JPH07100923A - Production of shrink film - Google Patents

Abstract

PURPOSE:To increase an emitting amt. and to efficiently provide stable shrinkage characteristics without performing water cooling after emission, the drying treatment of the water bonded to the surface of a tube and the reheating of the cooled tube. CONSTITUTION:In producing a shrink film by molding a film according to an inflation method, the molten resin eitted from the leading end of a die 2 is quenched to temp. within the range of + or -50 deg.C of the m.p. of the resin while the cooling air from the internal cooling cylinder 5 provided to the loading end of an inner mandrel part and the cooling air from the external cooling cylinder 7 provided around the internal cooling cylinder 5 in front of an outer die part are sprayed on both inner and outer surfaces of the molten resin to be raised so as to hold the diameter of the die and subsequently blown up so as to have a diameter of two or more times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a shrink film used for packaging foods and food containers.

[0002]

2. Description of the Related Art Conventionally, there are two types of shrink films, a single layer film made of one resin composition and a multilayer film made by laminating a plurality of resins. In the production of these films by an inflation method, the film is formed into a tubular shape. It is extruded into water, and once solidified by water cooling, it is pressure-bonded with pinch rolls, and while cooling and pressure-bonding the tube is reheated between two sets of pinch rolls, air is injected into the bubbles and expanded by its internal pressure. Was adopted. In this method, since the tube comes into contact with water, the addition of an antifogging agent, which is an indispensable property as a film for food packaging, is restricted in providing antifogging property, and sufficient antifogging property cannot be obtained. Since the water adhering to the surface needs to be dried, there is a decrease in the line speed, adhesion of water droplets after drying, etc., temperature control is required during the reheating process to expand the tube, water cooling or Because the control width during reheating is narrow, the amount of resin extruded and discharged is restricted.
For the same reason, there are drawbacks such as a narrow selection range of the resin constitution of the film to be formed, and there has been a problem that the shrinkage rate and shrinkage force as the shrink film are not stable.

[0003]

Therefore, the object of the present invention is to eliminate the drawbacks of the above-mentioned prior art such as water cooling after discharge, drying treatment of water adhering to the tube surface, and reheating of the cooling tube. Another object of the present invention is to provide a method for producing a shrink film that has a large discharge amount, is efficient, and has stable shrinkage characteristics.

[0004]

According to the method for producing a shrink film of the present invention, in forming a film by the inflation method, the molten resin discharged from the tip of the die is provided from both inside and outside, particularly at the tip of the inner mandrel portion. The cooling air from the internal cooling cylinder and the cooling air from the external cooling cylinder mounted around the internal cooling cylinder in front of the out die section rapidly cools the resin to a temperature within ± 50 ° C of the melting point of the die. After launching with the diameter unchanged,
It is characterized in that it is blown up to a diameter twice or more.

[0005]

In the method of manufacturing the shrink film of the present invention,
The molten resin discharged from the tip of the die is supplied from both inside and outside, especially by the cooling air from the internal cooling cylinder provided at the tip of the inner mandrel and the cooling air from the external cooling cylinder mounted in front of the out die part. , The die diameter is raised to a temperature within ± 50 ° C. of the melting point of the resin, and the die diameter is increased, so that the blow-up with a diameter twice or more can be stably performed.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the figure, 1 is an extruder, and 2 is an annular die, which comprises an inner mandrel portion 3 and an out die portion 4. Reference numeral 5 denotes an internal cooling cylinder attached to the front of the inner mandrel portion 3 of the die 2 and having a diameter smaller than the diameter of the die 2. A slit 6 for discharging cooling air is provided in the height direction on the outer peripheral side wall of the lower portion thereof. It is provided over steps. Reference numeral 7 denotes an annular external cooling cylinder attached to the front of the out-die portion 4 of the die 2 and having an inner diameter larger than the diameter of the die 2. The external cooling cylinder 7 has a height lower than that of the internal cooling cylinder 5 and has a slit 6 of the internal cooling cylinder 5. A number of partitions 8 at the position corresponding to
Is equipped with. 9 is a bubble, 10 is a take-up pinch roll, and 11 is a winder.

In the apparatus shown in the figure, molten resin is annularly discharged from the lip of the die 2 and the internal cooling cylinder 5 is used with the die diameter unchanged.
And the external cooling cylinder 7. The air discharged from each slit 6 of the internal cooling cylinder 5 is preferably blown at the same pressure from the direction perpendicular to the discharged film made of molten resin. In order to bring the passing film closer to the internal cooling cylinder 5 depending on the film forming conditions, air may be discharged parallel to the film along the moving direction of the film. By bringing the film closer to the internal cooling cylinder 5 in this way, the cooling efficiency can be increased and the film can be cooled to a predetermined temperature. At that time, the film can be in a molten, semi-molten or solidified state. On the other hand, the air from the external cooling cylinder 7 is discharged so as to be blown to the film passing therethrough, and the air from the external cooling cylinder 7 is squeezed at a position at the same height as each slit 6 of the internal cooling cylinder 5. It is also possible to balance the exhaust air pressures of the cooling tubes 5 and 7 and control so that the film stably passes between them. The air used for cooling is preferably air precooled to 20 ° C. or lower. As a result, the film is uniformly cooled at the position of the upper end of the external cooling cylinder 7 within ± 50 ° C. of the melting point of the resin. At this time, due to the air pressure in the bubble 9 and the wind speed at which the air from the external cooling cylinder 7 diffuses into the atmosphere, a force pulling the film to the outside is exerted, so that the film rapidly blows up to more than twice the die diameter. The stretching effect is obtained by the change in the film diameter, and the surface temperature of the film is cooled to 50 ° C. or lower to obtain the target shrink film.

After the time when the blow-up is suddenly doubled or more, there is no slit 6 in the internal cooling cylinder 5, and the blow-up is performed only by the air wind velocity from the external cooling cylinder 7. If the film temperature at the time of blow-up above is below -50 ° C from the melting point of the resin, it is difficult to blow up due to the internal pressure of air due to the effect of melt viscosity, and above + 50 ° C from the melting point of the resin, the above-mentioned stretching effect is reduced and shrink properties Is difficult to obtain. If the blow-up is less than 2 times, the shrinking force when the film is heat-shrinked is insufficient and it becomes difficult to obtain the shrink property.
It is preferably 50 times, particularly 4 to 20 times, and is appropriately set from the combination of air velocity and film temperature in accordance with the shrinkage characteristics required for the film. As the resin applied to the method for producing the shrink film of the present invention, any resin can be used as long as the film can be obtained by the inflation method, for example, an olefin resin, a polyvinyl chloride resin, a polypropylene resin, ethylene-acetic acid. Examples include vinyl copolymers, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, linear low-density polyethylene resins, low-density polyethylene resins, and high-density polyethylene resins. . According to the production method of the present invention using these resins, a shrink film having a single-layer structure or a multilayer structure of two or more layers can be obtained. In the case of a multi-layer, the temperature of the film varies depending on the constituent resin, but may be ± 50 ° C. which is the melting point of the resin that governs the shrinkage property.

[0009]

EFFECTS OF THE INVENTION According to the present invention, the shrinkage is simple and efficient without the need for water cooling after discharge, draining of cooling water, reheating treatment, etc., which are indispensable and disadvantageous in the conventional methods. A shrink film having stable characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory view showing one embodiment of a shrink film manufacturing method of the present invention.

2 is a partially enlarged explanatory view of the embodiment shown in FIG. 1. FIG.

[Explanation of symbols]

1 ... Extruder, 2 ... Die, 3 ... Inner mandrel part, 4 ... Out die part, 5 ...
Internal cooling cylinder, 6 ... Slit, 7 ... External cooling cylinder
8 ... Partition 9 ... Bubble, 10 ... Take-up pinch roll, 11 ... Winder.

Claims (2)

[Claims] 1. A method of forming a film by an inflation method, characterized in that the resin melt-discharged from the tip of the die is rapidly cooled from both inside and outside to start up with the die diameter, and then blown up to twice or more the diameter. Shrink film manufacturing method. 2. Rapid cooling from both inside and outside of the resin, cooling air from an internal cooling cylinder provided at the tip of the inner mandrel portion, and an external cooling cylinder mounted around the internal cooling cylinder in front of the out die part. The shrink film is manufactured by cooling to a temperature within ± 50 ° C of the melting point of the resin with cooling air from.