JPH06117583A - Composite pipe - Google Patents

Abstract

PURPOSE:To provide a composite pipe composed of an inner layer made of silane graft denaturated polyolefin and an outer layer made of metal which is excellent in adhesivity and which does not crack or break even though hot water flows through the pipe for a long time. CONSTITUTION:Silane graft denaturated amorphous polyolefin obtained by mixing vinyltrimetoxi-silane and di-t-butyl oxide into amorphous polyolefin such as cyclic polyolefin, and by heating and melting thus obtained mixture, is extruded into a metal pipe so as to cover the inner surface of the metal pipe therewith, thereby it is possible to provide a composite pipe composed of an inner layer made of silane graft denaturated polyolefin and an outer layer made of metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a composite pipe having a metal outer layer and a polyolefin inner layer.

[0002]

2. Description of the Related Art Composite pipes having a resin layer formed on the inner surface of a metal pipe have come to be used as pipe materials for hot water supply, hot water heating, drainage and the like. This is because the resin layer contributes to the improvement of the corrosion resistance and pressure resistance of the metal tube, and as the resin layer, chemically stable and inexpensive polyolefin is particularly preferably used. However, since polyolefin does not have a polar group in the molecule, there is a problem that it is difficult to adhere to a metal.

Therefore, in order to improve the adhesion of the polyolefin to the metal, Japanese Patent Application Laid-Open No. 52-78983 discloses that
A composite having improved adhesion to a metal by using a silane-grafted modified polyolefin with a silane coupling agent has been proposed.

The above-mentioned silane-grafted modified polyolefin has an alkoxysilane group (Si-OR group, where R is an alkyl group) in the molecule, and the alkoxysilane group undergoes a hydrolysis reaction with water or acid to produce a silanol group ( Si-OH group). Since the silanol group is a polar group, the adhesiveness to metal and the adhesive durability are improved.

[0005]

However, the above-mentioned Japanese Unexamined Patent Application Publication No.
The silane-grafted modified polyolefin specifically disclosed in JP-A-2-78983 is a graft-modified high density polyethylene having high crystallinity.

[0006] In such a composite pipe having a metal inner surface coated with a polyolefin obtained by silane-grafting modification of polyethylene having a high degree of crystallinity, when used for a long period of time, silane-grafting modification of the inner layer is caused by hot water or hot water flowing in the tube. The polyolefin is heated and its amorphous part gradually crystallizes.

By the way, since hot water and hot water usually flow intermittently in the composite pipe, when the inner layer silane-grafted modified polyethylene polyethylene contracts when the temperature of the inner layer decreases, the interface between the crystalline portion and the non-crystalline portion. The shrinkage stress concentrates on the and brittle fracture occurs, causing cracks and cracks to occur.

When such cracks or cracks occur, water penetrates through these cracks or cracks to reach the metal surface, and the corrosion of the metal proceeds to cause problems such as perforation and water leakage. Also,
There is a problem in that the resin layer falls off from the metal surface due to cracking due to brittle fracture and mixes into hot water and hot water.

The present invention has been made in view of the above points, and has excellent adhesiveness to metal and adhesive durability, but cracks and cracks are generated even when hot water is run for a long time. The purpose is to provide a composite tube without.

[0010]

The composite pipe of the present invention is characterized in that the silane-grafted modified amorphous polyolefin or the silane-grafted modified low-crystalline polyolefin serves as an inner layer and the metal serves as an outer layer.

Examples of the metal used as the outer layer include steel, aluminum and copper, and the surface laminated with the polyolefin is subjected to degreasing, pickling, etc. to obtain a surface state suitable for adhesion with the olefin. preferable.

In the present invention, the silane-grafted modified amorphous polyolefin is a silane-grafted modified polyolefin obtained by mixing an amorphous polyolefin with a silane coupling agent and an organic peroxide and reacting them by heating. Say. The amorphous polyolefin means a polyolefin having a crystallinity of substantially 0. Examples of such an amorphous polyolefin include a polyolefin having a molecular chain of a cyclic structure in its molecule. . The crystallinity in this invention is measured by an X-ray diffraction method or the like.

The silane-grafted modified low crystalline polyolefin is a silane-grafted modified polyolefin obtained by mixing a silane coupling agent and an organic peroxide with a polyolefin having a low degree of crystallinity and heating the mixture. Say. The crystallinity of the silane-grafted modified low crystalline polyolefin is preferably 40% or less.
When it exceeds 40%, polyethylene is further crystallized by hot water during use as a composite pipe, and cracks and cracks due to brittle fracture are likely to occur.

Examples of the low crystallinity polyolefin include a melt mixture of polyethylene and polypropylene, a melt mixture of polyethylene and polybutene, and a melt mixture of the same resins such as polyethylene and polypropylene having different physical properties such as density and molecular weight distribution. , A melt mixture of an amorphous polyolefin and another polyolefin, and the like.

Examples of the silane coupling agent include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, γ-methacryloxypropyltrimethoxysilane and the like.

Examples of the organic peroxide include dimethyl peroxide, di-t-butyl peroxide, dicumyl peroxide, dipropionyl peroxide, benzoyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide. Etc.

As the method for producing the composite pipe of the present invention, for example, a long strip-shaped sheet of metal is spirally wound and the side edges thereof are joined together to form a tubular shape, and the inner surface thereof is extruded from an extrusion die. An example of the method is a continuous molding method by extrusion coating an inner layer of a silane-grafted modified amorphous polyolefin or a silane-grafted modified low-crystalline polyolefin.

[0018]

[Function] The inner layer is made of a silane-grafted modified amorphous polyolefin or a silane-grafted modified low-crystalline polyolefin, and polar groups are introduced into these polyolefins, so that they have excellent adhesiveness with metals and are resistant to hot water and warm water. Even when the temperature is high, the crystallization of the above-mentioned polyolefin hardly progresses, brittle fracture does not occur, and the generation of cracks and cracks is suppressed.

[0019]

Embodiments of the composite pipe of the present invention will be described.

Example 1 Amorphous polyethylene (melt index 2 g / 10 minutes: 190 ° C., density 1.000)
Vinyl trimethoxysilane and di-t-butyl peroxide were mixed in g / cm ³ and crystallinity 0%, and the mixture was heated and melted, and silane graft-modified amorphous polyethylene (melt index 0.7 g / 10 min: 190 ° C, density 1.0
00 g / cm ³ , crystallinity 0%) was obtained.

Next, a cold rolled steel sheet hoop material having a thickness of 1.5 mm and a width of 271 mm was continuously unwound, degreased with a sodium phosphate-based degreasing agent, and then immersed in a nitric acid solution for etching. This cold-rolled steel sheet was heated and dried, and a roll forming device was used to form a circular pipe with the etched surface inside, while welding the abutting portions of the side edges to continuously produce a metal tube.

The silane-grafted amorphous polyethylene described above is extruded as an inner layer from a die attached to the end of the extruder, and the metal pipe is coated on the inner surface of the cold-rolled steel plate hoop material being formed to form a composite pipe (inner diameter). 80 mm, inner layer 1.0 mm) was produced.

The resulting composite pipe was cut into a width of 2 cm in the longitudinal direction, and the adhesive strength was measured by the T-type peeling method.
It was 2.3 kgf. The crystallinity of the silane graft-modified amorphous polyethylene of the inner layer is 0% (X-ray diffraction method)
Met.

Next, hot water of 95 ° C. was passed through the composite pipe (length 1 m) for 20,000 hours, and the presence or absence of cracks or cracks in the inner layer was visually observed, but no abnormality was found. When the adhesive strength of the composite pipe after passing water was measured in the same manner as above, it was 38.5 kgf.
Met. The crystallinity of polyethylene in the inner layer is 3%
Met.

Example 2 Polyethylene (melt index 30 g / 10 min: 190 ° C., density 0.954 g /
cm ³ , crystallinity 70%, and polypropylene (melt index 10 g / 10 min: 230 ° C., density 0.91)
4 g / cm ³ and crystallinity 80%) were melt mixed at a weight ratio of 7: 3 and a melt index of 12 g / 10 min: 230.
° C., a density 0.900 g / cm ^3, to obtain a crystallinity of 27% of the mixture. Vinyltrimethoxysilane and di-t-butylperoxide were added to this mixture and heated and melted to obtain a silane graft-modified low crystalline polyolefin (melt index 5 g / 10 min: 230 ° C.).

A composite pipe was produced in the same manner as in Example 1 except that this silane-grafted modified low crystalline polyolefin was used in place of the silane-grafted modified amorphous polyethylene of Example 1.

The adhesive strength and crystallinity of the obtained composite pipe are
When measured in the same manner as in Example 1, it was 34.4.
The kgf was 26%.

When a hot water flow test was conducted in the same manner as in Example 1, no cracks or cracks were found in the inner layer of the composite pipe, and the adhesive strength and crystallinity were each 31.8 kg.
f was 27%.

Comparative Example High density polyethylene (melt index 2.5 g / 10 min: 190 ° C., density 0.95
4 g / cm ³ and a crystallinity of 75%), vinyltrimethoxysilane and di-t-butyl peroxide were mixed and heated to melt, and silane-grafted modified high-density polyethylene (melt index 1.5 g / 10 min: 190). C., crystallinity 70%) was obtained. A composite pipe was produced in the same manner as in Example 1 except that this silane-grafted modified high-density polyethylene was used instead of the silane-grafted modified amorphous polyethylene of Example 1.

The adhesive strength and crystallinity of the obtained composite pipe are
When measured in the same manner as in Example 1, it was 37.3, respectively.
It was kgf and 70%.

A hot water flow test was conducted in the same manner as in Example 1, and it was found that the inner layer surface of the composite pipe had a length of 1 to 5 cm.
Some cracks were seen. The adhesive strength and crystallinity are
They were 31.3 kgf and 85%, respectively.

[0032]

As described above, the composite pipe of the present invention has an excellent brittleness resistance even if hot water is passed for a long period of time, the crystallinity of the silane-grafted modified polyolefin of the inner layer hardly progresses. Has no cracks or cracks and can withstand long-term use of hot water or hot water. Therefore, it can be suitably used as a piping material for hot water supply, hot water heating, drainage, and the like.

Claims (1)

[Claims] 1. A composite tube comprising a silane-grafted modified amorphous polyolefin or a silane-grafted modified low-crystalline polyolefin as an inner layer and a metal as an outer layer.