JPH0249216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cooling device for inflation molding that cools a tubular resin extruded into a tubular shape from an extrusion die from the inside, and particularly relates to an improvement in its cooling capacity.

In inflation molding of thermoplastic resins, there is an increasing demand for high-speed molding to improve productivity, but in order to achieve high-speed molding, even if extruders and extrusion dies are capable of high-speed extrusion, , it must be possible to sufficiently cool the extruded tubular resin. Furthermore, in order to improve the physical properties of the molded film, it is necessary to sufficiently cool the molten resin evenly inside and outside.

By the way, a method of blowing cooling air onto the outer peripheral surface of an extruded tubular resin using one or more air rings is widely used, but in order to improve the cooling effect, the volume of cooling air is increased. For example, when using resins with low melt tension such as high-density polyethylene, linear ethylene-α-olefin copolymer, and polypropylene, the molding stability is significantly inhibited, so cooling is performed from the outside of the tubular resin. There was naturally a limit to the improvement of the cooling effect in the case of cooling.

Therefore, in order to cool the tubular resin not only from the outside but also from the inside, a method is known in which cooling air is circulated from the outside inside the tubular resin. However, in such a method, the molten resin tubular body immediately after being extruded from the extrusion die requires rapid cooling, but on the other hand, the resin bubbles that have passed through the expansion section and become bubbles are not necessarily cooled. Although this method does not require rapid cooling, it only cools the entire tubular resin almost uniformly, and there is no particular rapid cooling effect on the molten resin tubular body, so only this method is adopted. However, a sufficient cooling effect to achieve high-speed molding could not be obtained.

Furthermore, according to JP-A-56-75829, a cooling device in which the evaporation part of a heat pipe is buried in the center of a core (mandrel) has been proposed. The evaporator cools the core, and the cooled core further cools the molten resin tubular body, so the heat transfer efficiency is not always sufficient, and the evaporation of the heat pipe Since the part and the core are constructed as separate bodies, the structure is also complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cooling device for blown film molding which has a large cooling effect and a simple structure.

The present invention provides a heat pipe in which an evaporating section is placed in contact with or close to the inner circumferential surface of the molten resin tubular body immediately after being extruded from an extrusion die, and the evaporating section moves the molten resin tubular body inside the molten resin tubular body. In addition to cooling the heat pipe from the side, a vapor flow path and a condensate flow path for the working fluid are provided separately and independently within the heat pipe to make the movement of the working fluid smoother and faster. The objective is to achieve the above object by further improving cooling efficiency.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the main parts of an inflation molding apparatus to which a first embodiment of the cooling apparatus for inflation molding according to the present invention is applied.

In this figure, an extrusion die 1 consists of a die body 2 having a cylindrical hollow part, and a die mandrel 3 fitted into the hollow part of the die body 2, and an annular slit at the upper end of the fitting part. 4 is constructed, and the molten resin 5 supplied into the extrusion die 1 is extruded into a tubular shape through the annular slit 4 to form a tubular resin 6.

Immediately after being extruded from the extrusion die 1, the tubular resin 6 is in the form of a molten resin tubular body 6A, but after that, it is expanded at a predetermined blow-up ratio by internal pressure in the expansion section 6B, and then thinned. After the resin bubble 6C is completely cooled and solidified, it is nipped and flattened by nip rolls (not shown), and then continuously wound up.

In the center of the extrusion die 1, an encapsulating tube 9 having an external pot 8 is penetrated so as to protrude toward the inside of the tubular resin 6 by a relatively short predetermined length from the upper end surface of the extrusion die 1 in the figure. The lower end center portion of a heat pipe 10 serving as a cooling device for inflation molding is fixed to the upper end portion of the enclosing tube 9.

The evaporation section 10A of the heat pipe 10 is formed in a cylindrical shape with a predetermined diameter and has approximately the same height as the expansion section 6B, and the molten resin is disposed on the outer periphery of the approximately lower half in the figure along the longitudinal direction. While the inner peripheral surface of the tubular body 6A is brought into contact with or approached, the evaporation section 10
A predetermined gap is provided between the lower end of the extrusion die 1 and the upper end surface of the extrusion die 1, and a sealing port 11 is formed in the sealing tube 9 located within this gap.

Inside the evaporator 10A, a cylindrical partition 12 with a predetermined wall thickness is disposed (see FIG. 2), and a condensate passage 13 for the working fluid is provided in the center of the partition 12. The outer peripheral surface of the partition body 12 and the evaporation section 10
A working fluid vapor flow path 14 is formed by the gap between the inner circumferential surface of A and the vapor flow path 14 for the working fluid. is adapted to rise within the steam flow path 14.

Further, a plurality of communication pipes 17 are passed through the wall thickness of the partition wall body 12 along the longitudinal direction, and the upper and lower ends of these communication pipes 17 are respectively opened at the upper and lower ends of the evaporator 10A. The partition body 12 is supported by the communication pipe 17 at a predetermined position within the evaporation section 10A. Here, instead of the communication pipe 17, a single circular pipe slit-shaped communication passage of a double pipe type may be used.

Further, the condensing section 10B of the heat pipe 10 is arranged at a position where the resin bubble 6C in the resin bubble 6C is cooled and solidified, and a heat radiation fin 18 is provided on the outer circumference near the upper end of the condensing section 10B. ing.

Note that an air ring 19 is provided on the extrusion die 1.
is arranged, and the evaporation section 1 of the heat pipe 10
A not-shown wick is provided over substantially the entire inner circumferential surface of 0A.

Next, the operation of this embodiment will be explained.

The molten resin 5 in the extrusion die 1 is continuously extruded through the annular slit 4 to form a tubular resin 6. Air at a constant pressure is introduced into the tubular resin 6 from the sealing tube 9 at the start of operation. The molten resin tubular body 6A of the sealed tubular resin 6 is expanded by the internal pressure at a predetermined blow-up ratio in the expansion section 6B, thereby forming a resin bubble 6C.

The molten resin tubular body 6A is cooled from the outside by the air ring 19, but is also cooled from the inside by the evaporation section 10A of the heat pipe 10.
That is, the evaporation section 10A is the molten resin tubular body 6.
It acts as a core to improve the stability of the evaporator A, and also absorbs heat from the inside of the evaporator 10A, that is, cools it, and the condensate 15 evaporates inside the evaporator 10A.

The evaporated condensate 15 becomes a vapor flow 16 and rises in the steam channel 14, is condensed in the condensing section 10B, becomes the condensate 15, and descends in the condensate channel 13. The steam flow path 14 and the condensate flow path 13 are provided independently, and since the steam flow path 14 is disposed on the molten resin tubular body 6A side, the steam flow 16 is heated. The rate of rise tends to increase, and
Since the condensate 15 and the vapor flow 16 do not interfere with each other, the circulation of the working fluid is extremely smooth and rapid.

Due to such circulation of the working fluid within the heat pipe 10, the molten resin tubular body 6A is constantly rapidly cooled in the evaporation section 10A, and since the expansion section 6B is also located close to the evaporation section 10A, the expansion section 6B The internal air in contact with is also cooled, and the expansion section 6B is also cooled.

On the other hand, in the condensing section 10B, resin bubbles 6C
However, since the condensing section 10B is located at a position where the resin bubbles 6C are completely cooled and solidified, the heat dissipated in the condensing section 10B does not adversely affect the resin bubbles 6C.

Note that when the molten resin 5 is made of high-density polyethylene or the like, the stability of the molten resin tubular body 6A is extremely low. However, in the case of linear ethylene-α-olefin copolymer, polypropylene, etc., the outer circumferential surface of the evaporating section 10A should be covered with a molten resin tubular body. It is not necessary to make contact with the inner circumferential surface of 6A, and it is sufficient to simply make it close to it. Further, the air in the resin bubble 6C is flowed down to the lower end side of the evaporation section 10A via the communication pipe 17, and this flowed down air flows into the gap between the outer peripheral surface of the evaporation section 10A and the inner peripheral surface of the molten resin tubular body 6A. , and flows toward the resin bubble 6C side, the molten resin tubular body 6A will not be welded to the evaporation section 10A, and stable molding will be ensured.

According to this embodiment, the heat pipe 1
Since the molten resin tubular body 6A is directly cooled by the evaporator 10A, the quenching effect is large, and therefore high extrusion rate and high speed inflation molding can be performed stably. Further, the increase in the quenching effect, together with the fact that the tubular resin 6 is cooled not only from the outside but also from the inside, can improve the physical properties of the molded film, such as improving the stretching effect.

Moreover, the condensate flow path 13 and the steam flow path 14
Since these are provided independently and separately, the condensate 15 and the vapor flow 16 do not interfere with each other, and the working fluid circulates extremely smoothly and quickly, further increasing the cooling effect. . Moreover, since the steam flow channel 14 is arranged on the side of the molten resin tubular body 6A, the steam flow 16 is easily heated, so that the rising speed of the steam flow 16 is increased. This has the effect of making circulation smooth and quick.

Furthermore, since the evaporation section 10A of the heat pipe 10 also serves as a bubble stabilizer, that is, a core, the structure is simple and assembly is easy.

In addition, in the above-mentioned embodiment, the wick is provided on the entire inner peripheral surface of the evaporator 10A, but the wick may be provided on the entire inner peripheral surface of the heat pipe 10.

Next, embodiments other than the above will be described.
The same reference numerals are used for parts that are the same as or similar to those in the above embodiment, and the description thereof will be simplified or omitted.

A second embodiment is shown in FIG. 3, and in this figure, the evaporator 10A has a spiral tubular vapor flow channel 14 with a relatively small pitch and a vapor flow channel 14 on the central axis of the vapor flow channel 14. and a straight tubular condensate flow path 13 located in the condensate flow path 1.
A condensing section 10B is continuously provided on the vertically upper side of the section 3. Further, the inner peripheral surface of the molten resin tubular body 6A comes into contact with or approaches the envelope outer peripheral surface of the spiral tubular steam flow path 14, and the connecting portion 14A at the upper end side of the steam flow path 14 is tilted downward. The condensate 15 is connected to the condensate flow path 13 in a state such that the condensate 15 descending within the heat pipe 10 does not enter the steam flow path 14 . Note that a wick may be provided over the entire inner circumferential surface of the heat pipe 10.

According to such an embodiment, the same functions and effects as in the first embodiment can be achieved, and there is no need to provide a communication pipe 17 for internal air circulation that communicates both the upper and lower ends of the evaporator 10A. Moreover, since the places where the molten resin tubular body 6A can come into contact with the molten resin tubular body 6A are extremely limited, the molten resin tubular body 6A
It has the effect that it is extremely difficult to weld to 0A and that stable molding is more easily performed.

In each of the above embodiments, the cooling device according to the present invention is applied to top-blown inflation molding, but it can also be applied to bottom-blown inflation molding.

In addition, by providing a cooling air supply/discharge mechanism that circulates cooling air from the outside in the tubular resin 6,
Further cooling effects can be expected.

Furthermore, the vapor flow path 14 does not necessarily include the evaporation section 1.
Although it does not have to be placed on the 0A molten resin tubular body 6A side, if it is placed on the molten resin tubular body 6A side, the working fluid in the heat pipe 10 can be circulated even more smoothly and quickly.

As described above, according to the present invention, it is possible to provide a cooling device for inflation molding that has a large cooling effect and a simple structure.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a first embodiment of the cooling device for inflation molding according to the present invention, FIG. 2 is an enlarged cross-sectional view taken along the line - in FIG. 1, and FIG. FIG. 2 is a sectional view showing a second embodiment. 1... Extrusion die, 6... Tubular resin, 6A... Molten resin tubular body, 6B... Expansion section, 6C... Resin bubble, 10... Heat pipe as a cooling device for inflation molding, 10A... Evaporation section, 10
B... Condensing section, 13... Condensate flow path, 14...
Steam flow path, 15... Condensate, 16... Steam flow.

Claims (1)

[Scope of Claims] 1. A cooling device for inflation molding that cools from the inside a tubular resin that is extruded into a tubular shape from an extrusion die, expanded by internal pressure, cooled and solidified, and then wound up. It consists of a heat pipe having an evaporation part and a condensation part, and the evaporation part is
A working fluid vapor flow channel and a condensate flow channel are provided independently, and are in contact with or close to the inner circumferential surface of the molten resin tubular body immediately after being extruded from the extrusion die. The cooling device for inflation molding is characterized in that the condensing section is located at a position within the resin bubble where the resin bubble is cooled and solidified. 2. In claim 1, the steam flow path is arranged on the molten resin tubular body side of the evaporation section, and the condensate flow path is arranged at the center of the evaporation section. A cooling device for inflation molding featuring: