JP2002286171A - Cross-linked polyethylenic resin pipe and method of manufacturing cross-linked polyethylenic resin pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cross-linked polyethylenic resin pipe for remarkably improving pressure-proof performance an flexibility, and a manufacturing method of the cross-linked polyethylenic resin pipe. SOLUTION: This cross-linked polyethylenic resin pipe is composed of a cross-linked polyethylenic resin by heating and cross-linking a polyethylenic resin composition having a base resin composed of a polyethylenic resin having 2 to 5 molecular weight distribution, and 0.938 g/cm<3> to 0.945 g/cm<3> density, and organic peroxide mixed at a rate of 1 pts.wt. to 5 pts.wt. to this base resin of 100 pts.wt. at a melting point or higher of the polyethylene resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross-linked polyethylene resin pipe and a method for producing a cross-linked polyethylene resin pipe, and more particularly, to a floor heating pipe and a lubricating oil which are excellent in short-term and long-term pressure resistance performance and excellent in flexibility. The present invention relates to a crosslinked polyethylene resin tube usable for pipes and the like and a method for producing a crosslinked polyethylene resin tube.

[0002]

2. Description of the Related Art Cross-linked polyethylene resin tubes have heat resistance,
It is excellent in pressure resistance, creep performance, flexibility, etc., and is used for floor heating piping, oil supply piping, etc., which require complicated piping. Conventionally, as a method of manufacturing a crosslinked polyethylene resin tube, a method of grafting an organic silane to a polyethylene resin and then crosslinking with hot water or a method of directly irradiating ionizing radiation (electron beam) to the polyethylene resin to perform crosslinking. Methods are known.

However, in the above-mentioned method, since the cross-linking between the molecules of the polyethylene resin is generally performed at a temperature lower than the melting point of the polyethylene resin, the cross-linking mainly occurs in the amorphous portion of the polyethylene resin. In other words, in the method described above, even if the crosslinking is carried out, since there is no influence on the crystal structure of the polyethylene resin, properties such as pressure resistance and flexibility of the obtained crosslinked polyethylene resin tube are almost used. It is determined by the characteristics of the raw material.

In order to improve the pressure resistance of a crosslinked polyethylene resin tube, it is necessary to increase the density (crystallinity) of the polyethylene resin as a raw material. When the polyethylene resin having the increased density is used as the raw material resin, the elastic modulus of the obtained cross-linked polyethylene resin tube can be increased to improve the pressure resistance, but the flexibility is impaired. This causes a problem. That is, in the above-mentioned method, it was not possible to dramatically improve flexibility while maintaining excellent pressure resistance performance of the crosslinked polyethylene resin tube.

[0005] Therefore, by using a polyethylene resin polymerized by a single-site catalyst as a base resin, it is possible to greatly improve the flexibility of the crosslinked polyethylene system while maintaining excellent pressure resistance performance. A method for manufacturing a resin tube is disclosed in Japanese Patent Application Laid-Open No. 2000-9265.

That is, the polyethylene resin polymerized by the single-site catalyst has a uniform crystal structure due to a uniform distribution of the degree of branching. Therefore, the number of tie molecules connecting the crystals increases, and the pressure resistance performance is reduced. Increased than polyethylene resin. That is, in the polyethylene resin polymerized by the single-site catalyst, the resin density can be reduced by an amount corresponding to the improvement in the pressure resistance. As described above, when the resin density is reduced (resin density is reduced), flexibility is improved accordingly. Therefore, the obtained crosslinked polyethylene resin tube can improve flexibility while securing its pressure resistance performance.

[0007]

However, Japanese Patent Laid-Open Publication
No. 9265 discloses a method in which a polyethylene resin having improved pressure resistance by being polymerized with a single-site catalyst is used.
Since the hydrothermal crosslinking is performed after the organic silane is grafted to the polyethylene resin, the crosslinking between the molecules of the crosslinked polyethylene resin is performed at a temperature lower than the melting point of the polyethylene resin.

[0008] Therefore, the performance of the obtained crosslinked polyethylene resin tube is determined only by the characteristic of the polyethylene resin that the pressure resistance is improved by being polymerized with a single-site catalyst. The pressure resistance and flexibility of the tube cannot be dramatically improved.

[0009] In view of such circumstances, an object of the present invention is to provide a crosslinked polyethylene resin pipe and a method for manufacturing a crosslinked polyethylene resin pipe which have significantly improved pressure resistance and flexibility. It was done.

[0010]

In order to achieve such an object, a crosslinked polyethylene resin pipe according to the first aspect of the present invention (hereinafter referred to as "a crosslinked polyethylene resin pipe of claim 1") is provided. Indicates that the molecular weight distribution is 2 or more and 5 or more.
Hereinafter, the density is 0.938 g / cm ³ or more and 0.945 g / cm ³ or more.
A polyethylene-based resin composition comprising a polyethylene-based resin having a molecular weight of ³ cm or less and an organic peroxide mixed in a proportion of 1 part by weight or more and 5 parts by weight or less with 100 parts by weight of the base resin, It is made of a cross-linked polyethylene resin which is heated and cross-linked at a temperature not lower than the melting point of the resin.

The method for producing a crosslinked polyethylene resin pipe according to the second aspect of the present invention (hereinafter referred to as “the production method of the second aspect”) has a molecular weight distribution of 2 to 5; Density is 0.938 g / cm ³ or more and 0.945 g
/ Cm ³ or less, and a polyethylene resin composition comprising a base resin composed of a polyethylene resin of not more than 1 part by weight and 100 parts by weight of the base resin and an organic peroxide mixed at a ratio of 1 part by weight or more and 5 parts by weight or less. And a crosslinking step of heating the polyethylene-based resin composition at a temperature equal to or higher than the melting point of the polyethylene-based resin to crosslink so that the gel fraction becomes 65% or more. Configuration.

The polyethylene resin used in the present invention includes not only a polymer obtained by polymerizing ethylene alone, but also a copolymer of ethylene and an α-olefin resin having 3 or more carbon atoms. Here, the α-olefin resin having 3 or more carbon atoms is not particularly limited.
Butene-1, hexene-1, 4-methylpentene-1,
Octene-1 and the like.

The polyethylene resin used in the present invention must have a molecular weight distribution of 2 or more and 5 or less. That is, the molecular weight distribution of the polyethylene resin is 2
If less, the temperature dependence of the fluidity of the molten polyethylene resin increases, and, for example, after melting the polyethylene resin with an extruder or the like, a mold for shaping the molten polyethylene resin into a tubular shape It is very difficult to control the temperature to make the flow distribution uniform when forming the polyethylene resin tube by supplying the resin to the tube. Further, when the molecular weight distribution of the polyethylene resin is larger than 5, the crosslinking by the organic peroxide is preferentially performed in the high molecular component, and the phenomenon that the crosslinking is not performed in the low molecular component occurs. As a result, the long-term pressure resistance performance is reduced. From the above, the molecular weight distribution of the polyethylene resin is 3
It is particularly preferred that the number be in the range of 4 to 4. In addition, the said molecular weight distribution means the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) obtained by gel permeation chromatography.

Further, the polyethylene resin used in the present invention has a density of 0.938 g / cm ³ or more and 0.945 g / cm ³ or more.
g / cm ³ or less. That is, when the density of the polyethylene resin is smaller than 0.938 g / cm ³ , the flexibility is improved, but the pressure resistance performance is reduced, and the balance of the crosslinked polyethylene resin pipe as a product is deteriorated. . On the other hand, if the density of the polyethylene-based resin is greater than 0.945 g / cm ³ , the pressure resistance performance is improved, but the flexibility is reduced, and the balance of the crosslinked polyethylene-based resin pipe as a product is deteriorated. . From the above, the density of polyethylene resin is
It is particularly preferred that it is 0.940 g / cm ³ or more and 0.943 g / cm ³ or less.

[0015] The polyethylene resin composition used in the present invention may optionally contain additives. Examples of the additives include antioxidants, light stabilizers, ultraviolet absorbers, lubricants, flame retardants, antistatic agents, and the like. These additives are used to improve desired physical properties. In addition, as a means for improving the physical properties, a small amount of a substance that can serve as a crystal nucleating agent may be added to the polyethylene-based resin composition to help refine the crystals and make the physical properties uniform.

The organic peroxide used in the present invention is not particularly limited, but can be appropriately selected from the viewpoint of the molding temperature and compatibility of the polyethylene resin used. Specifically, dicumyl peroxide, α, α′-
Bis (t-butylperoxy-m-isopropyl) benzene, cyclohexane peroxide, 1,1-di (t
-Butylperoxy) cyclohexane, 1,1-di (t
-Butylperoxy) 3,3,5-trimethylcyclohexane, 2,2-di (t-butylperoxy) octane, n-butyl-4,4-di (t-butylperoxy)
Berelate, di-t-butyl peroxide, benzoyl peroxide, cumyl peroxy neodecate,
t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-
Butylperoxyisopropyl carbonate, t-butylperoxyallyl carbonate, t-butylperacetate, 2,2-bis (t-butylperoxy) butane, di-t-butylperoxyisophthalate, t-butylperoxymalein Acid, diazoaminobenzene,
N, N'-dichloroazodicarbonamide, trichloropentadiene, trichloromethanesulfochloride, methyl ethyl ketone peroxide, 2,5-dimethyl-
2,5-di (t-butylperoxy) hexyne-3,
2,5-dimethyl-2,5-di (t-butylperoxy) hexane and the like, and dicumyl peroxide,
α, α′-bis (t-butylperoxy-m-isopropyl) benzene, t-butylcumyl peroxide, benzoyl peroxide, t-butylperoxybenzoate, methyl ethyl ketone peroxide, 2,5-
Dimethyl-2,5-di (t-butylperoxy) hexyne-3,2,5-dimethyl-2,5-di (t-butylperoxy) hexane is preferred, and dicumyl peroxide, α, α′- Bis (t-butylperoxy-m-isopropyl) benzene, methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3,2,5-dimethyl-2,5- Di (t-butylperoxy) hexane is more preferred.

It is necessary that the amount of the organic peroxide is 1 to 5 parts by weight based on 100 parts by weight of the polyethylene resin. That is, if the amount of the organic peroxide added is too small, the gel fraction of the finally obtained crosslinked polyethylene resin tube is not sufficiently increased, and the effect of crosslinking cannot be obtained. Therefore, the pressure resistance of the obtained cross-linked polyethylene resin pipe is reduced. On the other hand, if the amount of the organic peroxide is too large, the progress of crosslinking becomes too fast, and the possibility that unreacted organic peroxide remains in the system increases. Therefore, the obtained cross-linked polyethylene resin pipe has impaired safety and cannot be used as a pipe for drinking water or the like. From the above, the addition amount of the organic peroxide,
It is preferable that the organic peroxide be 1.5 to 3 parts by weight based on 100 parts by weight of the polyethylene resin.

Further, the polyethylene resin composition is preferably crosslinked such that the gel fraction is 65% or more as in the production method of the second aspect. That is, when the gel fraction of the polyethylene resin composition is less than 65%,
It cannot be said that the crosslinking has proceeded sufficiently, and there is a possibility that the pressure resistance of the obtained crosslinked polyethylene resin tube cannot be sufficiently secured. The gel fraction can be represented by the following equation (1). Gel fraction (%) = (sample weight before solvent extraction−sample weight after solvent extraction) / sample weight before solvent extraction × 100 (1) In the above equation, after the solvent extraction, The sample weight is the weight of only the remaining insoluble portion obtained by dissolving the uncrosslinked resin portion remaining in the sample using a solvent capable of dissolving the selected crosslinked thermoplastic resin.

The method for mixing the organic peroxide with the polyethylene resin serving as the base resin is not particularly limited.
For example, a method of impregnating a powdery polyethylene resin with an organic peroxide or kneading the organic peroxide with a polyethylene resin melted by an extruder or the like is mentioned. In order to uniformly and finely mix the polyethylene resin with the polyethylene resin, it is preferable to knead the organic peroxide with the polyethylene resin melted in the extruder.

In the present invention, the polyethylene resin composition needs to be cross-linked by heating at a temperature not lower than the melting point of the polyethylene resin. That is, when the crosslinking is performed at a temperature lower than the melting point of the polyethylene resin, the following problems occur. The molecular motion of the polyethylene resin is not sufficiently performed, and the crosslinking efficiency is reduced. As a result, an excessive amount of the organic peroxide must be supplied. Below the melting point of the polyethylene resin, the crystal structure of the polyethylene resin is maintained, and the crosslinking is performed only in the amorphous portion, and the introduction of the crosslinking cannot reduce the crystallization by inhibiting the crystallization of the polyethylene resin. . As a result, it becomes impossible to improve the flexibility of the obtained crosslinked polyethylene resin tube.

As a method of heating the polyethylene resin composition to a temperature not lower than the melting point of the polyethylene resin, for example, the resin contact surface in a mold for forming the polyethylene resin composition into a tube is heated or heated. A contact heating method in which heating is performed while adjusting the temperature with a medium or the like, and a non-contact heating method in which heating is performed using a near-infrared ray, ultrasonic wave, microwave, or the like without directly applying to the polyethylene-based resin composition, are exemplified. However, in the non-contact heating method, when heating is performed to a temperature equal to or higher than the melting point of the resin in a state where the crosslinking is not progressing in the polyethylene resin composition, a phenomenon called a draw occurs, and the pipe is thinned. It is preferable to perform heating by a contact heating method because there is a possibility of causing thickness unevenness. Further, as a method of shaping the crosslinked polyethylene resin composition into a tubular shape, a generally used method is to extrude the polyethylene resin composition into a mold for shaping a pipe using an extruder or the like. I just need. Further, as described above, the steps from shaping a cross-linked polyethylene resin tube to a polyethylene resin composition obtained by mixing an organic peroxide with a polyethylene resin are commonly used when forming an engel method or a resin tube. It is preferable that a series of steps be continuously performed using an extruder provided with a known extruder and a tube forming die, because the working efficiency can be improved. In the method for manufacturing a crosslinked polyethylene resin tube, the shaping step may be performed after the shaping step, or the shaping step may be performed after the crosslinking step. The steps may be performed simultaneously, but as in the manufacturing method of claim 2,
It is preferable that the shaping step is performed after the cross-linking step, since a cross-linked polyethylene resin tube can be continuously and efficiently manufactured.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
This will be described in detail with reference to the drawings. FIG. 1 is a schematic view of a manufacturing apparatus used for continuously manufacturing a crosslinked polyethylene resin tube of the present invention. FIG. 2 is a cross-sectional view for explaining the structure of a mold (hereinafter, simply referred to as “mold”) 2 for producing a crosslinked polyethylene resin tube in the production apparatus 1 shown in FIG.

As shown in FIG. 1, this manufacturing apparatus 1 is described as an extruder for extruding a mold 2 and a polyethylene resin composition containing an organic peroxide (hereinafter, referred to as “extruder for crosslinked resin”). ) 3, an inner layer coating extruder 4, and an outer layer coating extruder 5. The mold 2 is formed by the mold main body 21 and the mandrel 22, as shown in FIG. 2, and has a distribution zone A, a cross-linking zone B, and a shaping zone C.

As shown in FIG. 2, the mold body 21 has a crosslinked resin supply port 211 and non-crosslinked resin supply ports 211a and 211b. Further, in the direction in which the polyethylene-based resin composition is extruded, the distribution zone forming cylinder 212, the reduced diameter cylinder 214, the small diameter cylinder 213, and the shaped cylinder 2
15 are formed. The cross-linking resin supply port 211 is provided as shown in FIG.
And crosslinking the molecular weight distribution to be extruded from the resin extruder 3 is 2 to 5, the base resin density of from 0.938 g / cm ³ or more 0.945 g / cm ³ or less of the polyethylene resin as shown in, the base resin 100 It is an inlet for supplying a molten polyethylene-based resin composition comprising an organic peroxide mixed in a ratio of 1 part by weight or more and 5 parts by weight or less with respect to parts by weight. The polyethylene-based resin composition thus obtained is developed in the mold 2.

The non-crosslinked resin supply port 211a is a molten crosslinker-free thermoplastic resin extruded from the inner layer coating extruder 4 shown in FIG. 1 (hereinafter, referred to simply as "thermoplastic resin"). The thermoplastic resin supplied from the non-crosslinking resin supply port 211a is supplied from the non-crosslinked resin supply port 211a, and expands into a tubular shape from a substantially central position surface portion of a distribution zone forming shaft 222 described later through the inside of the mold 2. The polyethylene resin composition is developed so as to cover the inner layer portion.

The non-crosslinked resin supply port 211b is a molten crosslinker-free thermoplastic resin extruded from the outer layer coating extruder 5 shown in FIG. 1 (hereinafter, referred to simply as "thermoplastic resin"). The thermoplastic resin supplied from the non-crosslinking resin supply port 211b serves as a supply port for supplying the polyethylene-based resin composition which is tubularly developed from a substantially central position of the distribution zone forming cylindrical portion 212 of the mold body 21. It is developed so as to cover the outer layer portion.

The distribution zone forming cylinder 212 is provided in the mold body 2.
1 is provided from the end on the crosslinked resin supply port 211 side to the center. The small-diameter cylindrical portion 213 is provided at the center of the mold body 21, and is disposed between the distribution zone forming cylindrical portion 212 and the small-diameter cylindrical portion 213 between the distribution zone forming cylindrical portion 212 and the small-diameter cylindrical portion 213. There is provided a diameter-reducing cylinder 214 that gradually decreases in diameter. Further, the shaping tubular portion 215 is a crosslinked polyethylene resin tubular body obtained by heating and crosslinking the tubular polyethylene resin composition that has passed through the small diameter tubular portion 213 at a temperature equal to or higher than the melting point of the polyethylene resin. The diameter of the crosslinked polyethylene resin tube is reduced to a size corresponding to the outer diameter of the crosslinked polyethylene resin tube so as to shape the crosslinked polyethylene resin tube.

On the other hand, the mandrel 22 is formed by joining the distribution zone forming shaft 222, the reduced diameter shaft 224, the small diameter shaft 223, and the shaping shaft 225 in the direction in which the polyethylene resin composition is extruded. Have been.

The distribution zone forming shaft portion 222 is supported by the mold body 21 at a part of one end thereof.
A concave groove 226 is formed in a part of the outer peripheral surface of a portion from the portion facing 11 to the reduced diameter shaft portion 224. Small diameter shaft part 22
Numeral 3 is for forming a small-diameter thick-walled tubular gap with the small-diameter cylindrical portion 213 of the mold body 21.
The reference numeral 25 designates a gap having the same cross-sectional shape as the cross-sectional shape of the tube to be formed between the shaping tubular portion 215 of the mold main body 21 and the shaping tube portion 215. The diameter-reduced shaft portion 224 is gradually reduced in diameter from the distribution zone forming shaft portion 222 toward the small-diameter shaft portion 223.

The recessed groove 226 is provided for allowing the polyethylene resin composition supplied from the extruder 3 to flow through the distribution zone forming shaft portion 22.
2 and between the distribution zone forming cylinder 212,
A resin merging point for merging so as to have a tubular cross section is provided, and a resin outlet 6 for removing the merging portion of the polyethylene-based resin composition and the vicinity thereof at the resin merging point and discharging the resin to the outside of the mold 2 is provided. Is provided.

As shown in FIG. 3, the resin discharge port 6 is provided with a discharge amount adjusting mechanism 60, and is 0.1% by weight to 2% by weight of the polyethylene resin composition supplied into the mold 2. % Can be adjusted to be discharged to the outside of the mold 2.

The manufacturing apparatus 1 having the above configuration
First, in the crosslinked resin extruder 3, the molecular weight distribution is 2 or more and 5 or less, and the density is 0.938 g / cm ³ or more and 0.945 or less.
A polyethylene resin composition in which an organic peroxide is kneaded at a ratio of 1 part by weight or more and 5 parts by weight or less with respect to 100 parts by weight of a base resin made of a polyethylene resin of not more than g / cm ³ is extruded into a mold 2. It has become. In the mold 2, the polyethylene-based resin composition supplied from the extruder 3 for crosslinked resin is distributed from the distribution zone A into the mold 2 through the following steps. After the polyethylene resin composition extruded from the crosslinked resin extruder 3 is supplied from the crosslinked resin supply port 211, the distribution zone forming shaft 222 and the distribution zone forming cylinder 2
12 and joins to form a tubular cross section at the resin confluence point, the confluence of the crosslinkable raw material resin composition and its vicinity at this resin confluence point are taken out of the resin outlet 6.
To form a tubular cross-linked polyethylene resin composition. At this time, the amount of the merging portion of the tubular crosslinked polyethylene resin composition and the vicinity thereof discharged is 0.1% by weight or more and 2% by weight or less of the amount of the tubular crosslinked polyethylene resin composition supplied from the crosslinked resin supply port 211. As a guide.

After the thermoplastic resin extruded from the inner layer coating extruder 4 is supplied from the non-crosslinked resin supply port 211a, the thermoplastic resin passes through the inside of the mold and passes through the distribution zone forming shaft portion 22.
2 is developed so as to cover the inner layer portion of the tubular crosslinked polyethylene resin composition obtained in the process from the substantially central position surface portion, and the thermoplastic resin extruded from the outer layer coating extruder 5 is non-crosslinked. After being supplied from the resin supply port 211b, a three-layer structure was formed by spreading the outer layer portion of the tubular cross-linked polyethylene resin composition obtained in the process from a substantially central position of the distribution zone forming tubular portion 212 in a layered manner. A tubular resin composition is formed. The three-layer tubular resin composition obtained in the step is distributed to the cross-linking zone B such that the diameter of the tubular resin composition is reduced to a tubular body having an arbitrary diameter.

Next, the manufacturing apparatus 1 thermally crosslinks the tubular resin composition in the crosslinking zone B as follows. The resin contact surface of the small-diameter cylindrical portion 213 and the small-diameter shaft portion 223 forming the cross-linking zone B is heated to a temperature equal to or higher than the melting point of the polyethylene resin composition by a heater (not shown). The tubular resin composition passing through the resin flow path formed between 223 is crosslinked by the heat of the resin contact surface to form a crosslinked polyethylene resin tubular body. The crosslinked polyethylene resin tubular body thus obtained is shaped in the shaping zone C so as to match the diameter of the pipe to be a product to form a crosslinked polyethylene resin pipe.

The crosslinked polyethylene resin pipe formed as described above is crosslinked so as to be most suitable for the properties of the polyethylene resin, and is uniformly crosslinked, so that it has excellent pressure resistance over a long period of time. In addition, since it has excellent flexibility, it can be used for various applications such as floor heating pipes and hot water supply pipes. That is, when the polyethylene resin composition is crosslinked, the unevenness of the crosslinked structure is governed by the molecular weight distribution of the polyethylene resin as a raw material and the crosslinking method for crosslinking the polyethylene resin. If the molecular weight distribution of the polyethylene resin is wide, crosslinking on the high molecular weight side of the polyethylene resin occurs preferentially, and the crosslinked structure becomes uneven. Therefore, as a result, the low molecular weight portion remains in the crosslinked polyethylene resin tube as a product in an uncrosslinked state, and the long-term pressure resistance is reduced. In other words, the heterogeneity of the cross-linked structure causes non-uniformity of the crystal inhibition of the polyethylene resin, and the obtained cross-linked polyethylene resin tube has a non-uniform crystal structure. ,
As a result, the long-term pressure resistance of the crosslinked polyethylene resin pipe is reduced. Also, the heating temperature at the time of crosslinking the polyethylene resin,
If the melting point of the polyethylene-based resin is lower than the melting point, only the amorphous portion becomes a cross-linked structure, and the crystallinity of the polyethylene-based resin does not change. However, the properties of the polyethylene resin as the raw material are governed, and it is not possible to achieve a dramatic improvement in the performance of the crosslinked polyethylene resin tube.
As described above, the crosslinked polyethylene resin tube and the method for producing a crosslinked polyethylene resin tube according to the present invention use a polyethylene resin having a narrow molecular weight distribution and a predetermined density as a raw material, and a melting point of the polyethylene resin. Crosslinking is performed using an organic oxide that is crosslinked by heating to the above temperature. Therefore, the cross-linked structure can be made uniform, the long-term pressure resistance of the cross-linked polyethylene resin tube can be improved, and the cross-linking is performed at a temperature equal to or higher than the melting point of the polyethylene resin composition. The crystallization inhibition makes it possible to lower the degree of crystallinity and improve the flexibility.

The crosslinked polyethylene resin pipe and the method for producing the crosslinked polyethylene resin pipe according to the present invention are described below.
The present invention is not limited to the above embodiment. In the above-described embodiment, the outer layer and the inner layer of the tubular polyethylene-based resin composition are covered with the thermoplastic resin in layers, but a lubricant or the like may be used instead of the thermoplastic resin. .

In the above embodiment, as a means for crosslinking the tubular polyethylene resin composition, the resin contact surface of the mold contacting the inner and outer surfaces of the tubular polyethylene resin composition is heated by a heater. But
Instead, a non-contact heating device such as an infrared irradiation device may be used.

[0038]

Embodiments of the present invention will be described below in more detail.

(Example 1) A mold 2 as shown in FIG. 2 having the following dimensions and a cross-linked resin extruder 3 as shown in FIG. 1 were prepared. [Mold dimensions]-Inner diameter of small-diameter cylindrical part 213: 50.0 mm-Inner diameter of shaping cylindrical part 215: 43.0 mm [Mandrel dimension]-Outer diameter of small-diameter shaft part 223: 17.0 mm-Shaping shaft part 225 Outer diameter: 12.8 mm [Extruder]-TEX30α manufactured by Japan Steel Works, L / D = 51, caliber 3
2mm

Then, a linear low-density polyethylene (density 0.940, melt flow rate (MFR) 1.9, molecular weight distribution 3.7, melting point 127 ° C.) as a raw material polyethylene resin is charged into an extruder, and , L / D = 35
From the position of 2,5-dimethyl- as an organic peroxide
2,5-di (t-butylperoxy) hexine-3 (Perhexin 25B manufactured by NOF Corporation, 193 ° C half-life time 6
0 seconds) was added to the extruder at a ratio of 1.5 parts by weight to 100 parts by weight of the linear low-density polyethylene.
At a resin temperature of 70 ° C., a linear low density polyethylene and 2,5
-Dimethyl-2,5-di (t-butylperoxy) hexyne-3 was mixed and kneaded to obtain a polyethylene resin composition.

The obtained polyethylene resin composition was supplied to the mold 2 via a metering pump installed between the extruder 3 for crosslinked resin and the mold 2. The mold 2 is of a coat hanger type. The resin outlet 6 for discharging the polyethylene resin composition out of the mold 2 is φ5 at the resin confluence of the concave groove 226 which is the end of the manifold flow path.
A hole of mm was installed from outside the mold. The amount of the polyethylene resin composition discharged to the outside of the mold was adjusted so as to be 1.0% of the polyethylene resin composition supplied into the mold.

The thermal crosslinking is performed by adjusting the resin contact surfaces of the small-diameter cylindrical portion 213 and the small-diameter shaft portion 223 to 250 ° C. with a heater. Contact surface is 200 ℃ with heater
The temperature was adjusted so that In addition, the extruder 4 for coating the inner layer and the extruder 5 for coating the outer layer receive linear low-density polyethylene (density 0.945, melt flow rate (MFR)).
Multilayer extrusion was performed so as to cover the inner layer and the outer layer of a tubular polyethylene-based resin composition having a melting point of 5.5 ° C. and 127 ° C., respectively.

By performing the above operation, the outer diameter of 17.
A crosslinked resin tube having a diameter of 0 mm and an inner diameter of 12.8 mm was continuously obtained at a molding speed (line speed) of 15.0 mm / min.

In the extruder, the screw shaft moves from the upstream side to the downstream side in the first full flight shape section-first reverse full flight shape section-second full flight shape section-second reverse full flight shape section. The low pressure part (second full flight shape part) sandwiched between the high pressure part (first reverse full flight shape part) and the high pressure part (second reverse full flight shape part) using an extruder equipped with Supplied 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3.

Example 2 As raw material polyethylene resin, linear low density polyethylene (density 0.940, melt flow rate (MFR) 2.5, molecular weight distribution 4.1,
The same operation as in Example 1 was performed except that melting point was 127 ° C.).

Example 3 As raw material polyethylene resin, linear low density polyethylene (density 0.945, melt flow rate (MFR) 1.0, molecular weight distribution 4.2,
The same operation as in Example 1 was performed except that melting point was 127 ° C.).

Comparative Example 1 As a raw material polyethylene resin, a linear low-density polyethylene (density 0.940, melt flow rate (MFR) 2.3, molecular weight distribution 5.4,
The same operation as in Example 1 was performed except that melting point was 127 ° C.).

Comparative Example 2 As a raw material polyethylene resin, a linear low-density polyethylene (density 0.940, melt flow rate (MFR) 2.3, molecular weight distribution 1.9,
The same operation as in Example 1 was performed except that the melting point was 127 ° C.), but molding was impossible.

Comparative Example 3 As a raw material polyethylene resin, linear low density polyethylene (density 0.935, melt flow rate (MFR) 1.9, molecular weight distribution 3.7,
The same operation as in Example 1 was performed except that melting point was 127 ° C.).

Comparative Example 4 As a raw material polyethylene resin, a linear low density polyethylene (density 0.950, melt flow rate (MFR) 1.9, molecular weight distribution 3.7,
The same operation as in Example 1 was performed except that melting point was 127 ° C.).

(Comparative Example 5) 2,5 as an organic peroxide
-Dimethyl-2,5-di (t-butylperoxy) hexine-3 (Perhexin 25B manufactured by NOF Corporation, 193 ° C)
The half-life time is 60 seconds) and the linear low-density polyethylene 100
The same operation as in Example 1 was performed except that 0.8 parts by weight was added to the parts by weight.

(Comparative Example 6) As a raw material polyethylene resin, linear low-density polyethylene (density 0.940, melt flow rate (MFR) 1.9, molecular weight distribution 3.7,
(Melting point 127 ° C.)
The same operation as in Example 1 was performed except that the crosslinking was performed by performing a heat treatment with hot water of 95 ° C. for 24 hours.

The degree of crosslinking, the long-term pressure resistance of the crosslinked polyethylene resin tubes obtained in Examples 1 to 3 and Comparative Examples 1 to 6,
Short-term pressure resistance and flexibility were determined, and the results are shown in Table 1. The degree of crosslinking can be represented by a gel fraction (%) represented by the following formula (1) based on JIS K6769.

Gel fraction (%) = (sample weight before solvent extraction−sample weight after solvent extraction) / sample weight before solvent extraction × 100 (1) The weight of the sample after extraction is the weight of only the remaining insoluble portion obtained by dissolving the uncrosslinked resin remaining in the sample using a solvent capable of dissolving the selected crosslinked thermoplastic resin.

The long-term pressure resistance was measured by a method specified in a hot internal pressure creep test (JIS K6769) and visually observed for cracks and other defects. The evaluation was evaluated as を when no defect was observed, and as × when cracks and other defects were observed.

The initial withstand voltage performance and flexibility are determined by JI
It was evaluated based on the yield strength and elastic modulus determined by a tensile test specified in SK6769. From the viewpoint of workability, the elastic modulus was evaluated to be good if it was 0.4 GPa or less.

[0057]

[Table 1]

From the results in Table 1, it can be seen that a crosslinked polyethylene resin tube excellent in all of the long-term pressure resistance performance, the short-term pressure resistance performance, and the flexibility is obtained when manufactured under the conditions of Examples 1 to 3. I understand. Further, in Comparative Example 2, molding was impossible because the polyethylene resin having a too low molecular weight distribution was used, and thus crosslinking was considered to have progressed in an early stage.

[0059]

According to the crosslinked polyethylene resin pipe of the first aspect of the present invention, since both the uniform crosslinked structure and the reduction of the crystallinity are achieved, the short-term and long-term pressure resistance performance is improved. It can be secured at a standard and can have excellent flexibility. Therefore, construction can be easily performed even at a complicated construction site, and can be suitably used for a water supply hot water supply pipe used for a long time.

In the method for producing a crosslinked polyethylene resin tube according to the second aspect of the present invention, since the crosslinked structure can be made uniform and the degree of crystallinity can be reduced, short-term and long-term pressure resistance can be improved. It is possible to obtain a crosslinked polyethylene-based resin tube having a high level of flexibility and excellent flexibility.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of an apparatus for producing a crosslinked polyethylene resin tube according to the present invention.

FIG. 2 is a sectional view showing a mold in the manufacturing apparatus of FIG.

FIG. 3 is an explanatory diagram illustrating a structure of a resin discharge port.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 2 Die 3 (For crosslinked resin) Extruder

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // B29K 23:00 B29K 23:00 105: 24 105: 24 B29L 23:00 B29L 23:00 (72) Inventor Akihiro Ogawa 2-2 Sekisui Engineering Co., Ltd. F-term (reference) 2-2 Kamikaba Kaminokocho, Minami-ku, Kyoto 3H111 AA02 BA15 BA34 DA07 DB03 DB08 EA12 4F071 AA15 AA81 AA82 AC08 AH03 BB06 BC05 4F207 AA04D AB03 AG08 KA01KA KK01 KW33 4J002 BB031 BB051 EK036 EK046 EK056 FD146 GL00

Claims (2)

[Claims] (1) a molecular weight distribution of 2 to 5 and a density of 0.9;
A base resin made of a polyethylene resin of 38 g / cm ³ or more and 0.945 g / cm ³ or less;
A polyethylene-based resin composition comprising an organic peroxide mixed with 0 part by weight in an amount of 1 part by weight or more and 5 parts by weight or less is made of a cross-linked polyethylene-based resin which is heat-crosslinked at a melting point of the polyethylene-based resin or more. A crosslinked polyethylene resin tube characterized by the above-mentioned. 2. A molecular weight distribution of 2 to 5 and a density of 0.9.
A base resin made of a polyethylene resin of 38 g / cm ³ or more and 0.945 g / cm ³ or less;
A shaping step of shaping a polyethylene-based resin composition comprising an organic peroxide mixed at a ratio of 1 part by weight or more and 5 parts by weight or less to 0 parts by weight, and forming the polyethylene-based resin composition into polyethylene A cross-linking step of cross-linking so that the gel fraction becomes 65% or more by heating at a temperature equal to or higher than the melting point of the system resin.