JP2002113762A - Method for manufacturing polyethylene pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyethylene pipe which can effectively continuously stretch a thick item and prevent a resin from being crosslinked in an extruder even when high speed forming is conducted. SOLUTION: A method for manufacturing a polyethylene pipe comprises a raw material resin supply process of supplying a mixture obtained by kneading a raw material containing a polyethylene resin and a peroxide from an extruder into a die having a heat-crosslinking zone, a stretching zone and a cooling zone, a crosslinking process of heat-crosslinking the raw material resin in the heat-crosslinking zone to shape it into a pipe of the crosslinked resin, a stretching process of stretching it in the stretching zone to give a shape approximately similar to the formed item and a cooling process of cooling the shaped item to a temperature lower than an orientation relaxation temperature in the cooling zone, wherein an employed peroxide has one minute half life temperature of not lower than 190 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyethylene pipe capable of increasing strength and elastic modulus.

[0002]

2. Description of the Related Art A method of manufacturing an oriented product in which a resin is stretched during molding for the purpose of enhancing strength has already been disclosed in Japanese Patent Publication No. Hei.
No. 55379, Japanese Translation of PCT International Publication No. 5-501993,
It is disclosed in Japanese Patent Publication No. 2-58093. However, the manufacturing methods disclosed in the above publications have the following problems.

[Production method of Japanese Patent Publication No. 4-55379] In the production method of Japanese Patent Publication No. 4-55379, stretching is performed by pulling out from the downstream side of a die. Since the orientation in the circumferential direction imparted by expanding the diameter of the tube is alleviated by the pulling force in the axial direction, the orientation is preferentially oriented in the axial direction, and the orientation control is poor.

[Production method of Japanese Patent Publication No. 5-501993] The orientation state of a molded article is an orientation imparted only in the circumferential direction. There is low productivity.

[Production method disclosed in Japanese Patent Publication No. 2-58093] This is a method in which the material is pushed into the enlarged-diameter portion by the extrusion pressure, and since there is no need for a drawing force, the orientation control is arbitrarily high, and the control is easy and the production is easy. It has excellent properties. However, in the case of this production method, the film is stretched at a temperature equal to or higher than the glass transition temperature and equal to or lower than the melting point. In particular, in the case of a crystalline thermoplastic resin, a change in elastic modulus in this temperature region is sharp.

Therefore, in order to achieve uniform stretching, it is necessary to make the resin temperature distribution uniform, but it is not possible to achieve uniform temperature in thick products or high-speed molding. That is, there is a problem in the moldability of thick-walled products and high-speed molding.
In addition, since the elastic modulus is also at a high level in this temperature range, the necessary extrusion pressure is high, and it is impossible to continuously achieve high-viscosity resin or high-magnification stretching with an extruder.

On the other hand, a method for producing an oriented product by continuously stretching a resin is disclosed in Japanese Patent Publication No. Hei 11-513326. This production method is excellent in uniformity of orientation and continuous productivity because it is possible to achieve orientation at a temperature equal to or higher than the melting point by introducing crosslinking.

[0008]

However, in the above production method, no consideration is given to the 1 minute half-life temperature of the peroxide (crosslinking agent) used. The peroxide exemplified in the above publication is dicumyl peroxide. The one-minute half-life temperature of this dicumyl peroxide is as low as 171 ° C. Considering the fact that a polyethylene pipe is actually manufactured by using a peroxide having a low one-minute half-life temperature as a crosslinking agent as described above, when performing high-speed extrusion, the resin temperature cannot be suppressed in the extruder, and the extrusion is not performed. Crosslinking proceeds in the machine, making extrusion impossible.

In view of such circumstances, the present invention can efficiently perform continuous stretch molding of a thick product, and can crosslink a resin in an extruder even when performing high-speed molding. It is an object of the present invention to provide a method for producing a polyethylene pipe without any problem.

[0010]

In order to achieve such an object, a method for producing a polyethylene pipe according to the first aspect of the present invention (hereinafter referred to as the "method for producing the first aspect").
Is described), a kneaded material obtained by kneading a raw material containing a polyethylene resin and a peroxide, a heat crosslinking zone from an extruder,
A raw resin supply step of supplying the resin into a mold having a stretching zone and a cooling zone; and thermally cross-linking the polyethylene resin in the kneaded material in the heat-crosslinking zone, and applying the cross-linked resin tubular body along the cross-sectional shape of the mold. A cross-linking step of forming; a stretching step of shaping into a substantially molded article while orienting in the stretching zone at least one axis or more at an average temperature in the resin thickness direction at or above the softening temperature of the resin; And a cooling step of cooling the shaped article formed in the cooling zone to a temperature equal to or lower than the orientation relaxation temperature in a cooling zone, wherein a peroxide having a one-minute half-life temperature of 190 ° C. or more is used. Was adopted.

[0011] The method for producing a polyethylene pipe according to the second aspect of the present invention (hereinafter referred to as "the method for producing the second aspect") is the same as that of the first aspect.
The peroxide is 2,5-dimethyl-2,5-di (t-
(Butylperoxy) hexyne-3.

As the polyethylene resin used in the production method of the present invention, L-LDPE (linear low density polyethylene), LDPE (low density polyethylene), MD
Examples include PE (medium density polyethylene) and HDPE (high density polyethylene).

Further, in the production method of the present invention, the polyethylene resin is crosslinked by thermal crosslinking. At this time, the peroxide having a one-minute half-life temperature of 190 ° C. or more used as a crosslinking agent is not particularly limited. For example, t-butyl hydroperoxide, 1,1,3,
3, tetramethylbutyl hydroperoxide, p-menthane hydroperoxide, diisopropylbenzene hydroperoxide, 2,5-dimethylhexane-
2,5-dihydroperoxide, 2,5-dimethyl-
2,5-di (t-butylperoxy) hexyne-3 and the like. In particular, because of its excellent crosslinking efficiency,
As in the production method of claim 2, 2,5-dimethyl-2,
It is preferred to use 5-di (t-butylperoxy) hexyne-3. The amount of peroxide added is not particularly limited, but if it is too small, the gel fraction of the finally obtained thermal crosslinking will not be sufficiently high, so that the effect of crosslinking cannot be obtained. On the other hand, if the amount of the peroxide is too large, the progress of the crosslinking is not only accelerated, but also the possibility that unreacted peroxide remains after the crosslinking is performed. Therefore, the amount of peroxide added was 0.02 to 100 parts by weight of the polyethylene resin.
It is preferably not less than 2 parts by weight and not more than 0.1 part by weight,
It is more preferable that the amount be 5 parts by weight or more and 1.5 parts by weight or less.

Additives may be appropriately added to the raw materials used in the production method of the present invention. Additives such as antioxidants, light stabilizers, ultraviolet absorbers, lubricants, flame retardants, antistatic agents and the like are appropriately used to obtain desired physical properties. It is also possible to add a small amount of a substance that can serve as a crystal nucleating agent to refine the crystal and to help uniform the physical properties. In addition, fillers and pigments can be used in a range that does not cause deterioration in physical properties. For example, fibrous fillers such as glass fiber, carbon fiber, and asbestos, talc, mica, montmorillonite, and aluminum oxide are exemplified.

The degree of crosslinking of the crosslinked resin tubular body immediately before the stretching zone is preferably 40% or more and 70% or less. That is, if the degree of cross-linking is less than 40%, the molecular chains may pass through by stretching at a temperature higher than the melting point, and sufficient molecular orientation may not be achieved. If the degree of cross-linking exceeds 70%, the elongation of the resin may be reduced. This is because there is a possibility that high-magnification stretching may not be performed because the degree is lowered. In the present invention, the degree of crosslinking can be represented by a gel fraction (%) represented by the following formula. Gel fraction (%) = sample weight after solvent extraction / sample weight before solvent extraction × 100

In the above formula, the weight of the sample after the solvent extraction means that the uncrosslinked resin remaining in the sample is dissolved by using a solvent capable of dissolving the selected uncrosslinked raw material resin. It is the weight of only the insoluble matter.

Further, the average temperature in the thickness direction of the resin means an average value of the temperatures of both wall surfaces and the center of the thickness in the thickness direction. However, it is preferable that the difference between the maximum temperature and the minimum temperature is within 10 ° C. from the viewpoint of uniformity of the quality of the final alignment product. The term “above the softening temperature” means, in the case of polyethylene resin which is a crystalline thermoplastic resin, above the crystallization peak temperature, preferably above the melting peak temperature. In addition, in the case of polyethylene resin, the term “below the orientation relaxation temperature” means below the temperature at which extrapolation crystallization ends. The temperature relating to crystallization referred to here is based on JIS.
K 7121 is the temperature defined. Cooling is performed to cool the stretched shaped article and freeze the orientation.

As a method of supplying the polyethylene resin into the mold, there is a method of pressure-feeding using a pressure pump capable of continuously applying heat to the polyethylene resin. As such a pressure pump, a method using an extruder is most preferably used.

As the extruder, a single-screw extruder, a twin-screw extruder, a multi-screw extruder and the like can be used. When the polyethylene resin and the peroxide are kneaded in the extruder, polyethylene extruder is preferably used. A twin-screw co-rotating extruder which melts the resin and has excellent mixing ability with peroxide is preferred.

If there is a portion where the pressure becomes zero in the extruder, the screw may be unfilled at that portion and a problem of peroxide adhesion may occur. Therefore, when the polyethylene resin and the peroxide are mixed in the extruder and supplied to the mold, the screw arrangement in the extruder is sequentially formed with a high-pressure part, a low-pressure part, and a high-pressure part, and a liquid peroxide is formed in the low-pressure part. It is preferable to supply and knead with the polyethylene resin in the extruder. That is, since the high pressure section is provided on the upstream side and the downstream side of the low pressure section to which the peroxide is supplied, the outflow of the peroxide to the upstream side and the downstream side is prevented, and the pressure of the low pressure section becomes zero. So that it is kept. Therefore, it is possible to prevent the retention of peroxide adherence to the screw.

As described above, the method for controlling the pressure gradient in the extruder is not particularly limited.
In the case of a coaxial co-rotating extruder, in order to increase the pressure, use a kneading disk in which a disk having a cross section of a self-wiping shape is intermittently connected or a reverse full flight shape that transports resin to the upstream side. Can be lowered by using a normal full-flight shape and arranging them so as to have the above-mentioned pressure gradient. One example is a full flight from downstream to upstream in a part of the screw axis direction.
A structure in which reverse full flight, full flight, and reverse full flight are arranged in this order, and peroxide is supplied to a third full flight portion that is a low pressure portion.

Further, as means for supplying the kneaded material from the extruder into the mold, a press-in device may be used. The pressurizing press-in device is not particularly limited as long as the device can press-in and press the kneaded material into the mold, and examples thereof include an extruder in which a gear pump and a screw shaft are incorporated. Among them, it is particularly preferable to use a gear pump that can press and push a resin into a mold despite its small size. As the gear pump, a gear pump having a spur gear having parallel gear teeth or a helical gear having an angle can be used, but a gear pump having a helical gear is preferable from the viewpoint of appearance and the like.

The apparatus for supplying the peroxide to the low-pressure section is not particularly limited as long as the liquid can be supplied against the pressure of the low-pressure section, and examples thereof include a plunger pump and a diaphragm pump.

In the production method of the present invention, it is preferable that a lubricant is interposed between the resin contact surface in the mold and the crosslinked resin. As a method of interposing a lubricant,
Although not particularly limited, for example, (1) a method in which a low-molecular-weight lubricant is preliminarily mixed into a raw material, and (2) a method in which a lubricant is supplied to a resin contact surface in a mold, are exemplified.
The method (2) is more preferable from the viewpoint of the stability of the lubricating effect and the long-term performance of the molded article.

Examples of the lubricant used in the method (1) include waxes and oligomers. Examples of the lubricant used in the method (2) include ethylene oligomer, silicone oil, stearic acid, polyethylene glycol, liquid paraffin, and a low melting point polymer. Considering the stability of forming a lubricating film and the heat resistance,
Polyethylene glycol is preferred.

Considering the removability of the lubricant from the formed oriented product, the shear rate is not less than the flow start temperature of the polyethylene resin and not more than (flow start temperature + 50 ° C.) and not less than 10 / sec and not more than 200 / sec. Melt viscosity at 300 poi
It is preferable to use a low melting point thermoplastic resin (hereinafter, referred to as “resin lubricant”) in a range from se to 3000 poise. Such a resin lubricant is not particularly limited, but its melting point is not higher than the temperature at which the molecular motion of the raw material resin is fixed, there is no heat-fusibility with the raw material resin, and if it can be peeled off after cooling, Although not particularly limited, for example, polycaprolactone or polyamide is preferable. These resin lubricants may be used alone or in combination of two or more.

The polycaprolactone is represented by the following general formula H- (OCH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CO) _n -H (n is a positive integer). The weight average molecular weight of this polycaprolactone is preferably from 20,000 to 70,000.

As the polyamide, general polyamides can be used and are not particularly limited.
Nylon 20 and the like. The weight average molecular weight of the polyamide is preferably from 1,000 to 5,000.

These polycaprolactones and polyamides can be used alone or individually with polymers whose viscosity can be adjusted, such as polyethylene, polystyrene, polypropylene, ethylene-vinyl acetate copolymer, and ethylene-ethyl (meth) acrylate copolymer. Two or more kinds may be added. The addition ratio of these polymers is 1 to 100 parts by weight of polycaprolactone and / or polyamide.
It is preferably from 0 to 50 parts by weight, particularly preferably from 20 to 40 parts by weight.

The melt viscosity of the lubricant is 300 poise or more and 3000 poise or less at a shear temperature of 10 / sec or more and 200 / sec or less at a temperature not lower than the flow start temperature of the polyethylene resin (flow start temperature + 50 ° C.). The reason is that the melt viscosity is 300
If it exceeds 0 poise, there will be no lubrication effect and 300 po
If it is less than ise, the cohesive force will be small, and it may be broken when peeled off in a solidified state from the molded product extruded from the mold.

Here, the temperature at which the molecular motion is fixed indicates the crystallization end temperature. The flow start temperature is
It shows the temperature at which the indentation load becomes infinite when a capillary with a diameter of 1 mm and a length of 10 mm is used in a capillary rheometer. That is, in the case of polyethylene resin, the flow start temperature means a melting point.

As a method of supplying the lubricant to the resin contact surface, at least a portion to be the resin contact surface of the mold is formed of a porous material, and pressure is applied to the lubricant to allow the resin contact from the back side of the porous material. A method in which the lubricant is exuded toward the surface of the surface, a method in which the lubricant is developed by a manifold and supplied to the shape of a molded product, and the like. The device for supplying the lubricant is not particularly limited as long as the lubricant can be supplied against the pressure in the mold, and examples thereof include a plunger pump and a diaphragm pump.

In the production method of the present invention, uniaxial stretching can be achieved by expanding at least one of the inner diameters and reducing the thickness. Depending on the magnitude of these actions, the draw ratio can be arbitrarily controlled,
It is selected in the range of 5 times or more and 50 times or less in the area reduction rate at which the stretching effect appears.

Incidentally, by performing the stretching in the stretching step, the degree of orientation of the resin can be represented by the “degree of orientation”. The “degree of orientation” is a numerical value indicating how many molecular chains of polyolefin molecules are arranged in that direction, and can be said to be substantially proportional to the refractive index of the resin. That is,
The higher the refractive index in a particular direction is higher than the refractive index (nn) in the non-oriented state, the higher the degree of orientation in that direction.

Therefore, the degree of orientation can be determined by measuring the refractive index using infrared spectroscopy (hereinafter referred to as “IR”), X-ray analysis, a deflection microscope, or microwave.

However, in order to measure the refractive index, an Abbe refractometer that irradiates a sodium D line (wavelength 589 nm) is often used because the measuring method is simple. It is necessary to sufficiently transmit the sample, and it is not appropriate to measure the refractive index of the optically opaque polyolefin resin tubular body using an Abbe refractometer. Therefore, in the microwave region where dielectric relaxation due to local motion such as twisting of the molecular main chain of a polymer material such as polyolefin resin is observed,
Among them, the dielectric constant (ε ′) is measured by irradiating a microwave around 19 GHz to the polyolefin-based resin tubular body, and the Maxwell's formula ((refractive index (n) =
It is appropriate to determine the refractive index from √ (ε ′)).

The refractive index of the biaxially oriented polyolefin resin tubular body of the present invention is such that the average value of the refractive index (nh) in the circumferential direction and the average value of the refractive index (na) in the axial direction are each in the non-oriented state. 0.002 or more larger than the refractive index (nn), and the ratio (D / D) of the outer diameter (D) of the tube to the thickness (t) of the tube.
Preferably, t) is 100 or less. That is, either the average value of the refractive index (na) in the circumferential direction or the average value of the refractive index (nh) in the axial direction is the refractive index (n
If the value of n) is less than 0.002, the orientation of the polyolefin molecules is insufficient, and it is not possible to improve the elastic modulus.

Accordingly, resistance to the internal pressure applied to the pipe from the fluid flowing inside the pipe (hereinafter referred to as “internal pressure resistance”)
The resistance to pressure applied to pipes from soil and vehicles running on the ground (hereinafter referred to as “earth pressure resistance”) when the polyolefin resin tubular body is buried and the pipe cannot be improved. Can not.

As the refractive index (nn) in the non-aligned state, the refractive index of the polyolefin-based resin before alignment may be directly used as the refractive index (nn) in the non-aligned state. After stretching and orienting the tubular body, the tube is heated above its melting point + 40 ° C., and then cooled at a rate of about 10 ° C./min to change the refractive index of the tube whose orientation has been canceled to that of the non-oriented state. It is preferable to set the refractive index (nn).

As described above, the higher the refractive index, the higher the degree of orientation. Specifically, the refractive index (nh) in the circumferential direction is larger than the refractive index (na) in the axial direction, and Is preferably 0.004 or more, preferably 0.01 or more, greater than the refractive index (nn) in the non-aligned state. When the refractive index (nh) in the circumferential direction is smaller than the refractive index (na) in the axial direction, it goes without saying that the degree of orientation in the axial direction is larger than the degree of orientation in the circumferential direction. When the difference between the refractive index (nh) in the circumferential direction and the refractive index (nn) in the non-oriented state is less than 0.004, the orientation of the polyolefin molecules in the circumferential direction by stretching is insufficient. In some cases, the elastic modulus in the circumferential direction cannot be sufficiently improved, and the internal pressure resistance and the earth pressure resistance of the pipe cannot be improved.

The ratio of (refractive index in the circumferential direction (nh) -refractive index in the axial direction (na)) / (refractive index in the circumferential direction (nh)) is preferably 0.004 or more and 0.03 or less.
More preferably, it is 0.01 or more and 0.02 or less.
If it is less than 0.004, the orientation of the polyolefin molecules in the circumferential direction by stretching is insufficient, the elastic modulus in the circumferential direction cannot be sufficiently improved, and the internal pressure resistance and the earth pressure resistance of the pipe cannot be improved. There are cases.

On the other hand, if it exceeds 0.03, the polyolefin molecules are stretched too much so as to be oriented in the circumferential direction too much, so that the deformation followability of the pipe is deteriorated. When an earthquake occurs when used as a buried pipe, the pipe tends to break easily.

The molecular weight of the polyethylene resin is not particularly limited.
0000 is preferable, and 10,000 to 1,000,000 is more preferable.

[0044]

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 schematically shows one embodiment of a manufacturing apparatus used for manufacturing the polyethylene pipe of the present invention, and FIG. 2 shows a mold in a cross section.

As shown in FIG. 1, the manufacturing apparatus A is provided with an extruder 8, a mold 1, and a resin flow path 9 connecting the extruder 8 and the mold 1. As shown in FIG.
Has a hopper 81 for charging polyethylene resin and a peroxide charging port 82.

The resin flow path 9 has a gear pump 91 as a pressurizing and pushing device in the middle thereof, and the extruder 8 and the gear pump 9
1, a pressure detection sensor 92a is provided between the gear pump 91 and the mold 1. The gear pump 91 is connected to a drive motor 93 for driving the gear pump 91, a control panel 94 for the drive motor 93, and a rotation speed setting device 95 for setting the rotation speed of the drive motor 93.

The mold 1 is, as shown in FIG.
And a mandrel 3. The mold body 2 is shown in FIG.
A resin supply port 21 for supplying a kneaded material in a molten state in which a raw material containing a polyethylene resin and a peroxide sent from the extruder 8 through the resin flow path 9 shown in FIG.
A lubricant supply port 22 is provided, a small-diameter cylindrical portion 23 is provided from the end on the resin supply port 21 side toward the center, and a large-diameter cylindrical portion 24 is provided from the outlet side of the mold body 2 toward the center. A large-diameter tube portion 25 is provided between the small-diameter tube portion 23 and the large-diameter tube portion 24 and gradually increases in diameter from the small-diameter tube portion 23 to the large-diameter tube portion 24.

The mandrel 3 is a small-diameter cylindrical portion 2 of the mold body 2.
A fitting portion 31 that fits the small-diameter cylindrical portion 23 in a watertight manner from the end of the small-diameter cylindrical portion 23 to a substantially central portion of the small-diameter cylindrical portion 23 to bring the mold body 2 and the mandrel 3 into an integrated state; 23 is a cross-sectional shape of a tube to be substantially formed between a small-diameter shaft portion 32 forming a small-diameter thick-walled tubular thermal crosslinking zone 4 and a large-diameter cylindrical portion 24 of the mold body 2. A large-diameter shaft portion 33 that forms a cooling zone 6 having the same cross-sectional shape as that of the above, and a stretching zone is gradually increased from the small-diameter shaft portion 32 toward the large-diameter shaft portion 33 and between the large-diameter cylindrical portion 25. 5 forming the enlarged diameter shaft portion 34
And

The fitting portion 31 has a spiral that guides the resin supplied from the resin supply port 21 to the thermal cross-linking zone 4 on the outer peripheral surface from the portion facing the resin supply port 21 to the boundary with the small diameter shaft portion 32. A groove 31a is provided. Also, mandrel 3
A lubricant supply passage 35 is formed from the fitting portion 31 toward the small-diameter shaft portion 32. The lubricant supply passage 35 extends from the outer peripheral surface of the small-diameter shaft portion 32 to the outer peripheral surface of the enlarged-diameter shaft portion 34. It communicates with a spirally-provided lubricant supply groove 36.

That is, the lubricant is supplied to the outer peripheral surfaces of the small-diameter shaft portion 32 and the large-diameter shaft portion 35 which are the resin contact surfaces via the lubricant supply groove 36 by a pressure pump or the like.

Next, an embodiment of a method for manufacturing a polyethylene pipe using the mold 1 will be described in the order of steps.

(1) A polyethylene resin having a one-minute half-life temperature of 190 ° C. or more is charged into the extruder 8 from the hopper 81 through the peroxide inlet 82, and is mixed and kneaded in the extruder 8. The kneaded material is melted and continuously supplied to the resin supply port 21 of the mold 1 via the resin flow path 9 provided between the extruder 8 and the mold 1. At the time of supply, the pressure detection sensor 92a detects the pressure on the upstream side of the gear pump 91 in the resin flow path 9, and according to the result, the rotation number setting device 95 is driven so that the pressure becomes equal to or less than the withstand pressure of the extruder 8. Motor 93
The number of rotations is controlled.

At the same time as supplying the raw material resin to the extruder 8, the inner peripheral surface of the mold main body 2 and the mandrel 3, which are the resin contact surfaces, via the lubricant supply port 22 and the lubricant supply path 37.
The melting point of the polyethylene resin is equal to or higher than the melting point of the polyethylene resin.
Melt viscosity at a temperature of 50 ° C. or less and a shear rate of 10 / sec or more and 200 / sec or less is 300 poise or more and 3000 p or more.
The lubricant composed of a thermoplastic resin within the range of oise or less is exuded.

(2) The kneaded material supplied to the resin supply port 21 is sent to the thermal cross-linking zone 4 through the spiral groove 31a, developed into a thick cylindrical shape, and the polyethylene resin in the kneaded material is reduced to 40% by peroxide. % And 70% or less. (3) The crosslinked resin tubular body that has been thermally crosslinked is sent to the stretching zone 5 where the diameter is increased by the taper of the enlarged diameter shaft portion 34, and the thickness is reduced to achieve uniaxial or more stretching.

(4) In the cooling zone 6, the tubular shaped material formed into a gap between the large-diameter shaft portion 33 and the large-diameter cylindrical portion 24 by stretching in the stretching zone 5 is subjected to the orientation relaxation temperature or less, that is, While maintaining the shape below the crystallization start temperature, cooling is performed, and the oriented resin is cooled and solidified, and the lubricant is solidified in a layer on the surface of the oriented resin. (5) The lubricant layer 7 solidified into a layer is peeled off to continuously obtain a polyethylene pipe P.

The polyethylene pipe P of the present invention thus obtained is stretched in a molten state as described above, so that the resin deformation force can be greatly reduced. And
Since the polyethylene resin is cross-linked to form a stitch structure between molecular chains, molecular orientation can be ensured by stretching even during melting. That is, in the above method, the timing at which crosslinking is performed is not performed before, during, and after stretching as in the production method of Japanese Patent Application Laid-Open No. 11-51326, but the strength can be improved most by orientation. Since the cross-linking is performed at a timing before performing the stretching step in consideration, a polyethylene pipe excellent in strength can be obtained.

Further, since thermal crosslinking is performed so as to have a degree of crosslinking of 40% or more and 70% or less, a polyethylene tube having excellent orientation can be obtained without passing through molecular chains. In addition, in the production method of the present invention, a peroxide having a one-minute half-life temperature of 190 ° C. or more is used. Therefore, even during high-speed molding, the progress of crosslinking of the kneaded product is suppressed until the thermal crosslinking zone 4 is reached. Therefore, the polyethylene pipe P can be stably produced without forming a gel in the extruder 8 or the like.

When the obtained polyethylene pipe is connected to a joint, if a lubricant is left on the surface, the adhesiveness is remarkably reduced. Therefore, in order to obtain a product, it is necessary to completely remove the lubricant. When a liquid lubricant that does not solidify at room temperature is used, the lubricant attached to the surface of the extruded extruded product must be wiped with a cloth or the like or washed with water, and the removal operation is troublesome. However, as described above, the lubricant is solidified on the surface of the molded article in the cooling step and then the lubricant layer is peeled off, so that the productivity is improved and the thermoplastic resin is used as the lubricant. Since the lubricant is used, the lubricant can be collected and reused, and the manufacturing cost can be reduced.

[0059]

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

(Example 1) As shown in FIG. 1, a metal mold 1 as shown in FIG.
And a manufacturing apparatus A provided with an extruder 8. [Die size]-Outer diameter of small diameter shaft portion 32: 11.8 mm-Inner diameter of small diameter cylindrical portion 23: 34.1 mm-Outer diameter of large diameter shaft portion 33: 58.8 mm-Inner diameter of large diameter cylindrical portion 24: 63.0mm

[Extruder] TEX30α manufactured by Japan Steel Works, L / D = 51, caliber 3
2mm

Then, high-density polyethylene (density 0.953, melt flow rate (MFR) 0.03, weight average molecular weight 268,000, melting point 132 ° C.) as a polyethylene resin is charged into the extruder, and L / D = 3.
From position 5, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 as a peroxide
(Perhexin 25B manufactured by NOF Corporation, 193 ° C., half-life time: 60 seconds) was added to the extruder 8 at a ratio of 0.1 part by weight to 100 parts by weight of the high-density polyethylene, and the resin at 170 ° C. in the extruder 8 was added. After high-density polyethylene and 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 are mixed and kneaded at a temperature, the obtained kneaded product is mixed with the extruder 8 and the mold 1. Through a pressure-indentation means (gear pump) provided in the resin flow path 9 between the resin supply port 21 of the mold body 2, the temperature of the thermal crosslinking zone 4 reaches 220 ° C., the stretching zone 5 reaches 160 ° C., and the cooling zone 5 reaches 80 ° C. It was continuously supplied into the set mold 1 to continuously obtain an oriented polyethylene tube having an outer diameter of 63 mm and an inner diameter of 58.8 mm.

In the extrusion stretching, polycaprolactone as a lubricant [viscosity of 1000 cps (at 160
° C)) was fed into the mold with a plunger pump so that it spread over the inner and outer surfaces of the resin just before the thermal crosslinking zone. In addition, as an extruder, a screw shaft is provided with a 1st full flight shape part-a 1st reverse full flight shape part-a 2nd full flight shape part-a 2nd reverse full flight shape part in order from the upstream side to the downstream side. From 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) 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3.

Comparative Example 1 An oriented polyethylene tube was continuously obtained in the same manner as in Example 1 except that dicumyl peroxide (one minute half-life temperature: 171 ° C.) was used as the peroxide. However, a gel was formed in the extruder 8 and continuous sampling was impossible.

Table 1 shows the circumferential strength, the axial strength and the continuous formability at 0.6 m / min of the oriented polyethylene pipe obtained in Example 1 above.

[0066]

[Table 1]

From the results shown in Table 1, the one-minute half-life temperature was 190
2,5-dimethyl-2, which is a peroxide at a temperature of at least
The use of 5-di (t-butylperoxy) hexyne-3 enables continuous production of oriented polyethylene pipes having excellent circumferential and axial strength even at a high speed of 0.6 m / min. I understand.

[0068]

The method for continuously producing an oriented product according to the present invention is configured as described above, so that orientation control and molding of a thick product are possible, and even if high-speed molding is performed, A polyethylene tube can be stably manufactured without forming a gel before reaching the thermal crosslinking zone.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing one example of a production apparatus used for a continuous production method of an oriented product according to the present invention.

FIG. 2 is a cross-sectional view illustrating a mold of the manufacturing apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Mold main body 3 Mandrel 4 Thermal crosslinking zone 5 Stretching zone 6 Cooling zone 8 Extruder A Manufacturing apparatus P Polyethylene pipe

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 23:00 B29L 23:00 C08L 23:04 C08L 23:04 (72) Inventor Junichi Yokoyama Minami-ku, Kyoto 2-2 Kamisoba Kamichocho Sekisui Chemical Co., Ltd. F-term (reference) 4F071 AA15 AC08 AE02 AG05 BB06 BC05 4F207 AA04 AB03 AG08 KA01 KA17 KK01 KK45 KK48 KL57 KL63 KL83 KL88 KM15

Claims (2)

[Claims] 1. A kneaded product obtained by kneading a raw material containing a polyethylene resin and a peroxide is subjected to a thermal crosslinking zone from an extruder,
A raw resin supply step of supplying the resin into a mold having a stretching zone and a cooling zone; and thermally cross-linking the polyethylene resin in the kneaded material in the heat-crosslinking zone, and applying the cross-linked resin tubular body along the cross-sectional shape of the mold. A cross-linking step of forming; a stretching step of shaping into a substantially molded article while orienting in the stretching zone at least one axis or more at an average temperature in the resin thickness direction at or above the softening temperature of the resin; And a cooling step of cooling the shaped article formed in the cooling zone to a temperature equal to or lower than the orientation relaxation temperature in a cooling zone, wherein a peroxide having a one-minute half-life temperature of 190 ° C. or more is used. A method for producing a polyethylene pipe. 2. The method according to claim 2, wherein the peroxide is 2,5-dimethyl-2,2.
The method for producing a polyethylene tube according to claim 1, wherein the method is 5-di (t-butylperoxy) hexine-3.