JP2639979B2 - Heat resistant and corrosion resistant multi-layer coated steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a relatively small-diameter pipe having an outer diameter of about 20 mm or less provided as a fluid transfer path in an automobile or other various mechanical devices. More particularly, the present invention relates to a heat-resistant and corrosion-resistant multilayer steel pipe having a protective layer capable of withstanding a severe corrosive environment.

[Prior Art] Conventionally, as a pipe used for automobiles and other mechanical devices, a product in which a Zn plating layer is formed on an outer surface of a steel pipe and a chromate treatment is performed on the Zn plating layer is often used.

However, for example, pipes for braking or fuel of automobiles are strictly used, and have high corrosion resistance as well as heat resistance in a high temperature environment such as around an engine.
Underfloor piping that is easily damaged is required to be able to withstand mechanical external forces such as scratch resistance and impact resistance.
In response to such demands, those obtained by further applying a plastic protective coating on a Zn plating layer have been used. Japanese Patent Publication No. 57-60434 and Japanese Patent Publication No. Zn plating on the surface by electrolytic method,
Next, a method has been proposed in which a relatively thick special chromate film is formed on the Zn layer using a chromic acid solution containing formic acid, and a fluorinated resin film is formed on the chromate film.

[Problems to be Solved by the Invention] However, in order to increase the corrosion resistance of the metal plating layer, the protective layer formed by the above-described method has a thickness of 25 μm for the Zn plating layer.
m is required to be formed as thick as 以上 m or more, which has the problem of greatly reducing productivity, and a relatively high concentration of chromic acid solution containing formic acid to achieve a close bond with the fluorinated resin. In addition, it is necessary to form a chromate film by using the method described above, and there is a problem that the chemical consumption of the treatment liquid is large, and the disposal cost of waste liquid containing hexavalent chromium which is a harmful substance increases.

The present invention solves the above-mentioned problems, and aims to improve the heat-resistant and corrosion-resistant performance of a metal plating layer in a corrosion-resistant protective film formed by laminating a metal plating layer applied to the surface of a steel pipe and a resin film. With good adhesion,
It is an object of the present invention to obtain a durable heat-resistant and corrosion-resistant multi-layer coated steel pipe under severe corrosive environment including mechanical external force.

[Means for Solving the Problems] The present inventor has conducted studies to solve the above problems and achieve the above object. As a result, when forming a fluorinated resin film on a metal plating layer, an epoxy resin was used. It has been found that the object can be achieved by forming a multilayer coating interposed as an intermediate layer, and the present invention has been completed. That is, the first embodiment of the present invention comprises a steel pipe, a Zn-Ni alloy plating layer adhered to the outer surface of the steel pipe, and an epoxy resin interposed as an intermediate layer on the Zn-Ni alloy plating layer. The second embodiment is a steel pipe, a Zn-Ni alloy plating layer adhered to the outer surface of the steel pipe, and a Zn-Ni alloy. A heat-resistant and corrosion-resistant multi-layer steel pipe comprising a chromate film formed on a plating layer and a polyvinyl fluoride film formed by interposing an epoxy resin as an intermediate layer on the chromate film.

 Next, the present invention will be described with reference to the accompanying drawings.

FIG. 1 is an enlarged cross-sectional view of a part of a heat-resistant and corrosion-resistant multi-layer coated steel pipe according to the present invention, and FIG. It is sectional drawing.

Reference numeral 1 denotes a steel pipe, which is made of, for example, material STPG and has an outer diameter of 20 mm or less, an electric resistance welded steel pipe having a thickness of 0.5 to 1 mm (FIG. 1), or a Cu plating layer previously applied to the surface of a strip steel sheet. Double winding and brazing the overlapped surface to form
This is a double-wound steel pipe (FIG. 2) having a Cu plating layer 2 of about 3 μm on its outer peripheral surface. Numeral 3 is a Zn-Ni alloy plating layer which is formed on the outer surface of the steel pipe by, for example, an electroplating method using a known chloride bath or sulfuric acid bath, and has a Ni content of 5 to 20%. It is preferable that the thickness be about 15 μm or less from the viewpoint of corrosion resistance and post-processability. Reference numeral 4 denotes a chromate film, which is formed on the Zn-Ni alloy plating layer 3 by a treatment solution obtained by adding sulfuric acid to low-concentration chromic acid or dichromic acid, or a commercially available chromate treatment solution for Zn-Ni plating. It is formed and can very effectively improve corrosion resistance. However, without forming the chromate film, a resin film to be an intermediate layer described later may be directly applied on the Zn—Ni alloy plating layer. Reference numeral 5 denotes an intermediate layer of an epoxy resin, on the chromate film 4 (first
(Fig. 2) or directly deposited on three layers of Zn-Ni alloy plating (second
It is applied by dipping or spraying using, for example, a primer based on an epoxy resin, and is dried by heating to form a film having a thickness of about 3 to 10 μm.
The intermediate layer 5 is provided between the lower Zn—Ni alloy plating layer 3 or the chromate film 4 formed thereon and the uppermost polyvinyl fluoride film so that the two layers can be strongly adhered to each other. is there. Reference numeral 6 denotes a vinyl fluoride film, which is applied by dipping or spraying using a liquid in which a solid of polyvinyl fluoride is dispersed in a high boiling solvent such as dimethyl or diethylene phthalate in a state where solids are not recognized.
It is dried by heating to about ° C and fixed to form a thickness of about 10 to 25 µm.

Since the heat-resistant and corrosion-resistant multi-layer coated steel pipe of the present invention is configured in this manner, the Zn-Ni alloy plating layer is more excellent in corrosion resistance with a thinner layer thickness than the conventional Zn plating layer, and even in a high temperature environment. It has heat and corrosion resistance that does not deteriorate,
In addition, since the epoxy resin is used as the intermediate layer, a polyvinyl fluoride resin that is mechanically tough, has high heat resistance, high weather resistance and excellent chemical resistance is adhered with good adhesion, and has excellent scratch resistance and impact resistance. As a protective layer under severe corrosive environment, it will exhibit extremely excellent performance.

[Example] Next, an example of the present invention will be described.

Example 1 1) Steel pipe a Material SPCC, using a steel strip having a copper plating layer with a thickness of 3 μm on both sides, outer diameter 8 mm, wall thickness 0.7 mm, length 330 mm
Double-walled steel pipe.

2) Formation of Zn—Ni alloy plating layer An 8 μm-thick alloy plating layer was formed using a Zn—Ni alloy plating bath composed of a chloride bath (Zn-10MU manufactured by Ebara Cordierite).

3) Formation of resin film The steel pipe a with the Zn-Ni alloy plating layer obtained in 2) was
Epoxy resin and pigment are immersed in a paint prepared with a solvent, applied and heated at 350 ° C for 60 seconds to obtain a film thickness of about 5
An intermediate layer of an epoxy resin having a thickness of μm was formed, and then dipped in a solution in which polyvinyl fluoride was dispersed in diethyl phthalate, coated with polyvinyl fluoride, and heated and dried at 350 ° C. for 60 seconds to form a film having a thickness of about 15 μm. A polyvinyl fluoride film was formed.

4) Heat and corrosion resistance test One end of the multi-layer coated steel pipe obtained as above
80 ° bending process into a stick shape, after continuous heating for 24 hours at a heating atmosphere of 150 ° C, let cool in the air, JIS
One hundred and forty hours of salt spray test based on Z 2371
The cycle was repeated, and the number of cycles until the generation of rust was measured to determine the heat and corrosion resistance.

5) Impact corrosion resistance test A stick having a particle size of 9 to 15 mm was spray-blasted at an air pressure of 5 kg onto a stick-shaped sample formed by bending one end side at 25 R by 180 °, and then salt water based on JIS Z 2371 140 spray tests
The cycle of time was repeated as one cycle, and the number of cycles until the generation of rust was measured to determine the impact corrosion resistance. The results of 4) and 5) are shown in the following table.

Example 2 1) Steel pipe b ERW steel pipe having a material of STPG 38, an outer diameter of 8 mm, a wall thickness of 0.7 mm, and a length of 330 mm.

2) Formation of Zn-Ni alloy plating layer and formation of resin film
The test was performed in the same manner as in Example 1, and various tests were performed in the same manner as in Example 1. The results are shown in the following table.

Example 3 1) Formation of Zn-Ni alloy plating layer and chromate treatment Using a steel pipe a, a Zn-Ni alloy plating layer was formed in the same manner as in Example 1, and then a chromate treatment solution (manufactured by Ebara Cordierite) (ZN-80YMU) to form a chromate film.

2) Thereafter, a resin film was formed in the same manner as in Example 1,
Various tests were performed in the same manner as in Example 1. The results are shown in the following table.

Example 4 In the same manner as in Example 3 except that steel pipe b was used, Zn was used.
A multi-layer coated steel pipe comprising a Ni alloy plating layer, a chromate film, an intermediate layer of an epoxy resin, and a polyvinyl fluoride film was manufactured, and various tests were performed in the same manner as in Example 1. The results are shown in the following table.

Comparative Example 1 After a Zn plating layer having a thickness of 25 μm was formed under conventional conditions using a steel pipe a, chromate treatment was performed with a commercially available chromate treatment solution for Zn plating. Various tests were performed on the obtained product in the same manner as in Example 1. The results are shown in the following table.

Comparative Example 2 A product was obtained in the same manner as in Comparative Example 1 except that the steel pipe b was used, and various tests were performed in the same manner as in Example 1. The results are shown in the following table.

Comparative Example 3 Using a steel pipe a, a Zn plating layer was formed in the same manner as in Comparative Example 1, a chromate film was formed with a chromic acid solution containing formic acid at a pH of 2.1 to 2.6, and then polyfluoroethylene was added to diethyl phthalate. Dipped in a liquid in which vinyl chloride is dispersed, coated with polyvinyl fluoride, and dried by heating at 350 ° C for 60 seconds to a film thickness of about 1
A 5 μm polyvinyl fluoride film was formed to obtain a product. Various tests were performed on the obtained product in the same manner as in Example 1. The results are shown in the following table.

Comparative Example 4 A product was obtained in the same manner as in Comparative Example 3 except that the steel pipe b was used, and various tests were performed in the same manner as in Example 1. The results are shown in the following table.

[Effects of the Invention] Since the present invention is obtained by forming a fluorinated resin film on a Zn-Ni alloy plating layer via a resin intermediate layer, it can be compared with conventional Zn plating regardless of the presence or absence of chromate treatment. Excellent heat resistance, has the same or higher corrosion resistance even when the overall layer thickness is reduced, can form a resin film with good adhesion, can reduce manufacturing costs, and is a severe corrosive environment including mechanical external force Very selected effects are recognized, such as being extremely useful for piping used below.

[Brief description of the drawings]

FIG. 1 is a diametrical sectional view showing an enlarged part of an embodiment of a heat-resistant and corrosion-resistant multi-layer coated steel pipe of the present invention, and FIG.
It is a sectional view of the diameter direction which expands and shows another Example of this invention. 1 ... steel pipe, 2 ... Cu plating layer, 3 ... Zn-Ni alloy plating layer, 4 ... chromate film, 5 ... intermediate layer, 6 ... polyvinyl fluoride film

Claims (2)

(57) [Claims] 1. A steel pipe, and Zn-Ni deposited on an outer surface of the steel pipe.
A heat-resistant and corrosion-resistant multi-layer steel pipe comprising an alloy plating layer and a polyvinyl fluoride film formed by interposing an epoxy resin as an intermediate layer on the Zn-Ni alloy plating layer. 2. A steel pipe, and Zn-Ni adhered to an outer surface of the steel pipe.
An alloy plating layer, a chromate film formed on the Zn-Ni alloy plating layer, and a polyvinyl fluoride film formed on the chromate film by interposing an epoxy resin as an intermediate layer. Corrosion resistant multi-layer coated steel pipe.