JPH0790584B2 - Method for manufacturing polyolefin-coated metal tube - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyolefin-coated metal pipe, and more particularly, a polyolefin coated with a polyolefin resin having excellent adhesiveness to the surface of the metal pipe, which can be used even in extremely cold and severe heat. The present invention relates to a method for manufacturing a coated metal tube.

[0002]

2. Description of the Related Art Polyolefin has not only excellent corrosion resistance to acids, alkalis and certain organic solvents, but also electrical insulation and easy workability.
It is widely used for lining pipes, coating electric wires and coating electrical machinery.

Therefore, the polyolefin-coated metal pipes include gas pipes, crude oil or petroleum transfer pipes,
It is highly expected to be used as a metal pipe for laying or burying ground surface such as cable protection pipe.

In order to coat the outer surface of the metal tube with a polyolefin such as polyethylene using an adhesive, a coating device as shown in FIG. 2 is generally used. This device
A crosshead provided in the line with a primer coating device 2, a heating device 3, an extruder 4 containing an adhesive made of a polyolefin modified with maleic anhydride, and an extruder 5 containing a polyolefin serving as a corrosion-resistant layer. The die 6, the cooling device 7, and the cutting device 8 are arranged in order.

A plurality of metal pipes connected by using a connecting jig are passed through this apparatus, a primer made of a thermosetting epoxy resin is applied as a base layer by using a primer applying apparatus 2, and a metal is heated by a heating apparatus 3. The tube 1 is heated to cure the primer. After the heat treatment, these resins are co-extruded from the crosshead die 6 to cover the obtained primer layer so that the modified polyolefin is the inner layer and the polyolefin is the outer layer. The coated resin is cooled in the cooling device 7 by air cooling or water cooling. Thereafter, the traveling cutting machine 8 cuts the original metal tube unit to obtain a polyolefin-coated metal tube.

In such a polyolefin coating of a metal tube, in order to sufficiently bond the modified polyolefin serving as the adhesive layer on the primer layer serving as the underlayer, the surface temperature of the metal tube coated with the primer at the time of applying the adhesive is required. Should be maintained at the melting point of the modified polyolefin (for example, 80 to 160 ° C.) or higher. However, if this temperature is close to the melting point, the curing time of the adhesive becomes long and the production efficiency decreases. In addition, if the surface temperature of the metal tube is set to be much higher than the melting point in order to shorten the curing time,
It takes time to cool down after applying the adhesive layer and anticorrosion layer,
Since a cooling device of a scale normally used for a series of coating devices cannot cool in time, dents and the like due to the transport rollers are likely to occur on the surface of the anticorrosion layer. On the other hand, if the cooling time is lengthened, the production efficiency will decrease.

[0007]

The present invention has been made in view of the above problems, and a polyolefin coating having good adhesiveness and film uniformity is obtained, and the curing time of the adhesive and the cooling time of the anticorrosion layer are obtained. It is an object of the present invention to provide a method for producing a polyolefin-coated metal tube having a short length and good productivity.

[0008]

According to the method of the present invention, a step of removing rust on the surface of a metal pipe, a part of a corrosion-resistant layer consisting of an adhesive layer and a polyolefin resin on the rust-free metal surface is used with a crosshead die. Co-extrusion to form a first coating layer, and a step of coating a polyolefin resin on the first coating layer to form a second coating layer consisting of the remaining anticorrosion layer. In the method for manufacturing a metal tube, the film thickness of the first coating layer is 1/4 to 2/3 of the total film thickness of the first coating layer and the second coating layer, and
The surface temperature of the coating layer of the melting point is -70 ° C or higher, melting point +3
The second coating layer is formed after cooling to 0 ° C. or less.

That is, in the method for producing a polyolefin-coated metal pipe of the present invention, the anticorrosion layer is coated twice or twice or more several times, and the first layer is composed of an adhesive layer and a part of the anticorrosion layer. The film thickness of the coating layer is set to 1/4 to 2/3 of the total film thickness in view of its cooling efficiency. If it is less than ¼ or more than ⅔, the cooling efficiency becomes poor.

Before applying the second coating layer, the first coating
When cooling the coating layer of, the surface temperature of this first layer is
Set to a range that does not drop below 70 ° C. If the surface temperature is less than 70 ° C., the fusion between the first coating layer and the second coating layer will be incomplete, and an integrated anticorrosion layer cannot be obtained.
If the surface temperature exceeds the melting point + 30 ° C, it takes a long time to cool and the productivity is lowered.

The polyolefin resins used for the first anticorrosion layer and the second anticorrosion layer may be the same resin or different resins as long as they are fused to each other and have sufficient anticorrosion properties. It may be. For example, when both are polyethylene, they may have different densities or different color layers. The same applies when the coating is performed in three or more layers.

In carrying out the present invention, the metal tube to be provided is in the range of small and medium diameters that can be manufactured by using a co-extrusion crosshead die, and at least the surface thereof is at least a metal tube. It is necessary that the pickling and blasting performed at the time of manufacture be carried out sufficiently and uniformly. If, for example, oil or dirt remains on the surface of the metal tube depending on the result of this pretreatment, the adhesive may be repelled when the adhesive is applied, or the surface of the metal tube may not be sufficiently wetted.

A primer layer as a base layer is usually formed on the surface of the metal tube thus derusted. A thermosetting epoxy adhesive can be used as the primer layer. This primer has the advantage that the line speed can be increased because it cures faster than the solvent system.

Instead of forming the primer layer, the metal tube may be subjected to chemical conversion treatment to form the chromate layer. It is also possible to form a primer layer on the chromate layer.

In the present invention, an adhesive modified polyolefin can be used as an adhesive for the anticorrosion layer.
The adhesive modified polyolefin includes a polyolefin grafted with an unsaturated carboxylic acid or an acid anhydride thereof or a blend of this modified polyolefin with an unmodified polyolefin, and as a base polyolefin, polyethylene (low to high density) is used. ), Polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, and mixtures thereof. can give. Further, the unsaturated carboxylic acid or its acid anhydride, for example, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, citraconic acid,
Examples include citraconic anhydride, itaconic acid, and itaconic anhydride.

Since this adhesive modified polyolefin layer is provided to increase the tightness between the thermosetting epoxy adhesive and the polyolefin, the thickness of the film is not required so much and is generally 0.03 to. About 0.3 mm is sufficient. The polyolefin forming the outermost layer is usually a corrosion resistant layer and a protective layer, and therefore is usually formed to have a thickness of about 1 to 4 mm.

[0017]

When the method of the present invention is used, the polyolefin coating step is divided into two or more steps in a series of production lines,
By setting the film thickness of the first layer to 1/4 to 2/3 of the film thickness of all the coating layers, the thermal conductivity from the coating surface can be improved and the cooling can be efficiently performed. In addition, before coating the second layer, the surface temperature of the first layer has a melting point of −70 ° C. or higher and a melting point of +3.
By cooling to 0 ° C. or less, the cooling efficiency can be improved without impairing the film characteristics.

[0018]

Embodiments of the present invention will be described below with reference to the drawings to more specifically describe the present invention. The apparatus used in the following examples is configured, for example, as shown in FIG. That is, a primer coating device 2, a heating device 3, an extruder 4 containing an adhesive made of a polyolefin modified with maleic anhydride or the like, and an extruder 5 containing a polyolefin forming a part of a corrosion-resistant layer are provided in a line. A crosshead die 6 provided, a water-cooling type first cooling device 7, a die 10 for coating the remaining polyolefin serving as a corrosion-resistant layer,
The water-cooled second cooling device 9 and the cutting device 8 are arranged in order. Although not shown, a chemical conversion treatment device may be arranged in place of or in front of the primer applying device 2. Example 1

Using a device shown in FIG. 1, a thermosetting epoxy resin layer, a modified polyethylene layer, a first layer consisting of a part of the polyethylene layer, and the rest are attached to the metal tube from which the oxide film on the surface has been removed by shot blasting. To form a second layer consisting of the polyethylene layer. The melting point of the polyethylene used is 126 ° C. The moving speed of the metal tube in the line, the metal tube surface temperature before the first layer coating, the coating film thickness of the first and second layers, and the metal tube surface temperature before the second layer coating are under the conditions shown in Table 1. I did. Further, a cross-sectional view showing a part of the obtained polyolefin-coated metal tube is shown in FIG. As shown in FIG. 3, this polyolefin-coated metal tube 20 has a thickness of 34.0 mm.
Thermosetting epoxy resin layer 11 formed on the metal tube 1 having an outer diameter of, a modified polyethylene layer 12 and a polyethylene layer 13 applied as the first layer and formed on the epoxy resin layer 11, and a second layer It consists of a polyethylene layer 14 which is applied as a layer and is fused and substantially integrated with the polyethylene layer 13 on the polyethylene layer 13. The thickness of the obtained modified polyethylene layer 12 is 0.15.
mm, the total thickness of the polyethylene layers 13 and 14 is 1.6
It was 5 mm. The peel adhesion of the obtained coating layer was measured and the presence or absence of roll mark flaws was inspected. The results are shown in Table 1. Example 2

A polyolefin-coated metal tube was obtained in the same manner as in Example 1 except that chemical conversion treatment with chromate was carried out instead of coating the thermosetting epoxy resin and the coating conditions shown in Table 1 were used. A cross-sectional view of the obtained polyolefin metal tube is shown in FIG. As shown in FIG. 4, the polyolefin-coated metal tube 21 is applied as a chemical conversion treatment layer 14 formed on the metal tube 1 having an outer diameter of 60.5 mm as a first layer, and is applied on the chemical conversion treatment layer 14. The modified polyethylene layer 12 and the polyethylene layer 13 are formed, and the polyethylene layer 15 which is applied as the second layer and is fused and substantially integrated with the polyethylene layer 13 on the polyethylene layer 13. The resulting modified polyethylene layer had a thickness of 0.15 mm, and the polyethylene layers 13 and 15 had a thickness of 1.65 mm. The peel adhesion of the obtained coating layer was measured and the presence or absence of roll mark flaws was inspected. The results are shown in Table 1. Example 3

A polyolefin-coated metal tube was obtained in the same manner as in Example 1 except that the chemical conversion treatment with chromate was performed before applying the thermosetting epoxy resin and the application conditions shown in Table 1 were used. A cross-sectional view of the obtained polyolefin metal tube is shown in FIG. As shown in FIG. 5, the polyolefin-coated metal tube 22 includes a chemical conversion layer 14 formed on the metal tube 1 having an outer diameter of 34.0 mm.
The thermosetting epoxy resin layer 11 formed on the above, the modified polyethylene layer 12 and the polyethylene layer 13 formed on the epoxy resin layer 11 as the first layer, and the second layer formed on the epoxy resin layer 11, and the polyethylene layer 13 It comprises a polyethylene layer 15 which is fused and substantially integrated with this polyethylene layer 13. The modified polyethylene layer obtained had a thickness of 0.20 mm, and the polyethylene layers 13 and 15 had a thickness of 1.90 mm. The peel adhesion of the obtained coating layer was measured and the presence or absence of roll mark flaws was inspected. The results are shown in Table 1. Comparative Example 1

A polyolefin-coated metal tube was obtained in the same manner as in Example 1 except that the coating conditions shown in Table 1 were used and the second layer was not coated. A cross-sectional view of the obtained polyolefin metal tube is shown in FIG. As shown in FIG. 6, this polyolefin-coated metal tube 23 is a metal tube 1 having an outer diameter of 34.0 mm.
The thermosetting epoxy resin layer 11 formed on the upper side, and the modified polyethylene layer 12 and the polyethylene layer 13 applied as the first layer and formed on the epoxy resin layer 11 are formed. The thickness of the obtained modified polyethylene layer is 0.1.
The thickness of the polyethylene layer 13 was 5 mm and the thickness of the polyethylene layer 13 was 1.65 mm. The peel adhesion of the obtained coating layer was measured and the presence or absence of roll mark flaws was inspected. The results are shown in Table 1. Comparative example 2

A polyolefin-coated metal tube was obtained in the same manner as in Example 2, except that the coating conditions shown in Table 1 were used and the second layer was not coated. A cross-sectional view of the obtained polyolefin metal tube is shown in FIG. As shown in FIG. 7, this polyolefin-coated metal tube 24 is applied as a chemical conversion treatment layer 14 formed on the metal tube 1 having an outer diameter of 60.5 mm as the first layer. The modified polyethylene layer 12 and the polyethylene layer 13 are formed. The modified polyethylene layer 12 thus obtained had a thickness of 0.15 mm, and the polyethylene layer 13 had a thickness of 1.65 mm. The peel adhesion of the obtained coating layer was measured and the presence or absence of roll mark flaws was inspected. The results are shown in Table 1. Comparative Example 3

A polyolefin-coated metal tube was obtained in the same manner as in Example 3 except that the coating conditions shown in Table 1 were used and the second layer was not coated. A cross-sectional view of the obtained polyolefin metal tube is shown in FIG. As shown in FIG. 8, the polyolefin-coated metal tube 25 includes a chemical conversion treatment layer 14 formed on the metal tube 1 having an outer diameter of 34.0 mm, and the chemical conversion treatment layer 14
It is composed of a thermosetting epoxy resin layer 11, a modified polyethylene layer 12 and a polyethylene layer 13 formed above. The thickness of the obtained modified polyethylene layer is 0.15 mm,
The thickness of the polyethylene layer 13 was 2.15 mm. The peel adhesion of the obtained coating layer was measured and the presence or absence of roll mark flaws was inspected. The results are shown in Table 1.

As is clear from Table 1, the polyolefin-coated metal pipes obtained by the method according to the present invention (Examples 1 to 1)
In the case of 3), the peel adhesion was good and no flaws due to the roll were observed, but in Comparative Examples 1 to 3, flaws due to the roll were observed even if the peel adhesion was good.

[0026]

According to the present invention, 1/4 to 2/3 of the total thickness of the adhesive layer and the anticorrosion layer is formed as the first layer.
By cooling the surface temperature of the layer to a melting point of −70 ° C. or higher and a melting point of + 30 ° C. or lower, and forming the second layer, a polyolefin coating having good adhesion and film uniformity can be obtained.
Provided is a method for producing a polyolefin-coated metal tube, which has a short curing time for a primer layer and a cooling time for an anticorrosion layer and has good productivity.

[0027]

[Table 1]

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a polyolefin coating apparatus used in the present invention.

FIG. 2 is a schematic view showing a conventional polyolefin coating device.

FIG. 3 is a sectional view showing an example of a polyolefin-coated metal tube according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view showing another example of the polyolefin-coated metal tube according to the embodiment of the present invention.

FIG. 5 is a sectional view showing still another example of the polyolefin-coated metal tube according to the embodiment of the present invention.

FIG. 6 is a cross-sectional view showing an example of a polyolefin-coated metal tube of a comparative example.

FIG. 7 is a cross-sectional view showing another example of the polyolefin-coated metal tube of the comparative example.

FIG. 8 is a cross-sectional view showing still another example of the polyolefin-coated metal tube of the comparative example.

[Explanation of Codes] 1 ... Metal tube, 11 ... Primer layer, 12 ... Adhesive layer, 1
3 ... First polyolefin layer, 14 ... Chemical conversion treatment layer, 1
5: Second polyolefin layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location F16L 9/14 (56) References JP-A-3-114743 (JP, A) JP-A-3- 97546 (JP, A) JP 58-74336 (JP, A) JP 50-141663 (JP, A)

Claims (1)

[Claims] 1. A step of removing rust on a surface of a metal tube, a part of a corrosion-resistant layer consisting of an adhesive layer and a polyolefin resin is coextruded on the surface of the removed metal by a crosshead die to form a first coating layer. And a step of forming a second coating layer composed of the remaining anticorrosion layer by coating a polyolefin resin on the first coating layer, wherein the first coating layer comprises: The thickness of the coating layer is 1/4 to 2 of the total thickness of the first coating layer and the second coating layer.
/ 3 and the surface temperature of the first coating layer is equal to the melting point of −7.
After cooling to 0 ° C or higher and a melting point + 30 ° C or lower, a second coating layer is formed, and the second coating layer is fused with the anticorrosion layer of the first coating layer. Production method.