JP2020121444A - High-density polyethylene tube and joint - Google Patents

Abstract

To provide a high-density polyethylene tube or joint in which degradation due to external factors such as a radial ray, oxygen, ultraviolet or the like and chemical crack due to chemical materials are restrained.SOLUTION: A high-density polyethylene tube 10 or joint comprises: a conduit 1 comprising high-density polyethylene having a density of 0.940-0.980 g/cmas a main component; an inside gas barrier film 2a covering the inner surface of the conduit 1 and including ethylene-vinyl alcohol copolymer resin; an outside gas barrier film 2b covering the outer surface of the conduit 1 and including the above copolymer resin; a fusion-preventive film 3b made by a resin having a melting point of 150°C or more and covering the outer surface of the outside gas barrier film 2b; and an outer layer 4b including low-density polyethylene having the density of 0.910-0.930 g/cmas the main component and covering the outer surface of the fusion-preventive film 3b.SELECTED DRAWING: Figure 1

Description

The present invention relates to a high density polyethylene pipe and a joint used for applications such as nuclear power facilities.

The piping for nuclear facilities laid in nuclear facilities is required to have a performance capable of safely carrying a fluid containing a radioactive substance or a fluid under a high radiation dose for a long period of time. Conventionally, steel pipes have been used as pipes for nuclear facilities. However, in nuclear-related facilities where space and time constraints are assumed, steel pipes are not optimal because of the number of man-hours and equipment required for construction. Under such circumstances, substitution of resin pipes, which are easy to move and process and easy to join pipes and joints, is being promoted.

As the resin pipe, use of a high-density polyethylene pipe that is also used as a long-distance pipe for water supply is being considered. However, the high-density polyethylene pipe is inferior in radiation resistance to the steel pipe, and has a defect that brittle fracture is likely to occur under a high radiation dose. When the high-density polyethylene pipe deteriorates and causes minute defects in the resin, when pressure from fluid inside the pipe or earth pressure from outside the pipe is applied, stress concentrates on the defective portion, causing cracking or rupture. Cause

Further, under a high radiation dose, water flowing in the pipe is decomposed by radiation. Radiation decomposition of water mainly produces hydrogen and hydrogen peroxide, but also oxygen. The high-density polyethylene pipe can be exposed to oxygen gas staying in the gas phase portion inside the pipe or oxygen gas dissolved in the fluid inside the pipe. When chlorine or the like is present in the fluid in the pipe, a highly active chemical substance such as hypochlorous acid or perchloric acid may be produced.

Degradation of high-density polyethylene is promoted mainly by autoxidation involving radicals, but is accelerated not only by the action of radiation but also by ultraviolet rays and oxygen. Ultraviolet rays and oxygen present in the atmosphere degrade the high density polyethylene mainly from the outside of the pipe. On the other hand, oxygen generated in the pipe due to radiolysis of water mainly deteriorates the high density polyethylene from the inside of the pipe. Further, the chemical substance existing in the pipe becomes a factor for generating a chemical crack that causes minute defects in the resin.

It is important not to cause a leak event if the fluid transported in the high density polyethylene tubing contains radioactive material or is likely to be activated. Therefore, it is necessary to take measures to prevent deterioration due to external factors such as radiation, oxygen and ultraviolet rays, and chemical substances such as hydrogen peroxide, hypochlorous acid and perchloric acid.

For example, Patent Document 1 describes a technique in which a hydroaromatic deterioration inhibitor or propylfluoranthene is added to high-density polyethylene in an amount of 1 to 7 parts by mass.

Patent Document 2 describes a high-density polyethylene pipe, a joint that can be heat-sealed to the outer surface thereof, and a fluid transportation device including these. In the high-density polyethylene pipe, the tie molecules that connect the crystal structures that are likely to be the starting points of breakage are reinforced with a cross-linking structure. A non-crosslinkable polyethylene layer that can be heat-sealed is formed on the outer surface of the high-density polyethylene pipe.

JP, 2017-020628, A JP, 2017-101688, A

When a deterioration inhibitor is added to high-density polyethylene as in Patent Document 1 or when tie molecules are reinforced with a cross-linking structure as in Patent Document 2, the radiation resistance of the high-density polyethylene pipe is improved. be able to. Also, if the high-density polyethylene pipe has a double-pipe structure, it will be difficult for ultraviolet rays and oxygen in the atmosphere to reach the inside, so even if the outdoors is under a high radiation dose, the integrity of the pipe will be maintained for a long period of time. Can be kept.

However, these high-density polyethylene pipes cannot be said to have sufficient durability as compared with steel pipes that have a durable life of 40 years or more and do not require replacement in a short period of time. While high-density polyethylene exhibits the pressure resistance and hardness required for piping, it has poor ductility and has the essential drawback of easily brittle fracture when used under high radiation dose. There is. Although the radical reaction that deteriorates the resin is easily initiated by radiation, it is promoted by external factors such as oxygen and ultraviolet rays, and therefore advanced measures are required to prevent these.

Also, under a high radiation dose, when oxygen or a chemical substance is generated in the pipe due to radiation, or when a fluid containing a high concentration of oxygen or chemicals is flowed in the pipe, oxidation deterioration from the inside of the pipe or Since chemical cracks occur, it is essential to take measures against oxygen and chemical substances existing in the pipe. Also, pipe joints made of high-density polyethylene may be exposed to external factors such as radiation, oxygen, and ultraviolet rays, and chemical substances, and similar measures are required.

Therefore, an object of the present invention is to provide a high-density polyethylene pipe and a joint in which deterioration due to external factors such as radiation, oxygen, and ultraviolet rays and chemical cracks due to chemical substances are suppressed.

In order to solve the above-mentioned problems, a high-density polyethylene pipe according to the present invention comprises a conduit having a density of 0.940 g/cm ³ or more and 0.980 g/cm ³ or less as a main component, and an inner surface of the conduit. The inner gas barrier film containing ethylene/vinyl alcohol copolymer resin and the outer surface of the conduit, the outer gas barrier film containing ethylene/vinyl alcohol copolymer resin, and the outer surface of the outer gas barrier film. A fusion prevention film made of a resin having a melting point of 150° C. or higher and a low density polyethylene having a density of 0.910 g/cm ³ or more and 0.930 g/cm ³ or less, which covers the outer surface of the fusion prevention film. And an outer layer as a component.

Further, the joint according to the present invention has the same layer structure as that of the high-density polyethylene pipe described above.

According to the present invention, it is possible to provide a high-density polyethylene pipe and joint in which deterioration due to external factors such as radiation, oxygen, and ultraviolet rays and chemical cracks due to chemical substances are suppressed.

Sectional drawing which shows typically an example of the high-density polyethylene pipe|tube which concerns on this invention. The perspective view which shows typically an example of the high-density polyethylene pipe|tube which concerns on this invention. Sectional drawing which shows typically an example of the high-density polyethylene pipe|tube which concerns on this invention. The figure which shows the relationship between %CN of the oil used as an additive, and the elongation at the time of fracture. The figure which shows the relationship between %CN of the oil used as an additive, and the elongation at the time of fracture. The figure which shows the relationship between the% CA of the oil used as an additive, and the elongation at the time of fracture. The figure which shows the relationship between the% CA of the oil used as an additive, and the elongation at the time of fracture. The figure which shows the relationship between the MFR of the linear low density polyethylene used for the gas barrier film, and the elongation at break. The figure which shows the relationship between the MFR of the linear low density polyethylene used for the gas barrier film, and the elongation at break. The figure which shows the relationship between the total thickness of a gas barrier film, and the elongation at the time of breaking. The figure which shows the relationship between the total thickness of a gas barrier film, and the elongation at the time of breaking. The figure which shows the relationship between the thickness of the ethylene-vinyl alcohol copolymer resin used for the gas barrier film, and the elongation at break. The figure which shows the relationship between the thickness of the ethylene-vinyl alcohol copolymer resin used for the gas barrier film, and the elongation at break. The figure which shows the relationship between the thickness of a fusion prevention film, and the elongation at the time of breaking. The figure which shows the relationship between the thickness of a fusion prevention film, and the elongation at the time of breaking. The figure which shows the relationship between the thickness of an outer layer, and the elongation at the time of fracture. The figure which shows the relationship between the thickness of an outer layer, and the elongation at the time of fracture.

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 addition, in each of the following drawings, the same reference numerals are given to configurations having the same main function, and duplicate description will be omitted.

FIG. 1 is a sectional view schematically showing an example of the high-density polyethylene pipe according to the present invention. Further, 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 tube is exposed to show the layer structure of the high-density polyethylene tube.

As shown in FIGS. 1 and 2, a high-density polyethylene pipe 10 according to the present embodiment includes a tubular conduit 1 that forms a fluid passage, an inner gas barrier film 2a that covers the inner surface of the conduit 1, and a conduit. 1. An outer gas barrier film 2b covering the outer surface of No. 1, an outer fusion preventing 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 fusion preventing film 3b. ing.

Further, the high-density polyethylene pipe 10 is provided with an inner layer 4a which covers the inner surface of the inner gas barrier film 2a inside the conduit 1. Further, the high-density polyethylene pipe 10 is provided with an inner fusion preventing film 3a between the conduit 1 and the inner gas barrier film 2a. In the present specification, when "a layer covers an inner surface or an outer surface of another layer", those layers may be adjacent to each other and may cover one surface, or the layers may be adjacent to each other. One surface may be covered while sandwiching the other layer.

The high-density polyethylene pipe 10 is mainly used as a fluid transportation pipe for transporting fluid between devices and equipment. The high-density polyethylene pipe 10 has excellent radiation resistance and is caused by external factors such as radiation, oxygen in the atmosphere and ultraviolet rays, and oxygen caused in the fluid in the pipe due to radiation and radiation. Deterioration of the conduit 1 due to chemical substances such as hydrogen peroxide, hypochlorous acid, and perchloric acid generated in the fluid in the pipe, and chemical substances such as chemicals flowing in the pipe is suppressed. Therefore, the high-density polyethylene pipe 10 is suitably used for transporting a fluid containing a high concentration of radioactive substances, transporting a fluid under a high radiation dose, and particularly transporting a fluid containing high concentrations of oxygen and chemical substances. ..

The high-density polyethylene pipe 10 is a conduit for the fluid 1 in order to drastically improve the essential drawback of the high-density polyethylene, which is brittle fracture easily when used under a high radiation dose. It is a coating tube in which both the inner and outer surfaces are covered with the gas barrier film 2 (2a, 2b). Between the gas barrier film 2 on both the inner and outer sides and the outer layer (conduit 1, outer layer 4b), a layer structure sandwiching a fusion preventing film 3 (3a, 3b) so that the gas barrier film 2 is not damaged during resin molding. I am trying.

The conduit 1 is formed mainly of high density polyethylene (HDPE) having a density of 0.940 g/cm ³ or more and 0.980 g/cm ³ or less. Since high-density polyethylene has high tensile strength and impact resistance, it is low in brittleness. Therefore, the conduit 1 containing high-density polyethylene as a main component of the present invention provides pressure resistance and hardness required for piping.

The high-density polyethylene can contain 1-butene, 1-hexene, and the like as a monomer in addition to ethylene, as long as the physical properties such as density are not impaired. The density of high-density polyethylene is preferably 0.940 g / cm ³ or more 0.970 g / cm ³ or less, more preferably 0.945 g / cm ³ or more 0.965 g / cm ³ or less.

The high-density polyethylene may be polymerized with any catalyst such as Ziegler catalyst, metallocene catalyst, Phillips catalyst and the like. Further, the high-density polyethylene may be a mixed material blended with another resin or a recycled material in which a polyethylene product is reused as a raw material. The high-density polyethylene may contain other resin such as polypropylene as long as it is less than 50% by mass.

The high-density polyethylene, for example, the reaction pressure 5 kgf / cm ² or more 200 kgf / cm ² or less, the reaction temperature may be a resin obtained by polymerizing the following conditions 100 ° C. 60 ° C. or higher. Further, the melt index (Melt flow rate: MFR) determined in accordance with ISO1133 is 0.1 g/10 min or more and 3.0 g/10 min at a test temperature of 190° C. and a test load of 5.0 kgf (49.03 N). The following resins, more preferably 0.2 g/10 minutes or more and 0.5 g/10 minutes or less can be used. However, the high-density polyethylene forming the conduit 1 is not limited to the resin having such physical properties.

The conduit 1 may be added with a general additive such as an antioxidant, a heat stabilizer, a lubricant, etc. to a base material mainly composed of high density polyethylene, or a general additive may be added thereto. You don't have to. 1 and 2, the conduit 1 has a cylindrical shape, but the conduit 1 has an ellipticity, a cross-sectional shape, a longitudinal shape, and inner and outer diameters and wall thicknesses, which are not particularly limited. Not something.

At least one of the oil containing naphthene produced when refining crude oil and the oil containing aromatics produced when refining crude oil is used for the conduit 1 with respect to the base material mainly composed of high-density polyethylene. It is preferable that one of them is blended. When these oils are blended, as will be described later, the slipperiness of the polyethylene molecule is improved, and the deterioration of the high-density polyethylene due to craze destruction is suppressed.

As an oil containing naphthene, an oil obtained by refining naphthenic crude oil as a raw material can be blended. For example, a product obtained by distilling naphthene-based crude oil under reduced pressure and removing oil containing an aromatic component by solvent extraction can be used. In addition to the solvent extraction, an oil refined by adsorption treatment, clay treatment, deoxidation treatment, etc. may be used. Note that the naphthenic general _formula: means a cyclic hydrocarbon represented by C _{n H 2n.}

As the oil containing aromatics, oil obtained by refining paraffinic crude oil or naphthenic crude oil as a raw material can be blended. For example, a residual oil having a high specific gravity and a high viscosity generated in the refining process of paraffinic crude oil or naphthenic crude oil can be used. Note that the aromatics, the general formula: C n _{H 2n-6} represented by aromatic hydrocarbons, i.e., means a cyclic hydrocarbon unsaturated having conjugated double bonds.

The oil containing naphthene is preferably an oil having a% CN of 10% or more and 100% or less in a ring analysis by the ndM method, which is produced when a naphthene crude oil is refined, and 10% or more and 80% or less. Oil is more preferable, and oil of 10% or more and 60% or less is further preferable. When %CN is 10% or more and 60% or less, a high effect of suppressing deterioration of high-density polyethylene can be obtained.

The oil containing aromatics is preferably an oil having a% CA of 5% or more and 100% or less in a ring analysis by the ndM method, among the oils produced when refining a paraffinic crude oil or a naphthene crude oil, Oils of 5% to 80% are more preferable, and oils of 15% to 60% are further preferable. When %CA is 5% or more and 80% or less, a high effect of suppressing deterioration of high-density polyethylene can be obtained.

Examples of oils containing naphthenes and oils containing aromatics include, for example, among the oils produced when refining crude oil,% CN in ring analysis by the ndM method is 20% or more and 60% or less. Further, an oil having a% CA of 5% or more and 40% or less in the ring analysis by the ndM method may be used as an additive.

The n-d-M method is one method (ring analysis method) of structural group analysis of oil (oil) based on ASTM D 3238-85, and is generally used for composition analysis of base oil. According to the ndM method, based on the data of the oil density d20 at 20° C., the oil refractive index nD20 at 20° C., and the average molecular weight of the oil, the mass ratio of paraffin carbon to the total carbon amount (% CP), mass ratio of naphthene carbon to total carbon amount (%CN), mass ratio of aromatic carbon to total carbon amount (%CA), average number of naphthene rings per molecule (RN), and one molecule The average number of aromatic rings (RA) per unit is determined.

The gas barrier film 2 is preferably formed of a resin film containing at least ethylene-vinylalcohol copolymer (EVOH). According to the gas barrier film 2, diffusion and permeation of a gas such as oxygen or a chemical substance into the conduit 1 side is suppressed, so that oxidative deterioration and chemical cracking of the conduit 1 are suppressed.

Generally, the oxygen permeability coefficient of high-density polyethylene is about 0.4×10 ⁻¹⁰ cm ³ (STP)·cm/(cm ² ·s·cmHg), and the oxygen permeability coefficient of low-density polyethylene is 6.9. It is about 10 ⁻¹⁰ cm ³ (STP)·cm/(cm ² ·s·cmHg). On the other hand, the ethylene/vinyl alcohol copolymer resin has a small oxygen permeability coefficient of about 0.0001×10 ⁻¹⁰ cm ³ (STP)·cm/(cm ² ·s·cmHg) and a high oxygen permeability. It can be suppressed to 1/4000 for low density polyethylene and 1/67,000 for low density polyethylene.

The gas barrier film 2 may be composed of a single layer composed of an ethylene/vinyl alcohol copolymer resin, or may be composed of a plurality of layers including a layer composed 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 these may have the same layer structure or different layer structures. May be done.

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

The thickness of the ethylene/vinyl alcohol copolymer resin is preferably 0.5 μm or more, more preferably 1 μm or more, still more preferably 5 μm or more. Further, it is preferably 60 μm or less, more preferably 50 μm or less, still more preferably 30 μm or less. The thicker the ethylene/vinyl alcohol copolymer resin is 0.5 μm or more, the more excellent the gas barrier property is obtained, and the oxidative deterioration of the conduit 1 and the chemical crack are suppressed. In addition, since the pinholes are less likely to occur, the gas barrier property is kept sound. On the other hand, the thinner the thickness is 60 μm or less, the more flexible it is. Therefore, the gas barrier film 2 is less likely to be damaged when the high-density polyethylene pipe 10 is constructed or moved. When 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 another resin. Examples of other resins to be blended include ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, polyolefin, modified polyolefin, polyamide and polyester. 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 FIGS. 1 and 2, the gas barrier film 2 is a multilayer film including an intermediate layer 21 made of an ethylene/vinyl alcohol copolymer resin and surface layers 22 laminated on both surfaces of the intermediate layer 21. Is preferred. In the drawing, the surface layer 22 includes an inner layer 21a arranged inside the intermediate layer 21 and an outer layer 21b arranged outside, but these layers have the same layer structure. Alternatively, the layers may have different layer configurations, and the number and types of layers laminated 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, with polyethylene, a high neutron shielding ability is obtained by the resin itself, so that the radiation deterioration of the conduit 1 can be further suppressed.

In particular, when 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 precision. Further, it is possible to alleviate external pressure, impact, etc. applied to the high-density polyethylene pipe 10 to prevent damage to the conduit 1 and peeling or dropping of the gas barrier film 2. The low-density polyethylene means polyethylene having a density of 0.910 g/cm ³ or more and 0.930 g/cm ³ or less. The low-density polyethylene can contain 1-butene, 1-hexene, and the like as a monomer in addition to ethylene.

Further, when the surface layer 22 is formed of linear low-density polyethylene, higher tensile fracture strength, adhesion, cold resistance and the like can be obtained than low-density polyethylene. Note that the linear low density polyethylene, the density is not more than 0.910 g / cm ³ or more 0.925 g / cm ^3, the content ratio of the monomer having a branch means a polyethylene having few percent. The linear low-density polyethylene can include 1-butene, 1-hexene, 1-octene, and the like as a monomer in addition to ethylene. The linear low-density polyethylene may be polymerized with any catalyst such as Ziegler catalyst and Phillips catalyst.

The low-density polyethylene or linear low-density polyethylene that forms the surface layer 22 preferably has a solubility index (MFR) determined according to ISO 1133 of 0.5 g/10 minutes or more. Further, it is preferably 50 g/10 minutes or less, more preferably 20 g/10 minutes or less, further preferably 10 g/10 minutes or less, further preferably 5 g/10 minutes or less, 3 g /10 minutes or less is particularly preferable. It is known that the molecular weight of the resin and the MFR have a correlation. A resin layer having such an MFR can form a resin layer containing a small amount of low molecular weight components.

The surface layer 22 may have a layer structure in which other resin is laminated in addition to the layer made of low density polyethylene or the layer made of linear low density polyethylene. For example, from the viewpoint of strengthening the multilayer film and using it as a base material for forming the intermediate layer 21, polyamide (polyamide: PA) such as nylon 6 or polyester (polyester: PEs) such as polyethylene terephthalate is used. The layer structure may be included.

Specific examples of the multilayer film include LDPE/EVOH/LDPE, LLDPE/EVOH/LLDPE, and the like, but are not limited thereto. From the viewpoint of improving radiation resistance, it is preferable that the low-density polyethylene and the linear low-density polyethylene do not contain a low-molecular weight component that affects the resin density and the like. If necessary, another layer such as an adhesive layer may be provided between the intermediate layer 21 and the surface layer 22.

The thickness of the multilayer film is preferably 20 μm or more and 200 μm or less. Since the thicker the thickness is 20 μm or more, the higher the durability becomes. Therefore, when the high-density polyethylene pipe 10 is constructed or moved, or when it is laid in a harsh environment such as an outdoor environment where external force is easily applied, the gas barrier property becomes sound. Can be kept. Further, as the thickness is 200 μm or less, the flexibility is less likely to be lost, so that the handling property and the winding property are improved, and the damage of the film during handling is reduced.

The total thickness of the gas barrier film 2 when wound in a tubular shape is preferably 20 μm or more, 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. The thicker the total thickness is 20 μm or more, the higher the gas barrier property is, so that the oxidative deterioration of the conduit 1 and the chemical crack can be surely suppressed. On the other hand, the thinner the total thickness is 500 μm or less, the less the material cost and the winding labor. Further, when 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 conduit 1 by fusion bonding. When the conduit 1 and the gas barrier film 2 are surface-bonded by fusion bonding, when a force is applied in the length direction or the radial direction of the pipe, the conduit 1 and the gas barrier film 2 having different elongations generate opposite stresses. , The probability of occurrence of stress fracture or tearing increases. The gas barrier film 2 may be blended with an oil containing naphthene or an oil containing aromatics, as in the conduit 1.

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

The polyethylene pipe is widely used as a long-distance pipe for water supply because it is lighter in weight than steel pipe and is easy to move and process. However, unlike a steel pipe, a polyethylene pipe is formed of an organic polymer mainly composed of carbon and hydrogen. Polyethylene deteriorates due to external factors such as radiation, ultraviolet rays, and heat, and its elasticity, stress environment resistance to cracking, impact resistance, etc. decrease, so that internal pressure, external pressure, impact, etc. may be applied to the pipe, Brittle fracture is likely to occur when the pipe is scratched or the pipe is exposed to chemical substances.

It is known that organic polymers are excited by radiation, ultraviolet rays, heat, etc., and the bonds in the molecules are broken and decomposed. For example, when radiation or the like acts on polyethylene, hydrogen radicals (H.) and hydrocarbon radicals (R.) are generated. Radicals have high reactivity, and radicals bond with each other (recombine), radicals withdraw an element to generate another radical (extraction reaction), and radicals add to double bonds (addition reaction). At the same time that radicals are bound to each other, the molecular chain is broken (disproportionation reaction).

The recombination and addition reaction due to radicals bring about an increase in molecular weight called crosslinking, and the disproportionation reaction brings about a decrease in molecular weight called decay. In a polyethylene pipe, when the cross-linking or the collapse of the molecular chain proceeds, the resistance to impact and bending becomes low, and the physical properties change such that the pipe becomes brittle. When the tube becomes brittle, stress fractures such as cracks and cracks and creep fractures easily occur when internal pressure, external pressure, impact, load, etc. are applied, and cracks and brittle cracks occur on the pipe wall. It causes problems such as occurrence of a pipe or burst of the pipe.

As a pipe material such as a polyethylene pipe for water distribution, high-density polyethylene that has been improved in performance by using multistage polymerization or an improved catalyst is also used. In this type of high-density polyethylene, the high molecular weight region is increased and the number of tie molecules that connect the crystal structures to each other is increased to improve the long-term hydrostatic strength and environmental stress crack resistance.

It is generally known that the crystalline region is not easily affected even under a harsh environment, but the amorphous region is known to increase when the tie molecule is cleaved under the harsh environment. It is considered that when the cutting of the tie molecule progresses, stress concentration easily occurs inside the resin when an external force is applied, and long-term hydrostatic strength, environmental stress crack resistance, and impact resistance decrease.

In particular, it is known that in an atmosphere where oxygen is present, radicals cause a propagation reaction (chain reaction) of oxidation. When oxygen exists in the pipe, the oxidation propagation reaction proceeds not only outside the pipe in contact with the atmosphere but also inside the pipe. First, as shown in reaction formula (1), by reacting hydrocarbon radical (R ·) and oxygen _{(O 2)} is, peroxide radical (ROO ·) is generated.

The peroxide radical (ROO.) is highly reactive, and as shown in the reaction formula (2), hydrogen (H) is extracted from another molecule (RH) to give a peroxide (ROOH) and a new hydrocarbon radical. (R.) is generated.

Then, the newly-generated hydrocarbon radical (R.) produces another peroxide radical (ROO.) according to the reaction formula (1), and the peroxide radical (ROO.) becomes the reaction formula (2). According to the procedure, another peroxide (ROOH) is produced. Since the peroxide (ROOH) is also unstable, new oxy radicals (RO.), peroxide radicals (ROO.), etc. are generated as in the reaction formulas (3) to (5).

In the atmosphere where oxygen is present or in a pipe where oxygen is present, a hydrocarbon radical (R.) initially generated causes a large number of new radicals to proliferate due to such an oxidation propagation reaction, resulting in cross-linking of molecular chains and Proceed with the collapse. Therefore, the deterioration of the resin is accelerated, and stress fracture or creep fracture is likely to occur.

Further, in the atmosphere where oxygen is present or in the pipe where oxygen is present, ozone may be generated by radiation or ultraviolet rays. Ozone has a high reactivity with polyethylene having a double bond and produces ozonide by the reaction with polyethylene. Since ozonide is unstable, the O—O bond is cleaved to generate aldehyde, ketone, ester, lactone, peroxide 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 the polyethylene pipe is subjected to a fluid pressure or soil pressure of about 1 MPa or more, the molecular chains are likely to be in an elongated state, so that the permeability of ozone is increased and the stress is easily concentrated on a specific portion. In such a case, the possibility of occurrence of ozone cracks and the possibility of destruction originating from ozone cracks increase.

Further, hydrogen peroxide and oxygen may be generated by the radiolysis of water in a pipe through which water such as contaminated water and drainage flows. Hydrogen peroxide produces hypochlorous acid, perchloric acid and the like when chloride ions and the like are present in the pipe. These chemical substances diffuse and penetrate into the matrix of the resin, and when a fluid pressure or the like is applied to the resin, they act synergistically with the stress to generate a chemical crack. When a chemical crack occurs on the inner surface of the pipe, there is a high possibility that a crack or rupture will occur from the inside of the pipe.

Polyethylene tubing may also be used to transport hot fluids. The various elementary reactions that lead to the decomposition of molecules are also associated with molecular motion, ie, vibration and collision probability of molecules. Since molecular motion becomes more intense as the temperature rises, when polyethylene is exposed to high temperatures, the crosslinking and disintegration of molecular chains accelerate, and the deterioration of the resin significantly progresses.

Particularly, in a system involving an oxidation reaction, the temperature affects the thickness of the oxide layer, the diffusion rate of oxygen, and the reaction rate of oxidative decomposition, so that the oxidative decomposition of molecules is further accelerated. Generally, the reaction rate doubles as the temperature increases by 10°C. Therefore, when the polyethylene pipe is used for transporting a high-temperature fluid, when the polyethylene is exposed to high temperature, oxidative deterioration is accelerated and molecular chain cross-linking or disintegration proceeds, resulting in significant deterioration of the resin.

Such deterioration of polyethylene due to radiation, ultraviolet rays, heat, etc. deteriorates various properties such as elastic modulus, tensile strength, elongation, etc., and deteriorates stress environmental crack resistance, impact resistance, etc. Continued use of polyethylene pipes and fittings in harsh environments such as radiation environment, ultraviolet environment, and high temperature environment may cause stress destruction or stress damage when exposed to internal pressure, external pressure, shock, etc., or chemical substances. Creep failure occurs, causing problems such as cracks, cracks, and rupture of the pipe body, which causes problems such as fluid leakage.

On the other hand, when the inner and outer surfaces of the conduit 1 are covered with the gas barrier film 2, the permeation of oxygen gas is hindered and the oxidation propagation reaction is suppressed. Suppressed. Since the gas barrier film 2 also impedes the permeation of chemical substances such as hydrogen peroxide, hypochlorous acid, perchloric acid, etc., and the gas generated by the chemical substances, deterioration from the inside of the conduit 1 can be suppressed. Further, when an oil containing naphthene or an oil containing aromatics is mixed in the conduit 1, radicals generated by the action of radiation or ultraviolet rays can be captured by the oil component.

Generally, polyethylene causes cracks, cracks, etc. due to various external factors such as radiation, ultraviolet rays, heat, etc., but the elongation decreases regardless of the type of the external factors, regardless of the fracture mode. , There is a feature that whitening appears on the fracture surface. The fracture surface has whitening and cracks, and has voids and fibrils. Whitening is a phenomenon caused by Mie scattering of light due to the formation of voids. Bleaching indicates the occurrence of craze destruction, a damage pattern composed of voids and fibrils.

It is generally known that breakage of polyethylene due to tension proceeds in the order of (A) to (D) below.
(A) Propagation of a localized region of strain generated immediately after tensile yielding (B) Propagation of a craze fracture region (C) Molecular chain breakage or crack occurs at a concentrated portion of craze breakage (D) Polymer fracture

In addition, it is known that tensile causes the following changes at the crystal level.
(A) Destruction of crystals at the molecular level (molecular chain exfoliation)
(B) Block-like destruction of crystals (molecular chain exfoliation)
(C) Slip rotation of molecule in crystal (small change)

Of these, in (a) and (b), the crystalline region is destroyed and the amorphous region increases. In addition, the molecular chains are separated from the crystalline region, voids and fibrils are formed, and Craze destruction occurs. However, in (c), the damage to the crystalline region is small, and the amorphous region hardly increases.

The amorphous region increased by such a mechanism becomes a starting point of fracture including stress cracking. Therefore, formation of voids and fibrils and the occurrence of craze fracture are prevented as much as possible, and brittle fracture and creep fracture do not occur when fluid pressure from inside the pipe or earth pressure from the outside of the pipe is applied. Is desirable.

On the other hand, when the conduit 1 is blended with an oil containing naphthene or an oil containing aromatics, it is possible to greatly improve the slipperiness of the molecules present in the crystal of polyethylene. By converting the change in crystal level into the slip rotation of the molecule in the crystal, it is possible to reduce the formation of voids and fibrils and craze fracture, and it is difficult to expand the amorphous region. It is possible to reduce brittle fracture and creep fracture due to.

Further, the oil containing naphthene has an SP value close to that of polyethylene and has good compatibility. When oil containing naphthene is added to the conduit 1, the oil can be penetrated into the details of the molecule in the crystal, and the slip property of the molecule in the crystal can be greatly improved. Therefore, it is possible to facilitate the slip rotation of the molecules in the crystal while suppressing the breakage of the crystal at the molecular level and the block-like break of the crystal.

Further, oil containing naphthene exhibits fluidity close to room temperature even at low temperatures. In general, polymer materials are prone to low temperature embrittlement, and high-density polyethylene has the drawback of low impact resistance at low temperatures. Therefore, it is important to facilitate slip rotation of molecules within crystals and around tie molecules. .. When oil containing naphthene is added to the conduit 1, the oil that has permeated into the crystal and around the tie molecule maintains high fluidity even at low temperature and easily causes the molecule to slip and rotate. Resistance to heat and impact resistance at low temperatures can be improved.

On the other hand, oils containing aromatics have a high viscosity index and are difficult to exude from high-density polyethylene in a wide temperature range. Therefore, when the oil containing aromatics is added to the conduit 1, the effect of the addition of oil lasts for a long time.

In addition, oils containing aromatics are characterized by having a high flash point. Therefore, by using an oil containing aromatics as an additive, the high-density polyethylene pipe 10 can be manufactured safely.

In addition, oils containing aromatics often contain impurities such as sulfur and have a high acid value. Since the sulfur content, aldehyde, carboxylic acid, etc. easily participate in the radical reaction, the effect of suppressing the deterioration of the conduit 1 can be obtained by sacrificing the oil itself.

Oils containing naphthene and oils containing aromatics have the effect of softening polyethylene. Generally, polyethylene becomes hard and easily embrittles when it is continuously used in a radiation environment. However, when the conduit 1 is blended with an oil containing naphthene or an oil containing aromatics, the high-density polyethylene itself is softened, so that embrittlement due to radiation can be less likely to occur.

The addition amount of the oil containing naphthene or the oil containing aromatics is preferably 0.1 part by mass or more and 7 parts by mass or less, and preferably 1 part by mass or more and 7 parts by mass, relative to 100 parts by mass of high-density polyethylene. It is more preferable that the amount is not more than part. If the amount added exceeds 7 parts by mass, the oil will seep out, making it difficult to properly mix the components. On the other hand, if the addition amount is less than 0.1 part by mass, a sufficient effect due to the addition cannot be obtained. On the other hand, the larger the amount added within the above range, the higher the effect of suppressing the deterioration of the resin and the effect of improving the slipperiness of the polyethylene molecule.

The content of oil contained in the resin can be measured, for example, by infrared spectroscopy. Further, the increase or decrease of the crystalline region and the amorphous region in the resin can be examined by using, for example, a differential scanning calorimetry (DSC). In general high-density polyethylene, the heat of crystal fusion is greatly reduced due to deterioration of the resin. However, when an oil containing naphthene or an oil containing aromatics is added as an additive, the heat of crystal melting hardly decreases.

The fusion preventing film 3 is formed of a resin film made of a resin having a melting point of 150° C. or higher. According to the anti-fusing film 3, when the resin is thermoformed so as to cover the gas barrier film 2, fusion of the molten resin to the gas barrier film 2 and heat transfer from the molten resin to the gas barrier film 2 can be blocked. it can. If another layer is fused to the gas barrier film 2, a large tension is applied to the gas barrier film 2 when an external force or the like is applied. Further, when 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 fusion preventing film 3 blocks fusion and heat transfer, pinholes and cracks will not occur, so that the gas barrier property can be kept sound.

The anti-fusing film 3 may be composed of one kind of resin film or plural kinds of resin films. In the figure, the fusion preventing film 3 includes an inner fusion preventing film 3a and an outer fusion preventing film 3b, but these may have the same layer structure. The layers may be different from each other.

The fusion prevention film 3 is preferably formed of a polyethylene terephthalate stretched film, a polyimide film, or a polyamideimide film. Stretched polyethylene terephthalate and polyamide imide have a melting point of 150° C. or higher. Also, the polyimide does not melt until it is thermally decomposed at a temperature higher than 150°C (about 500°C). Therefore, according to these resins, it is possible to prevent the fusion preventing film 3 itself from melting at the heating temperature when the conduit 1 or the like is resin-molded. Since fusion and melting of the gas barrier film 2 to other layers are prevented, the gas barrier property can be kept sound.

In addition, stretched polyethylene terephthalate, polyimide, and polyamideimide have an aromatic ring, have high radiation resistance, and are unlikely to change physical properties even under a high radiation dose. Therefore, by using such a fusion prevention film 3, the conduit 1 and the gas barrier film 2 can be protected from radiation, impact, external pressure, etc. after the high density polyethylene pipe 10 is manufactured.

The fusion preventing film 3 has a total thickness of preferably 10 μm or more, more preferably 20 μm or more, still more preferably 50 μm or more when wound in a tubular shape. Further, it is preferably 300 μm or less, more preferably 200 μm or less, still more preferably 150 μm or less. The thicker the total thickness is 10 μm or more, the more the fusion and heat transfer can be suppressed, and the gas barrier property of the gas barrier film 2 can be kept sound. On the other hand, the thinner the total thickness is 300 μm or less, the less the material cost and the labor of winding. When 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 is preferably formed mainly of low density polyethylene (LDPE) having a density of 0.910 g/cm ³ or more and 0.930 g/cm ³ or less. Since low density polyethylene has high flexibility, impact resistance, moisture resistance, water resistance, chemical resistance, etc., according to the inner layer 4a containing low density polyethylene as a main component, the inside of the high density polyethylene pipe 10 can be protected against impact or shock. It is possible to protect from external pressure, generation of scratches, fluids and chemical substances in piping. In particular, under a high radiation dose, hydrogen peroxide generated in the fluid may generate hypochlorous acid or perchloric acid, and these chemical substances may cause chemical cracks, causing cracking or leakage. However, the provision of the inner layer 4a can prevent chemical substances such as hydrogen peroxide, hypochlorous acid, and perchloric acid from penetrating into the conduit 1 side.

The outer layer 4b is preferably formed mainly of low density polyethylene (LDPE) having a density of 0.910 g/cm ³ or more and 0.930 g/cm ³ or less. Since the low density polyethylene has high flexibility, impact resistance, moisture resistance, water resistance, chemical resistance and the like, according to the outer layer 4b containing low density polyethylene as a main component, the outside of the high density polyethylene pipe 10 can be exposed to impact and It is possible to protect from external pressure, generation of scratches, chemical substances outside the piping, steam, rainwater, dew condensation water, and the like.

A general two-layer pipe has a structure in which a conduit and a coating layer are fused and a resin matrix is continuous. Therefore, when the resin of the coating layer is deteriorated, the impact of brittle fracture and dynamic strain generated in the coating layer are easily propagated toward the conduit, and the conduit is liable to cause stress cracks and the like in a chain. In particular, when the covering layer is high-density polyethylene or medium-density polyethylene, the impact and dynamic strain propagating toward the conduit are larger than those of low-density polyethylene having high flexibility.

On the other hand, in the high-density polyethylene pipe 10, the gas barrier film 2 and the anti-fusing film 3 are interposed between the conduit 1 and the inner layer 4a and between the conduit 1 and the outer layer 4b. The gas barrier film 2 and the fusion prevention film 3 do not have a structure in which the layers are integrated by surface bonding like fusion, but the layers are formed by winding the film. Since the gas barrier film 2 and the fusion preventing film 3 function as a barrier that prevents the propagation of impact and dynamic strain and the development of cracks, the conduit 1 can be protected from both 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. As the carbon black, for example, furnace black, channel black, acetylene black, thermal black or the like can be used. When carbon black is blended, ultraviolet rays are absorbed, so that deterioration of the outer layer 4b itself and the conduit 1 can be suppressed.

The content of carbon black in the outer layer 4b is preferably 1.0% by mass or more, and more preferably 1.5% by mass or more. Further, it is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, and further preferably 2.5% by mass or less. The higher the content is 1.0% by mass or more, the higher the effect of absorbing ultraviolet rays can be obtained, and therefore the weather resistance of the high-density polyethylene pipe 10 can be sufficiently improved. Further, the smaller the content is 4.0% by mass or less, the more difficult it is for carbon black to form agglomerates in the resin, and thus it is possible to prevent the agglomerates from becoming the starting point of fracture.

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

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

The high-density polyethylene pipe 10 (see FIGS. 1 and 2) includes a step of resin-molding the cylindrical inner layer 4a, a step of winding the inner gas barrier film 2a on the outer surface of the molded inner layer 4a, and The step of winding the inner fusion preventing film 3a on the outer surface of the tubular body on which the gas barrier film 2a is wound, and the resin conduit tube 1 on the outer surface of the tubular body on which the inner fusion preventing film 3a is wound. The step of molding, the step of winding the outer gas barrier film 2b on the outer surface of the molded conduit 1, and the outer fusion preventing film 3b on the outer surface of the tubular body on which the outer gas barrier film 2b is wound. It can be manufactured by a manufacturing method including a winding step and a step of resin-molding the tubular outer layer 4b on the outer surface of the tubular body on which the outer fusion preventing film 3b is wound.

The inner layer 4a of the high-density polyethylene pipe 10 is formed by heating a resin prepared as pellets or the like, adding an additive if necessary, and kneading the molten resin composition into a tubular resin by extrusion molding, injection molding, or the like. It can be obtained by molding. In the conduit 1 and the outer layer 4b, a resin prepared as pellets or the like is heated, and if necessary, additives such as oil and carbon black are added and kneaded to form a molten resin composition as an inner layer. It can be obtained by coating the outer periphery of the tubular body.

Examples of the method for coating and molding the conduit 1 and the outer layer 4b include, for example, a method of coating and molding with a T-die or the like while rotating the tube, and a method of coating and molding with a die having an appropriate shape while rotating and taking the tube. Alternatively, a method of extruding the outer periphery with a round die or the like while taking the tubular body can be used.

The additives may be dry-blended at the time of manufacturing the resin composition used as the raw material or at the time of manufacturing the high-density polyethylene pipe, or may be preliminarily blended with the resin composition such as pellets. However, solid additives such as carbon black may agglomerate and become a starting point of breakage if the kneading is insufficient. Therefore, it is preferable to mix the additives in advance as a master batch, and it is particularly preferable to mix the additives as a master batch in a state of being mixed with oil.

For example, in the case of dry blending the additives during the production of the resin composition used as the raw material, the master batch pellets prepared by blending the additives and the resin pellets made of the resin are put into the hopper of the pellet production apparatus. Then, these are melt-kneaded. Then, the kneaded molten resin composition is extruded into water through a stainless disk having a large number of holes (for example, a diameter of about 3 mm), and a predetermined length ( For example, a resin composition pellet containing an additive can be obtained by cutting into a length of about 3 mm).

Alternatively, the oil blended as an additive during the production of the resin composition used as the raw material may be directly mixed alone with the molten resin composition. For example, master batch pellets or resin pellets are put into a hopper of a pellet manufacturing apparatus, oil is dropped at a constant dropping rate using a microtube 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 to obtain resin composition pellets containing an additive.

Further, when forming the inner layer 4a, only the resin composition pellets containing the additive may be used as the material, or the master batch pellets and the resin pellets prepared by adding the additive may be used as the material. For example, these pellets are supplied to the hopper of an extruder (pipe manufacturing device), heated and melted in the extruder, extruded into a cylindrical shape from a predetermined die, and then taken up by a taker, sized as necessary, and cooled. The cylindrical inner layer 4a can be formed by cooling through a water tank or the like.

Further, at the time of forming the conduit 1 or at the time of forming the outer layer 4b, only the resin composition pellets containing the additive may be used as a material, or the master batch pellets and the resin pellets prepared by mixing the additive may be used. You may use it as a material. For example, these pellets are supplied to an extruder, heated and melted in the extruder, extruded from a predetermined die to the outer surface of the tube body on which the inner layer is formed, sized if necessary, and cooled. Thus, the conduit 1 and the tubular outer layer 4b can be formed. When forming the conduit 1 or forming the outer layer 4b, it is preferable to perform resin molding while cooling the inner surface side of the tubular body in order to prevent melting of the inner layer and fusion of the film.

As the kneader, various kneaders such as a batch type kneader such as a Banbury mixer, a twin-screw kneader, a rotor-type twin-screw kneader, and a Busconida can be used. Further, 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 such as a straight head die, a cross head die, and an offset die. The sizing may be performed by any of a sizing plate method, an outside mandrel method, a sizing box method, an inside mandrel method and the like.

The kneading temperature of polyethylene is preferably 120° C. or higher and 250° C. or lower. When using a Banbury mixer, a sufficiently molten resin composition can be obtained by, for example, kneading at 180° C. for 10 minutes. The polyethylene resin composition may contain titanium oxide in the range of 0.1 to 5 parts by mass with respect to 100 parts by mass of polyethylene.

The gas barrier film 2 and the fusion preventing 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 laminating method. The multilayer film may be formed by any 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 a winding machine or manual winding so as to cover the outer surface of the tubular body on which the inner layer is formed. Before winding the gas barrier film 2, the inner layer 4a and the conduit 1 are preferably cooled by water cooling or air cooling to at least a temperature at which heat fusion does not occur. The gas barrier film 2 may be wound in any of single winding, multiple winding, and spiral winding. However, from the viewpoint of reliably exerting the gas barrier property, it is preferable to wind with an arbitrary overlapping width. For example, multiple winding or spiral winding provided with an overlapping width that is ½ or more of the film width is preferable.

The anti-fusing film 3 can be wound by a winding machine or manual winding so as to cover the outer surface of the gas barrier film 2 wound around the tubular body on which the inner layer is formed. The anti-fusing film 3 may be wound in any of single winding, multiple winding and spiral winding. However, from the viewpoint of avoiding fusion of the molten resin to the gas barrier film 2 or melting of the gas barrier film 2 by the heat of the molten resin when the outer layer is resin-molded, an arbitrary overlapping width is provided. It is preferable to wind it up. For example, multiple winding or spiral winding provided with an overlapping width that is ½ or more of the film width is preferable.

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

FIG. 3 is a sectional view schematically showing an example of the high-density polyethylene pipe according to the present invention.
As shown in FIG. 3, the high-density polyethylene pipe 10A according to the present embodiment, like the high-density polyethylene pipe 10 shown in FIG. 1, has a tubular conduit 1 forming a fluid passage and an inner surface of the conduit 1. Of the inner gas barrier film 2a that covers the outer surface of the conduit 1, the outer gas barrier film 2b that covers the outer surface of the conduit 1, the outer fusion preventing film 3b that covers the outer surface of the outer gas barrier film 2b, and the outer fusion preventing film 3b. And an outer layer 4b that covers the outer surface.

Further, the high-density polyethylene pipe 10A is provided with an inner layer 4a, which covers the inner surface of the inner gas barrier film 2a, inside the conduit 1. The high-density polyethylene pipe 10A shown in FIG. 3 differs from the high-density polyethylene pipe 10 shown in FIG. 1 in that it is not between the conduit 1 and the inner gas barrier film 2a but between the inner gas barrier film 2a and the inner layer 4a. In addition, the inner side is provided with the fusion preventing film 3a.

The high-density polyethylene pipe 10A (see FIG. 3) includes a step of resin-molding the tubular conduit 1, a step of winding the outer gas barrier film 2b on the outer surface of the molded conduit 1, and an outer gas barrier film 2b. A step of winding the outer fusion preventing film 3b on the outer surface of the tubular body around which is wound, and a tubular outer layer 4b on the outer surface of the tubular body around which the outer fusion preventing film 3b is wound. The step of molding, the step of winding the inner gas barrier film 2a and the inner anti-fusing film 3a and arranging it inside the conduit 1, and the step of winding the inner gas barrier film 2a and the inner anti-fusing film 3a It can be manufactured by a manufacturing method including a step of resin-molding the cylindrical inner layer 4a on the inner surface of the arranged tubular body.

The conduit 1 of the high-density polyethylene pipe 10A is formed by heating a resin prepared as pellets, kneading it with an additive such as oil if necessary, and kneading the molten resin composition by extrusion molding, injection molding or the like. It can be obtained by resin-molding into a shape. The outer layer 4b is formed by heating a resin prepared as pellets, kneading it with an additive such as carbon black as necessary, and kneading the molten resin composition to the outer periphery of the tubular body on which the inner layer is formed. Can be obtained by coating and molding. The inner layer 4a is formed by heating a resin prepared as a pellet or the like, adding an additive as necessary and kneading the resin composition, and coating the molten resin composition on the inner circumference of the tubular body on which the outer layer is formed. You can get it.

Examples of the method of coating and molding the inner layer 4a include a method of coating and molding the inner surface of the tubular body with a die having an appropriate shape that can be inserted into the tubular body while rotating the tubular body, and a parison inside the tubular body. It is possible to use a method in which a resin composition in the shape of a tube is inserted, and the resin composition is fused to the inner surface of the tubular body by gas blow from the inside of the tubular body and then cooled.

The gas barrier film 2a on the inner side of the high-density polyethylene pipe 10A and the fusion preventing film 3a on the inner side can be wound by a winding machine or manual winding so as to cover the inner surface of the pipe body on which the outer layer is formed. .. For example, the gas barrier film 2a may be placed on the inside of the conduit 1 while being wound by using a winding machine that can be inserted inside the conduit 1, or on the outer periphery of a tubular or columnar substrate that can be inserted inside the conduit 1. It is possible to use a method in which the anti-fusing film 3a is wound in advance, the base material is inserted inside the conduit 1, the wound film is attached to the inner surface of the conduit 1 and only the base material is pulled out. it can. As the base material, it is preferable to use a base material whose outer surface is coated with a fluororesin such as polytetrafluoroethylene or a release agent such as wax, or a base material around which a release sheet is wound.

According to the high-density polyethylene pipe 10A (see FIG. 3) in which the above layer structure is changed, the conduit 1 can be resin-molded by itself as compared with the high-density polyethylene pipe 10 (see FIG. 1). The conditions for resin molding of the conduit 1 and the degree of freedom in design are less likely to be restricted. In the production of the high-density polyethylene pipe 10A, the order of forming the layers on the inner and outer sides of the conduit 1 is not particularly limited. Further, the function of the high-density polyethylene pipe 10A, the main configuration of each layer, and other operations and devices used for manufacturing can be the same as those of the high-density polyethylene pipe 10 described above.

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

The joint according to this embodiment has the same layer structure as that of the high-density polyethylene pipes 10 and 10A. Specifically, the joint according to the present embodiment includes a tubular conduit portion (conduit 1) forming a fluid passage, an inner gas barrier film 2a covering an inner surface of the conduit portion (conduit 1), and a conduit portion. An outer gas barrier film 2b covering the outer surface of (conduit 1), an outer fusion preventing 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 fusion preventing film 3b. , Is provided.

Further, the joint according to the present embodiment can include an inner layer 4a that covers the inner surface of the inner gas barrier film 2a inside the conduit portion (conduit 1), similar to the high density polyethylene pipes 10 and 10A. .. In addition, like the high-density polyethylene pipes 10 and 10A described above, the inner fusion bonding is performed between the conduit portion (conduit 1) and the inner gas barrier film 2a or between the inner gas barrier film 2a and the inner layer 4a. The prevention film 3a can be provided.

The size, shape, connection method, etc. of the joint according to the present embodiment are not particularly limited. The connection method may be any of mechanical type, electrofusion type, screw type and the like. In the joint according to the present embodiment, like the high-density polyethylene pipes 10 and 10A described above, the body part to which the pipes are connected is made of a high-density polyethylene pipe part (conduit 1), a gas barrier film 2, and an anti-fusion film 3. As long as it has a flange, a nut, a saddle, a sealant, etc.

In the joint according to the present embodiment, for example, as in the case of the high-density polyethylene pipes 10 and 10A described above, the tubular inner layer 4a or the conduit portion (conduit 1) to be the body portion is resin-molded by extrusion molding, injection molding or the like. , Arranging the gas barrier film 2 and the anti-fusing film 3 wound on both inner and outer surfaces, resin-molding the outer layer 4b and the inner layer 4a on the surface of each anti-fusing film 3, and subjecting the pipe joint to the necessary secondary processing. Can be manufactured.

According to the high-density polyethylene pipe and the joint according to the present embodiment described above, the inner and outer sides of the conduit are covered with the gas barrier film, so that it is possible to suppress oxidative deterioration of the conduit due to oxygen in the atmosphere and oxygen in the pipe. Therefore, high-density polyethylene pipes and joints have high doses of radiation, oxygen in the atmosphere, oxygen in the gas phase inside the pipes, oxygen dissolved in the fluid inside the pipes, and strong such as outdoors in summer. Even if it is exposed to ultraviolet rays, acid rain, etc. for a long time, or if it is in contact with a fluid containing a high concentration or a high dose of radioactive material or a high temperature fluid for a long time, the propagation reaction of oxidation is suppressed and Deterioration of the conduit due to external factors such as ultraviolet rays, oxygen, and heat is significantly suppressed. Also, even if the fluid flowing in the pipe may generate highly active chemical substances due to radiolysis, etc., or chemical substances such as chemicals may flow into the pipe, these chemical substances diffuse to the conduit side.・Difficult to penetrate and chemical cracks are 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, damage to the gas barrier film is prevented when earth pressure, impact, load, etc. are applied from the outside. However, deterioration of the gas barrier film itself and the conduit due to radiation and ultraviolet rays is also suppressed. Further, since the gas barrier film on the inner side is covered with the inner layer, damage to the gas barrier film is prevented when foreign matter flowing in the pipe collides, or when fluid pressure is applied from the inner side of the pipe, and from the inner side of the pipe. Diffusion and permeation of the chemical substances are further suppressed. Further, since the outer side of the gas barrier film is covered with the fusion preventing film, the outer layer can be resin-molded with the heat-melted resin while maintaining the soundness of the gas barrier film. Unlike the case where the protective tape is wound on the outermost surface of the pipe, the resin-molded outer layer is less likely to have gaps/holes and is less likely to be peeled off, so that resistance to external factors is improved.

Therefore, even when fluid pressure, earth pressure, impact, load, etc. are applied to the high-density polyethylene pipe and joint, environmental stress cracking and creep fracture are less likely to occur, and cracks, brittle cracks, etc. occur. It is also possible to prevent the piping and the like from bursting. That is, it is possible to drastically improve the essential drawback of polyethylene, which is prone to brittle fracture cracking. Even if there are invisible microscopic defects, stress concentrates there and brittle fracture or stress cracks do not easily occur, and sufficient elongation and elasticity can be obtained, so stress environment crack resistance and impact resistance Can be improved.

Especially, not only in normal environment, but also in various harsh environments such as high-dose radiation environment, ultraviolet environment such as outdoors in summer, high temperature environment such as summer, environment exposed to high concentration of oxygen and acid rain, etc. High-density polyethylene pipes and joints in which brittle fracture and creep fracture due to deterioration of are reduced can be obtained. Further, a high-density polyethylene pipe or joint is obtained in which long-term hydrostatic strength, elasticity, environmental stress crack resistance, impact resistance, etc. are unlikely to decrease for a long period of time and brittle fracture cracking or rupture is unlikely to occur.

The use of the high-density polyethylene pipe and the joint according to this embodiment is not particularly limited. High density polyethylene tubing and fittings can be used in any suitable environment. Further, the high-density polyethylene pipe and the joint can be used for transporting an appropriate fluid such as water or seawater. In particular, high-density polyethylene pipes and joints are suitable for transporting water, seawater, contaminated water, accumulated water in buildings, etc. in nuclear facilities.

For example, in nuclear facilities, dozens to hundreds of pipes for nuclear facilities are stretched around and connected to a plurality of contaminated water retention areas. The total length of these pipes is generally about 10 to 20 km. The high-density polyethylene pipes and joints can be suitably used for the application of nuclear facility piping for treating such contaminated water and treating the drainage from the building.

According to the high-density polyethylene pipe and the joint, the fluid containing the radioactive substance and the fluid under a high radiation dose or outdoors can be transported soundly and reliably for a long period of time. Even when handling a fluid containing a high concentration of radioactive material, it can be used for a long period of time and the frequency of replacement and inspection is reduced. The risk of radiation exposure can be greatly reduced.

Although 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-described embodiments, and various modifications are included without departing from the technical scope. .. For example, the above embodiments are not necessarily limited to those having all the configurations described. Further, it is possible to replace part of the configuration of the embodiment with another configuration or add another configuration to the configuration of the embodiment. Further, it is possible to add another configuration, delete a configuration, or replace a configuration with respect to a part of the configuration of the embodiment.

For example, the above-mentioned high-density polyethylene pipe and joint are provided with the inner layer 4a on the inner side, but the type and thickness of the gas barrier film 2a and the fusion preventing film 3a on the inner side, the type of fluid flowing in the pipe, the fluid The inner layer 4a may not be provided depending on the concentration of foreign matter contained therein. When the inner layer 4a is not provided, the fusion preventing film 3a inside the gas barrier film 2a may not be provided.

When the inner layer 4a is not provided, the gas barrier film 2a is preliminarily wound around the outer periphery of the tubular or columnar base material that can be inserted inside the conduit 1, and the base material is inserted inside the conduit 1 and wound. A high-density polyethylene pipe can be manufactured by a method in which a film in a state is attached to the inner surface of the conduit 1 and only the base material is pulled out.

Further, the high-density polyethylene pipe and the joint include the conduit 1, the gas barrier film 2, the anti-fusion film 3, the inner layer 4a, and the outer layer 4b, but the conduit 1 and the outer gas barrier film 2b. It is also possible to provide a buffer layer or the like for buffering impact between the outer gas barrier film 2b and the outer fusion preventing film 3b. The buffer layer can be provided by, for example, a resin containing polyethylene as a main component and having a density of less than 0.940 g/cm ³ , or another film or tape.

Hereinafter, the present invention will be specifically described with reference to Examples, but the technical scope of the present invention is not limited thereto.

High-density polyethylene pipe test pieces were prepared by changing the amount of naphthene-containing oil and aromatics-containing oil added and the layer structure of the gas barrier film, and the tensile elongation at break after irradiation was evaluated.

The conduit used was a high density polyethylene produced using a Ziegler catalyst. An oil containing naphthene or an oil containing aromatics is added to a high-density polyethylene base material as an additive, and the mixture is kneaded for 10 minutes at 180° C. using a Banbury mixer to obtain pellets for high-density polyethylene pipes. Was granulated. Then, the pellets were put into an injection molding machine to mold a cylindrical conduit.

Subsequently, the gas barrier film was wound around the outer circumference of the molded conduit alone or both around the outer circumference and the inner circumference, and the fusion preventing film was wound around the outer circumference of the outer gas barrier film. Then, on the outer periphery of the anti-fusing film, a low density polyethylene having a carbon content of 0.910 g/cm ³ or more and 0.930 g/cm ³ or less is extruded to form an outer layer to obtain a high density polyethylene pipe. It was

From the produced high-density polyethylene pipe, a 1B type dumbbell-shaped test piece described in Japanese Industrial Standards JIS K 7162 was produced. Then, the produced test piece was irradiated with γ-rays emitted from a ⁶⁰ Co radiation source at a dose rate of 1 kGy/h. The absorbed dose was 1200 kGy.

<Tensile test>
The tensile test was conducted in accordance with the Japan Water Works Association standard “Polyethylene pipe for water supply and distribution JWWA K 144”. The tester was equipped with a device for indicating the maximum tensile force, and the device described in JIS B 7721 was used, which was equipped with a grip for tightening a dumbbell-shaped test piece. The thickness of the test piece and the width of the parallel portion were measured, and a reference line for measuring elongation was attached to the center of the parallel portion, and then a tensile test was performed at a test speed of 25 mm/min and room temperature. The distance between marked lines was 50 mm. A tensile test was performed to measure the distance between the marked lines at break of the test piece, and the elongation at break was calculated by the following mathematical formula (1). In the mathematical expression (1), EB indicates elongation at break (%), L0 indicates distance between marked lines (mm), and L1 indicates distance between marked lines at break (mm).

Hereinafter, the measurement results of the tensile elongation at break after the irradiation treatment of the test pieces produced by changing the addition amount of the oil containing naphthene will be shown.

The conduit used was high-density polyethylene having a density of 0.95 g/cm ³ . As the additive, among the oils produced when the crude oil was refined, the oils in which %CN of the ring analysis by the ndM method was a predetermined value and %CA was 30% were used. The blending amount of oil was 5 parts by mass with respect to 100 parts by mass of high-density polyethylene. As the gas barrier film, a LLDPE/EVOH/LLDPE multilayer film having a thickness of EVOH of 24 μm and a MFR of LLDPE of 3 g/10 min was used so that the total thickness when wound was 300 μm. .. As the anti-fusion film, a polyethylene terephthalate stretched film was used so that the total thickness when wound was 100 μm. As the outer layer, a low-density polyethylene layer having a thickness of 2 mm and containing 3% by mass of carbon was formed.

4A and 4B are diagrams showing the relationship between the% CN of oil used as an additive and the elongation at break.
In FIGS. 4A and 4B, the horizontal axis represents% CN (%) of oil used as an additive, and the vertical axis represents elongation (%) at break due to tension. 4A shows the result of winding the gas barrier film only on the outer circumference of the conduit, and FIG. 4B shows the result of winding the same kind of gas barrier film on both the outer circumference and the inner circumference of the conduit.

As shown in FIG. 4A, when an oil containing naphthene was added as an additive, the tensile fracture elongation was remarkably increased when %CN was 20% or more and 60% or less, and radiation deterioration was satisfactorily suppressed. Was obtained. As shown in FIG. 4B, when there is an inner gas barrier film, the tensile elongation at break is slightly higher than that in FIG. 4A, and the tensile elongation at break is large when %CN is 10% or more and 60% or less.

Next, the measurement results of the tensile elongation at break after the irradiation treatment are shown for the test pieces produced by changing the addition amount of the oil containing aromatics.

The conduit used was high-density polyethylene having a density of 0.95 g/cm ³ . As an additive, among the oils produced when the crude oil was refined, the oil in which %CA of the ring analysis by the ndM method was a predetermined value and %CN was 40% was used. The blending amount of oil was 5 parts by mass with respect to 100 parts by mass of high-density polyethylene. As the gas barrier film, a LLDPE/EVOH/LLDPE multilayer film having a thickness of EVOH of 24 μm and a MFR of LLDPE of 3 g/10 min was used so that the total thickness when wound was 300 μm. .. As the anti-fusion film, a polyethylene terephthalate stretched film was used so that the total thickness when wound was 100 μm. As the outer layer, a low-density polyethylene layer having a thickness of 2 mm and containing 3% by mass of carbon was formed.

5A and 5B are diagrams showing the relationship between the% CA of oil used as an additive and the elongation at break.
5A and 5B, the horizontal axis represents% CA (%) of the oil containing aromatics used as an additive, and the vertical axis represents the elongation (%) at break due to tension. 5A shows the result of winding the gas barrier film only on the outer circumference of the conduit, and FIG. 5B shows the result of winding the same kind of gas barrier film on both the outer circumference and the inner circumference of the conduit.

As shown in FIG. 5A, when an oil containing aromatics is added as an additive, the% CA is 5% or more and 60% or less, and particularly 5% or more and 40% or less, the tensile elongation at break becomes significantly large, The result was that the radiation deterioration was well suppressed. As shown in FIG. 5B, when the inner gas barrier film is present, the tensile elongation at break is slightly higher than that of FIG. Has become.

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

The conduit used was high-density polyethylene having a density of 0.95 g/cm ³ . As an additive, among the oils produced when the crude oil was refined, the oil having %CN of 40% and %CA of 30% in the ring analysis by the ndM method was used. The blending amount of oil was 5 parts by mass with respect to 100 parts by mass of high-density polyethylene. The gas barrier film was a multilayer film of LLDPE/EVOH/LLDPE, and a film having a thickness of EVOH of 24 μm was used so that the total thickness when wound was 300 μm. As the anti-fusion film, a polyethylene terephthalate stretched film was used so that the total thickness when wound was 100 μm. As the outer layer, a low-density polyethylene layer having a thickness of 2 mm and containing 3% by mass of carbon was formed.

6A and 6B are diagrams showing the relationship between the MFR of linear low-density polyethylene used for the gas barrier film and the elongation at break.
In FIGS. 6A and 6B, the horizontal axis represents the MFR (g/10 minutes) of the linear low-density polyethylene used as the surface layer of the gas barrier film, and the vertical axis represents the elongation (%) at break due to tension. 6A shows the result of winding the gas barrier film only on the outer circumference of the conduit, and FIG. 6B shows the result of winding the same kind of gas barrier film on both the outer circumference and the inner circumference of the conduit.

As shown in FIG. 6A, the linear low-density polyethylene used as the surface layer of the gas barrier film has an MFR of 0.8 g/10 minutes or more and 10 g/10 minutes or less, and a tensile elongation at break of more than 400%. The result was that the radiation deterioration was well suppressed. As shown in FIG. 6B, when there is an inner gas barrier film, the tensile elongation at break is slightly higher than that of FIG. 6A, and the tensile elongation at break becomes large at MFR of 3 g/10 minutes or less.

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

The conduit used was high-density polyethylene having a density of 0.95 g/cm ³ . As an additive, among the oils produced when refining crude oil, an oil having a% CN of 40% and a% CA of 30% in a ring analysis by the ndM method was used. The blending amount of oil was 5 parts by mass with respect to 100 parts by mass of high-density polyethylene. As the gas barrier film, a LLDPE/EVOH/LLDPE multilayer film having a thickness of EVOH of 24 μm and an MFR of LLDPE of 3 g/10 min was used. As the anti-fusion film, a polyethylene terephthalate stretched film was used so that the total thickness when wound was 100 μm. As the outer layer, a low-density polyethylene layer having a thickness of 2 mm and containing 3% by mass of carbon was formed.

7A and 7B are diagrams showing the relationship between the total thickness of the gas barrier film and the elongation at break.
In FIGS. 7A and 7B, the horizontal axis represents the total thickness (μm) when the gas barrier film is wrapped around the outer periphery of the conduit, and the vertical axis represents the elongation (%) at break due to tension. FIG. 7A shows the result of winding the gas barrier film only on the outer circumference of the conduit, and FIG. 7B shows the result of winding the same kind of gas barrier film on both the outer circumference and the inner circumference of the conduit.

As shown in FIG. 7A, when the total thickness of the gas barrier film was 50 μm or more and 400 μm or less, the tensile elongation at break was remarkably increased, and the result that radiation deterioration was favorably suppressed was obtained. As shown in FIG. 7B, the tensile elongation at break is slightly higher than that of FIG. 7A when the inner gas barrier film is present.

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

The conduit used was high-density polyethylene having a density of 0.95 g/cm ³ . As an additive, among the oils produced when the crude oil was refined, the oil having %CN of 40% and %CA of 30% in the ring analysis by the ndM method was used. The blending amount of oil was 5 parts by mass with respect to 100 parts by mass of high-density polyethylene. The gas barrier film was a multi-layer film of LLDPE/EVOH/LLDPE, and a film having an MFR of LLDPE of 3 g/10 min was used so that the total thickness when wound was 300 μm. As the anti-fusion film, a polyethylene terephthalate stretched film was used so that the total thickness when wound was 100 μm. As the outer layer, a low-density polyethylene layer having a thickness of 2 mm and containing 3% by mass of carbon was formed.

8A and 8B are diagrams 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 FIGS. 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 tension. 8A shows the result of winding the gas barrier film only on the outer circumference of the conduit, and FIG. 8B shows the result of winding the same kind of gas barrier film on both the outer circumference and the inner circumference of the conduit.

As shown in FIG. 8A, 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 becomes significantly large and the radiation deterioration is well suppressed. Results were obtained. As shown in FIG. 8B, the tensile elongation at break is slightly higher than that in FIG. 8A when the inner gas barrier film is present.

Next, the measurement results of the tensile elongation at break after the irradiation treatment with respect to the test pieces produced by changing the thickness of the fusion preventing film will be shown.

The conduit used was high-density polyethylene having a density of 0.95 g/cm ³ . As an additive, among the oils produced when the crude oil was refined, the oil having %CN of 40% and %CA of 30% in the ring analysis by the ndM method was used. The blending amount of oil was 5 parts by mass with respect to 100 parts by mass of high-density polyethylene. As the gas barrier film, a LLDPE/EVOH/LLDPE multilayer film having a thickness of EVOH of 24 μm and a MFR of LLDPE of 3 g/10 min was used so that the total thickness when wound was 300 μm. .. A polyethylene terephthalate stretched film was used as the fusion preventing film. As the outer layer, a low-density polyethylene layer having a thickness of 2 mm and containing 3% by mass of carbon was formed.

9A and 9B are diagrams showing the relationship between the thickness of the anti-fusing film and the elongation at break.
In FIGS. 9A and 9B, the horizontal axis represents the thickness (μm) of the anti-fusing film, and the vertical axis represents the elongation (%) at break due to tension. 9A shows the result of winding the gas barrier film only around the outer circumference of the conduit, and FIG. 9B shows the result of winding the same kind of gas barrier film around both the outer circumference and the inner circumference of the conduit.

As shown in FIG. 9A, when the thickness of the anti-fusing film was 20 μm or more and 200 μm or less, the tensile elongation at break was remarkably increased, and the result that radiation deterioration was favorably suppressed was obtained. As shown in FIG. 9B, when there is an inner gas barrier film, the tensile elongation at break is slightly higher than that in FIG. 9A.

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

The conduit used was high-density polyethylene having a density of 0.95 g/cm ³ . As an additive, among the oils produced when the crude oil was refined, the oil having %CN of 40% and %CA of 30% in the ring analysis by the ndM method was used. The blending amount of oil was 5 parts by mass with respect to 100 parts by mass of high-density polyethylene. As the gas barrier film, a LLDPE/EVOH/LLDPE multilayer film having a thickness of EVOH of 24 μm and a MFR of LLDPE of 3 g/10 min was used so that the total thickness when wound was 300 μm. .. As the anti-fusion film, a polyethylene terephthalate stretched film was used so that the total thickness when wound was 100 μm. As the outer layer, a low-density polyethylene layer containing 3% by mass of carbon was formed.

10A and 10B are diagrams showing the relationship between the thickness of the outer layer and the elongation at break.
In FIGS. 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 tension. 10A shows the result of winding the gas barrier film only on the outer circumference of the conduit, and FIG. 10B shows the result of winding the same kind of gas barrier film on both the outer circumference and the inner circumference of the conduit.

As shown in FIG. 10A, when the thickness of the outer layer was 0.5 mm or more and 3 mm or less, the tensile elongation at break became significantly large, and the result was that radiation deterioration was favorably suppressed. As shown in FIG. 10B, the tensile elongation at break is slightly higher than that in FIG. 10A when the inner gas barrier film is present.

Next, with respect to the test pieces produced by changing the layer structure of the gas barrier film, the measurement results of tensile break elongation after irradiation treatment and the confirmation results of chemical cracks are shown.

The conduit used was high-density polyethylene having a density of 0.95 g/cm ³ . As an additive, among the oils produced when the crude oil was refined, the oil whose% CN in the ring analysis by the ndM method was 32% and whose% CA was 10% was used. The blending amount of oil was 5 parts by mass with respect to 100 parts by mass of high-density polyethylene. As the gas barrier film, a multi-layer film having a thickness of EVOH of 6 μm was used so that the total thickness when wound was 300 μm. As the anti-fusion film, a polyethylene terephthalate stretched film was used so that the total thickness when wound was 100 μm. As the outer layer, a low-density polyethylene layer having a thickness of 2 mm and containing 3% by mass of carbon was formed.

As shown in Table 1, when linear low density polyethylene (LLDPE) was used as the surface layer of the gas barrier film, radiation deterioration was suppressed as compared with the case of low density polyethylene (LDPE). No matter what kind of gas barrier film was used, high radiation resistance was obtained and no chemical crack was observed.

1 conduit, conduit part 2 gas barrier film 3 fusion prevention film 4a inner layer 4b outer layer 10 high-density polyethylene pipe 21 intermediate layer 22 surface layer

Claims (15)

A conduit having a density of 0.940 g/cm ³ or more and 0.980 g/cm ³ or less and a high density polyethylene as a main component;
An inner gas barrier film that covers the inner surface of the conduit and contains an ethylene/vinyl alcohol copolymer resin,
An outer gas barrier film covering the outer surface of the conduit and containing an ethylene/vinyl alcohol copolymer resin,
A fusion preventing film which covers the outer surface of the outer gas barrier film and is made of a resin having a melting point of 150° C. or higher;
An outer layer that covers the outer surface of the anti-fusing film and has a low density polyethylene as a main component, the density of which is 0.910 g/cm ³ or more and 0.930 g/cm ³ or less;
High-density polyethylene pipe with. The high-density polyethylene pipe according to claim 1,
A high-density polyethylene pipe, which covers the inner surface of the gas barrier film on the inner side and includes an inner layer mainly composed of low-density polyethylene having a density of 0.910 g/cm ³ or more and 0.930 g/cm ³ or less. The high density polyethylene pipe according to claim 2, wherein
A high-density polyethylene pipe comprising an inner fusion preventing film made of a resin having a melting point of 150° C. or higher between the conduit and the inner gas barrier film. The high density polyethylene pipe according to claim 2, wherein
A high-density polyethylene pipe provided with an inner fusion-preventing film made of a resin having a melting point of 150° C. or higher between the inner gas barrier film and the inner layer. The high-density polyethylene pipe according to claim 1,
A high-density polyethylene pipe, wherein the conduit contains at least one of an oil containing naphthene produced when refining crude oil and an oil containing aromatics produced when refining crude oil. The high-density polyethylene pipe according to claim 1,
The oil in which the conduit contains naphthene having a% CN of 10% or more and 60% or less in a ring analysis by the n-d-M method among oils produced when the crude oil is refined, and an oil produced when the crude oil is refined A high-density polyethylene tube containing at least one of the oils containing aromatics having a% CA of 5% or more and 80% or less in the ring analysis by the n-d-M method. The high-density polyethylene pipe according to claim 1,
The inner gas barrier film and the outer gas barrier film are high-density polyethylene pipes in which the thickness of the ethylene/vinyl alcohol copolymer resin is 1 μm or more and 50 μm or less. The high-density polyethylene pipe according to claim 1,
The inner gas barrier film and the outer gas barrier film are multilayer films having an intermediate layer made of an ethylene/vinyl alcohol copolymer resin and surface layers laminated on both surfaces of the intermediate layer,
The surface layer is a high-density polyethylene pipe containing at least one of low-density polyethylene and linear low-density polyethylene as a main component. The high-density polyethylene pipe according to claim 8,
The multilayer film is a high-density polyethylene pipe having a total thickness of 50 μm or more and 400 μm or less when wrapped around the outer circumference. The high-density polyethylene pipe according to claim 1,
The fusion prevention film is a polyethylene terephthalate stretched film, a polyimide film, or a polyamide-imide film, which is a high-density polyethylene pipe. The high-density polyethylene pipe according to claim 1,
The fusion prevention film is a high-density polyethylene pipe having a total thickness of 20 μm or more and 200 μm or less when wrapped around the outer periphery. The high-density polyethylene pipe according to claim 1,
A high-density polyethylene pipe in which the outer layer contains carbon black. The high density polyethylene pipe according to claim 12,
The carbon black is a high-density polyethylene pipe in which the content of the outer layer is 1.0% by mass or more and 3.0% by mass or less. The high-density polyethylene pipe according to any one of claims 1 to 13,
High-density polyethylene pipe, which is a pipe for nuclear equipment used to transport fluids in nuclear facilities. A tubular conduit part having a density of 0.940 g/cm ³ or more and 0.980 g/cm ³ or less and a high density polyethylene as a main component;
An inner gas barrier film that covers the inner surface of the conduit portion and contains an ethylene/vinyl alcohol copolymer resin,
An outer gas barrier film that covers the outer surface of the conduit portion and contains an ethylene/vinyl alcohol copolymer resin,
A fusion preventing film which covers the outer surface of the outer gas barrier film and is made of a resin having a melting point of 150° C. or higher;
An outer layer that covers the outer surface of the anti-fusing film and has a low density polyethylene as a main component, the density of which is 0.910 g/cm ³ or more and 0.930 g/cm ³ or less;
A joint equipped with.