JPH10193532A - Stretched shrink film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film having excellent removal easiness (easy tearability) in the case or removing an object of a content from a product for packaging the object in a packaging film used together with a stretched package or shrink package. SOLUTION: The stretched shrink film comprises a core layer containing a mixture of 75wt.% to 97wt.% of linear low-density polyethylene and 25 to 3wt.% of syndiotactic polypropylene as main components, and an innermost outer layer containing ethylene-α-olefin copolymer and polyethylene resin as main components, so that at least one or more layers are used with polyolefin laminate added with 0.5 to 3wt.% of surfactant composition oriented in lateral and longitudinal directions at a draw ratio of 2 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stretch shrink film, and more particularly to a stretch shrink film and a shrink (heat shrink) package for a food placed in a container such as a tray. The present invention relates to a stretch shrink film that can be easily opened.

[0002]

2. Description of the Related Art With the expansion of convenience stores, various foods such as prepared foods and bento have been packaged using stretch films, including fresh foods such as meat, seafood, vegetables and fruits. Most often, these stretch films are made of plasticized polyvinyl chloride having properties such as moderate adhesiveness, excellent transparency, and soft touch. However, a stretch film made of plasticized polyvinyl chloride has a large amount of water vapor permeation due to a large amount of a plasticizer,
It has problems of safety and health and pollution, such as loss of quality and deterioration, and generation of harmful hydrogen chloride gas during waste incineration.

[0003] The present inventors have previously conducted studies using polyethylene having no problem of safety and health and pollution in order to solve the above-mentioned drawbacks of the stretch film, and proposed a polyethylene-based stretch shrink film ( JP-A-3-215034, JP-A-8-090737
No.). The film obtained by this proposal solves the above-mentioned problems, further has heat shrinkage, and can be used in an automatic packaging machine, so that a good packaging finish is obtained, and The production speed can be increased.

[0004]

On the other hand, recently, the ease of removal (easy opening) of a film package has been recognized as a problem. The same applies to the stretch packaging field,
In particular, there is a growing awareness of problems with prepared foods and bento boxes in lidded containers sold at convenience stores and the like. In film packages with poor opening properties, not only is it time-consuming to open, but also the tray, contents, etc., can be deformed, impairing the value of the product, or applying excessive force when opening the tray. You may be injured. The opening method differs depending on each packaging system, but for example, the film is provided with small holes connected like perforations,
Along with that, the one that is to be propagated by tearing, or one that cuts (notches) in a certain part of the film, puts an opening label indicating the opening direction, etc., pulls the label and tears and propagates the film, etc. Yes, the packaging film can be removed from the unsealed portion created by the tear propagation, and the contents can be taken out. In any case, the property that the packaged film easily tears and propagates in the opening direction (the tear strength in the opening direction is small) is important. However, the stretch-shrink film proposed above has not been able to adequately respond to these requirements for easy opening.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to develop a stretch shrink film in which a package can be easily opened. As a result, a mixture of a linear low-density polyethylene and a syndiotactic polypropylene has been developed. It has been found that a film obtained by subjecting a polyolefin-based laminate to a stretching treatment can be suitable for the purpose, and the present invention has been completed.

That is, the present invention provides: A core layer mainly composed of a mixture of 75 to 97% by weight of linear low density polyethylene and 25 to 3% by weight of syndiotactic polypropylene; and an innermost and outermost layer mainly composed of an ethylene-α-olefin copolymer and a polyethylene resin. Layer, and at least one layer of the surfactant composition
A stretch shrink film, characterized in that the polyolefin-based laminate to which -3% by weight has been added is subjected to a stretching treatment at least twice in both the vertical and horizontal directions. 2. Syndiotactic polypropylene, ¹³ C-NM
Syndiotactic pentad fraction by R measurement 0.7
The stretch shrink film according to the above item 1, characterized in that: It is.

Hereinafter, the present invention will be described in detail. The linear low-density polyethylene used for the core layer in the present invention includes ethylene and propylene, butene-1, hexene-1,4-
Copolymers with one or two or more α-olefins having 3 to 20 carbon atoms, including methyl-pentene-1, octene-1, decene-1, and dodecene-1 are exemplified. Preferably, a copolymer of ethylene and 4-methyl-pentene-1; a copolymer of ethylene and butene-1;
A terpolymer of -methyl-pentene-1, butene-1 and a terpolymer of ethylene, octene-1, and butene-1 are used. The density at 25 ° C. is 0.890
0.935 g / cm ³ , melt index (hereinafter, referred to as
MI is abbreviated to 0.1 to 7.0 g / 10 min. In order to obtain a film having better rigidity, heat resistance and stretchability, which is required for suitability of an automatic packaging machine, a film having a relatively high density and a relatively high density within the above-mentioned density and MI range. A combination of low linear low density polyethylene is preferred.

The syndiotactic polypropylene used in the core layer together with the linear low-density polyethylene is different from the syndiotactic polypropylene having a low syndiotacticity obtained by using a conventional vanadium catalyst, and is measured by ¹³ C-NMR. The synthesized syndiotactic pentad fraction is 0.7 or more and has good syndiotacticity.

The syndiotactic polypropylene is disclosed in, for example, JP-A-2-41303 and JP-A-2-41303.
41305, JP-A-2-274703, JP-A-2-274704, JP-A-3-179005
And a catalyst comprising a cross-linked transition metal compound having asymmetrical ligands and a cocatalyst as described in JP-A No. 3-179006 and JP-A-3-179006. A method for measuring a syndiotactic pentad fraction by ¹³ C-NMR is described in, for example, JP-A-2-4130.
It can be measured by a known method as described in Japanese Patent Publication No.

If the amount of the syndiotactic polypropylene added to the core layer is less than 3% by weight, the tear strength in the opening direction is not reduced so that easy opening property cannot be obtained. If the content exceeds 25% by weight, the effect of the easy-opening property does not change, and the antifogging property tends to decrease. When the stretching treatment is performed by the tubular method, an addition amount exceeding 25% by weight is not preferable from the viewpoint of the stretching stability of the tube.

As a means for lowering the tear strength, a commercially available propylene homopolymer or a copolymer with ethylene containing isotactic polypropylene as a main component may be similarly added. Although the openability can be achieved, the transparency is poor and it is not practical at all.

[0012] The innermost and outermost layers are formed of ethylene-ethylene from the viewpoint of simultaneously satisfying the heat sealing property by a hot plate and the slipping property with bag-making parts, as well as transparency and glossiness, which are required for suitability of an automatic packaging machine. A composition containing an α-olefin copolymer and a polyethylene resin as main components is used.

The ethylene-α-olefin copolymer has a function of imparting a low-temperature heat-sealing property particularly on a hot plate. In the present invention, a low-crystalline or amorphous ethylene-olefin copolymer is used.
An α-olefin copolymer is used. Specifically, for example, ethylene and propylene, butene-1, pentene-1,
Hexene-1,4-methyl-pentene-1, octene-
1, a copolymer with decene-1 or a mixture thereof. Further, in order to satisfy the above-mentioned properties required for the innermost and outermost layers, the density should be 0.870 to 0.900 g.
/ Cm ³ , MI of 0.1 to 20 g / 10 min, and a main peak temperature of 50 to 100 ° C. in a melting curve are more preferably used. The addition amount of the ethylene-α-olefin copolymer in the innermost layer and the outermost layer is 20 to 60% by weight, and if it is less than 20% by weight, the low-temperature heat sealability is poor. This is not preferable in that it tends to cause slippage and decrease in transparency before shrinkage.

The polyethylene resin used for the innermost and outermost layers is
In combination with the ethylene-α-olefin copolymer described above,
It acts as a second component that imparts transparency, gloss, and low-temperature heat sealability. As the polyethylene resin, linear low-density polyethylene and high-pressure polyethylene are used. Further, from the viewpoints of suppressing blocking that results in excessive tackiness and improving slipperiness, a high-pressure polyethylene or a linear low-density polyethylene having a relatively narrow molecular weight distribution obtained by using a metallocene catalyst is preferably used.

As the surfactant composition to be added to at least one or more layers, one or more nonionic surfactants which are generally commercially available as antifogging agents are used. The amount of addition is 0.1 to 100 parts by weight of the raw material of each layer.
5 to 3% by weight. If it is less than 0.5% by weight, the antifogging property is not exhibited. Even if it exceeds 3% by weight, the antifogging effect does not change. The layer to which the surfactant is added may be added to any layer as long as the amount is within the above range, but two or more layers,
Further, when added to all the layers, it is preferable in that good anti-fog performance can be stably obtained for a long period immediately after production.

In addition to the above components, each layer has an appropriate amount of a lubricant, an anti-blocking agent, an antistatic agent for the purpose of imparting a releasability from a roll of a film, and a slipperiness for improving the efficiency of packaging and packing operations. Commonly used additives such as agents can be appropriately added for the purpose of imparting their effective effects. Further, other resins and the like can be added as long as the object of the present invention is not hindered.

In addition, within the range not interfering with the object of the present invention, the purpose of the present invention is to adjust the recovery layer when recycled between the innermost and outermost layers and the core layer, or the stretchability and other film strengths. One or more layers may be included.

In the stretching treatment performed in the present invention, it is necessary to perform stretching at least twice or more in both the vertical and horizontal directions. Preferably 3 times or more, more preferably 4 times
Times or more, and a film having excellent heat shrinkage can be easily obtained. In order to effectively reduce the required tear strength in the opening direction, it is necessary to slightly increase the stretching ratio in the opening direction. After the stretching treatment, heat treatment, aging and the like can be performed as necessary.

[0019]

The present invention will be described below in detail with reference to examples. In addition, each physical property measurement shown in this example was based on the following methods. (1) Haze Measured according to JIS K6714. (2) Tear strength The tear strength measurement direction is the long side, the long side is 62 mm, and the short side is 50.
A rectangular sample of mm was prepared, and the longitudinal strength of the film was measured using a light load tear tester. (3) Openability Using a stretch automatic packaging machine equipped with a shrink tunnel,
A lunch container (with a lid) having a width of 120 mm, a length of 180 mm and a height of 45 mm was subjected to stretch shrink packaging. At that time, after the bag was made and before shrinking, a V-shaped cut was made in the film on the upper surface of the container, shrink-wrapped, and an opening label was stuck on the cut. The openability was evaluated by setting the reverse direction of the V-shape to the opening direction (corresponding to the vertical direction in the film). The evaluation was performed based on the following criteria. ：: The resistance at the time of opening is completely unnoticeable, the tear is smoothly propagated in the vertical direction, and the packaging film can be easily removed. ×: There is a portion where the resistance to tear propagation increases during opening, and the film is torn in an oblique direction while stretching, and the propagation is interrupted, or the opening label is peeled off from the film, making it difficult to remove the packaging film. . (4) Antifogging property After putting 30 ml of water at 18 ° C. into a 100 ml beaker,
Cover the top of the beaker with a film without wrinkles and fix it. Next, the beaker is placed in hot air adjusted to 110 ° C. for 5 seconds to be thermally contracted. Thereafter, the film was left in an open showcase at 5 ° C. for 1 hour, the degree of cloudiness of the film was observed, and the film was evaluated according to the following criteria. ：: No fogging. X: Water droplets are present on the inner surface of the film, but the inside of the beaker is difficult or invisible.

Example 1 80% by weight of linear low density polyethylene (A) having the characteristics shown in Table 1 and 20% by weight of syndiotactic polypropylene (syndiotactic pentad fraction 0.79, melt flow index 4.9) Of a core layer obtained by adding 0.6% by weight of diglycerin oleate and 0.4% by weight of polyoxyethylene oleylamine to 100% by weight of a mixture of 88 g / cm ³ , MI 3.6 g / 10 min) 30% by weight and linear low density polyethylene (density 0.916 g / c
(m ³ , MI 1.2 g / 10 min) 70 wt%, and 0.6 wt% of diglycerin oleate and 0.4 wt% of polyoxyethylene oleylamine were added, and three raw materials for the innermost and outermost layers were used. Melt kneading at 170 to 240 ° C. in each extruder (for the innermost layer, intermediate layer, and outer layer), so that each extruder has a thickness ratio of innermost layer: core layer: outermost layer = 1: 5: 1. The extruded amount was adjusted and extruded downward from a slit of a three-layer annular die maintained at 240 ° C. The diameter of the slit of the annular die was 75 mm, and the gap of the slit was 0.8 mm. The extruded three-layered molten tubular film is attached directly under the die. The outer surface of a cylindrical mandrel having an outer diameter of 76 mm and circulating cooling water at 20 ° C inside is slid while passing the outer surface through a water tank. The resultant was cooled with water, cooled at room temperature, and taken off to obtain a tubular unstretched film having a diameter of about 75 mm and a thickness of about 240 μ. This tubular unstretched film was guided to a tubular biaxial stretching apparatus as shown in FIG. 1 and expanded and stretched. At this time, the current of the annular infrared heater of the preheater 4 was adjusted to adjust the film temperature at the outlet of the preheater. The eight annular infrared heaters of the main heater 5 are divided into four sections to control the respective currents to heat the film, and the low-speed nip roll 2 and the high-speed nip roll are supplied while supplying air flowing along the tube from below the main heater. The pressurized air is sent to the annular film between the three, and depending on the air pressure and the peripheral speed ratio of the low-speed and high-speed nip rolls, the height is 5.0 times and the width is 4.0 times (area stretching ratio is 20 times)
And a stretched film having a thickness of about 13 μm was produced. The stability during stretching was good, there was no vertical movement of the stretching point, no sliding of the stretching tube, and no uneven stretching state such as necking was observed. The transparency of the obtained film was good, the tear strength in the longitudinal direction as the opening direction was low, and the package could be easily opened. The antifogging property was also good. Table 1 shows the evaluation results.

Examples 2 to 4 As shown in Table 1, a stretched film was produced in the same manner as in Example 1 except that the mixing ratio of the linear low-density polyethylene and the syndiotactic polypropylene as the raw materials for the core layer was changed. Then, each characteristic was evaluated. In each of the examples, the stability during stretching was good, there was no vertical movement of the stretching point, no sliding of the stretching tube, and no uneven stretching such as necking was observed. When the obtained films were evaluated in the same manner as in Example 1, as shown in Table 1, all of the films had good transparency, tear strength in the longitudinal direction, openability, and protection similar to the films obtained in Example 1. It showed cloudiness. Table 1 shows the evaluation results.

Comparative Example 1 As shown in Table 1, a stretched film was produced in the same manner as in Example 1 except that the mixing ratio of the linear low-density polyethylene and the syndiotactic polypropylene as raw materials for the core layer was changed.
Each characteristic was evaluated. The stability during stretching was good, there was no vertical movement of the stretching point, no sliding of the stretching tube, and no uneven stretching state such as necking was observed. When the obtained film was evaluated in the same manner as in Example 1, the transparency and the antifogging property were good, but the tear strength in the vertical direction was high, and the openability of the packaged product was poor. Table 1 shows the evaluation results.

Comparative Example 2 As shown in Table 1, a stretched film was produced in the same manner as in Example 1 except that the mixing ratio of the linear low-density polyethylene and the syndiotactic polypropylene as the raw materials for the core layer was changed. Each characteristic was evaluated. During the stretching, vertical movement of the stretching point and sliding of the stretching tube were slightly observed, and the thickness unevenness of the obtained film was somewhat large. When the obtained film was evaluated in the same manner as in Example 1, the tear strength in the longitudinal direction and the opening property of the packaged product were good, but the transparency and the antifogging property were poor. Table 1 shows the evaluation results.

[0024]

[Table 1]

[0025]

The stretch shrink film of the present invention has good transparency and anti-fogging property, and also has easy opening property.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a biaxial stretching device used in Examples.

[Description of Signs] 1 Unstretched film 2 Low speed nip roll 3 High speed nip roll 4 Preheater 5 Main heater 6 Cooling air ring 7 Folding roll group

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B65D 71/08 B65D 71/08 C // B29K 23:00 105: 02

Claims (2)

[Claims] 1. 75 to 97% by weight of linear low density polyethylene and 25 to 3% by weight of syndiotactic polypropylene
And a core layer mainly composed of a mixture of the above, and an innermost and outermost layer mainly composed of an ethylene-α-olefin copolymer and a polyethylene-based resin. A stretch shrink film, characterized in that the polyolefin-based laminate to which weight% has been added is subjected to a stretching treatment at least twice in both the vertical and horizontal directions. 2. The syndiotactic polypropylene,
The stretch shrink film according to claim 1, wherein the fraction is at least 0.7 in syndiotactic pentad fraction by ¹³ C-NMR measurement.