JP2005082623A - Non-chromate precoated metal plate excellent in corrosion resistance after deep drawing and method for producing the same, and coating composition for producing the precoated metal plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precoated metal plate which can stably maintain a high-level corrosion resistance without peeling of the coating and formation of blisters, even by not using a chromate rust preventive pigment and even after deep drawing exposed to a severe processing condition, and to provide a coating composition for over coating and under coating suitable for producing the precoated metal plate. <P>SOLUTION: The precoated metal plate, which has excellent coating adhesion and corrosion resistance even after deep drawing, is provided by subjecting a zinc-plated steel sheet, which has an amount of zinc plating per one side of 45 g/m<SP>2</SP>or more, to conversion treatment on both sides thereof, and on the resultant sheet, forming an under coat and an over coat, each having a specified glass transition temperature, a number average molecular weight and a hydroxyl value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-chromate precoated metal sheet excellent in coating film adhesion and corrosion resistance after deep drawing, a method for producing the same, and a coating composition suitable for the production of the precoated metal sheet. The type of the metal plate to which the present invention is applied is not particularly limited, and can be widely applied to all non-ferrous metal plates such as aluminum and non-ferrous alloy plates in addition to iron-based metal plates such as the most typical steel plates. In the description, the description will be made mainly on the case of applying to a typical steel plate.

  Conventionally, in the manufacture of home appliances using steel plates, for example, the post-coating method in which a steel plate provided by a steel plate manufacturer is formed into an arbitrary shape by a home appliance manufacturer and then degreased and then painted and baked is often used. It has been. However, as problems such as deterioration of work environment and air pollution due to the generation of solvent vapor (VOC) generated during painting and baking have recently been highlighted, the work environment at home appliance manufacturers has been improved, and degreasing and painting processes have been improved. In order to save labor, there are increasing examples of using only pre-coated steel sheets that have been coated and baked by steel sheet manufacturers (hereinafter referred to as “pre-coated steel sheets” in this specification) and that only home appliance manufacturers perform forming processing. ing.

  By the way, in the precoat steel plate, in order to ensure corrosion resistance, a rust preventive paint containing a chromium anticorrosive pigment has been widely used. However, in recent years, the demand for non-chromating of pre-coated steel sheets has been rapidly increasing as the environmental awareness has increased and the transition to non-chromic products that do not use harmful chromium-based substances has progressed.

  Under such circumstances, research on non-chromate-based precoated steel sheets has been actively promoted. For example, Patent Documents 1 and 2 are presented. The pre-coated steel sheets disclosed in these documents are formed by forming an organic undercoat film and topcoat film containing a base resin such as a polyester resin and a curing agent on the surface of the steel sheet that has been subjected to chemical conversion treatment. Demonstrates reasonable corrosion resistance without using anti-corrosion pigments. Further, in these documents, it has been clarified that by specifying the molecular weight and glass transition temperature of the base resin to be used, it is possible to enhance the processing adhesion of the coating film and the scratch resistance.

However, in the case of a pre-coated steel sheet coated with an organic non-chromate anticorrosive paint, there is no problem when a mild process such as a normal bending process is performed. When an organic non-chromate rust preventive paint is applied to a pre-coated steel sheet for deep drawing where the film is exposed to extremely severe processing conditions, satisfactory corrosion resistance is not always obtained. For example, if the product after deep drawing is subjected to a salt spray test, a coating film bulges and peels off from the end surface of the product where the steel substrate is exposed in the cutting or punching process. It has become clear that this is a product defect.
JP-A-11-221877 Japanese Patent Laid-Open No. 11-256099

  The present invention has been made in view of the above-mentioned problems, and its purpose is that after deep drawing without using a chromium-based anticorrosive pigment and after the coating film is exposed to severe processing conditions. Providing a pre-coated metal plate that can stably exhibit high levels of coating adhesion and corrosion resistance without peeling or blistering even when exposed to harsh corrosive environments. Another object of the present invention is to provide a coating composition for top coating and undercoating suitable for the production of such a precoated metal sheet.

The first configuration according to the present invention that has solved the above problems is a coating composition for undercoating used in the production of a non-chromate pre-coated metal sheet for deep drawing,
(A) It consists of one or more selected from polyester resins and epoxy-modified polyester resins, has a glass transition temperature (Tg) of 60 ° C. or higher, a number average molecular weight (Mn) of 15,000 or higher, and a hydroxyl value of 5 mgKOH / a resin that is less than or equal to g;
(B) including at least one curing agent selected from the group consisting of amino resins, blocked polyisocyanate compounds and epoxy resins,
The ratio of the resin (A) to 70 to 95 parts by mass and the ratio of the curing agent (B) to 5 to 30 in 100 parts by mass in terms of solid content of the resin (A) and the curing agent (B). There is a gist where it is part by mass.

  In the coating composition, as other components, (C) non-chromium rust preventive pigment: 40 to 100 parts relative to a total of 100 parts by mass in terms of solid content of the resin (A) and the curing agent (B) In addition, as another component, (D) non-chromium coloring pigment: 20 parts by mass with respect to 100 parts by mass of the total of the resin (A) and the curing agent (B) The following may be included.

In addition, the second configuration according to the present invention is a coating composition for top coating used for manufacturing a non-chromate pre-coated metal sheet for deep drawing,
(E) a polyester resin having a glass transition temperature (Tg) of 10 to 30 ° C., a number average molecular weight (Mn) of 10,000 to 30,000, and a hydroxyl value of 1 to 20 mgKOH / g or less;
(F) At least one curing agent selected from an amino resin and a blocked polyisocyanate compound, and the resin (E) in a total of 100 parts by mass in terms of solid content of the resin (E) and the curing agent (F) It is characterized in that the proportion occupied by 70 to 95 parts by mass and the proportion occupied by the curing agent (F) is 5 to 30 parts by mass.

  Also in the top coating composition, the non-chromium pigment (G) is preferably used as the other component, preferably 10 to 120 with respect to 100 parts by mass of the total solids of the resin (E) and the curing agent (F). You may include in the range of a mass part.

Further, the third configuration according to the present invention is positioned as a method for producing a non-chromate pre-coated metal plate having excellent corrosion resistance after deep drawing, and the plating adhesion amount per side is 45 g / m ² or more. After performing chemical conversion treatment on both surfaces of a certain zinc-based plated steel sheet and forming an undercoat film using the above-described undercoat paint composition, an overcoat film is further formed thereon using the above-mentioned overcoat paint composition There is a gist there.

Still another configuration according to the present invention defines a non-chromate pre-coated metal plate itself having excellent post-drawing corrosion resistance obtained by the above method, and the amount of plating adhesion per side is 45 g / m ² or more. The both surfaces of the galvanized steel sheet are subjected to chemical conversion treatment, and an undercoat film having a thickness of 5 to 15 μm composed of the above-described undercoat paint composition is further formed. A gist exists where an overcoat film having a thickness of 10 to 25 μm is formed.

  The topcoat and undercoat paint compositions of the present invention specify the type and number average molecular weight, the glass transition temperature, and the hydroxyl value of the base resin as the main component, and specify the type and blending ratio of the curing agent to be used in combination. In particular, the non-chromate pre-coated metal sheet subjected to deep drawing can be provided with excellent coating adhesion and corrosion resistance that cannot be obtained by conventional examples. As a result, it is possible to obtain a non-chromate-based precoated metal sheet that exhibits stable and excellent coating film adhesion and corrosion resistance even after deep drawing.

  The coating composition used for the production of the non-chromate pre-coated metal sheet for deep drawing according to the present invention is divided into two types, for undercoating and for overcoating, and those for undercoating are the following components (A), ( B) is contained as an essential component.

(A) It consists of one or more selected from polyester resins and epoxy-modified polyester resins, has a glass transition temperature (Tg) of 60 ° C. or higher, a number average molecular weight (Mn) of 15,000 or higher, and a hydroxyl value of 5 mgKOH / a resin that is less than or equal to g;
(B) At least one curing agent selected from the group consisting of amino resins, blocked polyisocyanate compounds and epoxy resins.

  The polyester resin used as the resin (A) is produced by polycondensation of a polybasic acid component and a polyhydric alcohol component. As is well known, as the polybasic acid, phthalic anhydride, isophthalic acid, terephthalic acid are used. Acid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic anhydride, succinic acid, fumaric acid, adipic acid and the like, and divalent alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, neopentyl glycol Examples include various polyester resins using a small amount of alcohol or a trihydric or higher polyhydric alcohol such as glycerin, trimethylolethane, pentaerythritol, etc., and the number average molecular weight (Mn) and glass transition temperature (Tg) described later. ) And hydroxyl value requirements If the, the combination thereof polybasic acid component and polyhydric alcohol component can be used all without any restrictions.

  As the epoxy-modified polyester resin used as the resin (A), the carboxyl group or hydroxyl group in the polyester resin as described above is reacted with an epoxy group-containing compound or epoxy resin by addition, condensation, grafting, or the like. Therefore, a preferable amount of epoxy modification for more effectively exhibiting the specificity due to epoxy modification is in the range of 0.1 to 30% by mass of the epoxy compound in the epoxy-modified polyester resin.

  In the present invention, the above-mentioned polyester resin and epoxy-modified polyester resin can be used alone as the resin (A), and two or more kinds can be used together as necessary. It is essential to use those having a glass transition temperature (Tg) of 60 ° C. or higher, a number average molecular weight (Mn) of 15,000 or higher, and a hydroxyl value of 5 mgKOH / g or lower.

  Incidentally, if the glass transition temperature (Tg) of the resin (A) used for undercoating is less than 60 ° C., the internal stress generated in the coating film after deep drawing becomes excessive, and the coating film peels off at the processed part. Not only is it easy to break, but an increase in internal stress generated in the coating film also adversely affects, for example, corrosion resistance after a salt spray test. However, if the glass transition temperature (Tg) is 60 ° C. or higher, such defects do not occur, and excellent coating film adhesion and corrosion resistance can be exhibited even after deep drawing.

  A more preferable glass transition temperature is 65 ° C. or higher for enhancing the adhesion and corrosion resistance of the coating film after deep drawing. However, if the glass transition temperature is too high, cracks tend to occur in the coating film when bending is performed, and therefore it is desirable that the glass transition temperature is preferably 83 ° C. or lower, more preferably 70 ° C. or lower.

  Further, the number average molecular weight (Mn) of the resin (A) needs to be 15,000 or more, and if it is less than 15,000, cracks are likely to occur in the coating film when bent, Satisfactory processability cannot be ensured. The number average molecular weight is more preferably 22,000 or more in order to achieve both corrosion resistance after deep drawing and bending workability as the undercoat film. However, when the number average molecular weight is excessively large, the dispersibility in the solvent tends to be deteriorated. Therefore, it is preferable to use a solvent having a molecular weight of 40,000 or less, more preferably 30,000 or less.

  Furthermore, the other characteristic calculated | required by the said resin (A) is a hydroxyl value of 5 mgKOH / g or less. By the way, if the hydroxyl value of the resin for the undercoat exceeds 5 mgKOH / g, the reaction point with the curing agent increases, the internal stress after deep drawing becomes excessive, and satisfactory corrosion resistance can be secured in the salt spray test. Disappear.

  The curing agent (B) used together with the resin (A) is an important component for enhancing the physical and chemical properties of the undercoat film by acting as a crosslinking agent on the resin (A). As the type thereof, one or more selected from amino resins, blocked polyisocyanate compounds and epoxy resins are used.

  Here, the amino resin is a methylolated amino resin obtained by condensation / polymerization of an amino component such as melamine, urea, benzoguanamine or acetoguanamine with an aldehyde (one obtained by etherifying a part of the methylol group with an appropriate alcohol). Among them, melamine resin and urea resin are particularly preferable among them.

  The blocked polyisocyanate compound is a compound in which a free isocyanate group in the polyisocyanate compound is protected with a blocking agent. Examples of the polyisocyanate compound include aliphatic diisocyanates such as hexamethylene diisocyanate and aromatics such as tolylene diisocyanate. Aliphatic diisocyanates such as aromatic diisocyanates, isophorone diisocyanates, etc. are exemplified, and as blocking agents for protecting the isocyanate groups of these compounds, for example, phenols such as phenol, monovalent or polyvalent such as methanol, ethanol, ethylene glycol, etc. Examples thereof include monohydric alcohols, lactams such as caprolactam, and oximes such as acetoxime.

  Further, typical epoxy resins used as other crosslinking agents are bisphenol type epoxy resins, novolac type epoxy resins, or various modified resins thereof. In addition, for example, glycidyl groups are included in molecules such as glycidyl methacrylate. It is also possible to use various copolymer resins and oligomers having an epoxy group introduced into the molecule by using the polymerizable monomer as a monomer component.

  The blending ratio of the resin (A) and the curing agent (B) used for the undercoat paint is that of the resin (A) in the total 100 parts by mass in terms of solid content of both components (A) and (B). The ratio should be set in the range of 70 to 95 parts by mass, and the ratio of the curing agent (B) should be 5 to 30 parts by mass. Reaction becomes insufficient, resulting in poor curing and a cured coating film cannot be obtained. On the other hand, when the blending ratio of the curing agent (B) is relatively large, the curing agents react with each other to cause a problem that the coating film becomes hard and processability deteriorates. A more preferable blending ratio of the resin (A) and the curing agent (B) is in the range of 10 to 20 parts by mass with respect to the former 80 to 90 parts by mass.

  In the undercoat coating composition containing the resin (A) and the curing agent (B), an appropriate amount of a non-chromium rust preventive pigment (C) may be contained as another component if necessary. The type of the non-chromium-based anticorrosive pigment (C) that can be used is not particularly limited, but preferred examples include aluminum dihydrogen triphosphate, silica, zinc oxide, or zinc phosphate, calcium phosphate, aluminum phosphite, Examples include zinc molybdate and those surface-treated with oxides such as silica, magnesia, and zinc oxide. When an appropriate amount of these non-chromium rust preventive pigments (C) is contained, the corrosion resistance of the undercoat film Is preferable because it is further improved. The blending amount of these non-chromium rust preventive pigments (C) is not particularly limited, but in order to effectively exhibit the effect of addition as a rust preventive pigment while avoiding a decrease in coating film adhesion due to excessive blending, the resin It is 10-100 mass parts with respect to 100 mass parts of sum total of solid content conversion of (A) and a hardening | curing agent (B), More preferably, it is the range of 20-60 mass parts.

  Furthermore, it is also effective to add a small amount of a non-chromium color pigment (D) such as titanium white, talc, barium sulfate, calcium carbonate or the like that exhibits an underlying concealing effect to the undercoat coating composition as another component. However, since these non-chromic color pigments (D) may adversely affect the adhesion of the coating film and the deformability of the coating film, the sum of the resin (A) and the curing agent (B) in terms of solid content is 100. It is desirable to suppress it to about 20 parts by mass or less with respect to parts by mass.

  In the coating composition for undercoat according to the present invention, the resin (A) and the curing agent (B), and if necessary, the non-chromium rust preventive pigment (C) and the non-chromium color pigment (D) are as described above. Although contained in a suitable blending ratio, it is of course possible to blend a proper amount of other additives known for coatings, such as antifoaming agents, anti-settling agents, dispersants, flow control agents and the like.

  Next, the top coat composition applied on the undercoat paint will be described.

  As the resin (E) used for the preparation of the top coating composition, a polyester-based resin is selected from the resins listed as the constituent materials of the undercoating paint. The resin (E) has a glass transition temperature (Tg). A material having a number average molecular weight (Mn) in the range of 10,000 to 30,000 and a hydroxyl value in the range of 1 to 20 mgKOH / g should be used.

  In the present invention, the glass transition temperature (Tg) is determined by differential scanning calorimetry (DSC) according to a conventional method, the number average molecular weight of the resin is determined by gel permeation chromatography (GPC), and the hydroxyl value is JIS K-0070. These are values obtained in compliance with each other.

  By the way, the top coat film does not require excellent adhesion to the base steel plate as much as the undercoat film, but it has excellent barrier properties against corrosive gas containing moisture and oxygen on the surface layer side of the paint film. It must be capable of exerting, and it must also have lubricity and workability sufficient to withstand deep drawing. For this reason, the top coating composition has a high level of barrier properties against corrosive gases and moisture, etc., in combination with the action of the curing agent (F), which will be described later. The glass transition temperature (Tg), the number average molecular weight, and the appropriate value of the hydroxyl value are defined as requirements for forming a coating film having a high degree of lubrication and workability that can be followed.

  By the way, if the glass transition temperature (Tg) of the polyester resin (E) is too lower than the range of 10 to 30 ° C., the rubber elasticity of the resin is likely to be generated and the pressure mark resistance is deteriorated. When the number average molecular weight (Mn) is too lower than the range of 10,000 to 30,000, the workability deteriorates, for example, cracks occur during deep drawing. Furthermore, when the hydroxyl value of the resin (E) exceeds the range of 1 to 20 mgKOH / g, if it is removed, the reaction point with the curing agent increases so that defects such as deterioration of workability appear, and the top coating film The above required characteristics cannot be satisfied.

  The glass transition temperature (Tg) of the resin (E) is more preferably 10 to 25 ° C., the number average molecular weight (Mn) is 14,000 to 20,000, and the hydroxyl value is 10 mgKOH / g or less to further improve the required properties of the top coat film. is there.

  The types of amino resins and blocked polyisocyanate compounds that are blended as the curing agent (F) in the top coating composition are exemplified again by those disclosed as the curing agent (B) used as the primer coating composition. One or more of these are appropriately selected and used.

  The preferable blending ratio of the resin (E) and the curing agent (F) constituting the top coating composition is the resin (E) in the total 100 parts by mass in terms of solid content of these components (E) and (F). The ratio of 70 to 95 parts by mass and the ratio of the curing agent (F) is in the range of 5 to 30 parts by mass. When the blending ratio of the resin (E) is too large, it does not completely react with the curing agent during the baking process. Therefore, it becomes difficult to obtain a healthy coating film due to insufficient curing, and conversely, if the blending ratio of the curing agent (F) becomes relatively large, the curing agents react with each other and the coating film becomes too hard and the workability deteriorates. Problems arise. In consideration of such advantages and disadvantages, a more preferable blending ratio of the resin (E) and the curing agent (F) is 15 to 25 parts by mass with respect to the former 75 to 85 parts by mass.

  In the top coating composition containing the resin (E) and the curing agent (F), it is also effective to contain an appropriate amount of the non-chromium pigment (G) as other components, if necessary. The type of the non-chromium pigment (G) is not particularly limited, and examples thereof include non-chromium rust preventive pigments and colored pigments as described above, and titanium white, carbon black, bengara are particularly preferable for the top coat film. Or the like. It is preferable to add an appropriate amount of these pigments because the top coat film can have a background hiding effect and the appearance as an intermediate product is improved. The blending amount of the non-chromium pigment (G) is not particularly limited, but the resin (E) is effective for effectively exhibiting the effect as the pigment (G) while avoiding a decrease in coating film adhesion due to excessive blending. It is good to mix | blend in the range of 10-120 mass parts with respect to 100 mass parts of total of solid content conversion of a hardening | curing agent (F), More preferably, it is the range of 20-80 mass parts.

  The top coating composition according to the present invention contains a resin (E), a curing agent (F), and, if necessary, a non-chromium pigment (G) in a suitable blending ratio as described above. As a component, it is of course possible to add a proper amount of additives known for coatings such as antifoaming agents, anti-settling agents, dispersing agents, flow control agents and the like.

  In producing a pre-coated steel sheet by coating the above-mentioned coating composition for undercoating and overcoating on a metal plate to be coated, for example, a steel plate, the base metal plate (steel plate) is subjected to zinc-based plating. After the surface is subjected to phosphate treatment or chromium-free chemical conversion treatment based on silica or zirconia, the above-mentioned undercoat coating composition is applied at an appropriate thickness to form an undercoat film. Further, a pre-coated metal plate (steel plate) is obtained by applying a top coating composition thereon and drying it.

  After applying the undercoat and topcoat, each may be heated to an appropriate temperature and baked and dried in two stages, or the undercoat and topcoat can be heated and dried simultaneously in one stage. It is.

Zinc plating applied to the surface of steel sheets is important in preventing local corrosion of steel sheets due to various factors by the so-called sacrificial anti-corrosion function, as is well known, such as electroplating, hot dip galvanizing, displacement plating, etc. However, in order to exert the function effectively, the adhesion amount per side should be 45 g / m ² or more, more preferably 45 g / m ² or more.

  Moreover, the film thickness of the undercoat film formed on the zinc-based plating layer subjected to the chemical conversion treatment should be in the range of 5 to 15 μm, more preferably 7 to 12 μm, and further formed thereon. The film thickness of the top coat film is desirably 10 to 25 μm, more preferably 15 to 18 μm. Incidentally, if the film thickness of the undercoat film is less than 5 μm, the corrosion resistance becomes insufficient. Conversely, if the film thickness is more than 15 μm, there is no problem in terms of performance, but the cost becomes high and it is not suitable for practical use. On the other hand, if the film thickness of the top coat film is less than 10 μm, the concealability is insufficient and the problem of see-through appears. Conversely, if the film thickness exceeds 25 μm and becomes too thick, the coating film is likely to be cracked or depressed.

  In the precoated metal sheet (steel plate) of the present invention thus obtained, a zinc-based plating layer having an appropriate thickness having a sacrificial anticorrosive action is formed on the surface of the substrate as described above, and an appropriate thickness is formed on the surface via a chemical conversion treatment layer. An undercoat film of an appropriate thickness and an overcoat film of an appropriate thickness are formed on it, and the zinc-based plating layer and the undercoat film are highly adhesive and strong on the galvanized layer, combined with the chemical conversion treatment effect. Furthermore, the undercoat film and the topcoat film are strongly bonded by the action of a resin and a curing agent having high affinity with each other. Moreover, the undercoat film and the topcoat film are laminated films with suitable molecular weights having an appropriate glass transition temperature, and are firmly adhered to the surface of the base steel sheet, exhibiting good gas barrier properties and excellent corrosion resistance, and The film itself exhibits excellent lubricity and workability even under severe processing conditions.

  Therefore, the pre-coated steel sheet obtained does not peel off or undergo shear failure even when exposed to high deep drawing conditions, and even after deep drawing, it is not only dry but also subjected to salt spray tests. Even in such a severe corrosive and humid environment, excellent corrosion resistance can be exhibited.

  Hereinafter, the present invention will be described in more detail with reference to examples showing specific examples.However, the present invention is not limited by the following examples, and is suitable within a range that can meet the purpose described above and below. Of course, it is possible to carry out the invention with modifications, and these are all included in the technical scope of the present invention. In the following examples, “parts” and “%” are based on mass.

  Using the base resin for the undercoat shown in Table 1 and the base resin for the top coat shown in Table 2, these are blended together with a curing agent in the ratios shown in Tables 3 and 4, and the base coat paints 1 to 13 and the top coat paint A to H was produced. The blending ratio of each component is a value in terms of solid content unless otherwise specified.

On the other hand, a chemical conversion treating agent (trade name “CT-E220” manufactured by Nihon Parker Rising Co., Ltd.) 100 mg / m on the surface of a hot dip galvanized steel sheet (plate thickness: 0.8 mm, coating amount: 60 g / m ^{2 on} one side). ² Prepare a galvanized steel sheet to be adhered, and coat the base coating for undercoating and the base coating for overcoating obtained above on the galvanized steel sheet with a bar coater so as to obtain a predetermined dry film thickness. The precoated steel sheets shown in Tables 5 and 6 were obtained. The coating and baking conditions for the undercoat paint were 50 seconds at an ultimate plate temperature of 210 ° C., and the coating and baking conditions for the topcoat paint were 50 seconds at an ultimate temperature of 230 ° C.

  About each obtained precoat steel plate, while performing the T bending test by the following method, the corrosion resistance after deep drawing was investigated, and the result was written together in Table 5,6.

[T-bending test]
Each pre-coated steel sheet is cut into a size of 50 mm in length × 50 mm in width, and the surface of each steel sheet is on the outside, and two steel sheets with a thickness of 0.8 mm are sandwiched inside the folded part, at room temperature (20 ° C) After bending 180 ° (2T processing) with a vise under the conditions, the bent portion is observed with a 10-fold magnifier, and the state of cracks generated in the precoat layer is evaluated according to the following criteria.

◎: No cracks are observed, ○: Very small cracks are observed,
Δ: Clearly cracks are observed, ×: Large cracks are observed.

[Corrosion resistance after deep drawing]
Deep drawing: Using each pre-coated steel plate obtained above, pressing conditions: 80 ton crank press (product name “NCL-80TS” manufactured by Aida Engineering Co., Ltd.) and deep drawing under the following pressing conditions I do.

Die: Cylindrical type, Die size: Blank diameter 110 mmφ, punch outer diameter 50 mmφ, die inner diameter: 51.64 mmφ, punch R: 5 mm, die R: 3 mm, clearance: 0.82 mm, processing speed: 40 spm, wrinkle presser pressure : 1 kgf / cm ²
Salt spray test: Each deep-drawn material is subjected to a salt spray test according to JIS Z2371, and the corrosion resistance of the coating film is evaluated by the swelling width (mm) of the coating film from the end face after 120 hours. The evaluation is based on the following criteria based on the coating film width from the end face in the longitudinal direction (T) and the lateral direction (M) of the coating film formed on the surface of each sample subjected to deep drawing as shown in FIG. Evaluate 5 points.

1 point: Longitudinal (T) paint film swelling width of 15 mm or more (see the appearance photograph in FIG. 2),
2 points: The film blister width in the longitudinal direction (T) is 10 or more and less than 15 mm (see the appearance photograph in FIG. 3),
3 points: The film blister width in the longitudinal direction (T) is 5 mm or more and less than 10 mm (see the appearance photograph in FIG. 4)
4 points: coating film swelling width in the longitudinal direction (T) is less than 5 mm (see the appearance photograph in FIG. 5),
5 points: The film swelling width in the lateral direction (M) is less than 5 mm (see the appearance photograph in FIG. 6).

  Table 5 is an example that satisfies all the prescribed requirements of the present invention, both of which show excellent results in both coating film adhesion (T-fold test result) and salt spray test (corrosion resistance) after deep drawing. ing. On the other hand, Table 6 is a comparative example lacking any of the requirements defined in the present invention, and one or both of the T-fold test result (coating adhesion) and the salt spray test result (corrosion resistance after processing) are Inferior and unable to achieve the object of the present invention

It is explanatory drawing which shows the evaluation criteria of the corrosion resistance after deep drawing employ | adopted in the Example. It is an external appearance photograph of the sample whose corrosion resistance evaluation after deep drawing is 1 point. It is an external appearance photograph of the sample whose corrosion resistance evaluation after deep drawing is 2 points. It is an external appearance photograph of the sample whose evaluation of corrosion resistance after deep drawing is 3 points. It is an external appearance photograph of the sample whose evaluation of corrosion resistance after deep drawing is 4 points. It is an external appearance photograph of the sample whose evaluation of corrosion resistance after deep drawing is 5 points.

Explanation of symbols

T Vertical bulge M Horizontal bulge

Claims (7)

A coating composition for undercoating used in the production of a non-chromate pre-coated metal sheet for deep drawing,
(A) It consists of one or more selected from polyester resins and epoxy-modified polyester resins, has a glass transition temperature (Tg) of 60 ° C. or higher, a number average molecular weight (Mn) of 15,000 or higher, and a hydroxyl value of 5 mgKOH / a resin that is less than or equal to g;
(B) including at least one curing agent selected from the group consisting of amino resins, blocked polyisocyanate compounds and epoxy resins,
The ratio of the resin (A) to 70 to 95 parts by mass and the ratio of the curing agent (B) to 5 to 30 in 100 parts by mass in terms of solid content of the resin (A) and the curing agent (B). An undercoat paint composition for producing a non-chromate precoated metal sheet for deep drawing, characterized by being part by mass.   The other component contains (C) non-chromium rust preventive pigment: 10 to 100 parts with respect to 100 parts by mass of the total of the resin (A) and the curing agent (B) in terms of solid content. Undercoat paint composition.   Furthermore, as another component, with respect to 100 mass parts of total of solid content conversion of the said resin (A) and a hardening | curing agent (B), (D) non-chromium coloring pigment: 20 mass parts or less are contained. 2. The undercoat paint composition according to 2. A coating composition for top coating used in the production of a non-chromate pre-coated metal sheet for deep drawing,
(E) a polyester resin having a glass transition temperature (Tg) of 10 to 30 ° C., a number average molecular weight (Mn) of 10,000 to 30,000, and a hydroxyl value of 1 to 20 mgKOH / g or less;
(F) At least one curing agent selected from an amino resin and a blocked polyisocyanate compound, and the resin (E) in a total of 100 parts by mass in terms of solid content of the resin (E) and the curing agent (F) A top coating composition for producing a non-chromate pre-coated metal sheet for deep drawing, wherein the proportion occupied by 70 to 95 parts by mass and the proportion occupied by the curing agent (F) is 5 to 30 parts by mass.   The top coat of Claim 4 which contains 10-120 mass parts of non-chromium pigments (G) as another component with respect to 100 mass parts of total of solid content conversion of the said resin (E) and a hardening | curing agent (F). Paint composition. 4. A chemical conversion treatment is performed on both surfaces of a zinc-based plated steel sheet having a coating adhesion amount of 45 g / m ² or more per one surface, and an undercoat coating film is formed using the undercoat paint composition according to any one of claims 1 to 3. A non-chromate pre-coated metal sheet having excellent corrosion resistance after deep drawing, wherein a top coating film is further formed thereon using the top coating composition according to claim 4 or 5 The manufacturing method. A thickness 5 of the undercoat paint composition according to any one of claims 1 to 3, wherein a chemical conversion treatment is applied to both surfaces of a zinc-based plated steel sheet having a coating adhesion amount per side of 45 g / m ² or more. An undercoating film of ˜15 μm is formed, and an overcoating film having a thickness of 10 to 25 μm comprising the topcoating composition according to claim 4 or 5 is further formed thereon. Non-chromate pre-coated metal sheet with excellent corrosion resistance after deep drawing.