JPH0687197A - Stretch film for packaging - Google Patents

Abstract

PURPOSE:To obtain a stretch film for packaging which is excellent in self- adhesion and transparency by a method wherein a layer of a specific ethylene-alpha- olefin copolymer is laid in lamination on a layer of a specific propylene-alpha-olefin copolymer. CONSTITUTION:As for a propylene-alpha-olefin copolymer, the one which contains 8 to 35mol% of 4C or higher alpha-olefin, of which the ethylene content is 5mol% or less and of which a cold-xylene-soluble part is 10 to 70wt.% is used. As to an ethylene-olefin copolymer, the one of which the ethylene content is 50mol% or above, of which the number of carbon atoms of the alpha-olefin is 6 to 12, of which the density is 0.870 to 0.935g/cm<3>, which has a melting peak at 100 deg.C or above in a temperature rise thermogram by a differential scanning calorimeter and of which the cold-xylene-soluble part is 1 to 25wt.%, is used. A layer constituted of the ethylene-alpha-olefin copolymer is laid in lamination at least on one surface of a layer constituted of the propylene-alpha-olefin copolymer and thereby a stretch film for packaging is obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a stretch film for packaging. More specifically, for packaging foods that are directly or on a plastic tray and are stretch-wrapped with a film. For stretch films with good safety and hygiene, transparency, mechanical strength, low odor, and flexibility. Regarding stretch film.

[0002]

2. Description of the Related Art Conventionally, vinyl chloride resin has been mainly used as a stretch film for packaging in which foods such as fruits and vegetables, fresh fish, fresh meat, and prepared foods are placed directly or on a plastic tray and stretch-wrapped with a film. ing. In recent years, from the viewpoint of safety and hygiene, development of low-density polyethylene resin and ethylene-based resin such as ethylene-vinyl acetate copolymer has been actively conducted in place of conventional polyvinyl chloride.

However, when a low-density polyethylene resin or the like is used alone, the desired uniformity of film elongation and film rigidity cannot be satisfied at the same time. Further, in the ethylene-vinyl acetate copolymer resin film, if the vinyl acetate content, the molecular weight, etc. are appropriately selected, the problems as in the above-mentioned low density polyethylene resin film can be solved, but when the corner of the tray is sharp When packaging foods with sharp edges, there is a problem of tearing like tearing.

Therefore, for example, as disclosed in Japanese Patent Laid-Open No. 61-44635, an ethylene-vinyl acetate copolymer is provided on both outer layers of a specific resin to simultaneously satisfy the required performance. A stretch film for packaging has been proposed. However, the ethylene-vinyl acetate copolymer generates an acetic acid odor and is easily broken due to the low strength of the film. Since the melting temperature is low at around 90 ° C, when the film is sealed at the bottom of the tray, it is melted by heat, There are problems such as easy tearing.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a stretch film for packaging foods, which is excellent in automatic packaging suitability for the slip property, self-adhesiveness, transparency, heat sealability, uniform stretchability and flexibility. Further, it is to provide a stretch film for packaging which is extremely excellent in low odor, mechanical strength and heat resistance.

[0006]

In view of the above-mentioned problems, the inventors of the present invention continue to diligently research a stretch film for packaging having conventional performance, low odor and better cuttability and suitability for an automatic packaging line. Came. As a result, they found that a film having various performances was obtained by laminating a layer made of a specific ethylene copolymer (linear low-density polyethylene) on a layer made of a specific propylene resin, and completed the present invention. Came to do.

That is, the present invention provides the following (a1) to (a)
On at least one surface of the layer comprising the propylene-α-olefin-based copolymer (A) having the properties of 3), the following (b)
The present invention relates to a stretch film for packaging, which comprises laminating layers made of an ethylene-α-olefin copolymer (B) having the properties 1) to (b5). (A1) The content of α-olefin having 4 or more carbon atoms is 8 to 3
5 mol%, (a2) ethylene content is 5 mol% or less,
(A3) 10 to 70% by weight of cold xylene-soluble portion. (B
1) the ethylene content is 50 mol% or more, the (b2) α-olefin is an α-olefin having 6 to 12 carbon atoms,
(B3) has a density of 0.870 to 0.935 g / cm ³ , (b4) has a melting peak at 100 ° C or higher in a temperature rising thermogram by a differential scanning calorimeter (DSC), and (b5) has a cold xylene-soluble portion of 1 ~ 25% by weight.

The propylene-α-olefin copolymer (A) used in the present invention means propylene and α-olefin having 4 or more carbon atoms, or propylene and α-olefin having 4 or more carbon atoms.
-A copolymer of olefin and ethylene, which has the following (a
It is a copolymer having the properties 1) to (a3). (A1) The content of α-olefin having 4 or more carbon atoms is 8 to 3
5 mol%, (a2) ethylene content is 5 mol% or less,
(A3) 10 to 70% by weight of cold xylene-soluble portion. Examples of the α-olefin having 4 or more carbon atoms include butene-1, pentene-1, hexene-1, 4-methyl-pentene-1, octene-1 and the like, alone or in combination. For example, when vapor phase polymerization is carried out, butene-1 is preferable because it is difficult to liquefy and can have a high partial pressure.

The content of the (a1) α-olefin having 4 or more carbon atoms in the propylene-α-olefin copolymer (A) used in the present invention is from 8 to 35 mol%, from 10 to 25
Mol% is preferred. When the content of (a1) is less than 8 mol%, flexibility as a film cannot be obtained, which is not preferable. Also,
When the content of (a1) exceeds 35 mol%, the rigidity of the film is lowered and a sticky phenomenon occurs, which is not preferable.

The ethylene content of (a2) in the propylene-α-olefin copolymer (A) used in the present invention is 5 mol% or less, more preferably 3 mol% or less. The (a
When 2) exceeds 5 mol%, the transparency of the film deteriorates with time, which is not preferable.

The (a3) cold xylene-soluble part (hereinafter also referred to as CXS) of the propylene-α-olefin copolymer (A) used in the present invention is 10 to 70% by weight, preferably 12 to 65% by weight. %. 10% by weight of (a3)
If it is less than the above range, flexibility as a film cannot be obtained, which is not preferable. On the other hand, if the content of (a3) exceeds 70% by weight, the rigidity of the film decreases, which is not preferable.

The propylene-α-olefin copolymer (A) used in the present invention is a so-called Ziegler-Natta catalyst which is a catalyst for stereoregular polymerization of α-olefins known as a catalyst system, that is, a periodical system. A group IV to VIII transition metal compound, an organic compound of a group I to II typical metal of the periodic table, and a third component of an electron donating compound are preferably used. It can be produced by any method such as a solvent polymerization method for polymerization or a gas phase polymerization method for polymerization in a gas phase. For example, JP-A-6
It can be obtained by the production method described in JP-A 3-19255 (Example 1), JP-A-60-76515 or the like.

In the present invention, the ethylene content is 3 mol% to 10 mol% with respect to the propylene-α-olefin copolymer (A) within a range that does not impair the effects of the present invention.
The ethylene-propylene copolymer and the polyethylene resin can be blended and used. The polyethylene-based resin referred to here is a known resin, such as polyethylene obtained by a high pressure method, a copolymer of ethylene and an α-olefin having 4 or more carbon atoms, and the like.

In the present invention, the ethylene content of the ethylene-α-olefin copolymer (B) (b1) used for the purpose of improving low odor, mechanical strength and heat resistance is 50 mol% or more. Yes, 70 mol% or more is more preferable.

In the ethylene-α-olefin copolymer (B) used in the present invention, the (b2) α-olefin has 6 carbon atoms.
.About.12 .alpha.-olefin, and the content of .alpha.-olefin is preferably 1 to 15 mol%. Examples of the α-olefin include hexene-1,4-methyl-pentene-
1, and octene-1 and the like, alone or in combination.

The ethylene-α-olefin copolymer (B) used in the present invention has a (b3) density of 0.870 to 0.935 g / c.
m ^3, preferably 0.890~0.935 g / cm ^3, more preferably 0.910~0.930 g / cm ^3. The (b3) is
When it is less than 0.870 g / cm ³ , the rigidity of the film is lowered, which is not preferable, and when (b3) is 0.935 g / cm ^3.
When it exceeds cm ³ , transparency and flexibility are deteriorated and balanced physical properties cannot be obtained, which is not preferable.

The ethylene-α-olefin copolymer (B) used in the present invention is (b4) differential scanning calorimeter (DSC).
It is necessary that the temperature rising thermogram has a melting peak at 100 ° C. or higher. Multiple melting peaks may be observed within the above temperature range. Further, another melting peak may be observed outside the above temperature range. (B4) 10
If it does not have a melting peak at 0 ° C. or higher, perforation tends to occur during heat sealing, which is not preferable.

The (b5) cold xylene-soluble part (CX) of the ethylene-α-olefin copolymer (B) used in the present invention.
S) is 1 to 25% by weight, preferably 3 to 20% by weight. If the content of (b5) is less than 1% by weight, the film will not have well-balanced physical properties, and the content of (b5) will be 2
If it exceeds 5% by weight, workability is deteriorated, which is not preferable. The CXS of the copolymer (B) has many components having a weight average molecular chain length of 100 to 900 nm and a molecular weight.

The stretch film for packaging according to the present invention is prepared by laminating a layer of the ethylene-α-olefin copolymer (B) on one side or both sides of the layer of the propylene-α-olefin copolymer (A). Although obtained, the configurations and thicknesses of the propylene-α-olefin copolymer (A) and the ethylene-α-olefin copolymer (B) can be changed depending on the purpose of use of the film.
In terms of the layer structure, it is preferable that the layer containing a propylene-α-olefin copolymer as a main component accounts for 10 to 80% of the whole from the viewpoint of the balance of various physical properties of the obtained film. The total thickness of the film is preferably 6 to 40 μm, and the layer containing the propylene-α-olefin copolymer (A) as a main component is preferably 2 to 20 μm.

In the present invention, the copolymer (A) or the copolymer (B) may further have, for example, a carbon number of 1 to 12 for the purpose of adjusting extensibility, self-adhesiveness and the like. A fatty acid ester, which is a compound of the fatty acid alcohol described above and a fatty acid having 10 to 22 carbon atoms, can be added.

The film of the present invention can be produced by a conventional method such as an inflation method or a T-die method, followed by heat-bonding, or a coextrusion type of two kinds of two layers or two kinds of three layers. It is possible to form a film with an inflation film molding machine or a T die film molding machine. It is also possible to form a film by laminating it on any of the formed films by a known method such as extrusion lamination.

In the present invention, when the packaging stretch film requires shrinkage, it is preferably stretched in at least uniaxial direction after the film formation. The stretching can be uniaxial or biaxial. In the case of uniaxial stretching, for example, a commonly used roll stretching method is preferable. Further, in the case of biaxial stretching, for example, a sequential stretching method in which uniaxial stretching is followed by biaxial stretching may be used, or a method in which simultaneous biaxial stretching such as tubular stretching is also possible.

[0023]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded. First, methods for measuring physical property values in the following examples and comparative examples will be described.

(1) Content of α-olefin in copolymer (A) It was determined from the mass balance. Regarding the content of butene-1, the absorbance of the characteristic absorption at 770 cm ^-1 was measured using an infrared spectrophotometer, and the result of the substance balance was confirmed by the calibration curve prepared by the quantitative value by ¹³ C-NMR. .

(2) Ethylene content in copolymer (A) It was determined from the mass balance. Furthermore, using an infrared spectrophotometer,
32cm ^-1, and measuring the absorbance of characteristic absorption of 720 cm ^{-1, 14}
The mass balance results were confirmed using a calibration curve prepared from the quantitative values of the C-labeled ethylene copolymer measured by radiation.

(3) Cold xylene soluble part (CXS) 5 g of the polymer is dissolved in 500 ml of xylene and gradually cooled to room temperature. Then, the mixture is left in a bath at 20 ° C. for 4 hours and then filtered, and the filtrate is concentrated, dried, dried and weighed.

(4) Melt Flow Rate (MFR) The ethylene-α-olefin copolymer was subjected to the method specified in JIS K6760.

(5) Density According to the method specified in JIS K6760. After annealing in water at 100 ° C. for 1 hour, the density was measured.

(6) Differential Scanning Calorimeter (DSC) DSC-7 manufactured by Perkin Elmer was used. About 1 cut out from a sheet with a thickness of about 0.5 mm created by hot pressing
Put 0 mg of the test piece in the sample pan for DSC measurement and
Preheat at 5 ° C for 5 minutes, cool down to 40 ° C at 1 ° C / minute,
After holding for 5 minutes, the temperature is raised to 150 ° C at a rate of 10 ° C / minute to obtain a thermogram.

(7) Haze (Haze) According to the method specified in ASTM D1003. The smaller this value is, the better the transparency is.

(8) Tensile Fracture Strength and Elongation According to the method specified in JIS K6781. MD / TD
Was measured.

(9) Young's modulus According to the method specified in ASTM D882. The smaller this value is, the more flexible it is. MD / TD was measured. However, test piece shape: 20 mm x 120 mm strip type chuck distance: 50 mm Peeling speed: 5 mm / min

(10) Heat-resistant temperature Wrap a high-impact styrene tray with a film, and make a section of 4 sheets of film and 2 sheets of stack on the bottom of the tray, and apply a force of ² g / cm ² for 3 seconds on a hot plate. Hold down the temperature to make a hole somewhere in the film.

Example 1 A professional obtained by the method described in JP-A-60-76515
Pyrene-butene-1 copolymer (A-1) [(a1) butene
-1 content 17.3 mol%, (a3) cold xylene soluble part 2
9.6 wt%] 100 wt% resin composition
200 using an extruder with 50 mm and screw L / D = 28
Kneaded at ℃, while ethylene-hexene-1 copolymer
(B-1) [Sumikasen α manufactured by Sumitomo Chemical Co., Ltd.
Trademark name) FZ201-0, MFR 2.0g at 190 ℃
/ 10 minutes, (b3) density 0.912 g / cm ³, (B4) DS
Melting peak temperature by C is 101 ° C, (b5) weight flat
A cold xylene-soluble part with a uniform molecular chain length of 100 to 900 nm has 10 layers.
Includes amount%. ] 98.0% by weight and monoglycerin oleate
A resin composition consisting of 2.0% by weight is used, which has a diameter of 50 mm and a screw.
Using an extruder with L / D = 28, kneading at 190 ° C.
Both types are 3-layer, 3-layer in with a die diameter of 150 mm and a die lip of 1.2 mm.
Inflatable film made by Placo Co., Ltd. equipped with Freddie
Supplied to a molding machine to obtain a propylene-butene-1 copolymer (A-
Ethylene-hexene is formed on both sides of the 5 μm-thick layer consisting of 1).
-1 Copolymer (B-1) -based layer having a thickness of 5 µm
The die temperature is 200 ℃
By inflation molding with a ratio of 3.0, the total thickness
A 15μ stretch wrapping film was produced. Obtained
The characteristic values of the film are shown in Table 1. Of this film
The odor was at a sufficiently low level with no practical problems.

Example 2 The ethylene-hexene-1 copolymer (B used in Example 1
-1) instead of ethylene-hexene-1 copolymer (B-
2) [Sumikasen α (registered trademark) FZ202-0 manufactured by Sumitomo Chemical Co., Ltd., MFR 2.0 g / 190 ° C. /
10 minutes, (b3) density 0.921 g / cm ³ , (b4) DSC
4% by weight of the cold xylene-soluble part having a melting peak temperature of 108 ° C. and (b5) a weight average molecular chain length of 100 to 900 nm.
Including. ] In the same manner as in Example 1 except that
A .mu. stretch wrapping film was produced. Various characteristic values of the obtained film are shown in Table 1. The odor of this film was at a sufficiently low level with no practical problems.

Comparative Example 1 The ethylene-hexene-1 copolymer (B used in Example 1
-1) instead of ethylene-vinyl acetate copolymer (Sumitomo Chemical Co., Ltd. Evatate [registered trademark] H2011, vinyl acetate content 15% by weight, MFR2.
0 g / 10 min) was used, and a film for stretch packaging having a total thickness of 15 μm was produced in the same manner as in Example 1 except that the temperature in the extruder was 170 ° C. Various characteristic values of the obtained film are shown in Table 1. This film was not suitable for practical use because it was accompanied by an acetic acid odor and was inferior in heat resistance.

Comparative Example 2 Propylene-butene-1 copolymer (A used in Example 1
-1) A propylene-ethylene copolymer obtained by the method described in JP-A-60-76515 (ethylene content 11.6 mol%, cold xylene soluble part 27.1 wt%) was used instead of -1). A stretch packaging film having a total thickness of 15 μm was produced in the same manner as in Example 1. Various characteristic values of the obtained film are shown in Table 1. The odor of this film was at a sufficiently low level that there was practically no problem, but the transparency was poor,
It was poorly flexible.

Comparative Example 3 Propylene-butene-1 copolymer (A used in Example 1
-1), a propylene-butene-1 copolymer obtained by the method described in JP-A-60-76515 (butene-1 content 14.8 mol%, cold xylene-soluble portion 9.5% by weight). )
A stretch packaging film having a total thickness of 15 μm was produced in the same manner as in Example 1 except that 100% by weight was used as the intermediate layer. Various characteristic values of the obtained film are shown in Table 1. The odor of this film was at a sufficiently low level without any practical problems, but was poor in flexibility.

[0039]

[Table 1]

[0040]

INDUSTRIAL APPLICABILITY The stretch film for packaging of the present invention is a combination of a propylene-α-olefin-based copolymer and a specific ethylene-α-olefin copolymer, which is suitable for automatic packaging. It has excellent heat sealability, uniform extensibility, flexibility, low odor, transparency and mechanical strength.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Kawakita 2-10-1, Tsukahara, Takatsuki City, Osaka Prefecture Sumitomo Kagaku Kogyo Co., Ltd. (72) Takanori Kume 2-10-1, Tsukahara, Takatsuki City, Osaka Prefecture Sumitomo Chemical Co., Ltd.

Claims (2)

[Claims] 1. Ethylene having the following properties (b1) to (b5) on at least one side of a layer comprising a propylene-α-olefin copolymer (A) having the following properties (a1) to (a3): A stretch film for packaging, which is formed by laminating layers made of an α-olefin copolymer (B). (A1) The content of α-olefin having 4 or more carbon atoms is 8 to 3
5 mol%, (a2) ethylene content is 5 mol% or less,
(A3) 10 to 70% by weight of cold xylene-soluble portion. (B
1) the ethylene content is 50 mol% or more, the (b2) α-olefin is an α-olefin having 6 to 12 carbon atoms,
(B3) has a density of 0.870 to 0.935 g / cm ³ , (b4) has a melting peak at 100 ° C or higher in a temperature rising thermogram by a differential scanning calorimeter (DSC), and (b5) has a cold xylene-soluble portion of 1 ~ 25% by weight. 2. The stretch film for packaging according to claim 1, wherein the (a1) α-olefin having 4 or more carbon atoms is butene-1.