JP2020157246A - Coated metal plate and manufacturing method of coated metal plate - Google Patents

Abstract

To provide a manufacturing method of a coated metal plate which has low glossiness even when the coated metal plate does not substantially contain gloss control agent particles as the coated metal plate having a colored resin layer containing a fluorine resin, and has a high working property even after long-term storage.SOLUTION: A manufacturing method of a coated metal plate, which has a metal plate and a colored resin layer arranged thereon, includes: a step of grinding and mixing acrylic resin and colored pigment to provide a pigment dispersion liquid which includes acrylic resin, colored pigment particles and solvent; a step of stirring and mixing the pigment dispersion liquid and fluorine resin particles to provide colored resin coating material which includes an aggregate of the fluorine resin particles, the acrylic resin, the colored pigment particles and the solvent; and a step of applying the colored resin coating material onto the metal plate and, thereafter, heating the applied colored resin coating material to form the colored resin layer.SELECTED DRAWING: None

Description

The present invention relates to a painted metal plate and a method for manufacturing a painted metal plate.

The painted metal plate is generally excellent in durability, weather resistance and design, and is preferably used for exterior building materials, for example. Among the coated metal plates for exterior building materials, the coated metal plate having a fluororesin coating is suitable for the coated metal plate that requires long-term durability.

A coated metal plate having a fluororesin coating film has a transparent coating film made of a mixed resin of polyvinylidene fluoride and an acrylic resin on the surface of the stainless steel sheet, and the transparent coating film has a specific crystallinity and hardness. Fluororesin-based coated stainless steel sheets are known (see, for example, Patent Document 1). Further, a fluororesin-based material having a fluororesin-based colored layer containing a fluororesin, an acrylic resin, an inorganic fired pigment, and an organic pigment on the front surface of the steel sheet and a coating film made of polyester having a specific glass transition temperature on the back surface of the steel sheet. Painted steel sheets are known (see, for example, Patent Document 2).

Fluororesin is known to undergo crystallization over time. That is, the fluororesin has a property that the molecule is relatively easy to move in a temperature range above the glass transition temperature (for example, about −40 ° C. in the case of polyvinylidene fluoride) and a property that it has crystallinity. Therefore, the fluororesin tends to change from an irregular molecular arrangement structure (amorphous structure) to a regular molecular arrangement structure (crystal structure) in the temperature range above the glass transition temperature.

Further, the fluororesin also has a property that when crystallized, the bonding force between the molecular chains becomes strong. Therefore, the fluororesin-based coating film may have a reduced ductility over time due to the progress of crystallization of the fluororesin over time.

Therefore, a coated metal plate having a fluororesin coating film has high ductility of the fluororesin-based coating film, and the coating film is less likely to break (coating cracking) during molding immediately after production, but is stored for a long period of time after production. If the fluororesin coating film is molded after the ductility is reduced, the coating film may be broken.

As a method for improving the processability of a fluororesin coating film, a method of suppressing crystallization immediately after production and preventing a deterioration of the processability of the coating film over time has been proposed (for example, Patent Document 3, Patent Document 4, Patent Document). Reference 5). Further, as a method for preventing the deterioration of processability of the fluororesin coating film over time, a method of graft-polymerizing a (meth) acrylic acid ester compound on the fluororesin has also been proposed (see, for example, Patent Document 6). Further, the coated metal plate having a colored coating film containing a fluororesin, or the coated metal plate having a colored coating film containing a fluororesin and a gloss adjusting coating film containing a fluororesin is slowly cooled to form α crystals. (For example, Patent Documents 7 and 8) disclose a method of forming irregularities on the surface of a colored coating film by pressing an embossing roll or adjusting the content of a gloss adjusting agent. In addition, as shown in Patent Documents 7 and 8, a colored resin paint containing a fluororesin is usually prepared by pulverizing and mixing a colored pigment and a resin component from the viewpoint of forming a uniform coating film, and then using a filter or the like. It is used by filtering to remove aggregates.

Japanese Unexamined Patent Publication No. 2001-09367 Japanese Unexamined Patent Publication No. 2008-0872242 Japanese Unexamined Patent Publication No. 61-114846 Japanese Unexamined Patent Publication No. 6-262139 Japanese Unexamined Patent Publication No. 8-131945 Japanese Unexamined Patent Publication No. 9-87575 JP-A-2018-167470 JP-A-2018-167471

In recent years, highly corrosion-resistant galvanized steel sheets to which magnesium has been added have begun to be used as original plates for painting. Since the magnesium-added zinc-plated layer of the highly-corrosion-resistant galvanized steel sheet is generally hard, the plating layer is formed during the molding process of a coated metal plate having a fluororesin coating formed on the highly-corrosion-resistant galvanized steel sheet. The crack width tends to be large. Then, as the crack width of the plating layer during the molding process increases, the cracking of the fluororesin coating film during the molding process also tends to increase. Therefore, it is particularly desired that the fluororesin coating film is less likely to be cracked even after long-term storage, and the workability is further improved.

Further, cracking of the fluororesin coating film is particularly likely to occur when the fluororesin coating film contains gloss modifier particles such as silica particles and glass beads.

The present invention has been made in view of the above circumstances, and is a coated metal plate having a colored resin layer containing a fluororesin, and has a low glossiness even if it does not substantially contain gloss adjusting agent particles. An object of the present invention is to provide a method for producing a coated metal plate and a coated metal plate having high workability even after long-term storage.

The present invention relates to the following coated metal plate and a method for manufacturing the coated metal plate.

The method for producing a coated metal plate of the present invention is a method for producing a coated metal plate having a metal plate and a colored resin layer arranged on the metal plate, wherein the acrylic resin and the colored pigment are pulverized and mixed. A step of obtaining a pigment dispersion containing an acrylic resin, colored pigment particles, and a solvent, and a 50% particle diameter (d50) of the first fluororesin particles and the volume-based particle size distribution is larger than that of the first fluororesin particles. A step of mixing the second fluororesin particles so that the first fluororesin particles: the second fluororesin particles = 60:40 to 0: 100 (mass ratio) to obtain fluororesin particles, and the above-mentioned step. The pigment dispersion liquid and the fluororesin particles are stirred and mixed to contain an aggregate of the fluororesin particles, the acrylic resin, the coloring pigment particles, and the solvent, and the content of the gloss adjusting agent particles is increased. It includes a step of obtaining a colored resin coating having a solid content of 1% by mass or less, and a step of applying the colored resin coating on a metal plate and then heating to form a colored resin layer.

The coated metal plate of the present invention is a coated metal plate having a metal plate and a colored resin layer arranged on the metal plate, and the colored resin layer comprises a cohesive fusion product of fluororesin particles, an acrylic resin, and the like. The content of the gloss adjuster particles in the colored resin layer including the colored pigment particles is 1% by mass or less with respect to the colored resin layer, and the 60 ° glossiness Gs of the colored resin layer is 20 or less. Is.

According to the present invention, it is a coated metal plate having a colored resin layer containing a fluororesin, which has low glossiness even if it does not substantially contain gloss adjusting agent particles, and has high processability even after long-term storage. A method for producing a coated metal plate and a coated metal plate can be provided.

As described above, when a coated metal plate having a fluororesin coating film containing gloss adjusting agent particles such as silica particles and glass beads is bent, coating film cracking is likely to occur starting from the gloss adjusting agent particles. When such a coating film crack occurs, moisture, oxygen, sea salt particles, etc. easily invade from the cracked portion, and the coating original plate (particularly a metal plate) is easily corroded. Therefore, it is desired to reduce the glossiness by imparting unevenness to the surface of the fluororesin coating film even if the gloss adjusting agent particles are not contained. The same applies when the fluororesin coating film is a colored resin layer further containing colored pigment particles in addition to a base resin such as a fluororesin.

On the other hand, the present inventors appropriately form a cohesive fusion product of fluororesin particles as a base resin (fused product of secondary particles) on the surface of the colored resin layer. It was found that unevenness derived from can be formed. Since the agglomerated and fused product of such fluororesin particles has a larger contact area with the acrylic resin than one fluororesin particle having a similar size and a large particle size, the compatibility with the acrylic resin is also high. It was also found that even if the coated metal plate is bent, cracks are unlikely to occur at the interface between the cohesive fusion product of the fluororesin particles and the acrylic resin.

Such a colored resin layer is formed by applying a colored resin paint containing an aggregate of fluororesin particles, an acrylic resin, a colored pigment particle, and a solvent on a metal, and then heating (baking) the metal. be able to. Specifically, the fluororesin constituting the fluororesin particles has a relatively low surface tension, and the acrylic resin has a relatively high surface tension. Therefore, in the process of heating (baking) the coating film of the colored resin paint, the agglomerates of the fluororesin particles on the surface in contact with the air and the acrylic resin are phase-separated (causing cissing) (other than the agglomerates of the fluororesin particles). A sea-island structure having a sea phase (continuous phase) in which a fluororesin (dissolved in a solvent) and an acrylic resin are compatible with each other and an island phase (dispersed phase) containing a cohesive fusion product of fluororesin particles as a main component. At the same time, it is considered that an uneven shape is formed such that the island phase mainly composed of the aggregated and fused product of the fluororesin particles is concave and the sea phase in which the fluororesin and the acrylic resin are compatible is convex.

Conventionally, as a colored resin paint containing a fluororesin, one in which fluororesin particles and a colored pigment are pulverized and mixed in the presence of a solvent and then filtered is used. On the other hand, in the present invention, a fluororesin particle prepared by stirring and mixing (without pulverization) separately from the coloring pigment is used. Thereby, agglomerates of fluororesin particles can be appropriately left (contained) in the colored resin paint.
Further, by using a mixture of the first fluororesin particles and the second fluororesin particles having different particle diameters in a predetermined ratio as the fluororesin particles, the size of the aggregates of the obtained fluororesin particles can be appropriately adjusted. Easy to adjust to range. Further, since the packing density of the obtained agglomerates of the fluororesin particles can be adjusted within an appropriate range, the acrylic resin can be easily permeated into the agglomerates of the fluororesin particles, and the agglomerates may crack or fall off. Can also be suppressed. The present invention has been made based on such findings.

1. 1. Method for manufacturing a coated metal plate The method for producing a coated metal plate of the present invention includes 1) a step of pulverizing and mixing an acrylic resin and a colored pigment to obtain a pigment dispersion, and 2) a first fluororesin particle and a second. A step of mixing the fluororesin particles in a predetermined ratio to obtain the fluororesin particles, a step of 3) stirring and mixing the obtained pigment dispersion and the fluororesin particles to obtain a colored resin paint, and 4) This includes a step of applying the obtained colored resin paint on a metal plate and then heating to form a colored resin layer.

About step 1) (preparation step of pigment dispersion liquid) Acrylic resin and color pigment are pulverized and mixed to obtain pigment dispersion liquid. By performing pulverization and mixing, the coarse particles of the coloring pigment having a high hardness can be made finer while mixing the acrylic resin and the coloring pigment particles.

Milling and mixing can be done by any method, for example by a bead mill (using beads). A bead mill is a mill that mixes raw materials while crushing them, and refers to a device that fills a container containing the raw materials with beads (media), rotates the beads, grinds the raw materials, and crushes and disperses the raw materials. Such bead mills include attritors, ball mills, vibration mills, SC mills and the like.

The bead mill may be a wet bead mill for refining the raw material in a liquid, or a dry bead mill for refining the raw material in air or an inert gas. A wet bead mill is preferable from the viewpoint of easy pulverization to a relatively small particle size.

That is, the pigment dispersion may be prepared, for example, by pulverizing and mixing (drying) the acrylic resin particles and the coloring pigment, and then dissolving them in a solvent; the acrylic resin particles and the coloring pigment are mixed. , It may be carried out by a method of pulverizing and mixing (wet) in the presence of a solvent; or by a method of pulverizing and mixing (wet) an acrylic resin (preliminarily dissolved in a solvent) and a coloring pigment. Above all, from the viewpoint that the acrylic resin and the coloring pigment can be easily mixed and crushed into a relatively small particle size, the acrylic resin previously dissolved in the solvent and the coloring pigment are crushed and mixed to form a pigment dispersion. It is preferable to obtain. Thereby, a pigment dispersion liquid containing an acrylic resin, colored pigment particles, and a solvent can be obtained.

Hereinafter, each component used for preparing the pigment dispersion will be described.

(acrylic resin)
The acrylic resin used for preparing the pigment dispersion has a viewpoint of suppressing the crystallization of the fluororesin constituting the fluororesin particles, a viewpoint of improving the dispersibility of the colored pigment particles, and a viewpoint of improving the adhesion of the base resin. Therefore, it is contained in the colored resin layer.

The acrylic resin is preferably a polymer containing a structural unit derived from (meth) acrylic acid ester, and is a homopolymer containing a structural unit derived from methyl methacrylate or a copolymer thereof and another copolymerization monomer. Is more preferable.

Examples of other copolymerizable monomers copolymerizable with methyl methacrylate include methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, butyl (meth) acrylate, and the like other than methyl methacrylate. (Meta) acrylic acid esters; unsaturated nitriles such as (meth) acrylonitrile; unsaturated carboxylic acids such as (meth) acrylic acid and crotonic acid; (meth) acrylamide, methyl (meth) acrylamide, ethyl (meth) acrylamide, (Meta) acrylamides such as propyl (meth) acrylamide; vinyls such as styrene and methylstyrene; acrylonitrile is included. Further, from the viewpoint of weather resistance, the acrylic resin preferably further has an ultraviolet absorbing group. The acrylic resin having an ultraviolet absorbing group can also be obtained by a method of copolymerizing an ultraviolet absorbing group-containing (meth) acrylate such as 3- (2H-benzotriazole-2-yl) -4-hydroxyphenethylmethacrylate. it can. These may be used alone or in combination of two or more.

From the viewpoint of making the weather resistance of the coated metal plate less likely to be impaired, it is preferable that the glass transition temperature of the acrylic resin is high. From such a viewpoint, the acrylic resin is preferably a polymer containing a structural unit derived from methyl methacrylate as a main component. The content of the structural unit derived from methyl methacrylate in the polymer is preferably 50% by mass or more, more preferably 70% by mass or more, based on all the structural units constituting the polymer. , 100% by mass is particularly preferable.

On the other hand, from the viewpoint of facilitating the workability of the coated metal plate, it is preferable that the glass transition temperature of the acrylic resin is low. From such a viewpoint, the acrylic resin is an ester compound of a structural unit derived from methyl methacrylate, a structural unit derived from ethyl acrylate, and (meth) acrylic acid and an alcohol having 1 to 6 carbon atoms (however, It is preferably a copolymer containing a structural unit derived from (excluding methyl methacrylate). The structural unit derived from methyl methacrylate imparts an appropriate hardness to the copolymer, and the structural unit derived from ethyl acrylate or the structural unit derived from an esterified product imparts an appropriate flexibility to the copolymer. Can be granted. Further, in the above-mentioned copolymer, the structural unit derived from ethyl acrylate and the structural unit derived from the esterified product enhance the compatibility with the fluororesin, while the ester compound appropriately lowers the compatibility with the fluororesin. By doing so, the compatibility between the acrylic resin and the fluororesin can be appropriately adjusted.

In the copolymer, the content of the structural unit derived from methyl methacrylate is 10 to 50% by mass, the content of the structure derived from ethyl acrylate is 40 to 80% by mass, and the above ester compound. The content of the structural unit derived from is preferably 10 to 50% by mass. Furthermore, the above-mentioned copolymer has a content of structural units derived from methyl methacrylate in an amount of 10 to 30% by mass and a content of structural units derived from ethyl acrylate in an amount of 60 to 80% by mass. The content of the structural unit derived from the ester compound is preferably 10 to 30% by mass.

Further, from the viewpoint of making it easier to improve the workability of the coated metal plate and making it difficult for the weather resistance to be impaired, the acrylic resin contains a structural unit derived from methyl methacrylate and a structural unit derived from ethyl acrylate (meth). ) In addition to the structural unit derived from an ester compound of acrylic acid and an alcohol having 1 to 6 carbon atoms, the copolymer may further contain a structural unit derived from an ultraviolet absorbing group-containing (meth) acrylate.

The glass transition temperature (Tg) of the acrylic resin is not particularly limited and may be, for example, 0 to 110 ° C. From the viewpoint of facilitating the improvement of the weather resistance of the colored resin layer, the Tg of the acrylic resin is preferably high, for example, preferably 50 to 110 ° C., more preferably 70 to 110 ° C. On the other hand, from the viewpoint of suppressing the crystallization of the fluororesin over time, making it easier to suppress cracking of the colored resin layer, and making it easier to improve the processability of the coated metal plate, a lower value is preferable, for example, 40 ° C. or lower. Is preferable, and the temperature is more preferably 30 ° C. or lower. The Tg of the acrylic resin can be measured by differential thermal analysis (DTA).

The Tg of the acrylic resin can be adjusted by the monomer composition of the acrylic resin. In order to increase the Tg of the acrylic resin, it is preferable to increase the content of the structural unit derived from methyl methacrylate, and it is preferable to decrease the content of the structural unit derived from ethyl acrylate.

The weight average molecular weight (Mw) of the acrylic resin is preferably 20000 to 20000, and more preferably 20000 to 150,000. The weight average molecular weight of the acrylic resin can be measured by the same method as described above.

The content of the acrylic resin is preferably 5 to 40% by mass with respect to the total of the fluororesin and the acrylic resin described later. When the content of the acrylic resin is 5% by mass or more, not only the crystallization of the fluororesin can be sufficiently suppressed, but also the adhesion to the metal plate is easily improved, so that the processability of the coated metal plate is sufficiently improved. sell. When the content of the acrylic resin is 40% by mass or less, the characteristics of the fluororesin such as weather resistance, corrosion resistance and stain resistance are not easily impaired. From the above viewpoint, the content of the acrylic resin is more preferably 10 to 30% by mass with respect to the total of the fluororesin and the acrylic resin.

(Coloring pigment)
The coloring pigment is coarse particles that become colored pigment particles after being pulverized and mixed. The colored pigment particles can give a color tone to the resin layer to form a colored coating film. The color pigment may be either an organic color pigment or an inorganic color pigment that is generally available as a color pigment for paints.

Examples of inorganic color pigments include titanium oxide, chromium oxide, carbon black, iron black, iron oxide yellow, titanium yellow, red iron oxide, dark blue, cobalt blue, cerulean blue, ultramarine blue, cobalt green, and molybdenum red.

Examples of organic coloring pigments include quinacridone red, resole red B, brilliant scarlet G, pigment scarlet 3B, brilliant carmine 6B, lake red C, lake red D, permanent red 4R, Bordeaux 10B, fast yellow G, fast yellow 10G. , Parared, Watching Red, Benzidine Yellow, Benzidine Orange, Bonmaroon L, Bonmaroon M, Brilliant Fast Scarlet, Vermilion Red, Phthalocyanine Blue, Phthalocyanine Green, Fast Sky Blue, and Aniline Black.

The coloring pigment may be a composite oxide fired pigment containing a metal component. Examples of fired pigments include CoAl, CoCrAl, CoCrZnMgAl, CoNiZnTi, CoCrZnTi, NiSbTi, CrSbTi, FeCrZnNi, MnSbTi, FeCr, FeCrNi, FeNi, FeCrNiMn, FeZn, CoCr, MnCo, and SnZnTi.

Moreover, the coloring pigment may be a metallic pigment. Examples of metallic pigments include Al flakes, resin coated Al flakes, metal oxide coated Al flakes, Ni flakes, Cu flakes, and stainless steel flakes.

Moreover, the coloring pigment may be a pearl pigment. Examples of pearl pigments include titanium oxide-coated mica, iron oxide-coated mica, and titanium oxide-iron oxide-coated mica.

The coloring pigment may be used alone or in two or more kinds.

The average particle size of the coloring pigment (coarse particles) used for preparing the pigment dispersion is not particularly limited, but may be, for example, more than 3 μm. That is, the average particle size of the colored pigment particles obtained after pulverization and mixing is 3 μm or less, preferably 2 μm or less, more preferably 0.01 to 1.5 μm, and further preferably 0.01 to 0.5 μm. Is preferable. When the average particle size of the obtained colored pigment particles is within the above range, it is easy to impart a sufficient color tone evenly to the colored resin layer.

The average particle size of the coloring pigment used for preparing the pigment dispersion can be obtained as the average value of the particle sizes of any 100 coloring pigments (coarse particles) observed by an electron microscope.

The content of the coloring pigment varies depending on the particle size of the coloring pigment, but is preferably 10 to 40% by mass with respect to the solid content of the coloring resin coating material, for example, from the viewpoint of color development of the coloring resin layer.

(solvent)
The solvent is not particularly limited as long as it can dissolve at least the acrylic resin. Examples of such solvents include hydrocarbons such as toluene and xylene, esters such as ethyl acetate and butyl acetate, ethers such as cellosolve, and ketones such as methyl isobutyl ketone, methyl ethyl ketone, isophorone and cyclohexanone. Among them, isophorone is preferable from the viewpoint that the acrylic resin can be dissolved and the affinity with the fluororesin particles is high.

In the present embodiment, an example is shown in which an acrylic resin and a coloring pigment are pulverized and mixed to obtain a pigment dispersion liquid containing the acrylic resin, the coloring pigment particles, and a solvent, but the present invention is not limited to this. , A commercially available pigment dispersion liquid in which an acrylic resin and colored pigment particles are pulverized and mixed may be obtained.

Regarding step 2) (step of obtaining fluororesin particles), the first fluororesin particles having a relatively small 50% particle diameter (d50) of the volume-based particle size distribution and the second fluororesin particles having a relatively large d50 , Fluororesin particles (mixture) are obtained by mixing at a predetermined ratio. Thereby, the packing density and size of the obtained aggregates of the fluororesin particles can be adjusted within an appropriate range.

The d50 of the first fluororesin particles is preferably 1 to 5 μm. When the d50 of the first fluororesin particles is 1 μm or more, the first fluororesin particles are unlikely to be excessively aggregated with each other, so that unevenness of an appropriate size is likely to be formed on the surface of the colored resin layer. When the d50 of the first fluororesin particles is 5 μm or less, the second fluororesin particles easily enter between the second fluororesin particles, and agglomerates having a high packing density are easily formed. Further, since the acrylic resin easily penetrates into the agglomerates of the first fluororesin particles, cracks are unlikely to occur at the interface between the acrylic resin and the agglomerates of the fluororesin particles. From the above viewpoint, the d50 of the first fluororesin particles is more preferably 3 to 5 μm.

The 10% particle diameter (d10) of the first fluororesin particles is preferably 0.2 to 4 μm, more preferably 0.5 to 3 μm. The 90% particle diameter (d90) of the first fluororesin particles is preferably 3 to 10 μm, and more preferably 4 to 8 μm.

The d50 of the second fluororesin particles is preferably 5.5 to 12 μm. When the d50 of the second fluororesin particles is 5.5 μm or more, the obtained aggregates (secondary particles) of the fluororesin particles can be appropriately enlarged, so that the surface of the colored resin layer has irregularities of an appropriate size. Easy to form. When the d50 of the second fluororesin particles is 12 μm or less, the acrylic resin can penetrate into the aggregates of the fluororesin particles, so that cracks are unlikely to occur at the interface between the acrylic resin and the aggregates of the fluororesin particles. From the above viewpoint, the 50% particle diameter (d50) of the fluororesin particles is more preferably 7 to 10 μm.

The 10% particle diameter (d10) of the second fluororesin particles is preferably 2 to 10 μm, and more preferably 3 to 8 μm. The 90% particle diameter (d90) of the second fluororesin particles is preferably 8 to 20 μm, more preferably 10 to 15 μm.

The d10, d50, and d90 of the first fluororesin particles and the second fluororesin particles can be measured by the following procedure.
1) The first fluororesin particles (or the second fluororesin particles) are dispersed in ion-exchanged water as a dispersion medium to obtain a particle dispersion liquid. This particle dispersion is set in a laser diffraction / scattering particle size distribution measuring device LA-950V2 manufactured by Horiba Seisakusho Co., Ltd., and ultrasonic waves are irradiated for 60 minutes as a pretreatment and ultrasonic waves for 2 minutes as a dispersion treatment.
2) Next, the volume-based particle size distribution of this particle dispersion is measured, and d10, d50, and d90 are obtained as the cumulative frequency% diameter.

The mixing ratio of the first fluororesin particles and the second fluororesin particles is preferably 1st fluororesin particles: 2nd fluororesin particles = 60:40 to 0: 100 (mass ratio), and 30:70 to 70. More preferably, it is 0: 100 (mass ratio). As described above, when the content ratio of the secondary fluororesin particles is high, the aggregates (secondary particles) of the secondary fluororesin particles can be appropriately increased, so that the surface of the colored resin layer has irregularities of an appropriate size. Easy to form. Thereby, the glossiness of the obtained colored resin layer can be lowered.

(1st fluororesin particles / 2nd fluororesin particles)
The first fluororesin particles and the second fluororesin particles are the main components of the base resin constituting the colored resin layer. The fluororesin constituting the first fluororesin particles and the second fluororesin particles is a polymer containing at least a structural unit derived from vinylidene fluoride (VDF). Such a fluororesin can impart durability, chemical resistance, heat resistance, abrasion resistance, weather resistance, corrosion resistance, stain resistance, and the like to the colored resin layer while reducing crystallization over time.

The fluororesin may be a homopolymer of vinylidene fluoride (VDF), or may be a copolymer of vinylidene fluoride (VDF) and another fluoromonomer copolymerizable therewith.

Examples of other fluoromonomers include trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene and hexafluoropropylene. Of these, hexafluoropropylene (HFP) is preferable from the viewpoint of facilitating the control of crystallinity.

The content of the structural unit derived from hexafluoropropylene in the above copolymer is not particularly limited, but from the viewpoint of reducing crystallization over time without impairing weather resistance, the structural unit derived from vinylidene fluoride It is preferably 1 to 15% by mass with respect to the total of the structural units derived from hexafluoropropylene and hexafluoropropylene. When the content of the structural unit derived from hexafluoropropylene is 1% by mass or more, crystallization over time is likely to be reduced, and when it is 15% by mass or less, the weather resistance is not easily impaired. The total amount of the structural unit derived from vinylidene fluoride and the structural unit derived from hexafluoropropylene is preferably 100% by mass with respect to all the structural units constituting the fluororesin.

The weight average molecular weight (Mw) of the fluororesin is preferably 100,000 to 700,000, more preferably 200,000 to 500,000. The weight average molecular weight (Mw) of the fluororesin can be measured in terms of polystyrene by gel permeation chromatography (GPC).

The content of the fluororesin particles is not particularly limited, but is preferably 60 to 95% by mass with respect to the total of the fluororesin particles and the acrylic resin. When the content of the fluororesin particles is 60% by mass or more, the characteristics of the fluororesin particles such as weather resistance, corrosion resistance and stain resistance can be sufficiently exhibited. When the content of the fluororesin particles is 95% by mass or less, not only the crystallization of the fluororesin can be sufficiently suppressed by the acrylic resin, but also the adhesion to the metal plate is not easily impaired, and the processability of the coated metal plate is not impaired. Is not easily damaged. From the above viewpoint, the content of the fluororesin particles is more preferably 70 to 90% by mass with respect to the total of the fluororesin particles and the acrylic resin.

Regarding step 3) (step of obtaining colored resin paint), the pigment dispersion obtained in 1) above and the fluororesin particles obtained in 2) above are stirred and mixed to obtain a colored resin paint.

(Other ingredients)
In addition to the pigment dispersion liquid and the fluororesin particles, other components may be further blended if necessary. Examples of other components include solvents, hardeners, hardeners and hydrophilic agents.

As the solvent, the same solvent as that used in the step 1) can be used. Of these, isophorone is preferable from the viewpoint of high affinity with fluororesin particles.

The curing agent is added to the colored resin paint when the base resin has crosslinkable groups such as hydroxyl groups, carboxyl groups, glycidyl groups, active halogen atoms, and isocyanate groups, and the base resin is used when the paint is baked. To bridge. The curing agent can be appropriately selected from known cross-linking agents, curing agents, and the like, depending on the type of the base resin, the baking conditions, and the like. For example, when the base resin has a hydroxyl group or the like, a melamine compound or an isocyanate compound can be used as the curing agent.

The curing catalyst is a component that promotes curing of the coating film or cross-linking of the base resin, and can be appropriately selected from known components having such a catalytic action.

The hydrophilizing agent is suitable as an additive for the colored resin layer, and can be contained in the colored resin paint from the viewpoint of preventing rain streak stains on the colored resin layer. Examples of hydrophilizers include partially hydrolyzed condensates of tetraalkoxysilane.

(Stirring and mixing)
Then, the pigment dispersion liquid prepared above and the fluororesin particles are stirred and mixed. As a result, a colored resin paint containing an aggregate of fluororesin particles, an acrylic resin, colored pigment particles, and a solvent is obtained. The acrylic resin may be dissolved in a solvent.

Stirring and mixing refers to mixing by a stirrer (mixer) and without pulverization by beads (media). In such stirring and mixing, the agglomerates (secondary particles) of the fluororesin particles are not excessively broken (or decomposed), so that the agglomerates of the fluororesin particles in the obtained colored resin paint are appropriately left. be able to.

The stirring and mixing conditions (stirring blade tip speed (peripheral speed), stirring time) are preferably relatively gentle conditions so that agglomerates of fluororesin particles can be appropriately left. The peripheral speed is, for example, preferably 8 m / s or less, and more preferably 1.5 to 6 m / s. The stirring time depends on the peripheral speed, but is preferably 30 to 180 minutes, more preferably 30 to 60 minutes, for example. When the peripheral speed or the stirring time is less than the upper limit, the stirring speed is not too high, the stirring time is not too long, and the agglomerates are not decomposed too much (to the primary particles). It can be made moderately easy to leave.

The content ratio of the agglomerates of the fluororesin particles in the obtained colored resin paint is preferably, for example, 30% by volume or more, more preferably 40 to 70% by volume, based on the solid content of the colored resin paint. At least a part of the fluororesin particles mixed by stirring becomes an agglomerate, and the rest can be dissolved or dispersed in a solvent.

The content ratio of the agglomerates of the fluororesin particles in the colored resin paint can be determined by observing the coating film obtained by applying the colored resin paint on the glass plate and then drying it with an electron microscope or the like. Specifically, arbitrary three points are photographed with a scanning electron microscope composition image (1000 times), an image analysis is performed in a range of 10000 μm ² each, and the average area ratio of the agglomerates of the fluororesin particles is obtained to obtain the volume fraction. Convert.

The agglomerates of the fluororesin particles are usually agglomerates of 500 to 300,000 fluororesin particles (primary particles), although it depends on the average particle diameter (d50) of the fluororesin particles.

The total amount of the fluororesin particles and the acrylic resin is preferably 80% by mass or more, more preferably 100% by mass, based on the base resin component contained in the colored resin paint.

Further, the colored resin coating material does not substantially contain the gloss adjusting agent particles. Specifically, the content of the gloss adjusting agent particles in the colored resin paint is 1% by mass or less, preferably 0% by mass, based on the solid content.

The gloss adjuster particles are particles such as silica particles and glass beads, and are different from colored pigment particles and fluororesin particles. Specifically, the gloss adjuster particles are usually transparent to translucent particles that do not affect the color tone, and are particles that reduce the gloss of the coating film, and thus are different from the colored pigment particles and the fluororesin particles. different. For example, pearl pigment particles and metallic pigment particles as colored pigment particles can be distinguished in that they are particles that increase the gloss of a coating film, whereas gloss adjuster particles are particles that reduce the gloss of a coating film.

About step 4) (step of forming colored resin layer) The obtained colored resin paint is applied on a metal plate.

(Metal plate)
The metal plate can be selected from known metal plates. Examples of metal plates include cold-rolled steel sheets, galvanized steel sheets, Zn-Al alloy-plated steel sheets, Zn-Al-Mg alloy-plated steel sheets, aluminum-plated steel sheets, and stainless steel sheets (austenite-based, martensite-based, ferrite-based, ferrite-based). Includes (including martensite two-phase systems), aluminum plates, aluminum alloy plates and copper plates.

The metal plate is preferably a plated steel sheet or a stainless steel sheet from the viewpoint of corrosion resistance and weight reduction, and is preferably a plated steel sheet from the viewpoint of cost effectiveness. Further, the metal plate is preferably a molten 55% Al—Zn alloy plated steel sheet, a Zn—Al—Mg alloy plated steel sheet or an aluminum plated steel sheet from the viewpoint of further enhancing corrosion resistance. Of these, galvanized steel sheets are preferable, and zinc-based galvanized steel sheets containing magnesium, such as Zn-Al-Mg alloy-plated steel sheets, are more preferable.

The thickness of the metal plate can be appropriately set according to the use of the painted metal plate. For example, when the coated metal plate is used as an exterior building material, the thickness of the metal plate is preferably 0.2 to 3.0 mm, for example, and 0.25 to 2.0 mm from the viewpoint of further improving workability. Is preferable.

(Application)
The coating material can be applied onto the metal plate by a known method such as roll coating, curtain flow coating, spray coating, and immersion coating.

(Heating (baking))
Next, the coating film of the colored resin paint applied on the metal plate is heated (baked).

Heating (baking) of the coating film volatilizes the solvent from the colored resin paint and bake it to solidify the coating film of the colored resin paint. When the colored resin paint contains a curing agent, the solvent is volatilized from the colored resin paint and baked to cure the coating film (specifically, the base resin).

The coating film may be heated (baked) at a temperature at which the fluororesin particles are sufficiently melted (or fused). Specifically, when the melting point of the fluororesin particles is Tm (° C.), the baking temperature is preferably (Tm + 25) ° C. or higher. From the viewpoint of suppressing the decomposition of the fluororesin particles, the temperature is preferably 300 ° C. or lower. The baking temperature is the temperature reached by the metal plate coated with the colored resin paint. For example, the ultimate temperature of the metal plate coated with the colored resin paint can be 130 to 300 ° C, preferably 180 to 280 ° C.

Then, in the process of heating (baking) the coating film, irregularities are formed on the surface of the colored resin layer. Specifically, the fluororesin constituting the fluororesin particles has a relatively low surface tension, and the acrylic resin has a relatively high surface tension. Therefore, in the process of heating (baking) the coating film, the fluororesin and acrylic resin on the surface in contact with air are phase-separated (causing cissing), and the fluororesin and acrylic resin are incompatible with each other (continuous phase). And a sea-island structure having an island phase (dispersed phase) containing a cohesive fusion product of fluororesin particles as a main component is formed, and an island phase mainly composed of a cohesive fusion product of fluororesin particles is concave and fluororesin. It is considered that an uneven shape is formed such that the sea phase in which the acrylic resin is compatible with the resin is convex. It is considered that the larger the particle size of the fluororesin particles, the larger the unevenness on the surface.

(cooling)
Then, the heated (baked) coating film is cooled to form a colored resin layer containing a cohesive fusion product of fluororesin particles, an acrylic resin, and colored pigment particles.

That is, the heated (baked) coating film is heated (baked) at 130 ° C./sec from a temperature (200 ° C.) higher than the melting temperature of the fluororesin to a temperature (70 ° C.) at which the molecular motion of the fluororesin is reduced and crystals are difficult to grow. Cool at the above cooling rate (crystallization step). From the viewpoint of suppressing a decrease in workability due to the formation of coarse crystals, the cooling rate is preferably faster, preferably 250 ° C./sec or higher.

The coating film can be cooled by a known method such as air cooling, water cooling, air cooling, contact with a cooling member, and a combination thereof.

The coating film may be cooled immediately after the coating film is heated (baked), or after the coating film heated (baked) at a temperature lower than the melting temperature is heated to a temperature equal to or higher than the melting temperature. ..

5) Other Steps The method for manufacturing a coated metal plate may further include steps other than the above, if necessary. Examples of the other steps include one or more of a chemical conversion treatment step of forming a chemical conversion treatment film, a step of forming an undercoat layer, and a step of forming an intermediate coating layer.

(Chemical conversion processing process)
The chemical conversion treatment step is a step of forming a chemical conversion treatment layer on a metal plate. The chemical conversion treatment layer may be arranged directly on the metal plate, that is, between the metal plate and the colored resin layer, for the purpose of improving the adhesion and corrosion resistance of the coated metal plate. The chemical conversion treatment layer is a layer formed in contact with the surface of the metal plate, and is composed of a composition adhered to the surface of the metal plate by pre-painting treatment. Examples of chemical conversion-treated layers include non-chromate coatings and chromate coatings. All of these are rust-preventive films.

The non-chromate film is preferable from the viewpoint of enhancing the corrosion resistance and the viewpoint of reducing the burden on the environment in the production and use of the coated metal plate, and the chromate film is preferable from the viewpoint of enhancing the corrosion resistance.

Examples of non-chromate coatings include Ti-Mo composite coatings, fluoroacid coatings, phosphate coatings, resin coatings, resin and silane coupling agent coatings, silica coatings, silica and silane coupling agent coatings. , Zirconium-based coatings, as well as zirconium and silane coupling agent-based coatings.

In such a chemical conversion treatment layer, an aqueous chemical conversion treatment liquid for forming a chemical conversion treatment film is applied to the surface of a metal plate by a known method such as a roll coating method, a spin coating method, or a spray method. It can be formed by drying the board without washing it with water. From the viewpoint of productivity, the drying temperature and drying time of the metal plate are preferably, for example, 60 to 150 ° C. for 2 to 10 seconds at the ultimate temperature of the metal plate.

(Undercoat layer forming process)
The step of forming the undercoat layer is a step of forming the undercoat layer between the metal plate and the colored resin layer from the viewpoint of improving the adhesion and corrosion resistance of the colored resin layer on the coated metal plate. The undercoat layer is formed on the surface of the metal plate or the surface of the chemical conversion treatment layer.

The step of forming the undercoat layer can be performed by applying a paint for the undercoat layer (resin composition for the undercoat layer) and solidifying (or curing) the film thereby.

The coating material for the undercoat layer can be a resin composition containing a thermoplastic resin. Examples of thermoplastic resins include fluororesins, polyester resins, modified silicone resins, acrylic resins, phenoxy resins, urethane resins, vinyl chloride resins and the like.

Further, the coating material for the undercoat layer may be a resin composition containing a curable resin and a curing agent. Examples of the curable resin include an epoxy resin, a curable polyester resin (for example, a hydroxyl group-containing polyester resin), a curable acrylic resin (for example, a hydroxyl group-containing acrylic resin), and a phenol resin. The epoxy resin may be a modified epoxy resin having an amino group or the like.

In the example of the curing agent, the curing agent can be appropriately selected depending on the type of the curable resin. For example, examples of curing agents such as curable resins having hydroxyl groups include melamine compounds and isocyanate compounds. Examples of the epoxy resin curing agent include amine compounds and imidazole compounds.

These resin compositions may further contain additives such as rust preventive pigment particles, colored pigment particles, metallic pigment particles, pearl pigment particles, extender pigment particles, and gloss modifier particles.

Examples of rust preventive pigment particles include non-chromic rust preventive pigment particles including modified silica, vanazine salt, magnesium hydrogen phosphate, magnesium phosphate, zinc phosphate, and aluminum polyphosphate, and chromate. It contains particles of a chromium-based rust preventive pigment containing strontium, zinc chromate, barium chromate, calcium chromate and the like. As the colored pigment particles and the metallic pigment particles, the same ones as described above can be used. Examples of extender pigment particles include particles of barium sulfate, silica and calcium carbonate. Examples of the gloss adjuster particles include particles of an inorganic material such as silica and calcium carbonate, and particles of a resin material such as an acrylic resin.

The content of these additives is not particularly limited. For example, the content of the extender pigment particles is preferably 0 to 30% by mass with respect to the solid content of the resin composition. The content of the rust preventive pigment is preferably 10 to 40% by mass with respect to the solid content of the resin composition.

These resin compositions may further contain solvents and additives, if desired.

These resin compositions are prepared by uniformly mixing and dispersing the above-mentioned materials. The coating film of the paint is produced by being baked onto the metal plate by heating the metal plate at a temperature of 180 to 260 ° C., for example, at the temperature reached by the metal plate.

(Intermediate coating layer forming process)
The step of forming the intermediate coating layer is a step of forming an intermediate coating layer between the undercoat layer and the colored resin layer from the viewpoint of enhancing the adhesion and corrosion resistance between the layers of the coated metal plate.

The step of forming the intermediate coating layer can also be performed by applying the coating material for the intermediate coating layer (intermediate coating coating) and solidifying the coating film by the same as described above.

However, in the present invention, it is assumed that there is no step of pulverizing and mixing the colored resin paint between the steps of 3) and 4). This is to appropriately leave agglomerates of fluororesin particles in the colored resin paint applied to the metal plate. Further, it does not matter before or after the steps 1) and 2).

2. 2. Painted metal plate The painted metal plate of the present invention is obtained by the above-mentioned method for manufacturing a painted metal plate. That is, the coated metal plate of the present invention has a metal plate and a colored resin layer arranged on the metal plate.

2-1. Colored Resin Layer The colored resin layer is arranged in contact with the surface of the metal plate or via another layer. The colored resin layer is preferably a layer constituting the outermost surface of the coated metal plate from the viewpoint of further enhancing the weather resistance of the coated metal plate.

The colored resin layer contains a coagulated and fused product of fluororesin particles, an acrylic resin, and colored pigment particles, and may further contain a fluororesin derived from fluororesin particles other than the coagulated and fused product.

The agglomerated fusion product of the fluororesin particles is derived from the agglomerates of the fluororesin particles remaining in the colored resin paint, and when the fluororesin particles (primary particles) constituting the agglomerates form the colored resin layer. It is fused by heating (baking) of. In such a coagulated and fused product of fluororesin particles, at least a part of the surface of each fluororesin particle is coated with acrylic resin, or the acrylic resin penetrates into the gap between the coagulated fluororesin particles. There is.

Whether or not it is a cohesive fusion product of fluororesin particles can be confirmed, for example, by observing the cross section of the colored resin layer with a transmission electron microscope or the like by a dyeing method. For example, by detecting a component derived from an acrylic resin in a part of a cross section of a cohesive fused product, it can be determined that, for example, agglomerates of fluororesin particles coated with an acrylic resin are fused. ..

As described above, the cohesive fusion product of the fluororesin particles forms irregularities on the surface of the colored resin layer. That is, the colored resin layer has a sea-island structure of a sea phase (continuous phase) in which a fluororesin and an acrylic resin are compatible with each other and an island phase (dispersed phase) containing a cohesive fusion product of fluororesin particles as a main component. It has an uneven shape such that the agglomerated fusion product of the fluororesin particles is concave and the fused portion of the fluororesin and the acrylic resin is convex. As a result, the colored resin layer has substantially no gloss adjusting agent particles (for example, the content of the gloss adjusting agent particles is 1% by mass or less, preferably 0% by mass, based on the colored resin layer. However, it is possible to form an uneven shape on the surface only with the base resin. Therefore, it is possible to suppress cracking of the colored resin layer even if the coated metal plate is bent while exhibiting a good matting effect.

Further, since the coagulated and fused product of the fluororesin particles is firmly adhered to the acrylic resin or the like around the fluororesin particles, it is difficult for the surface of the colored resin layer to come off even if it is rubbed, and corrosion or the like due to it is unlikely to occur. Further, when the gloss adjusting agent particles are used, the surface of the obtained colored resin layer is likely to have protrusions due to the gloss adjusting agent particles, so that the surface of the colored resin layer tends to be rough to the touch. On the other hand, the surface of the colored resin layer obtained by the method for producing a coated metal plate of the present invention is liable to form recesses due to the aggregated fusion of fluororesin particles, so that the surface of the colored resin layer feels soft. It becomes.

The composition of the colored resin layer is the same as the composition of the solid content of the colored resin paint. The average particle size of the colored pigment particles in the colored resin layer is the same as the average particle size of the colored pigment after pulverization and mixing in the method for producing a coated metal plate. That is, the average particle size of the colored pigment particles in the colored resin layer can be 3 μm or less, preferably 2 μm or less, more preferably 0.01 to 1.5 μm, and further preferably 0.01 to 0.5 μm. The average particle size of the colored pigment particles in the colored resin layer can be obtained by observing the cross section of the colored resin layer with an electron microscope and taking the average value of any 100 particle sizes.

(Glossiness)
The 60-degree mirror gloss Gs (60 °) on the surface of the colored resin layer of the coated metal plate is not particularly limited, but is preferably 20 or less, preferably 15 or less, from the viewpoint of enhancing the design by the matting effect. Is more preferable. The 60 degree mirror gloss Gs (60 °) can be measured according to JIS Z 8741: 1997.

The 60-degree mirror glossiness Gs (60 °) is the size, packing density, and amount of the coagulated and fused material of the fluororesin particles contained in the colored resin layer; that is, the first (before stirring and mixing) in the manufacturing process of the coated metal plate. 1 Mixing ratio of fluororesin particles and 2nd fluororesin particles, 50% particle diameter (d50) of 1st fluororesin particles and 2nd fluororesin particles, mixing time and peripheral speed at the time of preparing colored resin paint, composition of acrylic resin It can be adjusted by such as. In order to reduce the 60-degree mirror glossiness Gs (60 °), the size of the cohesive fusion product of the fluororesin particles contained in the colored resin layer should be appropriately increased, and the amount should be appropriately increased; that is, the first The mixing ratio of the 1-fluororesin particles and the 2nd fluororesin particles is preferably appropriately increased, and the mixing time and peripheral speed at the time of preparing the colored resin paint are preferably appropriately reduced.

(Thickness)
The thickness of the colored resin layer is appropriately set according to the use of the coated metal plate, and is preferably 10 to 50 μm, for example. When the thickness of the colored resin layer is 50 μm or less, it is not necessary to increase the amount of paint applied when producing the colored resin layer, and when the paint film is heated and solidified, armpits (foam-like blisters) or It is possible to prevent the occurrence of coating defects such as holes).

The thickness of the colored resin layer can be expressed by the average value of the distances from the bottom surface to the surface at a plurality of locations (for example, 10 arbitrarily selected locations) of the colored resin layer.

The thickness of the colored resin layer can be appropriately determined in consideration of the content of the colored pigment particles, the color tone and the degree of ultraviolet shielding, the degree of processing during the molding process of the coated metal plate, and the like.

For example, when the color tone brightness (L value specified in JIS) of the colored pigment particles in the colored resin layer is low, or when the degree of ultraviolet shielding of the pigment particles is high, the color development property of the colored resin layer by the colored pigment particles (their). The color hiding property against the color of the base) and the ultraviolet shielding rate to the base are increased. Therefore, in these cases, the thickness of the colored resin layer can be made smaller. Further, since the ductility required for the colored resin layer is low, such as when the degree of processing is low, the thickness of the colored resin layer can be reduced.

On the other hand, from the viewpoint of maintaining long-term adhesion between the colored resin layer and its base (suppressing interface breakage for a long period of time), it is preferable to reduce the ultraviolet transmittance of the colored resin layer, and for that purpose, the colored resin layer It is preferable to increase the thickness of.

As described above, the lower limit of the thickness of the colored resin layer cannot be unconditionally stated, but for example, the degree of processing is equivalent to the degree of processing of 4T, and the L value of the colored pigment particles (for example, titanium oxide particles) exceeds 80. If so, the thickness of the colored resin layer is preferably 20 μm or more, and more preferably 25 μm or more. Further, when the degree of processing is as described above and the L value of the colored pigment particles (for example, iron-chromium-based fired pigment particles) is 70 or less, the thickness of the colored resin layer is preferably 15 μm or more, preferably 18 μm or more. Is more preferable.

When arranging other layers, the thickness of the colored resin layer can be determined in consideration of the existence of the other layers. For example, when the coated metal plate has an undercoat layer and a colored resin layer, the thickness of the colored resin layer can be, for example, 10 to 35 μm from the viewpoint of enhancing designability, corrosion resistance, and processability over time.

2-2. Other Layers As described above, the coated metal plate may further have layers other than the colored resin layer. Examples of other layers include chemical conversion layers, undercoat layers, and intermediate coat layers. For example, the coated metal plate preferably has a metal plate, a chemical conversion treatment layer, an undercoat layer, and a colored resin layer in this order; a metal plate, a chemical conversion treatment layer, an undercoat layer, and an intermediate coating layer. It is more preferable to have the colored resin layer in this order.

2-2-1. Chemical conversion treatment layer As described above, the chemical conversion treatment layer can be arranged directly on the metal plate, that is, between the metal plate and the colored resin layer, for the purpose of improving the adhesion and corrosion resistance of the coated metal plate. As described above, examples of the chemical conversion treatment layer include a non-chromate film and a chromate film.

The amount of non-chromate film adhered can be appropriately determined according to the type. For example, the adhesion amount of the Ti-Mo composite coating is preferably 10 to 500 mg / m ² in terms of total Ti and Mo, and the adhesion amount of the fluoroacid-based coating is 3 to 100 mg in terms of fluorine or total metal elements. preferably / is ^{m 2,} and the adhesion amount of the phosphate coating is preferably 0.1-5 g / ^{m 2} in terms of phosphorus, deposition of resin coating is 1-500 mg of resin terms is preferably / ^{m 2,} the adhesion amount of the resin and the silane coupling agent-based coating is preferably 0.1 to 50 mg / ^{m 2} in terms of Si, the adhesion amount of the silica-based coating, in terms of Si is preferably 0.1 to 200 mg / ^{m 2,} the adhesion amount of silica and silane coupling agent-based coating is preferably 0.1 to 200 mg / ^{m 2} in terms of Si, adhesion quantity of the zirconium-based coating is preferably 0.1-100 mg / ^{m 2} in terms of Zr coating weight of zirconium and a silane coupling agent-based coating is preferably 0.1-100 mg / ^{m 2} in terms of Zr.

Examples of chromate-based coatings include coating-type chromate-treated coatings and phosphoric acid-chromic acid-based treated chromate rust-preventive coatings. The amount of adhesion of these chromate-based coatings is preferably ²⁰ to 80 mg / m ² in terms of chromium element.

2-2-2. Undercoat layer As described above, the undercoat layer can be arranged between the metal plate and the colored resin layer from the viewpoint of enhancing the adhesion and corrosion resistance of the colored resin layer in the coated metal plate. The undercoat layer is formed on the surface of the metal plate or the surface of the chemical conversion treatment layer.

As described above, the undercoat layer may be composed of a resin composition containing a thermoplastic resin or a cured product of a resin composition containing a curable resin and a curing agent.

The thickness of the undercoat layer is not particularly limited, but is preferably 1 to 10 μm, more preferably 3 to 7 μm, for example.

2-2-3. Intermediate coating layer As described above, the intermediate coating layer can be arranged between the undercoat layer and the colored resin layer from the viewpoint of enhancing the adhesion and corrosion resistance between the layers of the coated metal plate.

Similar to the undercoat layer, the intermediate coating layer may also be composed of a resin composition containing a thermoplastic resin or a cured product of a resin composition containing a curable resin and a curing agent. Further, the intermediate coating layer may further contain an additive in the same manner as the undercoat layer. As the additive, for example, the same additive as described in the colored resin layer can be used.

The thickness of the intermediate coating layer is not particularly limited, but is preferably, for example, 3 to 20 μm, and more preferably 5 to 15 μm.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

1. 1. Preparation of painted original plate (preparation of metal plate)
A molten Zn-6% Al-3Mg alloy-plated steel sheet having a plate thickness of 0.4 mm and a double-sided plating adhesion amount of 180 g / m ² was alkali degreased.

(Formation of chemical conversion treatment layer)
Next, a non-chromate rust preventive treatment liquid having the following composition was applied to the surface of the alkali degreased plated steel sheet, and the coated plated steel sheet was dried at 100 ° C. without washing with water. As a result, non-chromate rust prevention treatment (formation of chemical conversion treatment layer) with an adhesion amount of 10 mg / m ^{2 in} terms of Ti was performed.
Hexafluorosilicic acid 55g / L
Hexafluorosilicic acid 10 g / L
Amino Methyl Substituted Polyvinyl Phenol 72 g / L
Water residue

(Formation of undercoat layer)
Next, an epoxy resin-based undercoat coating having the following composition is applied to the surface of the plated steel sheet after the non-chromate rust prevention treatment, and then heated so that the ultimate temperature of the plated steel sheet reaches 200 ° C. to increase the dry film thickness. A 5 μm undercoat coating was formed to obtain a chromate-free plated steel sheet. This was used as the original coating plate. The clear paint is "NSC680" (a paint containing an epoxy resin and an isocyanate-based curing agent) manufactured by Nippon Paint Industrial Coatings Co., Ltd.
Phosphate mixture 23% by mass (based on solids)
Barium sulfate 15% by mass (based on solids)
Silica 1% by mass (relative to solid content)
Clear paint remaining

2. 2. Preparation of colored resin paint 2-1. Material preparation (fluororesin particles)
Fluororesin particles 1 (first fluororesin particles) and fluororesin particles 2 (second fluororesin particles) shown in Table 1 were prepared.

The d10, d50, and d90 of the fluororesin particles 1 and 2 were measured by the following procedure.
1) Fluororesin particles were dispersed in ion-exchanged water as a dispersion medium to obtain a particle dispersion. This particle dispersion was set in a laser diffraction / scattering particle size distribution measuring device LA-950V2 manufactured by Horiba Seisakusho Co., Ltd., and ultrasonic waves were irradiated for 60 minutes as a pretreatment and ultrasonic waves for 2 minutes as a dispersion treatment.
2) The volume-based particle size distribution of the obtained particle dispersion was measured by the above apparatus, and d10, d50, and d90 were obtained as cumulative frequency% diameters.

(acrylic resin)
As the acrylic resin, a polymer containing methyl methacrylate (MMA), ethyl acrylate (EA) and acrylonitrile (AN) in different compounding ratios was synthesized by a conventional method to obtain acrylic resins 1 to 4. In the preparation of the acrylic resins 1 and 2, the amount of the benzotriazole-based ultraviolet absorbing group shown in Table 2 below was further incorporated into the acrylic resin.

The weight average molecular weight (Mw) and the glass transition temperature (Tg) of the acrylic resins 1 to 4 were measured by the following methods, respectively.

[Weight average molecular weight]
The weight average molecular weight of the acrylic resin was calculated based on the molecular weight of standard polystyrene from the chromatogram measured by the gel permeation chromatograph according to JIS K 0124-2011.

〔Glass-transition temperature〕
The glass transition temperature of the acrylic resin was measured using DSC (Differential Scanning Colorimetry) according to JIS K 7121-2012.

(Coloring pigment)
Color pigment: Titanium oxide (JR-805 manufactured by TAYCA Corporation, average particle size 0.29 μm)

(Gloss adjuster particles)
Gloss adjuster particles 1: Silica particles (Silicia 436 manufactured by Fuji Silysia Chemical Ltd.), average particle diameter 4 μm
Gloss adjuster particles 2: Glass beads (EMB20 manufactured by Potters Barotini), average particle diameter 10 μm
Gloss adjuster particles 3: Acrylic particles (ENEOS Unipowder NMB-1020 manufactured by JXTG Energy Co., Ltd.), average particle diameter 10 μm

2-2. Preparation of colored resin paint (preparation of colored resin paint 1)
(1) Preparation of Pigment Dispersion Liquid 1 As a solid content, acrylic resin 1 and titanium oxide (coloring pigment) were blended so that acrylic resin: titanium oxide = 7:15 (mass ratio). The solid content and the solvent component (isophorone) are further blended so that the solid content: solvent component = 1: 1 (mass ratio), and the ready mill RMB-04 manufactured by Imex Co., Ltd. has a peripheral speed of 6 m / s. Was mixed for 30 minutes (crushing and mixing). Then, the obtained mixture was filtered through a filter of 500 mesh to remove agglomerated particles from the mixture to obtain a pigment dispersion liquid 1. As the beads (media), zirconia 0.5 mmφ was used.

(2) Preparation of Colored Resin Paint 1 Fluororesin particles 2 are blended in the obtained pigment dispersion so that the fluororesin particles: acrylic resin = 4: 1 (mass ratio), and further the same as the fluororesin particles. Further mass of isophorone was added. This was stirred and mixed for 30 minutes at a stirring blade tip speed (peripheral speed) of 1.5 m / s using a stirrer (NZ-1100 manufactured by Tokyo Rika Kikai Co., Ltd.) to obtain a colored resin coating material 1.

(Preparation of colored resin paints 2 to 6)
Colored resin paints 2 to 6 were obtained in the same manner as in the colored resin paint 1 except that the stirring and mixing conditions (peripheral speed, time) were changed as shown in Table 3.

(Preparation of colored resin paints 7 and 8)
Colored resin paints 7 and 8 were obtained in the same manner as the colored resin paint 1 except that the types of acrylic resins were changed as shown in Table 3.

(Preparation of colored resin paints 17 and 18)
The pigment dispersion 1 and the fluororesin particles shown in Table 3 are blended so that the fluororesin particles: acrylic resin = 4: 1 (mass ratio), and isophorone having the same mass as the fluororesin particles is further added. It was. This was pulverized and mixed at the peripheral speed and time shown in Table 3 using a ready mill RMB-04 manufactured by Imex (using zirconia beads 0.5 mmφ) to obtain colored resin paints 17 and 18.

(Preparation of colored resin paints 9 to 16)
Colored resin paints 9 to 16 were obtained in the same manner as in the colored resin paint 1 except that the mixing ratio of the first fluororesin particles and the second fluororesin particles was changed as shown in Table 3.

(Preparation of colored resin paints 19 to 21)
Colored resin paints 19 to 21 were obtained in the same manner as the colored resin paint 9 except that the types and amounts of gloss adjusting agent particles shown in Table 3 were further blended when the pigment dispersion liquid and the fluororesin particles were mixed.

(Preparation of colored resin paints 22 to 24)
When the pigment dispersion liquid and the fluororesin particles were mixed, colored resin paints 22 to 24 were obtained in the same manner as in the colored resin paint 1 except that the gloss adjusting agent particles of the type and amount shown in Table 3 were further mixed. ..

(Preparation of colored resin paint 25)
As the colored resin paint, a commercially available Dick Flow C white (fluororesin: acrylic resin = 70:30 mass ratio) manufactured by Nippon Paint Industrial Coatings Co., Ltd. was used.

(Evaluation)
The content ratio of the agglomerates of the fluororesin particles was measured by the following method for a part of the obtained colored resin coating materials 1 to 25.

(Agglomerate content ratio)
A colored resin paint was applied onto the glass plate and then dried to form a coating film. Arbitrary three parts of the obtained coating film were photographed with a scanning electron microscope composition image (1000 times), and an image analysis was performed in a range of 10000 μm ² each. Then, the average area ratio of the aggregates of the fluororesin particles was obtained and converted into the volume fraction. In addition, those in which 500 to 300,000 fluororesin particles (primary particles) were aggregated were referred to as "aggregates of fluororesin particles".

Table 3 shows the compositions and evaluation results of the obtained colored resin paints 1 to 25. In addition, "-" in the column of the content ratio of agglomerates indicates that it has not been measured.

3. 3. Fabrication and evaluation of painted metal plate (manufacture of painted metal plate 1)
After applying the above-prepared colored resin coating material 1 on the undercoat layer of the prepared coating original plate, the plated steel sheet was heated so as to reach a temperature of 140 ° C. Then, this was immersed in water at 20 ° C., cooled with water, taken out from the water, wiped off with gauze, and dried in a room at 23 ° C. At this time, the cooling rate of 200 ° C. to 70 ° C. was 250 ° C./sec. In this way, a coated metal plate 1 having a coating film (colored resin layer) of a colored resin paint having a thickness of 20 μm was produced on the undercoat layer of the coating original plate.

(Manufacturing of painted metal plates 2 to 8)
A painted metal plate was obtained in the same manner as the painted metal plate 1 except that the baking temperature was changed as shown in Table 4.

(Manufacturing of painted metal plates 9 to 32)
A painted metal plate was obtained in the same manner as the painted metal plate 1 except that the type of the colored resin paint was changed as shown in Table 4.

(Evaluation)
The glossiness and workability of the obtained coated metal plates 1-32 were evaluated by the following methods.

(Glossiness)
The 60-degree mirror glossiness Gs (60 °) of the obtained coated metal plate was measured according to JIS Z 8741: 1997.

(Workability)
(1) Initial (immediately after painting)
Within 2 hours after manufacturing, the obtained coated metal plate was sandwiched between plates having the same thickness as the test plate with the coating film on the outside, and bent at 23 ° C. to 180 °. At this time, the minimum number of plate scissors T at which cracks did not occur in the coating film was recorded. The smaller the number of scissors T, the better the workability.

(2) After storage The obtained coated metal plate is allowed to stand in an environment of 60 ° C. for 7 days, and then a 180 ° bending test is performed in the same manner as described above, and the minimum number of plate scissors that does not cause cracks in the coating film. T was recorded.

Table 4 shows the evaluation results of the coated metal plates 1-32.

As shown in Table 4, the content ratio of the fluororesin particles 1 and 2 was adjusted to a predetermined range to obtain fluororesin particles, and a paint obtained by stirring and mixing the pigment dispersion liquid and the fluororesin particles with a stirrer was used. The obtained coated metal plates 1 to 15 and 21 to 23 all have a moderately low 60 ° glossiness Gs (60 °) and high workability immediately after coating (initial) and after storage at 60 ° C for 7 days. I understand.

In particular, it can be seen that by raising the baking temperature (specifically, setting the melting point to + 25 ° C. or higher), the workability after storage becomes higher. It is considered that this is because the fluororesin particles are sufficiently melted.

Further, it can be seen that the glossiness can be further lowered by lowering the stirring speed (peripheral speed) (comparison between the painted metal plates 1 and 11 to 13). It is considered that this is because if the stirring speed (peripheral speed) is too high, the agglomerates (secondary particles) are gradually decomposed into the primary particles during the stirring and mixing, and the proportion of the agglomerates decreases.

Further, it can be seen that the glossiness can be further lowered by increasing the ratio of the fluororesin particles 2 (large particle size and copolymer) in the fluororesin particles (painted metal plates 21 to 23).

On the other hand, the coated metal plates 24 to 25 obtained by using a paint obtained by crushing and mixing the pigment dispersion liquid and the fluororesin particles with a bead mill have high 60 ° gloss Gs (60 °) and are coated metals. It can be seen that the plate 24 has low workability after being stored at 60 ° C. for 7 days. It is considered that the reason why the glossiness Gs (60 °) is high is that the content of the agglomerates is small and the convexity having an appropriate size cannot be formed correspondingly. It is considered that the reason why the coated metal plate 24 has low processability after storage is that the fluororesin particles 1 tend to crystallize and become hard.

In particular, it can be seen that when the peripheral speed is increased, the agglomerates are further decomposed and the particle size is further reduced, so that the glossiness is further increased (comparison between the coated metal plates 16 and 24).

Further, the coated metal plates 26 to 31 using the paint containing the gloss adjusting agent particles have a low glossiness, but in the bending process, the coating film cracks starting from the gloss adjusting agent particles occur both immediately after painting and after storage. However, it can be seen that the workability is reduced. Further, since the coated metal plate 32 using a commercially available paint contains gloss adjusting agent particles, cracks in the coating film starting from the gloss adjusting agent particles occur both immediately after coating and after storage in the bending process, and the processability Can be seen to decrease.

Even if the coated metal plate of the present invention has a colored resin layer containing a fluororesin, it exhibits high processability even after storage. Therefore, it is expected that the coated metal plate having a colored resin layer containing a fluororesin will be further spread, especially as a material for exterior building materials.

Claims (11)

A method for manufacturing a coated metal plate having a metal plate and a colored resin layer arranged on the metal plate.
A step of pulverizing and mixing an acrylic resin and a coloring pigment to obtain a pigment dispersion liquid containing the acrylic resin, the coloring pigment particles, and a solvent.
The first fluororesin particles and the second fluororesin particles having a larger 50% particle diameter (d50) in the volume-based particle size distribution than the first fluororesin particles are the first fluororesin particles: the second fluororesin particles. A step of mixing so as to have a ratio of 60:40 to 0: 100 (mass ratio) to obtain fluororesin particles, and
The pigment dispersion and the fluororesin particles are stirred and mixed to contain an aggregate of the fluororesin particles, the acrylic resin, the colored pigment particles, and the solvent, and the content of the gloss adjusting agent particles. In the process of obtaining a colored resin coating having a solid content of 1% by mass or less,
A step of applying the colored resin paint onto a metal plate and then heating to form a colored resin layer is included.
Manufacturing method of painted metal plate. The pulverization and mixing are carried out by a bead mill.
The method for manufacturing a coated metal plate according to claim 1. The stirring and mixing does not involve grinding by media.
The method for manufacturing a coated metal plate according to claim 1 or 2. The stirring and mixing is carried out at a peripheral speed of 8 m / s or less for 30 to 180 minutes.
The method for manufacturing a coated metal plate according to claim 3. The 50% particle diameter (d50) of the first fluororesin particles is 1 to 5 μm.
The 50% particle diameter (d50) of the second fluororesin particles is 5.5 to 12 μm.
The method for manufacturing a coated metal plate according to any one of claims 1 to 4. The glass transition temperature (Tg) of the acrylic resin is 40 ° C. or lower.
The method for manufacturing a coated metal plate according to any one of claims 1 to 5. The acrylic resin contains a structural unit derived from methyl methacrylate, a structural unit derived from ethyl acrylate, and a structural unit derived from an ester compound of (meth) acrylic acid and an alcohol having 1 to 6 carbon atoms. It is a copolymer,
The method for manufacturing a coated metal plate according to claim 6. A coated metal plate having a metal plate and a colored resin layer arranged on the metal plate.
The colored resin layer contains a cohesive fusion product of fluororesin particles, an acrylic resin, and colored pigment particles.
The content of the gloss adjusting agent particles in the colored resin layer is 1% by mass or less with respect to the colored resin layer, and the 60 ° glossiness Gs of the colored resin layer is 20 or less.
Painted metal plate. The glass transition temperature (Tg) of the acrylic resin is 40 ° C. or lower.
The coated metal plate according to claim 8. The acrylic resin contains a structural unit derived from methyl methacrylate, a structural unit derived from ethyl acrylate, and a structural unit derived from an ester compound of (meth) acrylic acid and an alcohol having 1 to 6 carbon atoms. It is a copolymer,
The coated metal plate according to claim 9. The metal plate, the chemical conversion treatment layer, the undercoat layer, and the colored resin layer are laminated in this order.
The coated metal plate according to any one of claims 8 to 10.