JP2002097408A - Coating film having excellent weatherability and metal plate coated therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a polyester-type baked coating film comprising a pigment and having a polyester resin crosslinked with a melamine or an isocyanate type crosslinking agent, wherein the film has an improved weatherability without addition of a UV stabilizer so that the film has excellent processability and is prevented from early loss of gloss and early discoloration. SOLUTION: Adsorption of the crosslinking agent onto the pigment is restricted so that the nitrogen concentration on a coating surface is controlled to >=3 at.%, by controlling the amount of the added pigment and/or the cross- linking agent or by treating the pigment surface. When this coating film is formed as a top coat on an under coat over a metal with a prepared surface, a coated metal plate having excellent processability and weatherability is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inexpensive and excellent weather-resistant coating film suitable for outdoor building materials or electric products used outdoors, and a coated metal excellent in weather resistance and workability using the coating film. With board. INDUSTRIAL APPLICABILITY The coating film and the coated metal sheet of the present invention are useful for applications such as outdoor construction materials such as metal roofs, parts around roofs, and wall materials, and outer panels of electric appliances such as air conditioner outdoor units and vending machines.

[0002]

2. Description of the Related Art For indoor and outdoor building materials, a coated steel sheet which has been coated on a plated steel sheet in advance has been used. Depending on the resin type of the top coating material, the coated steel sheet includes a polyester-based coated steel sheet called a color steel sheet, a highly durable fluorine-based coated steel sheet, a thick-film PVC steel sheet, and the like.

[0003] Fluorine-coated steel sheets have an overcoating film composed of vinylidene fluoride and an acrylic resin, exhibit extremely excellent weather resistance, but are expensive. A PVC steel sheet is a thick film, so it is not easily scratched and has good corrosion resistance.It also has excellent workability.However, weather resistance tends to be chalky, and it tends to change color and gloss. The drop is easy to occur.

[0004] The polyester-coated steel sheet is obtained by applying a baking-type paint by mixing a thermoplastic saturated polyester resin having a terminal hydroxyl group with a base resin and blending a crosslinking agent such as a melamine resin and a polyisocyanate with the base resin. .

[0005] In a polyester-coated steel sheet for building materials, a paint containing a polyester resin having a number average molecular weight of about 3,000 to 5,000 as a base resin is applied to a thickness of about 15 μm. The workability of this coated steel sheet was approximately 6 in a 180 ° bending test.
It is about T to 8T, which is sufficient for building materials that are not subjected to very severe processing, but insufficient in workability for electric products.

As a polyester-coated steel sheet for electric products, a paint containing a high-molecular-weight polyester resin having a number average molecular weight exceeding 10,000 as a base resin is used. Although this coated steel sheet has excellent workability to withstand 180 ° close bending (0T), it often has insufficient weather resistance.

[0007] JP-A-11-246821 discloses that in order to obtain a precoated steel sheet having excellent workability and weather resistance, a paint containing an aminoplast resin (melamine resin) or a polyisocyanate as a polyester polyol and a crosslinking agent is used. It discloses that a coating material to which a specific copolymerized acrylic polyol is added as an ultraviolet stabilizer is used. A similar technique using other ultraviolet stabilizers is disclosed in JP-A-10-19.
No. 3509, No. 11-246815, No. 11-291386, No. 11-2913
Nos. 87 and 11-291395. The incorporation of an ultraviolet stabilizer in the coating improves weatherability, but is expensive because the ultraviolet stabilizer is expensive.

Japanese Patent Application Laid-Open No. 7-284726 discloses that a polyester resin-based coating film containing a titanium pigment has excellent light resistance when the content of titanium is as small as possible and the resin is rich. . Specifically, it is stated that good light fastness can be obtained when the Ti / C spectral intensity ratio of the coating film surface is 1.1 or less.

Japanese Patent Application Laid-Open No. 11-104559 discloses that, in a polyester-coated metal plate having an irregular appearance in which resin beads are contained in a coating film obtained by crosslinking polyester with melamine, the nitrogen concentration on the coating film surface is an average of the entire coating film. It is disclosed that when the nitrogen concentration is twice or more, the stain resistance is particularly improved.

In a coloring material, 64 (1991), 52-57 [12], in a coating film in which polyester is melamine crosslinked, melamine concentrates on the coating film surface during baking and exists on the coating film surface after curing. It has been shown that the melamine concentration affects the adhesion and wettability of the coating.

[0011]

SUMMARY OF THE INVENTION According to the present invention, the weather resistance of a polyester-based baked coating film containing a pigment obtained by crosslinking a polyester resin with a melamine or isocyanate type crosslinking agent is measured by using an additive such as an ultraviolet stabilizer. It aims to improve without. As a result, it is possible to prevent the early gloss reduction and color change of the smooth and glossy polyester baking coating film that is excellent in workability and has a smooth surface coated metal plate that is excellent in both weather resistance and workability. Obtainable.

[0012]

Means for Solving the Problems The composition and structure of the coating film surface,
For example, it has been known that the concentration of a melamine crosslinking agent on the surface of a coating film determines the surface properties of the coating film such as adhesion, wettability, and stain resistance. However, weather resistance was considered to be the performance of the entire coating as a bulk.
Therefore, conventionally, a method of improving the weather resistance of the coating film by increasing the ultraviolet absorption of the coating film by adding an ultraviolet stabilizer to the coating film, that is, taking measures against the whole coating film has been taken.

The present inventors have found that the weather resistance of a polyester-based baked coating film obtained by crosslinking a polyester resin with a melamine or isocyanate-type crosslinking agent, particularly, a relatively early color change and a decrease in gloss, depend on the structure of the coating film surface. I found that it changed greatly. After examining this in detail,
It has been found that when the nitrogen concentration (contained in a crosslinking agent such as melamine or isocyanate) on the surface of the coating film is 3 at% or more, it is effective for improving weather resistance.

Here, the present invention is a method for improving the weather resistance of a polyester-based baked coating film containing a pigment by using a polyester resin having a terminal hydroxyl group and a crosslinking agent containing a nitrogen atom as a binder component, This method is characterized in that the nitrogen concentration on the surface of the coating film is 3 at% or more.

[0015] From another aspect, the present invention provides a smooth polyester baked coating film containing a pigment, comprising a polyester resin having a terminal hydroxyl group and a crosslinking agent containing a nitrogen atom as a binder component. Is a polyester-based baked coating film having excellent weather resistance, wherein the nitrogen concentration of the polyester is 3 at% or more.

[0016] From still another aspect, the present invention provides, in order from the bottom, at least one surface of a metal plate,
It is characterized by having one or two baking films selected from an epoxy system, a polyester system and a polyurethane system, and the above-mentioned polyester baking film containing a coloring pigment as an uppermost layer. It is a coated metal plate with excellent workability.

In general, it is known that the nitrogen concentration on the surface of a polyester-based baked coating film is different from the average nitrogen concentration of the coating film. However, it was found that the nitrogen concentration on the surface of the coating film changes depending on the type and the amount of the pigment, such as a coloring pigment or an extender, even with a non-polar cross-linking agent that tends to condense the surface. This is presumably because the resin and the crosslinking agent are adsorbed on the surface of the pigment, and the degree of concentration of the crosslinking agent on the surface of the coating film changes. Also, the nitrogen concentration on the surface of the coating film changes depending on the presence or absence of the surface treatment of the pigment and the type and degree thereof. Therefore, in the polyester-based baked coating film according to the present invention, depending on the type and amount of the pigment used, the presence or absence of surface treatment, etc., the amount of the crosslinking agent used, the surface nitrogen concentration of the cured coating film after baking. Set to be at least 3 at%.

The surface nitrogen concentration of the coating film means a value determined by the XPS method as described later. A smooth polyester baking coating film does not contain particles for imparting irregularities to the coating film appearance (eg, resin beads disclosed in JP-A-11-104559, generally having a particle size of 10 μm or more). Means coating.

A coating film having a smooth surface and a high gloss is liable to have a noticeable decrease in gloss and discoloration due to chalking, and therefore requires higher weather resistance than a yuzu skin coating film having an uneven appearance. According to the present invention, without adding an additive for improving weather resistance such as an ultraviolet stabilizer, by appropriately selecting the coating composition and the surface treatment of the pigment, a polyester-based baking coating having a smooth pigment-containing surface. The weather resistance of the film can be improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Since the baking type polyester coating film of the present invention aims at improving weather resistance, it is useful as the uppermost coating film of a coated metal plate. Hereinafter, this aspect will be described in detail.

The base metal plate of the coated metal plate is not particularly limited. For example, cold-rolled steel sheet, stainless steel, metal sheet such as aluminum sheet, further electric or hot-dip galvanized steel sheet, galvannealed steel sheet, hot-dip aluminum coated steel sheet, hot-dip 5% or 55% Al-Zn alloy coated steel sheet, Various types of plated steel sheets, such as electric Zn-Ni alloy plated steel sheets, can be used, and may be appropriately selected according to the required level of corrosion resistance and workability.

Before the coating, the surface of the metal plate is usually subjected to a coating base treatment in order to improve coating adhesion and corrosion resistance. As the base treatment, one or more kinds of chromate treatment (preferably, coating type chromate treatment), zinc phosphate treatment, and non-chromium silica treatment may be applied in the same manner as in the past, and the amount of adhesion may be the same as in the past. The same may be applied.

The coating is usually made of two layers, an undercoat and an overcoat, but an intermediate coat may be applied in some cases. As the undercoat paint, it is advantageous to use a paint having high adhesion to a metal plate. In that regard, it is preferable to use a baking type undercoat selected from epoxy, polyester, and polyurethane, which has been conventionally used as a primer. The undercoat paint is usually applied so as to have a dry film thickness of about 3 to 10 μm, and is baked so that the PMT (maximum reached plate temperature) is 200 to 220 ° C. to dry and harden the paint film. For coating, a bar coater, a roll coater, a curtain flow coater or the like can be used.

When the intermediate coating is applied, the intermediate coating is not particularly limited. The resin type may be the same as the undercoat paint, but the intermediate paint may contain pigments such as extender pigments, rust preventive pigments, and color pigments.

According to the present invention, as the top coat for forming the uppermost coating film, a thermoplastic saturated polyester resin is used as a base resin, and a nitrogen-containing crosslinking agent such as a melamine resin or a polyisocyanate is blended with the base resin. Use a polyester-based baking paint as a binder component.

As the polyester resin, a thermoplastic saturated copolymerized polyester resin is preferable. This polyester resin is produced by polymerizing a monomer containing an acid component such as terephthalic acid, isophthalic acid and adipic acid and a polyhydric alcohol component such as ethylene glycol and glycerin under reduced pressure. In order to impart reactivity with a crosslinking agent, an excess of an alcohol component is used to produce a polyester having a terminal hydroxyl group. In order to improve processability, the number average molecular weight of the polyester resin is 5000-25000
Is more preferable, and more preferably in the range of 10,000 to 20,000. Examples of commercially available polyester resins of this type include Toyobo's Byron resin and Bayer's alkynol resin.

As the nitrogen-containing crosslinking agent, a melamine resin or a polyisocyanate can be used as in the conventional case. The compounding amount of the crosslinking agent is usually in the range of 10 to 30% by mass based on the total amount with the polyester resin (that is, the entire binder). If the amount of the crosslinking agent is too large, the coating film becomes hard and the workability is reduced.

As the melamine resin, a melamine resin modified with methyl alcohol or butyl alcohol is preferable. When excellent workability is required, it is preferable to use hexamethoxymethylated melamine and cure the coating film using a melamine curing catalyst such as PTSA (paratoluenesulfonic acid). When excellent stain resistance is required, use of a butyl alcohol-modified melamine resin is effective. Instead of a melamine resin, a guanamine resin such as a butyl etherified benzoguanamine resin can be used.

The polyisocyanate is a compound having two or more isocyanate groups. The polyisocyanate is preferably a non-yellowing type, for example, isophorone diisocyanate (IPDI) and hexamethylene diisocyanate.
(HMDI). It is common to use so-called blocked isocyanates in which free polyisocyanates are blocked with ε-caprolactam or MEK oxime in order to impart storage stability to paints. Further, those obtained by prepolymerizing such a polyisocyanate can also be used.

The top coat generally contains a coloring pigment, and may further contain other pigments such as extender pigments, brilliant pigments and rust-preventive pigments. Color pigments include titania (white), carbon black and iron oxide (black), and chromium oxide (green)
Various substances can be used, including, for example, graphite (yellow), iron oxide (red), and cobalt oxide (blue). Examples of the extender include calcium carbonate, barium sulfate, silica and the like. As the glitter pigment, various metal foils (eg,
Aluminum foil) and sulfides such as cobalt sulfide. Examples of rust preventive pigments are chromates such as strontium chromate.

The present inventors have found that the presence of a pigment in a polyester-based baked coating film is a major cause of deteriorating the weather resistance of the coating film. In other words, the polyester-based baked coating film containing no pigment has good weather resistance, but the addition of a small amount of pigment significantly reduces the weather resistance of the coating film. In the case of a polyester-coated metal sheet coated with a polyester-based baking coating, the top-coating film contains a coloring pigment and other pigments, which deteriorates the weather resistance. The cause is considered as follows.

Since pigments are fine particles, they have a high surface activity. In particular, inorganic pigments easily adsorb polar components on the surface. Therefore, a crosslinking agent component having a higher polarity than the polyester resin is preferentially adsorbed on the pigment surface. When the cross-linking agent is adsorbed on the pigment surface, the cross-linking agent does not sufficiently concentrate on the coating film surface during baking, so that the nitrogen concentration on the coating film surface after baking decreases. When the nitrogen concentration on the surface of the coating film becomes lower than 3 at% due to the adsorption of the crosslinking agent on the pigment surface, the concentration of the crosslinking agent on the surface of the coating film is insufficient and the crosslinking density on the surface of the coating film becomes low. The molecular weight is easily reduced, and evaporation is likely to occur. For this reason, it is presumed that fine irregularities occur on the surface, leading to deterioration of weather resistance.

As described above, the surface concentration of the crosslinking agent component such as melamine resin and the resulting increase in the nitrogen concentration on the surface of the coating film affect the surface properties such as adhesion and stain resistance of the baked polyester coating film. Doing has been known for some time. However, as can be seen from the fact that it was conventionally secured by the blending of an ultraviolet stabilizer (ultraviolet absorber), the weather resistance of the coating, which was considered to be the performance of the coating as a bulk, depends on the properties of the coating surface. Is an unexpected finding that depends on the nitrogen concentration on the coating surface, which is a measure of the surface concentration of the crosslinker.

In the present invention, based on this finding, the surface nitrogen concentration of a polyester-based baked coating film containing a pigment is adjusted to 3%.
At% or more, the weather resistance of the coating film is improved. The surface nitrogen concentration is preferably at least 5 at%.

When the type of the polyester resin and the crosslinking agent and the type of the pigment are constant, the following means can be used to increase the surface nitrogen concentration. The pigment is subjected to a surface treatment that reduces the surface activity of the pigment so as to reduce the amount of the pigment added, increase the amount of the crosslinking agent added, and reduce the adsorption of the crosslinking agent.

As the surface treatment of the pigment, for example, a coupling agent treatment such as a silane coupling agent and a titanate coupling agent can be used. In particular, use of an amine silane coupling agent is preferred. Titania pigments have very high surface activity as they are, so commercial products are surface-treated with one or more of silica, alumina, zirconia, etc. It is effective in lowering. The material of this surface treatment also affects the adsorption capacity of titania, the surface adsorption capacity of silica treated material is high, the next is zirconia treated material,
The alumina treatment material has the lowest adsorption capacity. Therefore, the surface nitrogen concentration can be increased by appropriately selecting the material for the surface treatment. In the above example, the use of titania surface-treated with alumina is most effective for improving weather resistance.

The reduction in the amount of the pigment may adversely affect the appearance of the coating film, and the increase in the amount of the cross-linking agent may limit the coating film too hard and adversely affect the processability. Therefore, if necessary, the above methods are appropriately combined so that the nitrogen concentration on the surface of the coating film becomes 3 at% or more.

The application and baking of the polyester top coat may be carried out in the same manner as in the prior art. However, baking conditions also affect the surface concentration of the cross-linking agent, and thus the nitrogen concentration on the coating film surface. Insufficient baking results in poor coating film performance, and insufficient increase in surface nitrogen concentration due to surface concentration of the crosslinking agent. In general, it is preferable to perform baking so that the PMT is 220 to 250 ° C.

The surface analysis of the polyester-based baked coating film of the present invention is performed by XPS (X-ray photoelectron spectroscopy). For example, X
Using AlKα (hν = 1486.6 eV) as the source, the analyzer calibrates the binding energy of pure gold Au4f7 / 2 to 83.7 eV (half-width 1.25 eV). Because the coating is an insulator,
Charge-up occurs during XPS measurement. Therefore, C
The XPS spectrum of the sample is corrected by setting the Cls binding energy of the -H group to 284.7 eV.

The measurement in the present invention is based on the photoelectron take-out angle.
(The angle formed between the sample surface and the photoelectrons detected) was fixed at 70 °. In this case, the detection depth is estimated to be about 11 nm from the coating film surface.

The surface nitrogen concentration (at%) of the coating film was calculated from the area intensity of the XPS spectrum according to the following formula: C _N = (I _N / S _N ) / Σ (I _i / S _i ) C _N : Nitrogen atomic concentration of the element, I _N: peak area intensity of nitrogen element, S _N: relative sensitivity coefficient of nitrogen element, I _i: peak area intensity of element i, S _i: relative sensitivity coefficients of elements i.

Even if the coating film contains a pigment, there is no other component than the resin components (C, O, N) on the surface of the coating film. Therefore, the element i may be of three types, C, O, and N, and each element S _i
As values, Cls was 1.0, O1s was 2.61, and Nls was 1.71.

[0043]

[Example] Method of preparing test material A hot-dip galvanized steel sheet (sheet thickness 0.5 mm, zinc adhesion amount 60 g / m ² per side) was used as a base material, and NRC 300 (coating type chromate) manufactured by Nippon Paint was used as a base treatment. 30 m chromium deposit
The resultant was bar-coated to a g / m ² and dried for about 10 seconds so that the PMT was 100 ° C.

A polyester primer (P670) manufactured by Nippon Paint Co., Ltd. was used as an undercoating material. One surface of the hot-dip galvanized steel sheet was bar-coated so that the dry film thickness was 5 μm, and the PMT was set to 210 ° C. Baked on.

The overcoat was prepared under the conditions shown below, and was coated with a bar on the undercoat so that the dry film thickness would be 15 μm, and baked so that the PMT would be 230 ° C. Test material was prepared.

<Overcoat> In the case of melamine crosslinking: Crosslinking agent based on the total amount of solid content of Byron 63cs (high molecular weight saturated copolymerized polyester) manufactured by Toyobo and Cymel 303 (methyl alcohol-modified melamine resin) manufactured by Mitsui Cytec. 0.3 wt% of PTSA as a catalyst was added to a binder mixed so that the solid content of the melamine resin of Example 1 was as shown in Table 1.
Was added.

Various amounts of carbon black as a color pigment were added to the resin solution, uniformly dispersed in the resin solution, and provided for coating. Some carbon blacks have been previously surface-treated with an amine-based silane coupling agent.

In the case of isocyanate crosslinking: Sumitomo Bayer Urethane Alkinol 2013 (polyester polyol) and the company's isocyanate resin (HMDI)
Based on the total amount of both solid contents, a binder was prepared so that the solid content of the polyisocyanate as the cross-linking agent became the ratio shown in Table 1. To this resin liquid, added various amounts of titania subjected to various surface treatments as a color pigment,
The mixture was uniformly dispersed and provided for coating. Only one example used carbon black as the pigment.

The workability, weather resistance and surface nitrogen concentration of each test material were evaluated as follows, and the results are also shown in Table 1. When isocyanate and melamine crosslinking agent are used in combination Color pigment = carbon black (same as above) Toyobo Pylon 63CS (polyester) Sumitomo Chemical Smear M (melamine, methyl alcohol modified) Sumitomo Bayer Urethane (isocyanate, HMDI) Evaluation method Processability (Bendability) With the painted surface of the test material on the outside and a sample of the same thickness sandwiched on the inside, perform 180 ° bending at 23 ° C using a vise, and use a 30x loupe to The presence or absence of cracks was determined by observing the coating film of No. 1, and the evaluation was made with the minimum number of plate scissors that did not cause cracks. From 0T to 2T, workability was determined to be good.

Weather resistance Sunshine weatherometer 200 hours, 500 hours,
The gloss retention relative to the initial gloss was determined. The gloss was measured at a regular reflectance of 60 °.

Analysis of Coated Film Surface Using ESCA MK II manufactured by VG, the composition of the extreme surface of the coated film was analyzed by the XPS method described above, and the surface nitrogen concentration (at%) was determined.

[0052]

[Table 1]

As can be seen from Table 1, in the case of a melamine cross-linked polyester coating, the nitrogen concentration (at%) of the coating surface was about 20% even when the content of the cross-linking agent was changed without the addition of the pigment.
The degree is constant and the weather resistance and workability are good. On the other hand, when carbon black is added as a coloring pigment, the nitrogen concentration on the surface of the coating film drastically decreases even when the amount of addition is as small as 5% by mass, and the surface nitrogen concentration further decreases with an increase in the amount of pigment added. , Less than 3%, and the weather resistance was greatly reduced (the gloss retention was 70% or less at 200 hours and 50% or less at 500 hours). However, even in that case, when the amount of the cross-linking agent added was increased or when the surface of the cross-linking agent was treated with a silane coupling agent, the surface nitrogen concentration was increased to 3% or more, and the gloss retention was improved accordingly. No decrease in workability due to the addition of the pigment was observed.

The same tendency is observed in the case of an isocyanate crosslinked polyester coating. That is, although the surface nitrogen concentration of the coating film containing no pigment was as high as 15%, the addition of titania subjected to various surface treatments as a pigment drastically reduced the surface nitrogen concentration. However, since the titania pigment has been subjected to surface treatment in advance, it is possible to secure a surface nitrogen concentration of 3% or more unless the amount of the crosslinking agent is small and the amount of the titania pigment surface-treated with silica is large. And the weather resistance of the coating film was well maintained. When the amounts of the cross-linking agent and the pigment were compared under the same conditions, the surface nitrogen concentration was the lowest when the silica-treated titania pigment was used, followed by the zirconia-treated material, and the surface nitrogen concentration when the alumina-treated titania was used. The weather resistance increased in this order. When the pigment is changed to carbon black, even if the amount of the pigment added is small,
The surface nitrogen concentration became very low, and the weather resistance was reduced.

A similar tendency was observed when two kinds of crosslinking agents, melamine and isocyanate, were used in combination.

[0056]

EFFECTS OF THE INVENTION A polyester baked coating film formed from a coating material in which a melamine resin or a polyisocyanate is blended as a cross-linking agent with a saturated high molecular weight polyester resin has excellent workability, but when used for an overcoat, a colored pigment In addition, the weather resistance is remarkably reduced by the addition of the compound, and the glossiness and the color change are often caused at an early stage, and this has been a problem particularly in a coated metal plate having a smooth coating film in which the gloss change is conspicuous.

According to the present invention, the weather resistance of a baked polyester-based coating film can be maintained well by only appropriately controlling the surface composition of the coating film without adding an expensive additive such as an ultraviolet light stabilizer. It is possible to prevent early gloss reduction and color change. Therefore, according to the present invention, a polyester-coated metal sheet excellent in workability and weather resistance, which is optimal for electric products and building materials used outdoors, can be supplied at low cost.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B32B 15/08 104 B32B 15/08 104Z C09D 5/00 C09D 5/00 Z 161/28 161/28 163 / 00 163/00 175/04 175/04 C23C 28/00 C23C 28/00 C (72) Inventor Akito Yoshioka 4-33 Kitahama, Chuo-ku, Osaka City, Osaka Sumitomo Metal Industries, Ltd. (72) Invention Inventor: Sumitomo Metal Industries, Ltd., 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka, Japan (72) Inventor Katsu Takahashi 4-5-33, Kitahama, Chuo-ku, Osaka, Osaka, Japan Sumitomo Metal Industries, Ltd. (72 ) Inventor Sayo Matsuo 2nd Dejima Nishimachi, Sakai City, Osaka Prefecture Sumitomo Metal Construction Materials Co., Ltd. (72) Inventor Kenichiro Kobayashi 2nd Dejima Nishimachi, Sakai City, Osaka Sumitomo Metal Construction Materials Co., Ltd. F-term in Sakai Works (reference) 4D075 AE03 CA32 DA06 DB01 DC18 EB35 EB38 4F100 AA37H AB01A AK36H AK41C AK41D AK41J AK51C AK51H AK53C AL01 BA04 DA05 BA06 BA10A BA10D BA13 CA02J CAJD J00N001 CA13D J00N DD061 DD071 DD081 DG001 DG111 JB36 KA03 KA08 NA01 NA03 NA12 PA08 PA11 PA14 PA19 PC02 4K044 AA02 AB02 BA10 BA15 BA21 BC02 BC05 CA11 CA16 CA18 CA53

Claims (3)

[Claims] 1. A method for improving the weather resistance of a polyester-based baked coating film containing a pigment, wherein the polyester resin having a terminal hydroxyl group and a crosslinking agent containing a nitrogen atom are used as a binder component. A method characterized in that the concentration is 3 at% or more. 2. A smooth polyester baked coating film containing a pigment, comprising a polyester resin having a terminal hydroxyl group and a crosslinking agent containing a nitrogen atom as a binder component,
A polyester baked coating film having excellent weather resistance, wherein the nitrogen concentration on the coating film surface is 3 at% or more. 3. At least one side of a metal plate, in order from the bottom, a base coat for coating, one or two baking coatings selected from epoxy, polyester and polyurethane, and a coloring pigment as an uppermost layer A coated metal sheet having excellent weather resistance and workability, comprising the polyester-based baked coating film according to claim 2 containing: