JP3184949B2 - Painted steel sheet with excellent red rust resistance on the end face - 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 steel sheet having excellent red rust resistance on an end face used for home appliances, building materials and automobiles.

[0002]

2. Description of the Related Art Conventionally, coating of home electric appliances and the like has been performed after processing and forming a steel sheet. However, the use of the coated steel sheet has increased from the viewpoints of pollution problems and work environment.

[0003] Painted steel sheets are premised on being processed after painting, so they require a high degree of workability, and are also required to have the same hardness, stain resistance and weather resistance as conventional post-painting.
This has been the subject of much consideration and improving gradually.

Another major drawback of the coated steel sheet is that it is used as it is, so that it is difficult to ensure the corrosion resistance of the cut end face, which is one obstacle to using the coated steel sheet.

[0005]

At present, almost no measures have been taken to improve the corrosion resistance of the end face. The use of painted steel sheets has been increasing recently, especially in the field of home appliances. This is because the need for omission of painting has become particularly strong among home appliance manufacturers.

[0006] Conventionally, it has been used for products used indoors, such as a microwave outer box and a refrigerator outer box. However, in recent years, it has been used outdoors such as an air conditioner outdoor unit and a vending machine. There is a growing movement to apply painted steel sheets to products.

[0007] Painted steel sheets are widely used outdoors as building materials, but in the case of building materials, coating film cracking in the processed part does not become a major problem, and the coating amount is increased by increasing the amount of plating applied. , End face corrosion resistance was secured.

[0008] On the other hand, in the case of products for home appliances, cracks in the coating on the processed part tend to be disliked as deteriorating the commercial value. Therefore, it is necessary to ensure both the red rust resistance of the end face and the appearance of the coating on the processed part. However, the problem cannot be solved only by increasing the amount of plating.

In view of such circumstances, the present invention provides a coated steel sheet which achieves both the red rust resistance of the end face of the coated steel sheet, the appearance of the processed part and the corrosion resistance of the processed part, and which can be used for outdoor applications for home appliances. With the goal.

[0010]

According to the present invention, which solves the above-mentioned problems, the thickness t (mm) of the steel sheet and the coating weight w (g / m ² ) per side are t ≦ 1.6, w ≦ 130, w / t
A coated steel sheet having excellent red rust resistance on the end faces , characterized in that a coating film containing 25% or more of a rust-preventive pigment in the coating film is formed on both sides of a galvanized steel sheet satisfying both ≧ 60.

[0011]

The present invention will be described in detail below together with the operation.

The inventors have found that the red rust resistance of the end face of a coated steel sheet is remarkably improved when the relation between the sheet thickness and the coating weight is within a certain range. That is, a relation of w / t ≧ 60 is established between the thickness t (mm) of the steel sheet not containing the plating and the amount of plating w (g / m ² ) per one side of the steel sheet. , T ≦ 1.6.

If the plate thickness t exceeds 1.6 mm, the improvement of the red rust resistance of the end face is not so much observed even if the plating amount is increased. When w / t is less than 60, the red rust resistance of the end face is insufficient. Further, for the coating weight w, w ≦ 13
When 0 is satisfied, the degree of cracking of the coated film in the processed portion is small, and in home electric appliances, the red rust resistance of the end surface and the appearance of the coated film in the processed portion can be secured.

The types of plating include hot dip galvanizing,
Electro-galvanized and alloyed hot-dip galvanized contemplated.

Next, a coating film containing 25% or more of a rust-preventive pigment in the coating film is formed on both surfaces of the galvanized steel sheet. It is essential to contain at least 25% by weight of the rust preventive pigment in the dry weight of the coating film.

The content of the anticorrosive pigment is insufficient resistance to rust of the end face is less than 25%. On the other hand, there is no particular upper limit, but 5
If the content is 0% or more, workability may be reduced.

As the type of the rust preventive pigment, strontium chromate, zinc chromate, potassium chromate,
A chromium-based rust-preventive pigment such as calcium chromate has a large effect, and those containing strontium chromate and potassium chromate as the main components are particularly preferable. Other examples include phosphoric acid pigments, finely divided silica, vanadic acid, and combinations thereof.

As a binder resin for forming a coating film,
Examples include polyester resin, epoxy resin, acrylic resin, urethane resin, and the like, but are not particularly limited. Polyester resin is most preferable in terms of achieving both workability and corrosion resistance.

[0019] The film thickness is not particularly limited, the end face 耐赤
From the viewpoint of ensuring rust resistance, it is desirable that both surfaces have a thickness of 1 μm or more, and a film thickness of 15 μm or more may be disadvantageous in terms of cost. When the thickness is about 3 to 10 μm on both sides , red rust resistance, corrosion resistance in the processed portion, and appearance of the processed portion are most easily compatible with each other.

If this coating film is formed only on one side of a plated steel sheet, it has the effect of improving the red rust resistance of the end face , but is insufficient for long-term outdoor use, and must be formed on both sides of the steel sheet. Is required.

An overcoat film can be further formed on the coated steel sheet. As the kind of the coating film, a coating film having good weather resistance such as a polyester resin type, a fluororesin type, a urethane resin type, and an acrylic resin type is preferable. The film thickness may be determined according to the required performance. For example, the film thickness of the overcoat layer may be about 5 to 30 μm. Of course, two or more overcoat layers may be provided.

The production of the coated steel sheet can be performed by a normal plating process and a normal coating process, and no special equipment is required. For example, plating can be hot-dip or electroplating,
What is necessary is just to carry out in the existing continuous plating equipment, and to apply the coating in the existing continuous coating equipment.

[0023]

EXAMPLE A hot-dip galvanized steel sheet having a thickness of 0.8 mm and a coating weight per side of 30 to 100 g / m ² was applied to both sides of a steel sheet by a conventional method. After applying a coating type chromate treatment to both sides of the plated steel sheet, after drying, a coating material having a weight content of the rust preventive pigment in the coating film of 0 to 55% is applied by a roll coater, and then at 220 ° C. for 40 seconds. After baking and curing, a top coat is further applied on this coating film by a roll coater.
It was baked and cured under the conditions of ~ 250 ° C for 60 seconds. These steel sheets were exposed to the Okinawa area, and the corrosion status of the end face was investigated.

Table 1 shows that an undercoat film of a polyester resin containing strontium chromate at 30% by dry weight of the coating film was formed on both sides of a hot-dip galvanized steel sheet at a dry film thickness of 5 μm. A coated steel sheet having a polyester resin-based overcoating film of 18 μm and a polyester resin-based backcoating film of 8 μm on the back surface has a thickness t
(Mm) and the width (mm) of occurrence of red rust on the end face 3 years after exposure to Okinawa when the plating amount w (g / m ² ) was changed.

When w / t is 60 or more, no red rust is generated, and it can be seen that the corrosion resistance of the end face can be ensured. Even when w / t was 60, the material having a plate thickness t of 1.8 mm showed generation of red rust.

The coating weight per side is 130 g /
If it exceeds m ² , the initial coating crack of the 2T processed part is large,
There was a problem in appearance. In addition, 25%
When the coating layer containing the above was formed only on one side of the plated steel sheet, generation of red rust was observed on the end face in any case.

[0027]

[Table 1]

Table 2 shows a polyester resin-based undercoat layer having a thickness of 5 μm and a top coat of a plate having a thickness of 0.8 mm and a coating weight of 50 g / m ² (w / t = 62.5) on one side. Exposure to Okinawa in the case of a polyester resin-based coating having a film thickness of 18 μm on the front side and 8 μm on the back side, and changing the amount of strontium chromate in the undercoating film from 0 to 55% 3
The red rust occurrence width (mm) at the end face part after one year is shown.

When the amount of the rust-preventive pigment in the undercoat film layer is 25% or more of the dry weight of the paint film, the red rust width is 0 mm and the rust-preventive effect on the end face is remarkable. In Table 2, the same result was obtained when potassium chromate was used as the rust preventive pigment.

[0030]

[Table 2]

In Table 3, a plate having a thickness of 0.8 mm and a coating weight of 50 g / m ² (w / t = 62.5) on one side was used.
m, 8 μm on the back side, the thickness of the polyester resin-based undercoating layer, and the width of red rust occurrence at the end face after 3 years of Okinawa exposure (m) when the amount of strontium chromate in the coating film was changed (m
m).

[0032]

[Table 3]

The undercoat layer was formed on the front and back of the plated steel sheet, and the minimum thickness per side was 2 μm. The product of the total film thickness on the front and back surfaces of the undercoat film layer and the amount of strontium chromate in the undercoat film layer (same on both sides) is 20.
When 0 or more, especially resistance to red rust of the end face it can be seen that the better. That is, when the total amount of the rust-preventive pigments contained in the front and back coating films is equal to or more than a certain value, the rust-preventive force on the end face is increased.

[0034]

As described above, in the coated steel sheet of the present invention, the relationship between the thickness of the steel sheet and the amount of plating per one side is specified, and a coating film containing a rust-preventive pigment is formed thereon. As a result, it is possible to obtain a good coated steel plate that has both the red rust resistance of the end face and the appearance and corrosion resistance of the processed part, and it can be used for a long time even in harsh outdoor environment of high temperature and humidity, and for household appliances and building materials used outdoors As a steel sheet for automobiles, the service life can be improved.

──────────────────────────────────────────────────の Continuation of the front page (72) Inventor Hiroshi Kanai 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Works (56) References JP-A-59-14942 (JP, A) 67502 (JP, B2) Jiko 62-29233 (JP, Y2) (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 15/08 B05D 7/14

Claims (1)

(57) [Claims] 1. The steel sheet has a thickness t (mm) and a coating weight per side w (g / m ² ) of t ≦ 1.6, w ≦ 13.
A coated steel sheet excellent in red rust resistance on the end face , characterized in that a coating film containing at least 25% of a rust-preventive pigment in the coating film is formed on both sides of a galvanized steel sheet satisfying both 0, w / t ≧ 60. .