JPH10219182A - Coating composition excellent in scratch resistance, abrasion resistance and durability and metallic plate coated therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating composition which does not undergo breakage of a base resin or separation of an aggregate by abrasion or scratching, is very excellent in scratch resistance and abrasion resistance and is also excellent in processability, impact resistance, durability and staining resistance. SOLUTION: This composition is prepared by mixing a base being a vehicle containing at least 50wt.% (in terms of the resin solid) acrylic resin with 5-20wt.%, based on the total solid of the composition, inorganic aggregate (A) having a mean particle diameter of 3-30μm and 1-10wt.%, based on the total solid of the composition, organic lubricant (B). The weight ratio (A)/(B) should be in the range of 0.5-10. It is desirable that the vehicle contains 50-95wt.% acrylic resin having a hydroxyl value of 60-110mgKOH/g and a glass transition temperature of 70-110 deg.C and 5-50wt.% at least one curing agent selected among melamine resins and polyisocyanate compounds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention provides a coating film having very high hardness, excellent scratch resistance and abrasion resistance, and also excellent in stain resistance, chemical resistance, impact resistance and weather resistance. The present invention relates to a paint composition and a coated metal sheet coated with the paint composition, and particularly when applied to a building material used for an outer wall of a building, a road, a tunnel, or the like, when it is damaged by wind sand or exhaust gas. TECHNICAL FIELD The present invention relates to a coating composition and a coated metal plate having long-term durability against chemical erosion due to NOx, SOx, and the like.

[0002]

2. Description of the Related Art In recent years, painted metal plates used for roof materials and outer wall materials of buildings, and inner and outer wall materials of buildings have been developed to be maintenance-free and capable of withstanding long-term use. High performance such as improvement of corrosion resistance and weather resistance has been achieved. Further, design considerations such as color tone and gloss are pursued in consideration of harmonizing the appearance of buildings and the like with the local environment. Problems such as stain resistance, corrosion resistance, weather resistance, etc. described above are caused by damage to the coating film caused during transportation or processing of the coated metal plate, abrasion and damage of the coating film due to wind sand after construction, etc. Such as deposition of contaminants. For this reason, recently, there is an increasing need for higher hardness of the coating film surface. For example, a conventional organic resin-based coating film having a pencil hardness of 5H or more or a pencil hardness of 9H or more in a severely damaged portion of the coating film is required. Thus, a hardness that could not be obtained has been required.

As one measure to meet such a demand, there has been proposed a method in which an acrylic resin-based coating material from which a high-hardness coating film is easily obtained is hardened by electron beam curing to make it highly crosslinked (for example, Japanese Patent Publication No. 55-55). No. 5422, Japanese Patent Publication No. 56-
No. 8070, Japanese Patent Publication No. 1-229622 and Japanese Patent Publication No. 2-242863). However, in this electron beam curing method, since the paint is cured in the electron beam irradiation equipment, it is difficult to continuously process the metal plate, and it is necessary to control the oxygen concentration in the electron beam irradiation atmosphere. There are many disadvantages to line production, and there are major problems with productivity and production costs. Also, in terms of the performance of the coating film, since the coating film cured by electron beam is inferior in flexibility, there is a problem in workability and impact resistance when a splashed stone collides, or inferior in weather resistance. Therefore, it has drawbacks such as not being suitable for outdoor use.

As another measure, a method has been proposed in which a photocurable resin is continuously photopolymerized to continuously obtain a high-hardness coating film (Japanese Patent Publication No. 3-261551).
In this method, the equipment cost is remarkably higher than the bake hardening method, and the coating material is expensive, so that the production cost is high and the productivity is low. Further, the coating film performance itself is inferior in flexibility as in the case of the coating film obtained by the electron beam curing method, and is also inferior in workability and impact resistance.

[0005] On the other hand, many attempts have been made to meet the above-mentioned demands by a bake hardening method which is advantageous in terms of productivity and production cost. Many of these are intended to increase the hardness by adding an aggregate to the coating film to improve the performance. For example, Japanese Patent Publication No. 50-25485
JP, JP-B-51-8128, JP-B-56-4
No. 0544, JP-B-59-210980, JP-B-63-5938 and JP-B-4-11671, glass fibers or glass beads are added to the uppermost coating film to reduce the hardness of the coating film. Techniques for increasing the resistance to abrasion and abrasion are disclosed.

[0006] However, these coating films have insufficient strength of the base resin with respect to the added aggregate and glass beads, so that when the coating film is rubbed with a hard substance, the base resin is destroyed. There is a problem that the aggregate falls off from the coating film. Therefore, the coating film hardness (pencil hardness) is limited to about 5H at most, and a coated metal plate having a coating film hardness of 9H or more cannot be obtained. To deal with such a problem,
According to Japanese Patent No. 3926, by incorporating an aggregate in a bake-curable coating material containing a specific resin as a main component, there is no breakage of the base resin or falling off of the aggregate in the coating film, and the pencil hardness is 9H or more. Painted metal plates exhibiting excellent scratch resistance by obtaining high coating film hardness have been proposed.

[0007]

However, with respect to the abrasion resistance of such a coated metal plate, as the base resin wears, the aggregate also falls off from the coating film, so that the effect of adding the aggregate is apparent. Did not appear, and sufficient performance was not obtained. Accordingly, an object of the present invention is to provide a coating composition in which the hardness of a coating film is increased by including an aggregate. A coating composition which does not fall off, is extremely excellent in scratch resistance and abrasion resistance, and further has excellent workability, impact resistance, durability such as weather resistance and stain resistance, and this coating composition is applied. It is to provide a painted metal plate.

[0008]

In order to sufficiently improve both the scratch resistance and the abrasion resistance, the coating film of the coated metal sheet is repeatedly rubbed against the damage caused by a very hard substance. Against wear caused by
In each case, the coating resin must have sufficient strength and abrasion resistance so that the aggregate in the coating does not fall off.In addition, durability and resistance such as weather resistance, corrosion resistance, chemical resistance, etc. It is necessary to have the pollution property. In addition, it must be stable as a paint and have excellent paintability and bake hardenability. As a result of studying the composition of the coating film having these characteristics, the inorganic aggregate and the organic lubricant having an average particle diameter in a specific range are respectively contained in a specific ratio in a vehicle mainly composed of an acrylic resin. As a result, it was found that the scratch resistance, abrasion resistance, stain resistance, durability, flexibility, paintability, and bake hardenability can be improved to the maximum.

The present invention has been made based on such findings, and the features thereof are as follows. (1) A main component is a vehicle containing 50% by weight or more of an acrylic resin in a resin solid content.
0 [mu] m of the inorganic aggregate [A] and the organic lubricant [B] in the proportion of the total solid content of the coating composition [A]: 5 to 20% by weight,
[B]: 1 to 10% by weight and [A] / [B] in weight ratio
= 0.5-10, a coating composition having excellent scratch resistance, abrasion resistance and durability. (2) In the coating composition of the above (1), the hydroxyl value is 60 to 110 mgKOH / g in the ratio of the vehicle in the solid content of the resin.
And 50 to 95% by weight of an acrylic resin having a glass transition temperature of 70 to 110 ° C and at least one of 5 to 5 curing agents selected from a melamine resin and a polyisocyanate compound.
A coating composition having excellent scratch resistance, abrasion resistance and durability, characterized by containing a coloring agent containing 0% by weight as a main component.

(3) In the coating composition of the above (1) or (2), the inorganic aggregate is one or more inorganic fine powders selected from alumina, silicon carbide, glass beads, glass fibers and ceramic fibers. A coating composition having excellent scratch resistance, abrasion resistance, and durability. (4) The coating composition according to (1), (2) or (3), wherein the organic lubricant is a fine powder of ethylene tetrafluoride resin, and is characterized by scratch resistance, abrasion resistance and durability. Excellent paint composition. (5) At least one surface of the metal plate has a chemical conversion coating, has an undercoat coating on the upper layer, further above (1), (2), (3) or (4) A coated metal sheet having excellent scratch resistance, abrasion resistance and durability, characterized by having a coating film obtained by applying and baking a coating composition.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention and the reasons for limitation will be described below. The coating composition of the present invention is mainly composed of a color developing agent mainly composed of an acrylic resin, and furthermore, an inorganic aggregate and an organic resin are used in order to secure excellent scratch resistance and abrasion resistance which cannot be obtained only by the resin component. Add lubricant. An acrylic resin needs to be contained as a vehicle.
The acrylic resin forms a crosslinking point with a functional group in an oxide such as alumina added as an inorganic aggregate (Susumu Kadokura, Journal of Aluminum Research Society, No. 7, 239, p. 1 (19)
89)), the added inorganic aggregate is firmly adhered to the acrylic resin, and is less likely to fall off. It is necessary that the content of the acrylic resin in the vehicle is 50% by weight or more based on the solid content of the resin. Acrylic resin content is 50% by weight
If the amount is less than the above, the crosslinking with the oxide becomes insufficient, and the aggregate is likely to fall off.

As the inorganic aggregate, a ceramic aggregate or a glass aggregate can be used. Ceramic aggregate may be in any shape such as granular or fibrous, for example, silica, titania, alumina, zirconia, silicon carbide,
One or more of aggregates composed of silicon nitride, aluminum nitride, aluminum carbide, or a composite material thereof can be used. As the glass aggregate, soda-lime-based, borosilicate-based, alumina-silica-based glass beads, or the like can be used. Among these inorganic aggregates, one of the aggregates composed of alumina, silicon carbide, glass beads, glass fiber, ceramic fiber, or a composite material thereof in view of durability of the aggregate itself and hardness balance with a coating film. Alternatively, it is most preferable to use two or more kinds.
In order to improve the wettability and adhesion to the coating film, the inorganic aggregate may be subjected to a surface treatment such as a silane coupling agent treatment or a titanium coupling agent treatment.

The average particle size of the inorganic aggregate is 3 to 30 μm. When the average particle size is less than 3 μm, the aggregate is hardly exposed on the surface of the coating film, so that the effect of improving the scratch resistance is small. On the other hand, when the average particle size exceeds 30 μm, the dispersibility in the paint is poor, and Since the material is liable to settle in the paint, poor coating is likely to occur. When the inorganic aggregate is fibrous (glass fiber, ceramic fiber), the “average particle size” indicates the average fiber length. The amount of the inorganic aggregate to be added is in the range of 5 to 20% by weight in the total solid content of the coating composition. If the amount of the inorganic aggregate is less than 5% by weight, the scratch resistance and the abrasion resistance are insufficient. On the other hand, if the amount is more than 20% by weight, the flow characteristics of the coating material are reduced and the coating workability is impaired. Or reduces the flexibility of the coating film. From the viewpoints described above, the preferable addition amount of the inorganic aggregate is 5
１５15% by weight.

In the present invention, an organic lubricant is further added to the coating composition containing the inorganic aggregate. An acrylic resin-containing coating film containing an inorganic aggregate shows extremely excellent performance against scratching. However, with respect to the abrasion caused by repeated rubbing of the substance, the effect of adding the aggregate does not appear clearly because the aggregate falls off the coating film as the base resin wears, and sufficient performance is obtained. Absent. Therefore, as a result of examination, it was found that the inorganic aggregate [A] and the organic lubricant [B] were used.
It was found that by adding a specific proportion to the acrylic resin-containing coating film, extremely excellent wear resistance was obtained.
These two additional components have a synergistic effect on abrasion resistance, and the performance is greatly reduced even if either one of the additional components is missing. For example, when only inorganic aggregate is added,
Since the frictional resistance of the surface of the coating film increases, the wear energy due to surface friction increases more than the fracture strength of the coating film increases due to the addition of the aggregate, and therefore the amount of wear increases. On the other hand, organic lubricants, especially tetrafluoroethylene resin (PTF)
E) When only fine powder is added, the lubricating property of the coating film is enhanced, so that the friction coefficient is reduced. However, since the lubricant itself lacks resistance to abrasion, when a large pressure is applied, the lubricant is broken, The amount of wear increases rapidly.

An appropriate composition range in which the above effects can be obtained by the composite addition of the inorganic aggregate [A] and the organic lubricant [B] is as follows:
[A] / [B] = 0.5 to 10 by weight ratio of both.
If the weight ratio of [A] / [B] is less than 0.5, the abrasion resistance of the coating film surface is reduced due to the excessively high concentration of the organic lubricant on the coating film surface, and the coating film has poor wear resistance. . on the other hand,
When [A] / [B] exceeds 10, almost no organic lubricant is present on the coating film surface, so that the wear energy due to surface friction increases and the coating film has poor wear resistance.

Examples of the organic lubricant include olefin wax such as polyethylene and polypropylene, fluorine wax such as tetrafluoroethylene and hexafluoroethylene, amide wax, hydrocarbon wax, silicone wax and acrylic wax. And the like can be used, and one or more of these can be used as a mixture.
These organic lubricants are added to the paint in a state of being dispersed in a liquid, a dry solid powder, or an organic solvent. Among the above-mentioned organic lubricants, a tetrafluoroethylene resin fine powder is most preferable from the viewpoint of the durability of the lubricant itself and the balance of hardness with the coating film.

The amount of the organic lubricant to be added is in the range of 1 to 10% by weight based on the total solid content of the coating composition. If the amount of the organic lubricant is less than 1% by weight, the wear resistance is insufficient. On the other hand, if the amount exceeds 10% by weight, the concentration of the lubricant on the surface of the coating film increases, so that the abrasion of the coating film surface is increased. In addition to lowering the resistance and inferior abrasion resistance, it also lowers the flow characteristics of the paint, impairing the workability of the paint, and reduces the flexibility of the paint film. From the above viewpoints, a more preferable addition amount of the organic lubricant is 2 to 10% by weight.

Further, by using a coloring agent containing one or more curing agents selected from an acrylic resin having a specific hydroxyl value and a glass transition temperature, a melamine resin and a polyisocyanate compound, as the coloring agent. In addition, the coating film performance is further improved. Acrylic resins can form a very hard crosslinked structure by reacting with a curing agent. Such acrylic resins are those having a hydroxyl group in a side chain or those having a hydroxyl group and a carboxyl group in a side chain. It is necessary.

For introducing a hydroxyl group into the acrylic resin,
Examples of the acrylic monomer having a hydroxyl group include, for example, hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, glycerol methacrylate, 4-hydroxybutyl methacrylate, 3,4-dihydroxybutyl Methacrylate, trimethylolpropane methacrylate, trimethylolpropane dimethacrylate, hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, glycerol acrylate, 4-hydroxybutyl acrylate, 3,4-dihydroxybutyl Acrylate, trimethylolpropane acrylate, trimethylolpro Nji acrylate, N- methylol acryl amines. Examples of the acrylic monomer having a carboxyl group for introducing a carboxyl group into an acrylic resin include acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, and substituted derivatives thereof.

The acrylic monomer copolymerized with the acrylic monomer containing a hydroxyl group or a carboxyl group in order to form a very hard crosslinked structure includes, for example, methyl methacrylate and ethyl methacrylate. Methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, isobonyl methacrylate, methyl acrylate, ethyl acrylate N-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, t-butyl acrylate Alkyl methacrylate or alkyl acrylate monomers such as acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, and isobornyl acrylate; ethylenic monomers copolymerizable with these monomers; acrylonitrile, styrene, etc. Is mentioned.

In the production of the acrylic resin used in the present invention, for example, a mixture of each component of the acrylic monomer and a radical polymerization initiator is dropped into a heated organic solvent over a predetermined time, By maintaining the temperature at a constant temperature, a radical polymerization reaction is performed, and an acrylic resin having a desired composition can be obtained. Acrylic resin has a hydroxyl value of 60-
110 mgKOH / g, glass transition temperature 70-110
It is preferably in the range of ° C. When the hydroxyl value of the acrylic resin is less than 60 mgKOH / g, the cross-linking density of the coating film is low, so that the strength and hardness of the coating film are slightly low. On the other hand, when the hydroxyl value exceeds 110 mgKOH / g, the flexibility of the coating film is low. Since it is slightly inferior, a problem arises in impact resistance, baking hardenability is also poor, and even after curing, unreacted groups remain in the coating film, so that chemical resistance and stain resistance may be inferior.

The glass transition temperature of the acrylic resin is 7
If the temperature is lower than 0 ° C, the strength and hardness of the coating film are slightly low. On the other hand, if the glass transition temperature exceeds 110 ° C, the flexibility of the coating film is slightly inferior, the impact resistance is insufficient, and the coating properties and baking harden. The sex may be slightly inferior. Further, the acrylic resin having a number average molecular weight of 3,000 to 10,000 is particularly preferable. If the number average molecular weight is less than 3,000, the baking curability is inferior, and the coating film hardness tends to be insufficient. On the other hand, if the number average molecular weight exceeds 10,000, the resin becomes difficult to dissolve in the solvent and the solid content of the coating material decreases. Poor paintability.

As the curing agent, it is optimal to use one or more curing agents selected from melamine resins and polyisocyanate compounds. Melamine resin, after reacting melamine and formaldehyde, methanol, ethanol,
Alkyl etherified melamine obtained by etherifying a part or all of a methylol group with a monohydric alcohol such as propanol or butanol. As the melamine resin, a methylated melamine resin, a butylated melamine resin, and a methylated-butylated mixed melamine resin are particularly suitable.

Further, as the polyisocyanate compound, a polyisocyanate compound obtained by a general production method can be used. Considering the application as paint for pre-coated steel sheet, blocked polyisocyanate such as phenol, cresol, aromatic secondary amine, tertiary alcohol, lactam, oxime etc. which can be used as one-pack type paint Compounds are desirable. More preferred polyisocyanate compounds include non-yellowing hexamethylene diisocyanate and its derivatives, tolylene diisocyanate and its derivatives, 4,4-diphenylmethane diisocyanate and its derivatives, xylylene diisocyanate and its derivatives, isophorone diisocyanate and its derivatives, and trimethylhexaene. Examples include methylene diisocyanate and its derivatives. In addition, commercially available polyisocyanate compounds such as “Sumidur” (manufactured by Sumitomo Bayer Urethane Co., Ltd.), “Desmodur” (manufactured by Sumitomo Bayer Urethane Co., Ltd.), and “Coronate” (manufactured by Nippon Polyurethane Co., Ltd.) are also used. it can.

The acrylic resin and the curing agent in the vehicle are as follows:
Acrylic resin in proportion to resin solid content of the vehicle: 50 to 9
5% by weight, curing agent: preferably 5 to 50% by weight. If the curing agent component is less than 5% by weight, the coating film hardness and abrasion resistance are insufficient, and the chemical resistance and the stain resistance are also poor.
On the other hand, if the curing agent component exceeds 50% by weight, the flexibility is poor, so that a problem arises in the impact resistance. Also particularly preferably,
When the curing agent is mainly composed of melamine resin, acrylic resin: 60 to 70% by weight and curing agent: 30 to 40% by weight. When the curing agent is mainly composed of polyisocyanate compound, acrylic resin: 70 to 70%. 90% by weight and curing agent:
The content is preferably set to 10 to 30% by weight.

Next, a coated metal plate coated with the above-described coating composition will be described. The coated metal plate used in the coated metal plate of the present invention includes a cold-rolled steel plate, a stainless steel plate,
In addition to an aluminum plate and a copper plate, various metal plates such as zinc, a zinc-based alloy, aluminum, chromium, nickel or a plated steel plate plated with these alloys can be used. On the surface of the above-mentioned metal plate, a chemical conversion treatment film is formed in order to secure adhesion to the coating film. The chemical conversion coating may be formed by a pre-coating treatment suitable for each metal plate, and may be performed by applying or spraying chromate, phosphate, or silane coupling agent, or by using an acid or alkali such as phosphoric acid, nitric acid, or hydrofluoric acid. In addition to those formed by an activation process or the like, those formed by an electrolytic process may be used.

An undercoating film is formed on the upper layer of the above-mentioned chemical conversion treatment film, and an overcoating film formed by applying and baking the coating composition of the present invention on the upper layer is formed. The undercoat film is formed to enhance the adhesion between the metal plate and the overcoat film, or to improve durability and impact resistance in a special environment such as high humidity. Lacquer-based or oil-based undercoats can also be used as the undercoat, and commonly used undercoats such as urethane resin-based paints and polyester resin-based paints besides epoxy resin-based paints for synthetic resin-based paints be able to.

Further, when a high degree of corrosion resistance or coating film adhesion is required, it is preferable to add a chromate compound as a rust preventive pigment in the undercoating film. As the chromate compound, zinc chromate, strontium chromate, calcium chromate, barium chromate and the like are preferable, and the content thereof is 1 in the solid content of the coating film.
It is appropriate that the content is in the range of 60 to 60% by weight. In addition, the dry coating thickness of the undercoat coating is 5 to obtain the above-mentioned effect.
It is preferable to set it to about 20 μm.

The top coat is formed by applying the above-mentioned coating composition and then baking. The dry coating thickness of the top coat is preferably 15 to 50 μm. When the coating thickness is less than 15 μm, the hard coating layer becomes thin, and the wear resistance, corrosion resistance, and chemical resistance are reduced. On the other hand, when the thickness of the coating film exceeds 50 μm, the coating film becomes brittle, and the coating film adhesion and impact resistance are poor. More preferably, the thickness of the coating film is adjusted to 70 to 150% of the average particle size of the inorganic aggregate contained. Within this range, the appearance of the coating is the most beautiful and the performance of the coating film is the highest. If the coating thickness is too small with respect to the average particle size of the aggregate, the smoothness of the coating is inferior because the aggregate is largely exposed on the coating surface, while the coating thickness is small relative to the average particle size of the aggregate. If the particle size is too large, the aggregate sinks deeply into the coating film, so that the scratch resistance, abrasion resistance and the like are reduced, and the coating film performance may be insufficient.

The baking treatment after the coating composition is applied is, for example, 30 seconds when drying is performed for a short time in a coil coating line.
It is preferable to perform the heating by heating for 180 seconds to reach a metal plate temperature of 220 to 300 ° C. When the temperature of the metal plate is lower than 220 ° C., the drying and curing of the resin component is insufficient. On the other hand, when the temperature exceeds 300 ° C., thermal degradation including the undercoat paint component starts. In addition, if the baking time is less than 30 seconds, the drying and curing of the resin component is insufficient, and since the curing speed of the resin exceeds the evaporation speed of the solvent, defects such as cracks are generated in the coating film, and the appearance is easily deteriorated. If the time exceeds 180 seconds, thermal deterioration including the undercoat paint component starts, and in any case, the original performance of the paint is not exhibited, which is not preferable.

In the case where drying is performed for a long time in a cut sheet coating line such as a post coat line, the temperature of the metal plate is set at 1 point.
It is preferable to hold at 50 to 240 ° C. for 10 to 30 minutes. The reason is the same as in the case of short-time curing. There is no particular limitation on the heating method at the time of baking, and methods such as a hot air heating method and a high frequency heating method can be applied. In addition, a plasticizer, a desiccant, a dispersant, a curing catalyst, a pigment, and the like can be added to the above-mentioned top coating film and undercoat film as needed. It is effective to add. As the pigment, an extender pigment, a rust preventive pigment, and a lubricant can be added in addition to various color pigments. The coating method is not particularly limited, and a conventional coating method such as a roll coater method, a curtain flow coater method, or a spray method can be applied.

[0032]

EXAMPLE A stainless steel sheet, a hot-dip galvanized steel sheet or a hot-dip 55% aluminum-zinc alloy-plated steel sheet (both having a thickness of 0.5 mm) is subjected to a coating type chromate treatment or a phosphate treatment, and then an epoxy resin is used as a base coat. Paint (Nippon Oil & Fats Co., Ltd. product name "Precolor WP-
3)) after coating, reached plate temperature: 190 ° C, baking time:
A baking treatment was performed for 40 seconds, and then a coating composition prepared as described below was applied as a top coat, followed by a baking treatment (baking time: 90 seconds), and the obtained coated metal plate was subjected to the following various tests. Tables 1 and 2 show the production conditions and characteristics of the acrylic resin copolymer used in the coating composition, Tables 3 to 10 show the composition of the top coating composition, and Tables 11 to 17 show the coatings of the examples. The production conditions of the metal plate and the results of various tests are shown.

[Production of acrylic resin copolymer]
In a four-necked flask equipped with a reflux condenser, a stirrer, a dropping funnel and a nitrogen gas inlet tube, 20 parts by weight of Solvesso # 100 and 10 parts by weight of n-butanol were charged under a nitrogen gas stream, and heated to reflux under stirring. During the reaction, a monomer and polymerization initiator mixture (dropping component) 55 having the composition shown in Tables 1 and 2 was used.
Parts by weight were dripped at a constant speed from the dropping funnel over 24 hours.
After completion of the dropwise addition, the mixture was kept under reflux for 2 hours.
After adding 15 parts by weight of 100 and cooling, the mixture was filtered through a 200-mesh wire gauze, whereby acrylic resin copolymers A-1 to A-1 having the properties described in Tables 1 and 2, respectively.
A solution of A-8 was obtained. The number average molecular weight of each acrylic resin copolymer was measured by gel permeation chromatography using a standard polystyrene calibration curve.

[Production of Top Coating Composition] Tables 3 to 1
According to the compounding ratio shown in 0, a part of the acrylic resin copolymer and a part of the mixed solvent are mixed, and then titanium dioxide is added and uniformly mixed, and then the particle size is reduced to 10 μm or less using an attritor. Dispersed. Further, the remaining of the acrylic resin copolymer, the curing agent and the acid catalyst were added, and the inorganic aggregate and the organic lubricant were added and mixed with stirring. .
4 to 120 ± 10 seconds (25 ° C.).
The following coating compositions T-1 to T-32 were obtained. Table 3
In Table 10, T-1 to T-20 are the coating compositions of the present invention, and T-21 to T-32 are the coating compositions of the comparative examples.

[Test / Evaluation Method] (1) Pencil Hardness Test The scratch resistance of the coating film was measured by changing the hardness of the pencil lead according to the method of JIS-K5400 8.4.1 (1993). The film was examined for scratches, and the highest hardness at which no scratches were observed in the coating film was defined as the pencil hardness of the coating film. In this test, those having a pencil hardness of 9H or more passed, and those having a pencil hardness of less than 9H were rejected. (2) Wear resistance test (Taber method) According to the method of 8.9 (1993) of JIS-K5400, a load of 9.81 N was applied to the sample and the wear loss when the CS10 wear wheel was rotated 2000 times. (Mg) was measured. In this test, those having a weight loss of 30 mg or less were passed, and those exceeding 30 mg were rejected.

(3) Coating film adhesion test (cross-cut tape method) According to the method of JIS-K5400, 8.5. Make a 1 x 10 square grid,
Immediately after the adhesive tape was firmly adhered to the grid, the adhesive tape was instantaneously peeled off from the coating film surface, and the adhesion was evaluated by the number of grids of the coating film remaining without being peeled off.
In this test, the number of crosscuts remaining without peeling was 100, and the number of crosscuts was 99 or less.

(4) Impact Deformation Test (DuPont Type) The method of JIS-K5400, 8.3.2 (1993) is applied, and the test piece has a coating surface facing upward under the conditions of a weight of 500 g and a height of 50 cm. The case and the downward case were tested and evaluated according to the following criteria. ：: no adhesive tape peeling (pass) ○: adhesive tape peeling area is 10% or less (pass) △: adhesive tape peeling area exceeds 10% and less than 50% (fail) ×: adhesive tape peeling area 50% or more (fail)

(5) Chemical resistance test According to the method of JIS-A5707, a 5% nitric acid aqueous solution
1 mL of a 5% sulfuric acid aqueous solution and a 5% sodium hydroxide aqueous solution are dropped on the coating film, left in a constant temperature and humidity room of 20 ° C. and 50 RH% for 24 hours, washed with water and dried, and visually observed changes in the coating film surface. And evaluated according to the following criteria. ◎: No change in coating film surface (pass) ○: Slight discoloration and blistering on coating film surface (pass) △: Discoloration and blistering are slightly noticeable on coating film surface (fail) ×: Coating surface Discoloration, blistering, and peeling are clearly noticed (failed)

(6) Carbon Contamination Resistance Test 1 mL of a dispersion having a carbon black / water ratio of 5/95 (weight ratio) was placed on the coating film and left in a constant temperature and humidity room at 20 ° C. and 50% RH for 24 hours. Thereafter, the film was washed with water, and the degree of discoloration of the coating film surface on which the dispersion was placed was visually observed, and evaluated according to the following criteria. ◎: No trace at all (pass) ○: Slight trace is recognized (pass) △: Slight traces are noticeable (fail) ×: dark trace remains (fail) (7) Accelerated weathering test (Sunshine Carbon) (Arc lamp type) According to the method of 9.8.1 (1993) of JIS-K5400, the gloss retention (%) of the coating film surface after 2,000 hours of sunshine weatherometer was evaluated. Passed, less than 80% was rejected.

As is clear from the results of the above embodiments,
The coated metal plates of Comparative Examples 1 to 12 deviating from the conditions of the present invention are:
It was rejected for any of abrasion resistance, coating film hardness, impact resistance, stain resistance, workability, and other characteristics. On the other hand, the coated metal plates of Examples 1 to 23 of the present invention are excellent in abrasion resistance, have a coating film hardness of 9H or more, and are excellent in all properties including chemical resistance and impact resistance. ing.
Among them, an acrylic resin having a specific hydroxyl value and a glass transition temperature, a melamine resin, and a specific ratio of at least one curing agent selected from polyisocyanate compounds as a vehicle are included in the present invention. Particularly excellent performance is obtained in Nos. 1 to 18, and among them, the inorganic aggregate is at least one kind of inorganic fine powder selected from alumina, silicon carbide, glass beads, glass fiber, and ceramic fiber, and organic In Examples 1 to 15 of the present invention in which the system lubricant is a fine powder of tetrafluoroethylene resin, the most excellent performance was obtained.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

[Table 5]

[0046]

[Table 6]

[0047]

[Table 7]

[0048]

[Table 8]

[0049]

[Table 9]

[0050]

[Table 10]

[0051]

[Table 11]

[0052]

[Table 12]

[0053]

[Table 13]

[0054]

[Table 14]

[0055]

[Table 15]

[0056]

[Table 16]

[0057]

[Table 17]

Note that * 1 to * 8 in Tables 3 to 10 indicate the following contents. * 1: Acrylic resin copolymer symbol shown in Tables 1 and 2. * 2: Nonvolatile content 55 wt% * 3: Nonvolatile content 100 wt% * 4: Nonvolatile content 75 wt% * 5: Butyl cellosolve / isophorone = 1/1 * 6 : 20 wt% solution of p-toluenesulfonic acid

* 7: Kind of inorganic aggregate Al: Alumina (average particle size 5 μm) SC; silicon carbide powder (average particle size 10 μm) GB; glass beads (average particle size 22 μm) GF; glass fiber (fiber length 10) ３０30 μm, fiber diameter 0.5
PT: potassium titanate fiber (fiber length: 10 to 30 μm, fiber diameter: 0.5 to 2.0 μm) MI: mica (average particle diameter: 10 μm) GC: glass beads (average particle diameter: 30 μm) SA: haze Feldspar powder (white powder, average particle diameter 2.3 μm) GD; glass beads (average particle diameter 41 μm) * 8: Type of organic lubricant PF; fine powder of tetrafluoroethylene resin PE; polyethylene wax SI; silicone wax

* 1 to * 4 in Tables 11 to 17 indicate the following contents. * 1: Kind of metal sheet SUS; SUS304 stainless steel sheet GI; Hot-dip galvanized steel sheet (coating weight; Z-25) GL; Hot-dip 55% aluminum-zinc alloy coated steel sheet (galvalume steel sheet, coating weight; AZ-150) * 2: Type of chemical conversion treatment Cr; Coating type chromate treatment P; Zinc phosphate treatment * 3: Coating composition symbol described in Tables 3 to 10 * 4: Ultimate plate temperature

[0061]

As described above, according to the coating composition of the present invention, there is no damage to the base resin and no falling off of the aggregate, not only to the damage but also to the abrasion. It is possible to obtain a coating film which is extremely excellent in properties, and further excellent in workability, impact resistance, durability such as weather resistance and stain resistance. Therefore, the coated metal sheet of the present invention exhibits excellent scratch resistance, abrasion resistance, durability, contamination resistance and the like as materials for exterior building materials and tunnel interior boards.

Claims (5)

[Claims] 1. An acrylic resin having a ratio of 5 to the resin solid content
A main component is a vehicle containing 0% by weight or more, and an inorganic aggregate [A] and an organic lubricant [B] having an average particle diameter of 3 to 30 μm are added thereto in a ratio of the total solid content of the coating composition. [A]: 5
-20% by weight, [B]: 1-10% by weight, and contained in a weight ratio of [A] / [B] = 0.5-10. A coating composition with excellent durability. 2. An acrylic resin having a hydroxyl value of 60 to 110 mg KOH / g and a glass transition temperature of 70 to 110 ° C. in a proportion of 50% to 95% by weight in the resin solid content of the vehicle.
The scratch resistance according to claim 1, wherein the main component is a coloring agent containing 5 to 50% by weight of at least one curing agent selected from a melamine resin and a polyisocyanate compound. A coating composition having excellent abrasion and durability. 3. The method according to claim 1, wherein the inorganic aggregate is at least one kind of inorganic fine powder selected from alumina, silicon carbide, glass beads, glass fiber and ceramic fiber. A coating composition having excellent scratch resistance, abrasion resistance and durability. 4. A coating composition having excellent scratch resistance, abrasion resistance and durability according to claim 1, wherein the organic lubricant is fine powder of tetrafluoroethylene resin. Stuff. 5. The coating composition according to claim 1, which has a chemical conversion coating on at least one surface of the metal plate, has an undercoat coating on an upper layer thereof, and further has an upper layer thereon. A coated metal sheet having excellent scratch resistance, abrasion resistance and durability, having a coating film obtained by applying and baking.