JPH091656A - External cooling apparatus - Google Patents

Abstract

PURPOSE: To increase even the extrusion amt. of a resin material low in melt tension and to enhance productivity by providing an air ring above a molding die in concentric relation to an annular emitting orifice and providing a pressure chamber above the annular air blowoff port for cooling a resin bubble provided to the inner peripheral surface thereof. CONSTITUTION: A tubular resin bubble 50 is extruded from the extrusion lip (annular emitting orifice) of a spiral die 3. Lower and upper air rings 11, 12 are provided to the external cooling apparatus 10 provided to the upper part of the die 3 and the lower air ring 11 is continued to the die 3 in the vicinity of the outside of the extrusion lip 3a thereof and has an air lip (annular air blowoff port) 11a. A pressure chamber 21 consisting of lower, middle and upper stage pressure chambers 21a, 21b, 21c is provided to the inner peripheral surface of the lower stage air ring 11. Cooling air A blown out of the lower stage air lip 11a is reduced in flow velocity within the pressure chambers 21a-21c without disturbing air flow to flow in a second pressure chamber 22 along with the cooling air A blown out of the upper stage air lip 12a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an external cooling device for air-cooling a resin bubble molded by an inflation molding method from the outer peripheral surface side.

[0002]

In the inflation molding method, molten resin is extruded through a die having an annular discharge port to form a tubular resin bubble, and the resin bubble is expanded by air blown inward (expansion air). And a tubular film having a desired diameter and thickness. In a molding apparatus that performs such an inflation molding method, an external cooling device that cools the expanding resin bubbles from the outer peripheral surface side is arranged above the die.

As an external cooling device, for example, a real fair 5
No. 13551, Japanese Patent Publication No. 4-66172, and Japanese Patent Laid-Open No. 6-872. Each of these external cooling devices has an air ring formed so that a blowout port for blowing out cooling air for cooling the resin bubbles is located outside the extrusion passage of the die. The air ring is formed so as to concentrically spread radially outward of the extrusion passage of the die and increase in height toward the outside (so-called "mortar shape").

Above the air ring, an air guide or a plurality of straightening cylinders, etc., which are formed so as to concentrically expand radially outwardly of the air ring and increase in height toward the outer side, etc. Is provided. As a result, the resin bubbles extruded from the die
The expansion air expands radially outward as it goes upward, and moves along the upper ends of the air guides and the straightening cylinders.

The cooling air blown out from the outlet flows along the outer peripheral surface of the resin bubble, that is, in the gap between the inner peripheral surface of the air ring or the upper end of each rectifying cylinder and the resin bubble, and the cooling device. Is discharged to the outside. During this time, the cooling air draws heat from the resin bubbles and cools them. further,
Since the flow velocity of the cooling air is increased when the resin bubble flows through a portion where the inner peripheral surface of the air ring and the upper end of each rectifying cylinder are close to each other, the attraction force of the resin bubble due to the Venturi effect is generated in this portion. As a result, the resin bubbles are attracted toward the air ring and the upper ends of the flow straightening cylinders at a plurality of radial positions and are stably supported.

Here, if the flow velocity of the cooling air is slow, the resin bubbles cannot be sufficiently cooled and also cannot be sufficiently attracted. On the contrary, if the flow velocity of the cooling air is too fast, the resin bubbles will be in a wavy state, resulting in a product in which the bubble thickness fluctuates. Therefore, in each of the above air rings, in particular, the resin bubbles immediately after being discharged from the molding die, which is likely to be in a wavy state due to the high flow velocity of the cooling air, are cooled, and an example thereof is shown in FIG. Thus, the annular air outlet 61 formed in the air ring 61 disposed above the die 3 is
A pressure chamber (air chamber) 62 is formed above a.
The flow velocity of the cooling air A is reduced at this portion.

As described above, when the pressure chamber 62 is formed in such a shape that the bottom surface 62b and the wall surface 61c are substantially perpendicular to each other, when the cooling air A flows into the pressure chamber 62, as indicated by an arrow. Disturbance occurs in the flow of the cooling air A.

[0008]

Here, in order to improve the productivity of the blown film, the resin bubble 5 is used.
When the molding speed of 0 (the amount of material extruded from the die per unit time) is increased (the amount of extrusion is increased), the resin bubble 5
A large amount of air is required to cool 0. For this reason,
It is necessary to increase the flow velocity of the cooling air A from the annular air outlet 61a. However, if the flow velocity of the cooling air A is increased, the turbulence of the air flow in the pressure chamber 62 becomes large even if the flow velocity decreases in the pressure chamber 62. Therefore, the formed resin bubble 5
There is a problem that 0 is easily wavy. Furthermore, the material forming the resin bubble 50 is a resin material having a weak melt tension (for example, "linear low-density polyethylene resin").
If it is, there is a problem that it is more likely to be in a wavy state.

The present invention has been made in view of the above problems, and improves the productivity of a tubular film by the inflation molding method even if the material forming the resin bubble is a resin material having a low melt tension. An object is to provide an external cooling device that can be achieved.

[0010]

In order to achieve the above-mentioned object, in the present invention, a tubular resin bubble that expands radially outward while being extruded upward through the annular discharge port of the molding die is used. In an inflation forming device that performs formation, an external cooling device that causes cooling air to flow to the outer peripheral surface side in order to cool the formed resin bubbles is provided with an inner peripheral surface that extends upward from the outer peripheral side of the annular discharge port and is radially outward. An air ring formed in a conical taper shape that widens toward the side is arranged above the molding die and concentrically with the annular discharge port. On the inner peripheral surface of the air ring, an annular air outlet that blows out cooling air for cooling the resin bubbles is formed concentrically with the annular outlet, and above the annular air outlet, the bottom of the bottom surface is formed. At least a portion forms an annular pressure chamber substantially parallel to the inner peripheral surface of the air ring.

According to such an external cooling device, the cooling air blown from the annular air outlet flows upward between the inner peripheral surface of the air ring and the formed resin bubble, and the resin bubble And the air ring is pulled toward the inner peripheral surface. At this time, the flow rate of the blown cooling air becomes slow due to flowing into the pressure chamber. In addition, the cooling air flowing into the pressure chamber
As it flows out of the pressure chamber and flows upward (passes through the pressure chamber), it flows along the bottom surface formed almost parallel to the inner circumferential surface of the inclined air ring, so that the flow of cooling air in this portion Disturbances can be suppressed to a minimum, and the resin bubbles do not undulate.

The external cooling device may be constructed by providing an air ring in which the pressure chamber has an arcuate cross section. Even in the external cooling device having the pressure chamber having such a shape, the turbulence of the flow of the cooling air passing through the pressure chamber can be suppressed to be small.

Further, in the air ring, at least two upper and lower annular air outlets are formed and whether at least a part of the bottom surface is substantially parallel to the inner peripheral surface of the air ring at least between the annular air outlets. Alternatively, a plurality of annular pressure chambers each having a circular arc cross section may be formed in a stepwise manner.

According to the external cooling device having such a structure, since the pressure chamber is formed above the annular air outlet located below, the pressure from the lower annular air outlet from which the bubble is easily waving is increased. It is possible to secure the air volume necessary for cooling without increasing the flow velocity of the cooling air and reduce the turbulence of the flow of the cooling air above the lower annular air outlet.

[0015]

Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows an inflation molding device equipped with an external cooling device according to the present invention. This inflation molding apparatus includes a hopper 1 into which a resin material (linear low-density polyethylene resin or the like) for inflation molding is charged, and a screw 2a connected to the hopper 1 to melt-knead and extrude the resin material. The extruder 2 and the spiral die 3 that receives the molten resin supplied from the extruder 2 are configured. The spiral die 3 has a ring-shaped extrusion lip (annular discharge port) 3a.
(See FIG. 1) is formed, and the molten resin is extruded as a tubular resin bubble 50 through the extrusion lip 3a.

Air is blown into the inside of the resin bubble 50 through a passage (not shown) formed inside the spiral die 3, whereby the resin bubble 50 is expanded and deformed in the radial direction. An external cooling device 10 according to the present invention is attached to the upper part of the die 3. The external cooling device 10 includes a lower air ring 11, an upper air ring 12, and first, second, third, fourth rectifying cylinders 15,
The resin bubble 50, which is composed of 16, 17, and 18 and expands as described above, is air-cooled from the outside.

The lower air ring 11 will be described in detail with reference to FIGS. 1 and 2. The lower air ring 11 is attached to the upper surface of the die 3, and is continuous in the shape of a ring in the vicinity of the outside of the extrusion lip 3a of the die 3 (below the inner peripheral surface of the lower air ring 11) and opens upward. It has an annular air outlet) 11a.

A blower (not shown) is connected to the connection port 13 attached to the lower air ring 11, and cooling air A is supplied from the blower to form inside the lower air ring 11. It blows upward from the air lip 11a through the formed flow path 11m. In addition, in the flow path 11m, a plurality of rectifying plates 11j, 11k,
11ι is provided to rectify the cooling air A blown from the air lip 11a.

The inner peripheral surface of the lower air ring 11 is formed in a conical taper shape that extends upward from the air lip 11a and spreads outward in the radial direction. At least a part of the bottom surface of this inner peripheral surface is the lower air ring. An annular pressure chamber 21 that is substantially parallel to the inner peripheral surface of 11 is formed. This pressure chamber 2
Reference numeral 1 denotes a lower pressure chamber 21a formed immediately above the air lip 11a, a middle pressure chamber 21b formed above the lower pressure chamber 21a, and an upper pressure chamber formed further above the middle pressure chamber 21b. 21c.

The lower pressure chamber 21a includes a bottom surface 11e and a wall surface 1.
It is formed surrounded by 1f. Here, the bottom surface 11e extends horizontally outward in the radial direction and then inclines upward,
It is connected to a wall surface 11f that extends vertically upward. The inclination angle of the bottom surface 11e is such that the upper end portion of the air lip 11a and the ridge line 11b at the inner end portion of the bottom surface 11e, the upper end portion of the wall surface 11f of the lower pressure chamber 21a and the middle pressure chamber 2
A line R connecting the inner edge of the bottom surface 11g of 1b and the ridgeline 11c.
It is formed at an angle of 1, that is, an angle substantially parallel to the angle of the inner peripheral surface of the lower air ring 11.

Further, the inclination angle of the bottom surface 11g of the middle pressure chamber 21b is also formed substantially parallel to the angle of the line R2 connecting the ridge line 11c and the ridge line 11d, and the bottom surface 11i of the upper pressure chamber 21c has the same inclination angle. Has been formed. In the lower air ring 11 formed in this manner, since three pressure chambers 21a, 21b, and 21c are formed on the inner peripheral surface, the portion existing as the inner peripheral surface has each ridge portion 11
b, 11c, 11d.

An upper air ring 12 is arranged above the lower air ring 11. The upper air ring 12 also has a channel 12e formed therein.
2e also has an air lip 12a whose one end opens upward.
And the other end is connected to the connection port 14.
The connection port 14 has a connection port 13 for the lower air ring 11.
A blower that is different from the blower that is connected to (also not shown)
Are connected, and the air A is supplied from this blower and blows upward from the air lip 12a.

A bottom surface 12b is formed above the air lip 12a and extends horizontally outward in the radial direction.
An inner wall surface 12c is formed to extend vertically upwards inside, and an outer wall surface 12d is formed to extend vertically upwards outside the bottom surface 12b.

On the bottom surface 12b, the first rectifying cylinder 15 is arranged along the outer wall surface 12d. This first straightening cylinder 1
The upper end surface 15a of No. 5 is formed so as to be inclined inward (so-called "chamfering") so as to draw a straight line or a parabolic line and connect with each ridge line portion 11b, 11c, 11d in the lower air ring 11. There is.

The upper air ring 12 constructed in this way
Also in, the second pressure chamber 22 surrounded by the bottom surface 12b, the inner wall surface 12c, and the first flow straightening cylinder 15 is formed. In the second pressure chamber 22, unlike the structure of the first pressure chamber 13, the bottom surface 12b is not inclined.

On the upper part of the upper air ring 12, a straightening tube support plate 1 is formed in a ring shape that extends horizontally outward in the radial direction.
9 is attached to the upper surface of the rectifying cylinder support plate 19, and a second rectifying cylinder 16 formed with a diameter larger than that of the first rectifying cylinder 15 is provided near the middle portion in the radial direction on the upper surface of the rectifying cylinder support plate 19. Has been done. A third rectifying cylinder 17 having a diameter larger than that of the second rectifying cylinder 16 is arranged at the outer peripheral end of the rectifying cylinder support plate 19 so as to extend upward. On the upper end surface 17a of the third rectifying cylinder 17, a fourth rectifying cylinder 18 having a bottom surface 18b and having an L-shaped cross section is provided.

The upper end surfaces 16a and 18a of the second rectifying cylinder 16 and the fourth rectifying cylinder 18 are also the upper end surface 1 of the first rectifying cylinder 15.
It is formed to be inclined similarly to 5a. The outside air supply / discharge hole 1 is provided below the second rectifying cylinder 16 and the third rectifying cylinder 17.
A plurality of 6b and 17b are formed.

In the rectifying cylinders 15 to 18 thus constructed, the third pressure chamber 23 is formed between the first rectifying cylinder 15 and the second rectifying cylinder 16, and the second rectifying cylinder 16 and the third rectifying cylinder are formed. A fourth pressure chamber 24 is formed between the cylinder 17 and the fifth pressure chamber 25 in a space surrounded by the fourth rectifying cylinder 18.

The external cooling device 10 configured as described above
In, the resin bubble 50 extruded from the die 3 and in the expansion process moves upward. At this time, the outer peripheral surface of the resin bubble 50 has the ridgelines 11b, 11c, 11
d and the upper end surfaces 15a, 1 of the rectifying cylinders 15, 16, 18
It moves close to 6a and 18a. Lower air lip 11
The cooling air A blown from a and the upper air lip 12a removes heat from the bubble 50 while flowing upward along the outer peripheral surface of the bubble 50 to cool it.

Here, the cooling air A is transferred to each of the ridgelines 11b, 11
When passing through the gaps between the c, 11d and the respective upper end surfaces 15a, 16a, 18a, the flow velocity of the cooling air A becomes faster, so that the so-called Venturi effect causes the resin bubbles 5 to flow.
0 is attracted to the upper and lower air rings 11 and 12 and the upper end surfaces 15a, 16a and 18a of the flow straightening cylinders. As a result, the resin bubbles 50 are stably supported at a plurality of radial positions (positions indicated by B in FIG. 1) where the upper and lower air rings 11 and 12 and the flow control cylinders 15, 16 and 18 are located. . The cooling air A passes through the gap between the upper end surface 18 a of the fourth rectifying cylinder 18 and the resin bubble 50,
It is discharged to the outside of the external cooling device 10.

Since the resin bubble 50 immediately after being extruded from the die 3 is not sufficiently cooled, the shape is unstable due to the cooling air A blown out from the lower air lip 11a, and it is easy to be in a wavy state. Cooling air A
If the flow of is too fast or is disturbed, it is likely to be wavy. Therefore, in the present external cooling device 10, as described above, the shape of the bottom surface of the pressure chamber 21 formed above the lower air lip 11a is an inclined surface, so that the flow velocity of the cooling air A is reduced and the flow turbulence is disturbed. I try to suppress it.

That is, the cooling air A blown out from the lower air lip 11a first flows into the lower pressure chamber 21a in the first pressure chamber 21. Here, the lower pressure chamber 21
The cooling air A flowing into the inside a flows upward along the inclination of the bottom surface 11e toward the ridgeline 11c as shown by the arrow. As a result, the cooling air A flowing into the lower pressure chamber 21a has a reduced flow velocity and is not significantly disturbed in the lower pressure chamber 21a.
0 is prevented from becoming a wavy state.

The flow rate of the cooling air A flowing out through the lower pressure chamber 21a becomes high again at the ridgeline 11c, so that the resin bubble 50 is attracted. Then, the cooling air A that has passed through the ridge line 11c flows into the middle pressure chamber 21b to reduce the flow velocity again, and then passes through the ridge line 11d and flows into the upper pressure chamber 21c. In this way, the flow velocity is reduced without disturbing the flow of air in each pressure chamber 21a to 21c, and the flow velocity is increased at each ridgeline 11b to 11d, so that the resin bubble 50 immediately after being extruded from the die 3 is removed. It can be attracted to the inner peripheral surface of the lower air ring 11 without being wavy.

The cooling air A flowing upward from the upper pressure chamber 21c flows into the second pressure chamber 22 together with the cooling air A blown out from the upper air lip 12a. The bottom surface 12b of the second pressure chamber 22 is not inclined as described above. Therefore, the turbulence becomes larger than the flow of the cooling air A in the first pressure chamber 21, but the resin bubble 50 moving on the second pressure chamber 22 is cooled to some extent by the cooling air blown out from the lower air lip 11a. Therefore, there is no wavy state.

As will be described later in detail, the bottom surface 12b of the second pressure chamber 22 is also dependent on the material characteristics and the like.
It is needless to say that at least a part of the above may be formed obliquely.

The cooling air A blown out from the upper and lower air lips 11a, 12a flows along the outer peripheral surface of the resin bubble 50, and the upper end surfaces 15a, 16 of the respective rectifying cylinders 15, 16, 18 are formed.
The flow velocity becomes faster when passing between the a and 18a and the resin bubble 50. Due to this increase in the flow velocity, the pressure inside the third pressure chamber 23 to the fifth pressure chamber 25 is reduced, and the outside air is sucked through the outside air supply / discharge holes 16a and 17a. A part of the sucked outside air flows upward together with the cooling air A flowing along the outer peripheral surface of the resin bubble 50 to efficiently cool the resin bubble 50 and to support the resin bubble 50 in a stable state without causing a wavy state. it can.

Next, the other external cooling device 30 according to the present invention will be described with reference to FIG. The external cooling device 30 is the same as the external cooling device 10 except for the configuration of the lower air ring 31. Therefore, the components other than the lower air ring 31 are designated by the same reference numerals and the description thereof is omitted.

The lower air ring 31 is also provided with the connection port 13, and a plurality of flow rectifying plates 3 are provided in the flow path 31m.
1j, 31k, 31ι are arranged. Then, the cooling air A blown out from the air lip 31a flows into the first pressure chamber 41. This first pressure chamber 41 is also composed of upper, middle and lower pressure chambers 41a, 41b, 41c, and has a bottom surface 31
The e, 31g and 31i are formed so that their cross-sectional shapes are arcuate. Then, the lower and middle pressure chambers 41
In a and 41b, the bottom surfaces 31e and 31f are connected to the wall surfaces 31f and 31h.

In the lower air ring 31 in which the first pressure chamber 41 is formed in this way, the cooling air A blown out from the lower air lip 31a has a reduced flow velocity in the first pressure chamber 41 and has an arc shape. Formed bottom surface 31
Since it flows upward along e, 31g, and 31i, the flow is not greatly disturbed. As a result, like the lower air ring 11, the formed resin bubble 50 can be cooled without being wavy, and can be attracted to the inner peripheral surface of the lower air ring 31.

Lower air ring 1 constructed as described above
External cooling device 10 or 30 having 1 or 31
When the inflation molding is performed by using, the resin bubble 50 in which the state immediately after being extruded from the die 3 is unstable (is likely to be in a wavy state) is cooled by the cooling air A blown only from the lower air lip 11a, The cooling air A does not disturb the flow in the first pressure chambers 21 and 41 and generates an appropriate tensile force, so that the resin bubble 50 does not become wavy.
An inflation film can be formed.

The resin bubble 50, which is slightly stable as it passes through the first pressure chambers 21 and 41 and is cooled, may be undulated by the cooling air A blown from the upper air lip 12a. Instead, a large amount of cooling air A can be used for more efficient cooling, and each upper end surface 15a,
6a, 18a. Therefore, the resin bubble 5
Even when the material forming 0 is a material such as a linear low-density polyethylene resin having a weak melt tension and the extrusion amount of the material from the die per unit time is large, the resin bubble 50 is in a wavy state. It is possible to supply the cooling air A sufficient for cooling without causing the above.

In each of the above-mentioned embodiments, a pressure chamber having a bottom surface which is inclined so as to be substantially parallel to the inner peripheral surface or whose cross-sectional shape is arcuate is formed in the first pressure chambers 21 and 41. Although the case where the lower three steps are formed in a step shape has been described, the present invention is not limited to this, and four or more step shapes or two steps are formed depending on the characteristics of the material of the resin bubble to be formed and the extrusion amount. It may be stepped. Further, the first pressure chambers 21 and 41 may be configured to have one inclined bottom surface or arc-shaped bottom surface without being divided into steps.

Further, in each of the above-mentioned embodiments, in the external cooling devices 10 and 30 having the lower air lip 11a and the upper air lip 12a, both air lips 11 are provided.
The case where the first pressure chambers 21 and 41 are provided between a and 12a (above the lower air lip 11a) has been described.
The present invention is not limited to this.

For example, when a material that can sufficiently cool the resin bubbles is used only by the cooling air blown out from the lower air lip 11a, or when the discharge amount is set, the upper air lip 12a is not necessarily provided. . On the other hand, when a material or the like that is likely to undulate by the cooling air blown from the upper air lip 12a is used, an annular pressure chamber formed similarly to the first pressure chambers 21 and 41 is also provided above the upper air lip 12a. It may be provided.

The external cooling device may have a structure in which three or more air lips are provided in the vertical direction. In this case, at least one of the air lips is formed similarly to the first pressure chambers 21 and 41. A ring-shaped pressure chamber may be provided.

In each of the above embodiments, cooling air is supplied to the lower air ring 11 and the upper air ring 12 from different blowers.
Each air ring 11,1 with two pipes from one blower
2 to supply cooling air to the flow path 11m,
A part of 12 m may be communicated with each other to supply cooling air to each of the air rings 11 and 12 from a single blower.

Furthermore, in each of the above embodiments, a plurality of rectifying cylinders 15 to 18 are provided above the upper air ring 12, but the present invention is applicable to an external cooling device having such rectifying cylinders. The present invention is not limited to this, and when the diameter of the resin bubble to be formed is small, such as when the width of the molded product is narrow, the rectifying cylinder is not necessarily provided.

Depending on the characteristics of the material of the resin bubble to be formed, instead of the rectifying cylinder, a cone extending from the inner peripheral surface of the lower air ring 11 continuously upward and expanding outward in the radial direction. Air guides formed in a tapered shape (Japanese Utility Model Publication No. 5-13551 and Japanese Patent Publication No. 4-66712)
An air guide formed in the same manner as the tapered air guide used in the external cooling device described in Japanese Patent Laid-Open Publication No. 2003-242242, and formed in the same manner as the air guide 63 shown in FIG. .

[0049]

As described above, in the external cooling device of the present invention, at least a part of the bottom surface of the external cooling device is blown above the annular air outlet for blowing the cooling air for cooling the resin bubbles. An annular pressure chamber having an arc-shaped cross section is formed so as to be substantially parallel to the inner peripheral surface of the ring. Therefore, the flow velocity can be reduced by suppressing the turbulence of the flow of the cooling air in the portion where the resin bubbles are not sufficiently cooled, and the air volume necessary for cooling can be ensured. Even if the material forming the bubble is a resin material with a low melt tension, the resin bubble does not become wavy above the annular air outlet, so the amount of material extruded from the die per unit time can be increased. The productivity of the blown film can be improved.

Further, at least two upper and lower annular air outlets are formed in the air ring, and at least a part of the bottom surface is substantially parallel to the inner peripheral surface of the air ring at least between the annular air outlets. An annular pressure chamber or a pressure chamber having an arcuate cross-sectional shape may be formed. According to the external cooling device configured in this way, the flow rate of cooling air is not increased and the air volume required for cooling is secured. Since the pressure chamber is formed above the annular air outlet located below, it is possible to reduce the turbulence of the flow of the cooling air above the lower annular air outlet, which is likely to cause the bubbles to undulate. You can

[Brief description of the drawings]

FIG. 1 is a side sectional view of an external cooling device according to the present invention.

FIG. 2 is a side sectional view of a lower air ring portion in the external cooling device.

FIG. 3 is a side sectional view of a lower air ring portion having a different configuration in the external cooling device.

FIG. 4 is a configuration diagram of an inflation molding device using the external cooling device.

FIG. 5 is a schematic view of a conventional external cooling device.

[Explanation of symbols]

 3 Spiral die 10,30 External cooling device 11,31 Lower air ring 11a, 31a Air lip (annular air outlet) 12 Upper air ring 15-18 Straightening cylinder 50 Resin bubble

Claims (3)

[Claims] 1. In an inflation molding apparatus, cooling air is cooled by flowing cooling air to the outer peripheral surface side of a tubular resin bubble that expands radially outward while being extruded upward through an annular discharge port of a molding die. An external cooling device, disposed concentrically with the annular discharge port above the molding die, and having an inner peripheral surface that extends upward from the outer peripheral side of the annular discharge port and expands radially outward in a conical taper shape. An air ring is formed, and on the inner peripheral surface of the air ring, an annular air outlet for blowing out the cooling air for cooling the resin bubbles is formed concentrically with the annular outlet, and the bottom surface is formed. An external cooling device in which an annular pressure chamber, at least a part of which is substantially parallel to the inner peripheral surface of the air ring, is formed above the annular air outlet. 2. In an inflation molding device, cooling air is cooled by flowing cooling air to the outer peripheral surface side of a tubular resin bubble that expands radially outward while being extruded upward through an annular discharge port of a molding die. An external cooling device, disposed concentrically with the annular discharge port above the molding die, and having an inner peripheral surface that extends upward from the outer peripheral side of the annular discharge port and expands radially outward in a conical taper shape. An air ring is formed, and an annular air outlet for blowing out the cooling air for cooling the resin bubbles is formed on the inner peripheral surface of the air ring concentrically with the annular outlet, and An external cooling device, wherein an annular pressure chamber having an arcuate cross-sectional shape is formed above the annular air outlet. 3. The annular air outlets are formed in at least two upper and lower stages, and the plurality of pressure chambers are formed in a stepwise manner between at least one of the annular air outlets. The external cooling device according to claim 1 or 2.