JPH11179860A - Film for stretch packaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film for stretch packaging which has excellent strength, transparency, flexibility, stretchability, etc., without using a plasticized PVC and provides both excellent self-adhesiveness and excellent shape-restoring properties without abrupt restoration from deformation. SOLUTION: On both faces of an intermediate layer formed of a polypropylene resin with a wt. average mol.wt. of 150,000-500,000 and wt. of elution at 0 deg.C, at higher than 0 deg.C to at most 90 deg.C and at higher than 90 deg.C to at most 130 deg.C respectively of 30-60, 30-55 and 5-20 wt.% by means of cross fractional chromatography, skin layers formed of a linear low density polyethylene resin polymerized by using a catalyst with a single polymn. active point and with a density of 0.885-0.920 g/cm<3> are laminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for stretch wrapping which is suitably used mainly for tray wrapping.

[0002]

2. Description of the Related Art Stretch packaging films are used for packaging various materials, and in particular, are widely used for tray packaging of fresh foods such as fruits and vegetables, fish, meat, and prepared foods.

[0003] When fresh foods and the like are to be packed in trays using the stretch packaging film, the fresh foods and the like are usually put in a plastic container made of styrene foam or the like.
The container is wrapped while stretching the stretch packaging film, and the film is wrapped and packaged while pulling the end.

Accordingly, stretch wrapping films include:
In addition to excellent transparency, flexibility, extensibility, etc., it is required to have excellent self-adhesive properties, deformation recovery properties, and the like.

Conventionally, as a film for stretch packaging used for packaging of fresh foods and the like, a vinyl chloride resin (plasticized PVC) plasticized with a plasticizer as a main component is used in view of cost and ease of use. Those that do have been widely used.

However, stretch packaging films containing plasticized PVC as a main component generate hydrogen chloride gas, dioxin and the like when incinerated, and therefore have a problem in terms of environmental hygiene.

For this reason, recently, as an alternative to plasticized PVC, for example, linear low-density polyethylene resin (L-
LDPE), ethylene / vinyl acetate copolymer resin (EV
A) The development of stretch packaging films using polyolefin-based resins such as polybutadiene resins has been actively conducted.

However, stretch wrapping films using a polyolefin resin generally have poor properties such as self-adhesion (self-adhesion) and deformation recovery (eg, elongation recovery) required at the time of packaging. However, there are problems such as that the wrapped film easily comes off the packaged object such as a plastic container and the film is wrinkled and the aesthetic appearance is impaired, and thus cannot be said to be satisfactory in practical use.

Various studies have been made to address the problems of stretch wrapping films using the above-mentioned polyolefin-based resins. For example, Japanese Patent Application Laid-Open No. 61-44635 discloses that "propylene and various α- EV on both surfaces of an intermediate layer mainly composed of a random copolymer resin with olefin
A stretch packaging film in which a layer mainly composed of A is laminated "has been proposed.

In Japanese Patent Application Laid-Open No. Sho 62-51440,
"EVA-based layers are formed on both surfaces of an intermediate layer mainly containing a hydrogenated derivative of a block copolymer composed of a polymer block of a monovinyl-substituted aromatic hydrocarbon and an elastomeric polymer block of a conjugated diene. "Laminated films for stretch packaging" have been proposed.

However, in the stretch packaging films as proposed in the above two proposals, those having low deformation recovery after packaging are liable to wrinkle, and those having high deformation recovery rapidly recover deformation. For this reason, there is a problem that the object to be packaged is easily deformed and the like, and none of them is satisfactory as a film for stretch packaging. Further, there is a problem that the cost is increased when the elastomer is used.

That is, at present, a polyolefin resin-based stretch packaging film that can sufficiently satisfy the demands of the market has not been put into practical use as a substitute for a stretch packaging film containing plasticized PVC as a main component.

[0013]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned conventional problems by using plasticized PVC without using strength, transparency, flexibility, extensibility and the like. An object of the present invention is to provide a stretch packaging film having both self-adhesiveness and excellent deformation recovery without causing rapid deformation recovery.

[0014]

The stretch packaging film according to the present invention has a weight-average molecular weight of 150,000 to 500,000, and the elution amount at 0 ° C. of the total elution amount by cross fractionation chromatography. 30-60% by weight, 0 ° C
The elution amount at 90 ° C. or less is more than 30 to 55% by weight, and the elution amount at 90 ° C. or less at 130 ° C. or less is 5 to 20% by weight. It is characterized in that a skin layer formed from a linear low-density polyethylene resin having a density of 0.885 to 0.920 g / cm ^3, which is polymerized using a single catalyst at a polymerization active site, is laminated. And

The weight average molecular weight of the polypropylene resin forming the intermediate layer of the stretch wrapping film according to the present invention and the elution amount at a predetermined temperature or temperature range by a cross fractionation chromatograph were measured by the following methods. .

In the method for measuring the elution amount by cross fractionation chromatography, first, a polypropylene resin is dissolved in o-dichlorobenzene at a temperature at which the polypropylene resin is completely dissolved, and the solution is cooled at a constant rate. A thin polymer layer is formed on the surface of the previously prepared inert carrier in the order of high crystallinity and high molecular weight.

Next, the temperature is raised continuously or stepwise, the concentration of the polypropylene resin component eluted sequentially at a predetermined temperature or in each predetermined temperature range is detected, and the composition distribution (crystallinity distribution) is measured ( Temperature rise elution fractionation).

More specifically, the measurement method is described below. First, a polypropylene-based resin is completely dissolved in o-dichlorobenzene at a temperature at which the polypropylene-based resin is completely dissolved. Cooled to 0 ° C. over 24 hours in the presence of active carrier. Next, while flowing o-dichlorobenzene over the carrier on which the polymer was deposited on the surface layer, the temperature was raised at a rate of 2 ° C./min to a temperature at which the polypropylene resin was completely dissolved, and the polymer was eluted at each temperature. The minute was measured as the elution amount every 2 ° C.

The apparatus used for the above measurement is not particularly limited, but for example, a cross-separation chromatograph (model "T150A" manufactured by Mitsubishi Yuka Co., Ltd.) and the like are preferably used.

The polypropylene resin forming the intermediate layer of the stretch packaging film according to the present invention is not particularly limited. For example, a propylene homopolymer or at least one kind of α-polymer other than propylene and propylene may be used. Examples thereof include copolymers with olefins, and one or more of these are suitably used. The above homopolymer or copolymer may be a random polymer or a block polymer.

The α-olefin is not particularly restricted but includes, for example, ethylene, 1-butene,
Examples thereof include 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and the like, and one or more of these are suitably used. Among them, ethylene and 1-butene are preferable. Etc. are more preferably used.

Specific examples of the copolymer of propylene and at least one α-olefin other than propylene include:
Although not particularly limited, for example, propylene /
Ethylene copolymer, propylene / 1-butene copolymer,
2 such as propylene / 4-methyl-1-pentene copolymer
Terpolymers such as propylene / ethylene / 1-butene copolymer and propylene / 1-butene / 4-methyl-1-pentene copolymer;
Species or two or more species are suitably used.

The copolymer of propylene and at least one α-olefin other than propylene is generally a copolymer of 2
In the presence of a titanium compound and an organoaluminum compound catalyst, for example, propylene or propylene and at least one α-olefin other than propylene are first polymerized in a multistage polymerization. Preliminarily polymerized in the second stage, and then obtained in the second and subsequent stages by copolymerizing propylene and at least one α-olefin other than propylene in the presence of the generated titanium-containing polyolefin and the organoaluminum compound catalyst. For example, a propylene / ethylene copolymer, an α-olefin copolymer other than propylene / ethylene / ethylene, and the like. The titanium-containing polyolefin produced in the first stage is, for example, a propylene homopolymer, a propylene / ethylene copolymer. Α-olefin other than propylene / ethylene It may be combined or the like.

The polypropylene resin used in the present invention has a weight average molecular weight of 150,000 to 5 as measured by the method described above.
It must be 10,000.

If the weight average molecular weight of the polypropylene resin is less than 150,000, the strength and extensibility of the obtained stretch packaging film will be insufficient, and if the weight average molecular weight of the polypropylene resin exceeds 500,000. The flexibility of the obtained stretch packaging film is poor.

Further, the polypropylene resin used in the present invention has an elution amount at 0 ° C. of 30 to 60% by weight, preferably 33 to 55% by weight, of the total elution amount by the above-mentioned cross fractionation chromatography. The elution amount at a temperature exceeding 0 ° C and 90 ° C or less is 30 to 55% by weight, preferably 35 to 50% by weight and 15% by weight or less in an arbitrary range of 1 ° C, and is higher than 90 ° C and 130 ° C or less. The elution amount at
It needs to be 20% by weight, preferably 7 to 10% by weight.

If the elution amount at 0 ° C. of the total elution amount of the polypropylene resin by cross separation chromatography is less than 30% by weight, the flexibility of the obtained stretch packaging film becomes insufficient, and conversely, 0%. If the elution amount at 60 ° C. exceeds 60% by weight, the strength of the stretch packaging film obtained will be insufficient.

If the amount of elution at more than 0 ° C. and 90 ° C. or less is less than 30% by weight of the total eluted amount of the polypropylene resin by cross fractionation chromatography, the flexibility of the obtained stretch packaging film is insufficient. Conversely, if the elution amount at more than 0 ° C. and 90 ° C. or less exceeds 55% by weight, the resulting stretch packaging film will have insufficient deformation recovery. On the other hand, if the elution amount in an arbitrary range of 1 ° C. in the range of more than 0 ° C. and 90 ° C. or less exceeds 15% by weight, the obtained stretch packaging film may have insufficient deformation recovery.

If the amount of elution at 90 ° C. or more and 130 ° C. or less is less than 5% by weight of the total elution amount of the polypropylene resin by cross fractionation chromatography, the strength of the obtained stretch packaging film becomes insufficient. 90 ° C
If the elution amount at 130 ° C. or less exceeds 20% by weight, the obtained stretch packaging film will have insufficient deformation recovery.

Further, in the stretch packaging film according to the present invention, it is preferable that the intermediate layer formed of the polypropylene resin has a flexural modulus of 1500 kg / cm ² or less. The bending elastic modulus of the intermediate layer is 1500
If it exceeds kg / cm ² , the flexibility of the obtained stretch packaging film may be reduced.

The stretch packaging film according to the present invention is obtained by polymerizing both surfaces of the intermediate layer formed of the above-mentioned polypropylene resin using a catalyst having a single polymerization active site, and having a density of 0.885-0. It has a three-layer structure in which skin layers formed of a linear low-density polyethylene resin (L-LDPE) of 920 g / cm ³ are laminated.
The catalyst having a single polymerization active site used for the polymerization of L-LDPE is not particularly limited, but typically includes, for example, a metallocene catalyst. In the L-LDPE used in the present invention, the structure of the catalyst, the method of polymerization, and the like are not particularly limited.

The L-LDPE forming the skin layer of the stretch packaging film according to the present invention has a density of 0.885 to 0.885.
It needs to be 0.920 g / cm ³ . LL
When the density of the DPE is less than 0.885 g / cm ³ , the strength of the obtained stretch packaging film becomes insufficient, and when it exceeds 0.920 g / cm ³ , the transparency and the transparency of the obtained stretch packaging film become poor. Deformation recovery and the like become insufficient.

The L-LDPE used in the present invention is:
In the measurement of the melting point by DSC, it is preferable that the temperature range from the start of melting to the end of melting of all the crystal components is 20 ° C. or less, and that the melting peak is single.

The L-LDPE used in the present invention may contain, for example, an α-olefin resin for improving flexibility, and a self-adhesive property, as long as the object of the present invention is not hindered. Contains one or more of various additives such as a tackifying resin, an anti-fogging agent for improving transparency, a stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, and a coloring agent. Is also good.

In the stretch packaging film according to the present invention, the thickness of the intermediate layer formed of the polypropylene resin is preferably 50 to 80%, and more preferably 65 to 80% of the total thickness of the film. More preferred.

The method for producing a stretch packaging film according to the present invention is not particularly limited. For example, a conventionally known method such as coextrusion by inflation molding or T-die molding or extrusion lamination using a plurality of extruders. What is necessary is just to carry out by the film forming method.

[0037]

The stretch packaging film according to the present invention comprises a polypropylene resin having a specific weight-average molecular weight and a specific elution amount at a specific temperature or temperature range in a cross-separation chromatograph as an intermediate layer, and a polymerization active site on both surfaces thereof. Has a three-layer structure in which a linear low-density polyethylene resin having a specific density, polymerized using a single catalyst, is laminated as a skin layer, so that strength, transparency, flexibility, and extensibility are achieved. It has both excellent self-adhesiveness and excellent deformation recovery without causing rapid deformation recovery.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, "molecular weight" means "weight average molecular weight", and "elution amount" means "elution amount of the total elution amount by cross fractionation chromatography".

(Example 1)

(1) Preparation of stretch packaging film As a resin for forming the intermediate layer, the molecular weight is 28,000, the elution amount is 0 ° C .: 49.0% by weight, and it is more than 0 ° C. and 90 ° C. or less: 4
0.1% by weight and not more than 15% by weight in an arbitrary range of 1 ° C.
Over 90 ° C. and 130 ° C. or less: 10.9% by weight of a polypropylene resin (trade name “NXO-30304”, density 0.878 g / cm ³ , MFR 1.5 g / 10 min, manufactured by Showa Denko KK) As a resin for forming a layer, the polymerization active site was polymerized using a single catalyst, and had a density of 0.905.
g / cm ³ linear low density polyethylene resin (trade name “Evolue SP0540”, MFR 3.6 g / 10
Mint, manufactured by Mitsui Petrochemical Industries, Ltd.)
R-2 "(manufactured by Riken Vitamin Co., Ltd.) added and mixed at 20% by weight, and the whole layer thickness was 15 μm by the co-extrusion method by inflation molding, and the layer thickness ratio (skin layer /
A stretch packaging film having an intermediate layer / skin layer ratio of 1/8/1 was obtained.

(2) Evaluation The performance of the film for stretch packaging obtained above (breaking strength and elongation at break, haze (haze value), elongation recovery rate, packaging finish) was evaluated by the following method. The results were as shown in Table 1. The evaluation was performed in an atmosphere of 20 ° C. and 65% RH unless otherwise specified.

Breaking strength and breaking elongation According to JIS K-6758 "Testing method for polypropylene", a tensile test of a film for stretch packaging was performed at a tensile speed of 50 mm / min using an autograph (manufactured by Shimadzu Corporation). The breaking strength (kg / cm ² ) and the breaking elongation (%) were measured. In addition, the measurement was performed in both the vertical direction and the horizontal direction of the film.

Haze (haze value) The haze (haze value,%) of the film for stretch packaging was measured in accordance with JIS K-7105 "Testing method for optical properties of plastics".

Elongation recovery rate After stretching the stretch packaging film by 50% and leaving it to stand for 5 minutes, the elongation recovery rate (%) was measured. In addition, the measurement was performed in both the vertical direction and the horizontal direction of the film.

After the plastic container is wrapped with the stretch packaging film, the state of peeling and wrinkling of the film is visually observed.
The packaging finish was evaluated according to the following criteria. [Evaluation criteria] ○ ‥‥ Neither peeling nor wrinkling was observed △ ‥‥ Peeling was not observed, but slight wrinkling was observed × ‥‥ Peeling or severe wrinkling was observed

Example 2 In the production of a film for stretch wrapping, as a resin for forming a skin layer, a polymerization was conducted using a catalyst having a single polymerization active site.
20 cm ³ of a low-density linear polyethylene resin (trade name “Affinity PL1845”, MFR 3.5 g / 10 min, manufactured by Dow Chemical Co., Ltd.) and 20 parts of the above-mentioned anti-fogging agent “EAR-2”
In the same manner as in Example 1 except that a mixture of the components added by weight% was used, the thickness of all the layers was 15 μm, and the layer thickness ratio (skin layer / intermediate layer / skin layer) was 1/8/1. A film for stretch packaging was obtained.

(Comparative Example 1) In the production of a film for stretch wrapping, ethylene / ethylene was used as a resin for forming a skin layer.
Vinyl acetate copolymer resin (trade name "Evaflex P-1"
405 ", vinyl acetate content 14% by weight, density 0.930
g / cm ³ , MFR 3.5 g / 10 min, manufactured by DuPont-Mitsui Polychemical Co., Ltd.), except that the thickness of all layers was 18 μm and the layer thickness ratio (skin layer /
A stretch packaging film having an intermediate layer / skin layer ratio of 1/8/1 was obtained.

Comparative Example 2 In the production of a film for stretch packaging, a resin having a density of 0.9 was used as a resin for forming a skin layer.
30 g / cm ³ linear low density polyethylene resin (trade name “Ultzex 3021F”, MFR 2.1 g / 1
0 min, manufactured by Mitsui Petrochemical Industry Co., Ltd.) except that the thickness of all layers was 18 μm and the layer thickness ratio (skin layer / intermediate layer / skin layer) was 1/8. / 1 was obtained.

The performance of the three types of stretch packaging films obtained in Example 2 and Comparative Example 1 or 2 was evaluated in Example 1.
The evaluation was performed in the same manner as described above. The results were as shown in Table 1.

[0050]

[Table 1]

As is clear from Table 1, the stretch wrapping film of Example 1 or 2 according to the present invention was excellent in all of strength, flexibility, transparency and the like. In addition, since it has excellent self-adhesiveness and excellent deformation recovery without causing rapid deformation recovery, peeling and wrinkling after packaging the packaged object (plastic container) are hardly observed. And excellent packaging finish.

On the other hand, the stretch packaging film of Comparative Example 1 using an ethylene / vinyl acetate copolymer resin as the resin for forming the skin layer had low strength and extremely poor transparency. In addition, the deformation recovery was insufficient, and the packaging finish was poor.

The resin for forming the skin layer has a density of 0.5.
The stretch packaging film of Comparative Example 2 using a linear low-density polyethylene resin exceeding 920 g / cm ³ was insufficient in both strength and transparency. In addition, deformation recovery was poor, and the packaging finish was poor.

[0054]

As described above, the stretch packaging film according to the present invention is excellent in strength, transparency, flexibility, extensibility, etc., and has excellent self-adhesiveness and rapid deformation recovery. Since it has both excellent deformation recovery properties and the like, it is suitably used for various applications including tray packaging of fresh foods and the like. Further, since a plasticized vinyl chloride resin is not used, there is no generation of hydrogen chloride gas, dioxin and the like at the time of incineration, and there is no adverse effect on the environment.

Claims (1)

[Claims] 1. The weight-average molecular weight is 150,000 to 500,000, and the elution amount at 0 ° C. is 30 to 60% by weight of the total elution amount by cross fractionation chromatography. The elution amount at 30 ° C. or lower is 30 to 55% by weight,
The elution amount at more than 90 ° C and 130 ° C or less is 5 to 20% by weight.
A linear low-density polyethylene having a density of 0.885 to 0.920 g / cm ³ , polymerized on both surfaces of an intermediate layer formed of a polypropylene resin having a density of 0.885 to 0.920 g / cm ^3. A film for stretch packaging, wherein a skin layer formed of a resin is laminated.