JP2021146636A - Easily openable film, co-extrusion easily openable film, and package of the same - Google Patents

Abstract

To provide an easily openable film which has good adhesion to a polypropylene-based resin packaging material of an adherend, has cohesive failure type easy peelability, prevents significant stringiness on a peeled and opened surface, and is excellent in transparency.SOLUTION: An easily openable film has at least a seal layer, in which the seal layer is composed of a resin composition that contains a polypropylene-based resin (a) produced using a single-site catalyst as a main component and contains a linear low density polyethylene resin (b) having a melt flow rate (MFR) of 5.0 g/10 min or less.SELECTED DRAWING: None

Description

The present invention relates to an easy-to-open film having a sealing function, a co-extruded easy-to-open film, and a package using these films.

Easy-to-open plastic packaging materials that can be easily opened are used as packaging containers for foods and beverages. As a general method for imparting easy-opening property, a delamination type that adjusts the sealing strength by adjusting the interlayer strength between the sealing layer of the lid material or the container and the adjacent resin layer, and the composition of the resin constituting the sealing layer are used. By changing the adhesiveness and adhesiveness to the adherend, the interface peeling type that peels off the interface between the seal layers to open the seal, and the seal layer is an incompatible polymer blend. An example is a coagulation break type in which the seal layer is coagulated and broken to open the seal. Among them, a coagulation-breaking type easy-opening sealant having a contaminated sealing property is often used for contents containing water or packaging containing liquid or the like.

The required characteristics of such food packaging materials are the sealing property (heat sealing property) of the contents, the light peeling property (easy peeling property) that can be easily opened, the filming on the peeled surface, the absence of stringing, and the contents being visible. The required level is very high, such as the transparency that can be achieved. In particular, various studies have been conducted so far as a coagulation fracture type lid material for polypropylene containers.

Patent Document 1 describes a support layer made of a polyolefin resin and a polypropylene resin 30 to, for example, a melt flow rate (MFR) of 1.0 g / 10 minutes or more, in order to achieve both low-temperature sealing property, heat resistance, and easy opening property. A sheet layer composed of a mixture of 90% by weight and, for example, 10 to 70% by weight of a polyethylene resin having an MFR of 0.5 to 2.0 g / 10 minutes, for packaging in which the ratio of the MFR of the polypropylene resin to the polyethylene resin is specified. Composite multilayer sheets are disclosed.

In Patent Document 2, for the purpose of sealing and easy opening, the first layer is a high-density polymerization method with an MFR of 1 to 7 g / 10 minutes, 20 to 60 parts by weight of a low-density polyethylene resin, and polypropylene-ethylene having an MFR of 1 to 15 g / 10 minutes. Random copolymer of 40 to 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, and on the surface of the second layer. A lid material for laminating a base film is disclosed.

In Patent Document 3, the sealant film for pillow packaging bags has a three-layer structure, the intermediate layer is made of low-density polyethylene and an ethylene-α-olefin copolymer, and the seal layer is manufactured by using a metallocene catalyst. A coextruded multilayer film composed of a propylene-α-olefin copolymer and a linear low density polyethylene is disclosed.

However, the technique for disclosing the seal layer of Patent Document 1 has a configuration in which many types of polypropylene-based resins and many types of polyethylene resins are listed, and most of the combinations of both resin types result in poor transparency and haze. Met.

Further, when the inventor of the present application examined the first layer (seal layer) composed of a combination of the high-pressure polymerization method low-density polyethylene resin and polypropylene-ethylene random copolymer disclosed in Patent Document 2, Patent Document 2 With the same layer composition as in Example 3, the cohesive failure of the seal layer is insufficient, and remarkable stringiness occurs on the surface after opening, which causes problems in terms of foreign matter mixed in the contents and hygiene safety. It turned out (see Comparative Example 3 of the present application). In addition, stringing the film is considered to be a major improvement because it may cut the lips when the beverage in the container is eaten.

Further, Patent Document 3 is a propylene-ethylene copolymer produced in Examples 1 and 2 using a metallocene catalyst in the seal layer (density 0.900 g / cm ³ , melting point 125 ° C., MFR 7 g / 10 minutes). Seal using a mixture of 90 parts by mass and 10 parts by mass of linear low-density polyethylene (melting point 68 ° C., density 0.880 g / cm ³ , MFR 8.0 g / 10 minutes) manufactured using a metallocene catalyst. The pillow packaging in which the layers are in close contact with each other shows easy opening, but when the inventor of the present application examined a similar layer structure, the cohesive failure of the seal layer was insufficient, and the surface of the seal layer after opening was markedly covered with resin. It was found that stringing occurs, and there are problems in terms of contamination of the contents with foreign matter and hygiene (see Comparative Example 1 of the present application).

Japanese Unexamined Patent Publication No. 2000-272064 Japanese Unexamined Patent Publication No. 2006-256637 Japanese Unexamined Patent Publication No. 2007-136866

In a packaging material using a packaging material made of polypropylene resin in the field of manufacturing plastic packaging, the contents can be sealed and packaged, and a coagulation-breaking type easy peel can be generated at the time of peeling, which is remarkable on the coagulation-broken surface. There is a demand for a highly transparent film that does not cause stringing, has no problem in terms of foreign matter mixed in the contents and hygiene, and can visually recognize the contents.

In view of the above circumstances, the subject of the present invention is to have good adhesion to the polypropylene resin packaging material of the adherend, coagulation fracture type easy peeling property, and a remarkable thread on the peeled and opened surface. An object of the present invention is to provide an easily openable film that does not cause pulling and has excellent transparency.

As a result of diligent studies, the present inventors have made a linear low-density polyethylene resin containing a polypropylene-based resin (a) produced using a single-site catalyst as a main component and having a specific melt flow rate (MFR). It has been found that the above-mentioned problems can be solved by a film having a sealing layer composed of a resin composition containing b), and the following invention has been completed.

In the first invention, in a film having at least a seal layer, the seal layer contains a polypropylene-based resin (a) produced by using a single-site catalyst as a main component, and melt flow rate (MFR) is 5.0 g. It is an easy-to-open film characterized by being composed of a resin composition containing a linear low-density polyethylene resin (b) of 10 minutes or less.

In the first invention, it is preferable that the resin composition further contains a low-density polyethylene resin (c) having an MFR of 1.0 g / 10 minutes or less.

In the first invention, the polypropylene resin (a) preferably has an MFR of 1.0 g / 10 minutes or more and 20 g / 10 minutes or less.

In the first invention, the linear low-density polyethylene resin (b) contains an ethylene monomer as a main component by an ion polymerization method using a single-site catalyst, and as a comonomer, butene-1, hexene-. 1. It is preferable that the α-olefin of octene-1,4-methylpentene is copolymerized.

In the first invention, when the total content of the polypropylene-based resin (a), the linear low-density polyethylene resin (b), and the low-density polyethylene (c) is 100% by mass, the polypropylene-based resin (a). ) Is 90 to 50% by mass, the low-density polyethylene resin (b) is 10 to 50% by mass, and the low-density polyethylene resin (c) is preferably 0 to 25% by mass.

In the first invention, it is preferable to have a polyolefin-based resin layer adjacent to the seal layer.

In the first invention, it is preferable that the seal layer has a thickness of 1 to 10 μm and the easy-to-open film is a co-extruded film.

The second invention is a package made by using the easy-to-open film of the first invention.

The third invention is a packaging body obtained by heat-sealing a lid material made of the easy-to-open film of the first invention and a container made of polypropylene resin.

The film of the present invention (hereinafter, may be referred to as the present film) is obtained by heat-sealing an adherend made of a polypropylene resin, for example, a container such as a cup or a tray to prepare a package. It can be sealed and packaged, and when it is opened, the seal layer of this film coagulates and breaks, and it can be easily opened with a light force. Excellent in sex. Therefore, it is useful as an easy-to-open film for polypropylene-based resin containers.
In addition, since this film has transparency, the visibility of the contents of the package using this film is good, and the state of the contents can be confirmed when manufacturing, transporting, storing, selling, etc. of the package. Excellent in ease.

Hereinafter, the film of the present invention as an example of the embodiment of the present invention will be described. However, the scope of the present invention is not limited to the embodiments described below.
In the present application, easy peeling property is synonymous with easy opening property and easy peeling property. Further, the sealant film may be referred to as a heat-sealing film or a heat-sealing film. Peeling strength is synonymous with sealing strength and opening strength, and is a measure of easy opening property and sealing sealing property (adhesion).
Further, "for polypropylene resin container" refers to a container made of polypropylene resin, the shape of which is not particularly limited, for example, a container such as a cup or a tray, or a container whose inner surface on the content side is made of polypropylene resin. It means that the film of the present invention can be heat-sealed on the flange portion of the above and used as a lid material.
When the numerical range is indicated by "○○ to △△", it means "○○ or more and △△ or less".

<Easy-to-open film>
This film has a seal layer, and the seal layer contains a polypropylene-based resin (a) produced using a single-site catalyst as a main component, and has a melt flow rate (MFR) of 5.0 g / 10 minutes or less. It is composed of a resin composition containing the linear low-density polyethylene resin (b). The resin composition constituting the seal layer preferably further contains a low-density polyethylene resin (c) having an MFR of 1.0 g / 10 minutes or less, and in this case, the cohesive fracture property can be improved. The form of this film may be a single-layer film composed of only the seal layer or a multilayer film provided with other layers as long as it has the seal layer.

(Polypropylene resin (a))
The polypropylene-based resin (a) constituting the seal layer of this film is not particularly limited as long as it is a polypropylene-based resin produced by using a single-site catalyst, and homopolypropylene, random polypropylene, or the like can be used. From the viewpoint of flexibility and transparency, a propylene-ethylene random copolymer is preferable. The polypropylene-based resin polymerized using the single-site catalyst has a narrower molecular weight distribution, a narrower composition distribution, and fewer low-regular components than the case of using the Ziegler-Natta catalyst. Therefore, the film-formed film has excellent low-temperature sealing properties, high rigidity, high tensile strength and impact resistance, and also exhibits high transparency even in the air-cooled inflation film-forming method. It also has a feature of excellent blocking resistance.

The type of single-site catalyst is not particularly limited, but a typical example is a metallocene catalyst. In the production of metallocene-based polypropylene, (i) a transition metal compound of Group 4 of the periodic table containing a ligand having a cyclopentadienyl skeleton (so-called metallocene compound) and (ii) a metallocene compound are generally reacted. Use a co-catalyst that can be activated into a stable ionic state. If necessary, this co-catalyst may be subjected to a reaction treatment with an organoaluminum compound or the like. The metallocene compound is preferably a crosslinked metallocene compound capable of polymerization having stereoregularity of propylene, and more preferably a crosslinked metallocene compound capable of polymerization having isotactic regularity of propylene.

The method for producing the polypropylene-based resin (a) produced using the single-site catalyst is not particularly limited, and a known slurry polymerization method, bulk polymerization method, gas phase polymerization method, or the like can be used. It can also be produced by using a multi-stage polymerization method.

The melt flow rate (MFR) of the polypropylene-based resin (a) produced using the single-site catalyst is preferably 1.0 to 20 g / 10 minutes, more preferably 2.0 to 15 g / 10 minutes, and 5.0. 10 g / 10 minutes is more preferable. When the MFR is less than 1.0 g / 10 minutes, the adhesion becomes strong when the adherend made of polypropylene resin is heat-sealed, and it is difficult to obtain easy opening. In addition, the film has poor fluidity on the molded surface, making it difficult to form a thin film layer.
The melting point of the polypropylene-based resin (a) is preferably 120 to 160 ° C., the upper limit is more preferably 150 ° C. or lower, and even more preferably 140 ° C. or lower in order to obtain a sealing property that adheres sufficiently in a short heat sealing step. The density of the polypropylene resin (a) is generally preferably ^{880~920kg / m 3, 890~910kg / m} 3 and more preferably.

The MFR of the polypropylene resin (a) is measured under the conditions of a test temperature of 230 ° C. and a load of 2.16 kg based on the JIS K7210-1: 2014 method.
The melting point is measured based on the JIS K7121: 2012 method.
Density is measured according to JIS K7112: 1999 method.

Since this film is used as an easy-to-open film for an adherend made of polypropylene-based resin, the polypropylene-based resin (a) is used as a reference (100% by mass) based on the entire resin composition constituting the seal layer of this film. Formulated as the main component. The "main component" here has a lower limit of preferably 50% by mass or more, more preferably 60% by mass or more, and an upper limit of preferably 90% by mass or less, more preferably 80% by mass or less.

(Linear low density polyethylene resin (b))
The resin composition constituting the seal layer of this film contains linear low-density polyethylene (b) having a melt flow rate (MFR) of 5.0 g / 10 minutes or less.
The polymerization method and branched structure of the linear low-density polyethylene (b) are not particularly limited, and are low to medium pressure radical polymerization methods using Ziegler-based catalysts and metallocene catalysts, medium pressure methods using Philips type catalysts, and others. It can be produced by a known method. Above all, the method by the ion polymerization method using a single-site catalyst is preferable. Further, the linear low-density polyethylene (b) may be produced from a petroleum-derived raw material or a plant-derived raw material.

The linear low-density polyethylene (b) is obtained by copolymerizing ethylene monomer as a main component with α-olefins such as butene-1, hexene-1, octene-1, and 4-methylpentene as comonomer. Is preferable, and among them, an ethylene / hexene-1 copolymer (C6 linear low-density polyethylene) is preferable in terms of the balance between transparency and cohesive destruction.
The comonomer content in the linear low-density polyethylene (b) is preferably in the range of 0.5 to 20 mol%, more preferably in the range of 1 to 18 mol%. When the content of the comonomer is within the above range, the linear low-density polyethylene (b) is appropriately compatible with the propylene-based resin (a) produced by using the single-site catalyst which is the main component of the seal layer. , A transparent sealant film having a relatively fine dispersed particle size can be obtained. When used as a seal layer, it exhibits good easy peeling properties when peeled off from the adherend.

As the single-site catalyst, various single-site catalysts such as a metallocene catalyst system such as a combination of a metallocene compound of the periodic table IV or V transition metal and an organic aluminum compound and / or an ionic compound can be used. can. In addition, since the single-site catalyst has a uniform active site, the molecular weight distribution of the obtained resin is sharper than that of the multi-site catalyst having a non-uniform active site. It is preferable because a film having physical properties with less precipitation and excellent seal strength stability and impact resistance can be obtained.

The linear low-density polyethylene (b) constituting the seal layer of this film has an MFR of 5.0 g / 10 minutes or less, preferably 4.0 g / 10 minutes or less, and more preferably 3.0 g / 10 minutes or less. preferable. When the MFR is 5.0 g / 10 minutes or less, the linear low-density polyethylene (b) has an appropriate dispersion diameter in the propylene resin (a) produced by the single catalyst which is the main component of the seal layer. It is a sealing layer having an excellent balance between transparency and cohesive breaking property.
The lower limit of the MFR of the linear low-density polyethylene (b) is preferably 0.6 g / 10 minutes or more, and more preferably 0.8 g / 10 minutes or more. As a result, the transparency of the seal layer and the film formation stability can be ensured.

The melting point of the linear low-density polyethylene resin (b) is preferably 90 to 140 ° C, more preferably 100 to 130 ° C. When the melting point is 90 ° C. or higher, heat resistance is easily obtained, which is preferable for packaging applications. Further, when the melting point is 140 ° C. or lower, it is preferable because it does not impair the low temperature sealing property.

The MFR of the linear low-density polyethylene resin (b) is measured under the conditions of a test temperature of 190 ° C. and a load of 2.16 kg based on the JIS K7210-1: 2014 method.
The melting point is measured based on the JIS K7121: 2012 method.
Density is measured according to JIS K7112: 1999 method.

(Low density polyethylene resin (c))
In addition to the propylene-based resin (a) and the linear low-density polyethylene resin (b), the seal layer of this film may further contain a non-linear low-density polyethylene resin (c). The MFR of the low-density polyethylene resin (c) is preferably 1.0 g / 10 minutes or less, more preferably 0.9 g / 10 minutes or less, and even more preferably 0.8 g / 10 minutes or less. When the MFR is 1.0 g / 10 minutes or less, a relatively coarse dispersed particle size can be formed in the polypropylene-based resin (a), and the cohesive fracture property is excellent. The lower limit is not particularly limited, but is preferably 0.1 g / 10 minutes or more, and more preferably 0.2 g / 10 minutes or more.

The low-density polyethylene resin (c) may be a polyethylene resin having a density of less than ^{930 kg / m 3} , preferably ^{a density of 910 to 925 kg / m 3.} Within this range, the film-forming property of the film is good, and as a result, good easy peeling property can be obtained.
The melting point of the low-density polyethylene resin (c) is preferably 90 to 140 ° C, more preferably 100 to 130 ° C. By setting the melting point to 140 ° C. or lower, good film-forming property can be obtained and secondary molding becomes possible. Further, by setting the melting point to 90 ° C. or higher, heat resistance can be easily obtained, and after heat-sealing, there is no stringiness even when peeled, and the peeled appearance is excellent.

Further, the low-density polyethylene resin (c) may be produced from a petroleum-derived raw material or a plant-derived raw material. The polymerization method and the branched structure are not particularly limited, and low-density polyethylene resins produced by a high-pressure radical polymerization method, a Ziegler-based, Philips-type, high-medium-low-pressure method using a metallocene catalyst, or other known methods can be used. Can be used. Of these, low-density polyethylene obtained by the high-pressure polymerization method is preferable because it has less fish eyes during film formation. Since the low-density polyethylene produced by the high-pressure polymerization method has long side chain branches, it has strong incompatibility with the polypropylene-based resin (a) and can form a domain having excellent fragility.

The easy-to-open property of this film is that the phase interface dissociation between the sea phase and the island phase of the sea / island (matrix / domain) dispersion structure due to the incompatibility of the polypropylene resin and the polyethylene resin of the seal layer propagates in the horizontal direction of the film. It is caused by coagulation failure. Therefore, the domain diameter (dispersed particle diameter) can be controlled by the incompatibility due to the molecular structure of the polypropylene resin and the polyethylene resin and the melt viscosity of each resin, and the cohesive fracture property can be exhibited. Since the seal layer of this film is mainly composed of the polypropylene resin (a), the island phase of the linear low-density polyethylene resin (b) is dispersed as a domain in the sea phase of the polypropylene resin (a). Has.

In the present invention, while investigating the structure of the resin composition and the mechanism of expressing the cohesive destruction function, a polypropylene-based resin (a) and a linear low-density polyethylene resin (b) having a specific melt flow rate (MFR) are used. ), It has been found that a film having both transparency, heat-sealing property, and cohesive breaking property of the film can be obtained. Specifically, it is easy to have a seal layer composed of a polypropylene-based resin (a) produced by a single catalyst and a resin composition composed of a linear low-density polyethylene resin (b) having an MFR of 5.0 g / 10 minutes or less. Regarding openable films.

The larger the particle size of the dispersed particles, the more likely it is that cohesive failure will occur. In comparison, transparency is maintained by creating a form in which a large number of islands of the linear low-density polyethylene resin (b) having small dispersed particles exist between the islands of the low-density polyethylene resin (c) having a large dispersed particle size. At the same time, it becomes possible to efficiently propagate the cohesive fracture. Further, the presence of the islands of the low-density polyethylene resin (c) having large dispersed particles makes it easy for cohesive fracture to occur regardless of the peeling direction, and is expected to have an effect of contributing to the improvement of isotropic property of easy opening. Further, since the island phases of the linear low-density polyethylene resin (b) and the low-density polyethylene resin (c) are dispersed in the sea phase of the polypropylene-based resin (a), the difference in dispersibility between the two is cohesive destructiveness. That is, it contributes to easy peeling.

(Composition ratio)
The seal layer of this film contains a polypropylene-based resin (a) produced using a single-site catalyst as a main component, and is a linear low-density polyethylene resin (melt flow rate (MFR) 5.0 g / 10 minutes or less). It is composed of a resin composition containing b), and the resin composition may further contain a low-density polyethylene resin (c) having an MFR of 0.1 g / 10 minutes or less.
When the total content of the resin composition constituting the seal layer is 100% by mass, the total amount of the polypropylene-based resin (a), the linear low-density polyethylene resin (b), and the low-density polyethylene resin (c) The mass ratio is preferably (a) :( b + c) = (90 to 50) :( 10 to 50), and more preferably (90 to 60) :( 10 to 40). Further, in (a): (b): (c), (90 to 50) :( 10 to 50): (0 to 25) is preferable, and (85 to 60) :( 10 to 40): (5 to 5). 20) is more preferable. By setting the polypropylene-based resin (a) to 50% by mass or more, sufficient adhesion to an adherend made of the polypropylene-based resin can be obtained, and heat resistance can also be imparted. Further, by setting the polypropylene resin (a) to 90% by mass or less, it is easy to obtain good easy peeling properties.

The composition ratio of each resin is analyzed by combining 1H-NMR method, FT-IR method, DSC method, high temperature GPC method, temperature elution fractionation method (TREF), crystallization elution fractionation method (CEF) and the like. Among them, TREF is preferably used as a method for analyzing polyolefin-based resins. The resin dissolved in the solvent is injected into a TREF column warmed to a predetermined temperature, and then the temperature is lowered at a constant rate to crystallize the column carrier. At this time, the component having high crystallinity and few branches is crystallized first, and the component having low crystallinity and many branches is crystallized as the temperature decreases. Then, by raising the temperature, the components having low crystallinity are eluted in order from the components having high crystallinity, and the fraction is separated according to the degree of short chain branching. Furthermore, by using a TREF column for a CFC that has the characteristics of a size exclusion chromatograph (GPC), it is possible to determine the two-dimensional distribution of crystallinity and molecular weight of a polyolefin resin, and polyethylene with different crystallinity and melt viscosity. Resin and polypropylene resin can be separated. Further, by expanding the measurement temperature range to −20 ° C., a thermoplastic elastomer having low crystallinity can be separated.

(Other resins)
(High density polyethylene resin)
The resin composition constituting the seal layer of the present film may further contain a high-density polyethylene resin as long as the effects of the present invention are not impaired. The density of high-density polyethylene resin is a resin 930~970kg / ^{m 3} or more, the lower limit is preferably 935 kg / ^{m 3} or more, the upper limit is more preferably equal to or less than 960 kg / ^{m 3.}
The melt flow rate (MFR) of the high-density polyethylene resin is preferably 4.0 g / 10 minutes or more. In general, since polyethylene resin has a correlation between density and melting point, high-density polyethylene resin has a higher melting point and heat of fusion than linear low-density polyethylene resin (b) and low-density polyethylene resin (c). However, if the MFR and density values of the high-density polyethylene resin are within this range, good adhesion can be obtained without hindering the adhesion with the polypropylene resin as the adherend even in a low-temperature heat seal at 140 ° C. can get. Further, since the high-density polyethylene resin has a relatively high melting point, the presence of dispersed particles (domains) in the seal layer causes polypropylene of the seal layer and the adherend to be adhered even under a high temperature seal temperature condition of, for example, 200 ° C. Adhesion with the resin does not become too strong, and good easy peelability can be easily obtained.

The high-density polyethylene resin may be produced from a petroleum-derived raw material or a plant-derived raw material. The polymerization method and the branched structure are not particularly limited, and a resin produced by a low to medium pressure radical polymerization method using a Ziegler-based catalyst or a metallocene catalyst, a medium pressure method using a Philips type catalyst, or another known method is used. be able to.

(Hydrogenated petroleum resin)
The resin composition constituting the seal layer of this film may contain other resins for the purpose of improving the fragility, and among them, the cohesive fracture property of the seal layer is improved without impairing the transparency. It may contain a hydrogenated petroleum resin which can be contained. Examples of petroleum resins include C4 to C10 aliphatic olefins and diolefins obtained from by-products by thermal decomposition of naphtha, and C8 or higher aromatic compounds having an olefinically unsaturated bond. Examples thereof include aliphatic, aromatic and copolymerized petroleum resins obtained by singly or copolymerizing one or more of the contained compounds. Among them, aliphatic petroleum containing C5 distillate as a main raw material. Preferred examples thereof include a resin, an aromatic petroleum resin containing a C9 distillate as a main raw material, a copolymerized petroleum resin thereof, and an alicyclic petroleum resin. Hydrogenated petroleum resins are obtained by hydrogenating these petroleum resins by a conventional method. For example, hydrogenated aliphatic petroleum resins, hydrogenated aromatic petroleum resins, hydrogenated copolymerized petroleum resins and hydrogenation. Examples include alicyclic petroleum resin and hydrogenated terpene resin. Among them, as the hydride alicyclic petroleum resin, those obtained by copolymerizing a cyclopentadiene compound, an aromatic vinyl compound and an indene compound and hydrogenating them are particularly preferable.

The hydrogenation rate of the hydride petroleum resin is compatible with the polypropylene-based resin (a) constituting the seal layer, the linear low-density polyethylene resin (b), etc., particularly with the polypropylene-based resin (a). From the viewpoint of color tone, thermal stability, moisture permeation resistance, etc. of the formed film, 60% or more is preferable, 80% or more is more preferable, and 90% or more is further preferable. Further, the hydrogenated petroleum resin preferably contains substantially no polar group such as a hydroxyl group, a carboxyl group or a halogen, or an unsaturated bond such as a double bond.
The hydrogenated petroleum resin preferably has a softening point of 80 ° C. or higher and 150 ° C. or lower, and more preferably 90 ° C. or higher and 140 ° C. or lower. When the softening point is 80 ° C. or higher, the resin pellets are not fixed, and the film is not blocked or the surface is sticky during the film formation, the secondary processing of the film, the transportation and storage, and the like. Further, when the softening point is 150 ° C. or lower, the compatibility with the resin constituting the seal layer is good, and the film is bleeded out and the occurrence of powder blowing is reduced.
The softening point of the hydrogenated petroleum resin is measured by the JIS K6863: 1994 method.

The hydride petroleum resin is discharged from the crystal part of the resin in the crystallization process of the polypropylene-based resin (a), the linear low-density polyethylene resin (b), etc. in the film formation, and is mainly of the polypropylene-based resin (a). It comes to exist in the amorphous part, and the hydride petroleum resin acts to suppress the movement of the molecular chain of the amorphous part of the polypropylene-based resin (a), reduce the flexibility of the resin, and promote cohesive breakdown. .. As a result, it is possible to reduce the occurrence of stringing / filming phenomena in cohesive fracture.
Further, since the hydrogenated petroleum resin has good compatibility with the polypropylene-based resin (a), the cohesive fracture property can be improved without lowering the transparency of the film and the seal layer.

(Adjacent layer)
By having the polyolefin-based resin layer adjacent to the seal layer, this film can maintain the strength of the seal layer and effectively exhibit cohesive fracture.
The polyolefin-based resin used for the adjacent layer is not particularly limited, but when the polypropylene-based resin (a), the linear low-density polyethylene resin (b), or the low-density polyethylene resin (c) constituting the above-mentioned seal layer is used, It is preferable because the interlayer adhesion between the seal layer and the adjacent layer is increased. Of these, linear low-density polyethylene composed of low-density polyethylene and an ethylene / α-olefin copolymer is preferable from the viewpoint of film-forming property of the coextruded film. For example, when a coextruded film is formed by an inflation method, the bubbles are stable and it is easy to perform arbitrary blow-up.

Further, a modified adhesive resin can be used as the polyolefin resin of the adjacent layer. For example, a polyolefin resin modified with an unsaturated carboxylic acid or a derivative thereof is preferably used. As such unsaturated carboxylic acid, acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid and the like can be used. Further, as the derivative of the unsaturated carboxylic acid, the above-mentioned ester or anhydride of the unsaturated carboxylic acid can be used, and for example, methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate and the like can be used. , Butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, acrylamide, methacrylic acid, sodium acrylate and the like. In addition, vinyl acetate and the like can also be used. When the adjacent layer is made of an adhesive resin, the adhesion between the layers of the film can be improved when another layer is provided on the side opposite to the seal layer side of the adjacent layer.

(Other layers)
The film of the present invention may have at least a seal layer and the above-mentioned adjacent layer adjacent to the seal layer, but further has another layer on the side opposite to the seal layer side of the adjacent layer. You may.
Examples of the resin constituting the other layer include polyolefin resins such as polyethylene and polypropylene, gas barrier resins typified by ethylene-vinyl acetate copolymer saponified products and aromatic polyamides, polyamide 6, polyamide 66, and polyamide 6. , 66, Polyamide-based resins such as polyamide 6, 10 copolymers, polyester-based resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate, and adhesive resins can be used according to the film requirements. Further, a plurality of other layers may be provided.

(Other ingredients)
Each layer of the film of the present invention can appropriately contain additives as long as it does not impair its properties. For example, colorants, inorganic fillers, organic fillers, UV absorbers, light stabilizers, heat stabilizers, antioxidants, lubricants, blocking agents, hydrolysis inhibitors, plasticizers, flame retardants, antistatic agents, Antifogging agents and the like can be mentioned. The amount of these additives added is not particularly limited, and can be appropriately determined within a range that does not impair the desired physical properties of the present invention.

<Manufacturing method of easy-to-open film>
The film of the present invention is not particularly limited, and can be produced by a known T-die method, inflation method, or the like.
The method for producing a film by providing a polyolefin resin layer (adjacent layer) adjacent to the seal layer is not particularly limited, but is a known feed block method, a multi-manifold method, or a coextrusion method using a combination thereof. Can be preferably used.
As a method for producing a film by providing another layer on the side opposite to the seal layer side of the adjacent layer, the coextrusion method is similarly used, or the film is formed by a heat laminating method, an extrusion laminating method, or a dry laminating method. You can also do it.
The film of the present invention may be unstretched, uniaxially stretched, simultaneously biaxially stretched, or sequentially biaxially stretched.
Further, the film or coextruded film of the present invention can also be subjected to surface treatment or surface treatment such as corona treatment, printing, coating and vapor deposition, if necessary. Further, when the other layer is provided in the adjacent layer, the other layer can be laminated after performing a surface treatment such as a corona treatment on the adjacent layer.

When the present film is a single-layer film having only a seal layer, the thickness thereof is preferably 1 to 30 μm.
When this film is a co-extruded film, the thickness of the seal layer is preferably 1 to 10 μm, preferably 1 to 10 μm, from the viewpoints of both heat-sealing property, good cohesive peeling property without stringing and film pulling, and transparency. 8 μm is more preferable, and 2 to 5 μm is further preferable from the viewpoint that cohesive failure is easily propagated in the horizontal direction of the film and the easy-to-open property is improved. The total thickness of the coextruded film including the adjacent layer and other layers is preferably 10 μm or more, more preferably 15 μm or more, still more preferably 20 μm or more, from the viewpoint of film strength, handleability, and secondary processability. The upper limit is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.
The thickness of the film, the total thickness of the co-extruded film, and the thickness of each layer can be measured from a stylus type thickness gauge and film cross-section observation.

<Easy-to-open film characteristics>
The film of the present invention preferably has the following characteristics.
(Heat sealability, easy opening property)
This film is a cohesive failure type that has sufficient adhesion to an adherend made of polyolefin resin, especially polypropylene resin, under heat sealing temperature conditions of around 140 ° C and 160 ° C, and is excellent at the time of opening and peeling. It is preferable to combine the ease of opening. In particular, having sufficient adhesion to a polypropylene adherend in a low temperature region, for example, a heat seal temperature condition of 140 ° C. is beneficial in terms of production stability in packaging production. Further, it is preferable that the peeled surface after opening and peeling has no noticeable stringing or the like and has a beautiful peeled surface from the viewpoint of preventing foreign matter from being mixed in and protecting the safety and hygiene of consumers.
Examples of the polypropylene-based resin of the adherend include homopolypropylene and random copolymer polypropylene. This film can exhibit good heat-sealing properties and easy-opening properties even if the adherend is homopolypropylene having a high melting point.

The evaluation method of heat sealability and easy opening property is as follows, for example. A 300 μm-thick homopolypropylene sheet is used as an adherend, and this film is overlaid on it (for coextruded films, the seal layer side is overlaid), the seal temperature is 140 to 160 ° C, the seal width is 5 mm, and the seal pressure is 0. Heat-seal to prepare a sample for evaluation under the conditions of 2 MPa and 1 second of sealing. To measure the heat seal adhesion and easy opening property, a heat-sealed sample is cut into strips with a width of 15 mm to prepare a test piece, and based on JIS Z0238: 1998, the heat seal part is centered and the peeling angle is 180 degrees. , A tensile test is performed under the condition of a tensile speed of 300 mm / min, and the peel strength (unit: N / 15 mm width) is measured.

The lower limit of the peel strength is preferably 5N / 15mm width or more, and more preferably 8N / 15mm width or more. The upper limit is preferably 20 N / 15 mm width or less, more preferably 18 N / 15 mm width or less, and further preferably 16 N / 15 mm width or less. If it has a peeling strength in the above range, it adheres to the adherend with sufficient strength and has excellent sealing properties for impurities when packaging liquid contents such as water and soup, and at the time of use. Can be easily peeled and opened by hand. In this film, the inside of the seal layer is coagulated and broken and can be peeled and opened, and it is easily peeled without stringing or film pulling. It is preferable to obtain a beautiful peeled appearance without causing fluffing, and it is more preferable to obtain a beautiful peeled appearance without causing fluffing or tearing of the resin.

(transparency)
From the viewpoint of visibility, aesthetics, design, etc. of the contents, the transparency of this film is preferably 20% or less, more preferably 15% or less, the lower limit is not particularly limited, and the value is smaller. Is preferable because it has good transparency. All haze measurements are made in accordance with JIS K7136: 2000.

<Packaging body>
Since this film has good heat-sealing properties and easy peeling properties, it can be heat-sealed with an adherend in a shape suitable for the contents to form a package. In particular, a packaging body in which a lid material made of this film and a container made of polypropylene resin are heat-sealed is useful.
When a coextruded film is used, the seal layer side is set to the adherend (for example, container) side, and the package is heat-sealed with the container to prepare a package. Examples of the polypropylene-based resin constituting the container include homopolypropylene and random copolymer polypropylene. In this film, even if the adherend is homopolypropylene having a high melting point, good heat-sealing property and easy-opening property can be exhibited. Further, this film can be laminated with other plastic films and sheets, metal foil, paper and the like by a known method such as dry lamination to be used as a packaging material, and a packaging body can be produced using them.

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited by the following examples and the like.
Using the following raw materials, a film was prepared by the following method, and tested and evaluated. The resin composition of the seal layer and the evaluation results are summarized in Table 1.

<Raw material (seal layer)>
(Polypropylene resin)
PP1: Propylene-ethylene copolymer polymerized with a metallocene catalyst (MFR: 7.0 g / 10 minutes, melting point: 124 ° C., density 900 kg / m ³ )
(Linear low density polyethylene resin)
LLD1: C6 linear low density polyethylene resin (MFR: 0.8 g / 10 minutes, melting point: 124 ° C., density 926 kg / m ³ )
LLD2: C6 linear low density polyethylene resin (MFR: 1.5 g / 10 minutes, melting point: 121 ° C., density 923 kg / m ³ )
LLD3: C6 linear low density polyethylene resin (MFR: 4.0 g / 10 minutes, melting point: 122 ° C., density 923 kg / m ³ )
LLD4: C6 linear low density polyethylene resin (MFR: 6.0 g / 10 minutes, melting point: 116 ° C., density 919 kg / m ³ )
LLD5: C8 linear low density polyethylene resin (MFR: 2.1 g / 10 minutes, melting point: 119 ° C., density 919 kg / m ³ )

(High-pressure polymerization method low-density polyethylene)
LD1: High-pressure polymerization method low-density polyethylene resin (MFR: 0.7 g / 10 minutes, melting point: 112 ° C., density 924 kg / m ³ )
LD2: High-pressure polymerization method low-density polyethylene resin (MFR: 4.0 g / 10 minutes, melting point: 111 ° C., density 923 kg / m ³ )
LD3: High-pressure polymerization method low-density polyethylene resin (MFR: 8.4 g / 10 minutes, melting point: 107 ° C., density 923 kg / m ³ )

<Raw material (adjacent layer)>
Linear low density polyethylene resin (MFR: 1.5 g / 10 minutes, melting point: 121 ° C., density 923 kg / m ³ )

<Examples 1 to 6, Comparative Examples 1 to 4>
Using the above raw materials, the seal layer has the composition shown in Table 1, the raw material is supplied to each extruder for each layer, and the seal layer and the adjacent layer are co-extruded under the condition of an extrusion temperature of 200 ° C. by the T-die coextrusion method. , A water-cooled metal cooling roll at 40 ° C. was used to obtain a coextruded film having a seal layer thickness of 5 μm and an adjacent layer thickness of 25 μm.
Next, the surface of the adjacent layer of the coextruded film was subjected to corona discharge treatment, and dry-laminated with a 12 μm-thick biaxially stretched polyethylene terephthalate film using an ether-based polyurethane adhesive to obtain a laminated film.

<Evaluation method>
(1) Heat-seal test and peel-off test A 300 μm-thick homopolypropylene sheet as an adherend and the seal layer surfaces of the laminated films obtained in Examples and Comparative Examples are laminated so as to face each other, and one end thereof is used with a heat seal machine. Heat-sealed under the conditions of a sealing width of 5 mm, a sealing pressure of 0.2 MPa, and a sealing time of 1 second. The set seal temperature was tested in two ways, 140 ° C and 160 ° C.
After that, it was cut into strips with a length of 50 mm and a width of 15 mm, and according to JIS Z0238: 1998, the ends of the two films were attached to the grip of the tensile tester with the heat seal part at the center, and the peeling angle was 180 degrees. Under the condition of peeling speed of 300 mm / min, the strip piece is pulled in the length direction until it peels or breaks, and the measured maximum stress is measured as the heat seal strength (unit: N / 15 mm width), and the heat seal strength is 5 N. The cases of / 15 mm width or more and 20 N / 15 mm width or less were evaluated as having good adhesion and easy peeling property.

Next, the morphology of the peeled surface after the peeling test was observed and judged according to the following criteria, and when the seal layer was coagulated and fractured (⊚ and 〇), it was evaluated as having good cohesive fracture property.
◎: Aggregate fracture, no stringing, etc. 〇: Aggregate fracture, slight stringing, etc.
▲: Insufficient cohesive failure, remarkable stringing, filming, fluffing, etc. ■: The film does not peel off and the film tears ×: The film and the adherend are not in close contact

(2) Transparency With respect to the coextruded films obtained in Examples and Comparative Examples, the total haze was measured using a haze meter NDH5000 manufactured by Nippon Denshoku Kogyo Co., Ltd. in accordance with JIS K7136: 2000.
Those with a total haze of 20% or less were judged to be good.

The seal layers of Examples 1 to 4 contain a polypropylene-based resin (a) produced using a single-site catalyst as a main component, and have a melt flow rate (MFR) of 5.0 g / 10 minutes or less in a linear low density. It is composed of a resin composition containing a density polyethylene resin (b), and all of the films have a total haze of 10.0% or less, which is very excellent as an easy-to-open sealant film for an adherend made of a polypropylene resin. It was transparent. Further, at heat-sealing temperatures of 140 ° C. and 160 ° C., a beautiful peeled surface was obtained, which had sufficient adhesion and easy-opening property, and further, there was no remarkable stringing on the coagulated fractured surface.

The seal layers of Examples 5 and 6 are composed of a resin composition obtained by adding a high-pressure polymerization method low-density polyethylene resin (c) of MFR 0.7 g / 10 minutes to the seal layer compositions of Examples 2 and 3, respectively. The film exhibited a total haze of 20.0% or less in transparency and very excellent easy peeling without any stringiness. This is similar to Examples 5 and 6, as compared with Examples 1 to 4 in which only fine dispersed particles made of linear low-density polyethylene (b) are present in the polypropylene-based resin (a). In addition, due to the form in which large dispersed particles derived from the low-density polyethylene resin (c) are also present, the propagation of cohesive failure is efficiently performed, and a particularly excellent peeled appearance without stringing or the like can be obtained. it is conceivable that.

The seal layer of Comparative Example 1 is composed of a resin composition containing a polypropylene resin (a) produced by a single catalyst as a main component and a linear low-density polyethylene resin having an MFR of 5.0 g / 10 minutes or more, and the film thereof. The transparency was good because the low-viscosity linear low-density polyethylene resin was present as fine dispersed particles. On the other hand, in the peeling test, the polypropylene-based resin (a) phase of the matrix and the linear low-density polyethylene resin phase of the domain resin did not coagulate and break, and remarkable stringing occurred, resulting in easy peeling property. Was inadequate.

The seal layer of Comparative Example 2 is composed of a resin composition containing a polypropylene resin (a) produced by a single catalyst as a main component and a low density polyethylene resin having an MFR of 0.7 g / 10 min, and has a high viscosity and a low density. The presence of polyethylene as large domain particles showed excellent easy peelability, but the total haze was very high and the film had poor transparency.
The seal layers of Comparative Examples 3 and 4 contain a polypropylene resin (a) produced by a single catalyst as a main component, and contain low-density polyethylene resins of MFR 4.0 g / 10 minutes and 8.4 g / 10 minutes, respectively. The total haze of the film was 20.0% or less, but remarkable stringing, filming, and fluffing occurred under heat-sealing conditions of 140 ° C. and 160 ° C.

The film of the present invention exhibits sufficient adhesion strength when heat-sealed with an adherend made of a polypropylene resin, and has a contaminant sealing property. In addition, when the package is prepared and opened, the seal layer is coagulated and broken, and the package can be peeled and opened with a light force. At the same time, stringing, fluffing, and resin tearing are unlikely to occur, so that food safety and hygiene are good. It excels in. Further, since it has transparency, the visibility of the contents of the package is good.

Claims (9)

In a film having at least a seal layer, the seal layer contains a polypropylene-based resin (a) produced using a single-site catalyst as a main component, and has a melt flow rate (MFR) of 5.0 g / 10 minutes or less. An easy-to-open film characterized by being composed of a resin composition containing a low-density polyethylene resin (b). The easy-to-open film according to claim 1, wherein the resin composition further contains a low-density polyethylene resin (c) having an MFR of 1.0 g / 10 minutes or less. The easy-to-open film according to claim 1 or 2, wherein the polypropylene resin (a) has an MFR of 1.0 g / 10 minutes or more and 20 g / 10 minutes or less. The linear low-density polyethylene resin (b) is subjected to an ionic polymerization method using a single-site catalyst, and the ethylene monomer is used as a main component, and butene-1, hexene-1, octene-1, and 4 are used as comonomers. The easy-to-open film according to any one of claims 1 to 3, which is a copolymer of α-olefin of −methylpentene. When the total content of the polypropylene-based resin (a), the linear low-density polyethylene resin (b), and the low-density polyethylene (c) is 100% by mass, the polypropylene-based resin (a) is 90 to 50% by mass. The easy-to-open film according to any one of claims 1 to 4, wherein the low-density polyethylene resin (b) is 10 to 50% by mass, and the low-density polyethylene resin (c) is 0 to 25% by mass. An easy-to-open film having a polyolefin-based resin layer adjacent to the seal layer of the easy-to-open film according to any one of claims 1 to 5. The easy-to-open film according to claim 6, wherein the seal layer has a thickness of 1 to 10 μm and is a coextruded film. A package obtained by using the easy-to-open film according to any one of claims 1 to 7. A package obtained by heat-sealing a lid material made of the easy-to-open film according to any one of claims 1 to 7 and a container made of a polypropylene resin.