JP5047493B2 - Film and multilayer biaxially stretched film - Google Patents

Description

  The present invention relates to a film and a multilayer biaxially stretched film suitable for freshness-keeping packaging of fruits and vegetables.

  In general, polyolefin resin films are widely used as various packaging materials such as foods, daily necessities, and industrial products because of their excellent moldability, transparency, and mechanical properties. However, when vegetables and fruits and flowers are sealed and packaged with a film, the transpiration and respiration rate of the water are reduced in the initial stage, so that a certain freshness retention effect can be obtained, but the oxygen concentration inside the package decreases due to respiration, and carbon dioxide When the concentration increased, there was a problem that the freshness rapidly declined due to decay by anaerobic breathing.

  For this reason, low density polyethylene (LDPE and LLDPE) films with relatively high gas permeability are often used for packaging fruits and vegetables, but they are more transparent and rigid than polypropylene and polystyrene films. There was a problem of shortage. Polystyrene films are transparent and rigid, and have a relatively high gas permeability, so they are also used for packaging for the same purpose, but they are broken because they are less stretched than polypropylene or low-density polyethylene films. There was a problem that it was easy and the seal strength was low.

  On the other hand, since a polypropylene film is also excellent in transparency and rigidity, for example, a biaxially stretched polypropylene film imparted with antifogging properties is used for packaging fruits and vegetables and flowers (see, for example, Patent Document 1). However, the film made of polypropylene has a lower gas permeability than the film made of low density polyethylene or polystyrene, so that the freshness retention in the case of hermetically wrapping fruits and vegetables and flowers is inferior.

  Therefore, a technique has been proposed in which fruits and vegetables are sealed and packaged with a film provided with gas permeability by opening minute holes (see, for example, Patent Document 2). However, in this method, equipment and processing costs for punching are generated, and in addition to the problem that the productivity of the film is lowered, there is a possibility that contaminants may enter from the outside through the hole.

  In addition, an olefin-based resin film made of isotactic polypropylene and an ethylene-octene-1 copolymer has been proposed (see Patent Document 3). However, the present proposal is a thick surface cosmetic film having a thickness of 0.03 to 0.2 mm and a layer made of an ethylene-octene-1 copolymer. A thick film with a thickness of 0.1 mm is shown, and it was not suitable for packaging fruits and vegetables and flowers that emphasize transparency.

Further, there has been proposed a laminated film obtained by laminating a resin composition made of a specific syndiotactic polypropylene and an ethylene-octene copolymer on a base material layer made of isotactic polypropylene (see Patent Document 4). However, since syndiotactic polypropylene generally has a low crystallinity and is soft, its main application has been a heat seal material conventionally, and the proposed composition has also been aimed at improving heat sealability.

In addition, a coextruded laminated film including a resin layer made of an ethylene-1-octene copolymer and an ethylene-propylene copolymer has been proposed (see Patent Document 5). However, even in this proposal, the function of the resin layer is only heat-sealing, and the thickness ratio of the coextruded laminated film is 40% at the maximum.
JP 2003-291282 A JP-A-5-153907 Japanese Patent Laid-Open No. 10-330551 JP-A-9-39175 JP 2003-165572 A

  An object of the present invention is to provide a film having a large ratio of oxygen permeability, carbon dioxide permeability, and carbon dioxide permeability / oxygen permeability, and excellent in freshness retention when packaging fruits and vegetables and flowers. . Furthermore, this invention makes it a subject to provide the laminated | multilayer film suitable for the freshness maintenance packaging of fruits and vegetables and flowers which are excellent in sealing performance and transparency, and have moderate rigidity and high oxygen permeability.

As a result of intensive studies to solve the above problems, the present inventor has found that a film composed of polypropylene (A): 55 to 95 wt% and ethylene-1-octene random copolymer (B): 5 to 45 wt% is polypropylene. Of course, the ratios of oxygen permeability, carbon dioxide permeability, and carbon dioxide permeability / oxygen permeability are much larger than films made of polyolefin elastomers other than polypropylene and ethylene-1-octene random copolymers. The present invention has been completed by finding that it is extremely suitable for packaging for maintaining the freshness of fruits and vegetables.

The polypropylene (A) of the present invention is a propylene homopolymer (A1) and / or a propylene-α-olefin copolymer (A2), which is a 1-octene copolymer contained in the ethylene-1-octene random copolymer (B). The amount is preferably 2 to 20 mol%. The film of the present invention may be a single layer or a multilayer, but in the case of a multilayer, it is preferable that the thickness of the film layer comprising the composition of the present invention accounts for 50% or more with respect to the total thickness. The film or film layer having the composition of the present invention is desirably stretched at least in a uniaxial direction. The haze value of the gas permeation control film of the present invention is preferably less than 10%.

In addition, as a result of intensive studies, the inventor has a base material layer made of a specific resin composition (C) and at least one surface layer made of a specific propylene-based resin (D). The multilayer biaxially stretched film characterized by being 1 to 20% of the thickness of the base material layer per layer has been found to have appropriate rigidity and high oxygen permeability, and the present invention has been completed. It was.
That is, this invention consists of the base material layer which consists of the following resin composition (C), and the surface layer of at least 1 layer which consists of the following propylene-type resin (D), and the thickness of a base material layer is the thickness of one surface layer. 1 to 20% of the thickness, and relates to a multilayer biaxially stretched film.

<Resin composition (C)>
Propylene homopolymer (CA-1) and / or propylene-based random copolymer having a MFR measured at 230 ° C. of 1 to 10 g / 10 min and a melting point Tm determined from the melting peak of DSC of 155 ° C. or higher ( CA-2) An ethylene-1-octene random copolymer having 75 to 95 parts by weight, an MFR measured at 190 ° C. of 0.5 to 30 g / 10 min, and a 1-octene content of 5 to 20 mol% A resin composition comprising 5 to 25 parts by weight of combined (CB-1).

<Propylene resin (D)>
Propylene homopolymer (D1) and / or propylene random copolymer (D2) having an MFR measured at 230 ° C. of 1 to 20 g / 10 min and a melting point Tm determined from the melting peak of DSC of 120 to 150 ° C. ).
As long as the total amount of component CA-1 and component CA-2 is in the range of 75 to 95 parts by weight in the resin composition (C), either one may be used in combination. The ethylene-1-octene random copolymer CB-1 occupies 5 to 25 parts by weight of the resin composition (C).

The gas permeation control film of the present invention has significantly higher ratios of oxygen permeability, carbon dioxide permeability, and carbon dioxide permeability / oxygen permeability than conventional polypropylene films. In this case, the freshness retention period can be extended.
Furthermore, since the multilayer biaxially stretched film of the present invention is excellent in sealing properties and transparency, has an appropriate rigidity and high oxygen permeability, it is optimal for packaging for maintaining freshness of fruits and vegetables. Furthermore, since it is not necessary to provide a physical hole in the film of the present invention, entry of contaminants from the outside can be prevented.

(Gas permeation control film)
The gas permeation control film according to the present invention comprises polypropylene (A): 55 to 95 wt% and ethylene-1-octene random copolymer (B): 5 to 45 wt%.
The polypropylene (A) used in the present invention is a propylene homopolymer (A1) and / or a propylene-α-olefin copolymer (A2). Moreover, it is desirable that the polypropylene (A) used in the present invention is basically isotactic polypropylene. As the α-olefin used in the propylene-α-olefin copolymer (A2), for example,
Ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadodecene, 4-methyl-1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, diethyl-1-butene, trimethyl-1-butene, 3-methyl-1-pentene, ethyl-1- Pentene, propyl-1-pentene, dimethyl-1-pentene, methylethyl-1-pentene, diethyl-1-hexene, trimethyl-1-pentene, 3-methyl-1-hexene, dimethyl-1-hexene, 3,5 , 5-trimethyl-1-hexene, methylethyl-1-heptene, trimethyl-1-heptene, dimethyloctene, ethyl-1-octene, methyl-1-nonene, vinylcyclopentene, vinylcyclohexane, vinylnorvo For example, Renan. One or more of these α-olefins can be contained in the propylene-α-olefin copolymer (A2) in an amount of 10 mol% or less in total.

The melt flow rate (ASTM D1238, 230 ° C., load 2.16 kg) of the polypropylene (A) used in the present invention is usually 0.5 to 10 g / 10 minutes, preferably 1 to 4 g / 10 minutes, more preferably It is in the range of 1.5 to 3.5 g / min. A melt flow rate in this range is preferable because the moldability and mechanical strength of the film are good.

The ethylene-1-octene random copolymer (B) used in the present invention preferably contains a structural unit derived from 1-octene in an amount of 2 to 20 mol%. When the amount of 1-octene is within this range, the film has good rigidity and gas permeability, which is preferable.

The ethylene-1-octene random copolymer (B) used in the present invention preferably has an intrinsic viscosity [η] measured at 135 ° C. in decalin of 1.5 to 3.5 dl / g, more preferably Is 2.0 to 3.0 dl / g. Such an ethylene-1-octene random copolymer (B) can be produced using a known vanadium catalyst or metallocene catalyst.

The gas permeation control film of the present invention includes heat stabilizers, antioxidants, slip agents, antiblocking agents, plasticizers, colorants, nucleating agents, weathering stabilizers, and UV absorbers that are generally used as necessary. In addition to these, an antifogging agent, an antifogging agent, an antibacterial agent, an ethylene removing agent and the like can be contained.

The thickness of the gas permeation control film of the present invention is not particularly limited because it depends on the type and usage of the fruits and flowers to be packaged, but is usually 10 to 100 μm, preferably 10 to 60 μm. A more preferable thickness is 10 μm or more and less than 30 μm. In addition, when a multilayer film is formed by laminating with a heat seal layer, a reinforcing layer, a surface protective layer, etc., the thickness of the layer made of the gas permeation control film of the present invention is at least 50% of the total thickness, preferably 60% or more, more preferably 70% or more.

The resin used for lamination is not particularly limited. For example, polyethylene, ethylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-methacrylate copolymer, Examples include ionomer resins, polypropylene, propylene-α-olefin copolymers, polymethylpentene, polybutene, polybutadiene, and polystyrene.

The gas permeation control film of the present invention is formed by a T-die method, an inflation method, a calendar method, or the like. In the case of a multilayer film, the multilayer film is formed by coextrusion or by laminating another resin layer on the base film by an extrusion lamination method or a dry lamination method.

The gas permeation control film of the present invention is desirably stretched in at least a uniaxial direction, more preferably in a biaxial direction. By stretching, a film excellent in strength, optical properties and appearance can be obtained. Examples of the stretching method include a roll method, a tenter method, and a tubular method. Further, in the case of biaxial stretching, sequential biaxial stretching or simultaneous biaxial stretching can be performed. The stretching ratio is preferably in the range of 3 to 8 times in the case of uniaxial stretching and in the range of 10 to 60 times in the case of biaxial stretching.

The haze value measured according to JIS K7105 of the gas permeation control film of the present invention is preferably less than 10%, more preferably less than 7%. When the haze value is within this range, the visibility of the packaged vegetables and florets is not impaired, and the appearance is good.

In producing the gas permeation control film of the present invention, a dry blend method or a melt blend method can be used. That is, polypropylene (A) and ethylene-1-octene random copolymer (B) may be mixed in a solid state such as pellets or powder to form a composition, which may be melt-kneaded at the time of molding. A composition obtained by melt-kneading (B) in advance can also be used.

(Multilayer biaxially stretched film)
The multilayer biaxially stretched film of the present invention will be described. It consists of a base material layer composed of the resin composition (C) and at least one surface layer composed of the propylene-based resin (D), and the thickness of the surface layer is in the range of 1 to 20% of the thickness of the base material layer per layer It is in.

<Resin composition (C)>
Propylene homopolymer (CA-1) and / or propylene random copolymer (CA) having an MFR measured at 230 ° C. of 1 to 10 g / 10 min and a melting point Tm determined from the melting peak of DSC of 155 ° C. or higher. -2) An ethylene-1-octene random copolymer having an MFR measured at 75 to 95 parts by weight and 190 ° C. of 0.5 to 30 g / 10 min and a 1-octene content of 5 to 20 mol% ( CB-1) A resin composition comprising 5 to 25 parts by weight.
As long as the total amount of component CA-1 and component CA-2 is in the range of 75 to 95 parts by weight in the resin composition (C), either one may be used in combination. The ethylene-1-octene random copolymer CB-1 occupies 5 to 25 parts by weight of the resin composition (C).
<Propylene resin (D)>
Propylene homopolymer (D1) and / or propylene-based random copolymer (D2) having an MFR measured at 230 ° C. of 1 to 20 g / 10 min and a melting point Tm determined from the melting peak of DSC of 120 to 150 ° C. .

  The propylene random copolymer (CA-2) used for the base material layer is a propylene-α-olefin copolymer, and examples of the α-olefin include ethylene, 1-butene, 1-pentene, and 1-hexene. 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadodecene, 4-methyl-1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 3-methyl-1 -Butene, 3,3-dimethyl-1-butene, diethyl-1-butene, trimethyl-1-butene, 3-methyl-1-pentene, ethyl-1-pentene, propyl-1-pentene, dimethyl-1-pentene Methylethyl-1-pentene, diethyl-1-hexene, trimethyl-1-pentene, 3-methyl-1-hexene, dimethyl-1-hexene, , 5,5-trimethyl-1-hexene, methylethyl-1-heptene, trimethyl-1-heptene, dimethyloctene, ethyl-1-octene, methyl-1-nonene, vinylcyclopentene, vinylcyclohexane, vinylnorbornane and the like. It is done. One or more of these α-olefins can be contained in the propylene-α-olefin copolymer in a total amount of 10 mol% or less.

  The MFR measured at 230 ° C. of the propylene homopolymer (CA-1) and / or propylene random copolymer (CA-2) used for the base material layer of the present invention is usually 1 to 10 g / 10 min, preferably Is in the range of 2-7 g / 10 min, more preferably in the range of 2-5 g / 10 min. When the MFR is within this range, it is preferable because the balance between the moldability of the film and the mechanical strength is good.

  From the peak temperature of the melting curve measured by a differential scanning calorimeter (DSC) of the propylene homopolymer (CA-1) and / or the propylene random copolymer (CA-2) used for the base material layer of the present invention. The defined melting point (Tm, unit: ° C) is 155 ° C or higher, preferably 155 ° C or higher and 170 ° C or lower. It is preferable for the melting point Tm to be 155 ° C. or higher, since an appropriate rigidity can be imparted to the film.

  MFR measured at 190 degreeC of the ethylene-1-octene random copolymer (CB-1) used for the base material layer of this invention is 0.5-30 g / 10min normally, Preferably it is 0.5-5 g / min. More preferably, it is in the range of 1 to 5 g / 10 minutes. When the MFR is in this range, it is preferable because the transparency of the film is good.

  Moreover, 1-octene content of the ethylene-1-octene random copolymer (CB-1) used for the base material layer of this invention is 5-20 mol%, Preferably it is 10-20 mol%, More preferably, it is 12 It is in the range of ˜18 mol%. When the amount of 1-octene is within this range, the balance between the rigidity of the film and the gas permeability is good, which is preferable.

  The resin composition (C) constituting the substrate layer of the present invention is 75 to 95 parts by weight, preferably 80 to 90 parts by weight, of propylene homopolymer (CA-1) and / or propylene random copolymer (CA-2). Parts and 5 to 25 parts by weight, preferably 10 to 20 parts by weight of ethylene-1-octene random copolymer (CB-1). When the composition is within this range, the balance of transparency, rigidity, and gas permeability of the film is improved, which is preferable.

  The propylene random copolymer (D2) used for the surface layer of the present invention is a propylene-α-olefin copolymer similar to the propylene random copolymer (CA-2) used for the base material layer. As the α-olefin, for example, ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-hexadodecene, 4-methyl-1-pentene 2-methyl-1-butene, 3-methyl-1-butene, 3-methyl-1-butene, 3,3-dimethyl-1-butene, diethyl-1-butene, trimethyl-1-butene, 3-methyl -1-pentene, ethyl-1-pentene, propyl-1-pentene, dimethyl-1-pentene, methylethyl-1-pentene, diethyl-1-hexene, tri Tyl-1-pentene, 3-methyl-1-hexene, dimethyl-1-hexene, 3,5,5-trimethyl-1-hexene, methylethyl-1-heptene, trimethyl-1-heptene, dimethyloctene, ethyl- Examples include 1-octene, methyl-1-nonene, vinylcyclopentene, vinylcyclohexane, and vinylnorbornane. One or more of these α-olefins can be contained in the propylene-α-olefin copolymer in a total amount of 10 mol% or less.

  The MFR measured at 230 ° C. of the propylene homopolymer (D1) and / or propylene random copolymer (D2) used for the surface layer of the present invention is usually 1 to 20 g / 10 minutes, preferably 2 to 10 g / 10 minutes. More preferably, it exists in the range of 4-10 g / 10min. An MFR in this range is preferable because the moldability and appearance of the film are good.

  The melting point Tm of the propylene homopolymer (D1) and / or the propylene random copolymer (D2) used for the surface layer of the present invention is in the range of 120 to 150 ° C, preferably 130 to 145 ° C. When the melting point Tm is in this range, there is no stickiness of the film, transparency and sealing properties are good, and gas permeability is high, which is preferable.

  The surface layer of the multilayer biaxially stretched film of the present invention is laminated on one side or both sides of the base material layer. When the surface layer is laminated on both surfaces, the propylene homopolymer (D1) and / or the propylene random copolymer (D2) for the surface layer may be the same or different. The thickness of the surface layer is 1 to 20%, preferably 2 to 10%, more preferably 4 to 7% of the thickness of the base material layer for one layer. When the thickness of the surface layer is within this range, the resulting multilayer biaxially stretched film is preferable in terms of sealing properties and rigidity. When laminating on both surfaces, the thickness of each layer may be in the above range, and the thickness of each layer may be the same or different, but it is preferable to laminate the propylene random copolymer (D2) on both surfaces. .

  The haze value of the multilayer biaxially stretched film of the present invention is preferably 5% or less. A haze value of 5% or less is preferable because the visibility of the packaged contents is not impaired.

  The tensile elastic modulus in the MD direction of the multilayer biaxially stretched film of the present invention is preferably 1800 Mpa or more, more preferably 2000 MPa or more. When the tensile elastic modulus is in this range, the resulting multilayer biaxially stretched film has sufficient rigidity, and is not insufficient.

Further, the oxygen permeability of the multilayer biaxially stretched film of the present invention is preferably 1.6 × 10 ⁻¹¹ mol / m ² · s · Pa or more, more preferably 1.8 × 10 ⁻¹¹ mol / m ² · s. -Pa or more, Especially preferably, it is 2.0 * 10 < ^-11 > mol / m < ² > * s * Pa or more. When the oxygen permeability is within this range, the effect of maintaining freshness is enhanced, which is preferable.

As a manufacturing method of the propylene homopolymer (A1, CA-1 and D1) and the propylene-based random copolymer (CA-2 and D2) and the propylene-α-olefin copolymer (A2) used in the present invention, The method of manufacturing by a well-known polymerization method using a well-known polymerization catalyst is mentioned.
Known polymerization catalysts include, for example, a catalyst system comprising a solid catalyst component essentially containing magnesium, titanium and halogen, an organoaluminum compound, and a third component such as an electron-donating compound used as necessary. A catalyst system comprising a transition metal compound of group IV of the periodic table having a pentadienyl ring and an alkylaluminoxane, or an ionic complex by reacting with a transition metal compound of group IV of the periodic table having a cyclopentadienyl ring. Examples thereof include a catalyst system composed of a compound to be formed and an organoaluminum compound.

Known polymerization methods include, for example, a slurry polymerization method using an inert hydrocarbon solvent, a solution polymerization method, a liquid phase polymerization method using no solvent, and a gas phase polymerization method. Furthermore, a method of combining the above-described polymerization methods and continuously performing them, for example, a liquid phase-gas phase polymerization method and the like can be mentioned.
The ethylene-1-octene random copolymer (B) used in the present invention can be produced by a known polymerization method using a known vanadium catalyst or metallocene catalyst.

  The multi-layer biaxially stretched film of the present invention is a heat stabilizer, antioxidant, slip agent, anti-blocking agent, plasticizer, colorant, nucleating agent, weathering stabilizer, UV absorber, which are generally used as necessary. In addition to the agent, it may contain an antifogging agent, an antifogging agent, an antibacterial agent, an ethylene removing agent, and the like. In particular, the anti-fogging agent is useful because it has an effect of preventing the moisture content of the fruits and flowers from condensing on the inner surface of the packaging film to wet the contents or to deteriorate the transparency of the film. Examples of the antifogging agent include known glycerin fatty acid esters, diglycerin fatty acid esters, sorbitan fatty acid esters, ethylene oxide adducts of alkylamines, ethylene oxide adducts of aliphatic amides, and the like. The content of the antifogging agent is usually 0.5 to 2.0% by weight.

  As a method of mixing the resin and additives used when producing the multilayer biaxially stretched film of the present invention, a dry blend method of mixing with a tumbler mixer, a Henschel mixer, a ribbon blender or the like, or melt-kneading with an extruder A melt blending method is mentioned.

  There is no restriction | limiting in particular in the film forming of the multilayer biaxially stretched film of this invention, and the extending | stretching processing method. For example, there is a method of sequentially biaxially stretching or simultaneously biaxially stretching a sheet molded by a multilayer T-die molding machine using a roll or a tenter. Further, there is a tubular biaxial stretching method in which a tube molded using an annular die is expanded with pressurized air. Furthermore, after a surface layer is laminated on a base material layer that has been uniaxially stretched vertically, it can be stretched laterally.

  Although there is no restriction | limiting in particular in the thickness of the multilayer biaxially stretched film of this invention, Usually, 10-100 micrometers, Preferably it is 10-60 micrometers. More preferably, it is 10 μm or more and less than 30 μm. When the thickness is within this range, the balance of transparency, rigidity and oxygen permeability is excellent and preferable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to this. The physical property test was conducted by the following method.

(1) Melting point Tm
About 5 mg of a sample was weighed and heated to 200 ° C. at a heating rate of 10 ° C./min using a differential scanning calorimeter DSC6200 manufactured by Seiko Instruments Inc. After cooling to 30 ° C./minute and holding at 30 ° C. for 1 minute, the maximum peak temperature was determined as the melting point Tm from the heat of fusion curve when the temperature was raised again to 200 ° C. at a temperature increase rate of 10 ° C./minute. .
(2) Tensile Elastic Modulus Using an JIS K6781 dumbbell, an SS curve was drawn at a distance between chucks of 80 mm and a tensile speed of 50 mm / min, and the initial elastic modulus was measured.
(3) Gas permeability
Using a gas permeability measuring device MT-C3 type manufactured by Toyo Seiki Seisakusho Co., Ltd., measurement was performed under the conditions of 23 ° C. and 0% RH in accordance with A method of JIS K7126.
(4) Haze The haze of one film was measured according to JIS K7105.

(Single layer gas permeable film)
[ Reference Example 1]
Polypropylene (PP-1) [Mitsui Polypro (registered trademark) F113G, manufactured by Mitsui Chemicals, MFR (JIS K7210, 230 ° C.) = 3 g / 10 min] (PP-1) 75 parts by weight and the amount of 1-octene Is 15 mol% and MFR (JIS K7210, 190 ° C.) = 1 g / 10 min of ethylene-1-octene random copolymer (EOR-1) 25 parts by weight is mixed (dry blended) with a Henschel mixer to obtain a resin composition I got a thing.

   Next, using this resin composition, a T-die molding machine (die lip width: 200 mm, extruder: 30 mmφ, L / D = 25), extruder set temperature: 230 ° C., die set temperature: 230 ° C., chill roll temperature : 30 ° C., take-up speed: 1 m / min, molded on the condition of single-sided air cooling to obtain a 500 μm-thick original film. Next, this original film was simultaneously stretched 5 times in the longitudinal direction and 5 times in the transverse direction at a stretching speed of 10 m / min in a tenter in which hot air at 145 ° C. was circulated to obtain a biaxially stretched film having a thickness of 20 μm. It was. The oxygen permeability [GTR (O2)] and carbon dioxide permeability [GTR (CO2)] of this film were measured, and the ratio was calculated. The results are shown in Table 1.

[Comparative Examples 1-6]
A biaxially stretched film having a thickness of 20 μm was obtained in the same manner as in Reference Example 1, except that the content of the resin composition was changed to that shown in Table 1. The oxygen permeability and carbon dioxide permeability of this film were measured and the ratio was calculated. The results are shown in Table 1. The polymer used in place of the ethylene-1-octene random copolymer is shown below:
PER: propylene-ethylene random copolymer [ethylene content = 42 mol%, MFR (JIS K7210, 190 ° C.) = 2 g / 10 min]
EPR: ethylene-propylene random copolymer [propylene content = 22 mol%, MFR (JIS K7210, 230 ° C.) = 2 g / 10 min]
BPR: 1-butene-propylene random copolymer [propylene content = 28 mol%, MFR (JIS K7210, 190 ° C.) = 2 g / 10 min]
EBR: ethylene-1-butene random copolymer [1-butene amount = 15 mol%, MFR (JIS K7210, 190 ° C.) = 4 g / 10 min]
PB: Poly-1-butene [MFR (JIS K7210, 190 ° C.) = 2 g / 10 min]

[Comparative Example 7]
As a biaxially stretched film, the oxygen permeability and carbon dioxide permeability of a gas-permeable OPP film PORO PRESH F # 25 (thickness 25 μm) manufactured by Nimura Chemical Industry Co., Ltd. were measured, and the ratio was calculated. The results are shown in Table 1.

(Multilayer biaxially stretched film)
[Example 2]
A propylene-ethylene random copolymer 95 having an ethylene amount of 1.2 mol%, a melting point Tm determined from a DSC melting peak of 159.8 ° C., and an MFR (JIS K7210, 230 ° C.) of 3 g / 10 min. 2 parts by weight of an ethylene-1-octene random copolymer having an amount of 1-octene of 15 mol% and an MFR (JIS K7210, 190 ° C.) of 1 g / 10 min. , L / D = 31), and melt kneading at an extruder set temperature: 230 ° C. to obtain a resin composition for a base material layer.

Next, the resin composition obtained above was put into a substrate layer extruder (30 mmφ, L / D = 25) of a two-type three-layer T-die molding machine (die lip width: 200 mm), and a surface layer extruder (25 mmφ). L / D = 25), the amount of ethylene is 3.3 mol%, the amount of 1-butene is 1.5 mol%, the melting point Tm is 138.4 ° C., and the MFR (JIS K7210, 230 ° C.) is 7 g / The propylene-ethylene-1-butene random copolymer that is 10 minutes is charged, the extruder set temperature: 230 ° C., the die set temperature: 230 ° C., the chill roll temperature: 30 ° C., under the conditions of single-sided air cooling, An original film having a total layer thickness of 500 μm having a surface layer on both surfaces of the base material layer was obtained with an extrusion rate setting of 5.5% of the thickness of the base material layer for one layer. Next, this raw film was first stretched 5 times in the MD direction and then 5 times in the TD direction in a tenter in which hot air at 150 ° C. was circulated. A multilayer biaxially stretched film was obtained. The tensile elastic modulus, oxygen permeability and haze in the MD direction of this multilayer biaxially stretched film were measured. The results are shown in Table 2.

[Example 3]
The thickness is the same as in Example 2 except that the propylene-ethylene random copolymer contained in the resin composition for the base layer is 90 parts by weight and the ethylene-1-octene random copolymer is 10 parts by weight. A 20 μm multilayer biaxially stretched film was obtained.

[Example 4]
The thickness is the same as in Example 2 except that the propylene-ethylene random copolymer contained in the resin composition for the base layer is 85 parts by weight and the ethylene-1-octene random copolymer is 15 parts by weight. A 20 μm multilayer biaxially stretched film was obtained.

[Example 5]
In Example 4, a multilayer biaxial stretching of 20 μm in thickness was performed in the same manner as in Example 4 except that the total thickness of the raw film was 320 μm and the stretching ratio was 4 times in the MD direction and 4 times in the TD direction. A film was obtained.

[Example 6]
In Example 4, multilayer biaxial stretching of 20 μm in thickness was performed in the same manner as in Example 4 except that the total thickness of the raw film was 720 μm and the stretching ratio was 6 times in the MD direction and 6 times in the TD direction. A film was obtained.

[Example 7]
The thickness is the same as in Example 2 except that the propylene-ethylene random copolymer contained in the resin composition for the base material layer is 80 parts by weight and the ethylene-1-octene random copolymer is 20 parts by weight. A 20 μm multilayer biaxially stretched film was obtained.

[Example 8]
Except that the propylene-ethylene random copolymer contained in the resin composition for the base layer is 75 parts by weight and the ethylene-1-octene random copolymer is 25 parts by weight, the same as in Example 6, A multilayer biaxially stretched film having a thickness of 20 μm was obtained.

[Comparative Example 8]
A multilayer biaxially stretched film having a thickness of 20 μm was obtained in the same manner as in Example 2 except that only a propylene-ethylene random copolymer was used as the resin for the base material layer.

[Comparative Example 9]
Except that the propylene-ethylene random copolymer contained in the resin composition for the base layer is 70 parts by weight and the ethylene-1-octene random copolymer is 30 parts by weight, the same as in Example 6, A multilayer biaxially stretched film having a thickness of 20 μm was obtained.

The gas permeation control film provided by the present invention has a larger ratio of oxygen permeability, carbon dioxide permeability, and carbon dioxide permeability / oxygen permeability than conventional polypropylene films. The multilayer biaxially stretched film provided by the present invention is excellent in transparency, has an appropriate rigidity and high oxygen permeability, and also has a good sealing property. Furthermore, since no physical hole exists in the film of the present invention, entry of contaminants from the outside can be prevented. As a result, the gas permeation control film and multilayer biaxially stretched film provided by the present invention are optimal as packaging materials for maintaining the freshness of fruits and vegetables.

Claims (6)

In a multilayer biaxially stretched film comprising a substrate layer and at least one surface layer, the substrate layer is composed of the following resin composition (C), the surface layer is composed of the following propylene-based resin (D), and the thickness of the surface layer is 1. A multilayer biaxially stretched film characterized in that the layer is 1 to 20% of the thickness of the base material layer.
Resin composition (C):
Propylene single weight having a melt flow rate (ASTM D1238, load 2.16 kg, hereinafter abbreviated as MFR) measured at 230 ° C. of 1 to 10 g / 10 min and a melting point Tm determined from a melting peak of DSC of 155 ° C. or more 75-95 parts by weight of coalescence (CA-1) and / or propylene random copolymer (CA-2), MFR measured at 190 ° C. is 0.5-30 g / 10 min, and 1-octene content The resin composition which consists of 5-25 weight part of ethylene-1-octene random copolymer (CB-1) whose is 5-20 mol%.
Propylene resin (D):
Propylene homopolymer (D1) and / or propylene random copolymer (D2) having an MFR measured at 230 ° C. of 1 to 20 g / 10 min and a melting point Tm determined from the melting peak of DSC of 120 to 150 ° C. ). The multilayer biaxially stretched film according to claim 1 , wherein the haze value (JIS K7105) is 5% or less. The multilayer biaxially stretched film according to claim 1 or 2 , wherein a tensile elastic modulus in the MD direction is 1800 Mpa or more. Multilayer biaxially oriented film according to any one of claims 1 to 3 oxygen permeability, characterized in that it is ^{1.6 × 10 -11 mol / m 2} · s · Pa or more. A freshness-maintaining packaging film for fruits and vegetables and / or flowers comprising the multilayer biaxially stretched film according to any one of claims 1 to 4 . The multilayer biaxially stretched film according to any one of claims 1 to 4 , wherein the thickness is in a range of 10 to 100 µm.