JP3506480B2 - Method and apparatus for forming blown film - Google Patents

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY Since the present invention has a low melt tension,
Even in the case of a synthetic resin, it has been difficult to make the bubble shape into a so-called long neck type (meaning a bubble shape in which the position where the bubble expands is far away from the die) in the inflation film molding method. The present invention relates to a film forming method and a forming apparatus capable of producing a long-neck type blown film forming method and capable of producing a thermoplastic resin film excellent in transparency (haze, gloss, clarity) and strength with high productivity. Here, as the synthetic resin that has been difficult to be a long neck type, linear low density polyethylene (hereinafter referred to as LLDPE), low density polyethylene (hereinafter referred to as LDPE) or high density polyethylene (hereinafter referred to as HDPE). ), Ethylene-vinyl acetate copolymers, ethylene-based copolymers such as ethylene-acrylate-based monomer copolymers, polypropylene, polyamides, polyesters and the like.

[0002]

2. Description of the Related Art There are many proposals for producing an inflation film by an air-cooling method, and the shapes of resin bubbles for forming a film are roughly classified into three types by the proposals (FIGS. 3 and 6). , FIG. 7).

Factors that determine the shape of the molten resin bubble include cooling capacity, film take-up speed, molten resin temperature, etc., and linear polyethylene such as ultra high molecular weight high density polyethylene (hereinafter referred to as HMWHDPE). For polyethylene having a high melt tension, film formation by so-called long neck type bubbles shown in FIG. 3 or FIG. 4 is often adopted, and it is supplied in large quantities in the field of shopping bags and the like as a high-strength balance film.

However, in this method, the molten bubble is gradually cooled, so that a transparent film cannot be obtained.

On the other hand, the LLDPE currently on the market is
The melt tension is relatively small, the flow characteristics are significantly different from HMWHDPE, the stability of the bubble is poor, and it is difficult to form the bubble into a shape such as a long neck type.
Normally, the bubble shape of the type shown in FIG. 6 or the type shown in FIG. 7 (referred to as low frost line type) or T
-Molded by the die method. The same applies to other thermoplastic resins having a small melt tension.

In the production of the blown film by the low frost line type, the molten bubbles are rapidly cooled,
Although a transparent film can be obtained, the biggest problem with this method is that the stability of the bubble is poor at high-speed production, and the thickness and film width are easily varied due to the fluctuation of the bubble, and the film is produced at high speed. At this time, the orientation in the take-up direction becomes stronger and the strength in the longitudinal direction (machine direction) increases, while the strength in the direction perpendicular to this (lateral direction) tends to be significantly lost. It is difficult to increase the pick-up speed because it becomes easy, and the productivity is limited.

In order to form a film of synthetic resin having a small melt tension by the inflation method,
There was no choice but to adopt a low frost line type bubble shape capable of stable production even at a low speed, or to adopt production by the T-die method.

[0008]

DISCLOSURE OF THE INVENTION The present invention, when producing a film of a thermoplastic resin having a small melt tension by an air-cooled inflation method, melts a long neck type molding even when a low melt tension thermoplastic resin is used. To solve the instability of resin bubbles, to stabilize the bubbles, and to establish a highly productive molding method for films with excellent transparency (haze and clarity).

[0009]

The present invention provides [1] polyethylene, ethylene and a radical-polymerizable monomer.
Copolymer with polypropylene, polypropylene or a mixture thereof
The method for forming an inflation film of at least one thermoplastic resin according to claim 1, wherein the extrusion resin temperature of the thermoplastic resin is
The temperature is 40 ° C above the melting point and 120 ° C above the melting point
For the molten resin bubble extruded from the die outlet by adjusting the temperature range to a high temperature, cooling air is blown from the first air ring provided close to the die outlet to cool it.
The bubble is then taken off from the die surface 150
It is installed between 0 mm or less, parallel to the die surface, and its diameter
It was formed so that the center of the
2 to 500 disks and the diameter of the disk-shaped stabilizer are
0.5 ~ 1.5R with respect to diameter R, thickness D is 1 ~ 30
mm, and the side angle of the disc-shaped stabilizer is 30 to 170.
It consists of two annular surfaces that intersect at ° and has a thermal conductivity of 100k.
Cal / m hr Stabilizer group consisting of materials below ℃
To make the molten resin bubble expand rapidly.
A second plurality of annular slits formed at a position so as to blow out in a direction substantially parallel to the bubble withdrawing direction;
The bubble resin temperature just before entering the air ring is adjusted within the range of the melting point + 30 ° C and the melting point + 80 ° C of the thermoplastic resin, and the actual temperature is adjusted.
Quality expansion ratio (bubble diameter after expansion / bubble before rapid expansion)
Method of forming blown film of a thermoplastic resin, which comprises forming the Le diameter) in the range of 1.3 to 6.0, [2] a thermoplastic resin is a linear low density polyethylene,
Lip gap 2.5 to 5.5 mm, extruded resin temperature is 1
70 to 250 ° C., the resin temperature immediately before entering the second air ring is 125 to 220 ° C., and the thickness of the film to be produced is 10 to 80 μm.

[3] Polyethylene, ethylene and LA
Copolymer with dical polymerizable monomer, polypropylene or
Or at least one thermoplastic resin of a mixture thereof, in a blown film forming apparatus, wherein the extruder
And a circular datum for inflation installed at the tip of the extruder.
The chair and the first air lie provided near the exit of the die.
Between the die and the die surface within 1500 mm,
It is parallel to the die surface and the center of its diameter overlaps with the center of the die diameter.
2 to 500 discs and their
The diameter of the disc-shaped stabilizer is 0.5R to the die diameter R
Material having 1.5R, thickness D of 1 to 30 mm, two annular surfaces where the side surface of the disk-shaped stabilizer intersects at an angle of 30 to 170 °, and thermal conductivity of 100 kcal / m hr ℃ or less
It has a bubble stabilizer group that is
The molten resin bubble is expanded rapidly in the downstream direction.
Has a plurality of annular slits, and the annular slits are melted.
The second that blows out cooling air in the direction of taking out the molten resin bubbles
Reduce the winder through the air ring and nip roll.
Inflation film composition characterized by having
Forming apparatus , and [4] the inflation film molding apparatus according to the above [3], wherein a means for heating the surface of the molten resin bubble is provided between the first air ring and the second air ring. It was confirmed that

The thermoplastic resin targeted by the present invention is L
Polyethylene such as LDPE, HDPE, LDPE; ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer, etc. Copolymer of ethylene and radical polymerizable monomer; polypropylene, vinyl chloride, Even a thermoplastic resin having a low melt tension such as polyamide, polyester or a mixture thereof can be used. However, a polymer having a high melt tension as much as possible has a better bubble stability.

Even LLDPE has good bubble stability during molding and can be taken up at high speed, and the film molded by the method of the present invention is excellent in transparency and strength.
Its transparency is comparable to that of cast polypropylene film and can be used as an inexpensive film that can be used at low temperatures.

In the following description, LLDP is used as the thermoplastic resin.
Taking E as a representative, description will be made with reference to the drawings.

The inflation molding method usable in the present invention may be either upward blow (FIG. 3) or downward blow (FIG. 4).

The extrusion temperature of the resin varies slightly depending on the type of resin, but it is usually 40 ° C. higher than the melting point and 120 ° C.
Within the high temperature range. For example, 1 for LLDPE
It is preferable to mold in the temperature range of 70 to 250 ° C.

In the case of LLDPE, if the temperature is lower than 170 ° C., melt fracture tends to occur, and if the temperature is higher than 250 ° C., the melt tension becomes small, and the stability of bubbles tends to be impaired.

In particular, LLDPE or a resin composition containing it has a property of easily causing melt fracture, so that the lip gap of the die is 2.0 to 10.0 mm.
(Preferably 2.5 to 5.5 mm), which is larger than that in HDPE, or the surface of the molten resin bubble 3 is located between the first air ring 2 and the second air ring 5 (on the die side from the expansion point). Roughening of the surface can be avoided by taking measures such as providing a bubble heater (not shown in the drawing) for heating. As the lip gap becomes larger than 7.0mm, the uniformity of the film thickness is lost, so even if the melt fracture can be made smaller, it should not be made larger than 10.0mm and the bubble heater avoids the rough surface. Preferably.

The molten resin bubble 3 extruded at a relatively low temperature is cooled by the cooling air from the first air ring 2 in the vicinity of the die outlet.

The blowing direction of the cooling air of the first air ring 2 is
It may be blown out obliquely with respect to the take-up direction like a normal air ring, but it is preferable to make it nearly perpendicular.

A stabilizer group is inserted in the portion of the first air ring 2 onto which cooling air is blown, so that vibration of bubbles can be suppressed and stable molding can be performed. The presence of the stabilizer group is effective because the bubble shape of the bubble is maintained by the outlet stabilizer A even when the blowout pressure of the first air ring 2 is strong, and this portion is stabilized.

The molten resin bubble is cooled by the first air ring, taken up while increasing the melt tension, and rapidly expands after passing through the stabilizer group.

The disc-shaped stabilizer has a die diameter R of
It is necessary to have a diameter at the center of the thickness of 0.5R to 1.5R. More preferably, 0.7R to 1.3R
Is the range. Within this range, the substantial expansion ratio (the ratio of the bubble diameter after expansion / the bubble diameter before rapid expansion) can be increased even when films of the same size are manufactured using the same size die. Increasing this substantial expansion ratio has the effect of increasing the strength in the lateral direction (the direction perpendicular to the film take-up direction) and increasing the impact strength.
To 6.0, preferably 1.5 to 4.5
It is better to set the range.

The film obtained when the substantial expansion ratio is lower than this tends to cause longitudinal tearing and has a low impact strength. On the other hand, when the substantial expansion ratio exceeds 6.0, the transverse orientation is too strong, and the film tends to break easily.
It should be avoided as it may cause bubbles to break during production. The thickness of the disk-shaped stabilizer needs to be 1 mm to 30 mm, preferably 1 mm to 10 mm. If the thickness of the disk-shaped stabilizer is smaller than 1 mm, the stabilizer is easily deformed by the stress and heat from the resin applied to the disk-shaped stabilizer, and if it is larger than 30 mm, the friction with the resin is large and the stability of the bubble is impaired. .

The side surface of the disk-shaped stabilizer has an angle of 30 to 170.
It is necessary to be composed of two annular surfaces intersecting at an angle, and the angle is preferably in the range of 45 to 150 °. If the angle is smaller than 30 °, the stabilizer bites into the bubble during production, causing large friction with the resin, impairing the stability of the bubble.
It also causes uneven thickness of the obtained film (variation in film thickness). If the angle is larger than 170 °, the contact area with the bubble is large and the stability of the bubble is impaired. The central portion of the thickness where the two annular surfaces intersect may have an acute angle,
It may be rounded with a curvature.

The material of the disk-shaped stabilizer has a thermal conductivity of 100.
It must be made of a solid material having a temperature of “kcal / mhr ° C.” or less, and preferably has a thermal conductivity of 10 “kca.
1 / mhr ° C.] or less. Thermal conductivity of 100 "kcal
/ Mhr ° C], heat is likely to be accumulated in the disk-shaped stabilizer, and the stability of bubbles is impaired.

The disk-shaped stabilizer is 1500 m from the die surface.
It is necessary to insert 2 to 500 sheets within m or less, and it is preferable to form 2 to 200 sheets of the above stabilizer within 600 mm or less from the die surface. is there. If the height is larger than 1500 mm, the bubble becomes unstable from the viewpoint of the melt tension of the resin.
If one sheet is used, the stability of the bubble will be impaired, and if it is more than 500 pieces, the friction with the resin will be large and the stability of the bubble will be impaired.

The molten resin bubble temperature is one of the important requirements in the present invention. The molten resin bubble 3 extruded from the die 1 is cooled by the cooling air or the like from the first air ring 2, and is in the melting point of the resin used at the inlet of the second air ring 5 and in a temperature range higher than the melting point by 110 ° C. Necessary, preferably melting point + 30 ° C to melting point +80
C., more preferably the melting point + 40.degree. C. to melting point + 80.degree. C. temperature range. When the temperature is lower than the melting point, not only the melt bubble gradually cools and the transparency decreases, but also the expansion becomes impossible or incomplete, and the variation becomes large. Can't get Further, when the temperature is higher than this temperature, the expansion of the molten resin bubble 3 becomes non-uniform and the stability of the bubble is impaired, so that it becomes difficult to manufacture a film having uniformity.

For example, in the case of linear low density polyethylene, the resin temperature at the inlet of the second air ring is 125 to 22.
It must be in the range of 0 ° C. The molten resin bubble expands sufficiently in the second air ring 5 or expands immediately after leaving the second air ring 5 to form a film having a predetermined thickness and size, but with high transparency. When necessary, the film thickness is 50 μm or less, preferably 40 μm or less. According film thickness becomes thicker, which inevitably opacifying for the slow cooling. As a countermeasure, a bubble heater can be used to solve this problem to a considerable extent.

The outlets (52, 53, 54) of the plurality of annular slits of the second air ring 5 having the outlets having the concentric annular slits for blowing two or more cooling air,
The air may be blown out in the direction outside the bubble diameter, but if possible, it is preferable that the air is blown out substantially parallel to the bubble take-up direction.

The depressurized atmosphere created by the blowing of the cooling air from the annular slit of the air ring in the bubble taking-out direction affects the molten resin bubble, and the bubble starts to expand rapidly at this position.

Although the air outlets (52, 53, 54) of the second air ring are shown as double annular slits in FIG. 5, they may be double or more. Each outlet 5
The upper end wall surfaces of the air outlets 2, 53, 54 may be inclined so as to increase the degree of pressure reduction. Further, the cover 55 may be attached to the tip of the air ring also for the purpose of blocking the flow of external air and the reduced pressure atmosphere from the outside.

Therefore, the position of the frost line 8 which affects the properties of the obtained film can be freely changed by moving the position of the second air ring 5. The position of the second air ring 5 is usually required to be separated from the die surface by 50 mm or more, preferably 100 mm or more, and more preferably 200 mm or more. If they are too close to each other, the cooling effect is reduced and high-speed take-up becomes difficult.

When the molten resin bubble 3 expands rapidly, the resin film becomes thin and is rapidly cooled, and after solidification, air is squeezed by a nip roll like normal inflation and taken up by a winder to form a film.

[0034]

Function The present invention is an ordinary HMWHD for balance film.
This is an effective manufacturing method not only for thermoplastic resins with high melt tension such as PE, but also for thermoplastic resins that have low melt tension and are difficult to perform long neck type inflation molding with conventional inflation molding equipment. is there.

The reason why the resin obtained by the method of the present invention has high transparency is considered as follows.

It is well known that, in general, a molten resin bubble extruded from a die swells at the outlet due to the swell effect, and the outer diameter of the molten resin bubble is larger than the diameter of the die by a few percent to a few percent.

At the time of this swelling, the bubble surface is in a state of large irregularities. When a film is formed in the low frost line type bubble shape shown in FIG. 6 or 7, the film surface is rapidly expanded, and the film surface is strongly affected by the swell effect.

However, in the case of the long neck type, the molten resin bubble slowly moves to the expansion point, the unevenness of the surface generated by the swell is greatly alleviated, and the relaxed bubble rapidly expands. It is estimated that the effect of can be greatly reduced, which is one of the reasons for obtaining a film having a smoother surface.

For example, haze is one of the indexes of the transparency of the film, but most of the haze (for example, about 60 to 80%) of the film is opaque due to non-transmission of light due to external haze (unevenness of the film surface). It is known that

It is considered that the high transparency of the film in the present invention is obtained by using a part of the long neck type which alleviates the swell effect.

When the neck point (point immediately before the rapid expansion) is lowered to the crystallization temperature, crystals grow and haze deteriorates. In the present invention, however, the temperature at the inlet of the second air ring is regulated. This problem is also avoided, which is considered to be one of the reasons for obtaining a highly transparent film.

In the molding method of the present invention, the temperature of the molten resin bubble at the inlet of the second air ring 5 is regulated by the cooling by the first air ring 2, and the plurality of annular slits (52, 53, 54) of the second air ring. ), A method of rapidly expanding a molten resin bubble in a decompressed atmosphere accompanying the blowing of cooling air is used, and by using the stabilizer group, not only a resin having a high melt tension but also a low melt tension can be obtained. However, there is no problem, and it is estimated that inflation molding was completed.

The use of two stages of air rings improves the cooling capacity, which enables high-speed take-up, and has a synergistic effect such as rapid cooling of the molten resin due to rapid expansion, and haze, image clarity (clarity), etc. It seems that the transparency of the is significantly improved.

[0044]

【Example】

(Example 1) Density 0.923 g / cm ³ , JIS K-
Melt flow according to condition 4 of Table 1 of 7210 (hereinafter referred to as MFR
Say. ) 1.0 g / 10 min of linear polyethylene was extruded at a resin temperature of 200 ° C. using an upward inflation film molding apparatus equipped with a die having a lip gap of 3 mm and a diameter of 100 mmφ. The disk-shaped stabilizer has a diameter of 100 mm in diameter at the center of thickness and is 10 mm in thickness made of Teflon, and the side surface is cut so as to have two annular surfaces intersecting at an angle of 90 °. A stable body which is parallel to the die surface and whose center of the diameter is located at the center of the die diameter, and which is formed by inserting 10 sheets of the above-mentioned stabilizer within a distance of 500 mm or less from the die surface,
A film having a folding width of 314 mm and a thickness of 30 μm was formed at a take-up speed of 50 m / min. The molten resin bubble is cooled by the cooling air or the like from the first air ring, and is 167 at the second air ring inlet consisting of the double annular slit.
C. and 131.degree. C. at the outlet. The frost line is 650 mm from the die surface, and the frost line temperature is 11
It is 1 ° C. The evaluation of the obtained film is shown in Table 1.

The temperature at the inlet of the second air ring was measured with a model IR-AP thermometer manufactured by Chino Co., Ltd. at a distance of 15
0 cm, measurement area; diameter was 45 cmφ, and the portion closest to the air ring was measured. Haze, gloss, and clarity were measured by the method specified in JIS K-7105.

(Examples 2 to 6) Density 0.923 g / cm
³ , MFR 1.0 g / 10 min LLDPE 80% by weight, density 0.925 g / cm ³ , MFR 0.8 g / 1
Using a resin composition composed of 20% by weight of LDPE for 0 minutes,
Using the same apparatus as in Example 1 except for the stabilizer group, the conditions were changed to form a film. The evaluation of the obtained film is shown in Table 1.

Comparative Examples 1 to 7 Films were formed under the conditions shown in Table 1 by using the same resins as those in Examples 2 to 6 and using the same apparatus except for the stabilizer group. The molten resin bubble became unstable, and particularly when the bubble was unstable, frequent cutting occurred and molding was impossible.

[0048]

[Table 1]

[0049]

INDUSTRIAL APPLICABILITY According to the present invention, when forming a film of a thermoplastic resin by an inflation method, the molten resin bubble is cooled by a first air ring provided in the vicinity of the die outlet, and then a specific stabilizer group is formed. While supporting in contact with each other, the temperature of the inlet of the second air ring having a plurality of annular slits provided at a position where it is rapidly expanded is adjusted to a range of a melting point of the thermoplastic resin and a temperature 100 ° C. higher than the melting point, When forming a film with the long neck type, for example, even if it is a thermoplastic resin with a small melt tension such as LLD, the molten resin bubble is stable, and a film excellent in transparency (haze and clarity) can be produced at high speed. I found it.

The molding apparatus used for this purpose can be preferably used in the above-mentioned blown film molding method.

It has also been found that even if the thermoplastic synthetic resin is liable to cause melt fracture, it is possible to greatly improve the haze and clarity by providing a bubble heater in the middle of the first air ring and the second air ring. It was

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of a disk-shaped stabilizer according to the present invention.

FIG. 2 is a conceptual diagram showing an example of a stabilizer group according to the present invention.

FIG. 3 is a conceptual diagram showing an example of a blown film molding method according to the present invention.

FIG. 4 is a conceptual diagram showing another example of the blown film molding method according to the present invention.

FIG. 5 is a cross-sectional view showing an example of a second air ring.

FIG. 6 is a conceptual diagram of an example of a conventional blown film molding method using a low frost line type.

FIG. 7 is a conceptual diagram of another example of a conventional blown film molding method using a low frost line.

[Explanation of symbols]

1 die 2 First air ring 3 molten resin bubbles 4 stable groups 41 Support 42 Disc-shaped stabilizer 43 Diameter of disc-shaped stabilizer 44 Thickness of disc-shaped stabilizer 45 2 Angle at which annular surfaces intersect 46 Side of disk-shaped stabilizer 5 Second air ring 51 air passage 52 Outlet 53 Outlet 54 Outlet 55 cover 8 Frost line A exit stabilizer

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Taka 3-2, Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Showa Denko KK Kawasaki Plastics Research Laboratory (56) Reference JP-A-63-51124 (JP, A) JP 62-113530 (JP, A) JP 61-108531 (JP, A) JP 60-229733 (JP, A) JP 59-42931 (JP, A) JP 58-219021 (JP, A) JP 58-119824 (JP, A) JP 58-42431 (JP, A) JP 58-18226 (JP, A) JP 57-34920 (JP, A) JP-A-56-46729 (JP, A) JP-A-54-93057 (JP, A) JP-A-51-102053 (JP, A) JP-A-49-61252 (JP, A) JP-A-46-5744 ( JP, A) JP-A-5-286032 (JP, A) JP-A-5-138734 (JP, A) JP-A-2-34324 (J P, A) Actual development Sho 64-30219 (JP, U) European patent 583619 (EP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) B29C 55/00-55/30 B29C 47 / 00-47/96

Claims (4)

(57) [Claims] 1. Polyethylene, radical-polymerizable with ethylene
Copolymers with monomers, polypropylene or their
A method for forming an inflation film of at least one thermoplastic resin of a mixture, the method comprising extruding the thermoplastic resin.
The resin temperature is 40 ° C. higher than the melting point and 12 is higher than the melting point.
It is extruded from the die outlet after adjusting the temperature range to 0 ℃ higher.
Cooling air is blown against the molten resin bubble from the first air ring provided in the vicinity of the die outlet, and then the bubble is taken from the die surface while being taken up.
It is installed between 1500mm or less, parallel to the die surface,
Formed so that the center of the diameter overlaps the center of the die diameter
2 to 500 disks and the diameter of the disk-shaped stabilizer
Is 0.5 to 1.5R with respect to the die diameter R, and the thickness D is
1 to 30 mm, the side angle of the disk-shaped stabilizer is 30
It consists of two annular surfaces that intersect at ~ 170 °, and its thermal conductivity is
Stabilizers made of materials with a temperature of 100 kcal / m hr ℃ or less
The inner surfaces of the molten resin are brought into contact with each other, and the molten resin bubble is rapidly expanded.
The bubble resin temperature immediately before entering the second air ring having a plurality of annular slits formed so as to be blown out in a direction substantially parallel to the bubble withdrawing direction is set to the melting point of the thermoplastic resin + 30 ° C. Adjust to a range of + 80 ° C and expand substantially (bubble diameter after expansion / expand rapidly)
Molding method for blown film of thermoplastic resin , characterized in that the former bubble diameter) is molded in the range of 1.3 to 6.0 . 2. The plastic resin is linear low density polyethylene, the lip gap is 2.5 to 5.5 mm, the extruded resin temperature is 170 to 250 ° C., and the resin temperature is 125 to 220 immediately before entering the second air ring. The method for molding an inflation film according to claim 1, wherein the film is produced at a temperature of ℃ and the thickness of the film produced is 10 to 80 μm. 3. Polyethylene, radical polymerization with ethylene
Copolymers with reactive monomers, polypropylene or those
In blown film molding apparatus of at least one thermoplastic resin mixture, the extruder and the extruder
Inflation circular die installed at the tip,
First air ring and die provided near the die exit
It is provided within 1500mm or less from the die surface and on the die surface
Parallel, so that the center of the diameter overlaps the center of the die diameter.
Supported by 2 to 500 discs and its disc-shaped stability
The body diameter is 0.5R to 1.5R with respect to the die diameter R
A bubble having a thickness D of 1 to 30 mm, two annular surfaces intersecting at a side surface of the disc-shaped stabilizer at an angle of 30 to 170 °, and a thermal conductivity of 100 kcal / m hr ℃ or less.
Equipped with a group of stabilizers, and further downstream in the direction of molten bubble collection
At the position where the molten resin bubble expands rapidly,
It has an annular slit, and the annular slit is a molten resin bubble.
Air ring that blows out cooling air in the take-up direction
And at least a winder via a nip roll.
An inflation film forming apparatus characterized by: 4. The blown film molding apparatus according to claim 3, wherein a means for heating the surface of the molten resin bubble is provided between the first air ring and the second air ring.