JPH0687159A - Production of heat-shrinkable packaging film - Google Patents

Abstract

PURPOSE:To perform a heat-shrinkable package having no possibility of pinholing and a superior tightness in a wide packaging temperature range by a method wherein a composition of a branched polyethylene and a linear polyethylene or the like is formed into a film by an inflation method in which an external cooling is used concurrently with an internal cooling. CONSTITUTION:By an inflation method in which an external cooling is used concurrently with internal cooling, a composition of a branched polyethylene and linear polyethylene, a composition of an ethylene-vinyl acetate copolymer and linear polyethylene, or a composition of a branched polyethylene, ethylene- vinyl acetate copolymer and linear polymethylene is formed into a film. In addition, the inflation method ensures a high-speed molding by externally cooling a melt resin delivered from a die by a cooling medium, such as air or water, and further positively lowering a temperature inside a bubble 1 differently from a normal method, therefore realizing a heat-shrinkable package having no possibility of formation of pinholes or other trouble and a superior tightness in a wide packaging temperature range.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention enables heat shrink wrapping produced by an inflation method which uses both external cooling and internal cooling, in a wide packaging temperature range, without troubles such as perforation and excellent in tightness. And a method for producing a film for heat shrink packaging.

[0002]

2. Description of the Related Art Currently, as a film for heat shrink packaging,
Although branched polyethylene is produced by the external cooling inflation method, there is a problem that it cannot be produced at high speed because cooling is rate-determining. In order to solve this problem, a heat-shrinkable film is produced from branched polyethylene and / or ethylene / vinyl acetate copolymer by an inflation method in which external cooling and internal cooling are simultaneously used, and cooling efficiency is improved.

[0003]

However, the branched polyethylene and / or the film of ethylene and vinyl acetate copolymer produced by the inflation method in which the external cooling and the internal cooling are simultaneously used are easily punctured during the heat shrink wrapping. There was a problem. That is, with the conventional technology, it was difficult to produce a film having good productivity and few holes when heat-shrinking.

[0004]

[Means for Solving the Problems] In order to solve the above-mentioned problems, as a result of various studies, by combining a specific resin and a specific manufacturing method, the productivity and the perforation phenomenon at the time of heat shrinkage are significantly increased. The present invention has been completed and the present invention has been completed. That is, the present invention provides branched polyethylene and linear polyethylene, ethylene vinyl acetate copolymer and linear polyethylene, or branched polyethylene and ethylene vinyl acetate copolymer and linear by an inflation method in which external cooling and internal cooling are simultaneously used in combination. A method for producing a heat-shrinkable film, which comprises forming a film from a composition with polyethylene.

The present invention will be described below. The branched polyethylene used in the present invention is not limited at all, but from the viewpoint of film flexibility, the density is 0.935 g / cm 3.
^It is preferably ³ or less. Further, in order to improve film forming stability, the melt index (hereinafter, MI) measured based on ASTM D1238 is preferably 3.0 g / 10 minutes or less, and more preferably 1.0 g / 10 minutes or less. Is.

The ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of 30% by weight or less, more preferably 25% by weight or less, from the viewpoint of film handling due to tackiness. The linear polyethylene used in the present invention is a homopolymer of ethylene, a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, and a low density polyethylene having a density of 0.930 g / cm ³ or less, medium density polyethylene of 0.930~0.942g / cm ^3, a 0.942 g / cm ³ or more high-density polyethylene.

As for the required properties required for the film, it is preferable to use low-density polyethylene having a density of 0.930 g / cm ³ or less for a soft film, and 0.930 g / cm ³ or more for a hard film. in,
It is preferred to use high density polyethylene. The MI of the linear polyethylene is preferably 20 g / 10 minutes or less, and more preferably 10 g / 10 minutes or less in order to improve the stability during film formation.

Branched polyethylene and linear polyethylene,
Mixing ratio of ethylene vinyl acetate copolymer and linear polyethylene, or branched polyethylene, ethylene vinyl acetate copolymer and linear polyethylene, that is, branched polyethylene / linear polyethylene, ethylene vinyl acetate / linear polyethylene, or The weight ratio of branched polyethylene + ethylene vinyl acetate / linear polyethylene is 95/5 to 4
0/60 is preferable, and 90 / 10-6 is more preferable.
It is 0/40. If the mixing ratio of linear polyethylene is less than 95/5, the perforation property during heat shrink packaging may not be improved. If the mixing ratio of linear polyethylene is greater than 40/60, the hole Openability is improved, but there may be a problem with tightness after heat shrink packaging.

Branched polyethylene and linear polyethylene,
The ethylene-vinyl acetate copolymer and linear polyethylene, or the branched polyethylene, ethylene-vinyl acetate copolymer and linear polyethylene may be mixed in advance by melt-mixing or pellet-mixing directly to a film forming machine. You can throw it in.
The melt-mixing method may be a normal single-screw extruder, a twin-screw extruder, a Banbury, or any other batch method, and the melt-mixing method is not limited.

The ordinary inflation method is a method in which a molten resin discharged from a die is externally cooled by a refrigerant such as air or water to be solidified, and the width of the film is kept constant inside the bubble, Do not change the state inside the bubble positively except to change it. For this reason, a resin having a low thermal conductivity such as polyethylene cannot cool the resin at a high speed because the cooling rate of the resin is the rate limiting.

On the other hand, the inflation method used in the present invention, which uses both external cooling and internal cooling at the same time, is
This is an inflation method in which the molten resin discharged from the die is cooled from the outside with a refrigerant such as air or water, and the temperature inside the bubble is positively lowered unlike the conventional method to enable high-speed molding. There are no restrictions on the method of cooling the inside and outside of the bubble in this inflation,
From the viewpoint of operability and economy, it is desirable to use air for both external cooling and internal cooling.

Further, the cooling method used for external cooling is not limited, but the method using an air ring is preferable from the viewpoint of operability. There are no restrictions on the type of air ring, such as various air blowing methods such as a single blowing and a double blowing chamber method, and other blowing angles. As an internal cooling method, a method of replacing the gas inside the bubble with a gas inside the bubble, a method of exchanging heat between the gas inside the bubble and the outside of the bubble to circulate, and a heat exchanger for reducing the gas temperature inside the bubble to the inside of the bubble It is possible to use any of the methods of incorporating the.

In the case of the method of introducing gas into the interior and cooling it, there is no limitation on the position of introduction of the gas, and it is sufficient if the bubble is not made unstable. Further, there is no limitation on the position where the internal gas is guided to the outside of the bubble, as long as the bubble is not unstable. An example of the conventional ordinary inflation method and the external cooling / internal cooling simultaneous inflation method of the present invention will be shown below.

FIG. 2 is an example showing a normal inflation method, and FIG. 1 is an example showing an external cooling / internal cooling simultaneous combined use inflation method used in the present invention. In FIG. 2, 1: bubble, 2: air ring for external cooling, 3: branch pipe for external cooling, 4: blower for external cooling,
5: die, 6: guide plate, 7: first pinch roll, in FIG. 1, 1: bubble, 2: external cooling air ring, 3: external cooling branch pipe, 4: external cooling blower,
5: Die, 6: Guide plate, 7: First pinch roll, 8:
An internal cooling gas injection blower, 9: internal cooling gas discharge blower, 10: internal cooling cylinder, 11: internal cooling gas outlet, and 12: internal cooling gas outlet.

As is clear from a comparison between FIGS. 1 and 2, the simultaneous cooling inflation method using external cooling and internal cooling has a bubble cooling area approximately twice that of the normal inflation method. The rate-determining cooling is greatly improved, and high-speed molding is possible. The heat-shrinkable film of the present invention has a shrinkage in one direction of 60% or more, preferably 70% or more, and a shrinkage in the other direction of 20% or less,
Even with a uniaxial shrinkage film of preferably 15% or less, the shrinkage ratio of the film in the vertical direction (flow direction during film formation) and the horizontal direction (direction perpendicular to the flow direction during film formation) is 2.5 or less, preferably 2 A biaxial shrinkage film of 0.0 or less may be used.

The film forming method of the present invention is not particularly limited as long as it is an inflation method which uses both external cooling and internal cooling, but particularly in the case of a uniaxial shrink film, a blow-up ratio (film diameter 1 die diameter). 1.0 to 2.5,
In the case of a biaxial shrink film, it is desirable to perform inflation molding with a blow-up ratio of 3 or more. Antioxidants, slip agents, antiblocking agents, antistatic agents, antifog agents, weathering agents, inorganic substances, pigments and other additives may be added to the film of the present invention, if necessary.

As the heat shrink wrapping apparatus of the present invention, an ordinary heat shrink wrapping apparatus can be used. As a heating source, an electric heater, an infrared heater, an ultrasonic wave or the like is used, but there is no limitation as long as it can heat the heat shrinkable packaging film. From the viewpoint of productivity, it is preferable to use the shrink tunnel. The heating temperature depends on the type of device,
There are optimum conditions depending on the shape, size, etc., but generally 100 ° C to 200 ° C, preferably 110 ° C to 180 ° C.
And the residence time in the device is within 5 minutes, preferably 1
Within minutes.

[0018]

The present invention will be specifically described with reference to the following examples.

[0019]

Example 1 (Film forming apparatus and extrusion conditions) 65φ extruder: die diameter 160φ, die gap
0.8mm-For air ring 160mmφ for external cooling-Air ring blower for external cooling 5.5KW-Internal cooling tube for internal cooling 160φ Cylinder-Suction blower for internal cooling 5.5KW-Exhaust blower for internal cooling 5.5KW- Blow-up ratio 4.0 ・ Film thickness 40 μm ・ Film pulling speed 30 m / min. - branched polyethylene: (measured based on ASTM D1238) MI 0.25g / 10 min, density 0.922 g / cm ³ (ASTM D1505 measured on the basis of) Linear Polyethylene: MI 0.8 g / 10 min (ASTM D1238) Density 0.924g / cm ³ (Measured according to ASTM D1505) Butene 1 Copolymer 80 parts by weight of branched polyethylene and linear polyethylene 20
A part by weight was melt-mixed with an extruder having a diameter of 65 mm, and a film was formed under the above film forming conditions.

With this film below, 100 × 100 × 1
Wrap a 00 mm wooden mold, open air vent holes with a diameter of 1 mm on each side, use a hot air type shrink tunnel with an electric heater as a heating source, heat shrink shrink wrap at each temperature with a residence time of 20 seconds in the tunnel The tight method and perforation of the packaging were measured. (Criteria for tightness) ○: With tightness Δ: No tightness in part ×: No tightness in the whole (criteria for perforation) ○: Perforation with 3 mmφ or less Δ: Perforation with 3-10 mmφ ×: Holes of 10 mmφ or more Further, the overall judgment of the above two evaluations was evaluated based on the following criteria.

⊚: Very good ∘: Good ×: Impossible As shown in Table 1, the measurement results show that the tightness and the perforation property are
It was good in the range of 120 to 140 ° C.

[0022]

Example 2 As the linear polyethylene of Example 1, MI
Example 1 was repeated except that a butene copolymer having a density of 1.0 g / 10 min and a density of 0.920 g / 10 min was used. As a result of the measurement, as shown in Table 1, the tightness and the perforation property were good in the range of 120 to 145 ° C.

[0023]

Example 3 Example 1 was repeated except that the branched polyethylene of Example 1 was 70 parts by weight and the linear polyethylene was 30 parts by weight. The measurement results, as shown in Table 1,
Tightness and perforation were good in the range of 120 to 150 ° C.

[0024]

Comparative Example 1 The procedure of Example 1 was repeated except that the linear polyethylene was not used. The measurement results are shown in Table 1.

[0025]

Comparative Example 2 In Example 1, as the branched polyethylene, MI 0.6 g / 10 min, density 0.922 g / c.
The same procedure as in Example 1 was carried out except that m ³ polyethylene was used and linear polyethylene was not used. The measurement results are shown in Table 1.

[0026]

Comparative Example 3 In Example 1, as the branched polyethylene, MI 0.4 g / 10 min, density 0.922 g / 1.
The same procedure as in Example 1 was carried out except that 0 minute polyethylene was used and no linear polyethylene was used. The measurement results are shown in Table 1.

[0027]

Comparative Example 4 The procedure of Example 1 was repeated except that the internal cooling was not used, but the bubble formation was unstable and film formation was impossible.

[0028]

[Table 1]

[0029]

[Example 4] Instead of the branched polyethylene of Example 1,
MI 0.3 g / 10 min Example 1 except that ethylene and vinyl acetate copolymer having a vinyl acetate content of 6% by weight were used.
I went the same way. The measurement results are shown in Table 2.

[0030]

[Example 5] Instead of the branched polyethylene of Example 1,
MI 0.25 g / 10 minutes 40 parts by weight of branched polyethylene having a density of 0.922 g / cm ³ and MI 0.3 g / 10
In the same manner as in Example 1 except that 40 parts by weight of ethylene and a vinyl acetate copolymer having a vinyl acetate content of 6% by weight were used.

The measurement results are shown in Table 2.

[0032]

Comparative Example 5 The procedure of Example 4 was repeated except that the linear polyethylene was not used. The measurement results are shown in Table 2.
It was shown to.

[0033]

Comparative Example 6 The procedure of Example 5 was repeated, except that the linear polyethylene was not used. The measurement results are shown in Table 2.
It was shown to.

[0034]

[Table 2]

[0035]

EFFECT OF THE INVENTION The heat-shrinkable packaging film of the present invention enables heat-shrinkable packaging which has no perforation and is excellent in tightness in a wide packaging temperature range.

[Brief description of drawings]

FIG. 1 is a schematic diagram of inflation of the present invention in which both external cooling and internal cooling are simultaneously used.

FIG. 2 is a schematic view of a conventional ordinary-type inflation only with external cooling.

[Explanation of symbols]

 1 bubble 2 external cooling air ring 3 external cooling branch pipe 4 external cooling blower 5 die 6 guide plate 7 first pinch roll 8 internal cooling gas injection blower 9 internal cooling gas discharge blower 10 internal cooling cylinder 11 internal cooling Gas outlet 12 for internal cooling gas outlet

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Claims (1)

[Claims] 1. A branched polyethylene and a linear polyethylene, an ethylene vinyl acetate copolymer and a linear polyethylene, or a branched polyethylene and an ethylene vinyl acetate copolymer and a wire by an inflation method using both external cooling and internal cooling simultaneously. A method for producing a film for heat-shrinkable packaging, which comprises forming a film with a composition of polyethylene-like polyethylene.