JP7449688B2 - Easy-open films and packaging - Google Patents

Description

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

Conventionally, polyolefin resin container bottoms have been used for individually wrapped cup-shaped products such as jelly, steamed egg custard, and side dishes, deep-drawn packaging, and blister packs that store medical products such as disposable syringes, daily necessities, and stationery. has been used, and a film containing a sealing layer made of a polyolefin resin having a melting point similar to that of the container bottom material has been used as the lid material. For example, with the expansion of the market and the diversification of consumer needs, the sealing layer of the lidding film has to have transparency, oxygen barrier properties, and water vapor barrier properties that allow the contents to be viewed when stored as food packaging films and containers. Various properties are required, such as strength, impact resistance, and heat resistance.
In particular, the sealing layer of the lidding film for food packaging containers must have not only heat-sealability to seal the contents, but also unsealability. The requirements are extremely high, such as no film formation or stringiness, and constant peeling force over a wide range of heat-sealing temperatures.

Easy-peel forms include an interfacial peeling mechanism in which the heat seal layer peels off at the interface with an adherend such as a container, a delamination mechanism in which the sealing layer in a multilayer film peels off at the interface between the peeling layer, and a cohesive failure in the sealing layer. This can lead to a cohesive failure mechanism that results in light peeling. Among these, the cohesive failure type has a relatively simple structure and exhibits good contaminant sealing properties for packaging containers containing moisture, so it is especially suitable for cohesive failure type lids for polypropylene containers. Various studies have been carried out so far.

Patent Document 1 discloses that in order to achieve both low-temperature sealability, heat resistance, and easy-opening properties, a support layer made of a polyolefin resin and a polypropylene resin having a melt flow rate (MFR) of 1.0 g/10 minutes or more, for example, 30~ The MFR ratio of the polypropylene resin and the polyethylene resin was specified. A composite multilayer sheet for packaging is disclosed.

Patent Document 2 discloses that the first layer contains 20 to 60 parts by weight of a high-pressure polymerized low density polyethylene resin with a melt flow rate (MFR) of 1 to 7 g/10 minutes and an MFR of 1 to 15 g/10 minutes for sealability and easy opening. The second layer is composed 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 is disclosed in which a base film is laminated on the surface of the second layer.

Patent Document 3 discloses that the base material layer is composed of a resin composition mainly composed of medium density polyethylene, high density polyethylene or polypropylene for heat sealability, sealability and easy openability, and the sealing layer is made of a resin composition with a melt flow rate. (MFR) 10 to 40 g/10 minutes An easy peel sealant is disclosed that is comprised of a resin composition based on a mixture of polypropylene and low density polyethylene.

However, the technology disclosed for the sealing layer in Patent Document 1 has a configuration in which many types of polypropylene resins and many types of polyethylene resins are listed, and the combination of both resin types results in haze with poor transparency. It was something.
Furthermore, in the first layer (sealing layer) of the combination of high-pressure polymerized low-density polyethylene resin and polypropylene-ethylene random copolymer disclosed in Patent Document 2, the domains in the matrix in the incompatible polymer blend are relatively large. Because of the large size, if the number of domains is set to obtain good ease of opening, that is, the blending ratio of both resins, the surface of the sealing layer of the formed film will have a large external haze, making it impossible to obtain sufficient transparency. there were.
Furthermore, in the seal layer disclosed in Patent Document 3, the MFR of polypropylene is as high as 10 to 40 g/10 minutes, so the extrusion temperature during film formation cannot be raised, and therefore the seal layer is likely to crystallize. Further, since the MFR of polypropylene is similarly high, the polyethylene domain in the polypropylene matrix becomes large. Due to these factors, transparency was insufficient.

In addition, for packages using packaging materials made of polypropylene resin in the plastic packaging manufacturing field, heat sealing is generally performed at a sealing temperature of 140 to 180°C. There is a need for a film that can cause cohesive failure type easy peeling even at temperatures of .

Japanese Patent Application Publication No. 2000-272064 Japanese Patent Application Publication No. 2006-256637 Japanese Patent Application Publication No. 2007-168257

In view of the above-mentioned circumstances, an object of the present invention is to provide a cohesive failure type easy sealing material when heat sealing is performed at a relatively low sealing temperature (140 to 180°C) to a packaging material made of a polypropylene resin as an adherend. The object of the present invention is to provide an easily openable film that exhibits peelability and is transparent.

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

A first aspect of the present invention provides a film having at least a sealing layer, wherein the sealing layer contains as a main component a polypropylene resin (a) produced using a single-site catalyst, and has a melt flow rate (MFR) of 1.0 g. This is an easily openable film characterized by being composed of a resin composition containing a low density polyethylene resin (b) with an MFR of less than /10 minutes and a low density polyethylene resin (c) with an MFR of more than 5.0 g/10 minutes.

In the first aspect of the present invention, it is preferable that the melt flow rate (MFR) of the polypropylene resin (a) is 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 preferably 90 to 50% by mass, the low density polyethylene resin (b) is 5 to 25% by mass, and the low density polyethylene resin (c) is preferably 5 to 25% by mass.

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

In the first aspect of the present invention, it is preferable that the thickness of the sealing layer is 1 to 10 μm.

The second invention is a package using the easily openable film of the first invention.

The third invention is a package formed by heat-sealing a lid material using the easily openable film of the first invention and a bottom material made of a polypropylene resin.

The film of the present invention (hereinafter sometimes referred to as the present film) can be heat-sealed to an adherend made of polypropylene resin, such as the bottom material of a container, cup, tray, etc., to create a package, which is then opened. When the seal layer of the film is cohesively destroyed, the seal layer can be easily opened with a light force, and at the same time, no fluffing or stringiness occurs, resulting in excellent food hygiene and food safety. Therefore, it is useful as an easy-open sealant film for polypropylene resin bottom materials.
In addition, since the film of the present invention has transparency, the package of the present invention has good visibility of the contents, making it easy to check the condition of the contents during manufacturing, transportation, storage, sale, etc. of the package. Excellent.

Hereinafter, a film of the present invention as an example of an embodiment of the present invention will be described. However, the scope of the present invention is not limited to the embodiments described below.
In this application, easy peelability is synonymous with easy-openability and easy-peelability. Further, the sealant film is sometimes referred to as a heat seal film or a heat sealable film. Peel strength is synonymous with seal strength and unsealing strength, and is a measure of ease of opening and sealability.
In addition, "for polypropylene resin bottom material" refers to the bottom material of containers, cups, trays, etc., which are made of polypropylene resin, for example, the shape is not limited, 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 to the flange portion of the bottom material and used as a lid material.
"Contained as a main component" means 50% by mass or more based on the total amount, preferably more than 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more. When a numerical range is indicated by "~", it means the above and below.

<Easy-to-open film>
This film is a film having a sealing layer, and the sealing layer contains a polypropylene 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. The resin composition includes a low-density polyethylene resin (b) having a MFR of more than 5.0 g/10 minutes and a low-density polyethylene resin (c) having an MFR of more than 5.0 g/10 minutes. The form of the present film may be as long as it has the sealing layer, and may be a single-layer film consisting of only the sealing layer or a multilayer film including other layers.

(Polypropylene resin (a))
The polypropylene resin (a) constituting the seal layer of this film is produced using a single-site catalyst. There are no particular limitations, and homopolypropylene, random polypropylene, etc. can be used. From the viewpoint of flexibility and transparency, a propylene-ethylene random copolymer is preferred. Polypropylene resins polymerized using single-site catalysts have narrower molecular weight distributions, narrower compositional distributions, and fewer low-order components than when using Ziegler-Natta catalysts. Therefore, the produced film has excellent low-temperature sealing properties, high rigidity, high tensile strength and impact resistance, and exhibits high transparency even in the air-cooled inflation film production method. It also has excellent blocking resistance.

The type of single-site catalyst is not particularly limited, but a typical example is a metallocene catalyst. Generally, metallocene polypropylene is produced by reacting (i) a transition metal compound of Group 4 of the periodic table (so-called metallocene compound) containing a ligand having a cyclopentadienyl skeleton, and (ii) reacting with the metallocene compound. A co-catalyst is used that can be activated to a stable ionic state. This co-catalyst may be subjected to a reaction treatment with an organic aluminum compound or the like, if necessary. The metallocene compound is preferably a crosslinked metallocene compound that enables polymerization with stereoregularity of propylene, and more preferably a crosslinked metallocene compound that enables polymerization with isotactic regularity of propylene.

The method for producing the polypropylene resin (a) produced using a single-site catalyst is not particularly limited, and known slurry polymerization methods, bulk polymerization methods, gas phase polymerization methods, etc. can be used. Moreover, it is also possible to manufacture using a multi-stage polymerization method.

The melt flow rate (MFR) of the polypropylene resin (a) produced using a 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. If the MFR is less than 1.0 g/10 minutes, when heat-sealed with an adherend made of polypropylene resin, the adhesion will be too strong, making it difficult to easily open the seal. Furthermore, the film forming surface also has poor fluidity, making it difficult to form a thin film layer.
In order to obtain sufficient sealing properties in a short heat sealing process in a wide temperature range of 140 to 180°C, the melting point of the polypropylene resin (a) is preferably 120 to 160°C, and the upper limit is preferably 150°C or less. The temperature is preferably 140°C or lower, and more preferably 140°C or lower. The density of the polypropylene resin (a) is generally preferably 880 to 920 kg/m ³ , more preferably 890 to 910 kg/m ³ .

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 based on JIS K7112:1999 method.

Since this film is used as an easy-to-open sealant film for a bottom material made of polypropylene resin, polypropylene resin (a) is blended as a main component with respect to the total amount of resin constituting the sealing layer of this film. The amount is preferably more than 50% by weight, more preferably 60% by weight or more, even more preferably 70% by weight or more.

(Low density polyethylene resin (b), low density polyethylene resin (c))
The polyethylene resins that make up the sealing layer of this film are low-density polyethylene resin (b) with a melt flow rate (MFR) of less than 1.0 g/10 minutes, and low-density polyethylene resin (b) with an MFR of more than 5.0 g/10 minutes. (c).
The low density polyethylene resin may be a polyethylene resin having a density of 910 to 930 kg/m3, preferably a density of 915 to 925 kg/m3. Within this range, good easy peelability can be obtained. Furthermore, it may be manufactured from petroleum-derived raw materials or from plant-derived raw materials. Furthermore, the polymerization method and branched structure are not particularly limited, and low-density polyethylene resins manufactured by high-pressure radical polymerization methods, high-medium-low-pressure methods using Ziegler type, Phillips type, or metallocene catalysts, and other known methods may be used. Can be done. Among these, low-density polyethylene obtained by high-pressure polymerization is preferred because it produces fewer fish eyes during film formation. Low-density polyethylene produced by high-pressure polymerization has long branched side chains, so it is highly incompatible with the polypropylene resin (a) and can form domains.

The ease of opening of this film is due to the incompatibility between the polypropylene resin and the polyethylene resin in the sealing layer, which is caused by the phase interface dissociation between the sea phase and the island phase in the sea/island (matrix/domain) dispersed structure, which occurs in the horizontal direction of the film. It is caused by propagation and cohesive 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 resin melt viscosity, and cohesive failure property can be expressed. Since the sealing layer of this film is mainly composed of polypropylene resin (a), it has a form in which island phases of polyethylene resin are dispersed as domains in a sea phase of polypropylene resin (a).
As a result of studying the structure and function expression mechanism of the constituent resins, the present invention has developed a low-density polyethylene resin with a high melt viscosity and a low-density polyethylene resin with a low melt viscosity expressed in a specific melt flow rate (MFR) range. It has been discovered that by using two types, transparency and good cohesive failure and easy peelability can be obtained when heat sealing is performed at a relatively low sealing temperature. Specifically, two types are used: a low density polyethylene resin (b) with an MFR of less than 1.0 g/10 minutes, and a low density polyethylene resin (c) with an MFR of more than 5.0 g/10 minutes.

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, more preferably 0.8 g/10 minutes or less. Further, the lower limit is preferably 0.2 g/10 minutes or more, more preferably 0.3 g/10 minutes or more. By using a polyethylene resin (b) with a high melt viscosity and a low MFR, a large dispersed particle size on the μm order is generated, making it easy to cause cohesive failure of the sealing layer, making it possible to obtain easy peelability without stringiness. can. Furthermore, within this MFR range, film formation can be achieved without significant deterioration in film formability.
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, even more preferably It is more than 7.0 g/10 minutes. By using a polyethylene resin (c) with a low melt viscosity and a high MFR, finer dispersed particles can be produced and transparency can be increased.

The larger the particle size of the dispersed particles, the more likely cohesive failure will occur, but the opacity will increase due to haze due to incompatibility and haze due to roughening of the surface of the sealing layer. Therefore, compared to a form in which only large dispersed particles exist, by creating a form in which many islands of polyethylene resin (c) with a small dispersed particle size exist between islands of polyethylene resin (b) with a large dispersed particle size, Cohesive failure propagation can be carried out efficiently and transparency can be achieved. Furthermore, due to the presence of many islands of polyethylene resin (c) with small dispersed particle diameters, cohesive failure is likely to occur regardless of the peeling direction, contributing to an isotropic improvement in ease of 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 allows for good film formation and secondary molding, and a melting point of 90° C. or higher is preferable because heat resistance can easily be obtained.

The MFR of the low-density polyethylene resin (b) and the low-density polyethylene (c) is measured at 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 based on JIS K7112:1999 method.

In addition, since the island phases of low density polyethylene resin (b) and low density polyethylene resin (c) are dispersed in the sea phase of polypropylene resin (a), the melt flow rate (MFR) ratio of both becomes cohesive failure. 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, cohesive failure type easy peelability is likely to occur. Moreover, from the point of view of easy opening property (cohesive failure property) of the film, the MFR ratio (b/a) is preferably 0.2 or less.
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, it is possible to achieve both transparency and easy peelability.

(composition ratio)
The sealing layer of this film contains as a main component a polypropylene resin (a) produced using a single-site catalyst, and a low-density polyethylene resin (b) with a melt flow rate (MFR) of less than 1.0 g/10 minutes. It is composed of a resin composition containing a low density polyethylene resin (c) with an MFR of more than 5.0 g/10 minutes.
When the total amount of resin constituting the seal layer is 100% by mass, the mass ratio of polypropylene resin (a) to the total amount of polyethylene resin (b) and polyethylene resin (c) is (a): (b + c) =50:50 to 90:10 is preferred, and 60:40 to 80:20 is more preferred. When the content of the polypropylene resin (a) is 50% by mass or more, sufficient adhesion to the adherend made of the polypropylene resin can be obtained and heat resistance can also be imparted. Further, by controlling the content of the polypropylene resin (a) to 90% by mass or less, it is easy to obtain good easy peelability.
The mass ratio of polyethylene resin (b) and polyethylene resin (c) is preferably (b):(c) = 1:5 to 5:1, more preferably 1:3 to 3:1, and 1:2 to 2:1 is more preferred. By setting it as this range, it is easy to obtain both easy peelability and transparency.
More preferably, the mass ratio of the polypropylene resin (a), the low density polyethylene resin (b), and the low density polyethylene resin (c) is a:b:c=(80-60):(5-20). :(5-20).

The composition ratio of each resin is determined by 1H-NMR method, FT-IR method, DSC method, high temperature GPC method, cross fractionation chromatography (CFC), temperature rising elution fractionation method (TREF), crystallization elution fractionation method (CEF), etc. are analyzed by combining them.
Among them, TREF is preferably used as a method for analyzing polyolefin resins. A resin dissolved in a solvent is injected into a TREF column heated to a predetermined temperature, and then the temperature is lowered at a constant rate to crystallize on the column carrier. At this time, components with high crystallinity and few branches are crystallized first, and as the temperature decreases, components with low crystallinity and many branches are crystallized. Thereafter, by raising the temperature, components are eluted in order from components with low crystallinity to components with high crystallinity, and fractionation is performed based on the degree of short chain branching. Furthermore, by using a TREF column in a CFC that has the characteristics of size exclusion chromatography (GPC), it is possible to determine the two-dimensional distribution of crystallinity and molecular weight of polyolefin resins, and it is possible to determine the two-dimensional distribution of crystallinity and molecular weight of polyolefin resins. It is possible to separate polypropylene resin and polypropylene resin. Furthermore, by extending the measurement temperature range to -20°C, thermoplastic elastomers with low crystallinity can also be separated.

(Adjacent layer (polyolefin resin layer))
By having the polyolefin resin layer adjacent to the sealing layer, this film can maintain the strength of the sealing layer and effectively exhibit cohesive failure.
The polyolefin resin used for the adjacent layer is not particularly limited, but may be the polypropylene resin (a), low density polyethylene resin (b), low density polyethylene resin (c) that constitutes the above-mentioned sealing layer, or these resins (b). ), it is preferable to use a low-density polyethylene resin other than resin (c) because it increases the interlayer adhesion between the seal layer and the adjacent layer. Among these, low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) made of a copolymer of ethylene and α-olefin are preferred from the viewpoint of coextrusion film formability. For example, when a coextrusion film is formed by an inflation method, bubbles are stabilized and arbitrary blow-up is easily performed.

Moreover, a modified adhesive resin can be used as the polyolefin resin of the adjacent layer. For example, polyolefin resins modified with unsaturated carboxylic acids or derivatives thereof are preferably used. As such unsaturated carboxylic acids, acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, citraconic acid, etc. can be used. Further, as derivatives of unsaturated carboxylic acids, esters and anhydrides of the above-mentioned unsaturated carboxylic acids can be used, such as methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, and butyl acrylate. , butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, acrylamide, methacrylamide, sodium acrylate, and the like. In addition, vinyl acetate and the like can also be used. When the adjacent layer is made of adhesive resin, the adhesion between each layer 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 sealing layer and the above-mentioned adjacent layer adjacent to the sealing layer, but may further have another layer on the side opposite to the sealing layer side of the adjacent layer. It's okay.
Examples of resins constituting other layers include polyolefin resins such as polyethylene and polypropylene, gas barrier resins such as saponified ethylene-vinyl acetate copolymers and aromatic polyamides, polyamide 6, polyamide 66, and polyamide 6. , 66 copolymer, polyester resins such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, adhesive resins, etc. can be used depending on the required function of the film. Further, a plurality of other layers may be provided.

(Other ingredients)
Each layer of the film of the present invention may contain additives as appropriate, as long as the properties thereof are not impaired. For example, colorants, inorganic fillers, organic fillers, ultraviolet absorbers, light stabilizers, heat stabilizers, antioxidants, lubricants, anti-blocking agents, hydrolysis inhibitors, plasticizers, flame retardants, antistatic agents, Examples include antifogging agents. The amount of these additives to be added is not particularly limited, and can be appropriately determined within a range that does not impede the desired physical properties of the present invention.

<Method for producing 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 sealing layer is not particularly limited, but may include a known feed block method, multi-manifold method, or a coextrusion method using a combination thereof. It can be suitably used.
A method for manufacturing a film by providing another layer on the side opposite to the sealing layer side of the adjacent layer may be similarly formed using a coextrusion method, a thermal lamination method, an extrusion lamination method, or a dry lamination method. can.
The film of the present invention may be unstretched, uniaxially stretched, simultaneously biaxially stretched, or sequentially biaxially stretched.
Furthermore, the film of the present invention can be subjected to surface treatments and surface treatments such as corona treatment, printing, coating, and vapor deposition, if necessary.

When the present film is a single-layer film with only a sealing layer, its thickness is preferably 1 to 30 μm.
If the film is a multilayer film containing other layers such as adjacent layers, such as a coextruded film, it is necessary to achieve both heat sealability and good easy peelability without stringing or film formation, and transparency. From this point of view, the thickness of the sealing layer is preferably 1 to 10 μm, more preferably 2 to 8 μm, and even more preferably 2 to 5 μm, since cohesive failure can easily propagate in the horizontal direction of the film and ease of opening is better.
Further, the thickness of the adjacent layer is preferably 1 to 30 μm from the viewpoint of the strength and handleability of the entire film.
The lower limit of the total thickness of the multilayer film including adjacent layers and other layers is preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, from the viewpoint of film strength, handling properties, 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 a single layer film, and the total thickness and each layer thickness of a multilayer film can be measured using a stylus type thickness meter or by observing a cross section of the film.

<Film characteristics>
The film and multilayer film of the present invention (hereinafter, these may be collectively referred to as "this film") preferably have the following characteristics.
(heat sealability, easy opening)
The present film preferably has excellent heat-seal adhesion to an adherend made of polyolefin resin, particularly polypropylene resin, and excellent cohesive failure type ease of opening when peeled off. That is, it has a characteristic that cohesive failure occurs when it is heat-sealed to an adherend made of polypropylene resin at a sealing temperature of 140 to 180° C. and then peeled off. Furthermore, when heat-sealing at a sealing temperature of 140 to 180° C. and peeling off, it is more preferable that cohesive failure occurs under any sealing temperature condition, and that the peeled surface is beautiful without stringiness. Examples of the polypropylene resin of the adherend include homopolypropylene and random copolymerized polypropylene. This film can exhibit good heat-sealability and easy-opening properties even when the adherend is homopolypropylene with a high melting point.

As the evaluation method, for example, the following can be adopted. Using a homopolypropylene sheet with a thickness of 300 μm as an adherend, this film was superimposed on this (for coextruded films, the sealing layer side was superimposed), the sealing temperature was 140 to 180°C, the sealing width was 5 mm, and the sealing pressure was 0. A sample for evaluation is prepared by heat sealing under the conditions of .2 MPa and a sealing time of 1 second. To measure the heat seal adhesion and ease of opening, a test piece was prepared by cutting the heat sealed sample into 15 mm wide strips, and based on JIS Z0238:1998, the heat sealed part was placed in the center and the peel angle was 180 degrees. A tensile test is conducted at 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 8 N/15 mm width or more, more preferably 10 N/15 mm width or more. The upper limit is preferably 20N/15mm width or less, more preferably 18N/15mm width or less. If it has a peel strength within this range, it adheres to the adherend with sufficient strength and can be easily peeled and opened by hand. In addition, this film can be opened by peeling due to cohesive failure inside the sealing layer, and can be peeled off easily without stringing or film formation. It is more preferable that a beautiful peeled appearance is obtained without causing any peeling.

Furthermore, when the package using the film of the present invention is opened, the difference in peel strength depending on the opening direction is small, and easy opening with excellent isotropy can be obtained. TD/MD indicating the isotropy is preferably less than 1.5, more preferably less than 1.4. Due to its excellent isotropy, it is advantageous in production efficiency and universal design of films and packaging bodies.

(transparency)
The transparency of this film is preferably 15% or less for total haze and external haze from the viewpoints of visibility of contents, aesthetics, design, etc. The lower limit is not particularly limited, and the lower the value, the lower the transparency. Good and preferable.
Haze is measured based on JIS K7136:2000.

<Package>
Since this film has good heat-sealability and easy peelability, it can be heat-sealed to an adherend in a shape appropriate to the contents to form a package. Particularly useful is a package in which a lid material made of the present film and a bottom material (adherent) made of a polypropylene resin are heat-sealed.
In addition, when using a multilayer film, a package is produced by heat-sealing with the bottom material with the sealing layer side facing the adherend (for example, the bottom material). Examples of the polypropylene resin constituting the bottom material include homopolypropylene and random copolymerized polypropylene. In this film, even if the adherend is homopolypropylene having a high melting point, it is possible to exhibit good heat sealability and easy openability. In addition, this film can also be used as a packaging material by laminating it with other plastic films and sheets, metal foil, paper, etc. by a known method such as dry lamination, and a lid made of these materials can be used to create a packaging material. can be created.

The present invention will be explained in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited by the Examples and the like.
Films were produced using the following raw materials according to the methods described in the Examples and Comparative Examples, and the films were tested and evaluated. The results are summarized in Table 1.

<Raw materials (seal layer)>
(Polypropylene resin)
PP1: Propylene-ethylene copolymer polypropylene resin polymerized with metallocene catalyst (MFR: 7.0 g/10 min, 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 min, melting point: 121°C, density 923 kg/m ³ )

<Examples 1 to 3, Comparative Examples 1 to 5>
Using the above raw materials, the seal layer has the composition shown in Table 1, feed the raw materials to each extruder for each layer, and co-extrude the seal layer and adjacent layer at an extrusion temperature of 200°C using the T-die coextrusion method. The coextruded film was cooled with a water-cooled metal cooling roll at 40° C. to obtain a coextruded film having a seal layer thickness of 5 μm/adjacent layer thickness of 25 μm.
Next, the surface of the adjacent layer of the coextruded film was subjected to a 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 sealing test, peeling test A homopolypropylene sheet with a thickness of 300 μm as an adherend was stacked with the seal layer surfaces of the laminated films obtained in Examples and Comparative Examples facing each other, and one end was sealed using a heat sealing machine. Heat sealing was performed under the conditions of a seal width of 5 mm, a seal pressure of 0.2 MPa, and a seal time of 1 second. The test was conducted with four set sealing temperatures: 140°C, 150°C, 160°C, and 180°C.
Thereafter, it was cut into strips with a length of 50 mm and a width of 15 mm, and in accordance with JIS Z0238:1998, the ends of the two films were attached to the grip of a tensile tester with the heat-sealed part in the center, and the peeling angle was 180 degrees. , At a peeling speed of 300 mm/min, the strip was pulled in the length direction until it peeled or broke, and the measured maximum stress was measured as the heat seal strength (unit: N/15 mm width), and the heat seal strength was 8 N. /15mm width or more and 20N/15mm width or less was evaluated as having good adhesion and easy peelability.

Next, the peeled surface after the peel test was observed according to the following criteria, and cases where the sealing layer showed cohesive failure (◯ and △) were evaluated as having good easy peelability.
○: Cohesive failure, no stringing, etc. △: Cohesive failure, but stringing, filminess, fuzz, resin tearing
▲: Insufficient cohesive failure, noticeable stringing, etc. ■: No peeling, film tears ×: Film and adherend are not in close contact These heat seal tests and peel tests are shown in Examples and Comparison The peel strength ratio (TD/MD) of the coextruded film obtained in the example was calculated in both the film machine direction (MD) and the perpendicular direction (TD). If the peel strength ratio (TD/MD) is less than 1.5, it can be said that the isotropy of easy opening is high.

(2) Transparency Regarding the coextruded films obtained in Examples and Comparative Examples, total haze was measured in accordance with JIS K7136:2000, and internal haze was measured in accordance with JIS K7105. As a measuring device, a haze meter NDH5000 manufactured by Nippon Denshoku Kogyo was used. In order to exclude the influence of the unevenness of the film, ethanol with 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. External haze was calculated from the total haze and internal haze values.
A sample having a total haze of 15% or less was judged to be good.

Examples 1 to 3 are low-density polyethylene resins in which the sealing layer contains polypropylene 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. (b) and a low-density polyethylene resin (c) with an MFR of more than 5.0 g/10 minutes. This easy-peel sealant film for adherends has superior transparency compared to conventional films. In addition, it had both sufficient adhesion and easy openability under heat sealing at a wide range of temperatures from 140 to 180°C, and also had a beautiful peeling surface with no stringiness on the cohesive failure surface. Furthermore, the peel strength ratio in the MD and TD peel directions is at the same level of less than 1.5, and the isotropy of easy opening is high, so production efficiency when forming films and packages is significantly improved. It has the advantage of improving performance, and can be said to be excellent in universal design.

In Comparative Example 1, the sealing layer was composed only of the polypropylene resin (a), and the peel strength was strong and the easy peelability was insufficient.
In Comparative Example 2, the sealing layer was composed only of polyethylene resin (b), the total haze was high due to the influence of high external haze on the surface of the sealing layer, and the transparency was poor.
Comparative Example 3 had a high total haze and poor transparency. Furthermore, at sealing temperatures of 140°C, 150°C, and 160°C, the peel strength ratio (TD/MD) was 1.5 or more, and the isotropy of easy opening was insufficient.
In Comparative Example 4, cohesive failure was insufficient at sealing temperatures of 140° C., 160° C., and 180° C., and stringing occurred, and peel strength was high at sealing temperatures of 180° C., resulting in poor ease of opening.
Comparative Example 5 had a high peel strength from a low sealing temperature of 140° C. and poor ease of opening. Further, at sealing temperatures of 140°C, 150°C and 160°C, the isotropy 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 resin, and can obtain contaminant sealing properties. In addition, when making and opening a package, the seal layer will cause cohesive failure no matter which direction the package is opened, allowing it to be peeled off with light force, and will not cause fuzz or stringiness, ensuring food safety. Excellent in sex and hygiene. Furthermore, since it has transparency, it is effective for visibility of the contents of the package. As described above, the film of the present invention can be suitably used as a blister pack for storing food packaging, medical products, daily necessities, and stationery.

Claims (7)

In a film having at least a sealing layer, the sealing layer contains as a main component a polypropylene resin (a) produced using a single-site catalyst, and has a melt flow rate (MFR) of less than 1.0 g/10 minutes under high pressure. It is characterized by being composed of a resin composition containing a legally produced low-density polyethylene resin (b) and a high-pressure polymerized low-density polyethylene resin (c) having an MFR of more than 5.0 g/ ¹⁰ minutes and a density of 910 kg/m3 or more. Easy-to-open film. The easily openable film according to claim 1, wherein the polypropylene resin (a) has a melt flow rate (MFR) of 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 easily openable film according to claim 1 or 2, wherein the low density polyethylene resin (b) is 5 to 25% by mass, and the low density polyethylene resin (c) is 5 to 25% by mass. The easily openable film according to claim 1, further comprising a polyolefin resin layer adjacent to the sealing layer. The easily openable film according to claim 1, wherein the sealing layer has a thickness of 1 to 10 μm. A package comprising the easily openable film according to any one of claims 1 to 5. A package obtained by heat-sealing a lid material using the easily openable film according to any one of claims 1 to 5 and a bottom material made of a polypropylene resin.