JP2001105550A - Laterally tearable laminated polyolefin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laterally tearable laminated polyolefin film which has good tearability which is not deteriorated at relatively high temperatures and tear direction properties, has enough flexibility even at low temperatures, and does not discharge harmful substances when burned. SOLUTION: A laminated film has a substantially laterally uniaxially oriented propylene-α-olefin copolymer skin film layer (A layer) and a substantially laterally uniaxially oriented base film (B layer) containing more α-olefin units than the A layer as basic constituents.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a laminating polyolefin film having a transverse tearing property, in particular, excellent transverse tearing properties and tearing directionality. The present invention also relates to a transversely tearable laminated polyolefin film having flexibility, which is suitable for packaging foods and pharmaceuticals, and can economically provide a packaging material which can be easily opened. It is about.

[0002]

2. Description of the Related Art Products wrapped in a film must be opened at the time of use, and are generally torn by hand, and the demand for easy tearing is increasing. In addition, a biaxially stretched polypropylene laminated film may be used, but bags formed from this film are easily cut open from the opening for opening, but are difficult to tear with directionality, and when packaging liquid or powder. If the cut reaches the entire bag and the contents leak, or if fragile confectionery such as cookies are wrapped, the cut will be cut diagonally and the take-out will be small, making it difficult to take out the contents without breaking it. There are difficulties such as becoming.

[0003] Furthermore, in order to facilitate opening, an opening for opening is often provided on a bag or an outer package, but it is often difficult to tear the bag in a directional manner. A method of laminating a crystalline low molecular weight polyolefin film layer on a polypropylene film layer in order to improve tearability (Japanese Patent Application Laid-Open No. 58-18 / 1983)
No. 260) is known, but the laminated film obtained by this method has hand-cutting properties in any direction.
As in the case of the film, the film cannot be torn with directionality. Further, there is a method using a uniaxially stretched homopolypropylene film as a polypropylene film having a tearing direction, but it is poor in flexibility and cannot be used especially at a low temperature.

Further, a method using a uniaxially stretched linear low-density polyethylene film (JP-A-59-78844, etc.) is also known, but is stiff and poor in tearability when used at high temperatures. Further, since the resin is flexible, there is a problem that when the tearing direction is changed, sufficient tearability cannot be obtained.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the conventional easily tearable film, and has a good tearability and a good tearing direction. Provided is a transversely tearable laminated polyolefin film that does not deteriorate tearability even at high temperatures, has sufficient flexibility even at low temperatures, and does not discharge harmful substances during combustion. Aim.

[0006]

In order to achieve the above object, a transversely tearable laminated polyolefin film according to the present invention comprises a polypropylene-based polymer comprising substantially uniaxially stretched propylene and an α-olefin other than propylene. A substantially uniaxially stretched base comprising a combined skin film layer (layer A) and a polypropylene-based polymer having a higher proportion of α-olefins other than propylene in the constituent polymer than the polymer constituting the layer A And a film layer (B layer). Here, the ratio of α-olefins other than propylene means the ratio (weight ratio) of α-olefins other than propylene to the total amount of propylene and α-olefins other than propylene in the polypropylene-based polymer.

The transversely tearable laminated polyolefin film of the present invention having the above-mentioned structure has good tearability and tearing directionality, and does not deteriorate even at a relatively high temperature. Has sufficient flexibility and does not emit harmful substances during combustion.

[0008] In this case, the layer A and the layer B can be a film layer obtained by stretching both in the transverse direction by 2 to 15 times.

In this case, the thickness of the layer A is 0.3 to 2
It can be 0 μm.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of a transversely tearable laminated polyolefin film of the present invention will be described.

The transversely tearable laminated polyolefin film of the present invention is substantially uniaxially stretched, and comprises a polypropylene-based polymer skin film layer (layer A) comprising propylene and an α-olefin other than propylene; A transversely tearable laminated polyolefin having, as a basic structure, a base film layer (B layer) substantially horizontally uniaxially stretched made of a polypropylene-based polymer having a higher proportion of α-olefins other than propylene than the polymer constituting Film.

In the present invention, a polypropylene polymer skin film layer substantially composed of propylene and an α-olefin other than propylene is laminated on at least one surface of the base film layer.

In the present invention, the polymer forming the skin film layer has a melting point of 140 ° C. or higher, preferably 1
A polymer mainly composed of propylene at 50 ° C. or higher,
For example, an ethylene / propylene copolymer having an ethylene content of 9% by weight or less, a copolymer of propylene having a propylene content of 90% by weight or more and an α-olefin having 4 to 6 carbon atoms, and the like are preferable. Also, mixtures of these polymers are used. Here, the proportion of propylene residues in the polypropylene-based polymer (including a mixture of polymers) forming the skin film layer is usually 93%.
To 99% by weight, preferably 95 to 98% by weight, and the remainder is occupied by α-olefin residues other than propylene residues.

In the present invention, the polypropylene polymer constituting the substantially uniaxially stretched base film layer (layer B) mainly comprises propylene having a melting point of 140 ° C. or higher, preferably 150 ° C. or higher. It is a polymer, the melting point of the polypropylene-based polymer forming the skin film layer depends on the type of the propylene-α-olefin copolymer used, but as measured by DSC, it is almost the same or less It is usually about 20 ° C. lower. Further, the proportion of α-olefins other than propylene is larger than that of the polymer constituting the polypropylene-based polymer skin film layer. For example, ethylene / propylene copolymer having an ethylene content of 9% by weight or less, propylene is 90% by weight or more. A copolymer of propylene with an α-olefin having 4 to 6 carbon atoms or a mixture of these weights is also used. Here, the proportion occupied by propylene residues in the polypropylene-based polymer (including the case of being a polymer) forming the base film layer is usually 90 to 98% by weight, preferably 92 to 97% by weight, and the remainder is Α-olefin residues other than propylene residues occupy.

When selecting a raw material polymer for forming the skin film layer and the base film layer, as described above, the amount of α-olefin other than propylene in the polypropylene-based polymer for forming the skin film layer depends on the amount of the base film layer. Α- other than propylene in the propylene polymer to be formed
It must be less than the amount of olefin. If this is not satisfied, the cut properties are poor or the flexibility is poor. As the α-olefin other than propylene in the present invention, ethylene, butene, pentene, hexene, heptene, octene and the like can be used.

Each of the above-mentioned polypropylene polymers forming the base film layer and the skin film layer comprises:
Intrinsic viscosity (measured with 135 ° C. tetralin solution) of 1.6 to
It is preferably 3.0 deciliters / g, particularly preferably 1.
It is preferably from 6 to 2.5 deciliters / g. When the intrinsic viscosity is less than 1.6 deciliter / g, it is difficult to obtain a packaging material composed of a transparent transversely tearable laminated polyolefin film. On the other hand, when the intrinsic viscosity exceeds 3.0 deciliter / g, the extrudability decreases and the appearance is poor. It becomes a packaging material with low gloss and low commercial value.

In the present invention, the polypropylene polymer forming the base film layer includes other polymers such as a thermoplastic resin having a low molecular weight so as not to lower the mechanical or thermal properties of the polypropylene polymer. Agent, lubricant,
An automatic packaging property can be improved by including a blocking inhibitor or the like. As a low molecular weight thermoplastic resin, natural or synthetic wax, hydrocarbon resin, rosin, dammar, phenol resin, chlorinated aliphatic hydrocarbon wax,
And chlorinated polynuclear aromatic hydrocarbons.

The method for producing the transversely tearable laminated polyolefin film of the present invention includes coextrusion in which a polymer for forming a base film layer and a skin film layer is extruded from a separate extruder, and a composite stream is formed and molded in a molten state. And an extrusion lamination method in which the other film-forming polymer is melt-extruded and adhered to an unstretched film. Further, an adhesive resin layer such as maleic anhydride-modified polypropylene may be laminated between the two layers in order to improve the adhesion between the two layers.

The unstretched laminated film obtained by the above method is stretched 2 to 15 times, preferably 4 to 10 times in the transverse direction. When the stretching ratio is 2 times or less, there is a disadvantage that a sufficient molecular orientation cannot be obtained and the film cannot be linearly torn in the stretching direction.
Further, it is difficult to stretch the film more than 15 times in the transverse direction, and the flexibility of the obtained film at low temperature is deteriorated. Although the stretching method is not particularly limited, 90 to 165 ° C,
In particular, it is preferable to perform transverse stretching by a tenter stretching method at 100 to 150 ° C.

Although it is not substantially stretched in the longitudinal direction,
It does not prevent stretching to 3 times or less to the extent that the directionality of the tear is not lost.

The laminated polyolefin film obtained by stretching is subjected to a temperature of 100 to 165 ° C. in order to provide thermal dimensional stability.
For 1 to 60 seconds. Further, the film surface may be subjected to a surface treatment such as a corona discharge treatment as necessary.

The thickness of the laminating polyolefin film in the transverse direction according to the present invention is arbitrarily set depending on the application, but is usually in the range of 5 to 100 μm, and is generally 15 to 100 μm.
60 μm. The thickness of the inner skin film layer is preferably 0.3 to 20 μm, particularly preferably 0.5 to 15 μm, and is in the range of 0.2 to 50% of the total thickness of the transversely tearable laminated polyolefin film. If the thickness of the skin film layer is less than 0.3 μm, transverse tearing at high temperatures cannot be obtained, and if it is greater than 20 μm or more than 50% of the total thickness, the transverse tearing laminated polyolefin film will be obtained. The stiffness increases, the flexibility decreases, and the film breaks at low temperatures.

The transversely tearable laminated polyolefin film of the present invention can be used alone or as a composite film laminated with another film, aluminum foil, paper, etc., and has excellent transverse tearability and tear directionality. In addition, the packaging material can be stiff and have properties suitable for the application, for example, gas barrier properties, printing properties, decorative properties, and the like.

FIG. 1 (a) shows a lateral tearing laminated polyolefin film of the present invention. FIG. 1 (a) shows a lateral tearing film obtained by laminating a skin film layer A on one side of a base film layer B made of a polypropylene polymer. FIG. 1B is a side view of a functional laminated polyolefin film, and FIG. 2B shows a laterally tearable laminated polyolefin film in which a skin film layer A is laminated on both sides of a base film layer B made of a polypropylene-based polymer. (A) and (b) of FIG.
Is a basic lamination structure of the transverse tearable laminated polyolefin film of the present invention. (C) is an example in which a stretched film or paper is laminated on one side of the transverse tearable laminated polyolefin film shown in (a) via an adhesive, C is an adhesive layer, and D is a stretched film or paper. Layer. (D) shows an example in which an aluminum foil E and a stretched film or paper D are sequentially laminated on one surface of the transverse tearable laminated polyolefin film of (a) by an adhesive layer C.

Next, the present invention will be further described with reference to examples. In addition, the measuring method of each data in an Example was performed as follows.

1) MFR Measured according to ASTM-D-1238 method.

2) Tear resistance Measured according to JIS-P-8116 method.

3) Young's modulus Measured according to ASTM-D-882 method.

4) Direction of tearing A transversely tearable laminated polyolefin film is provided with a 5 mm opening cut in the longitudinal direction from the end of the laminated polyolefin film, and the force direction angle of the tear is changed within 60 ° with respect to the longitudinal direction. The film was torn, and the condition was evaluated as follows. ：: Even when the direction of the tearing force was changed, tearing occurred almost straight in the longitudinal direction. C: When the force direction of the tear deviated from the longitudinal direction, the tear did not occur in a straight line. X: It did not tear with the directionality in the longitudinal direction.

5) Hand tearability Evaluation was made as follows according to the difficulty of tearing when the laterally tearable laminated polyolefin film was torn with a fingertip.
(Evaluated at normal temperature of 23 ° C. and high temperature of 40 ° C.) ：: easily torn. Δ: The nail was set up, and it was torn when reinforced. ×: did not tear.

6) Flexibility A sensitivity test was conducted for flexibility at 0 ° C. ：: Soft △: Medium ×: Hard

(Example 1) A mixture of 75% by weight of MFR2.5 isotactic polypropylene and 25% by weight of an MFR2.7 ethylene-propylene copolymer (ethylene content 9% by weight) was used as a base film layer resin. As a skin film layer resin, 100 parts by weight of a mixture of 85% by weight of isotactic polypropylene having an MFR of 2.5 and 15% by weight of an ethylene / propylene copolymer having an MFR of 2.7 (an ethylene content of 9% by weight) was mixed with 0.1 part of silica. A mixture of 3 parts by weight was used.

Each of the above resins is co-extruded with two extruders,
A three-layer unstretched film having a base film layer of 272 μm and a skin film layer (total) of 48 μm was obtained. Then 15
The film was stretched 8 times in the transverse direction at 0 ° C. and heat-treated at 150 ° C. for 5 seconds while giving a relaxation rate of 5%.

The obtained laminated polyolefin film has a total thickness of 40 μm, and has physical properties as shown in Table 1.
The tearing property in the transverse direction, the directionality of the tearing, the tearing property at a high temperature, and the flexibility at a low temperature were also good.

(Comparative Example 1) The base film layer resin used was the same polymer mixture as in Example 1, and the skin film layer was MFR2.5 isotactic polypropylene 5.
0% by weight, 50% by weight of an ethylene / propylene copolymer having an MFR of 2.7 (ethylene content: 9% by weight) 10
A mixture of 0.3 parts by weight of silica and 0 parts by weight was used.

Each of the above resins was formed into a film and stretched in the same manner as in Example 1 to obtain a laminated polyolefin film having a thickness of 40 μm. The physical properties are as shown in Table 1. Although the flexibility at low temperatures was excellent, the tearability at high temperatures was poor, and the desired cut properties could not be obtained.

Example 2 A mixture of 80% by weight of MFR2.5 isotactic polypropylene and 20% by weight of an MFR2.7 ethylene-propylene copolymer (ethylene content 9% by weight) was used as a base film layer resin. 0.3 parts by weight of silica based on a mixture of 85% by weight of MFR2.5 isotactic polypropylene and 15% by weight of an ethylene / propylene copolymer (ethylene content 9% by weight) of MFR2.7 as a skin film layer resin And a film was formed and stretched in the same manner as in Example 1.

Comparative Example 2 An unstretched laminated film having a thickness of 1600 μm was prepared by the same resin composition and the same film forming method as in Example 1 for the base film layer and the skin film layer, and then stretched 5 times in the longitudinal direction at 120 ° C. And at 150 ° C for 8
The sheet was heat-treated at 150 ° C. for 5 seconds while being stretched twice to give a relaxation rate of 5%. The obtained laminated polyolefin film was a biaxially stretched laminated film having a total thickness of 40 μm, and the physical properties were as shown in Table 1 and were inferior in tear directionality, hand-cutting property and flexibility.

Comparative Example 3 Using only the base film layer of Example 1, a film having a thickness of 40 μm was obtained by the same film forming and stretching method. Although excellent in flexibility at low temperatures, tearability was poor at both normal temperature and high temperature.

Comparative Example 4 A 40 μm film was obtained by the same film forming and stretching method as in Example 1 using only MFR2.5 isotactic polypropylene (100% by weight). Although it was excellent in hand-cutting property and directionality at high temperature, it was inferior in flexibility.

As is clear from Table 1, the transverse tearable laminated polyolefin film of the present invention has good tearing directionality, hand-cutting properties at high temperature and flexibility, while those of the comparative examples are not so good. Poor tearing direction, hand-cutting properties or flexibility, resulting in undesired results when packaged.

[0042]

[Table 1]

[0043]

According to the transversely tearable laminated polyolefin film of the present invention, it has good tearability and tear directionality, and does not deteriorate even at a relatively high temperature.
In addition, it has sufficient flexibility even at low temperatures, and does not emit harmful substances during combustion.

[Brief description of the drawings]

FIG. 1 (a) is a cross-sectional view showing one example of a transversely tearable laminated polyolefin film of the present invention. (B) It is sectional drawing which shows the other example of the transverse direction lamination | stacking polyolefin film of this invention. (C) It is sectional drawing which shows the example of the transverse direction tearing laminated polyolefin film which laminated | stacked the stretched film or paper on one side of the transverse direction tearing laminated polyolefin film of (a) figure. (D) It is sectional drawing which shows the example of the lateral direction tearing laminated polyolefin film which laminated | stacked the aluminum foil and the stretched film or paper on one side of the lateral direction tearing laminated polyolefin film of (a) figure.

[Explanation of symbols]

 A skin film layer B base film layer C adhesive layer D stretched film or paper E aluminum foil

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F100 AK07A AK07B AK64A AK64B AK66A AK66B AL05A AL05B BA02 BA10A BA10B BA16 BA27 EJ37A EJ37B GB15 GB23 GB66 JA20A JA20B JK03 YY00A YY00B

Claims (3)

[Claims] 1. A polypropylene-based polymer skin film layer (layer A) comprising substantially horizontally uniaxially stretched propylene and an α-olefin other than propylene, and a polymer constituting the layer A rather than the polymer constituting the layer A Α other than propylene in
A substantially uniaxially stretched base film layer (B) made of a polypropylene-based polymer having a high olefin content;
Layer) as a basic structure. 2. Both the A layer and the B layer are 2-1 to 2 in the lateral direction.
The transversely tearable laminated polyolefin film according to claim 1, which is stretched 5 times. 3. The transversely tearable laminated polyolefin film according to claim 1, wherein the layer A has a thickness of 0.3 to 20 μm.