JPH0815769B2 - Polyolefin multi-coated metal tube and method for producing the same - 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 to a polyolefin-coated metal pipe which has a coating excellent in adhesion to the surface of the metal pipe and can be used even in extremely cold and severe heat. Manufacturing method.

[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.

[0003] The polyolefin-coated metal pipes are greatly expected to be used as metal pipes for laying or burying ground surfaces such as gas pipes, crude oil or petroleum transport pipes, and cable protection pipes. In order to protect the polyolefin coating layer during storage, such a polyolefin-coated metal tube is coated with a packaging polyolefin that can be peeled off during use.

A polyolefin-coated metal tube coated with such a packaging polyolefin is generally shown in FIG.
It is manufactured using a coating device as shown in FIG. This device includes a primer applying device 2, a heating device 3,
For example, a crosshead die 12 provided with an extruder 11 containing a coating polyolefin, a crosshead die 10 provided with an extruder 13 containing a packaging polyolefin,
The cooling device 9 and the cutting device 8 are arranged in order.

A plurality of metal pipes connected by a connecting jig are passed through this device, a primer made of thermosetting epoxy resin is applied by using a primer applying device 2, and the metal pipe 1 is heated by a heating device 3. Heat to cure the primer. After the heat treatment, the coating polyolefin is extruded and coated on the obtained primer layer using the die 12. A die 10 is used to extrude the polyolefin for packaging onto the coating, and the coated resin is cooled in the cooling device 9 by air cooling or water cooling. After that, the traveling cutting machine 8 cuts the original metal tube unit to obtain a metal tube.

In the polyolefin multi-coated metal tube thus obtained, as a coating polyolefin, for example, a polyethylene homopolymer, or a packaging polyethylene, a monomer structural unit different from that of the coating polyethylene is used so as not to be welded to the coating polyolefin. Polyolefins such as ethylene-propylene block copolymers are used. However, when the ethylene-propylene block copolymer has a large content of ethylene monomer, it is easily fused with the coating polyethylene, and it is difficult to adjust the blending ratio of the ethylene monomer and the propylene monomer and the molecular weight distribution of the ethylene-propylene random copolymer. Further, when polypropylene is used instead of the ethylene-propylene block copolymer, the impact resistance at low temperature is insufficient. Therefore, as the packaging polyolefin, an ethylene-propylene block copolymer having good impact resistance is used instead of polypropylene.

FIG. 3 is a graph showing the degree of welding and the impact resistance with respect to the blending ratio of ethylene in the ethylene-propylene block copolymer. Curve 101 shows the degree of welding, and shows that the degree of welding increases as the ethylene content increases. Curve 102
Indicates impact resistance at low temperature, for example, at −30 ° C., and as the ethylene content increases, the impact resistance becomes better. From the graph of FIG. 3, it can be seen that it is very difficult to adjust the degree of this welding and the impact resistance within the practical range indicated by the shaded portion 103.

[0008]

As described above, it is difficult to obtain a polyolefin multi-coated metal pipe in which the polyolefin for coating and the polyolefin for packaging are not welded while adopting polyolefin having sufficient impact resistance. Met.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a metal pipe having a polyolefin multiple coating which is excellent in impact resistance, has a low degree of welding, and is excellent in peelability.

[0010]

A polyolefin multi-coated tube according to the present invention comprises a metal tube and a first tube formed on the metal tube.
And a second polyolefin layer formed on the first polyolefin layer, and the first and second polyolefin layers are provided between the first and second polyolefin layers.
Also, a release layer made of a polyolefin that is easily welded to one of the second and second polyolefin layers and is difficult to be welded is interposed on the other.

Of the first polyolefin layer, the peeling layer, and the second polyolefin layer, two layers that are easily welded to each other contain common monomer components and are difficult to be welded to each other.
The layers preferably do not contain common monomers.

The first polyolefin, the second polyolefin and the release layer are, for example, polyethylene (low density to high density), polypropylene, poly-1-butene, poly-1-hexene, poly-4-methyl-1. It can be chosen from homopolymers such as pentene, poly-1-octene and poly-1-decene and copolymers thereof.

First polyolefin layer, release layer and second
Examples of the preferable combination of the polyolefin layer include ethylene-propylene copolymer / homopolypropylene / homopolyethylene and homopolyethylene / homopolypropylene / ethylene-propylene copolymer. In this case, the content of the ethylene monomer in the ethylene-propylene copolymer is preferably 25% by weight or less in order to ensure welding with the release layer.

Further, the method for producing a multi-layered polyolefin pipe of the present invention comprises a step of forming a first polyolefin layer on the surface of a metal tube, a step of forming a release layer on the first polyolefin layer, and this release layer. A step of forming a second polyolefin layer on the release layer, wherein the release layer is the first layer.
And a polyolefin that is easily welded to one of the second and second polyolefin layers and is difficult to be welded to the other, and is formed by coextrusion together with one of the polyolefin layers that is easily welded.

When a copolymer is used for the first layer, a polyolefin homopolymer which is easily welded to the first layer is used for the release layer and is subjected to co-extrusion. When a copolymer is used for the second layer, the release layer is used for the release layer. A polyolefin homopolymer that is easily welded to the second layer can be used for coextrusion. Also, the copolymer can be used as a release layer when the copolymer does not have a common monomer component with the second polyolefin homopolymer.

Further, a primer layer as a base layer can be provided on the metal pipe which has been removed from rust. A thermosetting epoxy adhesive can be used as such an underlayer. Instead of forming the primer layer, the metal tube may be subjected to chemical conversion treatment to form chromate. 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 coating polyolefin 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. ), Polypropylene, poly-1-butene, poly-4-
Methyl-1-pentene, ethylene-propylene copolymer, ethylene-1-butene copolymer, propylene-1-
Examples include butene copolymers and mixtures thereof. The unsaturated carboxylic acid or its acid anhydride, for example, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, citraconic acid, citraconic anhydride, itaconic acid,
Such as 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.

In carrying out the present invention, the metal tube used is in the range of small and medium diameters that can be manufactured using a co-extrusion crosshead die, and at least the surface thereof is at least the metal tube is manufactured. Pickling sometimes done,
It is necessary that the sandblasting process is 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.

[0020]

In the polyolefin multi-coated metal tube of the present invention,
A polyolefin that is welded to either one of the first and second polyolefin layers and is not welded to the other between the first polyolefin layer that serves as the coating polyolefin and the second polyolefin layer that serves as the packaging polyolefin. A release layer is provided. Therefore, when the second polyolefin layer is peeled off, peeling surely occurs at the interface between the peeling layer and the polyolefin layer which is not welded thereto.

[0021]

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 as shown in FIG. 2, for example. That is, a cross-head die 6 provided with a primer coating device 2, a heating device 3, an extruder 4 containing a coating polyolefin and an extruder 5 containing a peeling polyolefin, and an extruder 7 containing a packaging polyolefin in a line. The cross head die 10, the water cooling type cooling device 9 and the cutting device 8 are sequentially arranged. Example 1

A primer layer made of a thermosetting epoxy resin is formed on the metal tube from which the oxide film on the surface has been removed by shot blasting, using the apparatus shown in FIG. 4, and the co-extrusion of the crosshead die 6 is performed on this primer layer. To form an ethylene-propylene copolymer layer of ethylene monomer: propylene monomer = 20: 80 as a first polyolefin layer and a homopolypropylene layer as a release layer, and then, on the release layer, a crosshead die 10 as a second layer. A homopolyethylene layer was formed by the extrusion used. After that, the metal tube covered with the cutting device 8 was cut into a desired length. A cross-sectional view showing a part of the obtained polyolefin multi-coated metal tube is shown in FIG. As shown in FIG. 1, this polyolefin multi-coated metal tube 20 comprises a metal tube 1 having a diameter of 60.5 mm, a primer layer 21 made of a thermosetting epoxy resin, an ethylene-propylene copolymer layer 22, and a homopolypropylene. It has a structure in which a layer 23 and a homopolyethylene layer 24 are laminated.

With respect to the obtained multiple coating layer, ethylene-
The weldability between the propylene copolymer layer and the homopolypropylene layer welded to this layer, the releasability between the homopolypropylene layer and the homopolyethylene layer to be peeled off, and the impact resistance at low temperature were examined. Table 1 shows the results. The weldability, releasability and low temperature impact resistance in the table were evaluated as follows. Difficulty in welding… ○ Normal… △ Easy to perform… × Good peelability… ○ Normal… △ Bad… × Low temperature impact resistance Good ○ ○ Normal… △ Bad… × Example 2

In Example 1 using a device in which the crosshead die 6 and the crosshead die 10 are reversed in FIG.
A homopolyethylene layer was formed as the first polyolefin layer, a polypropylene layer was formed as the release layer, and an ethylene-propylene copolymer layer of ethylene monomer: propylene monomer = 50: 50 was formed as the second polyolefin layer in the same manner as in 1. The coating was inspected. The results are shown in Table 1. Comparative Example 1

Without the release layer, the first polyolefin layer is a homopolyethylene layer, and the second polyolefin layer is an ethylene monomer: propylene monomer = 50:
Fifty ethylene-propylene copolymer layers were formed and tested on the resulting multiple coating layers. The results are shown in Table 1. Comparative Example 2

Without the release layer, the first polyolefin layer is a homopolyethylene layer, and the second polyolefin layer is ethylene monomer: propylene monomer = 10:
90 ethylene-propylene copolymer layers were formed, and the obtained multiple coating layers were examined in the same manner as in Example 1. The results are shown in Table 1. Comparative Example 3

In the same manner as in Example 1, a homopolyethylene layer was formed as each of the first polyolefin layer and the second polyolefin layer, and a homopolypropylene layer was formed as the release layer, and the obtained multiple coating layers were inspected. The results are shown in Table 1. Comparative Example 4

A homopolyethylene layer was formed as each of the first polyolefin layer and the second polyolefin layer without providing a release layer, and the obtained multiple coating layer was used in Example 1
The inspection was performed in the same manner as in. The results are shown in Table 1.

As is clear from Table 1, the polyolefin-coated metal pipes of Examples 1 and 2 had good weldability, peeling property, and low-temperature impact resistance. However, when a homopolyolefin layer and a copolymer layer having the same monomer component as this layer are formed without providing a peeling layer, if the amount of the same monomer is large as in Comparative Example 1, the weldability and peelability become insufficient, It can be seen that when the amount of the same monomer is small as in Comparative Example 2, the low temperature impact resistance becomes insufficient and it is difficult to adjust the monomer ratio in the copolymer. Further, when the copolymer is not used for the first polyolefin layer, the release layer and the second polyolefin layer, it is not clear which interface is peeled off at the time of peeling as in Comparative Example 3, and a stable coating layer cannot be obtained. Furthermore, when the homopolyolefin of the same kind is formed separately in two layers without providing a peeling layer, the first layer and the second layer do not peel as shown in Comparative Example 4.

[0030]

As described above, according to the present invention,
A metal tube with excellent impact resistance, which does not require strict control of the monomer ratio of the copolymer used, has a low degree of welding between the coating polyolefin and the packaging polyolefin, and has good releasability. Can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a polyolefin-coated metal tube according to an embodiment of the present invention.

FIG. 2 is a schematic view showing an example of a polyolefin coating apparatus used in the present invention.

FIG. 3 is a graph showing the weldability with homopolyethylene and the low temperature impact resistance with respect to the ethylene monomer content in the ethylene-propylene copolymer.

FIG. 4 is a schematic view showing a conventional polyolefin coating device.

[Explanation of symbols]

1 ... Metal tube, 21 ... Primer layer, 22 ... First layer, 23
... peeling layer, 24 ... second layer.

[Table 1]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-49-31741 (JP, A) JP-B 63-4490 (JP, B2) JP-B 50-2083 (JP, Y2)

Claims (3)

[Claims] 1. A metal tube, and a first formed on the metal tube.
And a second polyolefin layer formed on the first polyolefin layer, and the first and second polyolefin layers are provided between the first and second polyolefin layers.
And a polyolefin multi-coated metal tube, wherein a release layer made of a polyolefin that is easily welded to one of the second polyolefin layers and that is not easily welded is interposed on the other. 2. The first polyolefin layer, a release layer,
And the second polyolefin layer which is easily welded to each other 2
The polyolefin multi-coated metal pipe according to claim 1, wherein the layers contain a common monomer component, and the two layers which are difficult to be welded to each other do not contain a common monomer. 3. A step of forming a first polyolefin layer on the surface of a metal tube, a step of forming a release layer on the first polyolefin layer, and a step of forming a second polyolefin layer on the release layer. And the release layer is the first
And a second polyolefin layer, which is made of a polyolefin that is easily welded to the other polyolefin layer and is difficult to be welded to the other polyolefin layer, and is formed by co-extrusion together with one of the polyolefin layers that is easily welded. Pipe manufacturing method.