JP2018009070A - Polyethylene resin composition and piping material, piping and joint containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent brittle fracture cracking and stress cracks, which are fundamental defects of polyethylene.SOLUTION: A polyethylene resin composition contains: a base material predominantly composed of polyethylene; and an additive, the additive containing a nonpolar material that is liquid at room temperature, a content of the additive being 0.1-10 pts.mass relative to the polyethylene 100 pts.mass.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a polyethylene resin composition and piping materials, piping and joints containing the same.

  Polyethylene piping is used to transport various fluids. For example, water and sewage pipes, gas pipes, water supply pipes, hot water supply pipes, chemical liquid pipes, oil pipes and the like can be mentioned. Safety requirements for each pipe are increasing year by year, and pipe materials that have acquired PE80 as a gas pipe and PE100 as a water and sewage pipe are used. In addition, cross-linked polyethylene having excellent heat resistance is used as a pipe material for the hot water supply pipe. Furthermore, polyethylene joints are also used for polyethylene pipes. This has a feature that a polyethylene pipe and a polyethylene joint can be integrated by a welding joint called electrofusion.

  The piping material made of polyethylene is stressed by the pressure from the inside of the piping or the earth pressure from the outside at the time of embedding, so if there are minute defects in the piping, the stress is concentrated there and brittle fracture Is known to happen. In particular, it is necessary to develop a material that does not cause brittle fracture cracking under severe conditions where stress is applied over a long period of time.

  Conventionally, for example, as disclosed in Patent Document 1 and Patent Document 2, in order to improve the mechanical properties of polyethylene over a long period of time, improvement of polyethylene itself such as broadening of molecular weight distribution and introduction of side chains has been performed.

  Furthermore, for example, as in Patent Document 3, polyethylene having a low melt mass flow rate composed of two molecular weight distributions has been proposed.

  Patent Document 4 also discloses a polyethylene pipe and a pipe joint obtained by molding a composition comprising two components of low molecular weight and high density polyethylene and high molecular weight and low density polyethylene.

Japanese Examined Patent Publication No. 61-42736 Japanese Patent Publication No. 61-43378 Japanese Patent Laid-Open No. 10-17619 JP-A-8-301933

  The improvement of the polymer itself in the above prior art does not improve the problems of brittle fracture cracking and stress cracking, which are essential defects of polyethylene.

  An object of the present invention is to prevent brittle fracture cracking and stress cracking, which are essential defects of polyethylene.

  The polyethylene resin composition of the present invention includes a base material mainly composed of polyethylene and an additive, the additive includes a nonpolar substance that is liquid at room temperature, and the ratio of the additive is 100 parts by mass of polyethylene. It is 0.1-10 mass parts with respect to.

  According to the present invention, there is provided a polyethylene resin composition having sufficient elongation without causing concentration of stress to cause brittle fracture cracks or stress cracks even if invisible minute defects exist. Can do.

It is a photograph which shows the example of the state which the test piece of the general polyethylene resin composition fractured | ruptured. It is an enlarged photograph which shows a part of FIG. It is a graph which shows the result of having measured the crystal melting calorific value of the polyethylene resin composition before and after a tensile test.

  The present invention relates to a long-life polyethylene resin composition that does not cause brittle fracture cracks and environmental stress cracks, and piping materials, pipes, and joints containing the same.

  An object of the present invention is to drastically improve the problems of brittle fracture cracking and stress cracking, which are essential defects of polyethylene. Polyethylene resin composition having sufficient elongation without causing concentration of stress to cause brittle fracture cracking or stress cracking even if invisible minute defects exist, and piping material, piping and joint including the same I will provide a. In general, hard products such as pipes and joints require strength over a long period of time.

  The polyethylene resin composition of the present invention has the following characteristics.

  (1) An additive is mixed with a base material mainly composed of polyethylene, and the additive contains a nonpolar solvent (nonpolar substance) that is liquid at room temperature, and the proportion of the additive is 100 parts by mass of polyethylene. It is 0.1-10 mass parts with respect to. Here, the room temperature refers to an environmental temperature of a factory or the like of about 15 to 35 ° C. In addition, the base material which has polyethylene as a main component may be the pellet of the polyethylene resin currently distribute | circulated, and may contain less than 50% of polypropylene etc. on a mass basis. Moreover, as long as it has polyethylene as a main component, it may be a mixed material or recycled material containing polyethylene and polypropylene.

  (2) The nonpolar solvent desirably contains oil. Here, the oil refers to a nonpolar or hydrophobic organic substance.

  (3) The oil preferably has a flash point of 140 ° C. or higher.

  (4) The oil contains at least one of oil obtained by refining naphthenic crude oil as a raw material and oil obtained by refining paraffinic crude oil as a raw material. desirable.

  (5) Further, it is desirable to include an oil containing an aromatic component.

  Said polyethylene resin composition is used suitably for piping material, piping, and a joint.

  Hereinafter, an embodiment of the present invention will be further described. However, the present invention is not limited to the following examples, and various improvements and modifications can be made without departing from the spirit of the invention.

  The polyethylene resin composition according to the present invention contains polyethylene as a main component, and contains 0.1 to 10 parts by mass of a nonpolar solvent that is liquid at room temperature as an essential additive with respect to 100 parts by mass of polyethylene. Moreover, it is preferable that oil is included as a nonpolar solvent. In particular, oil having a flash point of 140 ° C. or higher is preferably contained as a nonpolar solvent.

  Specifically, at least one of the following additives (A) and (B) is included. The total amount of the additives (A) and (B) is 0.1 to 10 parts by mass. Moreover, you may mix 0.1-10 mass parts of the following additives (C) or (D).

  The additive (A) is an oil (hereinafter referred to as “naphthenic oil”) obtained by refining a naphthenic crude oil as a raw material.

  As the naphthenic oil, naphthenic crude oil is distilled under reduced pressure, and oil containing an aromatic component is removed by solvent extraction. This may be a naphthenic oil that has been purified by deoxidation after performing an adsorption treatment, a clay treatment, or a pretreatment. Here, the “naphthenic oil” refers to an oil containing a large amount of cyclic hydrocarbons, and in particular, an oil having high solubility and compatibility with polyethylene and a close SP value is desirable. Specifically, the SP value is preferably within ± 10%.

  The additive (B) is oil (hereinafter referred to as “paraffinic oil”) obtained by refining paraffinic crude oil as a raw material.

  As the paraffinic oil, a paraffinic crude oil obtained by subjecting paraffinic crude oil to atmospheric distillation and then vacuum distillation is used as it is or after solvent removal to obtain a primary product. It may be a paraffinic oil that has been subjected to hydrogen reforming and passed through a dewaxing step. Alternatively, it may be a hydrorefined paraffinic oil after the dewaxing step. Alternatively, a product obtained by removing the oil containing the aromatic component from the primary product by solvent extraction is used. This may be a naphthenic oil purified by a dewaxing step after the finishing step. Here, “paraffinic oil” refers to an oil containing a large amount of chain hydrocarbons, and in particular, those having high solubility in polyethylene and close SP values indicating compatibility are desirable. Specifically, the SP value is preferably within ± 10%.

  The additive (C) is an oil obtained by refining naphthenic crude oil as a raw material and containing an aromatic component (hereinafter, referred to as “naphthenic crude oil-derived aroma oil”). .

  As the aroma-based oil derived from naphthenic crude oil, an oil containing an aromatic component obtained by subjecting naphthenic crude oil to distillation under reduced pressure and solvent extraction is used.

  The additive (D) is oil obtained by refining paraffinic crude oil as a raw material and containing an aromatic component (hereinafter referred to as “paraffinic crude oil-derived aroma oil”). .

  As the aroma-based oil derived from paraffinic crude oil, oil containing aromatic components obtained by solvent extraction after being subjected to atmospheric distillation after paraffinic crude distillation is used as it is or after solvent removal.

  The effect of the polyethylene resin composition of the present invention having the above configuration will be described.

  Polyethylene pipes are lighter than steel pipes and are easy to move and process, so they are also used as long-distance pipes such as water pipes. However, unlike metal materials such as steel pipes, polyethylene is a polymer composed of carbon and hydrogen. Among polymer materials, polyethylene is prone to brittle fracture cracking and stress cracking due to external factors in various environments, such as ultraviolet rays, radiation, heat, internal pressure, external pressure, drop, impact, scratches, and chemical substances. Has drawbacks. In polyethylene, due to the action of ultraviolet rays, radiation, heat, etc., highly reactive hydrogen radicals and hydrocarbon radicals are generated, and molecular weight increases called recombination by radicals and crosslinking due to addition reactions, Due to a decrease in molecular weight, which is called “collapse” due to a leveling reaction, the elasticity, stress resistance, crack resistance and impact properties are degraded.

  In general, it is known that a polymer material is excited by the action of ultraviolet rays, radiation, heat, and the like, whereby the molecule is excited and the bond is broken. When ultraviolet rays, radiation, heat, etc. act on polyethylene, hydrogen radicals or hydrocarbon radicals are generated. This radical is highly reactive, the radicals bond together (recombination), the radical pulls out the element to form another radical (drawing reaction), or the radical is added next to the double bond (addition) It is known that the molecular chain is cleaved (disproportionation reaction) at the same time as the radicals are bonded to each other. A recombination or addition reaction results in an increase in molecular weight called cross-linking, whereas a disproportionation reaction results in a decrease in molecular weight called decay.

  The elasticity of both the collapse and the cross-linking is reduced, and the physical properties such as resistance to impact and bending are reduced, and brittleness is caused. Therefore, there is a concern that when used as piping, there is a problem such as cracking or rupture. There is.

  The same applies to polyethylene for water pipes. Polyethylene for distribution pipes improves long-term hydrostatic strength and environmental stress crack resistance by increasing the high molecular weight region and increasing the number of tie molecules that connect the crystal structure. In general, under severe conditions such as ultraviolet rays, radiation, and heat, the molecular chain in the crystalline region is not significantly affected, but the increase in the amorphous part (non-crystalline part), that is, the oxidative cleavage of the tie molecular chain proceeds. It has been known. As the tie molecular chain breaks, stress concentration occurs in the resin when external stress is applied, and long-term hydrostatic pressure strength, environmental stress crack resistance, and impact properties are thought to deteriorate.

  In the atmosphere where oxygen is present, when ultraviolet rays, radiation, heat, or the like acts on polyethylene, radicals have a strong reactivity with oxygen, and thus the radicals react with oxygen. Since oxygen has a high affinity with hydrogen, it is extracted to generate a peroxide radical (ROO.), And a reaction such as the following chemical formula (1) that initiates an oxidation propagation reaction (chain reaction) proceeds. It is known.

  This peroxide radical is rich in reactivity and draws hydrogen from other molecules to change into a peroxide (ROOH) and a radical (R.) (see the following chemical formula (2)).

  The newly generated radical (R.) is changed to a new peroxy radical according to the chemical formula (1) in the presence of oxygen. Since peroxide (ROOH) is also unstable, it decomposes and eventually changes to peroxy radical (ROO.), Oxy radical (RO.), Radical (R.), etc. (the following chemical formula (3) To (5)).

  Thus, one radical (R.) generated first passes through peroxy radical (ROO.), And a large number of new radicals are propagated, and oxidation propagation reaction (chain reaction) proceeds in a chain manner. . As a result, the decomposition (crosslinking and collapse) of the molecular structure is increasingly promoted.

  In addition to the chain hydrocarbon component and cyclic hydrocarbon component contained in oil, in particular, the aromatic component binds to these radicals to suppress the propagation reaction of oxidation, or the radical (R.) Has the function of suppressing the generation itself. In order to further enhance this oxidation-inhibiting function, it is more preferable that the aromatic component is contained even when the% CA by ring analysis (ndM method) is a very small amount of about 0.1%. The aromatic component may have any structure as long as it is a polycyclic structure in which two or more rings having a resonance structure having a double bond are connected.

  Further, as additives having the effect of suppressing the generation of radicals (R.) and scavenging radicals, antioxidants such as primary antioxidants, secondary antioxidants, and light stabilizers such as Irganox 1010 (manufactured by Ciba Geigy) ) Etc. is also effective. Unlike oil, solidified antioxidants can be added according to the purpose without considering compatibility with the base polymer, and oil-based additives can be used from the functional aspect of antioxidants. It becomes possible to expand. However, solidified antioxidants are difficult to refine and knead to the intermolecular bond level, so considering that they become the starting point of voids as solid inclusions, added in a range that does not affect the required strength It is important to add with oil.

  Furthermore, it is known that ozone is generated in the atmosphere. Ozone acts strongly on polyethylene having a double bond in the molecular chain. For example, when ozone attacks the double bond portion, an ozonide is formed, which is unstable, so that the O—O bond is cleaved to form an aldehyde, ketone, ester, lactone, peroxide or the like. It is known that the decomposition of the molecular structure by ozone forms minute cracks (ozone cracks). In particular, when a pipe pressure of 1 MPa is applied, it is always in an extended state, which increases the ozone penetration rate, and there is a concern that ozone cracks grow due to stress concentration, leading to explosion.

  In some cases, a high-temperature fluid is transferred using a polyethylene pipe. In this case, various elementary reactions that cause the decomposition of the molecular structure described above are related to molecular motion, that is, vibration and collision probability. Since the molecular motion becomes more intense as the temperature becomes higher, the decomposition reaction is accelerated and the deterioration is remarkable. In particular, in a system involving an oxidation reaction, it is known that the temperature affects the thickness of the oxide layer in the sample, the diffusion rate of oxygen, and the reaction rate of oxidative decomposition, and the decomposition due to oxidation is increasingly accelerated. In general, the reaction rate doubles as the temperature increases by 10 ° C. Therefore, when a high-temperature fluid is transferred, the oxidative degradation is accelerated and the molecular structure is easily decomposed. Such a change in molecular structure leads to a decrease in various properties such as a decrease in elastic modulus, a decrease in tensile strength, and a decrease in elongation. When these characteristics are deteriorated, there is a possibility that a defect such as a crack or a micro crack enters the pipe or bursts.

  As described above, it is known that the piping material made of polyethylene causes cracks and cracks due to various external factors (external stress).

  FIG. 1 is a photograph showing an example of a state in which a test piece of a general polyethylene resin composition is broken by receiving external stress. Here, a tensile test is performed to break the test piece.

  Regardless of the type of external stress, and regardless of the density or molecular weight of the polyethylene, the failure modes of the test pieces of the polyethylene resin composition all decrease in elongation, and whitening appears on the fracture surface. It is a feature.

  FIG. 2 is an enlarged photograph of FIG.

  The fracture surface of the test piece of the polyethylene resin composition has cracks in addition to whitening, and voids and fibrils are present on the fracture surface. Whitening occurs by Mie scattering of light due to void formation. Thus, whitening indicates the occurrence of craze destruction, which is a damaged form composed of voids and fibrils.

  It is known that the breaking mechanism of a polyethylene resin composition by tension proceeds as follows.

(A) Propagation of strain localized region immediately after tensile yielding (B) Propagation of craze fracture region (C) Molecular chain breakage and cracks occur at the craze fracture concentration (D) Polymer breakage
Furthermore, it is known that the following deformation occurs due to tension at the crystal level.

(A) Molecular-level crystal breakage (molecular chain peeling)
(B) Block break of crystals (molecular chain peeling)
(C) Slip rotation of molecules in the crystal (small change)
Here, in (a) and (b), the crystal breaks and the non-crystal part increases. Molecular chains peel off, voids and fibrils are formed, and craze destruction occurs. However, in (c), the damage to the crystal is small and the non-crystal part hardly increases.

  In contrast to the essential problems of polyethylene, in this embodiment, the deformation due to tension at the crystal level causes sliding rotation within the crystal, thereby suppressing an increase in the non-crystalline portion. And it prevents molecular chain peeling and prevents formation of voids and fibrils, and does not cause craze destruction. This is because a non-polar solvent that is liquid at room temperature greatly improves the slipping property of molecules in the crystal, and easily causes slip rotation.

  As a result of trial and error, the present inventor has added a non-polar solvent that is liquid at room temperature to improve the slipping property by improving the slipping property in the polyethylene crystal, in the tie molecule, or in the periphery of the polyethylene crystal. I found out. For additives that are solid at room temperature, it has been found that all the additives act as inclusions and cause breakage from this point. Even if it is a liquid at room temperature, in the case of a polar solvent, the compatibility with the moisture in the air and the water of the internal fluid is higher than that of polyethylene of the piping material, so it can easily escape from the inside of the crystal. The effect was not seen.

  In addition, since polyethylene is nonpolar, polar solvents have not been adapted, and it has been difficult to put in a crystal, a tie molecule, or the periphery thereof. Furthermore, the polar solvent has a lower effect of improving the slipperiness than the nonpolar solvent, and has little improvement effect on the slipperiness of the molecules in the crystal.

  As a result of adding the nonpolar solvent in the crystal of the polyethylene piping material, the tie molecule or the periphery thereof, it was found that the addition amount of the nonpolar solvent which improves the slip property is preferably 0.1 to 10 parts by mass. When the amount was less than 0.1 parts by mass, a sufficient effect was not observed, and there was no significant difference from that without addition. On the other hand, when the amount exceeds 10 parts by mass, the oil oozes out from the surface of the polyethylene piping material, so it was found that the addition amount was excessive.

  Oil is particularly desirable as the nonpolar solvent for improving the slip property. Oil has a track record of being used as a lubricant for all materials. As a result of trial and error, the present inventor succeeded in putting oil in a polyethylene crystal, a tie molecule or its periphery. As a result, the oil causes deformation due to tension at the crystal level to cause slip rotation within the crystal, thereby suppressing an increase in the non-crystalline part, suppressing molecular chain separation and preventing formation of voids and fibrils, and crazing fracture. It turns out that it does not cause.

  The increase in the amorphous part can be examined using a differential scanning calorimeter (DSC).

  FIG. 3 shows the result of quantifying the amount of heat generated by crystal melting (the amount of heat of crystal melting) for the sample before the tensile test and the sample deformed after the tensile test and comparing the amount of heat per unit mass. . In the figure, the conventional antioxidant is added with 1 part by mass of Irganox 1010 (Ciba Geigy). The novel additive is the additive used in the present invention.

  As shown in the figure, in the polyethylene resin composition without an additive, the crystal melting heat generation amount is greatly reduced. Moreover, in the polyethylene resin composition containing the conventional antioxidant, the crystal melting calorific value is greatly reduced. On the other hand, there is almost no change in the polyethylene resin composition containing the novel additive. When the elongation after the tensile test was confirmed, as shown in the lower part of the figure, the one containing the new additive was transparent and no whitening occurred. Those without additives and those with conventional antioxidants are whitened.

  From this result, it can be seen that the polyethylene resin composition containing the novel additive does not increase the non-crystalline part even after deformation due to tension, and there is no crystal damage. This is considered to be due to slip rotation in the crystal. As a result, it can be considered that the increase in the non-crystalline part can be suppressed, the peeling of the molecular chain can be suppressed, the formation of voids and fibrils is prevented, and the crazing destruction is prevented.

  The oil used as an additive preferably has a flash point of 140 ° C. or higher. When the flash point is lower than 140 ° C., it almost evaporates at the melting temperature of polyethylene (120 to 140 ° C.), and the target addition amount cannot be left in the molded product.

  By using a polyethylene resin composition comprising at least one of additives (A) and (B) in a range of 0.1 to 10 parts by mass, craze failure is prevented, and stress cracking and brittleness Breaking cracks can be suppressed. In particular, the additives (A) and (B) have a particularly high effect because they have a particularly high compatibility with polyethylene and a high function as a lubricant. The larger the amount added, the better. However, the maximum amount that can be added to polyethylene is 10 parts by mass. When the amount is more than 10 parts by mass, bleeding occurs and the range of application of the molded product is limited. On the other hand, when the amount is less than 0.1 parts by mass, the amount of addition is small, and a sufficient effect of sliding rotation of crystals cannot be obtained.

  In addition to additives (A) and (B), the additives (C) and (D) have an effect of suppressing radical scavenging of aromatic components in addition to the effect of sliding rotation of polyethylene crystals of the additives (A) and (B), thereby suppressing cracks. Is recognized. In particular, the function of suppressing the generation of R · in the chemical formula (1) is remarkable.

  In summary, in the polyethylene resin composition of the present invention, craze fracture due to various external factors is suppressed, and therefore, long-term hydrostatic strength, elasticity, environmental stress crack resistance, and impact characteristics are prevented from being lowered. That is, the polyethylene resin composition of the present invention has a tensile stress under various harsh conditions such as high outside air temperature, environment such as ultraviolet rays, ozone, radiation, atmospheric oxygen and acid rain, and transportation of high-temperature fluid. It is possible to minimize the damage to the crystal that occurs when this occurs. And thereby, malfunctions, such as a crack and a rupture, can be suppressed for a long period of time. This also leads to the suppression of the probability of occurrence of cracks in the fluid transport piping due to impact, even when the fluid freezes in a low temperature environment in winter.

  Hereinafter, a method for producing a fluid transport pipe (hereinafter referred to as “pipe”) will be described.

The case where high-density polyethylene (the density is usually 0.945 to 0.965 g / cm ³ ) is used as the substrate will be described. In addition, polyethylene is not limited to a high density thing, Medium density or low density may be sufficient.

  As the kneader, a batch kneader such as a Banbury mixer, a twin-screw kneader, a rotor-type twin-screw kneader, a bus coneer, or the like can be used, but it is not particularly limited. In this specification, when mixing an additive with a base material, an example using a Banbury mixer is given. The kneading temperature is desirably 120 to 250 ° C. The additive desirably contains at least one of the additives (A), (B), (C), and (D).

  In the extrusion molding of the pipe, the polyethylene resin composition may contain 0.1 to 5 parts by mass of titanium oxide with respect to 100 parts by mass of the polyethylene resin. Polyethylene resin pellets are supplied to the hopper of the pipe manufacturing apparatus while dry blending, heated and melted in an extruder, extruded from a die into a cylindrical shape, and cooled to form a pipe. The prototyped pipe has a nominal diameter of 100A, but the present invention is not limited to this.

  As another method, in advance, master batch pellets and polyethylene resin pellets are put into a hopper of a pellet manufacturing apparatus, melt kneaded, and a large number of holes (diameter of about 3 mm) are opened in the molten resin composition. Pass through a stainless steel disk, extrude into water like udon, cut into a length of about 3 mm with a rotating knife placed parallel to the disk surface, and store as polyethylene resin composition pellets to produce high-density polyethylene pipes The polyethylene resin composition pellets stored at the time of feeding may be supplied to a hopper of a pipe manufacturing apparatus, heated and melted in an extruder, extruded from a die into a cylindrical shape, and cooled to form a pipe.

  In order to mold a polyethylene resin composition pellet into a pipe, the composition is extruded through a die from an extruder at a temperature of, for example, 150 to 250 ° C., sized, cooled in a cooling water tank, cut through a take-off machine, or The winding method is mentioned. The pipe may be a single layer pipe or a two layer pipe. Examples of the extruder include a single screw extruder and a twin screw extruder. Any type of die such as a straight head die, a cross head die, or an offset die can be used. As the sizing method, any method such as a sizing plate method, an outside mandrel method, a sizing box method, and an inside mandrel method can be used.

  When the additive was mixed with the base material by a Banbury mixer, the temperature was 150 ° C. for 10 minutes, and then granulated to form a pellet of the polyethylene resin composition.

  As another method, in advance, master batch pellets or polyethylene resin pellets are put into a hopper of a pellet manufacturing apparatus, and melt kneading is performed using a micro tube pump that can add oil at a constant dropping rate. The molten resin composition is dropped onto a stainless steel disk having a large number of holes (diameter of about 3 mm), extruded into water in the form of noodles, and lengthened by a rotating knife installed in parallel to the disk surface. It is good also as a polyethylene resin composition pellet cut | disconnected to about 3 mm. In addition, oil is heated so that it may become the temperature of 140 degreeC or more at the time of dripping. A pipe was formed using the pellets of the polyethylene resin composition.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples.

  In this example, test pieces were prepared by changing the type of additive, and the tensile elongation at break was evaluated. Below, the preparation methods of the test piece of a present Example are demonstrated.

In this example, high density polyethylene was used as the base material. This base material contains 0.5 parts by mass of titanium oxide with respect to 100 parts by mass of the polyethylene resin. Here, the high-density polyethylene is produced using a Ziegler catalyst, and has a density of 0.95 g / cm ³ and a melt flow rate of 0.5 g / 10 minutes.

  And 1 or more types of additives (A), (B), (C), and (D) were mixed with the base material. At this time, the mixture was kneaded at a temperature of 150 ° C. for 10 minutes using a Banbury mixer and then granulated to obtain polyethylene resin composition pellets.

  The polyethylene resin composition pellets were supplied to an injection molding machine to prepare a 1B-type dumbbell-shaped test piece described in Japan Industrial Standards JIS K 7162.

<Tensile test>
The tensile test was performed after the test piece was heated at 100 ° C. for 500 hours to cause thermal deterioration.

  The tensile test conforms to the Japan Water Works Association standard “polyethylene pipe for water distribution JWWA K 144”. The test machine 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 gripper for fastening a dumbbell-shaped test piece. After measuring the thickness of the dumbbell test piece and the width of the parallel portion, and further attaching a mark for measuring elongation to the center of the parallel portion, a tensile test is performed at room temperature using a tensile tester at 500 mm / min. The distance between the marked lines is 50 mm. In the tensile test, the elongation at break is measured. The elongation at break is measured by measuring the length between marked lines until the test piece breaks. The elongation at break of the test piece is calculated by the following calculation formula (1).

  In the calculation formula (1), EB indicates elongation (%) at break, L0 indicates distance between marked lines (mm), and L1 indicates distance between marked lines at break (mm).

<DSC measurement>
The DSC measurement was performed in accordance with JIS standard “Method for measuring transition temperature of plastic” JIS K7121. The melting peak area (J) of the polyethylene crystal was determined by DSC measurement, and the melting energy (J / g), which was a value obtained by dividing this by the sampling mass (g), was calculated. The sample was compared between a portion where no tensile stress was applied in the tensile test (no deformation) and a portion where the elongation stress was applied and the deformation occurred (with deformation).

  It shows that the larger the amount of change in melting energy (J / g), the greater the damage to crystals, the more non-crystal parts, and the occurrence of molecular chain debonding.

(Comparative example)
In the comparative example, a test piece was prepared and evaluated in the same manner as in the example except that the additive was not added.

  Table 1 shows the types and amounts of additives, the elongation at break as the evaluation results, and the melting energy depending on the presence or absence of deformation, for the test pieces of the examples. In this table, the amount of additive contained in the test piece of the same number and the elongation at break vary, and this indicates that the amount of additive was measured as a parameter. Test pieces 1 to 12 are examples, and “no addition” is a comparative example.

  In Table 1, with respect to the elongation at break, the example is larger than the comparative example. Also, when two or more additives are mixed, the elongation at break is large.

  The melting energy by DSC measurement is also greater in the examples than in the comparative examples. From this, it was proved that the damage of the crystal due to the tensile stress was very small in the examples.

  As described above, according to the present invention, it was demonstrated that a long-life polyethylene resin composition that does not cause brittle fracture cracking or environmental stress cracking can be provided.

  According to the present invention, even if a minute defect that is not visible is present, stress concentration is not caused to cause brittle fracture cracking or stress cracking, and piping material having sufficient elongation and impact strength, piping, A joint can be provided. More specifically, when polyethylene or ultraviolet rays act on polyethylene, highly reactive hydrogen radicals or hydrocarbon radicals are generated, and an increase in molecular weight called cross-linking by recombination or addition reaction by these radicals, It is possible to solve the problem that the elasticity, elongation, resistance to environmental stress cracking, impact properties and the like are lowered due to a decrease in molecular weight called disintegration due to disproportionation reaction. Therefore, resistance to brittle fracture cracks and stress cracks when used for piping, joints, etc. over a long period of time can be increased.

  Note that the above-described embodiments have been specifically described in order to help understanding of the present invention, and the present invention is not limited to having all the configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, a part of the configuration of each embodiment can be deleted, replaced with another configuration, or added with another configuration.

Claims (8)

A base material based on polyethylene;
An additive,
The additive includes a non-polar substance that is liquid at room temperature,
The ratio of the said additive is a polyethylene resin composition which is 0.1-10 mass parts with respect to 100 mass parts of said polyethylenes.   The polyethylene resin composition according to claim 1, wherein the nonpolar substance includes oil.   The polyethylene resin composition according to claim 2, wherein the oil has a flash point of 140 ° C. or higher.   The oil includes at least one of an oil obtained by refining naphthenic crude oil as a raw material and an oil obtained by refining paraffinic crude oil as a raw material. Or the polyethylene resin composition of 3.   The polyethylene resin composition according to claim 4, wherein the oil includes an oil containing an aromatic component.   Piping material containing the polyethylene resin composition as described in any one of Claims 1-5.   Piping containing the polyethylene resin composition as described in any one of Claims 1-5.   The joint containing the polyethylene resin composition as described in any one of Claims 1-5.

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