JPH04229251A - Laminated film having crosswise easily tearable property - Google Patents

Abstract

PURPOSE:To obtain a laminated film which is superior in tear property, tear direction stability, cutting resistance and transparency, has favorable low- temperature heat seal properties and is suitable for high-speed automatic packing. CONSTITUTION:The title film possesses three layer structure of layers A, B, C, which is substantially a laminated film stretched laterally uniaxially, the layer B is constituted of a propylene polymer having a low melt index as the intermediate layer B, a propylene polymer having a high melt index is laminated to a cooling roll surface side of the layer B as the layer C and a heat seal layer comprised of an olefin polymer having a low melting point is laminated to its opposite side as the layer A.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a laminated film for packaging that exhibits suitable heat-sealing properties for automatic packaging of various foods, pharmaceuticals, etc., and is easy to tear when opened.
In particular, it relates to a laminated film that has excellent tearability in the transverse direction and stability in the tear direction, and has good cut resistance during film formation and secondary processing, as well as excellent transparency and low-temperature heat sealability. It is something.

0002

2. Description of the Related Art Automation of film packaging has advanced significantly in recent years, and most of the bonding in this case is done by heat sealing. As automatic packaging machines become faster and more efficient, the low-temperature heat-sealability and stiffness required of packaging films are becoming increasingly strict.

[0003] On the other hand, products packaged in films must be opened before use and are generally torn by hand, so there is an increasing demand for easy tearability.

By the way, the most commonly used heat-sealable film at present is a composite film in which a biaxially stretched film such as polypropylene or polyester is laminated with an unstretched film such as low-density polyethylene or polypropylene as a heat-sealable layer. However, these composite films generally have high tear strength and are difficult to open.

[0005] Packaging films laminated with heat-sealable biaxially oriented polypropylene are also known, but this film has poor tear direction stability from the opening cut, so the tear direction is diagonal from the tear start end. There are disadvantages such as running and scattering the contents such as liquids and powders, or the opening part being cut diagonally, making the opening small and making it difficult to take out fragile contents such as cookies.

[0006]Also, as a means to improve tearability, a method of laminating crystalline low molecular weight polyolefins (Japanese Patent Application Laid-Open No. 18260/1983) has been proposed, but this method does not improve tearability in all directions. However, the stability in the tear direction is not improved at all.

On the other hand, as a heat-sealable polypropylene film having stability in the tear direction, a uniaxially stretched homopolypropylene film is used as a heat-sealing layer.
There is also a product in which this film is laminated onto a base film made of a high melting point polymer (Japanese Patent Publication No. 40551/1983), but this film has poor low temperature heat sealability and has problems in application to high speed automatic packaging machines.

Furthermore, a method using a uniaxially stretched linear low-density polyethylene film (JP-A-59-78844, etc.) is also known, but this film is weak and has poor heat resistance as a single film. , it is difficult to apply it to high-speed automatic packaging machines, and the resin is soft, so if the tearing direction is changed, good tearability cannot be obtained.

Furthermore, a method using a film obtained by stretching a laminate consisting of a heat-sealing layer and a polypropylene base layer in the transverse uniaxial direction is also known (Japanese Unexamined Patent Publication No. 132051/1983); There is a drawback that the film tends to break during subsequent processing.

0010

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems that have been pointed out in conventional automatic packaging films, and its purpose is to provide excellent tearability and tearability. It has directional stability and good cut resistance during film formation and secondary processing, so there is no risk of impairing workability. Furthermore, it has good transparency and low-temperature heat sealability, making it suitable for automatic packaging. The aim is to provide a packaging film that is highly suitable for machines.

[0011]

[Means for Solving the Problems] The structure of the laminated film according to the present invention that can solve the above problems is: (1) a heat-sealable film layer (layer A) made of an olefin polymer having a melting point of 145° C. or less; and (2) a film layer (layer B) made of a propylene polymer that has a higher melting point than the polymer constituting the layer A and has a melt index of 0.5 to 8 at 230°C, and (2) the layer A above. A propylene polymer film layer (layer C) which has a melting point higher than that of the polymer constituting the layer B, and has a melt index at 230°C of 4 to 20, and a melt index higher by one or more than the polymer constituting the layer B. ), and its laminated structure is such that the middle layer is composed of the B layer, and the side that is in contact with the B layer and directly in contact with the cooling roll after melt extrusion is composed of the C layer, and the B layer The gist is that the film is made of a substantially horizontally uniaxially stretched laminated film having a thickness of 10% or more of the total thickness.

0012

[Function] As described above, the present invention is a laminate film having a three-layer structure consisting of layers A, B, and C, which is substantially horizontally uniaxially stretched. In particular, by providing a C layer with a high melt index on the side in contact with the cooling roll after melt extrusion, and laminating a B layer with a low melt index as an intermediate layer, it is possible to achieve something that cannot be achieved with a single layer structure. It has properties such as cut resistance and transparency that cannot be achieved with other materials.

That is, when obtaining a film that is substantially uniaxially stretched horizontally, it is necessary to increase the withdrawal speed after melt extrusion in order to increase productivity, but under such withdrawal conditions, the melt extruded resin The adhesion with the cooling roll deteriorates. As a result, the cooling rate decreases, surface irregularities increase, and transparency also decreases.

[0014] In order to increase transparency, it is possible to use a resin with a high melt index, but if this is done, the film becomes brittle and has poor cut resistance.
Cutting occurs frequently during the next process.

Therefore, in the present invention, films made of two types of propylene polymers having different melt indexes are laminated as described above, and layer B constituting the intermediate layer is made of a polymer with a low melt index. In addition, by laminating a polymer with a high melt index as the C layer on the side that directly contacts the cooling roll, excellent transparency is achieved. Layer A constituting the heat-sealing layer is laminated on the opposite side of layer B to layer C, so as to obtain low-temperature heat-sealability applicable to high-speed automatic packaging machines.

Each of the laminated constituent materials of the laminated film according to the present invention will be described in detail below. First, the olefin polymer constituting the heat-sealable film layer (layer A) should have a melting point of 145°C or lower, more preferably 100°C to 140°C.
are used. If the melting point exceeds 145°C, the heat-sealing temperature must be increased, making it unsuitable for high-speed automatic packaging.

[0017] As the above-mentioned olefin polymer, homopolymers or copolymers of various olefins can be used, and more specifically, for example, low density polyethylene,
Polybutene-1, ethylene/propylene copolymer, copolymer of propylene and α-olefin having 4 to 10 carbon atoms, copolymer of ethylene and α-olefin having 4 to 10 carbon atoms, ethylene, propylene, and α-olefin having 4 to 10 carbon atoms
Preferable examples include a ternary copolymer of No. 10 with an α-olefin, a copolymer of butene with an α-olefin other than butene, and the like.

[0018] In addition, ionomers, ethylene/vinyl acetate copolymers, ethylene/acrylic acid copolymers, etc. can also be used, and in addition to being used alone,
A mixture of two or more types can also be used.

Particularly preferred among the above polymers are:
These include propylene/butene random copolymer, ethylene/butene random copolymer, ethylene/propylene/butene random copolymer, ethylene/propylene random copolymer, linear low density polyethylene, ionomer, and the like.

Next, a polypropylene polymer film layer (
The polymer constituting layer B) has a melt index at 230°C of 0.5 to 8, more preferably 2 to 8.
6 are used. If the melt index is too small, the fluidity during melting is insufficient, resulting in poor film forming processability, and if the melt index is too large, the film becomes brittle and sufficient cut resistance cannot be obtained.

[0021] Furthermore, the polymer constituting the C layer is heated at 230°C.
It is necessary that the melt index is 4 to 20 and higher than that of the polymer constituting layer B by 1 or more, and the more preferable melt index is 7 to 15.
and is 1.5 or more higher than that of layer B.

If the melt index is too small, the transparency of the film will deteriorate due to poor adhesion to the cooling roll, and the commercial value will be lost; if the melt index is too large, the thickness of the C layer will be uneven, making it difficult to form a film. Processability deteriorates. Furthermore, if a material whose melt index at 230° C. is not 1.0 or more higher than that of layer B is used, the flow of layer C within the die is likely to be disturbed, resulting in poor appearance of the entire laminated film.

[0023] Layer B constitutes the center layer of the laminated film, and its thickness should be at least 10%, more preferably at least 30% of the total thickness. When the thickness ratio occupied by the B layer is 10% or less, the cut resistance of the laminated film as a whole becomes poor, and the film is likely to be cut during film formation and processing.

The propylene polymer constituting the B layer and C layer is a propylene-based polymer having a melting point of 140° C. or higher, preferably 150° C. or higher, and has an isotactic index of 85% by weight, for example. Isotactic polypropylene with an ethylene content of 7% by weight or less, an ethylene/propylene copolymer with a propylene content of 9% by weight or less,
Preferred examples include a copolymer of 0% by weight or more of propylene and an α-olefin having 4 to 5 carbon atoms. These propylene polymers may be used alone or in combination of two or more.

[0025] The polymers constituting the above A, B, and C layers may contain other polymers such as low molecular weight thermoplastic resins, antistatic agents, lubricants, and anti-blocking agents within the range that does not impede the required properties of each layer. It is possible to improve the automatic packaging property by incorporating agents and the like.

[0026] The low-molecular thermoplastic resin used here includes natural or synthetic waxes, hydrocarbon resins,
Examples include rosin, dammar, phenolic resin, chlorinated aliphatic hydrocarbon wax, and chlorinated polynuclear aromatic hydrocarbon.

As described above, the laminated film of the present invention has the B layer constituent material as an intermediate layer, the C layer constituent material is laminated on the side that contacts the B layer and directly contacts the cooling roll after melt extrusion, and the opposite layer. Layer A constituent materials are laminated on the surface side, and as a lamination molding method, a coextrusion method, a method in which other laminated constituent materials are melt-extruded and laminated on an unstretched film or sheet, etc. can be adopted. .

[0028] For example, when laminating polyethylene resin as a heat-sealable film layer, it is also effective to interpose an adhesive resin such as maleic anhydride-modified polypropylene between the layers in order to improve interlayer adhesion. .

The laminated unstretched film or sheet thus obtained is 2 to 15 times larger in the transverse direction, preferably 4 to 10 times larger in the transverse direction.
When stretched twice, a laminated film with excellent stability in the tear direction in the transverse direction can be obtained. When the lateral stretching ratio is less than 2 times,
Due to insufficient molecular orientation, stability in the tear direction cannot be sufficiently improved, and on the other hand, stretching 15 times or more is not only technically difficult, but also may result in poor low-temperature heat sealability.

[0030] The stretching method is not particularly limited, but
The most common method is to carry out transverse stretching at 65°C, especially at 100 to 150°C, by tenter stretching.

[0031] In the present invention, uniaxial stretching in the transverse direction imparts molecular orientation and provides stability in the tear direction.Although, as a general rule, there is no substantial stretching in the longitudinal direction, stability in the tear direction This does not preclude longitudinal stretching to about 3 times or less as long as it does not impede.

[0032] In order to impart thermal dimensional stability to the transversely stretched laminated film, it is desirable to heat treat it at 100 to 165°C for about 1 to 60 seconds. Further, this laminated film may be subjected to surface treatment such as corona treatment, if necessary.

[0033] The preferred thickness of the laminated film according to the present invention varies slightly depending on the application, but is usually 5 to 100μ.
The most versatile range is 15 to 60 m.
It is μm.

[0034] The thickness of the heat seal layer is 0.3 to 2
It is preferably in the range of 0 μm, particularly in the range of 0.5 to 15 μm, and in the range of 0.2 to 50% of the total thickness of the laminated film. When the thickness of the heat seal layer is less than 0.5 μm,
It is difficult to obtain sufficient heat-sealability, and if the thickness is more than 20 μm or more than 50% of the total thickness, the stiffness of the entire laminated film becomes weak, reducing suitability for automatic packaging and poor tearability.

The thus obtained laminated film of the present invention has excellent tearability and stability in the tearing direction, as well as excellent transparency and low-temperature heat sealability, and can be used by itself as an automatic packaging film. In addition, it is also possible to laminate other films, metal foil, paper, etc. on the C layer side to create a composite film with properties suitable for the application, such as gas barrier properties, printability, decorative properties, etc. be.

[0036]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples. The measurement method for each data in the examples was as follows. Haze: Measured using a haze tester manufactured by Toyo Seiki Co., Ltd. according to the JIS-K6714 method. Young's modulus: Measured according to ASTM-D-882 method. Tear direction stability: 5m in the longitudinal direction from the edge of the laminated film
An opening cut of 1.5 m was made, and the tearing force was applied at various angles within 60 degrees with respect to the longitudinal direction, and the tear condition was evaluated as follows. ○: Even if the direction of tearing force was changed, the film was torn almost in a straight line in the longitudinal direction. Δ: When the direction of the tearing force deviated from the longitudinal direction, the tearing did not occur in a straight line. ×: No directional tearing in the longitudinal direction. Elmendorf tear strength: Measured according to JIS-P-8116 method. Heat-sealing strength: After heat-sealing with a tilted heat sealer manufactured by Toyo Seiki Co., Ltd. under the conditions of a pressure of 1 kg/cm 2 for 1 second, the peel strength was measured when peeling at a speed of 200 mm/min. Hand-tearability: The laminated film was evaluated as follows based on the degree of difficulty in tearing the laminated film with a fingertip. ○: Easily torn. △: If you put your nails on it and put pressure on it, it would tear. ×: Not torn. Suitability for automatic packaging: Using a horizontal pillow packaging machine manufactured by Fuji Kikai Seisakusho, packaging was carried out at 160° C. and at a rate of 120 pieces/min while automatically supplying packaging materials, and its suitability was evaluated based on the following criteria. ○: Packaging went smoothly. △: Meandering of the film and adhesion to the heater occurred, making it sometimes impossible to wrap the film. ×: Automatic packaging could not be performed continuously due to adhesion to the heater, insufficient heat sealing strength, etc. Cutting resistance: One end of a 50 mm wide, 1000 mm long film was fixed, the other end was hung with a load of 400 g, the height was changed, the load was dropped, and the height at which the film was cut was measured.

Example 1 A terpolymer of ethylene/propylene/butene-1 (layer A) having a melting point of 138°C and isotactic propylene (layer A) having a melting point of 165°C and a melt index of 2.0 at 230°C. B layer), and the melting point is 165°C, 230°C
Isotactic polypropylene (layer C) with a melt index of 10 at °C is melted and coextruded, and layer C is taken off while being in close contact with a cooling roll to form an unstretched three-layer structure consisting of layer A/layer B/layer C. Got the film. then 14
After stretching 8 times in the transverse direction at 0°C, it was heat treated at 150°C for 5 seconds while giving a relaxation rate of 5%. The total thickness of the obtained laminated film was 25 μm, and the respective thicknesses of layer A/layer B/layer C were 5 μm/17 μm/4 μm.

Comparative Example 1 Using the same polymer as the A layer and B layer in Example 1,
Example 1 except that the use of the polymer constituting the C layer was omitted.
Melt coextrusion and transverse uniaxial stretching were performed in the same manner as in A.
A laminated film consisting of layer/B layer was obtained. The total thickness of the obtained laminated film was 25 μm, and the thickness of each layer A/B was 5 μm.
It was μm/20 μm.

Comparative Example 2 Using the same polymer as the A layer and C layer in Example 1,
Example 1 except that the use of the polymer constituting layer B was omitted.
Melt coextrusion and transverse uniaxial stretching were performed in the same manner as in A.
A laminated film consisting of layer/C layer was obtained. The total thickness of the obtained laminated film was 25 μm, and the thickness of each layer A/C was 5 μm.
It was μm/20 μm. Its physical properties are shown in Table 1.

Comparative Example 3 Only the polymer constituting layer A in Example 1 was melt-extruded to obtain an unstretched film of 25 μm.

Comparative Example 4 An unstretched laminated film having the same composition as the layers A, B, and C in Example 1 and having a thickness of 1000 μm was prepared, and then 1
After stretching 5 times in the machine direction at 20°C, stretching 8 times in the transverse direction at 155°C, and then stretching 150 times while giving a relaxation rate of 5%.
A heat treatment was performed at ℃ for 5 seconds to obtain a longitudinally and transversely biaxially stretched laminated film. The thickness structure of each layer in the obtained laminated film is as follows:
It was the same as the laminated film of Example 1. Example 1 above
The physical properties of the films obtained in Comparative Examples 1 to 4 are collectively shown in Table 1.

[0042]

[Table 1] As is clear from Table 1, the laminated film of Example 1 that satisfies the specified requirements of the present invention has transparency, tear direction stability, heat seal strength, hand tearability, automatic packaging suitability, and durability. While all of the cutting properties were good, Comparative Example 1 had poor transparency, Comparative Example 2 had poor cut resistance, and Comparative Examples 3 and 4 had tear direction stability, manual tearability, and automatic packaging suitability. is inferior,
It can be seen that all of these films are insufficient as films for automatic packaging.

[0043]

Effects of the Invention The present invention is constructed as described above, and by forming a horizontally uniaxially stretched film with a three-layer structure in which each layer is made of individually specified polymers, tear properties, stability in the tear direction, and durability can be improved. It has now become possible to provide a packaging laminated film that has excellent cuttability and transparency, has good low-temperature heat sealability, and is suitable for high-speed automatic packaging.

Claims (1)

[Claims] Claim 1: ■ A heat-sealable film layer (layer A) made of an olefin polymer with a melting point of 145° C. or less;
A film layer (layer B) made of a propylene-based polymer having a melt index of 0.5 to 8 at °C;
A propylene polymer film layer (layer C) having a melt index at 30° C. of 4 to 20 and a melt index higher by one or more than the polymer constituting the layer B above.
The laminated structure is such that the intermediate layer is composed of the B layer, and the side that is in contact with the B layer and directly in contact with the cooling roll after melt extrusion is composed of the C layer,
A laminated film that is easily tearable in the transverse direction, characterized in that the thickness of the B layer accounts for 10% or more of the total thickness, and the laminated film is substantially uniaxially stretched in the transverse direction.