JP2005193609A - Multi-layer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layer film which has characteristics such as impact resistance including low temperature impact resistance, anti-blocking properties, transparency, and heat seal properties while keeping heat resistance necessary for a packaging material for pouch-packed food and is optimal for packaging pouch-packed food by retort treatment. <P>SOLUTION: The multi-layer film 1 includes (I) a layer 2 comprising a high density polyethylene resin 940-970 kg/m<SP>3</SP>in density, a soft polymer 800-900 kg/m<SP>3</SP>in density, and an anti-blocking agent, (II) a layer 3 comprising linear low density polyethylene 920-945 kg/m<SP>3</SP>in density and a soft polymer 800-900 kg/m<SP>3</SP>in density not containing a nucleating agent, and (III) a layer 4 comprising linear low density polyethylene 920-945 kg/m<SP>3</SP>in density. A substrate layer 5 can be laminated on the layer 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a multilayer film that can be used as a packaging material for packaging retort foods and the like.

  As a packaging material for retort food, for example, a laminated film obtained by laminating a polyolefin resin sealant layer on a base film such as polyamide (nylon) resin or polyester resin is widely used. Since such a retort food is subjected to a heat sterilization treatment (retort treatment) at a temperature of about 120 ° C. for about 30 minutes, the sealant layer of the laminated film as a packaging material also has heat resistance equal to or higher than the temperature, It was necessary to select a resin material having a high melting point. Therefore, a resin material having a high melting point such as a polypropylene resin or a high density polyethylene resin has been used for the sealant layer of the laminated film.

  However, if polypropylene resin or high-density polyethylene resin is used as the resin material for the sealant layer, the low-temperature impact resistance will be insufficient, and the bag may be broken during transportation at low temperatures. Such a phenomenon is remarkable when the size of the bag is increased and the weight of the entire contents is increased. In addition, since these resin materials have a high melting point, there are many cases where heat sealing properties are not sufficient, and there is a problem that bag breakage is likely to occur due to so-called seal omission.

  On the other hand, a laminated film having a sealant layer made of linear low-density polyethylene having good transparency, low-temperature impact resistance, and heat-sealing properties has also been studied. However, since the linear low density polyethylene has a low melting point of about 125 ° C., the sealant layers are heat-sealed during the retort treatment performed under the above-described conditions, resulting in poor opening and removal of the contents. It was difficult. In addition, there has been a problem that the film is whitened during the retort treatment, resulting in poor transparency.

  In contrast, the sealant layer is composed of a resin composition containing a high density polyethylene resin, a soft polymer and an antiblocking agent (AB agent), and the intermediate layer is made of a linear low density polyethylene resin such as a sorbitol derivative. There has been provided a multilayer sealant film for lamination formed by adding a nucleating agent (for example, Patent Document 1). This multi-layer sealant film for laminating prevents the whitening of the film after retorting by adding a nucleating agent to the linear low-density polyethylene resin that constitutes the intermediate layer, and as a resin material that constitutes the sealant layer. By adding an anti-blocking agent in addition to a mixture of a high-density polyethylene resin and a soft polymer, heat fusion at the time of retort treatment is prevented, and heat sealability at low temperatures is to be ensured.

Japanese Patent No. 3410219 (Claim 1, FIG. 1)

  However, the sealant film for laminating disclosed in Patent Document 1 is inferior in impact resistance of the entire film while adding a nucleating agent as an intermediate layer to suppress whitening of the film after retorting. In addition, the required properties as packaging materials for retort foods that require retort processing have not always been satisfactory.

  Accordingly, the object of the present invention is to maintain the heat resistance, which is a required characteristic of packaging materials for packaging retort foods, while also having impact resistance (including impact resistance at low temperatures), anti-blocking properties, transparency, and heat sealability. It is providing the multilayer film optimal for the packaging use of the retort foodstuff which has various characteristics, such as these, and requires the heat sterilization process (retort process) around 120 degreeC.

In order to achieve the above object, the multilayer film of the present invention includes the following three layers (I) to (III).
(I) and high density polyethylene resin having a density of 940~970kg / ^{m 3,} a layer comprising a soft polymer density 800~900kg / ^{m 3,} and from the anti-blocking agent,
(II) and linear low density polyethylene having a density of 920~945kg / ^{m 3,} density becomes such a soft polymer 800~900kg / ^{m 3,} and a layer containing no nucleating agent,
(III) Layer composed of linear low density polyethylene having a density of 920 to 945 kg / m ³

In the multilayer film of the present invention, the (II) layer constituting the film is blended with a linear low density polyethylene having a specific range of density and a soft polymer having a specific range of density. Since the composition does not contain an agent, it has excellent impact resistance (including impact resistance at low temperatures, hereinafter the same), and the transparency of the film is also good.
In addition, as the (I) layer sandwiching the (II) layer, a high density polyethylene resin having a specific range of density is used, and a soft polymer and an antiblocking agent having a specific range of density are blended, In addition to excellent heat resistance, heat fusion properties are improved, and low temperature sealing properties can be improved.
And since the linear low density polyethylene whose density is a specific range is used as the (III) layer, the impact resistance and transparency of the film can be maintained. .
Accordingly, a film having various properties such as heat resistance, impact resistance, anti-blocking property, transparency, and heat sealability can be suitably provided as the entire multilayer film.

  And the multilayer film of this invention provided with such various characteristics can provide the multilayer film optimal for the packaging use of the retort food which requires the heat sterilization process (retort process) around 120 degreeC.

The multilayer film of the present invention contains 5 to 30% by mass of a soft polymer and 0.4 to 5% by mass of an antiblocking agent with respect to the above-mentioned (I) layer, and is soft with respect to the (II) layer. It is preferable to contain 5-30 mass% of polymers.
According to the present invention, the content of the soft polymer and the antiblocking agent constituting the (I) layer, and the content of the soft polymer constituting the (II) layer are set in specific ranges, respectively. The heat resistance, impact resistance, and low-temperature sealability can be further improved.

In the multilayer film of the present invention, the soft polymer is preferably an ethylene / α-olefin copolymer and / or a styrene / diene copolymer, or a hydrogenated product thereof.
According to the present invention, since the kind of the soft polymer constituting the (I) layer and / or the (II) layer is specified, the impact resistance characteristics can be further improved.

  In the multilayer film of the present invention, the layer thickness ratio r of the multilayer film represented by the following formula (X) is preferably 0.08 to 0.5, and is in the range of 0.12 to 0.4. Is particularly preferred.

  According to this invention, since the layer thickness ratio of the multilayer film is in a specific range, the heat resistance and impact resistance of the multilayer film can be further improved.

The multilayer film of the present invention is preferably a laminate sealant film.
As described above, the multilayer film of the present invention is a film having various properties such as heat resistance, impact resistance, anti-blocking property, transparency, heat sealability, etc., and thus a laminate for packaging various retort foods and the like. It can be suitably used as a sealant film.

The multilayer film (laminated film) of the present invention is biaxially stretched nylon, biaxially stretched polyethylene terephthalate, biaxially stretched polypropylene, ethylene-vinyl alcohol copolymer, aluminum foil (aluminum foil) with respect to the layer (III). It is preferable to laminate a base material layer composed of one or more selected from the group consisting of the above.
According to the present invention, since a specific base material layer is laminated on the (III) layer of the multilayer film, the multilayer film has a high mechanical strength, a high barrier property, a surface printability, etc. Various effects can be imparted.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an embodiment of the multilayer film 1 of the present invention. In FIG. 1, 1 is a multilayer film, 2 is a (I) layer that is a sealant layer, 3 is a (II) layer that is a base layer, and 4 is a (III) layer that is a laminate layer. As shown in FIG. 2, the (I) layer 2 and the (III) layer 4 are arranged on both sides of the (II) layer 3 and sandwiched.

(I) Layer 2:
(I) Layer 2 is the innermost layer when the multilayer film 1 of the present invention is used as a packaging material for retort foods. When the multilayer film 1 is made into a bag, the (I) The layer 2 is used as a sealant layer, and (I) layers 2 to be the sealant layers are heat-sealed.
Moreover, in the multilayer film 1 of this invention, this (I) layer 2 consists of a resin composition comprised from a high density polyethylene-type resin, a soft polymer, and an antiblocking agent.

(I) The high-density polyethylene resin constituting the layer 2 can impart heat resistance to the (I) layer 2 or the multilayer film 1 and has a density of 940 to 970 kg / m ³ , preferably 940 to 960 kg. / M ³ . If the density of the high-density polyethylene resin is within such a range, the sealant layer 2 can be provided with heat resistance, low-temperature impact properties, and sealing properties, while if the density is less than 940 kg / m ³ , the heat resistance When the density exceeds 970 kg / m ³ , the impact resistance at low temperatures and the low-temperature sealability may deteriorate.
The melt flow rate of the high-density polyethylene resin (hereinafter sometimes referred to as “MFR” may be 1.18 N, measured at a temperature of 190 ° C. in accordance with JIS K7210, hereinafter the same) is 0.1 to 10 g. / 10 minutes is sufficient, and it is preferably 1 to 5 g / 10 minutes.

As such a high-density polyethylene-based resin, for example, “Hi-Zex (registered trademark) 3300F” (made by Mitsui Chemicals, Inc., density 950 kg / m ³⁾ , melt flow rate (abbreviated as MFR, hereinafter the same) is used. 1.1 g / 10 min) and “J-Rex (registered trademark) KL471A (manufactured by Nippon Polyolefin Co., Ltd., density 956 kg / m ³ , MFR 2 g / 10 min)” are commercially available. Good.

  In addition, what is necessary is just to mix | blend content of the high density polyethylene-type resin with respect to the whole (I) layer 2 as the remainder of the soft polymer and antiblocking agent which are mentioned later.

Moreover, the soft polymer which comprises the (I) layer 2 can generally improve impact resistance and low temperature sealing performance. As a resin material that can be used as a soft polymer, a resin material having a density of 800 to 900 kg / m ³ , preferably 850 to 900 kg / m ³ , for example, an ethylene-propylene copolymer (including amorphous), Examples thereof include resin materials such as ethylene / α-olefin copolymers such as ethylene-butene copolymers, low crystalline ethylene-butene 1 copolymers, styrene / diene copolymers, or hydrogenated products thereof. One kind can be used alone, or two or more kinds can be used in combination. As the (I) layer 2 constituting the multilayer film 1 of the present invention, it is particularly preferable to use an ethylene / α / olefin copolymer.

In addition, as such a soft polymer, for example, “Tuffmer (registered trademark) P0280” (manufactured by Mitsui Chemicals, Ltd., density: 867 kg / m ³ , MFR: 5.4 g / 10 min) and “Tuffmer ( (Registered trademark) A4085 (Mitsui Chemicals, density 885 kg / m ³ , MFR 3.6 / 10 min) is commercially available, and these may be used.

  (I) The content of the soft polymer with respect to the layer 2 is preferably 5 to 30% by mass, and particularly preferably 5 to 15% by mass. If the content of the soft polymer is less than 5% by mass, the impact resistance and low temperature sealing properties may not be sufficiently improved. On the other hand, if the content of the soft polymer exceeds 30% by mass, the heat resistance and anti-resistance The blocking property may be insufficient.

  And the antiblocking agent which comprises the (I) layer 2 can suppress blocking of the sealant layer 2, and can prevent the heat seal | fusing of the sealant layers 2 at the time of a retort process. There is no restriction | limiting in particular as an antiblocking agent which can be used, What is necessary is just to use 1 type of silica, synthetic silica, diatomaceous earth, talc, and mica individually or in combination of 2 or more types.

  (I) The content of the antiblocking agent with respect to the layer 2 is preferably 0.4 to 5% by mass, particularly preferably 0.8 to 3% by mass. When the content of the anti-blocking agent is less than 0.4% by mass, the anti-blocking property may be insufficient. On the other hand, when the content of the anti-blocking agent exceeds 5% by mass, the transparency and impact resistance of the multilayer film 1 are obtained. May adversely affect sex.

(B) (II) Layer 3:
The (II) layer 3 in the multilayer film 1 of the present invention also serves as a base layer of the multilayer film 1 and is composed of a linear low density polyethylene and a soft polymer.
(II) The linear low-density polyethylene constituting the layer 3 imparts transparency and impact resistance at low temperatures to the multilayer film 1 and may be of a multisite catalyst system, A single site catalyst system may also be used.
In addition, since the (II) layer which comprises the multilayer film 1 of this invention does not contain a nucleating agent, the impact resistance of the multilayer film 1 can be maintained in a favorable state.

The density of the linear low density polyethylene is 920 to 945 kg / m ³ , preferably 930 to 945 kg / m ³ . If the density of the linear low density polyethylene constituting the (II) layer 3 is within such a range, the heat resistance and impact resistance can be imparted to the (I) layer 2, while the density is 920 kg / If it is smaller than m ³ , heat resistance may be insufficient, and if the density exceeds 945 kg / m ³ , impact resistance may be deteriorated.
In addition, as MFR of a linear low density polyethylene, it may be about 0.1-10 g / 10min, and it is preferable to set it as 1-5 g / 10min.

As such a linear low density polyethylene, for example, “MORETECH (registered trademark) 0278G” (manufactured by Idemitsu Petrochemical Co., Ltd., density 938 kg / m ³ , MFR 2.0 g / 10 min) as a trade name, "More Tech (registered trademark) 0168N (produced by Idemitsu Petrochemical Co., Ltd., density 934 kg / m ³ , MFR 1.0 / 10 min.) Obtained with a multi-site catalyst, as well as a metallocene catalyst. Since things etc. are marketed, you may make it use these.
In addition, what is necessary is just to let content of the linear low density polyethylene with respect to the (II) layer 3 be the remainder of the soft polymer mentioned later.

The soft polymer constituting the (II) layer 3 is the same resin material as the soft polymer constituting the (I) layer 2 described above, that is, the density is 800 to 900 kg / m ³ , preferably 850 to 900 kg / m ³ resin material, for example, an ethylene / α-olefin copolymer such as ethylene-propylene copolymer or ethylene-butene copolymer, a styrene / butadiene copolymer, or a hydrogenated product thereof. be able to.

  (II) The content of the soft polymer with respect to the layer 3 is preferably 5 to 30% by mass, and particularly preferably 5 to 15% by mass. If the content of the soft polymer is less than 5% by mass, the impact resistance modification effect may not be sufficient. On the other hand, if the content of the soft polymer exceeds 30% by mass, the heat resistance and anti-blocking properties are insufficient. There is a case.

(III) Layer 4:
The (III) layer 4 is also a laminate layer in the multilayer film 1 of the present invention, and the linear low-density polyethylene constituting the above-described (II) layer 3, that is, a density of 920 to 945 kg / m ³ , Preferably, a linear low density polyethylene of 930 to 945 kg / m ³ can be suitably used.

  In addition, with respect to the resin materials constituting the (I) layer 2, (II) layer 3 and (III) layer 4 described above, an antioxidant and resin adhesion prevention are within the range not impeding the effects of the present invention. Additives such as an agent, an antibacterial agent, a freshness-keeping agent, and a colorant can be appropriately blended as necessary. These additives are blended as processing aids and functionality-imparting additives, and can improve the film forming processability of the multilayer film 1.

  The thickness of the entire multilayer film 1 of the present invention is preferably in the range of 30 to 150 μm, particularly preferably 50 to 100 μm.

  In the multilayer film 1 of the present invention, the layer thickness ratio r of the multilayer film 1 represented by the following formula (X) is preferably in the range of 0.08 to 0.5, preferably 0.12 to 0.4. A range is particularly preferred.

When the layer thickness ratio r of the multilayer film 1 is within such a range, the film has both heat resistance and impact resistance. On the other hand, if the layer thickness ratio r is smaller than 0.08, the (I) layer 2 is too thin with respect to the entire multilayer film 1, and the heat resistance of the multilayer film 1 may not be sufficient. On the other hand, if the layer thickness ratio r of the multilayer film 1 exceeds 0.5, the (I) layer 2 will be too thick and the impact resistance may not be sufficient.
In order to obtain such a layer thickness ratio, the ratio of (I) layer 2 / (II) layer 3 / (III) layer 4 should be 1/1/1 to 1/11/1. Is preferable, and 1/2/1 to 1/6/1 is particularly preferable.

  In order to prepare the multilayer film 1 of the present invention using the constituent materials of the respective layers described above, the (I) layer 2, (II) layer 3 and (III) layer 4 constituting the film 1 are separately produced. After film formation, the multilayer film 1 may be formed by laminating by means such as a known dry laminating method, but it is preferable to simultaneously form the constituent layers by a known coextrusion film forming method. As such a film forming means, a forming method such as a multi-layer inflation co-extrusion film forming method or a T-die cast co-extrusion film forming method used for normal multi-layer film forming can be employed.

The multilayer film 1 of the present invention thus obtained can be used as a laminate sealant film that is most suitable for retort food packaging applications that require heat sterilization treatment (retort treatment) at around 120 ° C.
Here, as an application form, a bag-like application form formed by heat-sealing the (I) layers 2 of the multilayer film 1 around each other, or using the multilayer film 1 as a sealant base material for a container lid. Various application forms are possible.

According to the multilayer film 1 of this embodiment described above, there are the following effects.
(1) Since the multilayer film 1 of the present invention has the specific configuration as described above for the (I) layer 2, (II) layer 3 and (III) layer 4 forming the film, Films with various properties such as heat resistance, impact resistance (including impact resistance at low temperatures), anti-blocking properties, transparency, heat sealability, etc. can be suitably provided, and heat sterilization treatment at around 120 ° C It becomes the multilayer film 1 optimal for the packaging use of the retort food which requires (retort process).

(2) 5 to 30% by mass of a soft polymer and 0.4 to 5% by mass of an antiblocking agent are contained with respect to (I) layer 2, and 5 with respect to (II) layer 3. If it is made to contain -30 mass%, the above-mentioned heat resistance, impact resistance and low temperature sealing property of the multilayer film 1 can be further improved.

(3) Furthermore, if the soft polymer that is a constituent material of the multilayer film 1 is a hydrogenated ethylene / α-olefin copolymer and / or styrene / diene copolymer, the impact resistance of the multilayer film 1 Can be further improved.

(4) If the layer thickness ratio r of the multilayer film 1 represented by the formula (I) is in the range of 0.08 to 0.5, preferably 0.12 to 0.4, Heat resistance and impact resistance can be further improved.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications and improvements within a scope that can achieve the object of the present invention are included in the present invention.
For example, in the above-described embodiment, an example in which the multilayer film 1 including the (I) layer 2, the (II) layer 3 and the (III) layer 4 is used alone as shown in FIG. Without being limited thereto, as shown in FIG. 2, another base material layer 5 may be laminated on the surface of the (III) layer 4 of the multilayer film 1.

  Examples of the material constituting the other base material layer 5 include biaxially stretched nylon (ONY), biaxially stretched polyethylene terephthalate (OPET), biaxially stretched polypropylene (OPP), aluminum foil (aluminum foil), ethylene- Examples thereof include vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), paper, and nonwoven fabric. These base material layers 5 may be a single layer, or may be a multilayer body in which two or more of these are combined. By laminating the base material layer 5 on the multilayer film 1 of the present invention, various effects such as high mechanical strength, high barrier properties, and surface printability can be imparted to the multilayer film 1.

  As an example of the aspect which laminated | stacked the base material layer 5 on the multilayer film 1, biaxially-stretched nylon (ONY) which is the base material layer 5 with respect to (III) layer 4 of the multilayer film 1 or the base material layer 5 The aspect which laminated | stacked the laminated body of a certain biaxially-stretched polyethylene terephthalate (OPET) and aluminum foil (aluminum foil) is mentioned. Alternatively, a laminate of biaxially stretched polyethylene terephthalate (OPET), biaxially stretched nylon (ONY) and aluminum foil (aluminum foil) as the base layer 5 is laminated on the (III) layer 4 of the multilayer film 1. May be. In addition, when applying the laminated body containing aluminum foil (aluminum foil) as the base material layer 5, it laminates | stacks so that the said aluminum foil (aluminum foil) and the (III) layer 4 of the multilayer film 1 may overlap. Is preferred.

The means for laminating the base material layer 5 on the (III) layer 4 of the multi-layer film 1 of the present invention is not particularly limited, but the multi-layer film 1 and the base material layer 5 are formed by a known dry laminating method. A method of laminating and laminating, a method of laminating the film 1 on the base material layer 5 using a known sandwich lamination method using a polypropylene resin, a polyethylene resin, or the like as an adhesive layer, The constituent material of the film 1 and the constituent material of the base material layer 5 can be formed by using a known coextrusion film forming method, for example, by simultaneously forming both of them.
In addition, the specific structure, shape, and the like in the implementation of the present invention may be other structures as long as the object of the present invention can be achieved.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to the content of an Example etc. at all.

First, resin materials used in Examples and Comparative Examples (a), (b) Film production methods, and (c) Evaluation methods are shown below.
(A) Resin material used:
(1) High density polyethylene-I (abbreviated as HD-I)
Grade: Hi-Zex 3300F (Mitsui Chemicals)
Density: 950 kg / m ³
MFR: 1.1g / 10min

(2) High density polyethylene-II (abbreviated as HD-II)
Grade: Jyrex KL471A (manufactured by Nippon Polyolefin Co., Ltd.)
Density: 956 kg / m ³
MFR: 2.0g / 10min

(3) Linear low density polyethylene-I (abbreviated as LL-I)
Grade: Moretec 0278G (manufactured by Idemitsu Petrochemical Co., Ltd.)
Density: 938 kg / m ³
MFR: 2.0g / 10min

(4) Linear low density polyethylene-II (abbreviated as LL-II)
Grade: Moretec 0168N (Idemitsu Petrochemical Co., Ltd.)
Density: 934 kg / m ³
MFR: 1.0 g / 10 min

(5) Linear low density polyethylene-III (abbreviated as LL-III)
Grade: Moretec 0138N (made by Idemitsu Petrochemical Co., Ltd.)
Density: 916 kg / m ³
MFR: 1.0 g / 10 min

(6) Random polypropylene (abbreviated as RPP)
Grade: F-534N4 (Idemitsu Petrochemical Co., Ltd.)
Density: 900kg / m ³
MFR: 6.0 g / 10 minutes

(7) Ethylene-α-olefin copolymer (abbreviated as EαCo-I)
Grade: Toughmer A4085 (Mitsui Chemicals)
Density: 885 kg / m ³
MFR: 3.6 g / 10 minutes

(8) Ethylene-α olefin copolymer (abbreviated as EαCo-II)
Grade: Toughmer P0280 (Mitsui Chemicals)
Density: 867 kg / m ³
MFR: 5.4 g / 10 minutes

(9) Anti-blocking agent (abbreviated as AB agent)
Master batch containing 15% by mass of synthetic silica (base resin, linear low-density polyethylene. Examples 1 and 2 and Comparative Examples 1 and 4: manufactured by Mitsui Chemicals, Inc. and Example 3 Fuji Silysia Chemical Co., Ltd. ))

(10) Nucleating agent Dibenzylidenesorbitol (6% masterbatch used, base resin: low density polyethylene)

(B) Manufacturing method of multilayer film:
(B-1) Production of Examples 1 and 2 and Comparative Examples 1 to 4 (layer thickness ratio is 1/2/1) Blended with resin materials and additives (AB agent and nucleating agent) shown in Table 1 ( 1 part by mass), and using an inflation extrusion molding machine, a three-layer film (thickness of the entire film: 70 μm) having the configuration shown in FIG. 1 was prepared according to the following molding conditions.

( Molding condition )
Die diameter: 250mm
Die slip interval: 2.5mm
Processing temperature: 200 ° C
Blow-up ratio: 1.6

  After the corona discharge treatment is applied to the surface of the laminate layer of this three-layer film by a conventional method, a biaxially stretched nylon film (Emblem ONM: manufactured by Unitika Ltd., thickness 15 μm) is bonded to a polyester urethane type adhesive ( A multi-layer film (thickness of the entire film: 88 μm) having the configuration shown in FIG. 2 was obtained by dry lamination using an adhesive for retort manufactured by Mitsui Takeda Chemical Co., Ltd.

(B-2) Production of Example 3 and Comparative Examples 5 and 6 (layer thickness ratio is 1/3/1, 1/5/1) The resin materials and additives (AB agent) shown in Table 1 were blended. Then, using a three-layer T die-cast extrusion molding machine, a three-layer film (thickness of the entire film: 70 μm) having the configuration shown in FIG. 1 was prepared according to the following molding conditions.

( Molding condition )
Die surface length: 800mm
Die slip interval: 1.5mm
Processing temperature: 250 ° C
Discharge rate: 80 kg / hour Cooling temperature: 40 ° C

  The surface of the laminate layer of this three-layer film was subjected to corona discharge treatment in the same manner as in (B-1) above, and then a biaxially stretched nylon film (emblem ONM: manufactured by Unitika Ltd., thickness 15 μm) was used. Then, by dry lamination using a polyester urethane type adhesive (adhesive for retort manufactured by Mitsui Takeda Chemical Co., Ltd.), a multilayer film (thickness of the entire film: 88 μm) having the structure shown in FIG. 2 was obtained.

(C) Evaluation method:
The multilayer films of Examples 1 to 3 and Comparative Examples 1 to 6 obtained in (b) were compared and evaluated according to the following evaluation items.
(C-1) Heat-sealability A bag body (size outside dimensions: 170 mm × 150 mm, inside dimensions: heat-sealed between the (I) layers (sealant layers) of the multilayer film in a circumferential shape to make the inside vacuum. 150 mm × 130 mm) was prepared.
Retort processing is performed on this bag body under two conditions of “120 ° C. × 30 minutes” and “123 ° C. × 30 minutes”, and the fused state of the inner surface after the retort processing is determined using the following criteria. And sensory evaluation.

(Criteria)
Evaluation Content ◎: Not fused at all.
○: Although there is some fusion, it peels off easily.
Δ: Fused but can be peeled off.
X: Fusion is extremely severe and cannot be peeled off.

(C-2) Bag breaking strength In the same manner as (c-1), the (I) layers (sealant layers) of the multilayer film are heat-sealed in a circumferential shape and filled with 150 cc of water inside. (Outer dimensions: 170 mm × 150 mm, inner dimensions: 150 mm × 130 mm) were prepared.
The bag was subjected to a retort treatment at 120 ° C. for 30 minutes, and then subjected to a “horizontal” and “vertical” drop test under the following conditions to evaluate the bag breaking strength. The test was performed with n = 10 in each direction.

( Measurement condition )
(I) Horizontal direction:
At a temperature of 0 ° C., the bag body was dropped from a height of 1 m in a horizontal state, the number of times until the bag body broke was confirmed, and the average value was evaluated as a result.

(Ii) Vertical direction:
At a temperature of 0 ° C., it was dropped from a height of 1.5 m as a vertical state with respect to the body surface of the bag body, the number of times until the bag body broke was confirmed, and the average value was obtained as a result. evaluated.

(C-3) Transparency About the multilayer film, the size was set to 150 mm × 150 mm and used as an evaluation sample. A retort treatment was performed at 120 ° C. for 30 minutes with the evaluation sample sandwiched between two aluminum plates, and the change in the transparency of the evaluation sample before and after the retort treatment was confirmed by measuring the haze value as an index.

(C-4) Anti-blocking property (AB property)
In a state where 10 evaluation samples having the same specifications as (c-3) are stacked, a retort treatment is performed at 120 ° C. for 30 minutes, and then a temperature of 50 ° C. is applied and a load of 0.49 MPa is applied for 24 hours. The degree of blocking of the evaluation sample was compared with the degree of blocking before the retort treatment. The degree of blocking was sensory evaluated using the following criteria.

(Criteria)
Evaluation Content ○: No blocking Δ: Blocking, but can be peeled off with fingers.
X: Blocking is extremely severe and difficult to peel off with a finger.

(Multilayer film specifications and evaluation results)

  As can be seen from the results shown in Table 1, the multilayer films of Examples 1 to 3 have the evaluation items of “heat-fusibility”, “bag breaking strength”, “transparency”, and “anti-blocking property (AB property)”. Good results were obtained for all items. Therefore, it is confirmed that the multilayer film of the present invention has various properties such as heat resistance (heat fusion resistance), impact resistance, anti-blocking property, transparency and the like, and has no problem as a packaging material for retort food. did it.

On the other hand, the multilayer film of Comparative Example 1 in which no soft polymer was blended with the (II) layer had poor bag breaking strength and was inferior in the low-temperature impact properties of the film.
In the multilayer film of Comparative Example 2 in which no anti-blocking agent is blended with the (I) layer (sealant layer), the (I) layer (sealant layer) is thermally fused to each other during the retort treatment. Wearability was not good and antiblocking properties were also poor.

The multilayer film of Comparative Example 3 in which the (I) layer (sealant layer) is composed only of a high-density polyethylene-based resin did not give good results for bag breaking strength (low temperature impact property) and transparency.
The multilayer film of Comparative Example 4 in which a nucleating agent was blended with the (II) layer had poor bag breaking strength and poor impact resistance.
The multilayer film of Comparative Example 5 in which the (I) layer (sealant layer) is composed only of linear low-density polyethylene and no soft polymer is blended with the (II) layer has a heat fusibility and a bag breaking strength ( Good results were not obtained for any of the items (low temperature impact property), transparency and antiblocking properties.
A comparative example in which an antiblocking agent is not added to the (I) layer (sealant layer), and the (I), (II) and (III) layers are resin compositions composed of a random polypropylene resin and a soft polymer. The multilayer film No. 6 had poor bag breaking strength and was inferior in the low temperature impact strength of the film.
Thus, it has confirmed that the multilayer film of the comparative example which does not comprise the requirements of this invention is not preferable as a packaging material of a retort food.

  The multilayer film of the present invention can be suitably used as a packaging material for retort food that can be heat-sterilized (retort treatment) at a temperature of 120 ° C. or higher.

It is sectional drawing which shows one Embodiment of the multilayer film of this invention. It is other aspect of the multilayer film of this invention, Comprising: It is sectional drawing which showed the structure which laminated | stacked the base material layer with respect to the (III) layer.

Explanation of symbols

1 multilayer film 2 (I) layer (sealant layer)
3 (II) layer (base layer)
4 (III) layer (laminate layer)
5 Base material layer

Claims (6)

A multilayer film comprising the following three layers (I) to (III):
(I) and high density polyethylene resin having a density of 940~970kg / ^{m 3,} a layer comprising a soft polymer density 800~900kg / ^{m 3,} and from the anti-blocking agent,
(II) and linear low density polyethylene having a density of 920~945kg / ^{m 3,} density is a soft polymer 800~900kg / ^{m 3,} and a layer containing no nucleating agent,
(III) Layer composed of linear low density polyethylene having a density of 920 to 945 kg / m ³ The multilayer film according to claim 1, wherein
The soft polymer is contained in an amount of 5 to 30% by mass and the antiblocking agent is contained in an amount of 0.4 to 5% by mass with respect to the layer (I).
A multilayer film comprising 5 to 30% by mass of a soft polymer with respect to the layer (II). The multilayer film according to claim 1 or 2,
The multilayer film, wherein the soft polymer is an ethylene / α-olefin copolymer and / or a styrene / diene copolymer, or a hydrogenated product thereof. The multilayer film according to any one of claims 1 to 3,
A multilayer film having a layer thickness ratio r of a multilayer film represented by the following formula (X) in the range of 0.08 to 0.5.

In the multilayer film in any one of Claims 1 thru | or 4,
A multilayer film characterized by being a sealant film for laminating. The multilayer film according to any one of claims 1 to 5,
For the layer (III),
A base material layer composed of one or more selected from the group consisting of biaxially stretched nylon, biaxially stretched polyethylene terephthalate, biaxially stretched polypropylene, ethylene-vinyl alcohol copolymer, and aluminum foil (aluminum foil). A multilayer film characterized by laminating layers.

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