JP7719745B2 - Polyethylene laminate for packaging material and packaging material made of said laminate - Google Patents

Description

The present invention relates to a polyethylene laminate for packaging materials and a packaging material made from the laminate.

Polyethylene film is used in a variety of packaging materials because it has moderate flexibility, excellent transparency, moisture resistance, and chemical resistance, as well as being inexpensive. The melting point of polyethylene varies slightly depending on the type, but is generally around 100-140°C, so it is commonly used as a heat-sealable film in the packaging material field.

On the other hand, polyethylene films have inferior rigidity compared to other thermoplastic resin films, making them less suitable for printing and making it difficult to form clear images on their surfaces. Furthermore, polyethylene films do not have the strength to meet the durability requirements for packaging exteriors.
Therefore, packaging materials are produced by laminating a resin film having excellent rigidity and strength, such as a polyester film or a nylon film, with a polyethylene film to form a laminate, and then heat-sealing the edges of the laminate so that the polyethylene film side of the laminate faces inward (for example, JP 2005-104525 A).

In recent years, with growing calls for the creation of a recycling-oriented society, attempts have been made to recycle and reuse packaging materials. However, when different types of resin films are bonded together as described above, it is difficult to separate the resin films, making them unsuitable for recycling. There has also been a demand for packaging materials that place less of a burden on the environment.

Japanese Patent Application Laid-Open No. 2005-104525

The present invention was made to solve the above problems, and its objective is to provide a polyethylene laminate for packaging materials that significantly reduces the burden on the environment while also exhibiting high printability and strength.

The polyethylene laminate for packaging materials of the present invention comprises at least an oriented polyethylene film, an adhesive layer, and a heat-sealable polyethylene layer, and is characterized in that the adhesive layer contains a solventless adhesive.

In one embodiment, the oriented polyethylene film comprises at least one of high density polyethylene (HDPE) and medium density polyethylene (MDPE).

In one embodiment, the stretching ratio in the machine direction (MD) of the stretched polyethylene film is 2 times or more and 10 times or less.

In one embodiment, the stretched polyethylene film is a biaxially stretched film.

In one embodiment, the thickness of the stretched polyethylene film is 9 μm or more and 50 μm or less.

In one embodiment, the stretched polyethylene film has a configuration consisting of a high-density polyethylene layer, a medium-density polyethylene layer, and a high-density polyethylene layer.

In one embodiment, the ratio of the thickness of the high-density polyethylene layer to the thickness of the medium-density polyethylene layer is 1/10 or more and 1/1 or less.

In one embodiment, an image is formed on at least one side of the stretched polyethylene film.

In one embodiment, the stretched polyethylene film is produced by a blown film extrusion process.

In one embodiment, the heat-sealable polyethylene layer comprises at least one of low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE).

The packaging material of the present invention is characterized by being composed of the above-mentioned laminate.

The present invention makes it possible to significantly reduce the burden on the environment while providing a polyethylene laminate for packaging materials that has high printability and strength.

1 is a cross-sectional schematic view showing one embodiment of a polyethylene laminate for packaging materials according to the present invention. 1 is a cross-sectional schematic view showing one embodiment of a polyethylene laminate for packaging materials according to the present invention.

<Polyethylene laminate for packaging materials>
The polyethylene laminate for packaging material according to the present invention will be described with reference to the drawings.
As shown in FIG. 1, the polyethylene laminate for packaging material 10 comprises at least an oriented polyethylene film 20 , an adhesive layer 30 , and a heat-sealable polyethylene layer 40 .
In one embodiment, a polyethylene layer 50 comprising a vapor-deposited film is provided between the stretched polyethylene film 20 and the heat-sealable polyethylene layer 40 .
Each layer of the polyethylene laminate for packaging materials will be described below.

<Stretched polyethylene film>
The stretched polyethylene film may be uniaxially stretched or biaxially stretched, but from the viewpoint of strength, biaxially stretched films are preferred.

The stretching ratio in the machine direction (MD) of the stretched polyethylene film is preferably 2 to 10 times, and more preferably 3 to 7 times. This can further improve the printability and strength of the polyethylene laminate. This can also improve the transparency of the stretched polyethylene film.
The stretching ratio in the transverse direction (TD) is preferably 2 to 10 times, and more preferably 3 to 7 times. This can further improve the printability and strength of the polyethylene laminate. This can also improve the transparency of the stretched polyethylene film.

Examples of polyethylene contained in the stretched polyethylene film include high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE). The stretched polyethylene film may contain two or more of these.
Among these, high density polyethylene (HDPE) and medium density polyethylene (MDPE) are preferred from the viewpoints of printability, strength, heat resistance and suitability for stretching of the polyethylene laminate, and medium density polyethylene is more preferred from the viewpoint of suitability for stretching.
In the present invention, high-density polyethylene refers to polyethylene having a density of 0.945 g/cm ³ or more, medium-density polyethylene refers to polyethylene having a density of 0.925 to 0.944 g/cm ³ , and low-density polyethylene refers to polyethylene having a density of less than 0.925 g/cm ³ .

Polyethylenes with different densities and branching levels as described above can be obtained by appropriately selecting the polymerization method. For example, it is preferable to use a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst as the polymerization catalyst, and to carry out the polymerization in one stage or two or more stages using one of the following methods: gas phase polymerization, slurry polymerization, solution polymerization, or high-pressure ionic polymerization.

The single-site catalyst is a catalyst capable of forming a uniform active species, and is typically prepared by contacting a metallocene transition metal compound or a non-metallocene transition metal compound with an activating cocatalyst. Single-site catalysts are preferred because, compared to multi-site catalysts, they have a uniform active site structure and can polymerize polymers with high molecular weights and highly uniform structures. Metallocene catalysts are particularly preferred as single-site catalysts. Metallocene catalysts are catalysts that contain the following catalytic components: a transition metal compound of Group IV of the periodic table containing a ligand with a cyclopentadienyl skeleton, a cocatalyst, and, optionally, an organometallic compound and a carrier.

In the above-mentioned transition metal compounds of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, the cyclopentadienyl skeleton may be a cyclopentadienyl group, a substituted cyclopentadienyl group, or the like. The substituted cyclopentadienyl group has at least one substituent selected from hydrocarbon groups having 1 to 30 carbon atoms, silyl groups, silyl-substituted alkyl groups, silyl-substituted aryl groups, cyano groups, cyanoalkyl groups, cyanoaryl groups, halogen groups, haloalkyl groups, and halosilyl groups. The substituted cyclopentadienyl group may have two or more substituents, and the substituents may bond to each other to form a ring, such as an indenyl ring, a fluorenyl ring, an azulenyl ring, or a hydrogenated version thereof. The rings formed by bonding the substituents to each other may further have substituents.

In the transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, the transition metal can be zirconium, titanium, hafnium, etc., with zirconium and hafnium being particularly preferred. The transition metal compound typically contains two ligands having a cyclopentadienyl skeleton, and the cyclopentadienyl ligands are preferably bonded to each other via a bridging group. Examples of bridging groups include alkylene groups having 1 to 4 carbon atoms, silylene groups, substituted silylene groups such as dialkylsilylene groups and diarylsilylene groups, and substituted germylene groups such as dialkylgermylene groups and diarylgermylene groups. Substituted silylene groups are preferred. The above-mentioned transition metal compounds of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton can be used as a catalyst component, either singly or in combination.

The co-catalyst refers to a catalyst that can effectively use the above-mentioned transition metal compounds of Group IV of the periodic table as a polymerization catalyst, or that can balance the ionic charge in a catalytically activated state. Examples of co-catalysts include benzene-soluble aluminoxanes of organoaluminum oxy compounds and benzene-insoluble organoaluminum oxy compounds, ion-exchangeable layered silicates, boron compounds, ionic compounds consisting of a cation with or without an active hydrogen group and a non-coordinating anion, lanthanoid salts such as lanthanum oxide, tin oxide, and phenoxy compounds containing a fluoro group.

The transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton may be used by being supported on an inorganic or organic support. The support is preferably an inorganic or organic porous oxide, and specific examples include ion-exchange layered silicates such as montmorillonite, SiO ₂ , Al ₂ O ₃ , MgO, ZrO ₂ , TiO ₂ , B ₂ O ₃ , CaO, ZnO, BaO, ThO ₂ , and mixtures thereof. Furthermore, examples of organometallic compounds that may be used if necessary include organoaluminum compounds, organomagnesium compounds, and organozinc compounds. Of these, organoaluminum compounds are preferred.

Copolymers of ethylene and other monomers can also be used as long as they do not impair the properties of the present invention. Examples of ethylene copolymers include copolymers of ethylene and an α-olefin having 3 to 20 carbon atoms. Examples of α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 3-methyl-1-butene, 4-methyl-1-pentene, and 6-methyl-1-heptene. Copolymers with vinyl acetate, acrylic esters, and the like can also be used as long as they do not impair the objectives of the present invention.

In addition, in the present invention, biomass-derived ethylene may be used as a raw material for obtaining the above-mentioned high-density polyethylene, instead of ethylene obtained from fossil fuels. Because such biomass-derived polyethylene is a carbon-neutral material, it can be used as a packaging material with even less environmental impact. Such biomass-derived polyethylene can be produced, for example, by a method such as that described in JP 2013-177531 A. Alternatively, commercially available biomass-derived polyethylene (such as Green PE, available from Braskem) may also be used.

The polyethylene content in the stretched polyethylene film is preferably 50% by mass or more, and more preferably 70% by mass or more.

The stretched polyethylene film may contain additives to the extent that they do not impair the properties of the present invention. Examples of such additives include crosslinking agents, antioxidants, antiblocking agents, slip agents, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins.

In one embodiment, the oriented polyethylene film has a multi-layer structure, preferably comprising a layer comprising high density polyethylene (HDPE) and a layer comprising medium density polyethylene (MDPE).
For example, the laminate may have a structure of a high-density polyethylene layer/a medium-density polyethylene layer/a high-density polyethylene layer. This structure can further improve the printability and strength of the polyethylene laminate. In this case, the thickness ratio of the high-density polyethylene layer to the medium-density polyethylene layer is preferably 1/10 or more and 1/1 or less, and more preferably 1/5 or more and 1/2 or less.

The thickness of the stretched polyethylene film is preferably 9 μm or more and 50 μm or less, and more preferably 12 μm or more and 30 μm or less. By keeping the thickness of the stretched polyethylene film within the above numerical range, the printability, strength, and heat resistance of the polyethylene laminate can be further improved.

In one embodiment, the stretched polyethylene film has, on one surface thereof, a vapor-deposited film containing a metal such as aluminum or an inorganic oxide such as aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, boron oxide, hafnium oxide, or barium oxide, thereby improving the gas barrier properties of the polyethylene laminate according to the present invention.
As the vapor deposition method, a conventionally known method can be used, and examples thereof include physical vapor deposition methods (PVD methods) such as vacuum deposition, sputtering, and ion plating, and chemical vapor deposition methods (CVD methods) such as plasma chemical vapor deposition, thermal chemical vapor deposition, and photochemical vapor deposition.

The thickness of the vapor-deposited film is preferably 0.002 μm or more and 0.4 μm or less, and more preferably 0.005 μm or more and 0.1 μm or less. By keeping the thickness of the vapor-deposited film within the above numerical range, it is possible to prevent cracks and other defects from occurring in the vapor-deposited film while maintaining gas barrier properties.

For example, a composite film consisting of two or more vapor-deposited layers of different inorganic oxides can be formed and used by combining physical vapor deposition and chemical vapor deposition. The vacuum level in the vapor deposition chamber is preferably approximately 10-2 to 10-8 mbar, particularly 10-3 to 10-7 mbar, before oxygen is introduced. After oxygen is introduced, the vacuum level is preferably approximately 10-1 to 10-6 mbar, particularly 10-2 to 10-5 mbar. The amount of oxygen introduced varies depending on the size of the vapor deposition machine. An inert gas such as argon, helium, or nitrogen may be used as a carrier gas for the introduced oxygen, provided this does not cause any problems. The film transport speed is preferably approximately 10 to 800 m/min, particularly 50 to 600 m/min.

The stretched polyethylene film may have images such as letters, patterns, symbols, etc. formed on its surface. It is preferable to form the image on the side of the stretched polyethylene film where the heat-sealable polyethylene layer is laminated, since this can prevent deterioration of the image over time.
The method for forming the image is not particularly limited, and examples thereof include conventionally known printing methods such as gravure printing, offset printing, flexographic printing, etc. Among these, flexographic printing is preferred from the viewpoint of environmental load.

Stretched polyethylene film can be obtained by melting a resin material containing polyethylene, forming it into a film using a melt extrusion method such as inflation molding or T-die molding, and then stretching it. Blown-film molding is preferred because it makes the stretching process easier. Stretched polyethylene film with a multilayer structure can be produced by melt co-extruding multiple resin materials.

The melt flow rate (MFR) of the resin material is preferably 0.5 g/10 min or more and 20 g/10 min or less, and more preferably 0.8 g/10 min or more and 5 g/10 min or less. By keeping the MFR of the resin material within the above numerical range, stretching can be carried out more easily.

<Adhesive layer>
The polyethylene laminate for packaging materials of the present invention comprises an adhesive layer containing a solventless adhesive between an oriented polyethylene film and a heat-sealable polyethylene layer.
Furthermore, when the polyethylene laminate for packaging materials of the present invention comprises a polyethylene layer having a vapor-deposited film, the adhesive layer is provided between the stretched polyethylene film and the polyethylene layer having a vapor-deposited film, and between the polyethylene layer having a vapor-deposited film and the heat-sealable polyethylene layer.
The adhesive layer of the polyethylene laminate for packaging materials of the present invention contains a solvent-free adhesive, thereby reducing the burden on the environment.

Examples of adhesives include polyvinyl acetate adhesives, polyacrylic ester adhesives, cyanoacrylate adhesives, ethylene copolymer adhesives, cellulose adhesives, polyester adhesives, polyether adhesives, polyamide adhesives, polyimide adhesives, amino resin adhesives, phenolic resin adhesives, epoxy adhesives, urethane adhesives, rubber adhesives, and silicone adhesives.

The thickness of the adhesive layer is not particularly limited, but can be 0.5 μm or more and 5 μm or less.

<Heat-sealable polyethylene layer>
The heat-sealable polyethylene layer contains at least one of high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and a copolymer of ethylene and another monomer. Among these, low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) are preferred from the viewpoint of heat-sealability. From the viewpoint of environmental impact, these polyethylenes are preferably derived from biomass.

The polyethylene content in the heat-sealable polyethylene layer is preferably 50% by mass or more, and more preferably 70% by mass or more.

The heat-sealable polyethylene layer may contain additives, such as crosslinking agents, antioxidants, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins, as long as they do not impair the properties of the present invention.

The thickness of the heat-sealable polyethylene layer is preferably 20 μm or more and 200 μm or less, and more preferably 30 μm or more and 150 μm or less. By keeping the thickness of the heat-sealable polyethylene layer within the above numerical range, its heat-sealability can be improved.

The heat-sealable polyethylene layer can be formed by producing a polyethylene film by forming a resin material containing polyethylene into a film using a melt extrusion molding method such as inflation molding or T-die molding, and then laminating this onto a polyethylene layer comprising a stretched polyethylene film or a vapor-deposited film via an adhesive layer.

<Polyethylene layer with vapor deposition film>
In one embodiment, the polyethylene laminate according to the present invention comprises a polyethylene layer comprising a vapor deposited film between an oriented polyethylene film and a heat-sealable polyethylene layer.
This can improve the gas barrier properties of the polyethylene laminate according to the present invention.

The polyethylene layer comprising the vapor-deposited film may be composed of a stretched or unstretched film, but from the standpoint of printability, strength, and heat resistance of the polyethylene laminate, it is preferable that it be stretched. It may also be uniaxially or biaxially stretched, but from the standpoint of strength, biaxial stretching is preferred.

The polyethylene layer comprising the vapor-deposited film contains at least one of high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and copolymers of ethylene and other monomers. Among these, from the viewpoints of printability, strength, and heat resistance, high-density polyethylene (HDPE) and medium-density polyethylene (MDPE) are preferred, with high-density polyethylene (HDPE) being more preferred. From the viewpoint of environmental impact, it is preferable that these polyethylenes are derived from biomass.

The polyethylene content in the polyethylene layer comprising the vapor-deposited film is preferably 50% by mass or more, and more preferably 70% by mass or more.

The polyethylene layer comprising the vapor-deposited film may contain additives, such as crosslinking agents, antioxidants, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins, as long as they do not impair the properties of the present invention.

From the viewpoint of productivity and economy, the thickness of the polyethylene layer having the vapor deposition film is preferably 9 μm or more and 50 μm or less, and more preferably 12 μm or more and 30 μm or less.
The thickness of the vapor-deposited film is preferably 0.002 μm or more and 0.4 μm or less, and more preferably 0.005 μm or more and 0.1 μm or less. By setting the thickness of the vapor-deposited film within the above numerical range, it is possible to prevent the occurrence of cracks and the like in the vapor-deposited film while maintaining the gas barrier properties.

The polyethylene layer having the vapor-deposited film may have an image formed on its surface. The image formation method is as described above.

The polyethylene layer having a vapor-deposited film can be formed by producing a polyethylene film by forming a resin material containing polyethylene using a melt extrusion method such as inflation molding or T-die molding, forming a vapor-deposited film on at least one side of the polyethylene film using the method described above, and then laminating the film on a stretched polyethylene film via an adhesive layer. In this case, the polyethylene film may be stretched before vapor deposition or lamination.

<Packaging materials>
In one embodiment, the packaging material according to the present invention can be produced by folding the polyethylene laminate in half, overlapping it so that the heat-sealable polyethylene layer is on the inside, and heat-sealing the edges.
Alternatively, it can be produced by overlapping two polyethylene laminates with the heat-sealable polyethylene layers facing each other and heat-sealing the edges.
Depending on the sealing method, various types of packaging materials can be produced by heat sealing using heat sealing forms such as side seal type, two-sided seal type, three-sided seal type, four-sided seal type, envelope seal type, palm seal type (pillow seal type), pleated seal type, flat bottom seal type, square bottom seal type, gusset type, and others.
Other examples include self-standing packaging bags (standing pouches), etc. Heat sealing can be performed by known methods such as bar sealing, rotary roll sealing, belt sealing, impulse sealing, high frequency sealing, and ultrasonic sealing.

Even though the polyethylene laminate of the present invention is a laminate made of only one type of resin (i.e., polyethylene), the oriented polyethylene film meets the strength and printability requirements for an outer film of packaging material, and the heat-sealable polyethylene layer makes it possible to form packaging. Therefore, it is extremely suitable as a material for constructing packaging materials that require recyclability.

The present invention will be explained in more detail using examples, but the present invention is not limited to these examples.

Example 1
Medium density polyethylene (density: 0.941 g/cm ³ , melting point: 129° C., MFR: 1.3 g/10 min, manufactured by Dow Chemical, trade name: Elite 5538G) was formed into a film by inflation molding to obtain a polyethylene film having a thickness of 100 μm.
This polyethylene film was stretched in the machine direction (MD) at a stretching ratio of 5 times to obtain a stretched polyethylene film having a thickness of 20 μm.

The above stretched polyethylene film was laminated with a 40 μm-thick unstretched linear low-density polyethylene (LLDPE) film (manufactured by Toyobo Co., Ltd., product name: L6100) via a two-component curing solventless polyester adhesive (manufactured by Rock Paint Co., Ltd., product name RN-920/HN:920) to obtain a polyethylene laminate.

Example 2
High-density polyethylene (density: 0.961 g/cm ³ , melting point: 135°C, MFR: 0.7 g/10 min, ExxonMobil, trade name: HTA108) and medium-density polyethylene (density: 0.941 g/cm ³ , melting point: 129°C, MFR: 1.3 g/10 min, Dow Chemical, trade name: Elite 5538G) were formed into a polyethylene film by inflation molding, consisting of a high-density polyethylene layer/medium-density polyethylene layer/high-density polyethylene layer. The high-density polyethylene layers were each 20 μm thick, and the medium-density polyethylene layer was 60 μm thick.
This polyethylene film was stretched in the machine direction (MD) at a stretching ratio of 5 times to obtain a stretched polyethylene film having a thickness of 20 μm.

The above stretched polyethylene film was laminated with a 40 μm-thick unstretched linear low-density polyethylene (LLDPE) film (manufactured by Toyobo Co., Ltd., product name: L6100) via a two-component curing solventless polyester adhesive (manufactured by Rock Paint Co., Ltd., product name RN-920/HN:920) to obtain a polyethylene laminate.

Example 3
Medium density polyethylene (density: 0.941 g/cm ³ , melting point: 129° C., MFR: 1.3 g/10 min, manufactured by Dow Chemical, trade name: Elite 5538G) was formed into a film by inflation molding to obtain a polyethylene film having a thickness of 100 μm.
This polyethylene film was stretched in the machine direction (MD) and the transverse direction (TD) at a stretching ratio of 2.24 to obtain a stretched polyethylene film having a thickness of 20 μm.
The stretched polyethylene film and a 40 μm-thick unstretched linear low-density polyethylene (LLDPE) film (manufactured by Toyobo Co., Ltd., trade name: L6100) were laminated together via a two-component curing solventless polyester adhesive (manufactured by Rock Paint Co., Ltd., trade name: RN-920/HN:920) to obtain a polyethylene laminate.

<Comparative Example 1>
Medium density polyethylene (density: 0.941 g/cm ³ , melting point: 129° C., MFR: 1.3 g/10 min, manufactured by Dow Chemical, trade name: Elite 5538G) was formed into a film by inflation molding to obtain a polyethylene film having a thickness of 20 μm.

The above polyethylene film was laminated with a 40 μm-thick unstretched linear low-density polyethylene (LLDPE) film (manufactured by Toyobo Co., Ltd., product name: L6100) via a two-component curing solventless polyester adhesive (manufactured by Rock Paint Co., Ltd., product name RN-920/HN:920) to obtain a polyethylene laminate.

<Comparative Example 2>
High-density polyethylene (density: 0.961 g/cm ³ , melting point: 135°C, MFR: 0.7 g/10 min, ExxonMobil, trade name: HTA108) and medium-density polyethylene (density: 0.941 g/cm ³ , melting point: 129°C, MFR: 1.3 g/10 min, Dow Chemical, trade name: Elite 5538G) were formed into a polyethylene film by inflation molding, consisting of a high-density polyethylene layer/medium-density polyethylene layer/high-density polyethylene layer. The high-density polyethylene layer had a thickness of 4 μm, and the medium-density polyethylene layer had a thickness of 12 μm.

The above polyethylene film was laminated with a 40 μm-thick unstretched linear low-density polyethylene (LLDPE) film (manufactured by Toyobo Co., Ltd., product name: L6100) via a two-component curing solventless polyester adhesive (manufactured by Rock Paint Co., Ltd., product name RN-920/HN:920) to obtain a polyethylene laminate.

<Printability evaluation>
An image was formed on one side of the stretched polyethylene film and polyethylene film produced in the above Examples and Comparative Examples by flexographic printing using a water-based flexographic ink (trade name: Aquariona, manufactured by Toyo Ink Co., Ltd.). The formed image was visually observed, and the printability of the stretched polyethylene film and polyethylene film was evaluated based on the following evaluation criteria. The evaluation results are summarized in Table 1.
(Evaluation criteria)
Good: The dimensional stability during printing was good, and a good image was formed without rubbing, bleeding, or the like.
x: The film expanded and contracted during printing, causing rubbing and bleeding in the formed image.

<Rigidity evaluation>
The stretched polyethylene films and polyethylene films prepared in the above Examples and Comparative Examples were cut into 15 mm wide test pieces, and their stiffness was measured using a loop stiffness tester (manufactured by Toyo Seiki Seisakusho, product name: Loop Stiffness Tester). The loop length was 60 mm. The measurement results are summarized in Table 1.

<Strength evaluation>
The stretched polyethylene films and polyethylene films produced in the above Examples and Comparative Examples were cut into 10 mm wide dumbbell-shaped test pieces. The tensile strength of these test pieces in the MD direction was measured using a tensile tester (Orientec Co., Ltd., RTC-1310A). The chuck distance was 10 mm, and the pulling speed was 300 mm/min. The measurement results are summarized in Table 1.

10: Polyethylene laminate for packaging materials, 20: Stretched polyethylene film, 30: Adhesive layer, 40: Heat-sealable polyethylene layer, 50: Polyethylene layer with vapor-deposited film

Claims (7)

The film comprises at least a stretched polyethylene film, an adhesive layer, and a heat-sealable film ,
the stretched polyethylene film is composed of a layer containing at least a high-density polyethylene having a melt flow rate of 5 g/10 min or less, or a layer containing at least a medium-density polyethylene having a melt flow rate of 5 g/10 min or less,
Printing is applied to at least one surface of the stretched polyethylene film,
the adhesive layer comprises a solventless adhesive,
the heat-sealable film is made of polyethylene,
A polyethylene layer having a vapor-deposited film is further provided between the stretched polyethylene film and the heat-sealable film.
A polyethylene laminate for packaging material, characterized in that: The polyethylene laminate for packaging materials according to claim 1, wherein the stretched polyethylene film has a stretch ratio in the machine direction (MD) of 2 times or more and 10 times or less. The polyethylene laminate for packaging materials according to claim 1 or 2, wherein the stretched polyethylene film is a biaxially stretched film. The polyethylene laminate for packaging materials according to any one of claims 1 to 3, wherein the thickness of the stretched polyethylene film is 9 μm or more and 50 μm or less. The polyethylene laminate for packaging materials according to any one of claims 1 to 4, wherein the stretched polyethylene film is produced by inflation molding. 6. The polyethylene laminate for packaging materials according to claim 1, wherein the heat-sealable film comprises at least one of low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). A packaging material comprising the laminate described in any one of claims 1 to 6.