JP2004345135A - Laminated polypropylene resin film and package using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated polypropylene resin film having heat-sealing strength sufficient to pack a heavy article, good in transparency, not curled unidirectionally and suitably usable for a packaging use, and a package using it. <P>SOLUTION: This biaxially stretched laminated polypropylene resin film is constituted by successively laminating a base material layer (A) comprising a crystalline polypropylene resin, an intermediate layer (B) and a heat sealing layer (C) with a melting point of 150°C or below and characterized in that the thickness μa of the base material layer (A), the thickness μb of the intermediate layer (B) and the thickness μc of the heat sealing layer (C) satisfy the relation: μb≥2(μa+μc)μc>μa. The intermediate layer (B) comprises a resin containing at least one kind of an α-olefin copolymer with a cold xylene soluble content of 3 wt.% or below. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３９】
【発明の効果】
本発明の積層ポリプロピレン系樹脂フイルムによれば、重量物を包装するのに十分なヒートシール強度を有し、腰感が良好でカールのない包装用途に好適なフイルムとして用いることができる。
【００４０】
本発明の包装体によれば、重量物の包装が可能な十分なヒートシール強度を有し、腰感がよく取り扱いが良好な包装体とすることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat-sealable laminated polypropylene resin film and a package, and more particularly, has a sufficient heat-sealing strength for packaging a heavy object, has good transparency, and is preferably used for packaging applications. The present invention relates to a heat-sealable laminated polypropylene resin film and a package using such a film.
[0002]
[Prior art]
Conventionally, as a heat sealable film used for packaging, generally, a co-extruded laminated polypropylene resin film in which a low melting point polyolefin resin is laminated on a polypropylene resin, a non-oriented polyethylene resin film or a polypropylene resin. A laminated polypropylene resin film obtained by laminating a film and a stretched polypropylene resin film is often used. However, a co-extruded laminated polypropylene resin film obtained by laminating a low melting point polyolefin resin on a polypropylene resin has a certain degree of sealing strength, but does not have the sealing strength required for packaging heavy objects such as water, and is not stretched. Laminated polypropylene resin film obtained by laminating a polyethylene resin film or a polypropylene resin film and a stretched polypropylene resin film has a sufficient sealing strength, but requires a laminating step using an organic solvent or the like, and is economical. However, it is not preferable from the viewpoint of affecting the global environment.
[0003]
Further, as a measure for improving the sealing strength of a co-extruded laminated polypropylene resin film, a polypropylene resin is used as a base layer, and a linear low-density polyethylene resin is used for a heat-sealing layer (for example, see Patent Document 1). However, since different materials are laminated, the interlayer strength is weak, and the sufficient heat sealing strength intended in the present case cannot be obtained.
[0004]
Furthermore, an adhesive layer is provided between the polypropylene-based resin layer and the linear low-density polyethylene-based resin layer (see, for example, Patent Document 2), but these are inferior in transparency and the appearance of the contents is poor. It worsens and lowers the value as a product. Further, when laminating different kinds of materials, there is a problem in that they are curled in one direction due to a difference in crystallization and a difference in shrinkage during molding into a molten or film-like shape, which hinders bag making and the like.
[0005]
[Patent Document 1]
JP-A-9-207294 [Patent Document 2]
Japanese Patent Application Laid-Open No. H10-76618
[Problems to be solved by the invention]
The present invention solves the problems of the above-mentioned conventional laminated polypropylene film, has a sufficient heat seal strength for packaging heavy objects, has good transparency, and does not curl in one direction. An object of the present invention is to provide a heat-sealing laminated polypropylene resin film that can be suitably used for packaging applications and a package using such a film.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the laminated polyolefin-based film of the present invention comprises a base material layer (A), an intermediate layer (B), and a heat-sealing layer (C) having a melting point of 150 ° C. or less, which are made of a crystalline polypropylene resin. A laminated biaxially stretched polypropylene resin film which is laminated in order, wherein the thickness μa of the base material layer (A), the thickness μb of the intermediate layer (B), and the thickness μc of the heat fusion layer (C) are as follows. Is characterized by satisfying
μb ≧ 2 (μa + μc)
μc> μa
The intermediate layer (B) is characterized by comprising a resin containing at least one kind of α-olefin copolymer having a cold xylene soluble content of 3% by weight or less.
[0008]
In this case, the content of the α-olefin copolymer contained in the intermediate layer (B) is from 10 to 70 parts by weight.
[0009]
In this case, it is preferable that the film is biaxially stretched.
[0010]
Furthermore, in this case, it is preferable that the intermediate layer (B) contains at least one kind of a resin forming the heat sealing layer (C) in an amount of 5 parts by weight or more.
[0011]
Further, in this case, it is preferable that the intermediate layer (B) contains at least one kind of resin forming the base material layer (A) in an amount of 10 parts by weight or more.
Further, in this case, a package using the laminated polypropylene resin film is preferable.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the heat-sealable laminated polypropylene resin film and package of the present invention will be described.
[0014]
In the present invention, the polypropylene resin used for the base material layer (A) may be an n-heptane-insoluble isotactic propylene homopolymer or a polypropylene containing 70% by weight or more of propylene, which is used in ordinary extrusion molding or the like. And other α-olefins. The α-olefin as the copolymerization component is preferably an α-olefin having 2 to 8 carbon atoms, for example, ethylene, butene-1, pentene-1, hexene-1, 4-methyl-1-pentene and the like. Here, the copolymer includes a random or block copolymer. The melt flow rate (MFR) is in the range of 0.1 to 100 g / 10 min, preferably 0.5 to 20 g / 10 min, and more preferably 1.0 to 10 g / 10 min. Further, the crystalline polypropylene resin of the base material layer A may be a mixture of two or more kinds.
[0015]
In the present invention, the resin used for the heat-sealing layer C is a thermoplastic resin having a melting point of 150 ° C. or less, and has a carbon number of 2 to 10 such as ethylene, propylene, butene, pentene, hexene, octene, and decene. A random copolymer or a block copolymer obtained by polymerizing two or more kinds selected from α-olefin-based monomers is preferable, and this copolymer can be used alone or as a mixture.
[0016]
Further, the melting point of the thermoplastic resin forming the heat-sealing layer C is desirably 150 ° C. or less, preferably 60 to 150 ° C. By doing so, sufficient heat seal strength can be given to the heat sealable laminated polypropylene resin film. If the melting point of the thermoplastic resin forming the heat-sealing layer C is less than 60 ° C., the heat resistance of the heat-sealed portion is poor, and if it exceeds 150 ° C., improvement in heat-sealing strength cannot be expected.
[0017]
The MFR is in the range of 0.1 to 100 g / 10 min, preferably 0.5 to 20 g / 10 min, and more preferably 1.0 to 10 g / 10 min.
[0018]
The intermediate layer B must contain at least one kind of α-olefin copolymer having a cold xylene solubles (CXS) of 3% by weight or less. When the α-olefin copolymer having a soluble content of cold xylene of 3% by weight or less is not contained, a problem such as curling occurs.
[0019]
The content of the α-olefin copolymer having a cold xylene soluble content of 3% by weight or less in the intermediate layer B is 10 to 70% by weight, preferably 15 to 60% by weight, and more preferably 20 to 50% by weight. If the amount is less than 10% by weight, the adhesive strength between the respective layers becomes insufficient, and a sufficient sealing strength may not be obtained. If the amount exceeds 70% by weight, the stiffness of the entire film is reduced. In addition, curling and the like may occur, which is not preferable.
[0020]
The resin forming the intermediate layer B is not particularly limited, except for the α-olefin copolymer having a cold xylene-soluble content of 3% by weight or less, but is not particularly limited. It is preferable to contain at least one resin used for C in order to obtain sufficient sealing strength.
The MFR is in the range of 0.1 to 100 g / 10 min, preferably 0.5 to 20 g / 10 min, and more preferably 1.0 to 10 g / 10 min.
[0021]
In the present invention, in the resin forming each layer, various additives and fillers, for example, a heat stabilizer, an antioxidant, a light stabilizer, an antistatic agent, as long as the properties of each layer are not impaired as necessary. Lubricants, nucleating agents, flame retardants, pigments, dyes, calcium carbonate, barium sulfate, magnesium hydroxide, mica, talc, clay and the like can be added. Furthermore, other thermoplastic resins, thermoplastic elastomers, rubbers, hydrocarbon resins, petroleum resins and the like may be blended within a range that does not impair the properties of the film of the present invention.
[0022]
The thickness constitution of each layer of the laminated polypropylene resin film of the present invention needs to satisfy the following expression.
μb ≧ 2 (μa + μc)
μc> μa
Here, μa means the thickness of the base material layer (A), μb means the thickness of the intermediate layer (B), and μc means the thickness of the heat sealing layer (C).
When μb <2 (μa + μc), problems such as insufficient sealing strength and curling occur.
In the case of μc ≦ μa, a curling problem occurs, which is not preferable in handling.
[0023]
More preferably, the thickness of each layer is, for example, 1 to 10 μm for the base material layer (A), 3 to 20 μm for the heat sealing layer (C), and 8 to 100 μm for the intermediate layer (B).
[0024]
The laminated polypropylene resin film of the present invention can be arbitrarily produced by a method known per se, and is not particularly limited. For example, using an extruder suitable for the number of laminations, melt-lamination by T-die method or inflation method, etc., then cool by cooling roll method, water cooling method or air cooling method to form a laminated film, sequential biaxial stretching method, simultaneous biaxial A method of stretching by a stretching method, a tube stretching method or the like can be exemplified.
[0025]
The laminated polypropylene resin film of the present invention may be further laminated with another resin layer, for example, a saponified ethylene-vinyl acetate copolymer, a gas barrier resin layer such as polyvinyl alcohol on the surface of the base material layer A, In addition, lamination between the base layer A and the intermediate layer B and between the intermediate layer B and the heat-sealing layer C are not particularly limited as long as their properties are not impaired.
[0026]
The laminated polypropylene resin film of the present invention can be subjected to a surface treatment in order to improve printability, laminability and the like. Examples of the surface treatment method include, but are not particularly limited to, corona discharge treatment, plasma treatment, flame treatment, and acid treatment. It is preferable to perform a corona discharge treatment, a plasma treatment, and a flame treatment which can be continuously performed and can be easily performed before the winding step in the film manufacturing process.
[0027]
The laminated polypropylene resin film of the present invention has a sufficient heat sealing strength for packaging heavy objects, has good transparency, and is excellent in flour, rice, wheat and other cereals and board / thread konjac, takuan pickles, It is suitable as packaging material for various pickles such as soy sauce pickles, nara pickles, various misos, soup stock, mentsuyu, soy sauce, sauces, ketchup, mayonnaise, etc., and these are also used for paper cartons, tubes, bags, etc. , Cups, standing packs, trays and the like.
[0028]
【Example】
Hereinafter, specific examples of the present invention will be further described with reference to examples, but the present invention is not limited to the following examples unless departing from the gist thereof. The properties in the present specification were evaluated by the following methods.
[0029]
(Heat seal strength)
Under the conditions of a heat seal temperature of 140 ° C., a pressure of 1 kg / cm ² , and a heat seal time of 1 ^second , the heat-sealed layers C of the laminated film were overlapped with each other to perform hot plate sealing, thereby producing a test piece having a width of 15 mm. The 180-degree peel strength of this test piece was measured and defined as heat seal strength (N / 15 mm).
[0030]
(Cold xylene solubles)
After completely dissolving 1 g of the sample in 100 ml of boiling xylene, the temperature is lowered to 20 ° C. and left for 4 hours. Thereafter, this was separated into a precipitate and a solution by filtration, and the filtrate was dried and dried at 70 ° C. under reduced pressure. The weight was measured, and the weight% was determined to be a cold xylene-soluble matter.
[0031]
(Curl properties)
A 100 mm square sheet test piece was prepared, and the degree of curl was measured visually.
：: no curl △: slightly curl ×: marked curl
(Waist: stress at 5% extension)
According to ASTM D882, the stress at 5% elongation in the TD direction was measured.
[0033]
(Example 1)
Using three melt extruders, a propylene homopolymer (density: 0.90 g / cm ³ , MFR: 2.5 g / 10 min, melting point: 157 ° C., cold xylene soluble matter: 3.3% by weight in the first extruder) ) As a base material layer (A) in a second extruder, a propylene / ethylene / butene random copolymer (density 0.89 g / cm ³ , MFR 4.6 g / 10 min, melting point 128 ° C, cold xylene available) 85 wt%, propylene / butene random copolymer density 0.89 g / cm ³ , MFR 9.0 g / 10 min, melting point 130 ° C., cold xylene soluble matter 14.0 wt%) Propylene / ethylene / butene random copolymer (density 0.89 g / cm ³ , MFR 3.1 g / 10 min, melting point 133 ℃, soluble in cold xylene 1.6 wt%) 30 wt%, a propylene homopolymer (density 0.90g ^/ cm 3, MFR2.5g ^/ 10 min, melting point 157 ° C., a cold xylene-soluble portion 3.3 wt%) to 70 wt% The mixed resin thus obtained is used as the intermediate layer B, and the base layer A, the intermediate layer B, and the heat fusion layer C are arranged in the die in this order so that the base layer A / intermediate layer B / heat fusion layer C are formed in the die. After melt co-extrusion by the method, it is cooled and solidified by a chill roll, stretched 4.5 times in the vertical direction and 8 times in the horizontal direction, and the thicknesses of the base material layer A, the intermediate layer B, and the heat fusion layer C are sequentially reduced, respectively. Laminated films of 3 μm, 20 μm and 7 μm were obtained. The obtained laminated film satisfied the requirements of the present invention and had sufficient heat seal strength, stiffness and curl resistance.
[0034]
(Comparative Example 1)
A laminated film was obtained in the same manner as in Example 1, except that the thicknesses of the base material layer A, the intermediate layer B, and the heat sealing layer C were 7 μm, 20 μm, and 3 μm, respectively. The obtained laminated film had a high thickness ratio of the base material layer, was curled, and had poor workability during bag making.
[0035]
(Comparative Example 2)
A laminated film was obtained in the same manner as in Example 1, except that the thicknesses of the base material layer A, the intermediate layer B, and the heat sealing layer C were 3 μm, 15 μm, and 14 μm, respectively. The obtained laminated film had a low thickness ratio of the intermediate layer, had no stiffness, was curled, had poor workability at the time of bag making, and had poor handleability of the actual bag-made package.
[0036]
(Comparative Example 3)
Change in propylene / ethylene / butene random copolymer (density: 0.89 g / cm ³ , MFR: 3.1 g / 10 min, melting point: 133 ° C., cold xylene solubles: 1.6% by weight) as the resin used for the intermediate layer B Example 1 except that a propylene / ethylene / butene random copolymer (density 0.89 g / cm ³ , MFR 4.6 g / 10 min, melting point 128 ° C., cold xylene soluble matter 4.6% by weight) was used. In the same manner as in Example 1, a laminated film was obtained. Since the resin used as the intermediate layer was a raw material having a large amount of soluble components in cold xylene and a large amount of amorphous portion, the obtained laminated film was curled and had poor workability during bag making.
[0037]
The results are shown in Table 1.
[0038]
[Table 1]

[0039]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the laminated polypropylene resin film of this invention, it has sufficient heat-sealing strength for packing heavy goods, and can be used as a film suitable for packaging use which has a good feeling of stiffness and has no curl.
[0040]
ADVANTAGE OF THE INVENTION According to the package of this invention, it has sufficient heat-sealing strength which can pack a heavy thing, and it can be set as a package with good stiffness and good handling.

Claims (6)

A laminated biaxially stretched polypropylene resin film comprising a base material layer (A) made of a crystalline polypropylene resin, an intermediate layer (B), and a heat fusion layer (C) having a melting point of 150 ° C. or less, which are sequentially laminated. A thickness μa of the base material layer (A), a thickness μb of the intermediate layer (B), and a thickness μc of the heat sealing layer (C) satisfy the following relationship:
μb ≧ 2 (μa + μc)
μc> μa
A laminated polypropylene resin film, wherein the intermediate layer (B) is made of a resin containing at least one kind of α-olefin copolymer having a cold xylene soluble content of 3% by weight or less. The laminated polypropylene resin film according to claim 1, wherein the content of the α-olefin copolymer in the intermediate layer (B) is 10 to 70 parts by weight. Film. 3. The laminated polypropylene resin film according to claim 1, wherein the film is biaxially stretched. 4. 4. The laminated polypropylene resin film according to claim 1, wherein the intermediate layer (B) contains at least one kind of a resin forming a heat-sealing layer (C) in an amount of 5 parts by weight or more. 5. Characterized laminated polypropylene resin film. 5. The laminated polypropylene resin film according to claim 1, wherein the intermediate layer (B) contains at least one kind of resin forming a base material layer (A) in an amount of 10 parts by weight or more. 6. The laminated polypropylene resin film according to claim 1, wherein: A package using the laminated polypropylene resin film according to claim 1, 2, 3, 4, or 5.