JP2742292B2 - Shrink packaging method using heat shrinkable synthetic resin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for heat shrink wrapping using a heat shrinkable synthetic resin film, and more particularly to a simplified and economical method.

(Prior art) Conventionally, as a method of packaging an object to be packaged with a heat-shrinkable synthetic resin film, first, both ends in the width direction of the film are fitted to each other in a palm-shape manner, or are fitted to an envelope to form a tubular film. Then, an object to be packaged is inserted into the package, and thereafter, it is fitted in the shape of a palm, or a portion fitted in the shape of an envelope is heat-sealed or melt-sealed, and in the case of melt-sealing, one of the blown films is removed.

The packaged product is packaged in a tubular shape by the above-described process, and thereafter, the front and rear portions of the packaged material at both ends of the cylindrical shaft are again melt-sealed and cut off, and the packaged product is an independent closed package. Create A hole for venting air is opened in the film of this package, and the film is passed through a hot air tunnel to shrink and adhere to a sufficient amount of the film to perform a packaging method using a heat-shrinkable synthetic resin film.

(Problems to be Solved by the Invention) In the above-mentioned packaging method, heat-sealing of the mating portions at both ends in the width direction of the film or fusing seal or heat-sealing of both ends of the cylindrical shaft of the film must be performed. No. This means that the packaging machine must be provided with the sealing equipment, and the operation becomes complicated and troublesome.

In addition, there is a problem that when the package is made by shrinking the film at the heat-sealed or blown-sealed portion, the shrinkage of the film causes uneven shrinkage, resulting in a keloid shape and unsightly appearance.

(Means for Solving the Problems) In the present invention, the above-mentioned problem is caused by the fact that the center layer arranged so as to cover the entire surface of the package with some dimensional margin has a higher softening point temperature than the outer layer. Using a heat-shrinkable synthetic resin multilayer film for sealing, form a temporary dense package of the article to be packaged, and form a package provided with a deaeration port, and then heat the film to allow for the margin. Is shrunk, and the film is brought into close contact with the outer surface of the article to be packaged.

More specifically, in general, when performing heat shrink wrapping with a heat shrinkable synthetic resin film, the package temporarily wrapped with the film first expands in the hot air tunnel in a hot air tunnel,
Thereafter, the temperature of the film rises and a force for shrinking the film acts, and the film shrinks along the shape of the article to be packaged to complete the packaging. In this case, the film is previously provided with a small vent. The role of this deaeration port is to adjust the contraction state of the film that contracts along the surface of the packaged object. For example, if the film shrinks without the film expanding and the deaeration port is too large, the film adheres to the package and the amount of heat of the hot air is deprived by the package and the contraction becomes uneven, The appearance becomes extremely poor.

On the other hand, if the deaeration port is too small and it becomes a closed system, the film shrinkage is completed with insufficient deaeration,
It cannot be contracted. Accordingly, the area of the vent is adjusted so that a step occurs in which the coating film once expands like a balloon before the film contracts.

The temporary dense package in the method of the present invention means that a self-sealing heat-shrinkable synthetic resin film is used as the heat-shrinkable synthetic resin film, and the strip-shaped film is stretched in the width direction as shown in FIG. Just superimposed in a cylindrical shape
Without heat sealing or fusing sealing.
As shown in (B) of the figure, the film at the opening at the distal end of each end of the cylindrical shaft is melt-sealed or folded and overlapped. In addition, the provisional dense package is provided with an air vent / deaeration port, and when passing through the hot air tunnel, the pressure of the gas in the coating package and the temperature of the film due to the temperature of the hot air increase the temperature of the film joining portion. The surface can be self-sealed, and the inside air can be evacuated from the deaeration port as appropriate to allow tight packing as shown in FIG. 1 (C).
In FIG. 1, reference numeral 2 denotes a fusing seal portion, and reference numeral 3 denotes a bent portion. Also, FIG. 2 shows a temporary dense packaging by folding the film shown in FIG. 2 (D) before, after, and right and left as shown in FIG. 2 (E), (F) and (G). Make up with the body.

The order of folding of the film in this case is not restricted. For example, four sides of the film shown in FIG. It is possible to make a temporary dense package by folding the film with the board and simultaneously releasing the grip of the film. In this case, the self-sealing heat-shrinkable synthetic resin film is a multilayer film having a central layer having a high heat-resistant temperature and a layer having a low optimum sealing temperature on both outer layers.

On the other hand, a heat-shrinkable synthetic resin film used for a conventional heat-shrinkable packaging is produced by stretching at a temperature as low as possible below the temperature at which the resin softens to orient the molecules. As a result, the produced heat-shrinkable synthetic resin film exhibits a contracting force in a temperature region lower than the temperature at which the film softens. For this reason, when trying to shrink package using a single heat-shrinkable synthetic resin film, the film shrinks at a temperature before reaching the softening point to seal unless a closed system is created before heating. However, the pressure of the gas in the package increases and the gas in the package escapes, so that an apparent closed system with a controlled internal pressure cannot be created.

Therefore, as described in the prior art, when performing heat shrink wrapping using a conventional heat shrinkable synthetic resin film, it is necessary to create a closed system in advance by performing heat sealing or fusing sealing.

As the self-sealing heat-shrinkable synthetic resin film, a multilayer film composed of a center layer and an outer layer is used. In this case, the center layer needs to have a higher softening point temperature than the outer layer.

The purpose of the multi-layer structure is two or more layers, and the purpose can be achieved. Even if the number of layers is as large as five, the purpose can be achieved.

For ease of understanding, the description will be made in a simplified manner of a center layer and both outer layers.

Regarding the temperature difference between the softening point temperature of the resin of the center layer and the softening point of the resin of both outer layers, it is naturally preferable that the temperature difference is large due to the mechanism described above.

Since a resin having a high softening point is used for the center layer, the temperature at which the resin stretched at the optimum stretching temperature shrinks is defined. However, the temperature at the time of stretching can be slightly changed depending on the film forming conditions, and thus cannot be defined only by the softening points of the resins of the central layer and the outer layers.

The multilayer film of a resin in which the center layer and the outer layers are different from each other can be prepared by a multilayer coextruded film or a laminating technique such as lamination and extrusion. As a special case, the softening points of the central layer and both outer layers can be changed by extruding a multilayer co-extruded film and making the central layer more cross-linked by post-processing. The temperature of the heat shrink tunnel is generally set at a temperature approximately 20 to 30 ° C. higher than the temperature at which the shrinking force of the center layer is generated, and when the center layer is a polyethylene resin, the temperature is 130 to 150 ° C. 120-140 ° C for vinyl chloride, 14 for polypropylene
This is performed at a temperature of about 0 to 170 ° C.

As the resin used for both outer layers, a resin having a low softening point such as an ethylene copolymer resin such as ethylene vinyl acetate copolymer (EVA) or a vinyl chloride copolymer is used.

Hereinafter, the present invention will be described with reference to examples.

Example 1 Both outer layers were made of ethylene-vinyl acetate copolymer (EVA, vinyl acetate content 15% by weight), and the ratio to make the total thickness 30%.
And a three-layer 250 μ sheet of polyethylene (PE), the center layer of which was cross-linked with an electron beam. This was heated to 150 ° C and stretched 5 times each in the vertical and horizontal directions to 10μ
Film was made.

This film was used to wrap carrots in a tubular shape, and the films were overlapped only in the width direction, and no fusing seal or heat sealing was performed. The superposition was 10% per whole folded diameter. In addition, the front and rear ends of the cylindrical shaft are bent so as to overlap with the lower side.
% Length, and two types in which the front and rear ends of both ends of the cylinder shaft are sealed by fusing.

One hole was made in the package with a needle per 50 mm length to provide a gas vent.

This package was passed through a hot air tunnel in which hot air at 140 ° C. was circulating.

As a result of observing the state in the tunnel, the package first expanded in the tunnel and then contracted to form a uniform contracted package. The joint of the films was completely sealed and the appearance was very good.

Example 2 Three curies were packaged using the multilayer stretched film of EVA and PE prepared in Example 1. The size of three cucumbers laid flat was 200 mm in length, 80 mm in width, and 30 mm in height. The size of the film is 350mm in length, 150, 160, 170mm in width
Then, a package was prepared by the packaging method shown in FIG.

The lengthwise film was not long enough to wrap the curry around one turn, and the film turned to the back had a shortage of 100 mm and the curry was exposed. The film in the width direction was long enough to be wound one turn, and the overlap of the remaining films after one turn was 10, 20, and 30 mm.

A hole was formed in the portion where the film did not overlap with the package with two worm pins, and a gas vent was provided.

This package was passed through the same hot air tunnel as in Example 1. As a result of observing the state in the tunnel, the package first expanded in the tunnel, and then the film contracted to form a uniform shrinkable package. The mating portion and the overlapping portion of the film were completely self-sealed, and the appearance was very good.

Comparative Example 1 A sheet made of polyethylene alone and crosslinked with an electron beam was formed and stretched in the same manner as in Example 1 to form a 10 μm film.

Using this film, it was wrapped in a tubular shape as in Example 1,
The fusing seal was provided only in the front and rear directions in the cylindrical flow direction.

In this case, superimpositions in the width direction of the film were prepared with lengths of 10%, 20%, 30%, and 50% per the entire folding diameter.

As in the case of Example 1, the state of the package provided with the deaeration port in the tunnel when passing through the hot air tunnel was observed. The results were as follows.

In the case of the overlapped portions of 10% and 20%, no expansion was observed, and only those having non-uniform shrinkage and poor appearance were obtained. In the case of the overlapped portions of 30% and 50%, expansions of 10% and 30% were recognized, respectively, and uniform shrinkage and good appearance were obtained.

Comparative Example 2 A sheet made of polyethylene alone and crosslinked with an electron beam was prepared and stretched in the same manner as in Example 1 to prepare a 10 μm sheet. Using this film, three curies were used in the same manner as in Example 2, and a film having the same size as in Example 2 was used to prepare a similar package. The package was similarly pierced with two worm pins and provided with a deaeration port.

This package was passed through the same hot air tunnel as in Example 1. As a result of observing the condition in the tunnel, only the package having the overlap of the 30 mm film showed expansion in 50% of the package, and a very good appearance similar to that of Example 2 was obtained. On the other hand, the package having an overlap of the 10 and 20 mm films did not show any swelling, had a non-uniform shrinkage, and had only a poor appearance.

(Effect of the Invention) According to the method of the present invention, good-looking crimp packaging can be easily performed.

[Brief description of the drawings]

FIG. 1 is an explanatory view for explaining one embodiment of the method of the present invention, and FIG. 2 is an explanatory view for explaining another embodiment of the method of the present invention. 1 ... joining part, 2 ... fusing seal part, 3 ... bending part

Claims (1)

(57) [Claims] 1. A self-sealing heat-shrinkable synthetic resin multilayer film having a softening point higher in a center layer arranged so as to cover the entire surface of the package with a slight dimensional margin compared to the outer layer. The article to be packaged is formed in a temporary dense package, and is formed in a package having a deaeration port, and then heated to shrink the film to the extent of the margin, and the film is formed on the outer surface of the article to be packaged. A shrink-wrapping method using a heat-shrinkable synthetic resin film, characterized in that: