JPH0249215B2 - - 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, the entire tubular resin is only coated almost uniformly, and no particular rapid cooling effect is observed 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 constitutes a cooling device for inflation molding using a heat pipe in which an evaporating section is placed in contact with or close to the inner peripheral surface of a molten resin tubular body immediately after being extruded from an extrusion die, and The object is to be achieved by cooling the molten resin from the inside using the evaporation section.

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

In the center of the extrusion 1, an enclosure tube 9 having an external tip 8 is penetrated into the tubular resin 6 so as to reach a predetermined height position of the resin bubble 6C. A heat pipe 10 serving as a cooling device for molding is held at the center of the extrusion die 1 along the resin extrusion direction, with the enclosure tube 9 inserted through the center.

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 outer circumferential surface of approximately the lower half along the longitudinal direction is evaporated by the melt. It is arranged in contact with or close to the inner peripheral surface of the resin tubular body 6A, and a predetermined interval is provided between the lower end of the evaporating section 10A and the upper end surface of the extrusion die 1. A flow port 11 is bored in the enclosed tube 9 located therein.

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 dissipating fin 12 is provided on the outer circumference near the upper end of the condensing section 10B. , the enclosure tube 9 is open at the upper end.

A wick 13 is provided over almost the entire inner circumferential surface of the evaporating section 10A of the heat pipe 10, and a condensing section 14 of the working fluid is moved through the wick 13. A fluid vapor stream 15 is raised. Further, an air ring 16 is arranged on the extrusion die 1.

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 16, and also from the inside by the evaporation section 10A of the heat pipe 10. That is, the evaporation section 10A functions as a core that improves the stability of the molten resin tubular body 6A, and also absorbs heat from the inside, that is, cools the evaporation section 10A. 14 will evaporate.

The evaporated condensing part 14 becomes a vapor flow 15 and rises in the heat pipe 10, is condensed in the condensing part 10B, becomes a condensed liquid 14, and is moved to the evaporating part 10A.

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 arranged at the position where the resin bubbles 6C are completely solidified, the heat dissipation in the condensing section 10B does not have an adverse effect on 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, so the outer circumferential surface of the evaporator 10A is brought into contact with the inner circumferential surface of the molten resin tubular body 6A. However, in the case of linear ethylene-α-olefin copolymers, polypropylene, etc.,
There is no particular need to bring the outer circumferential surface of the evaporator 10A into contact with the inner circumferential surface of the molten resin tubular body 6A, and it is sufficient to simply bring them close to each other. Furthermore, the air in the resin bubble 6C is introduced into the encapsulating tube 9 from the upper end opening and flows out to the lower end side of the evaporating section 10A through the rear flow hole 11, and this outflowing air flows into the evaporating section 10A. Since it flows to the resin bubble 6C side through the gap between the outer peripheral surface and the inner peripheral surface of the molten resin tubular body 6A, the molten resin tubular body 6A is not welded to the evaporation part 10A,
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.

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.

Furthermore, since no internal cooling means such as circulating cooling air between the inside and outside of the tubular resin 6 or cooling the core with cooling water are used, the structure is simple and small. The present invention can also be applied to an extrusion die with a large diameter, and can be easily operated.

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 first embodiment, and explanations thereof will be simplified or omitted.

A second embodiment is shown in FIG. 2, in which the enclosure tube 9 terminates at the lower end surface of the heat pipe 10 and is closed. Further, in the evaporation section 10A of the heat pipe 10, two communication tubes 22 having a communication path 21 that communicates the upper and lower ends of the evaporation section 10A are arranged (see FIG. 3). Then, the internal air on the resin bubble 6C side is introduced to the lower end side of the evaporation section 10A, and the introduced air flows back into the resin bubble 6C side through the gap between the evaporation section 10A and the molten resin tubular body 6A. It's summery.

This embodiment also provides the same functions and effects as those of the first embodiment.

FIG. 4 shows a third embodiment, in which the encapsulating tube 9 ends at the lower end surface of the heat pipe 10 and is closed, as in the second embodiment. A discharge pipe 30 having an external socket 29 is inserted into the enclosure pipe 9, and this discharge pipe 30
penetrates the central portion of the heat pipe 10 and opens at the upper end of the heat pipe 10. Further, a discharge pipe 30 in the evaporation section 10A of the heat pipe 10
An internal tube 31 with a predetermined wall thickness is fitted into the internal tube 31, and a plurality of communicating passages 32 are provided along the longitudinal direction of the internal tube 31.
are arranged along a virtual circumference centered on the discharge pipe 30 (see FIG. 5). The upper ends of these communication passages 32 are bent toward the discharge pipe 30 and are open at openings 33 bored at predetermined positions in the discharge pipe 30, and the lower ends of the communication passages 32 are open to the heat pipe 10. It is open at the lower end.

Further, the enclosure tube 9 and the discharge tube 30 are connected to a cooling air supply/discharge mechanism (not shown), and cooling air is circulated within the tubular resin 6 so as to maintain a constant pressure at all times. Note that reference numeral 40 in FIG. 4 is a heat insulating material surrounding the encapsulating tube 9.

According to the third embodiment, although the structure of the entire device is complicated, since the tubular resin 6 is always in contact with the cooling air from the inside, the tubular resin 6
Further, since the temperature around the condensing part 10B of the heat pipe 10 is always maintained at a low temperature, heat dissipation in the condensing part 10B is always performed smoothly, and as a result, the rapid cooling effect in the evaporating part 10A is also increased. I will do it.

A fourth embodiment is shown in FIG. 6, in which the heat pipe 10 is composed of a spiral tubular evaporator section 10A with a relatively small pitch and a straight tubular condensation section 10B. A molten resin tubular body 6A is placed on the envelope outer peripheral surface of the spiral tubular evaporation section 10A.
The inner circumferential surfaces of the two are in contact with or come close to each other. Further, the heat pipe 10 does not need to be particularly provided with a heat pipe.

According to such a fourth embodiment, the first,
The same effects as in the second embodiment can be achieved, and furthermore, there is no need to provide a communication path for internal air circulation that communicates both the upper and lower ends of the evaporation section 10A, and the molten resin tubular body 6A Since the places where the molten resin tubular body 6A can come into contact with are extremely limited, it is extremely difficult for the molten resin tubular body 6A to adhere to the evaporation section 10A, and stable molding is more likely to be 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. Furthermore, in the first to third embodiments, the wick 13 is the evaporator 1.
Although the heat pipe 10 is provided over substantially the entire inner circumferential surface of the heat pipe 10, it may be provided over the entire inner circumferential surface of the heat pipe 10.

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 sectional view showing a first embodiment of the cooling device for inflation molding according to the present invention, FIG. 2 is a sectional view showing the second embodiment, and FIG. 3 is a sectional view showing the second embodiment.
FIG. 4 is an enlarged cross-sectional view taken along the line - in the figure, FIG. 4 is a cross-sectional view showing the third embodiment of the present invention, and FIG.
FIG. 6 is an enlarged cross-sectional view taken along the line V--V in the figure, and is a cross-sectional view showing a fourth embodiment of the present invention. 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, 14... Condensate, 15... Steam flow.

Claims (1)

[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 rolled up. The evaporation section consists of a heat pipe having
The condensation section is placed in contact with or close to the inner peripheral surface of the molten resin tubular body immediately after being extruded from the extrusion die, and the condensation section is located at a position within the resin bubble where the resin bubble is cooled and solidified. A cooling device for inflation molding, characterized in that it is disposed in a cooling device for inflation molding.