JP2008036844A - Multilayered polyolefinic heat-shrinkable film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayered polyolefinic heat-shrinkable film excellent in low temperature shrinkability, heat resistance, film forming stability, hot slip properties, heat sealability and resource saving properties and forming no harmful gas even if combusted at the time of discarding treatment. <P>SOLUTION: The multilayered polyolefinic heat-shrinkable film is constituted by integrally laminating a surface layer, which comprises a polyethylenic resin with a density of 0.91-0.93 g/cm<SP>3</SP>, on both surfaces of an intermediate layer which is composed of 30-70 wt.% of the polyethylenic resin with the density of 0.91-0.93 g/cm<SP>3</SP>and 30-70 wt.% of a polypropylene resin which has a melt start temperature of 30°C or above and a melt completion temperature of 150°C or below and is characterized in that the total heat quantity absorbed within the range from the melt start temperature to a temperature lower than a melt peak temperature by 20°C is 40-60% of the whole heat quantity absorbed during the period from the melt start temperature to the melt completion temperature in the differential scanning calorimetry using DSC. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multilayer polyolefin heat-shrink film used for commercial packaging. More specifically, it is excellent in low-temperature shrinkage, heat resistance, film-forming stability, hot slip, heat sealability and resource saving, and multi-layer polyolefin heat shrink that does not generate toxic gas even when burned during disposal. Related to film.

  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. Moreover, although the heat-shrinkable film mainly composed of polypropylene is excellent in heat resistance, it has a problem that it cannot be thermally shrunk unless it is at a high temperature because the low-temperature shrinkage is low.

  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 above film has a drawback that the hot slip property (smoothness immediately after shrinkage) and the heat seal property are insufficient.

  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 film has the disadvantages that it is slightly inferior in shrinkability and insufficient in 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). Although this film was excellent in low-temperature shrinkage and heat resistance, the film-forming stability was insufficient.

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

  The present invention is excellent in low-temperature shrinkage, heat resistance, film-forming stability, hot slip, heat sealability and resource saving, and multi-layer polyolefin heat shrink that does not generate harmful gases even when burned during disposal. Provide film.

The multilayer polyolefin heat-shrinkable film of the present invention has a density of 0 to both sides of an intermediate layer composed of 30 to 70% by weight of a polyethylene resin having a density of 0.91 to 0.93 g / cm ³ and 30 to 70% by weight of a polypropylene resin. A multi-layer polyolefin heat-shrinkable film obtained by laminating and integrating a surface layer made of polyethylene resin of .91 to 0.93 g / cm ^{3, wherein} the polypropylene resin used a DSC (differential scanning calorimeter). In the differential scanning calorimetry, the total amount of heat absorbed between the melting start temperature is 30 ° C. and the melting end temperature is 150 ° C. or less and the melting start temperature is 20 ° C. lower than the melting peak temperature is It is characterized by being 40 to 60% of the total amount of heat absorbed between the melting start temperature and the melting end temperature.

  The polyethylene-based resin constituting the intermediate layer of the multilayer polyolefin heat-shrinkable film is not particularly limited, and examples thereof include low-density polyethylene, medium-density polyethylene, and a copolymer of ethylene and other monomers mainly composed of ethylene. And may be used alone or in combination of two or more. In addition, the copolymer of ethylene and other monomers having ethylene as a main component may be any of a block copolymer, a random copolymer, and a random block copolymer.

  The polyethylene resin constituting the intermediate layer of the multilayer polyolefin heat-shrinkable film is preferably a copolymer of ethylene having ethylene as a main component and other monomers, and among these, linear low density polyethylene Is more preferable. 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. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene and 1-octene.

When the density of the polyethylene resin constituting the intermediate layer is low, the heat-sealability and hot-slip property of the multilayer polyolefin heat-shrinkable film are lowered, while when high, the low-temperature shrinkage property of the multilayer polyolefin-based heat shrinkable film is reduced. and since the heat sealability is lowered, limited to 0.91~0.93g / cm ^3, preferably 0.915~0.925g / cm ^3. In addition, the density of the polyethylene-type resin in this invention says the value measured based on JISK7112.

  If the melt flow rate of the polyethylene resin constituting the intermediate layer is small, the thickness accuracy of the multilayer polyolefin heat-shrinkable film may be reduced. On the other hand, if the melt flow rate is large, the multilayer polyolefin heat-shrinkable film is formed. Since stability 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 of the polyethylene-type resin in this invention means what was measured on condition of 190 degreeC and load 21.18N based on JISK7210.

  Furthermore, the content of the polyethylene resin in the intermediate layer is limited to 30 to 70% by weight, and preferably 40 to 60% by weight. This is because if the content of the polyethylene resin in the intermediate layer is small, the low-temperature shrinkability of the multilayer polyolefin heat-shrinkable film may decrease, or the transparency of the multilayer polyolefin heat-shrinkable film may decrease. The compatibility between the resin composition comprising the polyethylene resin and the polypropylene resin constituting the intermediate layer and the polyethylene resin constituting the surface layer described later is reduced, and the intermediate layer and the surface layer of the multilayer polyolefin heat shrink film The adhesiveness with the lowering causes a problem that the heat-sealing property of the multilayer polyolefin heat-shrinkable film is lowered. On the other hand, if the content of the polyethylene resin is large, the film-forming stability of the multilayer polyolefin-based heat-shrinkable film and It is because heat resistance falls.

  In addition, the polypropylene resin constituting the intermediate layer is not particularly limited, and examples thereof include homopolypropylene, copolymers of propylene mainly composed of propylene and other monomers, and the like. Also, two or more kinds may be used in combination. The copolymer of propylene mainly composed of propylene and another monomer may be any of a block copolymer, a random copolymer, and a random block copolymer.

  And as a polypropylene resin which comprises the said intermediate | middle layer, the copolymer of the propylene which has a propylene as a main component, and another monomer is preferable, Among these, it is a melting temperature range by the kind and quantity of the alpha olefin to contain. A propylene-α-olefin copolymer is more preferable from the viewpoint that the pH can be adjusted. Examples of the α-olefin constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and the like. And ethylene is preferred.

  Moreover, the melting start temperature of the said polypropylene resin measured by DSC (differential scanning calorimeter) is limited to 30 degreeC or more. This is because if the melting start temperature of the polypropylene resin is lower than 30 ° C., the heat resistance and slipperiness of the multilayer polyolefin heat-shrinkable film are lowered.

  And the melting end temperature of the said polypropylene resin measured by DSC is limited to 150 degrees C or less. This is because when the melting start temperature of the polypropylene resin is higher than 150 ° C., the low temperature shrinkability of the multilayer polyolefin heat shrink film is lowered.

  Furthermore, as the polypropylene resin, in the differential scanning calorimetry using DSC, the total amount of heat absorbed between the melting start temperature and the temperature 20 ° C. lower than the melting peak temperature is the melting end temperature from the melting start temperature to the end of melting. It is limited to what becomes 40 to 60% of the total heat absorbed up to the temperature, and what becomes 45 to 55% is preferable. This is between the melting start temperature of the polypropylene resin and the temperature 20 ° C. lower than the melting peak temperature with respect to the total heat absorbed between the melting start temperature of the polypropylene resin and the melting end temperature, as measured by DSC. When the ratio of the total amount of heat absorbed in the film (hereinafter referred to as “low-temperature endothermic ratio”) is lower than 40%, the low-temperature shrinkage of the multilayer polyolefin heat-shrinkable film is lowered, while the low-temperature endothermic ratio is 60%. This is because the film forming stability and heat resistance of the multilayer polyolefin heat-shrinkable film are lowered when the temperature is higher.

  The differential scanning calorimetric analysis of the polypropylene resin by DSC is performed in a temperature range of 0 to 200 ° C. by a conventionally known method. In addition, it does not specifically limit as DSC used for the said differential scanning calorimetry, For example, DSC marketed by Seiko Electronic Industry Co., Ltd. by the brand name "SSC-5100" etc. are mentioned.

  In the endothermic curve of the polypropylene resin obtained by differential scanning calorimetry using DSC as described above, the peak temperature of the strongest endothermic peak is the melting peak temperature, and the inflection point on the lowest temperature side of the endothermic curve is The temperature was defined as the melting start temperature, and the temperature at the inflection point on the highest temperature side of the endothermic curve was defined as the melting end temperature.

  Also, if the melt flow rate of the polypropylene 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 is large, the film-forming stability of the multilayer polyolefin heat-shrinkable film is lowered. In some cases, 0.5 to 6.0 g / 10 min is preferable, and 0.8 to 2.0 g / 10 min is more preferable. In addition, the melt flow rate of the polypropylene resin in this invention means what was measured on condition of 230 degreeC and load 21.18N based on JISK7210.

  Furthermore, if the content of the polypropylene resin in the intermediate layer is small, the film-forming stability, heat resistance and hot slip property of the multilayer polyolefin heat-shrinkable film are insufficient, while if it is large, the resin having a high melting temperature. Since the components increase and the low temperature shrinkability of the multilayer polyolefin heat shrink film decreases, it is limited to 30 to 70% by weight, preferably 40 to 60% by weight.

  The multilayer polyolefin heat-shrink film of the present invention has a surface layer laminated and integrated on both surfaces of the intermediate layer as described above. The polyethylene resin constituting the surface layer of the multilayer polyolefin heat-shrinkable film is not particularly limited, and examples thereof include low-density polyethylene, medium-density polyethylene, and a copolymer of ethylene mainly composed of ethylene and other monomers. Examples thereof include a polymer, and a copolymer of ethylene having ethylene as a main component and another monomer is preferable, and linear low-density polyethylene is more preferable. In addition, these polyethylene-type resin may be used independently, or 2 or more types may be used together.

  Furthermore, the compositions of the polyethylene resins constituting both surface layers laminated and integrated on both surfaces of the intermediate layer of the multilayer polyolefin heat-shrinkable film may be different, but are preferably the same.

When the density of the polyethylene resin constituting the surface layer is low, the film-forming stability and heat sealability of the multilayer polyolefin heat-shrinkable film are lowered. since heat sealability is lowered, limited to ^{0.91~0.93g / cm 3, 0.915~0.925g / cm} 3 are preferred.

  If the melt flow rate of the polyethylene resin constituting the surface layer is small, the thickness accuracy of the multilayer polyolefin heat-shrinkable film may be reduced. On the other hand, if the melt flow rate is large, the multilayer polyolefin heat-shrinkable film is formed. Since stability may fall, 0.5-3.0 g / 10min is preferable and 0.8-1.5 g / 10min is more preferable.

  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.

  As described above, the multilayer polyolefin heat-shrink film has a surface layer laminated and integrated on both sides of the intermediate layer, the thickness of the intermediate layer and the surface layer, and the thickness of the intermediate layer and the surface layer. The ratio is not particularly limited, but from the viewpoint of mechanical strength and workability of the multilayer polyolefin heat-shrinkable film, the total thickness of the multilayer polyolefin heat-shrinkable film is preferably 5 to 50 μm, preferably 10 to 30 μm. It is more preferable that

  In addition, when the thickness ratio of the intermediate layer to the surface layer of the multilayer polyolefin heat shrink film (thickness of the intermediate layer / surface layer thickness) is small, the film formation stability and heat resistance of the multilayer polyolefin heat shrink film are reduced. On the other hand, if it is large, the low-temperature shrinkability 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, and when the thicknesses of both surface layers are different, The thickness ratio between the intermediate 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. In addition, it is preferable that the thickness of the said unstretched multilayer polyolefin-type film is 200-500 micrometers. Moreover, when extending | stretching the said unstretched multilayer polyolefin-type film, a multilayer polyolefin-type film is stretched | stretched 2-10 times each length and width on the conditions of a stretching speed of 10-100 m / min and a stretching temperature of 50-120 degreeC. 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 packaging body in which the packaging body is packaged with a multi-layer polyolefin heat-shrinkable film and is closely adhered along the shape of the packaged body.

  Since the multilayer polyolefin heat-shrinkable film of the present invention has the above-described configuration, it has the low-temperature shrinkage characteristic of the polyethylene-based resin. Even if the heat shrink temperature during packaging is relatively low, an unshrinked portion does not occur, and a heat shrink package excellent in tightness can be obtained. Therefore, the multilayer polyolefin heat-shrinkable film is suitably used for packaging products such as plastic molded products, raw meat, and frozen foods that change in quality under high temperature conditions.

  Moreover, since the multilayer polyolefin heat-shrinkable film of the present invention contains a polypropylene resin in the intermediate layer of the film as described above, the film-forming stability and heat resistance, which are the characteristics of the polypropylene resin, are achieved. Has been granted. Since the multilayer polyolefin heat-shrinkable film is provided with film-forming stability, the thickness accuracy of the produced film is improved, so that no thickness unevenness occurs. Furthermore, since the multi-layer polyolefin-based heat-shrinkable film is given heat resistance, the temperature range suitable for heat-shrinking the film is widened, so the temperature in the packaging machine need not be strictly controlled. Even when high-speed packaging can be performed by closely adhering to the shape of the package body and shortening the time required for heat shrinkage by heating the heat-shrinkable package body at a high temperature The surface of the multilayer polyolefin heat-shrinkable film of the heat-shrinkable package is hardly melted and broken.

  As described above, the multilayer polyolefin heat-shrinkable film of the present invention has excellent thickness accuracy, 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.

  In addition, since the multilayer polyolefin heat-shrinkable film has the same density or a small density difference between the polyethylene resins constituting the intermediate layer and the surface layer, the intermediate layer and the surface layer do not delaminate and can be obtained. Since no pinhole is generated on the surface of the shrink wrap, the heat sealability is excellent. Furthermore, since the multilayer polyolefin heat-shrinkable film is excellent in mechanical strength and hot slip property, when the heat-shrinkable package is transported, it is applied to the surface of the multilayer polyolefin heat-shrinkable film. There is almost no damage or tearing.

  Furthermore, 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.

  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)
Prepare a film forming device with the tip of three extruders connected to a circular multi-layer die. The two extruders of this film forming device are used for the surface layer, and the remaining one extruder is used for the intermediate layer. As an intermediate layer extruder, linear low-density polyethylene A (trade name “2045G” manufactured by DOW, density: 0.920 g / cm ³ , melt flow rate: 1.0 g / 10 min, which is a polyethylene resin) ) 50 parts by weight and 50 parts by weight of a propylene-ethylene copolymer (trade name “VERSIFY2300” manufactured by DOW, propylene content: 15% by weight, melt flow rate: 2.0 g / 10 minutes), which is a polypropylene resin to one each of the extruder for both surface layers linear low-density polyethylene a (DOW trade name "2045G", density: 0.920 g / cm ^3, melt flow rate: 1. g / 10 min), and a surface layer made of linear low density polyethylene was laminated and integrated on both sides of an intermediate layer made of linear low density polyethylene and propylene-ethylene copolymer by a water-cooled inflation method. A multilayer polyolefin film having a thickness of 375 μm was prepared.

  The propylene-ethylene copolymer had a melting start temperature measured by DSC of 35 ° C., a melting peak temperature of 120 ° C., and a melting end temperature of 145 ° C. Further, the proportion of endotherm absorbed between 35 ° C. and 100 ° C. of the propylene-ethylene copolymer as measured by DSC (low temperature endotherm proportion) was 55%.

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

(Comparative Example 1)
As the resin material constituting the intermediate layer, only linear low density polyethylene A (trade name “2045G” manufactured by DOW, density: 0.920 g / cm ³ , melt flow rate: 1.0 g / 10 min) was used. In the same manner as in Example 1, a multilayer polyolefin heat-shrinkable film having an overall thickness of 15 μm, the thicknesses of both surface layers being the same, and the thickness ratio of the intermediate layer to the surface layer being 4 was obtained. .

(Comparative Example 2)
Except that only a propylene-ethylene copolymer (trade name “VERSIFY2300” manufactured by DOW, melt flow rate: 2.0 g / 10 min) was used as the resin material constituting the intermediate layer, the same as in Example 1. In this way, a multilayer polyolefin heat-shrinkable film having a total thickness of 15 μm, the thickness of both surface layers being the same, and a thickness ratio of the intermediate layer to the surface layer of 4 was obtained.

(Comparative Example 3)
As the polyethylene resin constituting the intermediate layer, instead of 50 parts by weight of linear low density polyethylene A, linear low density polyethylene B (trade name “A4203” manufactured by DOW, density: 0.905 g / cm ³ , melt flow (Rate: 0.8 g / 10 min) Except for using 50 parts by weight, the whole thickness was 15 μm, both surface layers had the same thickness, and the intermediate layer and the surface layer were the same as in Example 1. A multilayer polyolefin heat-shrink film having a thickness ratio of 4 was obtained.

(Comparative Example 4)
As the polyethylene resin constituting the intermediate layer, linear medium density polyethylene C (density: 0.940 g / cm ³ , melt flow rate: 1.0 g / 10 min) instead of 50 parts by weight of linear low density polyethylene A A multilayer polyolefin system having a total thickness of 15 μm, the thicknesses of both surface layers being the same, and the thickness ratio of the intermediate layer to the surface layer being 4, except that 50 parts by weight are used A heat shrink film was obtained.

  The multilayer polyolefin heat-shrinkable films obtained in the above examples and comparative examples were evaluated for heat shrinkability, film-forming stability, heat sealability, hot slip properties and packaging properties in the following manner, and the results are shown in Table 1. It was shown in 1. In Comparative Example 1, the film-forming stability was poor and a homogeneous multilayer polyolefin heat-shrinkable film could not be obtained, so the heat sealability, hot slip property and packaging property could not be evaluated. It was. “MFR” in Table 1 indicates the melt flow rate of the resin.

(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. ○ that does not meet the three conditions that the thickness accuracy of the multi-layer polyolefin heat-shrinkable film after stretching is good, and × that does not satisfy any one of the above three conditions evaluated.

(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.

(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 just after heat shrink wrapping are rubbed together, and the slippery condition at that time is sensory evaluated. Was marked with 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. Each piece (140 mm long × 170 mm wide × 50 mm high) was heat-shrink wrapped.

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.
A: Insufficient shrinkage or heating / 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, heat-melting and tearing were observed, and the finished state was poor.

Claims (3)

Polyethylene having a density of 0.91 to 0.93 g / cm ^{3 on} both surfaces of an intermediate layer composed of 30 to 70% by weight of a polyethylene resin having a density of 0.91 to 0.93 g / cm ³ and 30 to 70% by weight of a polypropylene resin. A multilayer polyolefin heat-shrink film obtained by laminating and integrating surface layers made of a resin, and the polypropylene resin has a melting start temperature of 30 in a differential scanning calorimetry using a DSC (differential scanning calorimeter). The total amount of heat absorbed between the melting start temperature and the melting end temperature is lower than the melting peak temperature by a temperature between the melting start temperature and the melting end temperature. A multilayer polyolefin heat-shrinkable film characterized by being 40 to 60% of the total heat absorbed in the film. 2. The multilayer polyolefin heat-shrinkable film according to claim 1, wherein the polyethylene resin constituting the intermediate layer is a linear low density polyethylene. The multilayer polyolefin heat-shrinkable film according to claim 1 or 2, wherein the polyethylene resin constituting the surface layer is a linear low-density polyethylene.