WO2023166995A1 - Multilayer film for ultrasonic sealing and package - Google Patents

Abstract

The present invention relates to a multilayer film for ultrasonic sealing and a package. Provided is a multilayer film for ultrasonic sealing, the multilayer film comprising at least a thermoplastic resin layer containing a thermoplastic resin, and a sealing layer containing a linear low-density polyethylene and an α-olefin resin, the α-olefin resin containing a butene-based α-olefin resin, and the multilayer film being capable of sealing by ultrasonic waves. Thus, the multilayer film for ultrasonic sealing is applicable to mono-materialization, is such that ultrasonic welding is possible, has sufficient rigidity, has a narrow sealing width, and is capable of having uniform and stable ultrasonic sealing strength.

Description

Multilayer film for ultrasonic sealing and package

The present invention relates to a multilayer film for ultrasonic sealing and a package.

　The use of mono-materials (single materials) is progressing in order to promote recycling and reduce the environmental impact of food packaging films such as Western confectionery and snacks. In contrast to the conventional multi-layer laminate structure of different materials (e.g., oriented polyethylene terephthalate OPET/non-oriented polypropylene CPP multi-layer film), multi-layers such as biaxially oriented polyethylene/non-oriented polyethylene sealant are used to support monomaterials. Film is required.

However, with multilayer films made of biaxially oriented polyethylene and non-oriented polyethylene sealant, which are compatible with conventional mono-materialization, the heat resistance of the materials differs, so there is concern that the surface of the multilayer film will deteriorate in heat resistance and reduce packaging suitability. There is a problem that

On the other hand, a multilayer film that can be ultrasonically sealed using ultrasonic waves that can heat only the sealing surface is being studied. So far, as a laminated film that can be strongly welded even by ultrasonic welding, an outer layer made of a uniaxially oriented polypropylene film, a barrier layer and a resin intermediate layer, and a linear low density polyethylene may be used. Laminated films containing high sealant layers have been proposed (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2017-217902

However, with a multilayer film that uses polyethylene to support monomaterialization, it is difficult to obtain a uniform and stable seal strength when ultrasonically sealed due to differences in heat resistance between materials. In addition, in order to obtain packaging aptitude such as pillow packaging used for packaging foods such as western confectionery and snacks, it is necessary for the film to have both rigidity. However, the laminated film proposed above, which is suitable for ultrasonic sealing, includes an ethylene resin layer and a polypropylene resin layer, and cannot be used as a monomaterial. Therefore, there is a demand for a multilayer film resin structure that can be used as a monomaterial, has sufficient rigidity, and is suitable for ultrasonic sealing.

The object of the present invention is to solve the above-mentioned conventional problems and to achieve the following objectives. That is, the present invention provides a multi-layer ultrasonic seal that can be used as a monomaterial, has sufficient rigidity, can be ultrasonically welded, and has a narrow seal width and uniform and stable ultrasonic seal strength. The purpose is to provide a film.

The present invention is based on the above findings by the present inventors, and means for solving the above problems are as follows. i.e.
<1> a thermoplastic resin layer containing a thermoplastic resin;
a seal layer containing a linear low-density polyethylene resin and an α-olefin resin;
The α-olefin resin contains a butene-based α-olefin resin,
The multilayer film for ultrasonic sealing is characterized in that it can be sealed by ultrasonic waves.
<2> The multilayer film for ultrasonic sealing according to <1>, wherein the content of the linear low-density polyethylene in the seal layer is 50% by mass or more and 90% by mass or less.
<3> The multilayer film for ultrasonic sealing according to <1>, wherein the linear chain low-density polyethylene in the seal layer has a density of 0.900 kg/m ³ or more and 0.940 kg/m ³ or less.
<4> The multilayer film for ultrasonic sealing according to <1>, wherein the sealing layer contains the butene-based α-olefin resin in an amount of 10% by mass or more and 50% by mass or less.
<5> The multilayer film for ultrasonic sealing according to <1>, wherein the seal layer has a thickness of 15% or more.
<6> The multilayer film for ultrasonic sealing according to <1>, having a total thickness of 40 μm or more.
<7> The multilayer film for ultrasonic sealing according to <1>, having a heat of fusion of 60 mJ/mg or more as measured by differential scanning calorimetry.
<8> The multilayer film for ultrasonic sealing according to <1>, wherein the thermoplastic resin contains at least one of polyethylene and polypropylene.
<9> A package obtained by ultrasonically sealing the multilayer film for ultrasonic sealing according to any one of <1> to <8> and a thermoplastic resin film.

ADVANTAGE OF THE INVENTION According to this invention, the above-mentioned problems in the past can be solved, the above-mentioned objects can be achieved, it can be used as a monomaterial, ultrasonic welding is possible, it has sufficient rigidity, and the seal width is narrow. It is possible to provide a multilayer film for ultrasonic sealing that can have uniform and stable ultrasonic sealing strength.

FIG. 1 is a schematic cross-sectional view showing an example of the multilayer film for ultrasonic sealing of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of the multilayer film for ultrasonic sealing of the present invention. FIG. 3A is a schematic cross-sectional view (No. 1) showing an example of an ultrasonic sealing device used for ultrasonic welding of the multilayer film for ultrasonic sealing of the present invention. FIG. 3B is a schematic cross-sectional view (No. 2) showing an example of an ultrasonic sealing device used for ultrasonic welding of the multilayer film for ultrasonic sealing of the present invention. FIG. 3C is a schematic cross-sectional view (No. 3) showing an example of an ultrasonic sealing device used for ultrasonic welding of the multilayer film for ultrasonic sealing of the present invention.

(multilayer film for ultrasonic sealing)
The ultrasonic sealing multilayer film of the present invention has at least a thermoplastic resin layer and a sealing layer, and is ultrasonically sealable.

<Thermoplastic resin layer>
The thermoplastic resin layer contains a thermoplastic resin as a main resin component.
The thermoplastic resin layer may be a single layer or multiple layers.
Said thermoplastic layer may be a surface layer on which printing of the packaging film can be provided.

-Thermoplastic resin-
The thermoplastic resin is not particularly limited and can be appropriately selected from known thermoplastic resins depending on the intended purpose. Examples thereof include olefin resins, styrene resins, ester resins and acrylic resins. Among these, the olefin resin is preferable because it can be made into a monomaterial.
Examples of the olefin resin include homopolymers of olefin monomers (polyethylene homopolymer, polypropylene homopolymer, etc.); copolymers containing olefin monomers as main components (propylene-ethylene block copolymers, propylene-ethylene random copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, etc.). These may be used individually by 1 type, and may use 2 or more types together. Among these, ethylene homopolymers, propylene homopolymers, propylene-ethylene block copolymers, and propylene-ethylene random copolymers containing at least one of polyethylene and polypropylene are preferred.
The content of the olefin monomer in the olefin resin is preferably 50 mol % to 100 mol %, more preferably 70 mol % to 100 mol %.

A cyclic olefin resin can also be used as the thermoplastic resin.
Examples of the cyclic olefin-based resins include norbornene-based polymers, vinyl alicyclic hydrocarbon polymers, and cyclic conjugated diene polymers.
Among these, norbornene-based polymers are preferred.
Examples of norbornene-based polymers include ring-opening polymers (COP) of norbornene-based monomers, and norbornene-based copolymers (COC) obtained by copolymerizing norbornene-based monomers with olefins such as ethylene.
Hydrogenates of COP and COC are also particularly preferred.
The weight average molecular weight of the cyclic olefin resin is preferably 5,000 to 500,000, more preferably 7,000 to 300,000.

The norbornene-based polymer and the norbornene-based monomer as a raw material are alicyclic monomers having a norbornene ring.
Examples of such norbornene-based monomers include norbornene, tetracyclododecene, ethylidenenorbornene, vinylnorbornene, ethylidetetracyclododecene, dicyclopentadiene, dimethanotetrahydrofluorene, phenylnorbornene, methoxycarbonylnorbornene, methoxy carbonyltetracyclododecene and the like.
These norbornene-based monomers may be used alone or in combination of two or more.

The norbornene-based copolymer is obtained by copolymerizing the norbornene-based monomer with a copolymerizable olefin. cycloolefins such as cyclobutene, cyclopentene and cyclohexene; non-conjugated dienes such as 1,4-hexadiene;

The content of the cyclic olefin resin contained in the thermoplastic resin layer is 15 to 35 mass%, preferably 20 to 30 mass% of the resin component contained in the thermoplastic resin layer. Suitable easy tearability and straight cutability can be realized without impairing the properties.

The cyclic olefin resin used in the thermoplastic resin layer has a glass transition temperature of 100° C. or lower, preferably 90° C. or lower, more preferably 80° C. or lower.
Although the lower limit is not particularly limited, it is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher.
By using the cyclic olefin-based resin having the glass transition temperature, it is easy to obtain good heat resistance and rigidity, and it is easy to improve the bag breakage resistance against dropping and the like.
Moreover, it becomes easy to obtain favorable compatibility and it becomes easy to suppress appearance unevenness.
The glass transition temperature is a value obtained by measuring with DSC.

Examples of commercially available products that can be used as the cyclic olefin-based resin include ring-opening polymers (COP) of norbornene-based monomers, such as "ZEONOR" manufactured by Nippon Zeon Co., Ltd. Norbornene-based copolymers ( COC) includes, for example, "APEL" manufactured by Mitsui Chemicals, Inc., and "TOPAS" manufactured by Polyplastics.

The melt flow rate (MFR) of the thermoplastic resin is not particularly limited and can be appropriately selected according to the purpose. 50.0 g/10 minutes is preferred, 3.0 g/10 minutes to 45.0 g/10 minutes is more preferred, and 3.0 g/10 minutes to 12.0 g/10 minutes is even more preferred.
Here, the melt flow rate (MFR) is a value measured at 190° C. under a load of 2.16 kg (21.18 N) according to JISK7210.

The melt flow rate (MFR) of the cyclic olefin resin is preferably 0.2 to 30 g/10 minutes (230°C, 21.18N), more preferably 3 to 17 g/10 minutes (230°C, 21.18N). Preferably, 5 to 15 g/10 minutes (230° C., 21.18 N) is more preferable. When the MFR is within this range, it is preferable in that good film formability can be obtained in various multilayer film forming methods.

^The density of the thermoplastic resin is not particularly limited and can be appropriately selected according to the ^{purpose .} 93 g/cm ³ is more preferred.

The melting point of the thermoplastic resin is not particularly limited and can be appropriately selected according to the purpose. The melting point can be measured using a differential scanning calorimeter (DSC) (for example, DSC7020 manufactured by Hitachi High-Tech Science Co., Ltd.).

<Seal layer>
The seal layer contains a linear low-density polyethylene resin and an α-olefin resin as main resin components.

－Linear low-density polyethylene resin－
The linear low density polyethylene (LLDPE) is a copolymer of ethylene and α-olefin polymerized using a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst. It is a coalescence.
Among the resins that satisfy the linear low-density polyethylene, resins that satisfy the specifications of α-olefin resins, which will be described later, may also be included. Treat as density polyethylene resin.
The linear low-density polyethylene resin is not particularly limited and can be appropriately selected according to the purpose. Examples thereof include copolymers obtained by copolymerizing α-olefins such as pentene monomers and 1-octene. Among these, a copolymer obtained by copolymerizing at least one of 1-hexene and 1-octene with an ethylene monomer as a main component is preferable. These may be used individually by 1 type, and may use 2 or more types together.
The content of the ethylene monomer in the linear low-density polyethylene resin is preferably 20 mol % to 95 mol %, more preferably 30 mol % to 95 mol %.

The melt flow rate (MFR) of the linear low-density polyethylene resin is not particularly limited and can be appropriately selected according to the purpose. 0 g/10 minutes to 50.0 g/10 minutes is preferable, 3.0 g/10 minutes to 45.0 g/10 minutes is more preferable, and 3.0 g/10 minutes to 12.0 g/10 minutes is even more preferable.

The ^{density of} the linear low-density polyethylene resin is not particularly limited and can be appropriately selected according to the purpose. ³ to 0.935 g/cm ³ is more preferable.

The melting point of the linear low-density polyethylene resin is not particularly limited and can be appropriately selected according to the purpose. °C is more preferred.

The content of the linear low-density polyethylene resin is preferably 40% by mass or more and 95% by mass or less, preferably 50% by mass or more and 90% by mass or less, relative to the total amount of the resin components contained in the seal layer. 60% by mass or more and 80% by mass or less is more preferable.
When the content is 40% by mass or more and 95% by mass or less, it is advantageous in terms of exhibiting ultrasonic sealing properties. Further, when the content is 40% by mass or more and 95% by mass or less, it is particularly advantageous in terms of ensuring uniform and stable ultrasonic sealing performance over the entire sealing length.

-α olefin resin-
The α-olefin resin contains at least a butene-based α-olefin resin and, if necessary, other α-olefin resins other than the butene-based α-olefin resin.

--butene-based α-olefin resin--
The butene-based α-olefin resin refers to a copolymer containing 50 mol % or more of butene-1 monomer or a butene-1 monomer homopolymer. The butene-based α-olefin resin is not particularly limited and can be appropriately selected according to the purpose. -1-butene copolymer, propylene-1-butene copolymer containing 50 mol% or more of butene-1 monomer, ethylene-propylene-1-butene copolymer containing 50 mol% or more of butene-1 monomer A coalescence etc. are mentioned. Among these, propylene-1-butene copolymers containing 50 mol % or more of butene-1 monomer are preferred. These may be used individually by 1 type, and may use 2 or more types together.
When the butene-based α-olefin resin is a copolymer, the content of the butene-1 monomer in the butene-based α-olefin resin is preferably 50 mol% to 95 mol%, preferably 60 mol%. It is more preferably to 95 mol %, even more preferably 70 mol % to 95 mol %.

The melt flow rate (MFR) of the butene-based α-olefin resin is not particularly limited and can be appropriately selected according to the purpose. 10 minutes to 50.0 g/10 minutes is preferred, 3.0 g/10 minutes to 45.0 g/10 minutes is more preferred, and 3.0 g/10 minutes to 12.0 g/10 minutes is even more preferred.

The density of ^the butene-based α-olefin resin is not particularly limited and can be appropriately ^selected according to the purpose ^. 0.92 g/cm ³ is more preferred.

The melting point of the butene-based α-olefin resin is not particularly limited and can be appropriately selected according to the purpose. More preferred.

The content of the butene-based α-olefin resin is preferably 5% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less, based on the total amount of the resin components contained in the seal layer. It is more preferably 50% by mass or less, and particularly preferably 20% by mass or more and 50% by mass or less.
When the content is 5% by mass or more and 60% by mass or less, it is advantageous in terms of exhibiting ultrasonic sealing properties. Further, when the content is 20% by mass or more and 50% by mass or less, it is particularly advantageous in terms of ensuring uniform and stable ultrasonic sealing performance over the entire sealing length.

The mass ratio (b2/b1) of the butene-based α-olefin resin (b2) to the linear low-density polyethylene (b1) in the sealing layer is not particularly limited and can be appropriately selected according to the purpose. , preferably 5/95 to 60/40, more preferably 10/90 to 50/50, still more preferably 20/80 to 50/50, and particularly preferably 30/70 to 40/60.

--Other α-olefin resins--
The other α-olefin resin is not particularly limited as long as it contains an α-olefin and the content of the 1-butene monomer is less than 50 mol%, and can be appropriately selected according to the purpose. Examples include ethylene polymers containing olefins, propylene polymers containing α-olefins, ethylene-propylene copolymers containing α-olefins, ethylene-1-butene copolymers, propylene-1-butene copolymers, and the like. α-olefins include 1-butene, 1-hexene, 4-methylpentene, 1-octene and the like. Among these, copolymers containing 50 mol% or more of butene-1 monomer correspond to butene-based α-olefin resins, and copolymers containing less than 50 mol% of butene-1 monomer are other α It corresponds to olefin resin. In addition, for copolymers of ethylene and α-olefins polymerized using multi-site catalysts such as Ziegler-Natta catalysts or single-site catalysts such as metallocene catalysts, linear low-density polyethylene is used instead of α-olefin resins. Applicable.
Moreover, these may be used individually by 1 type, and may use 2 or more types together.
The content of the α-olefin monomer in the α-olefin resin is not particularly limited and can be appropriately selected according to the purpose.

The melt flow rate (MFR) of the other α-olefin resin is not particularly limited and can be appropriately selected according to the purpose. 10 minutes to 50.0 g/10 minutes is preferred, 2.0 g/10 minutes to 45.0 g/10 minutes is more preferred, and 2.0 g/10 minutes to 10.0 g/10 minutes is even more preferred.

The ^density of the other α-olefin resin ^is not particularly limited and can be appropriately selected according to the purpose ^. 0.90 g/cm ³ is more preferred.

The melting point of the other α-olefin resin is not particularly limited and can be appropriately selected according to the purpose, but is preferably 40°C to 120°C, more preferably 50°C to 100°C.

A cyclic olefin resin may also be used in the seal layer of the present invention. As the cyclic olefin-based resin, the same cyclic olefin-based resin that can be used in the thermoplastic resin layer can be used.

<Other ingredients>
The seal layer may contain other olefinic resins. Other olefin-based resins include various ethylene-based resins and propylene-based resins.
The resin of the thermoplastic resin layer and the seal layer contains other ingredients such as antioxidants, ultraviolet absorbers, antistatic agents, and lubricants (antiblocking agents, slip agents) commonly used in polyolefins. may be blended as appropriate.

[Layer structure of multilayer film for ultrasonic sealing]
The thermoplastic resin layer in the multilayer film for ultrasonic sealing may be a single layer or a plurality of layers. The plurality of thermoplastic resin layers may have the same composition or different compositions.
When the thermoplastic resin layer is a single layer, the multilayer film for ultrasonic sealing is a multilayer film laminated in the order of thermoplastic resin layer/seal layer.
When the thermoplastic resin layer is a plurality of layers, the thermoplastic resin layer has a base layer that serves as a surface layer of the multilayer film for ultrasonic sealing and an intermediate layer (one to multiple layers). The multilayer film for ultrasonic sealing is a multilayer film laminated in the order of base layer (thermoplastic resin layer)/intermediate layer (thermoplastic resin layer)/seal layer.

When the thermoplastic resin layer is a plurality of layers and there is an intermediate layer, the intermediate layer is also preferably a cyclic olefin resin layer. The said cyclic olefin resin layer refers to the layer which contains 60 mass % or more of cyclic olefin resins among the resin components of the said layer.
By using such a layer as an intermediate layer, in addition to improving the rigidity of the multilayer film, it is possible to prevent the migration of the adhesive component into the interior, and because it has good ultrasonic wave propagation properties, The seal strength is also improved.

The multilayer film for ultrasonic sealing may be a coextrusion multilayer film in which each layer is extruded and laminated together, or may be a laminate film in which some layers are adhered and laminated.
The adhesion method for laminating the additional base material layer is not particularly limited and can be appropriately selected according to the purpose. Examples thereof include dry lamination, wet lamination, non-solvent lamination and extrusion lamination.

The ultrasonic sealing multilayer film is preferably a non-stretched film. Since the sealant film for ultrasonic sealing can be obtained as a substantially unstretched multilayer film by the above coextrusion production method, secondary forming such as deep drawing forming by vacuum forming is also possible. In addition, when the multilayer film for ultrasonic sealing is a laminate film laminated by bonding some layers, the resin film may be a stretched resin film in which some layers are laminated, but a non-stretched resin Films are preferably used.

The multilayer film for ultrasonic sealing is basically transparent and has a smooth surface. The mixed resin layer on both sides or one side of the multilayer film for ultrasonic sealing may be subjected to a corona discharge treatment to impart printability. In addition, both sides or one side of the multilayer film for ultrasonic sealing may be embossed to give an aperture pattern such as a satin finish.

The total thickness of the multilayer film for ultrasonic sealing is not particularly limited and can be appropriately selected according to the purpose. The above is more preferable. Moreover, it is preferably 30 μm or more and 100 μm or less, and more preferably 40 μm or more and 90 μm or less.

The average thickness of a single layer or each layer of the thermoplastic resin layer is not particularly limited and can be appropriately selected according to the purpose.
When the thermoplastic resin layer is a plurality of layers, the total average thickness of each layer is not particularly limited and can be appropriately selected according to the purpose. .
The thickness of the thermoplastic resin layer is not particularly limited and can be appropriately selected according to the purpose. (%) is preferably 90% or less, more preferably 20% to 90%, even more preferably 50% to 80%.

The average thickness of the sealing layer is not particularly limited and can be appropriately selected depending on the intended purpose.
The thickness of the seal layer is not particularly limited and can be appropriately selected according to the purpose. 10% or more is preferred, 15% or more is more preferred, and 20% or more is even more preferred. Moreover, it is preferably 10% or more and 50% or less, more preferably 15% or more and 50% or less, and still more preferably 20% or more and 50% or less.
When the thickness is 10% or more, it is advantageous in that uniform and stable ultrasonic sealing performance is ensured over the entire sealing length.

Further, when part or all of the thermoplastic resin layer is the cyclic olefin resin layer, the thickness ratio thereof is preferably 5% or more and 30% or less, more preferably 5% or more and 20%, with respect to the total thickness of the multilayer film. The following is more preferable, and 8% or more and 18% or less is even more preferable. When the thickness ratio of the cyclic olefin-based resin layer is within the range, the rigidity and seal strength can be improved, and when the multilayer film is used as a laminate film, it is easily made into a monomaterial film, which is preferable. When the said cyclic olefin resin layer exists in multiple numbers, it is preferable in the total thickness ratio being the said range.

[Heat of fusion]
The heat of fusion measured by differential scanning calorimetry (DSC) in the multilayer film for ultrasonic sealing is preferably 60 mJ/mg or more, more preferably 65 mJ/mg or more, from the viewpoint of uniform weldability by ultrasonic sealing. , more preferably 75 mJ/mg or more. Also, it is preferably 60 mJ/mg or more and 115 mJ/mg or less, more preferably 60 mJ/mg or more and 110 mJ/mg or less, and even more preferably 60 mJ/mg or more and 100 mJ/mg or less.
The amount of heat of fusion measured by differential scanning calorimetry (DSC) is the amount of heat of fusion in the first temperature rise, and is measured in the following procedure using, for example, a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Co., Ltd., DSC7020). be able to.
First, about 5.0 mg of a multilayer film for ultrasonic sealing, which is a target sample, is placed in an aluminum sample container, the sample container is placed on a holder unit, and set in an electric furnace. Next, in a nitrogen atmosphere, the sample is heated from 30° C. to 200° C. at a temperature increase rate of 10° C./min (first temperature increase), and the DSC curve is measured using a differential scanning calorimeter.
From the obtained DSC curve, an analysis program for a differential scanning calorimeter is used to select the DSC curve at the time of the first temperature increase, and the heat of fusion [mJ/mg] of the target sample at the first temperature increase can be obtained. can.

When a cyclic olefin resin layer is provided as the thermoplastic resin layer, the heat of fusion measured by differential scanning calorimetry (DSC) in the multilayer film for ultrasonic sealing is preferably 55 mJ/mg or more, and preferably 60 mJ. /mg or more, and more preferably 70 mJ/mg or more. If the amount of heat of fusion when the cyclic olefin resin layer is provided as the thermoplastic resin layer is within the above range, uniform welding is facilitated in the case of ultrasonic sealing, and perforation or the like is less likely to occur during welding. .

The heat of fusion measured by differential scanning calorimetry (DSC) in the multilayer film for ultrasonic sealing of the present invention is 70 mJ / mg or more, or when a cyclic olefin resin layer is provided as the thermoplastic resin layer, the heat of fusion is If it is 55 mJ/mg or more, it becomes easier to perform uniform welding in the case of ultrasonic sealing, and the reason why perforation or the like is less likely to occur during welding is not clear, but the inventors speculate as follows. there is That is, polyethylene has relatively low rigidity, and the vibrational energy generated by ultrasonic waves during ultrasonic sealing tends to be attenuated, and high energy must be applied for uniform sealing. A multilayer film having a relatively high heat of fusion in the above range achieves a uniform seal, so even when the vibration energy of ultrasonic waves during ultrasonic sealing is high, a good sealing result can be obtained without perforation or the like. can.

[rigidity]
The rigidity of the multilayer film for ultrasonic sealing can be evaluated by 1% tangent modulus.
"1% tangent modulus" means the tangent modulus at 1% strain.
The 1% tangential modulus in the multilayer film for ultrasonic sealing is preferably 190 MPa or more, more preferably 200 MPa or more, and even more preferably 210 MPa or more.
The method for measuring the 1% tangential modulus is not particularly limited and can be appropriately selected according to the purpose. 1% tangential modulus (unit: MPa) at 23° C. using a Tensilon tensile tester (device name: RTC-1210A, manufactured by A&D Co., Ltd.).

The rigidity of the multilayer film for ultrasonic sealing of the present invention can be selected according to the application by adjusting the resin composition of the multilayer film. For example, when using the ultrasonic sealing multilayer film for applications that require flexibility such as horizontal pillow packaging, by using a polyethylene resin such as linear low density polyethylene for the thermoplastic resin layer, the The 1% tangential modulus in the multilayer film for ultrasonic sealing can be adjusted to 190 MPa or more and about 300 MPa. On the other hand, when using the ultrasonic sealing multilayer film for applications that require rigidity such as standing pouches and vertical pillow packaging, by using a cyclic olefin resin for the thermoplastic resin layer, the ultrasonic sealing multilayer The 1% tangential modulus of the film can be adjusted to 300 MPa or more and about 900 MPa.

[Ultrasonic seal]
The ultrasonic sealing method is not particularly limited, and a known ultrasonic sealing method, a method using a known ultrasonic sealing device, or the like can be appropriately selected according to the purpose.
Here, the "ultrasonic seal" is a combination of an "ultrasonic horn" that transmits vibration energy by ultrasonic waves and a fixing jig "anvil" using ultrasonic vibration amplitude that converts electrical energy into mechanical energy. It is a technology in which a film to be joined is sandwiched in between, and frictional energy is generated uniformly at the interfaces of the film materials, resulting in instantaneous fusion and welding. The terms "ultrasonic sealing", "ultrasonic welding", "ultrasonic fusion welding", and "ultrasonic fusion bonding" can be synonymous with each other.

The ultrasonic horn may be arranged vertically above the object to be welded and the anvil, or horizontally with respect to the object to be welded and the anvil. Ultrasonic horns vibrate with ultrasonic waves, typically between 20 kHz and 40 kHz, to transfer energy under pressure, typically in the form of frictional heat, to the joints to be joined. Due to the frictional heat and pressure, a portion of at least one of the objects to be joined softens or melts, thereby joining the objects to be joined together.

Here, in the present invention, the "bonding object" is not particularly limited as long as it contains at least the multilayer film for ultrasonic sealing of the present invention, and can be appropriately selected according to the purpose. Two multilayer films may be arranged so that the seal layers are in contact with each other, and a series (one sheet) of the multilayer film for ultrasonic sealing may be folded so that the seal layers are in contact with each other. Alternatively, the ultrasonic sealing multilayer film and the thermoplastic resin film are arranged such that the sealing layer of the ultrasonic sealing multilayer film is in contact with the thermoplastic resin film. may be
A laminate to be described later can be obtained by ultrasonically sealing the portions where the seal layers are in contact with each other and the portions where the seal layers are in contact with the thermoplastic resin film to form joints.

The ultrasonic waves in the ultrasonic seal are not particularly limited, and elastic vibration waves (sound waves) having a high frequency that cannot be heard by the human ear can be appropriately selected according to the purpose. The frequency of the ultrasonic waves is preferably 16 kHz or higher, more preferably 20 kHz or higher, and particularly preferably 20 kHz or higher and 40 kHz or lower.

Conditions such as pressure, amplitude, welding time, hold time, etc. in the ultrasonic sealing vary depending on the type of object to be welded and the combination of frequency and conditions, and cannot be univocally defined, but there are no particular restrictions. can be selected as appropriate depending on the purpose.
The pressure means the pressing pressure of the ultrasonic horn against the object to be joined in the ultrasonic sealing device, and is expressed in units such as [Pa] (pascal), [MPa] (megapascal), and the like. The pressure is preferably 0.15 [MPa] to 0.3 [MPa], more preferably 0.25 [MPa] to 0.3 [MPa].
The amplitude means the magnitude of ultrasonic vibration. The amplitude is preferably 20 μm or more and 50 μm or less, and more preferably 35 μm or more and 50 μm or less in order to have a uniform and stable seal strength.
The welding time indicates the oscillation time of ultrasonic waves, and means the time during which the ultrasonic horn contacts and welds the object to be welded. The welding time is preferably 0.2 seconds or more and 1 second or less, more preferably 0.5 seconds or more and 1 second or less.
The hold time means the holding time of the ultrasonic oscillator and the hardening time of the welded portion. The hold time is preferably 0.2 seconds or more and 1.0 seconds or less, more preferably 0.5 seconds or more and 1.0 seconds or less.

Suitable examples of the ultrasonic sealing device include a continuous ultrasonic sealing type device, a device having a rotary ultrasonic horn, and the like.
Such continuous ultrasonic sealing type devices are commonly known as "continuous ultrasonic fusion bonds". Continuous ultrasonic fusion bonding can generally be fed substantially continuously into an ultrasonic sealing device, and is used to substantially continuously seal objects to be bonded. In continuous ultrasonic fusion bonding, the ultrasonic horn is usually fixed and the object to be welded moves underneath it. One type of continuous ultrasonic fusion bond uses a stationary horn and a rotating anvil face. During continuous ultrasonic fusion bonding, the object to be welded is pulled between the ultrasonic horn and the rotating anvil. The ultrasonic horn typically extends longitudinally toward the object to be joined, and vibrations are transmitted axially along the ultrasonic horn to the material.

In the device with a rotating ultrasonic horn, the ultrasonic horn is of rotary type, cylindrical and rotates about its longitudinal axis. The input vibration is in the axial direction of the ultrasonic horn and the output vibration is in the radial direction of the ultrasonic horn. The ultrasonic horn is placed in close proximity to the anvil, and the anvil is typically also rotatable such that the object to be welded passes between the cylindrical surfaces at a linear velocity substantially equal to the tangential velocity of the cylindrical surfaces. .

Examples of ultrasonic seals include JP-A-2008-526552, JP-A-2010-195044, JP-A-2013-231249, JP-A-2015-16294, and US Pat. No. 5,976,316. and the disclosure of which is incorporated herein by reference.

(Laminate)
The multilayer film of the present invention can also be laminated with another substrate to form a laminate having the multilayer film of the present invention.
The laminate has another substrate and the multilayer film of the present invention laminated with the other substrate.
At this time, the other substrate that can be used is not particularly limited, but from the viewpoint of easily expressing the effects of the present invention, a thermoplastic resin film having high rigidity and high gloss, especially two It is preferable to use an axially stretched resin film. For applications that do not require transparency, substrates such as aluminum foil, paper, and coated paper can be used singly or in combination.
The adhesion method for laminating the multilayer film of the present invention to the other substrate is not particularly limited and can be appropriately selected according to the purpose. Examples include dry lamination, wet lamination, non-solvent lamination, and extrusion lamination. etc.

Examples of the biaxially oriented resin film include biaxially oriented polyester (BOPET), biaxially oriented polyethylene (BOPE), biaxially oriented polypropylene (BOPP), biaxially oriented polyamide (BOPA), and ethylene vinyl alcohol copolymer. Examples include coextrusion biaxially oriented polypropylene with a core layer of coalescence (EVOH), biaxially oriented ethylene vinyl alcohol copolymer (BOEVOH), and coextruded biaxially oriented polypropylene coated with polyvinylidene chloride (PVDC). These may be used singly, or two or more of them may be used in combination or in combination.

(package)
The package of the present invention includes at least the multilayer film for ultrasonic sealing of the present invention, and is a laminate obtained by arranging two sheets of the multilayer film for ultrasonic sealing so that the respective sealing layers are in contact with each other and sealing them by ultrasonic waves. It may be a laminate obtained by folding and arranging a series (one sheet) of the multilayer film for ultrasonic sealing so that the sealing layers are in contact with each other, and then sealing by ultrasonic waves, or A laminate obtained by arranging the multilayer film for ultrasonic sealing and a thermoplastic resin film so that the seal layer of the multilayer film for ultrasonic sealing is in contact with the thermoplastic resin film and sealing them by ultrasonic waves, good too.
The packaging body can be suitably used as various packaging bodies such as food packaging bodies for western confectionery, snacks, bread, Japanese confectionery, and seasonings.
The package body can be made of a monomaterial, and can be sealed by an ultrasonic seal capable of heating only the sealing surface, so that the width of the seal can be narrowed and the amount of material can be reduced.

<Thermoplastic resin film>
The material of the thermoplastic resin film is not particularly limited and can be appropriately selected from known thermoplastic resins according to the purpose, but olefin resins are preferable from the viewpoint of monomaterialization.
As the olefin resin, any of the olefin resins described in the thermoplastic resin layer can be appropriately employed.

The ultrasonic sealing multilayer film 10 of the present invention is, for example, a multilayer film composed of a thermoplastic resin layer 1 and a sealing layer 2 and having two layers laminated, as shown in FIG.
Further, as shown in FIG. 2, the multilayer film 10 for ultrasonic sealing of the present invention may have a plurality of thermoplastic resin layers, a thermoplastic resin layer (base layer) 1a, a thermoplastic resin layer ( It may be a multi-layer film consisting of an intermediate layer) 1b and a seal layer 2 and laminated in the order of base layer/intermediate layer/seal layer. In addition, although the intermediate layer is one layer in FIG. 2, the intermediate layer may be plural layers.

3A to 3C are schematic cross-sectional views showing an example of an ultrasonic sealing device used for ultrasonic welding of the multilayer film for ultrasonic sealing of the present invention. The ultrasonic sealing device 100 has an anvil 110 and an ultrasonic horn 120 facing the outer peripheral surface of the anvil 110 . Seal projections are formed in a predetermined seal pattern on the outer peripheral surface of the anvil 110, and the ultrasonic horn 120 moves in the direction of the arrow in FIG. You can hold the joint target.
The object to be joined passed between the anvil 110 and the ultrasonic horn 120 may be, for example, two layers of the ultrasonic sealing multilayer film 10 (FIG. 3A). The plastic resin film may be doubled (not shown), and the metal rod 130 is hooked and tension is applied in the direction of the arrow in FIG. It may be a multilayer film 10 for ultrasonic sealing (Fig. 3B). A portion of the object to be joined sandwiched between the seal projection on the outer peripheral surface of the anvil 110 and the ultrasonic horn 120 is melt-sealed by frictional heat generated by ultrasonic vibration transmitted from the ultrasonic horn 120, thereby ultrasonically sealing. A laminate 50 containing at least the multi-layer film 10 is produced (see FIG. 3C). The ultrasonic sealing device transmits vibration energy to the object to be welded from the tip of an ultrasonic horn in contact with the object to be welded, and welds the object to be welded by frictional heat. It is almost the same as the shape of the contact surface with the tip of the ultrasonic horn. In the ultrasonic sealing device of FIG. 3A, the seal projections on the outer peripheral surface of the anvil 110 have a shape of 200 mm×2 mm, thereby manufacturing the welded laminate 50 with a seal length of 200 mm×seal width of 2 mm. .

The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples. In addition, unless otherwise specified, "part" refers to "mass part" and "%" refers to "mass%".

(Example 1)
<Preparation of multilayer film for ultrasonic sealing>
Resins and resin mixtures for forming each layer using the following resins as resin components for forming each layer of the substrate layer (A), the intermediate layer (B), the intermediate layer (C) and the seal layer (D). adjusted.
Base layer (A): 100 parts of linear low-density polyethylene resin (density 0.933 g/cm ³ , MFR 3.6 g/10 min, melting point 123° C.) (hereinafter referred to as LLDPE (2)).
Middle layer (B): 100 parts of LLDPE (2).
Middle layer (C): 100 parts of LLDPE (2).
Sealing layer (B): 60 parts of linear low-density polyethylene resin (density of 0.920 g/cm ³ , MFR of 4.3 g/10 minutes, melting point of 112° C.) (hereinafter referred to as LLDPE (1)), and 1- Butene-propylene copolymer (density 0.900 g/cm ³ , MFR 9.0 g/10 min, melting point 100° C., content of 1-butene-derived component: 60 mol % to 95 mol %) (hereinafter referred to as BPR (1) ) and 40 parts.

A laminated film formed of a substrate layer (A)/intermediate layer (B)/intermediate layer (C)/seal layer (D) by supplying resins and resin mixtures forming each layer to three extruders, respectively. The average thickness ratio of each layer is 20%: 36%: 20%: 24%, coextruded from a T die at an extrusion temperature of 250 ° C., cooled with a water-cooled metal cooling roll at 40 ° C., and the total thickness A multilayer film for ultrasonic sealing of Example 1, which is a laminated film having a thickness of 40 μm, was molded.

<Production of package>
The obtained multilayer film for ultrasonic sealing was cut into 210 mm × 600 mm, and two thermoplastic resin films (biaxially oriented polypropylene, P2161, manufactured by Toyobo Co., Ltd.) cut into the same size were stacked so that the sealing layer was in contact. A total of three sides, two long sides and one short side, were ultrasonically sealed using the same apparatus and conditions as in the evaluation of "ultrasonic sealability" described later, except that the package of Example 1 was was made.

<Evaluation>
<<Ultrasonic sealability>>
The obtained multilayer film for ultrasonic sealing was cut into a size of 210 mm x 600 mm, and the sealing layer was hooked on a metal rod, folded into two layers, and placed on the anvil of the ultrasonic sealing device shown in FIG. It was set up so that it would stretch on the As an ultrasonic sealing device, an ultrasonic plastic welder W3080 (manufactured by Nippon Avionics, frequency: 20 kHz) was used. Set the parameters (pressure = 0.3 MPa, amplitude = 50 μm, welding time = 1 second, hold time = 1 second), turn on the switch, and set one side of the multilayer film for ultrasonic sealing with a length of 210 mm to a seal length of 200 mm × seal width. Ultrasonic sealed at 2 mm.
After a seal length of 210 mm was visually observed, peeling was performed, and the ultrasonic sealability was evaluated according to the following evaluation criteria. Table 1 shows the results.
[Evaluation criteria]
Good: 80% or more of the full length of the seal was welded.
△○: 50% or more and less than 80% of the total length of the seal was welded (practical level).
Δ: A portion (less than 50%) of the full length of the seal was welded.
x: The seal was not welded over the entire length of the seal, or was easily peeled off at 0.5 N/210 mm or less.

<<Measurement of seal strength>>
The obtained multilayer film for ultrasonic sealing of Example 1 was cut into a width of 210 mm, and two layers were stacked so that the sealing layers were in contact with each other. , pressure = 0.3 MPa, amplitude = 50 µm, welding time = 0.5 seconds, and hold time = 1 second. Cut the ultrasonically sealed laminate into a width of 15 mm, and peel it at 90 degrees at a speed of 300 mm / min using a tensile tester (manufactured by A&D Co., Ltd.) in a constant temperature room at 23 ° C. and 50% RH. The seal strength [N/15 mm] was measured by Table 1 shows the results.

<<Measurement of heat of fusion>>
For the obtained multilayer film for ultrasonic sealing of Example 1, the heat of fusion in the first temperature rise measured by differential scanning calorimetry (DSC) was measured by the following procedure. Table 1 shows the results.
The heat of fusion in the first temperature rise in differential scanning calorimetry (DSC) was measured using a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Co., Ltd.).
First, about 5.0 mg of a multilayer film for ultrasonic sealing, which is a target sample, is placed in an aluminum sample container, the sample container is placed on a holder unit, and set in an electric furnace. Next, in a nitrogen atmosphere, the sample is heated from 30° C. to 200° C. at a temperature increase rate of 10° C./min (first temperature increase), and the DSC curve is measured using a differential scanning calorimeter.
From the obtained DSC curve, the DSC curve at the time of the first heating was selected using a differential scanning calorimeter analysis program, and the heat of fusion [mJ/mg] of the target sample at the first heating was determined.

<<Measurement of stiffness>>
For the obtained multilayer film for ultrasonic sealing of Example 1, 1% tangential modulus (unit: MPa) at 23 ° C. in the extrusion direction during film production was measured using a Tensilon tensile tester (device name: : RTC-1210A, manufactured by A&D Co., Ltd.).
Stiffness was evaluated based on the 1% tangent modulus. In addition, "1% tangential modulus" means a tangential elastic modulus (Tangent Modulus) when a strain of 1% is applied, and in the present invention, it is preferably 190 MPa or more, more preferably 200 MPa or more, and further preferably 210 MPa or more. .

(Example 2)
In Example 1, as shown in Table 1, BPR (1) in the sealing layer (D) was a 1-butene-propylene copolymer (density 0.900 g/cm ³ , MFR 9.0 g/10 minutes, melting point 58°C, Content of 1-butene-derived component: 60 mol% to 95 mol%) (hereinafter referred to as BPR (2)) for ultrasonic sealing in the same manner as in Example 1 A multilayer film was produced and evaluated. Table 1 shows the results.

(Examples 3-4)
In Example 2, as shown in Table 1, except that the amount ratio of LLDPE (1) and BPR (2) in the seal layer (D) was changed, Examples 3 and 4 were prepared in the same manner as in Example 2. A multilayer film for ultrasonic sealing was produced and evaluated. Table 1 shows the results.

(Examples 5-6)
In Example 2, as shown in Table 1, LLDPE (1) in the sealing layer (D) was replaced with LLDPE (2) and linear low-density polyethylene resin (density 0.940 g/cm ³ , MFR 4.3 g/10 minutes, Melting point 124° C.) (hereinafter referred to as LLDPE (3)). . Table 1 shows the results.

(Example 7)
<Preparation of multilayer film for ultrasonic sealing>
The following resins are used as resin components for forming each layer of the substrate layer (A), the intermediate layer (B), the intermediate layer (C), and the seal layer (D), and the resin mixture forming each layer is prepared. did.
Base layer (A): A mixture of 60 parts of LLDPE (1) and 40 parts of high-density polyethylene (960 g/cm ³ , MFR 7.5 g/10 min, melting point 131° C.) (hereinafter referred to as HDPE).
Middle layer (B): a mixture of 70 parts LLDPE (1) and 30 parts HDPE.
Middle layer (C): 100 parts of LLDPE (1).
Seal layer (B): a mixture of 60 parts LLDPE (1) and 40 parts BPR (2).

A resin mixture forming each layer is supplied to each of three extruders, and each layer of a laminated film formed of a base layer (A)/intermediate layer (B)/intermediate layer (C)/seal layer (D). The average thickness ratio of 20%: 36%: 20%: 24% is co-extruded from a T die at an extrusion temperature of 250 ° C., cooled with a water-cooled metal cooling roll at 40 ° C., and the total thickness is 40 μm. The multilayer film for ultrasonic sealing of Example 7, which is a laminated film of , was molded.
The obtained multilayer film for ultrasonic sealing of Example 7 was evaluated in the same manner as in Example 1. Table 2 shows the results.

(Example 8)
In Example 7, as shown in Table 2, the ratio of the average thickness of each layer of the laminated film formed of base layer (A)/intermediate layer (B)/intermediate layer (C)/seal layer (D) was , 20%:36%:28%:16%, a multilayer film for ultrasonic sealing of Example 8 was produced and evaluated in the same manner as in Example 7. Table 2 shows the results.

(Examples 9-10)
In Example 2, as shown in Table 2, 60 parts by mass of LLDPE (1) in the seal layer (D) was changed to 40 parts by mass and 95 parts by mass, respectively, 40 parts by mass of BPR (2) was changed to 60 parts by mass, and The multilayer films for ultrasonic sealing of Examples 9 and 10 were produced and evaluated in the same manner as in Example 2, except that each was changed to 5 parts by mass. Table 2 shows the results.

(Examples 11-12)
In Example 2, as shown in Table 2, the LLDPE (1) in the seal layer (D) was replaced with a linear low-density polyethylene resin (density 0.903 g/cm ³ , MFR 3.0 g/10 minutes, melting point 98°C). (hereinafter referred to as LLDPE (4)), and linear low-density polyethylene resin (density 0.944 g/cm ³ , MFR 4.0 g/10 min, melting point 128° C.) (hereinafter referred to as LLDPE (5)). ), the multilayer films for ultrasonic sealing of Examples 11 and 12 were produced and evaluated in the same manner as in Example 2, except that each was changed to ). Table 2 shows the results.

(Example 13)
In Example 2, as shown in Table 3, the ratio of the average thickness of each layer of the laminated film formed of base layer (A)/intermediate layer (B)/intermediate layer (C)/seal layer (D) was , 20%:46%:20%:14%. Table 3 shows the results.

(Example 14)
In Example 2, as shown in Table 3, a multilayer film for ultrasonic sealing of Example 14 was produced in the same manner as in Example 2, except that the total thickness of the multilayer film for ultrasonic sealing was changed from 40 μm to 35 μm. , conducted an evaluation. Table 3 shows the results.

(Examples 15-23)
Ultrasonic sealing multilayer films of Examples 15 to 20 were produced and evaluated in the same manner as in Example 1 except that the composition and the layer ratio of each layer were changed to those shown in Tables 4 and 5. The results are shown in Tables 4 and 5.

(Comparative example 1)
In Example 1, as shown in Table 6, comparison was made in the same manner as in Example 1, except that the butene-based olefin resin was not included in the seal layer (D) and 60 parts of LLDPE (1) was changed to 100 parts. A multilayer film for ultrasonic sealing of Example 1 was produced and evaluated. Table 6 shows the results.

(Comparative Examples 2-5)
In Example 1, as shown in Table 6, in the sealing layer (D), BPR(1) was changed to PBR(1), PBR(2), EBR(1), and EBR(2) below. Except for this, multilayer films for ultrasonic sealing of Comparative Examples 2 to 5 were produced in the same manner as in Example 1 and evaluated. Table 6 shows the results.
- PBR (1): polypropylene-1-butene copolymer (density 0.900 g/cm ³ , MFR 7.0 g/10 min, melting point 98°C, propylene-derived component content: 85 mol%)
PBR (2): Polypropylene-1-butene copolymer (density 0.900 g/cm ³ , MFR 7.0 g/10 min, melting point 75°C, propylene-derived component content: 74 mol%)
EBR (1): polyethylene-1-butene copolymer (density 0.893 g/cm ³ , MFR 6.7 g/10 min, melting point 77° C., ethylene-derived component content: 70 mol % to 92 mol %)
EBR (2): polyethylene-1-butene copolymer (density 0.885 g/cm ³ , MFR 6.7 g/10 min, melting point 66° C., content of ethylene-derived component: 76 mol % to 90 mol %, 1 - butene-derived component content: 18 mol%)

(Comparative Example 6)
In Example 1, as shown in Table 6, a multilayer film for ultrasonic sealing of Comparative Example 6 was produced in the same manner as in Example 1, except that LLDPE (1) was changed to HDPE in the sealing layer (D). and evaluated. Table 6 shows the results.

From the results in Tables 1 to 6, it was found that the ultrasonic sealability was ensured by the sealing layer containing linear low-density polyethylene and butene-based α-olefin resin. In addition, when the content of the butene-based α-olefin resin in the sealing layer is 5% by mass or more, the seal strength is inferior, but the ultrasonic sealing performance is at a practical level, and when the content is 20% by mass or more, the ultrasonic sealing performance is obtained over the entire sealing length. was found to be guaranteed. It was found that when the total thickness of the multilayer film for ultrasonic sealing is 40 μm, the ultrasonic sealing performance is ensured over the entire sealing length when the thickness of the sealing layer is 14% or more of the total thickness. It was found that excellent rigidity of 200 MPa or more was obtained in all the examples.

Furthermore, in Examples 1 to 14 and Examples 20 to 22 in which a polyethylene-based resin such as linear low-density polyethylene was used for the thermoplastic resin layer, the rigidity of the multilayer film for ultrasonic sealing was increased from 190 MPa to about 300 MPa. It was possible to obtain a multilayer film for ultrasonic sealing which could be adjusted and which is useful for flexible packaging applications. Further, in Examples 15 to 19 and Example 23, in which a cyclic olefin resin was used as part of the thermoplastic resin layer, the rigidity of the multilayer film for ultrasonic sealing can be adjusted to 300 MPa or more and about 900 MPa. A multi-layer film for ultrasonic sealing useful for applications requiring rigidity such as standing pouches was obtained.

The MFR, density, melting point, and compound name of each resin used in the examples are shown below.

1 thermoplastic resin layer 1a thermoplastic resin layer (base material layer)
1b Thermoplastic resin layer (intermediate layer)
2 sealing layer 10 multilayer film for ultrasonic sealing 50 laminate 100 ultrasonic sealing device 110 anvil 120 ultrasonic horn 130 metal rod

Claims (9)

a thermoplastic resin layer containing a thermoplastic resin;
a seal layer containing a linear low-density polyethylene resin and an α-olefin resin;
The α-olefin resin contains a butene-based α-olefin resin,
A multilayer film for ultrasonic sealing, characterized in that it can be sealed by ultrasonic waves. The multilayer film for ultrasonic sealing according to claim 1, wherein the content of the linear low-density polyethylene in the seal layer is 50% by mass or more and 90% by mass or less. The multilayer film for ultrasonic sealing according to claim 1, wherein the linear chain low density polyethylene in the seal layer has a density of 0.900 kg/ ^m3 or more and 0.940 kg/ ^m3 or less. The multilayer film for ultrasonic sealing according to claim 1, wherein the content of the butene-based α-olefin resin in the seal layer is 10% by mass or more and 50% by mass or less. The multilayer film for ultrasonic sealing according to claim 1, wherein the thickness of the sealing layer is 15% or more. The multilayer film for ultrasonic sealing according to claim 1, which has a total thickness of 40 μm or more. The multilayer film for ultrasonic sealing according to claim 1, wherein the heat of fusion measured by differential scanning calorimetry is 60 mJ/mg or more. The multilayer film for ultrasonic sealing according to claim 1, wherein the thermoplastic resin contains at least one of polyethylene and polypropylene. A package obtained by ultrasonically sealing the multilayer film for ultrasonic sealing according to any one of claims 1 to 8 and a thermoplastic resin film.

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