JPH03180321A - Method and apparatus for cooling bubble of elastomer film - Google Patents

Abstract

PURPOSE:To stabilize the frost line of bubble and consequently enhance the quality of the film concerned by a method wherein the domain ranging from an air ring for cooling the neck part of bubble and its upper part above the frost line is surrounded with an inverted conical net and the surroundings of the net are cooled to a certain temperature. CONSTITUTION:Bubble 7 is formed by extruding molten thermoplastic elastomer composition through the annular orifice 11 of a die. At this time, the diameter of the bubble 7 just after extrusion is small due to low melt tension, resulting in forming the so-called neck part 71. In the neck part 71, the bubble 7 is stretched mainly in longitudinal direction (MD). Next, the bubble 7 expands itself abruptly so as to have the predetermined bubble diameter. In the expansion part 72, the bubble 7 is stretched not only in MD but also in lateral direction (TD). Near the almost upper end of the expansion part 72, a frost line is present and the thermoplastic elastomer composition turns into cooled and solidified state here. The bubble is further cooled with a second cooling ring 3 and a third cooling ring 4, both of which are provided in a bubble region 73, which lies above the frost line 74.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for cooling a noible when producing an elastomer film by an air-cooled inflation method, and in particular can stabilize frost lines. The present invention relates to a method and apparatus for cooling bubbles that provides improved film quality.

[Prior art and problems to be solved by the invention] Films of thermoplastic elastomer compositions made of elastomers and thermoplastic resins have elasticity and stretchability that thermoplastic resin films do not have, and are useful in many fields. It is expected to have many uses.

Films made of such thermoplastic elastomer compositions include a portion of ethylene-vinyl acetate copolymer (EV
Films containing the ^> component are formed by the inflation method, but most of them are formed by the casting method or extrusion method. However, in film production by casting or extrusion, although stretching in the MD direction (longitudinal direction of the device) is relatively easy, stretching in the transverse direction of the TD force direction is difficult, which is problematic for the production of two-wheel stretched films. There is. Furthermore, it is necessary to include a release paper to prevent blocking between the films, which poses an economical problem.

On the other hand, when forming a film using the inflation method, although there are no problems such as those mentioned above, it is difficult to stabilize the bubbles, especially the frost line, and the bubbles are not stable especially when shaping the bottom of a thin film (less than 30 μm). Therefore, there is a problem that a uniform film cannot be obtained.

Therefore, as a result of investigating the reasons why it is difficult to stabilize bubbles, especially frost lines, in the air-cooled inflation method, we found that although it is necessary to stretch and stretch the elastomer film at low temperatures, the air-cooled inflation method Air is blown out from 1 to 3 air rings provided in the cooling device to cool it to the desired temperature, so the cooling temperature changes due to the influence of ambient temperature, etc., and cannot necessarily be maintained at the desired temperature. It turns out that there is.

Therefore, in view of the above-mentioned problems, an object of the present invention is to create a bubble that can stabilize frost lines and thereby provide a film with improved quality when producing a film made of a thermoplastic elastomer composition. An object of the present invention is to provide a cooling method and apparatus for cooling.

[Means to solve the problem]

In view of the above issues, as a result of intensive research, the present inventors have discovered that when manufacturing a film of a thermoplastic elastomer composition by an air-cooled inflation method, an air ring that cools the neck of the bubble and an air ring that cools the area above the frost line are used. If you surround the bubble between it and the air ring with an inverted cone-shaped net, and then cool the area around this net to a constant temperature, and then cool the bubble with a cooling ring, the temperature of each part of the bubble can be expanded. The inventors have discovered that elongation can be maintained at an optimal level, frost lines are stabilized, and a uniform and thin biaxially stretched elastomer film can be obtained, leading to the invention.

That is, the bubble cooling method for an elastomer film of the present invention includes: (a) cooling the neck of the bubble with cooling air jetted from a first cooling ring provided near the annular die; (b) cooling the neck of the bubble. (c) Cooling air jetted out from a second cooling ring provided slightly above the frost line cools the bubble; (d) The temperature at which the bubble is cooled by the first cooling ring and the second cooling ring is stabilized by constantly cooling the temperature around the inverted conical net.

Further, the film bubble cooling device of the present invention includes (a) a first cooling ring provided near the annular die to cool the neck of the formed bubble, and (b) a first cooling ring provided slightly above the frost line of the bubble. (c) an inverted conical net provided between the first cooling ring and the second cooling ring and surrounding the bubble; (d) the inverted conical net; and a device for cooling the net.

The present invention will be explained in detail below.

In the present invention, examples of the thermoplastic elastomer composition that forms the base of the elastomer film include a composition containing an ethylene-thioolefin copolymer rubber and an ethylene-vinyl acetate copolymer.

The ethylene-small olefin copolymer rubber that can be used in the present invention is a copolymer rubber containing ethylene and a peolefin, such as evafuropylene, butene-11hexene-1, octene-1, etc. Polymer rubber (BPR), or terpolymer rubber made by copolymerizing an ethylene-propylene system with a non-conjugated diene as a third component, such as ethylidenenorbornene, dicyclopentadiene, l,4-hexadiene, etc. (hereinafter EP
DM). Among these, EP word of mouth is preferred.

The ethylene-propylene-diene copolymer (BPDM) used in the present invention has a content of repeating units derived from ethylene of 60 to 70 mol% and a content of repeating units derived from propylene of 30 to 40 mol%. %, and the content of repeating units derived from the diene compound is preferably 1 to 10 mol%. A more preferable range is 62 to 66 mol% of ethylene repeating units.
, 33 to 37 mol% of propylene-based repeating units, and 3 to 6 mol% of diene compound-based repeating units.

The number average molecular weight of the ethylene-propylene-diene copolymer is preferably 400,000 to 600,000, and the density is 0.87 g/CI
I! The following are preferred.

Furthermore, the melt index (190°C, 2.16 kg load) of the ethylene-propylene-diene copolymer is preferably in the range of 0.1 to 5.0 g/10 minutes, more preferably 0.30 to 1. It is 0g/lo min.

The ethylene-propylene diene copolymer ([!PDM) used in the present invention basically consists of the above-mentioned repeating units, but within a range that does not impair the properties of this copolymer, for example, butene- Other repeating units such as repeating units derived from olefins such as 1- or 4-methylpentene-1 may also be included.

The ethylene-vinyl acetate copolymer (εν^) used in the present invention has a vinyl acetate repeating unit content of 5 to 50%.
30% by weight, and the melt index (190℃
, 2.16 kg load) is 0.2-25 g/10 min of the copolymer. If the vinyl acetate content is less than 5% by weight, the rubber elasticity will be poor, while if it exceeds 30% by weight, the film will block, making film formation difficult. The preferred vinyl acetate content is 15 to 30% by weight. Regarding the melt index, if it is less than 0.2 g/10 minutes, the film forming processability will be poor, and if it exceeds 25 g/10 minutes, it will be difficult to form a film by the air-cooled inflation method. Preferred melt index is 0.5-25 g
/10 minutes.

The proportion of ethylene-propylene-diene copolymer (BPDM) in the thermoplastic elastomer composition is 30 to 70% by weight, especially 50 to 60% by weight, based on the resin component i1 (100% by weight). It is preferable to keep it within this range. If the blending ratio of the ethylene-propylene-diene copolymer (EPDM) is lower than 30% by weight,
The stretching ratio of the resulting elastomer film decreases, and when it is made into a composite film, it is insufficiently made microporous due to heat shrinkage. On the other hand, if it is higher than 70% by weight, the t-shape of the resulting elastomer film will decrease.

In contrast, the above ethylene-vinyl acetate copolymer (EV
The blending ratio of A) is 70 to 30% by weight, based on the resin component (100% by weight), and is particularly preferably within the range of 50 to 40% by weight.The above ethylene vinyl acetate copolymer (E! The reason for limiting the blending ratio of VA) is exactly the opposite of the reason for limiting the above-mentioned ethylene-propylene-diene copolymer; when it is lower than 30% by weight, moldability decreases,
Moreover, if it is higher than 70% by weight, the elongation of the elastomer film will be insufficient.

The rigidity and moldability of the thermoplastic elastomer composition used in the present invention can be improved by adding a thermoplastic polyolefin. Examples of the thermoplastic polyolefin include ethylene, fluoropylene, phthene-1, pentene-11hexene-1,4-methylpentene-1, etc. (7) α-olefin homopolymers, ethylene and propylene or other α-olefins; copolymer,
Alternatively, copolymers of two or more of these α-olefins may be mentioned. Among these, polyethylene and polypropylene such as low density polyethylene, linear low density polyethylene, medium density polyethylene, and high density polyethylene are preferred. Polypropylene is not limited to a homopolymer, and the propylene component is 50 mol% or more, preferably 80 mol%.
Random or block copolymers with other small olefins including those mentioned above can also be used. Comonomers copolymerized with propylene include ethylene and other small olefins, with ethylene being particularly preferred. Therefore, the term "polypropylene" used herein is not limited to homopolymers of propylene, but should be understood to include copolymers as well.

The amount of the thermoplastic polyolefin added is as follows:
Based on the weight of M+εν^ (100 parts by weight), 1 to
The amount is preferably 30 parts by weight. If it is less than 1 part by weight, it will not be effective in improving rigidity and moldability, and if it exceeds 30 parts by weight, the elastomer properties of the resulting composition will decrease.

By adding a powdered inorganic filler to this thermoplastic elastomer composition, blocking resistance and heat resistance can be improved, and when it is made into a composite film, it can be easily made microporous. I can do it. Inorganic fillers include talc, calcium carbonate, ceracola,
Carbon black, clay, kaolin, silica, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, calcium phosphate,
aluminum hydroxide, zinc oxide, magnesium hydroxide,
Calcium oxide, magnesium oxide, titanium oxide, alumina, mica, shirasu balloon, zeolite, clay silicate, cement, silica fume, mica powder, etc. can be used, but talc, titanium oxide, calcium carbonate, silica, etc. are particularly preferred. The average particle size of the inorganic filler is 5μm
Below, preferably it is 1-3 micrometers.

These powdered inorganic fillers can be used alone or in combination. The total amount of the powdered inorganic filler added is preferably 2 to 15 parts by weight based on the weight of the aforementioned EPDM + BVA (100 parts by weight).If it is less than 2 parts by weight, the powdered inorganic filler is The effect of adding the above-mentioned inorganic filler may not be noticeable, and if it exceeds 15 parts by weight, the strength of the resulting composition may actually decrease.However, if the above-mentioned inorganic filler is added, The amount of inorganic filler is determined depending on the use of the elastomer film, since the film forming properties and stretching processability of the elastomer film decreases.
It is preferable to select it appropriately within the above range.

In addition, in the present invention, in addition to the above-mentioned additives, heat stabilizers, ultraviolet absorbers, antistatic agents, antioxidants, colorants, etc. can also be appropriately blended.

The present invention is a method for stabilizing the cooling conditions of the baffle when producing an elastomer film from the above thermoplastic elastomer composition, but the cooling conditions are required due to various properties of the elastomer film. It is something.

In order to produce the elastomer film, first, the ethylene-propylene-diene copolymer (EPDM)
, ethylene-vinyl acetate copolymer (EV^), and desired additives, etc., are carried out at a resin temperature of 170°C or less. In particular, it is preferable to perform kneading at a resin temperature within the range of 145 to 165°C. If the crosstalk temperature is higher than 170℃,
Thermal deterioration of the resin progresses, causing it to emit a strange odor and become sticky. For this reason, when kneading is carried out in an extruder such as a twin-screw extruder, one having a screw structure that does not generate heat or one having an appropriate cooling device is used. As for the lower limit of the kneading temperature, if it is less than 145°C, the extrusion rate will become unstable, which is not preferable.

It is also necessary that the temperature of the resin immediately after being extruded from the annular inflation die is 170° C. or less. If the temperature of the bubble immediately after extrusion through the annular die exceeds 170°C, the bubble cannot be cooled down to 45°C or lower by the first cooling ring. Particularly preferably, the temperature of the bubble immediately after extrusion through the annular die is 145-165°C.

The bubble extruded from the annular die is cooled by the cooling device of the present invention and is stretched not only in the MD force direction but also in the TD force direction. This is schematically illustrated in FIG. 1, which is an embodiment of the invention.

In FIG. 1, the bubble cooling device of the present invention includes a first cooling ring 2 provided near the annular die l, a second cooling ring 3 provided above the first cooling ring 2, and a second cooling ring 3 provided above the first cooling ring 2. A third cooling ring 4 provided slightly above the ring 3, an inverted conical net 5 provided between the first cooling ring 2 and the second cooling ring 3, and a net 5 provided below the net 5. It has a cooling air blowing device 6.

In the apparatus having the above configuration, the arrangement of each cooling ring is determined by controlling the temperature of the bubbles formed by the air-cooling inflation method, so the shape and temperature distribution of the bubbles will be explained below.

The molten thermoplastic elastomer composition is extruded through the annular orifice 11 of the die 1 to form bubbles 7.
The bubble 7 immediately after being extruded has a small diameter due to its low melt tension, and forms a so-called neck portion 71 . In the neck portion 71, the bubble 7 is mainly stretched in the MD force direction. Next, the bubble 7 rapidly expands to a predetermined bubble diameter. In this expansion tfB72, the bubble 7 is MD
It is stretched not only in the force direction but also in the TD force direction. There is a frost line 74 near the upper end of the expansion section 72, where the thermoplastic elastomer composition is cooled and solidified. The bubbles are further cooled by the second cooling ring 3 and the third cooling ring 4 provided in the bubble region 73 above the frost line 74.

In order to obtain a biaxially stretched elastomer film by the air-cooled inflation method as in the present invention, it is preferable to control the temperature of each part of the bubble 7 as follows.

(a) The temperature immediately after extrusion from the annular die 1 is 170°C or less.

wa) Neck [71 cooled to below 120°C.

(c) In the frost line 74, it is cooled to 45°C or less.

(a) Cooled down to 35°C or less by the second cooling ring 3.

The above condition (a) is as described above, but regarding the condition (b), unless the neck part 71 is cooled to 120° C. or lower, TD force direction stretching can be sufficiently achieved in the next expansion part 72. I can't. That is, 1 at the neck portion 71
If it is not cooled down to 20° C. or lower, the expanding portion 72 will not have sufficient melt tension, and stretching will be mainly in the MD direction.

Note that in order to satisfy such temperature conditions, the neck portion 71 needs to be relatively long. The length (H2) of the neck portion 71 varies depending on the bubble diameter, wall thickness, temperature, flow rate of cooling air from the first cooling ring 2, etc., but in order to satisfy the above condition (3), The diameter of the neck portion is equal to or 5 to 15% smaller than the diameter of the die, and the take-off speed may be set such that the length is 1.0 to 4.0 times the diameter of the annular die. In addition, the blow-up ratio is 1.5 to 5.0.
is preferable, and 3.0 to 4.5 is particularly desirable.

Regarding condition (c), cold stretching of the bubbles 7 can be achieved by lowering the bubble temperature at the frost line 74 to 45° C. or lower. When the thermoplastic elastomer composition is stretched at about 35 to 50° C., a portion of the ethylene-propylene-diene copolymer component is stretched and crystallized.

Therefore, the bubble temperature at the frost line 74 is 4
If the temperature is higher than 5° C., the expansion of the bubble 4 in both the MD direction and the TD direction in the expansion portion 72 is insufficient.

Regarding condition (d), by cooling the bubble 7 above the frost line 74 to 35° C. or lower, the formation of uniform thin bubbles can be stabilized.

If the temperature of the bubble above the frost line 74 is kept higher than 35° C. without providing the second cooling ring 3, there is a risk that non-uniform stretching will occur, making the entire bubble unstable. In particular, it is preferable that the second cooling ring 3 cools the temperature of the region 73 of the bubble 7 to 25 to 30°C.

In the present invention, after cooling by the second cooling ring, it is preferable that the third cooling ring 4 is further cooled to 30° C. or lower as condition (e). If an attempt is made to completely cool the bubble 7 using only the second cooling ring 3, there is a risk that non-uniform cooling will occur. Bubble 7 caused by third cooling ring 4
The temperature is preferably 30°C or lower, and it is particularly preferable to cool the temperature to 20 to 25°C. Due to these second cooling ring 3 and third cooling ring 4, no stretching occurs in the bubbles above them.

In order to control the temperature of the bubble 7 as described above, the arrangement of the first cooling ring 2, the second cooling ring 3, the third cooling ring 4, the net 5, and the cooling air blowing device 6, as well as the take-up device (not shown) are necessary. The take-up speed of 1) is as follows.

(a) First cooling ring 2 Provided immediately near the annular die 1, so that the temperature of the neck part 71 is 1
Cooling air is blown out so that the temperature drops to 20°C or less. As a result, 70 strings 74 after the expansion part 72
At this time, the temperature of the bubble 7 is 45°C or lower.

I) Second cooling ring 3 Disposed above the annular die 1 by a distance H2 that is 5 to 10 times the diameter of the annular die 10, and blows out cooling air so that the temperature of the bubble 7 is 35°C or less.

(c) Third cooling ring 4 Disposed above the second cooling ring 3 by a distance H5 that is 0.5 to 5.0 times the diameter of the annular die 1, so that the temperature of the bubble 7 is 30°C or less. blows out cooling air.

(d) Net 5 It has an inverted conical shape, is located between the first cooling ring and the second cooling ring, and surrounds the bubble. The cooling air is cooled by the cooling air blowing device 6 (described later), and the cooling by the first cooling ring 2 and the second cooling ring 3 is controlled by the external environment (temperature, humidity, etc.).
The temperature around the bubble is maintained uniformly so that the temperature of the bubble is maintained under the conditions (b) to (d) described above.

(e) Cooling air blowing device 6 Provided on the outside of the lower part of the net 5, having a cooling air blowing device opening in a circular shape along the lower end of the net 5, the temperature around the net 5 is preferably 20 to 35°C. The cooling air is ejected diagonally upward to maintain a stable temperature within the range of 25 to 30°C. The cooling air blown diagonally upward blows up along the net 5 and cools the entire net (arrow in FIG. 1).

(f) Taking-off speed of the taking-off device The length H3 of the neck portion 71 is 1°0 to 1° of the diameter of the annular die l.
Set it to be 4.0 times. Thereby, the temperature of the neck portion 71 can be lowered to 120° C. or lower by the first cooling ring 2.

In the above method, it is preferable to use humidified air as the cooling air injected into the bubbles 7 from the first to third cooling rings 2 to 4 from the viewpoint of cooling efficiency. Humidified air is air that has been humidified and cooled with cold water, contains nearly saturated moisture, and has a cooling effect about 5° C. greater than that of simple cooling air.

Furthermore, if a stable cooling effect cannot be obtained, the bubble 7 will become unstable, so it is necessary to control the temperature and humidity of the cooling air so that they do not change as much as possible.

Further, the cooling air injected from the cooling air blowing device 6 to the net 5 may be humidified air as in the case of the first to third cooling rings 2 to 4 described above, or normal indoor air may be used as desired. You may use one adjusted to a temperature of .

Furthermore, as net 5, nylon, polypropylene,
Plastics such as polyester, metals such as stainless steel, copper, brass, nickel, etc. can be used, but those with a mesh size of 5 to 20 meshes are preferable, particularly those with 8 to 10 meshes. is preferred.

The quality of the elastomer film cooled in this way is always uniform because each part of the bubble (immediately after extrusion, neck part, expansion part, frost line) is maintained at the desired temperature.

Moreover, since the cooling temperature at the neck can be lowered than before, it is possible to obtain a highly transparent film.
Furthermore, since the cooling rate can be increased, high-speed film formation is possible.

[For production]

Thermoplastic elastomer compositions have excellent stretchability in a relatively low temperature range of 40 to 60°C.

Therefore, the film formability, thinning, and physical properties of the film are determined by whether or not bubbles can be formed in the stretching region. 40
In order to perform stretching using the air-cooled inflation method in the low temperature range of ~60°C, the neck is first formed in a temperature range that exhibits melt tension that allows stable film formation, and then biaxial stretching is performed from the neck to the frost line. It is necessary to cool and solidify while stretching.

In the present invention, the area between the neck of the bubble and the frost line is surrounded by a net, and the wall surface of the net is further cooled to maintain a predetermined temperature around the net, so that the external environment of the bubble is always kept constant. can do. .

Therefore, local cooling can be stably performed at a desired temperature, and uniform thin bubbles can be stably formed.

〔Example〕

The present invention will be explained in further detail by the following examples.

Example 1, Comparative Examples 1-2 Ethylene-propylene-diene copolymer (Vistaron 3
708, manufactured by Exxon Chemical ■) 60% by weight, and ethylene-
A composition consisting of 40% by weight of vinyl acetate copolymer (vinyl acetate content: 28% by weight, melt index: 20 g/10 min) was melt-kneaded using a twin-screw kneader, and the mixture was melt-kneaded in a first cooling ring as shown in FIG. A cooling device having a second cooling ring, a third cooling ring, a net, and a cooling air blowing device is used to supply cooling air from the first to third cooling rings and from the cooling air blowing device. The bubble was cooled and an elastomer film was molded using each cooling method, including when cooling air was used (Example 1) and when cooling air was not supplied from the cooling air blowing device (Comparative Example 1). In addition, using the cooling device shown in Fig. 1 without a net, cooling air is supplied from the first to third cooling rings and cooling air is supplied from the cooling air blowing device to prevent bubbles. It was cooled and an elastomer film was formed (Comparative Example 2).

At this time, the temperature of the elastomer composition at the die exit of the extruder was 155 °C, the blow-up ratio was 3.8,
The take-up speed was 22 m/min, and the thickness of the obtained elastomer film was 20 m/min in each case. It was caII.

In addition, the cooling air from the first to third cooling rings is 10
Humidified air at a temperature of 23°C is humidified with water adjusted to ~15°C, and the cooling air from the cooling air blowing device is indoor air adjusted to about 20°C by air conditioning.

The presence or absence of cooling air from the net and cooling air blowing device, and each part of the bubble from the neck to the second cooling ring (A-F
) are shown in Table 1. Moreover, the parts in the bubbles A to F are shown in FIG.

In Example 1 and Comparative Examples 1.2, the temperature at the rear of the neck after cooling by the first cooling ring was 60 to 80°C in Example 1, over 100°C in Comparative Example 1, and 85°C in Comparative Example 2. The temperature was ~90°C.

As is clear from Table 1, the temperature of each part of the bubble in the cooling method of Example 1 is lower than that of each comparative example due to the large cooling effect, and is also within the desired temperature range, with almost no variation in temperature. There wasn't. On the other hand, in the cooling method of Comparative Example 1 in which cooling air was not supplied from the cooling air blowing device, the temperature after cooling was high and the variation was large. Further, in the cooling method of Comparative Example 2 without a net, although the temperature after cooling was lower than that of Comparative Example 1, the variation was still large.

These results show that the cooling method of the present invention makes it possible to maintain each part of the bubble at a desired temperature without being affected by the external environment (temperature, humidity, etc.). In addition,
It is thought that the temperature increase at the portion E or F of the bubble is due to the solidification of the bubble.

〔Effect of the invention〕

As detailed above, by using the cooling method of the present invention, the temperature of each bubble part of the elastomer film (immediately after extrusion, neck part, expansion part, frost line) can be controlled almost constantly within the optimum range. Therefore, a biaxially stretched elastomer film having a uniform thickness can be stably obtained.

In addition, by using the cooling method of the present invention, the cooling temperature can be lowered, making it possible to produce highly transparent films.Furthermore, it is possible to form molds at higher speeds than conventional methods, resulting in good production efficiency. It is.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a cooling device of the present invention, and FIG. 2 is a schematic diagram showing each part of a bubble. l ・ 2 ・ 3 ・ 4 ・ 5 ・ 6 ・ 7 ・ 71 ・ 72 ・ 74・ ・Annular die・First cooling ring・Second cooling ring・Third cooling ring・Net・Cooling air blowing device・Bubble・Neck part・Expansion part/Frost line Applicant: Tonen Petrochemical Co., Ltd.

Claims (13)

[Claims] (1) A method for cooling bubbles when producing an elastomer film by an air-cooled inflation method, the method comprising: (a) cooling air jetted from a first cooling ring provided near an annular die to cool the neck of the bubble; (b) cooling air jetted out from a second cooling ring installed slightly above the frost line of the bubble;
(c) cooling the bubble to a constant temperature around an inverted conical net provided between the first cooling ring and the second cooling ring; (d) cooling the bubble; A method characterized in that the cooling temperature of the bubble by the first cooling ring and the second cooling ring is stabilized. (2) In the bubble cooling method according to claim 1, the cooling air blowing out from a cooling air blowing device provided at the bottom of the net is blown up along the outer surface of the inverted conical net. A method characterized by cooling the area around the net. (3) The bubble cooling method according to claim 2, characterized in that humidified air is used as the cooling air of the cooling air blowing device. (4) The bubble cooling method according to any one of claims 1 to 3, characterized in that the bubble is further cooled by a third cooling ring provided slightly above the second cooling ring. . (5) The bubble cooling method according to any one of claims 1 to 4, characterized in that humidified air is used as the cooling air for the first cooling ring, the second cooling ring, and the third cooling ring. How to do it. (6) A device for cooling bubbles when producing a film by an air-cooled inflation method, including (a) a first cooling ring provided near the annular die and cooling the neck of the formed bubble; (c) a second cooling ring provided slightly above the frost line of the bubble to cool the bubble; (c) an inverted conical net provided between the first cooling ring and the second cooling ring to surround the bubble; (d) a device for cooling the inverted conical net. (7) The device according to claim 6, wherein the net is
A device characterized by being a metal net. (8) The device according to claim 6, wherein the net is
A device characterized in that it is a plastic net. (9) The device according to any one of claims 6 to 8, wherein the net has a mesh size of 5 to 20 meshes. (10) The device according to any one of claims 6 to 9, wherein the cooling device for the inverted conical net is a cooling air blowing device provided at a lower part of the net. (11) The device according to claim 10, wherein humidified air at a temperature of 5 to 28° C. is used as the cooling air of the cooling air blowing device. (12) The apparatus according to any one of claims 6 to 11, further comprising a third cooling ring located slightly above the second cooling ring for further cooling the bubble. (13) In the device according to any one of claims 6 to 12, humidified air at a temperature of 5 to 28°C is used as cooling air for the first cooling ring, the second cooling ring, and the third cooling ring. A device featuring: