JP2012035466A - Multilayer polyolefin-based heat shrinkable film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer polyolefin-based heat shrinkable film which has excellent low-temperature shrink characteristics, heat resistance, mechanical strength, film-forming stability, hot slip properties, heat seal properties and resource-saving properties, from which a toxic gas is not produced even when it is burned during its disposal, and which has no poor external appearance due to stringiness and has high seal strength.SOLUTION: The multilayer polyolefin-based heat shrinkable film is obtained by forming a surface layer on both sides of an intermediate layer containing a polyethylene resin and integrating the surface layers with the intermediate layer into one body. The surface layer contains 30-50 wt.% of a polypropylene resin (A) which has a ≥30°C melt start temperature, <130°C melt peak temperature, ≤150°C melt end temperature and 40-60% ratio of a low temperature endothermic ratio, and 50-70 wt.% of another polypropylene resin (B) having a 130-145°C melt peak temperature, ≥90°C crystallization temperature and a 5-10 g/10 minute melt flow rate.

Description

  The present invention relates to a multilayer polyolefin heat-shrink film used for commercial packaging. More specifically, it has excellent properties such as low temperature shrinkage, heat resistance, mechanical strength, film formation stability, hot slip, heat sealability and resource saving, and does not generate toxic gas even when burned during disposal. It is related with the multilayer polyolefin heat-shrink film which does not have the appearance defect by stringing, and has strong sealing strength.

  Conventionally, polyvinyl chloride (PVC) having excellent shrinkage performance at a low temperature has been widely used as a raw material used for a heat-shrinkable film. However, in recent years, attention has been paid to the adverse effects on the environment caused by toxic gases such as dioxins generated during the combustion of PVC, and there is an active movement to review the use of plastic products made from PVC.

  Such movement is no exception in heat-shrinkable films, and heat-shrinkable films using polyethylene or polypropylene are widely used today as raw materials to replace PVC.

  However, although the heat-shrinkable film mainly composed of polyethylene is excellent in low-temperature shrinkability, it has a problem that its heat resistance is insufficient and the shrinkable temperature range is extremely narrow. In addition, heat-shrinkable film mainly composed of polypropylene is excellent in heat resistance, but has low low-temperature shrinkability and cannot be heat-shrinkable unless it is high temperature, and has poor mechanical strength. It had the problem of not being suitable for packaging applications.

  In view of this, a heat-sealable multilayer film having heat resistance by forming a linear low-density polyethylene as a main component and crosslinking the linear low-density polyethylene has been proposed (Patent Document 1).

  However, the heat-sealable multilayer film is cross-linked with the linear low-density polyethylene that constitutes the film. There was a problem that it could not be reused, the manufacturing cost was high, and the resource saving property was inferior.

  In addition, as a multilayer heat-shrinkable film excellent in low-temperature shrinkability and heat resistance, both outermost layers are made of a polypropylene-based resin, and at least one intermediate layer is a linear low-density polyethylene resin having a predetermined density, or the resin There has been proposed a polypropylene-based laminated heat-shrinkable film made of a resin composition mainly composed of (Patent Document 2). However, the film has the disadvantages of insufficient mechanical strength, hot slip property (slidability immediately after shrinkage) and heat sealability.

  And as a multilayer heat-shrinkable film excellent in hot slip property, a polyolefin-based heat-shrinkable laminate comprising a polyethylene-based heat-shrinkable film layer composed of two types of polyethylene having different densities and a propylene-based heat-shrinkable film layer A film has been proposed (Patent Document 3). However, the above film has the disadvantages that it is slightly inferior in mechanical strength and shrinkage, and has insufficient heat sealability.

  Further, the surface layer is composed of linear low density polyethylene and linear high density polyethylene satisfying predetermined conditions, and the core layer is composed of linear low density polyethylene and linear very low density polyethylene satisfying predetermined conditions. A polyethylene-based multilayer heat-shrinkable film has been proposed (Patent Document 4). However, although this film is excellent in low temperature shrinkage and heat resistance, the film formation stability is insufficient.

  As a method for solving such drawbacks, two types of polypropylene systems having different melting peak temperatures in differential scanning calorimetry analysis using DSC (differential scanning calorimeter) on both surfaces of an intermediate layer containing a polyethylene resin are used. A multilayer polyolefin heat-shrink film containing a resin has been proposed.

  For example, in Patent Document 5, the surface layer has a melting start temperature of 30 ° C. or higher, a melting peak temperature of less than 130 ° C., a melting end temperature of 150 ° C. or lower, and 20 ° C. lower than the melting peak temperature from the melting start temperature. 30 to 80% by weight of a polypropylene resin (A) in which the total amount of heat absorbed until the temperature is 40 to 60% of the total amount of heat absorbed between the melting start temperature and the melting end temperature; A multilayer polyolefin heat-shrinkable film comprising 20 to 70% by weight of a polypropylene resin (B) having a melting peak temperature of 130 to 145 ° C. is disclosed. Patent Document 5 discloses that the melt flow rate (MFR) of the polypropylene resin (B) is preferably 0.5 to 15 g / 10 minutes, and more preferably 1 to 10 g / 10 minutes. ing.

  The multilayer polyolefin heat-shrink film of Patent Document 5 is used for packaging an object to be packaged using a packaging machine. However, in this multilayer polyolefin heat-shrinkable film, when fusing and sealing is performed using an L-type seal-type half-fold packaging machine, the molten resin adheres to the seal bar and cradle of the L-type seal-type half-fold packaging machine. When the seal bar moves away from the base, the molten resin becomes threaded between the seal bar and the cradle (also referred to as “threading”), and a part of the molten resin that is thread-like remains in the seal part of the film was there. When such stringing occurs, cleaning of the seal bar is required, which not only decreases the production efficiency, but also impairs the aesthetic appearance of the obtained package.

  Further, since the L-type seal-type half-fold packaging machine is smaller in speed than the pillow-type packaging machine, but is small in size, the package is immediately conveyed into the tunnel and contracted after fusing and sealing. Accordingly, the multilayer polyolefin heat-shrinkable film is required to have a high sealing strength immediately after the fusing seal.

Japanese Examined Patent Publication No. 4-70987 Japanese Patent Publication No. 8-2625 Japanese Patent Publication No. 8-5172 JP 2002-370327 A JP 2009-39950 A

  The present invention is excellent in low temperature shrinkage, heat resistance, mechanical strength, film formation stability, hot slip property, heat sealability and resource saving, and does not generate toxic gas even when burned during disposal. A multilayer polyolefin heat-shrinkable film having a high sealing strength and no appearance defects due to stringing is provided.

  The multilayer polyolefin heat shrinkable film of the present invention is a multilayer polyolefin heat shrinkable film in which surface layers are laminated and integrated on both sides of an intermediate layer containing a polyethylene resin, and the surface layer is DSC (differential). In differential scanning calorimetry using a scanning calorimeter), the melting start temperature is 30 ° C. or more, the melting peak temperature is less than 130 ° C., the melting end temperature is 150 ° C. or less, and from the melting start temperature to the melting peak temperature of 20 30 to 50% by weight of a polypropylene resin (A) in which the total amount of heat absorbed up to a low temperature is 40-60% of the total amount of heat absorbed between the melting start temperature and the melting end temperature. In the differential scanning calorimetry using DSC (differential scanning calorimeter), the melting peak temperature is 130 to 145 ° C., and the crystallization temperature is 90 ° C. or higher. Ri, and the melt flow rate is characterized by containing 20 to 70 wt% polypropylene resin (B) 50-70 wt% polypropylene resin (B) is 5 to 10 g / 10 min.

  The polypropylene resin (A) constituting the surface layer is not particularly limited, and examples thereof include homopolypropylene and a copolymer of propylene and another monomer containing 50% by weight or more of a propylene component. May be used alone or in combination of two or more. The copolymer of propylene and another monomer containing 50% by weight or more of the propylene component may be any of a block copolymer, a random copolymer, and a random block copolymer.

  And as said polypropylene resin (A), the copolymer of a propylene and another monomer which contains a propylene component 50weight% or more is preferable. Among these, the melting start temperature, the melting peak temperature, the melting end temperature, and the melting end temperature in the differential scanning calorimetry using a DSC (Differential Scanning Calorimeter) depending on the type and amount of the α-olefin to be contained. In view of the fact that the ratio of the total amount of heat absorbed from the melting start temperature to the temperature 20 ° C. lower than the melting peak temperature with respect to the total heat absorbed up to the temperature can be adjusted, propylene-α- Olefin copolymers are more preferred.

  The α-olefin constituting the propylene-α-olefin copolymer is not particularly limited, and examples thereof include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1 -Heptene, 1-octene, etc. are mentioned, and may be used independently or 2 or more types may be used together.

  If the melt flow rate (MFR) of the polypropylene resin (A) is small, the thickness accuracy of the multilayer polyolefin heat-shrinkable film may be lowered. On the other hand, if the melt flow rate (MFR) is large, the multilayer polyolefin heat-shrinkable film is formed. Since stability may fall, 0.5-10 g / 10min is preferable, and 4.0-9.0 g / 10min is more preferable. In addition, the melt flow rate (MFR) of the polypropylene resin in the present invention refers to that measured under conditions of 230 ° C. and a load of 21.18 N in accordance with JIS K7210.

  The melting start temperature (hereinafter simply referred to as “melting start temperature”) in the differential scanning calorimetry using the DSC (differential scanning calorimeter) of the polypropylene resin (A) is limited to 30 ° C. or more, 40 ° C. is preferred. This is because when the melting start temperature of the polypropylene resin (A) is low, the heat resistance and hot slip property of the multilayer polyolefin heat shrinkable film are lowered, while when too high, the low temperature shrinkage of the multilayer polyolefin heat shrinkable film is reduced. This is because there is a case where the lowering may occur.

  When the melting peak temperature (hereinafter simply referred to as “melting peak temperature”) in the differential scanning calorimetry using the DSC (differential scanning calorimeter) of the polypropylene resin (A) is high, the multilayer polyolefin heat shrinkable film Since the low temperature shrinkage of the multilayer polyolefin heat-shrinkable film is limited to less than 130 ° C. and is too low, the heat resistance and hot slip property of the multilayer polyolefin heat-shrinkable film may be lowered.

  In addition, when the melting end temperature (hereinafter simply referred to as “melting end temperature”) in the differential scanning calorimetry using the DSC (differential scanning calorimeter) of the polypropylene resin (A) is high, the multilayer polyolefin heat shrinkable film Since the low temperature shrinkage of the multilayer polyolefin heat-shrinkable film is too low, the heat resistance and hot slip property of the multilayer polyolefin-based heat-shrinkable film may be lowered.

  Further, as the polypropylene resin (A), the melting peak from the melting start temperature to the total heat absorbed from the melting start temperature to the melting end temperature in the differential scanning calorimetry using a DSC (differential scanning calorimeter). The ratio of the total amount of heat absorbed up to a temperature 20 ° C. lower than the temperature (hereinafter referred to as “low temperature endothermic ratio”) is limited to 40-60%, and 45-55% Is preferred.

  This is because when the low-temperature endothermic ratio of the polypropylene resin (A) is low, the low-temperature shrinkability and mechanical strength of the multi-layer polyolefin heat-shrinkable film are lowered, while when it is high, the film formation stability of the multi-layer polyolefin heat-shrinkable film is stable. This is because the properties and heat resistance are reduced.

  In addition, the differential scanning calorimetry of the polypropylene resin in the present invention is performed using a DSC (differential scanning calorimeter) marketed by Shimadzu Corporation under the trade name “DSC-60”, with a temperature rising rate of 10 ° C./min. Perform under conditions. In the endothermic curve of the polypropylene resin obtained by the differential scanning calorimetry, the peak temperature of the strongest endothermic peak is the melting peak temperature, the inflection point temperature on the lowest end of the endothermic curve is the melting start temperature, and the endothermic temperature. The temperature at the inflection point on the highest temperature side of the curve was defined as the melting end temperature.

  As a commercial item of the above-mentioned polypropylene-type resin (A), the propylene-ethylene copolymer etc. which are marketed by the brand name "VERSIFY3000.01" from Dow Chemical company etc. are mentioned, for example.

  If the content of the polypropylene resin (A) in the surface layer of the multilayer polyolefin heat-shrinkable film is small, the stretchability of the multilayer polyolefin film described later decreases, and the multilayer polyolefin obtained by stretching this film While the mechanical strength of the heat-shrinkable film is reduced and the low-temperature shrinkability of the multi-layer polyolefin heat-shrinkable film is reduced, the film-forming stability, heat resistance, and hot slip properties of the multi-layer polyolefin heat-shrinkable film are high. Since it falls, it is limited to 30 to 50 weight%, and 35 to 45 weight% is preferable.

  And as a polypropylene resin (B) which comprises the said surface layer, it does not specifically limit, For example, the copolymer of propylene and another monomer etc. which contain 50 weight% or more of homopolypropylene, a propylene component, etc. And may be used alone or in combination of two or more. The copolymer of propylene and another monomer containing 50% by weight or more of the propylene component may be any of a block copolymer, a random copolymer, and a random block copolymer.

  Moreover, as said polypropylene resin (B), the copolymer of a propylene and another monomer which contains a propylene component 50weight% or more is preferable. Other monomers are preferably α-olefins such as ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene and 1-octene. These may be used alone or in combination of two or more. Of these, ethylene is preferable.

  As the polypropylene resin (B), a random copolymer of propylene and α-olefin is preferable, and a random copolymer of propylene and ethylene is more preferable. Such a random copolymer can be easily adjusted to have a desired crystallization temperature, melt flow rate, melting peak temperature, and the like.

  When the melting peak temperature of the polypropylene resin (B) is low, the heat resistance and film-forming stability of the multilayer polyolefin heat-shrinkable film are lowered. On the other hand, when the melting peak temperature is high, the low-temperature shrinkability of the multilayer polyolefin heat-shrinkable film is lowered. Therefore, it is limited to 130 to 145 ° C, and 135 to 145 ° C is preferable.

  Further, if the crystallization temperature of the polypropylene resin (B) is low, the crystallization speed is slowed and the melt adhesive strength is lowered, so that the sealing strength is lowered. .

  In addition, the crystallization temperature of the polypropylene resin in the present invention is polypropylene based on DSC (differential scanning calorimeter) marketed by Shimadzu Corporation under the trade name “DSC-60” in accordance with JIS K7121. Crystallization when 5.0 mg of resin is heated from 23 ° C. to 180 ° C. at a heating rate of 10 ° C./min, held for 10 minutes, and then cooled to 40 ° C. at 10 ° C./min for crystallization. Let it be the temperature at the peak of the maximum peak.

  If the melt flow rate (MFR) of the polypropylene resin (B) is small, the thickness accuracy of the multilayer polyolefin heat-shrinkable film may be reduced, or the motor load during melt extrusion may be high. And the film-forming stability of the multilayer polyolefin heat-shrinkable film may be lowered, or the fusing and sealing properties may be lowered to cause stringing, so it is limited to 5 to 10 g / 10 minutes, and 7 to 10 g / 10 minutes. Is more preferable.

  As a commercial item of the above-mentioned polypropylene-type resin (B), the propylene-ethylene random copolymer etc. which are marketed with the brand name "PC630A" from the Sun Allomer company etc. are mentioned, for example.

  If the content of the polypropylene resin (B) in the surface layer is small, the film formation stability, heat resistance, and hot slip property of the multilayer polyolefin heat-shrinkable film are deteriorated. Since the low-temperature shrinkability and mechanical strength of the shrink film are lowered, it is limited to 50 to 70% by weight, and preferably 55 to 65% by weight.

  In addition, although the structure of the both surface layers laminated | stacked and integrated on both surfaces of the intermediate | middle layer of the said multilayer polyolefin heat shrink film does not necessarily need to be the same, it is preferable that it is the same structure.

  The polyethylene-based resin constituting the intermediate layer of the multilayer polyolefin heat-shrinkable film of the present invention is not particularly limited. For example, low-density polyethylene, medium-density polyethylene, ethylene containing 50% by weight or more of ethylene, Copolymers with other monomers may be mentioned, and these may be used alone or in combination of two or more. The copolymer of ethylene and another monomer containing 50% by weight or more of the ethylene component may be any of a block copolymer, a random copolymer, and a random block copolymer.

  The polyethylene-based resin constituting the intermediate layer of the multilayer polyolefin heat-shrinkable film is preferably a copolymer of ethylene and another monomer containing 50% by weight or more of an ethylene component. Among these, Linear low density polyethylene is more preferred. The linear low-density polyethylene is obtained by copolymerizing ethylene and α-olefin using a single-site catalyst such as Ziegler catalyst or metallocene catalyst, and adjusting the type and amount of α-olefin. Can control the density range.

  In addition, examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, and the like. Two or more kinds may be used in combination.

If the density of the polyethylene resin is low, the heat-sealability and hot-slip property of the multilayer polyolefin heat-shrinkable film may be lowered. On the other hand, if the density is high, the low-temperature shrinkage property of the multilayer polyolefin-based heat shrinkable film is lowered. Therefore, 0.910 to 0.930 g / cm ³ is preferable, and 0.915 to 0.925 g / cm ³ is more preferable. In addition, the density of the polyethylene-type resin in this invention says the value measured based on JISK7112.

  If the melt flow rate (MFR) of the polyethylene resin is small, the thickness accuracy of the multilayer polyolefin heat-shrinkable film may be reduced. On the other hand, if the melt flow rate (MFR) is large, the film-forming stability of the multilayer polyolefin heat-shrinkable film is low. Since it may fall, 0.7-2.0 g / 10min is preferable, and 0.8-1.5 g / 10min is more preferable. In addition, the melt flow rate (MFR) of the polyethylene-type resin in this invention says the value measured on condition of 190 degreeC and load 21.18N based on JISK7210.

  The multilayer polyolefin heat-shrinkable film of the present invention includes a lubricant, an anti-blocking agent, an antistatic agent, an antifogging agent, an antioxidant, an ultraviolet absorber, a crystal nucleating agent and the like within a range not impairing its physical properties. These additives may be added.

  Furthermore, a layer such as an adhesive layer, a colored layer, and a printed layer may be laminated and integrated on the surface layer of the multilayer polyolefin heat-shrinkable film as long as the effects of the present invention are not impaired.

  And, as described above, the multilayer polyolefin heat-shrink film is formed by integrating the surface layers on both sides of the intermediate layer, and the thickness of the intermediate layer and the surface layer, or the thickness ratio between the intermediate layer and the surface layer. Is not limited, but the total thickness of the multilayer polyolefin heat-shrinkable film is preferably 5 to 50 μm, preferably 10 to 30 μm from the viewpoint of mechanical strength and workability of the multilayer polyolefin heat-shrinkable film. Is more preferable.

  Also, if the thickness ratio between the intermediate layer and the surface layer of the multilayer polyolefin heat shrink film (intermediate layer thickness / surface layer thickness) is small, the low temperature shrinkability of the multilayer polyolefin heat shrink film may be reduced. On the other hand, if it is large, the film-forming stability and heat resistance of the multilayer polyolefin heat-shrinkable film may be lowered, so 3 to 8 is preferable, and 3.5 to 6 is more preferable. The thicknesses of both surface layers laminated and integrated on both surfaces of the intermediate layer are preferably the same, but not necessarily the same. If the thicknesses of both surface layers are different, the intermediate layer The thickness ratio between the surface layer and the surface layer is calculated using the thickness of the thinner surface layer.

  Next, a method for forming a multilayer polyolefin heat-shrinkable film will be described. The method for forming a multilayer polyolefin heat-shrinkable film is not particularly limited. For example, an unstretched multilayer polyolefin film is formed by a known film-forming method such as a multilayer T-die casting method or a water-cooled inflation method using a multilayer die. A method of forming a multilayer polyolefin heat-shrinkable film by forming this unstretched multilayer polyolefin film by a stretching method such as roll uniaxial stretching, tenter biaxial stretching or tubular biaxial stretching after film formation. Is mentioned. Here, the thickness of the unstretched multilayer polyolefin film is preferably 200 to 500 μm. When stretching the unstretched multi-layer polyolefin film, the multi-layer polyolefin film is stretched 2 to 10 times in the longitudinal and transverse directions at a stretching speed of 10 to 100 m / min and a stretching temperature of 50 to 120 ° C. Is preferred. In addition, the said extending | stretching temperature means the temperature of the multilayer polyolefin-type film just before extending | stretching.

  The packaging method of the packaged body using the multilayer polyolefin heat-shrink film is not particularly limited. For example, a heat formed by packaging a packaged object such as a product with a multilayer polyolefin heat-shrink film with some clearance. The shrinkable packaging body is supplied to an L-shaped seal packaging machine, and the heat-shrinkable packaging body is heated to 130 to 160 ° C. to thermally shrink the multilayer polyolefin heat-shrinkable film of the heat-shrinkable packaging body. There is a method of obtaining a heat-shrinkable package obtained by closely adhering along the shape of the package, and packaging the package with a multilayer polyolefin heat-shrink film.

  The multilayer polyolefin heat-shrinkable film of the present invention is excellent in low-temperature shrinkage because it contains a polyethylene resin in the intermediate layer and the above-mentioned polypropylene resin (A) in the surface layer. Therefore, the multilayer polyolefin heat-shrink film of the present invention hardly produces an unshrinked portion even when the heat-shrink temperature is relatively low, and can obtain a heat-shrink package having excellent tension. It is suitably used for packaging products such as plastic molded products, raw meat, and frozen foods that change quality under high temperature conditions.

  And since the said multilayer polyolefin heat shrink film contains the above-mentioned polypropylene resin (B) in the surface layer, it is excellent in heat resistance. Accordingly, the multilayer polyolefin heat-shrinkable film has a wide temperature range suitable for heat-shrinking, and can be packaged in close contact with the shape of the packaged body without strictly controlling the temperature in the packaging machine. Even when high-speed packaging is performed by shortening the time required for heat shrinkage by heating the heat-shrinkable package at a high temperature, the multilayer polyolefin heat of the heat-shrinkable package is obtained. There is almost no melting break on the surface of the shrink film.

  Moreover, since the said multilayer polyolefin heat shrink film takes the structure as mentioned above, it is excellent in film forming stability. Therefore, the multilayer polyolefin heat-shrinkable film has improved thickness accuracy at the time of film formation, and is excellent in productivity with almost no film formation failure such as thickness unevenness.

  Thus, the multilayer polyolefin heat-shrinkable film of the present invention has excellent thickness suitability, a wide range of temperature suitable for heat-shrinkage, and is suitable for high-speed packaging. Therefore, according to the multilayer polyolefin heat-shrink film of the present invention, a heat-shrink package having excellent appearance can be obtained with high productivity.

  The multilayer polyolefin heat-shrinkable film has the above-described configuration and is excellent in mechanical strength and hot slip property. Therefore, the heat-shrinkable package is heat-shrinkable packaged by the multilayer polyolefin heat-shrinkable film. The body is hardly damaged or torn on the surface of the multilayer polyolefin heat-shrinkable film during the transfer.

  In addition, the multilayer polyolefin heat-shrinkable film of the present invention does not need to crosslink the resin component constituting the intermediate layer and the surface layer, and does not crosslink the intermediate layer and the surface layer. It is possible to recycle scraps generated from trimming of film edges and film, and is excellent in resource saving. Furthermore, since the multilayer polyolefin heat-shrinkable film has excellent physical properties as described above even if the resin component constituting the film does not contain polyvinyl chloride, it can be dioxin even if it is burned during disposal. The generation of harmful gases such as can be suppressed, and environmental sanitation is also excellent.

  Furthermore, since the multilayer polyolefin heat-shrinkable film of the present invention can stably maintain a high sealing strength immediately after performing the fusing seal, stringing occurs at the seal portion of the multilayer polyolefin heat-shrinkable film. Therefore, a package having a beautiful appearance can be provided.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
First, a film forming apparatus is prepared in which the tips of three extruders are connected to a circular multi-layer die. The two extruders of this film forming apparatus are used for the surface layer, and the remaining one extruder is an intermediate. For layers. Next, a propylene-ethylene copolymer A (trade name “VERSIFY3000.01” manufactured by Dow Chemical Co., Ltd.), a melting start temperature: 35 ° C., a melting peak temperature: 120, which is a polypropylene resin, is used for each of the extruders for both surface layers. 40 ° C., melting end temperature: 145 ° C., low-temperature endothermic ratio: 55%, melt flow rate: 8.0 g / 10 min), and propylene-ethylene copolymer B (manufactured by Sun Allomer Co., Ltd.), which is a polypropylene resin (Name: “PC630A”, melting peak temperature: 137 ° C., crystallization temperature 94 ° C., melt flow rate: 7.5 g / 10 min) While supplying 60 parts by weight, the intermediate layer extruder is a polyethylene resin linear low density polyethylene (Dow Chemical Corporation, trade name "Dowlex 2045G", density: 0.920g / cm ^3, Merutofu -Rate: 1.0 g / 10 min) 100 parts by weight was supplied, and a surface layer made of a polypropylene resin was laminated and integrated on both surfaces of an intermediate layer made of linear low-density polyethylene by a water-cooled inflation method. Thickness of 375 μm A multilayer polyolefin film was prepared.

  Then, the obtained multilayer polyolefin-based film is supplied to a tubular biaxial stretching device, and stretched 5 times in the longitudinal and lateral directions. The total thickness is 15 μm, both surface layers have the same thickness, and the intermediate layer and the surface layer A multilayer polyolefin heat-shrinkable film having a thickness ratio (intermediate layer thickness / surface layer thickness) of 4 was obtained.

(Comparative Example 1)
In each of the extruders for both surface layers, propylene-ethylene copolymer A (trade name “VERSIFY3000.01” manufactured by Dow Chemical Co., Ltd.), which is a polypropylene resin, melting start temperature: 35 ° C., melting peak temperature: 120 ° C., Melting end temperature: 145 ° C., low-temperature endothermic ratio: 55%, melt flow rate: 8.0 g / 10 minutes 20 parts by weight, and propylene-ethylene copolymer B (manufactured by Sun Allomer Co., Ltd.), which is a polypropylene resin PC630A ”, crystallization temperature 94 ° C., melting peak temperature: 137 ° C., melt flow rate: 7.5 g / 10 min), except that 80 parts by weight were supplied, in the same manner as in Example 1, a multilayer polyolefin heat shrink film Got.

(Comparative Example 2)
In each of the extruders for both surface layers, propylene-ethylene copolymer A (trade name “VERSIFY3000.01” manufactured by Dow Chemical Co., Ltd.), which is a polypropylene resin, melting start temperature: 35 ° C., melting peak temperature: 120 ° C., Melting end temperature: 145 ° C., low-temperature endothermic ratio: 55%, melt flow rate: 8.0 g / 10 min) 80 parts by weight, and propylene-ethylene copolymer B (manufactured by Sun Allomer Co., Ltd.), which is a polypropylene resin PC630A ”, crystallization temperature 94 ° C., melting peak temperature: 137 ° C., melt flow rate: 7.5 g / 10 min), except that 20 parts by weight were supplied, in the same manner as in Example 1, a multilayer polyolefin heat shrink film Got.

(Comparative Example 3)
In each of the extruders for both surface layers, propylene-ethylene copolymer A (trade name “VERSIFY3000.01” manufactured by Dow Chemical Co., Ltd.), which is a polypropylene resin, melting start temperature: 35 ° C., melting peak temperature: 120 ° C., Melting end temperature: 145 ° C., low-temperature endothermic ratio: 55%, melt flow rate: 8.0 g / 10 min) 40 parts by weight, propylene-ethylene copolymer B which is a polypropylene resin (trade name “PC630A” manufactured by Sun Allomer Co., Ltd.) 30 parts by weight of a crystallization temperature of 94 ° C., a melting peak temperature of 137 ° C., a melt flow rate of 7.5 g / 10 min), and a propylene-ethylene-butene terpolymer that is a polypropylene resin (manufactured by Sumitomo Chemical Co., Ltd.) Product name “Noblen S131”, melting start temperature: 110 ° C., melting peak temperature: 140 ° C., melting end temperature: 160 ° C., low Endothermic ratio: 15%, melt flow rate: 1.2 g / 10 min), except that were fed 30 parts by weight, to obtain a multi-layer polyolefin heat-shrinkable film in the same manner as in Example 1.

(Comparative Example 4)
In each of the extruders for both surface layers, propylene-ethylene copolymer A (trade name “VERSIFY3000.01” manufactured by Dow Chemical Co., Ltd.), which is a polypropylene resin, melting start temperature: 35 ° C., melting peak temperature: 120 ° C., Melting end temperature: 145 ° C., low-temperature endothermic ratio: 55%, melt flow rate: 8.0 g / 10 min) 40 parts by weight, and propylene-ethylene-butene terpolymer which is a polypropylene resin (Sumitomo Chemical Co., Ltd.) Product name “Noblen S131”, melting start temperature: 110 ° C., melting peak temperature: 140 ° C., melting end temperature: 160 ° C., low temperature endothermic ratio: 15%, melt flow rate: 1.2 g / 10 min) 60 parts by weight A multilayer polyolefin heat-shrink film was obtained in the same manner as in Example 1 except that was supplied.

  About the multilayer polyolefin heat-shrinkable film obtained as described above, its heat-shrinkability, film-forming stability, heat-sealability, heat-seal strength, stringiness, hot-slip property, film strength, and packaging properties are described below. The results were evaluated in the manner shown, and the results are shown in Table 1.

(Heat shrinkage)
The heat shrinkage rate (%) in the longitudinal and transverse directions at 100 ° C., 110 ° C. and 120 ° C. of the multilayer polyolefin heat shrink film is measured according to JIS Z1709 “Shrink Wrapping Film”. Was used as an index for evaluating the heat shrinkability of the multilayer polyolefin heat shrink film. The longitudinal direction refers to the extrusion direction during the production of the multilayer polyolefin heat-shrinkable film, and the transverse direction refers to the direction along the surface of the multilayer polyolefin-based heat shrinkable film and orthogonal to the extrusion direction.

(Film formation stability)
Regarding film formation stability, it is easy to operate from the time the extruder is operated until a stable multilayer polyolefin heat-shrinkable film is obtained, and almost no deformation of the multilayer polyolefin heat-shrinkable film due to shaking of the film-forming bubble. Evaluated as ◯ when the film satisfies the three conditions that the multilayer polyolefin heat-shrinkable film has good thickness accuracy after being stretched, and evaluated as x when the film did not satisfy any one of the above three conditions. did.

(Film strength)
The impact strength of the multilayer polyolefin heat shrink film was measured according to ASTM D3420, while the dirt strength of the multilayer polyolefin heat shrink film was measured according to JIS K7124. Moreover, the puncture strength of the multilayer polyolefin heat shrink film was measured as follows according to the Food Sanitation Law. The multilayer polyolefin heat-shrink film was fixed to a cylindrical jig, a semicircular needle having a diameter of 1 mm was pierced at a speed of 200 mm / min on the sample surface, and the maximum load until the needle penetrated was measured as the piercing strength. A case where the impact strength, the dart strength and the puncture strength were all sufficient was evaluated as ◯, and a case where the other strengths were evaluated as ×.

(Heat sealability)
Using L-shaped seal wrapping machine (trade name “HP-10” manufactured by Hanagata Co., Ltd.), 10 pieces of rectangular parallelepiped wooden boxes (length 130 mm × width 170 mm × height 50 mm) are each entirely multi-layer polyolefin heat shrink The film was continuously heat shrink-wrapped at 140 ° C. with a film.

  Next, the multilayer polyolefin heat-shrinkable film packaging each wooden box was visually observed, and the hole diameter of the largest hole (pinhole) generated in the multilayer polyolefin heat-shrinkable film was measured. In addition, the hole diameter of a pinhole was made into the minimum diameter of the perfect circle which can surround a pinhole.

And 5 points for multi-hole polyolefin-based heat-shrink film without pinholes, 3 points for pinholes with a hole diameter of less than 2 mm, 1 point for pinholes with a hole diameter of 2 mm or more and less than 5 mm, pinholes A sample having a hole diameter of 5 mm or more was scored with a maximum score of 50, and the heat sealability was evaluated according to the following criteria.
A: The total score was 40 points or more.
Δ: The total score was 35 points or more and less than 40 points.
X: The total score was less than 35 points.

(Heat seal strength)
Using an L-shaped seal wrapping machine (trade name “HP-10” manufactured by Hanagata Co., Ltd.) under the conditions of a fusing seal temperature of 200 ° C. and a fusing seal time of 1.0 second (130 mm length × 170 mm width) X 50 mm in height) is heat-shrink-wrapped entirely with a multilayer polyolefin heat-shrink film, and the heat seal strength (N / 15 mm) of any part of the part that is longitudinally or transversely sealed conforms to JIS Z1707 It was measured. The tensile speed was 500 mm / min.

(Threading property)
Using an L-shaped seal wrapping machine (trade name “HP-10” manufactured by Hanagata Co., Ltd.) under the conditions of a fusing seal temperature of 200 ° C. and a fusing seal time of 1.0 second (130 mm length × 170 mm width) 30 pieces of packaging samples were obtained by continuously heat-shrinking 30 pieces each with a multi-layer polyolefin heat-shrink film. Then, the fusing seal part of the packaging sample was visually observed, and the stringiness was evaluated according to the following criteria.
○: No stringing occurred in all the packaging samples.
(Triangle | delta): One or two thread | yarn generation | occurrence | production occurred on average in one packaging sample.
X: Three or more yarns were generated on average in one package sample.

(Hot slip)
Using an L-shaped seal wrapping machine (trade name “HP-10” manufactured by Hanagata Co., Ltd.), two cuboid shaped wooden boxes (length 130 mm × width 170 mm × height 50 mm) are each entirely multi-layer polyolefin heat shrink The film was continuously heat shrink-wrapped at 140 ° C. with a film. Next, the two wooden boxes immediately after being heat-shrink-wrapped were rubbed together, and after 20 seconds, 40 seconds, and 60 seconds, the slippery condition was sensory evaluated. The case where the slipperiness was poor was taken as x.

(Packaging)
Using an L-type seal wrapping machine (trade name “HP-10” manufactured by Hanagata Co., Ltd.), the tunnel temperature of this L-type seal wrapping machine is changed from 140 ° C. to 160 ° C. in increments of 10 ° C. Heat shrink-wrapped one by one with a multilayer polyolefin heat-shrink film (length 130 mm × width 170 mm × height 50 mm) one by one.

Next, the multilayer polyolefin heat-shrink film packaging each wooden box was visually observed, and the packaging property was evaluated based on the following criteria.
○: Insufficient shrinkage or heat-melting breakage was not observed, and the finished state was good.
Δ: Slightly insufficient shrinkage was observed, but there was no practical problem.
X: Insufficient shrinkage or heat-melting tear was observed, and the finished state was poor.

Claims (6)

  A multi-layer polyolefin heat-shrink film in which surface layers are laminated and integrated on both surfaces of an intermediate layer containing a polyethylene-based resin, wherein the surface layer is a differential scanning calorimetry using a DSC (differential scanning calorimeter). , The melting start temperature is 30 ° C. or more, the melting peak temperature is less than 130 ° C., the melting end temperature is 150 ° C. or less, and the amount of heat absorbed between the melting start temperature and the temperature 20 ° C. lower than the melting peak temperature 30 to 50% by weight of a polypropylene resin (A) whose total amount is 40 to 60% of the total heat absorbed between the melting start temperature and the melting end temperature, and DSC (differential scanning calorimeter) In the differential scanning calorimetry used, the melting peak temperature is 130 to 145 ° C., the crystallization temperature is 90 ° C. or higher, and the melt flow rate is 5 to 10 g / 10. Multilayer polyolefin heat-shrinkable film to polypropylene resin (B), characterized by containing 50 to 70% by weight is.   The multilayer polyolefin heat-shrinkable film according to claim 1, wherein the polypropylene resin (A) is a propylene-α-olefin copolymer.   The multilayer polyolefin heat-shrinkable film according to claim 1 or 2, wherein the polypropylene resin (B) is a propylene-α-olefin copolymer. The polyethylene resin has a density of 0.910 to 0.930 g / cm ³ and a melt flow rate (MFR) of 0.7 to 2.0 g / 10 min. The multilayer polyolefin heat-shrink film as described in any one of the above.   The multilayer polyolefin heat-shrinkable film according to any one of claims 1 to 4, wherein the polyethylene resin is a linear low-density polyethylene.   The multilayer polyolefin system according to any one of claims 1 to 5, wherein a thickness ratio between the intermediate layer and the surface layer (intermediate layer thickness / surface layer thickness) is 3 to 8. Heat shrink film.