JPH09154479A - Stretched film for wrapping food - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a non-vinyl chloride resin stretched film good in wrapping workability and wrapped finish. SOLUTION: This stretched film for wrapping foods has at least one of layers containing the below-described components (A) and (B), having a frequency of 10Hz by the measurement of dynamic viscoelasticity, a storage elastic modulus (E') of 5.0×10<8> to 5.0×10<9> dyn/cm<2> measured at a temperature of 20 deg.C, and a loss tangent (tan δ) of 0.2-0.8. (A) One or more kinds of propylenic polymers having a crystallization calorie of 10J/g to 60J/g measured with a differential scanning calorimeter, when cooled down to 0 deg.C at a scanning rate of 10 deg.C/min, after the crystals are melted. (B) A petroleum resin, a terpene resin, a chromane-indene resin, a rosin resin, or their hydrogenation derivatives.

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. However, it is difficult to satisfy all the characteristics such as wrapping workability, wrapping finish, elastic recovery, and bottom sealability.

[0004]

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 as follows (A) and 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 ℃ is 5.0 × 10 ⁸ ~
5.0 × 10 ⁹ dyn / cm ² , loss tangent (tan δ)
Is in the range of 0.2 to 0.8, which is a stretch film for food packaging.

(A) Propylene polymer homopolymer 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 scanning rate of 10 ° C./min after crystal melting. (B) Petroleum resin, terpene resin, coumarone-indene resin, rosin resin, or hydrogenated derivatives thereof

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
The stretch film of the present invention has the above-mentioned (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-based polymer as the component (A) is a resin containing 70 mol% or more of propylene, and includes polypropylene (homopolymer), propylene and ethylene, or α-olefin having 4 to 12 carbon atoms. Examples thereof include copolymers thereof, or a mixture thereof. Propylene-based polymers generally have high crystallinity and high strength. Among polyolefin polymers, they have relatively high melting points and good heat resistance, but due to their high crystallinity, they require a large force during stretching and It exhibits only 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-based copolymer having a relatively low crystallinity as at least a part of the propylene-based polymer. As the copolymer in this case, ethylene or α having 4 to 12 carbon atoms is added to propylene.
-The thing which copolymerized about 3 to 30 mol% of olefin is suitable. In addition, crystalline propylene polymers and amorphous propylene polymers (eg, adhesive polypropylene)
And the like may be a mixture of two or more kinds.

Applicable to the present invention are those which can achieve the below-mentioned viscoelastic properties when mixed with the component (B), and are relatively low crystalline propylene polymers as described above. is there. As a measure of crystallinity, when the component (A) consisting of a single resin or a mixture of two or more kinds is measured by a differential scanning calorimeter (DSC), a 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, and more preferably 20 to 50 J / g.

When the amount of heat of crystallization is less than 10 J / g, the crystallinity is too low and the film-forming property is extremely poor, and the film is too soft and has insufficient strength at room temperature, which is a problem in practical use. When the amount of heat of crystallization exceeds 60 J / g, a large force is required when the film is stretched, and only a nonuniform stretch is exhibited, which is not suitable for a stretch film.

Here, the characteristics intended by the present invention cannot be obtained only with the component (A). That is, the glass transition temperature of the propylene-based 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, as the component (B), a petroleum resin, a terpene resin, a coumarone-indene resin, a rosin resin, or a hydrogenated derivative thereof is mixed with the component (A). The component (B) has a high glass transition temperature and increases the glass transition temperature of the mixture. Further, the storage elastic modulus (E ') which is compatible with the component (A) in a fine order to reduce its crystallinity and also changes the stress behavior of the component (A), and exhibits suitable extensibility as a stretch film at room temperature. And loss tangent (tan showing moderate stress relaxation)
It is possible to satisfy both δ).

Among the components (B), the petroleum resins include alicyclic petroleum resins derived from cyclopentadiene or a dimer thereof and aromatic petroleum resins derived from the C ₉ component, and β-pinene is used as the terpene resin. Terpene resin and terpene-phenol resin from, as the rosin resin,
Examples thereof include rosin resins such as gum rosin and utudrosine, and esterified rosin resins modified with glycerin or pentaerythritol. The component (B) exhibits a relatively good compatibility when mixed with the component (A), but it is preferable to use a hydrogenated derivative from the viewpoints of color tone, thermal stability, and compatibility.

The component (B) may be one having various glass transition temperatures mainly depending on the molecular weight, but the glass transition temperature applicable to the present invention is 50 to 100 ° C, preferably 70 to 90 ° C. belongs to. Glass transition temperature is 5
When the temperature is lower than 0 ° C., the crystallinity of the mixed resin composition is lowered, but the elastic modulus becomes too low, and it becomes difficult to obtain the viscoelastic properties described later as the entire film.

On the other hand, when the glass transition temperature exceeds 100 ° C., the crystallinity of the component (A) remains when the amount added is small, and the mixing effect of the component (B) is small, and when the amount added is large, the mixed resin composition is obtained. As the glass transition temperature rises, the elastic modulus also increases, and the extensibility and low temperature properties required for the stretch film are impaired, making it difficult to obtain the viscoelastic properties described below. .

The film of the present invention is a layer comprising the above-mentioned components (A) and (B), or a layer containing the above-mentioned components (A) and (B) as main components and other resins mixed therein within a range not impairing transparency and the like. Is to have.

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 well formed. 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.

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 was measured 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. To this end, the mixing ratio of the component (A) and the component (B), or the material and thickness of another polymer layer combined with the mixed resin layer of the component (A) and the component (B) can be adjusted. Good.

In order to bring E'and tan δ of the film of the present invention into the above ranges, it is most effective to adjust the mixing ratio of both components (A) and (B), and generally (A) / (B). The mixing weight ratio may be approximately 80/20 to 50/50.

According to the present invention, the stretch film comprising the mixture layer described above can be obtained, but it can be laminated with another non-vinyl chloride material layer if desired. Other resin layers include, for example, polyolefin polymers and flexible styrene-butadiene elastomers, and when laminated with these, film film stability, blocking resistance, tackiness, and slipperiness are imparted. can do.

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 this 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 thickness of the film of the present invention is generally in the range used for ordinary stretch packaging, that is, about 8 to 30 μm, typically 1
It is in the range of about 0 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 an annular die and perform inflation molding. At that time, 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 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.

[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 ', 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 3 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) Stability of film formation The stability of bubbles during film formation was evaluated by an inflation film formation equipment. ◎ Extremely stable ○ Stable △ Slightly unstable × No film formation 4) Amount of heat of crystallization Using DSC-7 manufactured by Perkin Elmer Co., the amount of heat of crystallization was measured under the following conditions. Temperature conditions: -50 ° C (hold for 1 minute) → 200 ° C
(Hold for 1 minute) → -40 ° C (Hold for 1 minute) Scanning speed: 10 ° C / min

Example 1 Component (A) Low-Crystalline Propylene-Ethylene-Propylene Copolymer Elastomer (Propylene Content 88 mol%, 230 ° C. MFR = 1.5 g / 10 min, PER T- manufactured by Tokuyama Corp.) 310J): 70% by weight (B) component Hydrogenated derivative of cyclopentadiene-based petroleum resin (glass transition temperature 81 ° C, softening temperature 125 ° C): 30% by weight Above 100 parts by weight of a mixed resin composition of two components As an antifogging agent, 1.5 parts by weight of diglycerin monooleate was melt-kneaded and subjected to inflation molding to obtain a film having a thickness of 15 μm.

The characteristics measured with the component (A) alone are as follows: storage modulus E'at 0 ° C. 3.6 × 10 ⁹ dyn / cm ² storage modulus E'at 20 ° C. 2.1 × 10 ⁹ dyn / The loss tangent tan δ in cm ^{2 of} 20 ° C was 0.07, the glass transition temperature was -25 ° C, and the heat of crystallization was 31 J / g.

(Example 2) As an intermediate layer, a mixed composition of the propylene-based copolymer used in Example 1 and hydrogenated petroleum resin was 11 μm, and as front and back layers EVA (vinyl acetate content 15% by weight, 190 ° C MFR). = 2.0 g / 10 minutes) 1
Coextrusion inflation molding was performed by co-extrusion inflation molding a composition in which 3 parts by weight of diglycerin monooleate (3.0 parts by weight) as an anti-fog agent was kneaded in an amount of 2 μm each, and the total thickness was 15 μm.
A film of (2 μm / 11 μm / 2 μm) was obtained.

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

The characteristics measured with CAP alone are as follows: storage modulus E'at 0 ° C. 4.5 × 10 ⁹ dyn / cm ² 20 ° C. storage modulus E ′ 2.0 × 10 ⁹ dyn / cm ² 20 ° C. Loss tangent tan δ in 0.11 was 0.15, glass transition temperature was −15 ° C., and the heat of crystallization was 33 J / g.

The properties measured for the mixed composition of the intermediate layer are as follows: storage modulus E'at 0 ° C. 1.2 × 10 ¹⁰ dyn / cm ² storage modulus E'at 20 ° C. E'2.0 × 10 ⁹ dyn / was the loss tangent tan [delta 0.36 glass transition temperature 0 ℃ in cm ² 20 ° 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 copolymer elastomer alone used in Example 2 was used as the intermediate layer.
/ 2 μm) was obtained.

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 above, the total thickness is 15 μm (2 μm / 11 μm / 2
μm) film was obtained.

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

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

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

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 performances 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 petroleum resin was mixed with a low crystalline propylene polymer, and had viscoelastic properties within the range specified by the present invention and was excellent in various properties. It was The films of Examples 2 to 3 are EVA.
The laminated film with No. 1 had similar excellent properties.

[0042]

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 C08L 57/02 LMJ C08L 57/02 LMJ 93/04 LSK 93/04 LSK // C08J 5/18 CES C08J 5/18 CES

Claims (3)

[Claims] 1. A storage elastic modulus (E ′) measured by dynamic viscoelasticity measurement at a frequency of 10 Hz and a temperature of 20 ° C., which has at least one layer containing the following components (A) and (B). A stretch film for food packaging, which has a x10 ^{8 to} 5.0 x 10 ⁹ dyn / cm ² and a loss tangent (tan δ) of 0.2 to 0.8. (A) A propylene-based polymer, which is a single compound or a mixture of two or more compounds, and has a crystallization heat amount of 10 J / when measured with a differential scanning calorimeter and cooled to 0 ° C. at a scanning speed of 10 ° C./min after crystal melting. A propylene-based polymer having a content of g to 60 J / g. (B) Petroleum resin, terpene resin, coumarone-indene resin, rosin resin, or hydrogenated derivatives thereof 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. The glass transition temperature of petroleum resin, terpene resin, coumarone-indene resin, rosin resin, or hydrogenated derivative thereof is in the range of 50 to 100 ° C. Stretch film for food packaging.