JP3386945B2 - 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, 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 of the characteristics such as wrapping workability, wrapping finish, elastic recovery, and bottom sealability. Further, a non-vinyl chloride type stretch film having EVA laminated on both surfaces of a styrene-butadiene block copolymer hydrogenated material layer has also been proposed (Japanese Patent Publication No.
Although there is an advantage that the elastic recovery property against deformation is good, it is not yet sufficient in terms of packaging workability, packaging finish, bottom sealing property, and the like.

[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 as follows (A), The storage elastic modulus (E) having at least one mixed resin layer containing three components (B) and (C) as a main component and measured at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement (E
′) Is 5.0 × 10 ⁸ to 5.0 × 10 ⁹ dyn / c
m ² and loss tangent (tan δ) are in the range of 0.2 to 0.8, which is a stretch film for food packaging. (A) Copolymer of vinyl aromatic compound and conjugated diene or hydrogenated derivative thereof (B) Petroleum resin, terpene resin, coumarone-indene resin, rosin resin, or hydrogenated derivative thereof (C) propylene resin

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
The stretch film of the present invention comprises (A) a copolymer of a vinyl aromatic compound and a conjugated diene or a hydrogenated derivative thereof, and (B) a petroleum resin, a terpene resin, a coumarone-indene resin, a rosin resin, or a resin thereof. It has at least one hydrogenated derivative and a mixed resin layer containing (C) propylene-based resin as a main component, and has specific viscoelastic properties as the entire film.

Here, the copolymer of the vinyl aromatic compound and the conjugated diene, which is the component (A), or its hydrogenated derivative generally has rubber elasticity, is flexible, is not easily broken, and has good transparency. It is suitable for achieving the object of the present invention by balancing the rigidity of the vinyl aromatic compound and the elastomeric property of the conjugated diene depending on the polymerization form.

However, styrene-butadiene block copolymers and styrene-isoprene block copolymers are known as conventional copolymers of this type, and they are also used in some film applications. Viscoelasticity is not suitable for the present invention. That is, conventionally used copolymers of this type are usually much lower than 0 ° C., usually −
This is because it has a glass transition temperature near 50 ° C. and the loss tangent (tan δ) described below is extremely small at room temperature.

Therefore, in the present invention, as the component (A), those having a glass transition temperature higher than that of the conventionally used copolymers are preferable, and specifically, -30 ° C. or more,
Suitably, those of -20 ° C to 20 ° C are suitable.

As such a copolymer, the weight ratio of the vinyl aromatic compound to the conjugated diene is 40/60 to 10 /.
A block copolymer in the range of 90, in which the glass transition temperature of the conjugated diene block is higher than usual, may be mentioned.

Specifically, there are those having a block obtained by randomly copolymerizing styrene or the like with a conjugated diene, or those having a tapered block obtained by copolymerizing styrene with a certain concentration gradient of the conjugated diene. It is also effective to use isoprene block having a high 3,4-bond ratio as the conjugated diene block.

Further, in the present invention, a random copolymer of a vinyl aromatic compound and a conjugated diene can be used as long as the viscoelastic property is suitable. In that case, the weight ratio of the vinyl aromatic compound and the conjugated diene is generally in the range of 30/70 to 60/40. Furthermore, as these copolymers, hydrogenated conjugated dienes can be particularly preferably used. Hydrogenation suppresses the crosslinking reaction in the molding process such as melt extrusion, and improves the compatibility with the component (B) when the component (B) described below is mixed, thereby maintaining transparency. From this point of view, a suitable hydrogenation rate is 50% or more, preferably 60% or more.

Here, styrene is a typical vinyl aromatic compound, but o-styrene, p-styrene, α-methylstyrene and the like can also be used. In addition, examples of the conjugated diene include butadiene, isoprene, and 1,3-pentadiene.

By the way, it is difficult to raise the glass transition temperature of the component (A), which is a copolymer of a vinyl aromatic compound and a conjugated diene, particularly a hydrogenated derivative, to near room temperature.
It alone is often disadvantageous in practical use because it has a low storage elastic modulus (E ′) at 20 ° C. and is too soft, and the selection of materials is extremely limited. Therefore, in the present invention,
The components (B) and (C) are mixed so that the desired viscoelastic properties can be easily obtained in practical use. Component (B), such as petroleum resin, increases the glass transition temperature of the composition to achieve desired viscoelastic properties, and component (C), the propylene resin, is mixed with components (A) and (B). In that case, the strength of the mixture is increased and the viscoelastic characteristics are adjusted without significantly impairing the transparency.

Among the components (B), the petroleum resin includes alicyclic petroleum resin derived from cyclopentadiene or a dimer thereof and aromatic petroleum resin 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. It is known that the above-mentioned component (B) exhibits a relatively good compatibility when mixed with the above-mentioned component (A), but a hydrogenated derivative is used from the viewpoint of color tone, thermal stability and compatibility. It is preferable.

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
If the temperature is lower than 0 ° C., it is necessary to add a large amount in order to obtain the viscoelastic properties described later when mixed with the above-mentioned component (A), and the material or film is likely to be blocked by bleeding on the surface. In addition, the mechanical strength of the film as a whole is insufficient and the film is easily torn, which may cause a problem in practical use. On the other hand, when the glass transition temperature is higher than 100 ° C., the compatibility with the component (A) is deteriorated and bleeding may occur on the film surface over time, leading to blocking and deterioration of transparency.

For the above reason, it is preferable that the content of the component (B) is as small as possible within the range where the viscoelastic properties described later can be achieved. For this purpose, as described above, the component (A) preferably has a higher glass transition temperature than that of a conventionally used copolymer.

By the way, only two components such as the copolymer of the vinyl aromatic compound and the conjugated diene as the component (A) and the petroleum resin as the component (B) have a narrow range in which a predetermined viscoelastic property can be secured, and A sufficient strength cannot be obtained as a stitch film, which is also disadvantageous in terms of cost.

Therefore, in the present invention, a propylene polymer as the component (C) is mixed with the above components (A) + (B).

The propylene-based polymer means propylene 7
Resin containing 0 mol% or more, polypropylene (homopolymer), propylene and ethylene or carbon number 4
Examples thereof include a copolymer of .about.12 with .alpha.-olefin, or a mixture thereof. Propylene content is 70
If it is less than%, the crystallinity is too low to control the viscoelastic property of the film as a whole or to attain strength up. It also lacks stability during film formation. Propylene-based polymers are generally
It has high crystallinity and high strength, and has a relatively high melting point and good heat resistance among the polyolefin polymers, but it requires a large amount of force during stretching due to its high crystallinity, and only shows non-uniform elongation. 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, a copolymer obtained by copolymerizing propylene with ethylene or α-olefin having 4 to 12 carbon atoms in an amount of about 3 to 30 mol% is preferable.

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 of the film with respect to elongation is instantaneous, so that the film is restored within a short time before the film is folded into the bottom of the tray, and the film is well conditioned. 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. Since many of vinyl aromatic compound / conjugated diene copolymers suitable for the present invention have a higher glass transition temperature than usual ones, care should be taken to satisfy the above-mentioned properties in order to secure flexibility such as low temperature elongation. Is preferred.

For that purpose, the ratio of the diene component of the vinyl aromatic compound / conjugated diene copolymer, (A),
The mixing ratio of the components (B) and (C) may be adjusted.

In order to bring E'and tan δ of the present invention into the above ranges, it is most effective to adjust the mixing ratio of the three components (A), (B) and (C). A mixture of the component (A) and the component (B) in an appropriate amount is generally 0.7 to 1.5 at around room temperature.
Tan δ in the range. The propylene-based polymer as the component (C) generally has a t of 0.01 to 0.10.
Since it has an δ, it is 0.2 to 0.8 as a mixture.
To have tan δ in the range of (A),
The mixing ratio of each of the components (B) and (C) may be 30 to 60% by weight of the component (A), 10 to 40% by weight of the component (B), and 20 to 50% by weight of each of the components (C).

According to the present invention, the stretch film composed of 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 a 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.

In practice, 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 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.

[0032]

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 (Example 1) Component (A) Polyisoprene 80 having 20% by weight of styrene and 55% of 3,4-bond ratio Hydrogenated derivative of styrene-isoprene-styrene triblock copolymer (glass transition temperature -19 ° C, hereinafter abbreviated as "HSIS") consisting of 50% by weight: 45% by weight (B) component Hydrogenated derivative of cyclopentadiene-based petroleum resin (Glass transition temperature 81 ° C, softening temperature 125 ° C): 25% by weight (C) component Propylene-ethylene random copolymer (ethylene content 4 mol%, MFR at 230 ° C = 0.5 g / 10 minutes): 30% by weight To 100 parts by weight of the mixed resin composition consisting of the above three components, 2.0 parts by weight of diglycerin monooleate as an antifogging agent was melt-kneaded, and inflation was performed. Thickness by Chillon molding 15
A film of μm was obtained.

The characteristics measured by HSIS alone are as follows: storage modulus E'at 0 ° C. E × 2.0 × 10 ⁹ dyn / cm ² 20 ° C. storage modulus E ′ 2.1 × 10 ⁸ dyn / cm ² 20 The loss tangent tan δ at 0 ° C was 0.44, and the glass transition temperature was -19 ° C. Further, the properties measured only with the mixture of HSIS and hydrogenated petroleum resin are as follows: storage modulus E'at 0 ° C E 1.4 x 10 ⁹ dyn / cm ² storage modulus E at 20 ° C E'6.0 x 10 ⁸ dyn / was the loss tangent tan [delta 1.20 glass transition temperature of 5 ° C. in cm ² 20 ° C..

The characteristics measured only with the propylene-based polymer are as follows: Storage elastic modulus at 0 ° C. E'1.7 × 10 ¹⁰ dyn / cm ² Storage elastic modulus at 20 ° C. E'9.0 × 10 ⁹ dyn / cm was the loss tangent tan [delta 0.06 glass transition temperature -5 ° C. at ² 20 ° C..

Example 2 The same as Example 1 except that the mixing ratio of the three resins used in Example 1 was changed to A component 35% by weight B component 25% by weight C component 40% by weight. A film having a thickness of 15 μm was obtained.

Example 3 EVA (vinyl acetate content 15% by weight, 190 ° C. MFR = 2.0 g / 10 min) 10 was used as an intermediate layer of the mixed composition of the three resins used in Example 1.
A composition obtained by kneading 2.0 parts by weight of diglycerin monooleate as an antifogging agent in 0 parts by weight was used as front and back layers by coextrusion inflation molding to give a total thickness of 15 μm (2.5 μm /
A film of 10 μm / 2.5 μm) was obtained.

Example 4 A total thickness of 15 μm (2.5 μm / 10 μm / 2.5) was obtained in the same manner as in Example 3 except that the mixed composition of the three kinds of resins used in Example 2 was used as the intermediate layer.
μm) film was obtained.

(Comparative Example 1) HSIS1 used in Example 1
A total thickness of 15 .mu.m (2.5 .mu.m / 1) was obtained in the same manner as in Example 3 except that a composition obtained by kneading 2.0 parts by weight of diglycerin monooleate as an antifogging agent in an amount of 00 parts by weight was used as an intermediate layer.
A film of 0 μm / 2.5 μm) was obtained. (Comparative Example 2) The HSIS used in Example 1 was 65% by weight,
In the same manner as in Example 3 except that an intermediate layer was prepared by kneading 2.0 parts by weight of diglycerin monooleate as an antifogging agent into a composition obtained by mixing 35% by weight of hydrogenated petroleum resin,
Total thickness 15μm (2.5μm / 10μm / 2.5μm)
I got a film.

(Comparative Example 3) The same procedure as in Example 3 was repeated except that the mixing ratios of the three resins used in Example 3 were changed to A component 30% by weight B component 15% by weight C component 55% by weight. , Total thickness 15μ
m (2.5 μm / 10 μm / 2.5 μm) film was obtained.

(Comparative Example 4) Linear ethylene-butene-1
Copolymer (butene-1 content 14% by weight, density 0.90
5) as an intermediate layer of 7 μm, EVA used in Example 3
The composition is 4 μm as the front and back layers, and the total thickness is 15 μm.
m (4/7/4 μm) film was obtained.

Comparative Example 5 Commercially available polyvinyl chloride stretch film (thickness: 15 μm) was evaluated.

Tables 1 and 2 show the results of measuring and evaluating the characteristics and performances of these films.

[0045]

[Table 1]

[Table 2]

[Table 3]

It can be seen that all the films of Examples have viscoelastic properties within the range specified by the present invention and are excellent in various properties.

[0047]

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, and the bottom sealing property is good, and the film tension can be improved. 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 front page (51) Int.Cl. ⁷ identification code FI C08L 93/04 C08L 93/04 (58) Fields investigated (Int.Cl. ⁷ , DB name) C08L 53/02 C08L 23/10 C08L 45/02 C08L 57/02 C08L 93/04 C08J 5/18

Claims (2)

(57) [Claims] 1. Storage elasticity measured by dynamic viscoelasticity measurement at a frequency of 10 Hz and a temperature of 20 ° C., having at least one mixed resin layer containing the following three components (A), (B) and (C) as a main component. The rate (E ') is 5.0 × 10 ⁸ to 5.0 × 10
⁹ dyn / cm ² , loss tangent (tan δ) is 0.2 to
A stretch film for food packaging, which is in the range of 0.8. (A) Copolymer of vinyl aromatic compound and conjugated diene or hydrogenated derivative thereof (B) Petroleum resin, terpene resin, coumarone-indene resin, rosin resin, or hydrogenated derivative thereof (C) propylene resin 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.