JPH0999527A - Stretch packaging film - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a film for stretch packaging, which has excellent appearance and excellent packaging suitability such as tear strength and deformation recovery. A base material comprising at least one resin selected from a low-density polyethylene resin, a crystalline polypropylene resin, and a linear ethylene-α-olefin copolymer resin having a density of 0.910 g / cm ³ or more. At least one surface of the layer (A) has a density of 0.908 g / cm ³ or less,
A stretch packaging film comprising a surface layer (B) made of a linear ethylene-α-olefin copolymer resin having a Q value (Mw / Mn) of 4.0 or less.

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 foods, and more particularly to a stretch packaging film having excellent appearance and excellent packaging suitability such as tear strength and deformation recovery.

[0002]

2. Description of the Related Art In recent years, foods such as fruits and vegetables, fresh fish, fresh meats, side dishes, etc. are placed directly or on a plastic tray, and these are stretch-wrapped with a film, so-called pre-packaging film, which is environmentally friendly. In place of the conventional polyvinyl chloride film, development of a polyolefin resin has been actively carried out.

For example, in Japanese Examined Patent Publication No. 2-12187 and Japanese Examined Patent Publication No. 2-18983, ethylene is polymerized with an α-olefin selected from butene-1, hexene-1, 4-methylpentene-1, and octene-1. A stretch packaging film has been proposed in which a first layer containing an ethylene-α-olefin copolymer resin as a main component and a second layer containing an ethylene-vinyl acetate copolymer resin as a main component are laminated.

In Japanese Patent Publication No. 4-50904,
Ethylene-vinyl acetate was used on both surfaces of a layer containing propylene-α-olefin random copolymer resin as a main component, which was obtained by polymerizing propylene and at least one α-olefin selected from ethylene and α-olefins having 4 to 8 carbon atoms. A stretch packaging film formed by laminating a layer containing a copolymer resin as a main component has been proposed.

However, the above-mentioned stretch wrapping film is inferior in appearance, particularly glossiness, to be used as a stretch wrapping film for foods, and the food to be packaged does not look good at the time of display at a store. Further, since the tear strength of the film is weak, there is a problem that if the food to be packaged has sharp corners or if the tray on which the food to be packaged is mounted has sharp corners, it will break from this contact part. .

Further, since the deformation recovery property is inferior, there is a problem that wrinkles are likely to occur at the time of transporting a package or displaying it at a store, and it has not always been possible to sufficiently meet the demands of the market.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in stretch packaging films for foods, and has as its object the object of the present invention is to provide a film having a moderate slip property.
It is an object of the present invention to provide a stretch packaging film having not only self-adhesiveness and antifogging property but also excellent appearance and excellent packaging suitability such as tear strength and deformation recovery.

[0008]

In order to solve the above problems, the invention according to claim 1 of the present invention provides a low density polyethylene resin, a crystalline polypropylene resin and a density of 0.
A density of 0.9 or more on at least one side of the base material layer (A) made of at least one resin selected from linear ethylene-α-olefin copolymer resins of 910 g / cm ³ or more.
08 g / cm ³ or less and a Q value (Mw / Mn) of 4.0
The present invention relates to a stretch packaging film comprising a surface layer (B) composed of the following linear ethylene-α-olefin copolymer resin.

Hereinafter, the present invention will be described in detail. The stretch packaging film of the present invention is configured to include two types of layers, a base layer (A) and a surface layer (B). Base material layer (A)
Is at least one resin selected from a low-density polyethylene resin, a crystalline polypropylene resin, and a linear ethylene-α-olefin copolymer resin having a density of 0.910 g / cm ³ or more.

The low-density polyethylene resin has a density of 0.915 to 0.930 g / cm ³ , MFR (JIS
K-7210: 190 ° C, 2.16Kg load) is 0.3
A low density polyethylene resin of ~ 15 g / 10 min is preferred. As the crystalline polypropylene resin, a homopolymer of propylene, a binary copolymer containing propylene as a main component and ethylene or an α-olefin having 4 to 8 carbon atoms, and a content of 74 to 96 wt% Of propylene and content of 1-10% by weight of ethylene and content of 3-25% by weight
And a ternary copolymer with an α-olefin having 4 to 8 carbon atoms. Examples of the α-olefin having 4 to 8 carbon atoms include butene-1, hexene-1, octene-1, pentene-1,4-methylpentene-1,3-methylpentene-1 and the like.

As the crystalline polypropylene resin, M
FR (JIS K-7210: 230 ° C, 2.16 Kg
Load) is 0.5 to 40 g / 10 minutes, preferably 0.5 to
It is 20 g / 10 minutes. Density is 0.910g / c
The linear ethylene-α-olefin copolymer resin having m ³ or more is mainly composed of ethylene
.About.8 α-olefin copolymer. 4 to 4 carbon atoms
Examples of the α-olefin of 8 include butene-1, hexene-1, 4-methylpentene-1, octene-1, and the like, and these can be used alone or in combination of two or more. The content of α-olefin in the resin is 5 to 15
% By weight is preferred. The density of the linear ethylene-α-olefin copolymer resin is 0.910 to 0.930 g /
cm ³ is preferable, and MFR is preferably 0.5 to 10 g / 10 minutes.

The surface layer (B) has a density of 0.908 g / c.
It is composed of a linear ethylene-α-olefin copolymer resin having m ³ or less and a Q value (Mw / Mn) of 4.0 or less. Preferably, the density is 0.865 to 0.905 g / cm ^{3, the} Q value (Mw / Mn) is 2.0 to 3.0, and the MFR is 0.5 to 5 g / 10 minutes. Density 0.908g / c
When it exceeds m ³ , the appearance of the film is deteriorated, and the Q value is 4.0 even when the density is 0.908 g / cm ³ or less.
If it exceeds, the film appearance is not necessarily good, and the packaging suitability such as tear strength is also deteriorated, and it may be difficult to use in an automatic stretch wrapping machine, which is not preferable.

The linear ethylene-α-olefin copolymer resin is a copolymer containing ethylene as a main component and α-olefin alone or as a mixture of two or more kinds. The α-olefin is an α-olefin having 4 to 8 carbon atoms, and for example, butene-1, hexene-1, 4-
Methyl pentene-1, octene-1, etc. are mentioned. α
-The content of olefin is 10 to 30% by weight, preferably 12 to 26% by weight.

When the α-olefin content is less than 10% by weight, the obtained film is hard and tear strength and the like are deteriorated, and good packaging suitability cannot be obtained. On the other hand, when it exceeds 30% by weight,
Film forming tends to be difficult. The linear ethylene-α-olefin copolymer is obtained by ionic polymerization of ethylene and α-olefin and uses a transition metal compound as a catalyst, a so-called Ziegler-Natta type catalyst,
Alternatively, a so-called metallocene catalyst using an organometallic complex can be given.

Further, as the manufacturing process, a high pressure method, a gas phase method, a solution method, which is used in general polyolefin manufacturing,
A slurry method and the like can be mentioned. The linear ethylene-α-olefin copolymer of the present invention is preferably a metallocene catalyst because of the relationship between the density and the Q value.

The metallocene catalyst is a transition metal (F
e, Ti, Zr, Hf, etc.) are sandwiched between unsaturated cyclic compounds, enabling precise control of stereoregularity, molecular weight, copolymerizability, and the like. A conventional Ziegler-Natta type catalyst is called a multi-site catalyst (MSC) because active sites having different properties are mixed, and low-molecular-weight components other than the target molecular weight can be obtained at the same time. Deteriorates sealing performance.

On the other hand, the metallocene catalyst is called a single-site catalyst (SSC) because it has a uniform catalytic active site, and a polymer having a uniform sandwiching molecular weight distribution can be obtained, which contributes to the processability-related molecular weight distribution and product physical properties. The composition distribution can be controlled arbitrarily. Such linear ethylene-α-olefin copolymers of metallocene catalysts are available from Mitsubishi Chemical Corporation “KERNEL” and from Dow Chemical Japan Ltd. “AFFINITY” and “ENGAGE”.
It is sold under the brand name.

In the surface layer (B), an ethylene-vinyl acetate copolymer (vinyl acetate content is 5 to 40% by weight), an ethylene-acrylic acid copolymer (acrylic acid content) within a range not deteriorating the appearance of the film. The amount is 5 to 20% by weight), a metal salt of an ethylene-methyl methacrylate copolymer, a copolymer of an α-olefin such as ethylene and propylene and a monomer selected from acrylic acid, methacrylic acid, maleic acid and the like. (Zn, Na, K, Li, Mg, etc.), maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, etc. 1 to 40% by weight, preferably 1 to 30% by weight, for the purpose of improving

Further, the above substances may be added to the base material layer (A) in an amount of 1 to 40% by weight as in the case of the surface layer (B). Further, the surface layer (B) has an antifogging property and an appropriate slip property,
In order to impart self-adhesiveness and antistatic property, for example, a compound of an aliphatic alcohol having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms and a fatty acid having 10 to 22 carbon atoms, preferably 12 to 18 carbon atoms Is an aliphatic alcohol fatty acid ester, specifically, monoglycerin oleate, polyglycerin oleate, glycerin triricinoleate, glycerin acetyl ricinoleate, polyglycerin stearate, polyglycerin laurate, methyl acetyl ricinoleate, ethyl Acetyl ricinoleate, butyl acetyl ricinoleate, propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, polyethylene glycol oleate, polypropylene glycol oleate, sorbitan oleate, sorbitan laurate , Polyethylene glycol sorbitan oleate, polyethylene glycol sorbitan laurate, etc., and polyalkylene ether polyols, specifically polyethylene glycol, polypropylene glycol, etc., and at least one compound selected from paraffin oils. It is preferable to add 0.1 to 10% by weight, preferably 1 to 5% by weight.

These additives may be added to the base material layer (A) in an amount of 0.1 to 10% by weight. The stretch packaging film of the present invention comprises at least one selected from the low-density polyethylene resin, the crystalline propylene-based resin, and the linear ethylene-α-olefin copolymer resin constituting the base material layer (A). The linear ethylene-α-olefin copolymer resin constituting the resin and the surface layer (B) is subjected to a known method such as a coextrusion method by inflation molding or T-die molding using a plurality of extruders, or an extrusion laminating method. Are laminated and molded.

In the inflation molding,
Either a method of cooling from the outer surface of the tube or a method of cooling from both the outer surface and the inner surface of the tube may be used. Above all, a coextrusion method by inflation molding is preferable in order to obtain a laminated film in which mechanical strength such as tear strength in the machine direction and the transverse direction is well balanced, and the blow ratio at that time is 3 to 2
It is 0 times, preferably 5 to 18 times.

The blow ratio here means the ratio of the circumferential length of the final blown film to the circumferential length of the die slit of the die. Further, the film obtained as described above is heated to a temperature not higher than the crystallization temperature of the resin and is drawn 1.2 to 5 times in the machine direction of the film by utilizing the speed difference between the nip rolls, or the film It may be biaxially stretched 1.2 to 5 times in both longitudinal and transverse directions.

The total thickness of the stretch wrapping film is 8 to 30 μm, of which the base layer (A) is 1 to 15 μm and the surface layer (B) is preferably 3 to 10 μm. . The stretch packaging film of the present invention,
It is suitable not only as a stretch film for food packaging, but also as a pallet stretch film in which a film is wrapped around a package loaded on a pallet for packaging.

[0024]

EXAMPLES The contents and effects of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the following examples, the physical properties and packaging suitability of the obtained stretch packaging film were determined by the following methods, and Table 1 shows the evaluation and packaging suitability of the stretch packaging film.

<Haze> JIS Z-6714 <Glossiness> JIS Z-8471 <Tear strength> JIS Z-1702 <Deformation recovery strain> Using the device shown in FIG.
After pressing a mmφ piston rod into the center of the film at a speed of 500 mm / min, the piston rod was retracted and the amount of strain at which the scratches caused by the piston rod disappeared after 3 minutes was taken as the deformation recovery strain amount.

<Expandability> The croquettes are placed on trays made of expanded polystyrene, expanded polystyrene, and impact-resistant polystyrene, respectively, and packed by a stretch automatic packing machine, A-18X [trade name] manufactured by Fujikikai Co., Ltd. The result of visually observing the stretched state of the film at that time was evaluated as follows. When the film stretched almost uniformly: ○, when the film stretched unevenly: ×.

<Rate of Occurrence of Breakage> Packaging was performed in the same manner as in the extensibility evaluation, and the presence or absence of breakage of the film at that time was visually observed. <Situation of Wrinkles> Packaging was performed in the same manner as in the extensibility evaluation, and the presence or absence of wrinkles in the film at that time was visually observed.

Example 1 As a resin for the base material layer (A), a low density polyethylene resin [density 0.924 g / cm ³ , MFR 0.7 g / 10
Min; Mitsubishi Chemical Co., Ltd., trade name "Mitsubishi Polyethylene-LD"
LF240 "] is kneaded at 190 ° C. using an extruder having a diameter of 65 mm and L / D25, and on the other hand, a linear ethylene-α-olefin copolymer resin [density 0.895 g / cm ³ , Q value 2.26, MFR
1.6 g / 10 minutes, α-olefin: octene-1 (content: 14.5% by weight); Dow Chemical Japan Co., Ltd.
Product name "AFFINITY PF1140"] 9
A resin composition consisting of 8.5% by weight and 1.5% by weight of diglycerin oleate (Riken Vitamin Co., Ltd., trade name "Rikemar O71D") was used.
The extruder was used to knead the mixture at 190 ° C., and the two were supplied to a single annular three-layer die to form a surface layer (a) on both sides of the resin layer having a thickness of 6.5 μm made of the base material layer (A). Insulation molding was performed at a die temperature of 190 ° C. and a blow ratio of 10 times so that the resin layers of B) each having a thickness of 3.25 μm were laminated, and the total thickness was 13 μm (3.25 μm / 6.5 μm).
m / 3.25 μm) was produced.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Example 2 In Example 1, the resin for the base material layer (A) was a linear ethylene-α-olefin copolymer resin [density 0.917 g
/ Cm ³ , MFR 1.8 g / 10 min, α-olefin:
Butene-1; manufactured by Mitsubishi Chemical Co., Ltd., trade name "Mitsubishi Polyethylene-LL X729"] was used to produce a stretch-wrapping film having a three-layer structure in the same manner as in the same example.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Example 3 In Example 1, the resin for the base material layer (A) was a linear ethylene-α-olefin copolymer resin [density 0.910 g
/ Cm ³ , MFR 3.6 g / 10 min, α-olefin:
4-methylpentene-1; manufactured by Mitsui Petrochemical Co., Ltd., trade name "Ultox X 1030F"] 98.5% by weight and replaced with the resin composition comprising 1.5% by weight of diglycerin oleate used in Example 1 In addition, a three-layer stretch wrapping film was manufactured in the same manner as in the above example.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Example 4 The linear ethylene-α-olefin copolymer resin 7 used in Example 3 was used as the resin for the base material layer (A) in Example 1.
0% by weight and propylene-ethylene random copolymer resin [density 0.890 g / cm ³ , MFR 17 g / 10
Min; Mitsubishi Chemical Co., Ltd., trade name "Mitsubishi Polypro MR0
2R "] except that the resin composition is 30% by weight,
A stretch packaging film having a three-layer structure was produced in the same manner as in the same example.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Example 5 In Example 1, the resin for the base material layer (A) was a propylene-ethylene-butene-1 random copolymer resin [density 0.890 g / cm ³ , MFR 5 g / 10 min; Mitsubishi Chemical Corporation, Product name "Mitsubishi Polypro SPX4400G"]
A stretch packaging film having a three-layer structure was produced in the same manner as in the above example except for the above.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Example 6 In Example 1, the resin for the base material layer (A) was replaced with the linear ethylene-α-olefin copolymer resin used in Example 2, and the linear resin was used as the resin for the surface layer (B). Ethylene-α-olefin copolymer resin [Density 0.895 g / cm
³ , Q value 2.0, MFR 3.5g / 10 minutes, α-olefin: hexene-1; manufactured by Mitsubishi Chemical Corporation, trade name "KE
RNEL 54FT "] 98.5 wt% and Example 1
A stretch packaging film having a three-layer structure was produced in the same manner as in the same example except that the resin composition consisting of 1.5% by weight of diglycerin oleate used in Example 1 was used.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Comparative Example 1 In Example 1, the resin for the base material layer (A) was a linear ethylene-α-olefin copolymer resin [density 0.920 g
/ Cm ³ , Q value 3.3, MFR 2.1 g / 10 minutes, α-olefin: butene-1; manufactured by Mitsubishi Chemical Corporation, trade name “Mitsubishi Polyethylene-LL UF240”], and
The surface layer (B) resin is an ethylene-vinyl acetate copolymer resin [vinyl acetate content 15% by weight, density 0.938 g
/ Cm ³ , MFR 2.0g / 10 minutes; Mitsubishi Chemical Corporation
Product name, "Mitsubishi Polyechie EVALV440"] 9
A three-layer stretch wrapping film was produced in the same manner as in Example 1 except that the resin composition was changed to 8.5 wt% and diglycerin oleate 1.5 wt% used in Example 1.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Comparative Example 2 In Example 1, the resin for the base material layer (A) was a propylene-ethylene random copolymer resin [density 0.90 g / c
m ³ , MFR 7.0 g / 10 min; manufactured by Mitsubishi Chemical Corporation, trade name “Mitsubishi Polypro FX4”], and the resin for the surface layer (B) was replaced with the resin composition used in Comparative Example 1. Outside, a three-layer structure stretch-wrapping film was produced in the same manner as in the same example.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Comparative Example 3 In Example 1, the resin for the base material layer (A) was replaced with the linear ethylene-α-olefin copolymer resin used in Example 2, and the resin for the surface layer (B) was linear. Ethylene-α
-Olefin copolymer resin [density 0.890 g / c
m ³ , Q value 5.29, MFR 0.8 g / 10 min, α-olefin: butene-1; Sumitomo Chemical Co., Ltd., trade name “Excellen VL EUL 130”] 98.5 wt% and used in Example 1. A stretch packaging film having a three-layer structure was produced in the same manner as in the same example except that the resin composition was changed to 1.5% by weight of diglycerin oleate.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to.

[0038]

[Table 1]

[0039]

The film for stretch packaging of the present invention comprises:
It has excellent appearance and excellent packaging suitability such as tear strength and deformation recovery, and it has a particularly advantageous effect as a stretch packaging film, and its industrial utility value is extremely large.

[Brief description of drawings]

FIG. 1 is a plan view of an apparatus for measuring a deformation recovery strain amount of a film.

[Explanation of symbols]

 1 Piston rod 2 Film (sample) 3 Load cell

Claims (2)

[Claims] 1. A group comprising at least one resin selected from low-density polyethylene resin, crystalline polypropylene resin, and linear ethylene-α-olefin copolymer resin having a density of 0.910 g / cm ³ or more. On at least one side of the material layer (A), a surface layer comprising a linear ethylene-α-olefin copolymer resin having a density of 0.908 g / cm ³ or less and a Q value (Mw / Mn) of 4.0 or less ( A film for stretch packaging, characterized in that B) is laminated. 2. The linear ethylene-α-olefin copolymer resin constituting the surface layer (B) has a carbon number of α-olefin of 4 to 8, and the content of the α-olefin in the resin is 10 to 30% by weight. %, The stretch packaging film according to claim 1.