JPH09216956A - Wrapping film and shrink-wrapped article using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shrink wrapping film which gives a good finish in a wide temp. range, decreases breaking at a vent hole or a sealed section, and has improved clarity and unsealability by specifying the heat shrinkage, equilibrium heat shrinkage stress, and tear strength and haze after the shrinkage of the film. SOLUTION: An ethylene copolymer having a density of 0.890-0.940g/cm<3> is melt extruded through a circular die and quenched. The resultant unstretched tube is cross-linked by the irradiation with a 2-10 Mrad electron beam, heated to the m.p. of the polymer or higher, stretched in both the longitudinal and transverse directions, and cooled to solidify, thus giving a wrapping film which has a heat shrinkage (according to ASTM D-2732) at 120 deg.C of 30% or higher in both the longitudinal and transverse directions, an equilibrium heat shrinkage stress (according to ASTM D-2838) at 120 deg.C after 10% shrinkage of 30-140g/mm<2> in both the longitudinal and transverse directions, a tear strength (according to ASTM D-1922) after 10-50% shrinkage of 3-10g in both the longitudinal and transverse directions, and a haze (according to ASTM D-1003) after 10-50% shrinkage of 3% or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a three-side sealed packaging film that covers a packaged object such as a container with a lid for a lunch box or a side dish or a tray without a lid such as meat or fresh vegetables, and is covered by heat shrinkage. The present invention relates to a shrink package that is tightly attached to a package and is tensioned, and a packaging film used for the shrink package.

[0002]

2. Description of the Related Art A shrink wrapping body has advantages in that a wrapping film is not intimately stuck to a wrapping object and is bulky, and various wrapping objects having different shapes can be beautifully wrapped without wrinkles. It is used as a package in a wide range of fields such as foods such as meat, fresh vegetables and cup ramen, as well as toys and daily necessities.

Further, as a packaging film used for the shrink package, a polyolefin resin such as low-density polyethylene, linear low-density polyethylene or polypropylene, or a stretched polyvinyl chloride resin is generally used. . As a method of obtaining a shrink wrap, the film is made into a tubular shape, the overlapping portion of the film is sealed, and the article to be wrapped is inserted into it, and then the opening of the tubular film is folded into the bottom of the article to be wrapped with hot air. Overlap shrink wrap that passes through the tunnel, three-way seal pillow shrink wrap that passes through the hot-air tunnel after fusing and sealing without folding the opening of the tubular film, fold one film in half, and between the films After inserting the object to be packaged into the package, three-way seal packaging that seals the open three sides and passes through the hot air tunnel, L-type seal packaging that continuously performs this, two-film covering the object to be packaged There is a four-way seal packaging that seals the opening and then passes through a hot air tunnel.

In any of the packaging methods, when the object to be packaged is wrapped and sealed, a small hole is generally formed in the film using a needle or the like in order to allow the sealed air to escape at the time of contraction. . Among them, the three-way sealed pillow shrink wrapping and the L-shaped seal wrapping are suitable for high-speed packaging of standard sized items and the latter are advantageous for wrapping irregularly shaped items, and are the most popular in the shrink wrapping field. This is a commonly used packaging method.

However, in the shrink wrap, the wrapping film is strained and adheres to the article to be wrapped,
There are few clues to break the packaging film at the time of opening, it is difficult to open, and since the packaging film is greatly shrunk by using hot air etc., the transparency of the packaging body is a packaging body by another packaging method, for example, a plasticized PVC film. There was a problem that it was inferior to the stretch package used. In addition, when trying to impart high shrinkability, the shrinkage stress also becomes too large, and there is also a problem that breakage may occur during shrink-wrapping from a small hole for venting air during shrinkage, or breakage from the seal part, etc. Was there.

The first method for improving these problems is
JP-A-4-229251 discloses a film in which the tearability in the stretching direction can be improved by laminating an olefin polymer and a propylene polymer and stretching the film in a uniaxial direction. In JP-A 3-28864, a linear low-density polyethylene layer and a blend layer of a linear low-density polyethylene and a propylene-based copolymer are laminated,
A film which discloses that the tearability can be improved by stretching in a specific direction, and thirdly, JP-A-2-283445.
The publication discloses that a crosslinked stretched film having a resin having a relatively high melting point as an outer layer and a resin having a relatively low melting point as a core layer can improve optical characteristics and achieve high shrinkage performance. There is a description of the film.

[0007]

However, although the tearability of the first and second films is improved, the tearability is only in one direction, and conversely, the tearability in the direction perpendicular to the stretching direction is poor. The improvement in openability was insufficient. In addition, these films have a poor balance of shrinkability, do not have wrinkles on the objects to be packaged of various shapes which are fields of use of the present invention, are insufficient for beautiful shrink packaging, and have poor transparency. there were. In addition, since the balance of tearability was poor, it was easy to break through the small holes for air release during contraction.

The third film has a high shrinkage property and can be beautifully packaged without wrinkles and can be improved in optical characteristics, but has a large tear propagation resistance and is difficult to open. It was a thing. As a result of studies to solve the problems of the above-mentioned conventional techniques, the inventors of the present invention have found that a packaging film having certain specific characteristics has a length of 10% to 50% of the length of a packaged item. A shrink that is obtained by tightly adhering to the packaged object by heat shrinkage by opening a small hole for venting air in the packaging film of this packaged object by sealing on three sides with a margin of It has been found that the package has excellent transparency after shrinkage, excellent tearability, and has no anisotropy, thereby greatly improving the openability.

[0009]

[Means for Solving the Problems] That is, the present invention is a packaging film for use in shrink packaging, wherein the packaging film is made of a crosslinked ethylene-based polymer resin and has the following characteristics (a) to (d): (A) The heat shrinkage rate at 120 ° C. measured by ASTM D-2732 is 30% or more in both longitudinal and transverse directions (b) Measured by ASTM D-2838 1 at 120 ℃
Equilibrium heat shrinkage stress after shrinking by 0% is 30 to 140 g / mm ² in both longitudinal and transverse directions (c) 10 to 50% measured by ASTM D-1922
Tear strength after shrinkage is 3 to 10 g in both longitudinal and transverse directions (d) 10 to 50% measured by ASTM D-1003
Haze after shrinkage is 3% or less. Also, it is 10 for each of the length and width of the package.
The packaged item was covered with a packaging film that was sealed on three sides with a margin of ~ 50%, and a small hole for venting air was opened in the packaged item of the packaged item. In the shrink package, the packaging film is made of a cross-linked ethylene-based polymer resin and has the following (a)
It is a shrink packaging body characterized by being a film having the characteristics (d) to (d).

(A) The thermal shrinkage at 120 ° C. measured by ASTM D-2732 is 30% or more in both longitudinal and transverse directions. (B) At 120 ° C. measured by ASTM D-2838 1
Equilibrium heat shrinkage stress after shrinking by 0% is 30 to 140 g / mm ² in both longitudinal and transverse directions (c) 10 to 50% measured by ASTM D-1922
Tear strength after shrinkage is 3 to 10 g in both longitudinal and transverse directions (d) 10 to 50% measured by ASTM D-1003
The haze after shrinkage is 3% or less. Hereinafter, the present invention will be described in detail.

An example of the process for obtaining the shrink package of the present invention from the packaging film of the present invention is as follows. Firstly, the packaging object is covered with a packaging film which is sealed on three sides with a margin ratio of 10 to 50% with respect to the length of the packaging object in the longitudinal direction and the transverse direction. The method of covering the article to be packaged with the packaging film may be either the pillow shrink or the L-type packaging described above. Here, the length of the packaged product in the vertical direction is
The length of the package in the flow direction when the package is flowed to the packaging machine is half the length of the package, and the lateral length is the circumference of the package in the direction perpendicular to the vertical direction. It means half the length, and the margin ratio of 10 to 50% means that the film length between the seals is made 10 to 50% longer than the length of the packaged object. is there.

The allowance ratio is set to 10 to 50% because there are various shapes such as a conical shape, a truncated cone shape, and an irregular shape having a protrusion, in addition to the rectangular parallelepiped or cubic shape. is there. If the allowance ratio is smaller than 10%, stress may be concentrated on the seal portion and the small holes for venting air at the time of contraction, and peeling or tearing of the seal may occur. Further, if the allowance rate is larger than 50%, it tends to be difficult to obtain a tensioned shrink wrapping body that is in close contact with the object to be packaged, and a beautiful shrink wrapping body cannot be obtained. Therefore, raising the temperature of hot air or the like causes a decrease in transparency.

The three-way seal may be selected in accordance with a packaging film that uses a normal sealing method such as impulse sealing, heat sealing, and fusion sealing, and these sealing methods may be used in combination. Secondly, a small hole for venting air is made in the packaging film of the article to be packaged to form a shrink package which is tightly attached to the article to be packaged by heat shrinkage.
The small hole for venting air can be opened by using a needle, a hot needle, a laser, or the like, but this step may be performed before the step of performing the first three-way sealing. Although hot air, steam or the like can be used for heat shrinkage, hot air that does not require post-treatment is usually used.

The packaging film of the present invention will be described in detail.
The packaging film of the present invention comprises a crosslinked ethylene polymer resin. Ethylene polymer resin is α ray, β ray, γ
It can be easily cross-linked by irradiation with ionizing radiation such as an electron beam, a neutron beam or an electron beam. Proper cross-linking is effective in improving the transparency of the packaging film after shrinkage, and also in preventing the film from breaking due to melting when shrinking by heating above the melting point of the resin that constitutes the packaging film. Is also effective.

The degree of irradiation is 2 megarads to 10 megarads, preferably 4 megarads to 7 megarads. When the degree of irradiation is less than 2 megarads, improvement in transparency after shrinkage is insufficient and it is difficult to impart high shrinkability to the packaging film, so that a beautiful shrink package cannot be obtained. Further, when the irradiation degree is higher than 10 megarads, the transparency after shrinkage is improved, but when high shrinkage is imparted, the shrinkage stress becomes too large, and tears from small holes for air release and peeling of the seal portion are caused. It occurs and it is difficult to obtain a beautiful shrink package.

Examples of the ethylene-based copolymer constituting the packaging film of the present invention include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene and ultra-low-density polyethylene using a Ziegler-type multisite catalyst. Resins such as a copolymer of ethylene and a vinyl compound that can be copolymerized, or an ethylene copolymer using a single-site catalyst, which has been rapidly developed in recent years, can be used. Among these ethylene-based copolymers, linear low-density polyethylene which is a copolymer of ethylene and α-olefin using a Ziegler-based catalyst, ultra-low density polyethylene, or ethylene and α using a single-site catalyst. -Copolymers with olefins are preferably used.

The density of the ethylene copolymer constituting the packaging film of the present invention is 0.890 to 0.9.
40 g / cm ³ is used, but preferably 0.
It is 900 to 0.930 g / cm ³ . 0.89 density
When it is less than 0 g / cm ³ , the packaging film is not stiff, and when the density exceeds 0.940 g / cm ³ , the transparency of the packaging film becomes poor.

The packaging film of the present invention may be either a monolayer film or a multilayer film, and particularly has a density of 0.8.
90 to 0.925 g / cm ³ of two outer layer films made of an ethylene-based polymer resin and a density of 0.925 to
A multilayer film comprising 0.940 g / cm ³ and at least one inner layer film comprising an ethylene polymer resin is desirable for obtaining a shrink package having excellent transparency and easy opening after shrinkage. Also, the density is 0.910
Two outer layer films made of an ethylene-based polymer resin having a density of 0.920 g / cm ³ and a density of 0.925 to 0.94
A multi-layer film comprising at least one inner layer film comprising an ethylene-based polymer resin of 0 g / cm ³ ;
It is more preferable in order to obtain a shrink package having excellent transparency and easy opening after shrinkage.

Among the characteristics of the packaging film of the present invention, the shrinkage characteristics will be described. The shrink wrap of the present invention has 3
It is intended to cover the object to be packaged with the one-side sealed packaging film and bring it into a state of being tightly adhered to the object to be packaged by heat shrinkage, but there are various shapes of the object to be packaged. The following shrinkage characteristics are required.

Firstly, it has a high shrinkage as measured by ASTM D-2732, in which the thermal shrinkage at 120 ° C. is 30% or more in both the longitudinal and transverse directions. In the present invention, the packaging film is provided with a margin ratio of 10 to 50% before heat shrinkage. In this case, it is used as a reference temperature for heat shrinkage.
It is necessary that the shrinkage rate at 0 ° C. is 30% or more in both the vertical and horizontal directions. If the shrinkage rate in both the vertical and horizontal directions is less than 30%, the packaging film will not adhere to the packaged object to form a tight package, and even if the shrinkage rate in one of the vertical and horizontal directions is less than 30%, the corners of the packaged object, etc. Wrinkles are left behind and it does not result in a beautiful package. It is difficult to impart such a high shrinkage property to a conventional polyethylene-based shrinkable film, and if the shrinkage temperature is raised to increase shrinkage, the film melts or the transparency deteriorates.

[0021] Part 2, ASTM D-2838 30~140g / mm 2 balanced heat shrinkage stress after shrunk by 10% at 120 ° C. were measured in the longitudinal and transverse directions both at, preferably 30 to 100 g / mm ² Is to be. If the equilibrium heat shrinkage stress after shrinking 10% at 120 ° C. is less than 30 g / mm ² in both the longitudinal and transverse directions, it seems that a tight and tight shrink package can be obtained immediately after shrink packaging. However, loosening occurs due to transportation, stacking, etc., and the commercial value is reduced. Further, when the equilibrium heat shrinkage stress exceeds 140 g / mm ² in both the vertical and horizontal directions, the stress concentrates on the seal portion and the small holes for air venting, resulting in peeling of the seal portion and tearing of the film from the small holes. further,
If the object to be packaged is a crushable tray or the like, it may be deformed or wrinkles may be generated.

The opening property of the packaging film of the present invention will be described. Generally, in the shrink wrapping body, since the wrapping film is in close contact with and in a tense state, there is no clue at the time of opening and there is a problem in the easy-opening property as described above.
For this reason, conventional shrink packaging has been devised such as notching the packaging film or attaching a cut tape. However, even if a clue to break the film with a notch or a cut tape is provided, the tear propagation resistance of the film is large, or the direction of tear is anisotropic, so easy opening can be imparted only by these measures. Not not.

The tear strength of the packaging film of the present invention after shrinking by 10 to 50% is 3 to 10 g in both longitudinal and transverse directions, preferably 4 to 10 g. If the tear strength is in this range, there is no resistance when opening and the anisotropy is small, so opening is very easy. The tear strength of the packaging film of the present invention is smaller than the tear strength of conventional polyethylene shrink films, but the shrink method of the shrink package of the present invention has a large margin ratio of 10 to 50%.
It does not cause problems such as tearing during packaging.

However, if the tear strength after shrinking by 10 to 50% is less than 3 g, tearing occurs in the process of running the packaging film on the machine, and the packaging efficiency is reduced. Also, the tear strength after 10-50% shrinkage is 10g
If it exceeds the limit, the resistance when opening will increase. Conventionally, when trying to reduce the tear strength and improve the openability, there was a problem that the shrinkage stress became too large and tearing and peeling of the seal part occurred at the small holes for air venting,
INDUSTRIAL APPLICABILITY The packaging film of the present invention is very useful while having an easy-opening property without tearing in small holes for air venting and peeling of the seal portion.

This characteristic is that the packaging film of the present invention is crosslinked, the heat shrinkage at 120 ° C. is 30% or more in both the longitudinal and transverse directions, which is high shrinkability, and 10% at 120 ° C.
Equilibrium heat shrinkage stress after 30% shrinkage is 30-140 g / m
It is due to m ² . Since the packaging film of the present invention is crosslinked, stable stretching can be easily performed due to the large tension of the film even at a temperature above the melting point of the resin constituting the film, and the stretching temperature and the stretching ratio are adjusted. This is because it is possible to produce a film having high shrinkability and low shrinkage stress.

The transparency of the packaging film of the present invention will be described. The packaging film of the present invention is ASTM D-1003.
The haze after shrinkage of 10 to 50% as measured by 1. is 3% or less. The haze is an important property that determines the visibility and commercial properties of the shrink package. Haze after shrinkage is 3%
If it exceeds, the visibility of the packaged product deteriorates, and as a result, the commercial property of the shrink package is deteriorated. Since the packaging film of the present invention is cross-linked, it can be used without melting even if the shrinking temperature is raised above the melting point of the resin constituting the film, and the transparency is less deteriorated even when cooled after shrinking.

The method for producing the packaging film of the present invention will be described. The non-anisotropic shrinkable film can be obtained by using, for example, a tubular biaxial stretching method.
First, a resin is extruded in a molten state from an annular die and rapidly cooled with a liquid refrigerant such as water to manufacture a non-stretched tube. Next, this tube is irradiated with an electron beam to crosslink the resin, and then the tube is heated to a temperature above the melting point of the resin by heat transfer heating with hot air or radiant heating with an infra heater, etc. While stretching in the machine flow direction with a velocity ratio between the two, air is injected into the tube and stretched in the direction perpendicular to the machine flow direction.

Irradiation with an electron beam varies depending on the type of resin, but usually 4 to 7 megarads is preferable for the packaging film used in the present invention. The reason why the tube after the cross-linking treatment is heated to the melting point of the resin or higher is to adjust the heat shrinkage stress of the stretched film so that the packaged article does not deform during packaging. Stretching below the melting point of the resin may cause deformation of the object to be packaged or break the film from the small holes for venting air during contraction. In order to stably perform stretching at a temperature equal to or higher than the melting point of the resin, a cross-linking treatment is necessary. If the cross-linking treatment is not performed, the tension of the tube before stretching is extremely reduced, and it is impossible to stretch at all.

In order to obtain the shrink wrap of the present invention, the wrapping film used is 5 at maximum in each of the vertical and horizontal directions.
It is necessary to shrink by 0%. In order to obtain such a packaging film, the stretching ratio also needs to be relatively large,
Specifically, a stretching ratio of 6 times or more is preferable in both the machine flow direction and the direction perpendicular thereto.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION The measuring method and the evaluating method in the present invention are as follows. (1) Heat shrinkage ratio Measured according to ASTM D-2732. (2) Equilibrium heat shrinkage stress Measured in accordance with ASTM D-2838. In addition, 1
10% shrinkage at 20 ° C means cutting a film into 200 mm square, fixing the film in a 180 mm square wooden frame with the four corners of the film slackened, and then shrinking the tunnel in the furnace at 120 ° C ( Keiyu System Co., Ltd. MS-8441 type) is passed through for 5 seconds to shrink the film by 20% in the machine and transverse directions. The equilibrium heat shrinkage stress is the value of the shrinkage stress 60 seconds after the start of measurement.

(3) Tear strength The tear strength was measured according to ASTM D-1922. 10-5
The contraction of 0% means that the film is fixed in a wooden frame in a state in which the film is slackened in the longitudinal and lateral directions by 10 to 50%, and then passed through a contraction tunnel for 5 seconds to contract. The tear strength is measured 10 minutes after passing through the shrink tunnel.

(4) Haze Measured according to ASTM D-1003. In addition, 1
Shrinkage of 0 to 50% means, similarly to the above (2), fixing the film in the wooden frame in a state that the film is slackened in the longitudinal and lateral directions by 10 to 50%, and then shrinking by passing through a shrinking tunnel for 5 seconds. Say. (5) Density Measured according to ASTM D-1505.

(6) MI (melt index) Measured in accordance with ASTM D-1238 E conditions.
Temperature 190 ° C, load 2.16Kg (7) Packaging evaluation-Finish of shrink package ○: Wrinkle-free packaging film adheres tightly to the packaged product △: No wrinkles on the top surface of the packaged product Has wrinkles around it. ×: Wrinkles remain on the upper surface and the periphery of the object to be packaged. ・ Breakage of the air vent hole and seal part ○: No air vent hole and seal part tear △: No air vent hole breakage Part of the seal part broke ×: Both the air vent hole and the seal part broke ・ Transparency (take out the film from the shrink package,
It was measured. ) ○: Haze of less than 3% △: Haze of 3 to 4% ×: Haze of more than 4% ・ Opening property ○: Tear resistance is small and there is no direction of tearing △ : Tear resistance is small, but there is a tear direction x: Tear resistance is large and there is a tear direction

[0034]

Example 1 Using the resins shown in Table 1, two extruders were used to melt a tube having a three-layer structure consisting of two surface layers of the same resin composition and one intermediate layer from a ring die. It was extruded and quenched with water as a liquid refrigerant to obtain a 400-micron-thick unstretched tube. At this time, the ratio of the two surface layers to the intermediate layer was 30:70, and the surface layer had 1% of diglycerin monooleate as a surfactant and 0.5% of glycerin monooleate and 0% of mineral oil as a lubricant. 0.75% was added.

The obtained non-stretched tube was irradiated with an electron beam accelerated by an accelerating voltage of 500 KV for 4 megarads to carry out a crosslinking treatment, followed by radiant heating by an infra heater to heat the non-stretched tube to 140 ° C., and to set two sets. Depending on the speed ratio between the nip rolls, the flow rate of the machine is 6 times, and by injecting air into the tube, it is stretched 6.5 times in the direction perpendicular to the machine flow direction, and the maximum diameter of the bubble formed by the air ring is increased. A cold air of 25 ° C. was applied to the part to cool and fix the stretching, and then it was folded to obtain a packaging film having a thickness of 10.3 μm.

The characteristics of the obtained packaging film are shown in Table 2. The obtained packaging film has high shrinkability, but does not show large shrinkage stress, tear strength does not increase even after shrinkage, and transparency does not deteriorate. It turns out to be a thing. Using this packaging film, a shrink wrapping body was prepared using a commercially available horizontal pillow shrink wrapping machine. As the article to be packaged, a lunch box container having a foamed polystyrene tray and a cover made of a stretched polystyrene transparent sheet is used, and the film is cylindrically sent around the lunch box container, and the seam of the film at the bottom of the article to be packaged is heat-sealed. Subsequently, both ends of the tubular film are fused and sealed. At this time, sealing was performed with a margin ratio of 30% in both the vertical and horizontal directions. The small holes for venting air were created by needle-like protrusions on the bottom of the package. Subsequently, it was conveyed to a heating tunnel and contracted for a residence time of 5 seconds to obtain a shrink package. Packaging was performed by changing the temperature of the heating tunnel from 110 ° C to 180 ° C, and the results are shown in Table 3. It can be seen that the shrink package of the present invention has a good finish in a wide temperature range, has little breakage in the air vent hole and the seal portion, is excellent in transparency and is easy to open.

In Table 1, VLDPE is an ethylene-octene-1 copolymer (ethylene content 90% by weight).
Ultra-low density polyethylene, LLDPE indicates linear low-density polyethylene (ethylene content: 95 wt%) linear low-density polyethylene, and LDPE indicates high-pressure low-density polyethylene (homopolymer).

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

Examples 2 to 4 A packaging film having a thickness of 10.5 μm was obtained in the same manner as in Example 1 except that the resins shown in Table 4 were used. The properties of the obtained packaging film are shown in Table 5, which is 1 even though each film has high shrinkability.
It can be seen that the equilibrium heat shrinkage stress after 10% shrinkage at 20 ° C. is small, the tear strength after shrinkage does not increase, and the haze after shrinking does not decrease.

Packaging was carried out in the same manner as in Example 1 using these packaging films to obtain a shrink package. The results are shown in Table 6, and it can be seen that any shrink package has a wide temperature range in which it can be packaged, has excellent transparency, and is easy to open. In particular, the shrink wrap of Example 2 was excellent in transparency after shrinkage, and was as transparent as a stretch wrap that was not subjected to shrink treatment.

In Table 4, VLDPE2 is ethylene-octene-1 copolymer (ethylene content 86% by weight) single-site catalyst ultra low density polyethylene,
VLDPE3 is an ethylene-octene-1 copolymer (ethylene content 90% by weight), a very low density polyethylene using a single site catalyst, and LLDPE4 is ethylene-octene-.
1 shows a copolymer (ethylene content 94% by weight) and a very low density polyethylene by a single site catalyst.

In Table 6, A is the finish of the shrink package, B is the breakage of the air vent hole and the seal, and C is C.
Indicates transparency and D indicates openability.

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

[Table 6]

[0048]

Examples 5 to 7 A packaging film was obtained in the same manner as in Example 1 except that the irradiation dose was changed to 2 megarads, 5 megarads and 7 megarads. The characteristics of the obtained packaging film are shown in Table 7. Using these films, packaging was performed in the same manner as in Example 1 to obtain shrink packages. Table 8 shows the results. It can be seen that the shrink package of the present invention has a good finish in a wide temperature range, has little breakage at the air vent hole and the seal portion, has excellent transparency, and is easy to open.

In Table 8, A is the finish of the shrink package, B is the breakage of the air vent hole and the seal, and C is.
Indicates transparency and D indicates openability.

[0050]

[Table 7]

[0051]

[Table 8]

[0052]

[Comparative Examples 1 and 2] Films were prepared in the same manner as in Example 1 except that the resins shown in Table 9 were used.
A 5 micron packaging film was obtained. The characteristics of the obtained packaging film are shown in Table 10. Using these films, the same packaging as in Example 1 was performed to obtain a shrink package. The results are shown in Table 11. The shrink package of Comparative Example 1 had excellent packaging finish and transparency, but had a large tear strength after shrinkage and poor openability. Further, the shrink package of Comparative Example 2 was liable to be broken at the air vent hole or the seal portion and was inferior in transparency.

In Table 9, VLDPE5 is ethylene-octene-1 copolymer (ethylene content 80% by weight), and HDPE7 is high density polyethylene. Further, in Table 11, A indicates the finish of the shrink package, B indicates the breakage of the air vent hole and the seal portion, C indicates the transparency, and D indicates the openability.

[0054]

[Table 9]

[0055]

[Table 10]

[0056]

[Table 11]

[0057]

Comparative Example 3 A packaging film was prepared in the same manner as in Example 1 except that the non-stretched tube was not irradiated. However, when heated above the melting point of the resin composition of the tube, stretching was not stable, Moreover, only a film having extremely poor transparency was obtained. Therefore, a commercially available non-crosslinked polyethylene-based shrinkable film having the properties shown in Table 12 was used as the packaging film, and the same packaging as in Example 1 was performed.
A shrink package was obtained. Table 13 shows the results. The shrink wrap of Comparative Example 3 obtained was excellent in transparency, but had a very narrow temperature range of the heating tunnel capable of achieving a good finish, and had a too large tear strength after shrinkage, resulting in poor openability. It was

[0058]

[Table 12]

[0059]

[Table 13]

[0060]

[Comparative Examples 4 to 5] A packaging film was prepared in the same manner as in Example 1 except that the irradiation amount to the non-stretched tube was 1 megarad and 11 megarad.
A 0.5 micron packaging film was obtained. The characteristics of the obtained packaging film are as shown in Table 14. Using these films, packaging was performed in the same manner as in Example 1 to obtain a shrink package. Table 15 shows the results. Obtained Comparative Example 4
Although the shrink wrapping of No. 1 had less breakage from the air vent hole and the breakage of the seal part, it had poor transparency after shrinkage and had a narrow temperature range of the heating tunnel capable of achieving a good finish. Further, Comparative Example 5 was excellent in transparency after shrinkage, but the temperature range of the heating tunnel capable of improving the finish was very narrow.

In Table 15, A is the finish of the shrink package, B is the breakage of the air vent hole and the seal,
C indicates transparency and D indicates opening property.

[0062]

[Table 14]

[Table 15]

INDUSTRIAL APPLICABILITY The packaging film of the present invention has high shrinkability but does not have large shrinkage stress, tear strength does not increase even after shrinkage, and transparency does not decrease, so that it can be preferably used for shrink packaging. . Further, the shrink package of the present invention has a good finish in a wide temperature range,
It is very useful in the shrink packaging field because it has little breakage at the air vent hole and the seal part, has excellent transparency, and is easy to open.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location B65B 53/02 B65B 53/02 D B65D 65/40 B65D 65/40 C C08J 3/28 CES C08J 3/28 CES // B29K 23:00 105: 02 105: 24 B29L 7:00 9:00 C08L 23:26

Claims (6)

[Claims] 1. A packaging film for use in a shrink package, wherein the packaging film is made of a cross-linked ethylene polymer resin and has the following characteristics (a) to (d). Packaging film. (A) Thermal contraction rate at 120 ° C. measured by ASTM D-2732 is 30% or more in both longitudinal and transverse directions. (B) 1 at 120 ° C. measured by ASTM D-2838
Equilibrium heat shrinkage stress after shrinking by 0% is 30 to 140 g / mm ² in both longitudinal and transverse directions (c) 10 to 50% measured by ASTM D-1922
Tear strength after shrinkage is 3 to 10 g in both longitudinal and transverse directions (d) 10 to 50% measured by ASTM D-1003
Haze after shrinkage is 3% or less 2. The packaging film according to claim 1, which is crosslinked by irradiation with an electron beam of 2 to 10 megarads. 3. Two outer layers of ethylene-based polymer resin having a density of 0.890 to 0.925 g / cm ^{3 as} measured by ASTM D-1505 and ASTM D-1505.
The packaging film according to claim 1, wherein the packaging film is a multilayer film including at least one inner layer made of an ethylene-based polymer resin having a density of 0.925 to 0.940 g / cm ³ measured in step ³ . 4. A packaging film for a packaged object, wherein the packaged object is covered with a packaging film which is sealed on three sides with a margin ratio of 10 to 50% with respect to the longitudinal and transverse lengths of the packaged object. In a shrink wrapping body in which a small hole for venting air is opened and which is tightly adhered to a packaged object due to heat shrinkage, the wrapping film is made of a crosslinked ethylene-based polymer resin, and the shrinkage of the following (a) to (d) A shrink package characterized by being a film having characteristics. (A) Thermal contraction rate at 120 ° C. measured by ASTM D-2732 is 30% or more in both longitudinal and transverse directions. (B) 1 at 120 ° C. measured by ASTM D-2838
Equilibrium heat shrinkage stress after shrinking by 0% is 30 to 140 g / mm ² in both longitudinal and transverse directions (c) 10 to 50% measured by ASTM D-1922
Tear strength after shrinkage is 3 to 10 g in both longitudinal and transverse directions (d) 10 to 50% measured by ASTM D-1003
Haze after shrinkage is 3% or less 5. The shrink package according to claim 4, wherein the packaging film is crosslinked by irradiation with an electron beam of 2 to 10 megarads. 6. The packaging film is ASTM D-1505.
Density measured at 0.890-0.925 g / cm^Threeso
Two outer layers made of an ethylene polymer resin and AST
The density measured by MD-1505 is 0.925 to 0.9.
40 g / cm ^ThreeWhich is an ethylene-based polymer resin
It is a multilayer film consisting of at least one inner layer.
The shrink wrapping body according to claim 4, wherein