阅读说明：本技术 涂装金属板及其制造方法 (Coated metal plate and method for producing same ) 是由 泷口庆子 佐藤正树 铃木成寿 杉田修一 于 2019-04-10 设计创作，主要内容包括：本发明的技术问题在于,提供具有耐雨痕污垢性及良好的外观的涂装金属板及其制造方法。为了解决上述技术问题,涂装金属板的制造方法具有：在金属板的表面上涂覆包含有机硅树脂和含氟树脂的涂料并使该涂料固化,以形成涂膜的工序；以及对所述涂膜进行火焰处理的工序。所述有机硅树脂包含相对于Si原子的总摩尔量为5摩尔％～50摩尔％的硅烷醇基。(The technical problem of the present invention is to provide a coated metal sheet having resistance to rain mark and dirt and good appearance, and a method for manufacturing the same. In order to solve the above-described problems, a method for manufacturing a coated metal sheet includes: a step of applying a coating material containing a silicone resin and a fluorine-containing resin on the surface of a metal plate and curing the coating material to form a coating film; and flame treating the coating film. The silicone resin includes 5 to 50 mol% of silanol groups relative to the total molar amount of Si atoms.)

1. A method for manufacturing a coated metal sheet, comprising the steps of:

a step of applying a coating material containing a silicone resin and a fluorine-containing resin on the surface of a metal plate and curing the coating material to form a coating film; and

a step of flame-treating the coating film,

the silicone resin contains 5 to 50 mol% of silanol groups relative to the total number of moles of Si atoms.

2. The coated metal sheet manufacturing method according to claim 1,

the silicone resin contains 50 to 100 mol% of Si atoms derived from trialkoxysilane relative to the total number of moles of Si atoms.

3. The method for producing a coated metal sheet according to claim 1 or 2,

the proportion of the number of moles of aryl groups directly bonded to Si atoms to the number of moles of alkyl groups directly bonded to Si atoms in the silicone resin is 20-80%.

4. A coated metal sheet having:

a metal plate; and

a fluorine-based coating film formed on the metal plate,

the coating film comprises a cured product of a silicone resin and a fluorine-containing resin,

when the surface of the coating film is analyzed by X-ray photoelectron spectroscopy using Al K.alpha.rays as an X-ray source, the ratio of Si atoms to the total amount of Si atoms, F atoms, C atoms and O atoms is defined as Si_aWhen the ratio of the amount of O atoms to the amount of C atoms is represented by x, Si is present_aAnd x respectively satisfy the following formulas:

Si_a≥8atm％

x≥0.8，

in the analysis of the X-ray photoelectron spectroscopyThe C1s peak top of the photoelectron spectrum was corrected to 285eV, and Si was added_2pWhen the energy spectrum is separated into a peak corresponding to 103.5eV and a peak corresponding to 102.7eV, the peak area of 103.5eV is compared with that of Si_2pWhen the ratio of the peak area of the entire spectrum is y, y satisfies the following formula:

y≥0.6。

5. the coated metal sheet as claimed in claim 4,

the sliding angle of diiodomethane on the surface of the coating film is 15 DEG to 50 deg.

6. The coated metal sheet according to claim 4 or 5,

the cured product of the silicone resin contains a structure derived from methyltrialkoxysilane or phenyltrialkoxysilane.

7. The coated metal sheet according to any one of claims 4 to 6,

the metal plate is a zinc-based plated steel plate.

Technical Field

The present invention relates to a coated metal sheet and a method for manufacturing the same.

Background

Coated metal sheets are often used in outdoor buildings, civil engineering structures, and the like. In addition, when long-term durability is required for a coated metal sheet, the following coated metal sheets are often used: a coated metal sheet using a fluororesin-based coating material having excellent weather resistance and mechanical properties as a coating material for a coating film disposed on the surface side thereof. In such a coated metal sheet, there is a problem that fouling occurs due to adhesion of carbon-based pollutants (hereinafter, also referred to as "hydrophobic carbon") contained in exhaust gas of automobiles, soot from factories, and the like. Among the stains, particularly, stains adhering along a raindrop (hereinafter, also referred to as "raindrop stains") are easily noticeable. Even when a coated metal sheet having a fluororesin-based coating material baked thereon is used, it is inevitable that raindrop stains become conspicuous within a relatively short period of time. Therefore, it is necessary to provide a coated metal sheet in which rain mark dirt is less likely to be generated.

In recent years, it has been proposed to prevent raindrop stains by making the contact angle of a coating film with water 60 ° or less, that is, making the coating film hydrophilic. It is considered that hydrophobic carbon is likely to float up to rainwater on the surface of a hydrophilic coating film having a low contact angle with water, and the surface of the coating film is likely to have a low contact angle with waterWhile the floating hydrophobic carbon is washed away. As one of the methods for hydrophilizing the surface of a coated metal sheet, there has been proposed a method in which a coating material contains tetraalkoxysilane or a condensate thereof (hereinafter, these are also referred to as "organosilicate") (patent documents 1 to 3). Further, a method of applying a coating material containing a vinyl group-containing silicone resin or the like to a metal plate and subjecting the coating film to corona discharge treatment has been proposed (patent document 4). Further, it has been proposed to apply a coating material containing a fluorine-containing resin to a metal plate and apply 200W/m to the coating film²A method of corona discharge treatment for a time of one minute or more (patent document 5). Further, it has been proposed to apply a coating material containing an organic silicate or the like to a metal plate and subject the coating film to flame treatment, plasma treatment, corona discharge treatment, or the like (patent document 6).

Documents of the prior art

Patent document

Patent document 1: international publication No. 1994/6870

Patent document 2: japanese laid-open patent publication No. 8-12921

Patent document 3: japanese laid-open patent publication No. 10-128232

Patent document 4: japanese laid-open patent publication No. 5-59330

Patent document 5: japanese patent laid-open publication No. 2000-61391

Patent document 6: japanese patent laid-open No. 2006-102671

Disclosure of Invention

Problems to be solved by the invention

The coating materials described in patent documents 1 to 3 include various resins and organic silicates. It can be considered that: when such a coating material is applied to the surface of a metal plate, the organosilicate migrates to the surface side of the film, and when the film is cured, the organosilicate reacts with moisture or the like in the air to generate silanol groups or siloxane bonds on the surface of the coating film, thereby hydrophilizing the surface of the coating film and suppressing rain mark fouling.

However, with any of the organosilicates, it is difficult to sufficiently suppress the occurrence of raindrop stains in a coated metal sheet obtained by using a paint after long-term storage, and the expression of raindrop stain prevention characteristics is not stable. In addition, as described above, it is difficult to sufficiently increase the hardness of the surface of a coating material containing a cured product of an organosilicate.

On the other hand, it is difficult to sufficiently prevent raindrop and dirt even by the techniques of patent documents 4 to 6. For example, in the technique of patent document 4, after a coating material containing a silicone resin is applied to the surface of a metal plate, corona discharge treatment is performed. However, it is difficult to hydrophilize the surface of a coating film uniformly by only subjecting the coating film of the coating material to corona discharge treatment. When a coating film containing a silicone resin is subjected to corona discharge treatment, hydrophilic regions and hydrophobic regions are formed on the surface of the coating film. Furthermore, the hydrophobic carbon adheres strongly to the hydrophobic region. On the other hand, in the hydrophilic region, the hydrophobic carbon floats by rainwater. However, the floating hydrophobic carbon moves closer to the hydrophobic carbon attached to the hydrophobic region, and the hydrophobic carbon gradually deposits from the hydrophobic region as a starting point. Therefore, even with the technique of patent document 4, it is difficult to obtain a coated metal sheet having high resistance to rain mark fouling.

In patent document 5, the surface of a coating film of a coating material containing a fluorine-containing resin or the like is subjected to corona discharge treatment, but even in this case, hydrophobic and hydrophilic regions are formed, and it is difficult to uniformly hydrophilize the surface of the coating film.

In addition, in the case of the coating material containing an organosilicate described in patent documents 1 to 3 or 6, when a film made of the coating material is heated, dried and baked, the organosilicate is likely to evaporate together with the solvent and adhere to a wall surface of a heating device or the like, thereby generating silica. Then, the silica comes into contact with the film being heated or peels off from the heating device and adheres to the film surface, and thus the resulting coated metal sheet is likely to have poor appearance.

The present invention has been made in view of such circumstances. That is, an object of the present invention is to provide a method for producing a coated metal sheet which is less likely to contaminate a heating device and which can easily form a coating film having high resistance to raindrop stains. It is another object of the present invention to provide a coated metal sheet having high resistance to raindrop dirt and good appearance.

Means for solving the problems

A first aspect of the present invention relates to the following method for producing a coated metal sheet.

[1] A method for manufacturing a coated metal sheet, comprising the steps of: a step of applying a coating material containing a silicone resin and a fluorine-containing resin on the surface of a metal plate and curing the coating material to form a coating film; and a step of flame-treating the coating film, wherein the silicone resin contains 5 to 50 mol% of silanol groups relative to the total number of moles of Si atoms.

[2] The method for producing a coated metal sheet according to [1], wherein the silicone resin contains 50 to 100 mol% of Si atoms derived from trialkoxysilane relative to the total number of moles of Si atoms.

[3] The method for producing a coated metal sheet according to [1] or [2], wherein a ratio of a number of moles of the aryl groups directly bonded to the Si atoms to a number of moles of the alkyl groups directly bonded to the Si atoms in the silicone resin is 20 to 80%.

A second aspect of the present invention relates to the following coated metal sheet.

[4]A coated metal sheet having: a metal plate; and a fluorine-containing coating film formed on the metal plate, the coating film comprising a cured product of a silicone resin and a fluorine-containing resin, wherein the ratio of Si atoms to the total amount of Si atoms, F atoms, C atoms and O atoms when the surface of the coating film is analyzed by X-ray photoelectron spectroscopy using Al Kalpha rays as an X-ray source is Si_aWhen the ratio of the amount of O atoms to the amount of C atoms is represented by x, Si is present_aAnd x respectively satisfy the following formulas:

Si_a≥8atm％

x≥0.8

the peak top of C1s in the X-ray photoelectron spectrum obtained by the analysis of the X-ray photoelectron spectroscopy was corrected to 285eV, and Si was added_2pWhen the energy spectrum is separated into a peak corresponding to 103.5eV and a peak corresponding to 102.7eV, the spectrum is separated intoThe peak area of 103.5eV was compared with that of Si_2pWhen the ratio of the peak area of the entire spectrum is y, y satisfies the following formula:

y≥0.6。

[5] the coated metal sheet according to [4], wherein a sliding angle of diiodomethane on the surface of the coating film is 15 ° or more and 50 ° or less.

[6] The coated metal sheet according to [4] or [5], wherein the cured product of the silicone resin contains a structure derived from methyltrialkoxysilane or phenyltrialkoxysilane.

[7] The coated metal sheet according to any one of [4] to [6], wherein the metal sheet is a zinc-based plated steel sheet.

Effects of the invention

The coated metal sheet of the present invention has high resistance to rain mark fouling and also has good coating appearance. Further, according to the manufacturing method of the present invention, a coated metal sheet which does not contaminate the heating device, has high resistance to rain mark fouling, and has good coating appearance can be manufactured.

Drawings

Fig. 1A is a side view of a burner head of a burner for flame treatment, fig. 1B is a front view of the burner head, and fig. 1C is a bottom view of the burner head.

Fig. 2A is a side view of a burner head of the burner for flame treatment, and fig. 2B is a bottom view of the burner head.

FIG. 3 is a schematic sectional view of a coated metal sheet according to the present invention.

Detailed Description

1. Method for manufacturing coated metal plate

The method for manufacturing a coated metal sheet according to the present invention includes: a step of applying a coating material containing a silicone resin to the surface of a metal plate and curing the coating material to form a coating film (hereinafter, also referred to as a "coating film forming step"); and a step of flame-treating the coating film (hereinafter, also referred to as "flame treatment step").

As described above, conventionally, attempts have been made to prevent the occurrence of raindrop stains on a coated metal plate by applying a paint containing an organosilicate or the like on the surface of the metal plate. It can be considered that: when the organosilicates are coated on the surface of the metal plate, they migrate to the surface side, and they are hydrolyzed to generate silanol groups or siloxane bonds, thereby exhibiting rainstain resistance. However, the organosilicate is liable to react with water in the coating material, and if the coating material is stored for a long period of time, the hydrophilicity of the coating film cannot be sufficiently improved, and it is difficult to obtain a high raindrop stain resistance property which is required for a coated metal sheet. When the film made of the coating material is heated, dried and baked, the organosilicate is easily evaporated together with the solvent to generate silica on the wall surface of the heating device. Then, the silica comes into contact with the cured film, or the exfoliated silica adheres to the film, and therefore, there is also a problem that the appearance of the obtained coated metal sheet tends to be poor.

On the other hand, it has been studied to apply corona treatment or the like to a coating film of a coating material containing an organic silicate or the like, but it is difficult to uniformly hydrophilize the surface of the coating film by the corona treatment.

In contrast, the method for manufacturing a coated metal sheet according to the present invention includes the steps of: a step of applying a coating material containing a specific silicone resin (containing 5 to 50 mol% of silanol groups relative to the total molar amount of Si atoms) and a fluorine-containing resin to form a coating film; and flame treating the coating film. The "silicone resin" in the present specification is a compound obtained by partial hydrolysis and condensation of alkoxysilane, which is not yet gelled, although mainly having a three-dimensional crosslinked structure, and is a polymer soluble in an organic solvent. The three-dimensional crosslinked structure contained in the silicone resin is not particularly limited, and may be any of a cage shape, a ladder shape, and a random shape, for example. In the present specification, the silicone resin does not contain tetraalkoxysilane, and a condensate (organosilicate) obtained by hydrolytic condensation of only tetraalkoxysilane.

Since the silicone resin contains a three-dimensional crosslinked structure, when the coating material is applied to the surface of the metal plate, the coating material is easily transferred to the surface side of the film, and is easily uniformly aligned along the surface of the film. When such a coating film is subjected to flame treatment, organic groups (for example, methyl groups, phenyl groups, etc.) contained in the silicone resin are uniformly removed, and silanol groups or siloxane bonds are introduced into the surface of the coating film. As a result, the hydrophilicity of the surface of the coated metal sheet is uniformly improved, and the rain mark fouling resistance is extremely improved.

The silicone resin contained in the coating material of the present invention contains 5 to 50 mol% of silanol groups relative to the total molar amount of Si atoms in the silicone resin. The silicone resin having a silanol group amount of 5 to 50 mol% relative to the total molar amount of Si atoms has an appropriate reactivity and is less likely to be excessively condensed by moisture contained in the coating material. Therefore, the silicone resin is not easily reacted in the coating, and the storage stability of the coating is very good. In addition, since the silanol group is moderately hydrogen-bonded to other components of the coating material, the silicone resin is less likely to evaporate when the film is dried by heating (baking or the like) after the coating material is applied. Therefore, the coating material of the present invention hardly contaminates a heating device, and appearance defects of a coated metal plate due to silica adhering to the heating device are less likely to occur.

The method for producing a coated metal sheet according to the present invention may further include a step other than the coating film forming step and the flame treatment step. Hereinafter, each step of the method for producing a coated metal sheet of the present invention will be described.

(1) Coating film forming step

In this step, a coating material containing a specific silicone resin, a fluorine-containing resin, or the like is applied to a metal plate and cured to obtain a coating film. The method for applying the coating material on the surface of the metal plate is not particularly limited, and can be appropriately selected from known methods. Examples of the coating method of the coating include: roll coating, curtain flow, spin coating, air spray, airless spray, and dip-draw. Among these, roll coating is preferred from the viewpoint of easily and efficiently obtaining a coating film having a desired thickness.

The curing method of the coating material is appropriately selected according to the kind of the resin in the coating material, and may be, for example, baking by heating. The temperature at the time of the baking treatment is preferably 100 to 300 ℃, more preferably 180 to 300 ℃, and further preferably 240 to 280 ℃ from the viewpoint of preventing decomposition of the resin and the like in the coating material and obtaining a uniform coating film. The baking treatment time is not particularly limited, but is preferably 3 seconds to 90 seconds, more preferably 10 seconds to 70 seconds, and further preferably 40 seconds to 60 seconds from the same viewpoint as described above.

Further, air may be blown so that the plate surface air velocity is 0.9m/s or more in order to cure the coating material in a short time at the time of baking the coating material. In the above-described coating, the silicone resin is bonded with hydrogen as the other component. Therefore, even if the coating material is cured while blowing air, the silicone resin is less likely to evaporate, and the heating device is less likely to be contaminated.

The thickness of the coating film formed on the metal plate may be appropriately selected depending on the application of the coated metal plate, and is usually in the range of 3 μm to 30 μm. The thickness is a value determined by a gravimetric method from the specific gravity of the baked coating film and the difference in weight between the coated metal sheet before and after the coating film is removed by sandblasting or the like. When the coating film is too thin, the durability and hiding property of the coating film may be insufficient. On the other hand, when the coating film is too thick, the production cost may increase, and foaming may easily occur during baking.

Here, as the metal plate to which the paint is applied, a metal plate generally used as a building plate can be used. Examples of such metal plates include: a coated steel sheet such as a hot-dip Zn-55% Al alloy coated steel sheet; steel plates such as ordinary steel plates and stainless steel plates; an aluminum plate; copper plate, etc. A chemical conversion coating film, an undercoat coating film, or the like may be formed on the surface of the metal plate within a range not to impair the effects of the present invention. The metal plate may be subjected to embossing, deep drawing, or other embossing processes as long as the effects of the present invention are not impaired.

The thickness of the metal plate is not particularly limited, and can be appropriately selected according to the use of the coated metal plate. For example, when a coated metal plate is used as the material of the metal wall plate, the thickness of the metal plate may be set to 0.15mm to 0.5 mm.

Here, the coating material for forming a coating film may contain at least a specific silicone resin, and may contain a fluorine-containing resin, a curing agent, inorganic particles, organic particles, a coloring pigment, a solvent, and the like in addition to the silicone resin.

As described above, the silicone resin is a compound obtained by partial hydrolytic condensation of an alkoxysilane, and generally contains one or two or more units selected from T-1 units to T-3 units derived from a trialkoxysilane (these units are also collectively referred to as "T units") in the molecular chain thereof, which are represented by the following general formula.

[ chemical formula 1]

In the above formula, R¹Represents a hydrocarbon group which may have a substituent. In addition, X¹Represents a hydrogen atom or a hydrocarbon group. The silicone resin may contain the above-mentioned R¹Or X¹A plurality of different kinds of T cells.

R¹Preferably C1-C12 hydrocarbon group, and specific examples thereof include: alkyl groups such as methyl, ethyl, propyl, hexyl, and octyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; cycloalkyl groups such as cyclohexyl, cyclobutyl and cyclopentyl; and the like. Among these, methyl and phenyl groups are particularly preferable.

On the other hand, X¹Preferably a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and examples of the hydrocarbon group include: alkyl groups such as methyl, ethyl, propyl, and hexyl; aryl groups such as phenyl, tolyl, and xylyl; cycloalkyl groups such as cyclohexyl, cyclobutyl and cyclopentyl; and the like. Among these, methyl and ethyl are particularly preferable.

Further, the silicone resin may contain either or both of a D-1 unit and a D-2 unit (these are also collectively referred to as "D unit") derived from a dialkoxysilane, which is represented by the following general formula, in the molecular chain.

[ chemical formula 2]

In the above formula, R²And R³Each independently represents a hydrocarbon group which may have a substituent. In addition, X²Represents a hydrogen atom or a hydrocarbon group. In addition, the silicone resin may contain the above-mentioned R²、R³、X²A plurality of kinds of D units different in kind.

R²And R³Each preferably a C1-12 hydrocarbon group, and specific examples thereof are: r with the above-mentioned T unit¹The same group. On the other hand, X²Preferably a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and specific examples thereof are: x with the above-mentioned T unit¹The same group.

The molecular chain of the silicone resin may contain one or more of Q-1 units to Q-4 units derived from tetraalkoxysilane (these units are also collectively referred to as "Q units") represented by the following general formula.

[ chemical formula 3]

In the above formula, X³Represents a hydrogen atom or a hydrocarbon group. Further, the silicone resin may contain the above-mentioned X³A plurality of kinds of Q units different from each other.

X³Preferably a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and specific examples thereof are: x with the above-mentioned T unit¹The same group.

The silicone resin has a structure in which at least the T units are three-dimensionally bonded, and the D unit and/or the Q unit may be bonded to the structure. As described above, the amount (number of moles) of silanol groups in the silicone resin contained in the coating material of the present invention is 5 to 50 mol%, more preferably 15 to 40 mol%, relative to the total molar amount of Si atoms. If the amount of silanol groups exceeds 50 mol% based on the total molar amount of Si atoms, the reactivity of the silicone resin tends to be high, and the storage stability of the coating material tends to be low. On the other hand, if the amount of silanol groups is less than 5 mol% relative to the total molar amount of Si atoms, the silicone resin is less likely to be hydrogen-bonded to other components (for example, an acrylic resin or the like) in the coating material, and the silicone resin is likely to evaporate during curing of the coating material.

On the other hand, when the amount of silanol groups in the silicone resin is in the above range, not only is the storage stability of the coating material improved as described above, but also the silicone resin is less likely to evaporate and contaminate the heating apparatus when the coating material is applied and then baked as described above.

Can pass through²⁹Si-NMR(²⁹Si nuclear magnetic resonance，²⁹Si-nuclear magnetic resonance) analysis, and¹H-NMR(¹H nuclear magnetic resonance，¹h-nuclear magnetic resonance) analysis, the number of moles of Si atoms contained in the silicone resin, and the amount of silanol groups contained in the silicone resin were determined. The amount of silanol groups in the silicone resin can be adjusted according to the charge ratio of the T unit, the D unit, and the Q unit, or the degree of condensation reaction. For example, in the case of using trialkoxysilane for the preparation of a silicone resin, the T-3 unit is increased and the amount of silanol groups is decreased by increasing the condensation reaction time or the like.

In addition, the silicone resin preferably contains 50 to 100 mol% of Si atoms derived from trialkoxysilane, that is, Si atoms constituting T units, relative to the total molar amount of Si atoms contained in the silicone resin, and more preferably contains 60 to 100 mol% of the aforementioned Si atoms derived from trialkoxysilane. When the amount of the T unit is less than 50 mol% (particularly, the amount of the D unit is more than 50 mol%), the silicone resin tends to form a micelle structure, and the silicone resin tends to be concentrated in an island shape on the surface of the coating film. As a result, it is difficult to uniformly improve the hydrophilicity of the coating film surface, and unevenness is likely to occur in the raindrop stain resistance of the coating film. Further, it was confirmed that the silicone resin was concentrated in islands on the surface of the coating film by analyzing the surface of the coating film after the flame treatment with an AFM (atomic force microscope). For example, the etching depth by the flame treatment differs between the sea portion and the island portion of the coating film surface. Therefore, the sea-island distribution of the silicone resin can be confirmed by the irregularities on the surface of the coating film.

On the other hand, when the T unit amount is 50 mol% or more, the silicone resin is less likely to form a micelle structure, and the silicone resin is likely to be uniformly concentrated on the surface of the coating film. As a result, the coated metal sheet obtained by applying the coating material had good rain mark fouling resistance. Can pass through²⁹Si-NMR analysis determines the amount of Si atoms constituting the T unit.

The number of moles of aryl groups directly bonded to Si atoms in the silicone resin is preferably 20% to 80%, more preferably 30% to 70%, relative to the number of moles of alkyl groups directly bonded to Si atoms in the silicone resin, that is, the ratio of aryl groups to alkyl groups. The greater the molar ratio of aryl groups, the more readily the silicone resin dissolves in the other ingredients in the coating. However, if the proportion of aryl groups is too high, the reaction rate at the time of forming a coating film may be greatly reduced, and it may be difficult to obtain a sufficient crosslink density. Can pass through¹H-NMR analysis determines the ratio of alkyl to aryl as described above.

The weight average molecular weight of the silicone resin is preferably 700 to 50000, and more preferably 1000 to 10000. If the weight average molecular weight of the silicone resin is less than 700, the silicone resin is likely to evaporate during the above baking after the coating material is applied, thereby contaminating a heating apparatus, or the amount of the silicone resin on the surface of the obtained coating film is reduced. On the other hand, when the weight average molecular weight exceeds 50000, the viscosity of the coating material tends to increase, and the storage stability tends to be low. The weight average molecular weight of the silicone resin is a polystyrene equivalent amount measured by Gel Permeation Chromatography (GPC).

The coating material preferably contains 1 to 10 parts by mass of the silicone resin, more preferably 2 to 6 parts by mass, per 100 parts by mass of the solid content thereof. When the silicone resin is contained in the range in the coating material, the hydrophilicity of the surface of the obtained coating film can be sufficiently improved, and rain mark fouling is less likely to occur.

The above silicone resin can be prepared by hydrolyzing and superposing trialkoxysilane or the like. Specifically, an alkoxysilane such as trialkoxysilane or a partial condensate thereof is dispersed in a solvent such as water or ethanol. Further, the alkoxysilane or the like is preferably hydrolyzed while the pH of the dispersion is adjusted to 1 to 7, more preferably 2 to 6. Thereafter, the hydrolyzates are subjected to dehydration condensation with each other, whereby a silicone resin can be obtained. The molecular weight of the obtained silicone resin can be adjusted by the dehydration condensation time or the like. The condensation of the hydrolysate can be continuously performed with the hydrolysis, and the condensation reaction can be promoted by distilling off ethanol or water produced by the hydrolysis.

The alkoxysilane used for the preparation of the silicone resin can be appropriately selected according to the structure of the desired silicone resin. Examples of trialkoxysilane compounds include: methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, propyltrimethoxysilane, propyltriethoxysilane, propyltriisopropoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, methyltrisinol, phenyltrisilanol, and the like.

Examples of dialkoxysilanes include: methylhydrodimethoxysilane, methylhydrodiethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methylethyldimethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, methylpropyldimethoxysilane, methylpropyldiethoxysilane, diisopropyldimethoxysilane, phenylmethyldimethoxysilane, diphenyldimethoxysilane, and the like.

And, examples of the tetraalkoxysilane include: tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetramethoxysilane, and the like.

In the production of the silicone resin, the partial condensate of trialkoxysilane, dialkoxysilane, and tetramethoxysilane may be used as a raw material.

Here, in the coating film obtained from the coating material, the fluorine-containing resin contained in the coating material functions as a binder. The fluorine-containing resin is not limited to a specific type as long as it contains fluorine in its molecule. Examples of the fluorine-containing resin include: (i) a copolymer of a fluoroolefin and a monomer copolymerizable therewith (hereinafter, also simply referred to as "(i) copolymer"), (ii) polyvinylidene fluoride, and the like.

(i) Examples of the fluoroolefin contained in the copolymer of the fluoroolefin and the monomer copolymerizable therewith include: fluoroolefins having 2 or 3 carbon atoms such as tetrafluoroethylene, chlorotrifluoroethylene, trifluoroethylene, hexafluoropropylene, pentafluoropropylene and the like. (i) The copolymer may contain only one of these, or may contain two or more of these.

Examples of the monomer copolymerizable with the above-mentioned fluoroolefin include: vinyl ethers, vinyl esters, allyl ethers, allyl esters, isopropenyl ethers, isopropenyl esters, methyl ethers, methyl esters, alpha-olefins, (meth) acrylic esters, and the like. (i) The copolymer may contain only one of these, or may contain two or more of these. In the present specification, (meth) acrylic acid means either or both of methacrylic acid and acrylic acid.

Examples of vinyl ethers include: alkyl vinyl ethers such as ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, fluoroalkyl vinyl ether, and perfluoro (alkyl vinyl ether). Examples of vinyl esters include: and fatty acid vinyl esters such as ethyl 2, 2-dimethyloctanoate, vinyl butyrate, vinyl acetate, vinyl pivalate, and vinyl versatate.

Examples of the above allyl ethers include: and alkylallyl ethers such as ethylallyl ether and cyclohexylallyl ether. Examples of allyl esters include: fatty acid allyl esters such as allyl propionate and allyl acetate. Examples of isopropenyl ethers include: alkyl isopropenyl ethers such as methyl isopropenyl ether. Examples of isopropenyl esters include: isopropenyl acetate, and the like. Examples of methyl ethers include: ethylene glycol monomethyl ether, etc., and examples of methyl esters include: beta-methyl acetate, and the like. Examples of alpha-olefins include: ethylene, propylene, isobutylene, and the like. Examples of (meth) acrylates include: methyl methacrylate, ethyl methacrylate, and the like.

Among the above monomers, vinyl ethers, vinyl esters, allyl ethers and allyl esters are preferred from the viewpoint of excellent copolymerizability with fluoroolefins. In addition, alkyl vinyl ether, fatty acid vinyl ester, alkyl allyl ether and fatty acid allyl ester having a linear, branched or alicyclic alkyl group having 1 to 10 carbon atoms are particularly preferable.

(i) The copolymer may further contain a structure derived from a monomer having a group crosslinkable with a curing agent described later. Examples of the monomer having a group crosslinkable with the curing agent include: hydroxybutyl vinyl ether, hydroxybutyl allyl ether, ethylene glycol monoallyl ether, cyclohexanediol monovinyl ether, acrylic acid, methacrylic acid, crotonic acid, undecylenic acid, glycidyl vinyl ether, glycidyl allyl ether, and the like. In addition, a compound having a carboxyl group, for example, succinic anhydride, may be reacted with the structure derived from the monomer to introduce the carboxyl group. Further, a double bond may be introduced by reacting a group having a double bond, for example, isocyanate alkyl methacrylate or the like, with the structure derived from the monomer.

The amount of the fluoroolefin-derived monomer contained in the copolymer (i) is preferably 30 to 70 mol%, more preferably 40 to 70 mol%, based on the total amount of the monomer units contained in the copolymer (i). When the amount of the monomer derived from the fluoroolefin is 30 mol% or more, the resulting coated metal sheet tends to have good weather resistance. On the other hand, when the amount of the fluoroolefin-derived monomer is 70 mol% or less, the compatibility with other components in the coating material is good.

(i) The weight average molecular weight of the copolymer is preferably 3000 to 500000, more preferably 5000 to 50000. When the weight average molecular weight of the copolymer (i) is within this range, the compatibility with other components in the coating material is good, and a film having high strength is obtained. The weight average molecular weight is a value (styrene equivalent) measured by gel permeation chromatography.

When the coating material contains the copolymer (i), a curing agent may be contained together. When the curing agent is contained, a crosslinked structure is easily formed, and the obtained coating film is easily made tougher. Examples of the curing agent include: aminoplast curing agents, isocyanate curing agents, polyacid curing agents, polyvalent amine curing agents, and the like. The coating material may contain only one kind of the above curing agent, or may contain two or more kinds of the above curing agents.

Examples of aminoplast-based curing agents include: methylolmelamines, methylolguanamines, methylolureas, and the like. Examples of methylol melamines include: methylolmelamines such as butylated methylolmelamine and methylated methylolmelamines, which are etherified with lower alcohols, epoxy-modified methylolmelamines, and the like. Examples of methylol ureas include: and alkylated methylol ureas such as methylated methylol urea and ethylated methylol urea.

Examples of the isocyanate-based curing agent include: a polyvalent isocyanate compound or a blocked product thereof. The polyvalent isocyanate compound may be a compound having 2 or more isocyanate groups. Examples of the polyvalent isocyanate compound include: aliphatic polyvalent isocyanate compounds such as ethylene diisocyanate, propylene diisocyanate, tetramethylene diisocyanate, hexamethylene triisocyanate and lysine diisocyanate; alicyclic polyvalent isocyanate compounds such as isophorone diisocyanate, dicyclohexylmethane diisocyanate, and diisocyanate methylcyclohexane; and aromatic isocyanate compounds such as m-xylylene diisocyanate and p-xylylene diisocyanate.

Examples of the modified or multimer of the polyvalent isocyanate compound include: urethane-modified products, urea-modified products, isocyanurate-modified products, biuret-modified products, allophanate-modified products, carbodiimide-modified products, and the like.

Examples of the polybasic acid-based curing agent include: long-chain aliphatic dicarboxylic acids, aromatic polyvalent carboxylic acids, and anhydrides thereof.

Examples of the polyvalent amine-based curing agent include: ethylenediamine, ethylenetriamine, and the like.

The coating material preferably contains the curing agent in an amount of 0.1 to 100 parts by mass, more preferably 1 to 50 parts by mass, based on 100 parts by mass of the copolymer (i). By setting the amount to 0.1 part by mass or more, the hardness of the coating film is easily improved. On the other hand, if it is 100 parts by mass or less, the obtained coated metal sheet is easy to have good workability and impact resistance.

On the other hand, (ii) the polyvinylidene fluoride may be a vinylidene fluoride homopolymer or a copolymer of vinylidene fluoride and another monomer. Among these monomers, the vinylidene fluoride-derived monomer is preferably contained in an amount of 50 mol% or more, and more preferably 60 mol% or more, based on the total amount of the monomers constituting the polyvinylidene fluoride.

Examples of the monomer copolymerizable with vinylidene fluoride include: the fluoroolefin, vinyl ether, vinyl ester and the like may be the same as those exemplified for the copolymer (i) above. (ii) The polyvinylidene fluoride may contain only one kind of structure derived from these, or may contain two or more kinds of structures derived from these.

(ii) The weight average molecular weight of the polyvinylidene fluoride is preferably 100000 or more, more preferably 200000 or more, and further preferably 400000 or more. When (ii) the weight average molecular weight of polyvinylidene fluoride is in this range, the coating film has good compatibility with other components in the coating material and high strength. The weight average molecular weight is a value (styrene equivalent) measured by gel permeation chromatography.

When the coating material contains the polyvinylidene fluoride (ii), the curing agent may be contained together. When the curing agent is contained, a crosslinked structure is easily formed, and the obtained coating film is easily made tougher. Examples of the curing agent include aminoplast curing agents, isocyanate curing agents and the like, and these curing agents may be the same as those used in combination with the copolymer (i) described above. The coating material may contain only one kind of the above curing agent, or may contain two or more kinds of the above curing agents. The amount of the curing agent may be the same as in the case of combining with the copolymer (i).

When the coating material contains the polyvinylidene fluoride (ii), it is preferable that the coating material further contains a (meth) acrylic resin from the viewpoint of fluidity, adhesion to a metal plate, and the like. The (meth) acrylic resin may be thermoplastic or thermosetting.

Examples of the thermoplastic (meth) acrylic resin include: a polymer comprising 70 mol% or more of a monomer derived from an alkyl (meth) acrylate ester, based on the total amount of monomer units constituting (meth) acrylic acid. Examples of the alkyl (meth) acrylate include: and alkyl (meth) acrylate monomers having 3 to 12 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, octyl (meth) acrylate, and the like. The (meth) acrylic resin may contain only one kind of structure derived from these, or may contain two or more kinds of structures derived from these.

The thermoplastic (meth) acrylic resin may contain a monomer structure derived from other than the above, and may contain a monomer derived from styrene, vinyl toluene, (meth) acrylonitrile, vinyl chloride, or the like.

The weight average molecular weight of the thermoplastic (meth) acrylic resin is preferably 40000 to 300000, more preferably 50000 to 200000. The weight average molecular weight of the thermoplastic (meth) acrylic resin is a value measured by GPC (in terms of styrene).

When the (ii) polyvinylidene fluoride is combined with the thermoplastic (meth) acrylic resin, the amount of the (meth) acrylic resin is preferably 150 parts by mass or less, and more preferably 10 to 50 parts by mass, relative to 100 parts by mass of the (ii) polyvinylidene fluoride. When the thermoplastic (meth) acrylic resin is mixed in this range, the fluidity of the coating material tends to be good.

On the other hand, the thermosetting (meth) acrylic resin may be a (meth) acrylic resin having a hydroxyl group or a crosslinkable reactive group such as a carboxyl group, a glycidyl group, an active halogen, and an isocyanate group. In this case, alkylated melamine, polyol, polyamine, polyamide, polyethylene oxide, or the like can be used as a curing agent for the thermosetting (meth) acrylic resin.

The weight average molecular weight of the thermosetting (meth) acrylic resin is preferably 1000 to 20000, and more preferably 2000 to 10000. The weight average molecular weight of the thermosetting (meth) acrylic resin is a value measured by GPC (in terms of styrene).

When the (ii) polyvinylidene fluoride is combined with the thermosetting (meth) acrylic resin, the amount of the (meth) acrylic resin is preferably 150 parts by mass or less, and more preferably 10 to 50 parts by mass, relative to 100 parts by mass of the (ii) polyvinylidene fluoride. When the thermosetting (meth) acrylic resin is mixed in this range, the fluidity of the coating material tends to be improved.

The amount of the fluorine-containing resin contained in the coating material can be appropriately selected depending on the use of the coating material. From the viewpoint of strength and the like of the obtained coating film, the coating material preferably contains the fluororesin by 20 to 95 parts by mass, more preferably 30 to 80 parts by mass, per 100 parts by mass of the solid content thereof.

In the coating material, a silicone resin curing catalyst may also be contained. In the coating film obtained from the coating material, the silicone resin curing catalyst functions as a catalyst for crosslinking the silicone resin or the fluorine-containing resin. As the silicone resin curing catalyst, a known metal-containing catalyst having catalytic activity in the dehydration condensation reaction of silanol groups (for example, aluminum, zinc, tin, or the like) or an amine-modified acid catalyst can be used.

As the silicone resin curing catalyst, commercially available catalysts can be used, for example, catalysts having the following trade names: CAT-AC, D-15 (manufactured by Nippon-Tempound chemical Co., Ltd.), NACURE2500, NACURE4167 (manufactured by King INDUSTRIES, U.S.A.) and the like.

The amount of the silicone resin curing catalyst contained in the coating material can be appropriately selected depending on the use of the coating material. The coating material preferably contains the silicone resin curing catalyst in an amount of 0.1 to 3.0 parts by mass, more preferably 0.5 to 1.0 part by mass, based on 100 parts by mass of the resin (total of the fluorine-containing resin and the (meth) acrylic resin). When the amount of the silicone resin curing catalyst is in the above range, the durability of the coating film obtained from the coating material is improved.

In addition, the coating material may contain inorganic particles or organic particles. When these are contained in the coating material, the surface roughness and the like of the obtained coating film can be easily adjusted. The average particle diameter of the inorganic particles or organic particles is preferably 4 to 80 μm, and more preferably 10 to 60 μm. The average particle diameter of the inorganic particles or the organic particles is a value measured by a coulter counter method. The shape of the inorganic particles or organic particles is not particularly limited, but is preferably substantially spherical from the viewpoint of easy adjustment of the surface state of the resulting coating film.

Examples of the inorganic particles include: silica, barium sulfate, talc, calcium carbonate, mica, glass beads, glass flakes. In addition, examples of the organic particles include resin beads composed of an acrylic resin or a polyacrylonitrile resin. These resin beads may be produced by a known method or may be commercially available. Examples of commercially available acrylic beads include: "TAFTIC AR650S (average particle size: 18 μm)", "TAFTIC AR650M (average particle size: 30 μm)", "TAFTIC AR650MX (average particle size: 40 μm)", "TAFTIC AR650MZ (average particle size: 60 μm)", and "TAFTIC AR650ML (average particle size: 80 μm)" manufactured by Toyo Boseki Kabushiki Kaisha. In addition, examples of commercially available polyacrylonitrile resin beads include: "TAFTIC A-20 (average particle size 24 μm)", "TAFTIC YK-30 (average particle size 33 μm)", "TAFTIC YK-50 (average particle size 50 μm)" and "TAFTIC YK-80 (average particle size 80 μm)" manufactured by Toyo Boseki K.K.K.K.K..

The amount of the inorganic particles and/or organic particles contained in the coating material can be appropriately selected according to the surface state of a desired coating film and the like. In general, the total amount of the inorganic particles and/or the organic particles may be 1 to 40 parts by mass with respect to 100 parts by mass of the solid content of the coating material.

The coating material may contain a coloring pigment as needed. The average particle diameter of the coloring pigment may be, for example, 0.2 to 2.0. mu.m. Examples of such coloring pigments include: titanium oxide, iron oxide, yellow iron oxide, phthalocyanine blue, carbon black, cobalt blue, and the like. When the coating material contains the coloring pigment, the amount thereof is preferably 20 to 60 parts by mass, and more preferably 30 to 55 parts by mass, based on 100 parts by mass of the solid content of the coating material for metal plates.

The coating material may contain wax as necessary. Examples of waxes include: polyolefin-based waxes (polyethylene, polypropylene, etc.), fluorine-based waxes (polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, etc.), paraffin-based waxes, stearic acid-based waxes, etc., but are not limited thereto. The amount of the wax may be appropriately selected depending on the kind of the wax, but may be about 2 to 15 mass% with respect to 100 parts by mass of the solid content of the coating material.

The coating material may contain an organic solvent as needed. The organic solvent is not particularly limited as long as it can sufficiently dissolve or disperse the silicone resin, the fluorine-containing resin or the curing agent thereof, the acrylic resin, the silicone resin curing catalyst, the inorganic particles, the organic particles, and the like. Examples of the organic solvent include: hydrocarbon solvents such as toluene, xylene, Solvesso (registered trademark) 100 (trade name, product of exxon mobil corporation), Solvesso (registered trademark) 150 (trade name, product of exxon mobil corporation), and Solvesso (registered trademark) 200 (trade name, product of exxon mobil corporation); ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol monoethyl ether acetate, and dimethyl phthalate; alcohol solvents such as methanol, isopropanol, and n-butanol; ether alcohol solvents such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether; and the like. The coating material may contain only one of these components, or may contain two or more of these components. Among these, isophorone, xylene, ethylbenzene, cyclohexanone, and dimethyl phthalate are preferable from the viewpoint of compatibility with the fluorine-containing resin.

The preparation method of the above-mentioned coating is not particularly limited. The coating composition can be prepared by mixing, stirring or dispersing the above materials in the same manner as in a known coating composition. Further, the silicone resin may be mixed with other components in advance. Further, a material other than the silicone resin may be mixed in advance, and then the silicone resin may be mixed.

(2) Flame treatment step

After the coating film forming step, a flame treatment step of flame-treating the coating film is performed. By performing the flame treatment of the coating film described above, the surface thereof is hydrophilized. When the coating film of the above-mentioned coating material is subjected to flame treatment, hydrocarbon groups (for example, methyl groups, phenyl groups, etc.) of the silicone resin on the surface of the coating film are decomposed to generate silanol groups or siloxane bonds. This improves the hydrophilicity of the coating film surface, and exhibits rain mark fouling resistance.

The flame treatment may be a method in which a metal sheet on which a coating film is formed is placed on a conveyor such as a belt conveyor and moved in a certain direction while a flame is emitted to the coating film by a flame treatment burner.

Here, the flame treatment amount is preferably 30kJ/m²～1000kJ/m²More preferably 100kJ/m²～600kJ/m². The "flame treatment amount" in the present specification means the amount of heat per unit area of the coated metal sheet calculated based on the amount of supply of a combustible gas such as liquefied petroleum gas (lpg). The amount of flame treatment can be adjusted by the distance between the burner head of the flame treatment burner and the surface of the coating film, the speed of conveying the coating film, and the like. The flame treatment capacity is less than 30kJ/m²In this case, treatment unevenness may occur, and it is difficult to uniformly hydrophilize the coating film surface. On the other hand, if the flame treatment amount exceeds 1000kJ/m²The coating film may be oxidized to turn yellow.

An example of a flame treatment burner that can be used for flame treatment of a coating film of the coating material of the present invention will be described below, but the flame treatment method is not limited to this method.

The burner for flame treatment comprises: a gas supply pipe for supplying a combustible gas, a burner head for burning the combustible gas supplied from the gas supply pipe, and a support member for supporting these components. Fig. 1 shows a schematic view of a burner head of a burner for flame treatment. Fig. 1A is a side view of a burner head, fig. 1B is a front view of the burner head, and fig. 1C is a bottom view of the burner head. Note that, although the portions corresponding to the flame ports 22B are highlighted by thick lines in fig. 1A and 1B for easy understanding, the flame ports 22B cannot be visually confirmed from the side and front in practice.

The burner head 22 has a substantially quadrangular prism-shaped housing 22a connected to the gas supply pipe 23 and a flame port 22b disposed on the bottom surface of the housing, and combusts the combustible gas supplied from the gas supply pipe 23 at the flame port 22 b.

The structure inside the casing 22a of the burner head 22 may be the same as that of a general burner for flame treatment, and for example, a flow path for flowing the combustible gas supplied from the gas supply pipe 23 to the flame ports 22b may be formed. The width of the case 22a when viewed from the front can be appropriately selected according to the width of the coating film to be subjected to flame treatment. The width of the case 22a when viewed from the side can be appropriately selected in accordance with the width of the flame ports 22b in the direction of conveyance of the coating film (the width indicated by L in fig. 1A).

On the other hand, the flame ports 22b are through holes provided in the bottom surface of the housing 22 a. The shape of the flame ports 22b is not particularly limited, and may be a rectangular shape or a circular hole shape. However, a rectangular shape is particularly preferable from the viewpoint of performing flame treatment uniformly in the width direction of the coating film. The width of the flame ports 22B in the direction perpendicular to the direction of conveyance of the coating film (the width indicated by W in fig. 1B) may be equal to or larger than the width of the coating film subjected to flame treatment, and may be, for example, about 50cm to 150 cm. On the other hand, the width of the flame ports 22b in the conveying direction of the coating film (the width indicated by L in fig. 1A) may be appropriately set in accordance with the ejection stability of the combustible gas, and may be, for example, about 1mm to 8 mm.

The gas supply pipe 23 is a gas flow path having one end connected to the burner head 22 and the other end connected to a gas mixing portion (not shown). The gas mixing section is connected to a combustible gas supply source (not shown) such as a combustible gas cylinder and a combustion-supporting gas supply source (not shown) for supplying air such as an air cylinder, an oxygen cylinder, an air compressor, and a blower, and is used to mix combustible gas and combustion-supporting gas in advance. It is preferable that the concentration of oxygen in the combustible gas (the mixed gas of the combustible gas and the combustion-supporting gas) supplied from the gas mixing portion to the gas supply pipe 23 is constant, and it is preferable that the gas mixing portion includes an oxygen supplier for supplying oxygen to the gas supply pipe 23 as needed.

Examples of the above combustible gas include: hydrogen gas, Liquefied Petroleum Gas (LPG), Liquefied Natural Gas (LNG), acetylene gas, propane gas, butane, and the like. Of these, LPG or LNG is preferable, and LPG is particularly preferable, from the viewpoint of facilitating formation of a desired flame. On the other hand, examples of the combustion-supporting gas include air and oxygen, and air is preferable from the viewpoint of operability and the like.

The mixing ratio of the combustible gas and the combustion-supporting gas in the combustible gas supplied to the burner head 22 through the gas supply pipe 23 can be appropriately set according to the types of the combustible gas and the combustion-supporting gas. For example, when the combustible gas is LPG and the combustion-supporting gas is air, the volume of air is preferably 24 to 27, more preferably 25 to 26, and still more preferably 25 to 25.5, with respect to 1 volume of LPG. When the combustible gas is LNG and the combustion-supporting gas is air, the volume of air is preferably 9.5 to 11, more preferably 9.8 to 10.5, and still more preferably 10 to 10.2, per 1 volume of LNG.

In the flame treatment burner, the flame treatment of the coating film is performed while the coating film is moved. In this case, the flame treatment can be performed by ejecting a combustible gas from the flame ports 22b of the burner head 22 toward the coating film and burning the combustible gas. The distance between the burner head 22 and the coating film can be appropriately selected according to the amount of flame treatment as described above, and is usually about 10mm to 120mm, preferably 25mm to 100mm, and more preferably 30mm to 90 mm. When the distance between the burner head and the coating film is too short, the coating film may come into contact with the burner head due to warping of the metal plate or the like. On the other hand, in the case where the distance between the burner head and the coating film is too far, a large amount of energy is required for flame treatment. In the flame treatment, although the flame may be emitted perpendicularly from the flame treatment burner to the surface of the coating film, the flame may be emitted from the flame treatment burner to the surface of the coating film at a certain angle to the surface of the coating film.

The moving speed of the coating film can be appropriately selected according to the above-mentioned flame treatment amount, and is usually preferably 5 m/min to 70 m/min, more preferably 10 m/min to 50 m/min, and still more preferably 20 m/min to 40 m/min. The flame treatment can be efficiently performed by moving the coating film at a speed of 5 m/min or more. On the other hand, when the moving speed of the coating film is too high, airflow is likely to be generated by the movement of the coating film, and the flame treatment may not be sufficiently performed.

In addition, although the burner head 22 having only one flame hole 22b in the casing 22a is shown in the above description, the structure of the burner head 22 is not limited to the above structure. For example, as shown in fig. 2, the burner head 22 may also have auxiliary flame ports 22c parallel to the flame ports 22 b. Fig. 2A is a side view of the burner head, and fig. 2B is a bottom view of the burner head. Note that, for the sake of easy understanding, in fig. 2A, portions corresponding to the flame ports 22b and the auxiliary flame ports 22c are highlighted by thick lines, but actually, the flame ports 22b and the auxiliary flame ports 22c cannot be visually confirmed from the side. Here, the interval between the flame ports 22b and the auxiliary flame ports 22c is preferably 2mm or more, and may be, for example, 2mm to 7 mm. In this case, the casing 22a has a structure in which a very small amount of combustible gas passes through the auxiliary flame ports 22 c. The amount of the combustible gas jetted from the auxiliary flame ports 22c is preferably 5% or less, and more preferably 3% or less, of the combustible gas jetted from the flame ports 22 b. The flame generated in the auxiliary flame ports 22c hardly affects the surface treatment of the coating film, but the presence of the auxiliary flame ports 22c increases the straightness of the combustible gas discharged from the flame ports 22b, and forms a flame with small fluctuation.

Before the flame treatment, a preheating treatment may be performed to heat the surface of the coating film to 40 ℃ or higher. When flame is irradiated to a coating film formed on the surface of a metal plate having high thermal conductivity (for example, a metal plate having a thermal conductivity of 10W/mK or more), water vapor generated by combustion of a combustible gas is cooled to become water, and temporarily accumulates on the surface of the coating film. Then, the water absorbs energy during the flame treatment and turns into water vapor, which may inhibit the flame treatment. On the other hand, by heating the coating surface (metal plate) in advance, the generation of water during flame irradiation can be suppressed.

The method of preheating the coating film is not particularly limited, and a heating device generally called a drying furnace may be used. For example, a batch-type drying furnace (also referred to as "safe furnace") may be used, and specific examples thereof include: a cryostat (model MINI CATALINA MRLV-11) manufactured by Isuzu institute, an automatic discharge dryer (model ATO-101) manufactured by Tokyo thermal corporation, and a simple explosion-proof dryer (model TNAT-1000) manufactured by Tokyo thermal corporation.

As described above, according to the method for producing a coated metal sheet of the present invention, the silicone resin can be uniformly concentrated on the surface of the coating film, and the hydrophilicity of the resulting coated metal sheet can be uniformly improved. In addition, by manufacturing a coated metal sheet using the above-described paint, the heating device is less likely to be contaminated when the paint is baked. Therefore, according to the method for producing a coated metal sheet of the present invention, a coated metal sheet which is applicable to exterior materials of various buildings and the like and is less likely to cause raindrop stains and the like can be efficiently produced. Further, the above-mentioned coating material also has an advantage of good storage stability.

2. About coating metal plate

As shown in fig. 3, a coated metal sheet 100 of the present invention includes: a metal plate 1; and a fluorine-based coating film 2 (hereinafter, also simply referred to as "coating film 2") formed on the metal plate 1 and containing a cured product of a silicone resin and a fluorine-containing resin. For example, the coated metal sheet 100 can be manufactured by the above-described method for manufacturing a coated metal sheet.

As described above, the silicone resin contains a three-dimensional crosslinked structure. Therefore, as described in the above-described method for producing a coated metal plate, when a paint containing a silicone resin is applied to the surface of the metal plate 1, the silicone resin is easily uniformly aligned along the surface of the film. Further, when the cured film of the silicone resin is subjected to hydrophilization treatment (flame treatment), organic groups contained in the surface of the cured film are uniformly removed, and silanol groups or siloxane bonds are introduced. As a result, the hydrophilicity of the surface of the coated metal sheet 100 (the surface of the coating film 2) is uniformly improved, and the raindrop stain resistance is very good.

Here, the coating film 2 produced as described above shows the following values when the surface thereof is analyzed by X-ray photoelectron spectroscopy (hereinafter, also referred to as XPS method). First, when the coating film surface is measured by XPS method using Al Kalpha rays as X-ray sources, the ratio of Si atoms to the total amount of Si atoms, F atoms, C atoms and O atoms_aIs more than 8 atm%. Si_aMore preferably 9 atm% or more, and still more preferably 10 atm% or more. Si_aIn proportion to the amount of the silicone resin concentrated on the surface of the coating film, if Si_aWhen the concentration is 8 atm% or more, the uniformity of the surface increases, and the rain mark fouling resistance after flame treatment tends to be good.

When the ratio of the amount of O atoms to the amount of C atoms (the amount of O atoms/the amount of C atoms) measured by the XPS method is x, x is 0.8 or more. x is more preferably 0.9 or more, and still more preferably 1.0 or more. x represents a ratio of the amount of O atoms derived from a siloxane bond or a silanol group present in the surface of the coating film with respect to the amount of C atoms derived from an organic group present in the surface of the coating film. That is, when the organic group derived from the silicone resin is removed by the flame treatment and a siloxane bond or a silanol group is introduced, x becomes large. When x is 0.8 or more, the hydrophilicity of the coating film surface (rain mark fouling resistance of the coated metal sheet) is particularly good.

Further, the peak top of C1s in the X-ray photoelectron spectrum obtained by XPS analysis of the surface of the coating film was corrected to 285eV, and Si was added_2pWhen the spectrum was separated into a peak corresponding to 103.5eV and a peak corresponding to 102.7eV, the peak area of 103.5eV (Si-Si_{Inorganic substance}) Relative to Si_2pRatio of peak area of the entire spectrum (Si)_{Inorganic substance}/Si_2pPeak area of the entire spectrum) is y, y is 0.6 or more. y is more preferably 0.65 or more, and still more preferably 0.7 or more.

Si_2pThe energy spectrum is observed in the vicinity of 101eV to 106eV when the peak top of C1s in the X-ray photoelectron spectrum is corrected to 285eV, and is a spectrum of the entire Si atom, that is, both the peak (102.7eV) containing the organic Si atom to which carbon is bonded (and the peak (103.5eV) containing the inorganic Si atom to which oxygen is bonded (which constitutes a siloxane bond or a silanol group). That is, y represents the proportion of inorganic Si atoms (Si atoms constituting siloxane bonds or silanol groups) relative to the total amount of Si on the surface of the coating film, and when y is 0.6 or more, the hydrophilicity of the surface of the coating film (the resistance to rain stain of the coated metal sheet) is particularly good.

Here, the analysis of the components (the amounts of Si atoms, F atoms, C atoms, and O atoms) on the surface of the coating film by the XPS method can be performed in the same manner as the analysis by the general XPS method using Al K α as an X-ray source, and can be performed, for example, by the following measurement apparatus and measurement conditions.

(measurement apparatus and measurement conditions)

A measuring device: AXIS-NOVA scanning type X-ray photoelectron spectrometer manufactured by KRATOS

An X-ray source: al Ka 1486.6eV

Analysis area 700 μm × 300 μm

Further, the above Si is preferable_2pThe energy spectrum was separated into a peak corresponding to 103.5eV and a peak corresponding to 102.7eThe peak of V can be obtained by the following method. First, the C1s peak top of the X-ray photoelectron spectrum was corrected to 285 eV. Then, Si observed in the vicinity of 101eV to 106eV is measured by a Linear (Linear) method_2pThe energy spectrum removes the background. Then, the energy spectrum from which the background was removed was processed by a complex function of a gaussian function and a lorentz function, and separated into a peak of an organic Si atom (102.7eV) and a peak of an inorganic Si atom (103.5 eV).

In the coated metal sheet 100 of the present invention, the sliding angle of diiodomethane on the surface of the coating film 2 is preferably 15 ° or more and 50 ° or less, and more preferably 35 ° or less. The coating film 2 of the coated metal sheet 100 of the present invention is subjected to flame treatment (hydrophilization treatment), but as described above, if the hydrophilization treatment is insufficient, it is difficult to obtain sufficient rain mark fouling resistance. Here, when the hydrophilicity of the surface of the coating film 2 is high, or when the roughness of the surface of the coating film 2 is large, the diiodomethane sliding angle is high. However, if the hydrophilicity of the surface of the coating film 2 is not uniform, it becomes too high. For example, in the case of surface treatment by corona treatment, the diiodomethane sliding angle may exceed 50 °. On the other hand, when subjected to flame treatment, the surface is uniformly hydrophilized, and the diiodomethane sliding angle is 50 ° or less.

The reason why the sliding angle of diiodomethane is larger than 50 ° when the hydrophilicity of the coating film surface becomes uneven by corona discharge treatment or the like is considered as follows. There are two kinds of coating films on the surface, the numbers of the hydrophilic groups and the hydrophobic groups on both the coating films being the same, provided that one of them has no deviation in the distribution of the hydrophilic groups and the hydrophobic groups, and the other has a deviation in the distribution of the hydrophilic groups and the hydrophobic groups. In this case, the static contact angles of the two are substantially the same, being less susceptible to the distribution of the hydrophilic group and the hydrophobic group. On the other hand, the dynamic contact angle (diiodomethane sliding angle) between the two is different from each other due to the distribution of the hydrophilic group and the hydrophobic group. When the distribution of the hydrophilic group and the hydrophobic group is not uniform in measuring the diiodomethane sliding angle, diiodomethane droplets are adsorbed to a portion having a high hydrophilic group density. That is, if the distribution of the hydrophilic group and the hydrophobic group varies, the diiodomethane droplet is less likely to move and the sliding angle is larger than in the case where the distribution is not uniform. Therefore, when a large amount of hydrophilic groups are introduced on the surface of the coating film as in the corona discharge treatment, but the distribution thereof is uneven, the diiodomethane sliding angle is a high value exceeding 50 °.

The diiodomethane sliding angle is a value measured in the following manner. First, 2. mu.l of diiodomethane was dropped onto the coating film 2. Thereafter, the tilt angle of the coating film 2 (the angle formed between the plane perpendicular to the gravity and the coating film) was increased at a rate of 2 degrees/second using a contact angle measuring apparatus. At this time, the droplet of diiodomethane was observed by a camera attached to the contact angle measuring apparatus. Then, the inclination angle at the moment when the droplets of diiodomethane slide was determined, and the average value of 5 times was set as the diiodomethane slide angle of the coating film 2. The moment when the droplet of diiodomethane slides means a moment when both the end point of diiodomethane (droplet) below in the direction of gravity and the end point above in the direction of gravity start moving.

Here, the metal plate 1 included in the coated metal plate 100 of the present invention may be the same as the metal plate described in the above-described method for manufacturing a coated metal plate. In the metal plate 1, a chemical conversion coating film, an undercoating film, or the like may be formed on the surface thereof within a range not to impair the effects of the present invention. The metal plate 1 may be subjected to embossing, deep drawing, or other embossing processes as long as the effects of the present invention are not impaired. The metal plate 1 is particularly preferably a zinc-plated steel plate from the viewpoint of a balance between cost and long-term durability.

On the other hand, the coating film 2 is not particularly limited as long as it contains the cured product of the silicone resin, the above-mentioned fluorine-containing resin or the cured product thereof (in the present specification, these are collectively referred to as "fluorine-containing resin"), and the like as described above and satisfies the above-mentioned limitations. The cured product of the silicone resin may be a cured product of the silicone resin contained in the coating material described in the above-described method for producing a coated metal sheet. In particular, a cured product of a silicone resin having a structure derived from methyltrialkoxysilane or phenyltrialkoxysilane is preferable. Methyl groups derived from methyltrialkoxysilane and phenyl groups derived from phenyltrialkoxysilane are easily removed during hydrophilization treatment (flame treatment) of the surface. Therefore, if the cured product of the silicone resin has such a structure, the hydrophilicity of the surface of the coating film 2 is likely to be improved, and the rain mark fouling resistance of the coated metal sheet 100 is likely to be improved. Whether or not the cured product of the silicone resin contained in the coating film 2 has a structure derived from methyltrialkoxysilane or phenyltrialkoxysilane can be determined by performing elemental analysis or structural analysis of the coating film 2.

The amount of the cured product of the silicone resin contained in the coating film 2 may be appropriately selected depending on the type of the coated metal sheet 100, but is preferably 1 to 10 parts by mass, more preferably 2 to 7 parts by mass, even more preferably 2 to 6 parts by mass, and particularly preferably 3 to 6 parts by mass, based on 100 parts by mass of the entire coating film 2. When the amount of the cured product of the silicone resin contained in the coating film 2 is within this range, the ratio of Si atoms in the surface of the coating film 2 is sufficiently increased, and a coated metal sheet in which raindrop stains are less likely to occur can be formed. In particular, the content of Si atoms in the coating film was measured by XPS method by setting the amount of the cured product of the silicone resin to 1 part by mass or more_aEasily become 8 atm% or more. On the other hand, by setting the content of the cured product of the silicone resin to 10 parts by mass or less, the coating film is less likely to be excessively hard, and the bending workability of the coated metal sheet 100 is likely to be good.

The coating film 2 may contain components other than the cured product of the silicone resin and the fluorine-containing resin, and may contain inorganic particles, organic particles, a coloring pigment, and the like. These inorganic particles, organic particles, coloring pigments, and the like may be the same as the components contained in the paint described in the above-mentioned method for producing a coated metal sheet. The amount of the fluororesin contained in the coating film 2 may be appropriately selected depending on the application of the coated metal sheet 100 and the kind of the resin, but from the viewpoint of the strength of the coating film 2, the amount of the fluororesin is preferably 25 to 60 parts by mass, more preferably 30 to 50 parts by mass, based on the entire mass of the coating film 2.

On the other hand, the amount of the inorganic particles and/or the organic particles contained in the coating film 2 can be appropriately selected according to the surface state of the coating film 2 and the like. Usually, the total amount of the inorganic particles and the organic particles can be set to 1 to 40 parts by mass with respect to 100 parts by mass of the coating film 2. The amount of the coloring pigment is preferably 20 to 60 parts by mass, and more preferably 30 to 55 parts by mass, based on the entire mass of the coating film 2.

The thickness of the coating film 2 may be appropriately selected according to the application of the coated metal sheet 100, and is usually in the range of 3 μm to 30 μm. The thickness is a value determined by a gravimetric method from the specific gravity of the baked coating film and the weight difference of the coated metal sheet 100 before and after the removal of the coating film 2, and the removal of the coating film 2 is performed by sandblasting or the like. When the coating film 2 is too thin, the durability and concealing property of the coating film 2 may be insufficient. On the other hand, when the coating film 2 is too thick, the production cost may increase, and foaming may easily occur during baking.

[ examples ]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

1. Preparation of the coating

Each coating was prepared by the following method.

1-1 Synthesis of methyl Silicone resin 1

A2L flask was charged with 408g (3.0 mol) of methyltrimethoxysilane, and 800g of water was added at 10 ℃ or lower, followed by thorough mixing. Then, 180g to 216g (10.0 mol to 12.0 mol) of a 0.05N hydrochloric acid aqueous solution was added dropwise at 5 ℃ to 25 ℃ for 20 minutes to 40 minutes under ice-bath cooling. After the dripping is finished, stirring for 0.6 to 6 hours at the temperature of between 5 and 25 ℃ to finish hydrolysis and dehydration condensation. Thus, 7 kinds of preparation solutions containing methyl silicone resins a to G having different silanol group contents were obtained. Further, the amount of silanol groups and the amount of constituent units in the methyl silicone resins a to G were adjusted by adjusting the reaction time (stirring time) and reaction temperature, and the amount of the aqueous hydrochloric acid solution added.

Then, methanol produced by hydrolysis was distilled off from the prepared solution at 70 ℃ under reduced pressure of 60mmHg for 1 hour. The preparation after the removal of methanol by distillation was turbid and separated into two layers by standing. The lower layer is a silicone resin that does not dissolve in water and settles. To the solution was added 469g of methyl isobutyl ketone (MIBK), and the mixture was stirred at room temperature for 1 hour. Thereby, the precipitated silicone resin was completely dissolved in MIBK. Then, the prepared solution was allowed to stand to separate an aqueous layer from an MIBK layer. Then, the lower water layer was removed from the flask with a stopper to obtain a colorless and transparent silicone resin solution having a solid content of 50 mass%.

To be provided with²⁹Si-NMR measured the structure of the obtained methyl silicone resin A, and two broad signals were observed. The chemical shifts of these signals are (1) δ -54ppm to-58 ppm and (2) δ -62ppm to-68 ppm. The chemical shifts are respectively ascribed to T represented by the following chemical formula_mIn cell, T_m-2 units and T_m-3 units of silicon atoms. That is, T is not contained in the methyl silicone resin A_m-1 unit. In addition, methyl silicone resin A was subjected to¹H-NMR analysis showed that: methoxy groups derived from methyltrimethoxysilane have been fully hydrolyzed to hydroxyl groups.

[ chemical formula 4]

Then, GPC analysis (in terms of polystyrene) was performed under the following conditions, and the weight average molecular weight Mw and the molecular weight distribution Mw/Mn of the silicone resin a were measured.

The measuring machine comprises: HLC-8320GPC manufactured by TOSOH corporation

Pipe column: shodex K-G + K-805 Lx 2 root + K-800D

Eluent: chloroform

Temperature: 40.0 ℃ of pipe column thermostatic bath

Flow rate: 1.0mL/min

Concentration: 0.2% by mass/volume

Injection amount: 100 μ l

Solubility: completely dissolve

Pretreatment: filtering with 0.45 μm filter

A detector: differential Refractometer (RI)

Similarly, the methyl silicone resins B to G are also prepared by²⁹Si-NMR and¹H-NMR analysis confirmed the structure. Further, the weight average molecular weight Mw and the molecular weight distribution Mw/Mn were measured by GPC analysis. The analysis results of the methyl silicone resins a to G are shown in table 1 below.

[ Table 1]

1-2 Synthesis of methyl Silicone resin 2

286g to 163g (2.1 to 1.2 mol) of methyltrimethoxysilane and 108g to 216g (0.9 mol to 1.8 mol) of dimethyldimethoxysilane were charged into a 2L flask, and 800g of water was added at 10 ℃ or lower and mixed thoroughly. Then, 180g to 216g (10.0 mol to 12.0 mol) of a 0.05N hydrochloric acid aqueous solution was added dropwise at 5 ℃ to 25 ℃ for 20 minutes to 40 minutes under ice-bath cooling. After the completion of the dropping, the mixture was stirred at 5 to 25 ℃ for 0.6 to 6 hours to undergo hydrolysis and dehydration condensation. After completion of the dropping, three kinds of silicone resin solutions containing methyl silicone resins H to J having a solid content of about 50 mass% were obtained in the same manner as in synthesis 1 of methyl silicone resin. The silanol groups and the amounts of the constituent units of the methyl silicone resins H to J were adjusted by adjusting the reaction time (stirring time), the reaction temperature, the amount of the aqueous hydrochloric acid solution added, and the amount of the charged solution.

The methyl silicone resins H to J obtained by²⁹Si-NMR and¹H-NMR analysis confirmed the structure. Further, the weight average molecular weight Mw and the molecular weight distribution Mw/Mn were measured by GPC analysis. Methyl-based silicone resinThe analysis results of H to J are shown in Table 2 below. In addition, D in Table 2_m-1 units and D_mThe-2 units are each a structural unit represented by the following chemical formula.

[ chemical formula 5]

[ Table 2]

1-3 Synthesis of methyl/phenyl Silicone resin 3

A2L flask was charged with 326 to 41g (2.4 to 0.3 mol) of methyltrimethoxysilane and 119 to 535g (0.6 to 2.7 mol) of phenyltrimethoxysilane, and then 800g of water was added thereto at 10 ℃ or lower to sufficiently mix them. Then, 180g to 216g (10.0 mol to 12.0 mol) of a 0.05N hydrochloric acid aqueous solution was added dropwise at 5 ℃ to 25 ℃ for 20 minutes to 40 minutes under ice-bath cooling. After the dripping is finished, stirring for 0.6 to 6 hours at the temperature of between 5 and 25 ℃ to finish hydrolysis and dehydration condensation. Five kinds of preparation liquids containing methyl/phenyl silicone resins K to O having a solid content of about 50 mass% were obtained in the same manner as in the synthesis 1 of methyl silicone resin. Further, the silanol group amount and the constituent unit amount of the methyl/phenyl silicone resins K to O were adjusted by adjusting the reaction time (stirring time), the reaction temperature, the addition amount of the aqueous hydrochloric acid solution, and the charging amount.

The methyl silicone K to O obtained by²⁹Si-NMR and¹H-NMR analysis confirmed the structure. In addition, to²⁹Si-NMR was carried out to measure the structure of the methyl/phenyl silicone resin L, and four signals were observed. The chemical shifts of these signals are (1) δ -52ppm to-61 ppm, (2) δ -62ppm to-71 ppm, (3) δ -67ppm to-75 ppm, and (4) δ -75ppm to-83 ppm, respectively, which are assigned to T represented by the following formula_mUnit and T_fIn a unit、T_m-2 units, T_m-3 units, T_f-2 units, and T_f-3 units of silicon atoms. In addition, the methyl/phenyl silicone resin L has been subjected to¹H-NMR analysis showed that: methoxy groups derived from methyltrimethoxysilane and phenyltrimethoxysilane have all been hydrolyzed to hydroxyl groups. Further, the weight average molecular weight Mw and the molecular weight distribution Mw/Mn were measured by GPC analysis. The analysis results are shown in Table 3.

[ chemical formula 6]

[ Table 3]

1-4 Synthesis of methyl/phenyl Silicone resin 4

A2L flask was charged with 109g to 27g (0.8 mol to 0.2 mol) of methyltrimethoxysilane, 198g (1.0 mol) of phenyltrimethoxysilane, and 144g to 216g (1.2 mol to 1.8 mol) of dimethyldimethoxysilane, and then 800g of water was added thereto at 10 ℃ or lower and mixed thoroughly. Then, 180g to 216g (10.0 mol to 12.0 mol) of 0.05N hydrochloric acid aqueous solution was added dropwise to the mixture at 5 ℃ to 25 ℃ for 20 minutes to 40 minutes under ice-bath cooling, and the mixture was stirred at 5 ℃ to 25 ℃ for 0.6 hours to 6 hours to complete hydrolysis and dehydration condensation. After completion of the dropping, the same operation as in synthesis 1 of a methyl silicone resin was performed, and three silicone resin solutions containing methyl/phenyl silicone resins P to R having a solid content of about 50 mass% were obtained. Further, the amount of silanol groups and the amount of constituent units in the methyl/phenyl silicone resins P to R were adjusted by adjusting the reaction time (stirring time), the reaction temperature, the amount of addition of the aqueous hydrochloric acid solution, and the amount of charge.

The methyl silicone P to R obtained by²⁹Si-NMR and¹H-NMR analysis confirmed the structure. And, via GPC analysis, the weight-average molecular weight Mw and the molecular weight distribution Mw/Mn are determined. The analysis results are shown in Table 4.

[ Table 4]

1-5 preparation of methyl silicate and ethyl silicate

The following commercially available products were used as methyl silicate and ethyl silicate.

[ methyl silicate S ]

Methyl silicate 53A (condensate of tetramethoxysilane, manufactured by COLCOAT corporation) weight average molecular weight (Mw): 840. number average molecular weight (Mn): 610. Mw/Mn of 1.4

[ Ethyl silicate T ]

Ethyl silicate 48 (condensate of tetraethoxysilane manufactured by COLCOAT Co., Ltd.) weight average molecular weight (Mw): 1300. number average molecular weight (Mn): 850. Mw/Mn of 1.5

1-6 preparation of coating

A composition containing a fluororesin as a base was obtained by mixing a polyvinylidene fluoride resin (product name: KYNAR500, weight-average molecular weight: 650,000, melting point: 160 ℃ C. to 165 ℃ C., manufactured by PENNWALT Co., Japan) with an acrylic resin (thermoplastic polymer of methyl (meth) acrylate). The mixing ratio of the polyvinylidene fluoride resin and the acrylic resin was 70/30 (mass ratio).

In the composition, 1 mass% of dodecylbenzene sulfonic acid as a catalyst was added to the solid content of the composition, and dimethylaminoethanol was added. The amount of dimethylaminoethanol added was such that the amine equivalent of the dimethylaminoethanol was 1.25 times the acid equivalent of the dodecylbenzene sulfonic acid.

As shown in tables 5 and 6, the methyl silicone resin, the methyl/phenyl silicone resin, the methyl silicate, or the ethyl silicate was added so that the amount of each of the components was 5 mass% based on the total solid content of the coating material. Further, triethyl orthoformate was added to the paint added with methyl silicate or ethyl silicate so as to be 5 mass% based on the total solid content of the paint.

1-7. preparation of Metal sheets

A plating film having a thickness of 0.27mm, an A4 size (210 mm. times.297 mm) and a single-side plating adhesion of 90g/m was prepared²The hot-dip Zn-55% Al alloy-plated steel sheet of (1) was used as a metal sheet, and the surface was subjected to alkali degreasing. Thereafter, a coating type chromate treatment liquid (NRC 300NS manufactured by Nippon paint Co., Ltd.) was applied to the surface so that the amount of Cr deposited was 50mg/m². An epoxy resin primer (800P, manufactured by FINE COATINGS, Japan) was applied by a roll coater so that the cured film thickness became 5 μm. Next, the substrate was fired so that the maximum reached plate temperature was 215 ℃, thereby obtaining a plated steel sheet having a primer coating film formed thereon (hereinafter, simply referred to as "plated steel sheet").

2. Production of coated Metal sheet (1)

In examples 1 to 16 and comparative examples 1, 2, 11 and 12, the following coating film forming step and flame treatment step were performed to obtain coated metal sheets. In comparative examples 6 to 8, the following coating film forming step and corona discharge treatment step were performed to obtain coated metal sheets. On the other hand, in comparative examples 3 to 5, 9 and 10, the following coating film forming process was performed to obtain coated metal sheets.

2-1. coating film Forming step

The coated steel sheets were baked for 60 seconds at a temperature of 260 ℃ at the maximum and a plate surface air speed of 0.9m/s by applying the coating materials of the types shown in tables 5 and 6 to the coated steel sheets by means of a roll coater so that the cured film thickness became 20 μm. Further, in order to confirm the stability of the coating material, coating was performed 24 hours after the preparation of the coating material.

2-2 flame treatment step (examples 1 to 16, comparative examples 1, 2, 11 and 12)

The coating film formed in the coating film forming step is subjected to flame treatment. F-3000 manufactured by Flynn Burner, Inc. (USA) was used as a Burner for flame treatment. In addition, as the combustible gas, liquefied petroleum gas (combustible gas) is used by a gas mixerAnd clean dry air (liquefied petroleum gas: clean dry air (volume ratio): 1: 25). In addition, 1cm relative to the flame port of the burner²The flow rates of the respective gases were adjusted as follows: liquefied petroleum gas (combustible gas) was 1.67L/min, and clean dry air was 41.7L/min. The length of the flame hole of the burner head in the direction of conveyance of the coating film (length indicated by L in fig. 1A) was set to 4 mm. On the other hand, the length of the flame ports of the burner head in the direction perpendicular to the conveying direction (length indicated by W in fig. 1B) was 450 mm. Further, the distance between the flame ports of the burner head and the surface of the coating film was set to 50mm in accordance with the desired amount of flame treatment. The flame treatment amount was adjusted to 212kJ/m by setting the conveying speed of the coating film to 30 m/min²。

2-3 Corona discharge treatment step (comparative examples 6 to 8)

In the corona discharge treatment, a corona discharge treatment apparatus of the following specification, manufactured by spring motors, was used.

(Specification)

-electrode ceramic electrode

Electrode length 430mm

Output 310W

The number of times of corona discharge treatment of the coating film was set to one. The corona discharge treatment amount was adjusted by adjusting the treatment speed. Specifically, the corona discharge treatment amount was set to 200 W.min/m by performing the treatment at 3.8 m/min²。

3. Test (1)

The following tests were performed on the coated metal sheets produced in the examples and comparative examples, or test pieces produced using the paints used in the examples and comparative examples. The results are shown in tables 5 and 6.

(1) Evaporation of silicone resin or silicate

The coating materials used in examples and comparative examples were applied to the surface of an aluminum plate (JIS A5052) having a thickness of 0.5mm so as to have a film thickness of 18 μm, thereby forming a coating film. Then, the coated aluminum plate on which the coating film was formed was cut into a 10cm × 10cm square, dissolved in a mixed acid solution of hydrofluoric acid, hydrochloric acid, and nitric acid, and further irradiated with microwaves for thermal decomposition. Thereafter, a constant volume was set with ultrapure water to prepare a detection solution. The Si atoms in the detection solution were quantitatively analyzed by an ICP-AES Analyzer model ICPE-9820, manufactured by Shimadzu corporation.

On the other hand, a coating material was prepared in the same manner as in examples and comparative examples except that no silicone resin or silicate was added, and a coating film was formed using the coating material. Then, the Si atoms in the detection solution were quantitatively analyzed in the same manner as described above.

By comparing these, the Si atomic weight derived from the silicone resin or the silicate in each coating film was determined. The Si atomic weight of the coating film was calculated assuming that the silicone resin or silicate did not evaporate at all. Then, the amount of evaporation of the silicone resin or silicate at the time of coating film formation was evaluated based on the ratio of the Si atomic weight when the coating film was completely not evaporated to the Si atomic weight of the coating film produced in the examples or comparative examples, according to the following criteria.

X: the evaporation capacity is more than 20%

And (delta): more than 10 percent and less than 20 percent

Good: more than 3 percent and less than 10 percent

Very good: less than 3 percent

In these, Δ, and ∈ are defined as pass.

(2) Evaluation of storage stability of coating Material

The coating materials used in examples and comparative examples were stored in a thermostatic chamber at 40 ℃ and the viscosity of the coating material after 15 days was measured with a type B viscometer. Then, the viscosities before and after storage were compared and evaluated according to the following criteria.

X: gelatinizing within 15 days of standing in thermostatic chamber

And (delta): before and after being stored in a constant temperature room, the viscosity increase rate of the coating is more than 100 percent

O: before and after being stored in a constant temperature chamber, the viscosity increase rate of the coating is more than 30 percent and less than 100 percent

Very good: before and after being stored in a constant temperature chamber, the viscosity increase rate of the coating is less than 30 percent

In these, Δ, and ∈ are defined as pass.

(3) Determination of contact Angle with Water

The contact angle with water of the surface of the coating film of each of the coated metal sheets prepared in examples and comparative examples was measured. The measurement method is as follows: in a constant temperature and humidity chamber at an air temperature of 23. + -. 2 ℃ and a relative humidity of 50. + -. 5%, 0.01cc of water droplets of purified water were formed and measured by using a contact angle meter DM901 manufactured by Kyowa Kagaku K.

(4) Evaluation of resistance to rain-stain fouling

The raindrop stain resistance was evaluated in the following manner.

First, the coated metal plates produced in examples and comparative examples were mounted on a vertical exposure platform, respectively. The corrugated plate was attached to the upper portion of the coated metal plate at an angle of 20 ° with respect to the ground. At this time, the corrugated plate is provided so that rainwater flows in a strip shape on the surface of the coated metal plate. In this state, an outdoor exposure test for six months was performed, and the adhesion state of dirt was observed. Evaluation of the rainstain resistance was performed using the lightness difference (Δ L) of the coated metal sheet before and after exposure in the following manner.

X: case where Δ L is 2 or more (conspicuous dirt)

And (delta): (ii) when Δ L is 1 or more and less than 2 (raindrop dirt is not conspicuous but can be visually recognized)

Good: case where Δ L is less than 1 (rain mark dirt is hardly visually recognized)

Very good: Δ L was less than 1 and rain mark dirt was completely visually undetectable.

In these, Δ, and ∈ are defined as pass.

As shown in tables 5 and 6, when a coating film was formed only with a coating material containing a silicone resin, the contact angle with water of the coating film was high and the resistance to rain stain of the coated metal sheet was poor similarly in the case of using any silicone resin (comparative examples 3 to 5). In addition, when the corona discharge treatment was performed after the coating film formation step, the contact angle with water was also high, and the resistance to rain mark fouling was also insufficient (comparative examples 6 to 8). The following presumptions can be made: it is difficult to uniformly perform the hydrophilization treatment by the corona discharge treatment.

On the other hand, with respect to a silicone resin in which the amount (number of moles) of silanol groups is 5 to 50 mol% relative to the amount (number of moles) of Si atoms, a coated metal sheet formed with a coating containing the silicone resin and subjected to flame treatment has a sufficiently low contact angle with water, and has satisfactory rain mark fouling resistance (examples 1 to 16). The silicone resin having the amount of silanol groups within the above range tends to be uniformly concentrated on the surface of the coating film. Further, phenyl groups bonded to Si atoms are generally difficult to remove by a general surface treatment (e.g., corona discharge treatment) (e.g., comparative examples 7 and 8), but not only methyl groups but also phenyl groups can be removed by flame treatment, and silanol groups and the like can be introduced to the surface of the coating film (e.g., examples 9 to 16). In addition, the flame treatment can uniformly hydrophilize the coating film surface.

In addition, the coating material containing the silicone resin was evaluated for good evaporation properties. That is, the silicone resin is less likely to evaporate during curing of the coating material, and the coating film is less likely to be contaminated by silica or the like adhering to the heating device, thereby obtaining a coated metal sheet having a good appearance.

On the other hand, when a coating film was formed using a coating material containing a silicone resin with an excessively small amount of silanol groups (less than 5 mol%), the rain mark fouling resistance was insufficient even when the flame treatment was performed (comparative example 1). The following presumptions can be made: if the amount of silanol groups is less than 5 mol%, the molecular weight of the silicone resin tends to increase, and the silicone resin will be polymerized by a slight reaction. Therefore, the silicone resin is difficult to be uniformly concentrated on the surface and is likely to be in the shape of a sea island. As a result, the surface of the coated metal sheet cannot be hydrophilized uniformly even by flame treatment, and the rain mark fouling resistance cannot be sufficiently improved.

On the other hand, when a coating film is formed from a coating material containing a silicone resin having an excessive amount (more than 50 mol%) of silanol groups, the rain mark fouling resistance is not sufficiently improved (comparative example 2). If the amount of silanol groups is too large, the silicone resin reacts with the paint over a long period of time from the preparation of the paint to the application of the paint, and it is considered difficult to uniformly hydrophilize the surface of the coated metal sheet.

Further, the storage stability of the coating material containing an organic silicate such as methyl silicate or ethyl silicate was insufficient, and the coating material was likely to evaporate during curing of the coating film (comparative examples 9 to 12). Further, the coated metal sheet produced using the paint containing methyl silicate had low resistance to rain mark fouling even when flame-treated (comparative example 11). The following presumptions can be made: the coating not only makes it difficult for the methyl silicate to concentrate on the surface of the film during coating, but also evaporates during curing of the film.

4. Preparation of the coating (2)

Each coating was prepared by the following method.

4-1. Synthesis of methyl-based Silicone resin U

A2L flask was charged with 408g (3.0 mol) of methyltrimethoxysilane, and 800g of water was added at 10 ℃ or lower, followed by thorough mixing. Then, 216g (12.0 mol) of a 0.05N aqueous hydrochloric acid solution was added dropwise thereto at 5 ℃ for 40 minutes under cooling in an ice bath. After completion of the dropping, the mixture was stirred at 10 ℃ for 6 hours to complete hydrolysis and dehydration condensation. Thus, a preparation solution containing a methyl silicone resin U was obtained.

Then, methanol produced by hydrolysis was distilled off from the prepared solution at 70 ℃ under reduced pressure of 60mmHg for 1 hour. The preparation after the removal of methanol by distillation was turbid and separated into two layers by standing. The lower layer is a silicone resin that does not dissolve in water and settles. To the solution was added 469g of methyl isobutyl ketone (MIBK), and the mixture was stirred at room temperature for 1 hour. Thereby, the precipitated silicone resin was completely dissolved in MIBK. Then, the prepared solution was allowed to stand to separate an aqueous layer from an MIBK layer. Then, the lower water layer was removed from the flask with a stopper to obtain a colorless and transparent silicone resin solution having a solid content of 50 mass%.

To be provided with²⁹Si-NMR measured the structure of the obtained methyl silicone resin U, and two broad signals were observed. The chemical shifts of these signals are (1) δ -54ppm to-58 ppm and (2) δ -62ppm to-68 ppm. The chemical shifts are respectively ascribed to T represented by the following chemical formula_mIn cell, T_m-2 units and T_m-3 units of silicon atoms. That is, T is not contained in the methyl silicone resin U_m-1 unit. In addition, methyl silicone resin U has been processed¹H-NMR analysis showed that: methoxy groups derived from methyltrimethoxysilane have been fully hydrolyzed to hydroxyl groups.

[ chemical formula 7]

Then, GPC analysis (in terms of polystyrene) was performed under the following conditions, and the weight average molecular weight Mw and the molecular weight distribution Mw/Mn of the silicone resin U were measured. The results are shown in Table 7.

The measuring machine comprises: HLC-8320GPC manufactured by TOSOH corporation

Pipe column: shodex K-G + K-805 Lx 2 root + K-800D

Eluent: chloroform

Temperature: 40.0 ℃ of pipe column thermostatic bath

Flow rate: 1.0mL/min

Concentration: 0.2% by mass/volume

Injection amount: 100 μ l

Solubility: completely dissolve

Pretreatment: filtering with 0.45 μm filter

A detector: differential Refractometer (RI)

4-2. Synthesis of methyl-series Silicone resin V

A2L flask was charged with 286g (2.1 mol) of methyltrimethoxysilane and 108g (0.9 mol) of dimethyldimethoxysilane, and 800g of water was added at 10 ℃ or lower to mix thoroughly. Then, 198g (11.0 mol) of a 0.05N aqueous hydrochloric acid solution was added dropwise thereto at 5 ℃ to 25 ℃ for 20 minutes under cooling in an ice bath. After completion of the dropping, the mixture was stirred at 15 ℃ for 6 hours to undergo hydrolysis and dehydration condensation. After completion of the dropping, the same operation as the synthesis of the methyl silicone resin U was performed, and a silicone resin solution containing the methyl silicone resin V and having a solid content of about 50 mass% was obtained.

The methyl silicone resin V obtained by²⁹Si-NMR and¹H-NMR analysis confirmed the structure. Further, the weight average molecular weight Mw and the molecular weight distribution Mw/Mn were measured by GPC analysis. The analysis results of the methyl silicone V are shown in table 7. In addition, D in Table 7_m-1 units and D_mThe-2 units are each a structural unit represented by the following chemical formula.

[ chemical formula 8]

[ Table 7]

4-3. Synthesis of methyl/phenyl Silicone resin W

A2L flask was charged with 272g (2.0 mol) of methyltrimethoxysilane and 119g (1.0 mol) of phenyltrimethoxysilane, and 800g of water was added at 10 ℃ or lower to sufficiently mix them. Then, 198g (11.0 mol) of a 0.05N aqueous hydrochloric acid solution was added dropwise thereto at 5 ℃ to 25 ℃ for 30 minutes under cooling in an ice bath. After completion of the dropping, the mixture was stirred at 10 ℃ for 6 hours to complete hydrolysis and dehydration condensation. After completion of the dropping, a preparation solution containing a methyl/phenyl silicone resin W having a solid content of about 50 mass% was obtained in the same manner as in the synthesis of the methyl silicone resin U.

The methyl/phenyl silicone resin W obtained by²⁹Si-NMR and¹H-NMR analysis confirmed the structure. In addition, to²⁹Si-NMR was carried out to measure the structure of the methyl/phenyl silicone resin W, and four signals were observed. The chemical shifts of these signals are (1) δ -52ppm to-61 ppm, (2) δ -62ppm to-71 ppm, (3) δ -67ppm to-75 ppm, and (4) δ -75ppm to-83 ppm, respectively, which are assigned to T represented by the following formula_mUnit and T_fIn cell, T_m-2 units, T_m-3 units, T_f-2 units, and T_f-3 units of silicon atoms. In addition, the methyl/phenyl silicone resin W is processed¹H-NMR analysis showed that: methoxy groups derived from methyltrimethoxysilane and phenyltrimethoxysilane have all been hydrolyzed to hydroxyl groups. Further, the weight average molecular weight Mw and the molecular weight distribution Mw/Mn were measured by GPC analysis. The analysis results are shown in Table 8.

[ chemical formula 9]

4-4. Synthesis of methyl/phenyl Silicone resin X

A2L flask was charged with 109g (0.8 mol) of methyltrimethoxysilane, 198g (1.0 mol) of phenyltrimethoxysilane, and 144g (1.2 mol) of dimethyldimethoxysilane, and then 800g of water was added thereto at 10 ℃ or lower to sufficiently mix them. Then, 216g (12.0 mol) of a 0.05N aqueous hydrochloric acid solution was added dropwise at 5 to 25 ℃ for 40 minutes under cooling in an ice bath, and the mixture was stirred at 10 ℃ for 6 hours to complete hydrolysis and dehydration condensation. After completion of the dropping, the same operation as the synthesis of the methyl silicone resin U was performed, and a silicone resin solution containing the methyl/phenyl silicone resin X and having a solid content of about 50 mass% was obtained.

The methyl/phenyl silicone resin X obtained by²⁹Si-NMR and¹H-NMR analysis confirmed the structure. And, all-purposeBy GPC analysis, the weight average molecular weight Mw and the molecular weight distribution Mw/Mn were determined. The analysis results are shown in Table 8.

[ Table 8]

4-5 preparation of methyl silicate and ethyl silicate

The following commercially available products were used as methyl silicate Y and ethyl silicate Z.

[ methyl silicate Y ]

Methyl silicate 53A (condensate of tetramethoxysilane, manufactured by COLCOAT corporation) weight average molecular weight (Mw): 840. number average molecular weight (Mn): 610. Mw/Mn of 1.4

[ Ethyl silicate Z ]

Ethyl silicate 48 (condensate of tetraethoxysilane manufactured by COLCOAT Co., Ltd.) weight average molecular weight (Mw): 1300. number average molecular weight (Mn): 850. Mw/Mn of 1.5

4-6 preparation of coating

A composition containing a fluororesin as a base was obtained by mixing a polyvinylidene fluoride resin (product name: KYNAR500, weight-average molecular weight: 650,000, melting point: 160 ℃ C. to 165 ℃ C., manufactured by PENNWALT Co., Japan) with an acrylic resin (thermoplastic polymer of methyl (meth) acrylate). The mixing ratio of the polyvinylidene fluoride resin and the acrylic resin was 70/30 (mass ratio).

In the composition, 1 mass% of dodecylbenzene sulfonic acid was added as a catalyst to the amount of the solid content of the composition. Also, dimethylaminoethanol was added. The amount of dimethylaminoethanol added was such that the amine equivalent of the dimethylaminoethanol was 1.25 times the acid equivalent of the dodecylbenzene sulfonic acid.

The methyl silicone resin, the methyl/phenyl silicone resin, the methyl silicate, or the ethyl silicate was added so that the proportions thereof with respect to the total solid content of the coating material were as shown in table 9. The coating was stored at 20 to 30 ℃ for 15 days. In the case of the paint to which methyl silicate Y or ethyl silicate Z was added, triethyl orthoformate was added as a dehydrating agent so as to be 5 mass% based on the total solid content of the paint at the time of paint preparation.

4-7. preparation of Metal sheets

A plating film having a thickness of 0.27mm, an A4 size (210 mm. times.297 mm) and a single-side plating adhesion of 90g/m was prepared²The hot-dip Zn-55% Al alloy-plated steel sheet of (1) was used as a metal sheet, and the surface was subjected to alkali degreasing. Thereafter, a coating type chromate treatment liquid (NRC 300NS manufactured by Nippon paint Co., Ltd.) was applied to the surface so that the amount of Cr deposited was 50mg/m². Then, an epoxy resin primer (800P, manufactured by FINE COATINGS Co., Ltd.) was applied by a roll coater so that the cured film thickness became 5 μm. Next, the substrate was fired so that the maximum reached plate temperature was 215 ℃, thereby obtaining a plated steel sheet having a primer coating film formed thereon (hereinafter, simply referred to as "plated steel sheet").

5. Production of coated Metal sheet (2)

In examples 17 to 26 and comparative examples 13, 16, 21 and 22, the following coating film forming step and flame treatment step were performed to obtain coated metal sheets. On the other hand, in comparative examples 14, 15, and 17 to 20, only the following coating film forming steps were performed, and a coated metal sheet was obtained.

5-1. coating film Forming step

The above-described plated steel sheet was coated with the paints of the types shown in Table 9 (all paints after 15 days from the preparation of the paints) by a roll coater so that the cured film thickness became 20 μm, and the steel sheet was baked at a maximum plate temperature of 260 ℃ and a plate surface air speed of 0.9m/s for 60 seconds.

5-2 flame treatment step (examples 17 to 26 and comparative examples 13, 16, 21 and 22)

The coating film formed in the coating film forming step is subjected to flame treatment. F-3000 manufactured by Flynn Burner, Inc. (USA) was used as a Burner for flame treatment. As the combustible gas, a mixed gas (liquefied petroleum gas) obtained by mixing liquefied petroleum gas (combustible gas) and clean dry air with a gas mixer is usedGas: clean dry air (volume ratio) 1: 25). In addition, 1cm relative to the flame port of the burner²The flow rates of the respective gases were adjusted as follows: liquefied petroleum gas (combustible gas) was 1.67L/min, and clean dry air was 41.7L/min. The length of the flame hole of the burner head in the direction of conveyance of the coating film (length indicated by L in fig. 1A) was set to 4 mm. On the other hand, the length of the flame ports of the burner head in the direction perpendicular to the conveying direction (length indicated by W in fig. 1B) was 450 mm. Further, the distance between the flame ports of the burner head and the surface of the coating film was set to 50mm in accordance with the desired amount of flame treatment. The flame treatment amount was adjusted to 319kJ/m by setting the conveying speed of the coating film to 20 m/min²。

6. Test (2)

The following measurements and evaluations were made on the coated metal sheets produced in examples and comparative examples, or on test pieces produced using the coating materials used in examples and comparative examples. The results are shown in Table 9.

(1) XPS assay

XPS measurement of the coating film surface was carried out using an AXIS-NOVA scanning X-ray photoelectron spectrometer manufactured by KRATOS. Then, the ratios of Si atoms to the amounts of Si atoms, F atoms, C atoms and O atoms on the surface of the coating film, respectively, Si was determined_aAnd a ratio x of the amount of O atoms to the amount of C atoms in the surface of the coating film. The C1s peak top of the obtained X-ray photoelectron spectrum was corrected to 285eV, and Si was added_2pThe energy spectrum was separated into a peak corresponding to 103.5eV and a peak corresponding to 102.7 eV. Further, the relative Si is calculated_2pThe ratio y of the peak area of the entire spectrum to the peak area of 103.5 eV. The measurement conditions in the XPS measurement are as follows. In addition, Si_2pAfter the background of the spectrum was removed by the Linear (Linear) method, the spectrum was processed by a complex function of a gaussian function and a lorentz function, and separated into a peak of an organic Si atom (102.7eV) and a peak of an inorganic Si atom (103.5 eV).

(measurement conditions)

An X-ray source: al Ka 1486.6eV

Analysis area: 700 μm × 300 μm

(2) Diiodomethane slide angle determination

On the horizontally held coating film, 2. mu.l of diiodomethane was dropped. Then, the tilt angle of the coating film (angle formed by the horizontal plane and the coating film) was increased at a rate of 2 degrees/sec using a contact angle measuring apparatus (DM 901, made by nippon interface science). At this time, the droplet of diiodomethane was observed by a camera attached to the contact angle measuring apparatus. Then, the inclination angle at the moment when the droplets of diiodomethane slide was determined, and the average value of 5 times was set as the diiodomethane slide angle of the coating film. Here, the moment when the droplet of diiodomethane slides means a moment when both the end point below the droplet of diiodomethane in the direction of gravity and the end point above the droplet of diiodomethane in the direction of gravity start moving.

(3) Evaluation of resistance to rain-stain fouling

The raindrop stain resistance was evaluated in the following manner.

First, the coated metal plates produced in examples and comparative examples were mounted on a vertical exposure platform, respectively. The corrugated plate was attached to the upper portion of the coated metal plate so as to form an angle of 20 ° with respect to the ground surface. At this time, the corrugated plate is provided so that rainwater flows in a strip shape on the surface of the coated metal plate. In this state, an outdoor exposure test for six months was performed, and the adhesion state of dirt was observed. Evaluation of the rainstain resistance was performed using the lightness difference (Δ L) of the coated metal sheet before and after exposure in the following manner.

X: case where Δ L is 2 or more (conspicuous dirt)

And (delta): (ii) when Δ L is 1 or more and less than 2 (raindrop dirt is not conspicuous but can be visually recognized)

Good: case where Δ L is less than 1 (rain mark dirt is hardly visually recognized)

Very good: Δ L less than 1 and rain mark dirt was completely invisible

In these, Δ, and ∈ are defined as pass.

As shown in Table 9 above, in Si_aWhen the amount of x is not less than 8.0 atm%, not less than 0.8 and y is not less than 0.6, all of the results of the rainstain fouling resistance were good (examples 17 to 26). In contrast, the ratio of Si atoms_aWhen the amount is less than 8.0 atm%, the rain mark fouling resistance is low (comparative examples 13, 16, and 19). The following presumptions can be made: since the surface of the coating film does not contain a sufficient amount of Si atoms, it is difficult to sufficiently increase the amount of siloxane bonds or silanol groups on the surface of the coating film, and it is difficult to increase the hydrophilicity.

In contrast, even the ratio of Si atoms Si_aThe content of the organic solvent is 8.0 atm% or more, and the raindrop stain resistance is poor even when x is less than 0.8 or when y is less than 0.6 (comparative examples 14, 15, 17, 18, 20 to 22). It is considered that when x is less than 0.8 or y is less than 0.6, the organic group derived from the silicone resin or the organic group derived from the organosilicate is not sufficiently removed, and the following presumption can be made: the hydrophilicity cannot be sufficiently increased because a large amount of organic groups remain on the surface.

The present application claims priority based on japanese patent application No. 2018-188120, filed on 3/10/2018. The contents described in the specification and drawings of this application are all incorporated in the specification of this application.

Industrial applicability

According to the method for producing a coated metal sheet of the present invention, a coated metal sheet having a good appearance and resistance to rain mark fouling can be easily produced without contaminating a heating apparatus. Therefore, the method for producing a coated metal sheet and the coated metal sheet obtained by the method can be suitably used as exterior building materials for various buildings.

Description of the reference numerals

22 burner head

22a housing

22b flame vent

22c auxiliary flame port

23 gas supply pipe