Polypropylene resin multi-layer film

Abstract

To provide a polypropylene-based resin multilayer film which has good automatic packaging suitability due to low temperature sealability and high heat seal strength, and has gusset packaging suitability, and thereby is usable for wide applications.SOLUTION: A polypropylene-based resin multilayer film has a base layer (A) composed of a polypropylene-based resin composition, and a surface layer (B) composed of the polypropylene-based resin composition on one surface of the base layer (A), has a seal layer (C) composed of the polypropylene-based resin composition on the surface of the base layer (A) that is opposite to the surface layer (B), has a film thickness of 10-100 μm, and satisfies the following a) to g) (only (a) is described). a) A mesopentad fraction of the polypropylene-based resin composition constituting the base layer (A) is 97.5% or more and 99.0% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a polypropylene-based resin multilayer film and a package using the same, and in particular to a polypropylene-based resin multilayer film that has heat sealability and an anti-fogging effect and is therefore suitable for packaging fresh produce (hereinafter, these will be referred to as "fruit and vegetables" in this specification) consisting of plants that require high freshness, such as vegetables, fruits, and flowers, and a package using the same. [Background technology]

[0002] Polypropylene-based resin multilayer films have been widely used in the field of packaging, such as food packaging and textile packaging, because of their excellent optical properties, mechanical properties, packaging suitability, etc. In particular, anti-fog films are widely used for packaging fruits and vegetables.

[0003] In the packaging of fruits and vegetables, the recent decline in the agricultural population has led to a demand for labor-saving farm work, and automatic packaging machines are becoming more widespread. The so-called pillow packaging method and gusset packaging method are used for automatic packaging machines for fruits and vegetables, and the process of making bags by heat sealing and filling the contents can be carried out simultaneously.

[0004] A laminated film for packaging fresh vegetables has been disclosed that can be used for automatic packaging such as pillow packaging, and comprises an outer layer made of a biaxially oriented film-like material whose main component is crystalline polypropylene, and a film-like material made of an olefin-based polymer having a melting point 10 to 90°C lower than that of the outer layer (see, for example, Patent Document 1). However, the film disclosed in Patent Document 1 uses a propylene-ethylene-butene-1 copolymer in the heat seal layer, and therefore has a problem in terms of achieving both low-temperature sealability and seal strength. In addition, a packaging film has been disclosed that is a laminate of two or more layers, having a base layer mainly made of a polypropylene-based resin and a heat seal layer mainly made of a polyolefin-based resin using a propylene-butene-1 copolymer and a propylene-ethylene-butene-1 copolymer (for example, see Patent Document 2). However, the film disclosed in Patent Document 2 has a problem in that its heat seal strength is insufficient.

[0005] Moreover, in recent years, gusseted bags with gussets are often used when packaging box-shaped or bulky items. In gusset packaging, the back is formed by heat sealing, and then a folded section is added to the side to increase the capacity. With regular bags, the contents are easily crushed, it is difficult to put things into the bag itself, and it is also difficult to close the bag, but with gusset bags there are no extra gaps and the contents can be neatly inserted. In addition, by heat sealing the surface layer of the back lining and the exterior surface to form a flat surface during bag manufacturing, the appearance of the gusset bag is improved when it is displayed. However, in gusset packaging, if the low-temperature sealing property of the sealing layer is insufficient and the heat-sealing temperature is too high when the opening is heat-sealed after the contents are inserted, the exterior surfaces of the products will stick to each other or to the exterior surface of the heat-sealed part and its neighboring exterior surface when the products are stacked together immediately after heat-sealing, and when the stuck parts are peeled off, the products may tear or develop holes, or their freshness-preserving function may be impaired. Such problems are particularly noticeable in high-speed packaging using a horizontal pillow packaging machine or the like.

[0006] A polypropylene-based resin multilayer film has been disclosed which has a base layer mainly made of a polypropylene-based resin, a surface layer on one side of the base layer mainly made of a polypropylene-based resin composition consisting of at least one copolymer selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer, and a seal layer on the opposite side of the surface layer mainly made of a polypropylene-based resin composition consisting of at least one polymer selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer (see, for example, Patent Document 3). However, the film disclosed in Patent Document 3 has insufficient low-temperature sealing properties, and does not make it possible to prevent exterior packaging from sticking to each other. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3104166 [Patent Document 2] Patent No. 4385443 [Patent Document 3] WO2017 / 170330 Summary of the Invention [Problem to be solved by the invention]

[0008] The objective of the present invention is to provide a polypropylene-based resin multilayer film which is less expensive than conventional films, has good suitability for automatic packaging due to its low-temperature sealability and high heat seal strength, and is also suitable for gusset packaging, making it suitable for a wide range of applications. [Means for solving the problem]

[0009] That is, the present invention has the following configuration. The laminate has a base layer (A) made of a polypropylene-based resin composition and a surface layer (B) made of a polypropylene-based resin composition on one side of the base layer (A), The polypropylene-based resin multi-layer film also has a sealing layer (C) made of a polypropylene-based resin composition on the opposite side of the surface layer (B) of the base layer (A), and satisfies the following a) to d). a) The thermal shrinkage rate in the longitudinal direction at 120°C is 3.0% or less. b) The heat seal strength rise temperature of the seal layer (C) is 100°C or higher and 115°C or lower. c) The heat seal strength rise temperature of the surface layer (B) is 125°C or higher and 140°C or lower. d) The thickness of the seal layer (C) is in the range of 5% to 15% of the total thickness of the film.

[0010] In this case, it is preferable that the polypropylene resin composition constituting the base layer (A) has a meso pentad fraction of 97.5% or more and 99.0% or less.

[0011] In this case, it is preferable that the ratio of the α-olefin monomer derived component to the total of the propylene monomer derived component and the α-olefin monomer derived component of the polypropylene resin composition constituting the base layer (A) is 0.25 mol % or more and 0.6 mol % or less.

[0012] In this case, it is preferable that the heat seal strength of the seal layer (C) of the polypropylene-based resin multilayer film is 3.0 N / 15 mm or more, and the heat seal strength of the surface layer (B) is 3.0 N / 15 mm or more.

[0013] In this case, it is preferable that the sealing layer (C) contains multiple polypropylene-based resins, the melting point of the polypropylene-based resin having the lowest melting point among the multiple polypropylene-based resins is in the range of 70 to 100°C, and the content thereof is in the range of 1% by weight or more and 50% by weight or less with respect to the entire sealing layer (C).

[0014] Furthermore, in this case, the sealing layer (C) contains a plurality of polypropylene-based resins, and the polypropylene-based resin having the highest melting point among the plurality of polypropylene-based resins. It is preferable that the polypropylene resin used has a melting point of 100° C. or higher and 140° C. or lower, and its content is in the range of 50 to 99% by weight.

[0015] Furthermore, in this case, it is preferable that the sealing layer (C) contains multiple polypropylene-based resins, the melting points of the multiple polypropylene-based resins are in the range of 70 to 140°C, the content of the polypropylene-based resins having a melting point of 70 to 100°C is 1% by weight or more and 50% by weight or less, and the content of the polypropylene-based resins having a melting point of 100 to 140°C is 50% by weight or more and 99% by weight or less.

[0016] Furthermore, in this case, it is preferable that the melting point of the polypropylene resin contained in the surface layer (B) is in the range of 120 to 140°C.

[0017] Furthermore, in this case, it is preferable to use the polypropylene-based resin multi-layer film to form a package. Effect of the Invention

[0018] The polypropylene-based resin multi-layer film of the present invention has been able to be endowed with better suitability for gusset packaging than conventional films by optimizing the composition and thickness of each layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (Base layer (A)) The base layer (A) in the present invention is made of a polypropylene-based resin composition, and preferably mainly uses at least one propylene-α-olefin copolymer selected from the group consisting of copolymers of propylene and other α-olefins containing 90 mol % or more of propylene, and a propylene homopolymer, and the content of propylene in the polypropylene-based resin composition constituting the base layer (A) is preferably 95 wt % or more, more preferably 97 wt % or more, and even more preferably 99 wt % or more.

[0020] (Propylene-α-olefin copolymer) The other α-olefin constituting the propylene-α-olefin copolymer is preferably an α-olefin having 2 to 8 carbon atoms, such as ethylene, butene-1, pentene-1, hexene-1, 4-methyl-1-pentene, etc. Among the propylene-α-olefin copolymers, a random or block copolymer obtained by polymerizing one or more of the above-listed α-olefins with propylene is preferred, and a propylene-ethylene copolymer, a propylene-butene-1 copolymer, a propylene-ethylene-butene-1 copolymer, or a propylene-pentene-1 copolymer is preferred. The lower limit of the melt flow rate (MFR) of the propylene-α-olefin copolymer measured at 230°C and 2.16 kgf is preferably 2.0 g / 10 min, more preferably 2.2 g / 10 min, even more preferably 2.5 g / 10 min, particularly preferably 2.8 g / 10 min, and most preferably 3.0 g / 10 min. If it is 2.0 g / 10 min or more, the mechanical load is small and stretching becomes easy. On the other hand, the upper limit of the MFR of the propylene-α-olefin copolymer is preferably 5 g / 10 min, more preferably 4.7 g / 10 min, even more preferably 4.5 g / 10 min, particularly preferably 4 g / 10 min, and most preferably 3.5 g / 10 min. If it is 5 g / 10 min or less, stretching becomes easy, thickness unevenness becomes small, and the stretching temperature and heat setting temperature are easily increased, resulting in a lower heat shrinkage rate.

[0021] The lower limit of the component derived from an α-olefin monomer in the propylene-α-olefin copolymer is preferably 0.1 mol% or more, more preferably 0.2 mol% or more, and even more preferably 0.25 mol% or more. When it is 0.1 mol% or more, the heat seal strength is easily increased, and when it is 0.2 mol% or more, the anti-fogging property is easily increased. On the other hand, the upper limit of the component derived from an α-olefin monomer in the propylene-α-olefin copolymer is preferably 0.6 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.4 mol% or less. When it is 0.6 mol% or less, the crystallinity is improved and the heat shrinkage rate at high temperatures is reduced.

[0022] The lower limit of the mesopentad fraction of the propylene-α-olefin copolymer is preferably 90%, more preferably 95%, and even more preferably 97%. If it is 90% or more, the crystallinity is improved and the heat shrinkage rate at high temperatures can be kept low. The upper limit of the mesopentad fraction is preferably 99.5%, more preferably 99%, and even more preferably 98%. If it is 99.5% or less, practical production becomes easy and anti-fogging properties become good.

[0023] (Propylene homopolymer) The propylene homopolymer is preferably an n-heptane insoluble isotactic propylene homopolymer. n-Heptane insolubility is an index of the crystallinity of polypropylene and also indicates its safety when used for food packaging. In the present invention, it is preferable to use polypropylene that satisfies the n-heptane insolubility criteria specified in Notification No. 20 of the Ministry of Health and Welfare of February 1982 (the eluted amount when extracted at 25°C for 60 minutes is 150 ppm or less [30 ppm or less for those used at temperatures exceeding 100°C]).

[0024] The lower limit of the melt flow rate (MFR) of an isotactic propylene homopolymer measured at 230°C and 2.16 kgf is preferably 5 g / 10 min. The lower limit of the MFR is preferably 6 g / 10 min, more preferably 6.5 g / 10 min, even more preferably 7 g / 10 min, and particularly preferably 7.3 g / 10 min. If it is 5 g / 10 min or more, the mechanical load is small and stretching becomes easy.

[0025] On the other hand, the upper limit of the MFR of the isotactic propylene homopolymer is preferably 10 g / 10 min, more preferably 9.5 g / 10 min, even more preferably 9 g / 10 min, particularly preferably 8.5 g / 10 min, and most preferably 8 g / 10 min. If it is 10 g / 10 min or less, stretching becomes easy, thickness unevenness becomes small, and the stretching temperature and heat setting temperature are easily increased, resulting in a lower heat shrinkage rate.

[0026] The lower limit of the mesopentad fraction of the isotactic propylene homopolymer is preferably 97%, more preferably 98%. Within this range, the crystallinity is improved, and the heat shrinkage rate at high temperatures can be kept low. The upper limit of the mesopentad fraction is preferably 99.5%, more preferably 99%. Within this range, practical production becomes easy, and antifogging properties tend to be good.

[0027] (Polypropylene resin composition constituting base layer (A)) The lower limit of the mesopentad fraction of the entire polypropylene resin composition constituting the base layer (A) is preferably 97.5% or more. The lower limit of the mesopentad fraction is more preferably 97.8%. When it is 97.5% or more, the crystallinity is improved and the heat shrinkage rate at high temperatures can be suppressed to a low level. The upper limit of the mesopentad fraction is preferably 99.0%, more preferably 98.8%, and even more preferably 99.5%. When it is 99.0% or less, practical production becomes easy.

[0028] The ratio of the α-olefin monomer derived component to the total of the propylene monomer derived component and the α-olefin monomer derived component of the entire polypropylene-based resin composition constituting the base layer (A) is preferably 0.1 mol% or more, preferably 0.2 mol% or more, more preferably 0.25 mol% or more, and particularly preferably 0.28 mol% or more. When it is 0.1 mol% or more, the anti-fogging property is good. On the other hand, the ratio of the α-olefin monomer derived component to the total of the propylene monomer derived component and the α-olefin monomer derived component is preferably 0.6 mol% or less, more preferably 0.5 mol% or less, and even more preferably 0.4 mol% or less. When it is 0.6 mol% or less, the crystallinity is improved and the heat shrinkage rate at high temperatures is small.

[0029] The lower limit of the melt flow rate (MFR) of the entire polypropylene resin composition constituting the base layer (A), measured at 230°C and 2.16 kgf, is preferably 3.0 g / 10 min. The lower limit of the entire MFR is more preferably 4.0 g / 10 min, and even more preferably 4.5 g / 10 min. Within the above range, the mechanical load is small and stretching is easy. On the other hand, the upper limit of the entire MFR is preferably 6.0 g / 10 min, more preferably 5.5 g / 10 min, even more preferably 5.0 g / 10 min, and particularly preferably 4.0 g / 10 min. Within the above range, stretching is easy, thickness unevenness is small, and the stretching temperature and heat setting temperature can be easily increased, resulting in a lower heat shrinkage rate.

[0030] The lower limit of the melting point of the entire polypropylene resin composition constituting the base layer (A) is preferably 158° C. or higher, more preferably 159° C. or higher. When it is 158° C. or higher, the effects of the present application, such as low heat shrinkage at high temperatures, are easily obtained.

[0031] It is preferable that the polypropylene resin composition constituting the base layer (A) contains an anti-fogging agent, and typical examples of the anti-fogging agent include fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, ethylene oxide adducts of amines or amides of higher fatty acids, etc. The amount of such an anti-fogging agent in the multilayer film is preferably 0.1 to 10% by weight, particularly 0.2 to 5% by weight, calculated on the basis of the total weight of the layers.

[0032] In addition, as long as the effects of the present invention are not impaired, the polypropylene resin composition constituting the base layer (A) may contain various additives for improving the qualities such as slipperiness and antistatic properties, for example, lubricants such as wax and metal soap for improving productivity, plasticizers, processing aids, and known heat stabilizers, antioxidants, antistatic agents, and ultraviolet absorbers.

[0033] (Sealing layer (C)) The sealing layer (C) in the present invention is made of a polypropylene-based resin composition, and it is preferable to mainly use a propylene-α-olefin copolymer, and the content of this copolymer in the polypropylene-based resin composition constituting the sealing layer (C) is preferably 95% by weight or more, more preferably 97% by weight or more, and even more preferably 99% by weight or more.

[0034] The α-olefin constituting the propylene-α-olefin copolymer is preferably an α-olefin having 2 to 8 carbon atoms, such as ethylene, butene-1, pentene-1, hexene-1, 4-methyl-1-pentene, etc. It is more preferable to mainly use at least one copolymer selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer as the propylene-α-olefin copolymer.

[0035] The heat seal strength rise temperature of the seal layer (C) is preferably 100° C. or more and 115° C. or less, more preferably 105° C. or more and 113° C. or less. The heat seal strength rise temperature of the seal layer (C) is the temperature at which the surfaces of the surface layers (B) of the film of the present invention are faced to each other and a heat seal pressure of 1 kg / cm is applied. 2 The temperature is the temperature at which the heat seal strength is 1N / 15mm when heat sealing is performed for 1 second.

[0036] If the heat seal strength rise temperature of the seal layer (C) is 115°C or less, sufficient strength can be maintained for heat sealing even at low heat seal temperatures, allowing high-speed operation during automatic packaging, and excellent sealing properties at the sealed portion, which, combined with the anti-fogging properties, maintains the freshness of fresh produce, makes the contents look good, and provides excellent handling of the package. In addition, the difference in melting point with the polypropylene resin of the base layer (A) is appropriately large, making it easy to sufficiently increase the operating speed of automatic packaging, and sufficient heat seal strength can be easily obtained even at low set temperatures, so the entire multilayer film is less likely to shrink during heat sealing, and wrinkles are less likely to occur in the heat sealed portion, making it less likely for poor sealing at the heat sealed portion to occur. Furthermore, the difference in melting point with respect to the polypropylene resin of the surface layer (B) is also appropriately large, making it difficult for the exterior surfaces of the products to stick to each other when they are stacked immediately after heat sealing.

[0037] When the heat seal strength rise temperature of the sealing layer (C) is 105°C or higher, the difference in melting point with the base layer (A) is not too large, peeling is unlikely to occur between the base layer (A) and the sealing layer (C), and sufficient seal strength for automatic packaging can be easily ensured. In order to set the heat seal strength rising temperature of the heat seal layer (C) to 105 to 115°C, a combination of a propylene-butene-1 copolymer and a propylene-ethylene copolymer is preferred.

[0038] The heat seal strength of the seal layer (C) is preferably 3.0 N / 15 mm or more, more preferably 4.0 N / 15 mm or more, and even more preferably 5.0 N / 15 mm or more. If it is less than 3.0 N / 15 mm, it is insufficient for preventing the contents from falling out as an automatic package. The heat seal strength is measured by placing the surfaces of the seal layers (C) of the film of the present invention face each other, using a thermal gradient tester (manufactured by Toyo Seiki Seisakusho), at a seal temperature of 100 to 150°C and a heat seal pressure of 1 kg / cm. 2 The heat seal strength indicated is the maximum value when the heat seal time is 1 second.

[0039] In the prior art, a propylene-butene copolymer with a low melting point has been added to the seal layer resin in order to develop low-temperature seal strength, but since the propylene-butene copolymer contains a large amount of butene and ethylene components, it has poor compatibility with the homopolypropylene resin of the core layer, and interfacial peeling is likely to occur. In addition, since the thickness of the seal layer is increased, interfacial peeling is more likely to occur, and sufficient seal strength cannot be developed. Therefore, in the present invention, it is preferable that the polypropylene resin composition constituting the seal layer (C) contains multiple polypropylene resins.

[0040] The polypropylene resin having the lowest melting point among the polypropylene resins in the polypropylene resin composition constituting the seal layer (C) preferably has a melting point of 70°C or higher and 100°C or lower. The polypropylene resin having the lowest melting point is preferably added in the range of 1% by weight or more and 50% by weight or less. More preferably, it is 1% by weight or more and 25% by weight or less, and even more preferably, it is 1% by weight or more and 20% by weight or less. When it is 50% by weight or less, interlaminar strength with the base layer (A) is easily obtained, and the seal strength is likely to be sufficient. When it is 1% by weight or more, the seal strength at low temperatures is likely to be sufficient.

[0041] The melting point of the resin having the highest melting point among the polypropylene resins in the polypropylene resin composition constituting the seal layer (C) is preferably 100°C or higher and 140°C or lower, and the content is preferably 50% by weight or higher and 99% by weight or lower. More preferably, it is 120°C or higher and 135°C or lower. At 140°C or lower, the heat seal strength at low temperatures tends to be sufficient, and the reliability of the package increases. At 100°C or higher, the interlaminar strength with the base layer (A) increases, and sufficient seal strength is easily obtained.

[0042] It is particularly preferred that the melting points of the multiple polypropylene resins in the polypropylene resin composition constituting the sealing layer (C) are in the range of 70 to 140°C, that the content of polypropylene resins having a melting point of 70 to 100°C is 1% by weight or more and 50% by weight or less, and that the content of polypropylene resins having a melting point of 100 to 140°C is 50% by weight or more and 99% by weight or less, and that the content of polypropylene resins having a melting point of 70 to 100°C is 1% by weight or more and 20% by weight or less, and that the content of copolymers having a melting point of 100 to 140°C is 80% by weight or more and 99% by weight or less.

[0043] The thickness of the seal layer (C) is preferably in the range of 5 to 15% of the total film thickness, more preferably 5 to 12%, and even more preferably 5 to 10%. If it is less than 5%, the heat seal strength is insufficient, and if it is thicker than 15%, the interlayer strength is insufficient.

[0044] It is preferable that the polypropylene resin composition constituting the sealing layer (C) contains an anti-fog agent. As described above, this is to prevent the inside of fruits and vegetables from becoming cloudy due to physiological effects of the contents when they are packaged and displayed or distributed in supermarkets. Typical examples of the anti-fog agent used include fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, and ethylene oxide adducts of amines and amides of higher fatty acids. The amount of such an anti-fog agent present in the film is preferably 0.1 to 10% by weight, particularly 0.2 to 5% by weight, calculated as the total layer.

[0045] In order to incorporate an anti-fog agent into the polypropylene-based resin composition constituting the sealing layer (C), during the production of the multilayer film, the anti-fog agent may be blended into the resins forming all layers of the packaging film of the present invention, the anti-fog agent may be blended into the polypropylene-based resin constituting the base layer (A) and the sealing layer (C), the anti-fog agent may be blended only into the polypropylene-based resin constituting the base layer (A), or the anti-fog agent may be blended only into the polypropylene-based resin constituting the sealing layer (C). If the polypropylene resin composition constituting the sealing layer (C) does not contain an anti-fog agent, the inside of the multilayer film will become cloudy when fruits and vegetables are wrapped in it, and they will be more likely to spoil, reducing their commercial value.

[0046] When an anti-fog agent is blended only in the polypropylene resin composition constituting the base layer (A), the anti-fog agent in the base layer (A) gradually migrates to the seal layer (C) during film production and storage after film formation, and then bleeds out onto the surface of the seal layer (C), thereby imparting anti-fog properties. This effect can be particularly exhibited when packaging fruits and vegetables, which are characterized by maintaining their physiological functions even after harvest. In order to maintain excellent anti-fogging properties over the long term during distribution, it is preferable to store the package at room temperature rather than in a frozen state. Therefore, taking into consideration temperature changes during storage and distribution, it is preferable to select an anti-fogging agent that will continue to exhibit anti-fogging properties over the course of repeated temperature changes between 5 and 30°C.

[0047] (Surface layer (B)) The surface layer (B) in the present invention is made of a polypropylene-based resin composition, and it is preferable to mainly use a propylene-α-olefin copolymer, and the polypropylene-based resin composition constituting the sealing layer (C) preferably contains 95% by weight or more of this copolymer, more preferably 97% by weight or more, and even more preferably 99% by weight or more. The α-olefin constituting the propylene-α-olefin copolymer is preferably an α-olefin having 2 to 8 carbon atoms, such as ethylene, butene-1, pentene-1, hexene-1, 4-methyl-1-pentene, etc. It is more preferable to mainly use at least one copolymer selected from the group consisting of propylene-ethylene-butene-1 copolymer, propylene-butene-1 copolymer, and propylene-ethylene copolymer as the propylene-α-olefin copolymer.

[0048] In addition, the heat seal strength rise temperature when the surface layers (B) are overlapped and heat sealed is preferably 125° C. or more and 140° C. or less, and more preferably 125° C. or more and 135° C. or less. In order to make the heat seal strength rise temperature of the surface layer (B) 125 to 140° C., it is preferable to select a copolymer containing a propylene-ethylene-butene-1 copolymer.

[0049] The heat seal strength rise temperature of the surface layer (B) is the temperature at which the surface layers (B) of the film are placed face to face with each other and the heat seal pressure is 1 kg / cm 2 This is the temperature at which the heat seal strength is 1N / 15mm when heat-sealed for 1 second. If the heat seal strength rise temperature of the surface layer (B) is 125°C or higher, the surface layer (B) is less likely to fuse to the seal bar during heat sealing of pillow packaging, making it easier to make bags. Also, if it is 140°C or lower, the back and fold-in parts are less likely to fuse to the exterior surfaces of the packaging after gusset packaging, resulting in a good appearance, and the back does not get caught when the packages are stacked, making it less likely for the seal to peel off.

[0050] The thickness of the surface layer (B) is preferably in the range of 1 to 10% of the total film thickness, more preferably 1 to 7%, and even more preferably 1 to 5%. If it is less than 1%, the heat seal strength of the back and fold-in parts is insufficient, and if it is thicker than 10%, problems such as sticking of the exterior parts to each other occurs when the products are stacked on top of each other immediately after heat sealing.

[0051] The heat seal strength of the surface layer (B) is preferably 3.0 N / 15 mm or more, more preferably 3.5 N / 15 mm or more. If it is less than 3.0 N / 15 mm, the seal strength of the folded-in portion of the gusset package is insufficient. The heat seal strength is measured by placing the surfaces of the surface layers (B) of the film of the present invention face to face with each other, using a thermal gradient tester (manufactured by Toyo Seiki Seisakusho), at a seal temperature of 100 to 150°C and a heat seal pressure of 1 kg / cm. 2 The heat seal strength indicated is the maximum value when the heat seal time is 1 second.

[0052] It is preferable that the surface of the surface layer (B) has anti-fogging properties. This is because when fruits and vegetables are packaged and displayed in supermarkets, etc., their appearance deteriorates if the surface becomes cloudy due to condensation, etc. Therefore, it is preferable to add an anti-fogging agent to the resin forming the surface layer (B). Typical examples of the antifogging agent added to the polypropylene resin composition constituting the surface layer (B) include fatty acid esters of polyhydric alcohols, amines of higher fatty acids, amides of higher fatty acids, ethylene oxide adducts of amines or amides of higher fatty acids, etc. The amount of such antifogging agent present in the film is preferably 0.1 to 10% by weight, particularly preferably 0.2 to 5% by weight, calculated based on the total layer.

[0053] In order to incorporate an anti-fog agent into the polypropylene-based resin composition constituting the surface layer (B), during the production of the multilayer film, the anti-fog agent may be blended into the resins forming all layers constituting the packaging film of the present invention, the anti-fog agent may be blended into the polypropylene-based resin constituting the base layer (A) and the surface layer (B), the anti-fog agent may be blended only into the polypropylene-based resin constituting the base layer (A), or the anti-fog agent may be blended only into the polypropylene-based resin constituting the surface layer (B). If the polypropylene resin composition constituting the surface layer (B) does not contain an anti-fogging agent, the exterior of fruits and vegetables will become foggy when wrapped in the multilayer film, reducing the commercial value.

[0054] When an anti-fog agent is blended only in the polypropylene resin composition constituting the base layer (A), the anti-fog agent in the base layer (A) gradually migrates to the surface layer (B) during film production and storage after film formation, and then bleeds out onto the surface of the surface layer (B), thereby imparting anti-fog properties. This effect can be particularly exhibited when packaging fruits and vegetables, which are characterized by maintaining their physiological functions even after harvest. In order to maintain excellent anti-fogging properties over the long term during distribution, it is preferable to store the package at room temperature rather than in a frozen state. Therefore, taking into consideration temperature changes during storage and distribution, it is preferable to select an anti-fogging agent that will continue to exhibit anti-fogging properties over the course of repeated temperature changes between 5 and 30°C.

[0055] In addition, as long as the effects of the present invention are not impaired, it is also possible to blend various additives for improving the quality of the polypropylene resin composition constituting the base layer (A) such as lubricants such as wax and metal soap, plasticizers, processing aids, and known heat stabilizers, antioxidants, antistatic agents, ultraviolet absorbers, etc., which are usually added to polypropylene films, in order to improve productivity, within the range of not impairing the effects of the present invention. It is also possible to blend inorganic or organic fine particles in order to ensure the blocking resistance and lubricity of the film.

[0056] Examples of inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, and zeolite, and the shape of these particles may be any type, such as spherical, elliptical, conical, or amorphous, and the particle size may be any type depending on the purpose and method of use of the film. As organic fine particles, crosslinked particles such as acrylic, methyl acrylate, and styrene-butadiene may be used, and similarly to inorganic fine particles, various shapes and sizes may be used. In addition, the surfaces of these inorganic or organic fine particles may be subjected to various surface treatments, and these may be used alone or in combination of two or more types.

[0057] (film thickness) The film thickness of the polypropylene-based resin multilayer film of the present invention varies depending on its application and method of use, but a polypropylene-based film used as a packaging film is generally about 10 to 100 μm, and from the standpoints of mechanical strength and transparency, it is more preferably about 15 to 50 μm.

[0058] (Heat shrinkage rate) It is important that the heat shrinkage rate of the polypropylene-based resin multilayer film of the present invention in the longitudinal direction at 120° C. is 3% or less, preferably 2.5% or less, and more preferably 2.0% or less. By making it 3% or less, it is possible to reduce heat-induced wrinkles during printing processing or heat sealing in bag making, and to reduce deformation of the heat-sealed portion during heat sealing, thereby suppressing sticking between the exterior surface and the surface of the surface layer (B) of the heat-sealed portion after packaging. The heat shrinkage rate of the polypropylene-based resin multilayer film of the present invention in the width direction at 120° C. is preferably 3% or less, more preferably 2.0% or less, and even more preferably 1.0% or less. By making it 3% or less, it is possible to reduce heat-induced wrinkles during printing or heat sealing in bag making, reduce deformation of the heat-sealed portion during heat sealing, and suppress sticking between the exterior surface and the surface of the surface layer (B) of the heat-sealed portion after packaging. Here, the "longitudinal direction" of the polypropylene-based resin multilayer film of the present invention is the direction corresponding to the machine direction in the film production process, and the "width direction" is the direction perpendicular to the machine direction in the film production process.

[0059] (Film forming method) The polypropylene-based resin multi-layer film of the present invention can be produced by the methods shown below, but is not limited thereto. For example, a method can be exemplified in which melt lamination is performed by a T-die method, an inflation method, or the like using an extruder suitable for the number of layers, followed by cooling by a cooling roll method, a water cooling method, or an air cooling method to form a laminated film, and then stretching by a sequential biaxial stretching method, a simultaneous biaxial stretching method, a tube stretching method, etc. Here, an example of conditions for production by the sequential biaxial stretching method is to produce a raw sheet by cooling and solidifying a resin melt-extruded from a T-shaped die in a casting machine. The temperature during melt lamination is preferably set in the range of 240° C. to 300° C. based on the melting point of the raw resin used for each layer. The temperature of the rolls used for casting is preferably set between 15° C. and 40° C. to suppress crystallization of the resin and improve transparency.

[0060] Next, the raw sheet is heated to a temperature suitable for stretching, and then stretched in the sheet flow direction by utilizing the speed difference between the stretching rolls. In this case, the stretching ratio is preferably set between 3 and 6 in order to ensure stable production without uneven stretching. The stretching temperature is also preferably set between 100°C and 150°C in order to ensure stable production without uneven stretching. Next, both edges of the longitudinally stretched sheet are held by tenter clips, and the sheet is stretched in the direction perpendicular to the flow of the sheet while being heated to a temperature suitable for stretching with hot air. The transverse stretching ratio at this time is preferably set between 7 and 10 times, taking into consideration thickness fluctuation and productivity. The stretching temperature is also preferably set between 130°C and 180°C, taking into consideration stable production without uneven stretching. Finally, the heat setting treatment is preferably carried out in the range of 150°C to 200°C.

[0061] The polypropylene-based resin multilayer film of the present invention can be surface-treated to improve printability, lamination with other members, etc. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, acid treatment, etc., and are not particularly limited. It is preferable to carry out corona discharge treatment, plasma treatment, or flame treatment, which can be performed continuously and can be easily performed before the winding step in the production process of this film. EXAMPLES

[0062] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples without departing from the gist of the present invention. The characteristics in this specification were evaluated by the following methods.

[0063] (1) DSC melting point The melting point was determined as the temperature of the maximum melting peak in the DSC curve of the polyolefin resin film obtained using a Shimadzu differential scanning calorimeter DSC-60 manufactured by Shimadzu Corporation. The starting temperature was 30°C, the heating rate was 5°C / min, and the end temperature was 180°C. Five samples were measured, and the average value was calculated.

[0064] (2) Mesopentad fraction The mesopentad fraction ([mmmm]%) of polypropylene resin is measured as follows: 13 The mesopentad fraction was calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973). 13 C-NMR measurements were performed using AVANCE500 manufactured by BRUKER, by dissolving 200 mg of a sample in a mixture of o-dichlorobenzene-d4 and benzene-d6 at a ratio of 8:2 at 135° C., and then at 110° C. Five samples were measured, and the average value was calculated. The mesopentad fraction of a polypropylene resin consisting of a mixture of a plurality of polypropylene resins is a value measured by the above-mentioned method for the mixture.

[0065] (3) Melt flow rate (MFR) The melt flow rate (MFR) was measured in accordance with JIS K7210 at a temperature of 230° C. and a load of 2.16 kgf. The isotactic mesopentad fraction of a polypropylene resin consisting of a mixture of a plurality of polypropylene resins is a value measured by the above-mentioned method for the mixture.

[0066] (4) Proportion of components derived from α-olefin monomers (mol%) The contents of propylene, butene-1, and ethylene in propylene-ethylene copolymer, propylene-butene-1 copolymer, and propylene-ethylene-butene-1 copolymer are determined by 13C-NMR spectroscopy according to the method described on pages 615-617 of Polymer Analysis Handbook (published by Kinokuniya Shoten in 1995). It is also possible to determine them by IR spectroscopy according to the method described on page 256 of the same book, section "(i) Random Copolymer." The mesopentad fraction of a polypropylene resin consisting of a mixture of a plurality of polypropylene resins is a value measured by the above-mentioned method for the mixture.

[0067] (5) Total film thickness The polypropylene resin multilayer film was cut into a size of 1 cm x 1 cm, a cross-sectional sample was prepared using a microtome, and the thickness of the base layer (A), surface layer (B), and entire film layer was measured using a differential interference microscope. Five points on the sample were measured, and the average value was calculated.

[0068] (6) Proportion of components derived from α-olefin monomers (mol%) The contents of propylene, butene-1, and ethylene in propylene-ethylene copolymer, propylene-butene-1 copolymer, and propylene-ethylene-butene-1 copolymer were measured by the method described on pages 615-617 of Polymer Analysis Handbook (published by Kinokuniya Shoten in 1995). 13 It is determined by C-NMR spectroscopy. It is also possible to determine it by IR spectroscopy according to the method described in the same book, page 256, section "(i) Random Copolymer." The mesopentad fraction of a polypropylene resin consisting of a mixture of a plurality of polypropylene resins is a value measured by the above-mentioned method for the mixture.

[0069] (7) Layer thickness The polypropylene resin multilayer film was cut into pieces measuring 1 cm x 1 cm, embedded in UV-curable resin, and cured by irradiating with UV for 5 minutes. After that, a cross-sectional sample was prepared using a microtome and observed using a differential interference microscope to measure the thickness of the surface layer (B) and the seal layer (C). Five points were measured on the sample, and the average value was calculated.

[0070] 8) Heat seal strength rise temperature of the seal layer (C) and the surface layer (B) The seal layers (C) of the polypropylene-based resin multi-layer film were stacked facing each other, and the heat seal pressure was 1 kg / cm using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). 2 The heat seal strength is the temperature at which the heat seal strength reaches 1N / 15mm when heat-sealed for 1 second. The heat seal layer surfaces of 5cm x 20cm films were placed face to face, and heat-sealed simultaneously with five heat seal bars (seal surface 1cm x 3cm) set at temperatures in 5°C increments. The center of each was cut to a width of 15mm, attached to the upper and lower chucks of a tensile tester, and pulled at a pulling speed of 200mm / min. The strength of each was measured and the heat seal strength was calculated (units: N / 15mm). A linear graph was drawn with temperature on the horizontal axis and heat seal strength on the vertical axis, and the temperature at which the heat seal strength exceeded 1N / 15mm was taken as the heat seal strength rise temperature of the seal layer (C). The surface layers (B) of the polypropylene-based resin multilayer films were laminated facing each other, and the heat seal strength rise temperature of the surface layers (B) was measured in the same manner as in the measurement of the heat seal strength rise temperature of the seal layer (C).

[0071] (9) Heat seal strength of the sealing layer (C) and the surface layer (B) The seal layers (C) of the polypropylene-based resin multi-layer film were stacked facing each other, and the heat seal pressure was 1 kg / cm using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). 2The heat seal strength was calculated (units: N / 15 mm) from the heat seal strength when the sample was pulled at a tensile speed of 200 mm / min. The upper limit of the heat seal temperature was set to 150°C, and the value at which the maximum strength was reached was regarded as the heat seal strength of the seal layer (C). The surface layers (B) of the polypropylene-based resin multi-layer films were laminated facing each other, and the heat seal strength of the surface layers (B) was measured in the same manner as in the measurement of the heat seal strength of the seal layer (C).

[0072] (10) Suitability for automatic packaging The heat seal layers of the polypropylene-based resin multi-layer film were stacked facing each other, and a heat-sealing pressure of 1 kg / cm was applied using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). 2 The heat sealing time was 1 second. At that time, the presence or absence of fusion of the surface layer (B) to the seal bar and the heat seal start temperature were evaluated according to the following criteria. ○: No adhesion to the seal bar. Start-up temperature: 115℃ to 125℃ △: No adhesion to the seal bar. Start-up temperature is less than 115℃ or more than 125℃. ×: There is adhesion to the seal bar

[0073] (11) Suitability for gusset packaging The heat seal layers of the polypropylene-based resin multi-layer film were stacked facing each other, and a heat-sealing pressure of 1 kg / cm was applied using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.). 2 The heat sealing time was 1 second. The heat seal start temperatures of the seal layer (C) and the surface layer (B) were evaluated according to the following criteria. ○: The heat seal start temperature of the seal layer is 100°C or higher and 115°C or lower, and the heat seal start temperature of the surface layer is 125°C or higher and 140°C or lower △: The heat seal rise temperature of the seal layer is less than 100° C. or more than 115° C., and the heat seal rise temperature of the surface layer is 125° C. to 140° C. Or, the heat seal rise temperature of the seal layer is 100° C. to 115° C., and the heat seal rise temperature of the surface layer is less than 125° C. or more than 140° C. ×: The heat seal rise temperature of the seal layer is less than 100°C or more than 115°C, and the heat seal rise temperature of the surface layer is less than 125°C or more than 140°C.

[0074] (12)Heat shrinkage rate The heat shrinkage was measured by the following method. The film was cut into a width of 20 mm and a length of 200 mm in both the longitudinal and transverse directions, and was hung in a hot air oven at 120°C and heated for 5 minutes. The length after heating was measured, and the heat shrinkage at 120°C was calculated as the ratio of the shrunken length to the original length. The heat shrinkage at 150°C was calculated in the same manner.

[0075] (13) Anti-fogging properties 1. Pour 300cc of 50°C warm water into a 500cc open-top container. 2. The opening of the container is sealed with the film, with the anti-fogging property measurement surface of the film facing inward. Leave in a cold room at 3.5°C. 4. After the warm water in the container had completely cooled to the ambient temperature, the degree of condensation on the film surface was evaluated on a 5-point scale. Grade 1: No dew on the entire surface (0 surface area) Grade 2: Some dew adhesion (up to 1 / 4 of the surface area) Grade 3: Dew adhesion on about 1 / 2 (up to 2 / 4 of the surface area) Grade 4: Almost all dew is attached (up to 3 / 4 of the surface area) Grade 5: Dew on the entire surface (3 / 4 or more of the surface area)

[0076] (Resin used) The resins constituting the respective layers used in the following production examples are as follows. [PP-1]: Propylene-ethylene random copolymer (FS2011GDG3 manufactured by Sumitomo Chemical Co., Ltd., MFR 2.5 g / 10 min, melting point 158°C, mesopentad fraction 97.0%, ethylene component 0.6 mol%), with anti-fogging agent (TBD-1 manufactured by Matsumoto Yushi Seiyaku Co., Ltd., stearylamine monostearate content 74 wt%, stearylamine content 12 wt%, glycerin monostearate content 11 wt%, glycerin distearate content 3 wt%) added in an amount of 1.14 wt%. %, and an antistatic agent (KYM-4K manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., stearylamine stearate content 100% by mass) was melt-mixed at a resin temperature of 240°C to give a concentration of 0.59% by weight.

[0077] [PP-2]: Isotactic propylene homopolymer (FS8052 manufactured by Japan Polypropylene Corporation, MFR 7.5 g / 10 min, melting point 162.5°C, meso pentad fraction 98.9%, ethylene component 0 mol%) was melt-mixed with antistatic agent (KYM-4K manufactured by Matsumoto Yushi Seiyaku Co., Ltd., stearylamine stearate content 100% by mass) to a resin temperature of 240°C to give 1.68% by weight.

[0078] [PP-3]: A mixture of propylene-butene copolymer and propylene-ethylene copolymer (SP7834 manufactured by Sumitomo Chemical Co., Ltd., butene content 12% by weight, ethylene content 2.5% by weight, MFR 7.0 g / 10 min, melting point 126°C) was mixed with 0.56% by weight of stearic acid monoglyceride (Rikemal S100 manufactured by Riken Vitamin Co., Ltd.), 0.39% by weight of amorphous silica, and 0.01% by weight of erucic acid amide. Melt-mixed at a resin temperature of 240°C to give a resin content of .17% by weight.

[0079] [PP-4]: Propylene-ethylene copolymer (Vistamax 3980FL manufactured by Exxon Mobil Corporation, ethylene content 9% by weight, MFR 8.3g / 10min, melting point 78℃)

[0080] [PP-5]: Propylene-butene copolymer (SPX78P9 manufactured by Sumitomo Chemical Co., Ltd., butene content 17% by weight, MFR 7.0 g / 10 min, melting point 128°C)

[0081] [PP-6]: Propylene-ethylene random copolymer (FS2011GDG3 manufactured by Sumitomo Chemical Co., Ltd., MFR 2.5 g / 10 min, melting point 158°C, meso pentad fraction 97.0%, ethylene component 0.6 mol%)

[0082] [PP-7]: Propylene-ethylene-butene-1 random copolymer (FSX66E8 manufactured by Sumitomo Chemical Co., Ltd., ethylene content 2.5 mol%, butene content 7 mol%, MFR 3.1 g / 10 min, melting point 133°C) was melt-mixed at a resin temperature of 240°C with 1.5% by weight of erucic acid amide particles (manufactured by Sumitomo Chemical Co., Ltd., weight average particle size 3.5 μm) as organic polymer fine particles and 0.45% by weight of glycerin monostearate (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., TB-123) as an anti-fogging agent, and then pelletized.

[0083] Example 1 The polypropylene resin used to form the base layer (A) was a mixture of 50% by weight of [PP-1] and 50% by weight of [PP-2]. The resin used to form the sealing layer (C) was a mixture of 90% by weight of [PP-3] and 10% by weight of [PP-4]. The resin used to form the surface layer (B) was 100% by weight of [PP-7].

[0084] Using three melt extruders, the resin forming the base layer (A) was melt extruded from the first extruder at a resin temperature of 280°C, the resin forming the surface layer (B) was melt extruded from the second extruder at a resin temperature of 250°C, and the resin forming the seal layer (C) was melt extruded from the third extruder at a resin temperature of 250°C. The resins were then extruded through a T-die in the order of surface layer (B) / base layer (A) / seal layer (C) from the contact surface with the chill roll, and then cooled and solidified on a cooling roll at 30°C to obtain an unstretched sheet. The film was then stretched 4.5 times in the longitudinal direction by utilizing the difference in peripheral speed between metal rolls heated to 130°C, and then introduced into a tenter stretching machine where it was stretched 9.5 times in the transverse direction. The temperature of the preheating zone of the tenter stretching machine was 168°C, and the temperature of the stretching zone was 155°C.

[0085] In the latter half of the tenter stretching machine, heat setting was performed at 163°C, and then the surface of the surface layer (B) was subjected to a corona discharge treatment using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., and then the seal layer (C) was similarly subjected to a corona discharge treatment, and the film was wound up by a film winder to obtain a polypropylene-based resin multilayer film that can be automatically packaged. The final film thickness was 25 μm. The thickness ratio of each layer in the obtained film was surface layer (B) / base layer (A) / sealing layer (C)=1.0 / 21.9 / 2.1 (μm). The obtained multilayer film satisfied the requirements of the present invention, and had sufficient heat seal strength and heat seal reach strength at low temperatures, and was suitable for automatic packaging and gusset packaging. The anti-fogging properties were also at a level that did not pose a problem when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0086] Example 2 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 55% by weight of [PP-1] and 45% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained laminated film had both suitability for automatic packaging and suitability for gusset packaging, similar to Example 1. The anti-fogging property was also at a level that would not cause problems when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0087] Example 3 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 60% by weight of [PP-1] and 40% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained laminated film had both suitability for automatic packaging and suitability for gusset packaging, similar to Example 1. The anti-fogging property was also at a level that would not cause problems when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0088] Example 4 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 65% by weight of [PP-1] and 35% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained laminated film had both suitability for automatic packaging and suitability for gusset packaging, similar to Example 1. The anti-fogging property was also at a level that would not cause problems when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0089] Example 5 A laminated film was obtained in the same manner as in Example 2, except that a mixture of 65% by weight of [PP-1] and 35% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained laminated film had both suitability for automatic packaging and suitability for gusset packaging, as in Example 2. The anti-fogging properties were also at a level that would not cause problems when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0090] Example 6 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 65% by weight of [PP-1] and 35% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A), and the thickness ratio of each layer in the obtained film was surface layer (B) / base layer (A) / seal layer (C) = 1.0 / 20.6 / 3.4 (μm). The obtained laminated film had both suitability for automatic packaging and suitability for gusset packaging, similar to Example 1. The anti-fogging property was also at a level that would not cause problems when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0091] Example 7 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 65% by weight of [PP-1] and 35% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained laminated film had both suitability for automatic packaging and suitability for gusset packaging, similar to Example 1. The anti-fogging property was also at a level that would not cause problems when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0092] Example 8 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 65% by weight of [PP-1] and 35% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A), and the thickness ratio of each layer in the obtained film was surface layer (B) / base layer (A) / seal layer (C) = 1.0 / 20.6 / 1.7 (μm). The obtained laminated film had both suitability for automatic packaging and suitability for gusset packaging, similar to Example 1. The anti-fogging property was also at a level that would not cause problems when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0093] Example 9 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 70% by weight of [PP-1] and 30% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained laminated film had both suitability for automatic packaging and suitability for gusset packaging, similar to Example 1. The anti-fogging property was also at a level that would not cause problems when packaging fruits and vegetables. The film composition and physical properties are shown in Table 1.

[0094] Example 10 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 45% by weight of [PP-1] and 55% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained film was suitable for both automatic long wrapping and gusset wrapping. The film composition and physical properties are shown in Table 1.

[0095] Example 11 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 75% by weight of [PP-1] and 25% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained film was suitable for both automatic packaging and gusset packaging. The film composition and physical properties are shown in Table 1.

[0096] Comparative Example 1 A laminated film was obtained in the same manner as in Example 1, except that 100% by weight of [PP-5] was used as the polypropylene-based resin constituting the seal layer (C). The obtained laminated film had a high heat seal start temperature of the seal layer (C), and was poorly suited for gusset packaging. The film composition and physical properties are shown in Table 2.

[0097] Comparative Example 2 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 50% by weight of [PP-6] and 50% by weight of [PP-7] was used as the polypropylene-based resin constituting the surface layer (B). The obtained laminated film had a high heat seal rise temperature of the surface layer (B) and was poor in suitability for gusset packaging. The film composition and physical properties are shown in Table 2.

[0098] Comparative Example 3 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 75% by weight of [PP-6] and 25% by weight of [PP-7] was used as the polypropylene-based resin constituting the surface layer (B). The obtained laminated film had a high heat seal rise temperature of the surface layer (B) and was poor in suitability for gusset packaging. The film composition and physical properties are shown in Table 2.

[0099] Comparative Example 4 A laminated film was obtained in the same manner as in Example 1, except that 100% by weight of [PP-6] was used as the polypropylene resin constituting the surface layer (B). The obtained laminated film had a high heat seal rise temperature of the surface layer (B) and a low heat seal rise temperature, and therefore had poor suitability for gusset packaging. The film composition and physical properties are shown in Table 2.

[0100] Comparative Example 5 A laminated film was obtained in the same manner as in Example 1, except that the thickness of the sealing layer (C) was set to 0.7 μm, so that the sealing layer thickness ratio was set to 3%. The obtained laminated film had a high heat seal rise temperature of the seal layer (C) and was poor in suitability for gusset packaging. The film composition and physical properties are shown in Table 2.

[0101] Comparative Example 6 A laminated film was obtained in the same manner as in Example 1, except that 100% of [PP-1] was used as the polypropylene resin constituting the base layer (A). The obtained laminated film had a high thermal shrinkage rate in the longitudinal direction, and it was not possible to reduce sticking during gusset packaging. The film composition and physical properties are shown in Table 2.

[0102] Comparative Example 7 A laminated film was obtained in the same manner as in Example 1, except that a mixture of 85% by weight of [PP-1] and 15% by weight of [PP-2] was used as the polypropylene-based resin constituting the base layer (A). The obtained laminated film had a high thermal shrinkage rate in the longitudinal direction, and it was not possible to reduce sticking during gusset packaging. The film composition and physical properties are shown in Table 2.

[0103] [Table 1]

[0104] [Table 2] [Industrial Applicability]

[0105] The polypropylene-based resin multilayer film of the present invention, which can be used for automatic packaging, has been able to provide good gusset packaging suitability at a lower cost than conventional films by optimizing the seal thickness and composition. In addition, since it has anti-fogging properties, it is particularly suitable for packaging of fruits and vegetables.

Claims

1. The polypropylene-based resin multilayer film for packaging fresh produce has a base layer (A) made of a polypropylene-based resin composition, a surface layer (B) made of the polypropylene-based resin composition on one side of the base layer (A), and a seal layer (C) made of the polypropylene-based resin composition on the opposite side of the surface layer (B) of the base layer (A), the film having a thickness of 10 to 100 μm, and satisfying the following a) to g), j), and k): a) The polypropylene resin composition constituting the base layer (A) has a mesopentane fraction of 97.5% or more and 99.0% or less. b) The proportion of the α-olefin monomer derived component relative to the total of the propylene monomer derived components and the α-olefin monomer derived components in the entire polypropylene-based resin composition constituting the base layer (A) is 0.4 mol % or less. c) The polypropylene resin composition constituting the surface layer (B) contains 95% by weight or more of a propylene-α-olefin copolymer. d) The thickness of the surface layer (B) is in the range of 1 to 10% of the total thickness of the film. e) The heat seal strength rising temperature of the surface layer (B) is 125° C. or higher and 140° C. or lower. f) The sealing layer (C) contains a plurality of polypropylene-based resins, the melting points of which are in the range of 70 to 140°C, the content of the polypropylene-based resin having a melting point of 70 to 100°C is 1% by weight or more and 50% by weight or less, and the content of the polypropylene-based resin having a melting point of 100 to 140°C is 50% by weight or more and 99% by weight or less. g) The thickness of the sealing layer (C) is in the range of 5 to 15% of the total thickness of the film. j) The heat seal ultimate strength of the seal layer (C) is 3.0 N / 15 mm or more. k) The heat seal ultimate strength of the surface layer (B) is 3.0 N / 15 mm or more.

2. The polypropylene-based resin multilayer film for packaging fruits and vegetables according to claim 1, which satisfies the following h): h) The heat seal strength rising temperature of the seal layer (C) is 100° C. or higher and 115° C. or lower.

3. 3. The polypropylene-based resin multi-layer film for packaging fruits and vegetables according to claim 1 or 2, which satisfies the following l): l) The polypropylene-based resin multi-layer film has a thermal shrinkage rate in the longitudinal direction at 120° C. of 3.0% or less.

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