JP2649638B2 - Blown film molding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a process for extruding a thermoplastic resin into a tubular shape and expanding the molten tubular resin (the tubular body before and after expansion is called a bubble) to form a film. The present invention relates to an inflation film forming apparatus which enables a so-called long neck forming method to be operated stably for a long time, and a method for forming an inflation film using the apparatus.

[0002]

2. Description of the Related Art There are many proposals for a method of producing an inflation film by an air cooling method, and the shape of a resin bubble for forming a film is large according to the proposal, and a so-called long neck type and a high pressure method low density polyethylene (L) are used.
(DPE) and the like, and can be classified into a so-called low frost line type which rapidly expands from a die outlet.

[0003] Which method is used for molding is mainly governed by the melt tension of a thermoplastic resin as a raw material. For a resin having a low melt tension, a low frost line type, ultra high molecular weight high density polyethylene (hereinafter, HMWHD) is used.
It is called PE. In the case of resins having a high melt tension such as (1) and (2), molding by a long neck type is often employed, and is generally used in the field of shopping bags and the like because it is a method suitable for obtaining a high-strength film.

On the other hand, currently available L-LDPE
Has a relatively low melt tension and a flow characteristic of HMWHDP
Unlike E, the stability of the bubble was poor, and it was difficult to form the bubble into a shape such as a long neck type. Usually, the bubble was formed by a low frost line type or by a T-die method. The same applies to other thermoplastic resins having a low melt tension.

[0005] In the production of blown film using this low frost line type, the melted bubble is rapidly cooled to obtain a transparent film. However, the biggest problem with this method is that when high-speed production is carried out, the stability of the bubble is poor, and the bubble is poor. The film thickness and film width are likely to vary due to shaking, and the orientation in the take-off direction increases when the film is produced at high speed, and the strength in the vertical direction (machine direction) increases. The strength in the direction (horizontal direction) is remarkably easily lost, so that the strength is unbalanced and it is easy to tear vertically, so that it is difficult to increase the take-up speed, and the productivity is limited.

In order to form a film of a synthetic resin having a low melt tension by the inflation method, a low frost line type bubble shape which enables stable production even at a low speed or a T-die method is used. I had no choice but to adopt.

Further, in a conventional long neck type blown film forming apparatus using a stabilizer, the stabilizer is formed by covering the surface of a metal stabilizer with felt in order to reduce the thermal conductivity of the stabilizer, or by using a metal ( There have been many proposals, such as knurling the surface of aluminum (Aluminum) and those using a spring as a stable body, and these have been put into practical use. When the resin is used, the molten resin bubbles adhere to the surface of the stable body, or are hardly formed on the surface of the stable body.

However, even when a resin having a high melt tension is used, if molding is continuously performed for a long period of time, impurities such as additives and a low molecular weight resin contained in the resin may be present on the felt surface and the knurled groove. This causes precipitation and bubble breakage. Usually, it was necessary to replace the surface material with a new one in about 5 days or to clean the knurled surface in a felt-made stabilizer.

[0009]

SUMMARY OF THE INVENTION The present invention relates to the instability of molten resin bubbles caused by molding with a long neck type even when a thermoplastic resin having a low melt tension is used in the production of a thermoplastic resin film by an air-cooled inflation method. To establish a molding method that enables high-speed molding of films with excellent physical strength, such as impact strength, and to develop an inflation film molding machine that can continuously mold over a long period of time for high melt tension resins. Aim.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a blown film forming apparatus for forming a molten resin bubble of a thermoplastic resin from an extruder while supporting the bubble with a bubble stabilizer attached to a die. The contact portion with the resin is smooth and the surface tension of the material is 30d
A blown film forming apparatus characterized by using a stable material having a diameter of less than yne · cm ⁻¹ , and in particular, a linear low density polyethylene (hereinafter referred to as L-LDPE) is formed into a film by a long neck type inflation method. The contact portion of the bubble stabilizer with the molten resin is smooth and the surface tension of the material is 30 dyne · cm ^−1.
The above object was achieved by developing a method for forming an inflation film, which is characterized by being formed using the following stabilizer.

As the thermoplastic resin usable in the molding apparatus to which the present invention is applied, not only HMWHDPE but also L-
LDPE, polyethylene such as LDPE; ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer and other copolymers of ethylene and radical polymerizable monomers; polypropylene, vinyl chloride, polyamide, A thermoplastic resin having a low melt tension such as polyester or a mixture thereof can be given. However, a high molecular weight material having as high a melt tension as possible has better bubble stability.

Since L-LDPE has good bubble stability during molding, it can be generally taken up at a higher speed than the low frost line method, and the film molded by the method of the present invention has excellent strength.

The blown film molding method of the present invention can be applied to both upward blow and downward blow.

As a stabilizer, it is necessary that the surface in contact with the molten or resin bubbles has a smooth surface and the surface tension of the material is smaller than the surface tension of the thermoplastic resin to be molded. The surface tension is 30 dyne · cm ⁻¹ or less, preferably 25 dyne · cm ⁻¹ or less, more preferably 20 dyne · cm ⁻¹ or less.
The material is dyne · cm ⁻¹ or less. Specifically, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkylvinyl ether terpolymer And resins having a melting point of 170 ° C. or higher, preferably 200 ° C. or higher, more preferably 230 ° C. or higher, such as fluorine-based resins such as polyvinylidene fluoride and polyhexafluoropropylene, and silicone resins such as polydimethylsiloxane. Surface tension is 30 dyne · c
When the material is m ⁻¹ or more, the molten resin bubbles easily stick, and high-speed molding becomes impossible.

The stabilizer may be made of the above-mentioned resin, or may be a metal stabilizer having a contact portion with the molten resin bubble coated with the above-mentioned resin.

The shape of the stabilizer is not limited as long as it does not give strong resistance to the molten resin bubbles.
It is preferable that a plurality of disks 3 as shown in FIG.

In this shape, it is possible to simply reduce the angle of the end face of the disk, but it is preferable to use a curved surface.

For example, a sheet of PTFE is punched out in a circular shape, and the corners of both sides are cut off to form an appropriate space (for example, 2 to 5c).
m) may be attached to the shaft 4 after opening. Alternatively, the ball may be crushed to have a thickness of 2 to 5 cm.

The stabilizer is manufactured according to the diameter of the die 1, but it can be used whether the diameter is smaller or larger than the diameter of the die. In theory, the length should be only the bubble contact portion. However, since the contact portion is changed by changing the operating conditions, the total length is preferably about 30 cm from the viewpoint of easy operation.

When the diameter of the stabilizer is smaller than the diameter of the die, the molten resin bubble extruded at the die outlet becomes larger than the die due to the swell. It is preferable to provide a disk or sphere of the same material as that of the above-mentioned stabilizer in a crushed shape, since this improves the stability of molding.

The shaft 4 has a vent hole 5 for introducing air through the die 1 into the molten resin bubble at the start of molding.
Is provided, and the expansion ratio of the bubble is adjusted. Alternatively, if a ventilation hole (not shown) is provided in the disk 3 for the stabilizer, the ventilation hole may be simply opened in the die surface.

Such a stabilizer requires a small contact area with the bubble, and has a sticky molten resin bubble such as L-
Even if the LDPE molten resin bubble adheres to the stable body and the phenomenon of cutting can be avoided, the operation can be performed without cutting the molten resin bubble even in high-speed molding.

In order to fix the stabilizer to the die 1, the shaft 4 is generally screwed in, but the invention is not limited to this.

Using such a stabilizer, L-LDPE
For example, to form the lip gap 2 of the die 1,
10 mm, extrusion temperature 170-250 ° C., substantial expansion ratio (diameter of product film / diameter of bubble immediately before expansion point) 1.3
6.0 or more, and a take-up speed of 40 m / min or more may be adopted.

[0025]

A long neck type blown film molding using a conventional stabilizer has been developed for molding HMWHDPE having high elasticity in a molten state (high melt tension). When attempting to mold a resin such as L-LDPE having low elasticity (low melt tension) and high adhesiveness in a molten state, the bubble stability is poor due to low elasticity, and even a small frictional resistance is required. However, there was a problem that bubbles were broken due to low melt tension.

In order to reduce the resistance of the stabilizer, a stabilizer having a rotating surface has also been proposed. In this case, the flatness of the product film may be due to the difference in temperature between the part that contacts the stabilizer and the part that does not. Was inferior.

Even when a smooth stabilizer was used, there were problems such as sticking to the stabilizer due to the stickiness of the molten resin and causing bubble breakage.

In the present invention, in order to avoid stickiness, the contact portion of the stabilizer with the molten resin bubble is smooth and the material has a surface tension of 30 dyne · cm ^-1 or less to avoid stickiness. succeeded in.

Further, by forming a plurality of disks on the stabilizer in a multi-layered shape with a space therebetween, the contact resistance was reduced, and high-speed molding was enabled.

[0030]

【Example】

(Example 1) 5 in which a die having a diameter of 100 mm was set
Using an inflation film forming apparatus having a 5 mmφ extruder, L-LDPE (MFR; 1.0 g / 10
min, a density of 0.921 g / cm ³ ), and a long neck type film is formed at a resin temperature of 190 ° C. under the conditions of a product film thickness of 28 μm and a folded width of 275 mm (substantial expansion ratio: 1.95). Was. In this case, a disk-shaped stabilizer made of PTFE (surface tension: 22 dyne · cm ⁻¹ ) (a 110 mmφ disk as an outlet stabilizer, then 100 mm, 100 mm, 98 m from the die side) as a stabilizer
m, 96mm, 96mm, 96mm, 94mm, 94m
m, 90 mm, and 90 mmφ, each having a 3 mm-thick disk whose surface was finished to a curved surface and fixed to a shaft at an interval of 3 cm). Up to 80
It was found that stable molding was possible even at a take-up speed of m / min or more. (The take-up speed of 80 m / min was the limit of the capacity of the extruder, but it was estimated that higher speed molding was possible because the stability of the bubble was not lost.) The characteristics of the obtained film were 238 kg · cm / impact. mm haze was 4.3%.

(Comparative Example 1) As a stabilizer, a length of 30 cm,
Example 1 except that an aluminum stabilizer (with a 110 mmφ exit stabilizer) having a diameter of 90 mm (the surface was knurled and the surface tension was 1648 dyne · cm ⁻¹ ) was used.
Inflation molding was performed under the same conditions as in the above. In this case, when the take-up speed exceeded about 50 m / min, the molten resin bubbles adhered to the stable body, and the bubbles were broken and molding was impossible. At a take-off speed of 40 m / min, the physical properties of the formed film were impact 213 kg · cm / mm haze 4.6%.

Example 2 As a stabilizer, a 30 cm long, 90 mmφ diameter cylindrical aluminum ballast having a surface coated with polyvinylidene fluoride (surface tension: 25 dyne · cm ⁻¹ ) (with a 110 mmφ exit stabilizer) The inflation molding was performed under the same conditions as in Example 1 except for using. When the take-up speed was 75 m / min or more, the molding became slightly unstable. This is presumed to be due to the loss of heat resistance of polyvinylidene fluoride and sticking.

(Embodiment 3) An inflation film forming apparatus and an HMWH in which the same stabilizer as in Embodiment 1 was set
DPE (MFR; 0.04 g / 10 min, density 0.9)
50 g / cm ³ ), resin temperature 190 ° C., product film thickness 20 μm, take-off speed 45 m / min, folding width 4
The film was formed under the conditions of 50 mm (substantial expansion ratio; 3.18). Under these conditions, 10 consecutive days (240
Time) Continuous operation was possible without bubble break.

(Comparative Example 2) The same blown film device as in Comparative Example 1 and the same HMW HDP as in Example 3
E, resin temperature 190 ° C, product film thickness 20μ
m, a take-up speed of 45 m / min, and a folding width of 450 mm (substantial expansion ratio; 3.18).
Under these conditions, a bubble break occurred on the fifth day of continuous molding. The cause is thought to be that impurities such as additives were precipitated in the knurled portions (three places) of the aluminum stable body, and it is considered that these precipitated impurities caused the bubble cutting. Molding was restarted without cleaning, but bubble cutting occurred after about 3 hours.

[0035]

According to the present invention, as a bubble stabilizer for an apparatus used for forming a long neck type air-cooled blown film, a contact portion with a molten resin bubble is smooth, and the surface tension of the material is 30 dyne · cm. By using a stabilizer of ^-1 or less, inflation molding can be stably performed even with a resin having a low melt tension,
In addition, when the resin is a high melt tension resin, continuous operation can be performed for a long period of time as compared with a conventionally used stabilizer.

Further, when a plurality of disks are stacked in a plurality of stages at intervals with a plurality of disks, the stabilizer can be formed at a high speed even with a resin having a low melt tension, which can be conventionally formed only at a relatively low take-off speed. We have developed an inflation molding machine capable of molding and a film manufacturing method using it.

The film produced by the method of the long neck type of the present invention has higher strength than the film produced by the low frost line type.

[Brief description of the drawings]

FIG. 1 shows an example of a bubble stabilizer in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Die nozzle 2 Outlet stabilizer 3 Disk 4 Shaft 5 Air supply hole D Dice body

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-279316 (JP, A) JP-A-52-102376 (JP, A) JP-A-59-171620 (JP, A) JP-A-61- 262115 (JP, A) JP-A-56-46729 (JP, A) JP-A-58-18226 (JP, A)

Claims (5)

(57) [Claims] A molten bubble of a thermoplastic resin is extruded from an extruder,
In an inflation film forming apparatus that forms while supporting with a bubble stabilizer attached to a die, a contact portion of the bubble stabilizer with a molten resin is smooth,
The surface tension of the material is Ri 30dyne · ^cm-1 der below, or
Squashed disks or spheres
An inflation film forming apparatus characterized by using a stable body attached to a shaft . 2. The blown film forming apparatus according to claim 1, wherein the stabilizer has a shape in which a plurality of disks are stacked in multiple stages at intervals. 3. When a thermoplastic resin is formed into a film by a long neck type inflation method, the contact portion of the bubble stabilizer with the molten resin is smooth, and the surface tension of the material is 30 dyne · cm ^{−. 1} Ri der below, and double
A method for forming an inflation film, comprising using a stable body having a number of disks or spheres crushed thereon. 4. The method according to claim 3, wherein the thermoplastic resin is a linear low-density polyethylene (hereinafter, referred to as L-LDPE). 5. The method of forming a blown film according to claim 3, wherein the stabilizer has a shape in which a plurality of disks are stacked in multiple stages at intervals.