JP2000094606A - Film for packaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyethylene warp film which is excellent in heat resistance, adhesiveness and drawing and cutting properties and does not generate bad smell even used in an electronic range. SOLUTION: This film for packaging is a film obtained by biaxially stretching longitudinally and laterally 2-5 times the film comprising a specific low density polyethylene resin laminated on both sides of a polypropylene resin layer by a co-extrusion process, and a film of a longitudinal/lateral ratio being in the range of 1.1-1.5 is adopted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packaging film which is excellent in tackiness, drawability, cutability, heat resistance and antifogging property and has no unpleasant odor.

[0002]

2. Description of the Related Art Wrap films for food packaging are used for wrapping food in ordinary households, restaurants and the like, storing them in a refrigerator or freezer, or heating them in a microwave oven (microwave cooker). It is also used for wrapping the contents of tableware before serving ramen, soba, soup, etc. Here, the food is wrapped to prevent the food from drying (preventing water from being scattered), prevent dust from entering, prevent the food from jumping out of tableware, and the like. Such a food packaging wrap film is wound around a paper tube with a width of 20 to 45 cm and a length of about 20 to 100 m and is housed in a paper carton box. Used after being cut in quantity.

[0003] As the wrap film, the following
Is required. The contents can be seen through, easy to pull out by hand from the carton box, sticky, have sufficient heat resistance so that the film does not dissolve when used in a microwave oven, do not fog during use, There is no unpleasant odor and the film is easy to cut.

At present, wrap films using vinylidene chloride resin are mainly used, but there is a drawback that, when cutting, they are not cut along the saw blade but cut diagonally. Ethylene-based resins have been actively developed in view of environmental problems such as generation of poisonous gas. However, the wrap film made of an ethylene-based resin is easy to stretch and hard to tear, so a considerable tensile force is required at the time of cutting, and the film cannot be pulled out well or the carton box is deformed. In addition, there are problems such as poor heat resistance when used in a microwave oven and low rigidity of the film, making it difficult to handle.Therefore, it cannot be replaced with vinylidene chloride resin and is used only in a part of the market. Absent.

In order to improve such disadvantages of the ethylene-based resin, Japanese Patent Application Laid-Open Nos.
Japanese Patent Application Laid-Open No. 7-189850 discloses a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer as a film capable of satisfying the cut property and the heat resistance. Laminated films with propylene homopolymer have been proposed, but these laminated films have no tackiness and cannot be used as household wrap films. Also, Japanese Patent Application Laid-Open No. 1-195043
In the publication, ethylene-propylene copolymer, or,
A heat-shrinkable film in which a linear low-density polyethylene (ethylene-α-olefin copolymer) is laminated on both surfaces of an ethylene-propylene-butene-1 copolymer has been proposed. The film adheres to each other when heat is applied in a microwave oven, and the workability is poor.
It is practically difficult to use as a household wrap film. Also, JP-A-7-52345, JP-A-7-52345
JP-A-196738, JP-A-8-80600, JP-A-9-29908, and the like disclose that ethylene-
Films having improved adhesiveness and heat resistance using an α-olefin copolymer or a propylene-based resin and a polyamide resin or an ethylene-vinyl acetate copolymer for an intermediate layer have been proposed.

JP-A-8-25596 discloses a crystalline propylene resin film layer comprising an ethylene-propylene-α-olefin copolymer and a linear ethylene-α-olefin copolymer on one or both surfaces. A film in which layers are laminated and which has excellent adhesiveness and heat resistance has been proposed. However, in the former case, since different materials are molded at the same time, molding is difficult, and the apparatus becomes complicated. For the latter, the tackiness is not always sufficient. On the other hand, some additives added to improve the tackiness may cause an unpleasant odor. Although there is no safety and health problem, it is uncomfortable and is a serious problem for use in food wrap films. There are also problems such as poor cut properties (film cut properties).

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in wrapping films for food packaging, and its object is to provide not only transparency but also heat resistance. Another object of the present invention is to provide a wrap film which is extremely excellent in adhesiveness, drawability, and cutability and does not have an unpleasant odor when used in a microwave oven or the like.

[0008]

According to the present invention, as a result of intensive studies to produce a packaging film in which the above-mentioned problems of the conventional wrapping film are solved, propylene-α was obtained.
-The above problems are solved by biaxially stretching a low-density polyethylene resin laminated on both sides of the olefin copolymer resin layer by co-extrusion, thereby improving heat resistance, adhesiveness, drawability, and cutability. The inventors have found that an excellent and unpleasant odor-free packaging film can be obtained, and arrived at the present invention. That is, the gist of the present invention is to co-extrude a laminate of at least three layers in which both surface layers are a low-density polyethylene resin and the intermediate layer is a propylene-α-olefin copolymer resin, and then quenched to obtain a raw film. A biaxially stretched film obtained by stretching the raw film in the longitudinal direction and the lateral direction in the range of 2 to 5 times, respectively, wherein the total thickness of the film is 5
５０50 μm, and the thickness of the intermediate layer comprising the propylene-α-olefin copolymer resin is in the range of 10 to 90% of the total thickness of the film.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further described below.
The packaging film of the present invention has at least three layers, for example, three layers of a surface layer / intermediate layer / surface layer (back layer). Of course, an adhesive layer may be provided between the surface layer and the intermediate layer and / or between the back layer and the intermediate layer. As such an adhesive layer, any material can be used as long as it can adhere the surface layer (including the back layer) and the medium-simplified layer. For example,
A resin having a composition close to that of the polyethylene resin used for the surface layer, for example, a mixture of the polyethylene resin (A) with an appropriate amount of polybutene (B) and a plasticizer (C), or a polypropylene resin used for the intermediate layer Those having a composition close to the above, for example, those obtained by mixing an appropriate amount of a propylene-butene-1 copolymer with a propylene-ethylene random copolymer, and the like are suitably used.

The low-density polyethylene resin constituting both surface layers of the self-adhesive film is not limited, and examples thereof include a linear low-density polyethylene and a high-pressure low-density polyethylene. preferable.
The physical properties of this low-density polyethylene resin may be selected according to the application, conditions, etc., but usually the melt flow rate (MF
R) 0.5-10 g / 10 min, density 0.920 g / cm
^A linear low density polyethylene of ³ or less is preferred. Melt flow rate is 190 in accordance with JIS K6758.
It was measured at 2.degree. By adding the following additives to the low-density polyethylene resin described above, excellent performance as a wrap film, that is, adhesiveness, heat resistance, and the like can be obtained. Polybutene (B) per 100 parts by weight of low-density polyethylene resin (A)
2 to 20 parts by weight and 0.1 to 10 parts by weight of the plasticizer (C) are added.

The component (B), polybutene, acts as a thickener and imparts excellent tackiness to the film. The butene is added in an amount of 2 to 20 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the low-density polyethylene resin as the component (A). If the amount is less than 2 parts by weight, sufficient viscosity increase will not be exhibited. Conversely, if it exceeds 20 parts by weight, stickiness due to a large amount of bleeding will occur, and heat resistance will decrease, which is not preferable. Note that the physical properties of the polybutene used here can be appropriately determined according to the blending amount, the type of the other components, the intended use of the composition, and the like.
Although there is no particular limitation, usually the number average molecular weight is 500 to 300.
0, preferably 600-2500, more preferably 7
Those having a range of 00 to 1500 are used.

The plasticizer, which is the component (C), increases the adhesiveness of the film when used in combination with polybutene. There is also an anti-fogging effect that fogging is unlikely to occur even when steam adheres. There is no smell. As the plasticizer, acetylated monoglyceride is preferably used. The acetylated monoglyceride is a compound in which one of the hydroxyl groups of glycerin is esterified with a fatty acid such as a higher fatty acid having 8 to 22 carbon atoms, and at least one is acetylated. The higher fatty acid may be saturated or unsaturated as long as it is a fatty acid having 8 to 22 carbon atoms, and is usually preferably a fatty acid having 10 to 18 carbon atoms. As acetylated monoglycerides, for example, glycerin diacetomonolaurate,
Glycerin diacetomonostearate, glycerin monoacetomonostearate and the like can be mentioned. Particularly, glycerin diacetomonolaurate is preferred. The amount of the acetylated monoglyceride is 0.1 to 10 parts by weight, preferably 0.2 to 5 parts by weight, based on the low-density polyethylene resin as the component (A). The blending amount is 0.
If the amount is less than 2 parts by weight, a synergistic effect with the polybutene as the component (B) does not occur. Conversely, if it exceeds 5 parts by weight, stickiness due to a large amount of bleeding may occur or gel may occur frequently. Not very good.

On the other hand, the propylene-α-olefin copolymer resin constituting the intermediate layer of the film for food packaging according to the present invention may be a copolymer with an α-olefin having 2 to 10 carbon atoms such as ethylene, butene, hexene and octene. Although a polymer is mentioned, a copolymer of propylene and an α-olefin having 2 to 10 carbon atoms is preferable. Particularly, a mixture of a propylene-ethylene copolymer and a propylene-butene copolymer is preferable. More preferably, the composition of the mixture is 70 to 90 parts by weight of a propylene-ethylene copolymer and 30 to 10 parts by weight of a propylene-butene copolymer, more preferably propylene-ethylene.
A composition comprising 75 to 85 parts by weight of an ethylene copolymer and 25 to 15 parts by weight of a propylene-butene copolymer. The ethylene content in the propylene-ethylene copolymer is 2 to 7
% By weight, and the butene content in the propylene-butene copolymer is preferably in the range of 5 to 30% by weight. The physical properties of the polypropylene-based resin may be selected according to the application, conditions and the like.
Those having 5 to 10 g / 10 minutes are preferred. Melt flow rate is 230 ° C 2.1 according to JIS K6758.
It was measured under a 6 kg load.

[0014] The polyolefin composition used for both the surface layer and the intermediate layer of the present invention contains a generally used heat stabilizer,
Additives such as a weather stabilizer, a lubricant, an antistatic agent, a nucleating agent, a filler, and an antiblocking agent may be contained in an amount of about 0.0005 to 5%. The food packaging film of the present invention comprises a low-density polyethylene resin and a propylene-α-olefin copolymer resin at least 2
A seed film having a layer structure of three seeds, for example, a laminated film of [low-density polyethylene resin / propylene-α-olefin copolymer resin / low-density polyethylene resin] is molded,
Next, the film is formed by biaxially stretching the film in both the longitudinal, transverse and longitudinal directions. The order of stretching may be vertical or horizontal, whichever may be first, or may be simultaneous vertical and horizontal stretching.

As the co-extrusion molding, a T-die molding method or a water-cooled inflation molding method is applied. That is, by rapidly cooling the melt-extruded resin by the above-mentioned molding method, a film having more excellent transparency and stretchability can be obtained as compared with an air-cooled inflation molding method which is usually used frequently. At the time of raw material forming, quenching can suppress the crystallinity to a low level, which improves transparency and stretchability. Although the air-cooled inflation molding method can be used in the present invention, it is necessary to pay sufficient attention to the fact that the cooling effect is so small that a break may occur during stretching. Careful attention is required, especially when the film is stretched in the transverse direction. In the case of the water-cooled inflation molding method, cooling may be performed by contacting cooling water having a temperature of 50 ° C. or less, preferably 30 ° C. or less. The unstretched multilayer film obtained by the co-extrusion molding is then stretched 2 to 5 times, preferably 2.5 to 4.5 in both longitudinal and transverse directions of the film.
Twice, the ratio of the stretching ratio in the longitudinal direction / the stretching ratio in the transverse direction is 1.1 to
The film is biaxially stretched in the range of 1.5, preferably in the range of 1.15 to 1.3.

If the stretching ratio is less than 2 times, the cutability of the film is insufficient, and if it is more than 5 times, the stretchability is reduced and breakage or uneven stretching of the film occurs.
When the ratio of the stretching ratio in the longitudinal direction / the stretching ratio in the lateral direction is less than 1.1, the cutability of the film deteriorates, and when it exceeds 1.5, the balance of the film performance deteriorates, which is not desirable.

In the case of tubular simultaneous biaxial stretching, the unstretched film is heated as it is, for example, by changing the peripheral speed of a stretching roll to stretch the film in the take-off direction, that is, in the longitudinal direction. The film is stretched in the lateral direction by changing the diameter of the tubular film by blowing air into the inside. The preheating temperature in the stretching treatment is generally a temperature lower than the melting point of the polyethylene resin by 20 ° C. or more, preferably 25 to 60 ° C.
It is preferred to work in a low temperature range. Moreover, you may heat-set after extending | stretching as needed. The heat setting temperature is not particularly limited, but is preferably a temperature that does not cause wrinkles,
Usually, it is preferable to carry out in the range of 40 to 110 ° C.

When the preheating and heat setting temperatures are higher than the appropriate temperature, the stability of the tube diameter becomes poor, and when the preheating temperature is lower than the appropriate temperature, the polypropylene-α-olefin copolymer resin is insufficiently preheated. Therefore, stretching becomes difficult and the film breaks, which is not desirable. In addition to the tubular simultaneous biaxial stretching method described above, a tenter simultaneous biaxial stretching method and a sequential biaxial stretching method can also be applied.
The preheating temperature and the heat setting temperature may be selected according to the above.

By performing this stretching step, the cutability of the film is greatly improved, and the film can be cut to a desired length with a light force using a saw blade. The total thickness of the packaging film of the present invention is in the range of 5 to 50 μm, preferably in the range of 5 to 30 μm, and more preferably in the range of 8 to 25 μm. If the total thickness of the packaging film is more than 50 μm, the tear strength at the time of cutting the film becomes too large, which is not suitable for the use of the wrap film. On the other hand, if the total thickness is less than 5 μm, the film does not have sufficient stiffness and tends to wrinkle, which is not suitable for a wrap film. The thickness ratio of the propylene-α-olefin copolymer resin layer of the intermediate layer is 10 to 9 with respect to the thickness of the entire film.
0%, preferably 15-80%.

If the thickness of the intermediate layer is less than 10% of the total thickness, the inherent heat resistance and mechanical strength of the propylene-α-olefin copolymer resin cannot be exhibited. 9
If the thickness is more than 0%, the thickness of the low-density polyethylene resin layer becomes too thin, and it becomes difficult to uniformly cover the intermediate layer by co-extrusion. The self-adhesive film of the present invention is used for various packaging applications such as food packaging. Further, by giving self-adhesiveness to both surface layers by the method described above, it can be suitably used as a wrap film.

[0021]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist thereof. The measurement in the examples was performed by the following method.

(1) Transparency (haze) Measured according to ASTM D-1003.

(2) Heat Resistant Temperature A strip film having a width of 30 mm and a length of 140 mm, a paper is placed on the upper and lower sides of a sample piece by 25 mm, and a weight of 10 g is lowered. The maximum ambient temperature that could not be cut in one hour was measured at 10 ° C intervals.

(3) Adhesion Two 80 mm-wide films are lightly overlapped, and the film is pressed three times with a roll of 25 mmφ and a width of 150 mm at a linear pressure of 0.3 kg / cm ² within 5 minutes. The force required for peeling in the 180-degree direction was measured with a push-pull scale (PSM2K manufactured by Imada Co., Ltd.), and the highest load g was determined.

(4) Pullability When a wrap film wound around a paper tube and having a width of 300 mm and a length of 20 m is put in a paper box, the end face of the film is sandwiched by clips, and the clips are pulled by a push-pull scale to pull out the film. Measure the maximum load.

(5) Odor A ceramic dish containing about 100 cc of warm soup was wrapped with a film, and after 30 minutes, the odor to the film was evaluated by smell. Those that did not smell were indicated by ○, and those that did not smell were indicated by x.

(6) Cutability A wrap film of 300 mm in width and 20 m in length wound on a paper tube is placed in a paper box, the end face of the film is sandwiched between clips, and the film is pulled by a push-pull scale, and the film is pulled out of the paper box. Measure the maximum load when cutting along the blade.

[Example 1] Water cooling system 3 with a diameter of 135 mm
The resin shown in Table 1 was simultaneously extruded from three extruders at a die temperature of 200 ° C. using a seed five-layer coextrusion annular die molding machine.
A three-layer film consisting of a surface layer (low-density polyethylene resin) / intermediate layer (polypropylene-α-olefin resin) / back layer (low-density polyethylene resin) was formed at a cooling water temperature of 20 ° C. and a take-up speed of 3 m / min. (230 μm thick,
(Layer ratio 1: 2: 1). Table 1 shows the composition of each raw material used.

[0029]

[Table 1]

Low density polyethylene resin: Ube Industries, Ltd.
Linear low density polyethylene, UBE polyethylene SPE2
040F (trade name) MFR 4.0 g / 10 min, density 0.
918 g / cm ³ , polybutene: manufactured by NOF Corporation Average molecular weight: 1000 Acetylated monoglyceride: glycerin diacetmonolaurate (manufactured by RIKEN Vitamin Co., Ltd.) Ethylene-propylene copolymer: PP FL-454 manufactured by Grand Polymer Co., Ltd. (Product name) MFR
2.7 g / min, Propylene-butene copolymer: Tuffmer A4085 (trade name) MFR 4.0 g / 10 manufactured by Mitsui Chemicals, Inc.
Min, density 0.890 g / cm ³

Next, the film was stretched 4.5 times in the machine direction and 4.0 times in the transverse direction at a preheating temperature of 80 ° C. and a stretching temperature of 100 ° C. The transparency (haze), heat resistance, tackiness, pull-out property, and cut property of the obtained film were evaluated by the methods described above. Table 2 shows the evaluation results.

[Example 2] 5.0 times in the vertical direction and 4.times. In the horizontal direction.
A fill was formed in the same manner as in Example 1 except that the film was stretched 0 times. Table 2 shows the evaluation results such as film performance.
Shown in

Example 3 A fill was formed in the same manner as in Example 2 except that the layer ratio was 1: 3: 1. Table 2 shows the evaluation results such as the performance of the film.

Comparative Example 1 Table 2 shows the physical properties of commercially available polyethylene resin wrap films.

Comparative Example 2 4.0 times in the vertical direction and 5.times. In the horizontal direction.
A fill was formed in the same manner as in Example 1 except that the film was stretched 0 times. Table 2 shows the evaluation results such as the performance of the film.

[0036]

[Table 2]

[0037]

The wrapping film of the present invention is excellent in heat resistance, adhesiveness, drawability and cutability, has no unpleasant odor, and has a toxic gas at the time of incineration because the whole film is a polyolefin resin. There is no generation of highly toxic combustion residues, and safety is excellent from environmental issues.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29K 23:00 B29L 9:00 F term (Reference) 3E086 AD13 BA04 BA15 BB15 BB22 BB41 BB57 BB90 CA01 CA17 CA18 CA22 CA25 4F100 AK06A AK06C AK09A AK09C AK64B AK66B AK67B AL03B AL05B BA03 BA06 BA10A BA10C BA13 CA04A CA04C EH20 EJ38 GB15 JA06A JA06C JA07A JA07C JA13A JA13C JA20 JA20B JJ03 JK06 JN01 YY00 YY00A YY00B YY00C 4F207 AA04E AA07 AA11E AA12 AA12E AB07 AG03 AH81 KA01 KB26 KK81 4F210 AA04E AA07 AA11E AA12 AA12E AB07 AG03 AH81 QA02 QA03 QC05 QL01 QN01

Claims (3)

[Claims] 1. A laminate comprising at least three layers in which both surface layers are made of a low-density polyethylene resin and an intermediate layer is made of a propylene-α-olefin copolymer resin, and then rapidly cooled to form a raw film. The anti-film is stretched in the longitudinal direction and the transverse direction in the range of 2 to 5 times each, and the longitudinal stretching ratio /
A biaxially stretched film obtained by stretching in a transverse stretching ratio of 1.1 to 1.5, wherein the film has a total thickness of 5 to 50 μm and a propylene-α-olefin copolymer. A packaging film, wherein the thickness of the intermediate layer made of the united resin is in the range of 10 to 90% of the total thickness of the film. 2. The low-density polyethylene resin of both surface layers is 2 to 20 parts by weight of polybutene (B) and 0.1 to 10 parts by weight of plasticizer (C) based on 100 parts by weight of low-density polyethylene resin (A).
10 parts by weight, and the intermediate layer propylene-α
-The olefin copolymer resin is composed of 70 to 90 parts by weight of a propylene-ethylene random copolymer and propylene-butene.
The packaging film according to claim 1, wherein the mixture is a mixture of 30 to 10 parts by weight of one copolymer. 3. The low-density polyethylene resin (A) in both surface layers is a linear low-density polyethylene having a density of 0.920 g / cm ³ or less and a melt flow rate of 0.5 to 10 g / 10 minutes, Polybutene (B) has a number average molecular weight of 5
The ethylene content in the propylene-ethylene random copolymer of the intermediate layer is 2 to 7% by weight, and the butene-1 in the propylene-butene-1 copolymer
3. The packaging film according to claim 2, wherein the content is in the range of 5 to 30% by weight.