JP3078445B2 - Painted metal plate with excellent light resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated metal sheet having excellent light resistance on the surface of a coating film when irradiated with light such as ultraviolet rays, which is used for home appliances, building materials, automobiles and the like.

[0002]

2. Description of the Related Art Conventionally, painted products that have been painted after processing are now coated with a pre-coated metal plate (hereinafter referred to as a painted metal) because of the needs of improving the working environment, preventing the occurrence of pollution problems, and omitting steps with low production efficiency. The use of painted metal plates has been increasing. Painted metal sheets are required to be formed and processed, so a high degree of workability is required.On the other hand, the performance required conventionally has to be satisfied, and the coating design is difficult. there were. In order to solve this, Japanese Patent Application Laid-Open No. 61-32351 and Japanese Patent Application Laid-Open
A method for improving the resin composition as seen in 2-21830 discloses, a method of devising the paint formulation as seen in Japanese Unexamined Patent Publication No. 2-269168 has been proposed.
However, in recent years, the required level for various performances such as workability and light resistance has become extremely high, and it is the present situation that conventional technologies cannot meet these requirements.

[0003]

SUMMARY OF THE INVENTION The present invention provides a coated metal sheet which meets such advanced requirements and has excellent workability and light resistance.

[0004]

Means for Solving the Problems The physical properties of the coating film such as workability and light resistance are closely related to the structure of the coating film, and it can be said that the coating film structure determines these physical properties. Therefore, analysis of the coating film structure is extremely important. However, since the organic substance forming the coating film is a complex, glow discharge emission spectroscopy (hereinafter, referred to as GDS), which is an analysis method generally used in the analysis of metals, cannot be used. Analytical means that require a vacuum have the problem of instrument contamination. Infrared spectroscopy is also an effective means for obtaining knowledge about the structure in the depth direction, but it is an inorganic substance (for example, titanium oxide;
At present, it cannot be used for the quantification of i) and the analysis in the depth direction of the coating film has not been sufficiently performed. But recently,
As can be seen in the catalog of Rigaku Denki Kogyo Co., Ltd., for example, “System 386” manufactured by Rigaku Denki Kogyo Co., Ltd.
GDS using a high frequency such as "0" can be measured, and elemental analysis in the depth direction of the organic film has become possible.

In the present invention, as a result of intensive studies on a coating film excellent in light resistance, particularly ultraviolet light resistance, deterioration of light resistance, particularly, a decrease in gloss due to ultraviolet irradiation is caused by decomposition and volatilization of a coating resin in a surface layer. This was caused by the exposure of the pigment component. That is, the thickness of the layer not containing the pigment component in the outermost layer of the coating film is large, and those having a sufficiently low content of Ti of the pigment component are excellent in light resistance as compared with C which is a main element of the resin by surface analysis. . Specifically, T
The element distribution of the coating outermost layer of the coated metal plate having the upper coating film containing the i-pigment is such that the ratio of Ti to C in the strength ratio observed by high-frequency GDS is 1.
It was found that a value of 1 or less was a coated metal plate having excellent light resistance.

[0006]

In the present invention, the polyester resin coating film means a coating film containing a polyester resin and an aminoplast resin as essential components. The polyester resin is a resin having an ester group in the resin, and is called an oil-free polyester resin, an alkyd resin, a linear high molecular weight polyester resin, or a branched high molecular weight polyester resin. In addition to polyester resin, other resins,
For example, epoxy resin, urethane resin, acrylic resin,
One kind of fluorine resin, silicone resin, amide resin, imide resin and the like may be used alone, or two or more kinds may be mixed.

The aminoplast resin is a melamine resin,
Benzoguanamine resin and the like. Examples of the melamine resin include a methylated melamine resin and a mixed etherified melamine resin such as butyl-methyl. In addition to aminoplast resins, isocyanate groups, epoxy groups, amino groups, etc.
The addition of a crosslinking agent component having a group that reacts with the component added to the coating film such as a polyester resin may be used. Also,
In addition to titanium oxide as a titanium pigment, color pigments such as red iron oxide, barium sulfate, silica, cyanine blue, etc. and extender pigments, additives such as resin beads, aluminum flakes, mica, etc. If necessary, additives such as an antifoaming agent and a leveling agent can be contained.

As the metal plate, for example, a steel plate, an aluminum plate,
Examples include a stainless plate, a titanium plate, and a copper plate. Examples of the steel sheet include cold-rolled steel sheet, hot-rolled steel sheet, hot-dip galvanized steel sheet, galvannealed steel sheet, electro-galvanized steel sheet, zinc-iron alloy coated steel sheet, zinc-aluminum alloy coated steel sheet, and aluminum-coated steel sheet Chrome-plated steel sheet, nickel-plated steel sheet, zinc-nickel alloy-plated steel sheet, tin-plated steel sheet, and the like.

Further, the metal plate can be subjected to a pretreatment as required. Examples of the pretreatment include water washing, hot water washing, pickling, alkali degreasing, grinding, polishing, chromate treatment, zinc phosphate treatment, composite oxide film treatment, and the like, and these are used alone or in combination to perform the painting pretreatment. The conditions for the pre-coating treatment may be appropriately selected. Next, if necessary, an undercoat paint is applied on a metal plate and cured and dried to form an undercoat film layer. As the undercoat paint, there are polyester, epoxy, urethane and the like, which are roll coater, curtain flow coater,
Roller curtain flow coater, electrostatic coating machine, brush,
Paint with a blade coater, die coater, etc. to the required film thickness, then dry at room temperature or hot air oven,
An undercoating film layer is obtained by curing and drying in an induction heating furnace, a near-infrared ray furnace, an energy ray curing furnace, or the like.

Although the film thickness is optional, a dry metal film thickness of about 1 to 30 μm, particularly 3 to 12 μm is generally used for a coated metal plate. Drying conditions may be appropriately selected according to the content of the paint and the required performance, but the hot plate furnace, induction heating furnace, near-infrared furnace, etc. have a maximum reached plate temperature of 150 ° C to 230 ° C and a reaching time of about 10 to 200 seconds Conditions are common. In the present invention, the number of coating film layers to be formed is not limited at all, and after forming several coating films as needed, the polyester resin film according to the present invention may be formed on the outermost layer. The thickness of each coating layer, the resin composition, the pigment composition, and the like are not limited.

After the pretreatment and the formation of the undercoat film layer if necessary, the coating film of the present invention is formed. The method of formation is not particularly limited, but the paint is applied by a roll coater, a curtain flow coater, a roller curtain flow coater, an electrostatic coating machine, a brush, a blade coater, a die coater, or the like so as to have a required film thickness. The coating layer according to the present invention can be obtained by standing drying or curing and drying in a hot air oven, induction heating oven, near infrared oven, energy ray curing oven, or the like. Although the film thickness is optional, a dry film thickness of about 1 to 50 μm, particularly 5 to 30 μm is generally used for a coated metal plate. Drying conditions may be appropriately selected according to the contents of the coating material.
A condition of about 200 seconds is generally used.

The coating film thus formed is analyzed using a high-frequency GDS. The measurement conditions of the high-frequency GDS are not particularly limited. For example, the discharge power is 20 to 60 W, the argon flow rate is 150 to 350 ml / min, the photomultiplier voltage for detecting carbon is 400 to 500 V, and the photomultiplier voltage for detecting titanium is 700 to 900 V. , Sampling interval 3
It is measured at 00 to 2500 msec. Note that these values are fixed in one measurement and are not changed during the measurement. From the spectrum obtained by the measurement of the high-frequency GDS, the intensity of the spectrum peaks of Ti and C observed within 0.5 μm from the surface of the polyester resin coating film in contact with the air was measured, and the intensity ratio was Ti / C Calculate.

[0013]

EXAMPLES The method of high frequency discharge glow discharge emission spectroscopy was carried out under the following conditions. Equipment: System manufactured by Rigaku Denki Kogyo Co., Ltd.
3860 Anode inner diameter: 4 mmφ Analysis mode: high-frequency constant voltage mode Discharge power: 50 W Ar flow rate: 200 ml / min Measurement time: 800 sec Sampling interval: 500 msec Number of output points: 400 Photomultiplier voltage: C; 420 V, Ti; 800 V

According to this method, a chart is obtained in which the horizontal axis represents the sputtering time of the sample from the surface and the vertical axis represents the spectral intensity of the element. Here, from the value of the thickness of the surface layer measured by another method such as a gravimetric method or an electromagnetic film thickness measuring method and the sputtering time when the Ti concentration of this chart rapidly decreases, the average sputtering in the film thickness direction of the coating film is obtained. Speed (μm
/ Sec). Here, the element Ti unique to the surface layer
Paying attention to, the surface layer thickness on the chart was determined as the position where the strength sharply decreases as the interface between the surface layer and the layer below, but the content greatly changed between the surface layer and the layer below, The type of element of interest does not matter as long as it is an element that indicates the interface between the surface layer and the lower layer. The calculated average sputtering rate (μ
(m / sec), focusing on a range of 0.5 μm from the surface, measuring the respective intensities from the spectral peaks of Ti and C located therebetween, and calculating the value of Ti / C.

FIG. 1 shows the light resistance of a coating film surface according to the present invention;
4 shows the relationship with the Ti to C intensity ratio observed by high frequency discharge glow discharge emission spectroscopy. This indicates that a Ti / C intensity ratio of 1.1 or less as a value of Ti / C indicates excellent light resistance. In this example, as a condition for irradiation with ultraviolet light, a 15 W germicidal lamp (manufactured by Toshiba) was placed at a position 200 mm from the coated plate at room temperature,
Irradiation was performed for 8 hours. The gloss retention is determined by measuring the value of the mirror reaction rate (60 °) before and after irradiation, and calculating each value by the formula “gloss after irradiation” / “gloss before irradiation” to obtain the gloss retention. In general, it is determined that if the gloss retention is 45% or more under the irradiation conditions, sufficient light fastness is obtained, and the value of Ti / C at that time is 1.1 or less.

[0016]

According to the present invention, as a coated metal plate having excellent light resistance, the element distribution of the outermost layer of the coating film of a coated metal plate having an upper coating film containing a Ti pigment can be determined by high frequency discharge glow discharge emission spectroscopy. Excellent light resistance is obtained when the intensity ratio of the spectrum peaks of Ti and C observed within 0.5 μm from the surface of the polyester resin coating film which is in contact with air is 1.1 or less as the value of Ti / C. It is possible to obtain a coated metal plate having properties.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the light fastness of the coating film surface according to the present invention and the Ti to C intensity ratio observed by high frequency discharge glow discharge emission spectroscopy.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-309324 (JP, A) JP-A-62-10077 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 1/00-7/26

Claims (3)

(57) [Claims] 1. A coated metal sheet pigment in which a polyester resin-based coating film containing a titanium pigment is formed on the outermost layer,
High frequency discharge glow discharge emission spectroscopy (hereinafter referred to as high frequency G
DS), when the elemental concentration analysis of the polyester resin coating film in the depth direction was measured, titanium (hereinafter referred to as Ti) which was found within 0.5 μm from the surface of the polyester resin coating film in contact with air. A coated metal plate excellent in light resistance, wherein the intensity ratio of a spectral peak of carbon (hereinafter, C) is 1.1 or less as a value of Ti / C. 2. The coated metal sheet having excellent light resistance according to claim 1, wherein a coating film containing a melamine-formaldehyde resin is formed on the outermost layer. 3. The coated metal sheet having excellent light resistance according to claim 1, wherein a high-frequency induction heating device is used as a method of heating and baking the upper coating film.