JPH07112513A - Stretch film for food packaging - Google Patents

Abstract

PURPOSE:To provide a polyolefin resin stretch film providing good packaging finish. CONSTITUTION:A stretch film wherein an ethylene-(alpha-olefin copolymer resin layer with a melt flow ratio of 0.2-2g/min, a density of 0.890-0.910g/cm<3> and a ratio of wt. average mol. wt. Mw and number average mol. wt. Mn (Mw/Mn) of 7-10 is made as a central layer and an ethylene-vinyl acetate copolymer resin layer with a melt flow ratio of 0.2-2 and vinyl acetate content of 10-20wt.% is respectively provided on both sides of the central layer is provided. This film has pref. a ratio of a stress(sigma150at 150% elongation to a stress sigma50 at 50% elongation (sigma150/sigma50) of 1.3-2.0 both in the longitudinal and transverse direction. It is possible thereby to obtain a stretch film with less wrinkle occurrence excellent elastic recovery even when deformation is applied by pushing it with a finger and good packaging finish.

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, and more particularly to a polyolefin resin stretch film capable of obtaining a good packaging finish.

[0002]

2. Description of the Related Art Conventionally, a polyvinyl chloride-based film has been used as a film for so-called prepackaging, in which fruits and vegetables, fresh fish, meat, side dishes, etc. are placed on a lightweight tray and overlapped with the film. Came. In addition to the packaging suitability that the packaging efficiency is good and the packaging finish is beautiful, even if deformation such as pushing the film after packing with a finger is applied, it has an excellent elastic recovery power that does not lower the commercial value, This is because it had a great commercial value that was recognized by both sellers and consumers.

However, in recent years, problems such as hydrogen chloride gas generated at the time of incineration and elution of the plasticizer contained in the polyvinyl chloride film have been regarded as problems. Therefore, various alternatives to polyvinyl chloride film have been studied, and in particular, stretch film of various constitutions using polyolefin resin has been proposed, but it has characteristics such as packaging workability, packaging finish, and elastic recovery. A polyolefin film-based stretch film for food packaging that satisfies all of the above requirements has not yet been put on the market.

Among the polyolefin type stretch films, ethylene-α-, such as linear low-density polyethylene, is used.
Although the multilayer film having the olefin polymer layer as the central layer exhibits relatively good properties, it still has difficulty in wrinkling and elastic recovery especially at the time of packaging as compared with the conventional polyvinyl chloride-based stretch film. there were.

[0005]

Means for Solving the Problems The present invention solves the above-mentioned problems, and its gist is that the melt flow lacquer is 0.2 to 2 g / 10 minutes and the density is 0.890 to 0.
Ethylene-α-having a weight average molecular weight Mw of 910 g / cm ³ and a number average molecular weight Mn (Mw / Mn) of 7 to 10;
A layer of olefin copolymer resin is used as a central layer, and a layer of ethylene-vinyl acetate copolymer resin having a melt flow rate of 0.2 to 2 and a vinyl acetate content of 10 to 20% by weight is provided on both sides thereof. The present invention is a stretch film for food packaging. In this film, the ratio of the stress σ ₁₅₀ at 150% elongation to the stress σ ₅₀ at 50% elongation (σ ₁₅₀ / σ ₅₀ ) was 1.3 to 2.
It is particularly preferably 0.

The present invention will be described in detail below. The stretch film of the present invention is a laminated film basically consisting of three layers, in which the central layer is an ethylene-α-olefin copolymer resin layer and both outer surface layers are ethylene-vinyl acetate copolymer resin layers. . The ethylene-α-olefin copolymer in the central layer is a so-called linear low-density polyethylene (LLDPE) having a linear main chain and substantially no long chain branching, and is a melt flow-ray copolymer. (MFR, 1
90 ° C., 2.16 kg load) 0.2 to 2 g / 10 minutes,
It is preferable that the density is 0.890 to 0.910 g / cm ³ .

When the MFR is less than 0.2, the extrusion moldability is deteriorated, and when it exceeds 2, the strength of the film is lowered and the film tends to be broken. When the density is less than 0.890, the strength is lowered and the film is easily torn, and when the density exceeds 0.910, the film is hard and difficult to stretch. As α-olefins copolymerized with ethylene, butene-1, hexene-1, 4-methyl-pentene-1, octene-1 and the like are available, but those mainly containing butene-1 as a copolymerization component are practical. And
The copolymerization ratio is generally 5 to 15% by weight.

In the present invention, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn, hereinafter referred to as Q value) of the ethylene-α-olefin copolymer resin of the central layer is 7 to 10. Use one within the range. When the Q value is less than 7, it is difficult to increase the blow-up ratio because the stability of bubbles during inflation molding is lowered, and the obtained film has a strong tendency to show a necking elongation. It's hard to get a good film. On the other hand, if the Q value exceeds 10, transparency is lowered and strength is lowered, so that the film is easily broken, which is not preferable.

Further, as the ethylene-vinyl acetate copolymer resin used on both sides of the central layer of the above-mentioned ethylene-α-olefin copolymer, Melt Flow-Reciyo (MFR) is available.
Is 0.2 to 2 g / cm ³ , and the vinyl acetate content is 10 to 2
It is preferably 0% by weight. Vinyl acetate content is 10%
If it is less than the above range, it is hard and difficult to stretch, and the transparency is lowered. If the content of vinyl acetate exceeds 20%, the strength is lowered and the package tends to be broken during the packaging work. When the MFR is less than 0.2, the extrusion moldability is deteriorated, and when it exceeds 2, the strength of the film is lowered and the film is easily broken.

Such a film can be obtained by co-extruding each layer and performing inflation molding. The blow-up ratio (diameter of bubble / diameter of die) at the time of inflation molding is 4 or more, preferably 5 to 7.

The film of the present invention has a stress σ ₁₅₀ and a stress 50% at the time of elongation of 150% when the laminated film is stretched.
The ratio (σ ₁₅₀ / σ ₅₀ ) to the stress σ ₅₀ during elongation is the longitudinal direction,
It is preferable to set the width in the range of 1.3 to 2.0 in the lateral direction.

In order to improve the wrapping workability, wrapping finish, and elastic recovery force of the film, it is necessary that the change in stress with respect to the amount of tensile deformation, that is, the shape of the SS curve is within a specific range. . This range varies depending on how the film is used, but if it is a packaging method or packaging machine that is usually used in the case of a stretch film for food packaging,
(Stress at 150% elongation σ ₁₅₀ / Stress at 50% elongation σ
_When expressed as a ratio of ₅₀ ), it is preferable that this ratio be in the range of 1.3 to 2 in both the vertical and horizontal directions.

When this ratio is less than 1.3, the film exhibits uneven elongation during packaging, and local elongation tends to cause breakage at the corner portion of the tray. Further, when the packaged product is pressed with a finger to be deformed, the mark of the finger remains forever and the value of the product being displayed is reduced. On the other hand, if this ratio exceeds 2.0, a strong force is required to extend the film during the packaging work and the workability is deteriorated, and the tray is deformed or crushed in the packaging by the automatic packaging machine.

When a film containing an ethylene-α-olefin copolymer layer is produced by the inflation method which is a general method for producing stretch films, σ ₁₅₀ / σ ₅₀ is large in the longitudinal direction and small in the transverse direction. In order to obtain a film that tends to have excellent wrapping suitability, σ especially in the lateral direction
It is important to set ₁₅₀ / σ ₅₀ to a specific range,
Therefore, as a result of various investigations, a film having good packaging suitability can be obtained by using an ethylene-α-olefin copolymer resin having a Q value of 7 or more as the central layer and increasing the blow-up ratio during inflation molding. I found it.

Ethylene-α-having a Q value of less than 7
Olefin copolymer resin is known to be preferable as a packaging film because it has high tear strength and tear strength, but on the other hand, as described above, the stability of the bubble in inflation-molding is lowered and the blow-up ratio is decreased. Difficult to raise. The obtained film has a lateral σ ₁₅₀ /
The σ ₅₀ was difficult to improve, showed non-uniform elongation, and wrinkles and breakage due to local elongation were likely to occur, which was not preferable.

Thus, ethylene having a Q value of 7 or more-α-
The film of the present invention can be obtained by using an olefin copolymer resin in the center layer and increasing the blow-up ratio, specifically 4 or more, particularly 5 to 7. The total thickness of the film of the present invention is 8 to 30 μm.
m, the central layer of the ethylene-α-olefin copolymer resin is preferably set to be about 20 to 60% of the total thickness.

In order to impart antifogging property and slipperiness to the film of the present invention, at least one surface active agent such as glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester and ethylene oxide adduct is mainly used on the outer surface. You may add 0.5 to 5 weight% to the ethylene-vinyl acetate copolymer resin which is a layer. Further, at least one kind of hydrogenated petroleum resin, hydrogenated terpene resin, rosin resin, liquid polybutene resin and the like is added to the ethylene-vinyl acetate copolymer resin, which is the outer surface layer, in order to impart tackiness. Is also good. Further, the ethylene-vinyl acetate copolymer resin layer of the outer layer may have a two-layer structure of an outermost layer containing a large amount of the above-mentioned additive and an intermediate layer containing no or a small amount of the additive.

The effects of the present invention will be clarified by the following examples.

[0019]

【Example】

(Example 1) MFR is 0.4 g / 10 minutes and density is 0.9.
00 g / cm ³ of ethylene-butene-1 copolymer resin (butene-1 content 14% by weight) having a Q value of 8 was melted with an extruder having a diameter of 40 mm and L / D = 28,
It was introduced into a circular die with a diameter of 80 mm, and an ethylene-vinyl acetate copolymer resin having an MFR of 0.5 g / 10 min and a vinyl acetate content of 15% by weight was provided on both sides of the die with another diameter of 50 m.
m, L / D = 26, induction of melting from extruder, die temperature 2
Inflation molding was performed at 00 ° C. and a blow-up ratio of 4, and the thickness of the ethylene-butene-1 copolymer resin central layer was 5 μm, and the thickness of the ethylene-vinyl acetate copolymer resin layers on both sides was 5 μm. A film having a thickness of 15 μm was obtained.

(Examples 2 to 3) In the same manner as in Example 1,
Inflation molding was performed with a blow-up ratio of 5 or 6 to obtain a film having a total thickness of 15 μm. (Comparative Examples 1 and 2) The ethylene-α-olefin copolymer resin in the center layer had a density of 0.905 g / cm ³ , an MFR of 0.
Example 8, except that the ethylene-butene-1 copolymer resin having a Q value of 4 (butene-1 content 12% by weight) was used.
A film having a total thickness of 15 μm was obtained under the same conditions as in 3.

(Comparative Examples 3 to 4) Under the same conditions as in Example, except that the center layer was the same ethylene-vinyl acetate copolymer resin as the both layers, only an ethylene-vinyl acetate copolymer having a total thickness of 15 μm was used. I got this film. Comparative Example 5 A commercially available polyvinyl chloride-based stretch film (thickness: 15 μm) was used.

Using these films, expanded polystyrene tray (length 200 mm, width 100 mm, depth 30)
mm) and a manual wrapper and a push-up type automatic wrapping machine (AW-2600JR manufactured by Teraoka Seiko Co., Ltd.). Table 1 shows the characteristics of each film, Table 2 shows the results of the evaluation of packaging suitability, and Table 3 shows the evaluation method of the packaging suitability. The σ ₁₅₀ / σ ₅₀ shown in Table 1 was measured at a tensile speed of 200 mm / min according to JIS-K-1702, and the tear strength was JIS-
It was measured according to K-7128.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

From the results shown in Tables 1 and 2, the films of Examples using the ethylene-α-olefin copolymer resin having the properties within the range specified in the present invention as the central layer showed the stress-
It has excellent elongation characteristics and excellent packaging suitability. In particular films of Examples 2-3 in which the Buroatsupu ratio was 5 or more and σ _{15 0} / σ ₅₀ becomes 1.35 or higher showed very excellent packaging quality.

On the other hand, in Comparative Examples 1 and 2 using the ethylene-α-olefin copolymer resin having a low Q value, when the blow-up ratio is increased, the inflation molding becomes unstable and stable film molding is performed. Even when the blow-up ratio was the same as that of the example, the stress-elongation property in the transverse direction of the film was unsuitable and a good packaging finish could not be obtained. Further, in Comparative Examples 3 to 4 in which the ethylene-α-olefin copolymer resin is not used in the central layer, the core layer is easily broken and the sealing property is poor.

[0028]

According to the present invention, there is provided a stretch film which has less wrinkles, has an excellent elastic recovery force to return to its original shape even if it is deformed by pushing with a finger, and is also excellent in sealing property and strength. Obtained stably.

Claims (2)

[Claims] 1. Melt flow lacquer is 0.2-2 g /
10 minutes, density 0.890 to 0.910 g / cm ³ , ratio of weight average molecular weight Mw to number average molecular weight Mn (Mw / M
n) has a layer of ethylene-α-olefin copolymer resin of 7 to 10 as a central layer, and has a melt flow ratio of 0.2 to 2 and a vinyl acetate content of 10 to 20% by weight on both sides thereof.
A stretch film for food packaging, which has a layer of the ethylene-vinyl acetate copolymer resin. 2. The ratio of the stress σ ₁₅₀ at 150% elongation to the stress σ ₅₀ at 50% elongation (σ ₁₅₀ / σ ₅₀ ) is 1.3 to 2.0 in both the longitudinal and transverse directions. The stretch film for food packaging according to claim 1.