阅读说明：本技术 高密度聚乙烯管、接头和密封材料 (High density polyethylene pipe, joint and sealing material ) 是由 本棒享子 寺尾圭论 永田纯也 于 2019-07-23 设计创作，主要内容包括：本发明涉及高密度聚乙烯管、接头和密封材料。具体地,[课题]本发明提供抑制由辐射线等外部因素导致的劣化的高密度聚乙烯管、接头和密封材料。[解决课题的手段]本发明的高密度聚乙烯管(10)、接头和密封材料具备：以密度为0.940g/cm<Sup>3</Sup>以上0.980g/cm<Sup>3</Sup>以下的高密度聚乙烯为主成分的内层(1),覆盖内层1的外表面的、含有乙烯-乙烯醇共聚树脂的气体阻挡膜(2),覆盖气体阻挡膜(2)的外表面的、含有熔点为150℃以上的树脂的防熔融粘接膜(3)、以及覆盖防熔融粘接膜(3)的外表面的、以密度为0.910g/cm<Sup>3</Sup>以上0.930g/cm<Sup>3</Sup>以下的低密度聚乙烯为主成分的外层(4)。(The present invention relates to high density polyethylene pipes, joints and sealing materials. Specifically, [ problem ]]The invention provides a high-density polyethylene pipe, a joint and a sealing material which can inhibit the deterioration caused by external factors such as radiation. [ means for solving problems]The high-density polyethylene pipe (10), joint, and sealing material of the present invention are provided with: with a density of 0.940g/cm 3 Above 0.980g/cm 3 An inner layer (1) mainly composed of the following high-density polyethylene, a gas barrier film (2) containing an ethylene-vinyl alcohol copolymer resin and covering the outer surface of the inner layer (1), an anti-melt adhesive film (3) containing a resin having a melting point of 150 ℃ or higher and covering the outer surface of the gas barrier film (2), and a resin having a density of 0.910g/cm and covering the outer surface of the anti-melt adhesive film (3) 3 Above 0.930g/cm 3 The outer layer (4) mainly composed of low-density polyethylene.)

1. A high-density polyethylene pipe comprising:

with a density of 0.940g/cm ³Above 0.980g/cm ³The inner layer mainly composed of the following high-density polyethylene,

a gas barrier film containing an ethylene-vinyl alcohol copolymer resin covering the outer surface of the inner layer,

an anti-fusion bonding film covering the outer surface of the gas barrier film and containing a resin having a melting point of 150 ℃ or higher, and

a density of 0.910g/cm covering the outer surface of the fusion-bond preventing film ³Above 0.930g/cm ³The outer layer mainly composed of the following low-density polyethylene.

2. The high density polyethylene pipe of claim 1, wherein the inner layer comprises at least one of:

an oil containing naphthenes formed when refining crude oil, and

an aromatic-containing oil produced when crude oil is refined.

3. The high density polyethylene pipe of claim 1, wherein the inner layer comprises at least one of:

an oil containing naphthenes and having a% CN of 20-60% in a ring analysis measured by an n-d-M method, among oils produced when crude oil is refined, and

an aromatic hydrocarbon-containing oil having a% CA of 5% to 40% in a ring analysis measured by an n-d-M method, among oils produced when crude oil is purified.

4. The high-density polyethylene pipe according to claim 1, wherein the ethylene-vinyl alcohol copolymer resin has a thickness of 1 μm or more and 50 μm or less.

5. The high density polyethylene pipe of claim 1,

the gas barrier film is a multilayer film having: an intermediate layer containing an ethylene-vinyl alcohol copolymer resin, and surface layers laminated on both sides of the intermediate layer,

the surface layer contains at least one of low-density polyethylene and linear low-density polyethylene.

6. The high-density polyethylene pipe according to claim 5, wherein the total thickness of the multilayer film when wound around the outer periphery is 50 μm or more and 400 μm or less.

7. The high-density polyethylene pipe according to claim 1, wherein the melt adhesion preventing film is a polyethylene terephthalate stretched film, a polyimide film, or a polyamideimide film.

8. The high-density polyethylene pipe according to claim 1, wherein the total thickness of the fusion-bond preventing film when wound around the outer periphery is 20 μm or more and 200 μm or less.

9. The high density polyethylene pipe of claim 1 wherein the outer layer comprises carbon black.

10. The high-density polyethylene pipe according to claim 9, wherein a content of the carbon black in the outer layer is 1.0 mass% or more and 3.0 mass% or less.

11. The high density polyethylene pipe as claimed in any one of claims 1 to 10, which is a pipeline for nuclear power equipment for fluid transportation in nuclear power-related facilities.

12. A joint, comprising:

with a density of 0.940g/cm ³Above 0.980g/cm ³The inner layer mainly composed of the following high-density polyethylene,

a gas barrier film containing an ethylene-vinyl alcohol copolymer resin covering the outer surface of the inner layer,

an anti-fusion bonding film covering the outer surface of the gas barrier film and containing a resin having a melting point of 150 ℃ or higher, and

a density of 0.910g/cm covering the outer surface of the fusion-bond preventing film ³Above 0.930g/cm ³The outer layer mainly composed of the following low-density polyethylene.

13. A sealing material, comprising:

with a density of 0.940g/cm ³Above 0.980g/cm ³The inner layer mainly composed of the following high-density polyethylene,

a gas barrier film containing an ethylene-vinyl alcohol copolymer resin covering the outer surface of the inner layer,

an anti-fusion bonding film covering the outer surface of the gas barrier film and containing a resin having a melting point of 150 ℃ or higher, and

a density of 0.910g/cm covering the outer surface of the fusion-bond preventing film ³Above 0.930g/cm ³The outer layer mainly composed of the following low-density polyethylene.

Technical Field

The present invention relates to a high-density polyethylene pipe, a joint, and a sealing material used for nuclear power plants and the like.

Background

The pipeline for nuclear power plant laid in a nuclear power-related facility is required to have a performance capable of safely carrying out the transport of a fluid containing a radioactive substance for a long period of time and the transport of the fluid at a high radiation dose. Conventionally, steel pipes have been used as pipelines for nuclear power plants. However, since many man-hours and machines are required for construction of nuclear facilities that are subject to space and time constraints, steel pipes cannot be said to be optimal. In this case, replacement with resin pipes is being performed in which movement and processing are easy, and joining between pipes and joints is also easy.

As a resin pipe, use of a high-density polyethylene pipe used as a long-distance pipe for a water pipe has been studied. However, high density polyethylene pipes have a disadvantage that they are inferior to steel pipes in radiation resistance and are likely to be brittle at high radiation doses. When a high-density polyethylene pipe deteriorates and a minute defect is generated in the resin, stress is concentrated at the defect portion and a fracture or a crack is generated when pressure from a fluid inside the pipe, earth pressure from the outside of the pipe, or the like is applied.

The deterioration of polyethylene progresses due to autoxidation mainly involving radicals, and the deterioration of polyethylene is promoted not only by the action of radiation but also by ultraviolet rays and oxygen. In the case where the fluid conveyed through the high-density polyethylene pipe contains a radioactive substance or has a possibility of being irradiated, it is important that no leakage event occurs, and therefore, it is necessary to take measures to prevent deterioration due to external factors such as radiation, oxygen, and ultraviolet rays.

For example, patent document 1 describes a technique of adding 1 to 7 parts by mass of a hydrogenated aromatic deterioration inhibitor or propylfluoranthene to high-density polyethylene.

Patent document 2 describes a high-density polyethylene pipe, a joint that can be thermally fusion-bonded (thermally bonded) to the outer surface of the high-density polyethylene pipe, and a fluid transfer device provided with these. In a high-density polyethylene pipe, tie molecules (tie molecules) that easily become the starting points of fracture and connect to a crystal structure are reinforced by a cross-linked structure. In addition, a non-crosslinked polyethylene layer that can be thermally melt-bonded is formed on the outer surface of the high-density polyethylene pipe.

Disclosure of Invention

Problems to be solved by the invention

When a deterioration preventing agent is added to high-density polyethylene as in patent document 1, or when tie molecules are reinforced with a crosslinked structure as in patent document 2, the radiation resistance of the high-density polyethylene pipe can be improved. Further, when the high density polyethylene pipe has a double pipe structure, it is difficult for ultraviolet rays and oxygen in the atmosphere to reach the inside, and therefore, the pipe integrity can be maintained for a certain period of time even outdoors or the like with a high radiation dose.

However, these high-density polyethylene pipes have a durability life of 40 years or more, and cannot be said to have sufficient durability as compared with steel pipes which do not need to be replaced in a short period of time. High density polyethylene, while having the compressive strength and hardness required for pipes, has the essential disadvantage of lacking ductility and being susceptible to brittle fracture when used continuously at high radiation doses. Radical reactions that degrade resins are easily initiated by radiation and are promoted by external factors such as oxygen and ultraviolet rays, and therefore, a high level of measures for preventing these factors are required.

Further, sealing materials such as high-density polyethylene pipe joints, gaskets, and circular rings used together with high-density polyethylene pipes are sometimes exposed to external factors such as ultraviolet rays, and countermeasures are also required. As a material of the sealing material, there are Ultra High Molecular Weight Polyethylene (UHPE) and the like, and long-term sealing of not only a piping material but also a radioactive solution in nuclear fuel facilities and the like is expected.

Accordingly, an object of the present invention is to provide a high-density polyethylene pipe, a joint, and a sealing material which can suppress deterioration due to external factors such as radiation.

In order to solve the above problems, a high density polyethylene pipe according to the present invention includes: with a density of 0.940g/cm ³Above 0.980g/cm ³An inner layer mainly composed of the following high-density polyethylene, a gas barrier film containing an ethylene-vinyl alcohol copolymer resin and covering the outer surface of the inner layer, a melt-resistant adhesive film (heat-resistant adhesive film) containing a resin having a melting point of 150 ℃ or higher and covering the outer surface of the gas barrier film, and a resin having a density of 0.910g/cm and covering the outer surface of the melt-resistant adhesive film ³Above 0.930g/cm ³The outer layer mainly composed of the following low-density polyethylene.

The joint and the sealing material of the present invention have the same layer structure as the high density polyethylene pipe.

Effects of the invention

According to the present invention, it is possible to provide a high-density polyethylene pipe, a joint, and a sealing material which can suppress deterioration due to external factors such as radiation.

Drawings

FIG. 1 is a sectional view schematically showing a high density polyethylene pipe of the present invention.

FIG. 2 is a perspective view schematically showing a high-density polyethylene pipe of the present invention.

FIG. 3 is a graph showing the relationship between% CN of oil used as an additive and elongation at break.

FIG. 4 is a graph showing the relationship between% CA of an oil used as an additive and elongation at break.

FIG. 5 is a graph showing the relationship between MFR and elongation at break of linear low density polyethylene used for a gas barrier film.

Fig. 6 is a graph showing the relationship between the total thickness of the gas barrier film and the elongation at break.

FIG. 7 is a graph showing the relationship between the thickness of an ethylene-vinyl alcohol copolymer resin used for a gas barrier film and the elongation at break.

FIG. 8 is a graph showing the relationship between the thickness of a fusion-bond preventing film (fusion-bond preventing film) and the elongation at break.

FIG. 9 is a graph showing the relationship between the thickness of the protective layer (outer layer) and the elongation at break.

Detailed Description

Hereinafter, a high-density polyethylene pipe, a joint, and a sealing material according to an embodiment of the present invention will be described with reference to the drawings.

Fig. 1 is a cross-sectional view schematically showing a high-density polyethylene pipe of the present invention. Fig. 2 is a perspective view schematically showing the high-density polyethylene pipe of the present invention. In fig. 2, the inside of the pipe body is exposed to show the layer structure of the high density polyethylene pipe.

As shown in fig. 1 and 2, the high-density polyethylene pipe 10 of the present embodiment includes: the pipe comprises a cylindrical inner layer 1 forming a pipe, a gas barrier film 2 covering the outer surface of the inner layer 1, an anti-melt adhesive film 3 covering the outer surface of the gas barrier film 2, and an outer layer 4 serving as a protective layer covering the outer surface of the anti-melt adhesive film 3.

The high-density polyethylene pipe 10 is mainly used as a fluid transport pipe for transporting fluid between machines and facilities. The high-density polyethylene pipe 10 has excellent radiation resistance and suppresses deterioration of the high-density polyethylene pipe (inner layer 1) due to external factors such as radiation, oxygen, and ultraviolet rays, and is therefore particularly suitable for use in the transport of fluids containing high-concentration radioactive substances and the transport of fluids at high radiation doses.

In order to fundamentally improve the intrinsic defect that high density polyethylene has that it is easily brittle-broken when continuously used at a high radiation dose, the high density polyethylene pipe 10 is a multilayer pipe in which the outside of a conduit (inner layer 1) through which a fluid flows is covered with a gas barrier film 2 and a protective layer (outer layer 4) for improving weather resistance. In resin molding into the protective layer (outer layer 4), the gas barrier film 2 and the protective layer (outer layer 4) are provided with a layer structure in which the fusion-bonding preventing film 3 is interposed therebetween so as not to cause cracking of the gas barrier film 2.

The density of the inner layer 1 is 0.940g/cm ³Above 0.980g/cm ³The following High Density Polyethylene (HDPE) was used as a main component. Since high-density polyethylene has low brittleness although it has high tensile strength and impact resistance, the inner layer 1 mainly composed of high-density polyethylene provides the compressive strength and hardness required for pipes.

The high-density polyethylene may contain 1-butene, 1-hexene, and the like as monomers in addition to ethylene, as long as the physical properties such as density are not impaired. The density of the high-density polyethylene is preferably 0.940g/cm ³Above 0.970g/cm ³Hereinafter, more preferably 0.945g/cm ³Above 0.965g/cm ³The following.

The high-density polyethylene can be obtained by polymerization using any of ziegler catalyst, metallocene catalyst, phillips catalyst, and the like. The high-density polyethylene may be a mixed material blended with another resin or a recycled material obtained by recycling a polyethylene product as a raw material. The high-density polyethylene may further contain other resins such as polypropylene as long as it is in a range of less than 50% by mass.

As the high-density polyethylene, for example, a polyethylene having a reaction pressure of 5kgf/cm can be used ²Above 200kgf/cm ²And a resin polymerized at a reaction temperature of 60 ℃ to 100 ℃ inclusive. Further, a resin having a Melt Flow Rate (MFR) determined in accordance with ISO1133 of 0.1g/10 min to 3.0g/10 min, more preferably 0.2g/10 min to 0.5g/10 min under the conditions of a test temperature of 190 ℃ and a test load of 5.0kgf (49.03N) can be used. However, the high-density polyethylene constituting the inner layer 1 is not limited to the resin exhibiting such physical properties.

In the inner layer 1, usual additives such as an antioxidant and a heat stabilizer may be added to the base material mainly composed of the high-density polyethylene, or usual additives may not be added. In fig. 1 and 2, the shape of the inner layer 1 is a cylindrical shape, but the dimensions of the inner layer 1, such as ovality, cross-sectional shape, longitudinal shape, inner and outer diameters, and wall thickness, are not particularly limited.

The inner layer 1 preferably contains at least one of an oil containing naphthenes produced during crude oil purification and an oil containing aromatic hydrocarbons produced during crude oil purification in a base material mainly composed of high-density polyethylene. When these oils are blended, the sliding property of the polyethylene molecules is improved as described later, and the deterioration of the high density polyethylene due to the breakage of the fine grains is suppressed.

The oil containing naphthenes may be an oil obtained by purifying a naphthene-based crude oil as a raw material. For example, there can be used an oil obtained by distilling a naphthenic crude oil under reduced pressure and removing an oil containing aromatic components by solvent extraction. In addition to solvent extraction, oil purified by adsorption treatment, clay treatment, deacidification treatment, or the like may be used. Here, cycloalkane means a compound represented by the general formula: c _nH _2nCyclic hydrocarbons are shown.

As the aromatic hydrocarbon-containing oil, a paraffinic crude oil and/or a naphthenic crude oil may be blended as a raw material, and these oils may be purified. For example, residual oil having a high specific gravity and a high viscosity, which is produced in the purification process of paraffinic crude oil or naphthenic crude oil, can be used. Aromatic hydrocarbons are defined by the general formula: c _nH _2n-6The aromatic hydrocarbon represented, that is, an unsaturated cyclic hydrocarbon having a conjugated double bond.

The oil containing naphthenes is preferably an oil having a% CN of 10% to 100% in a ring analysis measured by an n-d-M method, more preferably an oil having a% CN of 10% to 80%, and still more preferably an oil having a% CN of 20% to 60%, among oils produced when a naphthene-based crude oil is purified. When the% CN is about 20% or more and about 60% or less, a high effect of suppressing deterioration of the high density polyethylene is obtained.

Among oils produced when refining paraffinic crude oils or naphthenic crude oils, the aromatic-containing oils preferably have a% CA of 5% to 100%, more preferably have a% CA of 5% to 60%, and still more preferably have a% CA of 5% to 40%, as measured by the n-d-M method. When the% CA is about 5% to about 40%, a high effect of suppressing deterioration of the high density polyethylene is obtained.

Further, as the oils containing naphthenes and aromatics, for example, oils having a% CN of ring analysis measured by n-d-M method of 20% to 60% and a% CA of ring analysis measured by n-d-M method of 5% to 40% among oils produced when crude oil is refined can be used as additives.

The n-D-M method is a method of structure-based analysis of oils (Ring analysis method) according to ASTM D3238-85, and is generally used for compositional analysis of base oils. Based on the density d20 of the oil at 20 ℃, the refractive index nD20 of the oil at 20 ℃ and the average molecular weight data of the oil, the mass ratio of paraffinic carbons to the total carbon amount (% CP), the mass ratio of naphthenic carbons to the total carbon amount (% CN), the mass ratio of aromatic carbons to the total carbon amount (% CA), the average number of naphthenic rings per molecule (RN), and the average number of aromatic rings per molecule (RA) were determined by the n-d-M method.

The gas barrier film 2 is formed of a resin film containing at least ethylene-vinyl alcohol copolymer resin (EVOH). According to the gas barrier film 2 containing an ethylene-vinyl alcohol copolymer resin, oxygen in the outside air is shielded, and oxidative deterioration of the high-density polyethylene of the inner layer 1 is suppressed.

Typically, the high density polyethylene has an oxygen permeability coefficient of about 0.4X 10 ^-10cm ³(STP)·cm/(cm ²s-cmHg), the oxygen permeability coefficient of the low density polyethylene is about 6.9X 10 ^-10cm ³(STP)·cm/(cm ²S · cmHg). In contrast, the oxygen permeability coefficient of the ethylene-vinyl alcohol copolymer resin is as small as about 0.0001X 10 ^-10cm ³(STP)·cm/(cm ²S cmHg), the oxygen permeation can be suppressed to 1/4000 for high density polyethylene and 1/67000 for low density polyethylene.

The gas barrier film 2 may be formed of a single layer containing an ethylene-vinyl alcohol copolymer resin, or may be formed of a plurality of layers including a layer containing an ethylene-vinyl alcohol copolymer resin.

The average polymerization degree, ethylene content and saponification degree of the ethylene-vinyl alcohol copolymer resin are not particularly limited. For example, the average polymerization degree may be 500 to 3000. The ethylene content may be, for example, 20% to 80%. The ethylene content is preferably 25% or more from the viewpoint of improving flexibility and water resistance. The saponification degree may be, for example, 85% to 99%. From the viewpoint of ensuring gas barrier properties, the saponification degree is preferably 90% or more, and more preferably 95% or more.

The thickness of the ethylene-vinyl alcohol copolymer resin is preferably 0.5 μm or more, more preferably 1 μm or more, and still more preferably 5 μm or more. Further, it is preferably 60 μm or less, more preferably 50 μm or less, and further preferably 30 μm or less. When the thickness of the ethylene-vinyl alcohol copolymer resin is 0.5 μm or more, excellent gas barrier properties can be obtained as the thickness is larger, and oxidative deterioration of the resin of the inner layer 1 can be suppressed. Further, since pinholes are less likely to occur, it is easy to ensure gas impermeability satisfactorily. When the thickness is 5 μm or more and 50 μm or less, particularly high radiation resistance is obtained by the neutron shielding ability of the resin itself. On the other hand, when the thickness is 60 μm or less, the gas barrier film 2 is less likely to be broken when the high-density polyethylene pipe 10 is constructed, moved, or the like because it has flexibility as it is thinner.

The ethylene-vinyl alcohol copolymer resin may be a mixed material blended with other resins. Examples of the other resins to be blended include ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, polyolefins, modified polyolefins, polyamides, and polyesters. The ethylene-vinyl alcohol copolymer resin may be a resin modified with an epoxy compound or the like, or may be a copolymer containing a monomer other than ethylene and vinyl acetate.

As shown in fig. 1 and 2, the gas barrier film 2 is preferably a multilayer film including an intermediate layer 22 containing an ethylene-vinyl alcohol copolymer resin and surface layers (21, 23) laminated on both sides of the intermediate layer 22. In fig. 1 and 2, the surface layers (21, 23) include an inner layer 21 disposed inside the intermediate layer 22 and an outer layer 23 disposed outside the intermediate layer 22, but the number of layers stacked on both surfaces of the intermediate layer 22 is not particularly limited.

The surface layers (21, 23) preferably contain at least one of Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE). These polyethylenes can be coextruded with ethylene-vinyl alcohol copolymer resins. Further, according to the polyethylene, since a high neutron shielding ability can be obtained by the resin itself, radiation deterioration of the resin of the inner layer 1 can be suppressed.

In particular, when the surface layers (21, 23) are formed of low-density polyethylene, a multilayer film having high flexibility, impact resistance, cold resistance, moisture resistance and the like can be formed with high precision. Further, external pressure, impact, and the like applied to the high-density polyethylene pipe 10 can be alleviated, and damage of the inner layer 1, peeling, falling, and the like of the gas barrier film 2 can be prevented. Here, the low density polyethylene means a density of 0.910g/cm ³Above 0.930g/cm ³The following polyethylenes. The low density polyethylene may contain 1-butene, 1-hexene, and the like as monomers in addition to ethylene.

When the surface layers (21, 23) are formed of linear low-density polyethylene, higher tensile rupture strength, adhesiveness, cold resistance, and the like can be obtained than when the surface layers are formed of low-density polyethylene. Here, the linear low-density polyethylene means a polyethylene having a density of 0.910g/cm ³Above 0.925g/cm ³Hereinafter, the content of the monomer having a branched chain is a few%. The linear low-density polyethylene may contain 1-butene, 1-hexene, 1-octene, and the like as monomers in addition to ethylene. The linear low-density polyethylene can be polymerized by using any catalyst such as a ziegler catalyst or a phillips catalyst.

The melt index (MFR, melt flow rate) of the low-density polyethylene and the linear low-density polyethylene forming the surface layers (21, 23) is preferably 0.5g/10 min or more, as determined in accordance with ISO 1133. Further, it is preferably 50g/10 min or less, more preferably 20g/10 min or less, further preferably 10g/10 min or less, and particularly preferably 5g/10 min or less. It is known that the molecular weight of a resin has a correlation with MFR. When polyethylene exhibiting such MFR is used, the amount of low molecular weight components is small, and therefore high neutron shielding ability can be obtained by the resin itself.

The surface layers (21, 23) may be formed by laminating other resins as long as the layers containing low-density polyethylene or linear low-density polyethylene are provided on both sides of the intermediate layer 22. For example, from the viewpoint of toughening the multilayer film, the multilayer structure may be one containing Polyamide (PA) such as nylon 6 and Polyester (PE) such as polyethylene terephthalate.

Specific examples of the multilayer film include, but are not limited to, LDPE/EVOH/LDPE, LLDPE/EVOH/LLDPE, and the like. In view of improving the radiation resistance, it is preferable to exclude a low molecular weight component from the low density polyethylene and the linear low density polyethylene. Between the intermediate layer 22 and the surface layers (21, 23), another layer such as an adhesive layer may be provided as necessary.

The thickness of the multilayer film is preferably 20 μm to 200 μm. When the thickness is 20 μm or more, the greater the durability, the more the high density polyethylene pipe 10 is thick, and therefore, when it is laid in an excessively harsh environment where external force is easily applied, such as when it is used for construction, transportation, or the like, or outdoors, the gas barrier property can be satisfactorily ensured. Further, when the thickness is 200 μm or less, the thinner the film, the less flexibility is lost, so that the handling property and the winding property to the catheter (inner layer 1) are good, and the breakage of the film at the time of handling is reduced.

The total thickness of the gas barrier film 2 when wound on the outer periphery of the inner layer 1 is preferably 20 μm or more, and more preferably 50 μm or more. Further, it is preferably 500 μm or less, more preferably 400 μm or less, and further preferably 300 μm or less. When the total thickness is 20 μm or more, the greater the thickness, the higher the gas barrier property can be obtained, and therefore, the oxidative degradation of the resin of the inner layer 1 can be reliably suppressed. In addition, when the total thickness is 50 μm or more and 400 μm or less, particularly high radiation resistance can be obtained. On the other hand, when the total thickness is 500 μm or less, the thinner the film, the lower the material cost of the gas barrier film 2 and the labor for winding the film.

The gas barrier film 2 and the inner layer 1 may be fusion-bonded to each other or bonded by an adhesive, an adhesive material, or the like, but is preferably not fusion-bonded or bonded to the inner layer 1. When the inner layer 1 and the gas barrier film 2 are surface-joined by fusion bonding or adhesion, when a force is applied in the longitudinal direction or the radial direction of the pipe, stress is generated in opposite directions in the inner layer 1 and the gas barrier film 2 having different elongations, respectively, and thus the probability of occurrence of stress cracking or breakage increases. The gas barrier film 2 may contain an oil containing naphthene or an oil containing aromatic hydrocarbon, similarly to the inner layer 1.

Here, the action and effect of the oil and the gas barrier film 2 added to the inner layer 1 of the high-density polyethylene pipe 10 will be specifically described.

Polyethylene pipes are lighter in weight than steel pipes and are easy to move and process, and thus are widely used as long-distance pipes for water pipes and the like. However, unlike steel pipes, polyethylene pipes are made of organic polymers mainly composed of carbon and hydrogen. Polyethylene tends to undergo a brittle fracture when internal pressure, external pressure, impact, or the like is applied to a pipe, damage is caused to the pipe, or the pipe is exposed to a chemical substance, because deterioration progresses due to external factors such as radiation, ultraviolet rays, and heat, and elasticity, stress environment cracking resistance, impact resistance, and the like are reduced.

It is known that, in the case of an organic polymer, a molecule is excited by radiation, ultraviolet rays, heat, or the like, and bonds in the molecule are broken and decomposed. For example, when radiation or the like acts on polyethylene, hydrogen radicals (H) and hydrocarbon radicals (R) are generated. The reactivity of the radicals is high, and the radicals are bonded to each other (re-bonding), or the radicals are introduced to generate another radical (initiation reaction), or the radicals are added to a double bond (addition reaction), or a molecular chain is cut while the radicals are bonded to each other (disproportionation reaction).

The recombination and addition reactions of free radicals bring about an increase in the molecular weight called crosslinking, and the disproportionation reactions bring about a decrease in the molecular weight called disintegration. In a polyethylene pipe, when molecular chains are crosslinked and disintegrated, resistance to impact and bending is reduced, and physical properties such as brittleness of the pipe body are changed. As described above, when embrittlement of the pipe body progresses, the following problems occur when internal pressure, external pressure, impact, load, and the like are applied: stress cracking or creep rupture such as cracking or cracking, or cracking or brittle cracking in the pipe wall, or cracking of the pipe body, etc. are likely to occur.

As a pipe material such as a polyethylene pipe for water distribution, high-density polyethylene having been subjected to high performance by multi-stage polymerization or by an improved catalyst can be used. For such high density polyethylene, long term hydrostatic strength and environmental stress crack resistance can be improved by increasing the high molecular weight region, increasing the tie molecules connecting between the crystalline structures.

In general, it is known that the crystalline region is not easily affected even in an excessively severe environment, and the amorphous region is increasingly subjected to cleavage of tie molecules in an excessively severe environment. It is considered that if the tie molecules are cut, stress concentration is likely to occur in the resin when an external force is applied, and the long-term hydrostatic strength, environmental stress cracking resistance, and impact resistance are lowered.

In particular, in an atmosphere in which oxygen is present, it is known that propagation reaction (chain reaction) of oxidation proceeds by radicals. Initially, as in reaction formula (1), a hydrocarbon radical (R.cndot.) is reacted with oxygen (O) ₂) The reaction produces peroxygenated radicals (ROO.).

[ solution 1]

R·+O ₂→ROO·…(1)

The peroxygen radical (ROO. cndot.) is reactive, and as shown in the reaction formula (2), hydrogen (H) is extracted from other molecules (RH) to generate a peroxide (ROOH) and a new hydrocarbon radical (R. cndot.).

[ solution 2]

ROO.+RH→ROOH+R.…(2)

The newly formed hydrocarbon radical (R.cndot.) then forms another peroxidic radical (ROO.cndot.) according to equation (1), which forms another peroxide (ROOH) according to equation (2). The peroxide (ROOH) is unstable, and thus, as in the reaction formulas (3) to (5), a new oxygen radical (RO.), a peroxide radical (ROO.), and the like are generated.

[ solution 3]

ROOH→RO.+.OH…(3)

[ solution 4]

2ROOH→ROO.+RO.+H ₂O…(4)

[ solution 5]

RO.+RH→ROH+R.…(5)

In the atmosphere in the presence of oxygen, by such a propagating reaction of oxidation, the originally produced hydrocarbon radicals (R ·) propagate in large numbers into new radicals, and crosslinking and disintegration of the molecular chains progress. Therefore, deterioration of the resin is accelerated, and stress cracking and creep rupture are easily generated.

In addition, ozone is sometimes generated by radiation or ultraviolet rays in the atmosphere in which oxygen exists. Ozone has high reactivity with polyethylene having a double bond, and ozonides are produced by reaction with polyethylene. Since ozonides are unstable, the O-O bond is broken to produce aldehydes, ketones, esters, lactones, peroxides, and the like. It is known that molecular decomposition caused by such a reaction forms minute cracks (ozone cracks) in the resin.

In particular, when a fluid pressure, an earth pressure, or the like of about 1MPa or more is applied to a polyethylene pipe, the molecular chains tend to be stretched, so that the permeability of ozone is high and stress tends to concentrate on a specific site. In this case, the possibility of the occurrence of ozone cracks and the possibility of fracture starting from ozone cracks are increased.

In addition, polyethylene pipes are sometimes used for the transport of high temperature fluids. The various reactions that cause the decomposition of molecules are also related to molecular motion, i.e., the vibration and collision probability of the molecules. The more vigorous the molecular motion is at high temperature, and therefore, when polyethylene is exposed to high temperature, crosslinking and disintegration of molecular chains are accelerated, and deterioration of resin remarkably proceeds.

In particular, in a system involving an oxidation reaction, since the thickness of an oxide layer, the diffusion rate of oxygen, and the reaction rate of oxidative decomposition are affected by temperature, the oxidative decomposition of molecules is accelerated. Generally, the reaction rate is 2 times when the temperature is increased by 10 ℃. Therefore, in the case of using a polyethylene pipe for the transportation of a fluid at a high temperature, etc., when polyethylene is exposed to a high temperature, oxidative deterioration is accelerated, crosslinking and disintegration of molecular chains proceed, and deterioration of the resin becomes remarkable.

Such degradation of polyethylene by radiation, ultraviolet rays, heat, or the like deteriorates various properties such as elastic modulus, tensile strength, elongation, and the like, and deteriorates stress environment cracking resistance, impact resistance, and the like. In an excessively severe environment such as a radiation environment, an ultraviolet environment, a high-temperature environment, or the like, when a polyethylene pipe, a joint, or the like is continuously used, problems such as stress cracking, creep rupture, generation of undesirable phenomena such as cracking, or breakage of a pipe body, and fluid leakage are caused when internal pressure, external pressure, impact, or the like is applied, or when the pipe, the joint, or the like is exposed to a chemical substance.

On the other hand, when the inner layer 1 of the high density polyethylene pipe 10 is covered with the gas barrier film 2, the permeation of oxygen is inhibited, and the propagation reaction of oxidation is suppressed, so that the oxidative degradation of the resin of the inner layer 1 can be suppressed even at a high dose of radiation. When oil containing naphthene or oil containing aromatic hydrocarbon is blended in the inner layer 1, radicals generated by the action of radiation or ultraviolet rays can be trapped by the oil component.

In general, polyethylene has a characteristic that cracks, fissures, and the like are generated by various external factors such as radiation, ultraviolet rays, and heat, and the elongation is reduced and whitening occurs on the fracture surface in any fracture mode, although the polyethylene varies depending on the kind of the external factor. Whitening or cracking occurs on the fractured surface, and voids and fibrils exist. Whitening is a phenomenon caused by mie scattering of light due to void formation. Whitening indicates the occurrence of a form of damage consisting of voids and fibrils, i.e., a fine line break.

In general, it is known that the breakage of polyethylene by drawing proceeds in the following order of (a) to (D).

(A) Local area propagation of strain occurring just after tensile yield

(B) Propagation of fine-line fracture zone

(C) In the concentrated part of the fine grain breakage, molecular chain cutting and cracking occur

(D) Polymer fracture

In addition, for the crystal level, it is known that the change as described below is produced by stretching.

(a) Cracking of crystals at molecular level (molecular chain peeling)

(b) Bulk breaking of crystals (molecular chain peeling)

(c) Sliding rotation of molecules within a crystal (small variation)

Wherein in (a) and (b), the crystalline region is destroyed and the amorphous region is increased. In addition, the molecular chains are peeled off from the crystal region to form voids and fibrils, which cause fine line breakage. However, in (c), the crystal region is less damaged, and the amorphous region is hardly increased.

The amorphous region increased by this mechanism becomes a starting point of fracture typified by stress cracking. The following is therefore desirable: the formation of voids and fibrils, and the occurrence of fine crack are prevented as much as possible, and brittle crack and creep crack do not occur when pressure from a fluid inside the pipe, and/or earth pressure from outside the pipe, or the like is applied.

On the other hand, when the oil containing cycloalkane and/or the oil containing aromatic hydrocarbon is blended in the inner layer 1 of the high-density polyethylene pipe 10, the slidability of molecules present in the polyethylene crystal can be greatly improved. By converting the change in the crystal level into sliding rotation of molecules within the crystal, formation of voids and fibrils and fine grain fracture can be reduced, and the amorphous region is less likely to be enlarged, so brittle fracture and creep fracture caused by deterioration of high density polyethylene can be reduced.

Furthermore, oils containing naphthenes have SP values similar to those of polyethylene and are well compatible with polyethylene. When oil containing cycloalkane is added to the inner layer 1 of the high-density polyethylene tube 10, the oil penetrates into the fine parts of the molecules in the crystal, and the sliding properties of the molecules in the crystal can be greatly improved. Therefore, it is possible to suppress the cracking of the crystal at the molecular level and the bulk cracking of the crystal, while easily causing the sliding rotation of the molecules within the crystal.

In addition, oils containing naphthenes also exhibit fluidity at low temperatures close to normal temperatures. In general, a high-molecular material is likely to cause low-temperature embrittlement, and high-density polyethylene has a disadvantage of low impact resistance at low temperatures, and therefore it is important that sliding rotation of molecules is likely to occur in crystals and in the periphery of tie molecules. When oil containing cycloalkane is added to the inner layer 1 of the high-density polyethylene pipe 10, the oil penetrating into the crystal and around the tie molecules retains high fluidity even at low temperatures, and sliding rotation of the molecules in the crystal is easily caused, so that resistance to low-temperature embrittlement and impact resistance at low temperatures can be improved.

On the other hand, aromatic hydrocarbon-containing oils are characterized by high viscosity index and low tendency to bleed out of the high density polyethylene of the substrate over a wide temperature range. Therefore, when the aromatic hydrocarbon-containing oil is added to the inner layer 1 of the high-density polyethylene pipe 10, the effect of the oil addition can be maintained for a long time. In addition, the fluid flowing inside the pipe (inner layer 1) is less likely to be contaminated by the oil oozing out.

In addition, aromatic-containing oils are characterized by high lightning. Therefore, when the aromatic hydrocarbon-containing oil is used as the additive, the high-density polyethylene pipe 10 can be safely manufactured.

In addition, most of the aromatic hydrocarbon-containing oils contain impurities such as sulfur and have a high acid value. Sulfur, aldehyde, carboxylic acid, and the like are likely to participate in the radical reaction, and thus the oil itself deteriorates sacrificially, thereby obtaining an effect of suppressing deterioration of the inner layer 1 of the high-density polyethylene pipe 10.

In addition, oils containing cycloalkanes or oils containing aromatics show the effect of softening polyethylene. It is generally known that polyethylene becomes hard and easily embrittled when it is continuously used in a radiation environment. However, when the oil containing naphthenes or the oil containing aromatic hydrocarbons is blended in the inner layer 1 of the high-density polyethylene pipe 10, the high-density polyethylene itself of the base material is softened, and thus embrittlement by radiation is less likely to occur.

The amount of the naphthenic oil or aromatic oil added is preferably 0.1 to 7 parts by mass, more preferably 1 to 7 parts by mass, based on 100 parts by mass of the high-density polyethylene. When the amount exceeds 7 parts by mass, the oil bleeds out, and it is difficult to properly blend the oil. On the other hand, when the amount is less than 0.1 part by mass, a sufficient effect due to the addition cannot be obtained. On the other hand, in the above-mentioned range of the addition amount, the effect of suppressing the deterioration of the resin and the effect of improving the slidability of the polyethylene molecules are higher as the addition amount is larger.

The content of oil contained in the base material mainly composed of high-density polyethylene can be measured by, for example, infrared spectroscopic analysis. The increase or decrease in the crystalline region and the amorphous region in the substrate can be examined, for example, by using a Differential Scanning Calorimeter (DSC). In general polyethylene, the amount of heat generation due to the melting of crystals due to the deterioration of the resin is greatly reduced. However, when an oil containing cycloalkane or an oil containing aromatic hydrocarbon is blended as an additive, the calorific value of crystal melting hardly decreases.

The fusion-bond preventing film 3 is formed of a resin film containing a resin having a melting point of 150 ℃ or higher. According to the melt adhesion preventing film 3, when the outer layer 4 described later is resin-molded, the outer layer 4 is prevented from being directly melt-adhered to the gas barrier film 2, and heat transfer of the molten resin to the gas barrier film 2 can be prevented. Since it is possible to prevent a large tension from being applied to the gas barrier film 2 melt-bonded to another layer and the gas barrier film 2 itself from being melted, pinholes and cracks are less likely to be generated in the gas barrier film 2, and the gas barrier properties of the gas barrier film 2 can be satisfactorily ensured.

The fusion-bonding preventing film 3 is preferably formed of a polyethylene terephthalate stretched film, a polyimide film, or a polyamideimide film. The melting point of the stretched polyethylene terephthalate or polyamideimide is 150 ℃ or higher. In addition, the polyimide does not melt until it is thermally decomposed at a temperature higher than 150 ℃ (about 500 ℃). Therefore, according to these resins, the melt adhesion preventing film 3 itself is not melted at the melting temperature at the time of resin molding into the outer layer 4, and the melt adhesion of the gas barrier film 2 and the heat transfer to the gas barrier film 2 can be reliably suppressed.

Further, the stretched polyethylene terephthalate, polyimide and polyamideimide have an aromatic ring, have high radiation resistance, and are less likely to change physical properties even at a high radiation dose. Therefore, when the resin is molded into the outer layer 4, the gas barrier properties of the gas barrier film 2 are satisfactorily ensured by suppressing melt adhesion and heat transfer, and the inner layer 1 and the gas barrier film 2 can be protected from radiation, impact, external pressure, and the like after the production of the high-density polyethylene pipe 10.

The total thickness of the fusion-bond preventing film 3 when wound around the outer periphery of the gas barrier film 2 is preferably 10 μm or more, more preferably 20 μm or more, and still more preferably 50 μm or more. Further, it is preferably 300 μm or less, more preferably 200 μm or less, and further preferably 150 μm or less. When the total thickness is 10 μm or more, the thicker the film, the more the fusion bonding and heat transfer are suppressed, and the gas barrier property of the gas barrier film 2 can be ensured satisfactorily. In addition, when the total thickness is 20 μm or more and 200 μm or less, particularly high radiation resistance can be obtained by the neutron shielding ability of the resin itself. On the other hand, when the total thickness is 300 μm or less, the thinner the thickness, the lower the material cost of the anti-fusion bonding film 3 and the labor for winding.

The outer layer 4 has a density of 0.910g/cm ³Above 0.930g/cm ³The following Low Density Polyethylene (LDPE) is used as the main component. The outer layer 4 can be provided by resin molding by extrusion molding, injection molding, or the like so as to cover the outer peripheral surface of the melt adhesion preventing film 3. Since low density polyethylene has high flexibility, impact resistance, moisture resistance, water resistance, chemical resistance, and the like, the outer layer 4 mainly composed of low density polyethylene can protect the inner layer 1, the gas barrier film 2, and the fusion-bonding preventive film 3 from impact, external pressure, damage, chemicals, water vapor, rain water, dew water, and the like.

A typical double tube has a structure in which a guide tube and a covering layer are fusion bonded and a resin matrix is continuous. Therefore, the impact and dynamic strain of the brittle fracture generated in the coating layer are easily transmitted to the conduit, and cause a cracking phenomenon such as stress cracking in the conduit. In particular, when the covering layer is high density polyethylene or medium density polyethylene, the impact and dynamic strain transmitted to the catheter become large as compared with low density polyethylene having high flexibility.

In contrast, in the high-density polyethylene pipe 10, the gas barrier film 2 and the fusion-bonding preventing film 3 are provided between the guide pipe (inner layer 1) and the protective layer (outer layer 4), and the protective layer (outer layer 4) contains low-density polyethylene as a main component. Therefore, the gas barrier film 2 and the fusion-bonding preventing film 3 can prevent the impact, the propagation of dynamic strain, and the development of cracks from the outer layer 4 to the inner layer 1. Further, since the outer layer 4 contains low-density polyethylene as a main component, it can be easily joined to a joint by electrofusion or the like.

The outer layer 4 preferably contains carbon black as an additive. As the carbon black, for example, furnace black, channel black, acetylene black, pyrolytic carbon black, and the like can be used. When carbon black is blended, ultraviolet rays are absorbed, and therefore, deterioration of ultraviolet rays in the outer layer 4 and the inner layer 1 can be suppressed. That is, since the high density polyethylene pipe 10 itself has improved weather resistance, the fluid transport can be maintained well even outdoors or the like under a high radiation dose.

The content of carbon black in each outer layer 4 is preferably 1.0% by mass or more, more preferably 1.5% by mass or more. Further, it is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, and further preferably 2.5% by mass or less. When the content is 1.0 mass% or more, the greater the content, the higher the ultraviolet ray absorbing effect can be obtained, and therefore the weather resistance of the high density polyethylene pipe 10 can be sufficiently improved. When the content is 4.0% by mass or less, a large amount of carbon black is less likely to cause aggregates in the resin when the content is small. Therefore, the agglomerated masses can be prevented from becoming the starting points of environmental stress cracks or brittle fractures.

The thickness of the outer layer 4 is preferably 0.4mm or more, more preferably 0.5mm or more, and further preferably 0.8mm or more. Further, it is preferably 4mm or less, more preferably 3mm or less, and further preferably 2mm or less. When the thickness is 0.4mm or more, the protective performance of the outer layer 4 can be improved as the thickness is increased. When the thickness is 0.5mm or more and 3mm or less, particularly high radiation resistance is obtained by the neutron shielding ability of the resin itself. On the other hand, when the thickness is 4mm or less, the material cost of the outer layer 4 can be reduced as the thickness is thinner.

Next, a method for producing the high-density polyethylene pipe will be described.

The guide tube (inner layer 1) and the protective layer (outer layer 4) of the high-density polyethylene tube can be manufactured by the following method: polyethylene prepared as pellets or the like is heated and melted, and if necessary, additives such as oil and carbon black are added and kneaded, and the obtained polyethylene resin composition is used as a material for extrusion molding, injection molding, and the like.

In the production of the polyethylene resin composition and the production of the high-density polyethylene pipe, the additives may be dry blended or may be directly mixed with the resin. However, if the kneading of the solid additive such as carbon black is insufficient, the solid additive is coagulated to become a starting point of the fracture. Therefore, the additives are preferably prepared in advance as a master batch and then mixed, and particularly preferably prepared as a master batch in a state of being mixed with oil and then mixed.

For example, in the production of a polyethylene resin composition, when an additive is dry-blended, master batch pellets prepared by blending the additive and polyethylene resin pellets are put into a hopper of a pellet production apparatus and melt-kneaded. Then, the kneaded molten resin composition is extruded into water through a stainless steel disc having a plurality of holes (for example, a diameter of about 3mm) formed therein, and cut into a predetermined length (for example, a length of about 3mm) by a knife provided in parallel with the disc surface, whereby polyethylene resin composition pellets containing an additive can be obtained.

Alternatively, in the production of the polyethylene resin composition, the oil blended as the additive may be separately and directly mixed into the molten resin composition during melt kneading. For example, the master batch pellets and the polyethylene resin pellets are put into a hopper of a pellet production apparatus together, and at the same time, oil is dropped at a constant dropping rate using a micro-tube pump or the like, and they are melt-kneaded. Then, the kneaded molten resin composition is extruded in water and cut into a predetermined length, whereby polyethylene resin composition pellets containing an additive can be obtained.

In the production of the high-density polyethylene pipe, only the polyethylene resin composition pellets containing the additive may be used as the material, or the master batch pellets and the polyethylene resin pellets may be used as the material. For example, the catheter (inner layer 1) can be produced by feeding these pellets to a hopper of an extruder (tube production apparatus), heating and melting the pellets in the extruder, extruding the pellets in a cylindrical shape from a die, sizing the pellets as needed while taking out the pellets by a take-out machine, and cooling the pellets by introducing the pellets into a cooling water tank or the like.

As the kneader, various kneaders such as a batch kneader such as a Banbury mixer, a twin-screw kneader, a rotor type twin-screw kneader, and a Busco kneader can be used. As the extruder, for example, a single screw extruder, a twin screw extruder, or the like can be used. The mold may be any of a straight head mold, a crosshead mold, an offset (offset) mold, and the like. The sizing may be performed by any of a sizing plate method, an outer mandrel method, a size box method, an inner mandrel method, and the like.

The kneading temperature of the polyethylene is preferably 120 ℃ to 250 ℃. In the case of using a Banbury mixer, a molten resin composition is obtained by kneading at 180 ℃ for 10 minutes or the like, for example. The polyethylene resin composition may contain titanium oxide in an amount of 0.1 to 5 parts by mass per 100 parts by mass of polyethylene.

The gas barrier film 2 and the anti-fusion bonding film 3 may be film-formed by a suitable method such as coating forming. The multilayer film used as the gas barrier film 2 may be formed by a suitable method such as a coextrusion method or a lamination method. The multilayer film may be formed by any one of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film. The multilayer film is preferably formed by biaxially stretching a film from the viewpoint of obtaining high strength and excellent gas barrier properties.

The gas barrier film 2 may be wound around the outer circumference so as to cover the outer surface of the resin-molded duct (inner layer 1). The resin-molded inner layer 1 is preferably cooled in advance to a temperature at least not causing hot-melt adhesion by water cooling or air cooling before being wound with the gas barrier film 2. The winding method of the gas barrier film 2 may be any one of one-turn winding, multiple-turn winding, and spiral winding. Among them, a winding system having an arbitrary overlapping width is preferably provided from the viewpoint of reliably exhibiting gas barrier properties. For example, it is preferable to provide multi-turn winding or spiral winding having an overlapping width of 1/2 or more of the film width.

The fusion-bonding preventing film 3 may be wound around the outer circumference so as to cover the outer surface of the gas barrier film 2 wound around the pipe (inner layer 1). The winding form of the fusion-bonding preventing film 3 may be any one of one-turn winding, multiple-turn winding, and spiral winding. Among them, in the case of resin molding the outer layer 4, a winding system having an arbitrary overlapping width is preferably provided from the viewpoint of suppressing direct melt adhesion of the outer layer 4 to the gas barrier film 2 and suppressing heat transfer of the molten resin to the gas barrier film 2. For example, it is preferable to provide multi-turn winding or spiral winding having an overlapping width of 1/2 or more of the film width.

The protective layer (outer layer 4) can be formed by: the pipe (inner layer 1) around which the gas barrier film 2 and the melt adhesion preventing film 3 are wound is supplied to a jacket (sheath) extrusion molding apparatus as a core wire, and the polyethylene resin composition for the protective layer is extrusion molded on the outer periphery of the supplied core wire. The high-density polyethylene pipe 10 can be produced by heating and melting the polyethylene resin composition in a sheath extrusion molding device, covering the outer periphery of the core wire, extruding the composition from a die, sizing the composition as needed while taking out the composition with a take-out machine, and cooling the composition in a cooling water tank or the like.

Next, the joint and the sealing material made of high density polyethylene will be described.

The joint of the present embodiment has the same layer structure as the high density polyethylene pipe 10. Specifically, the joint of the present embodiment includes: the gas barrier film comprises a cylindrical inner layer 1 through which fluid flows, a gas barrier film 2 covering the outer surface of the inner layer 1, an anti-melt-bonding film 3 covering the outer surface of the gas barrier film 2, and an outer layer 4 covering the outer surface of the anti-melt-bonding film 3.

The size, shape, connection method, and the like of the joint of the present embodiment are not particularly limited. The connection method may be any of mechanical, electrofusion, screw, and the like. The joint of the present embodiment may have a flange, a nut, a bracket, a sealing material, and the like as long as the body portion has a layer structure including the inner layer 1, the gas barrier film 2, the melt adhesion preventing film 3, and the outer layer 4, as in the high density polyethylene pipe 10.

The joint of the present embodiment can be produced by the following method, for example, in the same manner as the high density polyethylene pipe 10 described above: after extrusion molding of the body (inner layer 1), winding of the gas barrier film 2 and the melt adhesion preventing film 3, and the like are performed using the polyethylene resin composition as a material, secondary processing is performed on the molded body up to the formation of the protective layer (outer layer 4).

The sealing material of the present embodiment has the same layer structure as the high-density polyethylene pipe 10. Specifically, the sealing material of the present embodiment includes: an inner layer 1 in contact with a fluid, a gas barrier film 2 covering an outer surface of the inner layer 1, an anti-melt adhesive film 3 covering an outer surface of the gas barrier film 2, and an outer layer 4 covering an outer surface of the anti-melt adhesive film 3.

As polyethylene used for the sealing material, ultra-high molecular weight polyethylene having a molecular weight of about 100 to about 700 ten thousand can be preferably used. Specifically, a resin having a melt index of less than 0.1g/10 min at a test temperature of 190 ℃ and a test load of 21.6kgf, which is determined in accordance with ISO1133, can be used. However, the polyethylene used for the sealing material is not limited to resins exhibiting such physical properties. In the case of using ultra-high molecular weight polyethylene, the inner layer 1 does not have to be high density polyethylene.

The sealing material of the present embodiment may be in the form of a gasket such as a flange gasket (flange packing) or a circular ring, and the size, shape, and the like are not particularly limited. The sealing material is constituted by a layer having the inner layer 1, the gas barrier film 2, the anti-fusion bonding film 3, and the outer layer 4, at least a part of a region between a surface in contact with the fluid and a surface exposed to the outside air or ultraviolet rays, as in the high-density polyethylene pipe 10 described above, and the entire surface of the sealing material does not necessarily need to be covered with the gas barrier film 2, the anti-fusion bonding film 3, or the outer layer 4.

The joint and the sealing material of the present embodiment are produced by, for example, the following methods in the same manner as the high density polyethylene pipe 10: the polyethylene resin composition is used as a material, and after injection molding of the base (inner layer 1), winding and sticking of a film, and the like, a protective layer (outer layer 4) is formed on the outside thereof.

According to the high-density polyethylene pipe, the joint, and the sealing material of the present embodiment described above, the inner layer is covered with the gas barrier film, and therefore, oxidative degradation of the inner layer resin due to oxygen in the outside air can be suppressed. Therefore, even when the high-density polyethylene pipe, joint, or sealing material is exposed to high radiation dose radiation, oxygen in the atmosphere, strong ultraviolet rays such as outdoors in summer, acid rain, or the like for a long time, or is in contact with a fluid containing a radioactive substance at a high concentration or a high radiation dose, a high-temperature fluid, or the like for a long time, the propagation reaction of oxidation is suppressed, and deterioration of the resin in the inner layer due to external factors such as radiation, ultraviolet rays, oxygen, and heat is greatly suppressed.

In addition, according to the high-density polyethylene pipe, joint, and sealing material of the present embodiment, since the gas barrier film is covered with the outer layer, when earth pressure, impact, load, or the like is applied from the outside, it is possible to suppress deterioration of the gas barrier film itself and the inner layer due to radiation and ultraviolet rays while preventing damage to the gas barrier film. Further, since the fusion-bonding preventing film is provided between the gas barrier film and the outer layer, the outer layer can be formed by resin molding using a molten resin on the outside of the gas barrier film, and in this case, the soundness of the gas barrier film can be ensured. Unlike the case where the protective tape is wound on the outermost surface, the outer layer of the resin molding is less likely to have gaps and holes and is less likely to peel off, and therefore, the resistance to external factors that degrade the resin can be improved.

Therefore, when fluid pressure, earth pressure, impact, load, or the like is applied to the high-density polyethylene pipe, joint, or sealing material, environmental stress cracking or creep rupture is less likely to occur, and cracking, brittle cracking, or the like, and cracking of the pipe or joint are prevented. That is, the intrinsic defect of polyethylene, which easily causes brittle fracture cracking, can be fundamentally improved. Even if minute defects invisible to the naked eye are present, brittle fracture and stress cracking are less likely to occur due to stress concentration thereon, and sufficient elongation and elasticity can be obtained, so that stress environment cracking resistance and impact resistance can be improved.

In particular, high density polyethylene pipes, joints, and sealing materials with reduced brittle fracture and creep fracture due to resin deterioration can be obtained not only in normal environments but also in various severe environments such as high-dose irradiation environments, ultraviolet environments such as outdoor environments in summer, high-temperature environments such as summer, and environments exposed to high concentrations of oxygen and acid rain. Further, a high-density polyethylene pipe, a joint, and a sealing material which are less likely to deteriorate in long-term hydrostatic strength, elasticity, environmental stress cracking resistance, impact resistance, and the like, and are less likely to cause brittle fracture cracking and cracking can be obtained.

The use of the high-density polyethylene pipe, the joint, and the sealing material according to the present embodiment is not particularly limited. The high-density polyethylene pipe, joint, and sealing material can be used in a suitable environment. In addition, high density polyethylene pipes and joints are used for the transport of suitable fluids such as water, seawater, and the like. The sealing material can be used for sealing a suitable fluid during storage, transportation, handling, and the like of the fluid.

In particular, high density polyethylene pipes and joints are used for the transport of fluids such as water, seawater, etc. in nuclear power related facilities. In the nuclear energy-related facility, tens to hundreds of nuclear energy facilities are surrounded by pipes and connected to a plurality of contaminated water retention zones. The total length of these pipes is generally from about 10km to about 20 km. The high-density polyethylene pipe and the joint can be suitably used for such a nuclear facility pipe. According to the high-density polyethylene pipe and the joint, it is possible to transport a fluid containing a radioactive substance, and to transport a fluid at a high radiation dose or outdoors, robustly and reliably for a long period of time.

The sealing material is effective for sealing a fluid in a nuclear power-related facility, a nuclear fuel facility, or the like, and is suitably used as a sealing material for a nuclear power facility pipe, a nuclear fuel facility pipe, a radioactive substance storage container, or the like. The sealing material can be particularly suitable for sealing a fluid containing a high concentration of radioactive substances and sealing a fluid at a high radiation dose.

According to the high-density polyethylene pipe, the joint, and the sealing material of the present embodiment, deterioration of the resin is greatly suppressed, and therefore, even at a high radiation dose at which radicals are likely to be generated, it is possible to reliably prevent occurrence of a leakage event while maintaining soundness of the resin molded body. When a fluid containing a high concentration of radioactive substance is treated, the fluid can be used for a long period of time, and the frequency of replacement and inspection can be reduced, so that the number of steps and materials for laying and installation, the risk of exposure of constructors and inspectors, and the like can be greatly reduced.

While the embodiments of the high density polyethylene pipe, joint, and sealing material of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications may be made without departing from the technical scope. For example, the above-described embodiments are not necessarily limited to the embodiments having all the configurations described above. Further, a part of the configuration of the embodiment may be replaced with another configuration, or another configuration may be added to the configuration of the embodiment. Further, as for a part of the configuration of the embodiment, addition of other configurations, deletion of the configuration, and replacement of the configuration may be performed.

For example, the high-density polyethylene pipe, the joint, and the sealing material are configured to include the inner layer 1, the gas barrier film 2, the fusion-bonding preventing film 3, and the outer layer 4 in this order, but functional layers such as a buffer layer for buffering impact may be provided between the inner layer 1 and the gas barrier film 2, and between the gas barrier film 2 and the fusion-bonding preventing film 3. The buffer layer may be formed, for example, by coating the buffer layer with a density of less than 0.940g/cm ³The resin molded article containing polyethylene as a main component, or other films or tapes.