JP2005104152A - Heat-sealable laminated polypropylene resin film and package - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-sealable laminated polypropylene resin film having heat-sealing strength sufficient to package a heavy article, good in stiffness feeling, capable of applying printing to a thermowelding layer and suitably usable in packaging, and a package using it. <P>SOLUTION: This heat-sealable laminated polypropylene resin film comprises a laminate having at least a three-layered structure composed of a base material layer comprising a crystalline polypropylene resin, an intermediate layer and the thermowelding layer with a melting point of 150°C or below and is characterized in that each of the tensile moduli in both directions crossing mutually at a right angle of the film is 1.45 GPa or above, the heat-sealing strength thereof is 10 N/15 mm or above and the wet tension of the surface of the thermowelding layer is 31 mN/m or above. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-sealable laminated polypropylene-based resin film and a package, and more specifically, has a heat-seal strength sufficient for packaging heavy objects, has good transparency, and is suitably used for packaging applications. The present invention relates to a heat-sealable laminated polypropylene resin film and a package using such a film.

  Conventionally, heat-sealable films used for packaging are generally co-extruded laminated polypropylene resin films, unstretched polyethylene resin films, or polypropylene resins obtained by laminating low melting point polyolefin resins to polypropylene resins. A laminated polypropylene resin film obtained by laminating a film and a stretched polypropylene resin film is often used. However, co-extrusion laminated polypropylene resin film in which low melting point polyolefin resin is laminated on polypropylene resin has some degree of seal strength, but does not have enough seal strength to package heavy objects such as water, and is not stretched A laminated polypropylene resin film in which a polyethylene resin film or a polypropylene resin film and a stretched polypropylene resin film are laminated has sufficient sealing strength, but requires a laminating process using an organic solvent, etc. Moreover, it is not preferable from the aspect of influence on the global environment.

  In addition, as a measure for improving the sealing strength of a co-extruded laminated polypropylene resin film, there is an example in which a polypropylene resin is used as a base layer and a linear low density polyethylene resin is used in a heat-sealing layer (for example, patents) Reference 1).

  However, since different materials are laminated, the interlayer strength is weak, and the sufficient heat seal strength intended in this case cannot be obtained.

  In addition, there is an adhesive layer provided between a polypropylene resin layer and a linear low density polyethylene resin layer (see Patent Document 2).

However, since these are laminated with a polyethylene resin, the feeling of the film is lost, and the handleability at the time of bag making processing and after filling the contents is hindered. In addition, what is shown here generally prints on the front side of the bag when it is made into a package, which loses the glossiness of the film and lowers the commercial value.
Japanese Patent Laid-Open No. 9-207294 Japanese Patent Laid-Open No. 10-76618

  The present invention solves the problems of the above-mentioned conventional laminated polypropylene film, has sufficient heat seal strength to package heavy objects, has a good feeling of waist, and can be printed on a heat-sealing layer. It is an object of the present invention to provide a heat-sealable laminated polypropylene resin film that can be suitably used for packaging applications and a packaging body using such a film.

  In order to achieve the above object, the packaging film of the present invention comprises a base material layer made of a crystalline polypropylene-based resin, an intermediate layer, and a laminate composed of three or more layers having a heat-sealing layer having a melting point of 150 ° C. or lower. A polypropylene-based resin film having a tensile modulus of elasticity of 1.45 GPa or more in each direction perpendicular to the film, a heat seal strength of 10 N / 15 mm or more, and a wetting tension on the surface of the heat-sealing layer of 31 mN / m or more. It is characterized by being.

  That is, by setting the tensile modulus of elasticity in both directions perpendicular to the film to 1.45 GPa or more, it is possible to give a feeling of waist to the film, and by making the heat seal strength 10 N / 15 mm or more, A substantial strength capable of packaging heavy objects can be ensured. Moreover, by setting the wetting tension on the surface of the heat-sealing layer to 31 mN / m or more, the wettability and adhesion with the ink are improved, and printing can be performed on the heat-sealing layer.

  The heat-sealable laminated polypropylene resin film of the present invention having the above-described structure has sufficient heat-seal strength to wrap heavy objects, has good handling of the package, and improves the appearance during product display. be able to.

  In this case, the film is preferably biaxially stretched.

  Furthermore, the package which uses the said film is also included by this invention.

  The heat-sealable laminated polypropylene resin film of the present invention has sufficient heat-seal strength to wrap heavy objects, has a good feeling of waist, can be printed on a heat-sealing layer, and is suitable for packaging applications It can be used as a secure film.

  The package of the present invention is a package that has sufficient heat seal strength capable of packaging heavy items, has a good waist feeling, is easy to handle, and has a glossy feeling.

  Hereinafter, embodiments of the heat-sealable laminated polypropylene resin film and the package of the present invention will be described.

  In the present invention, the crystalline polypropylene resin used for the base material layer is an isotactic propylene homopolymer used in ordinary extrusion molding or the like or a co-polymer with another α-olefin containing 70% by mass or more of propylene. It may be a polymer, more preferably n-heptane insoluble. The insolubility of n-heptane indicates the crystallinity of polypropylene and at the same time indicates the safety when used as a food packaging. It is a preferred embodiment to use one having an elution amount of 150 ppm or less when extracted at 25 ° C. for 60 minutes (30 ppm or less when the operating temperature exceeds 100 ° C.).

  The α-olefin as the copolymerization component is preferably an α-olefin having 2 to 8 carbon atoms, such as ethylene, butene-1, pentene-1, hexene-1, 4-methyl-1-pentene. Here, the copolymer includes a random or block copolymer. Moreover, a melt flow rate (MFR) is 0.1-100 g / 10min, Preferably it is 0.5-20 g / 10min, More preferably, the thing of the range of 1.0-10 g / 10min can be illustrated. Further, the crystalline polypropylene resin of the base material layer may be a mixture of two or more.

  In the present invention, the wetting tension on the surface of the heat-sealing layer needs to be 31 mN / m or more, more preferably 34 mN / m or more. If the wetting tension is less than 31 mN / m, ink adhesion during printing is not sufficient. Further, if the wetting tension is greater than 45 mN / m, the heat seal strength is lowered, which is not preferable.

  The resin used for the heat-sealing layer is a thermoplastic resin having a melting point of 150 ° C. or lower, and an α-olefin monomer having 2 to 10 carbon atoms such as ethylene, propylene, butene, pentene, hexene, octene, and decene. A random copolymer or block copolymer obtained by polymerizing two or more selected from the above is preferred. These copolymers can be used alone or in combination. Particularly preferred as the resin used for the heat-sealing layer is a propylene-α-olefin random copolymer, and more preferably a propylene-butene random copolymer. This is because the use of a propylene-α-olefin random copolymer further improves the fusing power during heat sealing.

  The propylene-α-olefin random copolymer used for the heat-sealing layer has a cold xylene soluble content of 10% by mass or more, more preferably 11% by mass or more, and further preferably 12% by mass or more. It is desirable to use a material having a mass% or less, more preferably 70 mass% or less, and still more preferably 60 mass% or less. This is because the use of a component having a cold xylene-soluble content of 10% by mass or more can suppress a decrease in heat seal strength after corona treatment of the heat-fusible layer. On the other hand, when the soluble content of cold xylene exceeds 80% by mass, the decrease in heat seal strength after corona treatment increases, and further, blocking or the like tends to occur. Here, the cold xylene-soluble matter means that 1 g of a sample is completely dissolved in 100 ml of boiling xylene, then the temperature is lowered to 20 ° C., left to stand for 4 hours, and then separated into a precipitate and a solution. The mass when dried and dried at 70 ° C. under reduced pressure is measured, and this is expressed as mass% relative to 1 g of the test sample. The cold xylene-soluble component can be controlled by appropriately setting the molecular weight of the resulting propylene-α-olefin random copolymer, the type of α-olefin to be copolymerized, the content, and the like.

  Further, the melting point of the thermoplastic resin forming the heat-sealing layer is 150 ° C. or less, preferably 60 to 150 ° C. By using such a thermoplastic resin, sufficient heat seal strength can be imparted to the heat sealable laminated polypropylene resin film. When the melting point of the thermoplastic resin forming the heat-sealing layer is less than 60 ° C., the heat resistance of the heat-sealed part becomes inferior, and when it exceeds 150 ° C., improvement in heat seal strength cannot be expected. The MFR of the thermoplastic resin forming the heat-sealing layer is preferably 0.1 to 100 g / 10 min, more preferably 0.5 to 20 g / 10 min, and still more preferably 1.0 to 10 g / 10 min.

  The resin used for the intermediate layer is not particularly limited, but preferably contains at least one α-olefin copolymer having a cold xylene soluble content (CXS) of 3% by mass or less. When the α-olefin copolymer having a cold xylene soluble content of 3% by mass or less is not included, the interlayer strength between the base material layer and the heat fusion layer tends to be lowered. Further, the blending amount of the α-olefin copolymer having a cold xylene soluble content of 3% by mass or less in the intermediate layer is preferably 10 to 70% by mass, and more preferably 15 to 60% by mass. Here, if the amount is less than 10% by mass, the adhesive strength between the respective layers may be insufficient, and a sufficient sealing strength may not be obtained. If the amount exceeds 70% by mass, the entire film is lowered. In some cases, it is not preferable. Here, the cold xylene solubles can be determined by the method described above.

  In addition to the α-olefin copolymer having a cold xylene soluble content of 3% by mass or less, the resin forming the intermediate layer contains at least one type of resin used for the base material layer. It is preferable in obtaining. The MFR of the resin forming the intermediate layer is preferably 0.1 to 100 g / 10 min, more preferably 0.5 to 20 g / 10 min, and still more preferably 1.0 to 10 g / 10 min.

  In the present invention, particularly preferred as the resin used for the intermediate layer is, for example, a mixture of a propylene-ethylene-butene random copolymer and a propylene homopolymer. The blending ratio of each resin component in the intermediate layer is preferably propylene-ethylene-butene random copolymer: propylene homopolymer = 1: 9 to 9: 1, more preferably 3: 7 to 7: 3. .

  The tensile modulus of elasticity in the longitudinal direction and the transverse direction perpendicular to the film in the present invention is 1.45 GPa or more, preferably 1.5 to 3.5 GPa. When it is less than 1.45 GPa, the film feels low, and the handleability of the package is significantly deteriorated. When it exceeds 3.5 GPa, cracks entering the film are likely to propagate when the package is opened, and the contents may be easily spilled, which is not preferable.

  The heat seal strength of the film in the present invention is 10 N / 15 mm or more, preferably 11 N / mm or more, and more preferably 12 N / mm or more. This is because heat seal strength is set to a certain level or more so that heavy objects such as water can be packaged. The upper limit of the heat seal strength is not particularly limited, but is preferably 35 N / 15 mm, more preferably 33 N / mm, still more preferably 30 N / mm. This is because if the heat seal strength exceeds 35 N / mm, the heat seal strength is too strong when the bag is opened, which makes it difficult to open the bag.

  In the present invention, the resin forming each layer includes various additives and fillers, for example, a heat stabilizer, an antioxidant, a light stabilizer, and an antistatic agent, as long as they do not impair the characteristics of each layer. A lubricant, a nucleating agent, a flame retardant, a pigment, a dye, 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 characteristics of the film of the present invention.

  As for the thickness constitution of each layer of the heat-sealable laminated polypropylene resin film of the present invention, the base material layer is 5 to 100 μm (more preferably 10 to 80 μm), and the heat fusion layer is 2 to 20 μm (more preferably 2.5 to 6.5 μm), and the intermediate layer is preferably 7 to 30 μm (more preferably 8 to 25 μm). In particular, when the thickness of the heat-fusible layer is less than 2 μm, the heat seal strength tends to decrease.

  Furthermore, in the present invention, the thickness of each layer is preferably such that the thickness of the base material layer is larger than that of the heat-fusible layer and the intermediate layer. If the intermediate layer or the heat-fusible layer is thicker than the base material layer, the tensile elastic modulus is lowered, the waist is lost, and the product handling property may deteriorate.

  The laminated polypropylene resin film having good heat sealability of the present invention can be arbitrarily produced by a known method and is not particularly limited. For example, after melt lamination by T-die method or inflation method using the number of extruders suitable for the number of layers, it is cooled by a cooling roll method, water cooling method or air cooling method to form a laminated film, and sequentially biaxial stretching method, simultaneous Examples of the stretching method include a biaxial stretching method and a tube stretching method.

  The laminated polypropylene resin film having good heat sealability of the present invention is preferably composed of the above-mentioned base material layer / intermediate layer / heat fusion layer, but the same type of polypropylene resin layer on the surface of the base material layer. And other resin layers, for example, a gas barrier resin layer such as saponified ethylene-vinyl acetate copolymer or polyvinyl alcohol may be further laminated. Similarly, the lamination between the deposited layers is not particularly limited as long as the characteristics are not impaired.

  The laminated polypropylene resin film having good heat sealability of the present invention is preferably subjected to surface treatment in order to improve the wetting tension of the heat-sealing layer. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, and acid treatment, and are not particularly limited. It is preferable to perform a corona discharge treatment, a plasma treatment, and a flame treatment on the heat-bonding layer, which can be continuously performed and can be easily performed before the winding step of the film production process. In particular, when the corona discharge treatment is performed, the propylene-α-olefin random copolymer used in the heat-sealing layer as described above has a cold xylene soluble content of 10% by mass to 80% by mass. By using it, the fall of the heat seal intensity | strength by a corona discharge process can be suppressed.

  The heat-sealable laminated polypropylene resin film of the present invention has sufficient heat-seal strength to wrap heavy objects, has good transparency, and grains such as flour, rice, and wheat, and plate / thread konjac. , Pickles such as takuan pickles, soy sauce pickles, Nara pickles, various miso soups, soup stock, noodle soup, soy sauce, sauces, ketchup, mayonnaise, etc. It can be used as a package for tubes, bags, cups, standing packs, trays, and the like.

  Hereinafter, specific examples of the present invention will be further described with reference to examples. However, the present invention is not limited to the following examples without departing from the gist thereof. In addition, the characteristic in this specification evaluated by the following method.

(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 sealing layer C surfaces of the laminated film were overlapped to perform hot plate sealing, and a test piece having a width of 15 mm was produced. The 180-degree peel strength of this test piece was measured and set as a heat seal strength (N / 15 mm).

(Tensile modulus)
It measured according to JIS-K-7127 method.

(Wetting tension)
It measured according to JIS-K-6768 method.

(Product handling)
A product in which rice confectionery with a mass of about 4 g and a size of 25 mm × 75 mm is twisted and wrapped with a polyethylene film with a thickness of 25 μm and a size of 80 mm × 140 mm is placed in a bag of size 190 mm × 250 mm made of the obtained film. Was prepared and evaluated for its handleability.
Evaluation grade 5: The film has a waist and can be easily packed, boxed, and displayed.
Evaluation grade 4: When you have a bag, it feels a little bit, but you can work without problems.
Evaluation grade 3: Feeling that there is no waist, it feels awkward when it is held in the hand, and the work is somewhat difficult.
Evaluation 2nd grade: Has no waist, feels warm when held in hand, and is difficult to work with.
Evaluation 1st grade: There is no waist and the work is difficult.

(Printability)
On the surface of the heat-sealing layer of the obtained film, gravure printing ink (Daiichi Seika Kogyo Co., Ltd./trade name UNIC160, 711 red) is used, and a PAS type gravure printing machine (manufactured by Totani Iron Works Co., Ltd.) is used. Then, a solid-printed sample was prepared with a 175 L × 35 μm gravure roll under the conditions of a line speed of 100 m / min and a drying temperature of 70 ° C., and ink adhesion was evaluated.
(Ink adhesion)
A grid-like parallel slit (25 pieces) having an interval of 2 mm in length and breadth is put into the printed matter subjected to the above printing, and then evaluated using a cellophane adhesive tape (manufactured by Nichiban: 18 mm width, hereinafter abbreviated as adhesive tape).

Hold the adhesive surface of the adhesive tape to the surface of the printed surface with a finger nail over a length of 3 cm and firmly adhere to the entire surface. Next, the edge of the film is fixed with a finger, the adhesive tape is peeled from one direction at a speed of 2 cm / sec at an angle of 90 degrees, and the amount of ink peeled off the printed film by adhering to the adhesive tape side (number of grids) ) With the naked eye.
A: No printing ink transfer on the adhesive tape side O: No more than 4 printing inks transferred to the adhesive tape side Δ: No more than 5-9 printing inks transferred to the adhesive tape side x: 10 or more printing inks transferred to the adhesive tape side.

(Example 1)
Using three melt extruders, the propylene homopolymer (density 0.90 g / cm ³ , MFR 2.5 g / 10 min, melting point 157 ° C.) as the base layer A in the first extruder, A ^third extruder using a propylene-butene random copolymer (density 0.89 g / cm ³ , MFR 8.0 g / 10 min, melting point 130 ° C., butene content 25%) as a heat-sealing layer C in an extruder. 50% by weight of propylene-ethylene-butene random copolymer (density 0.89 g / cm ³ , MFR 3.1 g / 10 min, melting point 133 ° C., ethylene content 2.5%, butene content 7%) A mixed resin containing 50% by mass of a homopolymer (density 0.90 g / cm ³ , MFR 2.5 g / 10 min, melting point 157 ° C.) as an intermediate layer B was used as a base layer A / intermediate layer B / in the die. Base material layer A so as to become heat-sealing layer C After melt coextrusion by the T-die method in the order of the intermediate layer B and the heat fusion layer C, it is cooled and solidified by a chill roll, 4.5 times in the longitudinal direction (film longitudinal direction), and 8 in the lateral direction (film width direction). The surface of the heat fusion layer C of the resulting film is subjected to corona discharge treatment, and the total of the wet tension of the corona discharge treatment surface is 35 mN / m, the base material layer A is 32 μm, the intermediate layer B is 10 μm, and the heat fusion layer C is 3 μm. A 45 μm three-layer laminated film was obtained. The evaluation results of the obtained film are shown in Table 1. The obtained laminated film satisfied the requirements of the present invention and had sufficient heat seal strength, low back feeling and ink adhesion.

(Comparative Example 1)
A laminated film was obtained in the same manner as in Example 1 except that the surface of the heat-sealing layer C was not subjected to corona treatment. The evaluation results of the obtained film are shown in Table 1. The obtained laminated film had insufficient ink adhesion to the heat-sealing layer C.

(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 fusion layer C were 3 μm, 35 μm, and 7 μm, respectively. The evaluation results of the obtained film are shown in Table 1. The obtained laminated film had no waist and was poor in handleability of the actual bag-making package.

(Comparative Example 3)
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 fusion layer C were 39 μm, 5 μm, and 1 μm, respectively. The evaluation results of the obtained film are shown in Table 1. The obtained laminated film had insufficient heat seal strength, and broke from the seal part during transportation and handling of the actual bag-making package, and had a problem in practical use.

(Comparative Example 4)
The thicknesses of the base material layer A, the intermediate layer B, and the heat-sealing layer C are respectively set to 32 μm, 10 μm, and 3 μm, and a propylene-butene random copolymer (density 0.89 g / cm ³ , MFR3. A laminated film was obtained in the same manner as in Example 1 except that 9 g / 10 minutes, melting point 138 ° C., butene content 18.7 mass%, cold xylene soluble content 8.5%). The evaluation results of the obtained film are shown in Table 1. The obtained laminated film had insufficient heat seal strength, and was broken from the seal part during transportation and handling of the actual bag-making package, and had practical problems.

The heat-sealable laminated polypropylene resin film of the present invention has sufficient heat-seal strength to wrap heavy objects, has good transparency, and cereals such as flour, rice, and wheat, and plate / thread konjac. , Pickles such as takuan pickles, soy sauce pickles, Nara pickles, miso soup, soup stock, noodle soup, soy sauce, sauces, ketchup, mayonnaise, etc. It can be used as a package for tubes, bags, cups, standing packs, trays, etc., and contributes greatly to the industry.

Claims (3)

  A stretched polypropylene resin film comprising a base material layer composed of a crystalline polypropylene resin, an intermediate layer, and a laminate of three or more layers having a heat-fusible layer having a melting point of 150 ° C. or lower, wherein the film is pulled in both directions perpendicular to each other A heat-sealable laminated polypropylene resin film having an elastic modulus of 1.45 GPa or more, a heat seal strength of 10 N / 15 mm or more, and a wetting tension of 31 mN / m or more on the surface of the heat-sealing layer.   The heat-sealable laminated polypropylene resin film according to claim 1, wherein the heat-sealable laminated polypropylene resin film is biaxially stretched. A package comprising the heat-sealable laminated polypropylene resin film according to claim 1 or 2.