JP4460441B2 - Painted metal plate - Google Patents

Description

  The present invention relates to a non-chromium-based painted metal plate that does not substantially contain chromium, which is considered toxic to living organisms. More specifically, the present invention relates to a coated metal plate that is excellent not only in corrosion resistance but also in so-called “enamel hair resistance”.

  In either case of a so-called post-coated metal plate or a pre-coated metal plate, a chromate film is usually provided for the purpose of providing sufficient corrosion resistance to these metal plates. However, since this chromate film contains harmful hexavalent chromium, in recent years, many attempts have been made to reduce the amount of hexavalent chromium in the chromate film in consideration of the environment.

  Although the above attempts to reduce the amount of hexavalent chromium have achieved a certain degree of results, the problem cannot be completely solved as long as the chromate film is used. Therefore, recently, an attempt has been made to exert a corrosion resistance improving effect equivalent to or higher than that of a chromate film by using a non-chromium film that does not contain chromium itself.

  Japanese Patent Application Laid-Open No. 53-9238 discloses a treatment technique using an aqueous solution containing thiourea and tannin or tannic acid as a non-chromium-based rust prevention treatment method instead of chromate treatment. When a pre-coated metal plate is produced using the above, there is a problem that the coating film adhesion at the processed part is greatly inferior when applied to household appliances, automobiles, etc., which have strict processing shapes. JP-A-59-116381 (Patent Document 1) discloses a technique for improving white rust resistance and paint adhesion by surface treatment with an aqueous solution containing tannic acid and a silane coupling agent. Has been.

  When using the above-mentioned conventional non-chromium-based rust-proofing treatment, separate coating and seizing operations (two coats and two bakes) for the first layer and the second layer are necessary to ensure sufficient corrosion resistance and top coatability. ) Is necessary, and as a result, “3 coats and 3 bake” is required, and the work process is very complicated. That is, “coating + heat drying after application” is required for any of the three types of layer formation of the non-chromic base coating, the non-chromic primer, and the top coating.

  Furthermore, in the case of such a three-layer structure, it is practically essential to contain an inhibitor in the underlayer. However, when such an inhibitor is contained in the underlayer, a painted metal plate is used. When cut, there is a problem that the beard-like spread of the resin (that is, so-called “enamel hair”) frequently occurs in the vicinity of the cut surface, particularly when the mold is bad. In other words, the non-chromium coated metal plate has a serious problem that enamel hair is unavoidably generated in order to improve the corrosion resistance.

JP 59-116381 A

  An object of the present invention is to provide a painted metal plate which has solved the above-mentioned drawbacks of the prior art.

  Another object of the present invention is to provide a coated metal plate having sufficient corrosion resistance and capable of suppressing the generation of enamel hair.

  As a result of diligent research, the present inventor is extremely effective for achieving the above-mentioned purpose to set the surface roughness (Ra) of the interface between the primer layer constituting the coated metal plate and the top layer to a specific range. I found out.

  The coated metal plate of the present invention is based on the above knowledge, and more specifically, the metal plate, the non-chromium base coating film disposed on the metal plate, and the non-chrome coating disposed on the base coating film. A coated metal plate comprising at least a primer layer and an upper coating film disposed on the primer layer; the Tg of the primer layer is 30 ° C. or lower, and the Tg of the upper coating film is 40 ° C. or higher. In addition, the surface roughness Ra of the interface between the primer and the upper layer coating film is 0.25 μm or more.

  According to the knowledge of the present inventor, in the coated metal plate of the present invention having the above-described configuration, the specific hardness of each of the above-described upper coating film and the primer layer and the specific interface Ra between the upper coating film and the primer layer Based on the combination, stress distribution between the upper coating film and the primer layer can be achieved even at the time of cutting. Therefore, it is presumed that the stress concentration on the primer layer is relaxed and the generation of enamel hair is suppressed. According to the knowledge of the present inventor, due to moderate unevenness of the interface, the hardness (and / or composition) in the vicinity of the interface changes in a gradient or continuously, so that the stress concentration described above is relaxed during processing. Presumed.

  On the other hand, in the case of the conventional non-chromic base paint, according to the knowledge of the present inventor, between the upper paint and the primer, the specific hardness of each of the upper paint film and the primer layer and the upper paint Due to the combination of small Ra between the film and the primer layer, it is presumed that enamel hair was generated due to concentration of stress on the primer layer based on the stress between the upper layer paint and the primer during cutting. .

  As described above, according to the present invention, it is possible to obtain a non-chromium coated metal plate in which enamel hair generation is suppressed even during processing.

  Furthermore, according to the present invention, even when a non-chromic primer (generally low adhesion) containing a large amount of anticorrosive pigment is used, the adhesion between the primer and the upper coating film is improved and good. Processability can be obtained.

Hereinafter, the present invention will be described more specifically with reference to the drawings as necessary.
(Painted metal plate)
The coated metal plate of the present invention includes a metal plate, a base coating film disposed on the metal plate, a primer layer disposed on the base coating film, and an upper coating film disposed on the primer layer. Is a painted metal plate containing at least The coated metal plate of the present invention may be a so-called post-coated product or a pre-coated metal plate. From the viewpoint of environmental protection, a precoated metal plate is preferable.

  In the present invention, the Tg of the primer layer is 30 ° C. or lower, the Tg of the upper coating film is 40 ° C. or higher, and the surface roughness Ra of the interface between the primer and the upper coating film is 0.25 μm or higher. It is a feature. This Ra is further preferably 0.3 to 0.7 μm (in the present invention, Ra can be measured by the same method for the interface between layers other than this interface). According to the experiment of the present inventor, Ra of 0.7 μm is obtained as the maximum value.

  In order to ensure better corrosion resistance using a non-chromate primer containing a non-chromate rust preventive pigment, it is preferable to add a large amount of a rust preventive pigment to the primer. For example, in the case of calcium silicate which is a kind of non-chromate type anticorrosive pigment, it is desirable to contain about 40% by weight of solid content.

  However, when coated with 2C2B (2 coats and 2 bake), when 40% of rust preventive pigment enters, the coating itself becomes brittle, and when a hard coating with a Tg of 40 ° C. or higher is applied to the upper layer, Enamel hair is generated. According to the knowledge of the present inventor, when coated with normal 2C2B, the Ra of the interface between the primer and the top coating is small, so the impact force concentrates on the interface during cutting, and the brittle primer breaks down. It is presumed to be caused.

  When coated with 2C2B, the enamel hair is reduced if the Tg of the upper layer coating is less than 40 ° C, but the upper layer coating with a Tg of 40 ° C or less is inferior in hardness and easily scratched. PCM) is not preferable.

  On the other hand, even if the same primer is used and a hard upper coating film having a Tg of 40 ° C. or higher is used, enamel hair is generated if Ra at the interface between the primer and the top coating film is 0.25 μm or more. It is suppressed. This is presumably because the stress concentration on the interface at the time of cutting was dispersed due to the large Ra of the interface between the primer and the top coating, and the primer was not destroyed. To obtain a large Ra value, 2C1B coating is useful.

As a result of various investigations on the conditions for suppressing enamel hair while ensuring the hardness of the upper coating film, the Tg of the primer layer was 30 ° C. or lower, the Tg of the upper coating film was 40 ° C. or higher, and It was found that Ra should be 0.25 or more.
On the other hand, when the Tg of the primer was higher than 30 ° C., it was found that 2C1B coating satisfied the condition that Ra was 0.25 μm or more, but did not lead to improvement of enamel hair.

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

  That is, the interface where the surface roughness Ra is to be measured was photographed, and a microscopic photograph (magnification: 3500 times) was obtained. The unevenness (roughness curve) of the interface was traced by a tracing device, and cut out along the unevenness. By measuring the weight of the paper, the center line average roughness Ra of this interface is determined according to a predetermined formula of JIS B 0601.

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

(Adjustment of interface Ra)
In the present invention, the method for adjusting the interface Ra is not particularly limited. The interface Ra is preferably adjusted, for example, by controlling the difference in surface tension between the upper layer and the lower layer located on both sides of the interface.

(Estimated mechanism of adjustment of interface Ra)
According to the knowledge of the present inventor, the mechanism by which the interface Ra can be adjusted by controlling the difference in surface tension between the upper layer and the lower layer is estimated as follows.
In general, in order for the upper-layer paint to spread on the lower-layer paint, it is considered necessary to establish the relationship of the following formula (1) from the balance of forces at the interface.
S = σ (lower layer) −σ (upper layer) −γ (upper layer and lower layer)> 0 (1) where S is the balance of forces at the interface, σ is the surface tension, and γ is the interfacial tension.

The above equation (1) can be transformed into the following equation (2).
σ (lower layer) −σ (upper layer) → γ (upper layer and lower layer) (2)
Therefore, it is considered that the surface tension of the upper layer does not increase unless the surface tension of the lower layer is larger than the surface tension. This force is thought to act in a direction that suppresses the force that disturbs the upper and lower interface caused by Marangoni convection to widen the interface.

(Leveler)
On the other hand, for example, the effect of adding a leveler (a kind of surfactant) as a surface conditioner as described later to the upper layer is considered to be similar to the effect of suppressing bannered cell convection in a conventional single layer. That is, it can be considered that the surface tension of the upper layer is uniformly reduced to suppress non-uniform evaporation of the solvent.

  Furthermore, as a new effect of the above-described “leveler addition to the upper layer”, the surface tension of the upper layer is uniformly reduced, thereby promoting the uniform spreading of the upper layer coating on the lower layer coating. It is thought that it works in the direction of uniformly suppressing the force to disturb the lower layer interface and widen the interface.

  Generally, there are a leveler and an antifoaming agent in the surfactant, and in particular, the antifoaming agent is used for releasing bubbles in the paint.

  In this invention, what can be used as a surface conditioner belongs to the kind called a leveler among these surfactants. Among these surfactants, those selected by performing the following determination can be used. In other words, the appropriate leveler can be determined simply by whether or not a soft skin-like repellency occurs in a wet state when a paint to which a surface conditioner is added is applied as a single layer (“Yuzu skin In the case where no “state repellency” occurs, it is determined that the “leveler” can be used).

  Levelers that can actually be used include leveler A: acrylic leveler and leveler B: silicon additive BYK141 (by BYK-Chemie). The leveler usable in the present invention is not particularly limited. That is, as long as the surface tension of each layer can be appropriately controlled for the paint to be applied and the condition that the coating appearance at the wet time in a single layer does not become a crushed skin-like repellency is optional. Can be used.

  For example, homogenol L18, homogenol L95, homogenol L1820, BYK057, BYK061, BYK052, BYE053, BYK055, BYK077, and the like as non-silicon-based levelers; BYK088 etc. are mentioned.

(Relationship between Ra and surface tension)
Regarding the relationship between the difference in surface tension between the upper layer and the upper layer and the unevenness (Ra) at the coating film interface, it is found that Ra, which is an index of the unevenness at the coating film interface, decreases as the difference in surface tension between the lower layer and the upper layer is doing. According to the knowledge of the present inventor, the difference in surface tension between the lower layer and the upper layer when the Ra of the interface is less than 0.3 μm is 5 mN / m or more when a leveler is inserted only in the upper layer. When a leveler is inserted in the upper layer and the lower layer, a difference of 3.7 mN / m or more is recognized. In the present invention, in order to achieve Ra of 0.25 μm or more at the interface between the upper layer and the lower layer, the difference in surface tension between the lower layer and the upper layer is 6 mN / m or less when a leveler is inserted only in the upper layer. When a leveler is inserted between the upper layer and the lower layer, the difference may be 4 mN / m or less.

  In addition, the surface tension in the present invention can be measured using a dynamometer (BYK-Chemie GmbH).

(Metal plate)
As long as non-chrome coating is possible, the metal plate usable in the present invention is not particularly limited. The metal plate may be subjected to a base treatment as necessary.

  Particularly effective are hot-dip galvanizing (GI, GA) and hot-dip zinc-Al-Si-Mg plating (SD). Since these plating surfaces have an oxide film, the base film and primer Has low adhesion and is likely to generate enamel hair.

(surface treatment)
In the present invention, for example, a cold-rolled steel sheet, a hot-rolled steel sheet, a hot-dip galvanized steel sheet, an electrogalvanized steel sheet, a hot-dip galvanized steel sheet, an aluminum-plated steel sheet, and an aluminum-zinc alloyed steel sheet Generally known steel plates and plated plates such as stainless steel plates can be applied. These metal plates may be used after being subjected to ordinary treatments such as washing with water and alkali degreasing before the surface treatment.

(Non-chromic base treatment)
The non-chromium base treatment usable in the present invention is not particularly limited as long as a non-chromium primer layer can be laminated on the base treatment. From the viewpoint of excellent adhesion, it is preferable that the base treatment is performed by applying a chemical solution containing tannin or tannic acid, a silane coupling agent and fine silica, and then drying.

  Many reports on tannin or tannic acid have been made so far, but their adhesion was greatly inferior to chromate treatment. However, for example, by using tannin or tannic acid in combination with a silane coupling agent and fine silica, the adhesion of the coating film can be synergistically improved. Moreover, also about corrosion resistance, the adhesiveness of a coating film can be improved by adding a particulate silica, for example.

(Tannin or tannic acid)
The tannin or tannic acid that can be used in the present invention is not particularly limited. That is, tannin that can be hydrolyzed or condensed tannin may be used, or a part of them may be decomposed. Tannin and tannic acid are not particularly limited, such as Hamametatannin, pentaploid tannin, gallic tannin, milobaran tannin, dibibi tannin, argaroviran tannin, valonia tannin, catechin, etc., but “tannic acid: AL” (Fuji When the chemical industry) is used, the processing adhesion of the coating film is particularly improved.

  The amount of tannin or tannic acid added is more preferably 2 to 80 g / l. If the amount of tannin or tannic acid added is less than 2 g / l, the rust prevention effect and coating film adhesion are not ensured. On the other hand, if it exceeds 80 g / l, the rust prevention effect and coating film adhesion are reduced, It does not dissolve.

(Silane coupling)
The non-chromium base treatment of the present invention may contain silane coupling as necessary.

  Examples of the silane coupling agent that can be used in the present invention include γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, and γ- (2-aminoethyl). Aminopropyltriethoxysilane, γ- (2-aminoethyl) aminopropylmethyldiethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyl Dimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (N- Vinylbenzylaminoethyl ) -Γ-aminopropylmethyldimethoxysilane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropyltriethoxysilane, N-β- (N-vinylbenzylaminoethyl) -γ-aminopropylmethyldi Ethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-mercaptopropyltrimethoxy Silane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysila , Vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltriethoxysilane, γ-chloropropylmethyldiethoxysilane, hexamethyldisilazane, γ-anilinopropyl Trimethoxysilane, γ-anilinopropylmethyldimethoxysilane, γ-anilinopropyltriethoxysilane, γ-anilinopropylmethyldiethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyldi Ethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride, octadecyldimethyl [3- (methyldimethoxysilyl) propyl] ammonium chloride, octade Sildimethyl [3- (triethoxysilyl) propyl] ammonium chloride, octadecyldimethyl [3- (methyldiethoxysilyl) propyl] ammonium chloride, γ-chloropropylmethyldimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, methyltrichlorosilane, Examples thereof include dimethyldichlorosilane and trimethylchlorosilane.

  Among the above, when γ-glycidoxypropyltrimethoxysilane and γ-glycidoxypropyltriethoxysilane having a glycidyl ether group are used, the processing adhesion of the coating film is particularly improved. Furthermore, when a triethoxy type silane coupling agent is used, the storage stability of the base treatment material can be improved. This is thought to be because triethoxysilane is relatively stable in an aqueous solution and the polymerization rate is slow.

  From the viewpoint of coating film adhesion or corrosion resistance, the addition amount of the silane coupling agent is more preferably 2 to 80 g / l.

  In the present invention, fine silica is a general term for silica that has a fine particle size and can stably maintain a water-dispersed state when dispersed in water. Examples of the fine silica include “Snowtex N”, “Snowtex C”, “Snowtex UP”, “Snowtex PS” (all manufactured by Nissan Chemical Industries), “Adelite AT-20Q” (Asahi Denka Kogyo) Commercial silica gel, etc., or powder silica such as Aerosil # 300 (manufactured by Nippon Aerosil Co., Ltd.). The fine silica may be appropriately selected according to the required performance. When fine silica such as “Snowtex C” that can be stably dispersed even at a pH of 4 or higher can be used, the storage stability of the base treatment agent can be improved. This is considered to be because the pH of the chemical solution can be adjusted to 4 or more, so that the reaction of the silane coupling agent having high reactivity at low pH can be suppressed.

  The addition amount of the fine silica is preferably 1 to 40 g / l from the viewpoint of work adhesion and corrosion resistance.

(Additive)
When the polyester resin is further contained in the chemical solution for base treatment in a solid content of 1 to 60 g / l, the processing adhesion is further improved.

  Examples of the polyester resin include “FINETEX ES-650”, “FINETEX ES-611”, “FINETEX ES-670”, “FINETEX ES-675” (all manufactured by Dainippon Ink & Chemicals, Inc.), “Vaironal MD-1200”, “Vaironal MD-1220”, “Vaironal MD-1250”, “Vaironal MD-1100”, “Vaironal MD-1330”, “Vaironal MD-1930” (all manufactured by Toyobo), etc. Can be used.

  In the chemical | medical solution of the surface treating agent of this invention, you may add an acid, an alkali, etc. for pH adjustment within the range which does not impair performance.

(Formation of ground treatment layer)
In order to form the base treatment layer on the metal plate, for example, the above-described base treatment agent may be applied to the metal plate, and heated and dried. As heating temperature, 50-250 degreeC is good. If it is less than 50 ° C., the evaporation rate of water is slow and sufficient film forming properties cannot be obtained, so that the rust prevention power is insufficient. On the other hand, when it exceeds 250 ° C., tannic acid, which is an organic substance, or the alkyl portion of the silane coupling agent undergoes denaturation such as thermal decomposition, and adhesion and corrosion resistance are reduced. 70-160 degreeC is more preferable. In hot air drying, drying for 1 second to 5 minutes is preferable.

  The coating method for the base treatment is not particularly limited, and generally known coating methods such as roll coating, air spray, airless spray, and immersion can be employed.

From the viewpoint of work adhesion, the adhesion amount is preferably 10 to 500 mg / m ² in terms of solid content.

(Non-chromium primer layer)
The non-chromium primer layer to be disposed on the non-chromic base coating film is not particularly limited as long as it can be used in combination with the base coating film and an upper coating film described later. As a component constituting such a non-chromium primer layer, a known component that has been conventionally used as a non-chromium primer layer can be used without particular limitation.

The components of the non-chromium primer layer that can be suitably used in the present invention are listed as follows.
Resin components such as polyester, fluorine, acrylic, silicon polyester, urethane, and epoxy.

  As ready-made products, for example, they can be obtained from Nippon Paint Co., Ltd.

(Upper coating)
As long as it can be disposed on the primer layer, the configuration of the upper layer coating film is not particularly limited. As a component constituting such an upper coating film, a known component that has been conventionally used in combination with a non-chromium primer layer can be used without particular limitation.

  In the present invention, the base resin of the upper coating layer to be disposed on the primer layer may be in any form such as aqueous, solvent-based, and powder-based. Generally known resins such as polyacrylic resins, polyolefin resins, polyurethane resins, epoxy resins, polyester resins, polybutyral resins, melamine resins, etc. may be used as they are or in combination. it can.

If necessary, a color pigment may be added to the upper coating layer. Examples of the color pigment include titanium oxide (TiO ₂ ), zinc oxide (ZnO), zirconium oxide (ZrO ₂ ), calcium carbonate (CaCO ₃ ), barium sulfate (BaSO ₄ ), alumina (Al ₂ O ₃ ), kaolin clay, Generally known color pigments such as inorganic pigments such as carbon black and iron oxide (Fe ₂ O ₃ , Fe ₃ O ₄ ) and organic pigments can be used.

  Moreover, you may add a rust preventive pigment other than the above-mentioned coloring pigment as needed. Commonly known antirust pigments such as (1) phosphate anticorrosion pigments such as (1) zinc phosphate, iron phosphate and aluminum phosphate, (2) calcium molybdate, aluminum molybdate, barium molybdate, etc. And (3) vanadium rust preventive pigments such as vanadium oxide, (4) fine silica such as water-dispersible silica and fumed silica, and the like.

  The thickness of the coating layer containing the color pigment is preferably 1 to 25 μm, and if it is less than 1 μm, the corrosion resistance is poor, and if it exceeds 25 μm, the processability of the coating film is poor. However, if the upper layer coating is an organic or inorganic coating such as a lubricating coating or anti-fingerprint coating, it will be used for so-called post-coating or as a surface-treated metal plate for applications where no further coating is applied. Accordingly, the type and film thickness of the upper coating film may be appropriately selected, and the film thickness is not particularly limited to 1 to 25 μm.

(Applying method for upper layer coating)
The upper layer coating can be applied by a generally known coating method such as roll coating, curtain flow coating, air spray, airless spray, dipping, bar coating, brush coating, and the like.

(Glass transition temperature Tg)
In the present invention, it is inevitable that the primer layer has a Tg of 30 ° C. or lower and the upper coating film has a Tg of 40 ° C. or higher from the viewpoint of stain resistance, hardness and workability. Such Tg can be measured by the needle penetration method. However, when a coating film of these combinations is produced with 2C2B, enamel hair may occur.

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

(Preferable coating method)
In the present invention, for example, both the above-described primer layer and the upper layer coating was simultaneously coated with slide curtain method, Ru can be heated and dried.

  In the present invention, from the viewpoint of improving the efficiency of the manufacturing process, a multilayer coater or wet-on-wet application (that is, a method of coating the upper layer without substantially passing through the drying step after coating the lower layer) is used. It is preferable to form both the primer layer and the upper layer coating film and to bake both coating layer layers simultaneously.

(Method using multilayer coater)
In the present invention, it is useful to use a multilayer coater from the viewpoint of more effectively preventing the generation of enamel hair in the Tg film structure. As such a multilayer coater, for example, a coater or a coating method described in JP-A-6-190335 can be suitably used.

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

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

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

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

  Examples of the present invention will be given below to specifically explain the present invention.

1. Preparation of test plate 1.1 Test material, electrogalvanized steel sheet (EG)
Plate thickness 0.6mm, zinc adhesion amount 20g / m ² per side (double-sided plating)
・ Hot galvanized steel sheet (GI)
Plate thickness 0.6mm, zinc adhesion amount 60g / m ² per side (double-sided plating)
・ Cold rolled steel sheet (cold rolled)
Plate thickness 0.6mm
1.2
The pretreatment specimen was immersed in an aqueous solution having a concentration of 20 g / L and a temperature of 60 ° C. for 10 seconds using an alkaline degreasing agent CL-N364S (manufactured by Nihon Parkerizing), washed with pure water and dried. .

Comparative Example 1
1.3 Ground Treatment / Example Using a ground treatment agent having the composition shown in the table described later, the film is applied with a roll coater so as to have a predetermined film thickness, and the ultimate plate temperature is 80 ° C. in a hot air drying furnace. Dried. As the base treatment layer, a mixed treatment agent of silane coupling agent, tannic acid, and silica was used.

1.4
The following coating materials were used as the lower layer film treatment primer coating material, applied with a roll coater so as to have a predetermined film thickness, and cured and dried in an induction heating furnace in which hot air was blown so that the ultimate plate temperature was 220 ° C.

<Lower layer coating primer>
A paint mainly composed of 20% by weight of a rust preventive pigment of polyester / melamine resin and calcium silicate was used.

1.5 Upper layer coating treatment Polyester / melamine resin (manufactured by Nippon Paint Co., Ltd.) is applied as an upper layer coating layer so as to have a predetermined film thickness with a roll coater, and the ultimate plate temperature is 230 in an induction heating furnace blown with hot air. It was cured and dried to 2 ° C. (2C2B treatment).

Comparative Example 2
Using the slide coater shown in FIG. 1, a non-chromium primer layer and an upper coating film were formed using the paint shown in Table 1. A coated metal plate was obtained under the same conditions as in Comparative Example 1 except that the top coating was produced under a condition where the Tg was 35 ° C.

Comparative Example 3
Using the slide coater shown in FIG. 1, a non-chromium primer layer and an upper layer coating film were formed using the paint shown in Table 1. A coated steel sheet was obtained under the same conditions as in Comparative Examples 1 and 2 except that the Tg of the primer coating was 35 ° C.

  That is, after the same base treatment as in Comparative Example 1, a non-chromium primer layer and an upper layer coating film were formed by simultaneous application using the slide coater shown in FIG. 1, and then these layers were simultaneously baked (230 ° C. ), A non-chromium primer layer (thickness 5 μm) and an upper coating film (thickness 15 μm) were formed (2C1B treatment).

Example A lower layer coating primer layer and an upper coating layer were formed on a base treatment agent layer in the same manner as in Comparative Example 2 except that the materials shown in Table 1 were used (2C1B treatment).

Description of Examples In order to ensure corrosion resistance with a non-chromate primer, it is extremely preferable to add a large amount of an antirust pigment to the primer.

  In the case of calcium silicate, it is desirable to contain about 40% by weight of solid content. However, when 40% rust preventive pigment is contained, the coating itself becomes brittle, and when a hard coating having a Tg of 40 ° C. or higher is applied to the upper layer, enamel hair is generated (Comparative Example 1). ).

  This is because it was painted with ordinary 2C2B, and because the Ra at the primer-top interface is small, the impact force concentrates on the interface during cutting, and the brittle primer breaks down.

  If the Tg of the upper coating film is less than 40 ° C., the enamel hair is reduced (Comparative Example 2), but the upper coating film having a Tg of 40 ° C. or less is inferior in hardness and easily scratched, and is precoated steel sheet (PCM) It is not preferable. On the other hand, even when the same primer is used and a hard upper coating film having a Tg of 40 ° C. or higher is used, the generation of enamel hair is suppressed when the Ra at the Pr-top interface is 0.25 μm or more ( Example 1). This is because the stress concentration at the interface at the time of cutting was dispersed due to the large Ra, and Pr was not destroyed.

  As a result of various investigations on the conditions for suppressing enamel hair while ensuring the hardness of the upper coating film, the Tg of the primer layer was 30 ° C. or lower, the Tg of the upper coating film was 40 ° C. or higher, and Ra may be 0.25 μm or more (Example 2). Since Examples 3 to 10 in the table satisfy this condition, all show good performance.

  On the other hand, in Comparative Example 3, since the Tg of the primer is high, the condition that Ra is 0.25 μm or more is satisfied by 2C1B coating, but the enamel hair has not been improved.

<2. Evaluation>
2.1 Coating film processing adhesion test (OT taping test)
The coated plate was subjected to a 180 ° bending process, and the coating film in the processed part was observed with a 20-fold magnifier to examine whether the coating film was cracked. Moreover, the adhesive tape was affixed on the process part, and the residual state of the coating film was observed visually when this was peeled off vigorously. In this test, the tape was peeled twice. The bending process was 0T in an atmosphere at 20 ° C. The evaluation of coating film cracking is ◎ when there is no coating film cracking, ◯ when there are about 1 to 3 tiny cracks in the coating film, △ when there are tiny cracks on the entire surface of the coating film, △ When a clear large crack was observed on the entire surface of the processed part, it was evaluated as x. Moreover, the evaluation of the coating film remaining state after peeling with a tape is ◎ when the coating film remains on the plated steel sheet without peeling at all, ○ when the coating film is partially peeled off, Was evaluated as Δ when the film was partly severely peeled, and × when the peel was observed over almost the entire bent portion. Further, the coated steel sheet was processed by 0T, immersed in boiling water for 1 hour, taken out and left for 24 hours, and then the tape was peeled off. The evaluation of the coating film remaining state is ◎ when the coating film remains on the plated steel plate without peeling at all, ○ when the coating film is peeled off slightly, and the coating film is peeled off violently. The case was evaluated as Δ, and the case where peeling was observed over almost the entire bent portion was evaluated as ×.

  The degree of enamel hair generation was evaluated as follows.

  It was cut with a shear adjusted to a 1.5 mm clearant (steel plate 0.6 mt) and the occurrence of enamel hair was observed to evaluate what percentage of the cut length enamel hair was generated. . The occurrence of enamel hair was defined as 5% or less.

Scratch resistance test The pencil hardness indicating the hardness of the coating film was evaluated by the home appliance manufacturer's scratched hardness method. In the scratch hardness method, 5 lines are drawn with a pencil lead at a 45 ° angle on the coating film, and the evaluation result is displayed with pencil hardness that does not damage the coating film more than once. The evaluation test was performed at 20 ° C. using a uni-pencil manufactured by Mitsubishi Pencil Co., Ltd.

It is a model perspective view which shows an example of the slide coater which can be used conveniently in this invention.

Claims (3)

At least a metal plate, a non-chromium base coating disposed on the metal plate, a non-chromium primer layer disposed on the base coating, and an upper coating disposed on the primer layer Including a painted metal plate,
The Tg of the primer layer is 5 to 30 ° C., the Tg of the upper layer coating is 40 to 60 ° C., and the surface roughness Ra of the interface between the primer and the upper layer coating is 0.25 to 0.7 μm A painted metal plate characterized by being.   The coated metal plate according to claim 1, which is a precoated metal plate. By simultaneously applying a primer having a Tg of 30 ° C. or lower and an upper layer paint having a Tg of 40 ° C. or higher on a metal plate coated with a non-chromic base coating using a multilayer coater. ,
At least a metal plate, a non-chromium base coating disposed on the metal plate, a non-chromium primer layer disposed on the base coating, and an upper coating disposed on the primer layer A coated metal plate containing the primer layer having a Tg of 5 to 30 ° C., an upper coating film having a Tg of 40 to 60 ° C., and a surface roughness Ra of the interface between the primer and the upper coating film. A method for producing a coated metal plate, comprising obtaining a painted metal plate having a thickness of 0.25 to 0.7 μm .

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