JP2023126271A - Polyethylene laminate and packaging material using the same - Google Patents

Abstract

To provide a polyethylene laminate that has high heat resistance and also has excellent recyclability while keeping heat sealability.SOLUTION: A polyethylene laminate has a base material layer and a heat seal layer. The base material layer comprises polyethylene with a density of 0.930 g/cm3 or more and the heat seal layer comprises polyethylene with a density of less than 0.930 g/cm3. Each of the base material layer and the heat seal layer is formed by co-extrusion molding of the polyethylene with a density of 0.930 g/cm3 or more and the polyethylene with a density of less than 0.930 g/cm3. The polyethylene with a density of 0.930 g/cm3 or more and the polyethylene with a density of less than 0.930 g/cm3 include biomass polyethylene. The base material layer is treated with electron beam irradiation.SELECTED DRAWING: Figure 1

Description

The present invention relates to a polyethylene laminate, and more particularly to a polyethylene laminate made of a single material, including a polyethylene base layer with heat resistance and a polyethylene layer with heat sealability, and the use of the same. Regarding packaging materials.

Films made of polyethylene have appropriate flexibility, excellent transparency, moisture resistance, chemical resistance, etc., and are inexpensive, so they are used in various packaging materials. In particular, since the melting point of polyethylene is approximately 100 to 140°C, although it varies somewhat depending on the type, it is generally used as a sealant film in the field of packaging materials.

On the other hand, as mentioned above, polyethylene has poor heat resistance, so when used as a packaging material, it deforms or even melts when processed into a heat sheet, so it does not have the same heat resistance as polyester film or nylon film. It is common to use a laminate obtained by laminating a superior base film and a polyethylene film as a packaging material. For example, bags are made by laminating a base material such as a polyester film and a polyethylene film and heat-sealing them so that the polyethylene film side is on the inside of the packaging bag (for example, Patent Document 1). .

Incidentally, in recent years, as calls for building a recycling-oriented society have been increasing, there has been a desire to move away from fossil fuels in the materials field as well as energy, and the use of biomass has been attracting attention. Biomass is an organic compound that is photosynthesized from carbon dioxide and water, and by using it, it becomes carbon dioxide and water again, so it is a so-called carbon-neutral renewable energy. In recent years, the practical use of biomass plastics made from these biomass raw materials is rapidly progressing, and attempts are also being made to produce various resins from biomass raw materials. As an example, a resin film for packaging products using biomass-derived polyethylene has been proposed (Patent Document 2).

Furthermore, attempts have been made to recycle and use conventional packaging materials made from fossil fuel-derived materials. However, the above-mentioned laminate in which different types of resin films are bonded together has a problem in that it is difficult to separate each type of resin, making it unsuitable for recycling.

In order to solve the above problem, the applicant has studied to realize a packaging material made of a single polyethylene film without using a base film with excellent heat resistance such as a polyester film, and found that one side of the polyethylene film proposed that a packaging material made of polyethylene film could be realized by imparting heat resistance to one side of the polyethylene film conventionally used as a heat-sealing layer by irradiating it with electrons (Patent Document 3).

Japanese Patent Application Publication No. 2005-104525 Japanese Patent Application Publication No. 2012-251006 JP 2017-031233 Publication

As mentioned above, the polyethylene film proposed in Patent Document 3 functions as a base material because one surface is given heat resistance by electron beam irradiation, and the other surface has heat sealability. Because it is a single film, it has both heat resistance and heat sealability, making it suitable for use as packaging material.Furthermore, since it is composed of a single polyethylene material, it has excellent recyclability. There is. However, upon further study by the present inventors, we found that when the above polyethylene film is heat-sealed during bag making, ) may shrink, and it was found that there is room for further improvement in heat resistance.

Therefore, an object of the present invention is to provide a polyethylene laminate that has high heat resistance while maintaining heat sealability and is also excellent in recyclability.
Another object of the present invention is to provide a packaging material using the polyethylene laminate.

The present inventors have developed a polyethylene laminate that uses two types of polyethylene with different densities on the surface that is irradiated with electron beams and the surface that is not irradiated with electron beams, thereby achieving remarkable heat resistance while maintaining recyclability. We found that improvements can be made. Furthermore, by using biomass-derived polyethylene as the polyethylene constituting the polyethylene laminate, the environmental load can be further reduced. The present invention is based on this knowledge.

The polyethylene laminate according to the present invention comprises:
A polyethylene laminate comprising a base layer and a heat seal layer,
The base layer contains polyethylene with a density of 0.930 g/cm ³ or more,
The heat-sealing layer comprises polyethylene with a density of less than 0.930 g/cm ³ ,
The base layer and the heat seal layer are formed by co-extrusion molding of polyethylene with a density of 0.930 g/cm ³ or more and polyethylene with a density of less than 0.930 g/cm ³ ,
The polyethylene with a density of 0.930 g/cm ³ or more or the polyethylene with a density of less than 0.930 g/cm ³ includes biomass polyethylene,
The base material layer is characterized in that it has been subjected to electron beam irradiation treatment.

The polyethylene laminate according to the present invention may include an intermediate layer between the base layer and the heat seal layer.

Moreover, in the polyethylene laminate according to the present invention,
The intermediate layer comprises polyethylene with a density of 0.942 g/cm ³ or more,
The base layer, the intermediate layer, and the heat seal layer are made of polyethylene with a density of 0.930 g/cm ³ or more, polyethylene with a density of 0.942 g/cm ³ or more, and polyethylene with a density of less than 0.930 g/cm ³ . It may be formed by coextrusion molding.

Further, in the polyethylene laminate according to the present invention, the polyethylene having a density of 0.942 g/cm ³ or more may include biomass polyethylene.

Furthermore, the polyethylene laminate according to the present invention may further include a printed layer on the surface of the base layer.

Furthermore, the polyethylene laminate according to the present invention may further include a barrier layer on the surface of the base layer.

Moreover, the packaging material according to another aspect of the present invention is made of a polyethylene laminate.

According to the present invention, in a laminate including a base layer and a heat seal layer, the base layer is made of polyethylene with a density of 0.930 g/cm ³ or more, and the heat seal layer is made of polyethylene with a density of 0.930 g/cm ^{3 or more} . The base layer side of the laminate of the coextruded base layer and heat seal layer is subjected to electron beam irradiation treatment, thereby further improving the heat resistance of the base layer. can. As a result, it is possible to realize a polyethylene laminate that has high heat resistance while maintaining heat sealability and is also excellent in recyclability. Furthermore, by using biomass-derived polyethylene as the polyethylene constituting the polyethylene laminate, the environmental load can be further reduced.

FIG. 1 is a schematic cross-sectional view of a polyethylene laminate according to one embodiment of the present invention. FIG. 1 is a schematic cross-sectional view of a polyethylene laminate according to one embodiment of the present invention. FIG. 1 is a perspective view showing one embodiment of a packaging material produced using the polyethylene laminate of the present invention. FIG. 1 is a perspective view showing one embodiment of a packaging material produced using the polyethylene laminate of the present invention.

[Polyethylene laminate]
The polyethylene laminate according to the present invention will be explained with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a polyethylene laminate 10 according to an embodiment of the invention. The polyethylene laminate 10 according to the first embodiment includes a base layer 1 and a heat seal layer 2. As will be described later, the polyethylene laminate of the present invention can be suitably used as a packaging material, and when the polyethylene laminate is used as a packaging material, the base layer 1 side is the packaging material. On the outer surface, a heat-sealing layer 2 is used located on the inner surface of the packaging material. Further, the polyethylene laminate 10 according to another embodiment of the present invention may include an intermediate layer 3 between the base layer 1 and the heat seal layer 2. As will be described later, by providing the intermediate layer 3, stiffness and strength can be further imparted to the polyethylene laminate. In addition to the layers described above, the polyethylene laminate of the present invention may also include a printed layer or a barrier layer (not shown) as appropriate to suit various uses of packaging materials. Each layer constituting the polyethylene laminate of the present invention will be explained below.

<Base material layer>
In the present invention, the base material layer contains polyethylene having a density of 0.930 g/cm ³ or more. As mentioned above, in Patent Document 2, the present applicant improves the heat resistance of the electron beam irradiated surface by irradiating one side of a single layer film made of polyethylene with a density of 0.91 g/cm ³ or less with an electron beam. Therefore, we proposed that even a single polyethylene film can be used as a packaging material by maintaining the heat sealability of the other side that is not exposed to electron beam irradiation. This is thought to be due to the fact that by irradiating polyethylene with a density of 0.91 g/cm ³ or less with an electron beam, the polyethylene on the surface irradiated with the electron beam is partially crosslinked, improving heat resistance. However, polyethylene with a density of 0.91 g/cm ³ or less has poor processing suitability such as stickiness, and the processing suitability is not improved even by electron beam irradiation. Furthermore, since the crosslinking density of the polyethylene differs between the surface irradiated with the electron beam and the surface not irradiated with the electron beam, wrinkles may occur in the film due to the difference in heat shrinkage rate between the front and back surfaces of the film. In the present invention, as described above, polyethylene with a density of 0.930 g/cm ³ or more is used as the base material layer disposed on the surface to be irradiated with an electron beam, and the heat seal layer is made of polyethylene with a density of 0.930 g/cm ^{3 or} more. By constructing polyethylene of less than be.

As the polyethylene having a density of 0.930 g/cm ³ or more, medium density polyethylene (MDPE) or high density polyethylene (HDPE) can be suitably used. In addition, medium density polyethylene refers to polyethylene having a density of 0.930 g/cm ³ or more and less than 0.942 g/cm ³ , and high density polyethylene refers to polyethylene having a density of 0.942 g/cm ³ or more. say. The density of the polyethylene constituting the base material layer is preferably 0.930 g/cm ³ or more and 0.950 g/cm ³ or less, more preferably 0.935 g/cm ³ or more and 0.945 g/cm ³ or less. It is. Polyethylene having such a density can be prepared by mixing the above-mentioned medium density polyethylene and high density polyethylene at an appropriate blending ratio. In addition to medium-density polyethylene and high-density polyethylene, high-density polyethylene and low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE) may be mixed in an appropriate blending ratio so that the density falls within the above density range. It may also be prepared by Note that low-density polyethylene refers to polyethylene having a density of less than 0.930 g/cm ³ .

In the present invention, the polyethylene having a density of 0.930 g/cm ³ or more that constitutes the base layer contains biomass polyester. Biomass polyethylene is a monomer polymer containing ethylene derived from biomass. Since biomass-derived ethylene is used as the raw material monomer, the polymerized polyolefin is biomass-derived. The content of biomass-derived ethylene in the raw material monomer does not need to be 100% by mass, and is, for example, preferably 50% or more, more preferably 80% or more. The raw material monomer may include ethylene derived from fossil fuels, and may include monomers of α-olefins such as butylene, hexene, and octene. Even in such a case, the obtained polymer is called biomass polyethylene. By including an α-olefin, the polymerized polyolefin has an alkyl group in a branched structure, so it can be made more flexible than a simple linear one.

For example, biomass-derived ethylene can be produced using biomass-derived ethanol as a raw material. In particular, it is preferable to use fermented ethanol derived from biomass obtained from plant materials. The plant raw material is not particularly limited, and conventionally known plants can be used. For example, corn, sugar cane, beets and manioc may be mentioned.

In the present invention, fermented ethanol derived from biomass refers to ethanol produced by contacting a culture solution containing a carbon source obtained from a plant material with a product derived from an ethanol-producing microorganism or its crushed product, and then purified. Conventionally known methods such as distillation, membrane separation, and extraction can be applied to purify ethanol from the culture solution. For example, methods include adding benzene, cyclohexane, etc. and azeotropically distilling the mixture, or removing water by membrane separation or the like.

As the above-mentioned biomass-derived polyethylene, commercially available products may be used, such as biomass-derived linear low-density polyethylene (trade name: SLL118, density: 0.916 g/cm ³ manufactured by Braskem). , MFR: 1.0 g/10 min, biomass degree 87%), linear low-density polyethylene derived from biomass manufactured by Braskem (trade name: SLL318, density: 0.918 g/cm ³ , MFR: 2.7 g/ 10 minutes, biomass degree 87%), biomass-derived linear low-density polyethylene manufactured by Braskem (trade name: SLH218, density: 0.916 g/cm ³ , MFR: 2.3 g/10 minutes, biomass degree 87%) ), biomass-derived high-density polyethylene manufactured by Braskem (trade name: SHE150, density: 0.948 g/cm ³ , MFR: 1.0 g/10 min, biomass degree 94%), and the like.

The polyethylene with a density of 0.930 g/cm ³ or more constituting the base material layer may be entirely composed of the above-mentioned biomass polyethylene from the viewpoint of reducing environmental load, but conventional fossil fuel-derived polyethylene and biomass-derived polyethylene may be used. It may also be a blend with polyethylene.
The content of biomass-derived polyethylene is preferably 50% or more, more preferably 80% or more.

In the present invention, polyethylenes having different densities and branches as described above, which can be used as polyethylene having a density of 0.930 g/cm ³ or more, can be obtained by appropriately selecting a polymerization method. For example, using a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst as a polymerization catalyst, by any of gas phase polymerization, slurry polymerization, solution polymerization, and high-pressure ionic polymerization, It is preferable to perform the reaction in one stage or in multiple stages of two or more stages.

The above-mentioned single-site catalyst is a catalyst that can form a uniform active species, and is usually prepared by bringing a metallocene transition metal compound or a non-metallocene transition metal compound into contact with an activation cocatalyst. . Single-site catalysts are preferable compared to multi-site catalysts because they have a more uniform active site structure and can polymerize a polymer with a high molecular weight and a highly uniform structure. As the single site catalyst, it is particularly preferable to use a metallocene catalyst. The metallocene catalyst is a catalyst containing a transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, a cocatalyst, an organometallic compound if necessary, and each catalyst component of a carrier. be.

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

In a transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, examples of the transition metal include zirconium, titanium, hafnium, etc., and zirconium and hafnium are particularly preferred. The transition metal compound usually has two cyclopentadienyl skeleton-containing ligands, and each of the cyclopentadienyl skeleton-containing ligands is preferably bonded to each other via a crosslinking group. Examples of the crosslinking group include alkylene groups having 1 to 4 carbon atoms, substituted silylene groups such as silylene groups, dialkylsilylene groups, and diarylsilylene groups, and substituted germylene groups such as dialkylgermylene groups and diarylgermylene groups. Preferably, it is a substituted silylene group. One or a mixture of two or more of the transition metal compounds of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton can be used as a catalyst component.

The co-catalyst is one that can make the transition metal compound of Group IV of the periodic table effective as a polymerization catalyst, or can balance the ionic charges in a catalytically activated state. As a co-catalyst, organoaluminumoxy compounds such as benzene-soluble aluminoxane, benzene-insoluble organoaluminumoxy compounds, ion-exchanged layered silicates, boron compounds, cations containing or not containing active hydrogen groups, and non-coordinating anions can be used. Examples include ionic compounds, lanthanoid salts such as lanthanum oxide, tin oxide, and phenoxy compounds containing fluoro groups.

A 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 compound carrier. The carrier is preferably a porous oxide of an inorganic or organic compound, and specifically, 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, _ThO2 , etc., or a mixture thereof. Furthermore, examples of organometallic compounds that may be used as necessary include organoaluminum compounds, organomagnesium compounds, organozinc compounds, and the like. Among these, organic aluminum is preferably used.

It is also possible to use copolymers of ethylene and other monomers. Examples of ethylene copolymers include copolymers of ethylene and α-olefins having 3 to 20 carbon atoms, and 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, 6-methyl- Examples include 1-heptene. Furthermore, copolymers with vinyl acetate, acrylic esters, etc. may be used as long as they do not impair the purpose of the present invention.

Furthermore, in the present invention, polyethylene made from biomass-derived ethylene may be used instead of ethylene obtained from fossil fuels. Since 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 as described in JP-A No. 2013-177531. Alternatively, commercially available biomass-derived polyethylene (for example, green PE commercially available from Braskem, etc.) may be used.

The base layer may contain a light stabilizer. As will be described later, in the polyethylene laminate of the present invention, since the polyethylene of the base layer is subjected to electron beam irradiation treatment, the polyethylene laminate constituting the base layer contains a light stabilizer. It is also possible to prevent deterioration over time. Note that when polyethylene is subjected to electron beam irradiation treatment, carbon-hydrogen bonds in the polyethylene are broken, and radicals are generated at the ends of the broken bonds. The generated radicals come into contact with other polyethylene molecular chains due to the molecular motion of the molecular chains, extract hydrogen atoms, and bond with carbon atoms in the polyethylene molecular chains. As a result, a crosslinked structure is formed in the polyethylene, but the remaining radicals gradually break the molecular chains, which is thought to lead to deterioration of the polyethylene. The light stabilizer has the function of trapping these remaining radicals.

As light stabilizers, antioxidants such as phenolic antioxidants, amine antioxidants, phosphoric acid antioxidants, sulfur antioxidants, hindered amine antioxidants, and hydroxylamine antioxidants; and ultraviolet absorbers such as benzotriazole ultraviolet absorbers, triazine ultraviolet absorbers, and benzophenone ultraviolet absorbers.

It is preferable to use an antioxidant because it is less likely to inhibit the crosslinking reaction that is carried out by irradiating the polyethylene film base material with an electron beam.

In addition, as an antioxidant, it is preferable to use both a primary antioxidant that captures generated radicals and a secondary antioxidant that decomposes hydroperoxide generated from the radicals. Antioxidants having both the functions of antioxidants may also be used.

Primary antioxidants include phenolic antioxidants, amine antioxidants, and hindered amine antioxidants, and secondary antioxidants include phosphorus antioxidants and sulfur antioxidants. Examples of the antioxidant having both the functions of a primary antioxidant and a secondary antioxidant include hydroxylamine antioxidants.

Furthermore, hydroxylamine-based antioxidants and phosphorus-based antioxidants are preferred because they can prevent coloring of the polyethylene film base material.

The content of the light stabilizer in the base layer is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, and 0.1% by mass or more and 10% by mass or less. More preferably, it is at least 8% by mass and at most 8% by mass.

Further, the base material layer may contain a crosslinking agent. As described later, the base material layer is subjected to electron beam irradiation treatment, and by including a crosslinking agent, the degree of crosslinking of polyethylene can be further improved. As a result, the heat resistance of the base layer constituting the polyethylene laminate can be further improved.

As a crosslinking agent, styrene elastomers such as styrene-polyisoprene elastomer, styrene-polybutadiene elastomer, styrene-polyisoprene-butadiene random copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl Examples include ethylene-acrylate copolymers such as acrylate copolymers, ethylene-acrylic acid ester-glycidyl methacrylate, and the like.

The content of the crosslinking agent in the base layer is preferably 1% by mass or more and 49% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and 15% by mass or more and 35% by mass. It is more preferable that it is the following.

The base layer may contain additives within a range that does not impair the characteristics of the present invention, such as fillers, reinforcing agents, antistatic agents, pigments, and modifying resins.

The thickness of the base material layer is arbitrary depending on its use, but is usually about 5 μm or more and 200 μm or less, preferably about 5 μm or more and 100 μm or less. As will be described later, the thickness can be appropriately adjusted by adjusting the screw rotation speed of the melt extruder, the rotation speed of the cooling roll, etc. when performing coextrusion molding to form a laminate.

<Heat seal layer>
The polyethylene laminate of the present invention includes a heat seal layer. When the polyethylene laminate of the present invention is used as a packaging material, the heat seal layer is used so as to be located on the inner surface of the packaging material.

The heat seal layer comprises polyethylene with a density of less than 0.930 g/cm ³ . A polyethylene laminate that uses the same material (polyethylene) as the base layer, but maintains heat sealability and is recyclable by using polyethylene, which has a lower density than the polyethylene used for the base layer, as the heat seal layer. It can be a body.

In the present invention, the polyethylene with a density of less than 0.930 g/cm ³ constituting the heat seal layer includes polyethylene derived from biomass. Since the polyethylene constituting the base material layer and the heat seal layer both contain biomass polyethylene, the environmental load of the polyethylene laminate as a whole can be reduced. As the biomass polyethylene, the same ones as those mentioned above can be used.

The polyethylene with a density of less than 0.930 g/cm ³ constituting the heat-sealing layer may be entirely composed of the above-mentioned biomass polyethylene from the viewpoint of reducing environmental impact, but conventional fossil fuel-derived polyethylene and biomass-derived polyethylene may be used. It may also be a blend with polyethylene. The content of biomass-derived polyethylene is preferably 50% or more, more preferably 80% or more.

For the heat seal layer, low density polyethylene or linear low density polyethylene may be used alone, or a mixture of both may be used as appropriate. Further, a mixture of low density polyethylene and medium density polyethylene may be used as long as the density is within the above density range, but from the viewpoint of heat sealability, it is preferable to have a density of less than 0.925 g/ ^cm3 . , more preferably a density of less than 0.920 g/cm ³ .

The polyethylene film layer can contain the above additives within a range that does not impair the characteristics of the present invention.

The thickness of the heat seal layer is arbitrary depending on its use, but is usually preferably 15 μm or more and 200 μm or less, more preferably 20 μm or more and 200 μm or less, and 25 μm or more and 160 μm or less. It is even more preferable. Thereby, the processability of the polyethylene laminate of the present invention can be improved while maintaining its heat sealability. As will be described later, the thickness of the heat-sealing layer can be appropriately adjusted by adjusting the screw rotation speed of the melt extruder, the rotation speed of the cooling roll, etc. when coextruding the laminate into a laminate.

Further, the ratio of the thickness of the base material layer to the heat seal layer is preferably 4:1 to 1:4, more preferably 2:1 to 1:2. The thickness ratio can be appropriately adjusted by adjusting the rotational speed of each screw of the coextrusion film forming machine, etc., as described later.

<Middle layer>
In the polyethylene laminate of the present invention, an intermediate layer may be provided between the above-described base layer and the heat seal layer. By providing the intermediate layer, the polyethylene laminate can be made to have more stiffness and improve shape stability. Further, by providing the intermediate layer, it is possible to prevent the polyethylene laminate from melting and becoming thinner during the heat sealing process for bag making.

From the viewpoint of recyclability, the intermediate layer is preferably made of polyethylene, which is the same type of material as the material forming the base layer and the heat seal layer. In that case, the intermediate layer preferably contains polyethylene with a density of 0.942 g/cm ³ or more, more preferably polyethylene with a density of 0.950 g/cm ³ or more and 0.970 g/cm ³ or less. High-density polyethylene can be preferably used as such polyethylene, but a mixture of medium-density polyethylene and high-density polyethylene in an appropriate blending ratio may also be used as long as the density is within the above-mentioned range.

In the present invention, from the viewpoint of further reducing environmental load, it is preferable that polyethylene with a density of 0.942 g/cm ³ or more also contains biomass-derived polyester. As the biomass-derived polyester, those similar to those described above can be used.

The polyethylene with a density of 0.942 g/cm ³ or more constituting the intermediate layer may be entirely composed of the above-mentioned biomass polyethylene from the viewpoint of reducing environmental load, but conventional fossil fuel-derived polyethylene and biomass-derived polyethylene may be used. It may also be a blend with polyethylene.
The content of biomass-derived polyethylene is preferably 50% or more, more preferably 80% or more.

The thickness of the intermediate layer is arbitrary depending on its use, but is usually about 5 μm or more and 100 μm or less, preferably about 10 μm or more and 80 μm or less, and more preferably about 10 μm or more and 60 μm or less.

The intermediate layer may contain ethylene/vinyl alcohol copolymer (EVOH) in addition to the polyethylene described above. By containing the ethylene/vinyl alcohol copolymer, the intermediate layer functions as a barrier layer, so that barrier properties can be imparted to the polyethylene laminate.

The thickness of the intermediate layer may be adjusted as appropriate within a range that does not impair the function of the intermediate layer. For example, the thickness ratio of the base layer and the intermediate layer may be in the range of 2:1 to 1:5, which is preferable. The range is 1:1 to 1:3. Further, the thickness ratio between the intermediate layer and the heat seal layer can be in the range of 1:2 to 5:1, and the preferred range is 3:1 to 1:1. The ratio of the thickness of each layer can be appropriately adjusted by adjusting the rotation speed of each screw of the coextrusion film forming machine, etc., as described later.

<Other layers>
The polyethylene laminate according to the present invention may be provided with layers other than the above-mentioned layers as long as recyclability is not impaired. For example, a printing layer or a barrier layer may be provided on the surface of the base layer. In the polyethylene laminate according to the present invention, since the surface of the base material layer is subjected to electron beam irradiation treatment, the adhesion between the printing layer or barrier layer and the base material layer is maintained even if no particular surface treatment is applied to the base material layer. However, surface treatments such as corona treatment, ozone treatment, low-temperature plasma treatment using oxygen gas or nitrogen gas, glow discharge treatment, oxidation treatment using chemicals, etc. may also be performed.

The printing layer contains letters, numbers, pictures, figures, symbols, patterns, etc. for decoration, display of contents, display of expiration date, display of manufacturer, seller, etc., and for giving a sense of beauty. This layer forms any desired printed pattern. The printing layer may be provided on the entire surface of the base layer or the barrier layer to be described later, or may be provided on a portion thereof.

The printing layer can be formed using conventionally known pigments and dyes, but from the viewpoint of further reducing environmental load, the printing layer may also be formed using biomass-derived materials. For example, in a printing ink containing a coloring agent such as a pigment or dye, a polyol, and an isocyanate compound, a printing layer is formed using a printing ink in which at least one of the polyol as the main ingredient and the isocyanate compound as a hardening agent contains a biomass-derived component. may be formed.

As the biomass-derived polyol, biomass-derived polyester polyols and biomass-derived polyether polyols can be suitably used. A biomass-derived polyester polyol is a reaction product of a polyfunctional alcohol and a polyfunctional carboxylic acid, and either or both of the polyfunctional alcohol and the polyfunctional carboxylic acid are made of biomass-derived materials. Moreover, a biomass-derived polyether polyol is a reaction product of a polyfunctional alcohol and a polyfunctional isocyanate, and either or both of the polyfunctional alcohol and the polyfunctional isocyanate are made of biomass-derived materials.

As the polyfunctional alcohol constituting the above-mentioned biomass-derived polyol, aliphatic polyfunctional alcohols obtained from plant materials such as corn, sugarcane, cassava, and sago palm can be used. Examples of biomass-derived aliphatic polyfunctional alcohols include polypropylene glycol (PPG), neopentyl glycol (NPG), ethylene glycol (EG), diethylene glycol (DEG), and butylene, which are obtained from plant materials by the following methods. Examples include glycol (BG) and hexamethylene glycol, any of which can be used. These may be used alone or in combination.

Biomass-derived polypropylene glycol is produced by converting glycerol into 3-hydroxypropyl aldehyde (HPA) using a fermentation method in which glucose is obtained by decomposing plant materials. Compared to polypropylene glycol produced using the EO method, polypropylene glycol produced using biomethods such as the fermentation method described above is safer and produces useful by-products such as lactic acid, and can also be produced at lower production costs. It is also preferable that it is possible. Butylene glycol derived from biomass can be produced by producing succinic acid obtained by producing glycol from plant materials and fermenting it, and then hydrogenating this. Biomass-derived ethylene glycol can be produced, for example, from bioethanol obtained by a conventional method via ethylene.

Biomass-derived polyfunctional carboxylic acids include reproducible plant-derived oils such as soybean oil, linseed oil, tung oil, coconut oil, palm oil, and castor oil, as well as recycled waste cooking oils based on these oils. Aliphatic polyfunctional carboxylic acids obtained from plant materials such as oils can be used. Examples of biomass-derived aliphatic polyfunctional carboxylic acids include sebacic acid, succinic acid, phthalic acid, adipic acid, glutaric acid, and dimer acid. For example, sebacic acid is produced by alkaline thermal decomposition of ricinoleic acid obtained from castor oil, with heptyl alcohol as a by-product. In the present invention, it is particularly preferable to use biomass-derived succinic acid or biomass-derived sebacic acid. These may be used alone or in combination of two or more.

Biomass-derived polyfunctional isocyanates are produced by converting plant-derived divalent carboxylic acids into acid amides, reducing them to terminal amino groups, and then reacting with phosgene to convert the amino groups into isocyanate groups. What is obtained can be used. The biomass-derived polyfunctional isocyanate is, for example, a biomass-derived diisocyanate. Examples of biomass-derived diisocyanates include dimer acid diisocyanate (DDI), octamethylene diisocyanate, decamethylene diisocyanate, and the like. Furthermore, a plant-derived diisocyanate can also be obtained by using a plant-derived amino acid as a raw material and converting its amino group into an isocyanate group. For example, lysine diisocyanate (LDI) is obtained by methyl esterifying the carboxyl group of lysine and then converting the amino group into an isocyanate group. Furthermore, 1,5-pentamethylene diisocyanate can be obtained by decarboxylating the carboxyl group of lysine and then converting the amino group into an isocyanate group.

Other methods for synthesizing 1,5-pentamethylene diisocyanate include a phosgenation method and a carbamate method. More specifically, the phosgenation method includes a method in which 1,5-pentamethylenediamine or a salt thereof is directly reacted with phosgene, and a method in which the hydrochloride of pentamethylenediamine is suspended in an inert solvent and reacted with phosgene. This method synthesizes 1,5-pentamethylene diisocyanate. In addition, in the carbamate method, 1,5-pentamethylene diisocyanate is first produced by carbamateing 1,5-pentamethylene diamine or its salt to produce pentamethylene dicarbamate (PDC), and then thermally decomposing it to produce 1,5-pentamethylene diisocyanate. It is something that is synthesized. In the present invention, the polyisocyanate preferably used includes 1,5-pentamethylene diisocyanate-based polyisocyanate (trade name: Stabio (registered trademark)) manufactured by Mitsui Chemicals, Inc.

The method for forming the printed layer is not particularly limited, and for example, printing methods such as an inkjet method, a gravure printing method, an offset printing method, a flexo printing method, a thermal transfer method, a transfer, and a hot stamp (foil stamping) can be used. .

The printed layer preferably has a thickness of 0.1 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less, and still more preferably 1 μm or more and 3 μm or less.

As the barrier layer, a metal foil or a vapor deposited layer of metal or inorganic oxide can be suitably used.

As the metal foil, a conventionally known metal foil can be used. Aluminum foil is preferable from the viewpoint of gas barrier properties that block the transmission of oxygen gas, water vapor, etc., and light shielding properties that block the transmission of visible light, ultraviolet rays, etc. Furthermore, since the packaging bag can be given metallic luster, the design can be improved. The thickness of the metal foil is, for example, 5 μm or more and 15 μm or less.

The vapor deposited layer of metal or inorganic oxide is a layer consisting of a vapor deposited film that can be formed by a conventionally known method. By providing the vapor deposited layer, it is possible to provide or improve gas barrier properties that prevent permeation of oxygen gas, water vapor, and the like. Note that the barrier layer may include two or more vapor deposited layers. When two or more vapor deposited layers are provided, they may have the same composition or different compositions.

Examples of metal vapor deposited films include aluminum (Al), magnesium (Mg), tin (Sn), sodium (Na), titanium (Ti), lead (Pb), zirconium (Zr), yttrium (Y), and gold ( A metal vapor deposition film such as Au) or chromium (Cr) can be used. In particular, for packaging bags, it is preferable to include a vapor-deposited aluminum film.

Although the thickness of the metal vapor deposition film varies depending on the type of metal used, it is desirable to arbitrarily select the thickness within the range of, for example, 50 Å or more and 2000 Å or less, preferably 100 Å or more and 1000 Å or less. More specifically, in the case of a deposited aluminum film, the film thickness is desirably 50 Å or more and 600 Å or less, and more preferably 100 Å or more and 450 Å or less.

Examples of the inorganic oxide vapor deposited film include silicon (Si), aluminum (Al), magnesium (Mg), calcium (Ca), potassium (K), tin (Sn), sodium (Na), boron (B), A vapor deposited film of an oxide such as titanium (Ti), lead (Pb), zirconium (Zr), or yttrium (Y) can be used. In particular, for packaging bags, it is preferable to include a vapor-deposited film of aluminum oxide or silicon oxide.

Inorganic oxides are expressed as MOX, such as SiOX, AlOX, etc. (wherein, M represents an inorganic element, and the value of X varies depending on the inorganic element.) . The value range of X is 0 to 2 for silicon (Si), 0 to 1.5 for aluminum (Al), 0 to 1 for magnesium (Mg), 0 to 1 for calcium (Ca), Potassium (K) is 0 to 0.5, tin (Sn) is 0 to 2, sodium (Na) is 0 to 0.5, boron (B) is 0 to 1.5, titanium (Ti) can take a value in the range of 0 to 2, lead (Pb) can take a value in the range of 0 to 2, zirconium (Zr) can take a value in the range of 0 to 2, and yttrium (Y) can take a value in the range of 0 to 1.5. In the above, when X=0, it is a completely inorganic substance (pure substance) and is not transparent, and the upper limit of the range of X is a completely oxidized value. Silicon (Si) and aluminum (Al) are preferably used for the packaging material, with silicon (Si) in the range of 1.0 to 2.0 and aluminum (Al) in the range of 0.5 to 1.5. You can use the value of .

The thickness of the inorganic oxide vapor deposited film varies depending on the type of inorganic oxide used, but can be arbitrarily selected within the range of, for example, 50 Å or more and 2000 Å or less, preferably 100 Å or more and 1000 Å or less. desirable. For example, in the case of a vapor deposited film of aluminum oxide or silicon oxide, the film thickness is desirably 50 Å or more and 500 Å or less, more preferably 100 Å or more and 300 Å or less.

A vapor deposited film can be formed on a base material layer or the like using the following formation method. Examples of methods for forming the deposited film include physical vapor deposition methods (PVD methods) such as vacuum evaporation methods, sputtering methods, and ion plating methods, or plasma chemical vapor deposition methods and thermochemical methods. Examples include a chemical vapor deposition method (CVD method) such as a vapor phase growth method and a photochemical vapor deposition method.

If necessary, a gas barrier coating film may be provided on the vapor deposited layer. A gas barrier coating film is a coating film that functions as a layer that suppresses the permeation of oxygen gas, water vapor, and the like. The gas barrier coating film has a general formula R ¹ nM(OR ² )m (wherein, R ¹ and R ² represent an organic group having 1 to 8 carbon atoms, M represents a metal atom, and n is , represents an integer of 0 or more, m represents an integer of 1 or more, and n+m represents the valence of M.), a polyvinyl alcohol-based resin, and/or ethylene. - A gas barrier composition containing a vinyl alcohol copolymer and further polycondensed by a sol-gel method in the presence of a sol-gel method catalyst, acid, water, and an organic solvent.

As the alkoxide represented by the above general formula R ¹ nM(OR ² )m, at least one of a partial hydrolyzate of an alkoxide and a condensate of hydrolysis of an alkoxide can be used. In addition, the partial hydrolyzate of the alkoxide described above does not necessarily have to have all the alkoxy groups hydrolyzed, and may be one in which one or more alkoxy groups have been hydrolyzed, or a mixture thereof. As the condensate of alkoxide hydrolysis, a dimer or more of partially hydrolyzed alkoxide, specifically a dimer to hexamer, is used.

In the alkoxide represented by the above general formula R ¹ nM(OR ² )m, silicon, zirconium, titanium, aluminum, and the like can be used as the metal atom represented by M. In this embodiment, preferable metals include silicon, titanium, and the like. Furthermore, in the present invention, alkoxides can be used alone or in combination of two or more alkoxides of different metal atoms in the same solution.

Further, in the alkoxide represented by the above general formula R ¹ nM(OR ² )m, specific examples of the organic group represented by R ¹ include methyl group, ethyl group, n-propyl group, i- Examples include alkyl groups such as propyl group, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, n-hexyl group, n-octyl group, and others. Further, in the alkoxide represented by the above general formula R ¹ nM(OR ² )m, specific examples of the organic group represented by R ² include methyl group, ethyl group, n-propyl group, i- Examples include propyl group, n-butyl group, sec-butyl group, and others. Note that these alkyl groups in the same molecule may be the same or different.

When preparing the above gas barrier composition, for example, a silane coupling agent or the like may be added. As the silane coupling agent, known organoalkoxysilanes containing organic reactive groups can be used. In this embodiment, organoalkoxysilane having an epoxy group is particularly preferably used, and specifically, for example, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β -(3,4-epoxycyclohexyl)ethyltrimethoxysilane and the like can be used. The above silane coupling agents may be used alone or in combination of two or more.

In the polyethylene laminate according to the present invention, each of the above-mentioned layers is formed by coextrusion molding. That is, using an inflation film forming machine for coextrusion or the like, polyethylene with a density of 0.930 g/cm ³ or more to constitute the base layer, polyethylene with a density of less than 0.930 g/cm ³ to constitute the heat seal layer, And if desired, it can be obtained by coextruding polyethylene or the like having a density of 0.942 g/cm ³ or more constituting the intermediate layer to form a film. In this way, after forming a polyethylene laminate comprising a base layer, a heat-sealing layer, and, if desired, an intermediate layer, the above-described printed layer and barrier layer are formed on the surface of the base layer, thereby producing the polyethylene of the present invention. Laminates can be manufactured.

Next, electron beam irradiation treatment will be explained. In the polyethylene laminate according to the present invention, the base layer is subjected to electron beam irradiation treatment. It is thought that by subjecting the base material layer to electron beam irradiation treatment, a portion of the polyethylene constituting the base material layer is crosslinked, thereby improving heat resistance. The presence or absence of crosslinking (that is, whether it has been subjected to electron beam irradiation treatment) can be determined by immersing the polyethylene laminate in an organic solvent such as methyl ethyl ketone, taking advantage of the fact that the crosslinked portion does not dissolve in solvents, and checking whether the crosslinked portion remains undissolved or not. The crosslinking density can also be determined by measuring the mass of the insoluble part after drying and calculating the gel fraction from the thickness (mass) of the base layer before dissolution and the mass of the insoluble part after drying. . The gel fraction of the polyethylene laminate is preferably 20% or more and 80% or less in terms of the mass of the base layer.

It is preferable that the irradiation energy of the electron beam is changed as appropriate depending on the intended use of the package. Normally, the higher the irradiation energy of the electron beam, the more radicals are generated, making it easier to form a crosslinked structure. However, if the irradiation energy is too high, the molecular chains of polyethylene are cut too much, resulting in poor film properties such as strength. It is on a declining trend.

The dose of the electron beam is preferably in the range of 10 to 2000 kGy, more preferably 20 to 1000 kGy, and the acceleration voltage of the electron beam is preferably in the range of 30 to 300 kV, more preferably 50 to 300 kV, particularly preferably 50 to 300 kV. It is 250kV. Further, the irradiation energy of the electron beam is preferably 20 to 750 keV, more preferably 25 to 400 keV, even more preferably 30 to 300 keV, and particularly preferably 20 to 200 keV.

As the electron beam irradiation device, conventionally known ones can be used, such as a curtain type electron irradiation device (LB1023, manufactured by I-Electron Beam Co., Ltd.) and a line irradiation type low energy electron beam irradiation device (EB-ENGINE, manufactured by Hamamatsu Co., Ltd.). (manufactured by Photonics Co., Ltd.), etc. can be suitably used. In particular, a line irradiation type low energy electron beam irradiation device (EB-ENGINE, manufactured by Hamamatsu Photonics Co., Ltd.) can be suitably used.

The oxygen concentration in the electron beam irradiation device is preferably 500 ppm or less, more preferably 100 ppm or less. By performing electron beam irradiation under these conditions, it is possible to suppress the generation of ozone, and it is also possible to suppress the radicals generated by electron beam irradiation from being deactivated by oxygen in the atmosphere. can. Such conditions can be achieved, for example, by creating an inert gas (nitrogen, argon, etc.) atmosphere inside the apparatus.

Since a polyethylene film tends to undergo thermal contraction, it is preferable that the electron beam irradiation be performed simultaneously with cooling using a cooling drum or the like.

<Packaging materials>
The polyethylene laminate described above can be suitably used as a packaging material. In one embodiment of the present invention, a packaging material 20 using the polyethylene laminate of the present invention has a bag-like shape, as shown in FIG.

In another embodiment, a packaging material 30 using the polyethylene laminate of the present invention has a stand-up pouch-like shape including a body 31 and a bottom 32, as shown in FIG. In this embodiment, even if only the trunk is formed of the polyethylene co-pressed film, or only the bottom is formed of the polyethylene co-pressed film, both the trunk and the bottom are formed of the polyethylene co-pressed film. may be formed.

The packaging material can be manufactured by folding the above-mentioned polyethylene laminate in half so that the base layer is on the outside and the heat-sealing layer on the inside, stacking them on top of each other, and heat-sealing the edges etc. . Alternatively, it can be manufactured by stacking two polyethylene laminates so that the base material layers face each other and heat-sealing the edges and the like.

For example, side seal type, two side seal type, three side seal type, four side seal type, envelope sticker type, gassho sticker type (pillow seal type), pleated seal type, flat bottom seal type, square bottom seal type, and gusset type. , etc., and can be heat-sealed to produce various types of packaging materials. In addition, for example, a self-supporting packaging bag (standing pouch) or the like is also possible. As the heat sealing method, for example, known methods such as bar sealing, rotating roll sealing, belt sealing, impulse sealing, high frequency sealing, and ultrasonic sealing can be used.

Since the packaging material made from the polyethylene laminate of the present invention is made of one type of material (namely, polyethylene), it is more recyclable than conventional packaging materials made of a combination of different materials. In addition, since the base material layer of the polyethylene laminate contains electron beam irradiated polyethylene with a density of 0.930 g/cm ³ or more, it has physical properties such as strength, dimensional stability, and printing characteristics required for the outer layer of packaging materials. can be fulfilled. Furthermore, the heat-sealing layer of the polyethylene laminate contains polyethylene with a density of less than 0.930 g/cm ³ and therefore has heat-sealing properties, and can be suitably used as a film for packaging materials. Furthermore, by using biomass-derived polyethylene as the polyethylene constituting the polyethylene laminate, the environmental load can be further reduced.

The present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Example 1>
Medium density polyethylene (density: 0.937 g/cm ³ , MFR: 1.8 g/10 min, manufactured by Prime Polymer Co., Ltd., product name: SP4020),
Biomass-derived high-density polyethylene (density: 0.948 g/cm ³ , MFR: 1.0 g/10 min, manufactured by Braskem, trade name: SHE150),
Linear low-density polyethylene (density: 0.916 g/cm ³ , MFR: 2.3 g/10 min, manufactured by Prime Polymer Co., Ltd., product name: SP2020) was 1:3:1 by inflation molding. A coextruded polyethylene laminate was obtained. The thickness of the obtained coextruded polyethylene laminate was 60 μm. In the obtained coextruded polyethylene laminate, the layer side of medium-density polyethylene with a density of 0.937 g/cm ³ is called the base layer, and the layer side of linear low-density polyethylene with a density of 0.916 g/cm ³ is called the heat seal layer.

The coextruded polyethylene laminate obtained as described above was subjected to corona treatment from the base layer side, and then subjected to the following using an electron beam irradiation device (line irradiation type irradiation device EZ-CURE, manufactured by Iwasaki Electric Co., Ltd.). An electron beam was irradiated under the following conditions to obtain a coextruded polyethylene laminate in which the base layer was irradiated with an electron beam.
(Electron beam irradiation conditions)
Voltage: 100kV
Irradiation dose: 280kGy
Oxygen concentration in the device: 100 ppm or less Line speed: 25 m/min

Gravure printing was performed on the surface of the base material layer side of the coextruded polyethylene laminate immediately after production obtained as described above using a solvent-type gravure ink (manufactured by DIC Graphics Corporation, product name: XOX-901). The image was formed by the method.

<Example 2>
A coextruded polyethylene laminate was obtained in the same manner as in Example 1 except that the electron beam irradiation conditions were changed to the following conditions.
(Electron beam irradiation conditions)
Voltage: 110kV
Irradiation dose: 280kGy
Oxygen concentration in the device: 100 ppm or less Line speed: 25 m/min

<Example 3>
A coextruded polyethylene laminate was obtained in the same manner as in Example 1, except that the thickness of the coextruded polyethylene laminate was 100 μm.

<Example 4>
A coextruded polyethylene laminate was obtained in the same manner as in Example 2, except that the thickness of the coextruded polyethylene laminate was 100 μm.

<Example 5>
A coextruded polyethylene laminate was obtained in the same manner as in Example 1, except that the printing method after electron beam irradiation onto the surface of the base material layer was changed as follows.
(Printing method)
First, OP varnish (manufactured by Showa Ink Kogyosho Co., Ltd., product name: ALEX peeler OP varnish) was applied to the untreated surface of a PET film (Toyobo Co., Ltd., product name: E5100, 12 μm), and a solvent-based gravure ink (trade name: E5100, 12 μm) was applied. An image was formed by a gravure printing method using ALEX (NT) pattern ink manufactured by Showa Ink Kogyo Co., Ltd. (trade name: ALEX (NT) pattern ink). The obtained image-formed PET film and the coextruded polyethylene laminate after electron beam irradiation obtained in the same manner as in Example 1 were placed so that the printed surface of the PET film and the electron beam irradiated surface (substrate layer surface) faced each other. Dry lamination was performed using a two-component curable urethane adhesive (manufactured by Rock Paint Co., Ltd., trade name: RU-40/Curing Agent H-4) to obtain a coextruded polyethylene laminate.
Thereafter, the PET film was peeled off, and an image was formed by transferring the printed layer to the surface of the coextruded polyethylene laminate on the base layer side.

<Example 6>
A coextruded polyethylene laminate was obtained in the same manner as in Example 3, except that the printing method after electron beam irradiation onto the surface of the base material layer was changed as follows.
(Printing method)
First, OP varnish (manufactured by Showa Ink Kogyosho Co., Ltd., product name: ALEX peeler OP varnish) was applied to the untreated surface of a PET film (Toyobo Co., Ltd., product name: E5100, 12 μm), and a solvent-based gravure ink (trade name: E5100, 12 μm) was applied. An image was formed by a gravure printing method using ALEX (NT) pattern ink manufactured by Showa Ink Kogyo Co., Ltd. (trade name: ALEX (NT) pattern ink). The obtained image-formed PET film and the coextruded polyethylene laminate after electron beam irradiation obtained in the same manner as in Example 3 were placed so that the printed surface of the PET film and the electron beam irradiated surface (substrate layer surface) faced each other. Dry lamination was performed using a two-component curable urethane adhesive (manufactured by Rock Paint Co., Ltd., trade name: RU-40/Curing Agent H-4) to obtain a coextruded polyethylene laminate.
Thereafter, the PET film was peeled off, and an image was formed by transferring the printed layer to the surface of the coextruded polyethylene laminate on the base layer side.

<Comparative example 1>
A coextruded polyethylene laminate was obtained in the same manner as in Example 1 except that the electron beam was not irradiated.

<Comparative example 2>
A coextruded polyethylene laminate was obtained in the same manner as in Example 3, except that the electron beam was not irradiated.

<Heat resistance evaluation>
The coextruded polyethylene laminates obtained in the above Examples and Comparative Examples were cut into 5 cm x 5 cm pieces to prepare three sample pieces. Each sample was heated for 5 seconds in a glycerin solution heated to 140°C. The size of the sample piece after heating was measured in the machine flow direction (MD direction) during inflation molding and in the width direction (TD direction) orthogonal thereto. The average value of the shrinkage rate from the time of cutting was as shown in Table 1 below.

<Seal strength evaluation>
The coextruded polyethylene laminates immediately after production obtained in the above Examples and Comparative Examples were cut into 10 cm x 10 cm pieces to prepare three sample pieces. Each sample piece was folded in half so that the side that was not irradiated with the electron beam, that is, the layer side made of polyethylene with a density of 0.916 g/cm3, was on the inside, and the temperature was set to 180°C using a heat seal tester. An area of 1 cm x 10 cm was heat-sealed under conditions of a pressure of 1 kgf/cm 2 and a duration of 1 second.

The heat-sealed sample piece was cut into strips with a width of 15 mm, both ends that were not heat-sealed were held in a tensile tester, and the peel strength (N/15 mm) was measured at a speed of 300 mm/min and a load range of 50 N. It was measured. It should be noted that the coextruded polyethylene laminates obtained in Comparative Examples 1 and 2 were rated "-" because they adhered to the heat seal bar and the peel strength could not be measured. The measurement results were as shown in Table 1 below.

<Printing aptitude test>
The formed images were visually observed, and the printability of the coextruded polyethylene laminates obtained in the above Examples and Comparative Examples was evaluated based on the following evaluation criteria.
Good: Dimensional stability during printing was good, and a good image without rubbing, bleeding, etc. could be formed.
×: The film expanded and contracted during printing, and the formed image had scratches and smudges.
The evaluation results were as shown in Table 1.

<Liquid sachet bag making evaluation>
Using a liquid pouch filling machine, liquid pouches measuring 100 mm in length and 80 mm in width were produced from the coextruded polyethylene co-extruded films obtained in the above Examples and Comparative Examples.
As for the bag making method, first, two coextruded polyethylene laminates were stacked on top of each other so that the heat seal layers faced each other, and three sides were heat sealed using a heat seal bar at 140°C. Next, the heat-sealed coextruded polyethylene laminate was cut into a size of 100 mm in length x 80 mm in width to produce a liquid pouch.
Bag-making suitability of the liquid sachets was evaluated based on the following evaluation criteria.
Good: A liquid pouch could be produced using the liquid pouch filling machine without the film being fused to the heat seal bar.
×: The film was fused to the heat seal bar, and liquid sachets could not be neatly produced using the liquid sachet filling machine.
The evaluation results were as shown in Table 1.

<Stand pouch bag making evaluation>
A stand-up pouch measuring 110 mm in length and 150 mm in width was produced from the coextruded polyethylene laminates obtained in the above Examples and Comparative Examples using a bag making machine.
As for the bag making method, first, one test piece of 110 mm in length x 60 mm in width was prepared from the coextruded polyethylene laminates obtained in Examples and Comparative Examples, and it was molded into a V-shape with the heat seal layer on the outside. A piece (length: 110 mm x width: 30 mm) was produced by bending it. Next, the two coextruded polyethylene laminates were stacked so that the heat-sealing layers faced each other, and the V-shaped test piece obtained above was sandwiched between one end and heat-sealed using a heat-sealing bar at 140°C. The bottom was formed by doing this. Subsequently, the two sides adjacent to the bottom were heat-sealed in the same manner to form a cylindrical body, and the body was cut into a size of 110 mm long x 150 mm wide to produce a stand pouch.
The bag-making suitability of the stand pouch was evaluated based on the following evaluation criteria.
○: A stand-up pouch could be produced using a bag making machine without the film being fused to the heat seal bar.
×: The film was fused to the heat seal bar, and the stand pouch could not be neatly produced using the bag making machine.
The evaluation results were as shown in Table 1.

Claims (6)

A polyethylene laminate comprising a base layer, a printing layer provided on the surface of the base layer, and a heat seal layer,
The base layer contains polyethylene with a density of 0.930 g/cm ³ or more,
The heat-sealing layer comprises polyethylene with a density of less than 0.930 g/cm ³ ,
The base layer and the heat seal layer are formed by co-extrusion molding of polyethylene with a density of 0.930 g/cm ³ or more and polyethylene with a density of less than 0.930 g/cm ³ ,
The polyethylene with a density of 0.930 g/cm ³ or more or the polyethylene with a density of less than 0.930 g/cm ³ includes biomass polyethylene,
A polyethylene laminate, wherein the base layer has been subjected to electron beam irradiation treatment. The polyethylene laminate according to claim 1, further comprising an intermediate layer between the base layer and the heat seal layer. The intermediate layer comprises polyethylene with a density of 0.942 g/cm ³ or more,
The base layer, the intermediate layer, and the heat seal layer are made of polyethylene with a density of 0.930 g/cm ³ or more, polyethylene with a density of 0.942 g/cm ³ or more, and polyethylene with a density of less than 0.930 g/cm ³ . The polyethylene laminate according to claim 2, which is formed by coextrusion molding. The polyethylene laminate according to claim 3, wherein the polyethylene having a density of 0.942 g/cm ³ or more includes biomass polyethylene. The polyethylene laminate according to any one of claims 1 to 4, further comprising a barrier layer on the surface of the base layer. A packaging material comprising the polyethylene laminate according to any one of claims 1 to 5.