JP3296532B2 - Stretch film for food packaging - Google Patents

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, as a stretch film for a so-called pre-package, fruits and vegetables, meat, prepared foods and the like are placed on a lightweight tray and overlapped with a film, a polyvinyl chloride type film has been mainly used. This has good packaging efficiency, good packaging finish, etc., and has excellent elastic recovery force that returns to its original state even after deformation such as pressing with a finger after packing, and good bottom sealing. This is because the merchandise and the consumer have the superiority of the quality that the value of the merchandise does not decrease such that the film is hardly peeled off during the transportation display.

[0003]

However, in recent years, problems such as hydrogen chloride gas generated during incineration of a polyvinyl chloride film and elution of a large amount of a plasticizer have been regarded as problems. For this reason, various alternatives to polyvinyl chloride films have been studied, and in particular, various stretch films using polyolefin resins have been proposed. For example, ethylene-vinyl acetate copolymer (EVA),
A stretch film having a constitution such as EVA / polybutene-1 / EVA, EVA / linear ethylene-α-olefin copolymer / EVA has been proposed. However, it is difficult to satisfy all properties such as packaging workability, packaging finish, elastic recovery force, and bottom sealability.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventors have succeeded in obtaining a non-PVC-based stretch film excellent in the above-mentioned various properties. It has at least one layer containing the component (B), and has a frequency of 10 Hz and a temperature of 20 by dynamic viscoelasticity measurement.
Storage elastic modulus (E ′) measured at 5.0 ° 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.

(A) Propylene polymer alone or 2
A mixture of more than one species, measured with a differential scanning calorimeter,
A propylene-based polymer having a heat of crystallization of 10 J / g to 60 J / g when the temperature is lowered to 0 ° C. at a scan rate of 10 ° C./min after crystal melting. (B) petroleum resin, terpene resin, cumarone-indene resin, rosin resin, or hydrogenated derivative thereof

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The stretch film of the present invention comprises the above (A) and (B)
Having at least one mixed resin layer containing the two components of
The film as a whole has specific viscoelastic properties.

The propylene polymer as the component (A) is a resin containing propylene in an amount of 70 mol% or more, such as polypropylene (homopolymer), propylene and ethylene or α-olefin having 4 to 12 carbon atoms. Or a mixture thereof. Propylene polymers generally have high crystallinity and high strength, and have relatively high melting points and good heat resistance among polyolefin polymers. It shows only a uniform elongation and these properties remain in the mixture. Therefore, in the present invention, in order to obtain a film having good elongation, it is preferable to use a propylene copolymer having relatively low crystallinity as at least a part of the propylene polymer. As the copolymer in this case, propylene may be ethylene or α having 4 to 12 carbon atoms.
-Olefin is preferably copolymerized at about 3 to 30 mol%. Also, a crystalline propylene polymer and an amorphous propylene polymer (for example, attack polypropylene)
Or a mixture of two or more.

What can be applied to the present invention is one that can achieve the viscoelastic properties described below when mixed with the component (B), and is a relatively low-crystalline propylene polymer as described above. is there. As a guideline of the crystallinity, when the component (A) consisting of a single resin or a mixture of two or more resins is measured by a differential scanning calorimeter (DSC), the scanning speed after crystal melting is 1
The heat of crystallization when the temperature is lowered to 0 ° C. at 0 ° C./min is 10 J
/ G to 60 J / g, more preferably 20 to 50 J / g.

If the heat of crystallization is less than 10 J / g, the crystallinity is too low, resulting in extremely poor film-forming properties. At room temperature, the film is too soft or has insufficient strength, which poses a practical problem. On the other hand, when the heat of crystallization exceeds 60 J / g, a large force is required at the time of film extension, and only non-uniform elongation is exhibited, which is not suitable for a stretch film.

Here, the properties intended by the present invention cannot be obtained by using only the component (A). That is, the glass transition temperature of the propylene polymer as the component (A) is generally -30 ° C to 0 ° C, and tan δ at 20 ° C is as small as less than 0.1.

Therefore, in the present invention, a petroleum resin, a terpene resin, a cumarone-indene resin, a rosin-based resin, or a hydrogenated derivative thereof is mixed with the component (A) as the component (B). Component (B) has a high glass transition temperature and increases the glass transition temperature of the mixture. Further, it is compatible with the component (A) in a fine order to lower its crystallinity, and also changes the stress behavior of the component (A), and exhibits a storage elastic modulus (E ') which exhibits suitable extensibility as a stretch film at ordinary temperature. Loss tangent (tan) showing moderate stress relaxation
δ) can be satisfied.

[0012] Here, as the (B) petroleum resin of the component, there are aromatic petroleum resins from alicyclic petroleum resins and C ₉ components from cyclopentadiene or its dimer, the terpene resin β- pinene From terpene resins and terpene-phenol resins, and as rosin-based resins,
Examples thereof include rosin resins such as gum rosin and utsdrodin, and esterified rosin resins modified with glycerin or pentaerythritol. The component (B) exhibits relatively good compatibility when mixed with the component (A), but it is preferable to use a hydrogenated derivative in terms of color tone, thermal stability, and compatibility.

As the component (B), those having various glass transition temperatures mainly depending on the molecular weight can be obtained, but those having a glass transition temperature of 50 to 100 ° C., preferably 70 to 90 ° C. are suitable for the present invention. belongs to. Glass transition temperature is 5
If the temperature is lower than 0 ° C., the crystallinity of the mixed resin composition is reduced, but the elastic modulus is too low, and it becomes difficult to obtain the viscoelastic properties described later as the whole film.

On the other hand, when the glass transition temperature exceeds 100 ° C., if the amount added is small, the crystallinity of the component (A) remains and the mixing effect of the component (B) is small. Crystallinity decreases, but the elastic modulus also increases with an increase in the glass transition temperature, and the extensibility and low-temperature properties required as a stretch film are impaired, making it difficult to obtain the viscoelastic properties described below. .

The film of the present invention comprises a layer comprising the above components (A) and (B), or a layer comprising the components (A) and (B) as the main components and other resins mixed within a range not impairing the transparency and the like. It has.

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 .about.0.8. Here, E 'is 5.0
If it is less than × 10 ⁸ dyn / cm ^2, it is soft and the stress for deformation is too small, so that the workability is poor, the film of the packaged product is not stretched, and it is not suitable as a stretch film. On the other hand, when E ′ exceeds 5.0 × 10 ⁹ dyn / cm ² , the film becomes hard and hard to expand, and the tray is easily deformed or crushed.

If the tan δ is less than 0.2, the film is restored instantaneously to the elongation of the film, so that the film is restored in a short time until the film is folded into the bottom of the tray. It is easy to wrinkle without stretching. Also, in the heat-sealed state of the bottom part, in the case of the stretch wrapping, it is difficult to perform sufficient fusion by heat, so that the bottom seal is likely to be peeled off during the transportation or during the display after the wrapping. When tan δ exceeds 0.8, the packaging finish is good, but plastic deformation is exhibited, and the tension against the external force of the packaged product is too weak. The film is easy to sag and the commercial value is apt to decrease. In the case of automatic packaging, problems such as poor chucking tend to occur because the packaging tends to stretch vertically. A particularly preferred range of tan δ is
It is 0.30 to 0.60.

The stretch film is sometimes used at a low temperature, and it is desirable that the stretch film has excellent low temperature characteristics (especially, elongation). For this purpose, the stretch film was measured by dynamic viscoelasticity at a frequency of 10 Hz and a temperature of 0 ° C. It is preferable that the storage elastic modulus (E ') of the film is in the range of 1.5 × 10 ¹⁰ dyn / cm ² or less. For this purpose, the mixing ratio of the component (A) and the component (B) or the material and thickness of another polymer layer to be combined with the mixed resin layer of the component (A) and the component (B) may be adjusted. Good.

In order to keep E 'and tan δ of the film of the present invention within the above ranges, it is most effective to adjust the mixing ratio of the two components (A) and (B). Generally, (A) / (B) May be approximately 80/20 to 50/50.

According to the present invention, a stretch film comprising the above-described mixture layer can be obtained, but it can be laminated with another non-PVC material layer if desired. Other resin layers include polyolefin polymers and flexible styrene-butadiene elastomers, and by laminating these, impart film forming stability, blocking resistance, adhesiveness, slipperiness, etc. can do.

Here, the polyolefin-based polymer as the laminate material includes low-density polyethylene, ultra-low-density polyethylene (copolymer of ethylene and α-olefin), ethylene-vinyl acetate copolymer (EVA), Alkyl acrylate copolymer, ethylene-alkyl methacrylate copolymer, ethylene-acrylic acid copolymer,
Ionomers such as ethylene-methacrylic acid copolymer and low-density polyethylene, and propylene-based elastomer materials are suitable.

In practice, for example, EVA can be suitably used, and the EVA has a vinyl acetate content of 5 to 5.
25% by weight, preferably 10 to 20% by weight, having a melt flow rate (MFR) of 0.2 to 2 g / 10 min (190
(C, 2.16 kg load) is preferable in terms of strength, flexibility, film formability, and the like. In general, the thickness of the film of the present invention is in the range used for ordinary stretch packaging, that is, about 8 to 30 μm, typically about 1 to 30 μm.
It is in the range of about 0 to 20 μm.

The film of the present invention can be obtained by melt-extruding a material from an extruder and forming the film by inflation molding or T-die molding. In the case of a laminated film, it is advantageous to co-extrude with a multilayer die. Practically, it is preferable to melt extrude the material resin from the annular die to form inflation, and the blow-up ratio (bubble diameter / die diameter) is preferably 4 or more, and particularly preferably in the range of 5 to 7. is there.

Various additives can be added to the film of the present invention in order to impart properties such as antifogging property, antistatic property and slip property. 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.

[0025]

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 ', tan δ Viscoelastic spectrometer VES- manufactured by Iwamoto Seisakusho Co., Ltd.
Using F3, vibration frequency 10 Hz, temperature 20 ° C. and 0
The temperature was measured in the transverse direction of the film at ℃.

2) Suitability for stretch wrapping Using a stretch film having a width of 350 mm, an automatic wrapping machine (ISHIDA / Wmin MK- manufactured by Ishida Koki Co., Ltd.)
II) Expanded polystyrene tray (200m long)
m, width 130 mm, height 30 mm) were packaged, and the items shown in Table 3 were evaluated. Using the same film and tray, a packaging test was performed using a hand wrapping machine (Diawrapper A-105 manufactured by Mitsubishi Plastics, Inc.).

3) Stability of Film Formation The stability of bubbles when the film was formed by the inflation film formation equipment was evaluated. ◎ Extremely stable ○ Stable △ Slightly unstable × Film formation impossible 4) Heat of crystallization The heat of crystallization at the time of cooling was measured under the following conditions using DSC-7 manufactured by PerkinElmer. Temperature condition: -50 ° C (hold for 1 minute) → 200 ° C
(1 minute hold) → -40 ° C (1 minute hold) Scanning speed: 10 ° C / minute

Example 1 Component (A) Low-crystalline propylene-ethylene-propylene copolymer elastomer (propylene content: 88 mol%, 230 ° C. MFR = 1.5 g / 10 min, PERT- manufactured by Tokuyama Corporation) 310J): 70% by weight (B) Component Hydrogenated derivative of cyclopentadiene petroleum resin (glass transition temperature: 81 ° C., softening temperature: 125 ° C.): 30% by weight Based on 100 parts by weight of the mixed resin composition of two or more components. 1.5 parts by weight of diglycerin monooleate was melt-kneaded as an antifogging agent, and a 15 μm thick film was obtained by inflation molding.

The properties measured for component (A) alone were: storage elastic modulus at 0 ° C. E ′ 3.6 × 10 ⁹ dyn / cm ² storage elastic modulus at 20 ° C. E ′ 2.1 × 10 ⁹ dyn / Loss tangent tan δ at cm ² 20 ° C. 0.07 Glass transition temperature −25 ° C. Heat of crystallization 31 J / g.

(Example 2) As the intermediate layer, a mixed composition of the propylene copolymer and the hydrogenated petroleum resin used in Example 1 was 11 μm, and as the front and back layers, EVA (vinyl acetate content 15% by weight, 190 ° C. MFR) = 2.0g / 10min) 1
A layer of a composition obtained by kneading 3.0 parts by weight of diglycerin monooleate as an anti-fogging agent in 00 parts by weight, each having a thickness of 2 μm, was subjected to coextrusion inflation molding, and the total thickness was 15 μm.
(2 μm / 11 μm / 2 μm) was obtained.

Example 3 As an intermediate layer, a 50/50% by weight mixed composition of crystalline polypropylene and amorphous propylene-butene-1 copolymer (MFR at 230 ° C. = 14)
g / 10 minutes, Ube Lexen Co., Ltd. CAP350) 7
0% by weight and the hydrogenated petroleum resin 30 used in Example 1
Wt.%, And a total thickness of 15 μm (2/11/2 μm) was prepared in the same manner as in Example 2 except that a composition obtained by kneading 1.5 parts by weight of diglycerin monooleate as an antifogging agent with a resin mixed with 0.1% by weight was used.
m) was obtained.

The properties measured by CAP alone were: storage elastic modulus at 0 ° C. E ′ 4.5 × 10 ⁹ dyn / cm ² storage elastic modulus at 20 ° C. E ′ 2.0 × 10 ⁹ dyn / cm ² 20 ° C. Loss tangent tan δ 0.11 Glass transition temperature −15 ° C. Heat of crystallization 33 J / g.

The properties measured for the mixed composition of the intermediate layer were as follows: storage elastic modulus at 0 ° C. E ′ 1.2 × 10 ¹⁰ dyn / cm ² storage elastic modulus at 20 ° C. E ′ 2.0 × 10 ⁹ dyn / The loss tangent tan δ at cm ² 20 ° C. 0.36 and the glass transition temperature was 0 ° C.

Comparative Example 1 A total thickness of 15 μm (2 μm / 11 μm) was obtained in the same manner as in Example 2 except that the propylene-based copolymer elastomer used in Example 2 was used as an intermediate layer.
/ 2 μm).

Comparative Example 2 A propylene-ethylene random copolymer (ethylene content 4 mol%, 230 ° C.) was used in place of the propylene copolymer elastomer used in Example 2.
Example 2 except that MFR = 0.5 g / 10 min) was used.
In the same manner as described above, the total thickness is 15 μm (2 μm / 11 μm / 2
μm).

The properties measured for the propylene-ethylene random copolymer alone were as follows: storage elastic modulus at 0 ° C. E ′ 1.7 × 10 ¹⁰ dyn / cm ² storage elastic modulus at 20 ° C. E ′ 9.2 × 10 ⁹ dyn / cm ² Loss tangent tan δ at 20 ° C. 0.06 Glass transition temperature −5 ° C. Heat of crystallization was 75 J / g.

The properties measured for the intermediate layer composed of the propylene-ethylene random copolymer and the petroleum resin are as follows: storage elastic modulus at 0 ° C. E ′ 2.1 × 10 ¹⁰ dyn / cm ² storage elastic modulus at 20 ° C. '9.0 × 10 ⁹ dyn / cm ² Loss tangent tan δ at 20 ° C. tan 0.14 Glass transition temperature 10 ° C.

Comparative Example 3 As an intermediate layer, an ethylene-butene-1 copolymer (ultra low density polyethylene, butene-1
Total thickness 15 μm (2/11/2) in the same manner as in Example 2 except that the content was 14% by weight and the density was 0.905 alone.
μm).

Comparative Example 4 A commercially available polyvinyl chloride stretch film (thickness: 15 μm) was evaluated.
Tables 1 and 2 show the measurement and evaluation results of the characteristics and performance of these films.

[0040]

[Table 1]

[Table 2]

[Table 3]

The film of Example 1 was composed of a layer in which a hydrogenated product of a petroleum resin was mixed with a low-crystalline propylene polymer, the viscoelastic properties were within the range specified in the present invention, and the properties were excellent. Was. The films of Examples 2 and 3 were EVA.
, But also had excellent properties.

[0042]

According to the stretch film of the present invention, when used in an automatic packaging machine or the like, the film can be cut / transported or wrapped without any problem, the bottom sealing property is good, and the film tension is good. A good package can be obtained, and it has a unique feature as a non-PVC-based stretch film.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI C08L 57/02 C08L 57/02 93/04 93/04

Claims (3)

(57) [Claims] 1. At least one layer containing the following components (A) and (B), and has a storage elastic modulus (E ′) of 5.0 at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement. × 10 ^{8 to} 5.0 × 10 ⁹ dyn / cm ² and a loss tangent (tan δ) in the range of 0.2 to 0.8. (A) A propylene polymer alone or a mixture of two or more thereof, and has a heat of crystallization of 10 J / when measured by a differential scanning calorimeter and cooled to 0 ° C. at a scan rate of 10 ° C./min after melting the crystal. g to 60 J / g. (B) petroleum resin, terpene resin, cumarone-indene resin, rosin resin, or hydrogenated derivative thereof 2. A dynamic viscoelasticity measurement at a frequency of 10 Hz,
2. The stretch film for food packaging according to claim 1, wherein the storage elastic modulus (E ') of the film measured at a temperature of 0 ° C. is in a range of 1.5 × 10 ¹⁰ dyn / cm ² or less. 3. The glass transition temperature of a petroleum resin, a terpene resin, a cumarone-indene resin, a rosin-based resin, or a hydrogenated derivative thereof in the range of 50 to 100 ° C. Stretch film for food packaging.