JP7036151B2 - Multilayer film, packaging material and packaging - Google Patents

Description

The present invention relates to multilayer films, packaging materials and packaging bodies. Specifically, the present invention is a polypropylene-based multilayer film having excellent heat resistance and transparency and can be suitably used as a sealant film for packaging bags in harsh treatments such as boiling water treatment and retort treatment, and the polypropylene-based multilayer film. The present invention relates to the packaging material and the packaging body obtained by using.

Since polypropylene-based films have excellent rigidity and heat resistance and are inexpensive, they may be used as sealant films in various packaging materials such as food packaging.

Patent Document 1 is a polypropylene-based composite film composed of three layers, characterized in that the intermediate layer is made of a propylene / ethylene block copolymer and both surface layers are made of a propylene-based random copolymer. System composite films have been proposed.

Patent Document 2 proposes a multilayer film including both surface layers containing an ethylene-α-olefin copolymer and a propylene-based polymer, and an intermediate layer containing a propylene polymer and an ethylene-propylene copolymer.

Japanese Unexamined Patent Publication No. 2017-132186 JP-A-2017-105174

Polypropylene-based multilayer films are required to have heat resistance that can withstand retort treatment such as sterilization and sterilization by performing pressure treatment at a high temperature of 120 to 135 ° C, and transparency that can maintain visibility of the contents. It has become like that. However, in the present situation, it is difficult for the conventional polypropylene-based multilayer film to achieve both excellent heat resistance and transparency.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polypropylene-based multilayer film capable of achieving both excellent heat resistance and transparency. It is also an object of the present invention to provide a packaging material and a package obtained by using the multilayer film.

As a result of diligent studies to solve the above problems, the inventors have found that it is important to appropriately adjust the mode of the resin in the inner layer of the polypropylene-based multilayer film, and have completed the present invention.

The multilayer film according to one aspect of the present invention includes a first outer layer containing 70 to 30% by mass of the propylene homopolymer (A) and 30 to 70% by mass of the propylene / ethylene random copolymer (B), and propylene. An inner layer containing an ethylene block copolymer (C) and an ethylene / propylene copolymer elastomer (D), 70 to 30% by mass of the propylene homopolymer (A), and a propylene / ethylene random copolymer (B). A second outer layer containing 30 to 70% by mass is provided in this order, and the weight of the ethylene-propylene copolymer with respect to the weight average molecular weight Mw (PP) of the propylene resin in the propylene / ethylene block copolymer (C). The ratio Mw (EPR) / Mw (PP) of the average molecular weight Mw (EPR) is 1.5 or less.

In the multilayer film, the outer layer contains the propylene homopolymer (A) and the propylene / ethylene random copolymer (B) in a specific amount ratio, and the inner layer contains the propylene / ethylene block copolymer (C). ), The ratio of the weight average molecular weights of the propylene resin and the ethylene-propylene copolymer is less than or equal to a specific value. As a result, it is possible to reduce the difference in the refractive index in the film, which is a factor that lowers the transparency of the film, while maintaining the heat resistance. Such an effect cannot be obtained with a conventional multilayer film (for example, Patent Document 1 and Patent Document 2), and is particularly suitable for retort processing applications.

In one embodiment, the inner layer may contain 90 to 50% by mass of the propylene / ethylene block copolymer (C) and 10 to 50% by mass of the ethylene / propylene copolymer elastomer (D). As a result, the flexibility of the film is maintained, the edge breakage of the heat-sealed portion can be suppressed after the retort treatment, and excellent heat-sealing properties can be easily obtained.

In one embodiment, the total thickness of the first outer layer and the second outer layer may be 16 to 42% based on the thickness of the multilayer film. This makes it easy to achieve both transparency and heat sealability.

In one embodiment, the thickness of the inner layer may be 20 μm or more. This makes it easy to maintain the flexibility of the film.

In one embodiment, the thickness of the ethylene-propylene copolymer present as a dispersion in the inner layer in the stacking direction may be 1.5 μm or less. This makes it easy to maintain the transparency of the film.

The packaging material according to one aspect of the present invention includes the above-mentioned multilayer film and a base material.

The package according to one aspect of the present invention is made from the above-mentioned packaging material.

According to the present invention, it is possible to provide a polypropylene-based multilayer film capable of achieving both excellent heat resistance and transparency. Further, according to the present invention, it is possible to provide a packaging material and a packaging body obtained by using the multilayer film.

FIG. 1 is a cross-sectional view of a multilayer film according to an embodiment of the present invention. FIG. 2 is a diagram showing the results of dividing the total heat of fusion of the propylene / ethylene random copolymer (B) used in Example 1 and the heat of fusion at 135 ° C. FIG. 3 is a cross-sectional photograph of the inner layer in Example 1. FIG. 4 is a cross-sectional photograph of the inner layer in Comparative Example 4.

<Multilayer film>
FIG. 1 is a cross-sectional view of a multilayer film according to an embodiment of the present invention. The multilayer film 10 includes a first outer layer 1a, an inner layer 2, and a second outer layer 1b in this order. The multilayer film can be used as a polypropylene-based non-stretched sealant film.

[First outer layer and second outer layer]
The first outer layer and the second outer layer contain a propylene homopolymer (A) and a propylene / ethylene random copolymer (B). The first outer layer and the second outer layer may be collectively referred to as an outer layer. The first outer layer and the second outer layer may have the same composition or may have different compositions.

(Propylene homopolymer (A))
The propylene homopolymer (A) can be obtained by a method of homopolymerizing propylene using, for example, a Ziegler-Natta type catalyst or a metallocene catalyst. When the outer layer contains the propylene homopolymer (A), excellent heat resistance can be imparted to the outer layer.

As the propylene homopolymer (A), one having a melting start temperature of 150 ° C. or higher and a melting peak temperature of 155 ° C. or higher when measured by differential scanning calorimetry (JIS K 7121) can be used. Those having both the melting start temperature and the melting point peak temperature within this range have excellent heat resistance, and for example, after retort treatment at a high temperature, fusion is unlikely to occur on the inner surface of the packaging bag.

As the propylene homopolymer (A), one having a melt flow rate (MFR: ISO 1133) (temperature 230 ° C., load 2.16 kg) in the range of 2.0 to 7.0 g / 10 minutes can be used. .. When the melt flow rate is equal to or higher than the lower limit, the load on the extruder during the forming process is reduced, the processing speed is less likely to decrease, and excellent productivity can be easily maintained. Further, when the melt flow rate is not more than the upper limit value, the outer layer tends to have excellent impact resistance.

(Propylene / ethylene random copolymer (B))
The propylene / ethylene random copolymer (B) can be obtained by copolymerizing ethylene as a comonomer into a main monomer composed of propylene, for example, using a Cheegler-Nutter type catalyst or a metallocene catalyst. When the outer layer contains the propylene / ethylene random copolymer (B), a multilayer film having excellent transparency can be obtained.

As the propylene / ethylene random copolymer (B), one having a melting start temperature of 140 ° C. or higher and a melting point peak temperature of 145 ° C. or higher when measured by differential scanning calorimetry (JIS K 7121) can be used. .. Those having both the melting start temperature and the melting point peak temperature within this range have excellent heat resistance, and for example, after retort treatment at a high temperature, fusion is unlikely to occur on the inner surface of the packaging bag.

As the propylene / ethylene random copolymer (B), the heat of fusion ΔH _h on the high temperature side of the measured temperature of 135 ° C. and the heat of fusion ΔH _l on the low temperature side when differential scanning calorimetry (JIS K 7121) was performed. Those having a ratio of ΔH _h / ΔH _l in the range of 1.5 to 2.5 can be used. When the above ratio is not more than the upper limit, the flexibility of the film is maintained, the edge breakage of the heat-sealed portion can be suppressed after the retort treatment, and the heat-sealed strength is unlikely to decrease. The lower limit of the above ratio can be 1.5 from the viewpoint that fusion is unlikely to occur on the inner surface of the packaging bag after the retort treatment.

The ethylene content of the propylene / ethylene random copolymer (B) may be 5% by mass or less. When the ethylene content is not more than the upper limit value, the heat resistance is not excessively lowered while maintaining the transparency, and it becomes easy to suppress the fusion on the inner surface of the packaging bag after the retort treatment. From this point of view, the ethylene content may be 4.5% by mass or less, and may be 4% by mass or less. The lower limit of the ethylene content is not particularly limited, but it can be set to 2% by mass from the viewpoint that the flexibility of the film is maintained, edge breakage can be suppressed at the heat-sealed portion after the retort treatment, and the heat-sealed strength does not easily decrease. ..

The ethylene content of the propylene / ethylene random copolymer (B) is described on pages 412 to 413 of the Polymer Analysis Handbook (May 10, 2013, 3rd print) edited by the Polymer Analysis Council of the Japan Society of Analytical Science. Can be measured according to the ethylene content quantification method (IR method).

The outer layer contains 70 to 30% by mass of the propylene homopolymer (A) and 30 to 70% by mass of the propylene / ethylene random copolymer (B). When the content of the propylene homopolymer (A) is 30% by mass or more, excellent heat resistance can be maintained. From this point of view, the content may be 35% by mass or more, and may be 40% by mass or more. Excellent transparency when the content of the propylene homopolymer (A) is 70% by mass or less, that is, the content of the propylene / ethylene random copolymer (B) is at least 30% by mass or more. , Heat sealability can be exhibited. From this viewpoint, the content of the propylene homopolymer (A) may be 65% by mass or less, and may be 60% by mass or less. From the above viewpoint, the content of the propylene / ethylene random copolymer (B) may be 35 to 65% by mass or 40 to 60% by mass.

[Inner layer]
The inner layer contains a propylene / ethylene block copolymer (C) and an ethylene / propylene copolymer elastomer (D).

(Propylene / ethylene block copolymer (C))
The propylene / ethylene block copolymer (C) is produced by producing a propylene polymer (C1) in the first step and then producing an ethylene-propylene copolymer (C2) by vapor phase polymerization in the second step. It is a copolymer that can be obtained. The propylene / ethylene block copolymer (C) is not a block copolymer in which a propylene polymer terminal and an ethylene-propylene copolymer terminal are bonded, but is a kind of blend-type copolymer. Since the inner layer contains the propylene / ethylene block copolymer (C), the flexibility of the film is maintained, the edge breakage of the heat-sealed portion can be suppressed after the retort treatment, and excellent heat-sealing properties can be easily obtained.

The propylene / ethylene block copolymer (C) contains a propylene polymer component (C1) and an ethylene-propylene copolymer component (C2) as constituent components as described above. The ratio of the weight average molecular weight Mw (EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw (PP) of the propylene polymer in the propylene / ethylene block copolymer (C) is Mw (EPR) / Mw (PP). It is 1.5 or less. This allows the inner layer to have suitable transparency. From this point of view, the ratio may be 1.3 or less, and may be 1.2 or less.

The weight average molecular weight ratio can be measured as follows. First, 200 ml of n-decane is added to 5 g of the propylene / ethylene block copolymer (C), and the mixture is completely dissolved at 145 ° C. Then, after allowing to cool to room temperature, the precipitate is separated and separated. The separated product is used as a propylene resin component, and the residual solution is completely removed from the solvent in a dryer to obtain an ethylene-propylene copolymer component. 20 ml of a mobile phase for GPC measurement is added to each of the obtained components, dissolved at 145 ° C., and then heat-filtered with a sintered filter having a pore size of 1.0 μm to prepare a filtrate as a measurement solution. As a measuring device, an HLC-8321GPC / HT type high temperature gel permeation chromatograph manufactured by Tosoh was used, the column size was 7.5 mm, the length was 300 mm, the temperature was 140 ° C., and the mobile phase was o-dichlorobenzene (stabilizer; 0.025 wt%). The molecular weight is measured using a simple PS conversion method under the conditions of BHT content) and a flow rate of 1.0 ml. Regarding the obtained results, the ratio of the weight average molecular weight Mw (PP) of the propylene resin component and the weight average molecular weight Mw (EPR) of the ethylene-propylene copolymer component was defined as the weight average molecular weight ratio Mw (EPR) / Mw (PP). do.

The thickness of the above ethylene-propylene copolymer present as a dispersion in the inner layer in the stacking direction may be 1.5 μm or less. The ethylene-propylene copolymer is a so-called elastomer component, and when the thickness in the laminating direction is within this range, it is easy to suppress an increase in the internal haze value. This suppresses fogging of the entire film and makes it easier to see the contents. From this point of view, the thickness may be 1.25 μm or less, and may be 1.0 μm or less.

As the propylene / ethylene block copolymer (C), one having a melt flow rate (MFR: ISO 1133) (temperature 230 ° C., load 2.16 kg) in the range of 0.5 to 2.5 g / 10 minutes is used. be able to. When the melt flow rate is equal to or higher than the lower limit, the load on the extruder during the forming process is reduced, the processing speed is less likely to decrease, and excellent productivity can be easily maintained. When the melt flow rate is not more than the upper limit value, the inner layer tends to have excellent flexibility, the edge breakage of the heat-sealed portion can be suppressed, and excellent heat-sealing property can be easily obtained.

The propylene / ethylene block copolymer (C) may contain 90 to 60% by mass of the propylene polymer (C1) and 10 to 40% by mass of the ethylene-propylene copolymer (C2). When each component is in this range, excellent heat-sealing properties can be easily obtained. From this point of view, the propylene / ethylene block copolymer (C) contains 87.5 to 65% by mass of the propylene polymer (C1) and 12.5 to 35% by mass of the ethylene-propylene copolymer (C2). It may contain 85 to 70% by mass of the propylene polymer (C1) and 15 to 30% by mass of the ethylene-propylene copolymer (C2).

The ethylene content of the ethylene-propylene copolymer (C2) contained in the propylene / ethylene block copolymer (C) is not particularly limited, but can be in the range of 20 to 40% by mass. When the ethylene content is not more than the upper limit, the tackiness of the product can be suppressed, the product is less likely to be contaminated by the tack during production, and excellent productivity can be easily maintained. When the ethylene content is at least the lower limit, the flexibility of the film is maintained, the edge breakage of the heat-sealed portion can be suppressed after the retort treatment, and excellent heat-sealing properties can be easily obtained.

(Ethylene / Propylene Copolymer Elastomer (D))
The ethylene / propylene copolymer elastomer (D) is a slurry polymerization method performed in the presence of an inert hydrocarbon such as hexane, heptane, kerosene, or a liquefied α-olefin solvent such as propylene, and a gas phase weight without solvent. It can be obtained legally. Specifically, the ethylene / propylene copolymer elastomer (D) can be obtained by using a known multi-stage polymerization method. That is, a polymerized high rubber that can be obtained by polymerizing propylene and / or a propylene-α-olefin polymer in the first-stage reactor and then copolymerizing propylene and α-olefin in the second-stage reaction. It is a polypropylene-based resin contained. Since the inner layer contains the ethylene / propylene copolymer elastomer (D), it is easy to impart flexibility to the film, it is possible to suppress edge breakage of the heat-sealed portion, and it is easy to obtain excellent heat-sealing properties.

As the ethylene / propylene copolymer elastomer (D), one having a melt flow rate (MFR: ISO 1133) (temperature 230 ° C., load 2.16 kg) in the range of 0.5 to 3.5 g / 10 minutes is used. be able to. When the melt flow rate is equal to or higher than the lower limit, the load on the extruder during the forming process is reduced, the processing speed is less likely to decrease, and excellent productivity can be easily maintained. When the melt flow rate is not more than the upper limit value, the compatibility between the propylene / ethylene block copolymer (C) and the ethylene / propylene copolymer elastomer (D) becomes good, and the impact resistance does not easily decrease.

As the ethylene / propylene copolymer elastomer (D), one having a ratio of propylene content to ethylene content (propylene content / ethylene content) in the range of 1.5 to 4 can be used. When the above ratio is at least the lower limit, the flexibility of the film is maintained, the edge breakage of the heat-sealed portion can be suppressed after the retort treatment, and excellent heat-sealing properties can be easily obtained. When the above ratio is not more than the upper limit value, the compatibility between the propylene / ethylene block copolymer (C) and the ethylene / propylene copolymer elastomer (D) becomes good, and the transparency does not easily decrease.

The inner layer may contain 90 to 50% by mass of the propylene / ethylene block copolymer (C) and 10 to 50% by mass of the ethylene / propylene copolymer elastomer (D). When the content of the propylene / ethylene block copolymer (C) is 50% by mass or more, it is easy to maintain excellent heat-sealing properties. From this point of view, the content may be 60% by mass or more, and may be 70% by mass or more. Further, the content of the propylene / ethylene block copolymer (C) is 90% by mass or less, that is, the content of the ethylene / propylene copolymer elastomer (D) is at least 10% by mass or more. It can exhibit excellent heat-sealing properties. From this viewpoint, the content of the propylene / ethylene block copolymer (C) may be 87.5% by mass or less, and may be 85% by mass or less. From the above viewpoint, the content of the ethylene / propylene copolymer elastomer (D) may be 12.5 to 40% by mass and may be 15 to 30% by mass.

When only the resin used for the inner layer is formed into a film having a thickness of 60 μm using an extruder under the condition of 250 ° C., the internal haze value measured as follows may be 5% or less. It may be 4% or less.
[Internal haze measurement]
Cut out the produced film to 70 mm x 70 mm, apply silicone oil to both surfaces of the light receiving range of the film, smooth the thickness with a smooth film, and use a haze meter (model number HM-150) manufactured by Murakami Color Technology Laboratory. It is measured according to JIS K 7136.

The thickness of the multilayer film is not particularly limited as long as it can be used as a film for packaging materials, but if the film is too thick, it becomes a cost disadvantage. Therefore, the thickness of the multilayer film can be 100 μm or less, and may be 50 to 70 μm.

The thickness of the outer layer (that is, the total thickness of the first outer layer and the second outer layer) may be 16 to 42% based on the thickness of the multilayer film. When the ratio of the thickness of the outer layer is at least the lower limit value, it is easy to obtain excellent transparency, and when it is at least the upper limit value, it is possible to suppress the deterioration of the heat sealability of the film, and practicality is obtained. Easy to get rid of. From this point of view, the ratio of the thickness of the outer layer may be 20 to 35%.

The thickness of the inner layer may be 20 μm or more. As a result, the flexibility of the film is maintained, the film is less likely to break after the retort treatment, and the heat seal strength is less likely to decrease. From this point of view, the thickness of the inner layer may be 25 μm or more, and may be 30 μm or more. The upper limit of the thickness of the inner layer is not particularly limited, but it can be set to 50 μm because it is a cost demerit.

<Characteristics of multilayer film>
The surface roughness of the multilayer film, that is, the arithmetic mean roughness Ra (JIS B 0601-2001) of the outer layer constituting the multilayer film may be 0.05 to 0.15 μm. When Ra is at least the lower limit value, the slipperiness between the multilayer films tends to be good, and excellent processability is easily maintained. When Ra is not more than the upper limit value, diffused reflection due to unevenness on the film surface is less likely to occur, and excellent transparency is easily obtained.

The haze value of the multilayer film having a thickness of 60 μm measured according to JIS K 7136 may be 15% or less. When the haze value is 15% or less, it means that the visibility of the contents can be easily maintained.

The fusion strength of the multilayer film in the fusion test conducted in accordance with the following may be 2.0 N / 15 mm or less. The fact that the fusion strength is 2.0 N / 15 mm or less means that the films are difficult to fuse with each other when the retort treatment is performed at a high temperature of 135 ° C.

[Fusion test]
Using a heat sealer manufactured by Tester Sangyo Co., Ltd., the multilayer films are heat-sealed under the conditions of a sealing pressure of 0.03 MPa, a sealing time of 30 seconds, a sealing width of 10 mm, and a sealing temperature of 135 ° C. After that, the heat-sealed multilayer film was cut into a 15 mm width x 80 mm, and T-shaped peeling was performed at a tensile speed of 300 mm / min using a tensile tester manufactured by Shimadzu Corporation to increase the fusion strength of the heat-sealed portion. Measure.

<Manufacturing method of multilayer film>
The method for producing the multilayer film is not particularly limited, and a known method can be used. For example, as a method of thermoforming, a melt-kneading method using a general miscible machine such as a single-screw screw extruder, a twin-screw screw extruder, or a multi-screw screw extruder, after melting or dispersing and mixing each component, Examples thereof include a method of heating and removing the solvent. When workability is taken into consideration, a single-screw screw extruder or a twin-screw screw extruder can be used. When a single-screw extruder is used, examples of the screw include a full flight screw, a screw having a mixing element, a barrier flight screw, a fluted screw, and the like, and these can be used without particular limitation. As the biaxial kneading device, a biaxial screw extruder that rotates in the same direction, a biaxial screw extruder that rotates in a different direction, or the like can be used, and the screw shape is not particularly limited, such as a full flight screw or a kneading disc type. Can be done.

In the above method, it is possible to use a method in which a multilayer film is melted by a single-screw extruder, a twin-screw extruder, or the like, and then formed with a T-die via a feed block or a multi-manifold.

The obtained multilayer film may be subjected to a surface modification treatment to improve suitability for the post-process as appropriate, if necessary. For example, in order to improve the printability when using a single film and to improve the laminating suitability when using a laminated film, a surface modification treatment may be performed on the printed surface or the surface in contact with the substrate. Examples of the surface modification treatment include treatments such as corona discharge treatment, plasma treatment, and frame treatment to generate functional groups by oxidizing the film surface, and reforming treatments by a wet process for forming an easy-adhesion layer by coating. ..

<Packaging material>
The multilayer film may be used as a single film or may be used by laminating it with a base material, and the method of using the multilayer film as a packaging material is not particularly limited.

When the multilayer film is used by laminating it with the base material, the packaging material can include the above-mentioned multilayer film and the base material. Specifically, such packaging materials include the above-mentioned multilayer film, biaxially stretched polyamide film (ONy), biaxially stretched polyester film (PET), printing paper, metal foil (AL foil), transparent vapor-deposited film, and the like. It can be obtained by laminating at least one layer of a base material to form a laminated body. As a method for manufacturing the laminate, a normal dry laminating method in which the film constituting the laminate is bonded to the film using an adhesive can be preferably adopted, but if necessary, a method of directly extruding and laminating the multilayer film onto the substrate is also possible. Can be adopted.

The laminated structure of the laminated body is appropriately adjusted according to the required characteristics of the package, for example, the barrier property that satisfies the quality retention period of the food to be packaged, the size / impact resistance that can correspond to the weight of the contents, the visibility of the contents, and the like. can do.

<Packaging>
The package may be made from the above-mentioned packaging material, and the bag making style is not particularly limited. For example, the above-mentioned packaging material (laminated body) can be used for a flat bag, a three-sided bag, a gassho bag, a gusset bag, a standing pouch, a pouch with a spout, a pouch with a beak, or the like, which uses a multilayer film as a sealing material.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

<Manufacturing of laminated film>
(Example 1)
The following propylene homopolymer (A), propylene / ethylene random copolymer (B), propylene / ethylene block copolymer (C), and ethylene / propylene copolymer elastomer (D) were prepared.

(Propylene homopolymer (A))
When the differential scanning calorimetry (JIS K 7121) was performed, the melting start temperature was 153 ° C, the melting peak temperature was 159 ° C, and the melt flow rate (MFR: ISO 1133) (temperature 230 ° C, load 2.16 kg). A propylene homopolymer having a temperature of 3.0 g / 10 min.

(Propylene / ethylene random copolymer (B))
When the differential scanning calorimetry (JIS K 7121) was performed, the melting start temperature was 142 ° C., the melting peak temperature was 147 ° C., ΔH _h / ΔH _l was 1.84, and the ethylene content was 3.4% by mass. A propylene / ethylene random copolymer that is.

The ethylene content is measured by the method for quantifying the ethylene content described on pages 412 to 413 of the Polymer Analysis Handbook (May 10, 2013, 3rd print) edited by the Polymer Analysis Council of the Japan Society for Analytical Science (May 10, 2013, 3rd print). The IR method) was followed.
ΔH _h / ΔH _l is the ratio of the heat of fusion ΔH _h on the higher temperature side than the measured temperature of 135 ° C. and the heat of fusion ΔH _l on the lower temperature side when the differential scanning calorimetry (JIS K 7121) is performed. FIG. 2 is a diagram showing the results of dividing the total heat of fusion of the propylene / ethylene random copolymer (B) and the heat of fusion at 135 ° C.

(Propylene / ethylene block copolymer (C))
The melt flow rate (MFR: ISO 1133) (temperature 230 ° C., load 2.16 kg) was 2.0 g / 10 minutes, and 77.1% by mass of the propylene polymer and 22.9% by mass of the ethylene-propylene copolymer. A propylene / ethylene block contained in which the ratio Mw (EPR) / Mw (PP) of the weight average molecular weight Mw (EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw (PP) of the propylene polymer is 1.25. Copolymer.

The weight average molecular weight ratio was measured as follows. 200 ml of n-decane was added to 5 g of the propylene / ethylene block copolymer (C), and the mixture was completely dissolved at 145 ° C. Then, after allowing to cool to room temperature, the precipitate was separated by separation and separated. The separated material was used as a propylene resin component, and the solvent was completely removed from the remaining solution in a dryer to obtain an ethylene-propylene copolymer component. 20 ml of a mobile phase for GPC measurement was added to each of the obtained components, dissolved at 145 ° C., and then heat-filtered with a sintered filter having a pore size of 1.0 μm to prepare a filtrate as a measurement solution. As a measuring device, an HLC-8321GPC / HT type high temperature gel permeation chromatograph manufactured by Tosoh was used, the column size was 7.5 mm, the length was 300 mm, the temperature was 140 ° C., and the mobile phase was o-dichlorobenzene (stabilizer; 0.025 wt%). The molecular weight was measured using a simple PS conversion method under the conditions of BHT content) and a flow rate of 1.0 ml. Regarding the obtained results, the ratio of the weight average molecular weight Mw (PP) of the propylene resin component and the weight average molecular weight Mw (EPR) of the ethylene-propylene copolymer component was defined as the weight average molecular weight ratio Mw (EPR) / Mw (PP). did.

(Ethylene / Propylene Copolymer Elastomer (D))
Ethylene-propylene copolymer elastomer having a melt flow rate (MFR: ISO 1133) (temperature 230 ° C., load 2.16 kg) of 0.6 g / 10 minutes and a propylene content / ethylene content of 2.7. ..

A resin mixture in which 70% by mass of the propylene homopolymer (A) and 30% by mass of the propylene / ethylene random copolymer (B) are mixed in a pellet state is used for forming the outer layer, and a propylene / ethylene block is used for forming the inner layer. A resin mixture in which 83% by mass of the copolymer (C) and 17% by mass of the ethylene / propylene copolymer elastomer (D) were mixed in a pellet state was used. Each raw material is supplied to an extruder whose temperature is adjusted to 250 ° C., kneaded in a molten state, and the thickness of the first outer layer and the second outer layer is 10 μm, respectively, in a T-die extruder having a feed block. , The film of Example 1 was prepared by laminating so that the thickness of the inner layer was 40 μm.

(Example 2)
A film of Example 2 was prepared in the same manner as in Example 1 except that the mixing ratio of the propylene homopolymer (A) and the propylene / ethylene random copolymer (B) was changed as shown in Table 1. ..

(Example 3)
A film of Example 3 was prepared in the same manner as in Example 1 except that the mixing ratio of the propylene homopolymer (A) and the propylene / ethylene random copolymer (B) was changed as shown in Table 1. ..

(Example 4)
The film of Example 4 was produced in the same manner as in Example 2 except that the thicknesses of the outer layer and the inner layer were changed as shown in Table 1.

(Example 5)
The following propylene / ethylene block copolymer (C') was used instead of the propylene / ethylene block copolymer (C), and the propylene / ethylene block copolymer (C') and ethylene / propylene copolymer weight were used. The film of Example 5 was prepared in the same manner as in Example 2 except that the mixing ratio of the combined elastomer (D) was changed as shown in Table 1.
(Propene / ethylene block copolymer (C'))
The melt flow rate (MFR: ISO 1133) (temperature 230 ° C., load 2.16 kg) was 1.8 g / 10 minutes, and 81.5% by mass of the propylene polymer and 18.5% by mass of the ethylene-propylene copolymer. A propylene / ethylene block contained in which the ratio Mw (EPR) / Mw (PP) of the weight average molecular weight Mw (EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw (PP) of the propylene polymer is 1.16. Copolymer.

(Example 6)
Example 6 is the same as in Example 5 except that the mixing ratio of the propylene / ethylene block copolymer (C') and the ethylene / propylene copolymer elastomer (D) is changed as shown in Table 1. A film was made.

(Example 7)
Example 7 is the same as in Example 5 except that the mixing ratio of the propylene / ethylene block copolymer (C') and the ethylene / propylene copolymer elastomer (D) is changed as shown in Table 1. A film was made.

(Example 8)
The film of Example 8 in the same manner as in Example 2 except that the mixing ratio of the propylene / ethylene block copolymer (C) and the ethylene / propylene copolymer elastomer (D) was changed as shown in Table 1. Was produced.

(Comparative Example 1)
A film of Comparative Example 1 was prepared in the same manner as in Example 1 except that the outer layer was formed using only the propylene / ethylene random copolymer (B).

(Comparative Example 2)
Except that the following elastomer resin was used instead of the propylene / ethylene random copolymer (B), and the mixing ratio of the propylene homopolymer (A) and the elastomer resin was changed as shown in Table 2. , The film of Comparative Example 2 was produced in the same manner as in Example 1.
(Elastomer resin)
It is an olefin-based elastomer that uses a metallocene catalyst and uses ethylene as the main monomer and butene-1 as the comonomer, and has a melt flow rate (MFR: ISO 1133) (temperature 190 ° C., load 2.16 kg) of 3.6 g / g. Elastomer resin for 10 minutes.

(Comparative Example 3)
Using a resin mixture obtained by mixing 83% by mass of the propylene / ethylene block copolymer (C) and 17% by mass of the ethylene / propylene copolymer elastomer (D) in a pellet state, a film of Comparative Example 3 having a thickness of 60 μm was obtained. Made.

(Comparative Example 4)
The film of Comparative Example 4 was produced in the same manner as in Example 1 except that the following propylene / ethylene block copolymer (E) was used instead of the propylene / ethylene block copolymer (C).
(Propylene / ethylene block copolymer (E))
The melt flow rate (MFR: ISO 1133) (temperature 230 ° C., load 2.16 kg) was 2.5 g / 10 minutes, and 81.0% by mass of the propylene polymer and 19.0% by mass of the ethylene-propylene copolymer. A propylene / ethylene block contained in which the ratio Mw (EPR) / Mw (PP) of the weight average molecular weight Mw (EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw (PP) of the propylene polymer is 1.65. Copolymer.

(Comparative Example 5)
The film of Comparative Example 5 was produced in the same manner as in Example 2 except that the propylene / ethylene block copolymer (E) was used instead of the propylene / ethylene block copolymer (C).

(Comparative Example 6)
The film of Comparative Example 6 was produced in the same manner as in Example 3 except that the propylene / ethylene block copolymer (E) was used instead of the propylene / ethylene block copolymer (C).

<Various evaluations>
The following evaluations were performed on the films obtained in each example. The results are shown in Tables 1 and 2.

[Dispersion thickness measurement method]
After the multilayer film obtained in each example was hardened with a photocurable resin, a cross section was cut out with an ultramicrotome manufactured by Leica, and the ethylene-propylene copolymer component was dyed with ruthenium tetroxide. Then, the cross section of the film was observed at a magnification of 10,000 times using a scanning electron microscope (model number S-4800) manufactured by Hitachi High-Technologies Corporation, and the thickness of the ethylene-propylene copolymer component as a dispersion was observed. Was measured. The measurement was carried out along the flow direction (MD) at the time of film preparation. FIG. 3 is a cross-sectional photograph of the inner layer in Example 1. FIG. 4 is a cross-sectional photograph of the inner layer in Comparative Example 4.

[Internal haze measurement]
Only the resin used for the inner layer was formed into a film having a thickness of 60 μm using an extruder under the condition of 250 ° C. This film is cut into 70 mm x 70 mm, silicone oil is applied to both surfaces of the light receiving range of the film, smoothed to a uniform thickness with a smooth film, and a haze meter (model number HM-150) manufactured by Murakami Color Technology Research Institute is used. The internal haze was measured according to JIS K 7136.

[Surface roughness measurement]
The surface roughness (surface roughness of the outer layer) of the film obtained in each example was measured. As a measuring device, a small surface roughness measuring machine surf test manufactured by Mitutoyo Co., Ltd. was used. The arithmetic average roughness Ra (JIS B 0601-2001) was measured with the cutoff value λc set to 0.25.

[Haze measurement]
The evaluation was carried out using a haze meter (model number HM-150) manufactured by Murakami Color Technology Research Institute in accordance with the haze measuring method described in JIS K7136.

[Heat sealability evaluation]
A biaxially stretched polyester film (PET) having a thickness of 12 μm, a biaxially stretched polyamide film (ONy) having a thickness of 15 μm, an AL foil having a thickness of 9 μm, and a film (polypropylene film) obtained in each example were used. A laminate having the following composition was formed by laminating by a normal dry laminating method using a urethane-based adhesive.
Laminated structure: PET / adhesive / ONy / adhesive / AL foil / adhesive / polypropylene film The polypropylene films of this laminate face each other and are sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. Heat sealing was performed under the conditions of a pressure of 0.2 MPa, a sealing time of 1 second, a sealing width of 5 mm, and a sealing temperature of 200 ° C. Then, the retort treatment was performed at 135 ° C. for 40 minutes. The retort-treated film was cut into a 15 mm width × 80 mm, and T-shaped peeling was performed at a tensile speed of 300 mm / min using a tensile tester manufactured by Shimadzu Corporation, and the heat seal strength was measured.

[Measurement of fusion strength]
Using a heat sealer manufactured by Tester Sangyo Co., Ltd., the films obtained in each example were heat-sealed under the conditions of a sealing pressure of 0.03 MPa, a sealing time of 30 seconds, a sealing width of 10 mm, and a sealing temperature of 135 ° C. After that, the heat-sealed film was cut into a 15 mm width x 80 mm, and T-shaped peeling was performed at a tensile speed of 300 mm / min using a tensile tester manufactured by Shimadzu Corporation, and the fusion strength of the heat-sealed portion was measured. did.

The polypropylene-based multilayer film of the present invention has both heat resistance and transparency at a high level, and can be suitably used as a sealant film for retort packaging.

10 ... Multilayer film, 1a ... First outer layer, 1b ... Second outer layer, 2 ... Inner layer.

Claims (7)

A first outer layer containing 70 to 30% by mass of the propylene homopolymer (A) and 30 to 70% by mass of the propylene / ethylene random copolymer (B) having an ethylene content of 5% by mass or less .
An inner layer containing a propylene / ethylene block copolymer (C) and an ethylene / propylene copolymer elastomer (D),
A second outer layer containing 70 to 30% by mass of the propylene homopolymer (A) and 30 to 70% by mass of the propylene / ethylene random copolymer (B) having an ethylene content of 5% by mass or less. Prepare in order,
The ratio of the weight average molecular weight Mw (EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw (PP) of the propylene resin in the propylene / ethylene block copolymer (C) is Mw (EPR) / Mw (PP). Multilayer film of 1.5 or less. The multilayer film according to claim 1, wherein the inner layer contains 90 to 50% by mass of the propylene / ethylene block copolymer (C) and 10 to 50% by mass of the ethylene / propylene copolymer elastomer (D). The multilayer film according to claim 1 or 2, wherein the total thickness of the first outer layer and the second outer layer is 16 to 42% with respect to the thickness of the multilayer film. The multilayer film according to any one of claims 1 to 3, wherein the inner layer has a thickness of 20 μm or more. The multilayer film according to any one of claims 1 to 4, wherein the ethylene-propylene copolymer present as a dispersion in the inner layer has a thickness of 1.5 μm or less in the stacking direction. A packaging material comprising the multilayer film according to any one of claims 1 to 5 and a base material. A package made from the packaging material according to claim 6.

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