JPH0156909B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to coextruded multilayer films. More specifically, the present invention relates to a polypropylene/polyethylene coextruded multilayer film with improved heat sealability and low-temperature impact resistance. Crystalline polypropylene film has tensile strength,
It is widely used in the food packaging field due to its mechanical properties such as rigidity, surface hardness, and impact strength, its optical properties such as gloss and transparency, and its excellent food hygiene properties as it is non-toxic and odorless. There is. However, polypropylene film has a high temperature at which it can be heat-sealed in a single layer, and the appropriate temperature range is narrow, so it is possible to improve heat-sealability by using polypropylene film as a base material and laminating a resin with a low melting point on it. It is being said. Ethylene-based resins such as high-pressure low-density polyethylene and ethylene-vinyl acetate copolymer are widely used as resins used to improve heat-sealing properties, as they can also improve the low-temperature impact resistance of polypropylene films. . However, since polypropylene film and ethylene resin film lack interlayer adhesion, delamination may occur during use. The inventors of the present invention conducted studies to improve this drawback, and found that a specific ethylene film was found between the polypropylene film and the ethylene resin film.
It was found that by interposing an α-olefin copolymer, a multilayer film with good interlayer adhesion between both films, excellent heat sealability, low-temperature impact resistance, easy boilability, etc., was obtained, leading to the present invention. did. That is, the present invention uses polypropylene (A) as an intermediate layer with a melt flow rate of 0.5 to 20 g/
10min, density: 0.910~0.940g/ ^cm3 , X-ray crystallinity: 40~70%, melting point: 115~
Copolymer (B) made from ethylene and α-olefin having 4 to 20 carbon atoms at 130°C, then melt flow rate: 0.5 to 30 g/10 min and density:
High density polyethylene (C) ranging from 0.950 to 0.970 g/ ^cm3 , melt flow rate: 0.5 to 40 g/cm3
High pressure low density polyethylene ^{(D) with a melt flow rate of 0.5 to 30 g/10 min, a density of 0.920 to 0.970 g/cm 3 and} a vinyl acetate content of 30% by weight.
The present invention provides a coextruded multilayer film characterized by laminating ethylene resins selected from the following ethylene/vinyl acetate copolymers (E). Polypropylene used in the multilayer film of the present invention
(A) is a homopolymer of propylene or a copolymer of propylene with up to 15% by weight of one or more other α-olefins, such as ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, etc. Polymers and multicomponent copolymers of propylene, ethylene and up to 5% by weight of polyene components, such as 5-ethylidene-2-norbornene or 5-methylene-2-norbornene or 1,4-hexadiene, usually with a melting point of 130 ℃ or higher and a melt flow rate of 0.5 to 30 g/10 min (ASTM D1238L). The ethylene/α-olefin copolymer (B) used for the intermediate layer of the multilayer film of the present invention has a melt flow rate of 0.5 to 20 g/10 min, preferably 1 to 5 g/10 min (ASTM D1238E), and a density of
0.910 to 0.940 g/10 min, preferably 0.915 to 0.935 g/cm ³ , X-ray crystallinity of 40 to 70%, preferably 50 to 60%, melting point of 115 to 130°C, preferably 115 to 125°C. It is a copolymer of ethylene and an α-olefin having 4 to 20 carbon atoms, preferably 6 to 18 carbon atoms. If the melt flow rate is less than 0.5g/10min, the melt viscosity is large and the surface is likely to become rough during molding, and polypropylene (A) film and ethylene resin (C) described below
It roughens the interface with the film, and if it exceeds 20g/10min, the peel strength will be weak, resulting in a decrease in the strength of the multilayer film. If the density is less than 0.910 g/cm ³ , the interlayer adhesion with the polypropylene (A) film and the ethylene resin film will be strong, but the heat resistance will be poor and there is a risk of interlayer peeling during boiling. If the density exceeds 0.940 g/cm ³ , the effect of improving interlayer adhesion is small and does not meet the purpose of the present invention. There is a correlation between the density of the ethylene/α-olefin copolymer used in the present invention and the degree of crystallinity measured by X-rays, and those with a degree of crystallinity of less than 40% have poor heat resistance and are 70%
If it exceeds 20%, the effect of improving interlayer adhesion is small.
Also, those with a melting point of less than 115°C have excellent interlayer adhesive strength but poor heat resistance, and those with a melting point of 125°C or higher have little effect on improving interlayer adhesive strength. α having 4 to 20 carbon atoms copolymerized with the ethylene
-Olefin specifically includes, for example, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 1-decene, 1-
-tetradecene, 1-octadecene, etc., and 1
It may be used as a seed or a mixture of two or more types. A copolymer of ethylene and propylene has poor interlayer adhesion and does not meet the purpose of the present invention. Also 1
Although a copolymer with -butene has sufficient interlayer adhesion to withstand practical use, a copolymer with an α-olefin having 6 or more carbon atoms is particularly preferred because it increases the mechanical strength and interlayer adhesion of the multilayer film. The ethylene resin used in the multilayer film of the present invention has a melt flow rate (ASTM D1238:
E) is 0.5 to 30g/10min, preferably 1 to 10g/10min and density is 0.950 to 0.970.
g/cm ³ , preferably in the range of 0.953 to 0.965 g/cm ³ , melt flow rate (ASTM D1238:E) of 0.5 to 40 g/10 min;
Preferably 1 to 20g/10min and density
0.910 to 0.930g/cm ³ , preferably 0.915 to 0.930g/cm 3
High pressure low density polyethylene in the range of 0.925g/ ^cm3
(D) or melt flow rate (ASTM
D1238:E) is 0.5 to 30g/10min, preferably 1 to 20g/10min, density is 0.920 to
0.970g/cm ³ , preferably 0.926 to 0.950g/cm ³
and an ethylene/vinyl acetate copolymer with a vinyl acetate content of 30% by weight or less, preferably 20% by weight or less
This is selected from (E). Among them, high-pressure low-density polyethylene (D) and ethylene/vinyl acetate copolymer (E) have excellent film transparency and low-temperature heat-sealability. B) It is preferable because the transparency of the multilayer film laminated with the film interposed therebetween is excellent. The multilayer film of the present invention comprising polypropylene (A), ethylene/α-olefin copolymer (B), and ethylene resin is obtained by a coextrusion method. In addition to the coextrusion method, examples of manufacturing methods for composite films include extrusion lamination, Sand-German tyro-laminate, etc.; Even when laminated, the adhesion between the films is weak and there is a risk of interfacial delamination during use.
A composite film with good performance cannot be obtained. Coextrusion molding methods include a T-die method using a flat die and an inflation method using a circular die. The flat die may be of either a multi-manifold format or a single manifold format using blackboxes. A known die can also be used for the inflation method. The thickness of each layer of the multilayer film of the present invention is not particularly limited, but usually a polypropylene film layer is used.
100 to 1μ, preferably 50 to 10μ, and the intermediate layer of ethylene/α-olefin copolymer layer has a thickness of 50μ
0.5μ to 0.5μ, preferably 30 to 2μ, ethylene resin film 100 to 1μ, preferably 50 to 2μ
The thickness is in the range of 10μ. The multilayer film of the present invention includes polypropylene (A),
A weathering stabilizer is added to either or both of the ethylene/α-olefin copolymer (B) and the ethylene resin.
Various compounding agents, such as heat-resistant stabilizers, antistatic agents, antifogging agents, antiblocking agents, slip agents, lubricants, pigments, dyes, and fluxing agents, which are usually added to polyolefins, can be used for the purpose of the present invention. It may be added as long as it does not cause any damage. In order to obtain a conventional multilayer film made of polypropylene/ethylene resin with strong interlayer adhesion, it is necessary to anchor-coat a preformed polypropylene film with an adhesive and then laminate it with ethylene resin, which requires a long process. In contrast, the multilayer film of the present invention can easily obtain a film with excellent interlayer adhesion by simultaneously extruding polypropylene, ethylene/α-olefin copolymer, and ethylene resin through a three-layer die. It has the advantage of being able to In addition, the multilayer film of the present invention can be used in various applications, such as frozen desserts, breads, marine products, etc., which require cold resistance or flexibility, similar to the conventional two-layer film made of polypropylene/ethylene resin.
It is suitable for packaging vegetables such as ramen noodles and green peppers, square bags for sweets, twist bags, and general food packaging. EXAMPLES Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples in any way unless it goes beyond the gist thereof. Example 1 Melt flow rate 7.0g/10min (ASTM
D1238L) polypropylene (PP-I), melt flow rate 2.35g/10min (ASTM D1238E),
Ethylene/4-methyl-1-pentene copolymer (EMC-I) and melt with a density of 0.922 g/cm ³ , a crystallinity of 51% by X-rays, and a melting point of 123°C (with peaks at 118°C and 105°C) Flow rate 2.5g/
10 min (ASTM D1238E), ethylene-vinyl acetate copolymer (EVA-I) with a density of 0.940 g/cm ³ and a vinyl acetate content of 19% by weight was extruded using a 65 mmφ extruder (cylinder temperature 240°C) using EMC-I as an intermediate layer. , 40
mmφ extruder (cylinder temperature 220℃) and 65mm
After melting in a φ extruder (cylinder temperature 220℃), it is fed to a multi-manifold type three-layer T-die (die temperature 220℃) to form a PP-I layer of 20μ, an EMC-
A coextruded multilayer film with a 5μ I layer and a 15μ EVA-I layer was obtained. Next, the physical properties were evaluated by the following method. Haze (%): ASTM D1003 Tensile test: ASTM D638 Impact strength (Kg・cm/cm): ASTM D3420 Peel strength of heat-sealed part (g/15mm): Overlap film surfaces, 90℃, 100℃, 110℃ , 120℃,
It was heat sealed at a temperature of 130° C. and 140° C. and a pressure of 2 Kg/cm ² for 1 second using a sealing bar with a width of 5 mm, and then allowed to cool. A test piece with a width of 15 mm was cut from this, and the strength was measured when the heat-sealed portion was peeled off at a crosshead speed of 200 mm/min. Flexibility (number of pinholes: 282.6mm x 220mm)
The sample was mounted on a cylinder with a diameter of 90 mmφ and a movable disk and a fixed disk with an interval of 180 mm, and the speed was 50 times/min.
After applying a reciprocating twisting motion 1500 times in an atmosphere of -10°C, the number of pinholes generated in the sample was measured. The stroke of the movable disc is 152.4mm.
The specimen was twisted by 440 degrees while traveling 88.9 mm, and then straight forward by 63.5 mm, bending the specimen. Boiling water resistance: overlapping film surfaces, 110℃, 120℃
℃, 130℃, 140℃ temperature, 2Kg/ ^cm2 pressure 1
Heat sealing was performed for 2 seconds using a sealing bar with a width of 5 mm. This sample was left in boiling water at 100°C for 30 minutes, then taken out and allowed to cool. A 15 mm wide test piece was cut from this, and the crosshead speed was 200 mm/
It is expressed as the strength when the heat-sealed part is peeled off at min. The results are shown in Table 1. Example 2 Melt flow rate 4.7g/10min (ASTM D1238:E) instead of EVA-I used in Example 1
The same procedure as in Example 1 was carried out except that high-pressure low-density polyethylene (LDPE-I) having a density of 0.921 g/cm ³ was used. The results are shown in Table 1. Example 3 Instead of EMC-I used in Example 1, the melt flow rate was 2.4 g/10 min, the density was 0.921 g/cm ³ ,
X-ray crystallinity 50% and melting point 124°C (118
The same procedure as in Example 1 was conducted except that ethylene/1-octene copolymer (EO-I) (with peaks at 105°C and 105°C) was used. The results are shown in Table 1. Comparative Example 1 Instead of EMC-I used in Example 1, melt flow rate was 3.6 g/10 min, density was 0.890 g/cm ³ ,
The same procedure as in Example 1 was carried out except that an ethylene/1-butene copolymer (EB-I) having a crystallinity of 17% by X-rays and a melting point of 72°C was used. The results are shown in Table 1. Comparative Example 2 Using LDPE-I and PP-I used in Example 2, a two-layer film consisting of LDPE-I/PP-I was molded in the same manner as in Example 1. However, the 40 mmφ extruder for the intermediate layer used in Example 1 was not used.
The results are shown in Table 1. Reference example: After applying an isocyanate adhesive (trade name: Titabond 600, manufactured by Nippon Soda) to a preformed film made of PP-I, a film made of PP-I/LDPE-I is made by extrusion laminating with LDPE-I. A layered film was obtained. The two-layer film was then evaluated using the method described in Example 1. The results are shown in Table 1.

【table】

【table】

Claims (1)

[Claims] 1. Polypropylene (A), as an intermediate layer, melt flow rate: 0.5 to 0.5
20g/10min, density: 0.910 to 0.940g/cm ³ ,
Crystallinity by X-ray: 40-70% and melting point:
Copolymer (B) consisting of ethylene and α-olefin having 4 to 20 carbon atoms at 115 to 130°C, then melt flow rate: 0.5 to 30 g/
10min and density: high density polyethylene (C) in the range of 0.950 to 0.970g/ ^cm3 , melt flow rate:
0.5 to 40g/ ^cm3 and density: 0.910 to 0.930
High-pressure low density polyethylene (D) in the range of g/cm ³ and melt flow rate: 0.5 to 30 g/cm ³ , density: 0.920 to 0.970 g/cm ² and vinyl acetate content of 30% by weight or less. copolymer
A coextruded multilayer film characterized by laminating ethylene resins selected from (E).