JP2001219461A - Method for manufacturing biaxially-stretched thermoplastic resin pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for a biaxially-stretched thermoplastic resin pipe which can control a stretch ratio in an axial direction using a single take-up machine without a lubricant at all in biaxially stretching a thermoplastic resin pipe, unnecessitates re-heating the thermoplastic resin pipe, greatly cuts down molding equipment and gives an excellent stretch ratio and accuracy of dimension. SOLUTION: A thermoplastic resin pipe 9 extruded from a die 2 of an extruder 1 is quickly chilled followed by being slowly cooled to adjust a temperature to a predetermined stretching temperature. The thermoplastic resin pipe 9 is enlarged by inserting a large diameter die 6 connected to the die 2, having a diameter gradually increasing toward a running direction of the thermoplastic resin pipe 9 and having a maximum diameter almost equal to the inner diameter of the stretched thermoplastic resin pipe 9 to be formed and is stretched by taking up the enlarged thermoplastic resin pipe 91 with a take-up machine 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 pipe is stretched,
The strength in the stretched direction increases. However, conventional stretching is mainly performed in the axial direction (longitudinal direction) of the thermoplastic resin tube, and although the strength in the axial direction increases, the strength in the circumferential direction, that is, the strength against internal pressure and external pressure is insufficient. was there.

Therefore, attempts have been made to increase the strength of the thermoplastic resin tube not only in the axial direction but also in the circumferential direction.

For example, 1) A hollow work piece (thermoplastic resin tube) containing a stretchable thermoplastic polymer is supplied from an inlet of a mold, and a cross-sectional area larger than an initial internal cross-sectional area of a die and a work piece in a solid phase is supplied. A method of applying a tensile stress through a former disposed inside the hollow workpiece and stretching the hollow workpiece, and collecting the stretched hollow workpiece from the exit side of the die (Japanese Patent Publication No. 4-553).
No. 79),

[0005] 2) Withdrawing from the mold of the extruder by a take-off machine, forming an original drawing pipe while stretching in the longitudinal direction,
A method of reheating this prototype pipe, inserting and holding a large-diameter mold connected to the extrusion die in the prototype pipe for drawing, pulling it out with a take-off machine, and forming it in the circumferential direction (Japanese Patent Laid-Open Publication No.
-59163),

[0006] 3) An expansion molding machine is passed through a hollow article made of stretchable thermoplastic resin without a liquid lubricant, so that no external force acts in a direction perpendicular to the axial direction of the article. A method for producing a biaxially stretched tubular member in which a tubular member is molded in a state (Japanese Patent Laid-Open No. 2-25832)
No. 3) has been proposed.

[0007]

However, these methods have the following problems. In the method 1), the thermoplastic resin is pulled out from the die while compressing the thermoplastic resin with the die (outer die) and the former (inner die), so that a large tensile force is applied in the axial direction. As a result, the stretching ratio in the axial direction is reduced. growing.

The thickness of the pipe is reduced. Then,
Lack of strength against external pressure makes it unsuitable for buried pipes. If the thickness of the workpiece before stretching is increased beforehand to solve the problem, (1) the dimensional accuracy of the thick workpiece before stretching will deteriorate, and (2) it will take time to control the temperature within the thickness. ,
Problems such as a decrease in productivity and (3) a greater tensile force is required at the time of stretching, resulting in a larger axial stretching.

In the method 2), two take-up machines are used, and speed control of the two take-up machines and reheating to the stretching temperature are required. Therefore, problems such as an increase in the length of the production line and a complicated control method of the molding equipment occur.

Furthermore, in the method 3), since no liquid lubricant is used, friction between the resin and the mold is increased, and it is difficult to control the stretching ratio in the axial direction to a low ratio. Also, when lubricating with air, since air is a compressible fluid, if the resin contracts during stretching, air will not flow if the air pressure is too low, and the resin will expand too much if the air pressure is too high. In addition, it is difficult to form an air film evenly by selectively bleeding air only through a weak portion of the resin. Therefore, it is difficult to uniformly control the thickness of the drawn pipe.

[0011] The present invention solves the above-mentioned problems. In biaxially stretching a thermoplastic resin tube, the stretching ratio in the axial direction can be controlled by a single take-off machine without using any lubricant. An object of the present invention is to provide a method for producing a biaxially stretched thermoplastic resin tube which does not require reheating of the tube, can largely omit molding equipment, and has excellent stretch ratio and dimensional accuracy.

[0012]

According to the method of the present invention for producing a biaxially stretched thermoplastic resin tube, a thermoplastic resin tube extruded from a die of an extruder is quenched on the surface of the tube, and then the entire tube is subjected to a predetermined process. Along with adjusting the stretching temperature, the outer diameter is gradually increased in the direction in which the thermoplastic resin pipe advances in the direction in which the thermoplastic resin pipe advances, and the maximum outer diameter of the stretched thermoplastic resin pipe to be molded is increased. A large-diameter mold approximately equal to the inner diameter is expanded into the thermoplastic resin pipe while being inserted into the thermoplastic resin pipe, and the expanded thermoplastic resin pipe is stretched while being taken up by a take-up machine. Things.

The thermoplastic resin used in the present invention includes, for example, vinyl chloride resins; olefin resins such as polyethylene and polypropylene; polyoxymethylene;
Polyvinylidene fluoride, polyester, polyamide, polyacetal and the like are used.

The stretching ratio of the thermoplastic resin tube in the present invention is preferably 3 times or less in the axial direction, usually 1.05 times or more in the present invention, and 1.3 to 4 times in the circumferential direction. It is more preferable that the axial direction is 1.1 times to 2 times.
Double and the circumferential direction is 1.5 to 2 times.

If the stretching ratio is too large, the thickness of the thermoplastic resin tube after stretching becomes smaller than the thickness before stretching. When the above-mentioned thermoplastic resin pipe is used, for example, as a buried pipe, it is necessary to have a wall thickness to withstand the earth pressure. To satisfy this, the thickness before stretching becomes too large, so that it is difficult to control the temperature, and furthermore, to perform uniform stretching. Therefore,
It is necessary to suppress the stretching ratio from becoming too large.
On the other hand, if the stretching ratio is too small, it is not possible to increase the strength by stretching. Further, according to the present invention, the stretching ratio in the axial direction is approximately 1.05 times or more.

According to the present invention, the stretching ratio in the circumferential direction is controlled by the outer diameter of the large-diameter die connected to the extrusion die, and the stretching ratio in the axial direction is controlled for uniform temperature control of the large-diameter die. The temperature is controlled by the temperature of the temperature adjusting fluid circulated through the air and the take-off speed.

In the present invention, first, the surface of the thermoplastic resin tube extruded from the mold of the extruder is rapidly cooled. The quenching method is not particularly limited. For example, a refrigerant set at a temperature much lower than the glass transition temperature (hereinafter, referred to as “Tg”) or the melting point of the resin forming the thermoplastic resin tube is used. A method of passing the above-mentioned thermoplastic resin tube through the stored cooling tank is exemplified. The coolant is not particularly limited, but water is preferred in terms of heat capacity and cost.

As described above, the temperature of the refrigerant is not particularly limited as long as it is much lower than the Tg or melting point of the resin forming the thermoplastic resin tube. When using a system resin (Tg: about 80 ° C.), the temperature is preferably 30 ° C. or less. If the temperature of the refrigerant is too high, the dimensional accuracy of the thermoplastic resin tube (before stretching) is poor, and uniform stretching is difficult.

Next, in the present invention, the entire thermoplastic resin tube whose surface has been quenched is adjusted to a predetermined stretching temperature.
The method for adjusting to the predetermined stretching temperature is also not particularly limited, and as described above during quenching, the thermoplastic resin is stored in a cooling tank in which a refrigerant set at a temperature suitable for stretching is stored. A method of passing through a tube may be used, or air cooling may be used. Although the above-mentioned refrigerant is not particularly limited,
A liquid refrigerant is preferable in that the temperature in the circumferential direction can be made more uniform, and water is preferable in terms of heat capacity and cost. However, when the set temperature is high, a refrigerant such as polyethylene glycol can be used. The temperature of the refrigerant also depends on the type of resin forming the thermoplastic resin tube, the amount of extrusion, the type and amount of the refrigerant, the length of the cooling tank, etc., but if it is too low, the resin solidifies and during the stretch molding. Pipe breakage occurs on large diameter mold.
On the other hand, if it is too high, the resin becomes too soft, the axial elongation on the large-diameter mold is large, and the tube is broken.

The surface of the large-diameter mold used in the present invention is preferably subjected to a surface treatment such as hard chromium plating to make it as flat as possible. The drawn thermoplastic resin tube is preferably cooled to prevent shrinkage. Although the cooling method is not particularly limited, it is sufficient to spray the refrigerant from the outside in consideration of simplification of the equipment.
In order to reduce the residual stress due to the temperature distribution of the stretched thermoplastic resin tube, it is preferable to perform cooling from both the inner surface and the outer surface of the stretched thermoplastic resin tube.

(Function) Since the method for producing a biaxially stretched thermoplastic resin tube of the present invention is configured as described above, first, the surface of the thermoplastic resin tube extruded from the die of the extruder is cleaned. The rapid cooling increases the dimensional accuracy of the tube before stretching, so that uniform stretching can be performed. And, since the stretching ratio in the axial direction of the tube greatly depends on the temperature of the tube before stretching, the entire surface of the thermoplastic resin tube whose tube surface has been quenched is adjusted to a predetermined stretching temperature, so that the stretching ratio of the tube before stretching is reduced. Temperature variation is reduced, and the accuracy of the stretching ratio in the axial direction is increased.
Therefore, since it is not necessary to use a take-off machine before stretching to control the stretching ratio in the axial direction, excessive cooling and reheating with respect to the stretchable temperature are not required, and the molding equipment is a conventional biaxially stretched thermoplastic resin pipe. It can be largely omitted compared to molding, and accordingly, the items to be controlled are reduced, and a biaxially stretched pipe excellent in stretch ratio and dimensional accuracy can be formed.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a biaxial stretching device used in the present invention. 1 and 2, 1 is an extruder, 2 is a mold (of the extruder), 4 is a water tank for quenching the pipe surface, 5 is a water tank for adjusting the temperature of the entire pipe, 6 is a large-diameter mold,
8 is a take-off machine, 9 is a thermoplastic resin tube, and 91 is a biaxially stretched thermoplastic resin tube.

As shown in FIG. 1, the biaxial stretching apparatus used in the present invention comprises an extruder 1, a pipe surface quenching water tank 4, a water tank 5 for adjusting the temperature of the entire pipe, a large-diameter mold 6, and a take-off machine. 9 The extruder 1 is provided with a mold 2 for molding a thermoplastic resin tube having a predetermined diameter, and between the mold 2 and the large-diameter mold 6,
They are connected by a connection pipe 3.

In the method for producing a biaxially stretched thermoplastic resin tube according to the present invention, first, a thermoplastic resin is supplied to an extruder 1 of the above-described biaxially stretching apparatus, and extruded into a tube by a mold 2 of the extruder 1 to form a tube. The plastic resin tube 9 is formed.

Next, the obtained thermoplastic resin pipe 9 is cooled by the pipe surface quenching water tank 4 while the connecting pipe 3 is inserted.
It is adjusted to a predetermined stretching temperature. Next, the quenched thermoplastic resin pipe 9 is cooled by the water tank 5 for temperature control of the entire pipe. Then, the large-diameter mold 6 is inserted into the cooled thermoplastic resin tube 9. Note that the large-diameter mold 6 gradually increases in outer diameter in the traveling direction of the thermoplastic resin pipe 9, and has a maximum outer diameter substantially equal to the inner diameter of the stretched thermoplastic resin pipe 91 to be molded. ing. Thus, the thermoplastic resin pipe 9
And stretch in the circumferential direction. Then, while taking up the thermoplastic resin pipe stretched in the circumferential direction by the take-up machine 7,
When stretch-molded, a biaxially stretched thermoplastic resin tube 91 stretched in the axial direction can be obtained. Since the large-diameter mold 6 is provided on the downstream side immediately after the entire-tube temperature-adjusting water tank 5, there is an effect that the resin surface temperature can be controlled in the stretching step on the large-diameter mold 6.

FIG. 2 is a schematic view showing another example of the biaxial stretching apparatus used in the present invention. This embodiment is the same as FIG. 1 except that the upstream side of the large-diameter mold 6 is provided in the entire-tube temperature adjusting water tank 5.
The same reference numerals are used and the description is omitted. By providing the upstream side of the large-diameter mold 6 in the entire-tube temperature-adjusting water tank 5 in this manner, there is an effect that the temperature can be adjusted more uniformly until the stretching step is completed.

[0027]

The present invention will be described below in more detail with reference to examples. (Examples 1 to 5, Comparative Examples 1 to 3) 100 parts by weight of a vinyl chloride resin (manufactured by Tokuyama Sekisui Co., product number "TS1000R", degree of polymerization 1050) using the biaxial stretching apparatus shown in FIG.
Dioctyltin-based stabilizer (manufactured by Sankyoki Gosei Co., Ltd., product number "ON
Z142F) 1 part by weight, stearic acid (Nippon Yuka Co., Ltd.)
0.5 parts by weight, polyethylene wax (manufactured by Mitsui Chemicals, Inc.
A vinyl chloride-based resin composition (glass transition temperature: 80 ° C.) obtained by mixing 0.5 parts by weight of a trade name “Hiwax220MP”) with a super mixer (manufactured by Kawata Seisakusho Co., Ltd.)
(Sekisui Koki Co., Ltd., 60 mm twin screw extruder, model "SLM6
0 "), and formed at an extrusion temperature of 185 ° C. and an extrusion rate of 30 kg / h, an outer diameter of 38 mm and a wall thickness of 3.5 m.
m of the thermoplastic resin tube 9 was obtained.

Next, the obtained thermoplastic resin pipe 9
Was quenched by passing it through a 20 cm long tube surface quenching water bath 4 covered with water at 20 ° C.
After passing through a 60 cm long water tank 5 for adjusting the temperature of the entire pipe, which is filled with a refrigerant having a high temperature, the pipe is gradually cooled. Further, a large-diameter mold 6 is inserted into the pipe while expanding the thermoplastic resin pipe. The drawn thermoplastic resin tube was stretched and formed while being taken up by a take-off machine while being cooled in the water tank 7 to obtain a biaxially stretched thermoplastic resin tube 91 having an outer diameter of 60 mm.

Evaluation The biaxially stretched thermoplastic resin tubes 91 obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to the following evaluations, and the results are summarized in Table 1.

(Stretching Magnification) The obtained biaxially stretched thermoplastic resin tube 91 was cut into a length of 200 mm, and the outer diameter was measured with a caliper. The outer diameter was measured with a vernier caliper, and (cut length / tube length after shrinkage) was taken as the axial stretching ratio, and (outer diameter before shrinkage / outer diameter of the tube after shrinkage) was taken as the circumferential stretching ratio. .

(Appearance) The inner surface of the obtained biaxially stretched thermoplastic resin tube 91 was visually observed.

[0032]

[Table 1]

[0033]

According to the method for producing a biaxially stretched thermoplastic resin tube of the present invention as described above, when the thermoplastic resin tube is biaxially stretched, the dimensional stability of the tube before stretching is reduced. Because it is excellent, the stretching ratio in the axial direction can be controlled with a single take-off machine without using any lubricant, low-magnification stretching becomes easy, and reheating of the thermoplastic resin tube is not required, and molding equipment is not required. Can be largely omitted, and a biaxially stretched thermoplastic resin tube excellent in stretch ratio and dimensional accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a biaxial stretching device used in the present invention.

FIG. 2 is a schematic diagram showing another example of a biaxial stretching device used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Extruder 2 Die (of an extruder) 4 Pipe surface quenching water tank 5 Water tank for temperature control of the whole pipe 6 Large-diameter mold 7 Take-off machine 9 Thermoplastic resin pipe (before stretching) 91 Biaxially stretched thermoplastic resin pipe (stretching) rear)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F207 AA15 AB06 AG08 AK02 AR06 KA01 KA17 KK13 KK54 KK76 KW41 4F210 AA15 AB06 AG08 AK02 AR06 QA09 QC05 QD46 QG02 QT03 QW33

Claims (1)

[Claims] 1. A thermoplastic resin tube extruded from a mold of an extruder, after quenching the surface of the tube, adjusting the entire tube to a predetermined stretching temperature, and connecting the thermoplastic resin tube to the mold, Insert a large-diameter mold in which the outer diameter gradually increases in the traveling direction of the pipe and the maximum outer diameter is substantially equal to the inner diameter of the stretched thermoplastic resin pipe to be molded, into the thermoplastic resin pipe. A method for producing a biaxially stretched thermoplastic resin tube, characterized in that the thermoplastic resin tube is expanded while the stretched thermoplastic resin tube is drawn by a take-off machine.