JP2003117995A - Method for manufacturing biaxially oriented thermoplastic resin pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a biaxially oriented thermoplastic resin pipe, by which a biaxially oriented molding process can be smoothly started and a finished product showing an outstanding strength in the axial and the peripheral direction can be continuously obtained. SOLUTION: This method for manufacturing a biaxially oriented thermoplastic resin pipe comprises the steps to adjust the temperature of a thermoplastic resin pipe 21 extruded from a mold 12 of an extruder 11 to a specified orientation temperature level, to expand the diameter of the pipe 21 by making it pass over a diameter expansion mold 17 connected to the mold 12, and to orientate/mold the diameter-expanded pipe 21 while taking it up with the help of at take-up unit. The diameter expansion mold 17 is of such as structure that headless conical parts 171 and 173 with diameter gradually expanded in a direction where the pipe 21 proceeds are separately formed in a multi-stepped fashion. In addition, the headless conical parts 171 and 173 are connected to each other by an intermediate columnar part 172 which maintains the same diameter in the direction where the pipe 21 proceeds.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a biaxially stretched thermoplastic resin tube.

[0002]

2. Description of the Related Art Generally, when a thermoplastic resin tube is stretched, its strength is increased. However, only by stretching the thermoplastic resin tube in the axial direction (longitudinal direction), although the strength in the axial direction is increased, only a product having insufficient circumferential strength, that is, strength against internal and external pressures can be obtained. Therefore, for example, the following method has been proposed as a method of increasing the strength of the thermoplastic resin pipe not only in the axial direction but also in the circumferential direction.

(1) A hollow processed article made of a stretchable thermoplastic resin is expansion-molded without a liquid lubricant inside by pulling by holding a nose machined at one end with a jaw and pulling it. A method for producing a biaxially stretched tubular member which is passed through a machine and molded into a tubular member in the state perpendicular to the axial direction of the processed article without any external force (Japanese Patent Laid-Open No. 2-258323).

(2) One end of a stretchable thermoplastic polymer hollow processed product (thermoplastic resin tube) is machined to form a nose, and then the processed product is enclosed in an oven in a state of being surrounded by a mandrel and a rod. The inserted and machined end is projected from the die exit, the end is gripped by a take-up jaw and subjected to a load, and is drawn through a mandrel having a cross-sectional area larger than its initial internal cross-sectional area inside the workpiece. A method of deforming (Japanese Patent Publication No. 4-55379).

(3) A drawing original pipe is formed by drawing it from the extrusion die by a take-up machine while extending in the longitudinal direction, and the original pipe is reheated, and a large-diameter die connected to the extrusion die is used as the original pipe. Inserted and held in the inside, and drawn out by a take-out machine and stretch-molded in the circumferential direction (Japanese Patent Laid-Open No. 6-58242).
0-59163).

However, these conventional methods include
There are the following problems. In the case of the methods (1) and (2), it is necessary to expand the diameter of the gripped end portion, so that the productivity is poor and it is not suitable for continuous production. Further, when carrying out continuous molding, if the stretching ratio in the circumferential direction is 2 times or more, the expansion molding machine or the mandrel cannot be overcome at the start of stretching, and cracks will occur in the original pipe, There is a problem that the stretch molding cannot be started.

Further, in the case of the method (3), at the time of starting the operation, the original pipe must be cut open to get over the large diameter die. For example, in the case of a resin that does not cause necking when stretched at a stretching temperature, such as a hard vinyl chloride resin, if the stretching ratio in the circumferential direction is set to 2 times or more, the original pipe will be cracked unless it is cut open. Occurs, and stretch molding cannot be started. Then, when the operation is started using the original pipe that has been cut open, the original pipe passes under the large-diameter die. In the circumferential direction which is the radial direction, the frictional resistance between the original pipe and the large diameter die is concentrated at the end of the slit line, and cracks propagate continuously, so there is a problem that stretch forming cannot be started. is there.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above problems of the prior art and provides a product which can smoothly start biaxial stretching and has excellent strength in the axial and circumferential directions. The object of the present invention is to provide a method for producing a biaxially stretched thermoplastic resin tube which can be continuously obtained.

[0009]

The invention according to claim 1 of the present application (invention 1) is that the thermoplastic resin tube extruded from the extrusion die is adjusted to a predetermined stretching temperature, and the extrusion die is extruded. The diameter is expanded by passing it over the diameter expansion die connected to
A method for producing a biaxially stretched thermoplastic resin tube for performing biaxially stretched molding in the circumferential direction and the axial direction while taking the expanded thermoplastic resin tube with a take-off machine, wherein the heat-expanding die is the heat A headless conical portion that gradually expands in diameter in the traveling direction of the plastic resin pipe is provided in multiple stages, and the headless conical portions have the same diameter in the traveling direction of the thermoplastic resin pipe. A method for producing a biaxially stretched thermoplastic resin pipe, wherein the thermoplastic resin pipes are biaxially stretch-molded by using those connected by an intermediate columnar portion to be maintained.

The invention according to claim 2 of the present application (invention 2)
Is a thermoplastic resin tube extruded from the extrusion die, adjusted to a predetermined stretching temperature, expanded by passing through a diameter expansion die connected to the extrusion die, the expanded heat A method for producing a biaxially stretched thermoplastic resin tube, wherein a biaxially stretched thermoplastic resin tube is biaxially stretched in a circumferential direction and an axial direction while being drawn by a take-up machine, wherein the thermoplastic resin tube progresses as the expanding die. Direction, the headless conical portion is divided into multiple stages, and the headless conical portions are connected by an intermediate columnar portion that maintains the same diameter in the traveling direction of the thermoplastic resin pipe. A stretched state and a shortened state in which the headless conical portions are brought close to each other to form a series of headless conical portions in which the intermediate cylindrical portion is not exposed. ,
After starting the biaxial stretching of the thermoplastic resin tube using the expanded diameter mold in the expanded state, the expanded diameter mold is brought into a contracted state, and the thermoplastic resin tube is biaxially stretched. This is a method for producing a biaxially stretched thermoplastic resin tube that continues molding.

The invention according to claim 3 of the present application (invention 3)
The headless conical portion of the expansion mold is composed of a first headless conical portion and a second headless conical portion, and the first headless conical portion is
The biaxial of the present invention 1 or the present invention 2 which is capable of performing circumferential stretch molding to approximately half the difference from the inner diameter of the thermoplastic resin pipe before stretch molding to the inner diameter of the biaxially stretched thermoplastic resin pipe after stretch molding. It is a method for producing a stretched thermoplastic resin tube.

Examples of the thermoplastic resin used in the present invention include vinyl chloride resins, olefin resins such as polyethylene and polypropylene, polyoxamethylene,
Polyvinylidene fluoride, polyester, polyamide, polyacetal, etc. are used.

The stretching ratio of the biaxially stretched thermoplastic resin tube in the present invention is preferably 1.05 to 3 times in the axial direction,
It is preferably 1.3 to 4 times in the circumferential direction, and more preferably 1.1 to 2 times in the axial direction and 1.5 to 3 times in the circumferential direction.

When the stretching ratio is too large, the thickness of the biaxially stretched thermoplastic resin tube becomes smaller than the thickness of the thermoplastic resin tube before stretching. When the biaxially stretched thermoplastic resin pipe is used as a buried pipe, for example, it is necessary to have a wall thickness to withstand earth pressure. In order to satisfy this, it is necessary to increase the wall thickness of the thermoplastic resin pipe before stretching, which makes it difficult to control the temperature and, by extension, uniformly stretch-mold. Therefore, it is necessary to suppress the stretching ratio from becoming too large. On the other hand, if the stretching ratio is too small, the strength cannot be increased by stretching. Further, according to the present invention, the draw ratio in the axial direction is approximately 1.05 times or more.

According to the present invention, the draw ratio in the circumferential direction is controlled by the maximum outer diameter of the expanding die connected to the extrusion die,
The axial draw ratio is controlled by the ratio of the speed of introduction into the diameter-expansion die and the speed of take-up.

In the present invention, in order to adjust the thermoplastic resin tube extruded from the extrusion die to a predetermined stretching temperature,
Usually, the thermoplastic resin tube extruded from the extrusion die is cooled in a cooling water tank, air-cooled before the drawing step, and reheated if necessary to adjust the tube wall to the specified drawing temperature. To do. At this time, the stretching temperature (resin temperature) is from the glass transition temperature to the glass transition temperature + 40 ° C. when the thermoplastic resin has a clear glass transition temperature, and when the thermoplastic resin does not have a clear glass transition temperature. Alternatively, the stretching may be performed at a temperature equal to or higher than the melting point obtained by preliminary experiments.

In order to adjust the tube wall to a predetermined stretching temperature, the water temperature of the cooling water tank, the length of the water tank, and the length of the zone for cooling are properly adjusted, although the amount of extrusion and the size of the tube differ. It is possible to If necessary, the outside of the outer wall of the tube may be reheated with a heater, warm air, warm water, etc. before entering the stretching step.

It is preferable that the surface of the diameter-expansion die used in the present invention is subjected to surface treatment such as hard chrome plating and made as flat as possible. If the surface is rough, the frictional resistance with the inner surface of the pipe will be large, and at the start of stretching, when the thermoplastic resin pipe is passed over the diameter-expansion mold, the thermoplastic resin pipe will not reach the end of the cut in the longitudinal direction. At times, stress tends to concentrate, which tends to hinder the smooth starting of the circumferential stretching process.

The number of steps of the headless conical portion of the diameter-expanding die used in the present invention is not particularly limited, but is preferably 2 to 3. The semi-vertical angle (angle of inclination of the surface with respect to the axis) of the headless conical portion of the diameter-expanding die used in the present invention is 15 ° to 45
Is preferably 25 °, more preferably 25 ° to 35 °.
If the half-vertical angle is too small, the contact area between the diameter-expanding die and the thermoplastic resin inner surface becomes large, so the friction resistance becomes too large, and even if the half-vertical angle becomes too large, the thermoplastic resin inner surface expands. Since the pressing force on the diameter mold becomes too large, the frictional resistance becomes too large, and in both cases, when the thermoplastic resin pipe is passed over the diameter expansion mold, the end part of the cut line in which the thermoplastic resin pipe is inserted in the longitudinal direction. The stress is likely to be concentrated at one time, and it tends to be an obstacle to the smooth start of the stretch forming step in the circumferential direction.

The axial length of the surface of the intermediate cylindrical portion of the diameter-expanding die used in the present invention is 0.3 to the axial length of the surface of the first step of the headless conical portion. It is preferably 4 times, more preferably 0.5 to 2 times. If the axial length of the surface of the intermediate columnar part is too long, the contact area between the diameter expansion die and the inner surface of the thermoplastic resin pipe will increase, so the friction resistance will increase too much, and the plastic resin pipe will increase in diameter. When passing through the mold, stress is likely to be temporarily concentrated at the terminal end of the cut in which the thermoplastic resin tube is inserted in the longitudinal direction, and this tends to be an obstacle to smoothly start the stretch forming step in the circumferential direction. If the axial length of the surface of the intermediate columnar part is too short, when the thermoplastic resin pipe is passed over the diameter expansion mold, the thermoplastic resin pipe is temporarily stressed at the end of the cut. Tend to concentrate, which tends to hinder the smooth start of the stretching process in the circumferential direction.

After the biaxial stretch molding, cooling is carried out to prevent shrinkage of the thermoplastic resin tube. The cooling method is not particularly limited, but it may be passed through a normal cooling water tank, or if the equipment is further simplified, water spray cooling may be performed from the outside of the pipe. However, in order to reduce residual stress due to uneven cooling, it is preferable to perform cooling from both the inner surface and the outer surface of the thermoplastic resin tube.

[0022]

In the method for producing a biaxially stretched thermoplastic resin pipe of the present invention 1, as the diameter-expanding mold, the headless conical portion gradually expanding in diameter in the traveling direction of the thermoplastic resin pipe is divided into multiple stages. And the headless conical portions are connected by an intermediate columnar portion that maintains the same diameter in the traveling direction of the thermoplastic resin pipe. By performing the biaxial stretch molding of, at the start stage of the biaxial stretch molding, when passing the thermoplastic resin tube adjusted to a predetermined stretching temperature on the diameter expansion mold, a part of the thermoplastic resin tube is Make a slit in the longitudinal direction, insert the slit so that it slides on the lower surface of the diametrical expansion mold, engage it with a take-up machine, and start taking-up continuously. When the cutout part of the plastic resin pipe passes over the diameter expansion mold, Since a plurality of headless conical portions separately provided are sequentially passed through the cylindrical portions between the headless conical portions, stress is temporarily concentrated at the end of the cut of the thermoplastic resin pipe. In this case, the thermoplastic resin pipe can be passed over the diameter-expanding mold without further expanding the cut, and the biaxial stretching process can be smoothly started. Then, continuing the secondary stretch molding consisting of the started extrusion step, temperature adjustment step and biaxial stretching step,
A biaxially stretched thermoplastic resin tube can be manufactured continuously and stably.

In the method for producing a biaxially stretched thermoplastic resin pipe according to the second aspect of the present invention, as the diameter-expanding die, the headless conical portion, which gradually expands in the traveling direction of the thermoplastic resin pipe, is provided in multiple stages. Separately, the extended state in which the headless conical portions are connected by an intermediate columnar portion that maintains the same diameter in the traveling direction of the thermoplastic resin pipe and the headless conical portions approach each other. The thermoplastic resin is produced by using the expanded die which is in an expanded state by using a series of headless conical portions which do not expose the intermediate cylindrical portion and can be in a contracted state. After starting the biaxial stretch molding of the resin pipe, the expanded mold is brought into a contracted state, and by continuing the biaxial stretch molding of the thermoplastic resin pipe, in the starting stage of the biaxial stretch molding, When a thermoplastic resin tube adjusted to a specified stretching temperature is passed over the diameter expansion mold, Cut a part of the fat pipe so as to make a notch in the longitudinal direction, pass the cut part so that it slides on the lower surface of the diameter expansion mold, bit it into the take-up machine, and take it off continuously. Although it starts, when the cutout portion of the thermoplastic resin tube and the subsequent portions pass over the diameter-expansion die, the first headless conical portion and the second headless conical portion provided separately in multiple stages are Since it sequentially passes through the cylindrical portion, stress does not temporarily concentrate at the end of the cut of the thermoplastic resin pipe, and the thermoplastic resin pipe can be mounted on the diameter-expansion die without expanding the cut. The biaxial stretching process can be smoothly started up, and in the continuous stage of the biaxial stretching after the start, the thermoplastic resin tube adjusted to a predetermined stretching temperature is Frustoconical part and second
Since it passes over a diameter-expanding mold in a contracted state with a series of headless conical parts, the take-up load can be small, and stretching at a high magnification in the circumferential direction can be performed without difficulty, and in the axial direction. Also, a biaxially stretched thermoplastic resin tube having excellent strength in the circumferential direction can be stably and continuously manufactured.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram for explaining an example of a method for producing a biaxially stretched thermoplastic resin tube of the present invention, together with an example of a biaxially stretched apparatus used. As shown in FIG. 1, the biaxial stretching device 1 includes an extruder 11, an extrusion die 12, a first water tank 14, a first take-up machine 15, a reheater 16, a diameter expansion die 17, a second water tank 18, and It consists of the second take-up machine 19.

The extruder 11 is provided with an extrusion die 12 for forming a thermoplastic resin pipe having a predetermined diameter.
A diametrical expansion die 17 is connected through a connecting rod 13 in the traveling direction of the thermoplastic resin tube. Extrusion die 12 and diameter expansion die 17
A first water tank 14, a first take-up machine 15, and a reheater 16 are provided between them. A second water tank 18 and a second take-up machine 19 are provided in the advancing direction of the thermoplastic resin pipe of the diameter expansion mold 17.

FIG. 2 is an enlarged front view of the diameter-expanding mold 17 used in the biaxial stretching device 1 shown in FIG. The diameter-expansion die 17 has a first headless conical section 1 having two stages of headless conical sections that gradually expand in diameter in the traveling direction of the thermoplastic resin tube.
71 and the second headless conical portion 173 are provided separately. First headless conical portion 171 and second headless conical portion 173
Are connected to each other by a first columnar portion (intermediate columnar portion) 172 that maintains the same diameter in the traveling direction of the thermoplastic resin pipe. A second cylindrical portion 174 is provided on the second headless conical portion 173 on the advancing direction side of the thermoplastic resin pipe and maintains the same diameter in the advancing direction.

The first columnar portion 172 has an outer diameter capable of being stretch-molded to a half of the difference from the inner diameter of the thermoplastic resin pipe before stretch molding to the inner diameter of the biaxially stretched thermoplastic resin pipe after stretch molding. . The second cylindrical portion 174 has an outer diameter corresponding to the inner diameter of the biaxially stretched thermoplastic resin tube. Therefore, the first headless conical portion 171 stretch-molds the thermoplastic resin tube 21 extruded from the extrusion die 12 to half the circumferential stretch ratio of the target biaxially stretched thermoplastic resin tube. The second headless conical portion 173 is a portion to be stretch-molded until the intended stretching ratio in the circumferential direction of the biaxially stretched thermoplastic resin tube is reached.

Next, an example of the method for producing the biaxially stretched thermoplastic resin pipe of the present invention will be described with reference to the same FIG. In the method of this example, biaxial stretch molding including the following extrusion step, temperature adjusting step and biaxial stretching step is started. First,
In the first extrusion step, the thermoplastic resin composition is supplied to the extruder 11 of the biaxial stretching device 1, the tubular thermoplastic resin tube 21 is continuously extruded from the extrusion die 12, and the first take-up machine 1
Extrusion molding is carried out while taking it at No. 5.

In the temperature adjusting step, the thermoplastic resin tube 21 extruded from the extrusion die 12 is passed through the first water tank 14 to be cooled. The thermoplastic resin tube 21 is reheated by the reheater 16
It is passed through the inside and adjusted to a predetermined stretching temperature.

In the biaxial stretching step, the thermoplastic resin tube 22 adjusted to a predetermined stretching temperature is passed over the diameter-expanding die 17 to first stretch in the circumferential direction. Next, while the thermoplastic resin tube 23 stretched in the circumferential direction is taken by the second take-up machine 19, the axial stretch molding is performed, and the second water tank 1
8 to cool the biaxially stretched thermoplastic resin tube 24.
And eggplant

At the start stage of this biaxial stretching,
When the thermoplastic resin tube 22 adjusted to a predetermined stretching temperature is passed over the diameter-expansion die 17, a part of the thermoplastic resin tube 22 is cut open so as to make a cut in the longitudinal direction, and the cut is made. The open portion is slidably passed through the lower surface of the diameter-expanding die 17, the tip thereof is engaged with the second take-up machine 19, and continuous take-up is started. Then, when the portion of the thermoplastic resin pipe 22 after the cut open portion passes over the diameter-expansion die 17, the first headless conical portion 171 and the second headless conical portion 173 which are separately provided in multiple stages. And the first cylindrical portion 17
Since it sequentially passes through 2 through, the stress is not temporarily concentrated at the end of the cut of the thermoplastic resin tube 22, and the thermoplastic resin tube 22 is not expanded further on the diameter expansion mold 17 Can be overcome, and the biaxial stretching process can be smoothly started up.

As described above, the biaxially stretched molding including the above-mentioned extrusion step, temperature adjustment step and biaxially stretched step started is continued to continuously and stably produce the biaxially stretched thermoplastic resin tube 24. can do. Also in this biaxial stretch forming continuous stage, the thermoplastic resin tube 22 adjusted to the predetermined stretch temperature has the first headless conical portion 171 and the second headless conical portion 171 provided in multiple stages on the diameter expansion mold 17. Since the headless conical portion 173 and the first columnar portion 172 are sequentially passed, it is possible to perform stretching at a high magnification in the circumferential direction without difficulty, and to obtain excellent strength in the axial direction and the circumferential direction. Axial stretched thermoplastic resin tube 24
Can be stably and continuously manufactured.

In the above example, the diameter-expansion die 17 shown in FIG. 3 may be used instead of the diameter-expansion die 17. This diameter-expansion die 37 has a three-stage first headless conical portion 37 in which the diameter of the headless conical portion is gradually increased in the traveling direction of the thermoplastic resin pipe.
First and second headless conical portion 373 and third headless conical portion 375
And a first columnar portion that maintains the same diameter between the first headless conical portion 371 and the second headless conical portion 373 in the traveling direction of the thermoplastic resin pipe. (Intermediate cylindrical portion) 372 connected so that the second headless conical portion 373 and the third headless conical portion 375 maintain the same diameter in the traveling direction of the thermoplastic resin pipe. A third columnar portion that is connected by a columnar portion (intermediate columnar portion) 374 and maintains the same diameter in the traveling direction of the thermoplastic resin pipe of the third headless conical portion 375. 376 is provided.

FIGS. 4 and 5 are schematic diagrams for explaining the steps of another example of the method for producing a biaxially stretched thermoplastic resin tube of the present invention, together with an example of a biaxially stretched apparatus used. As shown in FIGS. 4 and 5, the biaxial stretching device 4 includes an extruder 41,
The extrusion die 42, the first water tank 44, the first take-up machine 45, the reheater 46, the diameter expansion die 47, the second water tank 48, and the second take-up machine 49.

The extruder 41 is provided with an extrusion die 42 for forming a thermoplastic resin tube having a predetermined diameter.
A diameter expansion mold 47 is connected via a connecting rod 43 in the traveling direction of the thermoplastic resin tube. Extrusion die 42 and diameter expansion die 47
A first water tank 44, a first take-up machine 45, and a reheater 46 are provided between and. A second water tank 48 and a second take-up machine 49 are provided in the advancing direction of the thermoplastic resin pipe of the diameter expansion die 47.

FIG. 6 is an enlarged front view showing a diameter expansion die 47 used in the biaxial stretching device 4 shown in FIGS. 4 and 5. As shown in FIG. 6 (a), the diameter-expansion die 47 has a headless conical portion that gradually expands in diameter in the traveling direction of the thermoplastic resin tube and has a two-stage first headless conical portion 471. The first circle that is divided into the second headless conical portion 473 and maintains the same diameter between the first headless conical portion 471 and the second headless conical portion 473 in the traveling direction of the thermoplastic resin pipe. Columnar part (intermediate columnar part)
As shown in FIG. 6B, the first headless conical portion 471 and the second headless conical portion 47 are connected to each other in an expanded state connected by 472.
The first columnar portion 472 can be brought into a contracted state in which the first cylindrical portion 472 forms a series of headless conical portions which are not exposed,
In any of the states, the second headless conical portion 473 is provided with the second cylindrical portion 474 on the traveling direction side of the thermoplastic resin tube, which maintains the same diameter in the traveling direction. .

Next, steps of an example of manufacturing the biaxially stretched thermoplastic resin pipe of the present invention will be described with reference to the same FIGS. 4 and 5. In the method of this example, the stretch molding including the following extrusion step, temperature adjusting step and biaxial stretching step is started.
First, in the first extrusion step, as shown in FIG. 4, the thermoplastic resin is supplied to the extruder 41 of the biaxial stretching device 4, and the tubular thermoplastic resin pipe 51 is continuously supplied from the extrusion die 42. Extrusion is carried out while extruding and picking up by the first take-up machine 45.

In the temperature adjusting step, the thermoplastic resin tube 51 extruded from the extrusion die 42 is passed through the first water tank 44 to be cooled. The thermoplastic resin tube 51 is reheated by a reheater 46.
It is passed through the inside and adjusted to a predetermined stretching temperature.

At the start stage of the biaxial stretch forming process, the thermoplastic resin tube 5 adjusted to a predetermined stretch temperature is used.
When passing 2 over the expanded diameter mold 47 in the extended state, a part of the thermoplastic resin tube 52 is cut open so as to make a cut in the longitudinal direction, and the cut portion is expanded by the expanded diameter mold. The bottom surface of 47 is slidably passed through, and the tip of
It is caught in the take-up machine 49 to start continuous take-up. Then, when the cutout portion of the thermoplastic resin pipe 52 and the subsequent portions pass over the diameter-expanding die 47, the first headless conical portion 471 and the second headless conical portion 473 which are provided in multiple stages are provided. Since it sequentially passes through the first cylindrical portion 472, stress is not temporarily concentrated at the end of the cut of the thermoplastic resin pipe 52, and the thermoplastic resin pipe 52 is expanded without further expansion of the cut. It is possible to get over the diameter die 47 and smoothly start the biaxial stretching process.

After starting as described above, as shown in FIGS. 5 and 6 (b), the diameter-expanding die 47, the first headless conical portion 471, and the second headless conical portion 473. The first columnar portion 472 is brought closer to the side to be in a contracted state in which a series of headless conical portions in which the first cylindrical portion 472 is not exposed is formed. Then, while taking the thermoplastic resin pipe 53 stretched in the circumferential direction with the second take-up machine 49,
Axial stretch molding is performed, and the biaxially stretched thermoplastic resin pipe 54 is continuously obtained by passing through the second water tank 48 and cooling.

In the continuous stage of the stretch molding, the thermoplastic resin tube 52 adjusted to a predetermined stretch temperature has a series of the first headless conical portion 471 and the second headless conical portion 473. Since it passes over the diameter-expanding mold 47 in the contracted state, the take-up load is reduced, high-strength stretching in the circumferential direction can be reasonably performed, and biaxial stretching with excellent strength in the axial and circumferential directions. The thermoplastic resin tube 54 can be manufactured stably. In this manner, the biaxially stretched molding including the extrusion step, the temperature adjustment step and the biaxially stretched step can be continued to stably and continuously produce the biaxially stretched thermoplastic resin tube 54.

In the above example, instead of the diameter expansion mold 47, a diameter expansion mold 47 'shown in FIG. 7 may be used. As shown in FIG. 7 (a), the diameter expansion die 47 'has a first headless conical portion 471' having two stages of headless cones that gradually expand in diameter in the traveling direction of the thermoplastic resin pipe. And the second headless conical portion 473 ', and the first headless conical portion 471' and the second headless conical portion 473 'have the same diameter in the traveling direction of the thermoplastic resin pipe. As shown in FIG. 7B, the extended state in which the first columnar section (intermediate columnar section) 472 'is maintained, and the second headless conical section 473' has the first headless conical section. The first columnar portion 472 'can be brought into a contracted state in which the first cylindrical portion 472' forms a series of non-exposed headless conical portions by approaching the portion 471 'side. In any state,
The second headless conical portion 473 'is provided with a second cylindrical portion 474' that maintains the same diameter in the traveling direction of the thermoplastic resin tube.

(Examples) The present invention will be described below with reference to examples. (Example 1) Vinyl chloride resin (manufactured by Tokuyama Sekisui company, product number "TS1000R", degree of polymerization 1050) was used by using the biaxial stretching device 1 shown in FIG. 1 (using the diameter expansion mold 17 shown in FIG. 2).
00 parts by weight, dioctyl tin stabilizer (manufactured by Sankyo Machine Gosei Co., Ltd., product number “ONZ142F” 1 part by weight, stearic acid (manufactured by NOF Corporation) 0.5 part by weight, polyethylene wax (manufactured by Mitsui Chemicals, Inc., trade name “ Hiwax 220MP ")
Vinyl chloride resin composition (glass transition temperature 80 ° C.) obtained by mixing 0.5 with a super mixer (manufactured by Kawata Manufacturing Co., Ltd.)
Extruder 11 (manufactured by Sekisui Koki Co., Ltd., 60 mm twin-screw extruder,
Supply to a hopper of model "SLM60"), extrusion temperature 1
At 85 ° C. and an extrusion rate of 80 kg / h, extrusion molding is carried out while being taken by the first take-up machine 15, and an outer diameter of 66 mm and a wall thickness of 12 m.
A thermoplastic resin tube 21 of m was obtained.

Next, the thermoplastic resin pipe 21 is connected to the first water tank 1.
After passing through the inside of 4 and passing through the inside of the reheater 16, the outer surface is adjusted to 100 ° C. and the inner surface is adjusted to 110 ° C., and the thermoplastic resin tube 22 is partially cut in the longitudinal direction. After being cut open, it is passed under the diameter-expanding die 17, the tip thereof is bitten into the second take-up machine 19, and is continuously taken out, whereby the cut-out portion and the subsequent parts are provided in multiple stages. The first headless conical portion 171 and the second headless conical portion 172 were successively passed through the first cylindrical portion 173.

As a result, the stress is not temporarily concentrated on the end of the cut of the thermoplastic resin tube 22, and the diameter-expansion mold 1 is provided without expanding the cut of the thermoplastic resin tube.
7 could be overcome, and the initial stage of circumferential stretch forming could be smoothly started up. At the same time, while the thermoplastic resin tube 23 stretched in the circumferential direction is taken by the second take-up machine 19, the axial stretch molding is performed to
It was possible to smoothly start up the initial stage of the axial stretch forming with the biaxially stretched thermoplastic resin tube 24 by passing through the water tank 18 and cooling.

As described above, the biaxial stretch forming comprising the extrusion step, the temperature adjusting step and the biaxial stretching step is smoothly started, and then the biaxial stretch forming is continued to continuously and stably. The production of the biaxially stretched thermoplastic resin tube 24 could be continued.

Example 2 In the same manner as in Example 1 except that the diameter-expanding mold 37 shown in FIG. 3 was used, biaxial stretch molding including the above-mentioned extrusion step, temperature adjusting step and biaxial stretching step. Was smoothly started, and thereafter, the production of the biaxially stretched thermoplastic resin tube could be continued continuously and stably.

(Example 3) Using the diameter-expansion die 47 shown in FIG. 6, at the start stage of the stretch-molding, the stretching was started in the stretched state, and thereafter the diameter-expansion die 47 was reduced. In the same manner as in Example 1 except that the stretch forming was continued in a state, the biaxial stretch forming consisting of the extrusion step, the temperature adjusting step and the biaxial stretching step was smoothly started, and then continuously stabilized. It was possible to continue the production of the biaxially stretched thermoplastic resin tube. And, while the load of the second take-up machine 49 in the drawing start stage was 2.5 t,
The load of the second take-up machine 49 in the continuous stretching stage was 1.5 t.

(Embodiment 4) Using the diameter-expansion die 47 'shown in FIG. 7, at the start stage of biaxial stretch molding, the biaxial stretch molding was started in the stretched state, and thereafter the diameter expansion was performed. In the same manner as in Example 1 except that the mold 47 ′ was kept in the contracted state and the stretch forming was continued, the biaxial stretch forming including the extrusion step, the temperature adjusting step and the biaxial stretching step was smoothly started, and thereafter, It was possible to continuously and stably produce the biaxially stretched thermoplastic resin tube. And, while the load of the second take-up machine 49 in the drawing start stage was 2.5 t, the load of the second take-up machine 49 in the drawing continuation stage was 1.
It was 5t.

Comparative Example A biaxially stretched thermoplastic resin tube was manufactured in the same manner as in Example 1 except that the diameter-expanding mold a shown in FIG. 8 was used. This diameter expansion die a has a headless conical portion b whose diameter gradually increases in the traveling direction of the thermoplastic resin tube.
And on the advancing direction side of the thermoplastic resin pipe of the headless conical portion b,
It is provided with a cylindrical portion c that maintains the same diameter in the traveling direction. Stress is temporarily concentrated at the break of the thermoplastic resin tube, and the cut part expands, and it is not possible to climb over the diameter-expansion mold a, so that the stretch forming step in the circumferential direction can be started up smoothly. I couldn't.

[0051]

Since the method for producing a biaxially stretched thermoplastic resin pipe of the present invention has the above-mentioned constitution, the biaxially stretched molding can be smoothly started, and the strength in the axial direction and the circumferential direction can be increased. It is possible to continuously obtain excellent products.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating steps of an example of a method for producing a biaxially stretched thermoplastic resin tube of the present invention, together with an example of a biaxially stretched apparatus used.

FIG. 2 is an enlarged front view showing a diameter-expanding mold used in the example of the biaxial stretching device shown in FIG.

FIG. 3 is a front view showing another example of the diameter-expanding mold used in the example of the method for producing the biaxially stretched thermoplastic resin tube of the present invention.

FIG. 4 is a schematic diagram illustrating steps of another example of the method for producing a biaxially stretched thermoplastic resin tube of the present invention, together with an example of a biaxially stretched apparatus used.

FIG. 5 is a schematic view illustrating steps of another example of the method for producing a biaxially stretched thermoplastic resin tube of the present invention, together with an example of a biaxially stretched apparatus used.

FIG. 6 is an enlarged front view showing a diameter-expanding mold used in the example of the biaxial stretching device shown in FIG. 4.

FIG. 7 is a front view showing another example of the diameter-expanding mold used in another example of the method for producing a biaxially stretched thermoplastic resin tube according to the present invention.

FIG. 8 is a front view showing a diameter expansion mold used in a comparative example.

[Explanation of symbols]

1,4 Biaxial stretching device 11,41 Extruder 12,42 Extrusion die 13,43 Connecting rod 14,44 First cooling water tank 15,45 First take-up machine 16,46 Reheating machine 17,47,47 'Expansion Diameter mold 18,48 Second water tank 19,49 Second take-up machine 21-23,51-53 Thermoplastic resin pipe 24,54 Biaxially stretched thermoplastic resin pipe 171,471,471 'First headless conical portion 172, 472, 472 'First cylindrical portion (intermediate cylindrical portion) 173, 473, 473' Second headless conical portion 174, 474, 474 'Second cylindrical portion 475 Third headless conical portion 476 Second cylindrical part (intermediate cylindrical part)

Claims (3)

[Claims] 1. A thermoplastic resin tube extruded from an extrusion die is adjusted to a predetermined stretching temperature and is passed through a diameter-expanding die connected to the extrusion die to expand the diameter, thereby expanding the diameter. A method for producing a biaxially stretched thermoplastic resin tube for performing biaxially stretched molding in a circumferential direction and an axial direction while taking a thermoplastic resin tube with a take-up machine, wherein the thermoplastic resin is used as the diameter-expanding die. A headless conical portion that gradually expands in diameter in the traveling direction of the pipe is provided in multiple stages, and the same diameter is maintained between the headless conical portions in the traveling direction of the thermoplastic resin pipe. A method for producing a biaxially stretched thermoplastic resin pipe, characterized in that the thermoplastic resin pipe is biaxially stretch-molded by using those connected by an intermediate columnar portion. 2. A thermoplastic resin tube extruded from an extrusion die is adjusted to a predetermined stretching temperature, and is passed through a diameter-expansion die connected to the extrusion die to expand the diameter, thereby expanding the diameter. A method for producing a biaxially stretched thermoplastic resin tube for performing biaxially stretched molding in a circumferential direction and an axial direction while taking a thermoplastic resin tube with a take-up machine, wherein the thermoplastic resin is used as the diameter-expanding die. A headless conical portion that gradually expands in diameter in the traveling direction of the pipe is divided into multiple stages, and an intermediate cylindrical portion in which the headless conical portions maintain the same diameter in the traveling direction of the thermoplastic resin pipe. And an expanded state in which the headless conical portions are brought close to each other so that the intermediate columnar portion is not exposed to form a series of headless conical portions. Using the expanded metal mold in the expanded state, the biaxial of the thermoplastic resin pipe A method for producing a biaxially stretched thermoplastic resin pipe, characterized in that after the stretch molding is started, the diameter-expanding mold is brought into a contracted state and the biaxial stretch molding of the thermoplastic resin pipe is continued. 3. The headless conical portion of the expansion mold is composed of a first headless conical portion and a second headless conical portion, and the first headless conical portion is heat-treated before stretch forming. 3. The stretch molding in the circumferential direction can be performed in the circumferential direction up to about half the difference from the inner diameter of the plastic resin pipe to the inner diameter of the biaxially stretched thermoplastic resin pipe after stretch molding. A method for producing a biaxially stretched thermoplastic resin tube.