JP3252536B2 - Stretch film for 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 for packaging. More specifically, foods are placed directly or on a plastic tray, and these are stretch-wrapped with a film.The packaging stretch film has good safety and health, transparency, mechanical strength, low odor, and flexibility. Related to stretch film.

[0002]

2. Description of the Related Art Conventionally, polyvinyl chloride resin is mainly used as a packaging stretch film 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 health, development of a low-density polyethylene resin or an ethylene-based resin such as an ethylene-vinyl acetate copolymer has been actively performed instead of the conventional polyvinyl chloride.

However, when a low-density polyethylene resin or the like is used alone, the desired uniformity of film elongation, film rigidity and the like cannot be satisfied at the same time. In addition, in the ethylene-vinyl acetate copolymer resin film, if the vinyl acetate content, the molecular weight, and the like are appropriately selected, the above-described problems in the low-density polyethylene resin film can be solved, but when the corner of the tray is sharp, When packaging foods having sharp or sharp parts, there is a problem that the food is torn torn.

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

[0005]

SUMMARY OF THE INVENTION The present invention relates to a stretch film for packaging foods, which is excellent in slipperiness, self-adhesiveness, transparency, heat sealability, uniform extensibility and flexibility as a film suitable for automatic packaging. Another object of the present invention 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 present inventors have intensively studied a stretch film for packaging having conventional performance, low odor, good cutability and suitability for an automatic packaging line. Have been. As a result, the inventors have found that a film having various properties can be 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. I came to.

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

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

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

The propylene-α-olefin copolymer (A) used in the present invention has a (a2) ethylene content of 5 mol% or less, more preferably 3 mol% or less. The (a
If 2) is more than 5 mol%, the transparency of the film is undesirably deteriorated with time.

The (a3) cold xylene-soluble portion (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. %. (A3) is 10% by weight
If it is less than 10, flexibility as a film cannot be obtained, which is not preferable. On the other hand, if (a3) exceeds 70% by weight, the rigidity of the film is undesirably reduced.

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 periodic system. A compound comprising a transition metal compound of Tables IV to VIII, an organic compound of a typical metal of Groups I to II of the periodic table, and preferably a third component of an electron donating compound is 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
It can be obtained by the production method described in JP-A No. 3-19255 (Example 1), JP-A-60-76515 and the like.

In the present invention, the ethylene content of the propylene-α-olefin copolymer (A) is 3 mol% to 10 mol% as long as the effects of the present invention are not impaired.
And an ethylene-propylene copolymer or a polyethylene resin. The polyethylene resin referred to here is a known resin, such as a polyethylene obtained by a high-pressure method, a copolymer of ethylene and an α-olefin having 4 or more carbon atoms, or the like.

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

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

The (b3) density of the ethylene-α-olefin copolymer (B) used in the present invention is 0.870 to 0.935 g / c.
m ³ , preferably 0.890 to 0.935 g / cm ³ , more preferably 0.910 to 0.930 g / cm ³ . (B3) is
If it is less than 0.870 g / cm ³ , the rigidity of the film decreases, which is not preferable.
If it exceeds cm ³ , transparency and flexibility are undesirably reduced, and it is not preferable because balanced physical properties cannot be obtained.

The ethylene-α-olefin copolymer (B) used in the present invention comprises (b4) a differential scanning calorimeter (DSC)
It is necessary to have a melting peak at 100 ° C. or higher in the thermogram obtained by the above method. A plurality of melting peaks may be observed within the above temperature range. Further, another melting peak may be observed outside the above temperature range. (B4) 10
When there is no melting peak at 0 ° C. or higher, it is not preferable because holes are easily generated during heat sealing.

The (b5) cold xylene-soluble portion (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. When the content of the (b5) is less than 1% by weight, the film does not have well-balanced physical properties.
If it exceeds 5% by weight, the processability is undesirably reduced. The CXS of the copolymer (B) has many components having a weight average molecular chain length of 100 to 900 nm.

The stretch film for packaging according to the present invention is obtained by laminating a layer of ethylene-α-olefin copolymer (B) on one or both sides of a layer composed of propylene-α-olefin copolymer (A). Although it is obtained, the configuration and thickness of the propylene-α-olefin copolymer (A) and the ethylene-α-olefin copolymer (B) can be changed according to the purpose of use of the film.
As the layer constitution, it is preferable that the layer mainly composed of the propylene-α-olefin-based copolymer accounts for 10 to 80% of the whole in view of the balance of various physical properties of the obtained film. The total thickness of the film is preferably from 6 to 40 μm, and the thickness of the layer mainly composed of the propylene-α-olefin-based copolymer (A) is preferably from 2 to 20 μm.

In the present invention, if necessary, the copolymer (A) or the copolymer (B) may have, for example, a carbon number of 1 to 12 for the purpose of adjusting the extensibility, self-adhesion and the like. And a fatty acid ester, which is a compound of a fatty acid alcohol having 10 to 22 carbon atoms, and the like.

In the present invention, the film is produced by a conventional method such as an inflation method or a T-die method, followed by heat lamination after forming the film, or a co-extrusion type of two or two layers or two or three layers. It is possible to form a film with an inflation film forming machine or a T-die film forming 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, if the stretch film for packaging needs shrinkage, it is preferable to stretch the film in at least one axial direction after the film is formed. Stretching can be uniaxial or biaxial. In the case of uniaxial stretching, for example, a commonly used roll stretching method is preferable. In the case of biaxial stretching, for example, a sequential stretching method in which uniaxial stretching is performed and then biaxial stretching may be performed, or a method of simultaneously biaxial stretching such as tubular stretching is also possible.

[0023]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist thereof. First, methods for measuring physical properties in the following examples and comparative examples will be described.

(1) α-Olefin content in copolymer (A) It was determined from the material balance. For the butene-1 content, the absorbance at 770 cm ^-1 characteristic absorption was measured using an infrared spectrophotometer, and the result of the material balance was confirmed by a calibration curve prepared from quantitative values by ¹³ C-NMR. .

(2) Ethylene content in copolymer (A) It was determined from the material balance. Further, using an infrared spectrophotometer, 7
32cm ^-1, and measuring the absorbance of characteristic absorption of 720 cm ^{-1, 14}
The result of the material balance was confirmed using a calibration curve prepared from the quantitative value of the ethylene copolymer labeled with C by radiation measurement.

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

(4) Melt flow rate (MFR) The ethylene-α-olefin copolymer followed the method specified in JIS K6760.

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

(6) Differential Scanning Calorimeter (DSC) DSC-7 manufactured by PerkinElmer was used. Approximately 1 cut out from a sheet of about 0.5mm thickness created by hot pressing
0 mg of the sample was placed in a sample pan for DSC measurement, and 150
Preheating at 5 ° C for 5 minutes, cooling 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./min to obtain a thermogram.

(7) Haze (Haze) The method specified in ASTM D1003 was followed. The smaller the value, the better the transparency.

(8) Tensile breaking strength and elongation The method specified in JIS K6781 was used. MD / TD
Was measured.

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

(10) Heat-resistant temperature Wrap the high impact styrene tray with film, make a four-layer and two-layer film at the bottom of the tray, and apply a force of ² g / cm ² on a hot plate for 3 seconds. The temperature at which holes are opened somewhere in the film.

Example 1 A process obtained by the method described in JP-A-60-76515
Pyrene-butene-1 copolymer (A-1) [(a1)
(A3) cold xylene soluble part 2
9.6% by weight]
200 mm using an extruder with 50 mm screw L / D = 28
Kneaded at the same temperature, while ethylene-hexene-1 copolymer
(B-1) [Sumikasen α manufactured by Sumitomo Chemical Co., Ltd.
Registered trademark name) FZ201-0, MFR 2.0 g at 190 ° C
/ 10 min, (b3) density 0.912 g / cm ^Three, (B4) DS
The temperature of the melting peak by C is 101 ° C., and (b5) the weight average
10-fold cold xylene soluble part with average molecular chain length of 100 to 900 nm
% Included. 98.0% by weight and monoglycerin oleate
A resin composition consisting of 2.0% by weight is screwed with a 50 mm diameter
The mixture was kneaded at 190 ° C. using an extruder with L / D = 28.
Both are three types of three layers with a die diameter of 150 mm and a die lip of 1.2 mm.
An inflation film made by Placo Co., Ltd.
Propylene-butene-1 copolymer (A-
1) ethylene-hexene on both sides of a 5 μm thick layer
5 μm thick layers containing -1 copolymer (B-1) as a main component
Are stacked, and the die temperature is set to 200 ° C and blown.
By inflation molding at a ratio of 3.0, the total thickness
A 15μ stretch packaging film was produced. Obtained
Table 1 shows various characteristic values of the obtained film. Of this film
The odor was at a sufficiently low level without 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
(B5) 4% by weight of a cold xylene-soluble portion having a weight average molecular chain length of 100 to 900 nm.
Including. ] Except that the total thickness 15
μ was prepared for stretch packaging film. Table 1 shows various characteristic values of the obtained film. The odor of this film was at a sufficiently low level without practical problems.

Comparative Example 1 The ethylene-hexene-1 copolymer (B) used in Example 1
-1) instead of an ethylene-vinyl acetate copolymer (Evatate [registered trademark] H2011, manufactured by Sumitomo Chemical Co., Ltd.), a vinyl acetate content of 15% by weight, and an MFR of 190.degree.
0 g / 10 min) 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. Table 1 shows various characteristic values of the obtained film. This film was not practical because it had an acetic acid odor and was inferior in heat resistance.

Comparative Example 2 The propylene-butene-1 copolymer (A
-1) was replaced by a propylene-ethylene copolymer (ethylene content: 11.6 mol%, soluble xylene-soluble part: 27.1% by weight) obtained by the method described in JP-A-60-76515. In the same manner as in Example 1, a film for stretch packaging having a total thickness of 15 μm was produced. Table 1 shows various characteristic values of the obtained film. The odor of this film was at a sufficiently low level that there was no practical problem, but the transparency was poor,
Lack of flexibility.

Comparative Example 3 The propylene-butene-1 copolymer (A
In place of -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 part: 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 of the intermediate layer was used. Table 1 shows various characteristic values of the obtained film. The odor of this film was at a sufficiently low level without practical problems, but was poor in flexibility.

[0039]

[Table 1]

[0040]

The stretch film for packaging according to the present invention is made of a combination of a propylene-.alpha.-olefin copolymer and a specific ethylene-.alpha.-olefin copolymer. It has excellent heat sealability, uniform extensibility, flexibility, and low odor, transparency, and mechanical strength.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshio Kawakita 2-10-1 Tsukahara, Takatsuki-shi, Osaka Sumitomo Chemical Industries Co., Ltd. (72) Inventor Takanori Kume 2-1-1 Tsukahara, Takatsuki-shi, Osaka Sumitomo (56) References JP-A-61-44635 (JP, A) JP-A-4-292944 (JP, A) JP-A-3-86544 (JP, A) (58) Fields surveyed ( Int.Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (2)

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