JP2006212785A - Light barrier film, laminate and container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light barrier film having high impact resistance, prevented from the lowering of heat sealing strength after heat treatment and capable of concealing discoloration at the time of absorption of oxygen even in a case that an oxygen absorbing layer is provided. <P>SOLUTION: The light barrier film 10 comprises: an intermediate layer 11 containing a polypropylene block copolymer, which is composed of a polypropylene component and an elastomer component, and a sunproof agent as main components; and surface layers 12 which are formed on both sides of the intermediate layer 11 and contain the polypropylene block copolymer as a main component and have streak-like elastomer particles dispersed therein. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light-shielding film that blocks light transmission. Moreover, it is related with the laminated body and container which provided the oxygen absorption layer.

Examples of food containers such as cooked rice containers and porridge containers include containers having a container body made of paper or plastic and a lid material for sealing the opening of the container body, flat bags with four-side seals, and bag-like containers such as standing pouches. It is used. As a container lid, for example, a laminate having a sealant layer for heat sealing at the time of container molding and a gas barrier layer for shielding oxygen from entering the container is widely used. As the sealant layer, a layer made of a polyolefin-based resin such as polypropylene or polyethylene is mainly used from the viewpoint of easy heat sealability and chemical resistance (for example, see Patent Document 1).
In food packaging, particularly when reducing the oxygen concentration inside the container, an oxygen absorbing layer containing an iron-based oxygen absorbent is provided inside the container of the gas barrier layer. In this oxygen absorption layer, oxygen inside the container reacts with the iron-based oxygen absorbent to produce iron oxide, thereby reducing the concentration of oxygen inside the container. By these actions, the oxidation of the food is suppressed and the preservability of the food is improved.
JP 2003-103729 A

However, the oxygen absorbing layer containing the iron-based oxygen absorber turns reddish brown when iron oxide is generated. Therefore, in food containers using conventional laminates, discoloration of the oxygen absorbing layer may be visible from the sealant layer side inside the container.
In particular, in containers consisting of a lid and a container body, when the lid is peeled from the container body, the discoloration of the oxygen absorbing layer through the sealant layer on the back of the lid is easily seen compared to a bag-like container. Can do.
In addition, food containers are required to have impact resistance that can withstand impacts when dropped on a floor or the like. In particular, when the content is food, it is refrigerated or frozen to prevent spoilage, so low temperature impact resistance is required.
In addition, food containers filled with food are retorted and sterilized and are sold in the market. The food container is required to have heat resistance enough to withstand the heating during the retort treatment, and specifically, the food container is required to have a small change in heat seal strength before and after the retort without decreasing the heat seal strength after the retort.
The present invention has been made in view of the above circumstances, has high impact resistance, prevents a decrease in heat seal strength after heat treatment, and even when an oxygen absorption layer is provided, discoloration during oxygen absorption is achieved. It aims at providing the light-shielding film which can be concealed. Furthermore, it aims at providing the laminated body and container which are high in impact resistance, the fall of the heat seal intensity | strength after heat processing is prevented, and can discolor the discoloration of an oxygen absorption layer.

The present invention
(1) An intermediate layer containing a polypropylene block copolymer composed of a polypropylene component and an elastomer component and a light-shielding agent as main components, and in which streaky elastomer particles are dispersed,
A light-shielding film having a surface layer formed on both surfaces of the intermediate layer, containing a polypropylene block copolymer as a main component, and having streaky elastomer particles dispersed therein.
(2) The propylene content in the elastomer component in the polypropylene block copolymer is 50 to 80% by mass, and the intrinsic viscosity value of the elastomer component is not more than the value obtained by adding 0.5 to the intrinsic viscosity value of the polypropylene component (1) It is the light-shielding film of description.
(3) A laminate having the light-shielding film according to (1) or (2), an oxygen absorption layer, and a gas barrier layer.
(4) A container having the laminate according to (3), wherein the light-shielding film of the laminate is disposed on the innermost side.

The light-shielding film of the present invention has high impact resistance, prevents a decrease in heat seal strength after heat treatment, and can conceal discoloration during oxygen absorption even when an oxygen absorption layer is provided.
The laminate and container of the present invention have high impact resistance, prevent a decrease in heat seal strength after heat treatment, and can conceal the discoloration of the oxygen absorbing layer. Therefore, when the laminated body is peeled from the container main body, discoloration of the oxygen absorption layer is difficult to see.

(Light-shielding film)
The light-shielding film of the present invention will be described.
As shown in FIG. 1, the light-shielding film 10 of the present invention has an intermediate layer 11 and surface layers 12 and 12 formed on both surfaces of the intermediate layer 11.

[Middle layer]
The intermediate layer 11 is a layer that contains a polypropylene block copolymer and a light-shielding agent 11a as main components and in which streaky elastomer particles 11b are dispersed.
A polypropylene block copolymer consists of a polypropylene component and an elastomer component.
Here, the polypropylene component of the polypropylene block copolymer is homopolypropylene or a propylene-ethylene copolymer having an ethylene unit content of less than 5% by mass. The elastomer component is a component that is more flexible than the polypropylene component, and includes a propylene unit and an ethylene unit and / or an α-olefin unit having 4 to 12 carbon atoms, and the content of the ethylene unit and the α-olefin unit is 5 mass. % Of copolymer.
As the α-olefin in the elastomer component, 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, vinylcyclopentane And vinylcyclohexane. These α-olefins may be used alone or in combination of two or more.
In the elastomer component, a preferable unit copolymerized with the propylene unit is an ethylene unit.

  The polypropylene component and the elastomer component can be separated by the following method. A sample of 2.5 g is put into 250 ml of orthoxylene, stirred while heating, heated to the boiling temperature, and completely dissolved over 30 minutes. After confirming complete dissolution, the mixture is allowed to cool to 100 ° C. or lower while stirring, and is further held for 2 hours in a thermostatic bath maintained at 25 ° C. Thereafter, the xylene-insoluble matter obtained by filtering the precipitated components with a filter paper is the polypropylene component. The xylene-soluble component obtained by evaporating and drying xylene under a nitrogen stream while heating the filtrate is the elastomer component.

  The polypropylene block copolymer used in the present invention has a melt flow rate (hereinafter referred to as “MFR”) measured at a temperature of 230 ° C. and a load of 21.18 N in accordance with JIS K 7210, usually 0.1 to 20 g / 10. Minutes, preferably 0.2 to 15 g / 10 minutes, and more preferably 0.5 to 10 g / 10 minutes.

[Middle layer]
In the intermediate layer 11, streaky elastomer particles 11a are dispersed.
In order to form the streak-like elastomer particles 11a, the compatibility of the elastomer component with the polypropylene component may be increased, and the intrinsic viscosity of the elastomer component and the polypropylene component may be in a specific relationship. In order to increase the compatibility of the elastomer component with the polypropylene component, the propylene content in the elastomer component may be increased. As for the intrinsic viscosity, the intrinsic viscosity of the elastomer component may be the same as or lower than that of the polypropylene component. That is, by increasing the propylene content in the elastomer component, and setting the intrinsic viscosity value of the elastomer component to be equal to or less than the value obtained by adding 0.5 to the intrinsic viscosity of the polypropylene component, a streaky elastomer is formed when the intermediate layer 11 is formed. Particles 11a can be formed.
In the present invention, the fact that the streaky elastomer particles are dispersed means that the form observed in the form observation described later is a streak. The elastomer particles in the film are preferably dispersed in layers in parallel with the film surface. That is, it is preferably elongated in the take-up direction at the time of film production, and the width in the depth direction in FIG. 1 is wider than the width in the vertical direction in FIG.

Specifically, the propylene content in the elastomer component in the polypropylene block copolymer is preferably 50 to 80% by mass, and more preferably 55 to 70% by mass. If the propylene content in the elastomer component is less than 50% by mass, the elastomer component is hardly compatible with the polypropylene component, so that the elastomer component is less likely to be streaked and the impact resistance tends to be low. Further, when the elastomer component is an ethylene-propylene copolymer, the heat seal strength tends to be lowered because the polyethylene portion that is easily heat-shrinkable increases. On the other hand, when the amount exceeds 80% by mass, the flexibility of the elastomer component is lowered, and the impact resistance tends to be lowered.
The intrinsic viscosity [η] of the elastomer component of the polypropylene block copolymer is preferably 3.1 to 3.8 dl / g. When the intrinsic viscosity [η] of the elastomer component is less than 3.1 dl / g, the molecular weight of the elastomer component becomes small and the impact resistance tends to be low. On the other hand, when it exceeds 3.8 dl / g, the elastomer component is less likely to be streaked and the impact resistance tends to decrease. Here, the intrinsic viscosity is a value reflecting the molecular weight of the elastomer component. That is, the intrinsic viscosity increases as the molecular weight of the elastomer component increases, and the intrinsic viscosity decreases as the molecular weight of the elastomer component decreases.
The intrinsic viscosity [η] in the present invention is a value measured at 135 ° C. in decalin.

  The elastomer component content in the polypropylene block copolymer in the mid layer 11 is preferably 20 to 50% by mass, and more preferably 25 to 35% by mass. When the elastomer component content in the polypropylene block copolymer is less than 20% by mass, impact resistance tends to be low. On the other hand, when it exceeds 50 mass%, heat resistance may fall and the heat seal intensity | strength after a retort process may fall.

Furthermore, it is preferable that the elastomer particles having a width of 1 μm or less among all elastomer components in the intermediate layer 11 are 50% or more. If the elastomer particles having a width of 1 μm or less are 50% or more, impact resistance can be further improved.
Here, the width of the elastomer particles in the intermediate layer 11 refers to the width of the streak-like elastomer particles (the length in the thickness direction of the film out of the two lengths perpendicular to the length direction), This is the vertical direction in FIG.
In order to observe the morphology of the elastomer particles, first, a sample is prepared by cutting the polypropylene multilayer film of the present invention in liquid nitrogen in parallel to the film take-off direction at the time of film production. Then, the sample is immersed in xylene and heated to 50 to 60 ° C. in an ultrasonic cleaner to etch and dissolve the components mainly composed of elastomer particles from the fracture surface, thereby removing the traces that fall off. What is necessary is just to observe with a scanning electron microscope. According to this method, the polypropylene-based multilayer film of the present invention is observed, for example, as shown in FIG.
In addition, the morphology of the elastomer particles can be analyzed by image analysis of a photograph obtained by a scanning electron microscope using an image analyzer. Examples of the image analysis apparatus include commercially available products such as a TOSPIX-U type high-precision monitor particle analysis package (manufactured by Toshiba Corporation) and an IMAGE-PRO PLUS apparatus (manufactured by MEDIA CYBERNETICS).

Examples of the light shielding agent 11a included in the intermediate layer 11 include various inorganic pigments such as titanium oxide, nickel oxide, and calcium carbonate, and organic pigments such as phthalocyanine. Among these, titanium oxide is preferable because it is particularly excellent in light-shielding properties and can conceal discoloration of the oxygen absorbent.
As content of the light shielding agent 11a in the intermediate | middle layer 11, it is preferable that it is 3-15 mass%. If the content of the light shielding agent 11a in the intermediate layer 11 is less than 3% by mass, discoloration of the oxygen absorbing layer may not be shielded. In addition, dispersion of the light shielding agent may occur and the appearance may be impaired. When it exceeds 15% by mass, impact resistance tends to be low.

  The thickness of the intermediate layer 11 is preferably 20 to 80 μm. If the intermediate layer 11 is 20 μm or more, the discoloration of the oxygen absorbent can be concealed more. However, if it exceeds 80 μm, the concealability does not increase according to the thickness, which is uneconomical.

[Surface layer]
The surface layer 12 contains a polypropylene block copolymer as a main component, and is a layer in which streaky elastomer particles 12a are dispersed.
As the polypropylene block copolymer in the surface layer 12, the same one as in the intermediate layer 11 can be used. Since the surface layer 12 tends to reduce the heat seal strength, it usually does not contain a light shielding agent, but may contain a light shielding agent.

Further, the intermediate layer 11 and / or the surface layer 12 of the light-shielding film 10 has higher impact resistance and suppresses the generation of distorted skin after retorting, so that an elastomer constituting a polypropylene block copolymer is formed. In addition to the elastomer component derived from the components, it is also preferable to contain other elastomer components.
The other elastomer component may be the same polymer as the elastomer component constituting the polypropylene block copolymer, or may be a different polymer. Specifically, for example, ethylene elastomer such as ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-butene-propylene terpolymer, hydrogenated product of styrene-isoprene-styrene block copolymer Examples thereof include styrene-based elastomers such as (SEPS). Further, the other elastomer component is preferably compliant with JIS K 7210, and the MFR measured at a temperature of 190 ° C. and a load of 21.18 N is preferably 1 to 15 g / 10 minutes, and more preferably 2 to 8 g / 10 minutes. More preferred.
It is preferable that content of the other elastomer component in the intermediate | middle layer 11 and the surface layer 12 is 5-20 mass%. If the content of the other elastomer component is less than 5% by mass, the improvement in impact resistance is small, and if it exceeds 20% by mass, the heat seal strength after the heat treatment may decrease.

  In addition, the intermediate layer 11 and the surface layer 12 of the light-shielding film 10 may contain other resins and additives as necessary. Examples of the additive include an antioxidant, a weather resistance stabilizer, an antistatic agent, a lubricant, an antiblocking agent, an antifogging agent, a dye, a pigment, an oil, and a wax.

  The thickness of the light-shielding film 10 is usually 30 to 100 μm, preferably 40 to 90 μm, and particularly preferably 50 to 80 μm. If the thickness is less than 30 μm, the heat seal strength tends to be low, and if it exceeds 100 μm, the impact resistance tends to be low.

[Film Production Method]
The said light-shielding film 10 is obtained by laminating | stacking each layer using the well-known inflation molding method using the at least 3 extruder, the T-die extrusion molding method, etc. Usually, in the T-die molding method, the die temperature is 220 to 280 ° C. Moreover, cooling temperature is 30-90 degreeC normally, 50-85 degreeC is preferable and 60-80 degreeC is more preferable. If the cooling temperature is less than 30 ° C., it may result in itchy skin after retorting, and if it exceeds 90 ° C., the impact resistance tends to decrease.
Moreover, since the elastomer component of the intermediate layer 11 and / or the surface layer 12 is likely to be more streaked, the light-shielding film 10 is produced using a film forming apparatus in which a polymer filter is provided between the extruder and the die. It is preferable.

  The light-shielding film 10 described above is a layer in which the intermediate layer 11 and the surface layer 12 contain a polypropylene block copolymer as a main component and in which streaky elastomer particles are dispersed. Excellent impact resistance. Further, since the streak-like elastomer particles have many polypropylene portions and are difficult to heat shrink, generation of voids after the heat treatment can be suppressed. Accordingly, it is possible to prevent the heat seal strength from being lowered after the heat treatment. Moreover, since the intermediate layer 11 contains a light-shielding agent, discoloration of the oxygen absorbent can be concealed even when an oxygen absorbing layer is provided.

(Laminate)
Next, the laminated body of this invention is demonstrated.
In FIG. 2, an example of the laminated body of this invention is shown. The laminate 1 includes the above-described light-shielding film 10, the oxygen absorption layer 20, the gas barrier layer 30, and a support 40, and each layer is laminated via an adhesive 50.

[Oxygen absorbing layer]
The oxygen absorption layer 20 is a layer containing an iron-based oxygen absorbent and a thermoplastic resin as main components. Examples of the thermoplastic resin constituting the oxygen absorbing layer 20 include various polyethylenes such as polyethylene produced by a high pressure method, a medium pressure method, and a low pressure method, polyethylene produced using a metallocene catalyst, and ethylene-vinyl acetate copolymer. Various ethylene copolymers such as copolymers, ethylene-methyl acrylate copolymers, ethylene-ethyl acrylate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-methyl methacrylate copolymers Polymers, propylene homopolymer, propylene-ethylene block copolymer, propylene-ethylene random copolymer, various polypropylenes such as polypropylene produced by metallocene catalyst, ethylene-α olefin copolymer, polymethylpentene, ionomer, polystyrene , Polyethylene tele Tallates and a modified product thereof, a thermoplastic elastomer and the like, may be used singly or in combination. Of these, polyethylenes and polypropylenes are preferred.

The iron-based oxygen absorbent constituting the oxygen absorption layer 20 is not particularly limited as long as it causes an oxygen absorption reaction and can be dispersed in a thermoplastic resin. Preferably, an oxygen absorbent comprising a combination of an oxidizable main agent and an auxiliary agent is used.
The iron powder of the main agent is not particularly limited as long as it can cause an oxygen absorption reaction. For example, a part of the surface may already be oxidized, and contains a small amount of other metals. There may be. The iron powder is preferably granular, and examples thereof include iron powder such as reduced iron powder, sprayed iron powder, and electrolytic iron powder, and pulverized and ground products of various irons such as cast iron and steel materials. The average particle size of the iron powder is preferably 1 to 100 μm and more preferably 1 to 80 μm from the viewpoint of ease of handling and oxygen absorption efficiency.

Examples of the auxiliary agent for the oxygen absorbent include substances that promote the oxygen absorption reaction of the main agent, such as metal halides and alkali agents. The metal halide acts catalytically on the oxygen absorption reaction of the main agent. As the metal halide, for example, an alkali metal or alkaline earth metal chloride, bromide or iodide is used, and lithium, sodium, potassium, magnesium, calcium or barium chloride, bromide or iodide is preferred.
The metal halide is used together with the main component iron powder, but is preferably mixed with the iron powder in advance so as not to adhere to the iron powder and easily separate. For example, a method of mixing a metal halide and iron powder using a ball mill, a speed mill, etc., a method of embedding a metal halide in the uneven portion of the iron powder surface, a method of attaching a metal halide to the iron powder surface using a binder A method in which a metal halide aqueous solution and iron powder are mixed and then dried to directly attach the metal halide to the surface of the iron powder can be employed.
0.1-20 mass parts is preferable with respect to 100 mass parts of iron powder, and, as for the compounding quantity of a metal halide, 0.1-5 mass parts is more preferable.

The blending amount of the oxygen absorbent in the oxygen absorbing layer 20 is preferably 10 to 70% by mass, and more preferably 10 to 60% by mass. If the blending amount of the oxygen absorbent is less than 10% by mass, the oxygen absorbing ability is insufficient, and if it exceeds 70% by mass, it becomes difficult to form the oxygen absorbing layer 20, or the oxygen absorbing layer 20 and the gas barrier layer 30 are formed. The adhesive strength tends to decrease.
Further, the oxygen absorbing layer 20 may be provided with various additives such as a color pigment such as titanium oxide, an antioxidant, a slip agent, an ultraviolet ray inhibitor, an antistatic agent and a stabilizer, clay, mica, silica, Fillers such as calcium carbonate, calcium sulfate, barium sulfate, and alumina, deodorizers, and adsorbents such as activated carbon and zeolite may be added.
The thickness of the oxygen absorbing layer is preferably 85 to 200 μm, more preferably 90 to 170 μm. It is also preferable to use “Ageless Omak” manufactured by Mitsubishi Gas Chemical Co., Ltd., which is a commercially available oxygen absorbing film.

[Gas barrier layer]
Examples of the gas barrier layer 30 include a film made of metaxylylene adipamide, saponified ethylene / vinyl acetate copolymer (EVOH), an aluminum foil, an aluminum oxide vapor deposition film, a silica vapor deposition film, and the like.

[Support]
Examples of the support 40 include a biaxially stretched or unstretched polyamide film, a biaxially stretched or unstretched polyethylene terephthalate (PET) film, a polyethylene naphthalate (PEN) film, and a polybutylene terephthalate (PBT) film.

  The method for producing the laminate 1 is not particularly limited. For example, a plurality of layers are simultaneously formed by melt molding such as a water-cooled or air-cooled coextrusion multi-layer inflation method and a co-extrusion multi-layer T-die method, and these are laminated. A method of forming a single layer film or sheet, such as a dry laminating method, and laminating using an adhesive, etc., and one film or sheet, such as an extrusion laminating method, being previously formed. For example, a method in which the other is melt laminated.

Since the laminated body 1 has the gas barrier layer 30, it is possible to prevent oxygen from entering when the laminated body 1 is used as a lid member of the container body.
Moreover, since it has the light-shielding film 10, even when the oxygen absorption layer 20 discolors, the discoloration can be concealed.
Furthermore, since it has the said light-shielding film 10, the fall of the heat resistance after impact resistance and heat processing is prevented.
In addition, the laminated body of this invention is not limited to the said laminated body 1, The support body 40 does not need to be provided.

(container)
The container of the present invention will be described.
FIG. 3 shows an example of the container of the present invention. This container 2 is a so-called standing pouch, and is obtained by heat-sealing the end of the above-described laminate 1 into a shape in which a bottom is formed. In order to make the container 2 easy to open, it is preferable to form a notch in the heat-sealed portion of the upper part of the container 2.
FIG. 4 shows another example of the container of the present invention. In this container 3, the above-described laminated body 1 is provided as a cover material for the container body 3a. In the laminated body 1, the light-shielding film is arrange | positioned at the innermost side. Examples of the container body 3a include a molded product made of paper or plastic and a gas barrier material.
In this container 1, as a method of integrating the laminated body 1 and the container main body 3a, for example, the opening part of the container main body 3a is covered with the laminated body 1, and then the laminated body 1 and the container main body 3a are in contact with each other. There is a method of fusing by thermal fusion, high-frequency fusion, or ultrasonic fusion. Moreover, in this container 1, the layer which consists of an easy-peeling material is laminated | stacked inside the layer of the light-shielding film of this invention which uses the easy-peeling material for the method of setting a melt | fusion condition suitably, or an inner layer of a container. This makes it easy to open.

The container 2 is composed of the laminated body 1, and the container 3 uses the laminated body 1 as a lid for the container body 3a, so that oxygen can be prevented from entering. Moreover, since the laminated body 1 has a light-shielding film, even when an oxygen absorption layer discolors, the discoloration can be concealed. Therefore, when the laminated body is peeled from the container main body, discoloration of the oxygen absorption layer is difficult to see. Furthermore, the light-shielding film has high impact resistance and prevents a decrease in heat seal strength after heat treatment.
Specifically, such a container of the present invention can be suitably used as a food container such as a bean container or a rice container, a medical container, or the like. The shape of the container is not particularly limited, and specifically, any of a two-side sealed bag, a three-side sealed bag, a four-side sealed bag, a pillow packaging bag, a gusset bag, and the like may be used.

(Examples 1-7, Comparative Examples 1-4)
A light-shielding film was obtained using the following resin.
BPP1: MFR at a temperature of 230 ° C., a load of 21.18 N is 1.0 g / 10 min, the proportion of the ethylene-propylene elastomer component is 28% by mass, the intrinsic viscosity of the polypropylene component is 3.4 dl / g, in the ethylene-propylene elastomer Polypropylene block copolymer BPP2 manufactured by Sun Allomer Co., which has a propylene content of 68% by mass and an elastomer component having an intrinsic viscosity of 3.6 dl / g: MFR with a temperature of 230 ° C. and a load of 21.18 N of 1.5 g / 10 min. The proportion of the ethylene-propylene elastomer component is 19% by mass, the propylene content in the ethylene-propylene elastomer is 55% by mass, the intrinsic viscosity of the polypropylene component is 2.5 dl / g, and the intrinsic viscosity of the elastomer component is 3.8 dl / g. Some Sun Allomer Co., Ltd. polypropylene blocks Union

[Film forming]
Table 1 shows the thickness of the intermediate layer (B layer) and the thickness of the outer surface layers (A layer) at a temperature of 230 ° C. using a multi-layer molding machine manufactured by Toshiba Machine Co., Ltd. having an extruder with a diameter of 45 mmφ and a diameter of 65 mmφ. As shown, A / B / A type 2 type 3 layer film was formed. As the light-shielding agent, “trade name: PEX6800 White A” manufactured by Toyo Ink Co., Ltd., which is a masterbatch having a titanium oxide concentration of 60% by mass, was changed as shown in Table 1.

The obtained film was evaluated as follows. The results are shown in Table 1.
[Evaluation of light transmittance]
Based on JIS 7361-1, the light transmittance was measured about visible light region (360-830 nm) using the JASCO Corporation V-550 type ultraviolet and visible spectrophotometer.

[Impact strength]
The film was sampled to a size of 10 cm × 10 cm and left in a thermostatic chamber at −5 ° C. for 2 hours. After that, in this thermostatic chamber, a ½ inch radius strike core was attached to a film impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd., sandwiched between two plate-like sample holders with a circular opening diameter of 50 mm, and tested 10 times. Energy was measured. These impact energy values were divided by the thickness of the film, and the average value of the 10 points was taken as the film impact and used as a measure of impact resistance.

[Heat seal strength]
A 12 μm-thick PET film / adhesive resin / the above film were laminated in this order, and then two sets were laminated so that the above film was on the inside, and heat sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. Bar width 5 mm, sealing temperature 160 ° C., pressurizing at 0.2 MPa for 1 second, direction perpendicular to resin flow direction (MD) during molding.
After conditioning at room temperature for 48 hours, the heat-sealed film was sampled to a width of 15 mm, and the heat-sealed part was broken in a direction to open the heat-sealed part at 180 ° at a tensile speed of 300 mm / min. A tensile load was applied, and the average strength during that time was determined. The average value of the average strength of 7 points was defined as the heat seal strength. In addition, after retorting at 120 ° C. for 30 minutes, the heat seal strength was measured.

[Particle morphology observation]
The obtained film was cut in liquid nitrogen in parallel with the film drawing direction at the time of film production to prepare a sample. The sample was immersed in xylene at a temperature of 40 to 90 ° C. and placed in an ultrasonic cleaner to etch the elastomer component, and then photographed. The photograph was analyzed with a TOSPIX-U type high-precision monitor particle analysis package (manufactured by Toshiba Corporation), and the width of the elastomer particles was measured.
From this observation, it was found that streaky elastomer dispersed particles were formed in the film obtained using BPP1, and the ratio of streaky elastomer dispersed particles having a width of 1 μm or less was 72%. Further, it was found that spherical elastomer dispersed particles were formed on the film obtained using BPP2, and the ratio of the spherical elastomer dispersed particles having a width exceeding 1 μm was 85%.

The films of Examples 1 to 7 having an intermediate layer and a surface layer on which streak-like elastomer particles are formed, and the intermediate layer contains a light-shielding agent, have high impact resistance and a decrease in heat seal strength after heat treatment. Even when an oxygen absorbing layer is provided, discoloration during oxygen absorption can be concealed.
On the other hand, the films of Comparative Examples 1, 2, and 4 having the intermediate layer and the surface layer on which spherical elastomer particles were formed had low impact resistance, and the heat seal strength decreased after the heat treatment. In addition, the film of Comparative Example 3 that does not contain a light-shielding agent has a high light transmittance, and thus cannot discolor the oxygen absorbing layer.

It is sectional drawing which shows an example of the light-shielding film of this invention. It is sectional drawing which shows an example of the laminated body of this invention. It is sectional drawing which shows an example of the container of this invention. It is a perspective view which shows the other example of the container of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminated body 2,3 Container 10 Light-shielding film 11 Intermediate layer 12 Surface layer 20 Oxygen absorption layer 30 Gas barrier layer

Claims (4)

An intermediate layer containing a polypropylene block copolymer composed of a polypropylene component and an elastomer component and a light-shielding agent as main components, and in which streaky elastomer particles are dispersed,
A light-shielding film comprising a surface layer formed on both surfaces of the intermediate layer, containing a polypropylene block copolymer as a main component, and having streaky elastomer particles dispersed therein.   The propylene content in the elastomer component in the polypropylene block copolymer is 50 to 80% by mass, and the intrinsic viscosity value of the elastomer component is not more than a value obtained by adding 0.5 to the intrinsic viscosity value of the polypropylene component. Item 2. The light-shielding film according to Item 1.   A laminate comprising the light-shielding film according to claim 1, an oxygen absorption layer, and a gas barrier layer. A container comprising the laminate according to claim 3, wherein the light-shielding film of the laminate is disposed on the innermost side.

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