JP2002069369A - Coating film having excellent weather resistance and coated metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the weather resistance of the baked coating film of a polyester resin crosslinked with a melamine or isocyanate crosslinking agent in no need of ultraviolet stabilizer and inhibit the premature gloss deterioration and discoloration of the polyester baked paint film of high processability. SOLUTION: Vinylidene fluoride resin is admixed into the coating film, preferably baked so that the maximum temperature may reach >=220 deg.C and the vinylidene fluoride resin may be distributed thick on the coating film surface whereby the fluorine concentration is increased higher than 5 at.% on the surface of the paint film. When this coated layer is formed as a finishing layer after the surface-treated metal plate is put in the undercoat, the objective coated metal having excellent processability and resistance to weather 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. Further, since the coating film thickness is about 20 to 25 μm, which is not very thick, if there is any damage during handling, there is a disadvantage that the base steel sheet is easily exposed and the corrosion resistance is reduced.

A PVC steel sheet has a feature that it is hard to be damaged due to being a thick film and has good corrosion resistance and also has excellent workability. However, the weather resistance is liable to be chalky. Changes and gloss reduction are likely to occur.

[0005] 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 melamine resin and polyisocyanate with the base resin. .

In the case of 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.

[0007] As a polyester-based 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. This coated steel sheet had excellent workability to withstand 180 ° close bending (0T), but often had insufficient weather resistance.

Japanese Patent Application Laid-Open No. 11-246821 discloses that in order to obtain a precoated steel sheet excellent in workability and weather resistance, a paint containing an aminoplast resin (melamine resin) or a polyisocyanate as a crosslinking agent and a polyester polyol 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.

[0009] Of these, Japanese Patent Application Laid-Open No. 11-293181 discloses that
Specific acrylic resin [ie, polymerizable UV-stable monomer
(A) and a copolymerizable acrylic polyol resin obtained by copolymerizing a polymerizable monomer component essentially containing a cycloalkyl group-containing polymerizable monomer (B) and a hydroxyl group-containing polymerizable monomer (C) ( D)]
And a prepainted steel sheet paint containing fluorinated resin (E).

[0010] 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.

For coloring materials, 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.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to improve the weather resistance of a polyester baked coating film obtained by crosslinking a polyester resin with a melamine or isocyanate type crosslinking agent without using an expensive ultraviolet stabilizer. It is what we aimed for. 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.

[0014]

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 improved the weather resistance by adding a vinylidene fluoride resin, which is a resin having excellent weather resistance, to a polyester baked coating film obtained by crosslinking a polyester resin with a melamine or isocyanate type crosslinking agent. I considered it. As a result, it was found that the weather resistance of the obtained coating film largely depends on the baking temperature, and that a coating film with improved weather resistance was easily obtained when the maximum ultimate plate temperature (PMT) was increased. When the surface composition of the coating film having good weather resistance was examined, the surface fluorine concentration was 5 at% or more, and when the PMT was 220 ° C. or more, the surface fluorine concentration was calculated from the amount added. It was found that the concentration of fluorine was higher than the average fluorine concentration in the film, and the fluorine was concentrated on the surface of the coating film.

That is, the weather resistance, which was conventionally considered to be the bulk property of the coating film, is called the concentration of the fluororesin on the coating film surface.
It was found to be improved by the surface composition. When the fluorine concentration on the coating film surface is 5 at% or more, the weather resistance is improved because at this concentration or more, the properties of the coating film surface are mainly controlled by vinylidene fluoride. It is speculated that the weather resistance may have come to the fore.

Here, the present invention relates to a polyester baked coating film comprising a polyester resin having a terminal hydroxyl group and a crosslinking agent as a binder component, wherein the coating film contains a vinylidene fluoride resin, It is a polyester-based baked coating film having excellent weather resistance, characterized by having a fluorine atom concentration of 5 at% or more.

Such a polyester baked coating film is
It can be obtained efficiently by baking at a maximum temperature of the plate of 220 ° C. or more and concentrating fluorine on the surface of the coating film.

The present invention also provides, in order from the bottom, at least one side of a metal plate, a base coat for coating, an epoxy-based coating,
Characterized by having one or two baking films selected from polyester and polyurethane, and the above-mentioned polyester baking film as an uppermost layer,
We also provide painted metal sheets with excellent weather resistance and workability.

In general, in a polyester-based baked coating film, it is known that the surface nitrogen concentration is higher than the average nitrogen concentration of the coating film because a crosslinking agent component such as melamine and polyisocyanate concentrates on the surface during baking. I have. However, when the coating film contains vinylidene fluoride resin, when the baking temperature exceeds a certain temperature, the vinylidene fluoride resin concentrates on the surface during baking, and the weather resistance of the coating film is increased due to an increase in the surface fluorine concentration. The remarkable improvement is a new and unexpected finding found by the present inventors.

The surface fluorine concentration of the coating film means a value determined by the XPS method as described later. According to the present invention, it is possible to improve the weather resistance of a substantially smooth polyester-based baked coating film by adding a coating composition and a baking temperature without adding an additive for improving weather resistance such as an ultraviolet stabilizer. it can.

[0022]

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 coating, the surface of the metal plate is usually subjected to a coating base treatment for improving 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, the top coat for forming the uppermost coating film is made of a thermoplastic saturated polyester resin as a base resin and a suitable crosslinking agent such as a melamine resin or a polyisocyanate. Use a polyester baking paint.

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 8,000 to 15,000. Examples of commercially available polyester resins of this type include Toyobo's Byron resin and Bayer's alkynol resin.

As the cross-linking agent, a nitrogen-containing one such as a melamine resin or a polyisocyanate can be used as in the prior art. The compounding amount of the crosslinking agent is 10 to 10 based on the total amount with the polyester resin (that is, the entire binder).
Usually it is in the range of 30% by weight. If the amount of the crosslinking agent is too large, the coating film becomes too hard, and the processability is reduced.

As the melamine resin, a melamine resin modified with methyl alcohol or butyl alcohol is preferred. 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 preferably a non-yellowing type, for example, isophorone diisocyanate (IPD
I) and hexamethylene diisocyanate (HMDI). It is common to use so-called blocked isocyanates in which free isocyanate groups are blocked with ε-caprolactam or MEK oxime in order to impart storage stability to paints. Further, those obtained by prepolymerizing such an isocyanate 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. Examples of the glitter pigment include various metal pigments (eg, aluminum flake), mica flake, and the like.

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. The cause is considered as follows.

Pigments Since pigments are fine particles, they have 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 is not sufficiently concentrated on the surface of the coating film during baking, so that the cross-linking density on the surface of the coating film is reduced. It is presumed that this decrease in the crosslink density on the surface of the coating film facilitates the breaking of molecular chains by ultraviolet rays, leading to deterioration in weather resistance.

In the present invention, a vinylidene fluoride resin is contained in the polyester-based baked coating film so that the fluorine concentration on the surface of the coating film becomes 5 at% or more. In the coating film having such a surface fluorine concentration, as described above, the properties of the vinylidene fluoride resin strongly appear, and even when the amount of the vinylidene fluoride resin is small, the weather resistance of the coating film is significantly improved. Is done.

Unlike many other fluororesins, vinylidene fluoride resins have relatively good compatibility with other resins, and therefore have been used alone as a binder component of weather-resistant fluorine-coated steel sheets. Or, it has been used in combination with an acrylic resin. However, as described in connection with the prior art, this resin is expensive, and the thickness of the coating film is insufficient, so that the base material is exposed due to scratching and the corrosion resistance is reduced.

In the present invention, a small amount of vinylidene fluoride resin is contained in the polyester-based baked coating film, and preferably the resin is concentrated on the coating film surface during baking to improve the weather resistance of the coating film. Since the amount used is small, economy is not deteriorated. The polyester coating can be applied to a sufficient thickness. Therefore, the disadvantages of the above-mentioned fluorine-coated steel sheet are eliminated.

The vinylidene fluoride resin used is preferably a homopolymer of vinylidene fluoride (polyvinylidene fluoride), but a copolymer with another vinyl monomer (for example, ethylene) as long as the weather resistance is not impaired. You can also. Alternatively, to increase compatibility with the binder resin,
An acrylic resin or the like can be added as a compatibilizer.

The amount of the vinylidene fluoride resin to be added may be an amount sufficient for the surface fluorine concentration of the baked polyester film to be 5 at% or more. This amount varies depending on the type and the mixing ratio of the polyester resin and the crosslinking agent in the coating film. However, it has been found that even when these conditions are exactly the same, the surface fluorine concentration of the coating film greatly varies depending on the baking temperature.

More specifically, if the PMT is significantly lower than 200 ° C. (eg, 180 ° C.), the vinylidene fluoride resin becomes thicker than the surface, and the surface fluorine concentration becomes lower than the average fluorine concentration of the entire coating film. When the PMT is around 200 ° C., the surface fluorine concentration becomes almost the same as the average fluorine concentration of the coating film, and the vinylidene fluoride resin is uniformly present on the surface and inside. In contrast, when the PMT rises above 220 ° C,
The vinylidene fluoride resin becomes concentrated on the surface, and the surface fluorine concentration becomes significantly higher than the average fluorine concentration of the coating film.

For example, as shown in Examples described below, even if vinylidene fluoride resin is added in the same amount so that the average fluorine concentration of the coating film becomes 5 at% based on the resin solid content,
The nitrogen concentration on the surface of the coated film after baking is 3 at% when the PMT is 180 ° C., whereas it is 6 wt% when the PMT is 220 ° C.
And a double opening appears. In other words, even if vinylidene fluoride resin is added in such an amount that the average fluorine concentration becomes 5 at%, if the PMT is low, a coating film excellent in weather resistance having a surface fluorine concentration of 5 at% or more according to the present invention can be obtained. Can not.

The content of the vinylidene fluoride resin in the coating film is calculated as atomic% of fluorine in the vinylidene fluoride based on the resin solid content of the binder component composed of the polyester resin and the crosslinking agent and the vinylidene fluoride resin. The average fluorine concentration in the coating film to be formed is preferably in the range of 4.2 to 15 at%, and the average fluorine concentration is more preferably in the range of 5 to 10 at%. If the vinylidene fluoride resin is added in a larger amount, the weather resistance of the coating film is improved, but it is disadvantageous in terms of cost, and there is also a problem that the gloss is easily lowered.

As the solvent for the paint for forming the coating film of the present invention, one or more selected from ketones, esters, and other solvents compatible with these can be used. For example, since the above-mentioned commercially available polyester resin or melamine resin or polyisocyanate of a crosslinking agent is dissolved in such a solvent,
Mix them appropriately and add the pigment to the polyester-based baked paint, and solidify the vinylidene fluoride resin as it is,
Alternatively, when added after being dispersed in the above-mentioned solvent, the paint used in the present invention can be prepared.

The application of the top coat may be carried out in the same manner as described for the undercoat. Subsequent baking of the overcoated film is performed at a temperature such that the fluorine concentration on the surface of the coated film after baking becomes 5 at%. This temperature depends on the amount of vinylidene fluoride resin added. That is, when the average fluorine concentration of the above-mentioned coating film is as high as 10 at% or more, for example, the baking temperature is low, and even if the vinylidene fluoride resin is concentrated not on the coating film surface but inside the coating film, The fluorine concentration on the surface of the coating film is at least 5 at%, and good weather resistance can be secured. On the other hand, when the average fluorine concentration of the coating film is around 5 at%, it is necessary to raise the baking temperature to some extent so as to avoid concentration of vinylidene fluoride in the coating film.

However, in any case, the baking of the top coat is preferably performed at a temperature at which the PMT is 220 ° C. or higher. As a result, the vinylidene fluoride resin concentrates on the surface of the coating film, and the fluorine concentration on the surface of the coating film becomes higher than the average fluorine concentration of the coating film. Generally, weather resistance tends to improve as the surface fluorine concentration of the coating film increases,
Regardless of whether the average fluorine concentration is high or low, it is advantageous to concentrate the vinylidene fluoride resin on the surface of the coating film to improve the weather resistance.

Although the upper limit of PMT is not particularly specified, if it is too high, the polyester resin may turn yellow.
The temperature is preferably set to 260 ° C. or lower, more preferably 250 ° C.
It is below ° 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 Au4f7 / 2 to 83.7 eV (half-width 1.25 eV). Since the coating is an insulator, X
Charge-up occurs during PS measurement. Therefore, CH
XPS of the sample, with the Cls binding energy of the group being 284.7 eV
Correct the S spectrum.

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 fluorine concentration (at%) of the coating film was measured by XPS
From the integrated intensity of spectrum was calculated by the following _{equation: C F = (I F /} S F) / Σ (I i / S i) C F: atomic concentration of fluorine element, I _F: peak area intensity of the fluorine element, S _F : relative sensitivity coefficient of elemental fluorine, I _i : peak area intensity of element i, S _i : relative sensitivity coefficient of element i.

Even if the coating film contains a pigment, only the resin components (C, O, N, F) are present on the surface of the coating film, and there is no metal element derived from the pigment. Therefore, the element i is C,
Four types of O, N, and F may be used, and the _Si value of each element is C
ls used a value of 1.0, O1s used a value of 2.6, Nls used a value of 1.7, and F1s used a value of 3.4.

[0051]

[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 raised to 210 ° C. Baked on.

The top coat was prepared under the conditions shown below, and was bar-coated on the undercoat so that the dry film thickness was 15 μm, and the PMT was changed in the range of 180 to 250 ° C. The coating film was baked to prepare a test material of a coated steel plate.

<Overcoat> In the case of melamine crosslinking: The mass ratio of the solid content of Byron 63cs (high molecular weight saturated copolymerized polyester, solvent: cyclohexanone) manufactured by Toyobo and Cymel 303 (methyl alcohol-modified melamine resin) manufactured by Mitsui Cytec. Was added to a binder mixed at a ratio of 85:15, and 0.3% by mass of PTSA as a catalyst was added. To this, polyvinylidene fluoride resin (Deokin Chemical NEOFLON VD
A dispersion liquid obtained by dispersing F) in cyclohexanone was added in various amounts to prepare a resin liquid having a resin solid content of 50% by mass. To this resin liquid, carbon black as a coloring pigment was added in an amount of 5% by mass based on the solid content of the resin, uniformly dispersed in the resin liquid, and provided for coating.

In the case of isocyanate crosslinking: The weight ratio of the solid content of alkynol 2013 (polyester polyol, solvent: Solvesso 150) manufactured by Sumitomo Bayer Urethane and polyisocyanate (blocked by HMDI and MEK oxime, solvent: Solvesso 150) manufactured by Sumitomo Bayer Urethane is determined. Binders were mixed at a ratio of 60:40. The same vinylidene fluoride dispersion as described above was added to this binder solution. To this resin solution, titania as a coloring pigment was added in an amount of 45% by mass based on the resin solid content, and the glass beads were uniformly dispersed in the resin solution using glass beads, and then filtered through a stainless mesh to remove the glass beads. After that, it was subjected to coating.

Table 1 shows that the vinylidene fluoride resin (PVD
The addition amount of F) is shown as at% in the F element with respect to the total amount of the solid content of the binder and the vinylidene fluoride resin.
If the surface fluorine concentration is higher than this concentration, it means that fluorine is concentrated on the surface.

The workability, weather resistance and surface fluorine concentration of each test material thus prepared were evaluated as follows, and the results are also shown in Table 1. Evaluation method Workability (Bendability) With the painted surface of the test material on the outside and a sample of the same plate thickness on the inside, perform 180 ° bending at 23 ° C using a vice, and use a 30-fold loupe Then, the presence or absence of cracks was determined by observing the coating film of the processed portion, 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 Surface of Coating Film Using ESCA MK II manufactured by VG, the composition of the extreme surface of the coating film was analyzed by the XPS method described above, and the surface fluorine concentration (at%) was determined.

[0060]

[Table 1] As can be seen from Table 1, in the case of the melamine-crosslinked polyester-based baked coating film, the surface fluorine concentration of the coating film was 0 in Nos. 1 to 3 in which the vinylidene fluoride resin was not added.
%, And the weather resistance was low regardless of the baking temperature.

On the other hand, when the vinylidene fluoride resin is added so that the average fluorine concentration of the coating film becomes 5 at%,
The baking temperature (PMT) greatly changed the fluorine concentration on the surface of the coating film. That is, when the PMT is as low as 180 ° C., the surface fluorine concentration is lower than the average fluorine concentration, vinylidene fluoride is concentrated inside the coating film, and the fluorine concentration on the coating film surface is 5 at%.
Is not reached, so even if vinylidene fluoride resin is added,
The weather resistance was not significantly improved. Even with the same amount of vinylidene fluoride resin added, when the PMT is 200 ° C., the surface nitrogen concentration is 5 at%, which is the same as the average concentration, and the weather resistance is significantly improved. When the PMT is 220 ° C. or higher, the surface fluorine concentration is lower. When the concentration was higher than the average concentration, the vinylidene fluoride resin became concentrated on the coating film surface, and the weather resistance was further improved.

The vinylidene fluoride resin has an average fluorine concentration of
If added at 10at%, PMT should be 200 ℃
In this case, the vinylidene fluoride resin was concentrated inside the coating film, and the surface fluorine concentration was lower than the average concentration.
Greatly exceeded, the weather resistance was sufficiently high. Also in this case, when the PMT was 220 ° C. or higher, the surface fluorine concentration became higher than the average concentration, the vinylidene fluoride resin was concentrated on the coating film surface, and the weather resistance was further improved. But P
When the MT was as high as 260 ° C., the weather resistance was rather lowered. This is considered to be due to thermal degradation of the polyester resin.

The same tendency was observed in the case of the isocyanate crosslinked polyester coating film, and the average fluorine concentration of the coating film was 5 at.
%, The surface fluorine concentration of the coating film fluctuated due to PMT. When the surface concentration was 5 at% or more, significant improvement in weather resistance was obtained.

Regardless of the crosslinking agent, no decrease in workability was observed when the fluorine concentration on the coating film surface was 5 at% or more.

[0065]

The polyester baking type coating film having a high molecular weight saturated polyester resin, a crosslinking agent such as melamine resin or polyisocyanate, and a binder component is excellent in workability. As a result, weather resistance is remarkably reduced, and early gloss reduction and color change often occur. This is a problem particularly in a coated metal plate having a smooth coating film in which gloss change is conspicuous.

According to the present invention, a vinylidene fluoride resin is blended in a small amount without adding expensive additives such as an ultraviolet stabilizer, and preferably, the baking temperature is set to a higher temperature so that the vinylidene fluoride resin is coated on the surface of the coating film. By concentrating to
The weather resistance of the polyester-based baked coating film can be favorably maintained, and 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) C09D 5/00 C09D 5/00 D 127/16 127/16 163/00 163/00 175/04 175/04 C23C 28/00 C23C 28/00 C (72) Inventor Akihito Yoshioka 4-33, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Inside Sumitomo Metal Industries, Ltd. (72) Michiyasu Takahashi Kitahama, Chuo-ku, Osaka City, Osaka Prefecture 4-5-33 Sumitomo Metal Industries, Ltd. (72) Inventor Katsu Takahashi 4-5-33, Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (72) Inventor Sachio Matsuo Dejima, Sakai-shi, Osaka No. 2 Nishimachi Sumitomo Metal Building Materials Co., Ltd. Sakai Works Co., Ltd. (72) Inventor Kenichiro Kobayashi No. 2 Dejima Nishimachi Sakai City, Osaka Prefecture Sumitomo Metal Building Materials Co., Ltd. Sakai Works Co., Ltd. F-term (reference) 4D075 AE03 BB26Z BB93Z CA13 CA32 CA33 CB04 DA06 DB02 DB04 DB05 DB07 DC01 DC18 EA07 EB17 EB32 EB33 EB35 EB38 EB45 4J038 CD111 CD112 DA162 DD061 DD071 DD081 DG111 GA03 KA03 NA01 NA03 NA12 PA14 PA19 PC02 4K044 AA02 BAA13 BA14 BC CA16 CA18 CA62

Claims (3)

[Claims] 1. A polyester-based baked coating film comprising a polyester resin having a terminal hydroxyl group and a crosslinking agent as a binder component, wherein the coating film contains a vinylidene fluoride resin,
A polyester-based baked coating film having excellent weather resistance, characterized in that the fluorine atom concentration on the coating film surface is 5 at% or more. 2. The polyester-based baked coating film according to claim 1, which has been baked at a maximum ultimate plate temperature of 220 ° C. or higher. 3. The method according to claim 1, wherein at least one surface of the metal plate is, in order from the bottom, a base coat for coating, one or two baking coatings selected from epoxy, polyester and polyurethane, and a top layer. 3. A coated metal sheet having excellent weather resistance and workability, comprising the polyester-based baked coating film according to any one of (1) to (2).