JPS5936423Y2 - Multilayer synthetic resin pipe - Google Patents

Description

[Detailed description of the invention] The present invention is a multilayer synthetic resin pipe made of thermoplastic synthetic resin, in which the innermost layer is made of a crosslinked thermoplastic synthetic resin with a gel fraction of 40% or more, and the layers other than the innermost layer are made of gel. Made of thermoplastic synthetic resin with a fraction of 30% or less, and with a thickness greater than that of the pipe wall, it has superior chemical resistance, chlorine corrosion resistance, and cold resistance compared to conventional products. The present invention relates to a multilayer synthetic resin pipe that has many advantages such as heat insulation and heat retention, and is easy to weld.

Traditionally, pipes made of synthetic resins such as polyethylene have been used as water pipes and other fluid transport pipes, and these have good chemical resistance and
It is known that it has excellent cold resistance.

However, recently, problems have arisen, such as corrosion or peeling of the inner surface of the synthetic resin used for water supply pipes or water supply pipes, which can lead to clogging of water faucets.

The cause of this is thought to be that the synthetic resin pipes are eroded by the chlorine contained in the water, but this situation has become increasingly common in society, especially in recent years due to the increasing use of disinfectants due to the deterioration of water quality. This has become an even bigger problem, and immediate countermeasures are urgently needed.

On the other hand, it is well known that the above-mentioned properties are greatly improved by crosslinking thermoplastic synthetic resin with a crosslinking agent, but crosslinked synthetic resin pipes do not melt even when heated. However, it has the disadvantage that it cannot be welded.

In addition, metal joints are partially used to connect crosslinked synthetic resin pipes, but this method not only provides insufficient corrosion resistance, but also poses problems such as complicated and expensive piping construction.

As a result of intensive studies to solve the above drawbacks, the inventors of the present invention constructed the innermost layer from a crosslinked thermoplastic synthetic resin with a gel fraction of 40% or more, and the layers other than the innermost layer had a gel fraction of 30%. Multilayer synthetic resin pipes made of the following crosslinked or non-crosslinked thermoplastic synthetic resins, foamed thermoplastic synthetic resins, etc., and whose thickness is 72 or more times the thickness of the pipe wall, not only have excellent chlorine corrosion resistance, but also have excellent chlorine corrosion resistance. It was discovered that it has excellent heat insulation and heat retention properties, and is easy to weld.

The "gel fraction" described in this specification refers to extracting 0.3 g of a sample ground into 20 meshes using 150 ml of xylene solvent at 120 ± 2°C for 10 hours, washing with acetone, and then extracting the sample at 80°C. Insoluble content (%) after drying for 5 hours
It is.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

In the multilayer synthetic resin pipe shown in Fig. 1, the innermost crosslinked thermoplastic synthetic resin layer 1 may have a gel fraction of about 10 to 20% if the purpose is only to improve the chlorine corrosion resistance of the water pipe. Although this does not mean that it cannot be used, it is generally necessary to have a gel fraction of 40% or more when using it under harsher conditions.

Alternatively, the innermost layer may be made of crosslinked foam depending on the application.

The thickness of the innermost layer is sufficient to coat the inside of the tube.

The outer layer 2 is made of non-crosslinked thermoplastic synthetic resin or gel with a gel fraction of 30 to facilitate welding and improve the strength of the tube.
% or less, and the thickness is 2 or more times the thickness of the tube wall, welding becomes easy and the adhesive strength of the welded portion is improved.

Furthermore, depending on the application, the same effect as described above can be achieved even if the outer layer 2 is made of a non-crosslinked foam or a crosslinked foam.

The multilayer structure of the synthetic resin pipe of the present invention is shown in Figure 1 (inner layer: crosslinked thermoplastic synthetic resin/outer layer: non-crosslinked thermoplastic synthetic resin),
As represented in Figure 2 (inner layer: two crosslinked thermoplastic synthetic resins/outer layer: foamed thermoplastic synthetic resin) and Figure 3 (inner layer: crosslinked foamed thermoplastic synthetic resin/outer layer two non-crosslinked thermoplastic synthetic resins), It is not only possible to arbitrarily combine crosslinked bodies, non-crosslinked bodies, crosslinked foams, non-crosslinked foams, etc., but also to combine the same or different types of synthetic resins.

Furthermore, the multilayer structure of the present invention is not limited to just two layers, and a multilayer structure of three or more layers can be arbitrarily selected.

The thermoplastic synthetic resins used in the multilayer synthetic resin pipe of the present invention include high, medium, and low density polyethylene, ethylene-vinyl acetate copolymer, crystalline ethylene-propylene copolymer,
Ethylene-butene copolymers, polyolefins such as polypropylene, polyamides such as nylon 6.12,
Included are thermoplastic synthetic resins such as polyester and polyvinyl alcohol, either alone or in a blend of two or more.

Furthermore, additives such as pigments, stabilizers, ultraviolet absorbers, fillers, and reinforcing agents may be added as necessary.

There are no particular limitations on the method for manufacturing the multilayer synthetic resin pipe of the present invention, and conventionally known methods can be used.

For example, using a multilayer coextrusion molding method, ordinary polyethylene is supplied for the outer layer and polyethylene mixed with a crosslinking agent is supplied for the inner layer, and after shaping by coextrusion, a heated fluid is poured inside the tube to cause a crosslinking reaction. There are two methods: a method of completing the process, or a method of coating the surface of a pre-fabricated cross-linked synthetic resin pipe with polyethylene.

In order to more effectively improve the chlorine corrosion resistance using the former method, it is advantageous from an economic standpoint to carry out the crosslinking reaction using an inert gas, particularly nitrogen gas.

As a crosslinking method, in addition to the above methods, a radiation crosslinking method or a chemical crosslinking method using a crosslinking agent such as peroxide or silane can also be used.

As detailed above, the multilayer synthetic resin pipe of the present invention has excellent cold resistance, chemical resistance, and especially chlorine corrosion resistance, so it is useful as a pipe for transporting water or hot water, and the outer layer By making it into a foam or crosslinked body, it is possible to improve the heat insulation properties, heat retention properties, and stress cracking resistance.

Furthermore, since the welding process is easy, the piping process is easy, and taking all of the above factors into account, it can be said that the multilayer synthetic resin pipe is excellent in economical efficiency.

[Brief explanation of the drawing]

In Figure 1, the inner layer is a crosslinked thermoplastic synthetic resin and the outer layer is a non-crosslinked thermoplastic synthetic resin, in Figure 2 the inner layer is a crosslinked thermoplastic synthetic resin and the outer layer is a foamed thermoplastic synthetic resin, and in Figure 3, Figure 4 shows a cross-sectional view of a multilayer synthetic resin pipe in which the inner layer is a crosslinked foamed thermoplastic synthetic resin and the outer layer is a non-crosslinked thermoplastic synthetic resin. An example of a cross-sectional view of a synthetic resin pipe welded with plates is shown. DESCRIPTION OF SYMBOLS 1...Crosslinked thermoplastic synthetic resin layer, 2...Non-crosslinked thermoplastic synthetic resin layer, 3...Crosslinked thermoplastic synthetic resin layer, 4
... Foamed thermoplastic synthetic resin layer, 5... Crosslinked foamed thermoplastic synthetic resin layer, 6... Non-crosslinked thermoplastic synthetic resin layer,
7...Crosslinked thermoplastic synthetic resin layer, 8...Non-crosslinked thermoplastic base resin layer.

Claims (5)

[Scope of utility model registration request] (1) In a synthetic resin pipe made of thermoplastic synthetic resin,
The innermost layer is made of a crosslinked thermoplastic synthetic resin with a gel fraction of 40% or more, the thickness of layers other than the innermost layer accounts for 2 or more of the thickness of the tube wall, and the gel fraction is made of a thermoplastic synthetic resin with a gel fraction of 30% or less. Multilayer synthetic resin pipe. (2) The multilayer synthetic resin pipe according to claim 1, wherein the outer layer is made of a foamed thermoplastic synthetic resin. (3) The multilayer synthetic resin pipe according to claim 1 or 2, wherein the inner layer is made of a crosslinked and foamed thermoplastic synthetic resin. (4) The multilayer synthetic resin pipe according to any one of claims 1 to 3, wherein the thermoplastic synthetic resin is a polyolefin. (5) The multilayer synthetic resin pipe according to claim 4, wherein the polyolefin is polyethylene.