JP7132081B2 - Easy-open sealant film and package - Google Patents

Description

TECHNICAL FIELD The present application relates to an easily openable sealant film and a package using the film.

BACKGROUND ART Conventionally, various packaging bodies have been developed and provided that use a film made of a plastic material or a container-shaped molded body, contain contents, and seal an opening by heating. Contents include a wide range of items such as food, medical products, industrial parts, and daily necessities. Packages are available in various shapes, such as bags, cups, deep-drawn bottom materials, blister packs, skin packs, etc., depending on the contents and usage. used. In recent years, improvements have been made in the functions of easy-to-open packages that can be opened with a light force.

For example, in Patent Document 1, in order to achieve both low-temperature sealability, heat resistance, and easy-openability, a support layer made of a polyolefin resin, and a polypropylene resin of 30 to 90% by weight and a polyethylene resin of 10 to 70% by weight. A composite multi-layer sheet for packaging is disclosed which is composed of a sheet layer made of a mixture and which has a specific melt flow rate ratio of a polypropylene-based resin and a polyethylene-based resin.

In addition, in Patent Document 2, for sealing and easy opening properties, the first layer contains 20 to 60 parts by weight of a high-pressure polymerization low-density polyethylene resin with a melt flow rate (MFR) of 1 to 7 g/10 minutes and an MFR of 1 to 15 g. / 10 minutes propylene-ethylene tandem copolymer 40-80 parts by weight, the second layer is mainly composed of ethylene-α olefin copolymer polymerized using a single site catalyst, high density polyethylene or polypropylene resin , discloses a lid material in which a base film is laminated on the surface of the second layer.

Patent Document 1: JP-A-2000-272064 Patent Document 2: JP-A-2006-256637

However, according to the studies of the present inventors, it was found that in these conventional techniques, the difference in peel strength is large depending on the opening direction of the package. However, it has been necessary to limit the hermetic seal of the package to a specific direction or to limit the opening direction.
Therefore, an object of the present application is to provide a sealant film that has a small difference in peel strength depending on the direction of peeling and has excellent isotropy and easy opening property.

As a first aspect, the present application provides a coextruded film having at least a substrate layer and a seal layer, wherein the substrate layer is composed of a polyolefin resin, and the seal layer is produced using a single-site catalyst. 60 to 95% by mass of polypropylene resin (A) and 40 to 5% by mass of polyethylene resin (B) having a density of 930 kg/m ³ or less and a melt flow rate of less than 1.0 g/10 minutes Disclosed is an easy-peelable sealant film characterized by comprising a resin composition.

1st form WHEREIN: It is preferable that the melt flow rate of the said polyethylene-type resin (B) is less than 0.5 g/10 minutes.

1st form WHEREIN: It is preferable that ratio of the melt flow rate of the said polypropylene-type resin (A) with respect to the melt flow rate of the said polyethylene-type resin (B) is five or more.

In the first embodiment, both the peel strength in the machine direction (MD) and the peel strength in the vertical direction (TD) are preferably 8.0 to 20.0 N/15 mm width.

In the first embodiment, the ratio of the peel strength of the MD to the peel strength of the TD is preferably 0.65 or more and 1.54 or less.

The present application discloses, as a second form, a package using the easy-open sealant film of the first form.

According to the easy-open sealant film of the present application, since the difference in peel strength is small regardless of the opening peel direction, for example, when this film is used as a lid material for a cup or the like, it can be sealed in any direction. The package can be opened with a uniform light force from the beginning to the end of the package, and the contents do not fly out or are damaged when the package is opened. In the manufacture of the package, it is no longer necessary to limit the heat-sealing direction or the unsealing direction, which increases the degree of freedom in product design and manufacturing conditions and reduces the manufacturing cost. In particular, it can exhibit good easy-openability for adherends made of polypropylene-based resins.

In the present application, easy openability is synonymous with easy peelability and easy peelability. Moreover, the sealant film may be called a heat-sealable film or a heat-sealable film.
The peel strength used as an indicator of easy-openability is synonymous with seal strength, indicates the peelability between heat-sealed packaging materials and the adhesion of heat-sealed materials, and is sometimes referred to as opening strength.
When a numerical range is indicated by "-", it means more than or equal to or less than.
The easily peelable sealant film of the present disclosure (hereinafter sometimes referred to as the present film) is composed of a coextruded film having at least a base layer and a seal layer.

<Seal layer>
The seal layer of the present film contains 60 to 95% by mass of a polypropylene resin (A) produced using a single-site catalyst, a density of 930 kg/m ³ or less, and a melt flow rate of less than 1.0 g/10 minutes. It is composed of a resin composition containing at least 40 to 5% by mass of a polyethylene resin (B).

(Polypropylene resin (A))
The polypropylene-based resin (A) that constitutes the seal layer of this film has narrow molecular weight distribution and composition distribution, high tensile strength and impact strength, and is manufactured using a single-site catalyst that has excellent low-temperature sealing properties. A polypropylene resin is used. For example, in the molecular weight distribution, the ratio Mw/Mn of the weight average molecular weight to the number average molecular weight is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.0 or less. The composition distribution, for example, preferably has a degree of short chain branching (SCB) of 40 or less, more preferably 30 or less, and even more preferably 20 or less. The type of single-site catalyst is not particularly limited, but a typical example is a metallocene catalyst. Hereinafter, a polypropylene resin produced using a single-site catalyst may be referred to as "m-PP" for convenience.

Examples of the polypropylene-based resin (A) include homopolypropylene and copolymers of propylene and α-olefins, with propylene-ethylene copolymers being preferred.
The melt flow rate (MFR) of the polypropylene resin (A) is preferably 2.0 to 15.0 g/10 minutes, more preferably 5.0 to 10.0 g/10 minutes. If the MFR is less than 2.0 g/10 minutes, the adhesion by heat sealing becomes strong, making it difficult to obtain easy-openability. Further, the melting point of the polypropylene-based resin (A) is preferably 120 to 160°C, more preferably 125 to 140°C, for low-temperature sealing properties. The density of the polypropylene resin (A) is generally preferably 880-920 kg/m ³ , more preferably 890-910 kg/m ³ .

(Polyethylene resin (B))
The polyethylene resin (B) constituting the seal layer of the present film is a low-density polyethylene having a density of 930 kg/m ³ or less, preferably 900 to 930 kg/m ³ , more preferably 910 to 930 kg/m ³ , 920-930 kg/m ³ is more preferred. If the density exceeds 930 kg/m ³ , the dispersion structure with the polypropylene-based resin used for the seal layer is not formed satisfactorily, and sufficient easy peelability is not exhibited. On the other hand, the lower limit is not particularly limited, but from the viewpoint of versatility and availability, the density is preferably 900 kg/m ³ or more.

Examples of the polyethylene-based resin (B) include homopolyethylene and various copolymers of ethylene and α-olefin.
The melt flow rate (MFR) of the polyethylene resin (B) is preferably less than 1.0 g/10 minutes, more preferably less than 0.8 g/10 minutes, even more preferably less than 0.5 g/10 minutes, and 0.4 g /10 minutes or less is particularly preferred. Although the lower limit is not particularly limited, it is generally 0.1 g/10 minutes or more. When the MFR is 1.0 g/10 minutes or more, the anisotropy of the peel strength increases.

(Composition ratio of polypropylene resin (A) and polyethylene resin (B))
The composition ratio of the polypropylene-based resin (A) and the polyethylene-based resin (B) constituting the seal layer is (A):(B)=(60 to 95): (40-5), preferably (70-90):(30-10).

If the composition ratio of the polypropylene-based resin (A) is less than 60% by mass, the adhesiveness to an adherend made of the polypropylene-based resin, such as a container such as a cup, may be poor and sufficient heat seal strength may not be obtained. . On the other hand, when the composition ratio of the polyethylene-based resin (B) exceeds 40% by mass, the same problems are expected, and the heat resistance may be impaired. In addition, when the composition ratio of the polypropylene resin (A) is more than 95% by mass, or when the composition ratio of the polyethylene resin (B) is less than 5% by mass, the seal layer aggregates during unsealing peeling after heat sealing. Destruction is difficult to occur and it is difficult to obtain easy-openability.

(Relationship between MFR of polypropylene resin (A) and polyethylene resin (B))
In the present invention, the MFR ratio (MFR (PP) / MRF (PE)) of the polypropylene resin (A) to the polyethylene resin (B) is preferably 5 or more from the viewpoint of improving the isotropic peel strength. More preferably, more than 20, more preferably greater than 20. In the sealing layer, when 60 to 95% by mass of polypropylene resin (A) and 40 to 5% by mass of polyethylene resin (B) are blended and the resin composition is melt-kneaded, the polypropylene resin (A) becomes matrix (sea) and polyethylene. A sea-island dispersed structure in which the resin (B) is a domain (island) is formed, and when the resin composition is formed into a film, the domain shape of the finely dispersed polyethylene resin (B) has different vertical and horizontal lengths ( aspect ratio). As the aspect ratio increases, the difference in seal strength when sealing in the machine direction (MD) and the transverse direction (TD) of the film increases. It is considered to be

Therefore, the melt flow rate (MFR) indicating the melt fluidity of the polypropylene resin (A) is sufficiently high, and the smaller the MFR ratio between the polypropylene resin (A) and the polyethylene resin (B), the more the film formation. In some cases, the orientation of the resin composition in the machine direction becomes stronger, and the domain shape of the polyethylene resin (B) forms a more elongated structure. It is thought that a large difference appears between the horizontal direction and the lateral direction. On the other hand, by using a polyethylene-based resin (B) having a small MFR and increasing the MFR ratio between the polypropylene-based resin (A) and the polyethylene-based resin (B), the aspect ratio of the polyethylene-based resin (B) domain decreases, It is considered possible to form a sealing layer in which the difference in sealing strength between the longitudinal direction and the lateral direction of the film is less likely to appear.

<Base material layer>
The base layer of this film is composed of a polyolefin resin. For example, polyethylene-based resins and polypropylene-based resins are preferable in terms of economy and versatility.
Examples of polyethylene-based resins include low-density polyethylene, medium-density polyethylene, and high-density polyethylene. Examples of polypropylene-based resins include homopolypropylene and copolymers of propylene and α-olefins.

<Layer structure of film>
The film may be a coextruded film having at least a substrate layer and a sealing layer, and may have one or more other layers. For example, configurations such as other layer/base layer/seal layer, other layer/other layer/base layer/seal layer, and base layer/other layer/seal layer are included. Resins constituting other layers include polyolefin, polyamide, polyester, ethylene-vinyl alcohol, and the like.

The total thickness and layer thickness of the present film are not particularly limited, but the total thickness is preferably about 10 to 100 μm, more preferably about 20 to 50 μm, from the viewpoint of economy and versatility. The thickness of the seal layer is preferably 1 to 20 μm, more preferably 2 to 10 μm, from the viewpoint of adjusting the peel strength (seal strength). The thickness of the substrate layer is, for example, preferably about 5 to 80 μm, more preferably about 10 to 50 μm.

The substrate layer, sealing layer and other layers of the present film may contain known additives as long as the functions and effects of the present film are not impaired. Examples of additives include antifogging agents, antistatic agents, pigments, coloring agents, lubricants, fillers, antiblocking agents, and the like.

Further, another film may be laminated on the substrate layer side of the present film by a known method such as dry lamination. Other films include unstretched and stretched films of polypropylene, polyester, polyamide, etc., and films provided with a gas barrier layer such as a vinylidene chloride coat layer, an ethylene-vinyl alcohol layer, and an inorganic oxide deposition layer. .

<Heat sealability, easy openability>
The film has a peel strength of 8.0 to 20.0 N/15 mm width when heat-sealed with the seal layer facing the adherend and peeled off, so that it can be opened with a light force. It is preferable from the viewpoint of having both the property and the sealing property to sufficiently seal the contents. The upper limit is more preferably 18.0 N/15 mm width or less, even more preferably 15.0 N/15 mm width or less, from the viewpoint of easy opening.

Above all, it is preferable that the peel strength is 8.0 to 20.0 N/15 mm width both when the film is peeled in the machine direction (MD) and in the direction perpendicular to it (TD). In particular, the ratio of the MD peel strength to the TD peel strength is preferably 0.65 or more and 1.54 or less, more preferably 0.70 or more and 1.43 or less. By having these physical properties, the isotropy of the easy-open property is good, the package can be produced without restriction of directionality, and convenience of opening for consumers is enhanced.

In addition, it is preferable that the present film has a cohesive failure type mechanism in which the film is peeled from the adherend by cohesive failure inside the sealing layer, and that the peeled interface appearing after peeling is beautiful without roughening.
In addition, the heat-sealing temperature for producing a package using a packaging material made of polyolefin resin can shorten the heat-sealing process, stabilize the heat-sealing strength (peel strength), prevent the resin from adhering to the heat-sealing bar, and protect the packaging. From the viewpoint of the appearance of the seal portion of the material, the temperature is generally 140 to 180° C., and it is preferable to obtain the above peel strength and peel strength ratio in this temperature range. Furthermore, it is more preferable if sufficient sealability and easy-openability can be obtained by these peel strengths and peel strength ratios under sealing temperature conditions of less than 140 ° C., such as 130 ° C., and the above peeling in the temperature range of 130 to 180 ° C. It is more preferable to obtain strength and peel strength ratios.

Although the type of adherend and sealing conditions for heat sealing are not limited, in the evaluation of the present application, a non-stretched sheet made of a propylene homopolymer having a thickness of 300 μm was placed as an adherend against the seal layer of the present film. A test piece heat-sealed under the conditions of a predetermined sealing temperature, a sealing pressure of 0.2 MPa, a sealing time of 1 second, and a sealing width of 5 mm was subjected to a peel test at a peel angle of 180 degrees and a tensile speed of 300 mm/min for evaluation.

<Other film properties>
Various film mechanical properties of the present film are not particularly limited as long as they are within the range applicable as a sealant film. For example, the strength at break is preferably 25.0 MPa or more, more preferably 28.0 MPa or more. The elongation at break is preferably 250% or more, more preferably 280% or more. The yield point strength is preferably 14.0 MPa or more, more preferably 14.5 MPa or more. Young's modulus is preferably 200 MPa or more, more preferably 250 MPa or more. These film mechanical strengths can be adjusted by the layer structure, each layer composition, and thickness of the film.

<Film manufacturing method>
The film has at least a substrate layer and a sealing layer, and can be produced by a known coextrusion method. That is, it is preferable that each resin composition constituting the substrate layer and the seal layer is formed into a film by a co-extruder using a T-die method or an inflation method. In addition, each resin and additive may be put into each layer extruder at a predetermined composition ratio to form a resin composition, or each resin and additive may be melt-kneaded in advance to prepare a resin composition, and then each layer extruder. You can put it in

<Package>
Although the configuration, shape, and manufacturing method of a package using this film are not limited, for example, a bag or pouch in which the sealing layers of this film are opposed to each other, or a package made of other materials using this film as a lid material. Examples include cups, trays, packages using a deep-drawn product as a bottom material, and the like, which can be produced by known methods. In addition, it is preferable to use a polypropylene-based resin as the material constituting the bottom material from the viewpoint of exhibiting good easy-openability.

<Measurement method>
Melt flow rate (MFR) was measured according to JIS K7210-1;2014. The test conditions conformed to JIS K6922-1 and JIS K6921-1. The test temperature is 190° C. for polyethylene and 230° C. for polypropylene resin, and the test load is 2.16 kg for both polyethylene resin and polypropylene resin.
Density was measured according to JIS K7112:1999.
The melting point was measured according to JIS K7121:2012.
The peel strength was measured by the method shown in Examples.

<Resin Constituting Seal Layer>
PP1: Propylene-ethylene random copolymer produced using a metallocene catalyst, density 900 kg/m ³ , MFR 7.0 g/10 minutes, melting point 125°C.
PE1: low density polyethylene resin, density 924 kg/m ³ , MFR 0.7 g/10 min.
- PE2: low-density polyethylene resin, density 920 kg/m ³ , MFR 0.3 g/10 min.
PE3: low density polyethylene resin, density 923 kg/m ³ , MFR 2.2 g/10 min.
• PE4: low density polyethylene resin, density 919 kg/m ³ , MFR 8.2 g/10 min.

<Resin Constituting Base Material Layer>
PE5: Linear low-density polyethylene resin produced using a metallocene catalyst, density 922 kg/m ³ , MFR 1.5 g/10 minutes.

<Examples 1-3, Comparative Examples 1-2>
A coextruded film (total thickness: 30 μm) of two types and two layers (base layer: 25 μm thick/seal layer: 5 μm thick) having a base layer and a seal layer having the resin composition shown in Table 1 was produced by an air-cooled inflation coextrusion film forming machine. was made using The following evaluation was performed, and the results are shown in Tables 2 and 3.

<Evaluation of sealability and peelability>
A non-stretched sheet made of a propylene homopolymer having a thickness of 300 μm was opposed to the sealing layer of the obtained coextruded film as an adherend, and the sealing pressure was 0 at a predetermined sealing temperature of 120 to 200° C. shown in Table 2. It was heat-sealed using a heat seal tester manufactured by Tester Sangyo Co., Ltd. under conditions of 2 MPa, a sealing time of 1 second, and a sealing width of 5 mm, and stored at room temperature. After that, using a tensile tester (TEN-03-S3Q) manufactured by Orientec Co., Ltd., under the conditions of a peeling angle of 180 degrees and a tensile speed of 300 mm / min, the machine direction (MD) and its perpendicular Each peel test was performed with the peel direction along the direction (TD).
In addition, the peeled surface after peeling was visually observed, and whether or not it was beautiful was evaluated according to the following criteria.
○: There is no stringiness on the peeling surface of the adherend in both the MD and TD peeling tests, and there is no whitening unevenness ×; There is a pull or there is unevenness in the whitening

<Other physical property evaluation>
Based on JIS K7127: 1999, the obtained coextruded film was subjected to a tensile test using a tensile tester (TEN-03-S3Q) manufactured by Orientec Co., Ltd. at a tensile speed of 300 mm / min. , elongation at break, strength at yield point, and Young's modulus were measured.

<Evaluation results>
In all of Examples 1 to 3, films could be stably formed, and the film had a good appearance without resin unevenness, gels, pimples, or the like. In addition, in the heat sealing temperature range of 130 to 180°C, a peel strength of 8.0 to 20.0 N/15 mm width is obtained for both MD and TD, showing good sealing and easy opening properties, and a beautiful peel appearance. there were. Moreover, the peel strength ratio MD/TD was within the range of 0.65 to 1.54, indicating that the peel strength was isotropic.

Comparative Example 1 exhibited favorable peel strengths in both MD and TD at a sealing temperature of 140 to 180°C, but at 160°C or lower, the peel strength ratio MD/TD was less than 0.65, indicating insufficient isotropy. rice field. In Comparative Example 2, the heat sealing temperature that satisfies suitable peel strength in both MD and TD was only 130°C, and the peel appearance was poor at 130°C.

According to the easy-open sealant film of the present invention, since the difference in peel strength is small regardless of the peeling direction when opening, for example, when the film is used as a lid material for a cup or the like, the sealant film can be sealed in any direction. The package can be opened with a uniform light force from the beginning to the end of the package, and the contents will not be blown out or damaged when the consumer opens the package. In the manufacture of the package, it is no longer necessary to limit the direction of heat sealing and the opening direction, which increases the degree of freedom in product design and manufacturing conditions, and reduces the manufacturing cost. In particular, since it exhibits good easy-opening properties with respect to adherends made of polypropylene resin, it is highly useful as a lid material for polypropylene resin containers.

Claims (5)

In a coextruded film having at least a substrate layer and a sealing layer,
The base material layer is made of polyolefin resin,
The sealing layer contains 60 to 95% by mass of a polypropylene resin (A) produced using a single-site catalyst, a density of 930 kg/m ³ or less, and a melt flow rate of less than 1.0 g/10 minutes. An easy-open sealant film characterized by being composed of a resin composition containing 40 to 5% by mass of a polyethylene resin (B) ,
An easy-open sealant film, wherein the ratio of the melt flow rate of the polypropylene resin (A) to the melt flow rate of the polyethylene resin (B) is 5 or more . In a coextruded film having at least a substrate layer and a sealing layer,
The base material layer is made of polyolefin resin,
The seal layer contains 60 to 95% by mass of a polypropylene resin (A) produced using a single-site catalyst and a density of 930 kg/m. ³ below and a melt flow rate of less than 1.0 g/10 min. There is
The easy-open sealant film having a peel strength in the machine direction (MD) and a peel strength in the vertical direction (TD) of 8.0 to 20.0 N/15 mm width. 3. The easy-open sealant film according to claim 1, wherein the polyethylene resin (B) has a melt flow rate of less than 0.5 g/10 minutes. The easy-open sealant film according to claim 2 , wherein the ratio of the peel strength of the MD to the peel strength of the TD is 0.65 or more and 1.54 or less. A package using the easy-open sealant film according to any one of claims 1 to 4 .