JPH08258111A - Method and apparatus for molding inflation film - Google Patents

Abstract

PURPOSE: To efficiently mold an inflation film particularly even when a resin in which liquid additive is added is used. CONSTITUTION: Raw material resin is melted and kneaded by a twin-screw extruder 3, the pressure of the melted resin is raised by a pump 4, the pressurized melted resin is extruded via a circular die 5, and then expanded to mold into a tubular film 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inflation film molding method and molding apparatus for molding a tubular film by extruding a molten resin through a circular die and then expanding the resin.

[0002]

2. Description of the Related Art In the blown film molding method,
The pelletized raw material resin is melted and kneaded by an extruder, the molten resin is extruded through a circular die (spiral die, etc.) to form a tubular resin bubble, and air is blown into the resin bubble to form a resin bubble. It is expanded and cooled to form a tubular film having a required diameter.

The circular die used in such an inflation film molding method has a large pressure resistance due to its internal structure. Therefore, generally, a high extrusion pressure is required to extrude a molten resin having a high viscosity through the circular die. Therefore, conventionally, as an extruder for blown film molding, resin melting
A single screw extruder capable of kneading and generating a high extrusion pressure is used. This single-screw extruder is configured by arranging one screw in a cylinder having a required length, and by rotating the screw, the molten resin is advanced in the cylinder, and the molten resin is advanced to the front end of the cylinder. Generate extrusion pressure.

By the way, in the blown film molding method, various properties can be changed by adding various additives to the raw material resin. Examples of the additive include a pressure-sensitive adhesive that imparts tackiness to the film, an antifogging agent that prevents the film from fogging, and the like.

[0005]

However, when a liquid additive of various additives is added to the raw material resin, the additive causes the molten resin to slide on the inner surface of the cylinder. Here, the single-screw extruder has a structure in which the forward force is generated by the rotation of the screw only when there is sufficient friction between the inner surface of the cylinder and the molten resin. Therefore, if the molten resin slips on the inner surface of the cylinder, the necessary forward force cannot be obtained, and the extrusion of the molten resin becomes unstable. A method in which a twin-screw extruder is used as a melting / kneading machine to once form pellets containing an additive, and the pellets are melted again by a single-screw extruder and extruded through a circular die is conventionally used. Two extruders are required, and the problem of increasing the size of the apparatus and the problem of inefficiency remain.

The present invention has been made in view of the above circumstances, and in particular, an inflation film molding method and a blown film molding method capable of efficiently forming a film even when a raw material resin containing a liquid additive is used. It is an object of the present invention to provide a molding device using.

[0007]

In order to achieve the above object, the blown film molding method of the present invention comprises:
The raw material resin is melted and kneaded by a twin-screw extruder, the pressure of the molten resin is increased by a pump, the pressurized molten resin is extruded through a circular die, and then expanded to form a tubular film.

Further, the blown film molding apparatus of the present invention has a twin-screw extruder for melting and kneading the raw material resin, a pump for increasing the pressure of the molten resin melted by the twin-screw extruder, and a pressure increase by the pump. And a film forming means for forming a tubular film by extruding the molten resin through a circular die and then expanding the molten resin.

[0009]

In these blown film forming methods and forming apparatuses, the resin containing the liquid additive is sufficiently melted and kneaded by the twin-screw extruder and supplied to the suction side of the pump. Here, the twin-screw extruder does not generate a high forward force (pushing force) unlike the single-screw extruder, but is hardly affected by the magnitude of the friction between the molten resin and the cylinder, and is melted by the two screws. It has a structure that can reliably send the resin forward. Therefore, the molten resin to which the liquid is added can be smoothly supplied to the pump. Further, by using such a twin-screw extruder and a pump together, it is possible to obtain a sufficient extrusion pressure and a stable extrusion amount,
A high quality blown film can be formed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an inflation film molding apparatus according to the present invention. The molding apparatus 1 includes a drive machine 2 in which a motor and a speed reducer (neither of which are shown) are housed, a twin-screw extruder 3 driven by the drive machine 2, and a front side of the twin-screw extruder 3. The gear pump 4 is provided, and the circular die 5 is connected to the discharge port 4a of the gear pump 4.

The twin-screw extruder 3 accommodates a cylinder 3a extending in the left-right direction inside, as indicated by a dotted line in the figure, and further, inside the cylinder 3a, two cylinders extending in parallel with each other in the left-right direction. Screw 3b, 3b. These screws 3b, 3b have grooves (not numbered) formed in a spiral shape around the axis, and both screws 3b
b and 3b are meshed with each other such that a portion between the grooves on the opposite side protrudes into each groove. And
Both screws 3b and 3b are rotationally driven in the same direction by the driving machine 2.

The rear end of the twin-screw extruder 3 (right end in the figure)
A raw material feeder 7 is arranged in the section. The raw material supply device 7 stores a raw material resin in pellet form in advance, and a constant raw material resin is supplied to the cylinder 3a by a feeder (not shown).
Is supplied to the inside of the rear end. When both screws 3b and 3b are rotationally driven by the driving machine 2, each groove and the cylinder 3a are
The raw material resin existing in the space surrounded by the inner surface of the is conveyed forward (to the left in the figure) while circulating in the groove. Further, the cylinder 3a is heated by a heater (not shown), and the raw material resin is melted in the cylinder 3a.

Further, behind the twin-screw extruder 3, there are arranged additive feeders 8 and 8 '. A liquid additive is stored in advance in these additive feeders 8 and 8 ', and a liquid additive of a fixed ratio to the resin amount is supplied into the cylinder 3a by a discharge mechanism (not shown). Here, in this example, linear low-density polyethylene (LL) was used as the raw material resin.
DPE) is used to add 10% of an adhesive (polybutene) which is a liquid additive and 1% of an antifogging agent (surfactant) to this raw material resin. Therefore, the molten resin becomes slippery on the cylinder 3a to the extent that it cannot be extruded by the single-screw extruder. However, according to the twin-screw extruder 3, even the molten resin that is slippery with respect to the cylinder 3a can be smoothly conveyed. In this way, the molten resin to which the liquid additive is added is conveyed forward while being sufficiently kneaded by the rotation of the screws 3b and 3b, and is discharged from the outlet 3c of the extruder 3.

The gear pump 4 increases the pressure of the molten resin delivered from the extruder 3. The maximum front end pressure in the cylinder 3a cannot be increased so much in order to stably and continuously carry out the resin from the twin-screw extruder 3.
The extrusion pressure larger than the maximum front end pressure can be applied to the resin, and the resin can be supplied to the circular die 5. The gear pump 4 also has a role of constantly supplying a stable amount of molten resin to the circular die 5. The discharge side of the gear pump 4 has a filter 10
Is provided. The filter 10 filters and removes foreign matters contained in the molten resin discharged from the gear pump 4.

The circular die 5 comprises a spiral die, and the molten resin discharged from the gear pump 4 is extruded as a cylindrical resin bubble 11 through the die 5. Here, the spiral die generally has a large pressure resistance because a plurality of spiral flow passages are formed therein. However, if the pressure of the molten resin is increased by using the gear pump 4, the necessary extrusion pressure can be obtained. Obtainable.

An air supply path 5a is formed inside the circular die 5 as shown by a dotted line in the figure, and air is blown into the resin bubble 11 through the air supply path 5a to cause the resin bubble 11 to flow. The pressure inside increases, which expands radially. Also, the resin bubble 11
Is cooled by an external cooling device 6 arranged so as to surround the outer periphery of the resin bubble 11 in the vicinity of the upper surface (extrusion port) of the circular die 5. The tubular film thus formed to have a required diameter is pulled up by a pinch roller (not shown), folded into a sheet, and further wound by a winder (not shown).

In the above examples, the case where two kinds of liquid additives (for example, an antifogging agent and an adhesive agent) are added to the raw material resin has been described, but the inflation film molding method and molding apparatus of the present invention are It can be used when one kind of additive is added to the raw material resin or when no additive is added at all. Further, in the above embodiment, the case where the spiral die is used as the circular die has been described. However, in the molding method and the molding apparatus of the present invention, a circular die other than the spiral die can be used. Further, the molding method and the molding apparatus of the present invention are capable of extruding one layer of the resin when performing so-called multi-layer molding of resin (when a plurality of extruders are used to extrude the resin into a multilayer shape). It can also be used.

[0018]

As described above, the blown film molding method and molding apparatus of the present invention are capable of sufficiently melting a resin or the like containing a liquid additive by a twin-screw extruder.
It is configured to knead and apply an extrusion pressure necessary for extrusion through a circular die by a pump to the molten resin (and supply a fixed amount of the molten resin to the circular die). Therefore, by using the present molding method and molding apparatus, it is possible to reliably mold a high-quality inflation film even when a liquid-added resin or the like that is difficult to stably extrude with a single-screw extruder is used.

[Brief description of drawings]

FIG. 1 is an overall view of an inflation film molding apparatus according to the present invention.

[Explanation of symbols]

 3 Twin screw extruder 4 Gear pump 5 Circular die 8,8 'Additive supply machine 11 Resin bubble

Claims (2)

[Claims] 1. A raw material resin is melted and kneaded by a twin-screw extruder, the pressure of the molten resin is increased by a pump, the pressurized molten resin is extruded through a circular die and then expanded to form a tubular film. Inflation film molding method. 2. A twin-screw extruder for melting and kneading a raw material resin, a pump for increasing the pressure of the melted resin melted by the twin-screw extruder, and a method of extruding the melted resin whose pressure is increased by a pump through a circular die. An inflation film forming apparatus comprising a film forming means for expanding and forming a tubular film.