JPS59111819A - Formation of multi-layered inflation film - Google Patents

Abstract

PURPOSE:To obtain a multi-layered inflation film havng a high strength and a high uniformity with lesser directivity by a method in which a simple device is provided at the lower end part of a molten resin cylinder molded of a resin having a great frictional resistance when melted for its inner layer and a high- density polyester resin for its outer layer. CONSTITUTION:A resin (e.g., low-density polyethylene resin, etc.) having a great frictional resistance when melted for an inner layer and a highdensity polyethylene resin for an outer layer are extruded from the annular slit 3 of an annular die to form a molten resin cylinder 4. The molten resin cylinder 4 is then expanded and cooled from outside by airing to the outside of the annular die 2 to form a multi-layered inflation film. In this case, an air sucker 7 is provided to the lower end of the molten resin cylinder 4, and air is passed through the opening 8 for airing 5 and a rectifying cylinder 9 provided around the resin cylinder 4 for cooling the cylinder to obtain a desired molding.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a multilayer blown film, and more specifically, even if the inner layer is a laminated film using a resin that has high frictional resistance when melted, such as low-density polyethylene, the inner layer may be made of high-density polyethylene. The present invention relates to a method for forming a multilayer blown film, which can be formed to the same 70-line height and blow ratio as when using a core (stabilizer), and which can be operated and controlled with simple equipment to quickly inspect the product.

Generally, multilayer blown film is formed by extruding a laminated film consisting of at least two layers through an annular slit of an annular die to form a molten resin cylinder, which is then expanded and cooled by an air ring from the outer periphery.

By the way, high-density polyethylene film is strong.

Although it has excellent stiffness, it has drawbacks such as insufficient heat sealability and transparency. Therefore, in order to improve this drawback, a film made by laminating high-density polyethylene and low-density polyethylene is known. When forming these laminated multilayer films, it is necessary to use low-density polyethylene as the inner layer film in order to improve heat sealability. However, when the inner layer is made of low-density polyethylene, the frictional resistance of the low-density polyethylene increases because the inner surface is in a molten state.

Therefore, when forming such a multilayer film,
If a core, which is commonly used for molding high-density polyethylene films, is used, there is a major drawback in that the molten resin cylinder does not move smoothly due to friction, making it impossible to mold a multilayer film.

Therefore, in order to reduce this frictional resistance, the molten resin tube is cooled by a cooling mandrel or cooling ring that is further provided inside the annular slit of the annular die, and then vertically aligned along the surface of the stabilizer attached to the tip of the annular gouer. A method has been proposed in which a multilayer blown film is formed by moving the film in the direction of
No. 31).

However, this method has disadvantages in that the apparatus is complicated and cannot be applied to small dies, and furthermore, it is difficult to control the cooling process and stable molding cannot be achieved.

On the other hand, if a core is not used, stable multilayer inflation film molding cannot be achieved unless the 70-strain line of the bubble is lowered or the blow ratio is lowered. Therefore, if the 70-stripe line of the bubble is lowered in order to stabilize molding, the productivity is lowered, the TD force direction ratio is lowered, and the strength is not balanced, which is physically undesirable.

The present invention solves these conventional drawbacks, and even if the laminated film uses a resin with high frictional resistance when melted, such as low-density polyethylene, as the inner layer, high-density polyethylene is used as the inner layer, and the center core is 7 similar to using
It is an object of the present invention to provide a method for molding a multilayer blown film that can be molded with zero strain height and blow ratio, using simple equipment, and whose operation can be easily controlled.

That is, in the present invention, a laminated film consisting of at least two layers is extruded through an annular slit of an annular die to form a molten resin cylinder, and then expanded and cooled from the outer periphery by an air ring on the outside of the annular die to form a multilayer blown film. In this method, a resin having high frictional resistance when melted is used as the inner layer, a high-density polyethylene resin is used as the outer layer, and the molten resin cylindrical body has an air intake means at the lower end and an air ring. The present invention provides a method for forming a multilayer blown film, characterized in that the molten resin tube is cooled by passing through a rectifying tube provided to surround the molten resin tube.

In the method of the present invention, a resin having high frictional resistance when melted can be used as the inner layer. Examples of such resins include low density polyethylene resins and polypropylene resins. Here, the low density polyethylene resin has a density of 0900 to n94 oy/d and a melt index (M engineering) of 05 to 101 iL.
7/10 minutes is used. Such low-density polyethylene resins include ethylene homopolymers, copolymers of ethylene and other α-olefins, such as ethylene-propylene copolymers, and ethylene-4-methylpentene-1 copolymers. These include straight-line low-density polyethylene (LLDPI). Furthermore, ethylene-vinyl acetate copolymer.

Examples include ethylene-unsaturated ester copolymers such as ethylene-acrylic acid copolymers, and mixtures thereof. Note that the content of components copolymerized with ethylene in the copolymer, ie, α-olefin and unsaturated monoester, should be determined in the range of 1 to 60 mol%, preferably 1 to 20 mol%.

In addition, as a polypropylene resin, the density is (188~
A material having αq2ti-/cdt and a melt index (M engineering) of 1 to 20 f710 is used. Such polypropylene resins include propylene homopolymers, random or block copolymers of propylene and other α-olefins, and the like.

Next, in the method of the present invention, a high-density polyethylene resin is used for the outer layer of the inner layer. Such high-density polyethylene resin has a density of CL940~o, q 70
g-/crdO is used, and not only ethylene homopolymers but also copolymers of ethylene and other α-olefins (α-olefin unit content 10 mol% or less) are used.
, such as ethylene-propylene copolymer, ethylene-
Butene-1 copolymers and mixtures thereof can be used. Additionally, rubbers and other olefin polymers can be added as needed.

In the method of the present invention, another layer (such as a second outer layer) may be further laminated on the outside of the above-mentioned outer layer to form a multilayer film having three or more layers. As such a resin, a low density polyethylene resin similar to that of the inner layer should be used.
The transparency of the film can be improved. Also, gellipropylene.

Polyamide, ethylene vinyl acetate copolymer, saponified products thereof, etc. can also be used.

As shown in FIG. 1, the method of the present invention is to extrude a laminated molten resin 1 consisting of at least two layers through an annular slit 6 of an annular die 2 of an extruder to form a molten resin cylindrical body 4, and then expand the annular die 2. The multilayer blown film 6 is cooled from the outer periphery by an air ring 5 provided on the outside of the multilayer blown film 6.
When molding, the above-mentioned various resins are used as the inner and outer layer films, and the molten resin cylindrical body 4 has an air intake means 7 at the lower end and an opening 8 of the air ring 5.
The molten resin cylindrical body 4 is cooled by passing through a rectifying tube 9 provided to surround the molten resin cylindrical body 4.

That is, the molten resin is extruded from the annular slit 3 of the annular die 2 of the extruder to form a molten resin cylinder 4, and then air is blown into it to expand it. The multilayer blown film 6 is cooled from the outer periphery by the cooling air that is blown out, and a feature of the present invention is that a device provided with a rectifying cylinder 9 is used at this time.

The rectifying cylinder 9 used in the method of the present invention must be provided so as to completely surround the molten resin cylinder 4 and the opening 8 of the bore ring 5. Further, an air intake means 7 is provided at the lower end of the rectifier cylinder.

In this embodiment, as the air intake means 7, a hole of an arbitrary shape is bored in the rectifier tube 9 to serve as an air intake hole. This air intake means 7 effectively prevents the inside of the rectifying cylinder from being depressurized due to the Venturi effect, and can be provided at multiple locations as appropriate depending on the degree of depressurization. For example, depending on the size of the air intake hole, is 5 holes φ, 50~5(
It is preferable to provide 10 locations.

Further, the shape of the rectifying cylinder is not particularly limited as long as it is cylindrical, but a cylindrical one is usually used. The size of the rectifying cylinder is 1.5~, where D is the die diameter! 1. OXD, with a height of 2-8XD, preferably 3-6XD. There are no particular restrictions on the material of the rectifier tube.

The molten resin cylinder is cooled by passing through the rectifying cylinder 9, and then expanded by the air sealed inside the cylinder to form a multilayer blown film.

Note that the extrusion temperature (molding die temperature) is usually 170 to 210
℃, the thickness of the laminated film is 10 to 200μ, preferably 20 to 120μ, and the ratio of the inner and outer layer thickness is inner layer / outer layer = 5 to 50 / 95 to 50, preferably 15 to 3
o/a 5-7o. Moreover, the blow ratio is usually 4 to 5.

According to the method for molding a multilayer blown film of the present invention having such a configuration, even if the inner layer is a laminated film using a resin that has high frictional resistance when melted, such as low density polyethylene, high density polyethylene can be used as the inner layer. In addition, molding with a 70-strain height and blow ratio similar to that of 7 is possible using a core. Therefore, the resulting film has high strength, has little directionality, and is uniform.

Moreover, according to the method of the present invention, a multilayer blown film can be formed using simple equipment without using complicated equipment unlike conventional methods. Moreover, it has the great feature of being able to form films of various sizes, including those with a small gooey diameter, at a high blow ratio. Hence, equipment costs.

Operating costs are low and energy can be saved.

Furthermore, it has practical effects such as easy operation control such as cooling control, excellent molding stability, and high-speed molding.

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

Examples 1 and 2 The inner layer is made of low density polyethylene (density o, q 20 y-
/d.

M engineering=! Loy/1o min), the outer layer is high-density polyethylene (density (1955i/Cfft9M1 = αo5y/I
o minutes), and the second outer layer on the outside of the outer layer is made of low-density polyethylene (
density a92ofi-/d+M knee xoy71o), and the layer thickness ratio of inner layer/outer layer/second outer layer is 2/
(A multilayer inflation film of S/2 with a layer thickness of 40 μm was molded under the following conditions.

Each resin was extruded using an extruder with a diameter of 75 wφ.

The film was formed by extrusion and expansion at 1 m of Glylip and a die temperature of 180°C. At this time, as shown in FIG. 1, a rectifying cylinder having a diameter of 165 rtva and a height of 550 mm was used so as to surround the opening of the air ring and the molten resin cylinder. Note that there are 3 fittings at the bottom end of this rectifying cylinder.
200 intake holes were drilled.

Table 1 shows the evaluation results of the moldability and strength of the obtained film.

Comparative Example 1 In Example 1, when molding was performed using a core (stabilizer) commonly used in high-density polyethylene molding methods instead of the rectifying tube, the molten resin adhered to the core and the film formation was interrupted. I couldn't do it.

Comparative Example 2 In Example 1, a 150+++ mpl sample was prepared in which the straightening tube was not used, and the die had a first discharge slit in the resin extrusion direction and a second discharge slit in the upper part thereof in a direction approximately 20 degrees outward in the resin extrusion direction. A multilayer blown film was obtained by molding using a double slit air ring. Table 1 shows the evaluation results of the moldability and strength of the obtained film.

Table 1-z, based on TIS"Z 1702 ◆2 Film impact method (The film was fixed in a ring shape, the film was punched out with a pendulum with a 1-inch impact head, and the energy required was measured.) (Using Seiki Seisakusho film impact tester)

[Brief explanation of drawings]

FIG. 1 is a sectional view of essential parts of a molding apparatus used in the method for molding a multilayer blown film according to the present invention. 1... Laminated molten resin, 2... Annular die. 6... Annular slit, 4... Molten resin cylindrical body. 5... Air ring, 6... Multilayer blown film, 7... Intake means, 8... Air ring opening, 9... Rectifier tube patent applicant Idemitsu Petrochemical Co., Ltd.

Claims (2)

[Claims] (1) A laminated film consisting of at least two layers is extruded through the annular slit of an annular die to form a molten resin cylinder, and then expanded and cooled from the outer periphery by an air ring on the outside of the annular die to form a multilayer blown film. In this method, a resin having high frictional resistance when melted is used as the inner layer, a high-density polyethylene resin is used as the outer layer, and the molten resin cylindrical body has an air intake means at the lower end and an opening of the air ring. A method for forming a multilayer blown film, wherein the molten resin cylinder is cooled by passing it through a rectifying cylinder provided so as to surround it. (2) The method according to claim 1, wherein the resin having high frictional resistance when melted is a low-density polyethylene resin or a polypropylene resin.