JPH08259707A - Stretchable film for food packaging - Google Patents

Abstract

PURPOSE: To obtain a stretchable film which is not made of PVC and is satisfactory in packaging efficiency and package finish. CONSTITUTION: This film comprises at least one layer of a resin (blend) comprising repeating units of an α-olefin ingredient consisting mainly of ethylene and repeating units of a cycloolefin which are optionally bonded thereto. It has a storage elastic modulus (E') of 5.0×10<8> to 5.0×10<9> dyn/cm<2> and a loss tangent (tanδ) of 0.2-0.8, as determined at a frequency of 10Hz and 20 deg.C in a dynamic viscoelasticity measurement. It is suitable for use in an automatic packaging machine, has satisfactory bottom sealability and evenness of elongation, and hence can give a package in which the film is in a well stretched state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stretch film used for food packaging, and more particularly to a stretch film made of a chlorine-free material.

[0002]

2. Description of the Related Art Conventionally, a polyvinyl chloride type has been mainly used as a stretch film for so-called prepackaging, in which fruits and vegetables, meat, side dishes, etc. are placed on a lightweight tray and overlapped with the film. This has good packaging efficiency, good packaging finish, and other properties, as well as excellent elastic recovery to return to its original shape even if the film after pressing is pressed with a finger, and also has a good bottom sealing property. This is because it has the quality advantage recognized by both sellers and consumers that the product value does not decrease, such as the film peeling does not occur easily during transportation display.

[0003]

However, in recent years, problems such as hydrogen chloride gas generated during incineration and elution of plasticizer contained in a large amount have been regarded as problems with polyvinyl chloride films. For this reason, various materials have been studied as alternatives to polyvinyl chloride films, and in particular, various stretch films having a structure using a polyolefin resin have been proposed. For example, ethylene-vinyl acetate copolymer (EVA),
Stretch films having a structure such as EVA / polybutene-1 / EVA and EVA / linear ethylene-α-olefin copolymer / EVA have been proposed. Polyolefin resins are readily available, have excellent water and oil resistance, hygiene, easy post-use treatment, are easy to film form, and have excellent mechanical strength.

However, since the polyolefin resin as described above is generally crystalline, the elongation tends to be non-uniform. In addition, when tension is removed in the stretched state, it is restored instantly, which makes it difficult to perform packaging work, and it is difficult to satisfy all of the characteristics such as packaging workability, packaging finish, elastic recovery, and bottom sealability.

[0005]

As a result of intensive studies, the present inventors have succeeded in obtaining a non-vinyl chloride type stretch film excellent in the above-mentioned various properties, and the gist thereof is mainly ethylene. Dynamic viscoelasticity measurement having at least one layer of a single or mixed resin containing a repeating unit of α-olefin and a repeating unit of cyclic olefin linked or not bonded to the repeating unit of α-olefin. The storage elastic modulus (E ') measured at a frequency of 10 Hz and a temperature of 20 ° C. is 5.0 × 10 ⁸ to 5.0 × 10 ⁹ dy.
A stretch film for food packaging is characterized in that the loss tangent (tan δ) of n / cm ² is in the range of 0.2 to 0.8.

That is, according to the present invention, a repeating unit of bulky cyclic olefin is coexistent with a repeating unit of α-olefin mainly composed of ethylene, thereby reducing the crystallinity and exhibiting uniform elongation. By giving the viscoelastic property of
It was found that a film with a good packaging finish can be obtained.

The present invention will be described in detail below. The stretch film of the present invention is a single or mixed resin containing a repeating unit of α-olefin, which is mainly composed of ethylene, and a repeating unit of a cyclic olefin, which is bonded to the α-olefin repeating unit or is not bonded. It has at least one layer.

As a concrete example thereof, a polymer material mainly composed of repeating units of (A ₁ ) α-olefin having ethylene as a main component is mixed with a polymer material mainly composed of repeating units of (B ₁ ) cyclic olefin. The ones that have been done are listed.

Here, α mainly composed of ethylene of (A ₁ )
-The resin consisting of repeating units of olefin, a unit derived from ethylene or a unit derived from other α-olefin in addition to it, and / or a resin in which a unit derived from a monomer other than α-olefin is copolymerized, For example, low density polyethylene, ultra low density polyethylene, medium density polyethylene, ethylene-vinyl acetate copolymer (EV
A), ethylene-alkyl acrylate copolymer, ethylene-alkyl methacrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer,
Ethylene-propylene copolymer, ethylene-butene-1
Examples thereof include copolymers and polymers such as ionomers of these resins. In addition, a small amount (for example, within 5 mol%)
It may be an ethylene-cyclic olefin copolymer obtained by copolymerizing the above cyclic olefin.

As these resins, known resins for films can be used, and in general, the melt flow ratio M from the viewpoint of film moldability and film strength.
FR (190 ° C, 2.16kg load) 0.1-5g /
Resin of about 10 minutes can be used. Also, in order to obtain the flexibility required for a stretch film, the ethylene unit is 6
A resin of 0 mol% or more, preferably 80 mol% or more is suitable.

On the other hand, as the polymer material having a cyclic olefin unit (B ₁ ), a petroleum resin mainly composed of a repeating unit derived from cyclopentadiene represented by the following formula (1) or a hydrogenated product thereof,

Embedded image

A so-called coumarone-indene resin obtained by copolymerizing a small amount of coumarone with indene represented by the following formula (2),

Embedded image

A terpene resin mainly composed of a repeating unit derived from α-pinene represented by the following formula (3) or a hydrogenated product thereof.

Embedded image

The following can be exemplified. Here, the cyclic olefin has only to have at least one double bond, and examples thereof include cyclic diolefin.

The component (B ₁ ) exemplified here can have various characteristics depending on its polymerization degree, copolymerization component, hydrogenation rate, catalyst system used, etc., but it is suitable for the present invention. Has a glass transition temperature of 70 ° C. or higher, particularly preferably 80 ° C. or higher in relation to the component (A ₁ ).

Further, since the component (B ₁ ) generally tends to be less compatible with the component (A ₁ ) as the molecular weight increases, the molecular weight is generally 700 to 900 from the viewpoint of both the glass transition temperature and the compatibility. Those in the range of are preferable,
Further, those having a sharp molecular weight distribution are preferable.

This (B ₁ ) component is compatible with the (A ₁ ) component, which is originally crystalline, in a fine order to reduce its crystallinity, and also changes the stress behavior characteristics of the (A ₁ ) component. The following characteristics can be achieved.
The mixing ratio of the (A ₁ ) component and the (B ₁ ) component is determined so as to comply with the later-described criteria regarding viscoelasticity.

The film of the present invention has a storage elastic modulus (E) measured at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement.
′) Is 5.0 × 10 ⁸ to 5.0 × 10 ⁹ (dyn / cm
² ) and the loss tangent (tan δ) is 0.2
It is in the range of 0.8. E'is 5.0 here
When it is less than × 10 ⁸ dyn / cm ^2, it is not suitable as a stretch film because it is soft and the stress against deformation is too small, resulting in poor workability and no film tension of the packed product. On the other hand, when E'exceeds 5.0 × 10 ⁹ dyn / cm ² , the film becomes hard and difficult to stretch, and the tray is likely to be deformed or crushed.

When tan δ is less than 0.2, the restoring behavior with respect to the elongation of the film is instantaneous, so that the film is restored in a short time before the film is folded into the bottom of the tray, and the film is satisfactorily processed. Wrinkles tend to occur without stretching. Also in the heat-sealed state of the bottom portion, in the case of stretch packaging, it is difficult to perform sufficient fusion bonding due to heat, so that the bottom seal is likely to be peeled off gradually during transportation or display after packaging. Further, if tan δ exceeds 0.8, the packaging finish is good, but plastic deformation is exhibited, and the tension of the packed products against the external force is too weak, and the tray top surface may become stuck due to stacking during transportation or display. The film is slack and the commercial value is apt to decrease. Further, in the case of automatic packaging, problems such as a defective check are likely to occur because it tends to stretch vertically. A particularly preferable range of tan δ is
It is 0.30 to 0.60.

The component (A ₁ ) generally has a glass transition temperature of −
40 to 0 ° C., and tan δ at 20 ° C. is 0.1 to
It is about 0.15, and the characteristics intended by the present invention cannot be obtained by itself. Therefore, the glass transition temperature is high (B ₁ )
By including / dispersing the components, the glass transition temperature of the mixture becomes high, the tan δ at 20 ° C. becomes large, and the crystallinity is lowered, so that preferable properties as a stretch film can be obtained.

In order to satisfy the above characteristics, the mixing ratio of the (A ₁ ) component and the (B ₁ ) component is important. The mixing ratio of the (A ₁ ) component and the (B ₁ ) component differs depending on the combination of the materials used, so it is difficult to unconditionally define, but if the (B ₁ ) component is less than 20% by weight, the (A ₁ ) component Crystallinity remains strong and tan δ is low, which is not preferable. On the other hand, when it exceeds 35% by weight, the storage elastic modulus (E ') of the film is lowered and the strength is also lowered, so that the packaging workability is deteriorated. Furthermore, the problem that the component (B ₁ ) is blown out onto the film surface is likely to occur. The standard of the mixing ratio is to set the glass transition temperature of the mixture to be in the range of -10 to 10 ° C.

Since the stretch film is sometimes used at low temperature, it is desirable that the stretch film has excellent low temperature characteristics (especially elongation). For that purpose, the dynamic viscoelasticity measurement was carried out at a frequency of 10 Hz and a temperature of 0 ° C. The storage elastic modulus (E ′) of the film is preferably in the range of 1.5 × 10 ¹⁰ dyn / cm ² or less.

For that purpose, it has excellent low temperature characteristics (A ₁ ).
It is effective to increase the ratio of the components, and the mixing ratio of the (A ₁ ) component and the (B ₁ ) component should be such that the amount of the (A ₁ ) component becomes large within the range where the viscoelastic property at a temperature of 20 ° C. is satisfied. It is achieved by setting to. Also, the above (B ₁ )
Many of the components impart tackiness to the film. Therefore, since a blocking when large amounts are added as described above is likely to occur, (A ₁₎ component and the (B ₁₎ mixed resin layer of the components, (A ₁₎ component alone or (A ₁₎ component is extremely large surface The layers can also be laminated.

As another example of the material system of the film of the present invention, a layer made of a copolymer resin of (A ₂ ) ethylene as a main component of α-olefin units and cyclic olefin units, or (A ₂ ) ethylene as a main component Examples thereof include those having a layer made of a combination of a copolymer resin of α-olefin units and cyclic olefin units, and (B ₂ ) a property adjusting material.

Here, the ethylene-based α-olefin unit of the component (A ₂ ) is mainly ethylene and, if necessary, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1 -Containing α-olefin units such as octene. Examples of the cyclic olefin unit include a cyclic olefin represented by the following general formula (4).

[0026]

[Chemical 4]

Specifically, norbornene, 5-methylnorbornene, 5-ethylnorbornene, 5-propylnorbornene, 1-methylnorbornene, 7-methylnorbornene, 5,5,6-trimethylnorbornene, 5-
Examples thereof include phenyl norbornene and 5-benzyl norbornene. Further, this resin may contain other copolymerizable monomer as needed within a range not impairing the object of the present invention, and examples thereof include butadiene and isoprene.

In the case of having a layer comprising the component (A ₂ ), the type of the cyclic olefin unit and the copolymerization ratio are controlled within a specific range, or two or more copolymer resins having different copolymerization ratios are blended. Further, it can be adjusted so as to satisfy the conditions such as E ′ and tan δ by copolymerizing the third component.

However, in the range where the above characteristics are satisfied, the crystallinity of the copolymer resin is considerably low and the glass transition temperature is not high, so that the pellets of the copolymer resin are apt to block. May be disadvantageous. Further, in a range satisfying E ′ and tan δ at 20 ° C., E ′ at 0 ° C. becomes high, and it may not be said that the low temperature suitability is perfect.

From this point, it is also possible to use an ethylene-cyclic olefin copolymer resin having a high cyclic olefin content as the component (A ₂ ) and mix it with the (B ₂ ) property improving material.

An example of the property improving material (B ₂ ) is polybutene having a low degree of polymerization. That is, a resin having a glass transition temperature of 40 ° C. or higher, which is generally used as an ethylene-cyclic olefin copolymer resin, is mixed with a material having a low glass transition temperature and a good compatibility, such as low polymerization degree polybutene, to plasticize the resin. The effect imparts flexibility, lowers the glass transition temperature, and improves the stretch film in a more preferable direction.

As the low-polymerization degree polybutene, those having an average molecular weight of 100 or more and 1,000 or less are preferable in consideration of compatibility and blowing onto the film surface after molding. Further, the mixing ratio is preferably in the range of about 35 to 50 parts by weight with respect to 100 parts by weight of the component (A ₂ ) when the glass transition temperature of the component (A ₂ ) is 40 ° C. or higher.

In addition, as a material having a low glass transition temperature and good compatibility with an ethylene-cyclic olefin copolymer resin, a copolymer of a vinyl aromatic compound and a conjugated diene, for example, styrene-butadiene-styrene triblock. Examples thereof include a copolymer (SBS) and a styrene-isoprene-styrene triblock copolymer (S1S). In this case, the styrene ratio is preferably 30% by weight or less in order to maintain the flexibility at room temperature.

In the case of using the above-mentioned property improving material, tan δ at 20 ° C. tends to become too large only by the above modification, and plastic deformation is exhibited to weaken the tension of the packed product. It is suitable to stack another non-PVC material layer having a small tan δ. As the other resin layer, a polyolefin polymer is preferable, and by laminating it with such a polymer, it is possible to adjust the viscoelastic property and impart stability, blocking resistance, slipperiness, etc. of the film formation of the film.

Here, examples of the polyolefin-based polymer as the laminated material include low density polyethylene, ultra low density polyethylene (copolymer of ethylene and α-olefin), ethylene-vinyl acetate copolymer (EVA), ethylene- Alkyl acrylate copolymer, ethylene-alkyl methacrylate copolymer, ethylene-acrylic acid copolymer,
Preference is given to ethylene-methacrylic acid copolymers, ionomers such as low-density polyethylene, and propylene-based elastomer materials.

Practically, for example, EVA can be preferably used, and the EVA has a vinyl acetate content of 5 to 5.
25% by weight, preferably 10 to 20% by weight, a melt flow ratio (MFR) of 0.2 to 2 g / 10 minutes (190
(° C, 2.16 kg load) is preferable in terms of strength, flexibility, film forming workability, and the like. The film of the present invention further has a stress ρ at 150% elongation measured at a temperature of 20 ° C.
₁₅₀ and the ratio of the stress ρ ₅₀ of the elongation at 50% (ρ ₁₅₀ /
It is preferable to have stress-strain characteristics such that ρ ₅₀ ) is in the range of 1.3 to 2.0 in both the vertical and horizontal directions.

When the ratio (ρ ₁₅₀ / ρ ₅₀ ) is less than 1.3, uneven elongation is exhibited at the time of packaging, and local elongation tends to cause breakage at a corner of a tray or the like. On the other hand, if this ratio exceeds 2.0, a strong force is required to stretch the film during the packaging work, the workability deteriorates, and the tray is likely to be deformed or crushed in the packaging by the automatic packaging machine.

When an ethylene polymer film is produced by the inflation method, which is a general method for producing stretch films, ρ ₁₅₀ / ρ ₅₀ tends to be large in the vertical direction and small in the horizontal direction. It is important to set ρ ₁₅₀ / ρ ₅₀ of the direction to a specific range. To do so, blow-up ratio (bubble diameter /
It is effective to increase the die diameter, and the blow-up ratio can be selected from the range of generally 4 or more, preferably 5 to 6, although it depends on the raw material used. The thickness of the film of the present invention is generally in the range used for ordinary stretch packaging, that is, in the range of 8 to 30 μm, typically in the range of 10 to 20 μm.

The film of the present invention is obtained by melt-extruding a material from an extruder and molding it into a film by inflation molding or T-die molding. In the case of a laminated film, it is advantageous to coextrude with a multilayer die. Practically, it is preferable to melt-extrude the material resin from the annular die and perform inflation molding.

Various additives may be added to the film of the present invention in order to impart antifogging properties, antistatic properties, slip properties and the like. For example, a surfactant such as glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, and ethylene oxide adduct can be appropriately added.

[0041]

EXAMPLES The effects of the present invention will be clarified by the following examples. The characteristics and performance of the film were measured and evaluated by the following methods. 1) E ', tanδ Viscoelasticity spectrometer VES- manufactured by Iwamoto Manufacturing Co., Ltd.
Using F3, vibration frequency 10Hz, temperature 20 ° C and 0
It was measured in the transverse direction of the film at ° C.

2) Stretch wrapping suitability: Using a stretch film having a width of 350 mm, an automatic wrapping machine (ISHIDA Wmin MK-manufactured by Ishida Koki Co., Ltd.) is used.
II) Expanded polystyrene tray (200 m long)
m, width 130 mm, height 30 mm) were packaged and the items shown in Table 4 were evaluated. Further, using the same film and tray, a packaging test was carried out by a hand packaging machine (Dialapper A-105 manufactured by Mitsubishi Plastics, Inc.). 3) ρ ₁₅₀ / ρ _{50 According to} JIS K1702, a tensile test was performed at a tensile speed of 200 mm / min for calculation.

Example 1 Linear ethylene-butene-1
Copolymer (butene-1 content 14% by weight, density 0.90
5) A composition obtained by mixing 75% by weight with 25% by weight of a hydrogenated product of a petroleum resin mainly composed of cyclopentadiene (glass transition temperature 81 ° C., Alcon P125 manufactured by Arakawa Chemical Co., Ltd.) was used as an intermediate layer (thickness 9 μm). On the other hand, EVA (vinyl acetate content 15% by weight, 190 ° C MFR 2.0 g / 10 min) 10
A composition obtained by kneading 3 parts by weight of diglycerin monooleate as an antifogging agent with 0 parts by weight was used as front and back layers and each had a thickness of 3 μm.
m, and a total thickness of 15 μm (3/9/3 μ by blow extrusion ratio (BUR) 6.0 by co-extrusion inflation molding.
m) was obtained.

The properties measured with the linear ethylene-butene-1 copolymer alone were as follows: storage modulus E'at 0 ° C. 2.0 × 10 ⁹ dyn / cm ² storage modulus E'1 at 20 ° C. The loss tangent tan δ 0.12 was 0.2 × 10 ⁹ dyn / cm ^{2 at} 20 ° C. The properties measured only with the intermediate layer composition are as follows: storage modulus E'at 0 ° C. 6.5 × 10 ⁹ dyn / cm ² storage modulus E ′ at 20 ° C. 1.1 × 10 ⁹ dyn / cm ² 20 ° C. The loss tangent at tan δ was 0.35.

(Example 2) A total thickness of 15 μm (3/3) was obtained in the same manner as in Example 1 except that the blow-up ratio was 5.0.
A film of 9/3 μm) was obtained. (Example 3) A total thickness of 15 µm (3/9/3 µm) was obtained in the same manner as in Example 1 except that the blow-up ratio was 4.0.
I got a film.

Example 4 An ethylene / methacrylic acid copolymer (methacrylic acid content: 12% by weight, 19%) was used as the front and back layers.
0 ° C. MFR 7.0 g / 10 min) 100 parts by weight, and 3 parts by weight of diglycerin monooleate as an antifogging agent were used in the same manner as in Example 1 except that a total thickness of 15 was used.
A film having a thickness of 3 μm (3/9/3 μm) was obtained.

Comparative Example 1 A film having a total thickness of 15 μm (6/3/6 μm) was obtained in the same manner as in Example 1 except that the thicknesses of the front and back layers and the intermediate layer were 6 μm and 3 μm, respectively. (Comparative Example 2) A total thickness of 15 µm (3/9/3 µm) was obtained in the same manner as in Example 1 except that only the linear ethylene-butene-1 copolymer used in Example 1 was used as the intermediate layer. I got a film.

Example 5 100 parts by weight of an ethylene-cyclic olefin copolymer (a glass transition temperature of 80 ° C., Apel 6509 manufactured by Mitsui Petrochemical Co., Ltd.) consisting of ethylene and norbornene was added to liquid polybutene (molecular weight 500, manufactured by Nippon Oil Co., Ltd.). The resin layer in which 40 parts by weight of LV-100) was mixed was used as an intermediate layer (9 μm), while the same EVA as used in Example 1 was used.
The composition was placed as front and back layers in an amount of 3 μm, and a film having a total thickness of 15 μm (3/9/3 μm) was obtained in the same manner as in Example 1.

The characteristics measured with the ethylene-cyclic olefin copolymer alone are as follows: storage modulus E'at 0 ° C. 1.8 × 10 ¹⁰ dyn / cm ² storage modulus E'at 20 ° C. E'1.8 × 10 The loss tangent at ¹⁰ dyn / cm ² 20 ° C. was tan δ 0.01. Further, the properties measured by the composition alone in which liquid polybutene is mixed with ethylene-cyclic olefin copolymer are as follows: storage elastic modulus at 0 ° C. E ′ 1.2 × 10 ¹⁰ dyn / cm ² storage elastic modulus at 20 ° C. E ′ 2 The loss tangent at 0.5 × 10 ⁹ dyn / cm ² 20 ° C. was tan δ 0.60.

Example 6 A film having a total thickness of 15 μm (5/5/5 μm) was obtained in the same manner as in Example 4 except that the thicknesses of the front and back layers and the intermediate layer were 5 μm and 5 μm, respectively. (Comparative Example 3) The front and back layers and the intermediate layer each have a thickness of 6 μm,
The total thickness is 15 μm in the same manner as in Example 4 except that the thickness is 3 μm.
A film of m (6/3/6 μm) was obtained.

Comparative Example 4 A total thickness of 15 μm (3 μm) was obtained in the same manner as in Example 4 except that a composition obtained by mixing 100 parts by weight of ethylene-cyclic olefin copolymer with 30 parts by weight of liquid polybutene was used as the intermediate layer. / 9/3 μm) was obtained. The properties measured by the intermediate layer composition alone are as follows: storage modulus E ′ at 0 ° C. 1.8 × 10 ¹⁰ dyn / cm ² storage modulus E ′ at 20 ° C. E ′ 8.0 × 10 ⁹ dyn / cm ^{2 at} 20 ° C. The loss tangent was tan δ 0.22.

Comparative Example 5 A commercially available polyvinyl chloride stretch film (thickness: 15 μm) was evaluated. Tables 1 to 3 show the results of measurement and evaluation of characteristics and performances of these films.

[0053]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

The film of Example 1 has a linear ethylene-
By including a layer in which a hydrogenated product of a petroleum resin mainly containing cyclopentadiene is mixed with the butene-1 copolymer,
The viscoelastic property was within the range specified in the present invention, and the various properties were excellent. Also, the films of Examples 2 to 6 were similarly excellent, but the film of Example 3 had a ρ ₁₅₀ / ρ ₅₀ outside the preferred range, and was slightly inferior in wrapping suitability.

[0055]

EFFECTS OF THE INVENTION According to the stretch film of the present invention, when used in an automatic wrapping machine or the like, the film can be cut / conveyed or lapped without any problems, the bottom sealing property is good, and the film tension is high. A good package can be obtained, and it has a feature that has never been seen as a non-PVC-based stretch film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location // C08F 210/02 MJR C08F 210/02 MJR

Claims (3)

[Claims] 1. A layer of a single or mixed resin comprising at least a repeating unit of α-olefin mainly composed of ethylene and a repeating unit of a cyclic olefin linked or not bonded to the α-olefin repeating unit. Having one layer, frequency 10Hz, temperature 2 by dynamic viscoelasticity measurement
Storage elastic modulus (E ′) measured at 0 ° C. is 5.0 × 10 ⁸ to
5.0 × 10 ⁹ dyn / cm ² , loss tangent (tan δ)
Is in the range of 0.2 to 0.8, and a stretch film for food packaging. 2. A frequency of 10 Hz measured by dynamic viscoelasticity,
Storage modulus of the film measured at a temperature 0 ° C. (E') is 1.5 × ¹⁰ 10 dyn / cm ² or less of food packaging stress Tutsi film of claim 1, wherein a is in the range. 3. A layer of a single or mixed resin comprising a repeating unit of α-olefin containing ethylene as a main component, and a repeating unit of cyclic olefin linked or not bonded to the repeating unit of α-olefin. It has at least one layer and has a storage elastic modulus (E ′) of 5.0 × 10 ⁸ measured at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement.
~ 5.0 × 10 ⁹ dyn / cm ² , loss tangent (tan
δ) is in the range of 0.2 to 0.8, and the ratio (ρ ₁₅₀ / ρ ₅₀ ) of the stress ρ ₁₅₀ at 150% elongation and the stress ρ ₅₀ at 50% elongation measured at a temperature of 20 ° C. A stretch film for food packaging, characterized in that it is in the range of 1.3 to 2.0 in both the vertical and horizontal directions.