JP4613571B2 - Heat-sealable polypropylene resin laminated film and package - Google Patents

Description

  The present invention relates to a film having heat-sealing properties, and more particularly to a film suitable for packaging heavy objects centering on fruits and vegetables, and a package using such a film.

  In general, as a heat-sealable film used for packaging, a co-extruded polypropylene resin laminated film in which a low melting point polyolefin resin is laminated on a polypropylene resin, an unstretched polyethylene resin film or a polypropylene resin film, A polypropylene resin laminated film obtained by laminating a stretched polypropylene resin film is often used.

  Although the above co-extruded polypropylene resin laminated film has a certain degree of heat seal strength, it cannot withstand the packaging of heavy objects such as cut vegetables for business use, and is not necessary for the purpose of packaging heavy objects. A polypropylene resin laminated film obtained by laminating a stretched polyethylene resin film or a polypropylene resin film and a stretched polypropylene resin film is used. However, although these laminate films have sufficient heat seal strength, a laminate process using an organic solvent or the like is necessary, which is not preferable from the viewpoint of the influence on the global environment economically.

Therefore, various studies have been made on improving the heat seal strength of the coextruded polypropylene resin laminated film. For example, Patent Document 1 shows an example in which a polypropylene-based resin is used as a base material layer and a linear low-density polyethylene-based resin is used as a heat-sealing layer. One in which an adhesive layer is provided between linear low-density polyethylene resin layers has been proposed. Patent Document 3 reports that sufficient heat seal strength can be obtained by defining the MFR (melt flow rate) of the resin used for each layer.
Japanese Patent Laid-Open No. 9-207294 Japanese Patent Laid-Open No. 10-76618 Japanese Patent Laid-Open No. 2003-225979

  However, since the films disclosed in Patent Document 1 are laminated with different materials, the adhesive strength between the layers is weak, and it is difficult to obtain a heat seal strength sufficient for packaging heavy objects. Moreover, even if an adhesive layer is provided as in Patent Document 2, if a polyethylene resin is laminated, the film feels irritated, which may hinder handling during bag making or after filling the contents. Furthermore, it is difficult to obtain heat-seal energy required for heavy-weight packaging only by controlling the MFR of the resin constituting each layer of the laminated film, and in particular, it is insufficient for packaging root vegetables such as potatoes. .

  Conventionally, in addition to the above characteristics, packaging films have been required to have transparency in order to enhance the aesthetics of the contents. In recent years, especially when packaging fruits and vegetables, the film is formed by moisture from the respiration of fruits and vegetables. It becomes a problem that the content becomes difficult to see because of cloudiness and the contents are reduced. However, a film having sufficient heat seal strength and heat seal energy as well as antifogging properties has not existed so far.

  The present invention has been made paying attention to the above-mentioned problems, and has sufficient heat seal strength and heat seal energy for packaging heavy items such as fruits and vegetables, and has a good waist feeling. An object of the present invention is to provide a conductive polypropylene-based resin laminated film and a package using such a film.

The heat-sealable polypropylene-based resin laminated film of the present invention that has solved the above problems has a heat-sealable layer having a melting point of 150 ° C. or less on the surface layer, and the heat-sealable layer and the crystalline polypropylene-based resin A heat-sealable polypropylene-based resin laminate film comprising a laminate of three or more layers having an intermediate layer between the substrate layer and a direction (TD) perpendicular to the flow direction (MD) of the film ) Of the tensile elastic modulus is 3.1 to 6.0 (GPa) ² , and the film flow direction and the direction perpendicular to the flow direction are set so that the heat seal strength of the film is 8 N / 15 mm or more. It has a gist where the heat seal energy when sealed is 11 N · cm / 15 mm or more.

  In the present invention, the product of the tensile elastic modulus is an index of the waist feeling of the laminated film, and the heat seal energy is an index of the resistance to stress acting on the seal portion of the laminated film, and the heat of the film This is derived from the relationship between the heat seal strength until the film breaks and the elongation of the film at the time of measuring the seal strength (absorbed energy until the seal portion breaks). Here, “so that the heat seal strength of the film is 8 N / 15 mm or more” means that the laminated film of the present invention is used for packaging heavy items, and has such heat seal strength. This is because, if present, it is considered to have strength enough to withstand the packaging of heavy objects.

  The laminated film having the above-described configuration has an appropriate waist feeling, and has excellent heat seal strength and heat seal energy, and therefore can be suitably used for packaging heavy objects.

When the thickness of the base material layer is x and the thickness of the intermediate layer is y, the thickness of the base material layer and the intermediate layer preferably satisfies the following relational expression.
2x <y

  The intermediate layer preferably contains an α-olefin copolymer having a cold xylene soluble content of 3% by mass or less, and the α-olefin copolymer is contained in the intermediate layer in an amount of 10 to 70% by mass. It is desirable to be a thing.

  Furthermore, it is preferable that the intermediate layer includes a crystalline polypropylene resin that constitutes the base material layer and a resin that constitutes the heat-fusible layer because the adhesive strength between the respective layers constituting the laminated film is excellent. .

  It is preferable that the wetting tension after washing the surface of the heat-sealing layer is 31 mN / m or more, and that the anti-fogging agent is present on the surface of the heat-sealing layer before washing.

  The laminated film is preferably biaxially stretched.

  The package made of the laminated film can also be suitably used for packaging heavy objects.

  The heat-sealable polypropylene-based resin laminated film of the present invention has high heat-seal strength and heat-seal energy, and also has good waist feeling and excellent product handling properties. can do. Moreover, since it can also have anti-fogging property, it can be used as a packaging film for fruits and vegetables.

The heat-sealable polypropylene-based resin laminated film of the present invention has a heat-sealable layer having a melting point of 150 ° C. or less on the surface layer, and between the heat-sealable layer and a base material layer made of a crystalline polypropylene-based resin. A heat-sealable polypropylene-based resin laminated film comprising a laminate of three or more layers having an intermediate layer on the product, the product of the film flow direction (MD) and the tensile elastic modulus in the direction perpendicular to the flow direction (TD) Is 3.1 to 6.0 (GPa) ² and each heat when the film flow direction and the direction perpendicular to the flow direction are sealed so that the heat seal strength of the film is 8 N / 15 mm or more. It is characterized by a seal energy of 11 N · cm / 15 mm or more.

Since the laminated film of the present invention also takes into account the packaging of heavy objects as described above, the film flow measured in accordance with the provisions of JIS-K-7127 from the viewpoint of ensuring the handling at the time of product packaging. The product of the tensile elastic modulus in the direction (MD) and the direction (TD) perpendicular to the direction (MD) is required to be 3.1 (GPa) ² or more and 6.0 (GPa) ² or less. Preferably it is 3.3 (GPa) ² or more, more preferably 3.4 (GPa) ² or more, preferably 5.5 (GPa) ² or less, more preferably 5.0 (GPa) ² or less.

  In general, it is known that the tensile elastic modulus of a film used as a packaging material has a correlation with a low feeling during handling of the packaging material. In the present invention, the product of the tensile elastic modulus in MD and TD, not the tensile elastic modulus, is adopted as a criterion for judging the back of the film. For example, the film is used as a bag-like package. In this case, it is due to the need for a sense of waist in both the flow direction (MD) of the film and the direction (TD) perpendicular thereto.

  Therefore, when the product of the tensile elastic modulus is less than the above range, the feeling of the back of the film is lowered, and the handleability of the package tends to be deteriorated. On the other hand, when it exceeds the above range, the film tends to be hard, cracks entering the film are easily propagated when the package is opened, and the contents may be spilled during opening. On the other hand, if the tensile elastic modulus is too large, the film is difficult to stretch, and heat seal energy described later may be difficult to obtain.

  In addition, if the product of the tensile elastic modulus is included in the above range, the value of the tensile elastic modulus of each of MD and TD is not particularly limited, but the tensile elastic modulus in MD is preferably 1.40 GPa or more, More preferably, it is 1.45 GPa, and the tensile elastic modulus at TD is preferably 2.25 GPa or more, more preferably 2.35 GPa or more.

  The laminated film of the present invention has a heat seal strength of 8 N / 15 mm or more and a heat seal energy of 11 N when the flow direction of the laminated film and the direction orthogonal to the flow direction are sealed. -It needs to be cm / 15 mm or more. It is preferably 12 N · cm / 15 mm or more, more preferably 12.5 N · cm / 15 mm or more.

  Here, the heat seal energy is a value derived from the relationship between the heat seal strength and the elongation of the film at the time of heat seal strength measurement, and means the film absorbed energy until the seal portion breaks (or yields). It is.

  When the laminated film is used as a bag-shaped package, the seal portion may be broken due to vibration or impact during transportation or dropping during distribution. This phenomenon is particularly remarkable when heavy objects are packaged. Such breakage of the seal portion is greatly influenced not only by the strength of the seal portion (heat seal strength) but also by the elongation of the seal portion up to the breakage. Therefore, if the seal portion is extended, the impact during transportation and cargo handling work is dispersed, so that the seal portion can be prevented from being broken, that is, the package can be broken. In other words, a small heat seal energy means that the seal part is difficult to stretch. In such a case, the impact cannot be dispersed and a load is locally applied to the seal part. When a heavy article is packaged with a laminated film, bag breaking tends to occur.

  In addition, the above-mentioned regulation “when the heat seal strength is 8 N / 15 mm or more and the MD and TD of the laminated film are sealed” is used for packaging heavy objects if the heat seal strength is 8 N / 15 mm or more. It is because it can be judged that it has sufficient intensity. This is because, in specifying the heat seal temperature, the above heat seal strength may be difficult to obtain depending on the type of resin constituting each layer constituting the laminated film and the thickness of the layer. Therefore, in the present invention, a regulation of 8 N / 15 mm or more is provided as a value of heat seal strength that the package can withstand heavy weight packaging. Therefore, when the heat seal strength is less than the above value, the strength is insufficient, and bag breakage may occur during handling of the package.

  The regulation of heat seal strength and heat seal energy in the present invention means values measured by the following measurement method.

Heat seal strength:
The sample cut out so that the film flow direction is the length direction of the bag is heat-sealed (seal width: 10 mm) so that the cross-section of the sealed portion of the bag is T-shaped as shown in FIG. A center press seal bag having a size of 185 mm × 255 mm is formed. Heat sealing is performed under the conditions of a sealing temperature of 150 ° C., a pressure of 2 kg / cm ² , and a heat sealing time of 2 seconds.

  A test piece having a width of 15 mm and a length of 50 mm is cut out from the seal portion parallel to the length direction (MD) and the width direction (TD) of the obtained bag. Next, the test piece was left in an atmosphere of a temperature of 20 ° C. and a humidity of 65% RH for 24 hours, and then the distance between chucks was set to 20 mm using “Tensilon” (UTM-IIIL) manufactured by Toyo Seiki Co., Ltd. The strength when peeled 180 degrees at a speed of 200 mm / min (chart speed 200 mm / min) was measured to obtain a heat seal strength [N / 15 mm]. The schematic of the shape of the bag produced in FIG. 1 and the test piece for heat seal strength measurement is shown.

Heat seal energy:
The heat seal energy can be derived from a chart obtained by measuring the heat seal strength. In the present invention, the area surrounded by the curve indicating the heat seal strength and the chart moving distance is defined as heat seal energy [N · cm / 15 mm] (FIG. 2).

  Next, each layer which comprises the laminated | multilayer film of this invention is demonstrated.

  As the crystalline polypropylene-based resin used for the base material layer of the laminated film of the present invention, it is preferable to use n-heptane-insoluble isotactic polypropylene used in ordinary extrusion molding. The insolubility of n-heptane indicates the crystallinity of polypropylene and indicates safety when used for food packaging. In the present invention, the insolubility of n-heptane according to Notification No. 20 of the Ministry of Health and Welfare in February 1982 is used. It is a preferred embodiment to use a material that conforms to (the elution amount when extracted at 25 ° C. for 60 minutes is 150 ppm or less [the usage temperature exceeds 100 ° C. is 30 ppm or less]).

  The isotactic polypropylene may be homopolypropylene (propylene homopolymer), or may be a random copolymer or block copolymer of polypropylene and another α-olefin. When a copolymer with another α-olefin is employed, it is preferable to employ polypropylene containing 70% by mass or more of propylene, and the other α-olefin as the copolymer component includes ethylene. It is preferable to use an α-olefin having 2 to 8 carbon atoms such as butene-1, hexene-1, 4-methyl-1-pentene. Further, the base material layer may be one that uses the above-described crystalline polypropylene resin alone, or may be a mixture of two or more.

  The melt flow rate (MFR) of the polypropylene resin used for the base material layer is preferably 0.1 g / 10 min or more, more preferably 0.5 g / 10 min or more, and further preferably 1.0 g / 10 min or more. 100 g / 10 min or less, more preferably 20 g / 10 min or less, still more preferably 15 g / 10 min or less. When MFR is less than the said range, the fluidity | liquidity of resin may be scarce and manufacture of a film may become difficult. On the other hand, when the above range is exceeded, the film strength becomes small, and inconvenience is likely to occur in terms of handling.

  The laminated film according to the present invention has a heat fusion layer having a melting point of 150 ° C. or less on the surface layer. The resin constituting the heat-sealing layer is a thermoplastic resin having a melting point of 150 ° C. or lower, and is obtained by polymerizing two or more selected from α-olefin monomers having 2 to 10 carbon atoms. It is preferable to use a copolymer or a block copolymer. Examples of the α-olefin monomer having 2 to 10 carbon atoms include ethylene, propylene, butene, pentene, hexene, octene, and decene. In addition, the resin which comprises a heat-fusion layer can use the said copolymer individually or in mixture of 2 or more types.

  In particular, it is preferable that the resin constituting the heat-sealing layer contains a propylene-butene copolymer having a high butene content. Here, the butene content in the propylene-butene copolymer is preferably 20% by mass or more. The upper limit of the butene content is not particularly limited, but if the butene content is too much, the film surface may become sticky, and slipperiness and blocking resistance may be reduced. Good. Examples of the propylene-butene copolymer having a high butene content include “SPX78J1” manufactured by Sumitomo Chemical Co., Ltd.

  The propylene-butene copolymer is preferably blended in an amount of 65% by mass or more in the resin component constituting the heat-sealing layer. More preferably, it is 70% by mass or more, preferably 99% by mass or less, and more preferably 95% by mass or less. If the blending amount of the propylene-butene copolymer is too small, the fusion force at the time of sealing may be low, and it may be difficult to obtain sufficient heat sealing energy. Interlaminar strength may decrease.

  In order to give sufficient heat seal strength to the laminated film according to the present invention, the lower limit of the melting point of the resin component constituting the heat-sealing layer is preferably 60 ° C. When the lower limit of the melting point is too low, the heat resistance of the heat seal portion is poor, while when the melting point is too high, improvement in heat seal strength may not be expected. Therefore, the upper limit of the melting point was set to 150 ° C.

  Further, from the viewpoint of ensuring workability and strength during film production, the MFR of the resin constituting the heat-sealing layer is preferably 0.1 to 100 g / 10 min, and more preferably 0.5 to 20 g / It is 10 minutes, More preferably, it is 1.0-15 g / 10min.

  The laminated film of the present invention has an intermediate layer between the base material layer and the heat-sealing layer. This intermediate layer is provided in order to improve the interlayer strength between the base material layer and the heat-sealing layer, and to make the laminated film of the present invention have an appropriate waist feeling and heat seal energy.

  The resin constituting the intermediate layer preferably contains at least one α-olefin copolymer having a cold xylene soluble content (CXS) of 3% by mass or less.

  The above-mentioned “cold xylene-soluble matter” indicates the amount of amorphous part contained in the α-olefin copolymer, and it is said that “cold xylene-soluble matter is 3% by mass or less” It means an α-olefin copolymer with few crystal parts and high crystallinity.

  α-Olefin copolymers are excellent in mechanical strength such as impact strength and tearing properties, low temperature properties, weather resistance, etc., and by blending such components, it is possible to impart excellent properties to laminated films. it can. However, the α-olefin copolymer has a structure in which a different α-olefin is randomly introduced as the second or third component in the main α-olefin molecular chain. Therefore, the crystallinity is lower than that of an α-olefin homopolymer such as homopolypropylene, and the blending of the α-olefin copolymer results in lowering the feeling of the film. On the other hand, if there are too few amorphous parts, the film will be hard and difficult to stretch, making it difficult to obtain sufficient heat seal energy. Therefore, from these viewpoints, an α-olefin copolymer having a cold xylene-soluble content of 3% by mass or less in the intermediate layer is formed in order to obtain a laminated film that has an appropriate feeling of elasticity and can be stretched according to the load. It was decided to blend together.

  The blending amount of the α-olefin copolymer having a cold xylene soluble content in the intermediate layer of 3% by mass or less is preferably 10% by mass or more, more preferably 15% by mass or more, and 70% by mass or less. It is preferable that it is 60 mass% or less. When the blending amount of the α-olefin copolymer is too small, the adhesive strength between the layers constituting the laminated film may be insufficient and sufficient heat seal strength may not be obtained. On the other hand, when too much, there exists a possibility of reducing the waist feeling of the whole film. If the blending amount of the α-olefin copolymer is in the above range, the heat seal layer may be deformed (thinned) and heated when the heat seal is performed at a high temperature. It can suppress that sealing energy falls.

  Examples of the α-olefin having a cold xylene-soluble content of 3% by mass or less include a polymer synthesized by a continuous gas phase polymerization method described in JP-A No. 2003-277412. For example, “FSX66E8” (Sumitomo Chemical Industries) [Made by Co., Ltd.] can be used.

  The above-mentioned cold xylene-soluble matter means that 1 g of a sample is completely dissolved in 100 ml of boiling xylene, cooled to 20 ° C. and left for 4 hours, and then the solvent is distilled off from the filtrate obtained by filtering the precipitate. And dried at 70 ° C. under reduced pressure, and the value calculated from the mass of the resulting precipitate is shown.

  In the intermediate layer of the laminated film of the present invention, in addition to the α-olefin copolymer described above, at least one or more resins constituting each of the base material layer and the heat fusion layer are preferably blended. This is because, by blending these resins, the affinity between the base material layer-intermediate layer and the intermediate layer-heat fusion layer is increased, and the adhesive force between the laminated film layers is enhanced. The blending amount of these resins is preferably 6% by mass or more, more preferably 10% by mass or more, and preferably 69% by mass or less, in the resin component constituting the intermediate layer. Is 65% by mass or less. When the blending amount is small, the adhesive strength between layers tends to be insufficient. On the other hand, when the amount of the resin constituting the base material layer is large, the heat seal energy may be insufficient, and when the resin constituting the heat fusion layer is too much, the intermediate layer is softened. And the lower back may be impaired.

  Furthermore, you may mix | blend an antifogging agent with the said base material layer, an intermediate | middle layer, and a heat-fusion layer. As described above, in recent years, in particular, films used for packaging fruits and vegetables have been required to have antifogging properties. Antifogging has an effect of suppressing water rot of the contents due to water droplets generated by the physiological action of fruits and vegetables, in addition to appearance characteristics that make the contents easy to see. Moreover, since the slipperiness of the film is improved by the addition of the antifogging agent, the film production process and the packaging process using the film can be performed smoothly.

  Examples of the antifogging agent that can be blended in the laminated film of the present invention include glycerin monooleate, glycerin laurate, glycerin caprate, glycerin fatty acid ester such as diglycerin oleate, diglycerin laurate, triglycerin oleate, and sorbitan laurate. Higher fatty acids such as sorbitan fatty acid esters such as polyethylene glycol oleate, polyethylene glycol fatty acid esters such as polyethylene glycol fatty acid esters, polyhydric alcohol fatty acid esters, higher fatty acid amines, stearic acid amide, oleic acid amide, erucic acid amide, etc. Amides of higher fatty acids, amines of higher fatty acids, ethylene oxide adducts of amides, and the like.

  In addition, although an antifogging agent should just be mixed and used with the structural resin of each layer which comprises a laminated | multilayer film at the time of manufacture of a film, you may mix | blend only with a specific layer. Even when blended only in a specific layer, the antifogging agent is transferred to other layers sequentially (bleed out) during film production and storage after film production, and finally the surface of the heat-sealing layer This is because the heat sealing layer surface is in a state having antifogging properties.

  In order to cause the bleed-out of the antifogging agent smoothly as described above, it is preferable to provide a gradient in the antifogging agent concentration in each layer constituting the laminated film. That is, it is preferable that the antifogging agent concentration is gradually decreased from the base material layer toward the heat-sealing layer.

  The blending amount of the anti-fogging agent may be determined in consideration of the temperature change during storage or distribution, and the anti-fogging property is such that the anti-fogging property can be exhibited continuously throughout the temperature change between 5 and 30 ° C. It is desirable that the clouding agent is present on the surface of the heat-sealing layer. From such a viewpoint, the blending amount of the antifogging agent is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and more preferably 10% by mass or less in terms of all layers constituting the laminated film. It is preferable that it is 5 mass% or less. In addition, from the viewpoint of ensuring heat sealability, the blending amount of the antifogging agent in the heat fusion layer constituting component is preferably 5% by mass or less, more preferably 1.0% by mass or less, and 0 It is preferably 0.01% by mass or more.

  In order to sufficiently exhibit the effect of the antifogging agent as described above, the wetting tension after washing the surface of the heat-sealing layer constituting the laminated film of the present invention is 31 mN / m or more and 41 mN / m or less. Preferably there is. Here, the wetting tension of the surface of the heat-sealing layer after washing with water was used as an index for evaluating the anti-fogging property, as a matter of course, the surface of the heat-sealing layer before washing was prevented from bleeding out from the inside of the laminated film. This is because a clouding agent is present, and the wetting tension measured in this state includes the contribution of the antifogging agent in addition to the characteristics of the heat-sealing layer itself.

  When the wetting tension after surface cleaning is low, the diffusion effect of the antifogging agent on the surface of the heat-sealing layer tends to be insufficient, while when the wetting tension is too high, the heat of the heat-sealing layer There is a tendency for the sealing performance to decrease.

  Various additives and fillers may be added to each layer constituting the laminated film of the present invention, as necessary, within a range that does not impair the characteristics of each layer. For example, heat stabilizer, antioxidant, light stabilizer, antistatic agent, lubricant, nucleating agent, flame retardant, pigment, dye, calcium carbonate, barium sulfate, magnesium hydroxide, mica, talc, clay, zinc oxide, oxidation Examples include magnesium, aluminum oxide, antibacterial agents, and additives that impart natural degradability. Furthermore, other thermoplastic resins, thermoplastic elastomers, rubbers, hydrocarbon resins, petroleum resins, and the like than those described above can be blended within a range that does not impair the properties of the laminated film.

In the laminated film according to the present invention, it is preferable that the thickness of the base material layer and the intermediate layer satisfy the following relational expression when the thickness of the base material layer is x and the thickness of the intermediate layer is y. .
2x <y

  This is because, in addition to the above-described configuration, if the thicknesses of the base material layer and the intermediate layer satisfy the above relational expression, it is easy to obtain the heat seal energy and waist feeling of the laminated film.

  The laminated film of the present invention is not particularly limited as long as the thickness of the base material layer and the intermediate layer satisfies the above relationship, and the base material layer is 10% or more and 32% or less of the total thickness of the laminated film ( More preferably, it is preferably 15% or more and 30% or less), the heat fusion layer is 1% or more and 20% or less (more preferably 1.5% or more and 15% or less), and the intermediate layer is 30% or more, 89 % Or less (more preferably 40% or more and 83.5% or less). When the thickness of the base material layer is less than 10%, the heat fusion layer exceeds 20%, and the intermediate layer exceeds 89%, the laminated film tends to be difficult to obtain. It is not preferable. Further, when the thickness of the base material layer exceeds 50%, the heat-sealing layer is less than 1%, and the intermediate layer is less than 40%, the target heat seal strength and heat seal energy may be difficult to obtain. .

  The configuration of the laminated film according to the present invention is not particularly limited as long as it includes the base material layer, the intermediate layer, and the heat fusion layer. The same kind of polypropylene as the constituent resin of the base material layer is formed on the surface of the base material layer. A mode in which another resin layer (for example, a gas barrier resin layer such as saponified ethylene-vinyl acetate copolymer or polyvinyl alcohol) for imparting various properties to a resin-based resin layer or a laminated film is also included in the present invention. It is. Moreover, as long as the characteristics of the laminated film are not impaired, the lamination position of the other resin layer is not limited, for example, between the base material layer and the intermediate layer, and between the intermediate layer and the heat fusion layer. Other layers as described above can also be provided.

  The manufacturing method of the laminated | multilayer film concerning this invention is not specifically limited, It can manufacture arbitrarily by a conventionally well-known method. For example, after melt lamination by a T-die method or an inflation method using an extruder suitable for the number of laminations, and cooling by a cooling roll method, a water cooling method, or an air cooling method to produce an unstretched laminated film, Examples thereof include a method of stretching and producing by an axial stretching method, a simultaneous biaxial stretching method, a tube stretching method, and the like.

  The laminated film according to the present invention may be subjected to a surface treatment as necessary (for example, improvement of printability) as long as the properties of the film are not impaired. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, and acid treatment. Among the methods exemplified above, corona discharge treatment, plasma treatment, and flame treatment are preferable because they can be continuously processed and can be easily carried out before the winding process during film production. In particular, it is recommended to employ corona discharge treatment as a means for improving the wetting tension on the surface of the heat-sealing layer. Moreover, you may give special processes, such as a punching process, to a film according to a use. For example, a film subjected to 1 to 500 μm perforation can be used as a freshness-keeping package for fruits and vegetables.

  The heat-sealable polypropylene-based resin laminated film of the present invention has sufficient heat-seal strength to wrap heavy objects, as well as excellent handleability and transparency, so that flour, Cereals such as rice and wheat; Root vegetables such as potatoes, radish and carrots; Plates and konjacs, takuan pickles; Various pickles such as soy sauce and Nara pickles; Various miso; Dashimoto, noodle soup and soy sauce It is suitable as a packaging material for collective packaging in which several individual packagings such as sauces, ketchups, mayonnaises, and ramen are packaged together. In particular, it can be used as a packaging material optimal for packaging of cut vegetables for business use that requires anti-fogging properties. In addition, the laminated film of the present invention can be used not only for food packaging, but also for clothing such as underwear and clothes, shopping, and packaging such as pharmaceuticals and cosmetics.

  Furthermore, the laminated film of the present invention can also be used as a package for paper cartons, 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]
A sample cut out from the packaging film obtained in the following experimental example so that the flow direction of the film is in the length direction of the bag, the cross section of the seal portion of the bag becomes T-shaped as shown in FIG. In this way, heat sealing (sealing width: 10 mm) (center joint seal type) was performed to produce a center press seal bag of 185 mm × 255 mm. The heat seal was performed using a sealer “Test Sealer” manufactured by Seibu Kikai Co., Ltd. under the conditions of a seal temperature of 150 ° C., a pressure of 196 kPa (2 Kg / cm ² ), and a heat seal time of 2 seconds.

  A test piece having a width of 15 mm and a length of 50 mm was cut out from a seal portion parallel to the length direction (MD) and the width direction (TD) of the bag. Next, the test piece was left in an atmosphere of a temperature of 20 ° C. and a humidity of 65% RH for 24 hours, and then the distance between chucks was set to 20 mm using “Tensilon” (UTM-IIIL) manufactured by Toyo Seiki Co., Ltd. The strength when peeled 180 degrees at a speed of 200 mm / min (chart speed of 200 mm / min) was measured to obtain a heat seal strength (N / 15 mm). The schematic of the shape of the bag produced in FIG. 1 and the test piece for heat seal strength measurement is shown.

[Heat seal energy]
The area of the chart surrounded by the heat seal strength and the chart moving distance of the chart obtained by the measurement of the heat seal strength was measured to obtain heat seal energy (N · cm / 15 mm). FIG. 2 shows a chart shape example.

[Tensile modulus]
According to the JIS-K-7127 method, the tensile elastic modulus (GPa) in the film flow direction (MD) and the film flow orthogonal direction (TD) was measured. The measurement was performed three times in each direction, and the average value of these values was taken as the tensile elastic modulus in each direction.

[Product handling]
About 400 g of potatoes were put into a bag prepared in the same manner as in the above heat seal strength measurement method, the bag mouth was squeezed, and the position 2 cm from the bag mouth was pack-sealed with a tape having a tape width of about 1 cm. The bagging workability of the potato and the handling property of the product after bagging were evaluated according to the following evaluation criteria.
Evaluation criteria Evaluation grade 5: The film is thin and can be packed, boxed, unboxed and displayed easily.
Evaluation grade 4: Feels somewhat unreliable when holding a bag, but works without problems.
Evaluation grade 3: Feeling that there is no waist, it feels unreliable when it is held in the hand, and is somewhat difficult to work with.
Evaluation 2nd grade: Has no waist, feels unreliable when held in hand, and difficult to work with.
Evaluation 1st grade: There is no waist and work is difficult.

[Bracks resistance when handling products]
The potato-filled bag prepared in the product handling test was dropped from a position of 120 cm in height, and the presence or absence of broken bags and the number of drops until the broken bags were generated were confirmed.

[Anti-fogging property]
The antifogging properties of the films obtained in the following production examples were evaluated according to the following procedures.
300 cc of hot water at 50 ° C. is put into a 1.500 cc upper opening container (opening area: 78.5 cm ² ).
2. The film container opening is sealed with the heat-sealing layer (antifogging measurement surface) of the film inside.
Leave in a cold room at 3.5 ° C for 12 hours.
After leaving in a cold room at 4.5 ° C., move to a 30 ° C. environment and leave for 12 hours.
5.3. And 4. After repeating this operation for 2 days, the dew adhesion state on the surface of the heat-sealing layer of the film was evaluated according to the following evaluation criteria.
Evaluation criteria Evaluation grade 6: No dew on the entire surface (attachment area 0)
Evaluation grade 5: Slight dew adhesion (up to 1/5 of adhesion area)
Evaluation grade 4: Some dew adhesion (up to 1/4 adhesion area)
Evaluation grade 3: Dew adhesion of about 1/2 (up to 2/4 of adhesion area)
Evaluation grade 2: almost dew adhesion (up to 3/4 adhesion area)
Evaluation grade 1: Dew adhesion on the entire surface (adhesion area 3/4 or more)

[Wet tension]
The surface of the heat-sealing layer of the film obtained in the following production example was washed with distilled water for 40 to 50 seconds, and then the wetting tension of the film was evaluated according to the JIS-K-6768 method.

Resins constituting each layer used in the following production examples are as follows.
Propylene homopolymer: “FS2011DG3” manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.5 g / 10 min, melting point: 158 ° C., cold xylene solubles (CXS): 3.3 mass%
Propylene / ethylene / butene random copolymer-1: “FSX66E8” manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 2.5 mol%, butene content: 7 mol%, MFR: 3.1 g / 10 min. Melting point: 133 ° C., cold xylene solubles (CXS): 1.6% by mass
Propylene / ethylene / butene random copolymer-2: “W171” manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 4.6 mol%, butene content: 4.2 mol%, MFR: 4.6 g / 10 Min, melting point: 128 ° C., cold xylene solubles (CXS): 4.6% by mass
Propylene / ethylene / butene random copolymer-3: “WF584S” manufactured by Sumitomo Chemical Co., Ltd., ethylene: 2.6 mol%, butene content: 5.4 mol%, MFR: 4.0 g / 10 Min, melting point: 135 ° C., cold xylene solubles (CXS): 3.6% by mass (produced by solution polymerization method)
Propylene / Butene Copolymer-1: “SPX78J1” manufactured by Sumitomo Chemical Co., Ltd., butene content: 25 mol%, MFR: 8.5 g / 10 min, melting point: 128 ° C., cold xylene solubles (CXS) : 14.0 mass%
Propylene / butene copolymer-2: “SP8932” manufactured by Sumitomo Chemical Co., Ltd., butene content: 33 mol%, MFR: 9.0 g / 10 min, melting point: 130 ° C.

[Production Example 1]
Using three melt extruders, the base layer A (propylene homopolymer) was used in the first extruder, and the heat fusion layer C (propylene / ethylene / butene random copolymer was used in the second extruder. -1: 10 parts by mass, propylene / butene copolymer-1: 90 parts by mass of mixed resin) using a third extruder, intermediate layer B (propylene / ethylene / butene random copolymer-1: 40 parts by mass) %, Propylene homopolymer: 60% by mass mixed resin) at a resin temperature of 260 ° C., respectively, and laminated in a T die so as to be a base material layer A / intermediate layer B / heat fusion layer C This was cooled and solidified with a chill roll at 20 ° C. Next, the obtained unstretched film was stretched 4.5 times in the longitudinal direction and then stretched 8 times in the transverse direction, and the base layer A: 10 μm, the intermediate layer B: 28 μm, and the heat fusion layer C: 2 μm A laminated film for packaging 1 (40 μm) was obtained. In Table 1, the structure and evaluation result of the laminated film 1 are shown.

  The obtained laminated film 1 had a sufficient heat seal strength, heat seal energy, and waist feeling, and was excellent in all of handleability and bag breaking resistance after filling a heavy article.

[Production Example 2]
Using three melt extruders, the base layer A (propylene homopolymer: 100 parts by mass, polyoxyethylene (2) stearylamine monostearate: 0.8 parts by mass, Oxyethylene (2) stearylamine: 0.2 parts by mass, stearic acid monoglycerin ester: mixed resin containing 0.2 parts by mass) was heat-fusible layer C (propylene / ethylene / butene) in a second extruder. Copolymer-1: 10 parts by mass and propylene / butene copolymer-1: 90 parts by mass of mixed resin) was mixed with an intermediate layer B (propylene / ethylene / butene random copolymer) using a third extruder. 1: 40% by mass, propylene homopolymer: 60% by mass mixed resin, polyoxyethylene (2) stearylamine monostearate: 0.3 parts by weight, polyoxyethylene (2) Stearylamine: 0.1 parts by weight and stearic acid monoglycerin ester: 0.24 parts by weight of mixed resin) are each melt extruded at a resin temperature of 260 ° C. After being laminated so as to be / intermediate layer B / heat fusion layer C, this was cooled and solidified with a chill roll at 20 ° C. Subsequently, the obtained unstretched film was stretched 4.5 times in the longitudinal direction and 8 times in the transverse direction, and the base layer A: 10 μm, the intermediate layer B: 28 μm, and the heat fusion layer C: 2 μm A laminated film 2 for packaging (40 μm) was obtained.

  The surface of the heat-sealing layer C of the obtained laminated film 2 was subjected to corona discharge treatment so that the wetting tension of the surface of the heat-sealing layer C after corona discharge treatment (after water washing) was 36 mN / m. Table 1 shows the configuration of the laminated film and the evaluation results.

  The resulting laminated film 2 has anti-fogging properties in addition to heat seal strength, heat seal energy, and sensation, and has sufficient handling properties, resistance to bag breakage after filling heavy items, and appearance of products. Met.

[Production Example 3]
Laminated films 3 and 4 were obtained in the same manner as in Production Example 2 except that the degree of corona treatment was adjusted so that the wetting tension (after water washing) on the surface of the heat-sealing layer C was the value shown in Table 1. Table 1 shows the configuration of the laminated film and the evaluation results.

  The laminated films 3 and 4 were excellent in heat seal strength, heat seal energy, and waist feeling. Since the laminated film 4 had insufficient corona discharge treatment, the antifogging property was somewhat low.

[Production Example 4]
A laminated film 5 was produced in the same manner as in Production Example 1 except that the compounding ratio of the resins constituting each layer of the laminated film was changed as shown in Table 1.

  The obtained laminated film 5 was excellent in heat seal strength, heat seal energy, and waist feeling.

[Production Example 5]
Films 6 to 11 were produced in the same manner as in Production Example 1 except that the composition of the resin constituting the intermediate layer B and / or the heat fusion layer C and the thickness of each layer were changed as shown in Table 2. Tables 2 and 3 show the structures and evaluation results of the laminated films.

  The film 6 was inferior in the handleability of the product because the base material layer was too thin and a feeling of waist was not obtained. Furthermore, since the base material layer was thin, the strength of the laminated film itself was lowered, and the bag breaking resistance was poor. Further, the blending amount of the propylene-butene copolymer in the heat-sealing layer was small, and the heat seal energy was inferior.

  Although the film 7 and the film 8 have sufficient waist feeling, since the intermediate layer is too thin, the heat seal energy is low, and the package made from such a film has extremely poor bag breaking resistance.

  The laminated film 9 had a low feeling of the laminated film and was inferior in product handling because the blended amount of the α-olefin copolymer having a cold xylene soluble content in the intermediate layer of 3% by mass or less was too large. It was.

  The laminated film 10 is an example in which the amount of the α-olefin copolymer having a cold xylene soluble content in the intermediate layer of 3% by mass or less is small, and the laminated film 11 has a cold xylene soluble content in the intermediate layer of 3% by mass. This is an example in which the following α-olefin copolymer was not blended. All of these laminated films had low heat seal strength and heat seal energy, and were inferior in bag breaking resistance.

[Production Example 6]
A laminated film 12 was produced in the same manner as in Production Example 2 except that the thickness of each layer constituting the laminated film was changed as shown in Table 3. In Table 3, the structure and evaluation result of a laminated film are shown.

  Although the laminated film 12 was satisfactory in heat seal strength, the heat seal energy was small because the thickness of the intermediate layer was too thin, and the package made from this laminated film was inferior in bag breaking resistance.

[Production Example 7]
A laminated film 13 was obtained in the same manner as in Production Example 2, except that the degree of corona treatment was adjusted so that the wetting tension (after water washing) on the surface of the heat-sealing layer C was the value shown in Table 3.

  Since the laminated film 13 was over-treated by corona treatment, the wet tension became too large, the sealing performance was lowered, and the heat seal strength was at a satisfactory level, but the heat seal energy was low, and the laminated film 13 was prepared with such a laminated film. The package was inferior in bag resistance.

[Production Example 8]
Using three melt extruders, the base layer A (propylene homopolymer) was used in the first extruder, and the heat fusion layer C (propylene / ethylene / butene random copolymer was used in the second extruder. -3: 40% by mass of propylene / ethylene / butene random copolymer-2: 60% by mass of mixed resin) using a third extruder, intermediate layer B (propylene homopolymer: 40% by mass, propylene / After melt coextrusion of ethylene / butene random copolymer-3: 60% by mass mixed resin) in the die in the order of base layer A / intermediate layer B / thermal fusion layer C Then, it is cooled and solidified with a chill roll at 20 ° C., stretched 4.5 times in the longitudinal direction, and then stretched 8 times in the transverse direction. Base material layer A: 14 μm, intermediate layer B: 14 μm, thermal fusion layer C: 2 μm A laminated film 14 was produced. In Table 3, the structure and evaluation result of a laminated film are shown.

  The laminated film 14 does not contain an α-olefin copolymer having a cold xylene-soluble content of 3% by mass or less in the intermediate layer B, and since the intermediate layer is thin, the heat seal energy is low, and thus the laminated film 14 is prepared with such a laminated film. The packaged product was inferior in bag breaking resistance.

  The heat-sealable polypropylene-based resin laminated film of the present invention has sufficient heat-seal strength to wrap heavy objects, as well as excellent handleability and transparency, so that flour, Cereals such as rice and wheat; Root vegetables such as potatoes, radish and carrots; Plates and konjacs; Various pickles such as takuan pickles, soy sauce pickles, and Nara pickles; Various miso soups; Dashimoto, Mentsuyu and soy sauce It is suitable as a packaging material for collective packaging in which several individual packagings such as sauces, ketchups, mayonnaises, and ramen are packaged together. In particular, it can be used as a packaging material optimal for packaging of cut vegetables for business use that requires anti-fogging properties.

  The laminated film of the present invention can also be used as a package for paper cartons, tubes, bags, cups, standing packs, trays, and the like.

It is the schematic of the shape of the bag created in the Example, and the test piece for heat seal strength measurement. It is an example of the chart at the time of heat seal intensity | strength measurement.

Claims (6)

The heat melting which contains 2 or more types of random copolymers or block copolymers obtained by polymerizing 2 or more types selected from α-olefin monomers having 2 to 10 carbon atoms and having a melting point of 150 ° C. or less on the surface layer. An intermediate layer containing an α-olefin copolymer having a cold xylene-soluble content of 3% by mass or less between the heat- fusible layer and the base material layer made of a crystalline polypropylene resin. It consists of three or more laminated films ,
When the thickness of the base material layer is x and the thickness of the intermediate layer is y, the thickness of the base material layer and the intermediate layer satisfies the relational expression 2x <y,
The product of the tensile elastic modulus in the flow direction (MD) of the laminated film and the direction (TD) perpendicular to the flow direction is 3.1 to 6.0 (GPa) ² ,
The heat seal strength of the laminated film is 8 N / 15 mm or more , and the heat sealing energy when the flow direction of the laminated film and the direction orthogonal to the flow direction are sealed is 11 N · cm / 15 mm or more. A heat-sealable polypropylene-based resin laminated film characterized by   The laminated film according to claim 1, wherein the α-olefin copolymer is contained in the intermediate layer in an amount of 10 to 70% by mass. The laminated film according to claim 1 or 2 , wherein the intermediate layer includes a crystalline polypropylene resin constituting a base material layer and the copolymer constituting a heat-sealing layer. And the wetting tension after water washing of the heat sealable layer surface 31 mN / m or more, to any one of claims 1 to 3 is formed on the surface of the pre-water washing of the heat-fusible layer are those anti-fogging agent is present The laminated film as described. The film according to any one of claims 1 to 4 , wherein the laminated film is biaxially stretched. A package comprising the laminated film according to any one of claims 1 to 5 .

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