JP2020016323A - High-density polyethylene pipe, joint and sealant - Google Patents

Abstract

To provide a high-density polyethylene pipe that is restrained from being deteriorated by an external factor such as radiation, a joint and a sealant.SOLUTION: A high-density polyethylene pipe 10, a joint and a sealant include: an inner layer 1 that is composed predominantly of high-density polyethylene having a density of 0.940 g/cmto 0.980 g/cm; a gas barrier film 2 that coates an outer surface of the inner layer 1 and that includes an ethylene-vinyl alcohol copolymer resin; a fusion prevention film 3 that coats an outer surface of the gas barrier film 2 and that is made of a resin with a melting point of 150°C or more; and an outer layer 4 that coats an outer surface of the fusion prevention film 3 and that is composed predominantly of low-density polyethylene having a density of 0.910 g/cmto 0.930 g/cm.SELECTED DRAWING: Figure 1

Description

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

  BACKGROUND ART Piping for a nuclear facility laid in a nuclear facility is required to be capable of safely transporting 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 piping for nuclear facilities. However, in nuclear-related facilities where space and time constraints are assumed, steel pipes are no longer optimal due to the large number of man-hours and equipment required for construction. Under such circumstances, replacement with resin-made piping, which is easy to move and process, and easily joins pipes and joints, is being promoted.

  As a resin pipe, use of a high-density polyethylene pipe, which is also used as a long-distance pipe for water supply, is being studied. However, high-density polyethylene pipes are inferior in radiation resistance as compared with steel pipes, and have a drawback that brittle fracture easily occurs under high radiation dose. If the high-density polyethylene pipe deteriorates and causes minute defects in the resin, when pressure from the fluid in the pipe or earth pressure from the outside of the pipe is applied, stress concentrates on the defect, causing cracking or rupture. Is generated.

  Degradation of polyethylene proceeds mainly by autoxidation involving radicals, but is promoted not only by the action of radiation but also by ultraviolet rays and oxygen. If the fluid transported in the high-density polyethylene tube contains radioactive materials or is likely to be activated, it is important not to cause a leakage event, so external factors such as radiation, oxygen, and ultraviolet rays There is a need to take measures to prevent deterioration due to aging.

  For example, Patent Literature 1 describes a technique in which a hydroaromatic-type deterioration inhibitor or propylfluoranthene is added to high-density polyethylene so as to be 1 to 7 parts by mass.

  Patent Literature 2 describes a high-density polyethylene pipe, a joint that can be thermally fused to an outer surface thereof, and a fluid transport device including the same. In a high-density polyethylene pipe, a tie molecule connecting a crystal structure that is likely to be a starting point of destruction is reinforced by a crosslinked structure. In addition, a heat-fusible non-crosslinked polyethylene layer is formed on the outer surface of the high-density polyethylene pipe.

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

  The radiation resistance of a high-density polyethylene pipe is improved by adding a deterioration inhibitor to high-density polyethylene as in Patent Literature 1 or by reinforcing between tie molecules with a crosslinked structure as in Patent Literature 2. be able to. In addition, if the high-density polyethylene pipe has a double-pipe structure, it is difficult for ultraviolet rays and atmospheric oxygen to reach the inside. Can be kept.

  However, these high-density polyethylene pipes also have a durable life of 40 years or more, and are not sufficiently durable as compared with steel pipes that do not require replacement in a short period of time. High-density polyethylene has the essential drawback of having the compressive strength and hardness required for piping, but having poor ductility and easily brittle fracture when used under high radiation doses. I have. The radical reaction that deteriorates the resin is easily started by radiation, but is accelerated by external factors such as oxygen and ultraviolet rays. Therefore, advanced measures to prevent these are required.

  In addition, high-density polyethylene pipe joints used together with high-density polyethylene pipes, and sealing materials such as gaskets and O-rings are sometimes exposed to external factors such as ultraviolet rays, and countermeasures are required. Ultra-high molecular weight polyethylene (UHPE) or the like is also used as a material for the sealing material, and long-term sealing of a radioactive solution in a nuclear fuel facility or the like as well as piping materials is expected.

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

In order to solve the above-mentioned problems, a high-density polyethylene pipe according to the present invention includes an inner layer mainly composed of high-density polyethylene having a density of 0.940 g / cm ³ or more and 0.980 g / cm ³ or less, and an outer surface of the inner layer. A gas barrier film containing an ethylene / vinyl alcohol copolymer resin, an outer surface of the gas barrier film, and an anti-fusion film made of a resin having a melting point of 150 ° C. or more, and an outer surface of the anti-fusion film. And an outer 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.

  Further, the joint and the seal material according to the present invention have the same layer configuration as the high-density polyethylene pipe.

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

FIG. 1 is a cross-sectional view schematically illustrating a high-density polyethylene pipe according to the present invention. The perspective view showing typically the high-density polyethylene pipe concerning the present invention. The figure which shows the relationship between% CN of the oil used as an additive, and elongation at break. The figure which shows the relationship between% CA of the oil used as an additive, and elongation at break. It is a figure which shows the relationship between MFR of linear low density polyethylene used for the gas barrier film, and elongation at break. FIG. 3 is a diagram showing a relationship between the total thickness of the gas barrier film and the elongation at break. It is a 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. It is a figure which shows the relationship between the thickness of a fusion prevention film, and the elongation at the time of fracture | rupture. FIG. 4 is a diagram illustrating a relationship between the thickness of a protective layer (outer layer) and elongation at break.

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

FIG. 1 is a sectional view schematically showing a high-density polyethylene pipe according to the present invention. FIG. 2 is a perspective view schematically showing a high-density polyethylene pipe according to the present invention. In FIG. 2, the inside of the tube is exposed to show the layer configuration 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 cylindrical inner layer 1 forming a conduit, a gas barrier film 2 covering the outer surface of the inner layer 1, and an outer surface of the gas barrier film 2. And an outer layer 4 serving as a protective layer that covers the outer surface of the anti-fusion film 3.

  The high-density polyethylene pipe 10 is mainly used as a fluid transport pipe for transporting a fluid between devices and equipment. The high-density polyethylene tube 10 has excellent radiation resistance and suppresses deterioration of the high-density polyethylene conduit (inner layer 1) due to external factors such as radiation, oxygen, and ultraviolet rays. It is particularly suitably used for transporting a fluid containing the fluid or transporting the fluid under a high radiation dose.

  The high-density polyethylene tube 10 is provided with a conduit through which a fluid flows so as to drastically improve the essential disadvantage of high-density polyethylene, which can easily break when subjected to a high radiation dose. It is a multilayer pipe in which the outside of the inner layer 1) is covered with a gas barrier film 2 for improving weather resistance and a protective layer (outer layer 4). Between the gas barrier film 2 and the protective layer (outer layer 4), the protective layer (outer layer 4) has a layer structure in which the anti-fusing film 3 is sandwiched so that the gas barrier film 2 is not damaged when the resin layer is molded. .

The inner layer 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. High-density polyethylene has high tensile strength and impact resistance, but low brittleness. Therefore, according to the inner layer 1 containing high-density polyethylene as a main component, the pressure resistance and hardness required for piping can be obtained.

The high-density polyethylene may contain 1-butene, 1-hexene, and the like as a monomer in addition to ethylene as long as 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 a Ziegler catalyst, a metallocene catalyst, and a Phillips catalyst. The high-density polyethylene may be a mixed material blended with another resin or a recycled material obtained by reusing a polyethylene product as a raw material. The high-density polyethylene may contain another 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 (MFR) determined in accordance with ISO 1133 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 resin, more preferably, a resin of 0.2 g / 10 min or more and 0.5 g / 10 min or less can be used. However, the high-density polyethylene constituting the inner layer 1 is not limited to a resin having such physical properties.

  The inner layer 1 may have a general additive such as an antioxidant and a heat stabilizer added to a base material mainly composed of high-density polyethylene, or may have no general additive. You may. 1 and 2, the shape of the inner layer 1 is cylindrical. However, dimensions such as ellipticity, cross-sectional shape, longitudinal shape, inner and outer diameters, and wall thickness of the inner layer 1 are particularly limited. Not something.

  The inner layer 1 is, for a base material mainly composed of high-density polyethylene, an oil containing naphthenes generated when crude oil is refined, and at least an oil containing aromatics generated when refined crude oil. It is preferable that one is blended. When these oils are blended, as described later, the slipperiness of polyethylene molecules is improved, and deterioration of high-density polyethylene due to craze destruction is suppressed.

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

As the oil containing the aromatics, an oil obtained by refining a paraffinic crude oil or a naphthenic crude oil as a raw material can be blended. For example, a high specific gravity, high viscosity residual oil or the like generated in the process of refining 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, preferably 10% or more and 80% or less, in a ring analysis by the dn-M method, among oils produced when a naphthenic crude oil is refined. Is more preferable, and an oil of 20% or more and 60% or less is further preferable. When% CN is at least about 20% and at most about 60%, a high effect of suppressing deterioration of the 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 ring analysis by the n-d-M method among oils produced when a paraffinic crude oil or a naphthenic crude oil is refined, An oil of 5% to 60% is more preferable, and an oil of 5% to 40% is more preferable. When% CA is at least about 5% and at most about 40%, a high effect of suppressing deterioration of the high-density polyethylene can be obtained.

  Examples of the naphthene-containing oil and the aromatics-containing oil include, for example, oil having a CN of 20% or more and 60% or less in the ring analysis by the dn-M method among the oils generated when crude oil is refined. Oil having a% CA of 5% or more and 40% or less in ring analysis by the ndM method may be used as an additive.

  The ndm method is one method of analyzing the structural group of oil (oil) based on ASTM D 3238-85 (ring analysis method), and is generally used for analyzing the composition of base oil. According to the ndM method, based on data of the oil density d20 at 20 ° C., the refractive index nD20 of the oil at 20 ° C., and the average molecular weight of the oil, the mass ratio (% CP), mass ratio of naphthenic 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 formed of a resin film containing at least an ethylene-vinyl alcohol copolymer (EVOH). According to the gas barrier film 2 containing the ethylene / vinyl alcohol copolymer resin, oxygen in the outside air is shielded, and oxidative deterioration of the high-density polyethylene of the inner layer 1 is suppressed.

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 has 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 made of an ethylene / vinyl alcohol copolymer resin, or may be composed of a plurality of layers including a layer made of an ethylene / vinyl alcohol copolymer resin.

  The average polymerization degree, ethylene content, and saponification degree of the ethylene / vinyl alcohol copolymer resin are not particularly limited. For example, the average 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, and further preferably 5 μm or more. Further, it is preferably 60 μm or less, more preferably 50 μm or less, and still more preferably 30 μm or less. As the thickness of the ethylene / vinyl alcohol copolymer resin is 0.5 μm or more, more excellent gas barrier properties are obtained, and the oxidation deterioration of the resin of the inner layer 1 is suppressed. In addition, since pinholes do not easily occur, the gas barrier properties are easily maintained. When the thickness is 5 μm or more and 50 μm or less, particularly high radiation resistance can be obtained due to the neutron shielding ability of the resin itself. On the other hand, the thinner the thickness is 60 μm or less, the more flexible the gas barrier film 2 becomes when the high-density polyethylene pipe 10 is constructed or moved.

  The ethylene / vinyl alcohol copolymer resin may be a mixture blended with another resin. Other resins to be blended include, for example, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, polyolefin, modified polyolefin, polyamide, polyester and the like. The ethylene / vinyl alcohol copolymer resin may be a resin modified with an epoxy compound or the like, or may be a copolymer containing other monomers other than ethylene and vinyl acetate.

  As shown in FIGS. 1 and 2, the gas barrier film 2 has a multilayer structure including an intermediate layer 22 made of an ethylene / vinyl alcohol copolymer resin, and surface layers (21, 23) laminated on both surfaces of the intermediate layer 22. It is preferably a film. 1 and 2, the surface layers (21, 23) include an inner layer 21 disposed inside the intermediate layer 22 and an outer layer 23 disposed outside the intermediate layer 22. However, the number of layers laminated on both surfaces of the intermediate layer 22 is not particularly limited.

  It is preferable that the surface layers (21, 23) include at least one of low-density polyethylene (Low Density Polyethylene: LDPE) and linear low-density polyethylene (LLDPE). According to these polyethylenes, coextrusion with an ethylene / vinyl alcohol copolymer resin is possible. In addition, according to polyethylene, a high neutron shielding ability is obtained by the resin itself, so that radiation deterioration of the resin of the inner layer 1 is suppressed.

In particular, when the surface layers (21, 23) are formed of low-density polyethylene, a multilayer film having high flexibility, impact resistance, cold resistance, moisture resistance, and the like can be formed with high precision. In addition, the external pressure, impact, and the like applied to the high-density polyethylene pipe 10 can be reduced to prevent damage to the inner layer 1 and peeling and falling off of the gas barrier film 2. The low-density polyethylene means a 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 layers (21, 23) are formed of linear low-density polyethylene, higher tensile breaking strength, adhesion, cold resistance, etc. can be obtained than with 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 contain 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 a Ziegler catalyst or a Phillips catalyst.

  The low-density polyethylene or linear low-density polyethylene forming the surface layers (21, 23) preferably has a dissolution index (MFR) determined in accordance with ISO 1133 of 0.5 g / 10 min or more. Further, it is preferably 50 g / 10 min or less, more preferably 20 g / 10 min or less, further preferably 10 g / 10 min or less, particularly preferably 5 g / 10 min or less. It is known that there is a correlation between the molecular weight of the resin and the MFR. In the case of polyethylene having such an MFR, since the low molecular weight component is small, a high neutron shielding ability can be obtained by the resin itself.

  As long as the surface layers (21, 23) have a layer made of low-density polyethylene or a layer made of linear low-density polyethylene on both sides of the intermediate layer 22, even if they have a layer structure in which other resins are laminated. Good. For example, from the viewpoint of toughening a multilayer film, a multilayer structure composed of polyamide (polyamide: PA) such as nylon 6 or polyester (polyester: PEs) such as polyethylene terephthalate may be used.

  Specific examples of the multilayer film include, but are not limited to, LDPE / EVOH / LDPE and LLDPE / EVOH / LLDPE. The low-density polyethylene and the linear low-density polyethylene are preferably those excluding low-molecular-weight components from the viewpoint of improving radiation resistance. Another layer such as an adhesive layer may be provided between the intermediate layer 22 and the surface layers (21, 23) as necessary.

  The thickness of the multilayer film is preferably from 20 μm to 200 μm. When the thickness is 20 μm or more, the durability increases as the thickness increases. Therefore, when the high-density polyethylene pipe 10 is constructed or moved, or when laid in a harsh environment where external force is likely to be applied, such as outdoors, the gas barrier property is soundly improved. 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 on the conduit (inner layer 1) are improved, and the damage of the film during handling is reduced.

  The gas barrier film 2 preferably has a total thickness of 20 μm or more, more preferably 50 μm or more, when wound around the outer periphery of the inner layer 1. Further, it is preferably 500 μm or less, more preferably 400 μm or less, and still more preferably 300 μm or less. The thicker the total thickness is 20 μm or more, the higher the gas barrier property is obtained, so that the oxidative deterioration of the resin of the inner layer 1 can be reliably suppressed. Further, when the total thickness is 50 μm or more and 400 μm or less, particularly high radiation resistance is obtained. On the other hand, as the total thickness is 500 μm or less, the material cost and winding time of the gas barrier film 2 are reduced.

  The gas barrier film 2 can be fused to the inner layer 1 or bonded with an adhesive, an adhesive or the like. However, it is preferable that the gas barrier film 2 does not fuse or adhere to the inner layer 1. When the inner layer 1 and the gas barrier film 2 are surface-bonded by fusion or adhesion, when a force is applied in the length direction or the radial direction of the pipe, stresses in opposite directions are applied to the inner layer 1 and the gas barrier film 2 having different elongation rates. As a result, the probability of occurrence of stress fracture or breakage increases. Like the inner layer 1, the gas barrier film 2 may be blended with an oil containing naphthene or an oil containing aromatics.

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

  Polyethylene pipes are widely used as long-distance pipes for water supply and the like because they are lighter in weight and easier to move and process than steel pipes. 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, heat, etc., and its elasticity, stress resistance, crack resistance, impact resistance, etc. decrease. Brittle fractures are likely to occur when the pipe is scratched or when the piping is exposed to chemicals.

  It is known that molecules of an organic polymer are excited by radiation, ultraviolet rays, heat, or the like, and the bonds in the molecule are broken to be decomposed. For example, when radiation or the like acts on polyethylene, hydrogen radicals (H.) and hydrocarbon radicals (R.) are generated. Radicals are highly reactive and combine radicals (recombination), radicals extract elements to generate other radicals (extraction reaction), and radicals add to double bonds (addition reaction) At the same time, the radicals are bonded to each other, and at the same time the molecular chain is cut (disproportionation reaction).

  Recombination and addition reactions by radicals lead to an increase in molecular weight, called crosslinking, and disproportionation reactions lead to a decrease in molecular weight, called decay. In a polyethylene pipe, as the cross-linking and collapse of the molecular chain progresses, the resistance to impact and bending is reduced, and the physical properties such as the pipe become brittle. And, as the embrittlement of the tube progresses, when internal pressure, external pressure, impact, load, etc. are applied, stress and creep fractures such as cracks and cracks are likely to occur, and cracks and brittle cracks occur on the tube wall. Or a rupture of the pipe body.

  As a piping material such as a polyethylene pipe for water distribution, high-density polyethylene, which has been improved in performance using multistage polymerization or an improved catalyst, is also used. In this kind of high-density polyethylene, the long-term hydrostatic pressure strength and environmental stress crack resistance are improved by increasing the high molecular weight region and increasing the number of tie molecules connecting the crystal structures.

  Generally, it is known that the crystalline region is hardly affected even under a severe environment, but the amorphous region increases when a tie molecule is cut under a severe environment. It is considered that when the cutting of the tie molecules proceeds, stress concentration easily occurs inside the resin when an external force is applied, and the long-term hydrostatic pressure strength, environmental stress cracking resistance, and impact resistance decrease.

In particular, it is known that the propagation reaction of oxidation (chain reaction) proceeds by radicals in the atmosphere where oxygen is present. First, as shown in the reaction formula (1), a hydrocarbon radical (R ·) reacts with oxygen (O ₂ ) to generate a peroxide radical (ROO ·).

  The peroxide radical (ROO.) Is rich in reactivity, as shown in reaction formula (2), extracts hydrogen (H) from another molecule (RH), and forms a peroxide (ROOH) and a new hydrocarbon radical. (R.).

  Then, the newly generated hydrocarbon radical (R •) generates another peroxide radical (ROO •) according to the reaction formula (1), and the peroxide radical (ROO •) is generated according to the reaction formula (2). Produces another peroxide (ROOH). Since peroxide (ROOH) is also unstable, it generates new oxy radicals (RO.), Peroxide radicals (ROO.) And the like as shown in Reaction Formulas (3) to (5).

  In the atmosphere where oxygen is present, such a propagation reaction of oxidation causes the initially generated hydrocarbon radical (R.) to multiply a large number of new radicals, thereby promoting the cross-linking and collapse of molecular chains. For this reason, the deterioration of the resin accelerates, and stress and creep ruptures are likely to occur.

  In the atmosphere where oxygen is present, ozone may be generated by radiation or ultraviolet rays. Ozone has high reactivity with polyethylene having a double bond, and generates ozonide by reaction with polyethylene. Since ozonide is unstable, the OO 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 a fluid pressure, an earth pressure, or the like of about 1 MPa or more is applied to the polyethylene pipe, the molecular chains are likely to be in an elongated state, so that the ozone permeability is increased and stress is easily concentrated on a specific portion. In such a case, the possibility of generation of an ozone crack or the possibility of destruction starting from the ozone crack increases.

  Also, polyethylene tubes are sometimes used for transporting high-temperature fluids. The various elementary reactions that result in the decomposition of a molecule are also related to molecular motion, that is, the vibration and collision probability of the molecule. Since the molecular motion becomes more intense as the temperature becomes higher, when the polyethylene is exposed to the high temperature, the cross-linking and collapsing of the molecular chains are accelerated, and the deterioration of the resin remarkably progresses.

  In particular, 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. In general, a 10 ° C. increase in temperature doubles the reaction rate. Therefore, when the polyethylene tube is exposed to a high temperature, for example, when the polyethylene tube is used for transporting a high-temperature fluid, the oxidative deterioration is accelerated, and the crosslinking and collapse of the molecular chains proceed, and the deterioration of the resin becomes remarkable.

  Such deterioration of polyethylene due to radiation, ultraviolet rays, heat, etc., reduces various properties such as elastic modulus, tensile strength, elongation, etc., and deteriorates stress environment crack resistance, impact resistance, and the like. If polyethylene pipes and fittings are continuously used in severe environments such as radiation environment, ultraviolet environment, and high temperature environment, stress destruction may occur if internal pressure, external pressure, impact, etc. are applied, or if they are exposed to chemical substances. And creep destruction occur, causing problems such as cracks, cracks, and rupture of the pipe body, resulting in problems such as leakage of fluid.

  On the other hand, if the inner layer 1 of the high-density polyethylene pipe 10 is covered with the gas barrier film 2, the permeation of oxygen is prevented and the propagation reaction of oxidation is suppressed. Is suppressed from being oxidatively degraded. When an oil containing naphthene or an oil containing aromatics is blended in the inner layer 1, radicals generated by the action of radiation or ultraviolet rays can be captured by the components of the oil.

  In general, polyethylene generates cracks, cracks, etc. due to various external factors such as radiation, ultraviolet rays, and heat, but the elongation is reduced regardless of the type of external factors, regardless of the fracture mode. There is a feature that whitening appears on the fracture surface. Whitening and cracks have occurred on the fracture surface, and voids and fibrils are present. Whitening is a phenomenon caused by Mie scattering of light due to the formation of voids. Bleaching indicates that craze destruction, a form of damage composed of voids and fibrils, has occurred.

In general, it is known that the fracture of polyethylene due to tension progresses in the following order (A) to (D).
(A) Propagation of localized region of strain generated immediately after tensile yielding (B) Propagation of craze fracture region (C) Breakage of molecular chains and cracks at concentrated portion of craze fracture (D) Polymer fracture

At the crystal level, it is known that the following changes occur due to tension.
(A) Destruction of crystal at molecular level (molecular chain separation)
(B) Block-like fracture of crystal (molecule peeling)
(C) Slip rotation of molecules in a crystal (small change)

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

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

  On the other hand, when oil containing naphthene or oil containing aromatics is blended into the inner layer 1 of the high-density polyethylene pipe 10, the slipperiness of molecules existing in polyethylene crystals can be greatly improved. By converting the change in crystal level into the slip rotation of molecules in the crystal, the formation of voids and fibrils and the craze breakage can be reduced, making it difficult to expand the amorphous region. Brittle fracture and creep fracture can be reduced.

  In addition, the oil containing naphthene has an SP value close to that of polyethylene and has good compatibility. When an oil containing naphthene is added to the inner layer 1 of the high-density polyethylene tube 10, the oil can penetrate into the details of the molecules in the crystal, and the slipperiness of the molecules in the crystal can be greatly improved. Therefore, it is possible to easily cause the slip rotation of the molecule in the crystal while suppressing the destruction of the crystal at the molecular level and the block-shaped destruction of the crystal.

  Moreover, the oil containing naphthene exhibits fluidity close to normal temperature even at low temperatures. In general, polymer materials are susceptible to low-temperature embrittlement, and high-density polyethylene has the drawback of low impact resistance at low temperatures. Therefore, it is important to facilitate the occurrence of molecular slip rotation in crystals and around tie molecules. . When an oil containing naphthene is added to the inner layer 1 of the high-density polyethylene pipe 10, the oil that has penetrated into the crystal and around the tie molecules maintains high fluidity even at a low temperature, causing slip rotation of the molecule in the crystal. To facilitate this, the resistance to low-temperature embrittlement and the impact resistance at low temperatures can be improved.

  On the other hand, the oil containing the aromatics has a high viscosity index and has a characteristic that it hardly exudes from the high-density polyethylene of the base material in a wide temperature range. Therefore, when an oil containing aromatics is added to the inner layer 1 of the high-density polyethylene pipe 10, the effect of the addition of the oil lasts for a long time. Further, the fluid flowing inside the conduit (inner layer 1) is less likely to be contaminated by oil seepage.

  In addition, oils containing aromatics have a characteristic of having a high flash point. Therefore, when an oil containing aromatics is used as an additive, the high-density polyethylene pipe 10 can be manufactured safely.

  In addition, oils containing aromatics often contain impurities such as sulfur content or have a high acid value. Sulfur, aldehyde, carboxylic acid and the like are likely to take part in the radical reaction, so that the oil itself is sacrificed and deteriorated, so that the effect of suppressing the deterioration of the inner layer 1 of the high-density polyethylene pipe 10 is obtained.

  Oils containing naphthenes and oils containing aromatics have the effect of softening polyethylene. In general, it is known that polyethylene becomes hard and easily embrittles when used in a radiation environment. However, when an oil containing naphthene or an oil containing aromatics is blended into the inner layer 1 of the high-density polyethylene pipe 10, the high-density polyethylene itself as a base material is softened, so that embrittlement due to radiation is less likely to occur. it can.

  The amount of the naphthene-containing oil or the aromatics-containing oil is preferably 0.1 to 7 parts by mass, and more preferably 1 to 7 parts by mass, per 100 parts by mass of the high-density polyethylene. Parts or less is more preferable. If the amount exceeds 7 parts by mass, the oil will seep out, making it difficult to properly mix the oil. On the other hand, if the addition amount is less than 0.1 part by mass, a sufficient effect by the addition cannot be obtained. On the other hand, as the addition amount is larger in the above-mentioned addition amount range, the effect of suppressing the deterioration of the resin and the effect of improving the slipperiness of polyethylene molecules are increased.

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

  The fusion prevention film 3 is formed of a resin film having a melting point of 150 ° C. or higher. According to the anti-fusing film 3, when the outer layer 4 described later is molded with a resin, it is possible to prevent the outer layer 4 from directly fusing to the gas barrier film 2 or to prevent the heat of the molten resin from being transferred to the gas barrier film 2. it can. Since a large tension is prevented from being applied to the gas barrier film 2 fused to the other layer and the gas barrier film 2 itself is prevented from being melted, pinholes and cracks are not generated in the gas barrier film 2. 2 can keep the gas barrier property sound.

  The anti-fusing film 3 is preferably formed of a stretched polyethylene terephthalate film, a polyimide film, or a polyamideimide film. Stretched polyethylene terephthalate and polyamideimide have a melting point of 150 ° C. or higher. Further, polyimide does not melt until it is thermally decomposed at a temperature higher than 150 ° C. (about 500 ° C.). Therefore, according to these resins, the fusion preventing film 3 itself does not melt at the melting temperature when the outer layer 4 is molded with the resin, and the fusion of the gas barrier film 2 and the heat transfer to the gas barrier film 2 are reliably suppressed. be able to.

  Further, stretched polyethylene terephthalate, polyimide, and polyamide imide have an aromatic ring, have high radiation resistance, and hardly change in physical properties even under a high radiation dose. Therefore, when the outer layer 4 is molded with resin, fusion and heat transfer are suppressed, and the gas barrier properties of the gas barrier film 2 are kept healthy. On the other hand, after the high-density polyethylene pipe 10 is manufactured, the inner layer 1 and the gas barrier film 2 are It can protect against radiation, impact, external pressure, etc.

  The fusion prevention film 3 has a total thickness of preferably 10 μm or more, more preferably 20 μm or more, further preferably 50 μm or more when wound around the outer periphery of the gas barrier film 2. Further, it is preferably 300 μm or less, more preferably 200 μm or less, and further preferably 150 μm or less. As the total thickness is greater than or equal to 10 μm, fusion and heat transfer can be suppressed, and the gas barrier properties of the gas barrier film 2 can be kept sound. Further, when the total thickness is 20 μm or more and 200 μm or less, particularly high radiation resistance can be obtained due to the neutron shielding ability of the resin itself. On the other hand, the thinner the total thickness is 300 μm or less, the less the material cost of the anti-fusing film 3 and the trouble of winding.

The outer layer 4 is 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. The outer layer 4 can be provided by resin molding such as extrusion molding, injection molding, or the like so as to cover the outer peripheral surface of the fusion prevention film 3. Since low-density polyethylene has high flexibility, impact resistance, moisture resistance, water resistance, chemical resistance, and the like, according to the outer layer 4 containing low-density polyethylene as a main component, the inner layer 1, the gas barrier film 2, and the fusion prevention film are used. 3 can be protected from impact, external pressure, scratching, chemical substances, water vapor, rain water, dew water and the like.

  A general two-layer tube has a structure in which a conduit and a coating layer are fused and a resin matrix is continuous. Therefore, the impact and the dynamic strain of the brittle fracture generated in the coating layer easily propagate to the conduit, and cause a fracture phenomenon such as stress cracking in the conduit. In particular, when the coating layer is a high-density polyethylene or a medium-density polyethylene, the impact and dynamic strain transmitted to the conduit are larger than that of the low-density polyethylene having high flexibility.

  On the other hand, in the high-density polyethylene pipe 10, the gas barrier film 2 and the fusion prevention film 3 are interposed between the conduit (inner layer 1) and the protective layer (outer layer 4), and the protective layer (outer layer 4) is Low-density polyethylene as the main component. Therefore, the propagation of the impact, the dynamic strain, and the crack from the outer layer 4 to the inner layer 1 can be prevented by the gas barrier film 2 and the fusion prevention film 3. In addition, since the outer layer 4 contains low-density polyethylene as a main component, bonding with a joint can be easily performed by electrofusion or the like.

  The outer layer 4 preferably contains carbon black as an additive. As the carbon black, for example, furnace black, channel black, acetylene black, thermal black and the like can be used. When the carbon black is blended, the ultraviolet rays are absorbed, so that the deterioration of the outer layer 4 and the inner layer 1 due to the ultraviolet rays can be suppressed. That is, the weather resistance of the high-density polyethylene pipe 10 itself is improved, so that the fluid can be transported soundly even outdoors such as under a high radiation dose.

  The content of carbon black per outer layer 4 is preferably 1.0% by mass or more, more preferably 1.5% by mass or more. Further, it is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, and still more preferably 2.5% by mass or less. The higher the content is at least 1.0% by mass, the higher the effect of absorbing ultraviolet light can be obtained, so that the weather resistance of the high-density polyethylene pipe 10 can be sufficiently improved. Also, as the content is less than 4.0% by mass or less, a large amount of carbon black is less likely to form an aggregate in the resin. Therefore, it is possible to prevent the aggregate from becoming a starting point of environmental stress cracking or brittle fracture.

  The thickness of the outer layer 4 is preferably 0.4 mm or more, more preferably 0.5 mm or more, and still more preferably 0.8 mm or more. Further, it is preferably 4 mm or less, more preferably 3 mm or less, and still more preferably 2 mm or less. The higher the thickness is 0.4 mm or more, the higher the protection performance of the outer layer 4 is obtained. When the thickness is 0.5 mm or more and 3 mm or less, particularly high radiation resistance can be obtained due to the neutron shielding ability of the resin itself. On the other hand, as the thickness is less than 4 mm, the material cost of the outer layer 4 is reduced.

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

  The conduit (inner layer 1) and the protective layer (outer layer 4) of the high-density polyethylene pipe are prepared by heating and melting polyethylene prepared as pellets and the like, and adding and kneading additives such as oil and carbon black as necessary. It can be produced by performing extrusion molding, injection molding and the like using the obtained polyethylene resin composition as a material.

  During the production of the polyethylene resin composition or the production of the high-density polyethylene tube, the additives may be dry-blended or directly mixed with the resin. However, solid additives such as carbon black, if insufficiently kneaded, may aggregate and become a starting point of destruction. Therefore, it is preferable to mix the additive beforehand as a master batch, and it is particularly preferable to mix the additive as a master batch in a state of being mixed with oil.

  For example, when dry blending an additive during the production of a polyethylene resin composition, a master batch pellet prepared by blending the additive and a polyethylene resin pellet are put into a hopper of a pellet production apparatus, and these are melt-kneaded. I do. Then, the kneaded molten resin composition is extruded into water through a stainless steel disc having a large number of holes (for example, about 3 mm in diameter), and is extruded into a predetermined length (with a knife installed in parallel with the disc surface). For example, by cutting into a length of about 3 mm), it is possible to obtain a polyethylene resin composition pellet in which an additive is blended.

  Alternatively, at the time of producing the polyethylene resin composition, the oil to be blended as an additive may be directly directly mixed with the molten resin composition being melt-kneaded. For example, a master batch pellet or a polyethylene resin pellet is put into a hopper of a pellet manufacturing apparatus, and oil is dropped at a constant dropping rate using a microtube pump or the like, and these are melt-kneaded. Then, by extruding the kneaded molten resin composition into water and cutting it into a predetermined length, it is possible to obtain a polyethylene resin composition pellet in which an additive is blended.

  When manufacturing a high-density polyethylene pipe, only a polyethylene resin composition pellet containing an additive may be used as a material, or a master batch pellet and a polyethylene resin pellet may be used as a material. For example, these pellets are supplied to a hopper of an extruder (pipe manufacturing apparatus), heated and melted in the extruder, extruded into a cylindrical shape from a die, sized as needed while being taken up by a take-up machine, and a cooling water tank, etc. By cooling through, a conduit (inner layer 1) can be produced.

  As the kneader, various kneaders such as a batch kneader such as a Banbury mixer, a twin-screw kneader, a rotor-type twin-screw kneader, and a buscon kneader can be used. As the extruder, for example, a single screw extruder, a twin screw extruder, or the like can be used. The dice may be of any type such as a straight head dice, a cross head dice, and an offset dice. In addition, sizing may be performed by any method such as a sizing plate method, an outside mandrel method, a sizing box method, and an inside mandrel method.

  The kneading temperature of the polyethylene is preferably set to 120 ° C. or higher and 250 ° C. or lower. When a Banbury mixer is used, a molten resin composition is obtained by, for example, kneading at 180 ° C. for 10 minutes. The polyethylene resin composition may contain titanium oxide as long as it is 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 prevention film 3 can be formed into a film by an appropriate method such as coating and forming. The multilayer film used as the gas barrier film 2 can be formed by an appropriate method such as a coextrusion method and a lamination method. The multilayer film may be formed by any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film. From the viewpoint of obtaining high strength and excellent gas barrier properties, the multilayer film is preferably formed of a biaxially stretched film.

  The gas barrier film 2 can be wound around the outer periphery so as to cover the outer surface of the resin-molded conduit (inner layer 1). It is preferable that the resin-molded inner layer 1 is cooled by water cooling or air cooling to at least a temperature at which heat fusion does not occur before the gas barrier film 2 is wound. The gas barrier film 2 may be wound in any of single winding, multiple winding, and spiral winding. However, from the viewpoint of reliably exhibiting gas barrier properties, winding with an arbitrary overlapping width is preferable. For example, multiple winding or spiral winding having an overlapping width that is equal to or more than の of the film width is preferable.

  The anti-fusing film 3 can be wound on the outer periphery so as to cover the outer surface of the gas barrier film 2 wound on the conduit (inner layer 1). The winding method of the fusion prevention film 3 may be any of single winding, multiple winding, and spiral winding. However, when forming the outer layer 4 with a resin, an arbitrary overlapping width is provided from the viewpoint of suppressing the direct fusion of the outer layer 4 to the gas barrier film 2 and the transfer of heat of the molten resin to the gas barrier film 2. Winding is preferred. For example, multiple winding or spiral winding having an overlapping width that is equal to or more than の of the film width is preferable.

  The protective layer (outer layer 4) is supplied to the sheath extrusion device with the conduit (inner layer 1) around which the gas barrier film 2 and the anti-fusing film 3 are wound as a core wire, and a polyethylene resin for the protective layer is provided around the supplied core wire. It can be formed by extruding the composition. By heating and melting the polyethylene resin composition in a sheath extrusion molding apparatus, coating the outer periphery of the core wire, extruding from a die, performing sizing as needed while taking up with a take-up machine, and cooling by passing through a cooling water tank or the like, A high-density polyethylene tube 10 can be manufactured.

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

  The joint according to the present embodiment has the same layer configuration as the high-density polyethylene pipe 10 described above. Specifically, the joint according to the present embodiment includes a cylindrical inner layer 1 through which a fluid flows, a gas barrier film 2 covering the outer surface of the inner layer 1, and a fusion preventing film 3 covering the outer surface of the gas barrier film 2. And an outer layer 4 covering the outer surface of the anti-fusing film 3.

  The size, shape, connection method, and the like of the joint according to the present embodiment are not particularly limited. The connection method may be any of a mechanical method, an electrofusion method, a screw-in method, and the like. The joint according to the present embodiment has a flange, a nut, a saddle, and a flange as long as the trunk has the layer structure of the inner layer 1, the gas barrier film 2, the anti-fusion film 3, and the outer layer 4 as in the case of the high-density polyethylene pipe 10. A sealing material or the like may be provided.

  The joint according to the present embodiment is made of, for example, a polyethylene resin composition as in the case of the high-density polyethylene pipe 10, and is formed by extruding a body (inner layer 1), winding a gas barrier film 2 or a fusion-prevention film 3. After performing a round or the like, the molded body formed up to the protective layer (outer layer 4) can be manufactured by subjecting it to secondary processing.

  The sealing material according to the present embodiment has the same layer configuration as the high-density polyethylene pipe 10 described above. Specifically, the sealing material according to the present embodiment includes an inner layer 1 that comes into contact with a fluid, a gas barrier film 2 that covers the outer surface of the inner layer 1, a fusion prevention film 3 that covers the outer surface of the gas barrier film 2, And an outer layer 4 covering the outer surface of the anti-fusing film 3.

  As the polyethylene used for the sealing material, ultrahigh molecular weight polyethylene having a molecular weight of about 1,000,000 to 7,000,000 can be preferably used. Specifically, a resin having a dissolution index determined in accordance with ISO 1133 at a test temperature of 190 ° C. and a test load of 21.6 kgf, of less than 0.1 g / 10 minutes can be used. However, the polyethylene used for the sealing material is not limited to a resin having such physical properties. When ultrahigh molecular weight polyethylene is used, the inner layer 1 does not necessarily have to be high density polyethylene.

  The sealing material according to the present embodiment can be in the form of a gasket such as a flange packing or an O-ring, but the size and shape are not particularly limited. As in the case of the high-density polyethylene tube 10, at least a part of the sealing material between the surface that comes in contact with the fluid and the surface that is exposed to the outside air or ultraviolet rays, the inner layer 1, the gas barrier film 2, and the fusion prevention film 3 In addition, as long as it has the layer configuration of the outer layer 4, it is not always necessary that the entire surface of the sealing material is covered with the gas barrier film 2, the fusion prevention film 3, and the outer layer 4.

  The joint and the seal material according to the present embodiment are made of, for example, a polyethylene resin composition as the material of the high-density polyethylene pipe 10 and are subjected to injection molding of the base (inner layer 1), winding and sticking of a film, and the like. After that, it can be manufactured by forming a protective layer (outer layer 4) on the outside.

  According to the high-density polyethylene pipe, the joint, and the sealant according to the above-described embodiment, the inner layer is covered with the gas barrier film, so that the oxidative deterioration of the resin of the inner layer due to oxygen in the outside air can be suppressed. Therefore, high-density polyethylene pipes, fittings, and seals may be exposed to high doses of radiation, atmospheric oxygen, strong ultraviolet rays such as outdoors in summer, acid rain, etc. Even in the case of prolonged contact with fluids containing substances, high-temperature fluids, etc., the propagation reaction of oxidation is suppressed, and the deterioration of the resin in the inner layer due to external factors such as radiation, ultraviolet rays, oxygen, heat, etc. is greatly reduced. Is suppressed.

  In addition, according to the high-density polyethylene pipe, the joint, and the sealant according to the present embodiment, the gas barrier film is covered with the outer layer. Therefore, when an earth pressure, an impact, a load, or the like is applied from the outside, the gas barrier film is not damaged. In addition, it is possible to prevent the gas barrier film itself and the inner layer from being deteriorated by radiation or ultraviolet rays. Furthermore, since a fusion preventing film is provided between the gas barrier film and the outer layer, the outer layer can be resin-molded using a molten resin outside the gas barrier film. Can also be kept. Unlike the case where a protective tape is wound on the outermost surface, the resin-molded outer layer is unlikely to form gaps / holes and hardly peels off, so that it is possible to improve resistance to external factors that deteriorate the resin. .

  Therefore, even when fluid pressure, earth pressure, other impacts, loads, etc. are applied to high-density polyethylene pipes, joints and seal materials, environmental stress cracks and creep fractures are unlikely to occur, and cracks, brittle cracks, etc. Is prevented and the piping and joints are prevented from exploding. That is, the essential disadvantage of polyethylene, which is liable to cause brittle fracture cracking, can be drastically improved. Even if there are minute defects that are not visible, stress concentrates there and hardly causes brittle fracture or stress cracking.Sufficient elongation and elasticity can be obtained, so stress-resistant environment cracking and impact resistance Can be improved.

  In particular, not only in the normal environment, but also in various severe environments such as high-dose radiation environment, ultraviolet environment such as outdoor in summer, high temperature environment such as summer, environment exposed to high concentration of oxygen and acid rain, etc. A high-density polyethylene pipe, a joint, and a sealing material that reduce brittle fracture and creep fracture due to deterioration of the steel can be obtained. In addition, a high-density polyethylene pipe, a joint, and a sealing material, which hardly decrease in long-term hydrostatic pressure strength, elasticity, environmental stress crack resistance, impact resistance, and the like over a long period of time and hardly cause brittle fracture cracking or rupture, can be obtained.

  The use of the high-density polyethylene pipe, the joint, and the sealant according to the present embodiment is not particularly limited. The high-density polyethylene pipe, the joint, and the sealing material can be used in an appropriate environment. Further, the high-density polyethylene pipe and the joint can be used for transporting an appropriate fluid such as water or seawater. The sealing material can be used to seal an appropriate fluid during storage, transportation, handling, and the like of the fluid.

  In particular, high-density polyethylene pipes and joints can be used for transporting fluids such as water and seawater in nuclear facilities. In a nuclear-related facility, tens to hundreds of pipes for nuclear facilities are stretched and connected to a plurality of contaminated water retention areas. The overall length of these pipes is generally about 10 km to 20 km. High-density polyethylene pipes and joints can be suitably used for such applications of nuclear equipment piping. According to the high-density polyethylene pipe or the joint, the transport of a fluid containing a radioactive substance and the transport of a fluid under a high radiation dose or outdoors can be performed soundly and reliably over a long period of time.

  In addition, the sealing material is effective for sealing fluid in nuclear facilities, nuclear fuel facilities, and the like, and can be suitably used as a sealing material for nuclear equipment piping, nuclear fuel facility piping, a radioactive material storage container, and the like. This sealing material can be particularly suitably used for sealing a fluid containing a high concentration of a radioactive substance or for sealing a fluid under a high radiation dose.

  According to the high-density polyethylene pipe, the joint, and the sealant according to the present embodiment, since the deterioration of the resin is largely suppressed, the integrity of the resin molded body is maintained even under a high radiation dose where radicals are easily generated. However, it is possible to reliably prevent the occurrence of a leakage event. Even when handling fluids containing high concentrations of radioactive materials, it can be used for a long time and the frequency of replacement and inspection is reduced, so the man-hours and equipment for laying and installing, exposure to installers and inspectors And the like can be greatly reduced.

  As described above, the embodiments of the high-density polyethylene pipe, the joint, and the sealing material according to the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the technical scope. Is included. For example, the above embodiments are not necessarily limited to those having all the configurations described above. Further, a part of the configuration of the embodiment can be replaced with another configuration, or another configuration can be added to the configuration of the embodiment. Further, for a part of the configuration of the embodiment, it is also possible to add another configuration, delete the configuration, or replace the configuration.

For example, the high-density polyethylene pipe, the joint, and the sealing material have a layer configuration including an inner layer 1, a gas barrier film 2, a fusion prevention film 3, and an outer layer 4 in this order. A functional layer such as a buffer layer for buffering an impact may be provided between the gas barrier film 2 and between the gas barrier film 2 and the fusion prevention film 3. The buffer layer can be provided by, for example, a resin molded product containing polyethylene having a density of less than 0.940 g / cm ³ as a main component, or another film, tape, or the like.

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

  Specimens of high-density polyethylene pipes were prepared by changing the amounts of the naphthene-containing oil and the aromatics-containing oil and the layer constitution of the gas barrier film, and the tensile elongation at break after irradiation treatment was evaluated.

  As the base material for the inner layer, high-density polyethylene manufactured using a Ziegler catalyst was used. An oil containing naphthene or an oil containing aromatics is blended as an additive with a base material of high-density polyethylene and kneaded at 180 ° C. for 10 minutes using a Banbury mixer, and pellets for high-density polyethylene pipes Was granulated. Then, the pellets were put into an injection molding machine to form a cylindrical conduit (inner layer).

Subsequently, a gas barrier film was wound around the outer periphery of the formed conduit (inner layer) using a winding machine, and a fusion prevention film was wound around the outer periphery of the gas barrier film. Then, a protective layer (outer layer) is formed on the outer periphery of the gas barrier film by extrusion-molding low-density polyethylene containing carbon and having a density of 0.910 g / cm ³ or more and 0.930 g / cm ³ or less. I got

From the produced high-density polyethylene pipe, a 1B-type dumbbell-shaped test piece described in JIS K 7162 of Japanese Industrial Standards (Japanese Industrial Standards) was produced. Then, the prepared test piece was irradiated with a γ-ray emitted from a ⁶⁰ Co radiation source at a dose rate of 1 kGy / h. The absorbed dose was 1000 kGy.

<Tensile test>
The tensile test was carried out in accordance with the Japan Water Works Association standard "Polyethylene pipe for water distribution JWWA K144". The tester was provided with a device for indicating the maximum tensile force, and used a device described in JIS B 7721 provided with a gripper for fastening a dumbbell-shaped test piece. The thickness of the test piece and the width of the parallel portion were measured, and a marking line for elongation measurement was attached to the center of the parallel portion, and then a tensile test was performed at a test speed of 25 mm / min at room temperature. The distance between the marked lines was 50 mm. A tensile test was performed to measure the distance between the marked lines at the time of breakage of the test piece, and the elongation at break was calculated by the following equation (1). In Equation (1), EB indicates the elongation at break (%), L0 indicates the distance between mark lines (mm), and L1 indicates the distance between mark lines at break (mm).

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

In addition, as a base material of the conduit (inner layer), a high-density polyethylene having a density of 0.95 g / cm ³ was used. As an additive, an oil having a predetermined value of% CN and a% CA of 30% in a ring analysis by an ndM method was used among oils generated when crude oil was refined. The amount of the oil was 5 parts by mass with respect to 100 parts by mass of the high-density polyethylene. The gas barrier film is a multi-layer film of LLDPE / EVOH / LLDPE. The thickness of the EVOH is 24 μm, and the MLD of the LLDPE is 3 g / 10 min. Using. As the anti-fusing film, a polyethylene terephthalate stretched film was used such that the total thickness when wound around the outer periphery was 100 μm. As the protective layer (outer layer), a layer of low-density polyethylene having a thickness of 2 mm and containing 3% by mass of carbon was formed.

FIG. 3 is a diagram showing a relationship between% CN of oil used as an additive and elongation at break.
In FIG. 3, the horizontal axis represents% CN (%) of the oil used as an additive, and the vertical axis represents elongation at break (%) due to tension.

  As shown in FIG. 3, when an oil containing naphthene is added as an additive, when% CN is 20% or more and 60% or less, the tensile elongation at break becomes remarkably large, and the result that radiation deterioration is suppressed well is obtained. Obtained.

  Next, the measurement results of the tensile elongation at break after the irradiation treatment of the test piece prepared by changing the amount of the oil containing the aromatics are shown.

In addition, as a base material of the conduit (inner layer), a high-density polyethylene having a density of 0.95 g / cm ³ was used. As an additive, oil having a predetermined value of% CA in ring analysis by the ndM method and a% CN of 40% among oils generated when crude oil was refined was used. The amount of the oil was 5 parts by mass with respect to 100 parts by mass of the high-density polyethylene. The gas barrier film is a multi-layer film of LLDPE / EVOH / LLDPE. The thickness of the EVOH is 24 μm, and the MLD of the LLDPE is 3 g / 10 min. Using. As the anti-fusing film, a polyethylene terephthalate stretched film was used so that the total thickness when wound around the outer periphery was 100 μm. As the protective layer (outer layer), a layer of low-density polyethylene having a thickness of 2 mm and containing 3% by mass of carbon was formed.

FIG. 4 is a graph showing the relationship between% CA of oil used as an additive and elongation at break.
In FIG. 4, the horizontal axis represents% CA (%) of the oil containing the aromatics used as an additive, and the vertical axis represents the elongation at break (%) due to tension.

  As shown in FIG. 4, when an oil containing an aromatics is added as an additive, the tensile elongation at break is significantly increased when% CA is 5% or more and 60% or less, particularly 5% or more and 40% or less, The result that radiation deterioration was suppressed favorably was obtained.

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

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

FIG. 5 is a diagram showing the relationship between the MFR of the linear low-density polyethylene used for the gas barrier film and the elongation at break.
In FIG. 5, the horizontal axis shows 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 shows the elongation at break (%) due to tension.

  As shown in FIG. 5, the MFR of the linear low-density polyethylene used as the surface layer of the gas barrier film is 0.8 g / 10 min or more and 10 g / 10 min or less, and the tensile elongation at break exceeds 400%; The result that radiation deterioration was suppressed favorably was obtained.

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

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

FIG. 6 is a diagram showing the relationship between the total thickness of the gas barrier film and the elongation at break.
In FIG. 6, the abscissa indicates the total thickness (μm) when the gas barrier film is wound around the outer periphery of the inner layer, and the ordinate indicates the elongation (%) at break due to tension.

  As shown in FIG. 6, 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 suppressed well was obtained.

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

In addition, as a base material of the conduit (inner layer), a high-density polyethylene having a density of 0.95 g / cm ³ was used. As an additive, oil having a% CN of 40% and a% CA of 30% in ring analysis by the ndM method was used among the oils generated when the crude oil was refined. The amount of the oil was 5 parts by mass with respect to 100 parts by mass of the high-density polyethylene. The gas barrier film was a multilayer 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 around the outer periphery was 300 μm. As the anti-fusing film, a polyethylene terephthalate stretched film was used so that the total thickness when wound around the outer periphery was 100 μm. As the protective layer (outer layer), a layer of low-density polyethylene having a thickness of 2 mm and containing 3% by mass of carbon was formed.

FIG. 7 is a diagram showing the relationship between the thickness of the ethylene / vinyl alcohol copolymer resin used for the gas barrier film and the elongation at break.
In FIG. 7, the horizontal axis indicates the thickness (μm) of the ethylene / vinyl alcohol copolymer resin used as the intermediate layer of the gas barrier film, and the vertical axis indicates the elongation at break (%) due to tension.

  As shown in FIG. 7, when the thickness of the ethylene / vinyl alcohol copolymer resin used as the intermediate layer of the gas barrier film is 10 μm or more and 50 μm or less, the tensile elongation at break becomes remarkably large, and radiation deterioration is favorably suppressed. The result was obtained.

  Next, the results of measuring the tensile elongation at break after the irradiation treatment of the test piece prepared by changing the thickness of the anti-fusing film are shown.

In addition, as a base material of the conduit (inner layer), a high-density polyethylene having a density of 0.95 g / cm ³ was used. As an additive, oil having a% CN of 40% and a% CA of 30% in ring analysis by the ndM method was used among the oils generated when the crude oil was refined. The amount of the oil was 5 parts by mass with respect to 100 parts by mass of the high-density polyethylene. The gas barrier film is a multi-layer film of LLDPE / EVOH / LLDPE. The thickness of the EVOH is 24 μm, and the MLD of the LLDPE is 3 g / 10 min. Using. As the anti-fusing film, a polyethylene terephthalate stretched film was used. As the protective layer (outer layer), a layer of low-density polyethylene having a thickness of 2 mm and containing 3% by mass of carbon was formed.

FIG. 8 is a diagram showing the relationship between the thickness of the anti-fusing film and the elongation at break.
In FIG. 8, the horizontal axis indicates the thickness (μm) of the anti-fusing film, and the vertical axis indicates the elongation at break (%) due to tension.

  As shown in FIG. 8, 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 well suppressed was obtained.

  Next, the measurement results of the tensile elongation at break after the irradiation treatment of the test piece prepared by changing the thickness of the protective layer (outer layer) are shown.

In addition, as a base material of the conduit (inner layer), a high-density polyethylene having a density of 0.95 g / cm ³ was used. As an additive, oil having a% CN of 40% and a% CA of 30% in ring analysis by the ndM method was used among the oils generated when the crude oil was refined. The amount of the oil was 5 parts by mass with respect to 100 parts by mass of the high-density polyethylene. The gas barrier film is a multi-layer film of LLDPE / EVOH / LLDPE. The thickness of the EVOH is 24 μm, and the MLD of the LLDPE is 3 g / 10 min. Using. As the anti-fusing film, a polyethylene terephthalate stretched film was used such that the total thickness when wound around the outer periphery was 100 μm. As the protective layer (outer layer), a layer of low-density polyethylene containing 3% by mass of carbon was formed.

FIG. 9 is a diagram showing the relationship between the thickness of the protective layer (outer layer) and the elongation at break.
In FIG. 9, the horizontal axis indicates the thickness (mm) of the protective layer (outer layer), and the vertical axis indicates the elongation at break (%) due to tension.

  As shown in FIG. 9, when the thickness of the protective layer (outer layer) was 0.5 mm or more and 3 mm or less, the tensile elongation at break became remarkably large, and the result that radiation deterioration was suppressed well was obtained.

  Next, the results of measuring the tensile elongation at break after the irradiation treatment of test pieces prepared by changing the layer configuration of the gas barrier film and the type of the anti-fusion film are shown.

In addition, as a base material of the conduit (inner layer), a high-density polyethylene having a density of 0.95 g / cm ³ was used. As an additive, an oil having a% CN of 32% and a% CA of 10% in ring analysis by the ndM method was used among the oils generated when the crude oil was refined. The amount of the oil was 5 parts by mass with respect to 100 parts by mass of the high-density polyethylene.

  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). Although the anti-fusing film was of any type, high radiation resistance was obtained. Especially suppressed.

DESCRIPTION OF SYMBOLS 10 High density polyethylene pipe 1 Inner layer 2 Gas barrier film 21 Surface layer 22 Intermediate layer 23 Surface layer 3 Anti-fusion film 4 Outer layer

Claims (13)

An inner layer mainly composed of high-density polyethylene having a density of 0.940 g / cm ³ or more and 0.980 g / cm ³ or less;
A gas barrier film covering the outer surface of the inner layer and containing an ethylene / vinyl alcohol copolymer resin,
An anti-fusing film that covers the outer surface of the gas barrier film and has a melting point of 150 ° C. or higher.
An outer layer covering the outer surface of the anti-fusing film and having a density of 0.910 g / cm ³ or more and 0.930 g / cm ³ or less as a main component;
A high-density polyethylene tube. The high-density polyethylene tube according to claim 1,
A high-density polyethylene pipe in which the inner layer contains at least one of an oil containing naphthenes produced when crude oil is refined and an oil containing aromatics produced when refined crude oil. The high-density polyethylene tube according to claim 1,
The inner layer contains naphthenes having a% CN of 20% or more and 60% or less in ring analysis by the dn-M method among the oils produced when the crude oil is refined, and the oils produced when the crude oil is refined. A high-density polyethylene tube containing at least one of oils containing aromatics having a% CA of 5% or more and 40% or less in ring analysis by an ndM method. The high-density polyethylene tube according to claim 1,
A high-density polyethylene pipe wherein the thickness of the ethylene / vinyl alcohol copolymer resin is 1 μm or more and 50 μm or less. The high-density polyethylene tube according to claim 1,
The gas barrier film is a multilayer film having an intermediate layer made of an ethylene / vinyl alcohol copolymer resin and a surface layer laminated on both surfaces of the intermediate layer,
The surface layer is a high-density polyethylene tube containing at least one of low-density polyethylene and linear low-density polyethylene. The high-density polyethylene pipe according to claim 5, wherein
A high-density polyethylene pipe, wherein the multilayer film has a total thickness of 50 μm or more and 400 μm or less when wound around an outer periphery. The high-density polyethylene tube according to claim 1,
The high-density polyethylene pipe, wherein the anti-fusion film is a stretched polyethylene terephthalate film, a polyimide film, or a polyamideimide film. The high-density polyethylene tube according to claim 1,
A high-density polyethylene pipe, wherein the fusion prevention film has a total thickness of 20 μm or more and 200 μm or less when wound around an outer periphery. The high-density polyethylene tube according to claim 1,
A high-density polyethylene tube in which the outer layer contains carbon black. The high-density polyethylene tube according to claim 9,
A high-density polyethylene pipe, wherein the content of the carbon black per 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 10, wherein
High-density polyethylene pipes, which are pipes for nuclear facilities used for transporting fluids in nuclear facilities. An inner layer mainly composed of high-density polyethylene having a density of 0.940 g / cm ³ or more and 0.980 g / cm ³ or less;
A gas barrier film covering the outer surface of the inner layer and containing an ethylene / vinyl alcohol copolymer resin,
Said covering the outer surface of the gas barrier film, the anti-fusing film having a melting point consisting of 0.99 ° C. or more resins, covers the outer surface of the anti-blocking film, a density of 0.910 g / cm ³ or more 0.930 g / cm ³ An outer layer mainly composed of the following low-density polyethylene,
Fittings. An inner layer mainly composed of high-density polyethylene having a density of 0.940 g / cm ³ or more and 0.980 g / cm ³ or less;
A gas barrier film covering the outer surface of the inner layer and containing an ethylene / vinyl alcohol copolymer resin,
An anti-fusing film that covers the outer surface of the gas barrier film and has a melting point of 150 ° C. or higher.
An outer layer covering the outer surface of the anti-fusing film and having a density of 0.910 g / cm ³ or more and 0.930 g / cm ³ or less as a main component;
A sealing material.

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