JPS6015121A - Method of forming blown film - Google Patents

Abstract

PURPOSE:To obtain the titled film excellent in the balance of strength without using a core or the like, by cooling a high-density polyethylene melt resin tubular body extruded from an annular extrusion die by an air ring apparatus having a specified action. CONSTITUTION:After a high-density polyethylene melt resin that has been melted and kneaded in an extruder is extruded from an annular slit 2 of an annular die 1, the melt resin tubular body is cooled by an air ring apparatus 7 that has a blowing outlet 6 directed outward and upward with respect to the direction of the extrusion of the resin to obtain the intended film. Preferably, the direction of the blowing outlet 6 is tilted 5-60 deg. outward and upward with respect to the direction of the extrusion of the resin. EFFECT:High speed molding becomes possible, and a blown film can be produced inexpensively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for inflation molding high density polyethylene resin.

The method of forming blown film usually involves melting and kneading resin using an extruder, extruding it into a tubular shape from an annular extrusion die, expanding it under internal pressure, cooling and assimilating it, and then winding it continuously. It is widely used for manufacturing films.

The most common method of this molding method is the method used to mold films such as low-density polyethylene and polypropylene, in which the molten resin tubular body extruded from an annular extrusion die is blown into the mold by air blown inside. As soon as it leaves the tube, it expands laterally, and this expanded tubular body is cooled by an air ring.

However, when this general method is applied to the production of high-density polyethylene resin films, strong orientation occurs in the direction of film propagation due to its crystallization properties, resulting in large directional changes in film strength and increased susceptibility to tearing. There is a drawback that high quality film cannot be obtained.

Therefore, as a method for forming a blown film of high-density polyethylene resin, as shown in FIG. The method used is to raise the container and then expand it horizontally using air blown into the interior. By adopting this method, it has become possible to produce a film with a well-balanced orientation between the longitudinal direction and the circumferential direction, and with improved tearability.

However, in the molding method using this core,
It has problems such as requiring a core, poor workability at the start of operation, narrow range of change in folding diameter of the product film, and poor cooling efficiency. Therefore, especially in order to change the fold diameter of the product film, it is necessary to replace at least the core, which has the disadvantage that continuous operation must be interrupted. Another drawback is that a large number of sets of annular dies and cores must be prepared in accordance with the folding diameter of the product film.

On the other hand, high-density polyethylene film has excellent strength and rigidity, but has drawbacks such as insufficient heat-sealability, transparency, and gloss. Therefore, in order to improve these drawbacks, a film made by laminating high-density polyethylene and low-density polyethylene has been proposed, which has excellent heat sealability and transparency.

Laminated films with improved gloss and impact strength are already known. However, when forming these laminated films, especially multilayer films that have low-density polyethylene in the innermost layer, the frictional resistance of the molten low-density polyethylene on the inner surface is large, causing a stick-slip phenomenon between it and the core. , a major drawback is that stable molding cannot be achieved. Furthermore, the molding temperature of low-density polyethylene is 15 to 40 degrees Celsius higher than the normal molding temperature, and from this point of view, the frictional resistance is large.
This also causes poor molding stability.

Therefore, in order to reduce the frictional resistance of the inner layer of low-density IJ ethylene, the molten resin tubular body is cooled by a cooling mandrel or a cooling ring, and then moved along the surface of a stabilizer attached to the tip of the annular die. A method has been proposed in which the film is then expanded to form a multilayer blown film (Japanese Unexamined Patent Publication No. 57-45031).

However, this method requires complicated equipment, cannot be applied to small dies, and is difficult to control cooling, so it has the disadvantage that high-speed molding cannot be performed in a stable state.

As a result of intensive research to eliminate the drawbacks of the conventional method as described above, the present inventors have found that when using an air ring device with a specific function, without using a core,
It has been found that it is possible to obtain a high-density polyethylene blown film with good stability and strength balance that is comparable to that of the prior art. The present invention was completed based on these findings.

That is, the present invention provides a method for forming a blown film in which a high-density polyethylene molten resin is extruded into a tubular shape from an annular extrusion die, expanded by internal pressure, cooled and solidified, and then continuously wound. The present invention relates to a method for forming a blown film characterized by cooling with an air ring device that expands diagonally outward.

An example of the blown film forming method of the present invention is as shown in FIG. 2, in which a high-density polyethylene molten resin melt-kneaded in an extruder (not shown) is extruded into a tubular shape from an annular slit 2 of an annular die 1. The cooling air from the air ring 7 whose outer periphery is arranged concentrically is blown out from the air outlet 5.6, and the air blowing direction of the air outlet 6 is made obliquely outward with respect to the resin extrusion direction, thereby achieving the Venturi effect. As a result, the molten resin tubular body is forcibly expanded and cooled to form a resin pavfre 8. After complete assimilation, the molten resin tubular body is continuously wound up via nip rolls.

The feature of the present invention is that it has the function of forcibly expanding the molten resin tubular body, rather than using air 1) for normal cooling (air blowing direction is in the resin extrusion direction or diagonally inward). The present inventors are the first to use an air ring device to form a blown film of high-density polyethylene, and it is superior to conventional forming methods in terms of film properties, forming stability, etc. It was quite surprising that the results were so good.

The air ring device used in the molding method of the present invention includes:
Those shown in FIGS. 5(a) and 5(b) are preferably used.

The cooling air blowing direction of this double slit air ring is not particularly limited to the blower outlet 5, but it is preferable that the blower outlet 6 is tilted outward at an angle of 5 to 60 degrees with respect to the resin extrusion direction. Moreover, the air volume from the air outlet is preferably the same as that of the air outlet 6) and the air outlet 5. In the present invention, the air ring device is mainly a double slit type air ring, but it is not limited to this type, and can utilize the Venturi effect, and has the function of expanding the molten resin tubular body, which is a feature of the present invention. Any material may be used as long as it is suitable. FIG. 4 shows an example of another air ring device. Here, 10 is an air chamber, and by combining this with a normal air ring 7,
The bubble shape targeted by the present invention can be obtained. In addition, as for the position of the air ring, in Fig. 2, the one provided above the annular die is shown, but as another example, it is also possible to expand the cylindrical body by raising it above the guide and cooling it to some extent. However, even in this case, the air ring functions to expand and is placed υ apart from the die.

The high-density polyethylene resin used in the present invention is a homopolymer of ethylene, ethylene and propylene.

It is a copolymer with α-olefin such as butene-1 or a mixture containing these as the main component, and has a density of 0.940.
~0.970 f/cd, preferably ~0.945
a, 96of/-, melt index (M) 0.
01-5.0p/10min, preferably 0.02-1.0
It is 7/10 minutes. The mixture includes not only high-density polyethylene, but also low-density polyethylene, linear low-density polyethylene, polypropylene,
Ethylene-propylene copolymer elastomer, ethylene-propylene-diene copolymer elastomer, styrene-butadiene elastomer, etc. can also be added as appropriate.

In addition, the molding method of the present invention is applicable not only to single-layer high-density polyethylene resin, but also to multilayer blown films with two or more layers of high-density polyethylene as the main component layer, for which the same molding method as conventional high-density polyethylene resin was used. This includes the molding of

Some of these multilayer films have improved heat-sealability, impact strength, transparency, printability, etc. by laminating low-density polyethylene resin on the inner layer, outer layer, or inner and outer layers of a high-density polyethylene resin layer. Here, the low density polyethylene resin is a homopolymer of ethylene, a copolymer of ethylene with an α-olefin such as propylene, butene-1, hexene-1,4-methyl-pentene-1, octene-1, or ethylene. -Vinyl acetate copolymer.

Ethylene-(meth)acrylic acid copolymer and mixtures thereof, etc.), density 0.900-0.94 CIP
/DI, preferably 0.910-0.940 f/d,
M work 0.1-20i710 minutes, preferably 0.2-1
This is from 01/1o. In addition, a multilayer film having an inner layer of low-density polyethylene, an intermediate layer of high-density polyethylene, and an outer layer of polyamide, polyester, polyvinylidene chloride, saponified ethylene-vinyl acetate copolymer, polypropylene, ionomer, polystyrene, etc. You can also do it. The layer ratio of high-density polyethylene resin layers in these multilayer films is 30% or more, usually 50%.
That's all. In the molding method of the present invention, the raw resin must contain 9
Pigments, anti-blocking agents, and slip agents from VC.

Antistatic agents, stabilizers, etc. can also be added.

The present invention has the great feature that even a film in which a low-density polyethylene resin is laminated as an inner layer as described above can be molded stably and at high speed in the same manner as a single-layer film without using special equipment.

The molding method of the present invention has been described above, but in order to further enhance the effects of the present invention, the moldability is further improved by providing a rectifying cylinder on the air ring.

In addition, by changing the height and diameter of the straightening tube, the folded diameter of the product can be changed arbitrarily without interrupting the molding process, making it possible to meet diversifying demands. moreover,
If necessary, a guide for the resin bubble and a second air ring may be provided as appropriate.

As detailed above, the blown film forming method of the present invention does not require equipment such as a core by adopting an air ring device having a specific function.
Furthermore, even with a multilayer film that uses low-density polyethylene resin as the inner layer, not only is there no need for equipment for cooling the die, but even though the 70-strike rate is low,
The excellent effect of stable molding at high speed can be obtained.

Moreover, it has the feature that the blow-up ratio can be changed over a relatively wide range (2.5 to 6) with one air ring equipment.

Therefore, in combination with the excellent physical properties of the obtained film, it is possible to provide an inexpensive film with low equipment costs and operating costs.

The molding method of the present invention will be explained below using examples.

Example 1 High-density polyethylene (density 0.955 f/ad, M process, 4 f/1 o) was melt-blended in an extruder, l1l (resin temperature 200°C), and a die diameter of 75 m1. Die lip 1. Extrude through a 2-fin annular extrusion die, send air inside to expand it, and use a double slit air IJ ring (
150fiI! 1) was used to cool the resin tubular body while expanding it.

Note that the cooling air blowing direction of the air ring was at an angle of 0 degrees from the first outlet and 20 degrees from the second outlet with respect to the resin extrusion direction. In the molding process, bubbles as shown in FIG. 2 were formed, and a high-density polyethylene resin blown film (W thickness 40 μm) with good bubble stability was obtained at a blowing ratio of 4.0.

Example 2 High-density polyethylene (density 0.9559
A mixture of 80% by weight (L/m, Mco, o55c/1o min) and 20% by weight of ethylene-propylene-dienter polymer (Mooney viscosity ML, +4 (1o o °C) 90), low density as outer layer resin Polyethylene (density 0.92
The resin temperature was 195℃ (inner layer) and 170"c.
The (outer layer) was melt-kneaded, introduced into an annular die with internal adhesive, and molded according to Example 1, with a layer ratio (inner/outer = 8).
/2) A two-layer film with a thickness of 120 μm was obtained with good molding stability. Table 1 shows the results of measuring the physical properties of the obtained film.

Reference Example In Example 2, a two-layer film was obtained by a conventional molding method using a core. Table 1 shows the results of measuring the physical properties of the obtained film.

Example 3 Ethylene-octene-1 copolymer (L-'LDPIC) (density 0.955 f/cd,
M-work 4.5p/10 min), high-density polyethylene as intermediate layer resin (density o, 954 f/d, M-work 0.9)
p/10 min) 80 wt- and ethylene-4-methylpentene-1 copolymer (L-LDPI) (density 0.9207
/al, M12.1) 710 min) 20 wt.
.

The wires were melted and mixed at 175°C (middle) and introduced into an annular die of die bonding type, with a die diameter of 12 (Imm-) and a die lip of 1.5.
Molding was carried out in accordance with Example 1, except that m was used, and a two-layer, three-layer film having a layer ratio of C2/6/2) and a thickness of 50 μm was obtained with good molding stability. Table 1 shows the results of measuring the physical properties of the obtained film.

Example 4 A blown film was obtained in the same manner as in Example 1 except that the air ring device shown in FIG. 4 was used.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing a conventional method for forming a blown film. FIG. 2 is a sectional view of a main part showing a method for forming a blown film according to the present invention. FIG. 6(&)■) is a partial detailed view showing an embodiment of the air ring device. FIG. 4 is a sectional view of a main part showing a method of forming a blown film using another air ring device. 1-Annular die, 2-: Il-shaped slit. 3-- Molten resin cylindrical body, 4- Central core. 5.6-Cooling air outlet, 7-Air ring. 8- Bubble, 9- Rectifier tube, 10- Air chamber Patent applicant Idemitsu Petrochemical Co., Ltd. -1"--127- Figure 2 Figure 3 (b) (a) 128-

Claims (1)

[Claims] (In an inflation film forming method in which high-density polyethylene molten resin is extruded into a tubular shape from an annular extrusion die, expanded by internal pressure, cooled and assimilated, and then continuously rolled up,
A method for forming a blown film, which comprises cooling a molten resin tubular body using an air ring device that expands the molten resin tubular body diagonally outward with respect to the resin extrusion direction.