JP2011025432A - Polypropylene composite film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sealant film having easy opening properties, capable of obtaining sufficiently high sealing strength for protecting the content and suitable for a retort pouch, a medical infusion bag, a pouch for liquid food, or the like, and to provide a laminate thereof. <P>SOLUTION: A polypropylene composite film is constituted of a base material layer (A) comprising a propylene-ethylene block copolymer (a) and a seal layer (B) composed of 15-50 wt.% of a propylene-ethylene block copolymer (a) and 50-85 wt.% of a mixed resin (b) of a propylene-ethylene random copolymer and/or a propylene-ethylene-butene random copolymer and low-density polyethylene. Herein, (a)+(b) is 100 wt.%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polypropylene-based composite film useful as a sealant film for retort food packaging applications, and more particularly to a polypropylene-based composite film having a strong seal strength for easy opening and content protection.

  Conventionally, sealant films used for retort pouches, medical infusion bags, liquid food pouches, etc. have heat resistance that can withstand heat and pressure sterilization (retort treatment), and impact resistance that can withstand the impact of distribution processes (especially at low temperatures). Impact resistance), sufficient seal strength, blocking resistance, and moderate transparency have been required. In particular, the retort pouch film design has been designed for the purpose of satisfying other required characteristics in a well-balanced manner by placing the highest importance on heat resistance, low-temperature impact resistance and seal strength among these required characteristics. For example, when an unstretched film formed by melt-extrusion of a propylene / ethylene block copolymer or a resin containing a propylene / ethylene block copolymer and an ethylene-based elastomer is used for a retort pouch, it has a sufficiently strong seal strength. And when opening, it was opened with a flaw etc. (patent documents 1, 2). However, as the elderly population has increased in recent years, pouches that can be easily opened by the elderly themselves, medical infusion bags that do not need to be opened with a bag to facilitate quick work at the medical site, liquid food pouches, etc. The demand for has increased. Therefore, in order to solve this problem, using Patent Documents 1 and 2, assuming that no excessive impact or the like is applied to the transportation and handling of the packaging bag, the seal temperature is lowered only for the portions necessary for opening. Although attempts were made to reduce the seal strength and seal the other portions at normal high temperatures to ensure sufficient seal strength, the unstretched films of Patent Document 1 and Patent Document 2 have the desired seal strength in the low temperature region. The temperature dependence of the seal strength is too large (appropriate seal temperature range is too narrow), it cannot be processed stably, and the seal strength for good easy opening and content protection ( The content sealability) could not be achieved at the same time.

  In addition, for the purpose of low-temperature heat sealability and impact resistance, a laminated polypropylene-based unstretched film having a two-layer structure of a laminate layer and a seal layer has been proposed (Patent Document 3). However, although the film of Patent Document 3 is excellent in low-temperature sealing properties, the sealing strength for protecting the contents is low, and the bag dropping strength when the contents are packed and dropped is not satisfied.

Japanese Patent Laid-Open No. 2003-55510 JP 2003-96251 A JP 2007-237641 A

  An object of the present invention is to provide a polypropylene-based composite film that has an easy-opening property, provides a sufficiently strong seal strength for content protection, and is suitable for retort pouches, medical infusion bags, liquid food pouches, and the like. There is.

  The present invention for solving this problem is characterized by the following configuration.

  A composite film having a base material layer (A) and a sealing layer (B) provided on one side of the base material layer (A), wherein the base material layer (A) is a propylene / ethylene block copolymer ( a), the seal layer (B) is 15 to 50% by weight of a propylene / ethylene block copolymer (a), a propylene / ethylene random copolymer and / or a propylene / ethylene / butene random copolymer, low A polypropylene-based composite film comprising 50 to 85% by weight of a mixed resin of density polyethylene (b) [provided that (a) + (b) = 100% by weight].

  The polypropylene-based composite film of the present invention can be stably sealed over a wide temperature range, has good easy-openability, and provides a sufficiently strong seal strength for protecting the contents. Only necessary portions can be easily opened, and other portions can ensure sufficient sealing strength. Furthermore, by laminating at least one layer selected from a biaxially stretched polyamide film, a biaxially stretched polyester film, printing paper, and a metal foil on the base material layer side of the polypropylene-based composite film, only a portion necessary for opening is obtained. Packaging bags such as retort pouches, medical infusion bags, and liquid food pouches that are easy to open and have sufficient sealing strength in the other parts can be provided.

  The polypropylene composite film according to the present invention will be specifically described.

  The resin constituting the base material layer (A) in the present invention needs to be a propylene / ethylene block copolymer (a). The propylene / ethylene block copolymer in the present invention is a copolymer comprising a propylene polymer (a1) and an ethylene polymer (a2).

The density of the propylene / ethylene block copolymer is preferably 0.90 to 0.96 g / cm ³ . When the density is less than 0.90 g / cm ³ , the mechanical strength of the film is low, and the slit property after film formation and the film may be stretched in the process at the time of lamination, and the process passability may deteriorate. On the other hand, if the density exceeds 0.96 g / cm ³ , the crystallinity of the film increases and the impact resistance may deteriorate.

  The propylene / ethylene block copolymer has a melt flow rate (hereinafter abbreviated as MFR) at 230 ° C. in the range of 1 to 20 g / 10 minutes, preferably in the range of 1 to 10 g / 10 minutes. More preferably, it is the range of 2-5 g / 10min. If the MFR is less than 1 g / 10 minutes, the molten polymer is cooled and solidified to form a film, resulting in poor speed following at the time of casting, which is not preferable. Moreover, when MFR exceeds 20 g / 10min, a viscosity will become low too much, the neck-in of the film edge part at the time of casting may become large, and productivity may deteriorate.

  As a method for adjusting the intrinsic viscosity of the a1 component and the a2 component of the propylene / ethylene block copolymer (a) and the melt flow rate, a method of adding a molecular weight regulator such as hydrogen gas or a metal compound in each step during polymerization, Examples include a method of adding an additive when melt-kneading a polymer obtained in powder form, a method of adjusting kneading conditions when melt-kneading a polymer obtained in powder form, and the like.

  In addition, the base layer (A) has a specific additive, specifically an organic compound such as erucic acid amide, in order to ensure slipperiness and laminating suitability suitable for film processing within the range not impairing the object of the present invention. Lubricants, antioxidants, and inorganic fillers such as silica and zeolite may be selected and used. Moreover, if it is a range which does not inhibit the effect of this invention for a base material layer (A), the film edge part, slit waste, etc. which are produced when producing this invention film can also be mixed and used as needed.

Examples of the method for producing the propylene / ethylene block copolymer (a) include a method of polymerizing propylene, ethylene or the like as a raw material using a catalyst. As the catalyst, a Ziegler-Natta catalyst, a metallocene catalyst, or the like can be used. For example, those described in JP-A-07-216017 can be preferably used. Specifically, in the presence of an organosilicon compound having an Si—O bond and an ester compound, the general formula Ti (OR ₃ ) _a X _4-a (wherein R 3 is a hydrocarbon group having 1 to 20 carbon atoms, X represents a halogen atom, and a represents a number of 0 <a ≦ 4, preferably 2 ≦ a ≦ 4, particularly preferably a = 4). A solid catalyst containing a trivalent titanium compound obtained by treating the resulting solid product with an ester compound and then treating with a mixture of an ether compound and titanium tetrachloride or a mixture of an ether compound, titanium tetrachloride and an ester compound, Examples thereof include a catalyst system composed of an organoaluminum compound electron donating compound (dialkyldimethoxysilane or the like is preferably used).

  As a specific method for producing the copolymer (a) using the catalyst, from the viewpoint of productivity and low temperature impact resistance, a monomer mainly composed of propylene in the first step substantially in the absence of an inert solvent. Is a block copolymer obtained by producing a polymer part (a1 component) and then producing an ethylene copolymer part (a2 component) by polymerization in the gas phase in the second step, The content of the a2 component is preferably 10 to 30% by weight (provided that the total of the a1 and a2 components is 100% by weight), more preferably 15 to 25% by weight. When the content of the a2 component is less than 10% by weight, the interfacial adhesive strength with the seal layer (B) may be inferior, and the drop bag impact resistance may be inferior. When the content exceeds 30% by weight, the blocking resistance is poor. There is a case.

  The ratio of the intrinsic viscosity ([η] a2) of the a2 component to the intrinsic viscosity ([η] a1) of the a1 component ([η] a2 / [η] a1) is 1.0 to 2.0. Preferably there is. If η] a2 / [η] a1 is less than 1.0, the blocking resistance may be deteriorated, and if it exceeds 2.0, the drop bag impact resistance may be deteriorated.

  Next, the sealing layer (B) in the present invention comprises 15 to 50% by weight of the propylene / ethylene block copolymer (a), a propylene / ethylene random copolymer and / or a propylene / ethylene / butene random copolymer. And 50% to 85% by weight of the mixed resin (b) of low density polyethylene [where (a) + (b) = 100% by weight]. When the content of the mixed resin (b) is less than 50% by weight, the low temperature heat sealability is inferior, and when it exceeds 85% by weight, the films stick to each other when rolled up as a film and may cause blocking. Therefore, it is not preferable. As for content of this mixed resin (b), the range of 60 to 80 weight% is more preferable.

  The content of the low density polyethylene resin (b4) in the mixed resin (b) of the propylene / ethylene random copolymer and / or propylene / ethylene / butene random copolymer and the low density polyethylene of the seal layer (B) is: A range of 5 to 20% by weight is preferred. When the content of the low density polyethylene is less than 5% by weight, the heat seal strength in a high temperature region of 160 ° C. or higher is inferior, and when it exceeds 20% by weight, the blocking resistance may be inferior.

  The seal layer (B) can contain an antioxidant, a heat stabilizer, an antistatic agent, an antiblocking agent, a lubricant and the like.

  The propylene / ethylene random copolymer and / or propylene / ethylene / butene random copolymer may be prepared by, for example, using the same catalyst as the propylene / ethylene block copolymer, and then propylene is polymerized in the same polymerization tank. And / or a method of polymerizing butene or a method of polymerizing continuously in two or three stages. The copolymerization amount of the ethylene (b2) component and / or ethylene butene (b3) component to the propylene (b1) component is 2 to 20% by weight (provided that the total of the b1 component, the b2 component and / or the b3 component is 100 Wt%), more preferably 4 to 15 wt%. If the content of the b2 component and / or the b3 component is less than 2% by weight, the impact resistance may be inferior. If the content exceeds 20% by weight, the blocking resistance may be inferior.

  The polypropylene composite film of the present invention needs to have a base material layer (A) and a seal layer (B) provided on one side of the base material layer (A). The single-layer film having the composition of the sealing layer (B) satisfies the sealing strength at the sealing temperature in the high temperature region, but the sealing strength is too weak at the sealing temperature in the low temperature region of 145 ° C. or lower, resulting in poor sealing performance. .

  The polypropylene-based composite film of the present invention is essential to be a composite film composed of two layers of a base material layer (A) and a seal layer (B). If necessary, a third composite film is formed on the base material layer (A) side. It is good also as a composite film of three or more layers by laminating four polypropylene-based resin layers.

  The thickness of the polypropylene composite film of the present invention is preferably 30 to 100 μm, and the thickness of the seal layer (B) is preferably 3 to 20 μm. If the thickness of the seal layer (B) is less than 3 μm, the easy-openability in the low temperature seal temperature range will be poor, and if it exceeds 20 μm, the seal strength may be insufficient in the high temperature seal temperature range.

  In addition, the polypropylene composite film of the present invention is at least one selected from a biaxially stretched polyamide film, a biaxially stretched polyester film, a printing paper, and a metal foil on the side opposite to the seal layer (B) of the base material layer (A). The layers are preferably used alone or in combination as needed. Examples of the biaxially stretched polyamide film include nylon 6, nylon 11, nylon 66, etc. Among them, the biaxially stretched nylon 66 film is more preferable in terms of heat resistance and moisture resistance. Examples of the biaxially stretched polyester film include a polyethylene terephthalate film, a polyethylene naphthalate film, a polybutylene terephthalate film, and the like. Among these, a biaxially stretched polyethylene terephthalate film is more preferable in terms of heat resistance and film formation price. Examples of the metal foil include aluminum foil and copper foil, and aluminum foil is more preferable. Examples of the printing paper include synthetic paper, high-quality paper, medium-quality paper, art paper, coated paper, and reprint paper. Art paper is preferable from the standpoint of printing.

  The thickness of the biaxially stretched polyamide film and the biaxially stretched polyester film is in the range of 10 to 100 μm, and in particular, in the range of 12 to 50 μm from the impact resistance and handleability when the retort pouch is used. preferable.

  The thickness of the printing paper is in the range of 15 to 200 μm, and particularly preferably in the range of 20 to 100 μm, from the viewpoint of printability processability and impact resistance and handleability when a retort pouch is used.

  The thickness of the metal foil is preferably in the range of 5 to 30 μm from the viewpoint of impact resistance, handleability, and economy when a retort pouch is used.

  The method of laminating these layers on the side opposite to the sealing layer (B) of the base material layer (A) is not particularly limited, but a method of laminating via an adhesive, a hot melt agent, and a low-melting extrusion laminate resin Is mentioned.

  When the sealing layers (B) of the polypropylene-based composite film of the present invention are heat-sealed, the heat-sealing strength at 135 ° C. to 145 ° C. is in the range of 20 to 30 N / 15 mm, and the heat sealing at 160 ° C. to 180 ° C. The strength is preferably 55 N / 15 mm or more from the viewpoint of heat seal strength stability during pouch creation. When the heat seal strength at 135 ° C. to 145 ° C. is less than 20 N / 15 mm, the content is poorly sealed, and when it exceeds 30 N / 15 mm, the easy-open property may be inferior. Moreover, if the heat seal strength at 160 ° C. to 180 ° C. is less than 55 N / 15 mm, the bag drop impact resistance is inferior.

  Next, an example of a method for producing the polypropylene composite film of the present invention will be described.

  Using two extruders, the propylene / ethylene block copolymer (a) is melted and extruded at a temperature of 160 to 260 ° C. from one extruder [base material layer (A)], and the other extruder. 25% by weight of propylene / ethylene block copolymer (a), 75% by weight of mixed resin (b) of low density polyethylene and propylene / ethylene random copolymer and / or propylene / ethylene / butene random copolymer Extruded by melting at a temperature of 160 to 250 ° C. [seal layer (B)], laminated with a pipe composite or coextrusion multilayer die, the thickness of the base layer (A) is 50 μm, and the thickness of the seal layer (B) is 10 μm In this way, the film is extruded from a die into a film shape, cast and solidified with a cooling roll of 35 to 50 ° C. to obtain a composite film. Subsequently, if necessary, the surface of the base material layer (A) is subjected to corona discharge treatment, wound up, and further slit to a predetermined width and length. The polypropylene composite film of the present invention obtained as described above is laminated with at least one layer selected from a biaxially stretched polyamide film, a biaxially stretched polyester film, a printing paper, and a metal foil, and is used for general packaging and retort. It can also be used as a sealant film for food packaging bags, medical infusion bags, liquid food pouches and the like.

The present invention will be described based on examples, but the present invention is not limited thereto.
The characteristic measurement method and the effect evaluation method in the present invention are as follows.

(1) Melting point (Tm)
Using a DSC (DSC-60A) manufactured by Shimadzu Corporation, a 5 mg sample was heated to 250 ° C. at a rate of 10 ° C./min and held for 5 minutes in a nitrogen atmosphere, and then cooled at 10 ° C./min. When the temperature was cooled to 10 ° C. and the temperature was raised again at a rate of 10 ° C./min, the peak temperature of the endothermic peak accompanying the melting of the resin was defined as the melting point (Tm).

(2) Density of resin The density was measured according to the density gradient tube method specified in JISK7112-1980.

(3) Film thickness Using a dial gauge thickness gauge (JIS B-7509-1992, measuring element 5 mmφ flat type), 10 points were measured at 10 cm intervals in the longitudinal direction and the width direction of the film, and the average value was obtained. .

(4) Thickness of each layer Cut out with a cross-sectional microtome of the film, and use a cross-sectional photograph taken by magnifying the cross-section 1000 times using a scanning electron microscope S-2100A type (manufactured by Hitachi, Ltd.). The length of each layer in the thickness direction was measured, and the thickness of each layer was determined by calculating backward from the magnification. In determining the thickness of each layer, a total of five cross-sectional photometers arbitrarily selected from different measurement visual fields were used, and the average value thereof was calculated.

(5) Heat seal strength A sample is cut out to 100 mm × 15 mm, the seal layer surfaces are overlapped, and a flat plate heat seal tester (TP-701B) manufactured by Shape Tester Sangyo Co., Ltd. is used, and each seal temperature and seal pressure is 1 kg / cm. ^2. The heat seal strength was measured when the sample heat-sealed under the condition of a seal time of 1 second was peeled 90 ° at a tensile speed of 300 mm / min using Tensilon (RTC-1210A) manufactured by Orientec Co., Ltd. . At that time, the average value of the measured values of n number 10 for one sample was taken.

  Further, in order to achieve both the sealing property, the content protection property, and the easy-opening property, which are the objects of the present invention, the heat seal strength in the low temperature region of 135 ° C. to 145 ° C. is 20 to 30 N / 15 mm and 160 ° C. When the heat seal strength in the high temperature region of ˜180 ° C. is 55 N / 15 mm or more, “◯” is given, and “X” is given when the range is out of the range and the sealing property, the content protection property, and the easy-opening property are not compatible.

(6) Low-temperature bag dropability In the production of a laminated film for heat seal strength measurement obtained in (5), the shape is 130 mm × 170 mm under the conditions of a heat seal temperature of 160 ° C., a seal pressure of 1 kg / cm ² , and a seal time of 1 second. After filling the contents with 150 ml of a 50/50 blend of water and salad oil, the contents are sealed under conditions of a heat seal temperature of 140 ° C., a seal pressure of 1 kg / cm ² , and a seal time of 1 second. Then, it is dropped vertically from the height of 1.2 m to the concrete surface with the bottom side down in a 0 ° C. atmosphere. At that time, a test of n number 10 was performed on one sample, and the number of the pouch seal part opened or a part of the pouch was broken was determined as follows.
○: There was no opening, and the pouch was not torn.
Δ: Opening or tearing was less than 3.
X: Opening or tearing was 3 or more.

(7) Bag drop impact strength From the laminated film obtained in (5), a 130 mm × 170 mm shaped pouch was prepared, and the contents were filled and sealed with 150 ml of a solution in which water and salad oil were blended in 50/50, Under normal temperature atmosphere (24 ° C.), drop vertically from a height of 1.5 m to the concrete surface with the bottom side down. At that time, a test of n number 10 was performed on one sample, and the determination was made as follows by the number of unsealed pouch seals or broken pouches.
○: There was no opening, and the pouch was not torn.
Δ: Opening or tearing was less than 3.
X: Opening or tearing was 3 or more.

(8) Melt flow rate (MFR)
In accordance with JIS K-7210, the polypropylene resin was measured at 230 ° C., and the polyethylene resin was measured at 190 ° C.

(9) Retort treatment After processing the pouch obtained in (6) at a temperature of 130 ° C. for 30 minutes and a pressure of 2 kg / cm ² using an autoclave (SR-240) manufactured by Tommy Seiko Co., Ltd. Then, heating and pressure were returned to room temperature and normal pressure, and then taken out.

(10) Easy opening characteristics Using the pouch obtained in (6), the sealing performance before and after the retort and the opening performance were evaluated for the final sealing section (opening section) after filling the contents, and the following determination was performed. .
○: Even after retorting, there is no opening of the seal part, and it can be easily opened by hand.
Δ: The seal part is not opened even after retorting and can be opened by hand, but stringing occurs at the peeling part, and the peeling mark is not clean.
X: The seal part is opened after retorting, or it is difficult to open by hand.

[Examples 1 to 3]
As a resin for the base material layer (A), a propylene / ethylene block copolymer having a density of 0.92 g / cm ³ , a melt flow rate (hereinafter abbreviated as MFR) 3.0 g / 10 min, and a melting point of 161 ° C. (a ) Is fed to an extruder adjusted to a temperature of 260 ° C. and melted, and as the sealing layer (B), the same propylene / ethylene block copolymer (a) as the base material layer and MFR of 30 g / 10 min. Mixed resin of propylene / ethylene random copolymer and / or propylene / ethylene / butene random copolymer having a melting point of 141 ° C. and low density polyethylene (b) having a density of 0.89 g / cm ³ and an MFR of 7 g / 10 min. Are mixed at the ratio shown in Table 1, supplied to another extruder, melted at a temperature of 250 ° C., laminated into two layers with a multi-manifold die for coextrusion, and pressed into a film form , Cooled and solidified by a cooling roll of 40 ° C., the thickness of the base material layer (A) is 50 [mu] m, the thickness of the sealing layer (B) has a total thickness 60μm composite film 10 [mu] m.

A two-component cured adhesive (LX-903 / KL-manufactured by Dainippon Ink & Chemicals, Inc.) as a dry laminating agent on a biaxially stretched nylon 66 film having a thickness of 15 μm (“Emblem” ONM manufactured by Unitika Ltd.) 75 = 8/1) was applied at a solid coating thickness of 3 μm, and then laminated on the composite film and dried. Thereafter, the laminated composite film was aged at a temperature of 40 ° C. for 24 hours to promote the curing reaction of the adhesive layer, and then at the temperatures shown in Table 1, 135 ° C. and 145 ° C. in the low temperature region, Samples were prepared by heat-sealing the seal layer (B) layers with the seal pressure of 1 kg / cm ² and the seal time of 1 second at 160 ° C. and 180 ° C., and the heat seal strength was measured. .

Next, under the conditions of the heat seal temperature of 160 ° C., the seal pressure of 1 kg / cm ² , and the seal time of 1 second, the vertical and bottom sides are heat sealed to create a 130 mm × 170 mm shape pouch, Filled with 150 ml of a 50/50 blend of salad oil and sealed, the upper easy-open part was sealed at a heat seal temperature of 145 ° C., a seal pressure of 1 kg / cm ² , and a seal time of 1 second. Impact properties, bag drop impact properties, and easy-open characteristics were evaluated.

  In the film of the present invention, the unsealed part heat-sealed in the low-temperature seal region shows good easy-open characteristics and sealing properties, and the vertical and bottom sides heat-sealed in the 160 ° C. high-temperature seal region have sufficient heat seal strength. It was excellent in content protection. The evaluation results of each physical property are as shown in Table 1.

[Comparative Example 1]
A composite film and a laminate were obtained under the same conditions as in Example 1 except that the base material layer (A) was a homopolypropylene having a MFR = 8 g / 10 min (manufactured by Sumitomo Chemical Co., Ltd., FLX80E4). In this laminate, interfacial peeling occurred with the seal layer (B), and the low temperature impact resistance and drop bag impact resistance were inferior. The evaluation results of each physical property are as shown in Table 1.

[Comparative Example 2]
A single layer film and a laminate having a thickness of 60 μm were obtained under the same conditions as in Example 1 except that the sealing layer (B) was a single layer composed only of the constituent resin composition. The present film and laminate did not satisfy the scope of the present invention because the heat seal strength in the low-temperature seal region was too high, and was inferior in easy-openability. The evaluation results of each physical property are as shown in Table 1.

[Comparative Example 3]
10% by weight of propylene / ethylene block copolymer, 72% by weight of propylene / ethylene random copolymer and 18% of low density polyethylene in the sealing layer (B), and a composite having a thickness of 60 μm under the same conditions as in Example 1. A film and a laminate were obtained. The film and laminate are low in heat seal strength as described above in the high temperature seal region, do not satisfy the scope of the present invention, are inferior in low temperature impact resistance and drop bag impact resistance, and inferior in content protection. there were. The evaluation results of each physical property are as shown in Table 1.

[Comparative Example 4]
A composite having a thickness of 60 μm under the same conditions as in Example 1 with 60% by weight of the propylene / ethylene block copolymer, 32% by weight of propylene / ethylene random copolymer, and 8% by weight of low density polyethylene in the sealing layer (B). A film was obtained. The film and laminate had low heat seal strength in the low temperature seal region, did not satisfy the scope of the present invention, and were inferior in sealing performance, low temperature impact resistance, and drop bag impact resistance. The evaluation results of each physical property are as shown in Table 1.

[Comparative Example 5]
A composite film having a thickness of 60 μm was obtained under the same conditions as in Example 1 except that the propylene / ethylene block copolymer of the seal layer (B) was 60% by weight and the propylene / ethylene random copolymer was 40% by weight. The present film and laminate did not satisfy the scope of the present invention because the heat seal strength was low in the low-temperature seal region, and the easy-open characteristics before and after retort and the sealability were inferior. The evaluation results of each physical property are as shown in Table 1.

[Comparative Example 6]
A composite film having a thickness of 60 μm was obtained under the same conditions as in Example 1 except that the propylene / ethylene block copolymer of the seal layer (B) was 60% by weight and the low density polyethylene was 40% by weight. Since this film and laminate do not contain propylene / ethylene random copolymer and / or propylene / ethylene / butene random copolymer, heat seal strength is low in the high temperature seal region, and low temperature impact resistance and drop bag impact The sex was not satisfactory. The evaluation results of each physical property are as shown in Table 1.

  The polypropylene-based composite film of the present invention can be stably sealed over a wide temperature range, has an easy openability, and provides a sufficiently strong seal strength for content protection. Suitable as a packaging bag for retort pouches, medical infusion bags, liquid food pouches, etc. by forming a laminate on one side of at least one other layer of polyamide film, biaxially stretched polyester film, printing paper, metal foil Can be used.

Claims (3)

  A composite film having a base material layer (A) and a sealing layer (B) provided on one side of the base material layer (A), wherein the base material layer (A) is a propylene / ethylene block copolymer ( a), the seal layer (B) is 15 to 50% by weight of a propylene / ethylene block copolymer (a), a propylene / ethylene random copolymer and / or a propylene / ethylene / butene random copolymer, low A polypropylene-based composite film comprising 50 to 85% by weight of a mixed resin of density polyethylene (b) [provided that (a) + (b) = 100% by weight].   The biaxially stretched polyamide film, the biaxially stretched polyester film, the printing paper, and at least one layer selected from a metal foil is provided on the side opposite to the sealing layer (B) of the base material layer (A). Polypropylene composite film.   When the seal layers (B) are heat sealed, the heat seal strength at 135 ° C. to 145 ° C. is 20 to 30 N / 15 mm and the heat seal strength at 160 ° C. to 180 ° C. is 55 N / 15 mm or more. The polypropylene-based composite film according to claim 1 or 2.