JP3001668B2 - Shrink film for half wrap - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shrink film for half wrap, and more particularly to a shrink film for half wrap used for collecting and packaging cans, bottles, small boxes and the like using trays such as cardboard.

[0002]

2. Description of the Related Art There are two general methods for placing cans, bottles, small boxes and the like in a tray made of cardboard, etc., and performing integrated shrink packaging using a film made of biaxial heat shrinkage. is there. One is to cover the tray from the bottom side and the contents top side with a biaxially heat-shrinkable film (sheet), heat-bond and cut between both films at the outer periphery of the package and at the center in the height direction. It is a full wrap shrink packaging method to heat shrink the whole,
The other is a half-wrap which does not cover the heat-shrinkable film from the bottom side of the tray, but only covers the upper surface of the contents, and adhesively fixes the entire outer peripheral edge of the film to the side surface of the tray with an adhesive and then heat-shrinks. This is a shrink packaging method.

In the former case, as described above, the upper and lower two films are thermally bonded substantially all around the tray and at the center in the height direction. And the cut, almost no wrinkles are generated at the bonded portion, and when heat-shrinked in that state, the bonded portion comes into close contact with the package without any wrinkles around the heat bonded portion. This is considered to be based on the thermal bonding between the two sheets in a planar shape that is hardly three-dimensional as described above. This full-wrap shrink wrapping is not preferable in terms of packaging material cost because the film is also applied to the lower surface of the tray. In this regard, it can be said that the half-wrap shrink wrap is excellent.

However, half-wrap shrink wrapping is
It is necessary to cover the package with the biaxial heat-shrinkable film only from the upper surface of the package, and to fix the peripheral edge of the film to the side surface of the tray in advance before the heat shrinkage. In this case, if the adhesive is to be fixed to the entire periphery of the side surface of the tray with an adhesive, the film must be bent not toward a flat surface but toward the side surface of the tray (usually four surfaces). If it is bent over the entire circumference to form a three-dimensional shape, wrinkles are necessarily generated at the corners. That is, when the adhesive is fixed over the entire circumference, wrinkles are already formed on the bonding portion, particularly the corners of the tray, before the heat shrinkage, and after the heat shrinkage, many wrinkles are left on the side surface of the tray, making it unsightly. As a countermeasure, there is a method in which only the pair of opposite sides of the tray (usually a square) is bonded and fixed in advance and freely heat-shrinks. For example, on the side of the tray in that direction, a part of the packaged material appears uncovered due to the heat shrinkage of the film, or even if covered, the edge of the shrinked film is thermally bonded to the tray. It is not preferable because there is no cost.

An object of the present invention is to solve the above-mentioned problems in the half-wrap shrink packaging. Also, conventional half-wrap shrink films include a single-layer film made of a specific ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer, or an adhesive layer to a tray such as a cardboard box. A multilayer film or the like in which a specific low-density polyethylene is laminated on the adhesive layer side is used (Japanese Patent Publication No. 2-12735, etc.).

[0006] Such a conventional shrink film for half wrap improves the adhesion to corrugated cardboard by increasing the content of vinyl acetate or ethyl acrylate. However, an increase in the content of vinyl acetate or ethyl acrylate lowers the melting point of the film itself, lowers the shrinkage temperature of the film, and tends to cause blocking between the films. Therefore, at the time of actual packaging, the film shrinks before the film temperature required for bonding with the cardboard is reached, causing wrinkles at the sleeve opening and further blocking between the films, and sufficient bonding with the cardboard. The state may not be obtained, and the packaging finish may be poor.

Further, since the heat resistance of the film is impaired, the packaging temperature conditions are narrowed, holes are liable to be formed in the shrinking tunnel in the lapping process, and the packaging conditions must be extremely changed between summer and winter. And is easily affected by the environment, and many packaging troubles occur.

Further, as described above, in the method in which the film is preliminarily bonded and fixed only to a pair of opposite sides of the tray, and the other pair of the films is heat-shrinked in an open state in which the sleeve opening is formed. In order to reduce the generation of wrinkles and the blocking of wrinkles, it is necessary to suppress the contraction balance in the vertical direction and the horizontal direction to a certain range. That is, if the film shrinks greatly in both the vertical and horizontal directions when heated in the lapping process, the film at the mouth of the sleeve moves in a complicated manner, causing wrinkles in the film at that time and further causing blocking between the films. -172735).

Therefore, the present inventors have solved the above-mentioned drawbacks of the prior art, and at the time of half-wrapping, the sleeve opening can also be sufficiently hot-pressed to the side surface of the tray, and the packaging finish without wrinkles. We worked diligently to develop a good half-wrap shrink film.

[0010]

As a result, the shrinkage characteristics of the multilayer film made of a resin having specific components and characteristics are limited to a specific range in each of the vertical and horizontal directions. It has been found that the above object can be achieved by performing a discharge treatment on. The present invention has been completed based on such findings.

That is, according to the present invention, the melt flow rate is
0.1-2.5 g / 10 min, vinyl acetate content 3.5-1.5.
A low-density polyethylene or melt flow rate having a melt flow rate of 0.1 to 2.5 g / 10 min and a density of 0.930 g / cm ³ or less; A multilayer film comprising an ethylene-vinyl acetate copolymer having a vinyl acetate content of 0.1 to 2.5 g / 10 minutes and a vinyl acetate content of 2% by weight or less. The shrinkage rate in the direction is 35 to 65% at 110 ° C and 65% or more at 120 ° C, and the shrinkage rate in the lateral direction is 11 to -30% at 110 ° C and -1 at 120 ° C.
The present invention provides a shrink film for half wrap, wherein the adhesive layer has a corona treatment of 5 to -35%.

Here, the half-wrap shrink film (hereinafter simply referred to as a film) is a film used for the half-wrap shrink packaging, and as shown in FIG. It is provided so as to cover the upper surface of the cardboard tray 2 on which the package 1 is placed,
The film 3 is provided on both sides 2 a in the longitudinal direction of the cardboard tray 2.
Are adhered via the hot melt adhesive 4, and both short side surfaces 2b of the cardboard tray 2 are adhered by the hot-melt adhesive force of the film itself. That is, when wrapping the packaged object 1 with the shrink film 3 for half wrap, first, a hot-melt adhesive 4 is applied in a strip shape to both side surfaces 2 a in the longitudinal direction of the cardboard tray 2, and the adhesive property is applied to the adhesive 4. The top and bottom edges of the film 3 with the layer (adhesive layer) inside are pressed against and pressed against the film 3, and the upper side is covered with the film 1 from the side of the cardboard tray 2. Next, the film 3 is shrunk by heating, and the laterally opposite ends of the film 3 which has been heated to be in a semi-molten state are attached to both lateral side surfaces 2b of the cardboard tray 2.
Is pressed with a roll or the like to adhere.

Accordingly, since no hot-melt adhesive or the like is interposed between the lateral side surfaces 2b of the cardboard tray 2 and the film 3, the adhesion between the film itself and the cardboard is regarded as important. Is very important.

The shrink film for half wrap of the present invention has the above-mentioned range of characteristics. However, the ethylene-vinyl acetate copolymer of the adhesive layer on the adhesive side to the corrugated cardboard tray is particularly suitable for use in melt coating. The flow rate is
The content is preferably from 0.1 to 2.5 g / 10 min, and the vinyl acetate content is preferably from 3.5 to 15.0% by weight. If the melt flow rate of the ethylene-vinyl acetate copolymer in this adhesive layer is less than 0.1 g / 10 minutes, the productivity during film processing is poor, there is the disadvantage of bubble breakage, and the melt flow rate is 2.5 g / min. If the time exceeds 10 minutes, there is a problem that the film strength is low and the heat shrinkage ratio is poor. Further, when the content of vinyl acetate is less than 3.5% by weight, sufficient adhesiveness cannot be obtained. When the content exceeds 15% by weight, the shrinkage balance is deteriorated, and blocking and wrinkles are generated at the time of packaging. The adhesiveness is reduced.

On the other hand, the outer layer is made of low-density polyethylene or ethylene-vinyl acetate copolymer as described above. In particular, in the low-density polyethylene of the outer layer, the melt flow rate is preferably 0.1 to 2.5 g / 10 minutes, and the density is preferably 0.917 to 0.930 g / cm ³ . Further, in the ethylene-vinyl acetate copolymer of the outer layer, the melt flow rate is preferably 0.1 to 2.5 g / 10 minutes, and the vinyl acetate content is preferably 2% by weight or less. In the case of low density polyethylene, the melt flow rate is 0.1
If it is less than g / 10 minutes, the moldability will be poor, and 2.5 g /
If the time exceeds 10 minutes, the strength of the film becomes weak, and the heat shrinkage ratio becomes poor. In addition, the density is 0.930 g
If it exceeds / cm ³ , the low-temperature shrinkage and transparency will deteriorate.
Furthermore, when the outer layer is an ethylene-vinyl acetate copolymer, if the melt flow rate is less than 0.1 g / 10 minutes, the film processability is poor, and there is a disadvantage that a flow mark or the like is generated. If it exceeds 2.5 g / 10 minutes, there is a problem that the film strength becomes weak and the heat shrinkage becomes poor. If the vinyl acetate content exceeds 2% by weight, the heat resistance becomes poor, and blocking and holes in tunnels occur. The problem of empty space arises.

The lamination of the above-mentioned adhesive layer and the outer layer is not particularly limited, and can be performed by a commonly used coextrusion (multilayer film forming) method or the like. The shrinkage of the multilayer film after lamination must be within the above-mentioned range. If the shrinkage in the vertical direction is small, it is not suitable for shrink packaging, and if there is shrinkage in the horizontal direction, the short direction of the cardboard tray Since the film comes off from both sides,
A sufficient amount of heat cannot be applied, and as a result, sufficient cardboard adhesive strength cannot be obtained. 1 vertical shrinkage
By having a characteristic of 35 to 65% at 10 ° C and 65% or more at 120 ° C, the slip between the packaged object and the shrink film in the heat shrinking process is appropriately maintained, and the shrinkage is performed smoothly. Will be Although there is a problem as described above if there is shrinkage in the horizontal direction, conversely, even if there is thermal elongation (negative shrinkage), if the value is small, flapping occurs when hot air is blown through a tunnel for heat shrinkage. Is generated, and it becomes difficult to adhere to both side surfaces in the short direction.

For the purpose of the present invention, at 110.degree.
A film exhibiting a heat extensibility of -15 to -35% at 30% and 120 ° C is suitable for the heat bonding step. Such a shrinkage balance can be obtained by appropriately selecting film forming conditions and stretching conditions. The corona treatment of the adhesive layer is performed by pressing the both ends in the lateral direction of the film 3 which has been heated and in a semi-molten state to the lateral side surfaces 2b of the cardboard tray 2 with a roll or the like to adhere. The degree of corona treatment is desirably set so that the surface tension of the film is 35 dyne / cm or more, preferably 38 dyne / cm or more. The upper limit may be adjusted to such an extent that the films do not cause blocking when the film is wound into a roll.

If the thickness of the adhesive layer is more than twice the thickness of the outer layer, blocking and wrinkles are likely to occur. Therefore, it is preferable that the thickness of the adhesive layer be less than twice the thickness of the outer layer.
When packaging is performed using the film of the present invention, the steps can be performed in the same manner as in the conventional case, and the same adhesive can be used. The heating in the lapping step may be performed by setting the film temperature to about 110 to 120 ° C.

[0019]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. Example 1 An adhesive layer (layer A) was prepared by adding ethylene acetate content of 7% by weight and melt flow rate (MFR) of 2.0 g / 10 min.
Outer layer (layer B) using vinyl acetate copolymer (EVA)
A low-density polyethylene (LDPE) having an MFR of 0.6 g / 10 min and a density of 0.921 g / cm ³ was used. The thicknesses of the A layer and the B layer were 8 μm and 42 μm, respectively. A two-layer film was formed, and the A layer was subjected to corona treatment to obtain a film having a shrinkage balance shown in Table 1. The heating of the film is performed a packaging test at a film temperature of 110 to 115 ° C.
The adhesive strength of the cardboard and the finish of the packaging were observed, and all were good. The adhesive strength of the corrugated cardboard in Table 1 was determined by using a hot-plate type sheet sealing machine capable of adjusting the temperature, stacking a 50 mm-wide corrugated cardboard with a film of the same width with an adhesive layer,
Bonding was performed at a bonding width of 10 mm, a sealing time of 1 second, a pressing time of 0.5 second, and a pressing force of 1 kg / cm ² at each bonding temperature, and the bonding strength was measured using a tensile tester.

Example 2 As layer B, vinyl acetate content 2% by weight, MFR 2.0 g
Except for using an ethylene-vinyl acetate copolymer of / 10 min, a two-layer film was formed in the same manner as in Example 1, and the layer A was subjected to corona treatment to obtain a film having a shrinkage balance shown in Table 1. Obtained. Both the cardboard adhesive strength and the packaging finish in the packaging test were good.

Comparative Example 1 A film having the same resin composition as in Example 1 and having a shrinkage balance shown in Table 1 was obtained. In the packaging test, many wrinkles were generated at the sleeve mouth, the packaging finish was poor, and the cardboard adhesive strength was insufficient. When the heating temperature of the film was increased in order to increase the adhesive strength, the film shrunk in the lateral direction, and the margin for bonding with the cardboard was reduced.

Comparative Example 2 The thicknesses of the layer A and the layer B in Example 1 were 30 μm and 20 μm, respectively.
μm, and a film having a shrinkage balance shown in Table 1 was obtained. In the packaging test, as in Comparative Example 1, many wrinkles occurred at the sleeve mouth, and the cardboard adhesive strength was insufficient. When the heating temperature of the film was increased, the film shrinks in the horizontal direction and the adhesive margin with the cardboard decreases. I have.

Comparative Example 3 Vinyl acetate content: 2.0% by weight, MFR: 1.0 g / 10 minutes,
An ethylene-vinyl acetate copolymer monolayer film having a density of 0.920 g / cm ³ and a shrinkage ratio in the length and width directions shown in Table 1 was used. In the packaging test, the packaging finish was good,
The cardboard adhesive strength was insufficient.

Comparative Example 4 A vinyl acetate content of 4.0% by weight, an MFR of 0.5 g / 10 minutes,
An ethylene-vinyl acetate copolymer monolayer film having a density of 0.920 g / cm ³ and a shrinkage ratio in the length and width directions shown in Table 1 was used. In the packaging test, the vinyl acetate content in the whole was large, so that the shrinkage in the vertical direction was large, and there was a problem such as a hole at the time of packaging, and the cardboard adhesive strength was insufficient due to insufficient heat. Was.

Comparative Example 5 A vinyl acetate content of 7.0% by weight, an MFR of 2.0 g / 10 minutes,
An ethylene-vinyl acetate copolymer monolayer film having a density of 0.920 g / cm ³ and a shrinkage ratio in the length and width directions shown in Table 1 was used. In the packaging test, as in Comparative Example 4, since the vinyl acetate content was large, the shrinkage in the vertical direction was large, problems such as holes were generated during packaging, and the cardboard adhesive strength was insufficient due to insufficient heat. It was not enough.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

As described above, according to the present invention, it is possible to provide a half-wrap film having a sufficient cardboard adhesive strength and a good packaging finish when the packaging is performed. Further, since the film has heat resistance, it is not affected by the environment, and packaging trouble can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a use state of a half-wrap film.

[Explanation of symbols]

1: Packaged object 2: Cardboard tray 2a: Both sides in the longitudinal direction 2b: Both sides in the transverse direction 3: Film 4: Hot melt adhesive

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasushi Ota 1-3-15 Nihonbashi Horidomecho, Chuo-ku, Tokyo Inside Heisei Polymer Co., Ltd. (72) Inventor Masamitsu Tsukada 1-3-3 Nihonbashi Horidomecho, Chuo-ku, Tokyo No.15 Heisei Polymer Co., Ltd. (72) Inventor Keiichi Kobayashi 1-3-15 Nihonbashi Horidomecho, Chuo-ku, Tokyo No. Heisei Polymer Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 B29C 61/00-61/10

Claims (1)

(57) [Claims] 1. The melt flow rate is from 0.1 to 2.5 g / 1.
0 minutes, an adhesive layer composed of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 3.5 to 15.0% by weight, a melt flow rate of 0.1 to 2.5 g / 10 minutes, and a density of 0.1. 930g /
cm ³ or less of low density polyethylene or melt flow rate of 0.1~2.5g / 10 min, an ethylene vinyl acetate content of less 2 wt% - double constructed from an outer layer comprising a vinyl acetate copolymer A film having a longitudinal shrinkage in a glycerin bath of 35 to 65% at 110 ° C.
It is 65% or more at 20 ° C and the shrinkage in the lateral direction is 110 ° C
A shrink film for half wrap, wherein the adhesive layer is subjected to corona treatment.