JPH0321429A - Method for molding thermoplastic film and air ring used therefor - Google Patents

Abstract

PURPOSE:To make it possible to continuously mold high quality thermoplastic resin blown film over a long period of time by a method wherein the lip of an air ring is heated. CONSTITUTION:In a blow extrusion equipment using a dual lip type air ring equipped with a heating device, the lip 5 of a lower air ring is heated for molding low density polyethylene, to which oleic acid amide as lubricant and fatty polyhydric alcohol monoester as antistat are added, over a long period of time. Further, the heating device consists of an elastic heater 3, a temperature detector 4 and a temperature controller 6.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a blown film that can continuously form a high-quality film for a long period of time when a thermoplastic resin tubular film is formed by the inflation method. Regarding the molding method. [Prior art] Thermoplastic resin blown films are used for packaging,
It is widely used for agricultural purposes, industrial materials, etc. Such blown films are blended with various additives such as lubricants and antistatic agents depending on the intended use.

However, since these additives are low molecular weight substances, they partially vaporize immediately after leaving the tubular die during inflation molding, and this vapor comes into contact with the air ring lip and liquefies and adheres to the air ring lip. Moreover, this liquid becomes droplets due to the cooling air from the air ring and adheres to the film, resulting in a decrease in commercial value.

In order to prevent these problems, conventional methods have been to stop production after a certain period of time, remove the liquid additives that have adhered to the air ring lip, and then start production again, or to reduce the amount of additive added. It is being produced using plastic resin.

[Problems to be Solved by the Invention] However, if the liquid substance adhering to the air ring lip is removed after stopping production, there is a problem that a lot of loss occurs due to stopping production. Furthermore, if the amount of additives added is reduced, there is a problem that the commercial value of the resulting film decreases.

In view of the above, the present invention aims to solve these problems and provide a method for forming a blown film that can continuously form a high quality thermoplastic resin blown film for a long period of time.

[Means for Solving the Problem] As a result of intensive research to achieve the above object, the present inventors found that, immediately after the thermoplastic resin is extruded from the tubular die during inflation molding of Netsucho plastic resin, Some of the additives added to the thermoplastic resin, such as slip agents and antistatic agents, vaporize, contact the air ring lip, cool and liquefy, and adhere to the air ring lip as droplets. However, it was discovered that the cooling air from the air ring scattered the liquid and caused droplets to adhere to the film surface. Based on this knowledge, the inventors have discovered that by heating the lip of the air ring, the vapor of the additive can be prevented from coming into contact with the air ring lip and being cooled and liquefied, thereby completing the present invention.

That is, the present invention consists of: (1) extruding molten thermoplastic resin heat from a tubular die;
A method for forming a blown film that is cooled by an air ring, characterized in that the lip of the air ring is heated; This air ring features a heating device installed on the lip. Examples of the thermoplastic resin in the present invention include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl acetate copolymer,
Examples include polyolefin resins such as polybutene-1 and poly-4-methylbentene-1, polystyrene, nylon, and polyester.

The additives referred to in the present invention include lubricants such as oleic acid amide and erucic acid amide, fatty acid polyhydric alcohol monoesters,
IF1 of alkylamines, etc. They are organic low molecular weight substances such as antifogging agents, antifogging agents such as higher fatty acid amide, antioxidants such as 2,6-di-tert-butyl-4-methylphenol, and ultraviolet absorbers.

There is no upper limit to the temperature of the lip of the air ring of the present invention, but it is preferably not so high as to adversely affect the film and inflation molding. As an example, in the case of polyethylene, it is preferably 60°C to 250°C, more preferably 100°C to 180°C, even more preferably 1
The temperature is 40°C to 180°C.

In the present invention, methods for raising the temperature of the lip of the air ring include an external heating method of heating from the outside with infrared rays or the like, and an internal heating method of attaching an electric heater or the like to the lip of the air ring. The method of increasing the temperature of the lip of these air rings is not particularly limited, and any method may be used.

It is desirable to control the temperature of the air ring lip to a constant temperature, and it is more preferable to install a control device such as a temperature regulator.

The heating portion of the lip of the air ring of the present invention may be either outside or inside the lip.

Although the effects of the present invention do not depend on the type of air ring, it is particularly effective when using a rapidly cooling multi-stage blowout air ring. In the case of a multistage blowout air ring, only the lip of the upper ring may be heated, but it is preferable to heat the lips of all the rings or only the lip of the lower ring because the effect is greater.

[Function] Heating the lip of the air ring in the present invention serves to prevent the vaporized component of the additive from coming into contact with the area, being cooled, and liquefied.

[Example] The present invention will be explained in detail below with reference to Examples.

Example 1 In an inflation molding apparatus using a dual-lip air ring with a heating device as shown in FIG. , low-density polyethylene to which 0.1 wt% fatty acid polyhydric alcohol monoester was added as an antistatic agent was molded for 10 hours, and the additive droplets in the 5 parts of the lower air ring and the processing stability during molding were processed. observed. The results are shown in Table 1. In FIG. 1, 1 is a tubular die, 2 is a tubular resin, 3 is an electric heater, 4 is a temperature detector, and 6 is a temperature controller.

Example 2 The results shown in Table 1 were obtained in the same manner as in Example 1, except that the temperature of the air ring lip was 300°C.

Comparative Example 1 The results shown in Table 1 were obtained in the same manner as in Example 1 except that the air ring lip was not heated. The temperature of the lip at this time was 40°C. Table 1 (Note 1) Status of droplet adhesion on lip.

◎: No liquid adhesion.

O: The lip is slightly damp.

×: Droplets are attached.

(Note 2) Molding stability O: Extremely stable.

Δ: The tube is slightly swaying.

×: Cannot be molded.

[Effects of the Invention] The inflation molding method of the present invention allows high-quality films to be continuously formed for a long period of time.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of an air ring with a heating device according to the present invention. 1: Tubular die 2: Tubular resin 3: Electric heater 4: Temperature detector 5: Lower air ring lip 6: Temperature controller

Claims (2)

[Claims] (1) A blown film forming method in which molten thermoplastic resin heat is extruded from a tubular die and cooled by an air ring, the method comprising heating the lip of the air ring. (2) An air ring for an apparatus for inflation molding thermoplastic resin, characterized in that a heating device is provided on the lip of the air ring.