Multi-layer film, packaging material, and package

Abstract

To provide a polypropylene-based multilayer film that has excellent heat resistance, transparency and anti-blocking property.SOLUTION: Provided is a multilayer film that includes a first outer layer which is a heat seal layer and contains a propylene homopolymer (A), a propylene / ethylene random copolymer (B) and an anti-blocking agent, an inner layer containing propylene / ethylene block copolymer (C) and ethylene / propylene copolymer elastomer (D), and a second outer layer containing propylene homopolymer (A) and propylene / ethylene random copolymer (B) in this order, and in which the contained amount of the anti-blocking agent in the first outer layer is 1.8 to 3.7 pts.mass for 100 pts.mass of the total amount of the propylene homopolymer (A) and the propylene / ethylene random copolymer (B).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multilayer film, a packaging material, and a package. Specifically, the present invention relates to a polypropylene-based multilayer film that is excellent in heat resistance, transparency, and antiblocking property and can be suitably used as a sealant film for packages even in severe treatments such as boiling water treatment and retort treatment, and a packaging material and a package obtained by using the polypropylene-based multilayer film.

Background Art

[0002] Polypropylene-based films are sometimes used as sealant films in various packaging materials such as food packaging because they are excellent in rigidity and heat resistance and are inexpensive.

[0003] Since polypropylene-based films have poor slipperiness during processing, resulting in wrinkles, and antiblocking marks due to blocking becoming apparent, antiblocking property is required. Regarding polypropylene-based films having antiblocking property, for example, the following proposals have been made.

[0004] Patent Document 1 proposes a single-layer polypropylene-based film containing a propylene-ethylene block copolymer and a hydrogenated styrene-based thermoplastic elastomer, and having a center line average roughness (Ra) of the film of 0.10 to 0.30 μm.

[0005] Patent Document 2 proposes a single-layer packaging film containing a propylene-ethylene block copolymer, an ethylene / α-olefin copolymer, and an antiblocking agent.

[0006] In Patent Document 3, a polypropylene-based composite film composed of three layers is proposed as a packaging film. The surface layer contains a polypropylene resin with a melting peak temperature of 130 to 145°C and an antiblocking agent, and the intermediate layer contains a crystalline propylene-α-olefin random copolymer with a melting peak temperature of 120 to 145°C and an ethylene-α-olefin random copolymer elastomer.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] For polypropylene-based films, for example, heat resistance that can withstand retort processing such as sterilization and disinfection by performing pressure treatment at a high temperature of 120 to 135°C and transparency that can maintain the visibility of the contents have been increasingly required. In addition, as described above, antiblocking properties are also required for polypropylene-based films. However, at present, it is difficult for conventional polypropylene-based films to achieve all of excellent heat resistance, excellent transparency, and excellent antiblocking properties.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a polypropylene-based multilayer film having excellent heat resistance, transparency, and antiblocking properties. Another object of the present invention is to provide a packaging material and a package obtained using the multilayer film.

Means for Solving the Problems

[0010] As a result of intensive studies to solve the above problems, the inventors have found that it is important to adjust the surface state of a polypropylene-based multilayer film by mixing different propylene-based polymers in the outer layer and further including a predetermined amount of an antiblocking agent, and thus have completed the present invention.

[0011] A multilayer film according to one aspect of the present invention includes a first outer layer which is a heat-sealing layer containing a propylene homopolymer (A), a propylene-ethylene random copolymer (B), and an antiblocking agent, an inner layer containing a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D), and a second outer layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B), in this order. The content of the antiblocking agent in the first outer layer is 1.8 to 3.7 parts by mass with respect to 100 parts by mass of the total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B).

[0012] In the above multilayer film, the outer layer contains a high-melting-point propylene homopolymer (A) and a propylene-ethylene random copolymer (B). Here, the propylene homopolymer (A) has a higher melting point compared to the propylene-ethylene random copolymer, and the propylene-ethylene random copolymer (B) is likely to smooth the film surface. Therefore, by providing the outer layer having the above configuration in the multilayer film, it is possible to suppress the surface irregularities, which are a factor in reducing the transparency of the film, while maintaining heat resistance (a high level of heat resistance where the film is less likely to deform or fuse on the inner surface when used as a package). Further, by containing a predetermined amount of an antiblocking agent in the first outer layer, the antiblocking property of the film surface is improved while maintaining transparency, and adhesion between the films can be prevented. In addition, by providing an inner layer in the multilayer film that contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D), it becomes possible to maintain the flexibility of the multilayer film and ensure excellent cold impact resistance. Although the inner layer containing the above components is likely to have irregularities on the surface, by sandwiching the inner layer with the above-described outer layer, the irregularities on the surface of the inner layer can be filled with the outer layer, and excellent transparency can be ensured. Such effects cannot be obtained with the polypropylene-based films described in Patent Documents 1 to 3 above, and are particularly suitable effects in applications such as retort treatment (including high retort treatment).

[0013] For example, in the above Patent Document 1, the blocking resistance is improved by defining the center line average roughness (Ra) of the polypropylene-based film. However, since a propylene-ethylene block copolymer having an essentially opaque property is used, the transparency is insufficient. Further, in the above Patent Document 2, a single-layer film is formed of a propylene-ethylene block copolymer and an antiblocking agent, but the transparency is insufficient due to surface irregularities. Furthermore, in the above Patent Document 3, the blocking resistance is improved by using a polypropylene resin having a melting peak temperature of 130 to 145°C and an antiblocking agent in the outer layer. However, as shown in the examples, the heat seal temperature is around 130 to 140°C, and the heat resistance is insufficient for applications where retort treatment is performed at a high temperature around 135°C. On the other hand, according to the present invention, by providing the above configuration, it is possible to provide a polypropylene-based multilayer film excellent in all of heat resistance, transparency, and blocking resistance, which cannot be achieved in the above Patent Documents 1 to 3.

[0014] In one aspect, the first outer layer may contain 30 to 70% by mass of the propylene homopolymer (A) and 30 to 70% by mass of the propylene-ethylene random copolymer (B) based on the total amount of the first outer layer excluding the antiblocking agent. The second outer layer may contain 30 to 70% by mass of the propylene homopolymer (A) and 30 to 70% by mass of the propylene-ethylene random copolymer (B) based on the total amount of the second outer layer. Thereby, it is easier to achieve both high heat resistance and transparency at a higher level.

[0015] In one aspect, the propylene homopolymer (A) may satisfy the following requirement (a1), and the propylene-ethylene random copolymer (B) may satisfy the following requirement (b1). Thereby, it is easier to achieve both high heat resistance and transparency at a higher level. Requirement (a1): The melting start temperature is 150°C or higher and the melting peak temperature is 155°C or higher as measured by differential scanning calorimetry (JIS K 7121). Requirement (b1): The ethylene content is 5% by mass or less.

[0016] In one aspect, the inner layer may contain 50 to 90% by mass of the propylene-ethylene block copolymer (C) and 10 to 50% by mass of the ethylene-propylene copolymer elastomer (D) based on the total amount of the inner layer. Thereby, the flexibility of the film is more easily maintained sufficiently, and more excellent cold resistance impact resistance is more easily obtained.

[0017] The packaging material according to one aspect of the present invention includes the above-mentioned multilayer film and a base material.

[0018] The package according to one aspect of the present invention is formed into a bag from the above-mentioned packaging material.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a polypropylene-based multilayer film having excellent heat resistance, transparency, and blocking resistance. The present invention can also provide a packaging material and a package obtained using the multilayer film.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0021] <Polypropylene-based 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.

[0022] [First Outer Layer and Second Outer Layer] The first outer layer contains a propylene homopolymer (A), a propylene-ethylene random copolymer (B), and an antiblocking agent. The first outer layer can be said to be a layer formed from a resin composition containing a propylene homopolymer (A), a propylene-ethylene random copolymer (B), and an antiblocking agent. When used as a packaging material, the first outer layer serves as a heat-sealing layer (has heat-sealing properties) and is arranged to contact the contents. For this reason, the first outer layer has heat resistance such that the first outer layers do not fuse together during retort processing. Also, in order to suppress the appearance of wrinkles caused by poor slipperiness during processing and blocking marks due to blocking, the first outer layer has antiblocking properties such that it does not adhere tightly to other films or rolls, etc.

[0023] The second outer layer contains a propylene homopolymer (A) and a propylene-ethylene random copolymer (B). The second outer layer can be said to be a layer formed from a resin composition containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B).

[0024] By the first outer layer and the second outer layer having the above-described configurations, heat resistance, transparency, and antiblocking properties can be imparted to the multilayer film. The first outer layer and the second outer layer may be collectively simply referred to as the outer layer.

[0025] (Propylene homopolymer (A)) The manufacturing method of the propylene homopolymer (A) is not particularly limited, and it can be obtained, for example, by a method of homopolymerizing propylene using a Ziegler-Natta type catalyst, a metallocene catalyst, or a half-metallocene catalyst. By the outer layer containing the propylene homopolymer (A), excellent heat resistance can be imparted to the outer layer.

[0026] As the propylene homopolymer (A), those 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 peak temperature within this range have excellent heat resistance. For example, after performing a retort treatment at a high temperature, it is difficult for fusion to occur on the inner surface of the package.

[0027] As the propylene homopolymer (A), those 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 min can be used. The melt flow rate is a parameter indicating the fluidity of a polymer material during melting and is also a parameter indicating the molecular weight. Therefore, if the melt flow rate is too high, the impact resistance of the polymer material is likely to decrease. If it is too low, the extruder load during molding processing increases, the processing speed decreases, and the productivity is likely to decrease. From these viewpoints, the melt flow rate can be 2.0 to 7.0 g / 10 min, and it may be 2.0 to 5.0 g / 10 min.

[0028] (Propylene-ethylene random copolymer (B)) The production method of the propylene-ethylene random copolymer (B) is not particularly limited. For example, it can be obtained by copolymerizing ethylene as a comonomer in a main monomer composed of propylene using a Ziegler-Natta type catalyst, a metallocene catalyst, or a half-metallocene catalyst. By containing the propylene-ethylene random copolymer (B) in the outer layer, a multilayer film having excellent transparency can be obtained.

[0029] As the propylene-ethylene random copolymer (B), those having a melting start temperature of 140°C or higher and a melting 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 peak temperature within this range have excellent heat resistance. For example, after performing a severe retort treatment at 135°C for 40 minutes, it is difficult for fusion to occur on the inner surface of the package.

[0030] As the propylene-ethylene random copolymer (B), when differential scanning calorimetry (JIS K 7121) is performed, the heat of fusion ΔH on the higher temperature side than the measurement temperature of 135°C h and the heat of fusion ΔH on the lower temperature side l The ratio ΔH h / ΔH l in the range of 1.5 to 2.5 can be used. When the above ratio is below the upper limit value, the flexibility of the film is maintained, edge breakage of the heat seal part can be suppressed after retort treatment, and the heat seal strength is less likely to decrease. The lower limit value of the above ratio can be set to 1.5 from the viewpoint that fusion hardly occurs on the inner surface of the package after retort treatment.

[0031] The ethylene content of the propylene-ethylene random copolymer (B) can be 5% by mass or less. When the ethylene content is below the upper limit value, transparency is maintained while heat resistance does not excessively decrease, and it becomes easier to suppress fusion on the inner surface of the package after retort treatment. From this viewpoint, 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 from the viewpoint that the flexibility of the film is maintained, edge breakage can be suppressed at the heat seal part after retort treatment, and the heat seal strength is less likely to decrease, it can be 2% by mass.

[0032] The ethylene content of the propylene-ethylene random copolymer (B) can be measured according to the ethylene content quantification method (IR method) described on pages 412 to 413 of the Polymer Analysis Handbook edited by the Polymer Analysis Discussion Group of the Japan Society for Analytical Chemistry (May 10, 2013, 3rd edition).

[0033] The outer layer may contain 30 to 70% by mass of a propylene homopolymer (A) and 30 to 70% by mass of a propylene-ethylene random copolymer (B) based on the total amount of the outer layer (excluding the antiblocking agent in the first outer layer). When the content of the propylene homopolymer (A) is 30% by mass or more, it is easy to maintain excellent heat resistance. Also, when the content of the propylene homopolymer (A) is 70% by mass or less, that is, when the content of the propylene-ethylene random copolymer (B) is 30% by mass or more, it is easy to exhibit excellent transparency and heat sealability. From these viewpoints, the outer layer may contain 40 to 60% by mass of the propylene homopolymer (A) and 40 to 60% by mass of the propylene-ethylene random copolymer (B). The total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) based on the total amount of the outer layer (excluding the antiblocking agent in the first outer layer) does not have to be 100% by mass and may contain other resins and additives, but from the viewpoint of further improving transparency and heat resistance, the total amount may be 70% by mass or more, 90% by mass or more, or 100% by mass.

[0034] In the outer layer, the content of the propylene-ethylene block copolymer (C) may be 10% by mass or less, 5% by mass or less, or 0% by mass based on the total amount of the outer layer (excluding the antiblocking agent in the first outer layer). By reducing the content of the propylene-ethylene block copolymer (C) in the outer layer or by the outer layer not containing the propylene-ethylene block copolymer (C), it is possible to suppress the formation of unevenness on the surface of the multilayer film, which is a factor causing a decrease in transparency, and to further improve the transparency of the multilayer film.

[0035] (Antiblocking agent) An anti-blocking agent (AB agent, anti-blocking inhibitor) is an additive that has the effect of suppressing the adhesion (blocking) between films by imparting unevenness to the film surface, and is an additive that imparts anti-blocking properties by adding a small amount to a polymer compound. The anti-blocking agent is not particularly limited as long as it exhibits such an effect. Examples thereof include natural silica (diatomaceous earth), kaolin, talc, calcium carbonate, synthetic silica, alumina, zeolite, and polymer beads. Further, as the size of the anti-blocking agent, those having an average particle diameter of 0.5 to 10 μm as measured by a Coulter counter (ISO 13319) are preferably used.

[0036] By blending the anti-blocking agent into the first outer layer that becomes the heat-sealing layer, unevenness is imparted to the surface of the first outer layer, the contact area between films or between the film and the roll can be reduced, and the anti-blocking property is improved. Thereby, the slipperiness and anti-blocking property in the film processing step can be improved.

[0037] The content of the anti-blocking agent can be 1.8 to 3.7 parts by mass with respect to 100 parts by mass of the total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B). By the content being not less than the above lower limit value, excellent anti-blocking properties can be ensured. On the other hand, by the content being not more than the above upper limit value, transparency is maintained, and it becomes possible to achieve both transparency and anti-blocking properties. Further, by the content being not more than the above upper limit value, the cost can be suppressed. From these viewpoints, the content of the anti-blocking agent may be 2.0 to 3.5 parts by mass.

[0038] The surface roughness Sa of the surface on the side opposite to the inner layer of the first outer layer is not particularly limited, but from the viewpoint of achieving both transparency and anti-blocking property at a higher level, it may be 0.12 to 0.25 μm, and may be 0.15 to 0.20 μm. The surface roughness of the first outer layer can be measured as the arithmetic mean roughness Sa defined in ISO 25178 by a laser microscope.

[0039] [Inner layer] The inner layer contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D). It is desirable for the inner layer to be flexible in order to obtain impact resistance that does not cause the bag to burst in a low-temperature environment.

[0040] (Propylene-ethylene block copolymer (C)) The propylene-ethylene block copolymer (C) can be obtained by producing a propylene polymer (C1) in the first step and then producing an ethylene-propylene copolymer (C2) by gas-phase polymerization in the second step. The propylene-ethylene block copolymer (C) is not a block copolymer in which the propylene polymer terminal and the ethylene-propylene copolymer terminal are bonded, but a kind of blend-type copolymer. By containing the propylene-ethylene block copolymer (C) in the inner layer, the flexibility of the film is maintained and excellent cold impact resistance is easily obtained.

[0041] As the propylene-ethylene block copolymer (C), those 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 min can be used. If the melt flow rate becomes too high, the impact resistance of the film is likely to decrease. If it is too low, the extruder load during molding processing increases, the processing speed decreases, and the productivity is likely to decrease. From these viewpoints, the melt flow rate can be 0.5 to 2.5 g / 10 min, and may be 1.0 to 2.0 g / 10 min.

[0042] The propylene-ethylene block copolymer (C) may contain 60 to 90% by mass of the above propylene polymer (C1) and 10 to 40% by mass of the above ethylene-propylene copolymer (C2). When each component is within this range, excellent cold impact resistance is easily obtained.

[0043] The ethylene content of the ethylene-propylene copolymer (C2) contained in the propylene-ethylene block copolymer (C) is not particularly limited, but can be 20 to 40% by mass. By the ethylene content being below the upper limit value, the tackiness of the product can be suppressed, and it is difficult for contamination due to the tack of the product to occur during production, and it is easy to maintain excellent productivity. By the ethylene content being above the lower limit value, the flexibility of the film is maintained, and it is easy to obtain excellent cold impact resistance.

[0044] (Ethylene-propylene copolymer elastomer (D)) The ethylene-propylene copolymer elastomer (D) can be obtained, for example, by a slurry polymerization method carried out in the presence of an inert hydrocarbon such as hexane, heptane, kerosene, or a liquefied α-olefin solvent such as propylene, or a gas phase polymerization method without a solvent. Specifically, the ethylene-propylene copolymer elastomer (D) is obtained using a known multi-stage polymerization method. That is, it is a polymerized high rubber-containing polypropylene-based resin that can be obtained by polymerizing propylene and / or a propylene-α-olefin polymer in the first-stage reaction and then copolymerizing propylene and an α-olefin in the second-stage reaction. By the inner layer containing the ethylene-propylene copolymer elastomer (D), it is easy to impart flexibility to the film and easy to obtain excellent cold impact resistance.

[0045] As the ethylene-propylene copolymer elastomer (D), those 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 can be used. By the melt flow rate being above the lower limit value, the extruder load during molding processing becomes small, and it is difficult for the processing speed to decrease, and it is easy to maintain excellent productivity. By the melt flow rate being below the upper limit value, the compatibility between the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) becomes good, and it is difficult for the transparency to decrease.

[0046] As the ethylene-propylene copolymer elastomer (D), those with 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, and it is easy to obtain excellent cold impact resistance. When the above ratio is at most the upper limit, the compatibility between the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) becomes good, and the transparency is less likely to decrease.

[0047] The inner layer may contain 50 to 90% by mass of the propylene-ethylene block copolymer (C) and 10 to 50% by mass of the ethylene-propylene copolymer elastomer (D) based on the total amount of the inner layer. When the content of the propylene-ethylene block copolymer (C) is 50% by mass or more, it is easy to maintain excellent cold impact resistance. Also, when the content of the propylene-ethylene block copolymer (C) is 90% by mass or less, that is, when the content of the ethylene-propylene copolymer elastomer (D) is at least 10% by mass or more, more excellent heat sealability can be exhibited. From these viewpoints, the inner layer may contain 60 to 80% by mass of the propylene-ethylene block copolymer (C) and 20 to 40% by mass of the ethylene-propylene copolymer elastomer (D). The total amount of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) based on the total amount of the inner layer does not have to be 100% by mass and may contain other resins and additives, but from the viewpoint of further improving flexibility and cold impact resistance, the total amount may be 80% by mass or more, 90% by mass or more, or 100% by mass.

[0048] The thickness of the multilayer film is not particularly limited as long as it is within the range that can be used as a film for packaging materials, for example, but if the film is too thick, it will be a cost disadvantage. Therefore, the thickness of the multilayer film can be 100 μm or less, and may be 50 to 70 μm.

[0049] The thickness of the outer layer (i.e., 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, and may be 25 to 42%. By the proportion of the thickness of the outer layer being not less than the lower limit value, it is easy to obtain excellent transparency, and by being not more than the upper limit value, it is possible to suppress a decrease in the impact resistance and heat sealability of the film, and practicality can be easily obtained.

[0050] The thickness of the inner layer can be 20 μm or more, and may be 30 μm or more. Thereby, the flexibility of the film is maintained, the film is less likely to break after retort processing, and the heat seal strength is less likely to decrease.

[0051] <Manufacturing method of multilayer film> The method for manufacturing the multilayer film is not particularly limited, and known methods can be used. For example, as the method of thermoforming, there are a melt kneading method using a general mixer such as a single screw extruder, a twin screw extruder, a multi-screw extruder, etc., a method of heating and removing the solvent after dissolving or dispersing and mixing each component, and the like. Considering workability, a single screw extruder or a twin screw extruder can be used. When using a single screw extruder, examples of the screw include a full flight screw, a screw having a mixing element, a barrier flight screw, a fluted screw, etc., and these can be used without particular limitation. As the twin kneading device, a co-rotating twin screw extruder, a counter-rotating twin screw extruder, etc. can be used, and as the screw shape, a full flight screw, a kneading disk type, etc. can be used without particular limitation.

[0052] In the above method, after melting the multilayer film by a single screw extruder or a twin screw extruder, etc., it is possible to use a method of forming a film with a T-die through a feed block or a multi-manifold.

[0053] The obtained multilayer film may be subjected to a surface modification treatment to improve post-processing suitability as appropriate if necessary. For example, a surface modification treatment may be performed on the printing surface or the surface in contact with the base material in order to improve printing suitability when using a single film or to improve laminating suitability when using in a laminated state. Examples of the surface modification treatment include treatments that generate functional groups by oxidizing the film surface such as corona discharge treatment, plasma treatment, and flame treatment, and modification treatments by wet processes that form an easy-adhesion layer by coating.

[0054] <Packaging material> The multilayer film may be used as a single film or may be used in a laminated state with a base material, and the method of using it as the packaging material is not particularly limited.

[0055] When the multilayer film is used in a laminated state with a base material, the packaging material can include the above-mentioned multilayer film and the base material. Specifically, such a packaging material can be obtained by laminating at least one layer of a base material such as a biaxially stretched polyamide film (ONy), a biaxially stretched polyester film (PET), printing paper, a metal foil (AL foil), or a transparent vapor-deposited film on the above-mentioned multilayer film 10 to form a laminate. FIG. 2 is a cross-sectional view of a packaging material according to an embodiment of the present invention. The packaging material 100 shown in the figure includes a multilayer film 10, an adhesive layer 3, a base material film 4, an adhesive layer 5, and a transparent vapor-deposited film 6 in this order. As a method for manufacturing the laminate, a normal dry lamination method of bonding the films constituting the laminate using an adhesive can be preferably adopted, but a method of directly extrusion laminating the multilayer film on the base material can also be adopted if necessary.

[0056] The laminated structure of the laminate can be 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 and impact resistance corresponding to the weight of the contents, and the visibility of the contents.

[0057] <Package> The package may be formed into a bag from the above packaging material, and there is no particular limitation on the bag-making style. For example, the above packaging material (laminate) can be used for flat bags, three-side seal bags, gusseted bags, stand-up pouches, pouches with spouts, pouches with beaks, etc., using a multilayer film as the sealing material.

Examples

[0058] Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited only to the following examples.

[0059] <Preparation of various materials> The following propylene homopolymer (A) (resin (A)), propylene-ethylene random copolymer (B) (resin (B)), propylene-ethylene block copolymer (C) (resin (C)), ethylene-propylene copolymer elastomer (D) (resin (D)), and antiblocking agent were prepared.

[0060] (Propylene homopolymer (A)) A propylene homopolymer having a melting start temperature of 153°C, a melting peak temperature of 159°C, and a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 3.0 g / 10 min when measured by differential scanning calorimetry (JIS K 7121).

[0061] (Propylene-ethylene random copolymer (B)) A propylene random copolymer having a melting start temperature of 142°C, a melting peak temperature of 147°C, ΔH h / ΔH l of 1.84 and an ethylene content of 3.4 mass% when measured by differential scanning calorimetry (JIS K 7121).

[0062] The ethylene content was measured according to the quantitative method (IR method) of ethylene content described on pages 412 - 413 of the Polymer Analysis Handbook (May 10, 2013, 3rd edition) edited by the Polymer Analysis Discussion Group of the Japan Society for Analytical Chemistry. ΔH h / ΔHl is the ratio of the heat of fusion ΔH on the higher temperature side than the measurement temperature of 135°C h to the heat of fusion ΔH on the lower temperature side l when performing differential scanning calorimetry (JIS K 7121).

[0063] (Propylene-ethylene block copolymer (C)) A propylene-ethylene block copolymer having a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 2.0 g / 10 min, containing 77.1% by mass of a propylene polymer and 22.9% by mass of an ethylene-propylene copolymer, and having an ethylene content of 28.7% by mass in the ethylene-propylene copolymer.

[0064] (Ethylene-propylene copolymer elastomer (D)) An ethylene-propylene copolymer elastomer having a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 0.6 g / 10 min and a propylene content / ethylene content of 2.7.

[0065] (Antiblocking agent) Acrylic beads having an average particle diameter (measured by Coulter counter, ISO 13319) of 10 μm Silica particles having an average particle diameter (measured by Coulter counter, ISO 13319) of 5 μm

[0066] (Production of multilayer film) (Example 1) For forming the first outer layer, a resin mixture was prepared by mixing 50 parts by mass of a propylene homopolymer (A), 50 parts by mass of a propylene-ethylene random copolymer (B), and acrylic beads as an antiblocking agent in a pellet state. The addition amount of the acrylic beads was 2.0 parts by mass with respect to 100 parts by mass of the total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B).

[0067] For forming the second outer layer, a resin mixture was prepared by mixing 50 parts by mass of a propylene homopolymer (A) and 50 parts by mass of a propylene-ethylene random copolymer (B) in a pellet state.

[0068] For forming the inner layer, a resin mixture was prepared by mixing 67.8 parts by mass of a propylene-ethylene block copolymer (C) and 32.2 parts by mass of an ethylene-propylene copolymer elastomer (D) in a pellet state.

[0069] Each resin mixture was supplied to an extruder heated to 250 °C, kneaded in a molten state, and laminated using a T-die extruder with a feed block so that the thicknesses of the first outer layer and the second outer layer were each 10 μm and the thickness of the inner layer was 40 μm, to produce the film of Example 1.

[0070] (Example 2) A film of Example 2 was produced in the same manner as in Example 1, except that the blending ratio of the acrylic beads was changed as shown in Table 1.

[0071] (Examples 3 to 4) Films of Examples 3 to 4 were produced in the same manner as in Example 2, except that the blending ratios of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the resin mixtures for forming the first and second outer layers were changed as shown in Table 1.

[0072] (Example 5) A film of Example 5 was produced in the same manner as in Example 2, except that the blending ratios of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) in the resin mixture for forming the inner layer were changed as shown in Table 1.

[0073] (Example 6) A film of Example 6 was produced in the same manner as in Example 1, except that the blending ratio of the acrylic beads was changed as shown in Table 1.

[0074] (Examples 7 to 8) Films of Examples 7 to 8 were produced in the same manner as in Example 1, except that silica was used instead of acrylic beads and the blending ratio was adjusted as shown in Table 1.

[0075] (Comparative Example 1) A film of Comparative Example 1 was produced in the same manner as in Example 1, except that no antiblocking agent was blended.

[0076] (Comparative Example 2) A film of Comparative Example 2 was produced in the same manner as in Example 1, except that only the propylene-ethylene random copolymer (B) was used for forming the outer layer.

[0077] (Comparative Examples 3 to 4) Films of Comparative Examples 3 to 4 were produced in the same manner as in Example 1, except that the blending ratio of acrylic beads was changed as shown in Table 1.

[0078] <Various Evaluations> The following evaluations were performed on the films obtained in each example. The results are shown in Table 1.

[0079] [Haze Measurement] Using the films obtained in each example, bags of 297 mm × 420 mm were prepared, 800 g of water was put inside and sealed, and retort treatment was performed at 135°C for 40 minutes. A film sample of 50 mm × 50 mm was cut out from the bag after the retort treatment, and evaluation was carried out using a haze meter (model number COH7700) manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with the haze measurement method described in JIS K7136. Since the lower the haze value, the better the transparency, the haze value was judged according to the following four criteria. S: 15% or less A: More than 15% and 20% or less B: More than 20% and 25% or less C: More than 25%

[0080] [Fusion Strength Measurement] Using a heat sealer manufactured by Tester Sangyo Co., Ltd., the films obtained in each example were heat-sealed with the first outer layers facing each other 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. Then, the heat-sealed film was cut into 15 mm width × 80 mm, and T-peel was performed at a tensile speed of 300 mm / min using a tensile testing machine manufactured by Shimadzu Corporation to measure the fusion strength of the heat-sealed portion. Since the lower the fusion strength, the better the heat resistance, the fusion strength was judged according to the following four criteria. S: 3 N / 15 mm or less A: More than 3 N / 15 mm and 5 N / 15 mm or less B: More than 5 N / 15 mm and 10 N / 15 mm or less C: More than 10 N / 15 mm

[0081] [Blocking Strength Measurement] Four films obtained in each example were cut out into four pieces each with a width of 120 mm and a length of 300 mm. Using a slitter manufactured by Higashinobori Co., Ltd., a 100 mm-wide PET film (manufactured by Toyobo Film Solutions Co., Ltd., product name: G2#25) was wound around a 3-inch core at a winding speed of 10 m / min to a length of 10 m under a pressure of 0.3 MPa (measured by the pressure measurement film "Prescale" LLLW manufactured by Fuji Film Co., Ltd. and the press scale pressure image analysis system FPD-9210) so that the film was in a pressurized state. After that, the four cut films were inserted in a stacked state and further wound around 20 m under the same conditions to pressurize the four films. The four films were made into two sets of two films stacked with the first outer layer and the second outer layer facing each other, and they were stacked. After placing the wound roll in an aging room at 40°C for 7 days, the films were separated into two pieces each (the above two sets), cut into pieces with a width of 30 mm and a length of 100 mm, and then the adhered films were peeled off 35 mm in the length direction from both ends in the length direction. For the peeled parts, the upper film was cut off at one end side and the lower film was cut off at the other end side to prepare samples with an adhesion area of 30 mm × 30 mm. For the obtained samples, a shear peel was performed at a tensile speed of 300 mm / min using a tensile testing machine manufactured by Shimadzu Corporation, and the blocking strength was measured. The measurement was carried out 5 times, and the average value was taken as the measured value. Since the lower the blocking strength, the better the blocking resistance, the blocking strength was judged according to the following four criteria. S: 10 N / 900 mm 2 Below A: 10 N / 900 mm 2 Over 14 N / 900 mm 2 Below B: 14 N / 900 mm 2 Over 17 N / 900 mm 2 Below C: 17 N / 900 mm 2 Over

[0082]

Table 1

Industrial Applicability

[0083] The polypropylene-based multilayer film of the present invention has high levels of heat resistance, transparency, and antiblocking properties, and can be suitably used as a sealant film for retort packaging.

Explanation of symbols

[0084] 10... Multilayer film, 100... Packaging material, 1a... First outer layer, 1b... Second outer layer, 2... Inner layer, 3... Adhesive layer, 4... Base film, 5... Adhesive layer, 6... Transparent vapor deposition film.

Claims

1. A first outer layer which is a heat-sealing layer containing a propylene homopolymer (A), a propylene-ethylene random copolymer (B), and an antiblocking agent, An inner layer containing a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D), A second outer layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B), provided in this order, The propylene-ethylene block copolymer (C) is a blend copolymer containing 60 to 90% by mass of a propylene polymer (C1) and 10 to 40% by mass of an ethylene-propylene copolymer (C2), A multilayer film in which the content of the antiblocking agent in the first outer layer is 1.8 to 3.7 parts by mass with respect to 100 parts by mass of the total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B).

2. The first outer layer contains 30 to 70% by mass of the propylene homopolymer (A) and 30 to 70% by mass of the propylene-ethylene random copolymer (B) based on the total amount of the first outer layer excluding the antiblocking agent, The second outer layer contains 30 to 70% by mass of the propylene homopolymer (A) and 30 to 70% by mass of the propylene-ethylene random copolymer (B) based on the total amount of the second outer layer. The multilayer film according to claim 1.

3. The multilayer film according to claim 1 or 2, wherein the propylene homopolymer (A) satisfies the following requirement (a1) and the propylene-ethylene random copolymer (B) satisfies the following requirement (b1). Requirement (a1): The melting start temperature is 150°C or higher and the melting peak temperature is 155°C or higher in the measurement by differential scanning calorimetry (JIS K 7121). Requirement (b1): The ethylene content is 5% by mass or less.

4. The inner layer contains 50 to 90% by mass of the propylene-ethylene block copolymer (C) and 10 to 50% by mass of the ethylene-propylene copolymer elastomer (D) based on the total amount of the inner layer. The multilayer film according to any one of claims 1 to 3.

5. A packaging material comprising the multilayer film according to any one of claims 1 to 4 and a base material.

6. A package formed by bag-making from the packaging material according to claim 5.

Images