratio of the coating film was measured. Cycle conditions: [5% salt spray, 30 ° C, 0.5 hour →
95% RH wet, 30 ° C, 1.5 hours → 20% dry
H, 50 ° C., 2 hours → dry 20% RH, 30 ° C., 2 hours] as one cycle, and this is repeated a predetermined number of cycles. Evaluation method: The total length in the width direction of the portion where the coating film swells in the bent portion having a width of 50 mm except for both ends of 10 mm is represented by% (for example, 5 in 50 mm).
When there are two swellings with a width of mm, the swelling ratio is 20%). The evaluation is as follows. ：: The swelling rate is less than 10% ：: The swelling rate is 10% or more and less than 30% ：: The swelling rate is 30% or more and less than 70% ×: The swelling rate is 70% or more

According to Tables 1 and 2, the coated steel sheet of the present invention exhibited good properties in all of the workability, 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.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

[0059]

As described above, the coated steel sheet of the present invention is
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.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C09D 5/08 C09D 5/08 161/20 161/20 163/00 163/00 167/00 167/00 175/04 175 / 04 (72) Inventor Keiji Yoshida 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Masaaki Yamashita 1-2-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Yasuhiro Majima 6-1 Mizue-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa N72K Inventor Norio Inoue 6-1 Mizue-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa NK-K Steel (72) Inventor Shinji Hori 6-1 Mizue-cho, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture F-term (reference) 4D075 AE17 BB26Y BB26Z BB73X BB93Y BB93Z DB05 DB07 EB32 EB33 EB35 EB38 EB52 EB53 EB56 ECA3AB100AB AB18A AB31A AK35B AK35H AK41B AK41C AK51B AK51H AK53B AL06B BA03 BA07 BA10A BA10C CA02B CA02C EH462 EH71A EJ68A GB07 GB48 JA05B JA07B JB02 JK12 JK16 JL01 YY00A YY00B YY00C 4J038 DA142 DA162 DA172 DB061 DB161 DB471 DD071 DD081 DD131 DD241 DG161 KA03 MA13 MA14 NA03 NA11 PA07 PA12 PA19 PC02

Claims (6)

[Claims] 1. A coated steel sheet having a zinc-based or zinc-aluminum-based hot-dip coated steel sheet as a base steel sheet, having a chemical conversion treatment film on a plating film surface and an undercoat film (a) below on the plating film. A coated steel sheet having excellent workability and corrosion resistance in a processed portion, further comprising an overcoat film described in (b) above. (A) a number average molecular weight of 14,000 to 26000, a glass transition temperature of 0 to 30 ° C., obtained by a reaction between a polyester resin (A) and an epoxy resin (B), and
A dry coating film formed by applying a coating mainly composed of a modified polyester resin (C) having a k value of 0.7 to 2.5 represented by the formula (1) and a curing agent (D). Undercoat having a thickness of 2 μm or more k = [Wb × (Ma + 2 × Mb)] / [(Wa + Wb) × 2 × Mb] (1) where Wa: [polyester resin (A) + epoxy resin (B)] Weight ratio of solid content of polyester resin (A) to polyester resin (A) Wb: Weight ratio of solid content of epoxy resin (B) to [polyester resin (A) + epoxy resin (B)] Ma: Number average molecular weight of polyester resin (A) Mb: Number average molecular weight of epoxy resin (B) (b) Dry coating film thickness formed by applying a paint containing a polyester resin (E) having a number average molecular weight of 5,000 to 20,000 and a curing agent as a main component resin has a thickness of 5 to 5. 30μm top coat 2. The coated steel sheet according to claim 1, wherein the zinc-aluminum hot-dip coated steel sheet contains 20 to 95 mass% of Al in a plating film. 3. The processability and the corrosion resistance of a processed part according to claim 1, wherein the curing agent (D) contained in the paint for the undercoat coating film is an amino resin and / or an isocyanate compound. Excellent painted steel plate. 4. A method for producing a coated steel sheet using a zinc-based or zinc-aluminum-based hot-dip coated steel sheet as a base steel sheet, wherein a chemical conversion treatment is applied to the surface of the plating film, and then the undercoat paint described in the following (a) is formed on the upper layer. To reach plate temperature of 180 to 26
By baking at 0 ° C., an undercoating film having a coating thickness of 2 μm or more is formed, and the upper layer is coated with the following overcoating (b) and baked at a reaching plate temperature of 180 to 270 ° C. A method for producing a coated steel sheet having excellent workability and corrosion resistance in a processed part, wherein a topcoat having a thickness of 5 to 30 μm is formed. (A) a number average molecular weight of 14,000 to 26000, a glass transition temperature of 0 to 30 ° C., obtained by a reaction between a polyester resin (A) and an epoxy resin (B), and
An undercoat paint containing a modified polyester resin (C) having a k value of 0.7 to 2.5 represented by the formula (1) and a curing agent (D) as main components k = [Wb × (Ma + 2 × Mb) )] / [(Wa + Wb) × 2 × Mb] (1) where Wa: the solid content weight ratio of polyester resin (A) to [polyester resin (A) + epoxy resin (B)] Wb: [polyester resin ( A) + the weight ratio of the solid content of the epoxy resin (B) to the epoxy resin (B)] Ma: the number average molecular weight of the polyester resin (A) Mb: the number average molecular weight of the epoxy resin (B) (b) the number average molecular weight is 5000 Topcoat paint containing up to 20,000 polyester resin (E) and hardener 5. The production of a coated steel sheet according to claim 4, wherein the zinc-aluminum hot-dip coated steel sheet contains 20 to 95 mass% of Al in a plating film. Method. 6. The processability and corrosion resistance of a processed part according to claim 4, wherein the curing agent (D) contained in the coating material for the undercoat coating film is an amino resin and / or an isocyanate compound. Manufacturing method of excellent coated steel sheet.