JPH04173876A - Coating composition and method for forming coating film - Google Patents

Abstract

PURPOSE:To provide the coating composition having good corrosion resistance, preventing the swelling of coating films at the ends of processed articles and having excellent scratch resistance by adding chromate anti-rusting particles and inorganic particles to a coating. CONSTITUTION:The objective composition is characterized by adding (A) 5-70 pts.wt., preferably 5-24 pts.wt., of a chromate anti-rusting pigment (preferably strontium chromate or calcium chromate) and (B) (i) 5-30 pts.wt. of inorganic substance particles (e.g. mica, gypsum, glass or silica wherein the particle diameters of the substances excluding the silica are preferably 3-30mum, respectively, and the particle diameter of the silica is preferably <=5mum) and/or (ii) 0.5-5 pts.wt., preferably 0.5-2 pts.wt., of organic polymer particles (preferably polytetrafluoroethylene, polyamide resin or PE having a particle diameter of 0.1-10mum) to 100 pts.wt. of the solid content of the coating.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a coating composition and a method of forming a coating film using the same, and more specifically, it is capable of improving corrosion resistance, especially the corrosion resistance of the end surface of an object to be coated, and also improves scratch resistance. The present invention relates to a coating composition that can also improve properties and a coating film forming method using the same. [Prior Art and Problems to be Solved by the Invention] Conventionally, galvanized steel sheets, aluminum plated steel sheets, and the like have been widely used as durable steel sheets. Additionally, aluminum-zinc alloy plated steel sheets are attracting attention as they have both of these characteristics, and are used in a wide range of fields including building roofing materials, wall materials, and various home appliances. By the way, galvanized steel sheet, aluminized steel sheet,
Aluminum-zinc alloy plated steel sheets are often used as so-called pre-coated metal by applying an undercoat after chemical conversion treatment and then applying a topcoat on top of the undercoat. When painted, blisters were sometimes observed in the paint film, especially at the edges of the object being painted. This is thought to occur because the steel plate corrodes and the coating film is pushed up by corrosion products and hydrogen gas. Such corrosion is particularly severe in aluminum-zinc alloy plated steel sheets, and it has been desired to prevent it. Several attempts have been made to resolve this issue. For example, JP-A-58-120784 discloses that on an aluminum-zinc alloy plated steel sheet, a coating film-forming resin, an extender pigment, a chromate-based rust-preventive pigment with low water solubility, and a chromate-based rust-preventive pigment with high water solubility are used. This patent discloses a coated steel sheet using an aluminum-zinc alloy plated steel sheet as a substrate, which is coated with an undercoat mixed with the above, and a topcoat is applied on top of the undercoat. Also, JP-A-59-14
In No. 942, a chemical conversion treatment layer is formed by chemical conversion treatment of an aluminum zinc alloy plating layer on the surface of an aluminum zinc alloy plated steel sheet on which an aluminum zinc alloy plating layer is formed by hot dipping, and a chemical conversion treatment layer is formed on the surface of this chemical conversion treatment layer. A coated copper plate is disclosed in which an undercoat containing strontium chromate or calcium chromate in an amount of 30 to 70% by weight based on the nonvolatile content of the undercoat is applied, and a topcoat is applied over the undercoat. . By the way, as mentioned above, copper plates with aluminum-zinc alloy yD are widely used as pre-coated metals, but when various processing is applied to these pre-coated metals, scratches tend to occur on the coating film, reducing the product value. There were many things I had to do. The above-mentioned JP-A-58-120784 and JP-A-59-1
The scratch resistance of the coating film of the aluminum-zinc alloy plated copper plate No. 4942 was not yet sufficient. Therefore, the object of the present invention is to improve the corrosion resistance of durable steel sheets such as aluminum-zinc alloy plated copper sheets, aluminum-coated steel sheets, and zinc-coated steel sheets, especially the corrosion resistance of the end faces, and to provide coating films with improved scratch resistance. An object of the present invention is to provide a coating composition that can be applied and a coating film forming method using the same. [Means for Solving the Problems] In view of the above problems, as a result of intensive research, the present inventors have developed a method containing specific amounts of at least one kind of chromate-based rust preventive pigment, inorganic substance particles, and organic polymer particles. The inventors have discovered that good corrosion resistance and scratch resistance can be obtained by using a coating composition of this type, and have completed the present invention. That is, the coating composition of the present invention contains (a) 5 to 70 parts of at least one chromate-based rust-preventing pigment per 100 parts by weight of the solid content of the coating.
(b) (i) 5 to 30 parts by weight of inorganic material particles, and/or 01) 0.5 to 5 parts by weight of organic polymer particles. Furthermore, in the coating film forming method of the present invention, (a) 5 to 70 parts of at least one chromate-based rust-preventing pigment is added to 1.0 parts by weight of the solid content of the paint.
and (b) (i) 5 to 30 parts by weight of inorganic particles, and/or (11) 05 to 5 parts by weight of organic polymer particles, on at least one surface of the object to be coated. It is characterized by being applied. The present invention will be explained in detail below. First, the following thermosetting resins and thermoplastic resins can be used as the base resin of the coating composition of the present invention. Examples of thermosetting resins include epoxy resins, epoxyurethane resins, modified epoxy resins, phenokine resins, phenol resins, acrylic resins, acrylic epoxy resins, acrylic phenol resins, acrylic phenol epoxy resins, polyester resins, various modified polyester resins, Examples include coating film-forming resins such as alkyd resins, isocyanate-curable acrylic resins, urethane resins, and acid anhydride-modified polypropylene resins. If necessary, a crosslinking agent such as an amino resin or a blocked isocyanate is added to these materials. Moreover, the above-mentioned resin can be used as an alkyd resin imparted with flexibility by adding up to about 30% by weight of oil or fat or fatty acid, if necessary. Furthermore, epoxy resins and curing agents such as various amines, polyamides, acids, and acid anhydrides can be added. In addition, thermoplastic resins that can be used in the present invention include chlorinated olefin resins such as chlorinated polyethylene and chlorinated polypropylene, vinyl chloride resins, vinyl acetate, and vinylidene chloride, which are commonly used in the paint field. Examples include copolymerized vinyl resins, cellulose resins, acetal resins, alkyd resins, and chlorinated rubber resins. In the present invention, not only resins soluble in organic solvents but also water-based paints made of water-soluble, water-soluble, and emulsified resins can be used. In addition, active energy ray-curable paints may be used; in this case, the active energy ray-curable paints include - numerically, a polymer having a radically polymerizable double bond in its structure as a coating film-forming component; The main components are oligomers, monomers, etc., and if necessary, non-reactive polymers,
It may contain organic solvents, waxes, and other additives. In addition, examples of active energy rays include electron beams and ultraviolet rays, and preferred examples of the coating film-forming resin include:
Those having acrylate functional groups are included. The resins that can be used in the coating composition of the present invention have been described above, but when the coating composition of the present invention is used in a pre-coat method, epoxy resin,
It is preferable to use a resin in which a polyester resin is combined with a corresponding curing agent. Examples of the chromate-based rust-preventing pigment added to the above-mentioned coating film-forming resin (paint) include strontium chromate, calcium chromate, barium chromate, zinc chromate, etc. In particular, strontium chromate, calcium chromate, etc. It is preferable to use The amount of the chromate rust preventive pigment added is 5 to 70 parts by weight per 100 parts by weight of the solid content of the above-mentioned paint. If the content of the tetramate rust-preventing pigment is less than 5 parts by weight, the corrosion resistance will decrease. On the other hand, if the amount exceeds 70 parts by weight, the yellowness of the coating film obtained from this coating composition will increase, and the degree of freedom in hue of the top coat applied thereon will decrease. In addition, the storage stability of the paint decreases due to precipitation of chromate-based antirust pigments and the like. Furthermore, the amount of chromium eluted by water cooling (water quenching) after the coating film is baked increases, resulting in uneven appearance and chromium leaking into the cooling water, resulting in problems such as environmental pollution. The preferred amount of the chromate-based rust preventive pigment is 5 to 60 parts by weight, more preferably 5 to 60 parts by weight.
It is 24 parts by weight. The inorganic particles used in the present invention are not particularly limited as long as they improve the hardness of the coating film by being present in the coating film, but preferably have a Mohs hardness of 5 to 5.
8, more preferably 6 to 7. Specifically, the inorganic particles used include natural or synthetic mica, gypsum, diatomaceous earth, aluminum powder, aluminum flakes, glass,
Examples include feldspar, quartz, and fine silica powder such as wet silica, dry silica, and colloidal silica. In the case of such inorganic substance particles other than the various silica fine powders mentioned above, it is preferable to use ones with a particle size of 3 to 30 μm, and in the case of silica fine powders, those with a particle size of 5 μm or less are used. Good. The blending amount of these inorganic particles is 5 to 30 parts by weight per 100 parts by weight of the solid content of the paint. If the amount of inorganic particles is less than 5 parts by weight, scratch resistance will decrease. On the other hand, if the amount exceeds 30 parts by weight, coating film strength will not be obtained and processability will be poor. Moreover, the surface smoothness of the coating film formed may be reduced. The preferred amount of inorganic particles is 10 to 25 parts by weight. Note that a plurality of types of each of the above-mentioned inorganic substance particles may be used in combination, for example, silica fine powder and other inorganic substance particles may be used in combination. In this case, the blending ratio of the two (inorganic particles other than silica/fine silica powder) is preferably about 98/2 to 70/30. In the present invention, organic polymer particles are added instead of or together with the above-mentioned inorganic particles. Organic polymer particles that can be used include fluororesins including polytetrafluoroethylene, polyethylene, polypropylene, silicone, cellulose, urethane, nylon,
Examples include polyester, phenol resin, acrylic resin, amino resin, polyamide resin, and modified resin thereof. Such organic polymer particles have a particle size of 0, 0
It is preferable to use one with a diameter of 01 to 30 μm. Preferred organic polymer particles have a particle size of 0.1 to 10. ljm
These are polytetrafluoroethylene, polyamide resin, and polyethylene. The above-mentioned organic polymer particles are blended in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of the solid content of the paint. If the amount of organic polymer particles is less than 0.5 parts by weight, scratch resistance will be reduced. On the other hand, if the amount exceeds 5 parts by weight, the strength of the coating film will not be obtained and processability will be poor. The preferred amount of organic polymer particles is 0.5 to 2 parts by weight. In the present invention, the object is achieved by arbitrarily combining the above two components (b) (inorganic material particles and organic polymer particles), but more preferably, the inorganic material particles of component (i) and 01) It is used together with organic polymer particles as a component. Preferred combinations of both when used together include (a) feldspar and polytetrafluoroethylene powder, (ii) feldspar and wet silica and polytetrafluoroethylene powder, and (c) feldspar and colloidal silica and polytetrafluoroethylene powder. . As explained above, in the coating composition of the present invention, a chromate-based antirust pigment is added to improve the anti-caking property. Also,
Scratch resistance is improved by adding inorganic particles and/or organic polymer particles. The reason why the scratch resistance is improved by adding the above-mentioned inorganic substance particles and/or organic polymer particles is considered to be due to the following effect. In other words, due to the presence of the filler (inorganic particles and/or organic polymer particles) in the coating film, even if stress is applied to the coated copper plate, the point of application of the stress is between the coating film and the base (steel plate). (substrate), but migrates to the surface of the filler in the coating film. When the stress applied to the coating film is relaxed by the filler in this way, scratches are less likely to be formed on the coating film. Furthermore, even if a shearing force is applied to the coating film, the internal sliding caused by the filler (particularly organic polymer particles) becomes effective and the force is dispersed, making it difficult for the coating film to be destroyed. In this way, inorganic particles with a Mohs hardness of about 5 to 8 (
By using feldspar, wet silica, etc.) and polytetrafluoroethylene, polyimide, polyamide powder, etc., which have a lubricating effect through internal sliding, scratch resistance is improved without impairing general coating performance such as coating gloss and processability. be done. Furthermore, by adding such fillers, the coating film (
The surface of the undercoat film becomes appropriately rough, thereby improving interlayer adhesion with the topcoat film, and also has the advantage of preventing peeling of the paint film. The coating composition of the present invention contains the above-mentioned components as essential components, but may further contain coloring pigments, extender pigments, and other antirust pigments. Such pigments include, for example, titanium dioxide, phthalosyanine blue, phthaloshanine green, quinacudrine, indanthrone, isoindolinone, perylene, anthrapyrimidine, carbon black, benzimidacylon, graphite, yellow iron oxide, Examples include coloring pigments such as red iron oxide, and extender pigments such as clay. In addition, various catalysts such as dodecylbenzenesulfonic acid, paratoluenesulfonic acid, dibutyltin laurate, and dicyandiamide, benzophenol-based ultraviolet absorbers, surface conditioners such as silicone and organic polymers, anti-sagging agents, and thickeners, etc. Additives can be added. These additives can be incorporated into a paint in an amount of 5 parts by weight or less to improve paint performance and film performance. However, if the amount of these additives is too large, it is not preferable because there is a risk that repelling may occur during coating film formation or that interlayer adhesion may deteriorate. A solvent may be added as appropriate for viscosity adjustment (workability). The components are mixed using equipment such as a paint shaker, day silver, ball mill, sand grind mill, kneader, etc., which are commonly used in paint production. The above-mentioned coating composition of the present invention is suitably used as an undercoat paint for durable steel plates such as aluminum-zinc alloy coated steel plates, aluminum-plated steel plates, and galvanized steel plates. Coating using the coating composition of the present invention is carried out as follows. First, a steel plate to be coated (such as the above-mentioned aluminum-zinc alloy coated steel plate) is degreased and then chemically treated. Degreasing (surface cleaning) and chemical conversion treatment may be performed by known methods.
Select the method that is suitable for the steel plate used. Next, the coating composition of the present invention is applied. When painting, the reserved paint composition is adjusted to an appropriate viscosity as described above. The painting method is not particularly limited, and air spray painting,
Conventional painting methods such as airless painting and electrostatic painting can be used. In addition, when particularly seeking accuracy of coating thickness, smoothness of coating surface, etc., gravure coating method,
roll coating method, curtain coating method,
It is preferable to use a bar coating method or an offset gravure coating method. In addition, in the case of a pre-coating method, it is preferable to adopt a roll coating method). In the coating film forming method of the present invention, the above-mentioned coating composition is applied as an undercoat to the object to be coated, and the coating may be applied to one side of the object (copper plate) or both sides. If the coating composition of the present invention is applied to both sides of a copper plate, the corrosion resistance will be further improved, but it may be applied to one side of a steel plate in consideration of required performance, manufacturing cost, etc. When only one side is undercoated with the coating composition of the present invention, a conventional undercoat paint may be used as the undercoat on the other side. The coating composition of the present invention can also be applied to the back surface of a steel plate processed into a product. By applying the coating composition of the present invention to the back surface, corrosion current is suppressed even on the edge end surfaces on which no coating film is formed, and the edge creep properties on both surfaces can be further improved. The coating thickness of this undercoat is 2 to 1 when dry.
The thickness is 0 μm, preferably 3 to 8 μm. If the film thickness is as thick as 2 μm, the corrosion resistance will decrease. Moreover, if the film thickness exceeds 10 μm, the smoothness of the coating film surface may be reduced. In addition, on the surface that becomes the back surface when a steel plate is processed into a product, the film thickness is 5 to 25 μm, preferably 8 to 20 μm.
Let it be μm. Apply the undercoat as described above, and after drying, apply the undercoat at 190 to 230℃ for 20 minutes.
Perform baking for ~60 seconds. Next, oil-free polyester, vinyl chloride, silicone polyester, fluororesin, thermosetting acrylic resin,
A known top coating material made of melamine alkyd resin, silicone acrylic resin, etc. can be applied. Coating at this time may be done by a known method. In addition, the combination of the above-mentioned undercoat paint and resin for this topcoat paint is similar to the combination of paints whose main components are the same type of resin, but different types of resins can be used as long as there is no problem in the adhesion between the topcoat film and the undercoat film. It may also be a combination of paints as main components. The thickness of the topcoat film is 10~10 for materials other than vinyl chloride.
The thickness is preferably 20 μm, and in the case of a top coat mainly made of vinyl chloride, the thickness is preferably 100 to 200 μm. After applying the top coat, dry and heat at 190 to 250℃ for 20 minutes.
Perform baking for ~60 seconds. Note that an intermediate coat may be applied between the above-mentioned undercoat and topcoat, and depending on the required performance of the coating film, paints that are compatible with the undercoat and topcoat (topcoat or undercoat) may be applied as appropriate. Apply a similar type of paint). In this case, it is preferable to perform baking after applying the intermediate coat to create a so-called 3-coat, 3-bake process. [Example] The present invention will be explained in more detail with reference to the following specific examples. Examples 1 to 19, Comparative Examples 1 to 5 [1] Preparation of paint compositions Paints 1 to 13 having the compositions shown in Table 1 were prepared using the solvents shown in Table 2. Note that both numbers in Tables 1 and 2 indicate parts by weight. During preparation, first a part of the resin and solvent, a pigment component, and a filler component consisting of inorganic particles and/or organic polymer particles are dispersed using a dispersion machine, and then the remaining part of the resin and solvent is added to adjust the viscosity. After adjustment, paints 1 to 13 were obtained. Notes to Table 1: (1) Strontium chromate N1 manufactured by Kikuchi Shiki■. (2) Zinc chromate C1 made by Kikuchi Shiki■. (3) Calcium chromate D, manufactured by Kikuchi Color Co., Ltd. (4) Barium chromate, manufactured by Kikuchi Shiki. (5) Minex 7, Shiraishi calcium flank. (6) Crystallite VX-32, manufactured by Tatsumori. (7) Micromica C-1000, manufactured by Shiraishi Calcium. (8) GI3-210, manufactured by Toshiba Ballotini■. (9) Nip seal E-200A, manufactured by Nippon Silica. αQ Hakusol S-200, manufactured by Hakuto Chemical ■. Ql) LeBron L-2, manufactured by Daikin Industries ■. ■Viscol 5503P, manufactured by Mitsu Kasei Kogyo ■. α3 nylon 5P-500, manufactured by Toshi ■. Alpha Reclay No. 1, made by Maruo Calcium. 05) TITONE R-62N, manufactured by Sakai Chemical ■. 0ωIEF-7931, nonvolatile content 40%, manufactured by Mitsui Toatsu Chemical ■. αtsu Epicor) 1009, non-volatile content 40%, made by Yuka Shell. 0 mark Epicor) 1055, non-volatile content 40%, manufactured by Yuka Shell @. 00 vinyl chloride vinylic acid copolymer, VAGH1 non-volatile content 20%, manufactured by UCC. (Epo) -) YD7020, non-volatile content 40%,
Manufactured by Tobu Kasei. (21) Dianal LR-90, non-volatile content 30%, manufactured by Mitsubishi Rayon. (22) Byron GK780, nonvolatile content 40%, manufactured by Toyobo ■ (faded with cyclohexane and Tsurpez 150). (23) Two-color MW-24X, non-volatile content 80%, manufactured by three-phase chemical side. (24) Super Beckamine L-107-70, non-volatile content 70%, manufactured by Dainippon Ink & Chemicals @. (25) Coronate 2182, non-volatile content 80%, made by Japan Polyurethane. Table 2 Note 2 (1) Swazol 100, aromatic solvent, manufactured by Marugata Sekiyu@. An aluminum-zinc alloy plated steel plate, a zinc coated copper plate, and an aluminum plated copper plate shown below were prepared, degreased, and used as test plate substrates. Next, the coating surface of each test board was subjected to the chemical conversion treatment shown below. After the chemical conversion treatment, each test substrate was undercoated using paints 1 to 13 described above under the conditions shown below. Each test board and paint 1
-13 are shown in Table 3. After undercoating as described above, Example 16.17 as shown in Table 3.
In and 18, intermediate coating was performed under the conditions shown below,
For the others, a top coat was applied under the following conditions without performing an intermediate coat. [2] Steel plate (test plate) ■AI/2nl+aluminum-zinc alloy plated steel plate,
Aluminum content 5%. ■AI/Zn2 aluminum-zinc alloy plated steel sheet,
Aluminum content 55%. ■A1 aluminum plated steel plate. ■Zn hot-dip galvanized steel sheet. [3] Chemical conversion treatment Each of the above-mentioned steel plates was subjected to chemical conversion treatment by a known method. As shown in Table 3, in Example 8.9 and Comparative Example 5 (both zinc-coated steel sheets), a zinc phosphate-based treatment solution (Surfdyne ZIl 9200, manufactured by Nippon Paint ■) was used for the chemical conversion treatment. In other examples, by immersing the steel plate in this treatment liquid, a chromate-based treatment liquid (Surfcoat NR
C300, manufactured by Nippon Paint ■). [4] Undercoat Each of the coating compositions shown in Tables 1 and 2 was used as an undercoat paint to undercoat both sides (or one side) of each of the above-mentioned steel plates as shown in Table 3. This undercoat was applied by a roll coater method, and baked for 60 seconds at the temperatures shown in Table 2. The obtained dry film thickness is also shown in Table 3. [5] Intermediate coating As shown in Table 3, for the test plates of Examples 16, 17 and 18, an intermediate coating was applied on top of the single undercoat film described above. The epoxy paint Superlac DIF P-29 (manufactured by Nippon Paint) was used as the intermediate coating, and was applied using the barcode method to a dry film thickness of 3 μm.
Baking was performed at 00°C for 40 seconds. In Example 16, this intermediate coating was applied to both sides of the test plate. Further, in Examples 17 and 18, only one side was coated with an intermediate coat. [6] Top coats below the top coat were applied using a roll coater method. The amount of coating was adjusted so that the dry film thickness was as shown below. The baking conditions were as follows. The combinations of this top coat and test substrate were as shown in Table 3. A1 oil-free polyester paint, Superlac DIF F-60, white (manufactured by Nippon Paint)
: Dry film thickness 20μm: Baking conditions are maximum temperature reached 200μm
℃ for 40 seconds. A2: Silicone polyester paint, Super Lac DIF 5-30, white (manufactured by Nippon Paint):
Dry film thickness 20 μm: Baking conditions are maximum temperature reached 220
℃ for 40 seconds. A3: Thermosetting acrylic paint, Superlac DIF
A-55, White (manufactured by Nippon Paint ■): Dry film thickness 15 μm = Baking conditions are maximum temperature reached at 220℃ and 5
It was set to 0 seconds. A4: Vinyl chloride sol paint, vinyl sol 10000X-
20, White (manufactured by Nippon Paint): Dry film thickness 20
0 μm: The baking conditions were such that the maximum temperature reached was 200° C. and the baking time was 60 seconds. A5: Fluororesin paint, Duranaro, White (manufactured by Nippon Paint ■): Dry film thickness 20 μm: Baking conditions were a maximum temperature reached of 245° C. for 50 seconds. 6: Oil-free polyester paint (as a top coat when an intermediate coat is applied), Super Lac DI
FF-25, White (manufactured by Nippon Paint ■): Dry film thickness 15 μm: Baking conditions were as follows: maximum temperature reached was 200° C. for 50 seconds. Each of the test plates obtained by applying the above coating was tested for edge creep resistance, rust resistance in processed parts, and scratch resistance in the following manner. The results are also shown in Table 3. [7] Construction-resistance azalea creep The above-coated test plate was used for natural exposure tests.
0cm x 30cm, 7cm for salt spray test
It was cut to a size of 20cm x 20cm, and the three cut sides were sealed with polyester tape. Note that the seal width was 5 mm from the cut end. The above test board, whose three sides were sealed with polyester tape, was left outdoors in Okinawa Prefecture for 36 months as a natural exposure test. Further, as a salt spray test, a 750 hour test was conducted in accordance with JIS X2371. For the test panels that have completed each test, the maximum length of blisters that have formed on the coating film from the unsealed side (
mm) was measured. [8] White rust on processed parts Cut each painted board to a size of 7 x 18 cm,
On the cm-long side, bend 15 cm from the end and process it with 2T.
Bend this board at the 5cm part) and JIS Z2
A salt spray test was conducted in accordance with 371. After the 1,000-hour test was completed, the occurrence of white rust from the portions where the bending process was performed was evaluated based on the following criteria. 3 points: Occurrence of white rust less than 20% 2 points 2 Occurrence of white rust less than 40% 20% or more 1 point: Occurrence of white rust 40% or more The test results are shown in Table 2.

[9] Scratchability The test coating was scratched (with a force of 0.5 kg) with a 10 yen coin without burrs on the outer circumferential surface, and damage to the test coating was evaluated according to the following criteria. 3 points: Even if there are scratches and flakes on the surface, the extent of the scratches is small and some of the top coat remains, and the undercoat (or intermediate coat) does not appear. 2 points: Part of the undercoat film has been scraped off, and peeling can be seen in the undercoat film. 1 item: Both the top coat and undercoat have been scraped off, exposing the base (chemical conversion treated surface of the board). The results are also shown in Table 3. Notes to Table 3: (1) Chromate system; conducted by applying Surf Coat NRC300 to the substrate. Zinc phosphate: The substrate was immersed in Sur7 Dyne Z []9200. (2) Each paint corresponds to the paint shown in Table 1. [Effects of the Invention] As detailed above, the steel plate coated with the coating composition of the present invention has good corrosion resistance, prevents blistering of the coating film at processed edges, and improves scratch resistance. ing. Good corrosion resistance can be obtained by applying the coating composition of the present invention as an undercoat to at least one surface of various steel plates. The coating composition of the present invention is suitable for a pre-coated steel plate, and can produce pre-coated metal with excellent corrosion resistance and scratch resistance by a coil coating method. Such pre-coated metals are suitable for various home appliances such as washing machines, outdoor construction materials such as roofs and wall materials, and the like.

Claims (2)

[Claims] (1) Based on 100 parts by weight of the solid content of the paint, (a) 5 to 70 parts of at least one chromate-based rust-preventing pigment;
(b) (i) 5 to 30 parts by weight of inorganic particles, and/or (ii) 0.5 to 5 parts by weight of organic polymer particles. (2) Based on 100 parts by weight of the solid content of the paint, (a) 5 to 70 parts of at least one chromate-based rust-preventing pigment;
and (b) (i) 5 to 30 parts by weight of inorganic particles, and/or (ii) 0.5 to 5 parts by weight of organic polymer particles, to at least one of the objects to be coated. A coating film forming method characterized by coating on a surface.