JPH09109330A - Stretched packaging film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stretched packaging film having excellent packaging suitability such as excellent external appearance, tear strength, and deformation recovery. SOLUTION: A front surface layer made of a straight-chain ethylene-α-olefin copolymer resin having a density of 0.908g/cm<3> or less and Q value (Mw/Mn) of 4.0 or less is laminated on at least one side surface of a base material layer containing block copolymer of polymer block of monovinyl substituted aromiatic hydrocarbon and conjugated diene elastomer copolymer block or its hydrogen- added derivative as a main ingredient.

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, meat, and side dishes are placed directly or on a plastic tray, and these are stretch-wrapped with a film, which is a film for so-called pre-packaging, which is environmentally friendly. Instead of a conventional polyvinyl chloride film, a linear low-density polyethylene film (Japanese Patent Laid-Open No. 64-14018) or a linear low-density polyethylene is used as an intermediate layer, and an ethylene-vinyl acetate copolymer film is formed on the front and back surfaces. Packaging films based on ethylene resins, such as laminated three-layer laminated films (Japanese Patent Publication No. 2-18953 and Japanese Patent Laid-Open No. 3-258542), have been put to practical use.

[0003] These ethylene resin packaging films are:
There has been a problem in deformation recovery properties such as recovery from deformation on the film surface during transportation of the package and display at the store without leaving wrinkles. For the purpose of remedying these drawbacks, Japanese Patent Publication No. 5-59822 discloses a general formula A- (B
-A) a hydrogenated derivative of a block copolymer represented by n (A: a polymer block of a monovinyl-substituted aromatic hydrocarbon, B: an elastomeric polymer block of a conjugated diene, n: an integer of 1 to 5) There has been proposed a stretch packaging film in which a layer mainly composed of an ethylene-vinyl acetate copolymer resin having a vinyl acetate content of 5 to 25% by weight is laminated on both sides of a layer mainly composed of a layer.

However, the stretch wrapping film is
When used as a food stretch packaging film, the film tear strength is weak, so if the packaged food has sharp corners or if the tray on which the packaged food is placed has a sharp corner, it will break from this contact area. There was a thing. In addition, deformation recovery properties are still insufficient, and there are problems such as wrinkles during transportation of packages and display at stores, and the like, which has not always been able to sufficiently respond to market requirements.

[0005] Furthermore, there is a problem that the appearance of the packaged food at the time of display at the store is not good due to insufficient appearance.

[0006]

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.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention comprises a polymer block of a monovinyl-substituted aromatic hydrocarbon and an elastomeric polymer block of a conjugated diene. A density of 0.908 g / cm ³ or less and a Q value (Mw / Mn) of 4.0 or less on at least one side of the base layer (A) containing a block copolymer or a hydrogenated derivative as a main component. The present invention relates to a stretch packaging film comprising a surface layer (B) made of a linear ethylene-α-olefin copolymer resin laminated.

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 a block copolymer of a polymer block of a monovinyl-substituted aromatic hydrocarbon and an elastomeric polymer block of a conjugated diene, or a resin whose main component is a hydrogenated derivative thereof. Examples of the monomers constituting the polymer block of the monovinyl-substituted aromatic hydrocarbon include styrene, α-methylstyrene, vinyltoluene, other lower alkylenestyrenes, and vinylnaphthalene. Of these, styrene is preferred.

Examples of the monomer forming the elastomeric polymer block of the conjugated diene include butadiene, isoprene, vinyl isoprene, etc. These may be used alone or in combination of two or more. it can.
Specific examples of the block copolymer of a polymer block of a monovinyl-substituted aromatic hydrocarbon and an elastomeric polymer block of a conjugated diene or a hydrogenated derivative thereof include a styrene-butadiene block copolymer resin and a styrene-butadiene block copolymer resin. Polymer elastomer, hydrogenated product of styrene-butadiene block copolymer, styrene-isoprene block copolymer elastomer, hydrogenated product of styrene-isoprene block copolymer, styrene-vinylated polyisoprene block copolymer elastomer or hydrogenation thereof There are things such as these, by themselves,
Alternatively, two or more kinds can be used as a mixture.

The styrene-butadiene block copolymer resin is a thermoplastic resin having a styrene content of 60 to 95% by weight, and has a MFR (JIS K6871 200 ° C.,
A styrene-butadiene block copolymer elastomer having a styrene content of 10 to 45% by weight is used as the styrene-butadiene block copolymer elastomer, and MFR (ASTM D1238 190) is used.
A material having a temperature of 2.16 kg and a temperature of 1 to 6 g / 10 minutes is used.

Such a styrene-butadiene block copolymer resin is commercially available from Asahi Kasei Kogyo Co., Ltd. under the name "Asaflex".
In addition, the styrene-butadiene block copolymer elastomer is sold by the same company under the product name of "Tufprene". The hydrogenated product of the styrene-butadiene block copolymer has a styrene content of 10 to 45% by weight, and at least 50%, preferably 80% or more of the olefinic double bonds are hydrogenated.
R (ASTM D1238 200 ℃, 5kg load) is 1
The thing of -10g / 10min is used.

The hydrogenated product of the styrene-butadiene block copolymer is sold by Shell Japan Co., Ltd. under the trade name of "Clayton G" and by Asahi Kasei Kogyo Co., Ltd. under the trade name of "Tuftec". The hydrogenated product of the styrene-isoprene block copolymer has a styrene content of 10 to 65% by weight and at least 80% or more of the olefinic double bond is hydrogenated, and M
The FR (ASTM D1238 230 ° C., 2.16 Kg load) having a FR of 0.05 to 10 g / 10 min is used.

The hydrogenated product of the styrene-isoprene block copolymer is sold by Kuraray Co., Ltd. under the trade name of "Septon". Further, as the styrene-vinylated polyisoprene block copolymer elastomer,
The styrene content is 10 to 40% by weight, and the olefin type double bond is unhydrogenated or 80% or more is hydrogenated, and MFR (ASTM D1238 170
C., 10 kg load) 0.4 to 10 g / 10 min.

Such a styrene-vinylated polyisoprene block copolymer elastomer is sold by Kuraray Co., Ltd. under the trade name of "High Blur". The base material layer (A) is composed of a block copolymer of a polymer block of a monovinyl-substituted aromatic hydrocarbon and an elastomeric polymer block of a conjugated diene, or a resin whose main component is a hydrogenated derivative thereof. Here, the main component means a base material layer (A)
It is to be contained in an amount of more than 50% by weight of the resin constituting the.

The base layer (A) may be blended with the following olefinic resins within a range that does not deteriorate the appearance of the film. For example, an ethylene-vinyl acetate copolymer (vinyl acetate content is 5 to 40% by weight) and a density of 0.
915 to 0.930 g / cm ³ low density polyethylene,
An ethylene-α-olefin copolymer having a density of 0.910 to 0.935 g / cm ³ (α-olefin has 4 to 8 carbon atoms), polypropylene, a propylene-ethylene copolymer, a propylene-ethylene-α-olefin copolymer,
Ethylene-acrylic acid copolymer (acrylic acid content is 5
-20% by weight), a metal salt of a copolymer of an ethylene-methyl methacrylate copolymer, a copolymer of an α-olefin such as ethylene and propylene with a monomer selected from acrylic acid, methacrylic acid, maleic acid, etc. Na, K, Li, Mg
Etc.), maleic anhydride grafted ethylene-vinyl acetate copolymer, maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, hydrogenated petroleum resin and the like. One or more of these may be added in an amount of 1 to 45% by weight, preferably 1 to 30% by weight, for the purpose of improving the packaging suitability of the film.

Further, the above olefin resin may be added to the surface layer (B) in an amount of 1 to 45% by weight as in the case of the base material layer (A). Further, the base layer (A) may be blended with the following additives in order to impart antifogging property, moderate slip property, self-adhesive property and antistatic property. For example, an aliphatic alcohol having 1 to 12 carbon atoms, preferably 1 to 6 and 10 to 22 carbon atoms, preferably 12 to 18 carbon atoms.
Aliphatic alcohol fatty acid ester that is a compound with a fatty acid of, 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 paraffinic oils 0.1 to at least one compound selected from
It is preferable to add 30% by weight, preferably 1 to 20% by weight.

These additives may be added to the surface layer (B) in an amount of 0.1 to 30% by weight. Base material layer (A)
When both the olefin resin and the additive are blended, the total amount is less than 50% by weight, preferably 45% by weight or less. The surface layer (B) has a density of 0.908 g
/ Cm ³ or less and a Q value (Mw / Mn) of 4.0 or less, a linear ethylene-α-olefin copolymer resin.

Preferably, the density is 0.865 to 0.90.
5 g / cm ³ and a Q value (Mw / Mn) of 2.0 to
3.0 and MFR is 0.5-5g / 10min. When the density exceeds 0.908 g / cm ³ , the appearance of the film is deteriorated, and the density is 0.908 g / cm ³
Even if the Q value is below 4.0, the film appearance is not always good, and the packaging suitability such as tear strength is 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 is 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.

The stretch wrapping film of the present invention comprises a block copolymer of a polymer block of a monovinyl-substituted aromatic hydrocarbon and an elastomeric polymer block of a conjugated diene, which constitutes the base material layer (A), or a hydrogen thereof. The resin containing the added derivative as a main component and the linear ethylene-α-olefin copolymer resin constituting the surface layer (B) are coextruded by inflation molding or T-die molding using a plurality of extruders, or extruded. It is laminated and formed by a known method such as a laminating method.

In 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 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 overall thickness of this stretch wrapping film is 8 to 30 μm, of which the base layer (A) has a thickness of 1 to 30 μm.
It is preferably 15 μm. The stretch packaging film of the present invention is suitable as a stretch film for food packaging.

[0028]

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.

<Degree of haze> JIS Z-6714 <Glossiness> JIS Z-8471 <Tear strength> JIS Z-1702 <Deformation recovery strain amount> 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 packaging machine, made by Ishida Co., Ltd., Wmini Mark II [trade name]. The results of observing the stretched state of the film at that time with the naked eye were 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 evaluation of extensibility, 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 hydrogenated product of a styrene-vinylated polyisoprene block copolymer elastomer [styrene content 20% by weight, density 0.940 g / cm 3]
³ , MFR 0.6 g / 10 min; manufactured by Kuraray Co., Ltd., trade name "HIBLER HVS-3"], caliber 65 mm, L /
The resin was kneaded at 190 ° C. using an extruder of D25, and as a resin for the surface layer (B), a linear ethylene-α-olefin copolymer resin [density 0.895 g / cm ³ , Q value 2.
26, MFR 1.6 g / 10 min, α-olefin: Octene-1 (content: 14.5 wt%); Dow Chemical Japan KK, trade name “AFFINITY PF11
40 "] 98.5% by weight and diglycerin oleate [manufactured by Riken Vitamin Co., Ltd., trade name" Rikemar O71 "
D "] 1.5% by weight of a resin composition having a diameter of 50 m
m, L / D25 extruder was used to knead at 190 ° C., and both were supplied to one annular three-layer die to form the base material layer (A).
A resin layer having a thickness of 4 μm and made of the surface layer (B) is laminated on both surfaces of the resin layer having a thickness of 5 μm.
Inflation molding was performed at a die temperature of 190 ° C and a blow ratio of 10 times, and the total thickness was 13 μm (4 μm / 5 μm / 4 μ).
The film for stretch packaging of m) 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 the hydrogenated product of 55% by weight of the styrene-vinylated polyisoprene block copolymer elastomer used in Example 1 and a propylene-ethylene random copolymer resin [ Density 0.890g
/ Cm ³ , MFR 17g / 10 minutes, manufactured by Mitsubishi Chemical Corporation,
Same as the same example, except that the resin composition was 25% by weight of the product name "Mitsubishi Polypro MR02R" and 20% by weight of paraffin oil [made by Idemitsu Kosan Co., Ltd., product name "Diana Process Oil PW380"]. A three-layer stretch wrapping film was produced by various methods.

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 hydrogenated product of a styrene-butadiene block copolymer [styrene content 13% by weight, density 0.920 g / cm ³ , MFR8.
g / 10 min; manufactured by Shell Japan Co., Ltd., trade name "Clayton G1657"], except that a three-layer stretch packaging film was manufactured 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 4 In Example 1, the resin for the base material layer (A) was a styrene-butadiene copolymer resin [styrene content 70% by weight,
Density 1.01 g / cm ³ , MFR 5 g / 10 minutes; Asahi Kasei Kogyo KK, trade name "Asaflex 810F"]
In the same manner as in the same example, except for replacing
m (5.5 μm / 2 μm / 5.5), a three-layer structure stretch-wrapping film was produced.

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 the styrene-butadiene copolymer resin 60% by weight and the styrene-butadiene copolymer elastomer [styrene content 40% by weight, used in Example 4; Density 0.950 g / cm ³ , M
FR 5 g / 10 min; Asahi Kasei Kogyo Co., Ltd., trade name “Toughprene 125”] in place of the resin composition consisting of 40% by weight, linear ethylene-α as the resin for the surface layer (B)
-Olefin copolymer resin [density 0.895 g / c
m ³ , Q value 2.0, MFR 3.5 g / 10 min, α-olefin: hexene-1 (content 18% by weight); manufactured by Mitsubishi Chemical Co., Ltd., trade name “KERNEL 54FT”] 98.
5% by weight and diglycerin oleate used in the same example 1.
A total thickness of 13 μm (5.5 μm / 2 μm /) was obtained by the same method as in the example except that the resin composition was replaced by 5% by weight.
A stretch packaging film having a three-layer structure of 5.5) was produced.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Comparative Example 1 In Example 3, the resin for the surface layer (B) was an ethylene-vinyl acetate copolymer resin [vinyl acetate content 15% by weight, density 0.938 g / cm ³ , MFR 2.0 g / 10.
Min; Mitsubishi Chemical Co., Ltd., trade name "Mitsubishi Poly EVA
LV440 "]] and a diglycerin oleate used in Example 1 in place of the resin composition consisting of 1.5% by weight, except that the same method as in the same example except that a three-layer stretch packaging film was used. Manufactured.

The physical properties and packaging suitability of this film are shown in Table 1.
It was shown to. Comparative Example 2 In Example 3, the resin for the surface layer (B) was a linear ethylene-α-olefin copolymer resin [density 0.890 g /
cm ³ , Q value 5.29, MFR 0.8 g / 10 minutes, α-olefin: butene-1; Sumitomo Chemical Co., Ltd., trade name “Excellen VL EUL 130”] 98.5% by weight
Then, a stretch packaging film having a three-layer structure was produced in the same manner as in Example 1 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.

[0040]

[Table 1]

[0041]

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 the 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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mie Toyota 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Chemical Co., Ltd. Yokkaichi Research Institute

Claims (2)

[Claims] 1. A polymer of a monovinyl-substituted aromatic hydrocarbon
Elastomeric polymer block of block and conjugated diene
Mainly composed of block copolymer with
The density is 0.9 on at least one side of the base material layer (A).
08g / cm ^ThreeBelow, and Q value (Mw / Mn) is 4.0
Is the following linear ethylene-α-olefin copolymer resin
A surface layer (B) of
Film for stretch packaging. 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.