HK1079153A - Inner mandrel - Google Patents

Description

Internal core

Technical Field

The present invention relates to an internal core (マンドレル) for cooling, which can be cooled extremely rapidly by bringing a tubular molten film extruded from an annular die of an extruder into direct contact with the inside when a tubular film or sheet is produced from a thermoplastic resin.

Background

Various types of apparatuses have been proposed for cooling an extruded film by bringing the film into contact with a direct cooling liquid in a process of producing a tubular film from a thermoplastic resin.

For example, there are known a method of rapidly cooling and solidifying the overflow liquid flowing down along the outer wall of the internal overflow pipe while directly pressing and holding the overflow liquid (Japanese patent publication No. 45-35192), a method of improving the high-speed film forming property by providing a spiral groove for flowing another coolant at the lower part of a double-layer pipe for regulating the pipe diameter of the overflow liquid (Japanese patent publication No. 46-31473), a method of removing the adhering liquid by suction while cooling and solidifying the adhering liquid by contacting the coolant (Japanese patent publication No. 39-2072), and an internal core for tubular film cooling in which an annular slit nozzle for ejecting the upper coolant is provided with two or more stages (Japanese patent publication No. 6-47795).

The biggest technical point in producing a film excellent in ductility and stable for a long time is how to produce an amorphous film substantially continuously and stably. This is extremely important in a tubular (hollow method) film-forming apparatus using an internal core for cooling, and affects the efficiency of the entire apparatus and the quality of the production of a tubular film or sheet.

The present inventors have proposed that the cooling capacity can be improved by multistage cooling to significantly improve the high-speed film forming property (Japanese patent application laid-open No. 6-47795). This can greatly increase the production rate of the tubular molten thin film, but when the rate is further increased, there is a disadvantage that the amount of air generated accompanying the thin film or the amount of air contained in the coolant, which increases with the increase in the amount of coolant, starts to increase, and an air layer accumulates in the lower portion of the pipe diameter regulation ring.

This air layer adversely affects the formability of the molten film. That is, although the molten thin film maintains a balance between the head pressure of the external water tank (ヘッド pressure) and the water pressure of the internal coolant, the air layer breaks the balance. When the balance is unbalanced, the air layer passes through between the film and the tubular regulation ring and reaches the upper annular nozzle for spraying the cooling liquid, and the air layer bursts at a portion where the molten film enters the cooling liquid, thereby causing uneven cooling of the film and generation of pinholes.

These problems have considerable effects on the entire apparatus, such as a reduction in workability due to the inability to continuously stretch the film, and a reduction in quality of the tubular film or sheet due to uneven cooling.

The conventional cooling core is described in detail below with reference to the attached drawings.

Fig. 4 is a detailed explanatory diagram of a cooling portion of a conventional cooling core.

Conventionally, the inner surface of the tubular thin film 4 is cooled by the internal coolant and the coolant in the external cooling tank 22, which are uniformly distributed by the spiral groove 9 provided in the lower cooling portion 10.

The tubular thin film cooled at this time is balanced by the internal pressure of the lower cooling liquid and the head pressure of the external cooling groove, and enters the seal ring 15 so as not to reach the spiral groove 9 of the lower cooling portion 10 or so as not to be separated from the lower portion of the pipe diameter regulating ring 6.

However, the film forming speed increases, and the air generated along with the melting of the tubular thin film 4 or the air contained in the coolant from the upper coolant discharge annular nozzle 8 or the middle coolant discharge annular nozzle 7 and the lower cooling section 10 also increases.

These air layers 12 are formed during the film formation process and remain below the tubular regulating ring portion 6. The coolant flowing through the spiral groove 9 of the lower cooling portion 10 is discharged through the lower drain port 14, but the air layer 12 remaining in the lower portion of the tubular regulation ring 6 cannot be discharged toward the lower drain port 14, and thus the air layer 12 increases as the film forming time increases.

In the cooling inner core, the air layer 12 breaks the balance between the internal pressure of the lower coolant in the lower cooling portion 10 and the head pressure of the external cooling bath 22, and becomes bubbles to rise from the gap between the tubular film and the pipe diameter regulating ring 6 to the upper middle coolant discharge annular nozzle 7 or the upper coolant discharge annular nozzle 8. At this time, the air layer 12 rises to generate bubbles and burst near the annular nozzle portion for ejecting the upper or middle cooling liquid, which causes defects such as uneven thickness and pinholes due to uneven cooling in the molten tubular film 4.

Disclosure of Invention

The present inventors have made extensive studies on an internal core (a mandrel) for cooling in order to overcome the above-mentioned disadvantages, and have finally completed the present invention.

The invention will provide

(1) An internal core for cooling a tubular film, which is directly coupled to the lower side of an annular extrusion die for a thermoplastic resin, and which is used together with an external annular cooling groove to cool a tubular molten film extruded downward from an annular slit of the die from the inside, wherein an internal cooling liquid phase in the lowermost stage portion flows in a direction in which the tubular molten film flows in the opposite direction;

(2) the tubular film cooling internal core according to item (1) above, wherein the liquid discharge amount and pressure are adjusted by adjusting the annular ring by means of a discharge port having a screw structure in the liquid discharge portion of the cooling water in the lowermost section.

The present invention is characterized in that the inner core is provided with a cooling liquid flowing upward from the lowest section, and the cooling liquid is aligned with the direction of the rising air layer, so that the air layer is not generated at all at the lower part of the pipe diameter regulation ring.

This can successfully prevent the film from having uneven thickness or pinholes due to uneven cooling, and significantly improve the high-speed stable film forming performance.

The present invention can be applied to the lowermost portion of a multi-stage core in which an upper coolant-discharging annular nozzle and a middle coolant-discharging annular nozzle are connected, or a core formed solely by an upper coolant-discharging annular nozzle.

Drawings

Fig. 1 is a schematic view illustrating the entire structure of one embodiment of the internal core of the present invention.

Fig. 2 is a detailed explanatory view of a cooling portion of one form of the internal core of the present invention.

Fig. 3 is a detailed view of a cooling portion of another embodiment of the inner core of the present invention.

Fig. 4 is a detailed explanatory view of a cooling portion of a conventional cooling inner core.

Detailed Description

The embodiments of the present invention will be specifically described below with reference to the drawings.

Fig. 1 is a view illustrating an entire structure of one aspect of the internal core of the present invention, and fig. 2 is a detailed view illustrating a cooling portion of the internal core of the present invention.

Reference numeral 1 denotes an annular die which is mounted downward on an extruder, and a thermoplastic resin melted by the extruder is extruded downward from an annular slit 3 into a tubular shape through a resin passage 2 inside the die. Reference numeral 5 denotes a cooling inner core suspended from the annular mold. The cooling inner core 5 is substantially cylindrical and mainly composed of 6 parts such as a pressure air discharge nozzle part 18, an upper cooling liquid discharge annular nozzle 8, a middle cooling liquid discharge annular nozzle 7, a pipe diameter regulation ring part 6, a lower cooling part inner cylinder 10a, and a seal ring part 15.

A pressure-air ejection nozzle 18 and an exhaust port 17 for discharging generated gas are provided in the uppermost portion of the cooling inner core 5 to maintain the bubble shape. The upper bubble portion formed between the annular mold 1 and the cooling inner core 5 maintains its shape by a balance between the pressure space exhausted from the coolant discharge port 16, the pressure space exhausted from the exhaust port 17, and the pressure space supplied from the pressure space discharge nozzle 18.

An upper annular nozzle 8 for discharging the coolant and a middle annular nozzle 7 for discharging the coolant are provided below the compressed air discharge nozzle 18. The annular thin film 4 is cooled by the coolant from the upper coolant discharge annular nozzle 8 and the middle coolant discharge annular nozzle 7, is shaped into a uniform cylindrical thin film by the pipe diameter regulating ring 6, and is led to the lower cooling section 10 b.

In the cooling inner core 5 (fig. 2) of the present invention, a lower cooling portion inner cylinder 10a is provided at a lower portion of a pipe diameter regulation ring portion 6, and a lower cooling liquid flows out upward of a lower cooling portion 10b from a lower cooling liquid ejection port 13 provided radially on a side of a seal ring portion 15.

Further, the upper part of the lower cooling part inner cylinder 10a is provided with a discharge port adjusting ring 11 having a screw structure, so that the internal pressure of the lower cooling liquid having a tubular film spaced therefrom can be adjusted in balance with the head pressure difference of the cooling liquid in the external cooling tank 22. That is, the lower cooling liquid flows toward the molten tubular film 4 and overflows from the upper portion of the discharge port regulating annular ring 11.

In the case of the cooling inner core 5 having such a structure, even if the amount of air generated along with the molten tubular film 4, the amount of air generated along with the upper cooling liquid discharge annular nozzle 8 or the middle cooling liquid discharge annular nozzle 7, and the amount of air contained in the cooling liquid in the lower cooling portion 10b increase, the lower cooling liquid flows upward, and therefore, much of the air flowing in is discharged from the discharge port at the upper portion of the discharge port adjustment annular ring 11 to the cooling liquid discharge port 16 together with the lower cooling liquid, no matter how fast the film is formed. Therefore, no air layer is present at all at the lower part of the pipe diameter regulating ring part 6, and the defects of uneven thickness and pinholes caused by uneven cooling of the molten tubular film 4 due to the formation of bubbles and bursting of the air layer can be eliminated.

The present invention will be described in further detail with reference to the following examples, but the present invention is not limited thereto.

Example 1

Nylon 6 was extruded from an annular die having an extrusion aperture of 550mm phi at a temperature of 260 ℃ to form a molten tubular film, passed through the outer diameter of the cooling inner core 5 having the shape shown in FIG. 1 and folded by the folding roller group 23, and then drawn by the drawing roller 24 at a speed of 40m/min to form a film.

The maximum diameter of the shoulder portion of the pipe diameter regulating ring 6 shown in FIG. 2 is 548mm phi, the maximum diameter of the seal ring 15 is 548mm phi, and the discharge port regulating ring 11 of the lower cooling portion inner cylinder 10a is 500mm phi.

Further, groundwater at 20 ℃ was supplied to the inner upper coolant introduction hole 19 at 2.3 t/hr and to the middle coolant introduction hole 20 at 1.0 t/hr.

On the other hand, the same 20 ℃ ground water was supplied to the lower coolant introduction hole 21 at a flow rate of 3.0 t/hr, flowed out through a gap of 1.0mm between the discharge port regulating annular ring 11 attached to the upper portion of the lower cooling portion inner cylinder 10a and the root portion of the pipe diameter regulating ring 6, and then discharged to the coolant discharge port 16.

Further, the same 20 ℃ groundwater was supplied to the external cooling bath 22 at a flow rate of 4.5 t/hr, and the film 4 was cooled externally.

The thickness unevenness of the film having an average film thickness of 145 μm obtained as described above was in the range of 10 μm, and both of the planarity and transparency were excellent.

In addition, even after 48 hours of operation, no trouble caused by the stagnant air layer occurred, and the performance of the above-described thin film was stable.

Comparative example 1

In example 1, the structure of the lower cooling part 10 of fig. 4 was adopted in place of the lower cooling part inner tube 10a of fig. 2, and the tubular film 4 was cooled under the same conditions as in example 1, and as a result, cooling thickness unevenness due to the air layer was generated 10 hours after the start of operation. In addition, after 40 hours, pinholes due to the air layer appeared in the tubular film, and it was impossible to continue the stretching.

Possibility of industrial application

As described above, the internal core of the present invention does not have an air layer trapped under the tubular regulation ring even in a high-speed film forming process, and thus can prevent troubles due to the air layer and can produce a tubular film having a stable thickness and good flatness for a long time.

Therefore, in the tubular film-forming apparatus using the cooling internal core, the efficiency of the entire apparatus and the production of the tubular film or sheet are greatly facilitated.

Claims (2)

1. An internal core for cooling a tubular film, which is directly coupled to the lower side of an annular extrusion die for a thermoplastic resin and is used together with an external annular cooling groove to cool a tubular molten film extruded downward from an annular slit of the die from the inside, wherein an internal cooling liquid phase in the lowermost stage portion flows in a direction in which the tubular molten film flows in the opposite direction.

2. The tubular film-cooling inner core according to claim 1, wherein the discharge amount and pressure of the cooling water are adjusted by using a discharge port adjusting ring having a screw structure in a discharge portion of the cooling water in the lowermost portion.