CN111497352B

CN111497352B - High density polyethylene pipe and joint

Info

Publication number: CN111497352B
Application number: CN202010006814.1A
Authority: CN
Inventors: 本棒享子; 永田纯也; 寺尾圭论
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2019-01-30
Filing date: 2020-01-03
Publication date: 2022-02-08
Anticipated expiration: 2040-01-03
Also published as: KR102286902B1; JP2020121444A; JP7186103B2; CN111497352A; KR20200094625A

Abstract

The invention provides a high density polyethylene pipe and a joint, which can inhibit deterioration caused by external factors such as radioactive rays, oxygen, ultraviolet rays and the like and chemical cracks caused by chemical substances. The high-density polyethylene pipe (10) and the joint of the present invention are provided with: a catheter (1) which will have a density of 0.940g/cm³Above 0.980g/cm³The following high density polyethylene as a main component; an inner gas barrier film (2a) which covers the inner surface of the conduit (1) and contains an ethylene-vinyl alcohol copolymer resin; an outer gas barrier film (2b) which covers the outer surface of the guide tube (1) and contains an ethylene-vinyl alcohol copolymer resin; a heat-resistant adhesive film (3b) which covers the outer surface of the outer gas barrier film (2b) and is formed from a resin having a melting point of 150 ℃ or higher; and an outer layer (4b) which covers the outer surface of the heat-shielding adhesive film (3b) and has a density of 0.910g/cm³Above 0.930g/cm³The following low-density polyethylene was used as a main component.

Description

High density polyethylene pipe and joint

Technical Field

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

Background

A pipeline for nuclear power facilities installed in a nuclear power facility is required to be capable of safely carrying out the transport of a fluid containing a radioactive substance and the transport of a fluid under a high radiation dose for a long period of time. Conventionally, steel pipes have been used as pipelines for nuclear power plants. However, in nuclear facilities where space limitation and time limitation are anticipated, steel pipes cannot be said to be optimal because of the large number of man-hours, machines, and materials required for construction. Under such circumstances, replacement with resin pipes is promoted, which are easy to move and process, and which facilitate joining of pipes and joints.

As a resin pipe, use of a high-density polyethylene pipe which is also used as a long-distance pipe for a water pipe has been studied. However, the high density polyethylene pipe has a disadvantage that it is inferior in radiation resistance to the steel pipe and is liable to be broken by a high radiation dose. If the high-density polyethylene pipe deteriorates and a minute defect occurs in the resin, stress is concentrated on the defect portion when pressure from a fluid inside the pipe, soil pressure from the outside of the pipe, or the like is applied, and cracking or breakage occurs.

In addition, at high radiation doses, water flowing within the conduit undergoes radiolysis. If water is decomposed by radiation, hydrogen and hydrogen peroxide are mainly produced, but oxygen is also produced. The high-density polyethylene pipe may be exposed to oxygen remaining in the gas phase portion of the pipe or oxygen dissolved in the fluid in the pipe. When chlorine or the like is present in the fluid in the pipe, chemical substances exhibiting high activity, such as hypochlorous acid and perchloric acid, may be generated.

The deterioration of high density polyethylene is mainly caused by autoxidation due to radicals, and is promoted not only by the action of radiation but also by ultraviolet rays and oxygen. Ultraviolet rays and oxygen present in the atmosphere deteriorate high-density polyethylene mainly from the outside of the pipe. On the other hand, oxygen generated in the pipe due to the radioactive decomposition of water deteriorates the high density polyethylene mainly from the inside of the pipe. Further, the chemical substances present in the pipe cause chemical cracks that cause minute defects in the resin.

In the case where the fluid to be transported by the high-density polyethylene pipe contains radioactive substances or is likely to be activated, it is important to prevent the leakage phenomenon from occurring. Therefore, measures for preventing deterioration due to external factors such as radiation, oxygen, and ultraviolet rays, and chemical substances such as hydrogen peroxide, hypochlorous acid, and perchloric acid are required.

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

Patent document 2 describes a joint that can be thermally bonded to the outer surface of a high-density polyethylene pipe, and a fluid transfer device provided with the joint. In the high-density polyethylene pipe, tie molecules connecting the crystal structures, which are likely to become starting points of breakage, are reinforced by a crosslinked structure. Further, the outer surface of the high density polyethylene pipe is formed with a non-crosslinked polyethylene layer capable of thermal bonding.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-020628

Patent document 2: japanese patent laid-open publication No. 2017-101688

Disclosure of Invention

Problems to be solved by the invention

Radiation resistance of the high-density polyethylene pipe can be improved by adding a deterioration preventing agent to the high-density polyethylene as in patent document 1 or by reinforcing tie molecules with a crosslinked structure as in patent document 2. Further, if the high density polyethylene pipe has a double pipe structure, ultraviolet rays and oxygen in the atmosphere hardly reach the inside, and therefore, the pipe can be kept sound for a certain period of time even outdoors or the like under a high radiation dose.

However, these high-density polyethylene pipes cannot be said to have sufficient durability if compared with steel pipes that have a durability life of 40 years or longer and do not need to be replaced in a short period of time. High density polyethylene exhibits the compressive strength and hardness required for pipes, but on the other hand, has the essential disadvantage of being less ductile and susceptible to brittle failure 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 countermeasures for preventing them are required.

Further, in the case where oxygen or a chemical substance is generated in the pipe by radiation at a high radiation dose, or in the case where a fluid containing oxygen, a chemical substance, or the like at a high concentration flows in the pipe, oxidative deterioration or chemical cracking occurs from the inside of the pipe, and therefore measures against oxygen or a chemical substance existing in the pipe are also indispensable. In addition, even in the case of a pipe joint made of high density polyethylene, it may be exposed to external factors and chemicals such as radiation, oxygen, and ultraviolet rays, and measures for the same are also required.

Accordingly, an object of the present invention is to provide a high-density polyethylene pipe and a joint, which can suppress deterioration due to external factors such as radiation, oxygen, and ultraviolet rays, and chemical cracking due to chemical substances.

In order to solve the above problems, a high density polyethylene pipe according to the present invention includes: a conduit which will have a density of 0.940g/cm³Above 0.980g/cm³The following high density polyethylene as a main component; an inner gas barrier film covering an inner surface of the duct and containing an ethylene-vinyl alcohol copolymer resin; an outer gas barrier film covering an outer surface of the duct and containing an ethylene-vinyl alcohol copolymer resin; a heat-resistant adhesive film which covers the outer surface of the outer gas barrier film and is formed of a resin having a melting point of 150 ℃ or higher; and an outer layer covering the outer surface of the heat-shielding adhesive film and having a density of 0.910g/cm³Above 0.930g/cm³The following low-density polyethylene was used as a main component.

The joint according to the present invention has the same layer structure as the high density polyethylene pipe.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a high-density polyethylene pipe and a joint that can suppress deterioration due to external factors such as radiation, oxygen, and ultraviolet rays, and chemical cracking due to chemical substances.

Drawings

Fig. 1 is a cross-sectional view schematically showing an example of the high-density polyethylene pipe according to the present invention.

Fig. 2 is a perspective view schematically showing an example of the high-density polyethylene pipe according to the present invention.

Fig. 3 is a cross-sectional view schematically showing an example of the high-density polyethylene pipe according to the present invention.

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

Fig. 4B is a graph showing the relationship between% CN of the oil used as the additive and the elongation at break.

Fig. 5A is a graph showing the relationship between% CA of oil used as an additive and elongation at break.

Fig. 5B is a graph showing the relationship between% CA of the oil used as the additive and the elongation at break.

Fig. 6A is a graph showing the relationship between MFR and elongation at break of linear low density polyethylene used for a gas barrier film.

Fig. 6B is a graph showing the relationship between the MFR of the linear low density polyethylene used for the gas barrier film and the elongation at break.

Fig. 7A is a graph showing the relationship between the total thickness of the gas barrier film and the elongation at break.

Fig. 7B is a graph showing the relationship between the total thickness of the gas barrier film and the elongation at break.

Fig. 8A is a graph showing the relationship between the thickness of the ethylene-vinyl alcohol copolymer resin used for the gas barrier film and the elongation at break.

Fig. 8B is a graph showing the relationship between the thickness of the ethylene-vinyl alcohol copolymer resin used for the gas barrier film and the elongation at break.

Fig. 9A is a graph showing a relationship between the thickness of the heat-shielding adhesive film and the elongation at break.

Fig. 9B is a graph showing the relationship between the thickness of the heat-shielding adhesive film and the elongation at break.

Fig. 10A is a graph showing the relationship between the thickness of the outer layer and the elongation at break.

Fig. 10B is a graph showing the relationship between the thickness of the outer layer and the elongation at break.

Description of the symbols

1: catheter, catheter portion, 2: gas barrier film, 3: heat-protective mucosa, 4 a: inner layer, 4 b: outer layer, 10: high density polyethylene pipe, 21: intermediate layer, 22: a surface layer.

Detailed Description

Hereinafter, a high-density polyethylene pipe and a joint according to an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same reference numerals are used for the components having the same main functions, and redundant description thereof is omitted.

Fig. 1 is a cross-sectional view schematically showing an example of the high-density polyethylene pipe according to the present invention. Fig. 2 is a perspective view schematically showing an example of the high-density polyethylene pipe according to 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 according to the present embodiment includes: a tubular duct 1 forming a fluid passage, an inner gas barrier film 2a covering the inner surface of the duct 1, an outer gas barrier film 2b covering the outer surface of the duct 1, an outer heat-shielding adhesive film 3b covering the outer surface of the outer gas barrier film 2b, and an outer layer 4b covering the outer surface of the outer heat-shielding adhesive film 3 b.

The high-density polyethylene tube 10 further includes an inner layer 4a covering the inner surface of the inner gas barrier film 2a inside the guide tube 1. The high-density polyethylene tube 10 further includes an inner heat-shielding adhesive film 3a between the guide tube 1 and the inner gas barrier film 2 a. In the present specification, when a layer is referred to as "covering an inner surface or an outer surface of another layer", the layers may be adjacent to each other to cover one surface, and the layers may cover one surface with the other layer interposed therebetween.

The high-density polyethylene pipe 10 is mainly used as a fluid transport pipe for transporting fluid between devices and facilities. The high density polyethylene pipe 10 has excellent radiation resistance, and can suppress deterioration of the catheter 1 due to external factors such as radiation, oxygen in the atmosphere, ultraviolet rays, oxygen generated in the fluid in the pipe by radiation, chemical substances such as hydrogen peroxide, hypochlorous acid, perchloric acid, etc., generated in the fluid in the pipe by radiation, etc., and chemical substances such as chemicals flowing in the pipe. Therefore, the high-density polyethylene tube 10 is suitable for transporting a fluid containing a radioactive substance at a high concentration, transporting a fluid at a high radiation dose, and particularly transporting a fluid containing oxygen or a chemical substance at a high concentration.

In order to fundamentally improve the essential disadvantage of high-density polyethylene, which is easily brittle and breakable when used continuously at a high radiation dose, the high-density polyethylene pipe 10 is a coated pipe in which both the inner and outer surfaces of a conduit 1 through which a fluid flows are covered with gas barrier films 2(2a, 2 b). In order to avoid breakage of the gas barrier film 2 during resin molding, the gas barrier film is configured as a layer in which heat-resistant adhesive films 3(3a, 3b) are sandwiched between the gas barrier film 2 on both the inner and outer sides and the outer layers (the duct 1, the outer layer 4 b).

The catheter 1 will have a density of 0.940g/cm³Above 0.980g/cm³The following High Density Polyethylene (HDPE) was formed as a main component. Since the high-density polyethylene has high tensile strength and impact resistance, but has low brittleness, the pipe 1 containing the high-density polyethylene of the present invention as a main component can obtain compressive strength and hardness required for pipes.

The high-density polyethylene may contain 1-butene, 1-hexene, and the like as monomers other than ethylene, as long as the physical properties such as density are not impaired. The density of the high-density polyethylene is preferably 0.940g/cm³Above 0.970g/cm³Hereinafter, more preferably 0.945g/cm³Above 0.965g/cm³The following.

The high-density polyethylene can be polymerized by any catalyst such as a ziegler catalyst, a metallocene catalyst, or a phillips catalyst. The high-density polyethylene may be a mixed material obtained by blending it with another resin or a recycled material obtained by recycling a polyethylene product as a raw material. The high-density polyethylene may contain other resins such as polypropylene as long as the content is less than 50% by mass.

As the high-density polyethylene, for example, a polyethylene having a reaction pressure of 5kgf/cm can be used²Above 200kgf/cm²The resin obtained by polymerization at a reaction temperature of 60 ℃ to 100 ℃ is described below. Furthermore, a resin having a dissolution index (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 at a test temperature of 190 ℃ and a test load of 5.0kgf (49.03N) can be used. However, the high-density polyethylene constituting the catheter 1 is not limited to resins exhibiting such physical properties.

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

The conduit 1 preferably contains at least one of naphthenic oil and aromatic oil produced when crude oil is purified, with respect to a base material mainly composed of high-density polyethylene. When these oils are blended, the molecular sliding properties of the polyethylene are improved as described later, and the deterioration of the high-density polyethylene due to the craze (craze) failure can be suppressed.

As the oil containing naphthenes, naphthenic crude oil can be blended as a raw material, and the oil can be purified. For example, a product obtained by distilling naphthenic crude oil under reduced pressure and removing oil containing aromatic components by solvent extraction can be used. In addition to solvent extraction, purified oils subjected to adsorption treatment, clay treatment, deacidification treatment, and the like may be used. The term "cycloalkane" refers to a compound represented by the general formula: c_nH_2nCyclic hydrocarbons are shown.

As the aromatic hydrocarbon-containing oil, paraffin-based crude oil and naphthene-based crude oil can be blended as raw materials and refined to obtain oil. Example (b)For example, residual oil having a high specific gravity and a high viscosity, which is generated in the purification process of paraffinic crude oil or naphthenic crude oil, can be used. Further, the aromatic hydrocarbon means a compound represented by the general formula: c_nH_2n-6The aromatic hydrocarbon is an unsaturated and cyclic hydrocarbon having a conjugated double bond.

The oil containing naphthenes is preferably an oil having a% CN of 10% to 100%, more preferably 10% to 80%, and still more preferably 10% to 60% in a ring analysis obtained by an n-d-M method, among oils produced during the purification of naphthenic crude oil. When% CN is 10% or more and 60% or less, an excellent effect of suppressing deterioration of the high-density polyethylene can be obtained.

The aromatic hydrocarbon-containing oil is preferably an oil having a% CA of ring analysis obtained by the n-d-M method of 5% to 100%, more preferably 5% to 80%, and still more preferably 15% to 60% among oils produced in the refining of paraffinic crude oil and naphthenic crude oil. When the% CA is 5% to 80%, an excellent effect of suppressing deterioration of the high-density polyethylene can be obtained.

As the naphthenic-containing oil and aromatic-containing oil, for example, an oil having a% CN of ring analysis by n-d-M method of 20% to 60% and a% CA of ring analysis by n-d-M method of 5% to 40% among oils produced during crude oil purification can be used as an additive.

The n-D-M method is a method of structure-based analysis of oils (oils) according to ASTM D3238-85 (Ring analysis method), and is generally used for compositional analysis of base oils. From the n-d-M method, 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 (% CP) of paraffinic carbons to the total carbon amount, the mass ratio (% CN) of naphthenic carbons to the total carbon amount, the mass ratio (% CA) of aromatic carbons to the total carbon amount, the average Ring Number (RN) of naphthenic rings per molecule, and the average ring number (RA) of aromatic rings per molecule can be determined.

The gas barrier film 2 is preferably formed of a resin film containing at least an ethylene-vinyl alcohol copolymer resin (EVOH). The gas barrier film 2 can suppress diffusion and permeation of a gas or a chemical substance such as oxygen into the conduit 1, thereby suppressing oxidation degradation and chemical cracking of the conduit 1.

In general, the high density polyethylene has an oxygen transmission coefficient of 0.4X 10^-10cm³(STP)·cm/(cm²s.cmHg), and the oxygen permeability coefficient of low density polyethylene is 6.9X 10^-10cm³(STP)·cm/(cm²S cmHg). On the other hand, the ethylene-vinyl alcohol copolymer resin had a small oxygen permeability coefficient of 0.0001X 10^-10cm³(STP)·cm/(cm²S · 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 a single layer made of an ethylene-vinyl alcohol copolymer resin, or may be a multilayer including a layer made of an ethylene-vinyl alcohol copolymer resin. In the figure, the gas barrier film 2 includes an inner gas barrier film 2a and an outer gas barrier film 2b, but they may be formed of the same layer or different layers.

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 can be set to 500 or more and 3000 or less. The ethylene content can be, for example, 20% to 80%. From the viewpoint of improving flexibility and water resistance, the content of ethylene is preferably 25% or more. The saponification degree can be set to, for example, 85% to 99%. From the viewpoint of ensuring gas barrier properties, the degree of saponification 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. The thicker the ethylene-vinyl alcohol copolymer resin is, the more excellent the gas barrier properties can be obtained, and the more the oxidative deterioration and chemical cracking of the catheter 1 can be suppressed. Further, since pinholes (pinholes) are less likely to be generated, the gas barrier properties can be maintained well. On the other hand, since the gas barrier film 2 has flexibility as the thickness is smaller than or equal to 60 μm, the gas barrier film is less likely to be broken when the high-density polyethylene pipe 10 is constructed, moved, or the like. Further, if the thickness is 5 μm or more and 50 μm or less, effective radiation resistance can be obtained due to the neutron shielding ability of the resin itself.

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 21 made of an ethylene-vinyl alcohol copolymer resin and surface layers 22 laminated on both sides of the intermediate layer 21. In the figure, the surface layer 22 includes an inner layer 21a disposed on the inner side of the intermediate layer 21 and an outer layer 21b disposed on the outer side, but they may have the same layer configuration or different layer configurations, and the number and types of layers stacked on both the inner and outer sides are not particularly limited.

The surface layer 22 preferably contains at least one of Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE) as a main component. These polyethylenes can be coextruded with an ethylene-vinyl alcohol copolymer resin. Further, according to the polyethylene, since a high neutron shielding capability can be obtained from the resin itself, radiation deterioration of the catheter 1 can be further suppressed.

In particular, if the surface layer 22 is 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 accuracy. Further, external pressure, impact, and the like applied to the high-density polyethylene pipe 10 can be alleviated, and damage to the guide pipe 1, peeling, detachment, and the like of the gas barrier film 2 can be prevented. The low density polyethylene means a polyethylene having a density of0.910g/cm³Above 0.930g/cm³The following polyethylenes. In the low density polyethylene, 1-butene, 1-hexene, and the like can be contained as monomers other than ethylene.

Further, if the surface layer 22 is formed of linear low-density polyethylene, higher tensile strength at break, adhesiveness, cold resistance, and the like can be obtained than low-density polyethylene. The linear low-density polyethylene means a polyethylene having a density of 0.910g/cm³Above 0.925g/cm³Hereinafter, the polyethylene having a content of the monomer having a branch chain of several percent. The linear low-density polyethylene may contain, as a monomer, 1-butene, 1-hexene, 1-octene, and the like in addition to ethylene. The linear low-density polyethylene can be polymerized by any catalyst such as a ziegler catalyst and a phillips catalyst.

The dissolution index (MFR) of the low-density polyethylene or linear low-density polyethylene forming the surface layer 22, which is determined in accordance with ISO1133, is preferably 0.5g/10 min or more. Further, it is preferably 50g/10 min or less, more preferably 20g/10 min or less, further preferably 10g/10 min or less, further preferably 5g/10 min or less, and particularly preferably 3g/10 min or less. It is known that the molecular weight of a resin has a correlation with MFR. The resin exhibiting such MFR can form a resin layer containing a small amount of low-molecular-weight components.

The surface layer 22 may be formed by laminating another resin in addition to the layer made of low-density polyethylene and the layer made of linear low-density polyethylene. For example, from the viewpoint of toughening the multilayer film, from the viewpoint of use as a base material for forming the intermediate layer 21, and the like, a layer structure including polyamide (polyamide: PA) such as nylon 6, and polyester (polyester: PEs) such as polyethylene terephthalate can be used.

Specific examples of the multilayer film include, but are not limited to, LDPE/EVOH/LDPE, LLDPE/EVOH/LLDPE, and the like. In addition, from the viewpoint of improving radiation resistance, the low-density polyethylene and the linear low-density polyethylene preferably do not contain a low-molecular-weight component that affects the density of the resin and the like. Between the intermediate layer 21 and the surface layer 22, 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. Since the durability is improved as the thickness is 20 μm or more and the thickness is increased, the gas barrier property can be maintained satisfactorily when the high-density polyethylene pipe 10 is installed in a severe environment such as outdoors where it is likely to be subjected to an external force, for example, during construction, movement, or the like. Further, the thinner the thickness is 200 μm or less, the more difficult the flexibility is lost, so that the workability and windability are good, and the breakage of the film during handling is reduced.

The total thickness of the gas barrier film 2 when wound into a tube shape 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. Since the higher the total thickness is 20 μm or more, the higher the gas barrier properties can be obtained, the oxidative deterioration and chemical cracking of the conduit 1 can be reliably suppressed. On the other hand, the thinner the total thickness is 500 μm or less, the lower the material cost, the time and labor for winding. Further, if the total thickness is 50 μm or more and 400 μm or less, effective radiation resistance can be obtained.

The gas barrier film 2 is preferably not surface-bonded to the duct 1 by thermal bonding. When the duct 1 and the gas barrier film 2 are surface-bonded by thermal adhesion, stress in opposite directions is generated in the duct 1 and the gas barrier film 2 having different elongations when force is applied in the longitudinal direction and the radial direction of the duct, and therefore, the probability of occurrence of stress fracture, tearing, or the like increases. Similarly to the guide tube 1, the gas barrier film 2 may contain naphthenic oil or aromatic oil.

The effects of the oil and gas barrier film added to the high-density polyethylene pipe will be specifically described.

Polyethylene pipes are lightweight compared to steel pipes, and are easy to move and process, and therefore are widely used as long-distance pipes for water pipes. However, unlike steel pipes, polyethylene pipes are mainly formed of organic polymers composed of carbon and hydrogen. Polyethylene is deteriorated by external factors such as radiation, ultraviolet rays, and heat, and the elasticity, stress environment cracking resistance, impact resistance, and the like are reduced, so that brittle fracture is likely to occur when internal pressure, external pressure, impact, and the like are applied to a pipe, the pipe is damaged, or the pipe is exposed to chemical substances.

It is known that organic polymers are decomposed by breaking bonds in molecules of the organic polymers as the molecules are excited by radiation, ultraviolet rays, heat, and the like. 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 abstract elements to generate other radicals (abstraction reaction), or the radicals are added to a double bond (addition reaction), or the radicals are bonded to each other and a molecular chain is cut (imbalance reaction).

The recombination or addition reaction by radicals causes an increase in molecular weight called crosslinking, and the imbalance reaction causes a decrease in molecular weight called collapse. In a polyethylene pipe, if the molecular chains are crosslinked or collapsed, the resistance to impact or bending is reduced, and the pipe body becomes brittle, which causes a change in physical properties. Further, if embrittlement of the pipe body progresses, stress failure such as cracking or splitting or creep failure is likely to occur when internal pressure, external pressure, impact, load, or the like is applied, and a problem such as cracking or brittle splitting of the pipe wall or breakage of the pipe body occurs.

As a piping material for polyethylene pipes for water supply, high-density polyethylene having been subjected to multistage polymerization and improved in catalyst performance has been used. For such high density polyethylene, by increasing the region of high molecular weight, tie molecules connecting the crystal structures to each other are increased, thereby improving long-term hydrostatic strength and environmental stress crack resistance.

In general, it is known that a crystalline region is hardly affected even under a severe environment, but an amorphous region increases if tie molecules are cut under a severe environment. When the tie molecules are cut, stress concentration is likely to occur in the resin when external force is applied, and it is considered that the long-term hydrostatic strength, the environmental stress cracking resistance, and the impact resistance are reduced.

In particular, it is known that oxidation proceeds by radicals in the atmosphere in which oxygen is presentPropagation reactions (chain reactions). In addition, when oxygen is present in the pipe, not only the outside of the pipe in contact with the atmosphere but also the inside of the pipe undergo a propagation reaction of oxidation. First, as shown in reaction formula (1), a hydrocarbon radical (R.cndot.) and oxygen (O)₂) The reaction takes place to form peroxidic free radicals (ROO.).

R·+O₂→ROO····(1)

The peroxygen radical (ROO. cndot.) is rich in reactivity, and as in equation (2), hydrogen (H) is abstracted from other molecules (RH), and generates a new hydrocarbon radical (R. cndot.) with the peroxide (ROOH).

ROO·+RH→ROOH+R····(2)

The newly formed hydrocarbon radical (R.cndot.) generates another peroxidized radical (ROO.cndot.) according to the reaction formula (1), and the peroxidized radical (ROO.cndot.) generates another peroxide (ROOH) according to the reaction formula (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.

ROOH→RO·+·OH···(3)

2ROOH→ROO·+RO·+H₂O···(4)

RO·+RH→ROH+R····(5)

In the atmosphere in which oxygen is present or in the pipe in which oxygen is present, the initially generated hydrocarbon radicals (R ·) propagate a large amount of new radicals by such an oxidation propagation reaction, and crosslinking and collapse of the molecular chain proceed. Therefore, deterioration of the resin progresses at an accelerated rate, and stress failure and creep failure are likely to occur.

In addition, ozone may be generated by radiation or ultraviolet rays in the atmosphere in which oxygen exists or in the duct 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 cleaved to produce aldehydes, ketones, esters, lactones, peroxides, and the like. It is known that the decomposition of molecules caused by such a reaction forms minute cracks (ozone cracks) in the resin.

In particular, when a polyethylene pipe is subjected to a fluid pressure of about 1MPa or more, a soil pressure, or the like, molecular chains tend to be stretched, and therefore, the permeability of ozone is improved and stress tends to concentrate on a specific site. In such a case, the possibility of occurrence of ozone cracks and the possibility of destruction starting from ozone cracks are increased.

In addition, hydrogen peroxide and oxygen may be generated by radioactive decomposition of water in a pipe through which water such as contaminated water and drainage flows. When chlorine ions or the like are present in the pipe, hydrogen peroxide generates hypochlorous acid, perchloric acid, or the like. These chemical substances diffuse and permeate into the matrix of the resin, and when fluid pressure or the like is applied to the resin, they act in synergy with stress to cause chemical cracking. If the inner surface of the pipe is chemically cracked, the possibility of cracking or breaking from the inside of the pipe is increased.

Further, polyethylene pipes are sometimes used for the transport of high-temperature fluids. The various elementary reactions that bring about the decomposition of the molecule are also related to the molecular motion, i.e., the vibration and collision probability of the molecule. Since molecular motion is more vigorous at higher temperatures, if polyethylene is exposed to high temperatures, crosslinking and collapse of molecular chains are accelerated, and deterioration of the resin proceeds significantly.

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 gradually accelerated. In general, if the temperature rises by 10 ℃, the reaction rate becomes 2 times. Therefore, when the polyethylene pipe is used for transporting a high-temperature fluid, if the polyethylene pipe is exposed to a high temperature, oxidative deterioration is accelerated, and crosslinking and collapse of molecular chains progress, so that 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, and elongation, and deteriorates stress environment cracking resistance, impact resistance, and the like. If a polyethylene pipe or joint is continuously used in a severe environment such as a radiation environment, an ultraviolet environment, a high-temperature environment, or the like, problems such as stress fracture, creep fracture, cracking, or tube body fracture, and fluid leakage occur when internal pressure, external pressure, impact, or the like is applied or chemical substances are exposed.

On the other hand, if the inner and outer surfaces of the catheter 1 are covered with the gas barrier films 2, the oxygen gas transmission is prevented, and the propagation reaction of oxidation is suppressed, so that the oxidative deterioration of the catheter 1 can be suppressed even at a high dose of radiation. The gas barrier film 2 also prevents the permeation of gases generated from chemical substances such as hydrogen peroxide, hypochlorous acid, perchloric acid, and the like, and thus can prevent deterioration from the inside of the conduit 1. Further, if naphthenic oil or aromatic oil is blended in the conduit 1, radicals generated by the action of radiation or ultraviolet rays can be trapped by the components of the oil.

In general, polyethylene is cracked or cracked by various external factors such as radiation, ultraviolet rays, heat, and the like, but has a characteristic that the elongation is reduced and the cross section is whitened in any failure mode regardless of the kind of the external factor. Whitening and cracking occur in the fracture surface, and voids and fibrils exist. Whitening is a phenomenon caused by mie scattering of light due to the formation of voids. Whitening indicates that craze damage occurs as a form of damage composed of voids and fibrils.

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

(A) Propagation of strain in localized regions immediately after tensile yield

(B) Propagation of craze damage region

(C) The cutting and cracking of molecular chains occur at the concentrated part of the silver streak

(D) Polymer fracture

Further, it is known that at the level of crystallization, the following changes occur due to stretching.

(a) Disruption of crystallization at molecular level (molecular chain exfoliation)

(b) Bulk destruction of crystals (molecular chain exfoliation)

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

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 causes craze failure. However, in (c), the crystalline region is less damaged and the amorphous region is hardly increased.

The amorphous region increased by such a mechanism becomes a starting point of failure typified by stress cracking. Therefore, it is desired to prevent the formation of voids, fibrils, and crazing as much as possible and avoid the occurrence of brittle fracture and creep fracture when fluid pressure from the inside of the pipe, soil pressure from the outside of the pipe, or the like is applied.

On the other hand, if naphthenic oil or aromatic oil is added to the conduit 1, the slidability of molecules present in the crystal of the polyethylene can be greatly improved. By converting the change in the level of crystallization into sliding rotation of molecules within the crystal, the formation of voids, fibrils, and crazing can be reduced, and the amorphous region is made difficult to expand, so brittle fracture and creep fracture due to deterioration of high-density polyethylene can be reduced.

Further, the oil containing naphthenes has an SP value close to that of polyethylene and is excellent in compatibility. If naphthenic oil is added to conduit 1, the oil can penetrate into fine parts of molecules in the crystal, and the sliding properties of molecules in the crystal can be greatly improved. Therefore, it is possible to suppress the breakage of the crystal at the molecular level and the bulk breakage of the crystal and to easily cause the sliding rotation of the molecules in the crystal.

Further, the oil containing naphthenes exhibits fluidity close to normal temperature even at low temperature. 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 the crystal and around tie molecules. When naphthenic oil is added to conduit 1, the oil that has penetrated into the interior of the crystal and around the ligament molecules retains high fluidity even at low temperatures, and tends to cause slip rotation of the molecules in the crystal, thereby making it possible to improve resistance to low-temperature embrittlement and impact resistance at low temperatures.

On the other hand, the aromatic hydrocarbon-containing oil has a high viscosity index and is characterized by being hardly exuded from high-density polyethylene over a wide temperature range. Therefore, if an oil containing aromatic hydrocarbons is added to conduit 1, the effect of the addition of the oil will last for a long time.

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

In addition, the aromatic hydrocarbon-containing oil often contains impurities such as sulfur components or has a high acid value. Since sulfur components, aldehydes, carboxylic acids, and the like are likely to participate in the radical reaction, the oil itself sacrificially deteriorates, and the effect of suppressing deterioration of the catheter 1 can be obtained.

Further, oils containing naphthenes and oils containing aromatics exhibit the effect of softening polyethylene. In general, polyethylene becomes hard and easily embrittled when it is continuously used in a radiation environment. However, if naphthenic oil or aromatic oil is added to the pipe 1, the high-density polyethylene itself is softened, and embrittlement due to radiation can be made difficult to occur.

The amount of the naphthenic oil and the aromatic oil added is preferably 0.1 to 7 parts by mass, more preferably 1 to 7 parts by mass, per 100 parts by mass of the high-density polyethylene. If the amount exceeds 7 parts by mass, the oil will exude, making it difficult to properly blend. On the other hand, if the amount is less than 0.1 part by mass, a sufficient effect by the addition cannot be obtained. On the other hand, the effect of suppressing deterioration of the resin and the effect of improving the slidability of the polyethylene molecules are more enhanced as the amount added is larger within the above-mentioned range of the amount added.

The content of the oil contained in the resin can be measured by infrared spectroscopic analysis, for example. In addition, the increase or decrease of the crystalline region and the amorphous region in the resin can be checked by using, for example, a Differential Scanning Calorimeter (DSC). In the case of a general high-density polyethylene, the heat generation amount of crystal melting is greatly reduced due to deterioration of the resin. However, if naphthenic oil or aromatic oil is added as an additive, the amount of heat generated by crystal melting is hardly reduced.

The heat-shielding adhesive film 3 is formed of a resin film made of a resin having a melting point of 150 ℃. According to the heat-blocking adhesive film 3, when the resin is heat-molded so as to cover the gas barrier film 2, thermal adhesion between the molten resin and the gas barrier film 2 and heat transfer from the molten resin to the gas barrier film 2 can be blocked. If the gas barrier film 2 is thermally adhered to another layer, the gas barrier film 2 is subjected to a large tension when an external force or the like is applied. Further, if the heat of the molten resin is transferred to the gas barrier film 2, the gas barrier film 2 itself is melted. However, if the heat-blocking adhesive film 3 is used to block thermal adhesion and heat transfer, pinholes and cracks are not generated, and thus the gas barrier properties can be satisfactorily maintained.

The heat-shielding adhesive film 3 may be formed of one kind of resin film or may be formed of a plurality of kinds of resin films. In the figure, the heat-shielding adhesive film 3 includes an inner heat-shielding adhesive film 3a and an outer heat-shielding adhesive film 3b, and these may be formed of the same layer or different layers.

The heat-shielding adhesive film 3 is preferably formed of a polyethylene terephthalate stretch film, a polyimide film, or a polyamideimide film. The melting point of the stretched polyethylene terephthalate and the polyamide imide is 150 ℃ or higher. Further, the polyimide does not melt until it is thermally decomposed at a temperature higher than 150 ℃ (about 500 ℃). Therefore, according to these resins, the heat-shielding adhesive film 3 itself can be prevented from melting at the heating temperature at the time of molding the resin such as the catheter 1. Since the gas barrier film 2 can be prevented from being thermally adhered to or melted in another layer, the gas barrier properties can be satisfactorily maintained.

Further, stretched polyethylene terephthalate, polyimide, and polyamideimide have an aromatic ring, have high radiation resistance, and are difficult to change in physical properties even at a high radiation dose. Therefore, by using such a heat-shielding adhesive film 3, the catheter 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 tube 10.

The total thickness of the heat-shielding adhesive film 3 wound in a tubular shape 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. The thicker the total thickness is, the more 10 μm or more, the more heat adhesion and heat transfer can be suppressed, and the gas barrier properties of the gas barrier film 2 can be kept well. On the other hand, the thinner the total thickness is 300 μm or less, the lower the material cost, the time and labor for winding. Further, if the total thickness is 20 μm or more and 200 μm or less, effective radiation resistance can be obtained due to the neutron shielding ability of the resin itself.

The inner layer 4a preferably will have a density of 0.910g/cm³Above 0.930g/cm³The following Low Density Polyethylene (LDPE) was formed as a main component. Since low density polyethylene has high flexibility, impact resistance, moisture resistance, water resistance, chemical resistance, and the like, the inner layer 4a mainly composed of low density polyethylene can protect the inside of the high density polyethylene pipe 10 from impact, external pressure, damage, fluid and chemical substances in the pipe. In particular, hydrogen peroxide generated in a fluid at a high radiation dose generates hypochlorous acid and perchloric acid, and these chemical substances may be chemically cracked to cause cracking and leakage. However, if the inner layer 4a is provided, it is possible to suppress chemical substances such as hydrogen peroxide, hypochlorous acid, perchloric acid, and the like from penetrating into the catheter 1.

The outer layer 4b preferably will have a density of 0.910g/cm³Above 0.930g/cm³The following Low Density Polyethylene (LDPE) was formed as a main component. Since low-density polyethylene has high flexibility, impact resistance, moisture resistance, water resistance, chemical resistance, and the like, the outer layer 4b mainly composed of low-density polyethylene can protect the outside of the high-density polyethylene pipe 10 from impact/external pressure, damage, chemicals outside the pipe, water vapor, rain water, condensed water, and the like.

A typical double-layer pipe is formed by thermally bonding a pipe and a coating layer, and has a structure in which a resin matrix is continuous. Therefore, when the resin of the coating layer deteriorates, there is a disadvantage that the impact of the brittle fracture generated in the coating layer and the dynamic strain are easily propagated to the conduit, and the conduit is easily subjected to the stress cracking in a chain manner. In particular, when the coating layer is high-density polyethylene or medium-density polyethylene, the impact and dynamic strain transmitted to the catheter are increased as compared with low-density polyethylene having high flexibility.

In contrast, in the high-density polyethylene tube 10, the gas barrier film 2 and the heat-shielding adhesive film 3 are interposed between the guide tube 1 and the inner layer 4a, and between the guide tube 1 and the outer layer 4 b. The gas barrier film 2 and the heat-resistant adhesive film 3 are not integrated by surface-bonding the layers to each other as in the case of thermal bonding, but are formed by winding the films. These gas barrier film 2 and heat-shielding adhesive film 3 function as barriers to prevent propagation of impact and dynamic strain and progress of cracking, and therefore, the catheter 1 can be protected from both the inside and outside.

The outer layer 4b preferably contains carbon black as an additive when the high-density polyethylene pipe 10 is exposed to an ultraviolet environment such as outdoors. Examples of carbon black include furnace black, channel black, acetylene black, and thermal black. Since ultraviolet rays are absorbed if carbon black is added, deterioration of the outer layer 4b itself and the catheter 1 can be suppressed.

The content of carbon black in the outer layer 4b is preferably 1.0 mass% or more, and more preferably 1.5 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. The greater the content is 1.0 mass% or more, the more excellent effect of absorbing ultraviolet rays is obtained, and therefore the weather resistance of the high density polyethylene pipe 10 can be sufficiently improved. In addition, the less the content is 4.0 mass% or less, the more difficult the carbon black is to form agglomerates in the resin, and therefore, the agglomerates can be prevented from becoming a starting point of breakage.

The thickness of the inner layer 4a and the outer layer 4b is preferably 0.4mm or more, more preferably 0.5mm or more, further preferably 0.8mm or more, and further preferably 1.0mm or more. Further, it is preferably 4mm or less, more preferably 3mm or less, and further preferably 2mm or less. The thicker the thickness is 0.4mm or more, the higher the protection performance can be obtained. On the other hand, the thinner the thickness is 4mm or less, the sufficient inner diameter can be secured for a predetermined outer diameter, and the material cost is reduced. Further, if the thickness is 0.5mm or more and 3mm or less, effective radiation resistance can be obtained due to the neutron shielding ability of the resin itself.

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

The high-density polyethylene pipe 10 (see fig. 1 and 2) can be produced by a production method including the steps of: a step of resin-molding the cylindrical inner layer 4a, a step of winding the inner gas barrier film 2a around the outer surface of the molded inner layer 4 a; a step of winding the inner heat-shielding adhesive film 3a around the outer surface of the pipe body around which the inner gas barrier film 2a is wound; a step of resin-molding the catheter 1 on the outer surface of the pipe body around which the inner heat-shielding adhesive film 3a is wound; a step of winding the outer gas barrier film 2b around the outer surface of the molded catheter 1; a step of winding the outer heat-shielding adhesive film 3b around the outer surface of the pipe body around which the outer gas barrier film 2b is wound; and a step of resin-molding the cylindrical outer layer 4b on the outer surface of the pipe body around which the outer heat-shielding adhesive film 3b is wound.

The inner layer 4a of the high-density polyethylene pipe 10 can be obtained by heating a resin prepared in the form of pellets or the like, adding an additive as needed, kneading, and resin-molding a molten resin composition into a cylindrical shape by extrusion molding, injection molding, or the like. The pipe 1 and the outer layer 4b can be obtained by heating a resin prepared in the form of pellets or the like, adding an additive such as oil or carbon black as necessary, kneading, and coating and molding a molten resin composition on the outer periphery of a pipe body having an inner layer formed thereon.

As a method for coating and molding the catheter 1 and the outer layer 4b, the following method can be used: for example, a method of coating-molding a pipe body with a T-die while rotating the pipe body, a method of coating-molding a pipe body with a die having an appropriate shape while pulling the pipe body while rotating the pipe body, a method of extrusion-molding a pipe body with a circular die while pulling the pipe body, and the like are used.

In the production of a resin composition used as a raw material or in the production of a high-density polyethylene pipe, the additive may be dry blended or may be blended in advance with a resin composition such as pellets. However, if the solid additive such as carbon black is not sufficiently kneaded, it may aggregate to become a starting point of destruction. 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, when an additive is dry blended in the production of a resin composition used as a raw material, master batch pellets prepared by blending the additive and resin pellets made of a resin 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, about 3mm in diameter), and cut into a predetermined length (for example, about 3mm in length) by a knife provided in parallel with the disc surface, thereby obtaining resin composition pellets containing an additive.

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

In the formation of the inner layer 4a, only the resin composition pellets containing the additive may be used as the material, or master batch pellets prepared by adding the additive and the resin pellets may be used as the material. For example, these pellets can be supplied to a hopper of an extruder (tube manufacturing apparatus), heated and melted in the extruder, cylindrically extruded from a predetermined die, and if necessary, sized while being drawn by a drawing machine, and cooled by a cooling water tank or the like to form the cylindrical inner layer 4 a.

In the formation of the catheter 1 and the formation of the outer layer 4b, only the resin composition pellets containing the additive may be used as the material, or master batch pellets prepared by adding the additive and resin pellets may be used as the material. For example, the pellets can be supplied to an extruder, heated and melted in the extruder, extruded from a predetermined die onto the outer surface of the pipe body on which the inner layer is formed, and if necessary, sized and cooled to form the conduit 1 and the cylindrical outer layer 4 b. In the formation of the duct 1 and the formation of the outer layer 4b, resin molding is preferably performed while cooling the inner surface side of the pipe body in order to prevent melting of the inner layer and thermal adhesion of the film.

As the kneading machine, various kneading machines such as a batch kneading machine such as a banbury mixer, a twin-screw kneading machine, a rotor type twin-screw kneading machine, and a kneader (Buss co-kneader) can be used. As the extruder, for example, a single screw extruder, a twin screw extruder, or the like can be used. The die may be any type of straight head die, cross-head die, offset die (offset dies), and the like. The sizing can be performed by any method such as a slashing sheet method, an outer mandrel method, a sizing box method, and an inner mandrel method.

The mixing temperature of the polyethylene is preferably 120 ℃ to 250 ℃. When a Banbury mixer is used, a resin composition which is sufficiently melted can be obtained by kneading at 180 ℃ for 10 minutes, for example. Further, titanium oxide may be added to the polyethylene resin composition in an amount within a range of 0.1 to 5 parts by mass per 100 parts by mass of polyethylene.

The gas barrier film 2 and the heat-shielding adhesive film 3 can be obtained by an appropriate method such as coating molding. The multilayer film used as the gas barrier film 2 can be obtained by an appropriate method such as a coextrusion method or a lamination method. The multilayer film may be formed of any one of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film. The multilayer film is preferably formed of a biaxially stretched film from the viewpoint of obtaining high strength and excellent gas barrier properties.

The gas barrier film 2 can be wound by hand winding with a winder so as to cover the outer surface of the pipe body on which the inner layer is formed. The inner layer 4a and the duct 1 are preferably cooled to at least a temperature at which thermal fusion does not occur by water cooling or air cooling before the gas barrier film 2 is wound. The gas barrier film 2 may be wound by any of single winding, multiple winding, and spiral winding. However, from the viewpoint of reliably exhibiting gas barrier properties, a winding system provided with an arbitrary overlap width is preferable. For example, multiple winding or spiral winding with an overlap width of 1/2 or more of the film width is preferably provided.

The heat-resistant adhesive film 3 can be wound by a winding machine or by manual winding so as to cover the outer surface of the gas barrier film 2 wound around the pipe body on which the inner layer is formed. The heat-shielding adhesive film 3 may be wound by any of single winding, multiple winding, and spiral winding. However, in the case of molding the outer layer with a resin, a winding method provided with an arbitrary overlapping width is preferable from the viewpoint of avoiding the fusion of the molten resin with the gas barrier film 2 or the melting of the gas barrier film 2 due to the heat of the molten resin. For example, it is preferable to perform multiple winding or spiral winding with an overlap width of 1/2 or more as the film width.

Next, another mode in which the layer structure of the high-density polyethylene pipe according to the present embodiment is changed will be described.

As shown in fig. 3, the high-density polyethylene pipe 10A according to the present embodiment includes, in the same manner as the high-density polyethylene pipe 10 shown in fig. 1: a tubular duct 1 forming a fluid passage, an inner gas barrier film 2a covering the inner surface of the duct 1, an outer gas barrier film 2b covering the outer surface of the duct 1, an outer heat-shielding adhesive film 3b covering the outer surface of the outer gas barrier film 2b, and an outer layer 4b covering the outer surface of the outer heat-shielding adhesive film 3 b.

The high-density polyethylene tube 10A further includes an inner layer 4a covering the inner surface of the inner gas barrier film 2a on the inner side of the guide tube 1. The high-density polyethylene tube 10A shown in fig. 3 differs from the high-density polyethylene tube 10 shown in fig. 1 in that an inner heat-resistant adhesive film 3a is provided not between the guide tube 1 and the inner gas barrier film 2a but between the inner gas barrier film 2a and the inner layer 4 a.

The high-density polyethylene pipe 10A (see fig. 3) can be produced by a production method including the steps of: a step of resin-molding the tubular catheter 1; a step of winding the outer gas barrier film 2b around the outer surface of the molded catheter 1; a step of winding the outer heat-shielding adhesive film 3b around the outer surface of the pipe body around which the outer gas barrier film 2b is wound; a step of resin-molding the cylindrical outer layer 4b on the outer surface of the pipe body around which the outer heat-shielding adhesive film 3b is wound; a step of winding the inner gas barrier film 2a and the inner heat-shielding adhesive film 3a around the inside of the catheter 1; and a step of resin-molding the cylindrical inner layer 4a on the inner surface of the pipe body around which the inner gas barrier film 2a and the inner heat-shielding adhesive film 3a are wound.

The catheter 1 of the high-density polyethylene tube 10A can be obtained by heating a resin prepared in the form of pellets or the like, adding an additive such as oil if necessary, kneading the mixture, and resin-molding the molten resin composition into a tubular shape by extrusion molding, injection molding, or the like. The outer layer 4b can be obtained by heating a resin prepared in the form of pellets or the like, adding an additive such as carbon black if necessary, kneading the mixture, and coating and molding the molten resin composition on the outer periphery of the pipe body on which the inner layer is formed. The inner layer 4a can be obtained by heating a resin prepared in the form of pellets or the like, adding an additive as needed, kneading, and coating and molding a molten resin composition on the inner periphery of a pipe body on which an outer layer is formed.

As a method of coating and molding the inner layer 4a, the following method can be used: for example, a method of coating and molding the inner surface of a pipe body by a die of an appropriate shape that can be inserted into the inside of the pipe body while rotating the pipe body; a method of inserting a parison-shaped resin composition into the inside of a pipe body, thermally bonding the resin composition to the inner surface of the pipe body by blowing (gas blow) or the like from the inside of the pipe body, and then cooling the resin composition.

The inner gas barrier film 2a and the inner heat-shielding adhesive film 3a of the high-density polyethylene pipe 10A can be wound by hand using a winding machine so as to cover the inner surface of the pipe body on which the outer layer is formed. The following methods can be used: for example, a method of arranging the catheter 1 inside the catheter 1 while winding the catheter by using a winding machine that can be inserted inside the catheter 1; a method in which the gas barrier film 2a and the heat-shielding adhesive film 3a are wound around the outer periphery of a cylindrical or columnar base material that can be inserted into the inside of the catheter 1 in advance, the base material is inserted into the inside of the catheter 1, the wound film is attached to the inner surface of the catheter 1, and only the base material is pulled out. As the substrate, a substrate coated with a fluororesin such as polytetrafluoroethylene, a release agent such as wax on the outer surface, a substrate wound with a release sheet, or the like is preferably used.

According to the high-density polyethylene tube 10A (see fig. 3) having the modified layer structure, the catheter 1 alone can be resin-molded as compared with the high-density polyethylene tube 10 (see fig. 1), and therefore, the conditions for resin molding of the catheter 1 and the degree of freedom in design are not easily limited. In the production of the high-density polyethylene pipe 10A, the order of forming the layers on both the inner and outer sides of the catheter 1 is not particularly limited. The function of the high-density polyethylene pipe 10A, the main structure of each layer, and other operations and devices used for the production may be the same as those of the high-density polyethylene pipe 10.

Next, a joint made of high density polyethylene according to the present embodiment will be described.

The joint according to the present embodiment has the same layer structure as the high

density polyethylene pipes

10 and 10A. Specifically, the joint according to the present embodiment includes: a tubular duct portion (duct 1) forming a fluid passage, an inner gas barrier film 2a covering the inner surface of the duct portion (duct 1), an outer gas barrier film 2b covering the outer surface of the duct portion (duct 1), an outer heat-proof adhesive film 3b covering the outer surface of the outer gas barrier film 2b, and an outer layer 4b covering the outer surface of the outer heat-proof adhesive film 3 b.

Further, the joint according to the present embodiment may be provided with an inner layer 4a covering the inner surface of the inner gas barrier film 2a inside the pipe portion (pipe 1) as in the high

density polyethylene pipes

10 and 10A described above. Further, as in the high-

density polyethylene tubes

10 and 10A, the inner heat-shielding adhesive film 3a may be provided between the duct portion (duct 1) and the inner gas barrier film 2a or between the inner gas barrier film 2a and the inner layer 4 a.

The size, shape, connection method, and the like of the joint according to the present embodiment are not particularly limited. The joining method may be any of mechanical, electric melting, screwing, and the like. In the joint according to the present embodiment, as long as the pipe portion (pipe 1), the gas barrier film 2, and the heat-shielding adhesive film 3 made of high-density polyethylene are provided, the body portion connected to the pipe may be provided with a flange, a nut, a saddle (saddle), a sealing material, and the like, as in the case of the high-

density polyethylene pipes

10 and 10A.

The joint according to the present embodiment can be manufactured, for example, as follows: similarly to the high

density polyethylene pipes

10 and 10A, the cylindrical inner layer 4a or the pipe portion (pipe 1) to be a body portion is resin-molded by extrusion molding, injection molding, or the like, the gas barrier film 2 and the heat-resistant adhesive film 3 wound around are disposed on both the inner and outer surfaces, and the outer layer 4b and the inner layer 4a are resin-molded on the surface of each heat-resistant adhesive film 3 to perform secondary processing required for the pipe joint.

According to the high density polyethylene pipe and the joint according to the present embodiment described above, since both the inside and the outside of the pipe are covered with the gas barrier film, the oxidative deterioration of the pipe due to oxygen in the atmosphere and oxygen in the pipe can be suppressed. Therefore, even when the high-density polyethylene pipe or joint is exposed to high-dose radiation, oxygen in the atmosphere, oxygen present in a gas phase portion in the pipe, oxygen dissolved in a fluid in the pipe, strong ultraviolet rays, acid rain, or the like in summer, or is in contact with a fluid containing a high-concentration or high-dose radioactive substance, a high-temperature fluid, or the like for a long time, the propagation reaction of oxidation can be suppressed, and the deterioration of the pipe due to external factors such as radiation, ultraviolet rays, oxygen, and heat can be greatly suppressed. Further, even if a fluid flowing through the inside of the pipe generates a highly active chemical substance by decomposition of radiation or the like, or a chemical substance such as a chemical substance flows through the inside of the pipe, the chemical substance is less likely to diffuse or permeate into the pipe side, and therefore chemical cracking can be suppressed.

Further, according to the high density polyethylene pipe and the joint according to the present embodiment, since the outer gas barrier film is covered with the outer layer, when earth pressure, impact, load, or the like is applied from the outside, the gas barrier film can be prevented from being damaged, and deterioration of the gas barrier film itself and the pipe due to radiation or ultraviolet rays can be suppressed. Further, since the inner gas barrier film is covered with the inner layer, the gas barrier film can be prevented from being damaged when a foreign object flowing through the inside of the pipe collides with the inner layer, when fluid pressure is applied from the inside of the pipe, or the like, and diffusion and permeation of a chemical substance from the inside of the pipe can be further suppressed. Further, since the outside of the gas barrier film is covered with the heat-resistant adhesive film, the outer layer resin can be molded with the resin melted by heating while maintaining the soundness of the gas barrier film. Unlike the case where the protective tape is wound around the outermost surface of the duct, the outer layer after resin molding is less likely to have gaps or holes and is less likely to peel off, and therefore resistance to external factors is improved.

Therefore, even when fluid pressure, soil pressure, impact, load, or the like is applied to the high-density polyethylene pipe or joint, environmental stress cracking or creep rupture is less likely to occur, and cracking, brittle cracking, or the like, or cracking of the pipe or the like can be prevented. That is, the essential disadvantage of polyethylene that is liable to cause brittle fracture cracking can be fundamentally improved. Even if there are minute defects that cannot be observed with the naked eye, it is difficult for stress to concentrate on them, and brittle fracture and stress cracking occur, and sufficient elongation and elasticity can be obtained, so that stress environment cracking resistance and impact resistance can be improved.

In particular, a high-density polyethylene pipe or joint which can reduce brittle fracture and creep fracture due to deterioration of the resin can be obtained not only in a normal environment but also in various severe environments such as an environment exposed to high-dose radiation, an ultraviolet environment such as outdoor in summer, a high-temperature environment such as summer, and an environment of high concentration of oxygen and acid rain. Further, a high density polyethylene pipe or joint can be obtained which is less likely to deteriorate in long-term hydrostatic strength, elasticity, environmental stress cracking resistance, impact resistance, etc., and is extremely less likely to undergo brittle fracture cracking or fracture.

Further, the use of the high-density polyethylene pipe and the joint according to the present embodiment is not particularly limited. High density polyethylene pipes and fittings can be used in appropriate environments. Further, the high density polyethylene pipe and the joint can be used for transporting appropriate fluids such as water and seawater. In particular, the high density polyethylene pipe and the joint are suitable for transportation of water, seawater, polluted water, water retained in a building, and the like in nuclear-energy-related facilities.

For example, in a nuclear power plant, tens to hundreds of nuclear facility pipes are connected to a plurality of contaminated water retention areas. The total length of these pipes is generally around 10km to 20 km. The high-density polyethylene pipe and the joint can be suitably used for the purpose of treating such contaminated water or a pipe for nuclear power plant for treating drainage water from a building.

The high-density polyethylene pipe and the joint can transport a fluid containing a radioactive substance, a fluid under a high radiation dose, or an outdoor fluid, in a sound and reliable manner over a long period of time. Even when a fluid containing a radioactive substance at a high concentration is treated, the fluid can be used for a long period of time, and the frequency of replacement and inspection is reduced, so that the number of steps for laying and mounting, the number of machines and materials, the risk of exposure of a constructor and an inspector to radioactive energy, and the like can be significantly reduced.

While the embodiments of the high density polyethylene pipe and the joint according to the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are included without departing from the technical scope. For example, the above 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 can be performed.

For example, the high-density polyethylene pipe and the joint described above have the inner layer 4a on the inside, but the inner layer 4a may not be provided depending on the type and thickness of the inner gas barrier film 2a and the heat-shielding adhesive film 3a, the type of fluid flowing through the pipe, the concentration of foreign matter contained in the fluid, and the like. When the inner layer 4a is not provided, the heat-shielding adhesive film 3a inside the gas barrier film 2a may not be provided.

In the case where the inner layer 4a is not provided, the high-density polyethylene pipe can be produced by a method in which: the gas barrier film 2a is wound around the outer periphery of a cylindrical or columnar base material that can be inserted into the inside of the guide tube 1, the base material is inserted into the inside of the guide tube 1, the wound film is attached to the inner surface of the guide tube 1, and only the base material is pulled out.

Further, the high-density polyethylene pipe and the joint include the pipe 1, the gas barrier film 2, the heat-shielding adhesive film 3, the inner layer 4a, and the outer layer 4b, but a buffer layer for buffering impact may be provided between the pipe 1 and the outer gas barrier film 2b, between the outer gas barrier film 2b and the outer heat-shielding adhesive film 3b, and the like. The buffer layer can be, for example, formed at a density of less than 0.940g/cm³The resin containing polyethylene as a main component, other films, tapes, etc.

Examples

The present invention will be described in detail with reference to examples below, but the technical scope of the present invention is not limited thereto.

Test pieces of high density polyethylene tubes were produced by changing the amounts of naphthenic-containing oil and aromatic-containing oil added and the layer composition of the gas barrier film, and the tensile elongation at break after the irradiation treatment was evaluated.

As the conduit, high density polyethylene produced using a ziegler catalyst was used. A base material of high-density polyethylene was blended with a naphthenic oil or an aromatic oil as an additive, and kneaded at 180 ℃ for 10 minutes using a Banbury mixer to produce pellets for pipes of high-density polyethylene. Then, the pellets were put into an injection molding machine to mold a cylindrical catheter.

Next, using a winding machine, the gas barrier film is wound only on the outer periphery of the molded catheter or on both the outer periphery and the inner periphery, and the heat-proof adhesive film is wound on the outer periphery of the outer gas barrier film. Then, on the outer periphery of the heat-shielding adhesive film, carbon was blended to a density of 0.910g/cm³Above 0.930g/cm³The following low density polyethylene was extrusion-molded to form an outer layer, and a high density polyethylene pipe was obtained.

Made of high density polymerThe ethylene tube was used to prepare a dumbbell-shaped test piece of 1B type described in JIS K7162. Then, the test piece was irradiated at a dose rate of 1kGy/h⁶⁰Gamma rays emitted from a Co ray source. The absorbed dose was set at 1200 kGy.

< tensile test >

The tensile test was carried out in accordance with "polyethylene pipe for water supply for city water pipe JWWA K144" standard of japan city water pipe association. The testing machine used was the one described in JIS B7721, which was equipped with a device for indicating the maximum tension and a holder for clamping a dumbbell-shaped test piece. The thickness of the test piece and the width of the parallel portion were measured, and a reticle for measuring elongation was drawn along the center of the parallel portion, and then a tensile test was performed at room temperature at a test speed of 25 mm/min. The distance between the standard lines was set to 50 mm. The elongation at break was calculated by the following formula (1) by measuring the distance between standard lines at break of the test piece by performing a tensile test. In the formula (1), EB represents the elongation (%) at break, L0 represents the distance (mm) between standard lines, and L1 represents the distance (mm) between standard lines at break.

EB＝(L1-L0)/L0×100···(1)

Hereinafter, the results of measuring the tensile elongation at break after the radiation irradiation treatment are shown for the test pieces prepared by changing the amount of the naphthenic oil.

In addition, as the catheter, a catheter having a density of 0.95g/cm was used³The high density polyethylene of (1). As the additives, oils having a predetermined value of% CN and 30% CA in the ring analysis by the n-d-M method among oils produced during the purification of crude oil were used. The amount of the oil blended was 5 parts by mass per 100 parts by mass of the high-density polyethylene. As the gas barrier film, a multilayer film of LLDPE/EVOH/LLDPE was used in which the thickness of EVOH was 24 μm and the MFR of LLDPE was 3g/10 min, and the film was wound so that the total thickness became 300 μm. As the heat-blocking adhesive film, a polyethylene terephthalate stretched film was used so that the total thickness at the time of winding became 100 μm. As the outer layer, a low-density polymer having a thickness of 2mm and containing 3 mass% of carbon was formedA layer of ethylene.

Fig. 4A and 4B are graphs showing the relationship between% CN of oil used as an additive and elongation at break.

In fig. 4A and 4B, the horizontal axis represents% CN (%) of oil used as an additive, and the vertical axis represents elongation (%) at break due to stretching. Fig. 4A shows the result of winding the gas barrier film only around the outer circumference of the duct, and fig. 4B shows the result of winding the same gas barrier film around both the outer circumference and the inner circumference of the duct.

As shown in fig. 4A, in the case of adding the oil containing naphthenes as an additive, the following results were obtained: when% CN is 20% or more and 60% or less, the tensile elongation at break is significantly increased, and radiation deterioration is favorably suppressed. As shown in fig. 4B, when the inside gas barrier film is provided, the tensile elongation at break is slightly higher than that in fig. 4A, and when the% CN is 10% or more and 60% or less, the tensile elongation at break is increased.

Next, the results of measuring the tensile elongation at break after the radiation irradiation treatment are shown for the test pieces prepared by changing the amount of the aromatic hydrocarbon-containing oil added.

In addition, as the catheter, a catheter having a density of 0.95g/cm was used³The high density polyethylene of (1). As the additives, oils having a predetermined value of% CA and 40% CN in the ring analysis by the n-d-M method among oils produced during the purification of crude oil were used. The amount of the oil blended was 5 parts by mass per 100 parts by mass of the high-density polyethylene. As the gas barrier film, a multilayer film of LLDPE/EVOH/LLDPE was used in which the thickness of EVOH was 24 μm and the MFR of LLDPE was 3g/10 min, and the film was wound so that the total thickness became 300 μm. As the heat-blocking adhesive film, a polyethylene terephthalate stretched film was used so that the total thickness at the time of winding became 100 μm. As the outer layer, a layer of low density polyethylene having a thickness of 2mm and containing 3 mass% of carbon was formed.

Fig. 5A and 5B are graphs showing the relationship between% CA of oil used as an additive and elongation at break.

In fig. 5A and 5B, the horizontal axis represents% CA (%) of the aromatic hydrocarbon-containing oil used as an additive, and the vertical axis represents elongation (%) at break due to stretching. Fig. 5A shows the result of winding the gas barrier film only around the outer circumference of the duct, and fig. 5B shows the result of winding the same gas barrier film around both the outer circumference and the inner circumference of the duct.

As shown in fig. 5A, in the case of adding an aromatic hydrocarbon-containing oil as an additive, the following results were obtained: when the% CA is 5% to 60%, particularly 5% to 40%, the tensile elongation at break is significantly increased, and radiation deterioration is favorably suppressed. As shown in fig. 5B, in the case of the inner gas barrier film, the tensile elongation at break is slightly higher than that in fig. 5A, and the tensile elongation at break is increased when the% CN is 5% to 80%, particularly 15% to 60%.

Next, the measurement results of the tensile breaking elongation after the radiation irradiation treatment are shown for the test pieces produced by changing the MFR of the LLDPE of the gas barrier film.

In addition, as the catheter, a catheter having a density of 0.95g/cm was used³The high density polyethylene of (1). As the additives, oils having a% CN and a% CA of 40% and 30% of the ring analysis by the n-d-M method were used among oils produced during the purification of crude oil. The amount of the oil blended was 5 parts by mass per 100 parts by mass of the density polyethylene. As the gas barrier film, a multilayer film of LLDPE/EVOH/LLDPE was used, in which EVOH had a thickness of 24 μm and the total thickness of the film when wound was 300 μm. As the heat-blocking adhesive film, a polyethylene terephthalate stretched film was used so that the total thickness at the time of winding became 100 μm. As the outer layer, a layer of low density polyethylene having a thickness of 2mm and containing 3 mass% of carbon was formed.

Fig. 6A and 6B are graphs showing the relationship between MFR and elongation at break of linear low density polyethylene used for a gas barrier film.

In fig. 6A and 6B, the horizontal axis represents MFR (g/10 min) of the linear low density polyethylene used as the surface layer of the gas barrier film, and the vertical axis represents elongation (%) at break due to stretching. Fig. 6A shows the result of winding the gas barrier film only around the outer circumference of the duct, and fig. 6B shows the result of winding the same gas barrier film around both the outer circumference and the inner circumference of the duct.

As shown in fig. 6A, the following results were obtained: when the MFR of the linear low-density polyethylene used as the surface layer of the gas barrier film is 0.8g/10 min to 10g/10 min, the tensile elongation at break exceeds 400%, and radiation deterioration is favorably suppressed. As shown in fig. 6B, in the case of having the inner gas barrier film, the tensile elongation at break is slightly higher than that in fig. 6A, and the tensile elongation at break is increased when the MFR is 3g/10 min or less.

Next, the results of measuring the tensile elongation at break after the radiation irradiation treatment are shown for the test pieces produced by changing the total thickness of the gas barrier film.

In addition, as the catheter, a catheter having a density of 0.95g/cm was used³The high density polyethylene of (1). As the additives, oils having a% CN and a% CA of 40% and 30% of the ring analysis by the n-d-M method were used among oils produced during the purification of crude oil. The amount of the oil blended was 5 parts by mass per 100 parts by mass of the density polyethylene. As the gas barrier film, a multilayer film of LLDPE/EVOH/LLDPE was used, in which the thickness of EVOH was 24 μm and the MFR of LLDPE was 3g/10 min. As the heat-blocking adhesive film, a polyethylene terephthalate stretched film was used so that the total thickness at the time of winding became 100 μm. As the outer layer, a layer of low density polyethylene having a thickness of 2mm and containing 3 mass% of carbon was formed.

Fig. 7A and 7B are graphs showing the relationship between the total thickness of the gas barrier film and the elongation at break.

In fig. 7A and 7B, the horizontal axis represents the total thickness (μm) when the gas barrier film is wound around the outer periphery of the guide tube, and the vertical axis represents the elongation (%) at break due to stretching. Fig. 7A shows the result of winding the gas barrier film only around the outer circumference of the duct, and fig. 7B shows the result of winding the same gas barrier film around both the outer circumference and the inner circumference of the duct.

As shown in fig. 7A, the following results were obtained: when the total thickness of the gas barrier film is 50 μm or more and 400 μm or less, the tensile elongation at break is significantly increased, and radiation deterioration is favorably suppressed. As shown in fig. 7B, when the inside gas barrier film is provided, the tensile elongation at break is slightly higher than that in fig. 7A.

Next, the results of measuring the tensile elongation at break after the radiation irradiation treatment are shown for the test pieces produced by changing the thickness of the EVOH of the gas barrier film.

In addition, as the catheter, a catheter having a density of 0.95g/cm was used³The high density polyethylene of (1). As the additives, oils having a% CN and a% CA of 40% and 30% of the ring analysis by the n-d-M method were used among oils produced during the purification of crude oil. The amount of the oil blended was 5 parts by mass per 100 parts by mass of the density polyethylene. As the gas barrier film, a LLDPE/EVOH/LLDPE multilayer film having an MFR of LLDPE of 3g/10 min was used so that the total thickness at the time of winding the film was 300. mu.m. As the heat-blocking adhesive film, a polyethylene terephthalate stretched film was used so that the total thickness at the time of winding became 100 μm. As the outer layer, a layer of low density polyethylene having a thickness of 2mm and containing 3 mass% of carbon was formed.

Fig. 8A and 8B are graphs showing the relationship between the thickness of the ethylene-vinyl alcohol copolymer resin used for the gas barrier film and the elongation at break.

In fig. 8A and 8B, the horizontal axis represents the thickness (μm) of the ethylene-vinyl alcohol copolymer resin used as the intermediate layer of the gas barrier film, and the vertical axis represents the elongation (%) at break due to stretching. Fig. 8A shows the result of winding the gas barrier film only around the outer circumference of the duct, and fig. 8B shows the result of winding the same gas barrier film around both the outer circumference and the inner circumference of the duct.

As shown in fig. 8A, the following results were obtained: when the thickness of the ethylene-vinyl alcohol copolymer resin used as the intermediate layer of the gas barrier film is 6 μm or more and 50 μm or less, the tensile elongation at break is significantly increased, and radiation deterioration is favorably suppressed. As shown in fig. 8B, when the inside gas barrier film is provided, the tensile elongation at break is slightly higher than that in fig. 8A.

Next, the test piece prepared by changing the thickness of the heat-shielding adhesive film was measured for tensile elongation at break after the radiation irradiation treatment.

In addition, as the catheter, a catheter having a density of 0.95g/cm was used³Is highA density polyethylene. As the additives, oils having a% CN and a% CA of 40% and 30% of the ring analysis by the n-d-M method were used among oils produced during the purification of crude oil. The amount of the oil blended was 5 parts by mass per 100 parts by mass of the density polyethylene. As the gas barrier film, a multilayer film of LLDPE/EVOH/LLDPE was used in which the thickness of EVOH was 24 μm and the MFR of LLDPE was 3g/10 min, and the film was wound so that the total thickness became 300. mu.m. As the heat-blocking adhesive film, a polyethylene terephthalate stretch film was used. As the outer layer, a layer of low density polyethylene having a thickness of 2mm and containing 3 mass% of carbon was formed.

Fig. 9A and 9B are graphs showing the relationship between the thickness of the heat-shielding adhesive film and the elongation at break.

In fig. 9A and 9B, the horizontal axis represents the thickness (μm) of the heat-shielding adhesive film, and the vertical axis represents the elongation (%) at break due to stretching. Fig. 9A shows the result of winding the gas barrier film only around the outer circumference of the duct, and fig. 9B shows the result of winding the same gas barrier film around both the outer circumference and the inner circumference of the duct.

As shown in fig. 9A, the following results were obtained: when the thickness of the heat-shielding adhesive film is 20 μm or more and 200 μm or less, the tensile elongation at break is remarkably increased, and radiation deterioration is favorably suppressed. As shown in fig. 9B, when the inside gas barrier film is provided, the tensile elongation at break is slightly higher than that in fig. 9A.

Next, the results of measuring the tensile elongation at break after the radiation irradiation treatment are shown for the test pieces produced by changing the thickness of the outer layer.

In addition, as the catheter, a catheter having a density of 0.95g/cm was used³The high density polyethylene of (1). As the additives, oils having a% CN and a% CA of 40% and 30% of the ring analysis by the n-d-M method were used among oils produced during the purification of crude oil. The amount of the oil blended was 5 parts by mass per 100 parts by mass of the density polyethylene. As the gas barrier film, a multilayer film of LLDPE/EVOH/LLDPE was used in which the thickness of EVOH was 24 μm and the MFR of LLDPE was 3g/10 min, and the total thickness of the film at the time of winding was 300 μm. As a heat-proof adhesive film, to the total thickness when woundA stretched polyethylene terephthalate film was used to form a film having a thickness of 100. mu.m. As the outer layer, a layer of low density polyethylene containing 3 mass% of carbon was formed.

Fig. 10A and 10B are graphs showing the relationship between the thickness of the outer layer and the elongation at break.

In fig. 10A and 10B, the horizontal axis represents the thickness (mm) of the outer layer, and the vertical axis represents the elongation (%) at break due to stretching. Fig. 10A shows the result of winding the gas barrier film only around the outer circumference of the duct, and fig. 10B shows the result of winding the same gas barrier film around both the outer circumference and the inner circumference of the duct.

As shown in fig. 10A, the following results were obtained: when the thickness of the outer layer is 0.5mm or more and 3mm or less, the tensile elongation at break is remarkably increased, and radiation deterioration is favorably suppressed. As shown in fig. 10B, when the inside gas barrier film is provided, the tensile elongation at break is slightly higher than that in fig. 10A.

Next, the results of measuring the tensile elongation at break and the results of confirming the chemical cracks after the radiation irradiation treatment were shown for the test pieces produced by changing the layer composition of the gas barrier film.

In addition, as the catheter, a catheter having a density of 0.95g/cm was used³The high density polyethylene of (1). As the additives, oils having a% CN of 32% and a% CA of 10% of the ring analysis by the n-d-M method among oils produced during the purification of crude oil were used. The amount of the oil blended was 5 parts by mass per 100 parts by mass of the density polyethylene. As the gas barrier film, a multilayer film of 6 μm in thickness of EVOH was used so that the total thickness at the time of winding became 300 μm. As the heat-blocking adhesive film, a polyethylene terephthalate stretched film was used so that the total thickness at the time of winding became 100 μm. As the outer layer, a layer of low density polyethylene having a thickness of 2mm and containing 3 mass% of carbon was formed.

[ Table 1]

As shown in table 1, if Linear Low Density Polyethylene (LLDPE) is used as the surface layer of the gas barrier film, radiation deterioration is suppressed as compared with the case of Low Density Polyethylene (LDPE). In any of the gas barrier films, high radiation resistance was obtained, and no chemical crack was observed.

Claims

1. A high-density polyethylene pipe comprising:

a conduit which will have a density of 0.940g/cm³Above 0.980g/cm³The following high density polyethylene as a main component;

an inner gas barrier film covering an inner surface of the guide tube and comprising an ethylene-vinyl alcohol copolymer resin;

an outer gas barrier film covering an outer surface of the duct and including an ethylene-vinyl alcohol copolymer resin;

a heat-resistant adhesive film which covers the outer surface of the outer gas barrier film and is formed of a resin having a melting point of 150 ℃ or higher; and

an outer layer covering an outer surface of the heat-shielding adhesive film and having a density of 0.910g/cm³Above 0.930g/cm³The following low-density polyethylene was used as a main component.

2. The high-density polyethylene pipe according to claim 1, comprising:

an inner layer covering an inner surface of the inner gas barrier film and having a density of 0.910g/cm³Above 0.930g/cm³The following low-density polyethylene was used as a main component.

3. The high-density polyethylene pipe according to claim 2, comprising:

and an inner heat-shielding adhesive film which is provided between the duct and the inner gas barrier film and is formed of a resin having a melting point of 150 ℃ or higher.

4. The high-density polyethylene pipe according to claim 2, comprising:

and an inner heat-shielding adhesive film which is provided between the inner gas barrier film and the inner layer and is formed of a resin having a melting point of 150 ℃ or higher.

5. The high density polyethylene pipe according to claim 1,

the conduit includes at least one of a naphthenic-containing oil produced when refining crude oil and an aromatic-containing oil produced when refining crude oil.

6. The high density polyethylene pipe according to claim 1,

the conduit includes at least one of naphthenic oil having% CN of 10% to 60% in a ring analysis by an n-d-M method in oil produced during refining of crude oil, and aromatic oil having% CA of 5% to 80% in a ring analysis by an n-d-M method in oil produced during refining of crude oil.

7. The high density polyethylene pipe according to claim 1,

in the inner gas barrier film and the outer gas barrier film, the thickness of the layer formed of the ethylene-vinyl alcohol copolymer resin is 1 μm or more and 50 μm or less.

8. The high density polyethylene pipe according to claim 1,

the inner gas barrier film and the outer gas barrier film are multilayer films each having an intermediate layer made of 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 as a main component.

9. The high density polyethylene pipe according to claim 8,

the total thickness of the multilayer film when wound around the outer periphery is 50 [ mu ] m or more and 400 [ mu ] m or less.

10. The high density polyethylene pipe according to claim 1,

the heat-proof adhesive film is a polyethylene terephthalate stretching film, a polyimide film or a polyamide-imide film.

11. The high density polyethylene pipe according to claim 1,

the total thickness of the heat-shielding adhesive film when wrapped around the outer periphery is 20 to 200 [ mu ] m.

12. The high density polyethylene pipe according to claim 1,

the outer layer contains carbon black.

13. The high density polyethylene pipe according to claim 12,

the content of the carbon black in the outer layer is 1.0 mass% or more and 3.0 mass% or less.

14. The high density polyethylene pipe according to any one of claims 1 to 13,

which is a pipe for nuclear power plant used in the transport of fluids in nuclear power related facilities.

15. A joint, comprising:

a tubular conduit part having a density of 0.940g/cm³Above 0.980g/cm³The following high-density polyethylene is used as a main component,

an inner gas barrier film covering an inner surface of the duct part and containing an ethylene-vinyl alcohol copolymer resin,

an outer gas barrier film covering an outer surface of the conduit part and containing an ethylene-vinyl alcohol copolymer resin,

a heat-resistant adhesive film covering the outer surface of the outer gas barrier film and formed of a resin having a melting point of 150 ℃ or higher,