JPH05285451A - Method for painting pcm steel panel with powder paint and pcm steel panel used therein - Google Patents

Abstract

PURPOSE:To safely form a powder paint film on the surface and cut surface of a double-coated PCM steel panel with good production efficiency and to adapt the coated article even to a use wherein inner surface aesthetic appearance and high corrosion resistance are required. CONSTITUTION:A conductive film with surface resistivity of 10<12>OMEGA/sq or less is formed on the rear film of a double-coated PCM steel panel or the rear film of the double-coated PCM steel panel is constituted of the conductive film with surface resistivity of 10<12>OMEGA/sq or less and powder paint is electrostatically applied to the surface of the PCM steel panel to form a powder paint film on the surface and cut surface of the PCM steel panel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder paint coating method for PCM steel sheets and a PCM steel sheet used in the method.

[0002]

2. Description of the Related Art PCM (pre-coating) by electrostatic coating of powder coating has been applied in various fields such as home electric appliances, building materials, steel products and vehicle parts. This PCM
The conversion means that the assembled object is not painted, but the sheet-shaped steel plate is painted in advance, or the coiled steel plate is unwound and painted.
This means a method in which the coated steel plate is cut into a predetermined composition and then formed into a product.

The powder coating is used for this PCM, because the powder coating does not contain an organic solvent and thus does not cause environmental pollution, and the coating which has not been applied onto the object to be coated is recovered. Reusable and even 1
It is based on the advantage that a thick film can be formed by coating once.

By the way, in the conventional PCM method using powder coating material, in order to prevent the occurrence of spark discharge during the electrostatic coating, it is possible to ensure continuity with the supporting conveyor.
When the back surface of the PCM steel sheet is not coated, or when the back surface is coated, a method of electrostatically coating the powder coating material in a sheet shape having a large area has been adopted.

However, the coated steel sheet obtained as described above is not coated on the back surface, or even if the coated steel sheet is coated, when the coated steel sheet is cut into a predetermined composition, the cut surface is powdered. Since it does not have a body paint coating film, there is a problem that it cannot be applied to applications where aesthetics of the inner surface and strong corrosion resistance are required.

That is, for applications where the inner surface is required to have a beautiful appearance or strong corrosion resistance, both sides of the PCM steel sheet are coated and cut with a predetermined composition before electrostatic coating of the powder coating. And electrostatically apply powder paint to it,
It is necessary to form the powder coating film not only on the surface of the PCM steel sheet but also on the cut surface with a predetermined composition.

Therefore, in order to meet the above demands, when it is desired to form a powder coating film on the cut surface of a double-sided coated PCM steel sheet whose back surface is also coated, up to the lower end of the cut surface of the object to be coated. It is necessary to electrostatically paint while keeping the contact area between the object to be coated and the conveyor to the minimum necessary by using a conveyor in which the contact part with the object to be coated has a pin shape so that the powder paint spreads. However, in the case of such a method, that the back surface coating film has an insulating property, and that the contact area is small and the contact resistance is high, the conduction of static electricity is poor, and spark discharge occurs during electrostatic coating, Risk of fire and explosion.

Therefore, in order to safely perform electrostatic coating, a steel sheet is cut into a predetermined composition, and then formed into a predetermined shape.
In other words, it is necessary to sufficiently ground the ground in a three-dimensional state and electrostatically coat the powder coating, but this method requires a large equipment and area for the coating line, and also three-dimensional coating. However, the coating efficiency per unit time is poor, and in terms of factory maintenance cost, labor saving, production efficiency, etc., there is a great disadvantage compared to the sheet-shaped or coil-shaped coating.

[0009]

As described above, in the conventional powder coating method of PCM steel sheet, in order to avoid the generation of spark discharge during electrostatic coating of powder coating, the appearance of the inner surface and strong corrosion resistance are improved. If you cannot obtain a coated product that can be applied to the application that requires the product, or if you want to obtain a coated product that can be used for the application that requires the inner appearance and strong corrosion resistance, electrostatically paint with good production efficiency. There was a problem that I could not.

Therefore, the present invention provides a powder coating method for a PCM steel sheet which allows safe and production-efficient electrostatic coating of powder coating on the surface and cut surface of a double-coated PCM steel sheet without generating spark discharge. The purpose is to provide.

[0011]

SUMMARY OF THE INVENTION The present invention is a double-sided coated PC.
In electrostatic coating of powder coating for M steel sheet, conductive coating is applied on the back coating to form a conductive coating having a surface resistivity of 10 ¹² Ω / sq or less, or double-sided coating PC
The back surface coating film of M steel sheet is made of a conductive coating film having a surface resistivity of 10 ¹² Ω / sq or less by coating with a conductive coating material, and the powder coating material is electrostatically coated on the surface of this PCM steel sheet surface. And, the above object is achieved by forming a powder coating film on the cut surface.

That is, according to the present invention, since the conductive coating film is formed on the back surface of the PCM steel sheet,
Even if the contact area between the steel plate and the conveyor is small, the static electricity generated during electrostatic coating of the powder coating can be effectively grounded. As a result, no spark discharge is generated during electrostatic coating of the powder coating, so that electrostatic coating of the powder coating can be safely performed.

Further, since the conductive coating film is formed on the back surface of the PCM steel sheet, the powder coating material reaches the lower end of the cut surface of the PCM steel sheet during electrostatic coating of the powder coating material, or if only the surface of the PCM steel sheet is present. It is also possible to form a powder coating film on the cut surface.

Then, the electrostatic coating is applied to a sheet-shaped PCM.
The method can be performed in a manner substantially similar to the method of electrostatically coating the steel sheet with the powder coating material.

Therefore, according to the present invention, double-sided coating P
It is possible to form a powder coating film on the surface and cut surface of a CM steel sheet safely and with good production efficiency, and it is also possible to apply the coated object to applications where aesthetics of the inner surface and strong corrosion resistance are required.

The conductive paint for forming the above-mentioned conductive coating film is attached to an existing primer (usually, the coating film directly formed on the back surface of the steel plate is a primer coating film) or directly on the steel plate. It is paintable, has bending workability and strength for ordinary PCM, and has a surface resistivity of 10 ¹²
Any material capable of forming a conductive coating film having a resistance of Ω / sq or less may be used, and, for example, a commercially available product described below can be used.

The conductive coating film formed on the back surface of the PCM steel sheet may be directly formed on the back surface of the PCM steel sheet,
Further, it may be formed on a back surface coating film such as a primer coating film, but its surface resistivity is required to be 10 ¹² Ω / sq or less. This has a surface resistivity of 10 ¹² Ω / s
If it is higher than q, the half-life of static electricity becomes too long and the removability of static electricity is insufficient.

The smaller the surface resistivity of the conductive coating film is, the more convenient it is in terms of removing static electricity, but the higher the price is. Therefore, considering the performance and the price, the surface resistivity of the conductive coating film is The range of 10 ¹⁰ to 10 ⁴ Ω / sq is preferable.

As the conductive agent in this conductive coating,
For example, conductive carbon, potassium titanate or titanium whose surface is plated with tin-antimony, graphite, zinc oxide or the like, which are used in ordinary conductive paints, may be used alone or in combination of two or more kinds. Used in.
As the base resin in the conductive paint, various kinds such as alkyd resin, polyester resin, epoxy resin, urethane resin, acrylic resin, and those containing a curing agent suitable for them can be used. And, as the form of the conductive paint, liquid, powder,
It may be in a sheet form.

As described above, it can be attached to an existing primer or directly coated on a steel plate, has bending workability and strength for ordinary PCM, and has a surface resistivity of 10 ¹² Ω / s.
As a conductive paint capable of forming a conductive coating film having a thickness of q or less,
For example, Shelltron 6300 gray type (I) (coating surface resistivity 10 ⁵ Ω / sq level conductive paint) manufactured by Kawakami Paint Co., Ltd., Shelltron 6300 gray type (II) (coating surface resistivity) Conductive paints of 10 ⁹ Ω / sq level) and the like can be mentioned.

The above-mentioned conductive coating film is usually formed in a thickness of 3 to 10 μm.
Appropriate coating means such as a bar coater or a flow coater is adopted.

Conductive paints have been used so far to prevent static electricity in electronic parts and to prevent static electricity in clean rooms related to electronics and biotechnology. It has never been applied, and no PCM steel sheet having a back surface coating film formed of a conductive coating film or a PCM steel sheet having a back surface coating film formed with a conductive coating film has been produced.

In electrostatic coating of powder coating, the surface resistivity of the conductive coating film on the back surface of the double-coated PCM steel sheet is measured to confirm that it is within a predetermined range, and cutting is performed with a predetermined composition before molding. After that, it is placed on a conductive conveyor or a conveyor that is grounded as required and electrostatically coated with powder coating.

The powder coating material may be, for example, an acrylic type, a polyester type, an epoxy type or an epoxy type, depending on the application.
Various powder coating materials such as polyester type and polyester-block urethane type can be used. Further, in electrostatic coating, any type of coating machine can be used.

The coating conditions are not particularly limited, but the applied voltage is -40 kV to -90 kV or +40 kV.
The range of V to +90 kV is preferable, and the distance between the electrodes is 50 to 3
00 mm, the discharge amount is preferably in the range of 50 to 300 g / min, and in the case of industrial implementation by line formation,
The pattern width is preferably 50 to 500 mm, the operating speed of the gun is 1 to 30 m / min, and the conveyor speed is preferably 1 to 50 m / min. Suitable conditions may be selected from these ranges according to the purpose.

[0026]

EXAMPLES Next, the present invention will be described more specifically by way of examples. However, the present invention is not limited to those examples.

Preparation of test coated plate Example 1 As a raw material, a thickness of 0.35 mm and 210 mm × 300 m
m pentite B [alloyed hot-dip galvanized steel sheet manufactured by Nisshin Steel Co., Ltd.] is used as a primer for 161Y
-70 primer [modified epoxy resin-based rust preventive primer manufactured by Kawakami Paint Co., Ltd.] is used, and the conductive paint is Shelltron 6300 gray type (I) [Kawakami Paint Co., Ltd.]
A conductive coating material produced by using a surface resistivity of the coating film of 10 ⁵ Ω / sq level] was used to prepare a test coated plate as described below.

The above 161Y-70 primer was coated on both sides of the material Pentite B using a bar coater so that the dry film thickness (hereinafter abbreviated as DFT) was 5 μm, and Baking was performed at a temperature (hereinafter abbreviated as PMT) of 190 ° C. for 30 seconds.

Next, the conductive paint Shelltron 6300 gray type (I) is applied on the back coating of the double-sided coated steel sheet.
With a bar coater. F. T. To 5 μm, and apply P. M. T. It was baked at 225 ° C for 40 seconds.
The surface resistivity of the conductive coating film on this back surface is 3.5 × 10 ⁵ Ω
Was / sq. Then, two circular holes having a diameter of 50 mm were punched out on this coated plate to make two circular cut surfaces.

Example 2 As a material, a thickness of 0.35 mm and a size of 210 mm × 300 mm
Silver alloy [alloyed hot-dip galvanized steel sheet manufactured by Nippon Steel Corporation], 161Y-70 primer was used as a primer in the same manner as in Example 1, and Sheltron 6300 gray type ( II) [conductive paint manufactured by Kawakami Paint Co., Ltd., surface resistivity of coating film 10 ⁹ Ω /
sq level], under the same conditions as in Example 1, 161Y-70 primer was applied to both sides of the material silver alloy and baked, and then the conductive paint Shelltron 6300 gray type was applied on the back surface coating film. (II) was coated and baked, and two coated circular holes having a diameter of 50 mm were punched out in the coated plate obtained as in Example 1. The surface resistivity of the conductive coating film on the back surface of this coated plate was 4.2 × 10 ⁹ Ω / sq. F. T. Was 5 μm.

Example 3 Cold-rolled steel plate SP having a thickness of 0.35 mm and a size of 210 mm × 300 mm treated with Bonderite 114M (a zinc phosphate coating agent manufactured by Nippon Parkerizing Co., Ltd.) as a material.
After using a CD-SD material [cold-rolled steel sheet manufactured by Nippon Steel Corporation], one surface of this material was coated with the same primer as in Example 1 under the same conditions as in Example 1, and baked. , A shell coating 6300 gray type (I) similar to that of Example 1 was used as a conductive paint on the back surface of the same. F. T. Of 5 .mu.m and coated in the same manner as in Example 1. M. T. 22
Baking was performed at 5 ° C. for 40 seconds, and two circular holes having a diameter of 50 mm were punched out in the obtained coated plate in the same manner as in Example 1. The surface resistivity of the conductive coating film on the back surface of this coated plate is 1.6 × 10 ⁵ Ω /
It was sq.

Example 4 As a material, a thickness of 0.35 mm and a size of 210 mm × 300 mm
The same 161Y as in Example 1 was used as the primer for the primer using the same zinc coat (electrogalvanized steel sheet manufactured by Nippon Steel Corporation).
Example 2 was used as a conductive paint using -70 primer.
Similar to Example 3, using the same Shelltron 6300 gray type (II) as in Example 3, a primer was applied to one surface of the material, baked, and then a conductive coating was applied to the back surface in the same manner as in Example 3. Painted and baked directly. Two circular holes having a diameter of 50 mm were punched in the obtained coated plate in the same manner as in Example 1. The surface resistivity of the conductive coating film on the back surface of this coated plate is 2.3.
It was × 10 ⁹ Ω / sq.

Example 5 As a material, a thickness of 0.35 mm and a size of 210 mm × 300 mm
GI material (a galvanized steel sheet manufactured by Sumitomo Metal Industries, Ltd.) of No. 1 was used, and the GI material of this material was coated with the same primer as in Example 1 under the same conditions as in Example 1 and baked. Then, a conductive paint similar to that of Example 1 was applied on the back surface coating film and baked under the same conditions as Example 1. A circular hole having a diameter of 50 mm was formed on the obtained coated plate as in Example 1. Two pieces were punched out, and the surface resistivity of the conductive coating film on the back surface of this coated plate was 5.2 × 10 ⁵ Ω / sq.

Comparative Example 1 As in Example 1, as a material, Pentite B [an alloyed hot-dip galvanized steel sheet manufactured by Nisshin Steel Co., Ltd.] was used, and the same primer as in Example 1 was applied to both sides of this material. Example 1
After coating and baking under the same conditions as above, Sheltron 6300 gray type (III) [conductive paint manufactured by Kawakami Paint Co., Ltd., surface resistivity of the paint 10 ¹² Ω
/ Sq level) was coated and baked under the same conditions as in Example 1. The coated plate thus obtained has a diameter of 50 mm as in Example 1.
I punched out two holes. The surface resistivity of the coating film on the back surface of this coated plate was 2.2 × 10 ¹² Ω / sq.

Comparative Example 2 As in Example 4, Zincoat [electrogalvanized steel sheet manufactured by Nippon Steel Corp.] was used as a material, and the same primer as in Example 1 was used on both sides of this material as in Example 1. After coating and baking under the conditions of C., a coil coater 8200 gray [polyester paint manufactured by Kawakami Paint Co., Ltd.] was applied on the back surface coating film by D.P. F. T. Is 5μ
It is painted so that it becomes m. M. T. It was baked at 200 ° C. for 40 seconds. The coated plate thus obtained had a diameter of 50 in the same manner as in Example 1.
Two mm holes were punched out. The surface resistivity of the back surface coating film of this coated plate was 7.8 × 10 ¹⁴ Ω / sq.

Comparative Example 3 As a material, Pentite B [an alloyed hot-dip galvanized steel sheet manufactured by Nisshin Steel Co., Ltd.] was used as a material, and the same primer as in Example 1 was applied to both surfaces of the material. Example 1
As with D., with a bar coater. F. T. Paint so that the thickness is 5 μm, and apply P. M. T. After baking at 190 ° C. for 30 seconds, a coil coater 8200 gray similar to that in Comparative Example 2 was applied on the back surface coating film by a bar coater under the same conditions as in Comparative Example 2 and baked. The surface resistivity of the back surface coating film of this coated plate was 8.5 × 10 ¹⁴ Ω / sq.

Electrostatic Coating of Powder Coating PCM prepared in Examples 1-5 and Comparative Examples 1-3 above
For the primer coating surface of the steel plate surface, porcelain 3
000-38 white [polyester powder coating for PCM manufactured by Kawakami Paint Co., Ltd.] was electrostatically coated with the following three types of electrostatic coating machines (all coating conditions were the same) to hold the PCM steel sheet. The degree of spark discharge generated between the grounded portion (which will be referred to as the pin-shaped contact portion 5 of the conveyor 4 in the description of FIG. 1 described later) is compared.

Further, the coating film after electrostatic coating of the powder coating is P.
M. T. After baking at 225 ° C. for 60 seconds, the coated plate was subjected to a salt spray test to examine its corrosion resistance. However, Comparative Example 3
For the coated plate of No. 2, after forming a powder coating film by electrostatic coating, two holes having a diameter of 50 mm were punched out and used as samples for a salt spray test.

Sample coating machine Hand-blown electrostatic coating machine GX-3 manufactured by Onoda Cement Co., Ltd.
Type 75 Gema Hand-Blown Electrostatic Coating Machine 721 Type Sames Hand-Blown Electrostatic Coating Machine Star Jet JR
-50 Applied voltage: -80kV Distance between gun and object to be coated: 200mm Discharge rate: 100g / min, 10 seconds coating Electrostatic coating temperature 20 ° C, relative humidity 60%

FIG. 1 shows a state of the powder coating material during electrostatic coating. 1 in FIG. 1 is a steel plate as a raw material, and there are coating films on both sides of this steel plate 1. In Examples 1 to 5, the front surface coating film 2 is a primer coating film and the back surface coating film 3 is a primer coating film. It is composed of a laminate with a conductive coating or a conductive coating alone.
Then, this PCM steel plate is disposed on the pin-shaped contact portion 5 of the conveyor 4, and the powder coating material 7 is electrostatically coated on the surface thereof from the electrostatic coating machine 6.

A sectional view of the PCM steel plate after electrostatic coating of the powder coating is schematically shown in FIGS.

In FIG. 2, numeral 11 is a steel plate as a raw material,
Reference numeral 12 is a primer coating film, and the primer coating film 12 is formed on both surfaces of the steel plate 11. 13 is a conductive coating film,
It is formed on the primer coating film 12 on the back surface side of the steel plate 11. Explaining in relation to FIG. 1, the primer coating film 12 and the conductive coating film 13 on the back surface side of the steel plate 11 correspond to the back surface coating film 3 in FIG. Reference numeral 14 is a powder coating film, and this powder coating film 14 completely covers the lower end of the cut surface of the PCM steel plate, that is, the lower end of the conductive coating film 13 of the lowermost layer. In addition, explaining in relation to the embodiment,
The coated plates of Examples 1, 2 and 5 on which a powder coating film is formed correspond to those shown in FIG.

Next, the one shown in FIG. 3 will be described. In FIG. 3, the primer coating film 12 is formed only on the front surface side of the steel plate 11, the primer coating film is not formed on the back surface side, and the conductive coating film 13 is directly formed on the back surface of the steel plate 11. There is. Explaining in relation to FIG. 1, this conductive coating film 13 corresponds to the back surface coating film 3 in FIG. Also in the case shown in FIG. 3, the powder coating film 14
Completely covers the lower end of the cut surface of the PCM steel plate, that is, the lower end of the conductive coating film 13 of the back surface coating film. Explaining in relation to the examples, the coated plates of Examples 3 and 4 on which a powder coating film is formed correspond to those shown in FIG.

Tables 1 and 2 show the occurrence of spark discharge during electrostatic coating of powder coatings and the results of salt spray test of coated plates after electrostatic coating. Table 1 is the case of Examples 1-5, and Table 2 is the case of Comparative Examples 1-3.

There are two types of spark discharge during electrostatic coating: spark is emitted at the same time as coating is started, and thereafter sparks are not emitted and sparks are continuously emitted. In both cases, powder paint is ignited. It may cause an explosion or explosion, and it is considered dangerous if either of them is present. The expression at the start of painting is referred to as the initial, and the expression as continued is referred to as the continuation. The occurrence status of spark discharge is shown for each electrostatic coating machine (indicated by company name) used.

In the salt spray test, a sodium chloride aqueous solution having a concentration of 5.0% by weight was applied to a coated plate electrostatically coated with powder coating.
The state of the cut surface was observed by spraying at 1.0 ° C. and 1.0 kg / cm ² for 1000 hours.

[0047]

[Table 1]

[0048]

[Table 2]

As is clear from the results shown in Table 1, in Examples 1 to 5 of the present invention, spark discharge did not occur at all during electrostatic coating of powder coating, and electrostatic coating of powder coating was safe. Was showing that it could be done. In addition, it shows that the coated material after electrostatic coating of powder coating does not show any abnormality on the cut surface even after the severe salt spray test of 1000 hours, and can be applied to applications requiring strong corrosion resistance. Was there.

On the other hand, in Comparative Examples 1 to 3, as shown in Table 2, spark discharge occurred during electrostatic coating of the powder coating material, resulting in poor safety. In Comparative Examples 2 to 3, Occurrence of red rust and blisters on the cut surface of the coated plate after the salt spray test,
It has been shown to be difficult to apply to applications where strong corrosion resistance is required.

[0051]

As described above, according to the present invention, the surface resistivity of 10 ¹² Ω / s is provided on the back coating of the double-coated PCM steel sheet.
Form a conductive coating film of q or less, or double-sided coating PC
By forming the back coating film of M steel sheet with a conductive coating film having a surface resistivity of 10 ¹² Ω / sq or less, a powder coating film is formed safely and efficiently on the surface and cut surface of a PCM steel sheet coated on both sides. It has become possible to apply the coated object to applications in which aesthetics of the inner surface and strong corrosion resistance are required.

[Brief description of drawings]

FIG. 1 is a schematic view schematically showing a state in which powder coating is electrostatically coated on a double-sided coated PCM steel sheet according to the present invention.

FIG. 2 is a PCM having a powder coating film formed according to the present invention.
It is sectional drawing which shows an example of the coating film structure of a steel plate typically.

FIG. 3 is a PCM having a powder coating film formed according to the present invention.
It is sectional drawing which shows the other example of the coating film structure of a steel plate typically.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Surface coating film 3 Back surface coating film 4 Conveyor 5 Pin contact part 6 Electrostatic coating machine 7 Powder coating material 11 Steel sheet 12 Primer coating film 13 Conductive coating film 14 Powder coating film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keiji Mitsuda Inventor Keiji Mitsuda 2-41-1, Tsukaguchihonmachi, Amagasaki City, Hyogo Prefecture Kawakami Paint Co., Ltd. (72) Inventor Yoshio Iwata 2-41-1, Tsukaguchihonmachi, Amagasaki City, Hyogo Prefecture No. Kawakami Paint Co., Ltd.

Claims (4)

[Claims] 1. A double-sided coated PCM steel sheet is coated with a conductive coating on the back coating to form a conductive coating having a surface resistivity of 10 ¹² Ω / sq or less, and the powder coating is coated on the surface of the PCM steel sheet. A method for coating a powder coating on a PCM steel sheet, which comprises electrostatically coating to form a powder coating film on the surface and the cut surface. 2. A double-sided coated PCM steel sheet has a backside coating film of PCM.
A conductive coating film having a surface resistivity of 10 ¹² Ω / sq or less, which is formed by coating a non-coated surface of a steel sheet with a conductive coating,
PC characterized in that powder coating is electrostatically coated on the surface of M steel sheet and a powder coating film is formed on the surface and cut surface.
Powder coating method for M steel sheet. 3. A PCM steel sheet, characterized in that a conductive coating film having a surface resistivity of 10 ¹² Ω / sq or less is formed on the back surface coating film of a double-sided coated PCM steel sheet. 4. A PCM steel sheet, wherein the back surface coating film of the double-sided coated PCM steel sheet is a conductive coating film having a surface resistivity of 10 ¹² Ω / sq or less.