JP5476318B2 - Method for producing precoated metal sheet - Google Patents

Description

  The present invention is excellent in sticking property of the protective film, and expresses good tackiness and adhesiveness during adhesion and adhesion construction with various materials applied at the time of processing and assembling, building interior and exterior materials such as panels and siding, Or it is related with the manufacturing method of the precoat metal plate suitable for uses, such as a household appliance interior / exterior material.

  The pre-coated metal plate, which has various coatings formed on the surface of the metal plate via chemical conversion treatment and undercoat coating, has many advantages such as stability of quality and rationalization by omitting the painting process at the customer, Widely used in building materials, home appliances, kitchens and other fields. In particular, a pre-coated steel sheet in which a baked coating film is formed on the surface of a steel sheet plated with zinc or an alloy of zinc and aluminum (hereinafter referred to as a zinc-based plated steel sheet) through a chemical conversion treatment and an undercoat film is used for a roof. , Shutters, outer walls, various exterior panels, housings for home appliances and office equipment, furniture, etc. are already widely used.

  However, these precoated metal plates cannot be welded together like ordinary unpainted metal plates because the coating film formed on the surface is an insulator. Therefore, as a method for joining the pre-coated metal plate, a method in which the coating film is partially removed and welding is performed, followed by repair coating, or a method by mechanical joining such as caulking or rivet is conventionally employed. The problem is that the method is expensive. Such a problem is solved by a method of bonding the precoated metal plates or the precoated metal plate and other various materials by adhesive bonding. In this method, since adhesive bonding is performed using an adhesive, mechanical processing such as removal of a coating film and caulking is not required, which is extremely advantageous in terms of cost. Under the background as described above, a precoated metal sheet having better tackiness and adhesion is desired today.

  Further, when processing such as press molding is performed on the pre-coated metal plate, a protective film may be attached to the surface of the top coat film of the pre-coated metal plate for the purpose of preventing damage during processing. Or, when manufacturing a pre-coated metal plate, a protective film may be attached to the surface of the top coat film in the process before winding the coil to make the final product, thereby preventing damage that may be a concern during product transportation and storage. . At that time, if the pre-coated metal sheet is insufficient in tackiness and adhesiveness, wrinkles due to peeling of the protective film or partial lifting will occur. Therefore, the precoat metal plate which has more favorable adhesiveness and adhesiveness from a viewpoint of the sticking property of a protective film is desired.

  As a pre-coated steel sheet suitable for adhesive bonding, Patent Document 1 discloses that a polymer polyester resin having a branched structure is used as a top coat film to increase functional groups such as hydroxyl groups and carboxyl groups, and the adhesiveness of the resin itself. Techniques that improve the above have been proposed. Patent Document 2 proposes a technique of blending an adhesive pigment such as chitin or chitosan into the top coat film. Further, Patent Document 3 proposes a technique of blending urea-based resin beads for imparting adhesiveness into the top coat film.

Japanese Patent Laid-Open No. 58-120684 JP-A-8-267660 JP-A-10-128905

  However, the technique of Patent Document 1 has a problem that not only the tackiness and adhesiveness of the pre-coated steel sheet are insufficient, but also the application is limited because the resin to be used is limited. Moreover, although the technique of patent document 2 has the versatility applicable to various resin coating materials, there existed a problem of causing the fall of the storage stability as a coating material, and the stability fall of the coating finishing external appearance. Furthermore, the technique of Patent Document 3 has problems such that the appearance of the coating is limited to matte and the effect of improving the adhesiveness of the protective film is small.

  The object of the present invention is to advantageously solve the above-mentioned problems of the prior art, can be applied to various applications, can be applied to various resin coatings, and has excellent adhesiveness and adhesiveness that can be stably produced. It is providing the manufacturing method of a precoat metal plate.

  In order to solve the above-mentioned problems, the present inventors have intensively studied various factors affecting the tackiness and adhesiveness of a precoated metal sheet. As a result, it has been found that the adhesiveness and adhesiveness of the precoated metal sheet are dramatically improved by setting the water contact angle at the initial stage of the coating film formed on the outermost layer of the precoated metal sheet to 65 ° or less. Here, the “water contact angle at the initial stage of the coating film formed on the outermost layer” means the value of the water contact angle before the precoated metal plate is formed or processed, or the guard film ( When a protective film is attached, it means a value of a water contact angle in a state before a guard film (protective film) is attached. Further, the inventors further studied a means for setting the water contact angle at the initial stage of the top coat film to 65 ° or less in the precoat metal plate having the top coat film as the outermost layer. As a result, it was found that a top coating film having a water contact angle as described above can be obtained by forming a top coating film having a predetermined composition and applying a predetermined treatment to the top coating film. It came to complete.

That is, the gist of the present invention is as follows.
[1] In a method for producing a pre-coated metal sheet in which a chemical conversion film, an undercoat film, and an overcoat film are sequentially formed on at least one surface of a metal plate, an organosilicate and / or the organosilicate is formed on the surface of the undercoat film. After forming the top coat film by applying a top coat containing the condensate and baking, the surface of the top coat is contacted with water or steam at 80 ° C. or higher for 1 second to 30 seconds. The method for producing a pre-coated metal sheet is characterized in that the contact angle of water on the surface of the top coat film is set to 65 ° or less.

[2] In the above [1], the amount of the organosilicate and / or the condensate of the organosilicate contained in the top coat film is 1% by mass or more and 20% by mass or less in terms of solid content. A method for producing a precoated metal sheet.

[3] The method for producing a precoated metal sheet according to [1] or [2], wherein the top coat film contains a melamine curable polyester resin or a vinylidene fluoride-acrylic fluorine resin as a main component. .

[4] In any one of [1] to [3], after bringing the surface of the top coat film into contact with water or steam at 80 ° C. or higher for 1 second or more and 30 seconds or less , winding the metal plate A method for producing a precoated metal sheet.

  According to the production method of the present invention, it is possible to provide a pre-coated metal plate that can be attached to a protective film without causing peeling or wrinkles in a pre-process of molding or in a continuous coating line. In addition, according to the manufacturing method of the present invention, it is possible to provide a pre-coated metal plate capable of firmly adhering a sealing agent to be applied for various adhesive joining at the time of assembly at a consumer, water stoppage at a construction site, and the like. Can do. Furthermore, according to the production method of the present invention, the precoated metal plate excellent in adhesiveness and adhesion as described above can be produced industrially stably, and there is a remarkable industrial effect.

The details of the present invention and the reasons for limitation will be described below.
The method for producing a precoated metal sheet of the present invention is a method for producing a precoated metal sheet in which a chemical conversion treatment film, an undercoat film, and an overcoat film are sequentially formed on at least one surface of a metal plate. After applying the topcoat containing an organosilicate and / or a condensate of the organosilicate and baking it, the surface of the topcoat is formed with water or water vapor of 80 ° C. or higher. The contact angle of water on the surface of the top coat film is set to 65 ° or less by contacting for at least 2 seconds.

  As the base metal plate, in addition to various steel plates such as cold-rolled steel plates, galvanized steel plates, zinc-based steel plates such as zinc-5% aluminum alloy-plated steel plates and 55% aluminum-zinc alloy-plated steel plates, aluminum-plated steel plates, Any conventionally known metal plate used for the original plate of the coated plate such as various stainless steel plates or aluminum plates can be applied. Among these, a zinc-based plated steel sheet having a good balance of workability, corrosion resistance, paintability, and other performances is particularly preferable.

The chemical conversion treatment film formed on the surface of the metal plate is effective for improving the adhesion between the metal surface of the metal plate as the base and the undercoat film formed on the upper surface, and improving the corrosion resistance of the pre-coated metal plate. Act on.
In addition, the undercoat film formed on the upper layer of the chemical conversion coating film provides adhesion between the base metal plate (with chemical conversion coating film) and the upper coating film, and corrosion resistance of the precoated metal plate. Formed.
In the present invention, the types of the chemical conversion coating and the undercoat coating are not particularly limited, and any of them can be formed by a conventionally known method.

Next, the outermost coating film formed on the undercoat coating film, that is, the top coating film will be described.
The top coat film is formed for the purpose of obtaining various color appearances and protecting the layers below the undercoat film.
And this invention makes it essential to form a top coat film using the coating material containing the organosilicate and / or the condensate of this organosilicate.

In the present invention, the initial surface of the top coat film formed on the outermost layer as described above needs to be in a hydrophilic state with a water contact angle of 65 ° or less. When the water contact angle is larger than 65 °, the tackiness and adhesiveness of the precoated metal plate, that is, the tackiness and adhesiveness with a protective film, various adhesives, or a sealing agent cannot be sufficiently ensured.
Therefore, in the present invention, a top coat film is formed using a paint containing the organosilicate represented by the general formula (1) and / or a condensate thereof, and further a predetermined treatment described later is applied to the top coat film, The water contact angle of the initial surface of the top coat film is 65 ° or less.

[Chemical 1]
R ¹ _a -Si- (OR ² ) _4-a (1)

In the general formula (1), R ¹ and R ² are alkyl groups or aryl groups, and a is 0 or 1.
Preferred examples of the organosilicate represented by the general formula (1) include tetraalkoxysilanes such as tetrahydroxysilane, tetramethoxysilane, and tetraethoxysilane, dimethoxydiethoxysilane, methyltriethoxysilane, and phenyltriethoxysilane. These can be used, and one or more of these can be used.

  An organosilicate condensate (including a partial condensate) is obtained by adding water and a catalyst to the organosilicate and hydrolyzing it to condense. Commercially available products of organosilicate condensates include “Methyl silicate 51”, “Ethyl silicate 40”, “Ethyl silicate 48” (manufactured by Colcoat Co., Ltd.), “MKC silicate MS51”, “MKC silicate ES40” (hereafter Mitsubishi). Chemical Co., Ltd.) can be used, and one or more of these can be used.

  The organosilicate and / or its condensate may be used as a chelate derivative such as ethanolamine or β-diketone. In addition to organosilicates and / or condensates thereof, dehydrating agents such as trialkyl orthoformate and trialkyl orthoacetate are added to paints for top coats to ensure stable storage as paints for pre-coated metal sheets. It is also possible to increase the nature.

  By using the coating composition for the top coat film as described above, an overcoat film containing an organosilicate and / or a condensate of the organosilicate is formed. The organosilicate and / or the above-mentioned organosilicate contained in the top coat film The blending amount (content) of the organosilicate condensate is preferably 1% by mass or more and 20% by mass or less in terms of solid content with respect to the total mass of the top coat film. Further, it is more preferably 1% by mass or more and 15% by mass or less. When the blending amount (content) is less than 1% by mass, it is difficult to make the water contact angle of the initial surface of the top coat film 65 ° or less. On the other hand, when the blending amount (content) exceeds 20% by mass, the performance of the top coat film itself, particularly weather resistance and corrosion resistance, may be deteriorated.

In the present invention, the components other than the organosilicate and / or the condensate thereof are not particularly limited among the components constituting the top coat film, but in order to obtain a stable quality that can be applied to various molding and processing. Those having an organic resin as a main component and capable of forming a film on a continuous coating line are preferable.
Specific examples of the organic resin suitable for the main component of the top coat film include polyester resins, acrylic resins, and fluorine resins that are widely used as pre-coated metal plates. You may use individually or in combination of multiple types. Moreover, when using polyester-type resin and acrylic resin as a main component of top coat film, it is comprised with the main ingredient resin and the hardening | curing agent which bridge | crosslinks it.
In addition, a main component means 50 mass% or more in a coating film.

That is, a polyester resin suitable as an organic resin that is a main component of the top coat film is composed of a polyester resin that is a main resin and a curing agent that crosslinks the polyester resin.
As a polyester resin suitable for the main resin of the top coat film, for example, a number average molecular weight of 1000 to 30000, preferably 3000 to 20000 is desirable. If the number average molecular weight is less than 1000, the elongation of the coating film becomes low, sufficient workability cannot be obtained, and the desired coating film performance may not be obtained. On the other hand, if the number average molecular weight exceeds 30000, the resin has a high viscosity, so that an excessive dilution solvent is required, and the ratio of the resin in the paint is reduced, so that an appropriate coating film may not be obtained. In addition, the said number average molecular weight and the number average molecular weight mentioned later are polystyrene conversion molecular weights measured by gel permeation chromatography.

  The polyester resin is a polymer obtained by heating and reacting a polybasic acid component and a polyhydric alcohol by a known method. Examples of the polybasic acid component include phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, trimellitic anhydride, maleic acid, adipic acid, fumaric acid, etc. They can be used in combination. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, Glycerin, pentaerythritol, trimethylolpropane, trimethylolethane and the like can be used alone or in combination of two or more.

An acrylic resin suitable as an organic resin as a main component of the top coat film is composed of an acrylic resin as a main resin and a curing agent that crosslinks the acrylic resin.
An acrylic resin suitable as the main resin for the top coat film is a copolymer obtained by heating and reacting an acrylic monomer or methacrylic monomer having a hydroxyl group with an acrylic ester or methacrylic ester by a known method. It is. As the acrylic monomer or methacrylic monomer having a hydroxyl group, for example, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, or the like can be used. These may be used alone or in combination of two or more. Examples of the acrylic ester or methacrylic ester described above include, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, -n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, Isopropyl methacrylate, methacrylic acid-n-butyl, methacrylic acid-2-ethylhexyl, and the like can be used, and these may be used alone or in combination.

  The acrylic resin is preferably a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of 1500 to 20000. The number average molecular weight is more preferably 1700-15000. The hydroxyl groups in the molecule of the acrylic resin are randomly arranged in the acrylic resin main chain. When the number average molecular weight is less than 1500, the workability of the top coat tends to be remarkably lowered. On the other hand, if the number average molecular weight exceeds 20000, the coating film for the top coating film becomes highly viscous, so an excessive dilution solvent is required at the time of coating, and the proportion of the resin in the coating material decreases, so an appropriate coating film can be obtained. There is a risk that it will not be obtained. Furthermore, there is a concern that the compatibility with other compounding components is significantly reduced.

An amino resin can be used as a curing agent for crosslinking the polyester resin and / or acrylic resin, which is the main resin of the top coat film.
As the amino resin used as the curing agent for the top coat film, resins obtained by reaction of urea, benzoguanamine, melamine and the like with formaldehyde, and those obtained by alkyl etherification with alcohols such as methanol and butanol can be used. Specific examples include methylated urea resins, n-butylated benzoguanamine resins, methylated melamine resins, n-butylated melamine resins, iso-butylated melamine resins, and the like. You may use combining a seed.

  The blending ratio (mass ratio of solid content) of the main resin of the top coat film and the amino resin that is the curing agent of the main resin is [amino resin] / [main resin] = 5/95 to 35/65. It is preferably 10/90 to 25/75. When the blending ratio is less than 5/95, the blending amount of the amino acid resin is decreased and the coating film hardness is insufficient. On the other hand, when the blending ratio exceeds 35/65, the blending amount of the amino acid resin becomes excessive, the coating film hardness becomes too high, and the processability becomes insufficient.

  As a fluorine-based resin suitable as an organic resin as a main component of the top coat film, a so-called vinylidene fluoride-acrylic fluorine resin composed of a blend of a (poly) vinylidene fluoride resin and an acrylic resin is preferable. Mixing polyvinylidene fluoride resin and acrylic resin improves the durability and workability of the top coat by suppressing the crystallization of the polyvinylidene fluoride resin, which is a crystalline resin. It is for improving adhesiveness with a coating film. The vinylidene fluoride-acrylic fluororesin is preferably an organosol baking type fluororesin in which the polyvinylidene fluoride resin and the acrylic resin are in a mass ratio of polyvinylidene fluoride resin: acrylic resin = 85: 15 to 50:50.

  As the acrylic resin used in the vinylidene fluoride-acrylic fluororesin, thermoplastic and thermosetting resins can be used alone or in combination. As the thermoplastic acrylic resin, from the viewpoint of compatibility with polyvinylidene fluoride, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, (meth) A polymer of one or more monomers such as amyl acrylate, or a copolymer of these monomers with acrylic acid or styrene can be used.

  The thermosetting acrylic resin is composed of an acrylic resin having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, a glycidyl group or an isocyanate group and a curing agent such as an alkylated melamine, a polyol or a polyamide. Can be used.

  When the ratio of polyvinylidene fluoride resin contained in the above-mentioned vinylidene fluoride-acrylic fluororesin (mass ratio of solid content) exceeds 85%, the coating property as a pre-coated metal plate is reduced, and the crystallinity of the top coat film is reduced. Since it becomes too high and there is a concern about deterioration of workability, it is not preferable. On the other hand, if the ratio is less than 50%, the durability, particularly weather resistance, of the polyvinylidene fluoride may be significantly reduced, which is not preferable. Therefore, the ratio is preferably 50 to 85%. Moreover, it is more preferable to set it as 70 to 85%.

  The top coat film is composed of the above-described organosilicate and / or the condensate of the organosilicate, the organic resin as the main component, titanium oxide, petal, mica, carbon black and other various types according to the purpose and application. Colored pigments, metallic pigments such as aluminum powder and mica, extender pigments consisting of carbonates and sulfates, etc., fine particles such as silica fine particles, nylon resin beads, acrylic resin beads, p-toluenesulfonic acid, tin octoate, dibutyl An appropriate amount of a curing catalyst such as tin dilaurate, wax and other additives can be blended.

  The thickness of the top coat film is preferably 5 to 30 μm. If the thickness of the top coat film is less than 5 μm, it is difficult to stabilize the color appearance. On the other hand, if the thickness of the top coat film exceeds 30 μm, the processability of the top coat film may be reduced, which is not preferable.

  The coating material for the top coat film is prepared by diluting the above-described organosilicate and / or a condensate of the organosilicate, an organic resin as a main component, or a pigment with an organic solvent in which each resin can be dissolved and decomposed. Can be obtained.

  And the top coat film in the present invention is formed by continuously applying the paint for the top coat film to the surface of the undercoat film using a conventionally known equipment such as roll coater coating, curtain flow coating, etc., and then baking it. The In the above, it is preferable to use a hot air heating, infrared heating, induction heating, or the like as the baking means, and the coating film is baked at an ultimate plate temperature of about 180 to 250 ° C.

The top coat film formed as described above is usually baked and cured and then wound into a coiled state, but as it is, the initial water contact angle of the surface exceeds 65 °. Therefore, in the present invention, before winding the precoated metal plate on which the top coat film is formed in a coiled state, the surface of the top coat film after baking with water or steam at 80 ° C. or higher is contacted for 1 second to 30 seconds . Apply processing. By this treatment, the initial water contact angle on the surface of the top coat film can be made 65 ° or less, and the tackiness and adhesiveness of the pre-coated metal plate are dramatically improved. When a protective film is applied before winding the coil to form a precoated metal plate with a protective film, the above treatment is applied before the protective film is applied, and the initial water contact angle on the surface of the top coat film is set to 65. Keep the temperature below.

  In addition, as a method of making the surface of the coating film to be the outermost layer 65 ° or less at the initial water contact angle, a method of forming an inorganic hydrophilic coating on the surface of the coating film to be the outermost layer, or the outermost layer There is a method of treating the surface of the coating with corona discharge. However, in these methods, there are problems that characteristics other than the tackiness and adhesiveness of the precoated metal plate are deteriorated, and that the versatility is poor.

  When performing the above treatment, if the water to be brought into contact with the surface of the top coat is less than 80 ° C., the effect of lowering the water contact angle is small, and the initial water contact angle on the surface of the top coat is reduced to 65 ° or less. It becomes difficult. Further, if the water to be brought into contact with the surface of the top coat film is less than 80 ° C., the contacted water may remain on the surface of the top coat film, which is not preferable. Therefore, the temperature of water or water vapor brought into contact with the surface of the top coat film is set to 80 ° C. or higher. Preferably it is 90 degreeC or more. On the other hand, if the temperature of water or water vapor contacted with the surface of the top coat film becomes excessively high, there is a concern about the problem of thermal deterioration of the paint film, so the temperature of water or water vapor contacted with the surface of the top coat film is 250 ° C. It is preferable to set it as below, and it is more preferable to set it as 200 degrees C or less.

  Also, when performing the above treatment, if the time for contacting water or water vapor to the surface of the top coat film is less than 1 second, the effect of lowering the water contact angle is small, and the initial water contact angle on the surface of the top coat film is reduced. It becomes difficult to reduce to 65 ° or less. Therefore, the time for bringing water or water vapor into contact with the surface of the top coat film is 1 second or longer. On the other hand, if the time for which water or water vapor is brought into contact with the surface of the top coat film is excessively long, there is a concern that the treatment cannot be performed in the continuous coating line unless the treatment equipment is lengthened. The time for contacting water or water vapor is preferably 30 seconds or less, and more preferably 10 seconds or less.

In the present invention, the surface of the top coat film is brought into contact with the surface of the top coat film containing the organosilicate and / or the condensate of the organosilicate at 80 ° C. or higher for 1 second or longer, thereby bringing the initial surface of the top coat film into contact. The reason why the water contact angle decreases to 65 ° or less is not clear, but is estimated as follows.
When the surface of the top coating film containing the organosilicate and / or the condensate of the organosilicate is brought into contact with water or steam at 80 ° C. or higher for 1 second or longer, the alkoxy contained in the organosilicate and / or the condensate of the organosilicate The group is hydrolyzed to a hydroxyl group. And it is estimated by the hydroxyl group generated in this way that the fresh water on the surface of the top coating film is dramatically improved and the effect of reducing the water contact angle is obtained.

The precoated metal sheet of the present invention is produced by providing means (spray, shower, dip tank, etc.) for bringing water or water vapor into contact with the surface of the top coat film in a so-called continuous coating line for producing a normal precoated metal sheet. be able to. That is, when forming a coating film for chemical conversion treatment, undercoating, and overcoating, the coating composition is applied by a method such as roll coater coating or curtain flow coating, and then heating means such as hot air heating, infrared heating, induction heating, etc. Each of the coating layers is baked and dried. After that, contact with the surface of the top coat after baking water or steam at 80 ° C or higher by spraying, showering or dipping, etc. for 1 second or more and 30 seconds or less , and then apply a protective film if necessary. It is manufactured by winding in a coil shape.

As described above, in the present invention, when producing a pre-coated metal sheet, 80 ° C. or more of water or water vapor is applied for 1 second to 30 seconds on the surface of the top coat film containing the organosilicate and / or the condensate of the organosilicate. Contact below . As a result, the initial water contact angle on the surface of the top coat film, which is the outermost layer, is reduced to 65 ° or less, and the tackiness and adhesiveness of the precoated metal sheet are dramatically improved. Therefore, by using pre-coated metal plates manufactured according to the present invention when joining pre-coated metal plates or between pre-coated metal plates and other various materials using various adhesives and sealants in assembly and on-site construction. Good adhesion can be obtained.

  Moreover, since the precoat metal plate manufactured according to this invention is excellent in adhesiveness and adhesiveness, a protective film sticking property is very favorable. Therefore, when manufacturing a pre-coated metal plate with a protective film, or when a customer affixes a protective film to a pre-coated metal plate before processing, a good film can be obtained by using the pre-coated metal plate manufactured according to the present invention. Adhesion can be obtained.

Furthermore, according to the method of the present invention, as shown in the following examples, the tackiness and adhesiveness can be improved without causing deterioration of other properties (bending workability) of the precoated metal sheet. Further, in the present invention, the top coating film contains an organosilicate and / or a condensate of the organosilicate, and the surface of the top coating film is contacted with water or steam at 80 ° C. or higher for 1 second to 30 seconds. Thus, the initial water contact angle on the surface of the top coat film that is the outermost layer can be made 65 ° or less. Therefore, it can be applied to a pre-coated metal plate made of various coating films and has high versatility.

  As described above, the type of the chemical conversion coating in the present invention is not particularly limited. For example, a chemical conversion coating formed by performing a chromate treatment or a phosphate treatment, a chemical conversion coating mainly composed of silica, an organic Conventionally known chemical conversion treatment films such as resin films can be used.

Further, as described above, the type of the undercoat coating film in the present invention is not particularly limited, but it is preferable that the main component is an organic resin composed of a main resin and a curing agent that crosslinks the main resin.
The types of the main resin and the curing agent are not particularly limited, but it is preferable to use an epoxy resin and / or a polyester resin as the main resin and to cure the main resin with an amino resin or a polyisocyanate compound.

  Examples of the epoxy resin suitable for the base resin of the undercoat film include, for example, epoxy compounds composed of bisphenols such as bisphenol A, bisphenol F, and bisphenol AD and epihalohydrin or β-methyl epihalohydrin, or copolymers thereof. These may be used alone or in combination of two or more. Furthermore, monocarboxylic acid modified products or dicarboxylic acid modified products, mono, di or polyalcohol modified products (monoalcohol modified products, dialcohol modified products or polyalcohol modified products), mono or diamine modified products (monoamines) of these epoxy compounds. Modified products or diamine modified products), mono-, di- or polyphenol-modified products (monophenol-modified products, diphenol-modified products or polyphenol-modified products) can also be used as the above epoxy resins, and these can be used alone or in combination. May be used.

  The polyester resin suitable for the main resin of the undercoat coating film is a polymer obtained by subjecting a polybasic acid component and a polyhydric alcohol to a heat reaction by a known method. Examples of the polybasic acid component include phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, trimellitic anhydride, maleic acid, adipic acid, and fumaric acid. May be used alone or in combination. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and triethylene glycol. Glycerin, pentaerythritol, trimethylolpropane, trimethylolethane and the like can be used, and these may be used alone or in combination of two or more.

  When the number average molecular weight of the polyester resin is less than 1000, the elongation of the undercoat coating film becomes low and sufficient workability cannot be obtained, and a desirable coating film performance cannot be obtained. On the other hand, if the number average molecular weight exceeds 30000, the resin becomes highly viscous, so that an excessive dilution solvent is required at the time of coating, and the ratio of the resin occupying in the paint is lowered, making it impossible to obtain an appropriate coating film. Therefore, the number average molecular weight of the polyester resin is preferably 1000 to 30000, and more preferably 3000 to 20000.

An amino resin and / or a polyisocyanate compound can be used as a curing agent for crosslinking the main resin of the undercoat film, for example, the epoxy resin and / or the polyester resin.
As the amino resin used as the curing agent for the undercoat coating film, resins obtained by reaction of urea, benzoguanamine, melamine and the like with formaldehyde, and those obtained by alkyl etherification with alcohols such as methanol and butanol can be used. Specific examples include methylated urea resins, n-butylated benzoguanamine resins, methylated melamine resins, n-butylated melamine resins, iso-butylated melamine resins, and the like. You may use combining a seed.

  As the polyisocyanate compound used for the curing agent for the undercoat film, hexamethylene diisocyanate and derivatives thereof obtained by a general production method, tolylene diisocyanate and derivatives thereof, 4,4′-diphenylmethane diisocyanate and compounds thereof, xylylene diisocyanate and Compounds such as derivatives thereof, isophorone diisocyanate and derivatives thereof, trimethylhexamethylene diisocyanate and derivatives thereof, hydrogenated tolylene diisocyanate and derivatives thereof, hydrogenated 4,4'-diphenylmethane diisocyanate and derivatives thereof, hydrogenated xylylene diisocyanate and derivatives thereof These may be used alone or in combination of two or more. Particularly preferred are polyisocyanate compounds that can be used as one-component paints, for example, polyisocyanate compounds blocked with a blocking agent such as phenol, cresol, aromatic secondary amine, tertiary alcohol, lactam, oxime and the like. . By using this blocked polyisocyanate compound, it is possible to store the paint used for forming the undercoat film as a single solution, and it is easy to use it as a paint for a pre-coated metal sheet.

  The compounding ratio (mass ratio of solid content) of the curing agent contained in the undercoat coating film is a ratio in the resin solid content, and is 9 to 50% by mass (in terms of solid content with respect to the total mass of the undercoating film). It is preferable. When the blending ratio (mass ratio of solid content) is less than 9% by mass, the coating film hardness tends to be insufficient, and when it exceeds 50% by mass, the processability of the coating film may be deteriorated.

  In addition to the organic resin (an organic resin composed of a main resin and a curing agent that crosslinks the main resin), the undercoat coating film may be p-toluenesulfonic acid, depending on the purpose and application, A curing catalyst such as tin octoate and dibutyltin dilaurate can be contained. It can also contain extender pigments such as calcium carbonate, kaolin and clay, and colored pigments such as titanium oxide, dials, mica, carbon black, and aluminum powder. Rust preventive pigments such as pigments, phosphate pigments and phosphite pigments can also be contained. Furthermore, you may contain various additives, such as an antifoamer and a leveling agent.

  The thickness of the undercoat coating film is preferably 2 to 20 μm, and more preferably 2 to 10 μm. When the thickness of the undercoat coating film is less than 2 μm, there is a possibility that sufficient rust prevention properties cannot be obtained. On the other hand, if the thickness of the undercoat coating film exceeds 20 μm, the workability and scratch resistance of the finally obtained precoated metal sheet may be lowered, and the production cost will increase, which is not preferable.

  The undercoating film is formed by continuously applying to the surface of the chemical conversion coating film using a conventionally known equipment, and then baking, like the above-described top coating film.

The present invention will be further described based on examples.
A galvanized steel sheet with a thickness of 0.35mm (plating adhesion amount: Z18 specified in JIS G3302 (2010)) is used as a base plate, and a coating type chromate conversion solution is applied to this base plate using a roll coater in terms of metallic chromium (drying). after the state) was applied so as to 40 mg / m ^2, to form a chemical conversion coating was dried at peak metal temperature of 80 ° C. using a hot-air drying furnace. Next, a melamine curable polyester resin paint (made by Nippon Fine Coatings Co., Ltd., trade name: PX primer) was applied as an undercoat paint by a roll coater so that the film thickness after baking was 5 μm, and was kept at 220 ° C. for 35 seconds Baking and forming an undercoat film. Further, various top coat compositions shown in Table 1 are applied to the upper layer of the undercoat film by a roll coater, and baked at a temperature shown in Table 1 for 40 seconds to form a top coat film having a dry film thickness shown in Table 1. After cooling, water or water vapor was brought into contact with the surface of the top coating film under the conditions shown in Table 1 and wound into a coil to obtain various precoated metal plates of the present invention and comparative examples.

  About the various precoat metal plates obtained by the above, the initial water contact angle of the surface of top coat film, adhesiveness, adhesiveness, and bending workability were evaluated by the evaluation method shown below. The results are shown in Table 1 together with the production conditions for various precoated metal plates.

(1) Water contact angle An automatic contact angle meter (trade name: DM-500) manufactured by Kyowa Interface Science Co., Ltd. was used to measure the value 10 seconds after dropping pure water.

(2) Adhesive As a protective film, an acrylic adhesive coated on a polyethylene film (Mitsui Chemicals Tosero Co., Ltd., trade name: Mitsui Masking Tape, PE, T5010A) is attached with a laminator for 24 hours. The subsequent adhesion state was visually observed and evaluated according to the following criteria.
○: Protective film is adhered on the entire surface without generation of wrinkles, etc. Δ: Protective film is partially lifted or wrinkled ×: Protective film is lifted on almost the entire surface

(3) Adhesiveness Cut out two 25mm x 100mm test pieces from various pre-coated metal plates, and adhere the painted surfaces to each other with a one-component modified silicone sealant (Sunstar Giken Co., Ltd., trade name: 2550HM). And peeled after 24 hours. The peeled state was observed visually, and the area of cohesive failure of the sealing material and the area of interface peeling between the coating film and the sealing material were calculated and evaluated according to the following criteria.
○: The area of cohesive failure of the sealing material is 80% or more of the peeled surface △: The area of cohesive failure of the sealing material is 30% or more and less than 80% of the peeled surface ×: The area of cohesive failure of the sealing material is 30% of the peeled surface Less than

(4) Workability After cutting 40 mm × 150 mm test pieces from various precoated metal plates and performing 0T bending by the T bending method, the peeled state of the top coat film was visually observed and evaluated according to the following criteria.
In addition, Nichiban Co., Ltd. cello tape (trade name) was used as the tape for forced peeling of the 0T bending portion.
○: No peeling of coating film at bending part ×: Peeling of coating film at bending part occurs

  As is clear from Table 1, in Nos. 7 to 11 which are comparative examples, the initial water contact angle of the surface of the top coat film which is the outermost layer exceeds 65 °, and the tackiness or adhesiveness is insufficient. there were. On the other hand, in Invention Examples Nos. 1 to 6, the initial water contact angle on the surface of the top coat film, which is the outermost layer, was 65 ° or less, the tackiness and adhesion were good, and the workability was also good. It was.

Claims (4)

In the method for producing a precoated metal sheet in which a chemical conversion film, an undercoat film, and an overcoat film are sequentially formed on at least one surface of a metal plate, an organosilicate and / or a condensate of the organosilicate is formed on the surface of the undercoat film. After forming the top coating film by applying a baking treatment and applying a top coating composition containing water, the surface of the top coating film is contacted with water or steam at 80 ° C. or more for 1 second or more and 30 seconds or less , A method for producing a precoated metal sheet, wherein the contact angle of water on the surface of the top coat film is 65 ° or less.   2. The precoat according to claim 1, wherein the amount of the organosilicate and / or the condensate of the organosilicate contained in the top coat film is 1% by mass or more and 20% by mass or less in terms of solid content. A method for producing a metal plate.   The method for producing a precoated metal sheet according to claim 1 or 2, wherein the top coat film comprises a melamine curable polyester resin or a vinylidene fluoride-acrylic fluorine resin as a main component. 4. The metal plate is wound up after contacting the surface of the top coat film with water or water vapor at 80 ° C. or higher for 1 second or more and 30 seconds or less . 5. A method for producing a precoated metal sheet.