JP7712112B2 - Polypropylene sealant film and laminate and pouch using same - Google Patents

Description

The present invention relates to a polypropylene sealant film used as a sealant for packaging bags, and to laminates and pouches using the same.

Conventionally, non-oriented films (hereafter referred to as CPP) mainly composed of propylene-ethylene block copolymers have been used as sealant films for high-retort packaging that is sterilized in retort at high temperatures of 120°C to 135°C. The main method of use is to laminate substrate layers such as oriented polyethylene terephthalate film (hereafter referred to as PET), oriented nylon film (hereafter referred to as ONy), and aluminum foil (hereafter referred to as AL) to form laminates of PET/ONy/AL/CPP, PET/AL/ONy/CPP, or PET/AL/CPP configurations, which are then made into bags for use.

However, when the propylene-ethylene block copolymer resins described in Patent Documents 1 and 2 or non-oriented films formed by melt extrusion of resins in which propylene-ethylene block copolymers are blended with ethylene-based elastomers or the like are used in retort pouches, there is a problem that the pouches are poorly cut in a straight line when opened from the notch (the cut at the end), causing deformation or spillage of the contents.

Therefore, sealant films used in retort pouches are required to be able to be opened by tearing easily from the notch without using a blade (easy tearability).

As a polypropylene film having easy tearing properties, there is a uniaxially stretched film (Patent Document 3) that is stretched at a high ratio in the longitudinal direction. However, the film of Patent Document 3 has improved tearing properties in the stretching direction, but has poor tearing properties in all in-plane directions, and its low-temperature impact resistance is insufficient for retort applications. There are also films that contain sorbitol derivatives (Patent Document 4) and films that contain rosin metal salt compounds (Patent Document 5) for the purpose of increasing the crystallinity of the film and imparting tearing properties, but they have a lot of odor and extractives after retort processing and are not suitable for high retort applications. There are also films that contain crystalline polyethylene resins (Patent Document 6) and films that contain polybutene-1 as a crystal nucleating agent (Patent Document 7), but both of them have poor low-temperature impact resistance and are therefore insufficient for high retort applications.

As described above, in the prior art, there was no polypropylene-based unstretched film that had easy tearing in all in-plane directions, and also had low-temperature impact resistance, heat sealability, and blocking resistance, and could be widely used for high-temperature retort applications (sterilization at 125 to 135°C).

In recent years, pouches for commercial use have become larger, and the required level of low-temperature impact resistance has become higher. In addition, the required level of pouch appearance has also become higher, and it is desired to minimize the occurrence of the fine uneven appearance that occurs on the laminate surface after retort sterilization, known as yuzu skin.

In addition, because the slipperiness between the CPP of the laminate and the laminate base material layer is poor, the CPP of the laminate and the laminate base material layer stick to each other during the film forming process, slitting process, bag making process, content filling process, etc., resulting in a so-called blocking phenomenon. If the laminate film is stored for a long period of time or at high temperatures, it becomes difficult to unwind the film when it is used, and there is a problem that bag making and filling workability are significantly reduced.

To solve the above problems, a method of preventing blocking by sprinkling an anti-blocking agent, for example, a powder such as starch that has been surface-treated to be water-resistant, onto the sealant has been adopted, a method of avoiding blocking by using the so-called powdering method. However, the powdering method has the drawback of impairing the appearance of the bag, or of the powder being mixed into the food to be filled, adversely affecting the taste, thereby reducing the commercial value of the product. Therefore, there has been a strong demand for the development of a polypropylene film that does not require powdering, can be used without powder, and can also be used suitably for high-retort applications as a packaging bag or a sealant for a packaging bag.

JP 2003-105164 A JP 2000-186159 A Japanese Patent Application Publication No. 7-138423 Japanese Unexamined Patent Publication No. 1-299831 Japanese Patent Application Publication No. 11-255910 Japanese Patent Application Publication No. 10-316772 Patent No. 3813263

The objective of the present invention is to provide a polypropylene sealant film that has excellent tearability in all directions in the film plane as a sealant for packaging bags, has excellent heat sealability and low-temperature impact resistance, and excellent blocking resistance so that it can be used without powder, and has excellent resistance to yuzu peeling so that it can be used suitably for high-retort applications, as well as a laminate and a pouch using the same.

In order to solve the above problems, the present invention is as follows.
(1) A polypropylene-based sealant film comprising a polypropylene-based resin as a main component, the film having a tear strength of 30 N/mm or less in all in-plane directions per sheet as measured by the Elmendorf method in accordance with JIS K 7128-2 (1998).
(2) The polypropylene sealant film according to (1), having a yield stress of 25 MPa or more and 50 MPa or less in all in-plane directions, as measured by the yield stress measurement method in JIS K 7161 (2014).
(3) The polypropylene sealant film according to (1) or (2), which has a crystallinity of 60% or more as measured by infrared spectroscopy.
(4) The polypropylene sealant film according to any ^one of (1) to (3), wherein the blocking shear strength between the heat-sealed surfaces of the polypropylene sealant film after 24 hours at 80° C. is 5 N/12 cm2 or less.
(5) The polypropylene sealant film according to any one of (1) to (4), wherein at least one surface of the film has a centerline average roughness (Ra) of 0.25 μm or more.
(6) A polypropylene-based sealant film according to any one of (1) to (5), which is made of a resin composition containing a polypropylene-based resin as a main component and 1,500 to 10,000 ppm of a crystal nucleating agent.
(7) A polypropylene-based sealant film according to (6), comprising a base layer made of the resin composition and a layer mainly composed of an ethylene-propylene block copolymer laminated on at least one side of the base layer.
(8) A laminate in which the polypropylene sealant film according to any one of (1) to (7) is laminated on one side of a laminate substrate layer formed by laminating a single layer or two or more layers of films.
(9) A pouch formed by heat-sealing polypropylene sealant films of the laminate according to (8) to each other.
(10) A pouch as described in (9) above, which can be torn open in both the vertical and horizontal directions to allow the contents to be removed.

When polypropylene sealant films and laminates using the same are used as sealants for packaging bags, they have excellent tearability in all directions within the film surface, excellent heat sealability and low-temperature impact resistance, and excellent blocking resistance, so they can be used without powder, and can be used as high-retort packaging materials with excellent yuzu-peel resistance.

The polypropylene sealant film of the present invention is a film whose main component is a polypropylene resin, and the tear strength per film measured by the Elmendorf method in JIS K 7128-2 (1998) is preferably 30 N/mm or less in all in-plane directions, more preferably 25 N/mm or less. If it exceeds 30 N/mm, the film becomes less easily tearable.

Here, "all directions in the plane" refers to all 360-degree directions on the film surface parallel to the direction in which the resin is extruded from the extruder as a polypropylene sealant film, including the MD (hereafter abbreviated as MD). In particular, the main directions used are the in-plane MD direction, the film width direction perpendicular to the MD in the plane at 90 degrees (hereafter abbreviated as TD), and the directions at 45 degrees to the left and right of the MD in the plane.

In the yield stress measurement method in JIS K 7161 (2014), the yield stress is preferably 25 MPa to 50 MPa in all in-plane directions, and more preferably 30 MPa to 45 MPa. If it is less than 25 MPa, the tearability may be poor, and if it exceeds 50 MPa, the low-temperature impact resistance may be weakened.

The degree of crystallinity measured by infrared spectroscopy (hereinafter referred to as IR) is preferably 60% or more. If it is less than 60%, the tearability and resistance to citron peeling in all in-plane directions may deteriorate.

It is preferable that the blocking shear strength between the heat seal layer surfaces of the film after 24 hours at 80° C. is 5 N/12 ^cm2 or ^less . If the blocking shear strength exceeds 5 N/12 cm2, poor opening properties may occur when the film is made into a bag without powder.

It is preferable that the center line average roughness (Ra) of at least one side of the film is 0.25 μm or more. If it is less than 0.25 μm, the films may stick together when made into bags without powder, resulting in poor opening properties.

The above (1) to (5) can be achieved, for example, by combining a polypropylene resin and a crystal nucleating agent masterbatch.

As polypropylene-based resins, propylene-based polymers such as homopolypropylene (a), which is a propylene homopolymer, ethylene-propylene block copolymer (b), propylene-α-olefin random copolymers with small amounts of ethylene, α-olefins such as 1-butene and 1-hexene, and other comonomers are preferred, and more preferably, a mixture of homopolypropylene (a), which is a propylene homopolymer, and ethylene-propylene block copolymer (b) is preferred, as this will result in a film that satisfies the various characteristics described above.

Homopolypropylene (a)
The melt flow rate (MFR) of the homopolypropylene (a) at 230° C. (load 21.18 N) is preferably in the range of 1 to 20 g/10 min, more preferably in the range of 1 to 10 g/10 min, and even more preferably in the range of 5 to 8 g/10 min, from the viewpoints of dispersibility between resins and stable melt film-forming property.

Ethylene-propylene block copolymer (b)
The ethylene-propylene block copolymer (b) preferably has a proportion of xylene-insoluble matter at 20° C. of 75 to 85% by mass, an intrinsic viscosity ([η]H) of the insoluble matter of the copolymer of the present invention of 1.7 to 2.0 dl/g, and an intrinsic viscosity ([η]EP) of the soluble matter of the copolymer of the present invention of 2.8 to 3.4 dl/g.

The 20°C xylene insoluble portion and the soluble portion are obtained by completely dissolving the ethylene-propylene block copolymer pellets in boiling xylene, lowering the temperature to 20°C, leaving them for at least 4 hours, and then filtering them into a precipitate and a solution. The precipitate is called the 20°C xylene insoluble portion, and the solution portion (filtrate) is dried to dryness and dried under reduced pressure at 70°C, and the portion obtained is called the soluble portion.

If the insoluble portion of the ethylene-propylene block copolymer (b) has an intrinsic viscosity ([η]H) of less than 1.7 dl/g, the molecular weight of the polypropylene in the sea component is small, which may result in insufficient low-temperature impact resistance. Conversely, if it is greater than 2.0 dl/g, the molecular weight of the polypropylene may become too large, making cast molding difficult. If the intrinsic viscosity ([η]EP) of the xylene-soluble portion is less than 2.8 dl/g, the film may become sticky and the blocking resistance may deteriorate. If it is greater than 3.4 dl/g, the dispersed particle size of the island component consisting of ethylene and ethylene-propylene copolymer rubber components may become large, which may lead to the citrus peel phenomenon when oily foods are packaged.

The ethylene-propylene block copolymer (b) used in the present invention can be produced by polymerizing the raw materials propylene and ethylene using a catalyst. Here, the catalyst can be a Ziegler-Natta type or a metallocene catalyst, and for example, those described in JP-A-07-216017 can be suitably used.

Specific examples of such catalysts include (1) a solid catalyst containing a trivalent titanium compound obtained by reducing a titanium compound represented by the general formula Ti(OR) _{aX 4-a} (wherein R is a hydrocarbon group having 1 to 20 carbon atoms, X is a halogen atom, and a is 0<a≦4, preferably 2≦a≦4, and particularly preferably a=4) with an organomagnesium compound in the presence of an organosilicon compound having a Si—O bond and an ester compound, treating the resulting solid product with an ester compound, and then treating the resulting solid product with a mixture of the ester compound and titanium tetrachloride or a mixture of an ether compound and titanium tetrachloride; (2) an organoaluminum compound; and (3) a catalyst system comprising an electron-donating compound (dialkyldimethoxysilane, etc. are preferably used).

From the viewpoints of productivity and low-temperature impact resistance, it is preferable to use a method for producing the ethylene-propylene block copolymer (b) in which a polymer portion mainly composed of propylene is polymerized in the first step, and then the ethylene-propylene copolymer is polymerized in the gas phase in the second step.

Crystal nucleating agent masterbatch (c)
The crystal nucleating agent master batch (c) contains 3 to 10 mass % of a crystal nucleating agent containing a metal phosphate. The carrier resin of the master batch is preferably an olefin-based resin, such as a propylene-based random copolymer in which propylene is randomly copolymerized with ethylene or butene, homopolypropylene, a propylene-based block copolymer, or a polyethylene-based resin.

The resin composition of the polypropylene sealant film of the present invention contains 1500 ppm or more and 10,000 ppm or less of the crystal nucleating agent containing the above-mentioned metal phosphate, which can improve the ease of tearing in all directions within the plane. If the crystal nucleating agent is less than 1500 ppm, the ease of tearing is not satisfactory, and if it is more than 10,000 ppm, further improvement in the ease of tearing may not be observed and the heat sealability may deteriorate.

Although metal phosphates alone can provide satisfactory tearability, their use in combination with metal dicarboxylates further improves tearability, so these crystal nucleating agents may be used in combination.

Examples of the metal phosphate salts in the present invention include phosphate ester compounds, and among these, aromatic metal phosphate salts are preferred for the purposes of the present invention. Specifically, sodium bis(4-t-butylphenyl)phosphate, sodium bis(4-methylphenyl)phosphate, sodium bis(4-ethylphenyl)phosphate, sodium bis(4-i-propylphenyl)phosphate, sodium bis(4-t-octylphenyl)phosphate, potassium bis(4-t-butylphenyl)phosphate, calcium bis(4-t-butylphenyl)phosphate, magnesium bis(4-t-butylphenyl)phosphate, phenyl) phosphate, lithium bis(4-t-butylphenyl) phosphate, aluminum bis(4-t-butylphenyl) phosphate, sodium 2,2'-methylene-bis(4,6-di-t-butylphenyl) phosphate, sodium 2,2'-ethylidene-bis(4,6-di-t-butylphenyl) phosphate, lithium 2,2'-methylene-bis(4,6-di-t-butylphenyl) phosphate, lithium 2,2'-ethylidene-bis(4,6- di-t-butylphenyl) phosphate, sodium-2,2'-ethylidene-bis(4-i-propyl-6-t-butylphenyl) phosphate, lithium-2,2'-methylene-bis(4-methyl-6-t-butylphenyl) phosphate, lithium-2,2'-methylene-bis(4-ethyl-6-t-butylphenyl) phosphate, calcium-bis[2,2'-thiobis(4-methyl-6-t-butylphenyl) phosphate], calcium-bis[2,2'-thiobis(4 -ethyl-6-t-butylphenyl)phosphate], calcium bis[2,2'-thiobis-(4,6-di-t-butylphenyl)phosphate], magnesium bis[2,2'-thiobis(4,6-di-t-butylphenyl)phosphate], magnesium bis[2,2'-thiobis-(4-t-octylphenyl)phosphate], sodium 2,2'-butylidene-bis(4,6-dimethylphenyl)phosphate, sodium 2,2'-butylidene-bis(4,6 -di-t-butylphenyl) phosphate, sodium-2,2'-t-octylmethylene-bis(4,6-di-methylphenyl) phosphate, sodium-2,2'-t-octylmethylene-bis(4,6-di-t-butylphenyl) phosphate, calcium-bis[2,2'-methylene-bis(4,6-di-t-butylphenyl) phosphate], magnesium-bis[2,2'-methylene-bis(4,6-di-t-butylphenyl) phosphate], barium-bis[2,2 '-methylene-bis(4,6-di-t-butylphenyl)phosphate], sodium-2,2'-methylene-bis(4-methyl-6-t-butylphenyl)phosphate, sodium-2,2'-methylene-bis(4-ethyl-6-t-butylphenyl)phosphate, sodium-(4,4'-dimethyl-5,6'-di-t-butyl-2,2'-biphenyl)phosphate, calcium-bis[(4,4-dimethyl-6,6'-di-t-butyl-2,2'-biphenyl)phosphate phosphate], sodium 2,2'-ethylidene-bis(4-m-butyl-6-t-butylphenyl) phosphate, sodium 2,2'-methylene-bis(4,6-di-methylphenyl) phosphate, sodium 2,2'-methylene-bis(4,6-di-ethylphenyl) phosphate, potassium 2,2'-ethylidene-bis(4,6-di-t-butylphenyl) phosphate, calcium bis[2,2'-ethylidene-bis(4,6-di-t-butylphenyl) phosphate ], magnesium bis[2,2'-ethylidene-bis(4,6-di-t-butylphenyl)phosphate], barium bis[2,2'-ethylidene-bis(4,6-di-t-butylphenyl)phosphate], aluminum tris[2,2'-methylene-bis(4,6-di-t-butylphenyl)phosphate] and aluminum tris[2,2'-ethylidene-bis(4,6-di-t-butylphenyl)phosphate] and mixtures of two or more of these can be exemplified. Sodium 2,2'-methylene-bis(4,6-di-t-butylphenyl)phosphate is particularly preferred.

The dicarboxylate metal salt in the present invention is a compound represented by the following structural formula (i) which is disclosed in JP 2015-212078 A.

(In formula (i), M1 and M2 are sodium, hydrogen, calcium, strontium, or lithium, and may be the same or different. R2, R3, R4, R5, R6, R7, R8, R9, R10, and R11 are hydrogen atoms, halogen atoms, alkyl groups having 1 to 9 carbon atoms, hydroxyl groups, alkoxy groups having 1 to 9 carbon atoms, alkyleneoxy groups having 1 to 9 carbon atoms, amino groups, alkylamino groups having 1 to 9 carbon atoms, or phenyl groups, and may be the same or different. Any two of R2, R3, R4, R5, R6, R7, R8, R9, R10, and R11 may be bonded to form a saturated hydrocarbon ring having 3 to 6 carbon atoms together with the cyclohexane ring carbon atoms to which they are bonded depicted in formula (i). R2 and R3 may be in a trans or cis configuration.)
Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Examples of alkyl groups having 1 to 9 carbon atoms include methyl groups, ethyl groups, n-propyl groups, and isopropyl groups. Examples of alkoxy groups having 1 to 9 carbon atoms include methoxy groups, ethoxy groups, n-propoxy groups, and isopropoxy groups. Examples of alkylamino groups having 1 to 9 carbon atoms include methylamino groups, ethylamino groups, dimethylamino groups, and diethylamino groups. Examples of alkyleneoxy groups having 1 to 9 carbon atoms include groups represented by the following formulas:

R(R'O)n-
(In the formula, R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R' represents an alkylene group having 2 or 3 carbon atoms, and n represents an integer of 2 to 4, with the proviso that the total number of carbon atoms of R and R' is 9 or less.)
When the alkyleneoxy group having 1 to 9 carbon atoms is a group represented by the above formula, it is preferably H(CH ₂ CH ₂ O) ₂ --, H(CH ₂ CH ₂ O) ₃ --, H(CH ₂ CH ₂ O) ₄ --, CH ₃ (CH ₂ CH ₂ O) ₂ --, CH ₃ (CH ₂ CH ₂ O) ₃ --, CH ₃ (CH ₂ CH ₂ O) ₄ --, CH ₃ CH ₂ (CH ₂ CH ₂ O) ₂ --, CH ₃ CH ₂ (CH ₂ CH ₂ O) ₃ --, (CH ₃ ) ₂ CH(CH ₂ CH ₂ O) ₂ --, (CH ₃ ) ₂ CH(CH ₂ CH ₂ O) ₃ --, H((CH ₃ ) _CHCH O) ₂ -, H((CH ₃ )CHCH ₂ O) ₃ -, CH ₃ ((CH ₃ )CHCH ₂ O) ₂ -, or CH ₃ CH ₂ ((CH ₃ )CHCH ₂ O) ₂ -.

The present invention may further contain 0 to 5000 ppm of a saccharide-based nucleating agent. However, if the content is too high, the odor of the film after retort may become bad, so the content is preferably 2000 to 3000 ppm. In this case, better tearability can be achieved. The saccharide-based nucleating agent includes sorbitol-based, nonitol-based, xylitol-based, and the like. Specifically, bis-1,3:2,4-(3'-methyl-4'-fluoro-benzylidene) 1-propyl sorbitol, bis-1,3:2,4-(3',4'-dimethylbenzylidene) 1'-methyl-2'-propenyl sorbitol, bis-1,3,2,4-dibenzylidene 2',3'-dibromopropyl sorbitol, bis-1,3,2,4-dibenzylidene 2'-bromo-3'-hydroxypropyl sorbitol, bis-1,3:2,4-(3'-bromo-4'-ethylbenzylidene)-1-allyl sorbitol, mono 2,4-(3'-bromo-4'-ethylbenzylidene) 1,2,3-trideoxy-4,6:5,7-bis-[(4-propylphenyl)methylene]-nonitol, bis-1,3:2,4-(4'-ethylbenzylidene) 1-allyl sorbitol, bis-1,3:2,4-(5',6',7',8'-tetrahydro-2-naphthaldehyde benzylidene) 1-allyl xylitol, bis-1,3:2,4-(3',4'-dimethylbenzylidene) 1-propyl xylitol, etc.

Addition of 5 to 20 parts by mass of polypropylene polymer (d) or high melt tension polypropylene (e) to the resin composition of the polypropylene sealant film improves the ease of tearing in all in-plane directions.

If the content of polypropylene-based polymer (d) or high melt strength polypropylene (e) is less than 5 parts by mass, the effect of easy tearing may not be achieved, and if it is more than 20 parts by mass, melt fracture may occur, resulting in a significantly deteriorated appearance.

Polypropylene polymer (d)
The polypropylene polymer (d) is a propylene polymer consisting of two or more propylene polymers with different molecular weights, in which the component with the highest molecular weight (d1 component) has an intrinsic viscosity ([η]d1) of 5 dl/g or more and less than 10 dl/g, and is at least twice the intrinsic viscosity ([η]d) of the entire polypropylene polymer (d). The intrinsic viscosity ([η]d1) of the d1 component, which is the component with the highest molecular weight of this polypropylene polymer (d), must be 5 dl/g or more and less than 10 dl/g. If it is less than 5 dl/g, the improvement of the tearability is insufficient, and if it is 10 dl/g or more, foreign matter may be generated in the film, which is not preferable. If the intrinsic viscosity ([η]d1) of the d1 component is less than twice the intrinsic viscosity ([η]d) of the entire polypropylene polymer (d), the kneadability becomes poor and melt fracture is likely to occur. The proportion of the d1 component in the polypropylene polymer (d) is preferably 3 to 25% by mass (wherein the total of the polypropylene polymer (d) is taken as 100% by mass).

High melt strength polypropylene (e)
The high melt tension polypropylene (e) can be produced by known methods such as imparting long chain branches by electron beam irradiation, imparting long chain branches by modification in an extruder in the presence of peroxide and crosslinking monomer, or improving melt tension by imparting high molecular weight components by multi-stage polymerization. The composition may be any of propylene homopolymer, propylene-ethylene random copolymer, or propylene-ethylene block copolymer (b), but propylene homopolymer type is preferred from the viewpoint of heat resistance.

The MFR of the high melt strength polypropylene (e) at 230°C (load 21.18N) is preferably in the range of 0.1 to 18 g/10 min, and preferably in the range of 0.5 to 9 g/10 min, since this makes it easier to obtain favorable film-forming properties and good compatibility with the propylene-based block copolymer.

It is preferable that the melt tension (230°C) of the high melt tension polypropylene (e) is in the range of 3 to 26 g, since this increases the crystallinity of the film and further improves the ease of tearing.

Addition of 1 to 20% by mass of low-density polyethylene polymer (f) to the resin composition of the polypropylene sealant film further improves low-temperature impact resistance and orange peel resistance.

If the content of low-density polyethylene polymer (f) is less than 1% by mass, the effect of improving low-temperature impact resistance and orange peel resistance may not be obtained, and conversely, if it exceeds 20% by mass, tearability may deteriorate.

The density of the low-density polyethylene polymer (f) is preferably in the range of 0.910 to 0.940 g/ ^cm3 , since it is easily dispersible in the polypropylene resin. If the density of the low-density polyethylene polymer (f) is less than 0.910 g/ ^cm3 , blocking resistance may decrease, and if it is more than 0.940 g/ ^cm3 , low-temperature impact resistance may decrease. In addition, it is preferable to use one produced using a metallocene catalyst from the viewpoint of heat sealability.

Examples of the low-density polyethylene polymer (f) include ethylene alone or a copolymer of ethylene and an α-olefin having 3 or more carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, etc., and those produced by generally known methods can be used. Specifically, high-pressure low-density polyethylene and linear low-density polyethylene can be used, and linear low-density polyethylene is preferred among them because it has higher impact strength and higher heat sealability than high-pressure low-density polyethylene.

Furthermore, it is preferable to contain 1 to 5 parts by mass of high-density polyethylene polymer (g) since this improves low-temperature impact resistance without reducing tearability. If the high-density polyethylene polymer (g) is contained in an amount of more than 5 parts by mass, low-temperature impact resistance will not improve and heat sealability may decrease significantly.

The high-density polyethylene polymer (g) is an ethylene polymer having a density of 0.92 to 0.97 g/cm ³ and an MFR of 1 to 20 g/10 min at 190° C. and a load of 21.18 N, and is preferably an ethylene homopolymer having a density of 0.92 to 0.97 g/cm ³ , more preferably 0.92 to 0.97 g/cm ^3. When the density of the high-density polyethylene polymer (g) is less than 0.92 g/cm ³ , blocking resistance may deteriorate, and when it exceeds 0.97 g/cm ³ , heat sealability may deteriorate.

If the MFR of the high-density polyethylene polymer (g) at 190°C and a load of 21.18 N is less than 1 g/10 min, the transparency may deteriorate. On the other hand, if the MFR exceeds 20 g/10 min, the low-temperature impact resistance may deteriorate.

Furthermore, by adding a thermoplastic elastomer (h) to the resin composition of the polypropylene-based sealant film, the low-temperature impact resistance and heat sealability are further improved.

The above thermoplastic elastomer (h) refers to a high molecular weight material that has rubber elasticity at 25°C due to having a hard segment phase and a soft segment phase, while at the same time, in the temperature range of 100°C to 300°C, which is the general thermoplastic molding temperature range, the hard segment phase exhibits fluidity, making it possible to mold and process it in the same way as general thermoplastic resins. As the thermoplastic elastomer (h), for example, polyester-based elastomers, polyolefin-based elastomers, polyamide-based elastomers, polyurethane-based elastomers, styrene-based elastomers, and polyacrylic-based elastomers can be used alone or in combination. Among them, it is preferable to use polyolefin-based elastomers and hydrogenated styrene-based elastomers from the viewpoint of the heat sealability of the resulting film.

As the polyolefin-based elastomer, propylene-based elastomers and ethylene-based elastomers are preferred.

In addition, if the various properties described above can be satisfied, the polypropylene sealant film of the present invention may be a single layer film, but in order to satisfy all of the properties of easy tearing, heat sealability, blocking resistance, and low-temperature impact resistance, the above resin composition may be used as a base layer (B layer) on at least one side of which a sealing layer (A layer) and a surface layer (C layer) are laminated, forming a composite film consisting of two layers of A layer/B layer or three layers of A layer/B layer/C layer.

In this case, it is preferable that the A layer and the C layer contain the ethylene-propylene block copolymer (b) as the main component. Here, the main component means that it is composed of 50% by mass or more.

If the ethylene-propylene block copolymer (b) is less than 50% by mass, low-temperature impact resistance and heat sealability may deteriorate.

In addition, by combining the ethylene-propylene block copolymer (b) of the A layer and the C layer with the low-density polyethylene polymer (f), the high-density polyethylene polymer (g), and the thermoplastic elastomer (h), it is preferable because the low-temperature impact resistance, heat sealability, and orange peel resistance are improved.

However, if the intrinsic viscosity [η]EP) of the above-mentioned layer A is not 2.8 dl/g or more due to the addition of the low-density polyethylene polymer (f), the heat sealability may be significantly reduced. If the intrinsic viscosity [η] exceeds 3.4 dl/g, the orange peel phenomenon may be more likely to occur. The ethylene content of the xylene-soluble portion is preferably in the range of 20 to 50% by mass. If the content is less than 20% by mass, the low-temperature impact resistance at low temperatures may decrease, and conversely, if it is more than 50% by mass, the tearability and blocking resistance may be insufficient.

The resin composition constituting layers A and C preferably contains 1 to 20% by mass of the low-density polyethylene polymer (f). If the content of low-density polyethylene polymer (f) is less than 1% by mass, the effect of improving low-temperature impact resistance and orange peel resistance may not be obtained, and conversely, if it exceeds 20% by mass, tearability may deteriorate.

Each layer may contain antioxidants, heat stabilizers, neutralizing agents, antistatic agents, hydrochloric acid absorbers, antiblocking agents, lubricants, etc., to the extent that the object of the present invention is not impaired. These additives may be used alone or in combination of two or more.

Specific examples of antioxidants include hindered phenols such as 4-methyl-2,6-di-t-butylphenol (BHT), octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate ("Irganox" 1076, "Sumilizer" BP-76), and tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane ("Irganox" 1010, "Sumilizer" BP-76). "BP-101," tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate ("Irganox" 3114, "Adekastab" AO-20), and the like. Also, as a phosphite (phosphorus) antioxidant, tris(2,4-di-t-butylphenyl)phosphite ("Irgafos" 168, "Adekastab" 2112), tetrakis(2,4-di-t-butylphenyl)-4-4'-biphenylene-diphosphonite ("Sandstab" P -EPQ), bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite ("Ultranox" 626, "Adekastab" PEP-24G), distearyl pentaerythritol diphosphite ("Adekastab" PEP-8), etc., among which 2,4,8,10-tetra-t-butyl-6-[3-(3-methyl-4-hydroxy-5-t-butylphenyl)propionate, which has both the functions of these hindered phenols and phosphites, is particularly preferred. [1-[2-hydroxy-3,5-di-t-pentylphenyl]ethyl]-4,6-di-t-pentylphenyl acrylate ("Sumilizer" GS) are preferred, and the combined use of these two is particularly effective in suppressing the decomposition of the 20°C xylene solubles during film formation, and is preferred because it contributes greatly to achieving both low-temperature impact resistance and blocking resistance. If the decomposition of the xylene solubles is accelerated, blocking resistance may deteriorate.

The amount of antioxidant to be added may vary depending on the type of antioxidant used, but may be set appropriately within the range of 0.05 to 0.3% by mass.

As neutralizing agents, hydrotalcite compounds, hydroxides, etc. are preferred for reducing smoke generation during film formation.

Next, the polypropylene sealant film of the present invention can be produced by known film production methods such as the T-die method and the tubular method, but the T-die method for producing an unstretched film is particularly preferred because it is easy to control the birefringence and crystallinity of the film. The T-die method for producing the film of the present invention is described below, but is not limited to this method.

For example, the sealant film can be produced by mixing and melt-kneading raw materials selected from homopolypropylene (a), ethylene-propylene block copolymer (b), crystal nucleating agent masterbatch (c), polypropylene-based polymer (d), high melt tension polypropylene (e), low density polyethylene-based polymer (f), high density polyethylene (g), and thermoplastic elastomer (h) in a predetermined blending ratio using a single-screw or twin-screw melt extruder, filtering the resulting kneaded mixture through a filter, and extruding it into a film from a flat die (e.g., a T-die). The thickness ratio of each layer is preferably 50/50 to 5/95, more preferably 40/60 to 10/90, and even more preferably 30/70 to 20/80, because it is easy to adjust the tearability, heat sealability, low-temperature impact resistance, and yuzu-peel resistance of the sealant film when the sealant film is composed of a seal layer (A layer) and a base layer (B layer). The temperature of the molten polymer extruded from the melt extruder is usually 180 to 300°C, but in order to prevent polymer decomposition and obtain a good quality film, 200 to 270°C is preferred. The film extruded from the T-die is brought into contact with a cooling roll set at a constant temperature of 20 to 90°C, where it is cooled and solidified, and then wound up.

The film of the present invention may be formed, for example, using a multi-layer lamination die, into a two-layer structure of seal layer (A layer)/base layer (B layer), or a three-layer structure of seal layer (A layer)/base layer (B layer)/surface layer (C layer) laminated with a surface C layer (C layer). The thickness ratio of each layer is preferably seal layer (A layer):base layer (B layer):surface layer (C layer) = 1:2:1 to 1:8:1, and more preferably 1:4:1 to 1:6:1, because this makes it easy to adjust the tearability, heat sealability, and low-temperature impact resistance.

The polypropylene sealant film of the present invention may be stretched after cooling and solidifying, but is preferably a non-stretched film that is not substantially stretched. A non-stretched film that is not substantially stretched is preferable from the viewpoint of heat sealability because it can be torn in all in-plane directions. In the present invention, the non-stretched film refers to an extrusion cast film, but in an actual film-forming process, the film may be slightly oriented in the MD or TD direction of the film. Therefore, it is preferable that the birefringence of the polypropylene sealant film of the present invention (the difference in refractive index between the MD and TD directions of the film, Δn) is in the range of 3.5×10 ⁻³ to 8.0×10 ⁻³ in terms of heat sealability, thermal dimensional stability, and easy tearability. The birefringence (Δn) can be calculated by measuring the retardation R (nm) of a sample using a compensator method and calculating Δn=R/d from the thickness d (nm) of the film at the measurement portion.

The thickness of the film of the present invention thus obtained is preferably 20 to 300 μm, and more preferably 30 to 100 μm.

Here, in the present invention, an example of a method for controlling the birefringence is to melt the mixed resin at a low temperature in the range of 180°C to 270°C, preferably 200°C to 250°C, and then cool it on a casting drum kept at a high temperature of 50°C to 90°C, preferably 50°C to 70°C, and then wind it up at a speed of 10 to 100 m/min.

The polypropylene sealant film of the present invention obtained as described above can be used alone as a packaging film, but is preferably used as a sealant film for retort food packaging bags containing general AL. The constituent films of the laminate can be preferably laminated using an ordinary dry lamination method in which adhesives are used, but if necessary, a method of directly extruding and laminating a polyethylene resin or polypropylene resin can also be used to laminate the film of the present invention and other substrate layers. These laminates are processed into flat bags, standing pouches, etc., with the polypropylene unstretched film used as the sealing layer (inner surface of the bag). For example, the above polypropylene sealant film is laminated to a laminate substrate layer consisting of a 12 μm-thick biaxially oriented polyethylene terephthalate film (PET), a 15 μm-thick biaxially oriented polyamide film (ONy), and a 9 μm-thick aluminum foil (AL) by a dry lamination method using a urethane adhesive to create a laminate with a configuration of PET/adhesive/ONy/adhesive/AL/sealant film. Two sheets of this laminate are placed so that the sealant film forms the inner surface of the bag, and a three-sided pouch with a bag size of 50 mm x 150 mm can be created using a Fuji Impulse CA-450-10 heat sealer with a heating time of 0.8 seconds (sealing temperature: about 180°C) and a cooling time of 3.0 seconds.

The laminate structure of these laminates is appropriately selected according to the required characteristics of the packaging bag (e.g., barrier performance to meet the shelf life of the packaged food, size and low-temperature impact resistance to accommodate the weight of the contents, visibility of the contents, etc.).

The present invention will be specifically explained below with reference to examples, but the scope of the present invention is not limited thereto. In addition, the measured values of each evaluation item in the detailed description of the present invention and the examples were measured by the following methods.

(1) Content of soluble part in xylene at 20°C 5 g of polypropylene pellets were completely dissolved in 500 mL of boiling xylene (Kanto Chemical Co., Ltd. Grade 1), then cooled to 20°C and left for 4 hours or more. The precipitate and solution were then filtered to separate the soluble part and the insoluble part. The soluble part was solidified under reduced pressure, dried at 70°C, and the mass was measured to determine the content (mass%).

(2) Intrinsic Viscosity of the Part Insoluble and Part Soluble in Xylene at 20° C. Using the sample separated by the above method, measurement was carried out in tetralin at 135° C. using an Ubbelohde viscometer.

(3) Melt flow rate (MFR)
According to JIS K7210:1999, the propylene-ethylene block copolymer (b) was measured at a temperature of 230° C., and the polyethylene polymer was measured at a temperature of 190° C., with a load of 21.18 N, respectively.

(4) Melt tension (MS)
The melt tension (MS) at 230°C was measured using a Melt Tension Tester Model 2 manufactured by Toyo Seiki Seisakusho, Ltd., by heating polypropylene to 230°C in the device, extruding the molten polypropylene from a nozzle having a diameter of 2.095 mm at a speed of 20 mm/min into the atmosphere at 23°C to form a strand, and then measuring the tension of the filamentous polypropylene when this strand was taken up at a speed of 3.14 m/min, and this was taken as the melt tension (MS).

(5) Density: Measured by a density gradient tube method based on JIS K7112:1999.

(6) Low-temperature impact resistance PET having a thickness of 12 μm, ONy having a thickness of 15 μm, AL having a thickness of 9 μm, and the film of the present invention having a thickness of 70 μm were bonded together using a urethane-based adhesive by a conventional dry lamination method to prepare a laminate having a thickness of 115 μm and the following structure.

Laminate structure: PET/adhesive/ONy/adhesive/AL/adhesive/film of the present invention. Two sheets of this laminate were placed so that the film of the present invention was on the inner surface of the bag, and a standing pouch with a bag size of 150 mm x 285 mm was made using a Fuji Impulse CA-450-10 type heat sealer with a heating time of 1.4 seconds (sealing temperature: about 220 ° C.) and a cooling time of 3.0 seconds. This bag was filled with 1000 cm ³ of saline solution with a concentration of 0.1%, and then retorted at 135 ° C. for 30 minutes. The bag after the retort treatment was stored in a refrigerator at 0 ° C., and then dropped from a height of 55 cm onto a flat floor surface (n number 20 pieces), and the number of times until the bag broke was recorded. In this evaluation method, if the average value of n number 20 pieces was 5 times or more, the low-temperature impact resistance was good and was marked as ◯, and if it was less than 5 times, it was marked as x.

(7) Heat sealability: Two seal layers of the same laminate as in (6) were heat sealed together using a flat heat sealer under conditions of a sealing temperature of 180°C, a sealing pressure of 10 N/ ^cm2 , and a sealing time of 1 second, and the sample was retorted at 130°C for 30 minutes, after which the heat seal strength was measured at a pulling speed of 300 mm/min using a Tensilon manufactured by Orientec Co., Ltd. If the strength measured by this method was 45 N/15 mm or more, the sample could be used satisfactorily for retort food, and the heat sealability was evaluated as good and ◯, and if it was less than 45 N/15 mm, the heat sealability was evaluated as ×.

(8) Orange peel resistance PET having a thickness of 12 μm, ONy having a thickness of 15 μm, AL having a thickness of 9 μm, and the film of the present invention were laminated together using a urethane-based adhesive by a normal dry lamination method to prepare a laminate having a thickness of 115 μm and the following structure.

Laminate structure: PET/adhesive/ONy/adhesive/AL/adhesive/film of the present invention. Two sheets of this laminate were heat sealed with the film of the present invention on the inner surface of the bag using a flat heat sealer under the conditions of a sealing temperature of 180°C, a sealing pressure of 10 N/ ^cm2 , and a sealing time of 1 second to prepare a three-sided bag (flat bag, seal width 5 mm) with a size of 160 mm x 210 mm (inner dimensions). This bag was filled with commercially available retort curry (House Foods Industry Co., Ltd.'s retort curry "Kukure Curry Hot"), and the occurrence of unevenness on the surface of the laminate immediately after retorting at 135°C for 30 minutes was visually judged. The unevenness was evaluated as rank 1 if no unevenness was observed at all, rank 2 if slight unevenness was observed, rank 3 if slight unevenness was observed, rank 4 if clear unevenness was observed, and rank 5 if severe unevenness was observed. In this evaluation method, ranks 1, 2, and 3 were evaluated as good yuzu peel resistance, and ranks 4 and above were evaluated as x for yuzu peel resistance.

(9) Blocking shear force (N/12 cm ² )
A film sample 30 mm wide and 100 mm long was prepared, and the films were overlapped in an area of 30 mm x 40 mm, and a load of 5 N/12 ^cm2 was applied, followed by heat treatment for 2.0 hours in an oven at 80°C, and then leaving the sample in an atmosphere of 23°C and 65% humidity for 30 minutes or more. The shear peel strength was then measured at a pulling speed of 300 mm/min using a Tensilon manufactured by Orientec Co., Ltd. If the shear peel strength was 10 N/12 cm2 or ^less by this measurement method, the blocking resistance was good and the sample could be used in non-powder retort, so it was rated as ◯, and if it was higher than 10 N/12 ^cm2 , the blocking resistance was rated as x.

(10) Elmendorf tear strength (N/mm)
According to JIS K7128-2:1998 (Elmendorf tear method), the tear strength (N) was measured in the longitudinal direction (MD), width direction (TD), and 45 degrees to the left and right of the MD in a constant temperature room at 23°C, and the tear strength was calculated by dividing by the film thickness (mm). A polypropylene sealant film alone was judged to have easy tearability if it had a tear strength of 30 N/mm or less per film in all in-plane directions.

The components used in the examples and comparative examples are as follows:

[Homopolypropylene (a)/PP1]
The homopolypropylene used had an MFR of 4.0 g/10 min at 230° C. and contained 0.0015% by mass of “Irganox” 1010 as an antioxidant. The homopolypropylene (a) is hereinafter referred to as PP1.
[Propylene-ethylene block copolymer (b)/B-PP1]
A propylene-ethylene block copolymer (b) pellet was used, which had a 20°C xylene insoluble content of 80% by mass, an intrinsic viscosity ([η]H) of 1.90 dl/g, a 20°C xylene soluble content of 15% by mass, an intrinsic viscosity ([η]EP) of 3.00 dl/g, an MFR at 230°C of 2.5 g/10 min, and contained 0.0002% by mass of "Sumilizer" GP and 0.00080% by mass of "Sumilizer" GS as antioxidants. Hereinafter, the propylene-ethylene block copolymer (b) is referred to as B-P1.

[Master batch (c)/MB1 containing a crystal nucleating agent of a metal phosphate]
A masterbatch (PPMST-0024 manufactured by Tokyo Ink Co., Ltd., carrier resin: homopolypropylene (a), MFR: 7 g/10 min) containing 6% by mass of a crystal nucleating agent, sodium 2,2'-methylene-bis(4,6-di-t-butylphenyl)phosphate ("ADEKA STAB" NA-11 manufactured by ADEKA), which is a phosphate metal salt, was used. Hereinafter, the crystal nucleating agent masterbatch of the phosphate metal salt is referred to as MB1(c). [Polypropylene-based polymer (d)/PP2]
Using the polymerization catalyst described in Example 1 of JP-A-11-228629, and following the polymerization method and polymerization conditions described in the same Example, propylene was polymerized in a first step to produce a first component, and then, without deactivating the catalyst, the catalyst and the first component were transferred to a second step, and propylene was polymerized in the second step to produce a component having a molecular weight different from that of the first component, thereby obtaining a polypropylene-based polymer (d) having an overall intrinsic viscosity of 2.0 dl/g, which was composed of 11 mass% of a propylene polymer component having an intrinsic viscosity of 7.6 dl/g and 89 mass% of a component having an intrinsic viscosity of 1.2 dl/g. 100 parts by mass of this polypropylene-based polymer (d) was mixed with 0.2 parts by mass of an antioxidant IRGANOX1010 (trade name, manufactured by Ciba Specialty Chemicals), 0.25 parts by mass of an antioxidant IRGAFOS168 (trade name, manufactured by Ciba Specialty Chemicals), and 0.05 parts by mass of calcium stearate, and melt-mixed at 200°C with a discharge rate of 300 kg/h and a screw rotation speed of 250 rpm using a twin-screw extruder TEM75 (trade name, manufactured by Toshiba Machine Co., Ltd.) to obtain pellets. The MFR of this pellet at 230°C and a load of 21.18 N was 10 g/10 min. Hereinafter, the polypropylene-based polymer (d) is referred to as PP2.

[High melt strength polypropylene (e)/HMS-PP]
EX6000 manufactured by Japan Polypropylene Corporation was used, which has a density of 0.90 g/ ^cm3 , an MFR of 2.9 g/10 min at 230°C and a load of 21.18 N, and a melt tension (MS) of 9 g at 230°C. Hereinafter, it is referred to as HMS-PP(e).

[Low-density polyethylene polymer (f)/low-density PE]
A linear low-density polyethylene (FV201 manufactured by Sumitomo Chemical Co., Ltd.) having a density of 0.925 g/ ^cm3 , MFR of 1.9 g/10 min, and a copolymerization component of 1-hexene was used. The low-density polyethylene polymer (f) is hereinafter referred to as low-density PE1.

[Low density polyethylene polymer (f)/Low density PE2]
A linear low-density polyethylene (SP1071C manufactured by Prime Polymer Co., Ltd.) having a density of 0.910 g/ ^cm3 , MFR of 10.0 g/10 min, and a copolymerization component of 1-hexene was used. The low-density polyethylene polymer (f) is hereinafter referred to as low-density PE2.

[High density polyethylene polymer (g)/High density PE1]
Commercially available high density ethylene pellets were used, which had a density of 0.950 g/ ^cm3 and an MFR of 16.0 g/10 min at 190° C. and a load of 21.18 N. Hereinafter, the high density ethylene pellets are referred to as HDPE1.

[Examples 1 to 25]
The resins in pellet form in the resin compositions of Tables 1 and 2 were mixed in a blender, fed to two or three extruders adjusted to a temperature of 260°C, melt-kneaded, filtered, and then extruded into a film shape by a multi-manifold die for co-extrusion in a single layer, two layers, or three layers, and then cooled and solidified by contacting with a cooling roll at a temperature of 50°C and a speed of 60 m/min. The cooling roll contact surface side was then corona discharge treated to obtain a film with a thickness of 70 μm. In the case of a single-layer film, layer B was 100%, and in the case of a two-layer film, the thickness ratio of layers A and B was 30% for layer A and 70% for layer B. In the case of a three-layer film, the thickness ratio of layers A, B, and C was 20% for layer A, 60% for layer B, and 20% for layer C.

As a result of evaluating the film properties, as shown in Tables 1 and 2, a film was obtained that was well-balanced and satisfactory in all respects, including tear strength in all directions in the plane, low-temperature impact resistance, blocking shear resistance, yuzu-peel resistance, and heat sealability. In particular, it was confirmed that as a laminate, it has excellent tear strength in all directions in the plane, excellent blocking resistance, and can be used without powder as a sealant for packaging bags.

[Comparative Examples 1 to 3, 5, and 6]
The resins in pellet form in the resin compositions of Tables 3 and 4 were mixed in a blender, fed to two or three extruders adjusted to a temperature of 260°C, melt-kneaded, filtered, and then extruded into a film shape by a multi-manifold die for co-extrusion in a single layer, two layers, or three layers, and then cooled and solidified by contacting with a cooling roll at a temperature of 50°C and a speed of 60 m/min. The cooling roll contact surface side was then corona discharge treated to obtain a film with a thickness of 350 μm. In the case of a single-layer film, layer B was 100%, and in the case of a two-layer film, the thickness ratio of layers A and B was 30% for layer A and 70% for layer B. In the case of a three-layer film, the thickness ratio of layers A, B, and C was 20% for layer A, 60% for layer B, and 20% for layer C.

The film properties were evaluated, and the results are shown in Tables 3 and 4. The tear strength in all in-plane directions was not satisfactory.

[Comparative Example 4]
The resins in pellet form with the resin composition shown in Table 3 were mixed in a blender, fed to two or three extruders controlled at a temperature of 260°C, melt-kneaded, filtered, extruded into a single-layer film using a multi-manifold die for coextrusion, cooled and solidified by contacting with a cooling roll at a temperature of 50°C and a speed of 20 m/min, and then the side in contact with the cooling roll was subjected to a corona discharge treatment to obtain a film with a thickness of 350 μm. The obtained film was stretched 5 times in a longitudinal stretching machine to obtain a film with a thickness of 70 μm.

The film properties were evaluated, and the results are shown in Table 3. The tear strength in all in-plane directions was unsatisfactory, and the low-temperature impact resistance and heat sealability were poor.

We provide a polypropylene sealant film that has excellent tearability in all directions within the film plane, and has excellent heat sealability, low-temperature impact resistance, blocking resistance, and orange peel resistance, as well as a laminate using the same.

Claims (8)

A film mainly composed of a polypropylene-based resin,
The polypropylene-based resin is any one of a homopolypropylene (a) which is a propylene homopolymer, an ethylene-propylene block copolymer (b), and a propylene-α-olefin random copolymer with an α-olefin comonomer selected from ethylene, 1-butene, and 1-hexene;
The tear strength per film according to the Elmendorf method in JIS K 7128-2 (1998) is 30 N/mm or less in all in-plane directions;
A polypropylene-based sealant film having a yield stress of 25 MPa or more and 50 MPa or less in all in-plane directions, as measured by the yield stress measurement method in JIS K 7161 (2014) . A film mainly composed of a polypropylene-based resin,
The polypropylene-based resin is any one of a homopolypropylene (a) which is a propylene homopolymer, an ethylene-propylene block copolymer (b), and a propylene-α-olefin random copolymer with an α-olefin comonomer selected from ethylene, 1-butene, and 1-hexene;
The tear strength per film according to the Elmendorf method in JIS K 7128-2 (1998) is 30 N/mm or less in all in-plane directions;
The polypropylene-based sealant film is made of a resin composition containing a polypropylene-based resin as a main component and 1,500 to 10,000 ppm of a crystal nucleating agent;
A polypropylene-based sealant film comprising a base layer made of the above resin composition and a layer mainly composed of an ethylene-propylene block copolymer laminated on at least one side of the base layer. The polypropylene sealant film according to claim 1 or 2, which has a crystallinity of 60% or more as measured by infrared spectroscopy. The polypropylene sealant film according to any one of claims 1 to ³ , wherein the blocking shear strength between heat-sealed surfaces of the polypropylene sealant film after 24 hours at 80°C is 5 N/12 cm2 or less. A polypropylene sealant film according to any one of claims 1 to 4, in which the centerline average roughness (Ra) of at least one surface is 0.25 μm or more. A laminate comprising the polypropylene sealant film according to any one of claims 1 to 5 laminated on one side of a laminate substrate layer comprising a single layer or two or more layers of films laminated together. A pouch produced by heat-sealing two polypropylene sealant films of the laminate according to claim 6 to each other. 8. The pouch of claim 7 , which can be torn open in both the longitudinal and transverse directions to allow removal of the contents.