JP2021095162A - Easily openable film and packaging body - Google Patents

Abstract

To provide an easily openable film which shows a cohesive failure type easy peeling property in the case where heat seal is performed at a comparatively low seal temperature (140-180°C) with respect to a polypropylene resin packaging material of a body to be adhered, and which has transparency.SOLUTION: In an easily openable film, in the film which at least includes a seal layer, the seal layer is constituted by a resin composition which includes polypropylene resin (a) manufactured by using a single-site catalyst as a main component, and also includes low-density polyethylene resin (b) having a melt flow rate (MFR) of below 1.0 g/10 min and low-density polyethylene resin (c) having MFR of over 5.0 g/10 min.SELECTED DRAWING: None

Description

The present invention relates to an easily openable film having a sealing function and a package using the film.

Conventionally, container bottom materials made of polyolefin resin have been used for individually wrapped cup-shaped products containing jelly, steamed tea, prepared foods, medical products such as deep-squeezed packages and disposable injectors, daily necessities, and stationery. Has been used as the lid material, and a film containing a seal layer made of a polyolefin resin having a melting point similar to that of the container bottom material has been used. For example, with the expansion of the market and the diversification of consumer needs, the sealing layer of the lid film has transparency, oxygen barrier property, and water vapor barrier that allow the contents to be visually recognized when stored as a food packaging film or container. Various properties such as property, impact resistance, and heat resistance are required.
Above all, the sealing layer of the lid film of the food packaging container needs to have opening property in addition to heat sealing property for sealing the contents, and it is a light peeling (easy peel) that can be easily opened, and the peeling surface The required level is very high, such as no filming and stringing, and constant peeling force at a wide range of heat seal temperatures.

The form of easy peel includes an interfacial peeling mechanism that peels off at the interface between the heat seal layer and an adherend such as a container, an delamination mechanism that peels off at the interface between the seal layer and the peeling layer in the multilayer film, and the seal layer is coagulated and broken. An example is a coagulation-breaking mechanism that results in light peeling. Of these, the coagulation-breaking type has a relatively simple structure and exhibits good contaminant sealing properties for packaging containers containing water-containing contents. Therefore, the coagulation-breaking type lid material is particularly suitable for polypropylene containers. As a result, various studies have been conducted so far.

In Patent Document 1, in order to achieve both low-temperature sealing property, heat resistance, and easy-opening property, a support layer made of a polyolefin resin and a polypropylene resin 30 to, for example, melt flow rate (MFR) 1.0 g / 10 minutes or more are described. The sheet layer was 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, and the ratio of the MFR of the polypropylene resin to the polyethylene resin was specified. Composite multilayer sheets for packaging are disclosed.

In Patent Document 2, for the purpose of sealing and easy opening, the first layer is 20 to 60 parts by weight of a high-density polymerization low-density polyethylene resin having a melt flow rate (MFR) of 1 to 7 g / 10 minutes and an MFR of 1 to 15 g / 15 g /. It consists of 40 to 80 parts by weight of a 10-minute polypropylene-ethylene random copolymer, and the second layer is mainly composed of an ethylene-α / olefin copolymer polymerized using a single-site catalyst, high-density polyethylene or a polypropylene-based resin. A lid material for laminating a base film on the surface of the second layer is disclosed.

In Patent Document 3, the base material layer is composed of medium-density polyethylene, high-density polyethylene, or a resin composition containing polypropylene as a main component for heat-sealing property, sealing property, and easy-opening property, and the sealing layer is melt flow rate. (MFR) An easy peel sealant composed of a resin composition containing a mixture of polypropylene at 10 to 40 g / 10 min and low density polyethylene as a main component 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-based resins are listed, and most of them become hazy with poor transparency in the combination of both resin types. It was a thing.
Further, the first layer (seal layer) of the combination of the high-pressure polymerization method low-density polyethylene resin and the polypropylene-ethylene random copolymer disclosed in Patent Document 2 has a relatively large domain in the matrix in the incompatible polymer blend. Since it is large, the outer haze of the surface of the seal layer of the film-formed film becomes large and sufficient transparency cannot be obtained when the domain quantity for obtaining good easy-opening property, that is, the compounding ratio of both resins is used. there were.
Further, in the seal layer disclosed in Patent Document 3, since the MFR of polypropylene is as high as 10 to 40 g / 10 minutes, the extrusion temperature at the time of film formation cannot be increased, and therefore the seal layer is easily crystallized. Also, since polypropylene also has a high MFR, the polyethylene domain in the polypropylene matrix becomes large. Due to these factors, transparency was insufficient.

Further, in a packaging material using a packaging material made of polypropylene resin in the field of manufacturing plastic packaging, heat sealing is generally performed under the condition of a sealing temperature of 140 to 180 ° C. Therefore, any of the sealing temperatures of 140 to 180 ° C. There is a demand for a film capable of causing coagulation-breaking type easy peel even at the above temperature.

Japanese Unexamined Patent Publication No. 2000-272064 Japanese Unexamined Patent Publication No. 2006-256637 JP-A-2007-168257

In view of the above circumstances, an object of the present invention is an easy coagulation-breaking type when a packaging material made of polypropylene-based resin as an adherend is heat-sealed at a relatively low sealing temperature (140 to 180 ° C.). It is an object of the present invention to provide an easily openable film which exhibits peeling property and has transparency.

As a result of diligent studies, the present inventors have made a low-density polyethylene resin (a low-density polyethylene resin) in which the seal layer contains a polypropylene-based resin (a) produced by using a single-site catalyst as a main component and has a specific melt flow rate (MFR). It has been found that the above problems can be solved by a film composed of a resin composition containing b) and (c), 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 1.0 g. An easy-to-open film characterized by being composed of a resin composition containing a low-density polyethylene resin (b) of less than / 10 minutes and a low-density polyethylene resin (c) of MFR 5.0 g / more than 10 minutes.

In the first invention, the melt flow rate (MFR) of the polypropylene-based resin (a) is preferably 1.0 g / 10 minutes or more and 20 g / 10 minutes or less.

In the first invention, when the total amount of the polypropylene resin (a), the low density polyethylene resin (b) and the low density polyethylene resin (c) is 100% by mass, the polypropylene resin (a) Is 90 to 50% by mass, the low-density polyethylene-based resin (b) is preferably 5 to 25% by mass, and the low-density polyethylene-based resin (c) is preferably 5 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, the thickness of the seal layer is preferably 1 to 10 μm.

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 using the easy-to-open film of the first invention and a bottom material made of a polypropylene resin.

The film of the present invention (hereinafter, may be referred to as the present film) is heat-sealed with an adherend made of polypropylene resin, for example, a bottom material such as a container, a cup, or a tray to prepare a package, and the package is opened. The seal layer of the film coagulates and breaks, and the film can be easily opened with a light force. At that time, fluffing and stringing are less likely to occur, and the film is excellent in food hygiene and food safety. Therefore, it is useful as an easy-to-open sealant film for polypropylene-based resin bottom materials.
Further, since the film of the present invention has transparency, the package of the present invention has good visibility of the contents, and it is easy to confirm the state of the contents when manufacturing, transporting, storing, selling, etc. of the package. Excellent.

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 and sealing sealing.
Further, "for polypropylene resin bottom material" is made of polypropylene resin, and the shape is not particularly limited, but for example, the bottom material of containers, cups, trays, etc., and the inner surface of the bottom material on the content side is made of polypropylene resin. This means that the film of the present invention can be heat-sealed on the flange portion of the bottom material to be used as a lid material.
"Containing as a main component" means 50% by mass or more with respect to the total amount of the constituents, preferably more than 50% by mass, more preferably 60% by mass or more, still more preferably 70% by mass or more. When the numerical range is indicated by "~", it means the above and the following.

<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 less than 1.0 g / 10 minutes. It is composed of a resin composition containing the low-density polyethylene-based resin (b) of the above and a low-density polyethylene-based resin (c) having an MFR of 5.0 g / 10 minutes or more. 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 produced by using a single-site catalyst. Homopolypropylene, random polypropylene and the like can be used without particular limitation. 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 reacted with an organoaluminum compound or the like. The metallocene compound is preferably a crosslinked metallocene compound capable of polymerizing with stereoregularity of propylene, and more preferably a crosslinked metallocene compound capable of polymerizing with isotactical 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, and the upper limit is particularly preferably less than 10 g / 10 minutes. 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 fluidity is poor on the molded surface of the film, and it is difficult to form a thin film layer.
The melting point of the polypropylene-based resin (a) is preferably 120 to 160 ° C, and the upper limit is 150 ° C or less in order to obtain a sealing property that adheres sufficiently in a short heat sealing step in a wide temperature range of 140 to 180 ° C. It is preferable, and 140 ° C. or lower is more preferable. 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 sealant film for a bottom material made of polypropylene-based resin, polypropylene-based resin (a) is blended as a main component with respect to the total amount of resin constituting the seal layer of this film. The amount is preferably more than 50% by mass, more preferably 60% by mass or more, still more preferably 70% by mass or more.

(Low density polyethylene resin (b), low density polyethylene resin (c))
The polyethylene-based resin constituting the seal layer of this film is a low-density polyethylene-based resin (b) having a melt flow rate (MFR) of less than 1.0 g / 10 minutes and a low-density polyethylene-based resin having an MFR of more than 5.0 g / 10 minutes. (C) and is included.
Low-density polyethylene resin may be a polyethylene resin density 910~930kg / ^{m 3,} preferably a density 915~925kg / ^{m 3.} Within this range, good easy peeling properties can be obtained. Further, it 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 low-density polyethylene resin produced by a high-pressure radical polymerization method, a high-medium-low pressure method using a Ziegler-based, Phillips-type or metallocene catalyst, or other known method is used. Can be done. Of these, low-density polyethylene and linear low-density polyethylene obtained by the high-pressure polymerization method are preferable because they have 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.

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 is in the horizontal direction of the film. It is produced by propagating and coagulating and breaking. Therefore, the domain diameter (dispersed particle diameter) can be controlled by the incompatibility due to the molecular structure of the polypropylene-based resin and the polyethylene-based resin and the melt viscosity of the resin, and the cohesive fracture property can be exhibited. Since the seal layer of this film is mainly composed of the polypropylene resin (a), it has a form in which the islet phase of the polyethylene resin is dispersed as a domain in the sea phase of the polypropylene resin (a).
As a result of examining the structure and function expression mechanism of the constituent resin, the present invention shows a low-density polyethylene resin having a large melt viscosity and a low-density polyethylene resin having a low melt viscosity, which are represented in a specific melt flow rate (MFR) range. It has been found that by using the above two types, transparency and good coagulation-breaking easy peeling property can be obtained when heat-sealed at a relatively low sealing temperature. Specifically, two types of low-density polyethylene resin (b) having an MFR of less than 1.0 g / 10 minutes and a low-density polyethylene resin (c) having an MFR of more than 5.0 g / 10 minutes are used.

The melt flow rate (MFR) of the low-density polyethylene resin (b) is less than 1.0 g / 10 minutes, preferably 0.9 g / 10 minutes or less, and more preferably 0.8 g / 10 minutes or less. The lower limit is preferably 0.2 g / 10 minutes or more, and more preferably 0.3 g / 10 minutes or more. By using the polyethylene resin (b) having a large melt viscosity and a small MFR, a dispersed particle size on the order of μm is generated, cohesive failure of the seal layer is likely to occur, and easy peeling without stringing can be obtained. it can. Further, within the range of this MFR, a film can be formed without significantly deteriorating the film forming property.
The melt flow rate (MFR) of the low-density polyethylene resin (c) is more than 5.0 g / 10 minutes, preferably 6.0 g / 10 minutes or more, more preferably 7.0 g / 10 minutes or more, still more preferably. It is over 7.0 g / 10 minutes. By using the polyethylene resin (c) having a small melt viscosity and a large MFR, finer dispersed particles can be generated and the transparency can be increased.

The larger the particle size of the dispersed particles, the more likely it is that cohesive fracture will occur, but the haze due to incompatibility and the haze due to the coarsening of the surface of the seal layer increase the opacity. Therefore, by creating a form in which a large number of islands of the polyethylene resin (c) having a small dispersed particle size are present between the islands of the polyethylene resin (b) having a large dispersed particle size, as compared with a form in which only large dispersed particles are present. Propagation of coagulation failure can be performed efficiently and can also have transparency. Further, since a large number of islands of the polyethylene resin (c) having a small dispersed particle size are present, cohesive fracture is likely to occur regardless of the peeling direction, which contributes to the improvement of the isotropic property of easy opening.

The melting points of the low-density polyethylene resin (b) and the low-density polyethylene resin (c) are preferably 90 to 140 ° C, more preferably 100 to 130 ° C. A melting point of 140 ° C. or lower enables good film formation and secondary molding, and a melting point of 90 ° C. or higher makes it easy to obtain heat resistance, which is preferable.

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

Further, since the island phases of the 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 melt flow rate (MFR) ratio of both becomes cohesive and destructive. Affect.
The ratio (b / a) of the MFR of the polyethylene resin (b) to the MFR of the polypropylene resin (a) is preferably 0.01 to 1.0. The lower limit is more preferably 0.05 or more, and even more preferably 0.08 or more. Within this range, the cohesive failure type easy peeling property is likely to be exhibited. The MFR ratio (b / a) is preferably 0.2 or less from the viewpoint of easy opening (aggregation fracture property) of the film.
The ratio (c / a) of the MFR of the polyethylene resin (c) to the MFR of the polypropylene resin (a) is preferably 0.25 to 20. The lower limit is more preferably 0.5 or more, and the upper limit is more preferably 10 or less. From the viewpoint of film transparency, the MFR ratio (c / a) is preferably 1.0 or more.
Since the seal layer of this film has two types of MFR ratios, both transparency and easy peelability can be achieved.

(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 low-density polyethylene resin (b) having a melt flow rate (MFR) of 1.0 g / less than 10 minutes. It is composed of a resin composition containing 5.0 g of MFR / low density polyethylene resin (c) of more than 10 minutes.
When the total amount of the resin constituting the seal layer is 100% by mass, the mass ratio of the polypropylene resin (a) to the total amount of the polyethylene resin (b) and the polyethylene resin (c) is (a) :( b + c). = 50:50 to 90:10 is preferable, and 60:40 to 80:20 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, when the polypropylene-based resin (a) is 90% by mass or less, good easy peelability can be easily obtained.
The mass ratio of the polyethylene resin (b) to the polyethylene resin (c) is preferably (b): (c) = 1: 5 to 5: 1, more preferably 1: 3 to 3: 1, and 1: 2 to 2. 2: 1 is even more preferred. Within this range, it is easy to obtain both easy peeling and transparency.
More preferably, the mass ratio of the polypropylene-based resin (a), the low-density polyethylene resin (b), and the low-density polyethylene-based resin (c) is a: b: c = (80 to 60) :( 5 to 20). : (5 to 20).

The composition ratio of each resin is 1H-NMR method, FT-IR method, DSC method, high temperature GPC method, cross fractionation chromatograph (CFC), temperature elution fractionation method (TREF), crystallization elution fractionation method (CEF), etc. Is analyzed by combining.
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 components are separated according to the degree of short chain branching. Furthermore, by using a TREF column for the CFC that has the characteristics of a size exclusion chromatograph (GPC), it is possible to determine the two-dimensional distribution of the crystallinity and molecular weight of the polyolefin resin, and polyethylene with different crystallinity and melt viscosity. It is possible to separate based resin and polypropylene based resin. Further, by expanding the measurement temperature range to −20 ° C., a thermoplastic elastomer having low crystallinity can be separated.

(Adjacent layer (polyolefin resin 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 is the polypropylene-based resin (a), the low-density polyethylene resin (b), the low-density polyethylene resin (c), or these resins (b) constituting the above-mentioned seal layer. ), It is preferable to use a low-density polyethylene resin other than the resin (c) because the interlayer adhesion between the seal layer and the adjacent layer is increased. Among them, low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) composed of a copolymer of ethylene and α-olefin are preferable from the viewpoint of coextrusion film film forming property. For example, when the coextruded film is formed by the 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 resins such as copolymers, polyethylene terephthalates, polyethylene naphthalates, polyester resins such as polybutylene terephthalates, adhesive resins and the like 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 method for producing the film of the present invention is not particularly limited, and the film 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 a known feed block method, a multi-manifold method, or a coextrusion method using a combination thereof can be used. It 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 may be similarly used, or the film may be formed by a heat laminating method, an extrusion laminating method, or a dry laminating method. it can.
The film of the present invention may be unstretched, uniaxially stretched, simultaneous biaxially stretched, or sequentially biaxially stretched.
Further, the film of the present invention can be subjected to surface treatment such as corona treatment, printing, coating, and vapor deposition, and surface treatment, if necessary.

When the present film is a single-layer film having only a seal layer, the thickness thereof is preferably 1 to 30 μm.
In the case of a multilayer film containing other layers such as adjacent layers, such as a coextruded film, this film has both heat sealability and good peelability without stringing or filming, and transparency. From this point of view, the thickness of the seal layer is preferably 1 to 10 μm, more preferably 2 to 8 μm, and further preferably 2 to 5 μm from the viewpoint that cohesive failure is easily propagated in the horizontal direction of the film and the easy opening property is improved.
The adjacent layer is preferably 1 to 30 μm from the viewpoint of the strength and handleability of the entire film.
The total thickness of the multilayer film including the adjacent layer and other layers is preferably 3 μm or more, more preferably 5 μm or more, still more preferably 10 μm or more, from the viewpoint of film strength, handleability, and secondary processability. The upper limit is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 50 μm or less.
The thickness of the single-layer film, the total thickness of the multilayer film, and the thickness of each layer can be measured from a stylus-type thickness system meter and film cross-section observation.

<Film characteristics>
The film and the multilayer film of the present invention (hereinafter, these may be collectively referred to as "the present film") preferably have the following characteristics.
(Heat sealability, easy opening property)
It is preferable that this film has excellent heat seal adhesion to an adherend made of a polyolefin resin, particularly a polypropylene resin, and an excellent cohesive failure type easy-opening property at the time of opening and peeling. That is, it has a characteristic that it coagulates and breaks when it is heat-sealed and peeled off from an adherend made of polypropylene-based resin at a sealing temperature of 140 to 180 ° C. Further, when heat-sealed and peeled at a sealing temperature of 140 to 180 ° C., it is more preferable that the peeling surface is coagulated and broken under any sealing temperature condition, and the peeled surface is beautiful without stringing or the like. 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.

As the evaluation method, for example, the following can be adopted. 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 180 ° 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 a seal time of 1 second. 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. , Perform a tensile test under the condition of a tensile speed of 300 mm / min, and measure the peel strength (unit: N / 15 mm width).

The lower limit of the peel strength is preferably 8N / 15mm width or more, and more preferably 10N / 15mm width or more. The upper limit is preferably 20 N / 15 mm width or less, and more preferably 18 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 can be easily peeled and opened by hand. In addition, this film can be peeled and opened by coagulating and breaking the inside of the seal layer, and it can be easily peeled without stringing or film pulling. It is more preferable that a beautiful peeled appearance is obtained without causing.

Further, the package using the film of the present invention has a small difference in peel strength depending on the opening direction at the time of opening, and can be easily opened with excellent isotropic properties. The TD / MD exhibiting the isotropic property is preferably less than 1.5, more preferably less than 1.4. Due to its excellent isotropic properties, it is superior in the production efficiency of films and packages and the design of universal design.

(transparency)
From the viewpoint of visibility, aesthetics, design, etc. of the contents, the transparency of this film is preferably 15% or less for all haze and external haze, the lower limit is not particularly limited, and the smaller the value, the more transparent. Good and preferable.
Haze is measured according to 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 the present film and a bottom material (adhesive body) made of a polypropylene resin are heat-sealed is useful.
When a multilayer film is used, the seal layer side is set to the adherend (for example, bottom material) side, and the package is heat-sealed with the bottom material to produce a package. Examples of the polypropylene-based resin constituting the bottom material 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. In addition, this film can be laminated with other plastic films and sheets, metal foil, paper, etc. by a known method such as dry laminating to be a packaging material, and a packaging material using a lid material made of these can also be used. Can be produced.

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, films were prepared by the methods described in each Example and Comparative Example, and tests and evaluations were carried out using the films. The results are summarized in Table 1.

<Raw material (seal layer)>
(Polypropylene resin)
PP1: Metallocene-catalyzed propylene-ethylene copolymer polypropylene resin (MFR: 7.0 g / 10 minutes, melting point: 124 ° C., density 900 kg / m ³ )
(Polyethylene resin)
PE1: Polyethylene resin polymerized by high-pressure polymerization method (MFR: 0.7 g / 10 minutes, melting point: 112 ° C., density 924 kg / m ³ )
PE2: Polyethylene resin polymerized by high-pressure polymerization method (MFR: 2.2 g / 10 minutes, melting point: 115 ° C., density 925 kg / m ³ )
PE3: Polyethylene resin polymerized by high-pressure polymerization method (MFR: 4.0 g / 10 minutes, melting point: 111 ° C., density 923 kg / m ³ )
PE4: Polyethylene resin polymerized by high-pressure polymerization method (MFR: 8.4 g / 10 minutes, melting point: 107 ° C., density 919 kg / m ³ )
PE5: Polyethylene resin polymerized by high-pressure polymerization method (MFR: 12 g / 10 minutes, melting point: 110 ° C., density 925 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 3 and Comparative Examples 1 to 5>
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, peeling 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 four ways of 140 ° C, 150, 160 ° C, and 180 ° 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 8 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 peeled surface after the peeling test was observed according to the following criteria, and when the seal layer was cohesively broken (◯ and Δ), it was evaluated as having good peelability.
◯: Aggregate fracture and no stringing, etc. Δ: Aggregate fracture, but there is stringing, filming, fluffing, resin tearing, etc.
▲: Insufficient coagulation failure, remarkable stringing, etc. ■: No peeling, film tears ×: No adhesion between film and adherend These heat seal tests and peeling tests are compared with examples. The ratio (TD / MD) of the peel strength was calculated in both the film flow direction (MD) and the vertical direction (TD) of the coextruded film obtained in the example. If the peel strength ratio (TD / MD) is less than 1.5, it can be said that the isotropic property of easy opening is high.

(2) Transparency The coextruded films obtained in Examples and Comparative Examples were measured for all hazes according to JIS K7136: 2000, and for internal hazes according to JIS K7105. As a measuring instrument, a haze meter NDH5000 manufactured by Nippon Denshoku Kogyo was used. For the internal haze, in order to exclude the influence of the unevenness of the film, ethanol having a purity of 99.5% was dropped on both sides of the film, the film was sandwiched between slide glasses, and the internal haze was measured. The external haze was calculated from the values of the total haze and the internal haze.
Those with a total haze of 15% or less were judged to be good.

In Examples 1 to 3, a low-density polyethylene resin in which the seal layer contains a polypropylene-based resin (a) produced by using a single-site catalyst as a main component and has a melt flow rate (MFR) of 1.0 g / less than 10 minutes. It is composed of a resin composition containing (b) and a low-density polyethylene resin (c) having an MFR of more than 5.0 g / 10 minutes, and all of the films have a total haze of 15.0% or less and are made of polypropylene-based resin. As an easy-peel sealant film for adherends, it has excellent transparency as compared with conventional films. Further, in a wide temperature range of 140 to 180 ° C., the heat seal has sufficient adhesion and easy opening property, and a beautiful peeled surface is obtained without stringing or the like on the surface that has been coagulated and broken. Furthermore, the ratio of the peel strength in the peeling direction of MD and TD is at the same level as less than 1.5, and the isotropic property of easy opening is high, so that the production efficiency when forming the film and the package is remarkably high. It can be said that it has the advantage of improving and is also excellent in the design of universal design.

In Comparative Example 1, the seal layer was composed of only the polypropylene-based resin (a), the peel strength was strong, and the easy peel property was insufficient.
In Comparative Example 2, the seal layer was composed of only polyethylene resin (b), and the total haze was high due to the high external haze on the surface of the seal layer, resulting in poor transparency.
In Comparative Example 3, the total haze was high and the transparency was poor. Further, at the sealing temperatures of 140 ° C., 150 ° C. and 160 ° C., the peel strength ratio (TD / MD) was 1.5 or more, and the isotropic property of easy opening was insufficient.
In Comparative Example 4, the cohesive failure was insufficient at the sealing temperatures of 140 ° C., 160 ° C. and 180 ° C., causing stringing and the like, and the peeling strength was high at the sealing temperature of 180 ° C., and the easy opening property was poor.
In Comparative Example 5, the peel strength was high from the low temperature region of the seal temperature of 140 ° C., and the easy-to-open property was poor. Further, at the sealing temperatures of 140 ° C., 150 ° C. and 160 ° C., the isotropic property of easy opening was insufficient.

The film of the present invention has sufficient adhesion strength by heat-sealing with an adherend made of a polypropylene-based resin, and has a contaminant sealing property. In addition, when the package is prepared and opened, regardless of the direction in which the package is opened, the seal layer is coagulated and broken, and the package can be peeled and opened with a light force, and fluffing and stringing are unlikely to occur, so food safety. Excellent in sex and hygiene. Further, since it has transparency, it is effective for visibility of the contents of the package. From the above, the film of the present invention can be suitably used as a blister pack for accommodating food packaging, medical products, daily necessities, and stationery.

Claims (7)

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 low density of melt flow rate (MFR) of less than 1.0 g / 10 minutes. An easy-to-open film characterized by being composed of a resin composition containing a polyethylene resin (b) and a low-density polyethylene resin (c) having an MFR of more than 5.0 g / 10 minutes. The easy-to-open film according to claim 1, wherein the melt flow rate (MFR) of the polypropylene-based resin (a) is 1.0 g / 10 minutes or more and 20 g / 10 minutes or less. When the total amount of the polypropylene resin (a), the low density polyethylene resin (b) and the low density polyethylene resin (c) is 100% by mass, the polypropylene resin (a) is 90 to 50% by mass. The easy-to-open film according to claim 1 or 2, wherein the low-density polyethylene-based resin (b) is 5 to 25% by mass, and the low-density polyethylene-based resin (c) is 5 to 25% by mass. The easy-to-open film according to any one of claims 1 to 3, which has a polyolefin-based resin layer adjacent to the seal layer. The easy-to-open film according to any one of claims 1 to 4, wherein the thickness of the seal layer is 1 to 10 μm. A package using the easily openable film according to any one of claims 1 to 5. A package obtained by heat-sealing a lid material using the easy-to-open film according to any one of claims 1 to 5 and a bottom material made of a polypropylene resin.