JP2002067235A - Polyolefin stretch film and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin stretch film that reduces buckling in manufacturing the film by inflation and also has sufficient self-adhesive properties on the occasion of overlap packaging. SOLUTION: In a multilayer film formed at least of three layers, surface layers are constituted of a resin composition of an ethylene-vinyl acetate copolymer, and as to the resin used therefor, the weight composition of a vinyl acetate of either one of the surface layers is less by 3-10 wt.% than that of the other layer. In the film thus obtained, the adhesion between films in manufacturing the film is low relatively and the buckling in winding the film is reduced, while the film has a sufficient adhesion in overlap packaging.

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 food packaging in which a layer comprising a polyolefin composition is laminated, and a method for producing the same.

[0002]

2. Description of the Related Art A stretch film for food packaging is a so-called business type in which foods such as fruits and vegetables, fresh fish, meat, prepared dishes and the like are placed directly or on a lightweight plastic tray such as polystyrene paper (PSP) to overlap the stretch films. As the stretch film, a polyvinyl chloride (hereinafter referred to as "PVC") type stretch film has been mainly used. This is because the film has good transparency, it is easy for workers to stretch and it is hard to get tired, the finish is clean without wrinkles, etc. In addition to deformation suitability, it recovers without deforming the film surface without leaving wrinkles In addition, it has the superiority of quality recognized by both sellers and consumers that the product value does not decrease, such as the peeling of the bottom of the stretch film hardly occurs during transportation and display. is there.

However, in recent years, problems such as hydrogen chloride gas generated during incineration of a PVC stretch film and elution of a contained plasticizer have been regarded as problems. For this reason, olefin-based stretch films have been studied and used as alternatives to PVC.

[0004] For example, JP-A-60-171148 and JP-A-3-258542 disclose a resin composition in which the surface layer is composed of an ethylene-vinyl acetate copolymer (hereinafter referred to as EVA) and the intermediate layer is composed of ethylene-α-olefin and polypropylene. A polyolefin-based stretch film composed of a product is disclosed.

[0005] These polyolefin-based stretch films are generally formed by inflation and then produced. If the peel strength between individual films is high, the film is formed and wound. It is easy to wrinkle in, causing a problem in commercial properties as a stretch film,
Yield decreases. If the peel strength is weak,
When this film is used for overlapping packaging, the self-adhesive strength is not sufficient, and there is a problem that the film gradually peels off after overlapping.

On the other hand, additives are generally added to olefin-based stretch films in order to impart anti-fogging properties, moderate slip properties, and self-adhesiveness. After that, the concentration distribution in the film changes over time. This also changes the peel strength between the films, making it more difficult to adjust the peel strength between the films.

[0007]

DISCLOSURE OF THE INVENTION The present invention relates to a transparent film having a sufficient self-adhesive property when curling wrinkles during film formation by an inflation method and when performing overlap packaging using this film. Another object of the present invention is to provide a polyolefin-based stretch film having excellent mechanical wrapping properties.

[0008]

In order to solve the above-mentioned problems, the cause of the occurrence of wrinkles during film formation by the inflation method was examined, and the peel strength between the outer surface and the inner surface of the film during film formation was examined. By optimizing each,
The generation of wrinkles during film formation is suppressed, and a polyolefin-based stretch film excellent in the above-mentioned various properties can be obtained, thus completing the present invention.

That is, the present invention relates to a multilayer film comprising at least three layers, wherein the surface layer is made of EVA, and the content of vinyl acetate in one of the surface layers is smaller than the content of the other surface layer. It is a polyolefin-based stretch film characterized by a small amount.

More preferably, the intermediate layer is a polyolefin-based stretch film comprising 60 to 80% by weight of a crystalline polypropylene resin, 20 to 30% by weight of a propylene-butene copolymer, and 10 to 30% by weight of an ethylene-propylene copolymer. is there.

In producing the above-mentioned polyolefin-based stretch film, when the film is formed by an inflation method, the peel strength between the outer surfaces of the film is as follows.
A method for producing a polyolefin-based stretch film, wherein the peel strength between inner surfaces is 1.2 to 2 times.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The polyolefin-based stretch film of the present invention has at least three layers. The surface layer of the film of the present invention is EVA
And the melt flow rate at 190 ° C. is 0.3
g / 10 min to 5 g / 10 min, vinyl acetate content of 5-2
5% by weight.

It is preferable that both surface layers of the present invention be a resin having an adhesive property, since the self-adhesive property at the time of overlapping packaging is good.

In order to produce the polyolefin-based stretch film of the present invention, a polyolefin-based resin composition is supplied to a plurality of extruders, and the resin melt-kneaded in the extruders is formed into an annular shape by means of one or more annular dies. The film is extruded, air bubbles are blown into the film, and the expanded bubble is air-cooled, the annular film is folded into a crushed state, and both ends are trimmed (cut and removed). Immediately after passing through the pinch roll, the two folded films are peeled off and wound separately.

In order to suppress the occurrence of wrinkles in the film, it is effective to reduce the peel strength between the inner surfaces of the annular film when the annular film is crushed. That is, the two films formed by folding are easily peeled off,
Since it is wound up smoothly and separately, wrinkles hardly occur. The peel strength between the films is related to the content of vinyl acetate in the EVA of the inner surface layer of the annular film. That is, when the content of vinyl acetate is reduced, the peel strength between the inner surfaces of the folded film tends to decrease, which has an effect of preventing wrinkles from occurring during the production of the film.

The content of vinyl acetate in EVA of the inner surface layer is preferably 3 to 10% by weight lower than that of the outer surface layer. If the content exceeds 10% by weight, the adhesive strength between the films is too much reduced, so that when the film is overlapped and packaged, the overlapped portion is easily peeled off, resulting in poor packaging suitability. When the content is 3% by weight or less, no effect is observed.

On the other hand, EV of the outer surface layer of the film of the present invention
The content of vinyl acetate in A is higher than that in the inner surface layer. When the film is overlap-wrapped using the film, the necessary adhesiveness is ensured by the E of the outer surface layer of the film.
This is achieved by increasing the content of vinyl acetate in VA. In order to simultaneously suppress the wrinkles generated during the film formation and secure the adhesiveness during the overlap packaging, compared with the outer surface layer as described above, the content of vinyl acetate in the inner surface layer is as follows. It is preferable to reduce the amount by 3 to 10% by weight.

An antifogging agent and additives can be added to the surface layer of the present invention. As the antifogging agent of the present invention, for example, glycerin fatty acid (C8-22) ester, sorbitan fatty acid (C8-22) ester, propylene glycol fatty acid (C8-22) as a surfactant conforming to the PL standard (list of food additives) Esters, sucrose fatty acids (C8-2
2) esters, citric acid mono (di or tri) stearic acid esters, pentaerythritol fatty acids (C8-2
2) Ester, polyglycerin fatty acid (C8-22) ester, polyoxyethylene (20) glycerin fatty acid (C8-22) ester, polyethylene glycol fatty acid (C8-22) ester, polypropylene glycol fatty acid (C8-22) ester, poly Oxyethylene (9.5) dodecyl ether, polyoxyethylene (4
-14.30-50) alkyl (C4, 9, 12) phenyl ether, condensation product of N, N-bis (2) -hydroxyethyl fatty acid (C12-18) with diethanolamine, polyoxypropylene polyoxyethylene block Polymer, polyethylene glycol (molecular weight 20
0-9500), polypropylene glycol and the like.

The intermediate layer of the present invention is composed of a polyolefin-based resin composition and is not particularly limited, but preferably comprises 60 to 80% by weight of a crystalline polypropylene resin and 20 to 30% of a propylene-butene copolymer. It is a resin composition consisting of 10% to 30% by weight of an ethylene-propylene copolymer.

The crystalline polypropylene resin used in the intermediate layer resin composition is a polymer obtained by polymerizing a propylene monomer as a main component.
Those copolymerized with an α-olefin such as butene and 4-methylpentene-1 may be used. Each copolymer may be either a random copolymer or a block copolymer. Above all 23
It is preferable that the melt flow rate at 0 ° C. and a load of 2.16 kg is 0.1 g / 10 min to 20 g / 10 min,
More preferably, it is 0.4 g / 10 min to 10 g / 10 min. If it exceeds 20 g / 10 minutes, the melt tension becomes low during the film formation by the inflation method, resulting in poor film-forming properties. The crystalline propylene-based resin contains 60 to 80 in the intermediate layer.
It is contained in weight%. When the content is less than 60% by weight, the stretch film is soft and has no waist, so that the cutting property in an automatic packaging machine is poor. The cutting property here means that when the stretch film is fed out by the conveyor belt in the automatic packaging machine, the cut blades installed between the conveyor belts protrude, so that the stretch film is perforated, and then the conveyor belt stretches the stretch film. Means torn from the perforation by being pulled.
If the stretch film is soft and does not have a waist, it will be difficult to perforate because the blade will stretch when it protrudes. If it is at least 80% by weight, the transparency will be reduced.

The propylene-butene copolymer used in the intermediate layer of the present invention has a butene-1 content of 30 to 50% by weight.
And those having a number average molecular weight of 1,500 to 10,000 can be used. The propylene-butene copolymer is contained in the intermediate layer at 20 to 30% by weight. As this action, transparency and flexibility can be obtained by finely dispersing the crystals of the crystalline polypropylene resin. If the stretch film is not flexible with an automatic packaging machine, the tray will be deformed when wrapped. If the propylene-butene copolymer is at most 20% by weight, it will be difficult to obtain transparency and the flexibility will be insufficient. If the content is 30% by weight or more, the stretch film is too soft and loses its waist.

The ethylene-propylene copolymer used in the intermediate layer of the present invention may have a propylene content of 20 to 30% by weight. The ethylene-propylene copolymer is contained in the intermediate layer at 10 to 30% by weight. This action can provide flexibility, recoverability and piercing strength. If there is no recovery in the automatic packaging machine, wrinkles will occur when packaging, and if there is no piercing strength, the stretch film will break when folded. When the ethylene-propylene copolymer is 10% by weight or less, these properties are hardly obtained, and when the ethylene-propylene copolymer is 30% by weight or more, the stretch film is too soft and loses its stiffness.

If necessary, a stabilizer, an antistatic agent, a processability improver, and a tackifier may be added to the stretch film of the present invention. For example, 2,6-di-t-butyl-p-cresol (BHT), tetrakis [methylene-3- (3,5-di-tbutyl-4-hydroxyphenyl) propionate] methane, n-octadecyl-3-
A phenolic stabilizer represented by (4'-hydroxy-3,5'-di-t-butylphenyl) propionate;
Bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite and tris (2,4-di-t-butyl)
(Butylphenyl) phosphite; phosphite-based stabilizers; antistatic agents such as glycerin esters, sorbitan acid esters, and polyethylene glycol esters of fatty acids having 8 to 22 carbon atoms; and fatty acid metal salts such as calcium stearate. Processability improvers can be added.

On the other hand, the stretch film of the present invention can return the scrap to the intermediate layer up to 30 parts by weight.
At this time, both surface layer components are included in the intermediate layer. However, up to the above-mentioned amount, there is almost no decrease in the transparency of the film and no generation of gel or the like.

Further, the thickness of the stretch film of the present invention is in the range used as a normal stretch film,
That is, it is about 5 to 30 μm, preferably 8 to 20 μm
Range.

[0026]

The present invention will be described in more detail with reference to the following examples. The properties and properties of the stretch film were measured and evaluated by the following methods.

1) Wrinkling Wrinkling when the film was formed and wound into a roll was visually observed. 2) Transparency (Haze%) Measured according to ASTM-D1003. 3) Peel strength The outer and inner surfaces of a film having a width of 100 mm and a length of 60 mm are overlapped over 10 mm, and pressed at 23 ° C. and a pressure of 2.5 kPa. So that the distance between the chucks is 50 mm,
Tensile stress was measured at a crosshead speed of 50 mm / min to determine the peel strength. 4) Suitability for automatic wrapping machine Using a stretch film having a width of 350 mm, a PSP tray (length: 196 mm, width: 153 mm, height: 2) by an automatic wrapping machine (AW-2600JrPE manufactured by Teraoka Seiko Co., Ltd.)
5 mm) packaging test. The self-adhesiveness, cuttability, wrinkles, tear, and tray deformation shown in Table 2 were evaluated.

Example 1 EVA (vinyl acetate content 15% by weight, MFR = 1.5 g / 10 min (1
90 ° C., 2.16 Kg)) A composition obtained by adding 3 parts by weight of diglycerin oleate as an anti-fog agent to 100 parts by weight of EVA (vinyl acetate content 10% by weight, MF
R = 1.5 g / 10 min (190 ° C., 2.16 Kg) 1
A composition obtained by adding 3 parts by weight of diglycerin oleate as an antifogging agent to 00 parts by weight was used. The intermediate layer is made of a propylene-ethylene random copolymer (ethylene-containing 4 mol%, MFR = 0.5 g / 10 min (230 ° C., 2.16 K
g)) A propylene / butene-1 copolymer (trade name REXTAC®) having 62.5% by weight, a weight ratio of propylene / butene-1 of 65/35 and a number average molecular weight Mn of 6500.
T2780) 22.5% by weight, ethylene-propylene random copolymer (propylene content 26 mol%, MFR
= 3.2 g / 10 min (230 ° C, 2.16 Kg) 15
A stretch film having a total thickness of 12 μm (3 μm / 6 μm / 3 μm) was obtained by co-extrusion inflation molding using a composition obtained by mixing 2% by weight of diglycerin oleate as an anti-fogging agent with 2% by weight.

The molding conditions are as follows: extrusion temperature 200 ° C. die slip gap 1.0 mm take-off speed 30 m / min blow-up ratio 7.0 times

Example 2 EVA (vinyl acetate content 15% by weight, MFR = 1.5 g / 10 min (1
90 ° C., 2.16 Kg)) A composition obtained by adding 3 parts by weight of diglycerin oleate as an anti-fogging agent to 100 parts by weight, and EVA (vinyl acetate content 8% by weight, M
FR = 1.5 g / 10 min (190 ° C., 2.16 Kg)
100 parts by weight of diglycerin oleate as antifogging agent
A stretch film was formed under the same conditions as in Example 1 except that the composition added in parts by weight was used.

Example 3 The resin composition of the intermediate layer was 85% by weight of the same propylene-ethylene random copolymer used in Example 1, and the same propylene / butene as in Example 1. A stretch film was formed under the same conditions as in Example 1 except that the -1 copolymer was changed to 15% by weight.

Comparative Example 1 The same EVA (vinyl acetate content: 15% by weight, MFR = 1.5 g / 10 min (190 ° C., 2.16K) was used for both the outer surface layer and the inner surface layer.
g)), except that the stretch film was formed under the same conditions as in Example 1.

Comparative Example 2 The resin composition of the intermediate layer was 85% by weight of the polypropylene used in Example 1 and 15% by weight of the propylene / butene-1 copolymer. The same EVA (vinyl acetate content 15% by weight, MFR = 1.5 g / 10 min (190 ° C.,
A stretch film was formed under the same conditions as in Example 1 except that 2.16 kg)) was used.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

According to the polyolefin stretch film of the present invention, the peel strength of the inner surface layer is made lower than that of the outer surface layer, whereby curling wrinkles at the time of film formation are suppressed. Has a sufficient self-adhesiveness, and provides a stretch film excellent in transparency, moderate flexibility, recoverability and piercing strength.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // (C08L 23/10 (C08L 23/10 23:14 23:14 23:16) 23:16) B29K 23:00 B29K 23:00 B29L 9:00 B29L 9:00 F term (reference) 3E086 AB01 AD17 BA04 BA15 BB66 CA01 DA08 4F071 AA15X AA20 AA20X AA21X AH04 BB09 BC01 4F100 AH02H AK07C AK09C AK64 BA10A23ABABAB23A23A23A23A23A30 JK06 JL13 JN01 YY00C 4F210 AA03 AA04E AA10 AA11E AA12E AB09 AH54 QA01 QC07 QG15 QG18 QK23 4J002 BB121 BB142 BB153 GG02

Claims (4)

[Claims] 1. A multilayer film comprising at least three layers, wherein a surface layer comprises an ethylene-vinyl acetate copolymer,
A polyolefin-based stretch film, characterized in that the content of vinyl acetate in one of the ethylene-vinyl acetate copolymers in the surface layer is higher than the content in the other surface layer. 2. The method according to claim 1, wherein the content of vinyl acetate in one of the surface layers is 5 to 25% by weight, and 3 to 10% by weight lower than the content in the other surface layer. Item 7. The polyolefin-based stretch film according to Item 1. 3. A crystalline polypropylene resin 60 to 80% by weight, a propylene-butene copolymer 20 to 30% by weight,
The polyolefin-based stretch film according to claim 1 or 2, having an intermediate layer composed of 10 to 30% by weight of an ethylene-propylene copolymer. 4. The peel strength between the outer surface of the film and the peel strength between the inner surfaces when the film is formed by an inflation method in producing the polyolefin-based stretch film according to claim 1 or 2 or 3. Strength 1.
A method for producing a polyolefin-based stretch film, characterized in that the stretch ratio is 2 to 2 times.