JPS61286117A - Molding of blown film and equipment thereof - Google Patents

Abstract

PURPOSE:To stabilize a bubble and consequently mold a blown film with favorable thickness accuracy at high speed by a method wherein the diameter of the bubble formed by being extruded from a die is once expanded and, after that, contracted by blasting cooling air against the bubble and finally expanded again at the blow-up ratio of 2 or more. CONSTITUTION:A bubble is formed by extruding polyethylene, especially high density polyethylene with melt flow rate (MFR) of 0.01-2.0, from a die 1. Firstly, the diameter of the bubble is expanded 1.0-1.19 times or preferably 1.05-1.15 times as large as the lip bore A of the die by means of a first stabilizer 3. Secondly, the diameter of the bubble is contracted on the downstream side of the first stabilizer 3 by blasting cooling air from an air ring 2 against the bubble. Finally, the resultant bubble is expanded again at the blow-up ratio of 2 or more in order to obtain a blown film. A blown film with favorable thickness accuracy can be molded at high speed by employing the amount of blown-off air and take-off speed, which are respectively about 2.2 times as large as those used in the conventional method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming a blown film and an apparatus therefor, which are capable of forming a blown film at high speed.

[Prior art] When attempting to form a blown film at high speed using the inflation method, for example, Japanese Patent Publication No. 55-2180
A method using a bubble stabilizer as in the publication No. 1 is known. However, although high-speed molding is possible to some extent with this method, if higher-speed molding is attempted, it is necessary to discharge a large amount of air at a higher speed than the air ring in order to cool the bubbles. In that case, the bubble shakes and becomes unstable where the air hits the bubble, reducing thickness precision and hindering high-speed molding.

In addition, in JP-A-55-154126, the position of the first stabilizer is downstream of the air ring outlet, and a phenomenon similar to the above occurs between the die and the first stabilizer, especially near the die outlet, resulting in high speed. Bubbles tend to become unstable during molding.

This is because the melt tension of the bubble is smaller as it approaches the die exit, and if the diameter of the first stabilizer is in the range of 1.2 to 2.5 times the diameter of the die slip, the friction between the bubble and the stabilizer increases. This is because the resistance is large and the bubbles get caught on the stabilizer during molding.

[Object of the Invention] Accordingly, an object of the present invention is to provide a method and apparatus for forming a blown film that can stabilize bubbles and form a blown film with good thickness and thinness precision at high speed.

[Structure of the Invention] According to the present invention, when forming a blown film by the inflation method, the diameter of the bubble extruded from the die and formed is expanded to 1.0 to 1.19 times the die slip diameter, and then A method for forming a blown film is provided, which comprises applying cooling air to reduce the diameter of bubbles, and then expanding the bubbles to a blow-up ratio of 2 or more.

Further, according to the present invention, a disk-shaped first stable body with a diameter of 1.0 to 1.19 times the die slip diameter is provided upstream of the air ring outlet, and a disk-shaped first stable body with a diameter of 1.0 to 1.19 times the diameter of the die slip is provided downstream of the first stable body. is the first
A cylindrical second stable body smaller than the stable body is provided, and the diameter is 1.1 times to 1.1 times the diameter of the second stable body on the downstream side of the second stable body.
There is provided a blown film forming apparatus characterized in that a disk-shaped third stabilizer with a magnification of 5 times is provided so that its end surface is in contact with the bubble.

[Operations and Effects of the Invention] Therefore, the first stabilizer stabilizes the bubble, the second stabilizer prevents the bubble from shaking, and the third stabilizer stabilizes the frost line of the bubble, improving the cooling effect. As a result, a blown film with good thickness and thinness accuracy can be formed at high speed with an air blowing amount and take-up speed that is approximately 2.2 times the normal amount.

[Preferred Embodiment] In carrying out the present invention, the raw material is polyethylene, especially MF
It is preferable to use high-density polyethylene having an R of 0.01 to 2.0.

In practicing the invention, it is preferred that the diameter of the first stabilizer is 1.05 to 1.15 times the diameter of the die slip.

In the practice of the present invention, the second stabilizer is brought into contact with the constriction of the bubble and preferably has a diameter of 1.05 to 1.5 times the diameter of the constriction in the absence of any stabilizer.

[Example] The present invention will be described in detail below with reference to the drawings.

In FIG. 1, an air ring 2 for blowing out cooling air is provided downstream of a die 1 having a lip diameter A that is connected to an extruder (not shown). On the upstream side of the air outlet of the air ring 2, there is a first stable member 3 in the form of a disc, the diameter B of which is 1.0 to 1.19 times, preferably 1.05 to 1.15 times, the diameter A of the die slip. is provided. On the downstream side of the first stabilizer 3, the diameter C is smaller than the diameter B of the first stabilizer 2, and the diameter G of the constriction F of the bubble E when no stabilizer is present as shown in FIG. 1°05 to 1
．． A cylindrical second stabilizer 4 of five times the size is provided. The downstream side, that is, the upper edge of the second stable body 4 has a second diameter.
A third stable member 5 having a disk shape and having a diameter C of 1°1 to 1.5 times the diameter C of the stable member 4 is provided so that its end surface is in contact with the bubble E.

For molding, preferably polyethylene, especially MFR 0
．． 01 to 2.0 high density polyethylene is extruded through the die 1 to form a bubble, and the diameter of the bubble is adjusted by the first stabilizer 2 to 1.0 to 1.19 times the diameter of the die slip, preferably 1.05. Or give 18 doses to 1815 times. At this time, if it is smaller than 1°0 times, the stabilizing effect of the bubble will be small, and if it is larger than 1°19 times, the molten bubble will get caught on the first stabilizer 2, making it impossible to form.
5 to 1.15 times, and since the first stabilizer 2 is disc-shaped, the gm resistance with the bubble is small, so the stabilizing effect of the bubble is large.

Next, cooling air is blown onto the bubble from the air ring 2 on the downstream side of the first stabilizer 2 to reduce the diameter of the bubble. On this occasion,
The second stabilizer 4 prevents the bubble from swinging, and the bubble is narrowed to contact the second stabilizer 4 at the constriction F. Note that if the diameter C of the second stabilizer 4 is made smaller than the diameter G of the constriction part F of the bubble in the case where no stabilizer is present, the effect of preventing vibration of the bubble will be reduced, and if it is made larger, the strength of the blown film will be reduced. Next, the bubble is expanded to a blow-up ratio of 2 or more to obtain a blown film. At this time, the third stabilizer 5 stabilizes the 70 lines H of bubbles and improves the cooling effect. In this way, a high quality blown film with good thickness and thinning precision is obtained.

Normally, when forming a 25 μm blown film, there was a conventional take-up speed limit of 30 m/min in order to obtain a high quality product, but the method of the present invention allows the air blowing speed to be reduced to approximately 30 m/min. 2.2, and the take-up speed was 657 FL/min.

In other words, even if the speed is 2.2 times, it is possible to perform molding at a sufficiently high speed. Note that even if the third stabilizer 5 is omitted, the take-up speed is still 60%.
If it is about m/min, a high quality blown film can be formed.

The present invention will be explained in more detail by giving examples and comparative examples below. Examples 1 to 3, Comparative Examples 1 to 7 Using the high-density polyethylene HDPE shown in Figure 2, bubbles were extruded and expanded from a die with a die slit diameter of 75 m installed in an extruder with a heat insulating extrusion type of 60 Φ, and air rings were formed. The diameter of the bubble was made thinner by applying cold 1fi, and the molding of a 25 μm thick blown film with a blow-up ratio of 4 was attempted under various molding conditions. The symbols indicating the obtained stability (score) are as follows.

Continuous production possible △ Possible to produce but slightly unstable X Production difficulties [summary]

Claims (2)

[Claims] (1) When forming an blown film using the inflation method, the diameter of the bubble extruded from the die is 1.0 to 1.19 of the die slip diameter.
A method for forming a blown film, which comprises expanding the film to twice its original size, then applying cooling air to reduce the diameter of the bubble, and then expanding the film to a blow-up ratio of 2 or more. (2) A disk-shaped first stable body with a diameter of 1.0 to 1.19 times the die slip diameter is provided upstream of the air ring outlet, and a first stable body with a diameter of 1.0 to 1.19 times the diameter of the die slip is provided downstream of the first stable body. A cylindrical second stable body smaller than the body is provided, and a disk-shaped third stable body with a diameter of 1.1 to 1.5 times that of the second stable body is provided on the downstream side of the second stable body. 1. A blown film forming apparatus, characterized in that the blown film is provided so as to be in contact with a bubble.