JP2000167482A - Pre-coated metal sheet with excellent coating adhesion - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a non-chromium-based precoated steel sheet excellent in coating film adhesion, which does not contain a chromate-treated film and a chromium-based rust-preventive pigment having a problem in toxicity. SOLUTION: At least one side of a metal plate has the following (1) to
The coating layer of (2), that is, (1) 100 parts by weight of aqueous resin as solid content, tannin or tannic acid 0.2 to 5
A coating layer containing 0 parts by weight; and (2) a coating layer containing 10 to 500 parts by weight of finely divided silica as a solid component in the above (1), as a base treatment layer, and further provided thereon. A colored film layer is provided as an upper film.
Further, a film layer containing a rust-preventive pigment may be provided as a lower film between the undercoating layer and the upper film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoated metal sheet having excellent coating film adhesion, and more particularly to a precoated metal sheet containing no toxic hexavalent chromium.

[0002]

2. Description of the Related Art In the fields of building materials, home appliances, sundries, automobiles, etc., a prepainted metal plate (pre-coated metal plate (pre-coated metal plate ( PCM) is preformed by molding and joining to form a product. PCM is a metal plate coated with an organic film on a rust-proofing treatment, and has the property of having good workability, good workability, and good corrosion resistance.

[0003] For example, Japanese Patent Application Laid-Open No. 8-168723 discloses a technique for obtaining a precoated steel sheet having excellent workability, anti-contamination property and hardness by defining the structure of a film. Japanese Patent Application Laid-Open No. Hei 3-100180 discloses a precoated steel sheet having improved end face corrosion resistance by using a specific chromate treatment liquid.

[0004] These pre-coated metal sheets have not only corrosion resistance, but also workability and paint adhesion due to the combined effect of the organic film to which plating, chromate and chromium-based rust-preventive pigments are added. The purpose is to improve the properties and quality.

[0005]

In such a pre-coated metal plate, chromate-based treatment is mainly performed for imparting coating film adhesion and corrosion resistance. In addition, chromium-based rust-proofing is included in the organic coating. Pigment is incorporated. Hexavalent chromium contained in the chromate-treated film and the chromium-based pigment is water-soluble, and has a property of repairing a scratch of the film generated on the film by elution thereof. In addition, trivalent chromium contained at the same time is water-insoluble and contributes to ensuring the adhesion of the coating film. Therefore, especially in the rust prevention application of a zinc-based plated steel sheet, a chromate-treated film has been exclusively used to date as a film for imparting coating film adhesion and corrosion resistance. However, due to the toxicity problem of hexavalent chromium which may be eluted from the chromate-treated film and the organic film containing the chromium-based rust-preventive pigment, there has recently been an increasing demand for a non-chromium rust-proof treated film and a non-chromium organic film.

Accordingly, it is an object of the present invention to provide a non-chromium-based precoated metal sheet which meets such demands, has excellent adhesion, and has a practically usable level of corrosion resistance.

[0007]

According to the present invention, there is provided a coating layer of the following (1) or (2) on at least one side of a metal plate:
(1) a coating layer containing 100 parts by weight of an aqueous resin, 0.2 to 50 parts by weight of tannin or tannic acid as a solid content,
(2) In addition to the above (1), one of the coating layers containing 10 to 500 parts by weight of finely divided silica as a solid content is further provided as a base treatment layer, and a colored coating is further provided thereon as an upper coating. A precoated metal sheet having a layer. Corrosion resistance is further improved by having a coating layer containing a rust-preventive pigment as a lower coating layer between the base treatment layer and the upper coating layer.

[0008] The precoated metal sheet has a coating film adhesion comparable to that of a conventional chromate-treated precoated metal sheet, and has the advantage that no chromium is used or the amount of chromium can be reduced.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The pretreatment agent used for the precoated metal sheet of the present invention has been developed for the purpose of preventing rust of various metal sheets (including plated metal sheets) including steel sheets. Cold-rolled steel sheet, electro-galvanized steel sheet, hot-dip galvanized steel sheet, galvannealed steel sheet, galvanized steel sheet, aluminum-plated steel sheet, chrome-plated steel sheet, nickel-plated steel sheet, nickel-plated steel sheet, etc., stainless steel sheet, It can be applied to a known metal plate such as an aluminum plate, a copper plate, and an aluminum alloy plate. The metal plate can be subjected to ordinary treatment such as hot water washing and alkali degreasing before the base treatment.

The undercoating layer for the purpose of the rust prevention treatment of the present invention is characterized by containing tannin or tannic acid based on an aqueous resin. As described above, the undercoat layer is a coating layer based on an aqueous resin.

Here, the term "aqueous resin" refers to not only a water-soluble resin, but also a water-insoluble resin (water-dispersible resin) which is originally water-insoluble but can be in a finely dispersed state in water such as an emulsion or a suspension. Include it. Examples of resins that can be used as such an aqueous resin include polyolefin resins, acrylic olefin resins, polyurethane resins, acrylic resins, polycarbonate resins, epoxy resins, polyester resins, phenol resins, and other thermosetting resins. And the like, and a crosslinkable resin is more preferable. Particularly preferred resins are acrylic olefin-based resins, polyurethane-based resins, and mixed resins of both. Two or more of these water-soluble resins may be used as a mixture.

The tannin or tannic acid may be a tannin which can be hydrolyzed or a condensed tannin, or a partially decomposed tannin. The tannins and tannic acids are not particularly limited, such as hamametantan, quintuple tannin, gallic tannin, myrobalan tannin, dividibine tannin, argarovilla tannin, baronia tannin, and catechin. (Manufactured by Fuji Chemical Co., Ltd.).

The content of tannin and tannic acid is 100 parts by weight of the resin, and tannin or tannic acid is added in an amount of 0.1 part by weight.
The amount is preferably 2 to 50 parts by weight. If the content of tannin or tannic acid is less than 0.2 parts by weight, the rust-preventing effect and coating film adhesion are not ensured. On the other hand, if the content exceeds 500 parts by weight, the rust-preventing effect decreases, In some cases, gelation may occur, causing problems.

Further, when fine silica is added, the rust prevention effect (corrosion resistance) is further promoted. Moreover, in addition to the corrosion resistance, the drying property, the scratch resistance, and the coating film adhesion are also improved.

In the present invention, the term "fine silica" is a generic term for silica having a characteristic such that when it is dispersed in water, it has a fine particle size and can stably maintain a water-dispersed state, and semi-permanently no sedimentation is observed. That's what I mean. The finely divided silica is not particularly limited as long as it has a small amount of impurities such as sodium and is weakly alkaline. For example, commercially available silica such as "Snowtex N" (manufactured by Nissan Chemical Industries, Ltd.) and "Adelite AT-20N" (manufactured by Asahi Denka Kogyo KK) can be used.

The content of the finely divided silica is preferably 10 to 500 parts by weight based on 100 parts by weight of the aqueous resin in terms of solid content. If it is less than 10 parts by weight, the effect of addition is small, and if it exceeds 500 parts by weight, the effect of improving corrosion resistance is saturated and uneconomical.

Further, the undercoating layer of the present invention has another composition.
Minutes may be included. For example, pigments, surfactants
And so on. Examples of such pigments include
For example, titanium oxide (TiO)_Two), Zinc oxide (ZnO),
Zirconium oxide (ZrO_Two), Calcium carbonate (Ca
CO_Three), Barium sulfate (BaSO)_Four), Alumina (A
l_TwoO_Three), Kaolin clay, carbon black, oxidation
Iron (Fe_TwoO_Three, Fe _ThreeO_Four) And other organic pigments and organic face
Various coloring pigments such as pigments can be used. Ma
In order to further improve coating adhesion, silane cups
A ring agent may be blended. As a silane coupling agent
For example, γ-aminopropyltrimethoxysila
Γ-aminopropylethoxysilane, γ-glycidin
Xypropyltrimethoxysilane, γ-glycidoxyp
Propyl ethoxysilane, N- [2- (vinylbenzyl
Mino) ethyl] -3-aminopropyltrimethoxysila
And the like.

In order to form a base treatment layer on a metal plate, a base treatment agent (coating agent) containing the above components is prepared in water, applied to a steel plate, and the coating film is heated and dried. When the resin is crosslinkable or curable, the resin is crosslinked and cured by this heating. The heating temperature is preferably 50 to 250C. 50 ℃
If it is less than 10%, the evaporation rate of water is too slow to obtain a sufficient film-forming property, so that the rust-preventive force is insufficient. On the other hand, when the temperature exceeds 250 ° C., thermal decomposition of the aqueous resin occurs, so that there is a problem that the SST property and the water resistance are reduced and the appearance is yellowed. 70
~ 160 ° C is more preferred. In hot air drying, drying for 1 second to 5 minutes is preferable.

The adhesion amount after drying of the base treatment is 10 mg / m ²
The above is preferable. If it is less than 10 mg / m ² , the rust-preventing ability is insufficient. On the other hand, if the amount of adhesion is too large, it is uneconomical as a base treatment layer, and the adhesion of the coating film decreases. Therefore, the upper limit of the film thickness is preferably 3000 mg / m ² or less.

The method of applying the undercoating is not particularly limited.
Generally known coating methods, for example, roll coating, air spray, airless spray, immersion and the like can be adopted.

In the precoated metal plate of the present invention, the base resin of the colored coating layer coated on the undercoating layer may be any one of an aqueous type, a solvent type, a powder type and the like. As the type of resin, generally known ones, for example, polyacrylic resin, polyolefin resin, polyurethane resin,
Polyepoxy resins, polyester resins, polybutyral resins, melamine resins, and the like can be used.

As the coloring pigment, titanium oxide (Ti
O ₂ ), zinc oxide (ZnO), zirconium oxide (Zr
O ₂ ), calcium carbonate (CaCO ₃ ), barium sulfate (BaSO ₄ ), alumina (Al ₂ O ₃ ), kaolin clay, carbon black, iron oxide (Fe ₂ O ₃ , Fe ₃
Commonly known coloring pigments such as inorganic pigments such as O ₄ ) and organic pigments can be used. Further, in addition to the above-mentioned coloring pigment, a rust preventive pigment may be added as necessary. Generally known rust preventive pigments, for example, (1) phosphoric acid rust preventive pigments such as zinc phosphate, iron phosphate and aluminum phosphate, (2) calcium molybdate, aluminum molybdate, barium molybdate and the like Molybdic acid rust preventive pigments, (3) vanadium rust preventive pigments such as vanadium oxide, (4) strontium chromate, zinc chromate, calcium chromate, potassium chromate,
Chromate-based rust preventive pigments such as barium chromate,
(5) Finely divided silica such as water-dispersed silica and fumed silica can be used. However, since the chromate-based rust preventive pigment of (4) is environmentally toxic,
It is desirable to use a rust preventive pigment other than the chromate rust preventive pigment of (4).

The thickness of the coating layer containing the color pigment is 1 to 30 μm.
m is suitable, and if it is less than 1 μm, the corrosion resistance is deteriorated, and if it is more than 30 μm, the workability of the coating film is poor.

[0024] The method for applying the coating containing the color pigment can be performed by a generally known coating method, for example, roll coating, curtain flow coating, air spray, airless spray, dipping, bar coating, brush coating and the like.

The precoated metal sheet of the present invention can have a coating layer to which a rust-preventive pigment is added as a lower coating between the undercoat layer and the colored coating layer.

The base resin of the lower layer coating may be any of water-based, solvent-based, powder-based, and the like. Further, it may be an adhesive layer. As the kind of the resin, generally known ones, for example, polyacrylic resin, polyolefin resin, polyurethane resin, polyepoxy resin, polyester resin, polybutyral resin, melamine resin and the like can be used.

As the rust preventive pigment for the lower layer coating, generally known rust preventive pigments, for example, (1) phosphate rust preventive pigments such as zinc phosphate, iron phosphate and aluminum phosphate, (2) calcium molybdate, molybdenum Molybdic acid-based rust preventive pigments such as aluminum oxide and barium molybdate; (3) vanadium-based rust preventive pigments such as vanadium oxide; Rust pigments, (5) finely divided silica such as water-dispersed silica and fumed silica can be used. However, since the chromate-based rust preventive pigment of (4) is environmentally toxic, it is desirable to use a rust-preventive pigment other than the chromate-based rust preventive pigment of (4). The amount of the rust preventive pigment to be added is 1 to the weight of the total solid content of the lower layer coating.
40% by weight is preferred. If it is less than 1% by weight, the effect of corrosion resistance is small, and if it is more than 40% by weight, the processability of the coating film is deteriorated, which is not suitable.

The thickness of the film containing the rust preventive pigment is 1 to 30 μm
Is preferred, and if it is less than 1 μm, the corrosion resistance becomes poor,
If it exceeds 30 μm, the processability of the coating film is inferior.

The method for applying the film containing the rust-preventive pigment can be performed by a generally known coating method, for example, roll coating, curtain flow coating, air spray, airless spray, immersion, bar coating, brush coating, or the like.

[0030]

The present invention will be described below with reference to examples. A galvanized steel sheet having a galvanized coating weight of 20 g / m ² per side and a thickness of 0.6 mm plated on both sides (described as EG in the table below) and a galvanized coating weight of 6
A hot-dip galvanized steel sheet having a thickness of 0.6 mm and plated on both sides at 0 g / m ² (described as GI in the table below) was FC-3
64S (manufactured by Nippon Parkerizing) 2% by weight, 6
It was degreased by immersing it in an aqueous solution at a temperature of 0 ° C. for 10 seconds, washed with water, and dried. Next, the undercoating agents having the compositions shown in the first and second compositions were applied with a coal coater and dried in a hot air drying oven. As tannic acid, "tannic acid AL"
(Manufactured by Fuji Chemical Industries), "BREWTAN" (manufactured by Omnichem) and "TANAL1" (manufactured by Omnichem) were used. As the silica, "Snowtex N" (described as ST-N in the table below) and "Snowtex NS"
(Described as ST-NS in the table below) (manufactured by Nissan Chemical Industries, Ltd.) was used. The reached plate temperature during drying was 150 ° C.

Next, Nippon Paint P641 primer paint (polyester resin type, described in the following table as polyester), Nippon Paint P108 primer paint (epoxy resin type, described in the following table as epoxy),
Nippon Paint's P304 primer paint (urethane resin type, described as urethane in the table below) was changed to the rust-preventive pigment shown in the table below, and was applied with a roll coater and blown with hot air. It was cured and dried in an induction heating furnace so that the reached plate temperature was 220 ° C. to form a lower layer film. The amount of the rust preventive pigment used was 15% by weight based on the total solid content of the lower layer coating.

Next, Nippon Paint FL100HQ (polyester resin, white color) was further applied on the lower layer film containing the rust-preventive pigment, and the ultimate plate temperature was raised to 220 ° C. in an induction heating furnace into which hot air was blown. The film was cured and dried to form an upper layer film.

The plate was water-cooled after each curing and drying process.

The following evaluation was performed on the precoated steel sheet manufactured as described above. 1. Coating film adhesion The coated plate was cut into a 1 mm square grid on the coating surface with a cutter knife, extruded 7 mm with an Erichsen tester so that the coating surface became convex, and then subjected to a tape peeling test. Regarding how to put in a grid, how to extrude Erichsen, and how to peel off the tape, JIS-K5400.8.2 and JIS
It carried out according to the method of -K5400.88.5. The evaluation after tape peeling was performed according to the figure of the evaluation example described in 8.5.
-, When the score was 6 or more and less than 9 points, it was evaluated as Δ, and when it was less than 6 points, it was evaluated as x. In addition, JIS-
In accordance with the description of K5400.8.20, after immersion, taking out and leaving for 24 hours, crosscut Ericksen and tape peeling were carried out by the above-mentioned method, and the same evaluation was performed.

2. Folding workability test The coated plate was bent at 180 °, and the coating film of the processed portion was observed with a 10-fold loupe to check for cracks in the coating film. Further, an adhesive tape was attached to the processed portion, and the remaining state of the coating film when the adhesive tape was vigorously peeled off was visually observed. The bending was performed in a 20 ° C. atmosphere with a 0.6 mm spacer interposed therebetween. The evaluation of coating film cracking was evaluated as ○ when there was no coating film cracking, Δ when there was some cracking in the coating film, and X when the coating film had clear cracking visually.
In addition, the evaluation of the remaining state of the coating film after peeling off with the tape was evaluated as follows: ○ when the coating film remained on the plated steel sheet without peeling at all; Δ when the coating film was partially peeled; The case where peeling was observed over the entire surface was evaluated as x. Further, the coated steel sheet is heated in boiling water according to JIS-K5400.8.20.
After immersion, taking out and standing for 24 hours, the above-mentioned bending was carried out, and the peeling of the coating film and the remaining state of the coating film after the tape peeling test of the processed portion were evaluated in the same manner.

3. Corrosion resistance The coated plate was subjected to a salt spray test according to the method described in JIS-K5400.9.1. The test time was 120 hours for an electrogalvanized steel sheet and 240 hours for a galvanized steel sheet. The method of evaluating the coating film in the cross-cut portion is as follows: when the maximum swollen width on one side of the cross-cut is less than 1 mm, ○ when the width is 1 mm or more and less than 2 mm;
When it was less than 3 mm, it was evaluated as x, and when it was 3 mm or more, it was evaluated as x. In addition, the above-mentioned salt water spray test was also performed on a flat plate manufactured so that the return (burr) at the time of cutting was on the evaluation surface side of the coated steel plate (to be the upper burr), and the swelling of the coating film from the end surface was performed. The width was observed. The evaluation method of the end face part is as follows: ○ when the swollen width from the end face is 3 mm or less; did.

The evaluation results are shown in Tables 3 and 4. The coating film adhesion, bending workability, and bending work adhesion of the precoated metal sheet (Examples 1 to 29) according to the present invention have almost the same performance as the conventional chromate-based precoated steel sheet (Comparative Examples 11 to 13). are doing. Although the corrosion resistance is slightly inferior, there is no problem in practical use. Those in which a coating layer containing a rust-preventive pigment was not coated between the undercoating layer and the colored coating layer (Examples 6 and 7), and those in which the undercoating layer did not contain silica (Examples 11, 15, 17, 25) is slightly inferior in corrosion resistance, but this is also practically no problem.

In the comparative examples, when the tannic acid content of the undercoat layer was too small (Comparative Examples 1 and 2) and when the amount of the undercoat layer was too small (Comparative Examples 5 and 6), the corrosion resistance was large. Poor and unsuitable. Conversely, when the tannic acid content of the undercoat layer is too large (Comparative Examples 3 and 4), the corrosion resistance is rather deteriorated. When the amount of the undercoat layer is too large (Comparative Examples 7 and 8), the adhesion of the coating film is reduced, and the corrosion resistance is lowered, which is not suitable. Further, when the thickness of the undercoat layer (the coating layer containing the rust-preventive pigment) is too thick (Comparative Example 9,
10) is inferior in bending workability and is unsuitable. In addition, since the chromium which is environmentally toxic is used about Comparative Examples 11-13, this is also unsuitable.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

According to the present invention, it has become possible to provide a precoated metal sheet which is excellent in the adhesion of the coating film, the workability of the coating film, and the corrosion resistance without using environmentally toxic chromium. Therefore, it can be said that the present invention is an invention having extremely high industrial value.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiromasa Nomura 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Akira Takahashi 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Inside Kimitsu Works, Ltd. AB01A AB11C AB11E AH10B AH10D AK01B AK01C AK01D AK01E AK03 AK03J AK25 AK25J AK41 AK51 AK53 AL01 BA03 BA05 BA06 BA26 CA13B CA13C CA13D CA13E DE01C DE01E GB07 GB32 JB05J10B10 J05B10

Claims (2)

[Claims] 1. The method according to claim 1, wherein at least one side of the metal plate has
The coating layer of (2), that is, (1) 100 parts by weight of aqueous resin as solid content, tannin or tannic acid 0.2 to 5
A coating layer containing 0 parts by weight; and (2) a coating layer containing 10 to 500 parts by weight of fine silica as a solid component in the above (1) as a base treatment layer. A precoated metal sheet having a colored film layer as an upper film. 2. The precoated metal sheet according to claim 1, wherein a coating layer containing a rust-preventive pigment is provided as a lower coating between the undercoating layer and the upper coating.