JPH04329131A - Polyolefin multiple coated metal pipe and preparation thereof - Google Patents

Abstract

PURPOSE:To improve the impact resistance and releasability of a polyolefin multiple coating layer without strictly controlling the monomer ratio of a polyolefin copolymer. CONSTITUTION:A first polyolefin layer and a second polyolefin layer are formed to a metal pipe and a release layer composed of polyolefin easily welded to either one of the layers but hardly welded to the other layer is interposed between both layers.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing polyolefin-coated metal tubes, and more specifically, the present invention relates to a method for manufacturing polyolefin-coated metal tubes, and more specifically, polyolefin-coated metal tubes that have a coating that has excellent adhesion to the surface of the metal tube and can be used even in extremely cold or extremely hot temperatures. Relating to a manufacturing method.

0002

[Prior Art] Polyolefins not only exhibit excellent corrosion resistance against acids, alkalis, and certain organic solvents, but also have electrical insulation properties and are easy to process. Widely used for coatings and electrical machinery equipment.

Polyolefin-coated metal pipes are highly expected to be used as metal pipes for laying on the ground or buried, such as gas pipes, pipes for transferring crude oil or oil, and cable protection pipes. Such a polyolefin-coated metal tube is coated with a packaging polyolefin that can be peeled off during use in order to protect the polyolefin coating layer during storage.

[0004] Such a polyolefin-coated metal tube coated with polyolefin for packaging is generally used as shown in FIG.
It is manufactured using the coating equipment shown in . This device includes a primer coating device 2, a heating device 3,
For example, a crosshead die 12 equipped with an extruder 11 for accommodating polyolefin for coating, a crosshead die 10 equipped with an extruder 13 for accommodating polyolefin for packaging,
It has a configuration in which a cooling device 9 and a cutting device 8 are arranged in sequence.

A plurality of metal tubes connected using a connecting jig are passed through this device, a primer made of thermosetting epoxy resin is applied using a primer coating device 2, and the metal tube 1 is coated with a heating device 3. Heat to cure this primer. After the heat treatment, a coating polyolefin is extruded and coated on the obtained primer layer using a die 12. A packaging polyolefin is extruded and coated onto this using a die 10, and the coated resin is cooled by air cooling or water cooling using a cooling device 9. Thereafter, the traveling cutter 8 cuts the original metal tube into units to obtain metal tubes.

In the polyolefin multi-coated metal pipe thus obtained, the coating polyolefin is usually a polyethylene homopolymer, and the packaging polyethylene is a monomer structural unit different from that of the coating polyethylene to prevent welding with the coating polyolefin. Polyolefins such as ethylene-propylene block copolymers are used. However, when the ethylene monomer content of the ethylene-propylene block copolymer is large, it tends to fuse with the coating polyethylene, making it difficult to adjust the blending ratio of ethylene monomer and propylene monomer and the molecular weight distribution of the ethylene-propylene random copolymer. Furthermore, when polypropylene is used instead of the ethylene-propylene block copolymer, impact resistance at low temperatures is insufficient. Therefore, as the polyolefin for packaging, 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 impact resistance with respect to the blending ratio of ethylene in an ethylene-propylene block copolymer. A curve 101 indicates the degree of welding, and indicates that as the ethylene content increases, the degree of welding increases. Curve 102 shows the impact resistance at a low temperature, for example -30°C, and indicates that the higher the ethylene content, the better the impact resistance. From the graph in FIG. 3, it can be seen that it is very difficult to adjust the degree of welding and impact resistance to a practical range shown by the shaded area 103.

[0008]

[Problems to be Solved by the Invention] As described above, it is difficult to obtain a polyolefin multi-coated metal tube in which the coating polyolefin and the packaging polyolefin do not weld together while using a polyolefin with sufficient impact resistance. Met.

The present invention was made in view of the above-mentioned problems, and it is an object of the present invention to provide a metal tube having multiple polyolefin coatings that have excellent impact resistance, a low degree of welding, and good peelability.

0010

[Means for Solving the Problems] The polyolefin multiple cladding tube of the present invention comprises a metal tube and a first tube formed on the metal tube.
a polyolefin layer formed on the first polyolefin layer, and a second polyolefin layer formed on the first polyolefin layer;
and the second polyolefin layer, a peeling layer made of a polyolefin that is easily welded to one of them and difficult to be welded to the other is interposed therebetween.

Among the first polyolefin layer, the release layer, and the second polyolefin layer, the two layers that are easily welded to each other contain a common monomer component, and the two layers that are difficult to weld to each other contain a common monomer component.
Preferably, the layers do not contain any common monomers.

[0012] The first polyolefin, second polyolefin and release layer are made of, for example, polyethylene (low density to high density), polypropylene, poly-1-butene, poly-1-hexene, poly-4-methyl-1 - Can be selected from homopolymers such as pentene, poly-1-octene and poly-1-decene and copolymers thereof.

[0013] The first polyolefin layer, the release layer and the second
Preferred combinations of polyolefin layers include, for example, ethylene-propylene copolymer/homopolypropylene/homopolyethylene and homopolyethylene/homopolypropylene/ethylene-propylene copolymer. In this case, the content of ethylene monomer in the ethylene-propylene copolymer is preferably 25% by weight or less in order to ensure welding with the release layer.

The method for producing a polyolefin multiple cladding tube of the present invention also includes a step of forming a first polyolefin layer on the surface of the metal tube, a step of forming a release layer on the first polyolefin layer, and a step of forming a release layer on the first polyolefin layer. forming a second polyolefin layer on top of the first polyolefin layer;
and the second polyolefin layer, and is made of a polyolefin that is easily welded to one of the second polyolefin layers and is difficult to weld to the other, and is characterized in that it is formed by coextrusion with either one of the polyolefin layers that is easy to weld.

When a copolymer is used for the first layer, a polyolefin homopolymer that easily welds with the first layer is used for coextrusion, and when a copolymer is used for the second layer, the release layer A polyolefin homopolymer that is easily welded to the second layer can be used and subjected to coextrusion. The copolymer can also be used as a release layer if the copolymer has no monomer components in common with the second polyolefin homopolymer.

[0016] Furthermore, a primer layer as an underlayer can be provided on the rust-removed metal pipe. As such a base layer, a thermosetting epoxy adhesive can be used. Instead of forming a primer layer, the metal tube may be subjected to a chemical conversion treatment to form chromate. It is also possible to form a primer layer on the chromate layer.

In the present invention, adhesively modified polyolefins can be used as adhesives for the coating polyolefin layer. Adhesive modified polyolefins include polyolefins grafted with unsaturated carboxylic acids or their acid anhydrides, or blends of this modified polyolefin with unmodified polyolefins.The base polyolefin is polyethylene (low to high density). ), polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer,
Examples include ethylene-1-butene copolymers, propylene-1-butene copolymers, and mixtures thereof. Also,
Examples of the unsaturated carboxylic acid or its acid anhydride include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, citraconic acid, 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 to be very thick, and is approximately 0.03~0. A thickness of about 0.3 mm is sufficient.

[0019] 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 crosshead die for coextrusion, and the surface thereof is at least Pickling, which is sometimes carried out
It is necessary that sandblasting is carried out sufficiently and uniformly. Depending on the result of this pretreatment, for example, if oil or dirt remains on the surface of the metal tube, the adhesive may be repelled during application of the adhesive, or the surface of the metal tube may not be sufficiently wetted.

[0020]

[Function] In the polyolefin multiple coated metal tube of the present invention,
Between the first polyolefin layer serving as the coating polyolefin and the second polyolefin layer serving as the packaging polyolefin, the polyolefin is made of a polyolefin that is welded to either one of the first and second polyolefin layers but not to the other. A release layer is provided. Therefore, when the second polyolefin layer is peeled off, peeling occurs reliably at the interface between the release layer and the polyolefin layer that is not welded.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be explained in more detail by showing examples of the present invention with reference to the drawings. The apparatus used in the following examples is configured as shown in FIG. 2, for example. That is, the line includes a primer coating device 2, a heating device 3, an extruder 4 containing polyolefin for coating, an extruder 5 containing polyolefin for peeling, and a crosshead die 6, and an extruder 7 containing polyolefin for packaging. A crosshead die 10 provided with a crosshead, a water-cooled cooling device 9, and a cutting device 8 are arranged in this order. 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. An ethylene-propylene copolymer layer of ethylene monomer:propylene monomer = 20:80 was formed as the first polyolefin layer, and a homopolypropylene layer was formed as the release layer, and then a crosshead die 10 was formed as the second layer on the release layer. A homopolyethylene layer was formed using extrusion. Thereafter, the coated metal tube was cut into a desired length by a cutting device 8. FIG. 1 shows a cross-sectional view of a part of the obtained polyolefin multi-coated metal tube. As shown in FIG. 1, this polyolefin multi-coated metal tube 20 consists of 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 copolymer layer 22. It has a structure in which a layer 23 and a homopolyethylene layer 24 are laminated.

[0023] Regarding the obtained multiple coating layers, ethylene-
Weldability between the propylene copolymer layer and the homopolypropylene layer welded to this layer, peelability between the homopolypropylene layer and the homopolyethylene layer to be peeled off, and impact resistance at low temperatures were tested. The results are shown in Table 1. In addition, the weldability, peelability, and low-temperature impact resistance in the table were evaluated as follows. Hard to weld…○ Normal…△ Easy to weld…× Good peelability…○ Normal…△ Poor…× Good low-temperature impact resistance…○ Normal…△ Poor…× Example 2

Example 1 was carried out using an apparatus in which the crosshead die 6 and the crosshead die 10 are arranged in reverse in FIG.
In the same manner as above, a homopolyethylene layer was formed as the first polyolefin layer, a polypropylene layer was used as the release layer, and an ethylene-propylene copolymer layer with an ethylene monomer:propylene monomer ratio of 50:50 was formed as the second polyolefin layer. The coating layer was inspected. The results are shown in Table 1. Comparative example 1

[0025] Without providing a release layer, the first polyolefin layer was a homopolyethylene layer, and the second polyolefin layer was made of ethylene monomer: propylene monomer = 50:
Fifty ethylene-propylene copolymer layers were formed and the resulting multiple coatings were tested. The results are shown in Table 1. Comparative example 2

[0026] Without providing a release layer, the first polyolefin layer is a homopolyethylene layer, and the second polyolefin layer is made of ethylene monomer:propylene monomer = 10:
90 ethylene-propylene copolymer layers were formed and the resulting multiple coatings were tested as in Example 1. The results are shown in Table 1. Comparative example 3

In the same manner as in Example 1, homopolyethylene layers were formed as the first polyolefin layer and second polyolefin layer, and homopolypropylene layers were formed as the release layer, and the resulting multiple coating layers were examined. The results are shown in Table 1. Comparative example 4

Example 1 Regarding the multiple coating layer obtained by forming homopolyethylene layers as the first polyolefin layer and the second polyolefin layer without providing a release layer.
The test was conducted in the same manner. The results are shown in Table 1.

As is clear from Table 1, the polyolefin-coated metal tubes of Examples 1 and 2 had good weldability, peelability, and low-temperature impact resistance. However, when a homopolyolefin layer and a copolymer layer having the same monomer components as this layer are formed without providing a peeling layer, if the amount of the same monomer is large as in Comparative Example 1, weldability and peelability will be 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 a copolymer is not used in the first polyolefin layer, the release layer, and the second polyolefin layer, it is not clear which interface will be peeled off at the time of peeling, as in Comparative Example 3, and a stable coating layer cannot be obtained. Furthermore, when the same type of homopolyolefin is formed into two separate layers without providing a release layer, the first layer and the second layer do not separate as shown in Comparative Example 4.

[0030]

[Effects of the Invention] As explained above, according to the present invention,
A metal tube with polyolefin multi-coating that has excellent impact resistance and has a low degree of welding between coating polyolefin and packaging polyolefin and good peelability without requiring strict control of the monomer ratio of the copolymer used. can be obtained.

[Brief explanation of drawings]

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

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

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

FIG. 4 is a schematic diagram showing a conventional polyolefin coating apparatus.

[Explanation of symbols]

1... Metal tube, 21... Primer layer, 22... First layer, 23
...Release layer, 24...Second layer.

[Table 1]

Claims (3)

[Claims] 1. A method comprising: a metal tube; a first polyolefin layer formed on the metal tube; and a second polyolefin layer formed on the first polyolefin layer; A polyolefin characterized in that a peeling layer made of a polyolefin that is easily welded to one of the first and second polyolefin layers and difficult to weld to the other is interposed between the polyolefin layer No. 2 and the polyolefin layer No. 2. Multi-coated metal tube. 2. Among the first polyolefin layer, the release layer, and the second polyolefin layer, two layers that are easily welded to each other contain a common monomer component, and two layers that are difficult to weld to each other contain a common monomer component. The polyolefin multi-coated metal tube according to claim 1, characterized in that the polyolefin multi-coated metal tube is not coated with polyolefin. 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. The release layer is made of a polyolefin that is easily welded to one of the first and second polyolefin layers and is difficult to weld to the other, and is formed by coextrusion with either one of the polyolefin layers that is easy to weld. A method for producing a polyolefin multiple coated metal tube.