JP2017105174A - Multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer film capable of providing a packaging bag excellent in transparency, drop-bag strength and blocking resistance.SOLUTION: There is provided a multilayer film having an intermediate layer between two surface layers and satisfying all of following requirement (1), requirement (2) and requirement (3), wherein the intermediate layer is a layer containing at least two kinds of olefin polymers forming a sea-island type phase separation structure, the surface layer is a layer containing an ethylene-α-olefin copolymer having a constitutional unit derived from ethylene and an α-olefin having 4 to 20 carbon atoms and a propylene polymer (II). Requirement (1): haze is 25% or less. Requirement (2): heat seal strength when the films each other are heat sealed at 200°C is 35 N/15 mm or more. Requirement (3): heat seal strength when the films each other are heat sealed at 170°C is 35 N/15 mm or less.SELECTED DRAWING: None

Description

  The present invention relates to a multilayer film.

  Polypropylene films are widely used in the fields of films, sheets, containers and the like because they are excellent in heat resistance and rigidity, and are also used as heat sterilized food packaging films taking advantage of their properties. In recent years, transparency is also required for heat-sterilized food packaging films so that the packaged contents can be seen. For example, the following patent documents describe films with improved transparency.

  Patent Document 1 is a polypropylene-based laminated film composed of three layers of a surface layer and an intermediate layer, the intermediate layer comprising a polypropylene-based composition composed of crystalline polypropylene and a propylene-α-olefin copolymer, A polypropylene-based laminated film is described in which both surface layers are made of a crystalline propylene-α-olefin copolymer.

  Patent Document 2 includes a laminate layer made of a propylene-α-olefin random copolymer resin and a propylene-ethylene block copolymer resin, an intermediate layer made of propylene-α-olefin random copolymer resin and a propylene-ethylene block copolymer resin, And a laminated polypropylene film composed of a seal layer made of a propylene-α-olefin random copolymer resin and a propylene-ethylene block copolymer resin.

JP 2006-35516 A JP2007-237641

However, the packaging bags made of the above-described film having excellent transparency are not sufficient in dropping bag strength and blocking resistance.
The subject of this invention is providing the multilayer film which can obtain the packaging bag excellent in transparency, bag drop strength, and blocking resistance.

  As a result of intensive studies, the present inventors have found that the above problems can be solved, and have completed the present invention.

The present invention is a multilayer film having an intermediate layer between two surface layers and satisfying all of the following requirements (1), (2) and (3):
The intermediate layer contains at least two types of olefin polymers, and the two types of olefin polymers form a sea-island type phase separation structure,
The surface layer is a layer containing an ethylene-α-olefin copolymer having a structural unit derived from ethylene and a structural unit derived from an α-olefin having 4 to 20 carbon atoms, and a propylene-based polymer (II). This relates to a multilayer film.
Requirement (1): The haze measured according to JIS K7105-1981 is 25% or less.
Requirement (2): The heat seal strength when the films are heat sealed at 200 ° C. is 35 N / 15 mm or more.
Requirement (3): The heat seal strength when the films are heat sealed at 170 ° C. is 35 N / 15 mm or less.

  If the multilayer film of this invention is used, the packaging bag excellent in transparency, bag drop strength, and blocking resistance can be obtained.

The multilayer film of the present invention is a multilayer film having an intermediate layer between two surface layers,
The intermediate layer contains at least two kinds of olefin polymers, and the two kinds of olefin polymers form a sea-island type phase separation structure.
In the present invention, the sea-island type phase separation structure means that at least two types of olefin polymers are phase-separated, one of the olefin polymers forms a continuous phase, and the other olefin polymer is a discontinuous phase. It is the phase-separation structure which forms. The phase separation structure can be observed using a transmission electron microscope. For example, after a test piece including a cross section perpendicular to the film surface is cut out and dyed with ruthenium tetroxide, the test piece can be observed with a transmission electron microscope at a magnification of about 5000 times.
Examples of the olefin polymer contained in the intermediate layer include a propylene polymer and an ethylene polymer.

  The surface layer of the multilayer film of the present invention has an ethylene-α-olefin copolymer (hereinafter referred to as ethylene-α-olefin copolymer) having a structural unit derived from ethylene and a structural unit derived from an α-olefin having 4 to 20 carbon atoms. A layer containing a polymer (E)) and a propylene-based polymer (II).

  The ethylene-α-olefin copolymer (E) is a copolymer having a structural unit derived from ethylene and a structural unit derived from an α-olefin having 4 to 20 carbon atoms. Examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-hexadecene, 1-eicosene, 4- Examples include methyl-1-pentene and 4-methyl-1-hexene. It is a C 4-20 α-olefin, preferably propylene, 1-butene, or 1-hexene. The ethylene-α-olefin copolymer (E) may have two or more structural units derived from an α-olefin having 4 to 20 carbon atoms. The content of structural units derived from ethylene contained in the ethylene-α-olefin copolymer (E) is preferably 75% by weight to 99% by weight, more preferably 80% by weight to 99% by weight. More preferably, it is 90% by weight or more and 99% by weight or less (provided that the total amount of the ethylene-α-olefin copolymer (E) is 100% by weight).

The density of the ethylene -α- olefin copolymer (E) is preferably not 860 kg / ^{m 3} or more 950 kg / ^{m 3} or less, more preferably 880 kg / ^{m 3} or more 930 kg / ^{m 3} or less.

  The melt flow rate of the ethylene-α-olefin copolymer (E) is preferably 0.5 g / 10 min to 30 g / 10 min, more preferably 1 g / 10 min to 10 g / 10 min. More preferably, it is 1 g / 10 min or more and 5 g / 10 min or less. The melt flow rate is a value measured at a temperature of 190 ° C. and a load of 21.18 N according to the method defined in JIS K7210.

  The molecular weight distribution of the ethylene-α-olefin copolymer (E) is preferably 1 or more and less than 3, more preferably 1.5 or more and less than 2.5, from the viewpoint of excellent impact resistance at low temperatures. is there. The molecular weight distribution is the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by gel permeation chromatography (hereinafter sometimes referred to as “GPC”). .

  As a method for producing an ethylene-α-olefin copolymer (E) having a molecular weight distribution of 1 or more and less than 3, for example, a method of copolymerizing ethylene and an α-olefin having 4 to 20 carbon atoms using a metallocene catalyst. Can be mentioned.

  As a method for producing the ethylene-α-olefin copolymer (E), ethylene and an α-olefin having 4 to 20 carbon atoms are copolymerized using a solid catalyst component in which the catalyst component is supported on a particulate carrier. How to do. Examples of the solid catalyst component include a promoter support in which a compound that ionizes a metallocene complex such as an organoaluminum oxy compound, boron compound, or organozinc compound to form an ionic complex is supported on a particulate carrier. Can be used.

  The propylene polymer (II) used for the surface layer is a polymer having a structural unit based on propylene. The propylene polymer (II) is preferably one or more propylene polymers selected from the group consisting of a propylene homopolymer (C) and an ethylene-propylene copolymer (D), preferably a propylene homopolymer. It is a mixture of the polymer (C) and the ethylene-propylene copolymer (D).

The ethylene-propylene copolymer (D) is a copolymer composed of a structural unit derived from propylene and a structural unit derived from ethylene.
The content of the structural unit derived from propylene contained in the propylene copolymer (D) is preferably 94% by weight or more and 99% by weight or less, and more preferably 94% by weight or more and 97% by weight or less. The content of structural units derived from ethylene contained in the propylene copolymer (D) is preferably 1% by weight to 6% by weight, more preferably 3% by weight to 6% by weight (provided that The total amount of the ethylene-propylene copolymer (D) is 100% by weight).

As a method for producing the propylene polymer (II), propylene is homopolymerized by using a Ziegler-Natta type catalyst or a metallocene catalyst, or one or more olefins selected from olefins other than propylene are combined with propylene. The method of superposing | polymerizing etc. is mentioned. The Ziegler-Natta type catalyst includes a catalyst system using a combination of a titanium-containing solid transition metal component and an organometallic component. Examples of the metallocene catalyst include a catalyst system using a combination of a transition metal compound of Group 4 to Group 6 having at least one cyclopentadienyl skeleton and a promoter component.
Examples of the polymerization method include a slurry polymerization method and a solution polymerization method performed in an inert hydrocarbon solvent, and a liquid phase polymerization method and a gas phase polymerization method performed in the absence of a solvent.

  The content of the ethylene-α-olefin copolymer (E) contained in the surface layer is preferably 5% or more from the viewpoint of excellent transparency of the multilayer film and surface state after heat treatment of the composite film. The content of the ethylene-α-olefin copolymer (E) contained in the surface layer is preferably 20% by weight or less from the viewpoint of excellent heat sealability, blocking resistance, and impact resistance at low temperatures, More preferably, it is 15% by weight or less (provided that the total content of the ethylene-α-olefin copolymer (E) and the propylene polymer (II) contained in the surface layer is 100% by weight).

When the propylene-based polymer (II) in the surface layer is a mixture of a propylene homopolymer (C) and an ethylene-propylene copolymer (D), the propylene homopolymer (C) contained in the surface layer is contained. The amount is preferably 50% by weight or more and 85% by weight or less, more preferably 65% by weight or more and 85% by weight or less, and still more preferably 65% by weight or more and 75% by weight or less from the viewpoint of excellent heat sealability and blocking resistance. The total content of propylene homopolymer (C), ethylene-propylene copolymer (D) and ethylene-α-olefin copolymer (E) contained in the surface layer is 100% by weight or less. %).
The content of the ethylene-propylene copolymer (D) contained in the surface layer is preferably 10% by weight or more and 30% by weight or less, more preferably 15% by weight from the viewpoint of excellent heat sealability and blocking resistance. % Of the content of the propylene homopolymer (C), ethylene-propylene copolymer (D) and ethylene-α-olefin copolymer (E) contained in the surface layer. The total is 100% by weight).

Requirement (1)
The multilayer film of the present invention has a haze measured according to JIS K7105-1981 of 25% or less, preferably 20% or less, more preferably 15% or less.

Requirement (2)
The multilayer film of the present invention has a heat seal strength of 35 N / 15 mm or more, preferably 40 N / 15 mm or more and 80 N / 15 mm or less when the films are heat sealed at 200 ° C.

Requirement (3)
The multilayer film of the present invention has a heat seal strength of 35 N / 15 mm or less, preferably 15 N / 15 mm or less, more preferably 10 N / 15 mm or less when the films are heat sealed at 170 ° C.

  The intermediate layer is preferably a propylene polymer (A) in which the content of structural units derived from propylene is 95% by weight or more (provided that the total amount of the propylene polymer (A) is 100% by weight), ethylene Ethylene-propylene copolymer (B) in which the content of structural units derived from is 20 wt% or more and 60 wt% or less (provided that the total amount of ethylene-propylene copolymer (B) is 100 wt%); It is a layer containing.

  The propylene polymer (A) is a propylene homopolymer (A-1) or the following propylene copolymer (A-2). The propylene homopolymer (A-1) is a homopolymer composed of structural units derived from propylene.

  The propylene polymer (A) is preferably a propylene homopolymer (A-1).

The propylene copolymer (A-2) is a copolymer composed of a structural unit derived from propylene and a structural unit derived from ethylene or an α-olefin having 4 to 12 carbon atoms. Examples of the α-olefin having 4 to 12 carbon atoms include 1-butene, 1-hexene, 1-octene, and the like, and preferably 1-butene. The propylene copolymer (A-2) may have two or more structural units derived from ethylene or an α-olefin having 4 to 12 carbon atoms.
The content of the structural unit derived from propylene in the propylene copolymer (A-2) is preferably 95% by weight or more, more preferably 98% by weight or more (provided that the propylene-based copolymer (A- The total amount of 2) is 100% by weight). The content of structural units derived from ethylene or an α-olefin having 4 to 12 carbon atoms in the propylene copolymer (A-2) is preferably 5% by weight or less, more preferably 2% by weight or less ( However, the total amount of the propylene copolymer (A-2) is 100% by weight).

  The ethylene-propylene copolymer (B) is a copolymer composed of a structural unit derived from ethylene and a structural unit derived from propylene. The content of the structural unit derived from ethylene in the ethylene-propylene copolymer (B) is preferably 20% by weight or more and 60% by weight or less from the viewpoint of excellent blocking resistance and impact resistance at low temperature. It is preferably 25% by weight or more and 50% by weight or less (provided that the total amount of the ethylene-propylene copolymer (B) is 100% by weight). The content of structural units derived from propylene in the ethylene-propylene copolymer (B) is 40% by weight to 80% by weight, preferably 50% by weight to 75% by weight (provided that ethylene- (The total amount of the propylene copolymer (B) is 100% by weight.)

  The intrinsic viscosity ([η] B) of the ethylene-propylene copolymer (B) is preferably 2.5 dl / g or more and 4.5 dl from the viewpoint of suppressing the number of fish eyes while maintaining excellent heat seal strength. / G or less, more preferably 3.5 dl / g or more and 4.5 dl / g or less.

  The ratio ([η] B / [η] A) of the intrinsic viscosity ([η] B) of the ethylene-propylene copolymer (B) to the intrinsic viscosity ([η] A) of the propylene polymer (A) is excellent. It is preferably 1.0 or more and 3.0 or less, more preferably 1.5 or more and 3.0 or less, from the viewpoint that the number of fish eyes can be suppressed while maintaining the heat seal strength.

  The content of the propylene polymer (A) contained in the intermediate layer is preferably 60% by weight or more and 90% by weight or less, more preferably from the viewpoint of excellent balance between heat sealability, blocking resistance and bag drop strength. Is not less than 65% by weight and not more than 90% by weight, more preferably not less than 65% by weight and not more than 85% by weight, particularly preferably not less than 65% by weight and not more than 75% by weight (provided that the weight of propylene contained in the intermediate layer) (The total content of the union (A) and the ethylene-propylene copolymer (B) is 100% by weight.) The content of the ethylene-propylene copolymer (B) contained in the intermediate layer is preferably 10% by weight or more and 40% by weight or less from the viewpoint of excellent balance between heat sealability, blocking resistance and bag drop strength. More preferably, it is 10 wt% or more and 35 wt% or less, more preferably 15 wt% or more and 35 wt% or less, particularly preferably 25 wt% or more and 35 wt% or less (however, in the intermediate layer) The total content of the propylene polymer (A) and the ethylene-propylene copolymer (B) contained is 100% by weight.

  When the intermediate layer contains the propylene polymer (A) and the ethylene-propylene copolymer (B), a propylene polymer comprising the propylene polymer (A) and the ethylene-propylene copolymer (B). The melt flow rate of the combined composition is preferably 1.5 g / 10 min or more and 10 g / 10 min or less, more preferably 2 g / 10 min, from the viewpoint of improving the processability and hygiene of the film. It is 8 g / 10 minutes or less. The melt flow rate is a value measured at a temperature of 230 ° C. and a load of 21.18 N according to the method defined in JIS K7210.

Examples of the production method of the propylene polymer (A) and the ethylene-propylene copolymer (B) include a method of polymerizing propylene and ethylene as raw materials using a Ziegler-Natta catalyst or a metallocene catalyst. It is done. For example, a method of polymerizing in an inert solvent such as hexane, heptane, toluene, xylene, a method of polymerizing in liquid propylene or ethylene, a method of polymerizing by adding a catalyst to gas propylene or ethylene, or these The method of superposing | polymerizing combining these methods is mentioned.
From the viewpoint of productivity, the propylene polymer (A) and the ethylene-propylene copolymer (B) are preferably produced in the first step and then in the second step. It is preferable to produce the ethylene-propylene copolymer (B) by phase polymerization.
As a method for adjusting the ethylene content in the propylene polymer (A) and the ethylene-propylene copolymer (B), a method of adding a molecular weight regulator such as hydrogen gas or a metal compound and ethylene in each step during the polymerization, The method of adjusting the temperature, pressure, etc. is mentioned.
In order to remove a residual solvent of propylene as a raw material, an ultra-low molecular weight oligomer generated as a by-product during production, drying may be performed at a temperature lower than the temperature at which polypropylene melts. Examples of the drying method include the methods described in JP-A Nos. 55-75410 and 2565753.

  The intermediate layer may further contain an ethylene-α-olefin copolymer (F) having a structural unit derived from ethylene and a structural unit derived from an α-olefin having 4 to 20 carbon atoms. Examples of the ethylene-α-olefin copolymer (F) include the copolymers described as the ethylene-α-olefin copolymer (E).

  When the intermediate layer contains a propylene polymer (A), an ethylene-propylene copolymer (B), and an ethylene-α-olefin copolymer (F), the bag drop strength and processability are excellent. From the above, the total content of the propylene polymer (A) and the ethylene-propylene copolymer (B) is preferably 70% by weight to 98% by weight, more preferably 70% by weight to 95% by weight. More preferably 75 wt% or more and 95 wt% or less (provided that the ethylene-α-olefin copolymer (F), the propylene polymer (A) and the ethylene-propylene copolymer contained in the intermediate layer) The total content of (B) is 100% by weight). The content of the ethylene-α-olefin copolymer (F) is preferably 2% by weight or more and 30% by weight or less, more preferably 5% by weight or more and 30% by weight from the viewpoint of excellent bag drop strength and workability. %, More preferably 5% by weight or more and 23% by weight or less (provided that the ethylene-α-olefin copolymer (F), the propylene polymer (A) and the ethylene-propylene contained in the intermediate layer) The total content of the copolymer (B) is 100% by weight).

The intermediate layer and the surface layer may contain additives and other resins.
Examples of the additive include an antioxidant, a neutralizer, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an adhesive, an antifogging agent, an antiblocking agent, and a melt flow rate adjusting agent. Examples of the antioxidant include a phenolic antioxidant, a phosphorus antioxidant, and a sulfur antioxidant. In addition, a composite type antioxidant that functions as a phenol-based antioxidant and a phosphorus-based antioxidant can also be used.
Examples of other resins that may be contained in the intermediate layer include styrene-butadiene-styrene copolymers, styrene-isoprene-styrene copolymers, and hydrogenated products thereof.
Other resins that may be contained in the surface layer include high-density polyethylene, low-density polyethylene, and ethylene-α-olefin copolymer having a structural unit content derived from α-olefin of more than 10% by weight (provided that The total amount of the ethylene-α-olefin copolymer is 100% by weight), and these are produced with a homogeneous catalyst such as a metallocene catalyst, even if they are produced with a heterogeneous catalyst. Examples thereof include styrene-butadiene-styrene copolymers, styrene-isoprene-styrene copolymers, and hydrogenated products thereof.

Each polymer contained in the intermediate layer and the surface layer may be previously melt-kneaded by the following known method to form a composition. For example, each component and various additives are mixed using a mixing apparatus such as a Henschel mixer, a ribbon blender, a tumble mixer, and then melt-kneaded;
After a homogeneous mixture is obtained by continuously supplying each component and various additives at a constant ratio using a fixed amount feeder, the mixture is supplied to a single-screw or twin-screw extruder, Banbury. Examples thereof include a melt kneading method using a mixer, a roll kneader or the like.

  The temperature during the melt kneading is preferably 180 ° C. or higher and 350 ° C. or lower. More preferably, it is 180 degreeC or more and 320 degrees C or less.

  The ethylene-α-olefin copolymer (E) contained in the intermediate layer in the multilayer film of the present invention and the ethylene-α-olefin copolymer (F) contained in the surface layer are the same or different. It may be.

  The ratio of the thickness of the intermediate layer in the multilayer film of the present invention is preferably 45% or more and 85% or less, more preferably from the point that the bag fall strength and transparency are excellent and the surface layer can be prevented from peeling from the intermediate layer. 55% or more and 85% or less (provided that the thickness of the multilayer film is 100%).

  The thickness of the multilayer film of the present invention is preferably 5 μm or more and 500 μm or less, and more preferably 30 μm or more and 150 μm or less.

  As a manufacturing method of the multilayer film of this invention, a well-known film manufacturing method is mentioned, For example, a T-die method, a tubular method, etc. are mentioned. The method for producing the multilayer film of the present invention is preferably a T-die method.

  In the multilayer film of the present invention, as a method of laminating the intermediate layer and the surface layer, a method of combining molten resins flowing from a plurality of extruders in layers in a die and a molten resin flowing from a plurality of extruders are separated. Can be fed into the manifold and combined in layers just before the lip of the die.

  The multilayer film of the present invention may be subjected to surface treatment such as corona discharge treatment, flame treatment, plasma treatment, ozone treatment and the like.

  Applications of the multilayer film of the present invention include packaging applications and the like, for example, packaging applications for foods, fibers, sundries and the like. Preferably, it is for retort food packaging. For retort food packaging, it can be used in retort food packaging bags.

  The multilayer film of the present invention is also excellent in heat resistance and heat sealability. In addition, the composite film of the present invention has few irregularities (hereinafter sometimes referred to as “Yuzu skin”) on the film surface that occurs after heat treatment.

  The multilayer film of the present invention may be a composite film in which a gas barrier layer and a base material layer are laminated.

  Examples of the gas barrier layer include an ethylene-vinyl alcohol copolymer, an organic silicon compound, an inorganic layered compound, a layer containing a metal or a metal oxide, and preferably an ethylene-vinyl alcohol copolymer or an organic silicon compound. It is a layer containing.

  Examples of the base material layer include a biaxially stretched polyester resin layer, a biaxially stretched polyamide resin layer, and a biaxial polyolefin resin layer. Of these, the substrate layer may be a multilayer of two or more.

Examples of the method of laminating the multilayer film of the present invention, the gas barrier layer, and the base material layer include a dry laminating method and an extrusion laminating method.
Applications of the composite film include heavy goods packaging applications.

Hereinafter, the present invention will be described using examples and comparative examples. In addition, the measured value of each item in an Example and a comparative example was measured with the following method.
(1) Content of propylene polymer (A) and ethylene-propylene copolymer (B) contained in the propylene polymer composition (unit:% by weight)
From the material balance during the polymerization of the propylene polymer (A) and the ethylene-propylene copolymer (B), the content of the propylene polymer (A) (P _A ) and the content of the ethylene-propylene copolymer (B) (P _B ) was obtained.

(2) Content of structural units derived from ethylene in the ethylene-propylene copolymer (B) (unit:% by weight)
The IR spectrum of the propylene polymer composition was measured, and the propylene polymer composition was determined according to “(ii) Method for Block Copolymer” described on page 616 of the Polymer Analysis Handbook (1995, published by Kinokuniya). The content of structural units derived from ethylene in the product was determined, and the content of structural units derived from ethylene in the ethylene-propylene copolymer (B) was determined from the following formula (1).
E _B = 100 E _T / P _B Formula (1)
(However, the content of the structural unit E _T is derived from ethylene in the propylene polymer composition, E _B is an ethylene - propylene copolymer content of structural units derived from ethylene in (B), P _B Indicates the content of the ethylene-propylene copolymer (B).)

(3) Melt flow rate (MFR, unit: g / 10 minutes)
The melt flow rates of the propylene polymer composition, the propylene homopolymer, and the ethylene-propylene copolymer were measured at a temperature of 230 ° C. and a load of 21.18 N according to the method defined in JIS K7210. The melt flow rate of the ethylene-α-olefin copolymer was measured at a temperature of 190 ° C. and a load of 21.18 N in the method defined in JIS K7210.

(4) Density (Unit: kg / m ³ )
The density of the ethylene-α-olefin copolymer was measured according to the method defined in Method A of JIS K7112-1980. The sample was annealed according to JIS K6760-1995.

(5) Molecular weight distribution (Mw / Mn)
The weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured by gel permeation chromatography (GPC) under the following conditions to obtain Mw / Mn. The baseline on the chromatogram is a stable horizontal region with a sufficiently long retention time than the appearance of the sample elution peak and a stable horizontal region with a sufficiently long retention time than the solvent elution peak was observed. A straight line formed by connecting the points.
Apparatus: Waters 150C manufactured by Waters
Separation column: TOSOH TSK-GEL GMH6-HT
Measurement temperature: 140 ° C
Carrier: Orthodichlorobenzene Flow rate: 1.0 mL / min Injection volume: 500 μL
Detector: Differential refraction Molecular weight reference material: Standard polystyrene

(6) Intrinsic viscosity of propylene polymer (A) ([η] A (unit: dL / g))
[Η] A was measured in a tetralin at 135 ° C. using a Ubbelohde viscometer after extracting the polymer powder from the polymerization tank after the polymerization of (A).

(7) Polymerization ratio of ethylene-propylene copolymer (B) to propylene polymer composition (χ (unit:% by weight))
After the sample was poured into an aqueous sulfuric acid solution (1 mol / liter), the metal component was extracted by applying ultrasonic waves, and the obtained liquid portion was quantified by ICP emission spectrometry to measure the magnesium content of each polymer. Χ was calculated from the following equation.
χ = 1−Mg (T) / Mg (P)
Mg (P): Magnesium content of propylene polymer (A)
Mg (T): Magnesium content of propylene copolymer comprising propylene polymer (A) and ethylene-propylene copolymer (B)

(8) Intrinsic viscosity of ethylene-propylene copolymer (B) ([η] B (unit: dL / g))
The intrinsic viscosity ([η] T) of a propylene polymer composition comprising a propylene polymer (A) and an ethylene-propylene copolymer (B) is measured at 135 ° C. in tetralin using an Ubbelohde viscometer. did. Polymerization ratio (χ) of the obtained [η] T, [η] A obtained in the above (6), and the ethylene-propylene copolymer (B) obtained in the above (7) to the propylene polymer composition From this, [η] B was determined by the following equation.
[Η] B = [η] T / χ− (1 / χ−1) [η] A
[Η] A: Intrinsic viscosity of propylene polymer (A) (dL / g)
[Η] T: Intrinsic viscosity (dL / g) of a propylene polymer composition comprising a propylene polymer (A) and an ethylene-propylene copolymer (B)
χ: polymerization ratio of ethylene-propylene copolymer (B) to propylene polymer composition (% by weight)

(9) Haze (Unit:%)
It measured according to JIS K7105. The lower the haze, the better the transparency.

(10) Heat seal strength (unit: N / 15mm)
Using a heat sealer manufactured by Toyo Tester Kogyo Co., Ltd., the multilayer films were heat sealed under the following conditions.
Seal bar: Heating on both sides of the surface Sealing temperature: 200 ° C, 170 ° C
Seal pressure: 1.0 kg / cm ²
Sealing time: 1.0 sec
Seal width: 10mm
For a sample obtained by heat sealing, a test piece having a width of 15 mm was cut out in a direction perpendicular to the seal width direction. Next, the heat seal strength of the test piece was measured at a peeling angle of 90 ° and a tensile speed of 200 mm / min using a tensile tester (Orientec Tensilon).
The lower the heat seal strength when heat sealed at a seal temperature of 170 ° C., the better the heat resistance.

(11) Permeability The multilayer film was placed 10 cm away from the paper on which the characters were printed, and whether the characters printed through the multilayer film could be read was determined according to the following four criteria.
1 ... Characters can be clearly read.
2 ... Characters are slightly blurred but can be read.
3 ... The characters are totally blurred, and some characters cannot be read.
4 ... Most characters are unreadable.

(12) Bag drop strength evaluation Standing pouch made by Seibu Kikai Co., Ltd. using a composite film in which a multilayer film, a biaxially stretched nylon film with a thickness of 7 μm, and a polyethylene terephthalate film with a thickness of 12 μm are bonded together by a dry laminating method Using a bag machine, a packaging bag having a multilayer film surface on the inside and heat-sealed on three sides was produced. After filling the obtained packaging bag with 200 g of water, one side that was not heat-sealed was heat-sealed and sealed to prepare a water-filled bag. After the water-filled bag was conditioned at 5 ° C. for 24 hours, the test was carried out by repeatedly dropping the filled bag 20 times from a height of 70 cm. The test was performed with a total of 10 bags, and the falling bag strength was evaluated based on the total number of times of no cracking (remaining number of times). 200 points were given when no cracks occurred, and 0 points were given when all cracks were made.

(13) Yuzu skin evaluation (12) After filling the packaging bag produced in the above-mentioned (12) bag drop strength evaluation with “bon curry gold dry” (trade name) manufactured by Otsuka Foods Co., Ltd., heat seal one side that was not heat sealed. And sealed to prepare a curry filled bag. Using an ALP small retort sterilizer, the curry-filled bag is retorted for 30 minutes under the condition of 120 ° C. Method for visual judgment.
1 ... Yuzu skin is not generated at all.
2 ... Yuzu skin is slightly generated, but there is no problem in practical use.
3 ... Some yuzu skin is observed, and there are some problems in practical use.
4 ... Yuzu skin is slightly observed, and there is a problem in practical use.
5 ... Yuzu skin is considerably observed and cannot be practically used.

(14) Blocking resistance (unit: N / 12 cm ² )
Using a multilayer film of 150 mm × 30 mm (collected so that the film forming direction and the long side direction coincide with each other), the seal layers of the multilayer film were overlapped, and a load of 500 g was applied to a range of 40 mm × 30 mm. Conditioning was performed at 24 ° C. for 24 hours. Thereafter, the multilayer film is left in an atmosphere of 23 ° C. and 50% humidity for 30 minutes or more, peeled off at a rate of 200 mm / min using a tensile tester manufactured by Toyo Seiki, and the strength required for peeling the sample ( That is, the blocking strength was measured. The lower the blocking strength, the better the blocking resistance.

(15) Impact strength (unit: kJ / m)
At −15 ° C., the impact strength of the multilayer film was measured using a film impact tester manufactured by Toyo Seiki, using a hemispherical impact head having a diameter of 15 mm. The higher the impact strength, the better the impact resistance.

Each component used in Examples and Comparative Examples is as follows.
[Propylene polymer composition (1)]
Using a Ziegler-Natta type catalyst, propylene is polymerized in the gas phase in the first step, and then in the second step, propylene and ethylene are copolymerized in the gas phase, and the propylene polymer (A) and ethylene- A propylene polymer composition comprising the propylene copolymer (B) was obtained. The resulting propylene polymer composition had a propylene polymer (A) content of 68 wt%, [η] A of 1.73 dl / g, and an ethylene-propylene copolymer (B) content of 30 wt%. %, [Η] B was 4.28 dl / g, and the content of structural units derived from ethylene in the ethylene-propylene copolymer (B) was 30% by weight.
With respect to 100 parts by weight of the obtained propylene polymer composition, 0.005% by weight of calcium hydroxide, Sumizer GP (2,4,8,10-tetra-t-butyl-6- [3- (3-methyl -4-hydroxy-5-t-butylphenyl) propoxy] dibenzo [d, f] [1,3,2] dioxaphosphine, manufactured by Sumitomo Chemical Co., Ltd.) 0.075% by weight, Sumitomo Chemical Co., Ltd. Sumilyzer GS (2,4-di-t-amyl-6- [1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl] phenyl acrylate, manufactured by Sumitomo Chemical Co., Ltd.) 0.03 An appropriate amount of 2,5-dimethyl-2,5-di (tertiary-butylperoxy) hexane as a weight% and melt flow rate adjusting agent was mixed with a Henschel mixer, and then melt-extruded and pelletized. The melt flow rate measured at 230 degreeC of the obtained pellet was 2.5 g / 10min. Hereinafter, it may be referred to as BCPP1.

[Propylene polymer composition (2)]
Using a Ziegler-Natta type catalyst, propylene is polymerized in the gas phase in the first step, and then in the second step, propylene and ethylene are copolymerized in the gas phase, and the propylene polymer (A) and ethylene- A propylene polymer composition comprising the propylene copolymer (B) was obtained. The obtained propylene polymer composition had a propylene polymer (A) content of 79% by weight, [η] A of 2.77 dl / g, and an ethylene-propylene copolymer (B) content of 21% by weight. %, [Η] B was 2.77 dl / g, and the content of structural units derived from ethylene in the ethylene-propylene copolymer (B) was 35% by weight.
With respect to 100 parts by weight of the resulting propylene polymer composition, 0.05% by weight of calcium stearate, 0.05% by weight of vitamin E and 2,5-dimethyl-2,5di (tertiary-butyl) as a melt flow rate modifier A suitable amount of peroxy) hexane was mixed with a Henschel mixer, and then melt-extruded and pelletized. The melt flow rate measured at 230 degreeC of the obtained pellet was 2 g / 10min. Hereinafter, it may be referred to as BCPP2.

[Propylene homopolymer (1)]
Propylene was polymerized in the gas phase using a Ziegler-Natta type catalyst to obtain a propylene homopolymer. To 100 parts by weight of the resulting propylene homopolymer, 0.002% by weight of calcium hydroxide and 0.15% by weight of Irganox 1010 (manufactured by BASF) were mixed with a Henschel mixer, and then melt-extruded to produce pellets. Turned into. The melt flow rate measured at 230 degreeC of the obtained pellet was 8.0 g / 10min. Hereinafter, it may be referred to as HPP.

[Ethylene-propylene copolymer (1)]
Using a Ziegler-Natta type catalyst, ethylene and propylene were copolymerized in the gas phase to obtain an ethylene-propylene copolymer. Content of the structural unit derived from ethylene of the obtained ethylene-propylene copolymer was 4.0% by weight.
Calcium stearate 0.045% by weight, Irganox 1010 (manufactured by BASF) 0.2% by weight, Irgaphos 168 (manufactured by BASF) 0.03% by weight with respect to 100 parts by weight of the obtained ethylene-propylene copolymer Further, an appropriate amount of 2,5-dimethyl-2,5-di (tertiary-butylperoxy) hexane as a melt flow rate modifier was mixed with a Henschel mixer, and then melt-extruded and pelletized. The melt flow rate measured at 230 ° C. of the obtained pellet was 3.3 g / 10 min. Hereinafter, it may be referred to as RPP.

[Ethylene-α-olefin copolymer (1)]
Sumikacene E FV405 (trade name) (manufactured by Sumitomo Chemical Co., Ltd.), which is an ethylene-1-hexene copolymer, was used. The melt flow rate measured at 190 ° C. was 3.8 g / 10 min, the density was 924 kg / m ³ , and the molecular weight distribution (Mw / Mn) was 2.2. Hereinafter, it may be referred to as PE1.

[Ethylene-α-olefin copolymer (2)]
Toughmer A4085s (trade name) (manufactured by Mitsui Chemicals, Inc.), which is an ethylene-butene copolymer, was used. The melt flow rate measured at 190 ° C. was 3.6 g / 10 min, the density was 885 kg / m ³ , and the molecular weight distribution (Mw / Mn) was 1.9. Hereinafter, it may be referred to as PE2.

[Ethylene-α-olefin copolymer (3)]
Sumikacene L FS240 (trade name) (manufactured by Sumitomo Chemical Co., Ltd.), which is an ethylene-butene copolymer, was used. The melt flow rate measured at 190 ° C. was 2.2 g / 10 min, the density was 920 kg / m ³ , and the molecular weight distribution (Mw / Mn) was 3.4. Hereinafter, it may be referred to as PE3.

[Example 1]
As the resin composition for the intermediate layer, a mixture obtained by pellet blending 80% by weight of the propylene polymer composition (1) and 20% by weight of the ethylene-α-olefin copolymer (1) is used. A mixture obtained by pellet blending 70% by weight of the homopolymer (1), 20% by weight of the ethylene-propylene copolymer (1) and 10% by weight of the ethylene-α-olefin copolymer (1) was used.
One of the three extruders using a metal filter with a filtration accuracy of 40 μm is used to melt and knead the mixture, and the two are melt-kneaded with the surface layer resin composition. (Die width 1250 mm, lip opening 0.8 mm), and melt extrusion was performed at a die temperature of 240 ° C. so that the intermediate layer ratio was 60%.
The extruded molten film was cooled and solidified with a chill roll rotating at 50 m / min and having a cooling temperature of 50 ° C. to obtain a multilayer film having a thickness of 70 μm. Table 1 shows the content of each component contained in the surface layer and the intermediate layer of the multilayer film. The haze of the film was measured using the obtained multilayer film. The intermediate layer of the obtained multilayer film formed a sea-island type phase separation structure.
Subsequently, the obtained multilayer film, a biaxially stretched nylon film having a thickness of 7 μm, and a polyethylene terephthalate film having a thickness of 12 μm were laminated by a dry lamination method to obtain a composite film. The heat seal strength of the multilayer film was measured using this composite film.
Further, a 15 cm × 18 cm packaging bag was prepared using this composite film, and 200 g of water was sealed therein to obtain a water-filled bag. Using this water-filled bag, the falling bag strength was evaluated.
In addition, “bon curry gold dry” (trade name) manufactured by Otsuka Foods Co., Ltd., which is a commercially available retort food, was enclosed in the packaging bag to obtain a curry filled bag. Yuzu skin evaluation was performed using this curry filling bag. The results are shown in Table 2.

[Example 2]
A multilayer film was obtained and evaluated in the same manner as in Example 1 except that 100% by weight of the propylene polymer composition (2) was used as the intermediate layer resin composition. The results are shown in Table 2. The intermediate layer of the obtained multilayer film formed a sea-island type phase separation structure.

[Example 3]
As in Example 1, except that a mixture obtained by pellet blending 95% by weight of propylene polymer composition (2) and 5% by weight of ethylene-α-olefin copolymer (2) was used as the intermediate layer resin composition. A multilayer film was obtained by the method described above and evaluated. The results are shown in Table 2. The intermediate layer of the obtained multilayer film formed a sea-island type phase separation structure.

[Example 4]
As the resin composition for the intermediate layer, 100% by weight of the propylene polymer composition (1) was used, and as the resin composition for the surface layer, 90% by weight of the propylene homopolymer (1) and the ethylene-α-olefin copolymer (1 ) A multilayer film was obtained and evaluated in the same manner as in Example 1 except that a mixture obtained by pellet blending of 10% by weight was used. The results are shown in Table 2. The intermediate layer of the obtained multilayer film formed a sea-island type phase separation structure.

[Example 5]
As in Example 4, except that a mixture obtained by pellet blending 95% by weight of propylene polymer composition (1) and 5% by weight of ethylene-α-olefin copolymer (2) was used as the intermediate layer resin composition. A multilayer film was obtained by the method described above and evaluated. The results are shown in Table 2. The intermediate layer of the obtained multilayer film formed a sea-island type phase separation structure.

[Example 6]
As the resin composition for the intermediate layer, 100% by weight of the propylene polymer composition (1) was used, and as the resin composition for the surface layer, 90% by weight of the propylene homopolymer (1) and the ethylene-α-olefin copolymer (3 ) A multilayer film was obtained and evaluated in the same manner as in Example 1 except that a mixture obtained by pellet blending of 10% by weight was used. The results are shown in Table 2. The intermediate layer of the obtained multilayer film formed a sea-island type phase separation structure.

[Comparative Example 1]
A film was obtained and evaluated in the same manner as in Example 1 except that 100% by weight of the ethylene-propylene copolymer (1) was used as the intermediate layer resin composition and the surface layer resin composition. It was. The results are shown in Table 2. The obtained film did not form a sea-island type phase separation structure.

[Comparative Example 2]
As the resin composition for the intermediate layer and the resin composition for the surface layer, 70% by weight of the propylene homopolymer (1), 20% by weight of the ethylene-propylene copolymer (1), and the ethylene-α-olefin copolymer (1 ) A film was obtained and evaluated in the same manner as in Example 1 except that a mixture obtained by pellet blending of 10% by weight was used. The obtained film did not form a sea-island type phase separation structure.

[Comparative Example 3]
A film was obtained and evaluated in the same manner as in Example 1, except that 100% by weight of the propylene polymer composition (1) was used as the intermediate layer resin composition and the surface layer resin composition. . The obtained film formed a sea-island type phase separation structure.

[Comparative Example 4]
A film was obtained and evaluated in the same manner as in Comparative Example 3 except that 100% by weight of the propylene homopolymer (1) was used as the surface layer resin composition. The intermediate layer of the obtained film formed a sea-island type phase separation structure.

[Comparative Example 5]
The same method as in Comparative Example 3 except that a mixture obtained by pellet blending 75% by weight of propylene homopolymer (1) and 25% by weight of ethylene-α-olefin copolymer (1) was used as the resin composition for the surface layer. A film was obtained and evaluated. The obtained film formed a sea-island type phase separation structure.

[Comparative Example 6]
As the intermediate layer resin composition and the surface layer resin composition, a mixture obtained by pellet blending 90% by weight of propylene homopolymer (1) and 10% by weight of ethylene-α-olefin copolymer (1) was used. Were obtained by the same method as in Example 1 and evaluated. The results are shown in Table 2. The obtained film did not form a sea-island type phase separation structure.

Claims (7)

A multilayer film having an intermediate layer between two surface layers and satisfying the following requirements (1), (2) and (3):
The intermediate layer contains at least two types of olefin polymers, and the two types of olefin polymers form a sea-island type phase separation structure,
The surface layer is a layer containing an ethylene-α-olefin copolymer having a structural unit derived from ethylene and a structural unit derived from an α-olefin having 4 to 20 carbon atoms, and a propylene-based polymer (II). Is a multilayer film.
Requirement (1): The haze measured according to JIS K7105-1981 is 25% or less.
Requirement (2): The heat seal strength when the films are heat sealed at 200 ° C. is 35 N / 15 mm or more.
Requirement (3): The heat seal strength when the films are heat sealed at 170 ° C. is 35 N / 15 mm or less. The intermediate layer is
A propylene polymer (A) in which the content of structural units derived from propylene is 95% by weight or more (provided that the total amount of the propylene polymer (A) is 100% by weight);
Ethylene-propylene copolymer (B) in which the content of structural units derived from ethylene is 20 wt% or more and 60 wt% or less (provided that the total amount of ethylene-propylene copolymer (B) is 100 wt%) And a layer containing
The content of the propylene polymer (A) contained in the intermediate layer is 60 wt% or more and 90 wt% or less, and the content of the ethylene-propylene copolymer (B) is 10 wt% or more and 40 wt%. (However, the total content of the propylene polymer (A) and the ethylene-propylene copolymer (B) contained in the intermediate layer is 100% by weight),
The surface layer propylene polymer (II) is one or more propylene polymers selected from the group consisting of a propylene homopolymer (C) and an ethylene-propylene copolymer (D),
The content of the ethylene-α-olefin copolymer contained in the surface layer is 5% by weight or more and 20% by weight or less, and the content of the propylene-based polymer (II) is 80% by weight or more and 95% by weight or less. (However, the total content of the ethylene-α-olefin copolymer and the propylene polymer (II) contained in the surface layer is 100% by weight). The intermediate layer further contains an ethylene-α-olefin copolymer (F) having a structural unit derived from ethylene and a structural unit derived from an α-olefin having 4 to 20 carbon atoms,
The content of the ethylene-α-olefin copolymer (F) contained in the intermediate layer is 2% by weight or more and 30% by weight or less,
The multilayer film according to claim 2, wherein the total content of the propylene polymer (A) and the ethylene-propylene copolymer (B) contained in the intermediate layer is 70 wt% or more and 98 wt% or less. The total content of the ethylene-α-olefin copolymer (F), the propylene polymer (A) and the ethylene-propylene copolymer (B) contained in the intermediate layer is 100% by weight).   The multilayer film according to any one of claims 1 to 3, wherein the thickness ratio of the intermediate layer is 45% or more and 85% or less when the thickness of the multilayer film is 100%. The multilayer film as described in any one of Claims 1-4 which satisfies the following requirements (1 ').
Requirement (1 ′): The haze measured according to JIS K7105-1981 is 15% or less. A composite film comprising the multilayer film according to any one of claims 1 to 5, a gas barrier layer, and a base material layer,
A composite film in which the gas barrier layer is a layer containing an ethylene-vinyl alcohol copolymer, an organic silicon compound, an inorganic layered compound, a metal or a metal oxide.   The composite film according to claim 6, wherein the base material layer is at least one layer selected from the group consisting of a biaxially stretched polyester resin layer, a biaxially stretched polyamide resin layer, and a biaxially stretched polyolefin resin layer. .