JP2019142018A - Heat shrinkable laminate film - Google Patents

Abstract

To provide a heat shrinkable laminate film which is excellent in shrinkability at low temperature, heat resistance, mechanical strength, and transparency and allowing for suppression of pinhole-like seal failures at a sealed part by melt-cut when sealed by melt-cut by an automatic packaging machine or the like.SOLUTION: A heat shrinkable laminate film 1 is provided which is formed by laminating surface layers 3 on both surfaces of a core layer 2, and in which the core layer is made of a polyethylene-based resin composition (A) composed of 60-95 wt.% of linear low-density polyethylene (a-1) having a density of 0.915-0.930 g/cmand 5-40 wt.% of linear high-density polyethylene (a-2) having a density of 0.935-0.965 g/cmand high-density polyethylene (a-3), the surface layer is made of a polypropylene-based resin composition (B) including a polypropylene-based resin (b) as a main component, and the polypropylene-based resin composition (B) has a crystallization temperature lower than 106°C in differential scanning calorimetry using a differential scanning calorimeter.SELECTED DRAWING: Figure 1

Description

  The present invention is a heat-shrinkable film having a laminated structure used for packaging, in particular, low-temperature shrinkage, heat resistance, mechanical strength, and transparency, and a pinhole-like seal defect occurs in the fusing seal part. The present invention relates to a heat-shrinkable laminated film that can be suppressed.

  Conventionally, after covering a package with a heat-shrinkable film, fusing and sealing the joint, the heat-shrinkable film is thermally shrunk by a method such as passing through a heat-shrink oven or blowing hot air. Heat-shrinkable film packaging has been performed. This heat-shrinkable film packaging is excellent in economy, workability, and high speed and is actively used in the packaging field. Various heat-shrinkable films made of polyvinyl chloride resin, polyethylene resin, polypropylene resin, etc. are known as heat-shrinkable films used for heat-shrinkable film packaging, but they are inexpensive and easy to dispose of after use. In view of the above, polyolefin heat-shrinkable films such as polyethylene resin and polypropylene resin are particularly preferred.

  However, the polyethylene heat-shrinkable film can shrink at a relatively low temperature. In particular, in the case of a heat-shrinkable film using linear low density polyethylene, the impact resistance of the fusing seal part is excellent, However, it has disadvantages such as difficulty in stretching and inferior heat resistance. On the other hand, polypropylene-based heat-shrinkable films are poor in low-temperature shrinkage, impact resistance, and tear resistance, but are excellent in stretch processability and heat resistance. The heat-shrinkable film which laminated | stacked is used.

For example, in Patent Document 1, as a laminated heat-shrinkable film excellent in low-temperature shrinkability and heat resistance, both outermost layers are made of a crystalline polypropylene resin, and the intermediate layer has a density of 0.890 to 0.905 g / cm. ³ , a polyolefin-based laminated heat-shrinkable film using a linear low-density polyethylene resin having a Vicat softening point of 60 to 80 ° C. or a resin composition containing the resin as a main component is described.

Patent Document 2 discloses an ethylene copolymer having a density of 0.90 to 0.93 g / cm ³ and a density of 0.87 as a laminated heat-shrinkable film having excellent stretch processability, low-temperature shrinkage, and slip properties. Polyolefin-based heat-shrinkable film layer composed of a polyethylene-based heat-shrinkable film layer composed of an ethylene-based copolymer of ˜0.91 g / cm ^{3 and} a polypropylene-based heat-shrinkable film layer composed of a resin mainly composed of propylene. A film is described.

JP 63-214446 A JP 63-173641 A

  The polyolefin-based laminated heat-shrinkable film described above is characterized by excellent low-temperature shrinkage and heat resistance and relatively high mechanical strength. However, the fusing sealability in an automatic packaging machine is not always satisfactory. For example, in an L-shaped half-fold automatic packaging machine, after passing through a heat shrink oven or the like, there is a problem that a pinhole-like seal defect (hole) is generated in the fusing seal part. When these pinhole-shaped holes occur, air leakage occurs when the heat-shrinkable film heat-shrinks, causing shrinkage defects (wrinkles and avatar patterns), resulting in deterioration of the packaging finish, and the occurrence of holes makes the package to be dustproof. , Causing problems such as impaired display properties.

  In addition, the L-shaped half-fold automatic packaging machine is slower but smaller than the pillow-type automatic packaging machine, and after the fusing and sealing, the package is immediately transported to the heat shrink oven and the film is shrunk. It is required that the sealing strength immediately after sealing, that is, the melt adhesive strength (hot tack property) of the fusing seal portion is strong.

  The present invention has been made in view of such problems, and is excellent in low-temperature shrinkage, heat resistance, mechanical strength, and transparency, and has a pinhole in the fusing seal portion even when fusing and sealing with an automatic packaging machine or the like. An object of the present invention is to provide a heat-shrinkable laminated film capable of suppressing the occurrence of a seal defect having a shape.

  First, the present inventors examined the cause of the occurrence of pinhole-like seal defects in the fusing seal part, and this problem has a variation in the sealing strength of the fusing seal part, and there are places where the sealing strength is partially weak. When present, it was found to be generated by stress during film shrinkage. In other words, the fusing seal of an automatic packaging machine, etc., cuts the film at the tip of a heated sharp cutting blade (metal wire, metal blade) and simultaneously melts and seals the cut surface at the side of the heated fusing blade. Therefore, when the cutting blade is separated from the film, strictly speaking, there are a portion where the molten resin is partially taken by the cutting blade and a portion where the molten resin is not. Then, since the resin puddle in the fusing seal part becomes non-uniform, the fusing seal part has a part with a strong seal strength and a part with a weak seal strength. It becomes a pinhole-like seal defect.

  Therefore, the present inventors have made it possible to prevent the molten resin from being partially taken by the fusing blade during fusing sealing, and to prevent the resin puddle in the fusing seal portion from becoming nonuniform, the crystallization temperature and crystallization speed of the film. As a result of intensive investigation based on the consideration that reducing the molten resin taken by the cutting blade is effective in suppressing pinhole-like seal defects in the fusing seal part, By blending linear low density polyethylene with a relatively low crystallization temperature into linear low density polyethylene with a high crystallization temperature, high crystallization temperature of the core layer is increased, and crystallization is performed. The present inventors have found that the film can be speeded up and can be made into a film having a small seal strength variation at the fusing seal portion and excellent in the seal strength, and the present invention has been completed.

According to the present invention,
(1) A surface layer is laminated on both surfaces of the core layer, and the core layer has a linear low density polyethylene (a-1) having a density of 0.915 to 0.930 g / cm ³ and 60 to 95% by weight; Polyethylene resin composition (A) comprising linear high-density polyethylene (a-2) and / or high-density polyethylene (a-3) of 5 to 40% by weight with a density of 0.935 to 0.965 g / cm ³ And the surface layer is composed of a polypropylene resin composition (B) containing a polypropylene resin (b) as a main component, and the polypropylene resin composition (B) is a differential using a differential scanning calorimeter (DSC). There is provided a heat shrinkable laminated film characterized in that the crystallization temperature in scanning calorimetry is less than 106 ° C.,
(2) Linear low density polyethylene (a-1), linear high density polyethylene (a-2) and / or high density polyethylene (a-3) contained in the polyethylene resin composition (A) The heat-shrinkable laminated film according to (1), wherein the density difference is 0.010 g / cm ³ or more,
(3) The polyethylene resin composition (A) is characterized in that the crystallization temperature in differential scanning calorimetry using a differential scanning calorimeter (DSC) is 106 ° C. or higher (1) or (2) The heat-shrinkable laminated film described is provided,
(4) The heat shrinkage according to any one of (1) to (3), wherein the polypropylene resin (b) is a propylene-ethylene random copolymer having an ethylene content of 3 to 7%. Functional laminated film is provided,
(5) The heat-shrinkable laminated film according to any one of (1) to (4), wherein the ratio of the polyethylene resin contained in the entire heat-shrinkable laminated film is more than 50% by weight. ,
(6) When the thickness of the core layer is ta and the thickness of the surface layer is tb ₁ and tb ₂ , respectively, tb ₁ + tb ₂ ≦ ta ≦ 2 (tb ₁ + tb ₂ ) A heat-shrinkable laminated film according to any one of (1) to (5) is provided,
(7) The heat-shrinkable laminated film according to any one of (1) to (6), which is used for a half-fold automatic packaging machine.

  The heat-shrinkable laminated film of the present invention is excellent in low-temperature shrinkage, heat resistance, mechanical strength, and transparency, and has a pinhole shape in the fusing seal part even when fusing and sealing using an automatic packaging machine or the like. Since generation | occurrence | production of a seal | sticker defect can be suppressed, a very favorable packaging finish can be obtained. Moreover, since the heat-shrinkable laminated film of the present invention is excellent in hot tack property, it can be suitably used as a packaging material for use in an L-shaped half-fold automatic packaging machine or the like.

It is an expanded sectional view of the heat-shrinkable laminated film which concerns on Embodiment 1 of this invention. It is an expanded sectional view of the heat-shrinkable laminated film according to Embodiment 2 of the present invention.

  Hereinafter, the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, In the range with the effect of this invention, it can take a various form.

[Heat-shrinkable laminated film (Embodiment 1)]
FIG. 1 is an enlarged cross-sectional view of a heat-shrinkable laminated film according to Embodiment 1 of the present invention. As shown in FIG. 1, the heat-shrinkable laminated film 1 of the present invention has a multilayer structure in which surface layers 3 are laminated on both surfaces of a core layer 2. In addition, it is also possible to provide another layer between each layer in the range which can achieve the objective of this invention.

[Core layer]
The core layer is formed from the polyethylene-based resin composition (A), and is a layer mainly contributing to the low temperature shrinkability, mechanical strength, fusing sealability, hot tackiness, etc. of the heat shrinkable laminated film.

<Polyethylene resin composition (A)>
The polyethylene-based resin composition (A) has a density of 0.935 to 0.965 g of linear low density polyethylene (a1) having a density of 0.915 to 0.930 g / cm ³ and 60 to 95% by weight. The linear high-density polyethylene (a2) and / or the high-density polyethylene (a3) that are / cm ³ are composed of 5 to 40% by weight. In the present invention, linear low-density polyethylene (a1) having a relatively low crystallization temperature and excellent low-temperature shrinkability, linear high-density polyethylene (a2) and / or high-density polyethylene (/ By blending with a3), the crystallization temperature of the core layer can be increased, the crystallization speed can be increased, and the sealing strength of the fusing seal portion is small, and the film has excellent sealing strength. It is something that can be done.

<Linear low density polyethylene (a1)>
The linear low density polyethylene (a1) contained in the polyethylene resin composition (A) is a polymer in which a monomer unit based on ethylene and a monomer unit based on α-olefin are copolymerized. The content of the monomer unit based on the polymer is 50% by weight or more based on the total weight (100% by weight) of the linear low density polyethylene (a1). Examples of the α-olefin in the linear low density polyethylene (a1) include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene and the like. However, 1-hexene and 1-octene are desirable from the viewpoint of film forming stability.

The linear low density polyethylene (a1) has a density of 0.915 to 0.930 g / cm ³ . Preferably the density is 0.915~0.925g / cm ^3, more preferably 0.915~0.923g / cm ^3. The linear low density polyethylene (a1) having a density in the above range has a relatively low crystallization temperature, low temperature shrinkage, mechanical strength (tensile rupture strength, tensile elastic modulus, elongation, tear load, resistance to fusing seals). Excellent impact). When the density is smaller than the above range, the mechanical strength is lowered, which is not preferable. When the density is larger than the above range, the low temperature shrinkability may be deteriorated. In addition, the density in this invention says the value measured based on JIS-K7112.

  The linear low density polyethylene (a1) preferably has a crystallization temperature of 90 to 110 ° C. in differential scanning calorimetry using a differential scanning calorimeter (DSC). The crystallization temperature is more preferably 92 to 107 ° C, and further preferably 95 to 105 ° C.

  The measurement of the crystallization temperature in the differential scanning calorimetry using a differential scanning calorimeter (DSC) is basically performed in accordance with JIS-K7121, but in the present invention, the crystallization temperature is determined as follows. And First, about 10 mg of a sample is sealed in an aluminum pan, heated to 230 ° C. at a rate of 10 ° C./min under a nitrogen stream, held for 1 minute, and then cooled to 0 ° C. at a rate of 10 ° C./min. The temperature at the top of the crystallization peak on the highest temperature side when crystallization is performed.

  The MFR (melt flow rate: melt flow rate) of the linear low density polyethylene (a1) is not particularly limited, but is 0.1 to 10 g / 10 min from the viewpoint of film forming and stretching stability. It is preferable that The MFR is more preferably 0.3 to 8 g / 10 minutes, and particularly preferably 0.5 to 5 g / 10 minutes. If the MFR is smaller than the above range, there is a problem that the motor load at the time of extrusion becomes large. If the MFR is larger than the above range, the stretching stability may be lowered. In addition, MFR in this invention says the value measured based on JIS-K7210.

<Linear high-density polyethylene (a2)>
The linear high-density polyethylene (a2) contained in the polyethylene resin composition (A) is a polymer in which a monomer unit based on ethylene and a monomer unit based on α-olefin are copolymerized. The content of the monomer unit based on the polymer is 50% by weight or more based on the total weight (100% by weight) of the linear high-density polyethylene (a2). Examples of the α-olefin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene and 1-dodecene. Hexene and 1-octene are desirable from the viewpoint of film forming stability.

The linear high-density polyethylene (a2) has a density of 0.935 to 0.965 g / cm ³ . Preferably the density is 0.935~0.955g / cm ^3, more preferably 0.935~0.945g / cm ^3. The linear high-density polyethylene (a2) having a density in the above range has a high crystallization temperature and a high crystallization speed, and thus has excellent hot tack properties. If the density is less than the above range, the resulting film is excellent in low temperature shrinkage, but the core layer has a low crystallization temperature, and the seal strength may vary widely. There is a risk that the sex becomes small.

  The linear high density polyethylene (a2) preferably has a crystallization temperature of 108 ° C. or higher in differential scanning calorimetry using a differential scanning calorimeter (DSC). The crystallization temperature is more preferably 110 ° C. or higher, and further preferably 112 ° C. or higher.

  The MFR of the linear high-density polyethylene (a2) is not particularly limited, but it is preferable that the MFR is 0.1 to 10 g / 10 min from the viewpoint of film forming processing and stretching process stability. The MFR is more preferably 0.3 to 8 g / 10 minutes, and particularly preferably 0.5 to 5 g / 10 minutes. If the MFR is smaller than the above range, there is a problem that the motor load at the time of extrusion becomes large. If the MFR is larger than the above range, the stretching stability may be lowered.

<High-density polyethylene (a3)>
The high-density polyethylene (a3) is a polymer obtained by polymerizing ethylene as a monomer unit, and is a polymer bonded in a straight chain with few molecular chain branches.

The high density polyethylene (a3) has a density of 0.935 to 0.965 g / cm ³ . Preferably the density is 0.945~0.965g / cm ^3, more preferably 0.955~0.965g / cm ^3. The high density polyethylene (a3) having a density in the above range has a high crystallization temperature and a high crystallization speed, and thus has excellent hot tack properties. If the density is smaller than the above range, the crystallization temperature of the core layer may be low, and the hot tack property may be deteriorated. If the density is larger than the above range, the low temperature shrinkability may be decreased.

  The high-density polyethylene (a3) preferably has a crystallization temperature of 110 ° C. or higher in differential scanning calorimetry using a differential scanning calorimeter (DSC). The crystallization temperature is more preferably 112 ° C. or higher, and further preferably 115 ° C. or higher.

  The MFR of the high-density polyethylene (a3) is not particularly limited, but it is preferable that the MFR is 0.1 to 10 g / 10 minutes from the viewpoint of the stability of the film forming process and the stretching process. The MFR is more preferably 0.3 to 8 g / 10 minutes, and particularly preferably 0.5 to 5 g / 10 minutes. If the MFR is smaller than the above range, there is a problem that the motor load at the time of extrusion becomes large. If the MFR is larger than the above range, the stretching stability may be lowered.

The density difference between the linear low density polyethylene (a1) and the linear high density polyethylene (a2) and / or the high density polyethylene (a3) contained in the polyethylene resin composition (A) is 0.010 g / cm ^3. The above is preferable. More preferably a density difference is 0.015 g / cm ³ or more, still more preferably 0.020 g / cm ³ or more, and particularly preferably 0.035 g / cm ³ or more. When the density difference is smaller than the above range, the crystallization temperature of the polyethylene resin composition (A) is low and the crystallization speed is low, so that the seal strength varies greatly and the seal strength may be lowered.

  The blending ratio of the linear low density polyethylene (a1) to the linear high density polyethylene (a2) and / or the high density polyethylene (a3) in the polyethylene resin composition (A) is 60 to 95% by weight: 40 ~ 5% by weight. The blending ratio is preferably 65 to 90% by weight: 35 to 10% by weight, more preferably 70 to 85% by weight: 30 to 15% by weight, and particularly preferably 70 to 83% by weight: 30 to 17% by weight. When the blending ratio of the linear high-density polyethylene (a2) and / or the high-density polyethylene (a3) is less than the above range, the crystallization temperature of the core layer is low, the seal strength varies greatly, and the seal strength decreases. There is a fear. If the blending ratio is higher than the above range, the film may be cut, whitened, necked, etc. in the stretching process, and the film may not be stably obtained.

  The polyethylene resin composition (A) preferably has a crystallization temperature of 106 ° C. or higher in differential scanning calorimetry using a differential scanning calorimeter (DSC). If the crystallization temperature of the polyethylene-based resin composition (A) is 106 ° C. or higher, it is possible to obtain a film having a small variation in seal strength and excellent in seal strength. After the package is passed through a heat shrink oven or the like, it is possible to suppress the occurrence of pinhole-like seal defects (holes) in the fusing seal part. The crystallization temperature is more preferably 108 ° C. or higher, further preferably 109 ° C. or higher, and particularly preferably 110 ° C. or higher. The upper limit of the crystallization temperature is not particularly limited, but linear high-density polyethylene (a2) has a crystallization temperature of about 114 ° C., and high-density polyethylene (a3) has a crystallization temperature of about 117 ° C. This is the upper limit at the present time of the crystallization temperature of the polyethylene resin composition (A) in the present invention. In addition, the crystallization temperature of the polyethylene resin composition (A) may be measured from a pellet or a film obtained by kneading each component contained in the polyethylene resin composition (A) in a molten state, For example, a value measured from a sample obtained by kneading each component under the conditions of a processing temperature of 200 ° C. and a rotation speed of 60 rpm using a lab plast mill manufactured by Toyo Seiki Seisakusho may be used.

  The polyethylene resin composition (A) may contain other thermoplastic resins in addition to the linear low density polyethylene (a1), the linear high density polyethylene (a2), and the high density polyethylene (a3). Examples of other thermoplastic resins include low density polyethylene, medium density polyethylene, polypropylene, ethylene-propylene copolymer, and copolymers of ethylene or propylene and other α-olefins. Can be used alone or in combination of two or more. When the polyethylene-based resin composition (A) contains another thermoplastic resin, the blending amount of the other thermoplastic resin is linear low density polyethylene (a1) and linear high density polyethylene (a2) and / or The total amount (100 parts by weight) with the high-density polyethylene (a3) is preferably 0.1 to 30 parts by weight, more preferably 0.5 to 20 parts by weight, More preferably, it is 10 parts by weight.

[Surface layer]
The surface layer is formed from the polypropylene-based resin composition (B), and is a layer mainly contributing to the heat resistance of the heat-shrinkable laminated film, the stability of film formation / stretching, and the like.

<Polypropylene resin composition (B)>
The polypropylene resin composition (B) contains the polypropylene resin (b) as a main component. In the present invention, “main component” means that the constituent ratio of the resin component constituting the resin composition is 50% by weight or more, preferably 60% by weight or more. More preferably 80% by weight or more, still more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

<Polypropylene resin (b)>
The polypropylene resin (b) is a homopolypropylene or a copolymer obtained by copolymerization of a monomer unit based on propylene and a monomer unit based on α-olefin, and contains a monomer unit based on propylene The amount of the propylene-α-olefin copolymer is 50% by weight or more based on the total weight (100% by weight) of the polypropylene resin (b). The propylene-α-olefin copolymer is classified into a block copolymer, a random copolymer, and a random block copolymer depending on the arrangement of the monomers, and any of these may be used in the present invention. Examples of the α-olefin copolymerized with propylene include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, and the like. -Desirable from the viewpoint of stability of stretching.

  The polypropylene resin (b) is preferably a propylene-ethylene random copolymer (b1), and a polypropylene resin composition (B) containing the propylene-ethylene random copolymer (b1) as a main component is used as a surface layer. The heat-shrinkable laminated film used is excellent in film forming / stretching stability. The propylene-ethylene random copolymer (b1) preferably has an ethylene content of 2 to 10% by weight, more preferably 3 to 7% by weight, and 4 to 6% by weight. More preferably. If the ethylene content is smaller than the above range, the shrinkage rate may be insufficient, and a heat-shrinkable laminated film having a desired shrinkage rate may not be obtained. When covered with a shrinkable laminated film and thermally shrunk, there is a possibility that a tight packaging finish cannot be obtained.

  The MFR of the polypropylene-based resin (b) is not particularly limited, but the MFR is preferably 0.1 to 10 g / 10 minutes from the viewpoint of the stability of film formation and stretching. The MFR is more preferably 0.3 to 8 g / 10 minutes, and particularly preferably 0.5 to 5 g / 10 minutes. If the MFR is smaller than the above range, there is a problem that the motor load at the time of extrusion becomes large. If the MFR is larger than the above range, the stretching stability may be lowered.

  The polypropylene resin (b) preferably has a crystallization temperature of 90 to 106 ° C. in differential scanning calorimetry using a differential scanning calorimeter (DSC). The crystallization temperature is more preferably 95 to 104 ° C, further preferably 97 to 102 ° C.

  Polypropylene resin composition (B) has a crystallization temperature of less than 106 ° C. in differential scanning calorimetry using a differential scanning calorimeter (DSC). The crystallization temperature is preferably less than 105 ° C, more preferably less than 104 ° C, and particularly preferably less than 102 ° C. The reason is not clear, but if the crystallization temperature of the polypropylene resin composition (B) is 106 ° C. or higher, pinhole-shaped seal defects may easily occur in the fusing seal portion. The lower limit of the crystallization temperature is not particularly limited, but the polypropylene resin (b) having a crystallization temperature of about 90 ° C. is available, and this is the polypropylene resin composition (B) in the present invention. This is the current lower limit of the crystallization temperature. In addition, what is necessary is just to measure the crystallization temperature of a polypropylene resin composition (B) by the method mentioned above.

  In the polypropylene resin composition (B), the amount of the nucleating agent contained in the composition is preferably less than 2500 ppm. The reason is not clear, but if the blending amount of the nucleating agent contained in the polypropylene resin composition (B) exceeds 2500 ppm, pinhole-like seal defects may easily occur in the fusing seal part. The nucleating agent contained in the polypropylene resin composition (B) is more preferably less than 2000 ppm. The type of the nucleating agent is not particularly limited, and conventionally known nucleating agents can be used. For example, benzoic acid metal salts, aromatic phosphate metal salts, aromatic phosphate metal salts and alkalis can be used. Examples include mixtures with metal salts, organic nucleating agents such as dibenzylindene sorbitols, amino acid metal salts, and rosin acid metal salts, and inorganic nucleating agents such as talc, clay, and calcium carbonate.

  The polypropylene resin composition (B) may be blended with other thermoplastic resins in addition to the polypropylene resin (b). Examples of other thermoplastic resins include low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-propylene copolymer, and copolymers of ethylene or propylene and other α-olefins. Can be used alone or in combination of two or more.

  The heat-shrinkable laminated film preferably contains more than 50% by weight of the polyethylene resin contained in the entire heat-shrinkable laminated film (100% by weight). By making the polyethylene resin contained in the entire heat-shrinkable laminated film more than 50% by weight, it has excellent low-temperature shrinkage, heat resistance, mechanical strength and transparency, high crystallization temperature, and high crystallization speed. It can be set as a heat-shrinkable laminated film, and by extension, the heat-shrinkable laminated film can be made into a seal-strength laminated film having a small variation in the sealing strength of the fusing seal part and excellent in the sealing strength. In addition, when a package is covered with a heat-shrinkable laminated film, the joint is melt-sealed and heat-shrinked with a heat shrink oven or the like, a substantially conical bulge is generated at the end of the melt-sealed seal. However, if the horn is hard, consumers may be injured. Therefore, the horn is required to be small and soft. If it is a heat-shrinkable laminated film containing more than 50% by weight of a polyethylene resin, the horn generated at the end of the fusing seal part can be made small and soft.

  The thickness of the heat-shrinkable laminated film is not particularly limited, but is preferably 5 to 50 μm and more preferably 7 to 30 μm from the viewpoints of mechanical strength and workability.

The thickness ratio of each layer of the heat-shrinkable laminated film is not particularly limited. For example, when the thickness of the core layer is ta and the thicknesses of both surface layers are tb ₁ and tb ₂ , respectively, tb ₁ + tb It is preferable that ₂ ≦ ta ≦ 2 (tb ₁ + tb ₂ ). By setting the thickness of the core layer to be equal to or greater than the thickness of both surface layers, a heat shrinkable laminated film having a high crystallization temperature and a high crystallization speed can be obtained. A heat-shrinkable laminated film having small variations and excellent sealing strength can be obtained. Note that the thicknesses of both surface layers laminated and integrated with the core layer are preferably the same, but not necessarily the same.

  In each layer constituting the heat-shrinkable laminated film of the present invention, known antioxidants, lubricants, anti-blocking agents, nucleating agents, anti-fogging agents, which are usually used for thermoplastic resins, as long as the object of the present invention is not impaired. Additives such as an agent, an antistatic agent, a plasticizer, a light stabilizer, an ultraviolet absorber, a filler, and a colorant can be blended.

[Heat-shrinkable laminated film (Embodiment 2)]
FIG. 2 is an enlarged cross-sectional view of a heat-shrinkable laminated film according to Embodiment 2 of the present invention. As described above, the heat-shrinkable laminated film of the present invention is formed by laminating and integrating the surface layers on both sides of the core layer. The core layer and the surface layer are considered in consideration of interlayer adhesion strength, regeneration reduction, and the like. An intermediate layer may be provided between them. Specifically, as shown in FIG. 2, the heat-shrinkable laminated film 11 is laminated in the order of the first surface layer 13 / first intermediate layer 14 / core layer 12 / second intermediate layer 14 / second surface layer 13. Multi-layer configuration. In addition, it is also possible to provide another layer between each layer in the range which can achieve the objective of this invention.

[Middle layer]
The intermediate layer is obtained by melting and regenerating a nonconforming product generated during production, and the intermediate layer includes a polyethylene-based resin composition (A) that forms a core layer and a polypropylene-based resin composition that forms a surface layer ( B) is included, but the intermediate layer preferably contains more than 50% by weight of the polyethylene resin composition (A).

The thickness of the intermediate layer may be determined in consideration of the amount of nonconforming product or the like generated during production, and is not particularly limited. For example, the thickness of the entire intermediate layer is t, and the thickness of the first intermediate layer is tc. ₁ , where tc ₂ is the thickness of the second intermediate layer, 0.2t ≦ (tc ₁ + tc ₂ ) ≦ 0.4 t is preferable. In addition, although it is preferable that the thickness of an intermediate | middle layer is respectively the same, it does not necessarily need to be the same.

[Method for producing heat-shrinkable laminated film]
The production method of the heat-shrinkable laminated film of the present invention can employ a conventionally known method, and is not particularly limited. For example, the polypropylene resin composition (B ), A polyethylene-based resin composition (A) for forming the core layer, and a regenerated reducing resin for forming the intermediate layer as necessary are supplied from separate extruders and pressed from one die. Examples thereof include a method in which an unstretched multilayer film is formed by an inflation coextrusion method, a T-die coextrusion method, or the like, and is stretched in the next step. The thickness of the unstretched multilayer film is not particularly limited, but is, for example, 200 to 500 μm.

  Moreover, the unstretched multilayer film formed by the said coextrusion method can be made into the film which has heat shrinkability by performing a extending | stretching process. As the stretching method, a conventionally known method can be adopted and is not particularly limited, and examples thereof include a tenter type biaxial stretch molding method and a tubular type biaxial stretch molding method. The stretching conditions of the unstretched multilayer film may be appropriately determined according to the required performance and the like, and are not particularly limited. For example, the stretching speed is 10 to 100 m / min and the stretching temperature is 90 to 130 ° C. The multilayer film may be stretched 2 to 10 times in length and width.

  Hereinafter, the packaging film of this invention is demonstrated based on an Example. In addition, the measurement / evaluation method performed in each heat-shrinkable laminated film is as follows.

(1) Crystallization temperature It measured by the method described in the text of the specification.
(2) Tensile strength, tensile elongation, tensile modulus According to ASTM D882, the tensile speed was 5 mm / min and the initial gripping interval was 50 mm.
(3) Tear load Measured according to ASTM D 1922.
(4) Haze The haze was measured with “NDH2000” manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K7105. Note that D65 was used as the light source.
(5) Thermal contraction rate It measured based on JISZ1709-1995. The thermal shrinkage at 90 ° C., 100 ° C., 110 ° C., and 120 ° C. was measured with a thermal solvent of glycerin and an immersion time of 10 seconds.
(6) Evaluation of seal defects in the fusing seal part Using an L-shaped half-fold automatic packaging machine (Hanagata Co., Ltd., product name “HP-10”, fusing blade: sharp metal blade at the tip, blade holder: Teflon sheet) Twenty packaging boxes (width 200 mm × depth 120 mm × height 30 mm) are continuously covered with a film and fused and sealed (melting blade temperature: 190 ° C., sealing time: 1 second), and then heat shrink oven (oven temperature: oven temperature: 160 ° C., passage time: 6 seconds), and heat shrink-wrapped, and the occurrence of seal defects in the fusing seal portion in each package was visually confirmed. The evaluation criteria are as follows.
<Evaluation criteria>
The total number of points for each package, with 5 points indicating no abnormalities in the seal part, 1 point where a seal defect such as a pinhole has occurred in the seal part, and 0 point when the seal part is torn across the entire width Evaluation in terms of points.
◎: Over 70 points, 100 points or less ○: Over 50 points, 70 points or less △: Over 30 points, 50 points or less ×: Over 10 points, 30 points or less XX: 10 points or less

The raw materials used in each example and comparative example are as follows.
<Linear low density polyethylene>
LLDPE (1) [Density: 0.916 g / cm ³ , Crystallization temperature: 102.2 ° C.]
LLDPE (2) [density: 0.912 g / cm ³ , crystallization temperature: 93.3 ° C.]
<Linear high density polyethylene>
LHDPE [density: 0.940 g / cm ³ , crystallization temperature: 113.6 ° C.]
<High density polyethylene>
HDPE [density 0.957 g / cm ³ , crystallization temperature: 116.7 ° C.]
<Polypropylene resin>
R-PP [propylene-ethylene random copolymer, MFR: 2.3 g / 10 min, ethylene content: 4.2 to 5.0%, crystallization temperature: 101.7 ° C.]
The density is a value measured according to JIS-K7112, and the MFR is a value measured according to JIS-K7210.

[Examples 1 to 5, Comparative Examples 1 to 4]
Using the resin composition shown in Table 1, an unstretched film of the first surface layer / first intermediate layer / core layer / second intermediate layer / second surface layer was formed by inflation coextrusion, Then, simultaneous biaxial stretching (length 4.3 times, width 4.5 times) was performed by a tubular stretching method to obtain a film having a thickness of 13.5 μm. The evaluation results of the obtained film are shown in Table 1. The thicknesses of the first surface layer and the second surface layer and the thicknesses of the first intermediate layer and the second intermediate layer are the same.

As shown in Table 1, linear density of 0.935 to 0.965 g / cm ³ is added to linear low density polyethylene having a density of 0.915 to 0.930 g / cm ³ contained as a main component in the core layer. The heat-shrinkable laminated films of Examples 1 to 3 blended with chain high-density polyethylene are excellent in low-temperature shrinkage, mechanical strength, and transparency, and the crystallization temperature of the core layer exceeds 106 ° C. In the fusing seal by the half-fold automatic packaging machine, the result of effectively suppressing the pinhole-like seal defect generated in the fusing seal part was shown. Further, a high density polyethylene having a density of 0.935 to 0.965 g / cm ³ was blended with a linear low density polyethylene having a density of 0.915 to 0.930 g / cm ³ contained as a main component in the core layer. The heat-shrinkable laminated films of Examples 4 and 5 are excellent in low-temperature shrinkage, mechanical strength, and transparency, and the crystallization temperature of the core layer exceeds 106 ° C. The results of effectively suppressing pinhole-like seal defects occurring in the fusing seal part are shown.

On the other hand, as shown in Table 1, the density contained as a main component in the core layer to the linear low density polyethylene 0.915~0.930g / cm ^3, density of 0.935~0.965g / cm ³ The heat-shrinkable laminated films of Comparative Examples 1 and 2 in which no linear high-density polyethylene or high-density polyethylene was blended had the same low-temperature shrinkage, mechanical strength, and transparency as those of Examples 1 to 5. However, since the crystallization temperature of the core layer is less than 106 ° C, in the fusing seal by L-shaped half-fold automatic packaging, the result that pinhole-like seal defects occur in the fusing seal part of almost all samples is shown. It was. Moreover, in order to raise the crystallization temperature of a surface layer, the heat-shrinkable film of the comparative example 3 which mix | blended the nucleating agent with the polypropylene resin contained as a main component in a surface layer is low temperature shrinkability, mechanical strength, and transparency. Although the same as in Examples 1 to 5, the crystallization temperature of the core layer is less than 106 ° C., and the crystallization temperature of the surface layer exceeds 106 ° C. The result of the melt-sealed seal portion of this sample was shown to tear across the entire width.

Furthermore, as shown in Table 1, the density contained as a main component in the core layer to the linear low density polyethylene 0.915~0.930g / cm ^3, density of 0.935~0.965g / cm ³ The heat-shrinkable film of Comparative Example 4 in which a high-density polyethylene was blended and a nucleating agent was blended into a polypropylene resin contained as a main component in the surface layer was the same as in Example 1 in terms of low-temperature shrinkage, mechanical strength, and transparency. However, since the crystallization temperature of the surface layer exceeds 106 ° C., pinhole-like seal defects are generated in the fusing seal portions of all samples in the L-type half-fold automatic packaging fusing seal. Or the result that tearing occurred over the entire width was shown.

1, 11: Heat-shrinkable laminated film 2, 12: Core layer 3, 13: Surface layer 14: Intermediate layer

Claims (7)

The surface layer is laminated on both sides of the core layer,
The core layer is a density 0.915~0.930g / cm ³ linear low-density polyethylene (a-1) 60~95% by weight, a density of 0.935~0.965g / cm ³ linear high A polyethylene resin composition (A) comprising 5 to 40% by weight of density polyethylene (a-2) and / or high density polyethylene (a-3),
The surface layer is made of a polypropylene resin composition (B) containing a polypropylene resin (b) as a main component,
The polypropylene resin composition (B) has a crystallization temperature of less than 106 ° C. in a differential scanning calorimetry using a differential scanning calorimeter (DSC). Density of linear low density polyethylene (a-1) and linear high density polyethylene (a-2) and / or high density polyethylene (a-3) contained in the polyethylene resin composition (A) The heat shrinkable laminated film according to claim 1, wherein the difference is 0.010 g / cm ³ or more.   The heat shrinkability according to claim 1 or 2, wherein the polyethylene-based resin composition (A) has a crystallization temperature of 106 ° C or higher in a differential scanning calorimetry using a differential scanning calorimeter (DSC). Laminated film.   The heat-shrinkable laminated film according to any one of claims 1 to 3, wherein the polypropylene resin (b) is a propylene-ethylene random copolymer having an ethylene content of 3 to 7%.   The heat-shrinkable laminated film according to any one of claims 1 to 4, wherein the ratio of the polyethylene resin contained in the whole heat-shrinkable laminated film is more than 50% by weight. 2. The thickness of the core layer is ta, and the thickness of the surface layer is tb ₁ and tb ₂ , respectively, and tb ₁ + tb ₂ ≦ ta ≦ 2 (tb ₁ + tb ₂ ). The heat-shrinkable laminated film according to any one of 5 to 5. The heat-shrinkable laminated film according to any one of claims 1 to 6, wherein the heat-shrinkable laminated film is used in a half-fold automatic packaging machine.

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