Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
  • B32B7/02—Physical, chemical or physicochemical properties
  • B32B7/027—Thermal properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
  • B65D65/00—Wrappers or flexible covers; Packaging materials of special type or form
  • B65D65/38—Packaging materials of special type or form
  • B65D65/40—Applications of laminates for particular packaging purposes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/80—Packaging reuse or recycling, e.g. of multilayer packaging

Definitions

• the present invention relates to a multilayer film used for packaging food, medical products, etc.
• the reasons for the deterioration of the quality of recycled plastics include the fact that many of the plastic products currently in circulation are made using polymeric compounds (sometimes called resins or polymers) with multiple different structures, and that impurities are mixed into the plastic, causing it to become discolored.
• many packaging materials used for food and beverages are multifunctional, such as durable weather resistance during distribution and refrigeration, functions to protect the contents from processes such as heat sterilization, and long-term storage (gas barrier properties). These are given many functions by combining various raw materials with their own functions.
• the quality of recycled plastics deteriorates in order to provide these multifunctional functions.
• recycled materials are sometimes mixed with virgin materials (newly synthesized polymeric compounds that are not recycled).
• polypropylene film which is often used as packaging material along with polyethylene, has a specific gravity close to that of polyethylene, so it cannot be easily separated by specific gravity, and as a result, polyethylene and polypropylene end up mixed together in recycled materials.
• Mono-material films laminated with polyethylene have been disclosed (see, for example, Patent Documents 1 and 2).
• Patent Documents 1 and 2 Mono-material films laminated with polyethylene have been disclosed (see, for example, Patent Documents 1 and 2).
• ratio of polyethylene to polypropylene when collected after use and mixed with polypropylene to become recycled materials, have an unknown composition (ratio of polyethylene to polypropylene). This makes it difficult to produce the films stably or to obtain the desired physical properties when they are re-filmed, raising concerns about a decline in quality.
• composition analysis by simple quantitative methods such as infrared spectroscopy (IR) and differential scanning calorimetry (DSC) has been proposed (see Non-Patent Documents 1 and 2).
• IR infrared spectroscopy
• DSC differential scanning calorimetry
• Non-Patent Documents 1 and 2 had a large measurement error for recycled materials with a high polyethylene ratio.
• Polyethylene with few short-chain branches is thought to be less likely to affect the polypropylene peak when a mixture with polypropylene resin is measured by infrared spectroscopy (IR). Therefore, from the viewpoint of the accuracy of IR measurement of the polyethylene ratio of recycled materials in which polypropylene resin and polyethylene resin are mixed, it is preferable to use polyethylene with few short-chain branches, especially high-density polyethylene.
• high-density polyethylene film is difficult to use for packaging applications where the contents must be visible due to its poor transparency, and also has poor impact resistance at low temperatures, so it may not be suitable for packaging frozen foods or chilled foods that are stored in low-temperature environments.
• the inventors conducted extensive research into the development of a multilayer film that is an easily recyclable mono-material film, has good accuracy in measuring the polyethylene ratio by IR in recycled materials that are a mixture of polypropylene-based resin and polyethylene-based resin, can be used in low-temperature environments such as for frozen foods, and has excellent packaging suitability, and as a result, they arrived at the multilayer film of the present invention. In other words, they discovered that these problems could be solved by setting the high-density polyethylene content and medium-density polyethylene content in the entire multilayer film to specific ranges.
• the objective of the present invention is to provide a multilayer film that has excellent performance as a packaging material, is a monomaterial, and has excellent composition analysis accuracy using IR.
• the present invention solves the above problems by providing a multilayer film in which at least a surface layer (A), an intermediate layer (B) and a sealing layer (C) are laminated in this order, and in which 90% by mass or more of the components contained in the multilayer film are polyethylene resins, the content of high density polyethylene in the entire multilayer film is 5 to 40% by mass, and the content of medium density polyethylene in the entire multilayer film is 28 to 72% by mass.
• the multilayer film of the present invention is a polyethylene mono-material film, so it is easy to recycle and contributes to reducing the environmental impact. Furthermore, when recycled, the accuracy of the compositional analysis of the recycled material is not reduced, making it easier to clarify the composition of the recycled material and to obtain the targeted physical properties, which allows the amount of virgin material mixed into the recycled material to be reduced, thereby contributing to the realization of a recycling-oriented society.
• the multilayer film of the present invention also has excellent suitability for packaging machines and is suitable as a packaging material.
• the multilayer film of the present invention has excellent impact resistance at extremely low temperatures of -20°C, and is therefore suitable for use in packaging frozen foods, chilled foods, and other items that are transported or stored at low temperatures, as well as in packaging medical products.
• the packaging material can be made lighter, reducing the environmental impact and costs.
• the multilayer film of the present invention is a multilayer film in which at least a surface layer (A), an intermediate layer (B) and a sealing layer (C) are laminated in this order, and is characterized in that 90% by mass or more of the components contained in the multilayer film are polyethylene resins, the content of high density polyethylene in the entire multilayer film is 5 to 40% by mass, and the content of medium density polyethylene in the entire multilayer film is 28 to 72% by mass.
• the surface layer (A) of the multilayer film of the present invention is preferably a layer containing a polyethylene resin as a main resin component, although other resins that can be co-extruded may be used in combination therewith within the range that does not impair the effects of the present invention.
• "Main resin component” specifically means that 70 mass % or more of the resin components used in the surface layer (A) is a polyethylene-based resin, preferably 80 mass % or more is a polyethylene-based resin, and more preferably 90 mass % or more is a polyethylene-based resin.
• polyethylene resins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE) can be used.
• LDPE low-density polyethylene
• LLDPE linear low-density polyethylene
• MDPE medium-density polyethylene
• HDPE high-density polyethylene
• low density polyethylene is meant a homopolymer of ethylene having a density less than 0.935 g/cm 3 .
• the linear low density polyethylene (LLDPE) is a copolymer of ethylene and an ⁇ -olefin polymerized using a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst, and has a density of less than 0.925 g/cm 3. It is therefore distinguished from low density polyethylene (LDPE), which is a homopolymer of ethylene.
• the ⁇ -olefins that serve as comonomers for linear low density polyethylene are those having 3 or more carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, 4-methylpentene, 3,3-dimethylbutene, and mixtures thereof.
• the medium density polyethylene (MDPE) means a copolymer of ethylene and an ⁇ -olefin having a density of 0.925 g/ cm3 or more and less than 0.942 g/ cm3 .
• the high density polyethylene means a polyethylene having a density of 0.942 g/cm 3 or more.
• the comonomer ratio is preferably 0.5% or less.
• the comonomer ratio may not be disclosed, so linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene are distinguished by density, and low-density polyethylene and medium-density polyethylene are distinguished by whether they are homopolymers of ethylene or not.
• biomass-derived polyethylene may be used, such as, for example, biomass-derived low-density polyethylene manufactured by Braskem (product name: SBC818, density: 0.918 g/cm 3 , MFR: 8.1 g/10 min), biomass-derived low-density polyethylene manufactured by Braskem (product name: SPB681, density: 0.922 g/cm 3 , MFR: 3.8 g/10 min), and biomass-derived linear low-density polyethylene manufactured by Braskem (product name: SLL118, density: 0.916 g/cm 3 , MFR: 1.0 g/10 min).
• the surface layer (A) of the multilayer film of the present invention needs to have a higher melting point than the seal layer (C) of the multilayer film. Therefore, the surface layer (A) of the multilayer film of the present invention is preferably a layer in which a medium density polyethylene (a1) and a high density polyethylene (a2) are used in combination, and the ratio of the medium density polyethylene (a1) to the high density polyethylene (a2) is more preferably 30:70 to 85:15, and even more preferably 40:60 to 70:30.
• the surface layer (A) is such a layer, it can exhibit impact resistance in a very low temperature (e.g., ⁇ 20° C.) environment while maintaining suitable packaging suitability, and also has good resistance to puncture by frozen foods.
• a plurality of types of the medium-density polyethylene (a1) and the high-density polyethylene (a2) may be used in combination.
• the ratio of (a1-1)+(a1-2):(a2) falls within the above range.
• the surface layer (A) of the multilayer film of the present invention may further contain a polyethylene resin other than the medium density polyethylene (a1) and the high density polyethylene (a2).
• LDPE low density polyethylene
• LDPE low density polyethylene
• the surface layer (A) of the multilayer film of the present invention preferably has a melting point of 110 to 150°C, more preferably 115 to 145°C.
• a melting point of the surface layer (A) refers to the melting peak measured by a differential scanning calorimeter.
• the surface layer (A) is a resin layer made by mixing a plurality of resins, it is preferable to determine the blending ratio so that the melting point of the mixed resin composition is within the range.
• the melting point of the mixed resin composition is a melting point calculated from the content of each resin component and the melting point of each resin, and when the resins used in each layer are resin a, resin b, resin c, etc., the melting points of these resins are Ta, Tb, Tc, etc., and the masses of the resins used in the layers are Wa, Wb, Wc, etc., the melting point is calculated as (TaWa+TbWb+TcWc%)/(Wa+Wb+Wc).
• the surface layer (A) of the multilayer film of the present invention preferably has a density of 0.925 to 0.955 g/cm 3 , and more preferably 0.930 to 0.950 g/cm 3 .
• the density is a value measured in accordance with JIS K7112.
• the MFR (190°C, 21.18N) of the polyethylene resin used in the surface layer (A) is 0.5 to 50 g/10 min (190°C, 21.18N), preferably 1 to 30 g/10 min (190°C, 21.18N), more preferably 2 to 20 g/10 min (190°C, 21.18N). When the MFR is within this range, good film-forming properties can be obtained, which is preferable.
• various resins used in packaging films can be used as resins other than the above-mentioned polyethylene-based resins, and among them, olefin-based resins such as polypropylene-based resins can be preferably used.
• olefin-based resins such as polypropylene-based resins
• polypropylene-based resin propylene homopolymers, propylene- ⁇ -olefin random copolymers, propylene- ⁇ -olefin block copolymers, etc. can be used. These may be used alone or in combination.
• an olefin-based resin other than the above-mentioned polyethylene-based resin is used as the resin component used in the surface layer (A)
• its content is preferably 30 mass % or less of the resin components contained in the surface layer (A), more preferably 10 mass % or less, and even more preferably 5 mass % or less.
• a cyclic polyolefin-based resin may be used, but the content of the cyclic polyolefin-based resin in the resin component contained in the surface layer (A) is preferably 10 mass% or less, more preferably 5 mass% or less, and it is also preferable that no cyclic polyolefin-based resin is used substantially.
• the cyclic olefin resin include norbornene polymers, vinyl alicyclic hydrocarbon polymers, and cyclic conjugated diene polymers. Of these, norbornene-based polymers are preferred.
• norbornene polymers examples include ring-opening polymers (COP) of norbornene monomers, and norbornene copolymers (COC) obtained by copolymerizing norbornene monomers with olefins such as ethylene. Hydrogenated products of COP and COC are also particularly preferred.
• the weight average molecular weight of the cyclic olefin resin is preferably from 5,000 to 500,000, and more preferably from 7,000 to 300,000.
• the norbornene monomer used as the raw material for the norbornene polymer is an alicyclic monomer having a norbornene ring.
• Examples of such norbornene-based monomers include norbornene, tetracyclododecene, ethylidenenorbornene, vinylnorbornene, ethylidetetracyclododecene, dicyclopentadiene, dimethanotetrahydrofluorene, phenylnorbornene, methoxycarbonylnorbornene, and methoxycarbonyltetracyclododecene.
• These norbornene monomers may be used alone or in combination of two or more kinds.
• the norbornene copolymer is a copolymer of the norbornene monomer and a copolymerizable olefin.
• olefins include olefins having 2 to 20 carbon atoms, such as ethylene, propylene, and 1-butene; cycloolefins, such as cyclobutene, cyclopentene, and cyclohexene; and non-conjugated dienes, such as 1,4-hexadiene.
• thermoplastic elastomers such as polyethylene-based elastomers, such as ethylene-vinyl acetate copolymer (EVA) and ethylene- ⁇ -olefin copolymers, polypropylene-based elastomers, and butene-based elastomers; ethylene-based copolymers such as ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate (EMA) copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer (E-EA-MAH), ethylene-acrylic acid copolymer (EAA), and ethylene-methacrylic acid copolymer (EMAA); and further ionomers of ethylene-acrylic acid copolymers and ionomers of
• their content is preferably 30% by mass or less of the resin components contained in the surface layer (A), more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less.
• additives may be appropriately used in addition to the above-mentioned resin components.
• the additives include antioxidants, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, lubricants, nucleating agents, pigments, and biodegradability-promoting additives.
• these additives are used in an amount of preferably 5 parts by mass or less, more preferably about 0.01 to 3 parts by mass, per 100 parts by mass of the resin component used in the surface layer (A).
• the thickness ratio of the surface layer (A) of the multilayer film of the present invention to the total thickness of the multilayer film is preferably in the range of 10 to 45%, and more preferably in the range of 15 to 30%, since this makes it easier to obtain suitable heat resistance and excellent impact resistance at low temperatures.
• the intermediate layer (B) of the multilayer film of the present invention is preferably a layer containing a polyethylene resin as a main resin component, similar to the surface layer (A) of the multilayer film of the present invention, although other co-extrudable resins may be used in combination therewith within the scope not impairing the effects of the present invention.
• the intermediate layer (B) of the multilayer film of the present invention is preferably a layer using a medium density polyethylene (b1) and a high density polyethylene (b2) in combination, and the ratio of the medium density polyethylene (b1) to the high density polyethylene (b2) is more preferably 50:50 to 90:10, and further preferably 70:30 to 80:20.
• the intermediate layer (B) is such a layer, it is likely to exhibit impact resistance in a very low temperature (e.g., ⁇ 20° C.) environment.
• a plurality of types of medium-density polyethylene (b1) and high-density polyethylene (b2) may be used in combination. In that case, for example, when two types of medium-density polyethylene (b1) (b1-1 and b1-2) are used, it is preferable that the ratio of (b1-1)+(b1-2):(b2) is within the above range.
• the intermediate layer (B) of the multilayer film of the present invention may further contain a polyethylene resin other than the medium density polyethylene (b1) and the high density polyethylene (b2).
• LDPE low density polyethylene
• LDPE low density polyethylene
• the melting point of the intermediate layer (B) of the multi-layer film of the present invention is preferably from 110 to 150°C, and more preferably from 115 to 140°C. By setting the melting point of the intermediate layer (B) within the above range, it becomes easier to realize suitable impact resistance and packaging machine suitability. In addition, suitable heat resistance can be realized.
• the melting point of the resin refers to the melting peak measured by a differential scanning calorimeter.
• the intermediate layer (B) is composed of one type of resin
• the melting point of the intermediate layer (B) is the melting point of the resin.
• the intermediate layer (B) is a resin layer in which a plurality of types of resins are mixed, it is preferable to determine the blending ratio so that the melting point of the mixed resin composition is within the range.
• the melting point of the mixed resin composition is a melting point calculated from the content of each resin component and the melting point of each resin.
• the resins used in each layer are resin a, resin b, resin c, etc.
• the melting points of these resins are Ta, Tb, Tc, etc.
• the masses of the resins used in the layers are Wa, Wb, Wc, etc.
• the melting point is calculated as (TaWa+TbWb+TcWc%)/(Wa+Wb+Wc).
• the intermediate layer (B) of the multilayer film of the present invention preferably has a density of 0.925 to 0.955 g/cm 3 , and more preferably 0.930 to 0.950 g/cm 3 .
• the density is a value measured in accordance with JIS K7112.
• the MFR (190°C, 21.18N) of the polyethylene resin used in the intermediate layer (B) is 0.5 to 50 g/10 min (190°C, 21.18 N), preferably 1 to 30 g/10 min (190°C, 21.18 N), and more preferably 2 to 20 g/10 min (190°C, 21.18 N).
• MFR 0.5 to 50 g/10 min (190°C, 21.18 N), preferably 1 to 30 g/10 min (190°C, 21.18 N), and more preferably 2 to 20 g/10 min (190°C, 21.18 N).
• resins other than those mentioned above may be used in combination.
• the other resins include polypropylene-based resins such as propylene homopolymers, propylene- ⁇ -olefin random copolymers, and propylene- ⁇ -olefin block copolymers, cyclic olefin-based resins, thermoplastic elastomers such as ethylene-vinyl acetate copolymers (EVA), polyethylene-based elastomers, polypropylene-based elastomers, and butene-based elastomers; ethylene-based copolymers such as ethylene-methyl methacrylate copolymers (EMMA), ethylene-ethyl acrylate copolymers (EEA), ethylene-methyl acrylate (EMA) copolymers, ethylene-ethyl acrylate-maleic anhydride copolymers (E-EA-MAH), ethylene-acrylic acid copolymers
• EMMA ethylene-methyl methacrylate
• the content of the resin is 20% or less by mass of the resin components contained in the intermediate layer (B), more preferably 10% or less by mass, and even more preferably 5% or less by mass. If the content is within this range, it is easier to achieve a mono-material structure for the entire multilayer film, and recyclability is improved.
• additives may be appropriately used in addition to the above-mentioned resin components.
• the additives include antioxidants, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, lubricants, nucleating agents, pigments, and biodegradation-promoting additives.
• these additives are used in an amount of preferably 5 parts by mass or less, and more preferably about 0.01 to 3 parts by mass, per 100 parts by mass of the resin component used in the intermediate layer (B).
• the thickness ratio of the intermediate layer (B) to the total thickness of the multilayer film is preferably 30 to 70%, and more preferably 35 to 55%, from the viewpoints of good packaging machine suitability and low-temperature impact resistance.
• the sealing layer (C) of the multi-layer film of the present invention is preferably a layer containing linear low density polyethylene as a main resin component. By providing the sealing layer (C), good impact resistance and heat sealability can be achieved.
• the melting point of the sealing layer (C) of the multi-layer film of the present invention is preferably 75 to 125°C, more preferably 80 to 120°C, further preferably 80 to 100°C, and particularly preferably 83 to 97°C. By setting the melting point of the sealing layer (C) within this range, good sealing strength can be obtained.
• the melting point of a resin refers to the melting peak measured by a differential scanning calorimeter. When there are two peaks, the peak with the largest amount of heat absorption is taken as the melting point. When the seal layer (C) is made of one type of resin, the melting point of the seal layer (C) is the melting point of the resin.
• the melting point of the mixed resin composition is a melting point calculated from the content of each resin component and the melting point of each resin, and when the resins used in each layer are resin a, resin b, resin c, etc., the melting points of these resins are Ta, Tb, Tc, etc., and the masses of the resins used in the layers are Wa, Wb, Wc, etc., the melting point is calculated as (TaWa+TbWb+TcWc%)/(Wa+Wb+Wc).
• the density of the linear low-density polyethylene is preferably 0.880 to 0.924 g/ cm3 , and more preferably 0.890 to 0.920 g/ cm3 , because good sealability and impact resistance can be easily obtained.
• the density is within this range, it can be assumed that the number of short chain branches in the polyethylene is relatively small, and even when the polyethylene is mixed with polypropylene as a recycled material, the blend ratio can be easily identified by infrared spectroscopy (IR).
• the linear low density polyethylene has an MFR of 0.5 to 50 g/10 min (190° C., 21.18 N), preferably 1 to 30 g/10 min (190° C., 21.18 N), and more preferably 2 to 20 g/10 min (190° C., 21.18 N).
• MFR 0.5 to 50 g/10 min (190° C., 21.18 N), preferably 1 to 30 g/10 min (190° C., 21.18 N), and more preferably 2 to 20 g/10 min (190° C., 21.18 N).
• the content of linear low-density polyethylene in the sealing layer (C) of the multilayer film of the present invention 70 mass% or more of the resin components contained in the sealing layer (C), it becomes easier to obtain suitable sealing properties and excellent impact resistance at low temperatures.
• the content is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, of the resin component contained in the sealing layer (C).
• 100% by mass of the resin component contained in the seal layer (C) may be linear low-density polyethylene.
• two or more kinds of linear low density polyethylenes having different densities, MFRs, etc. may be used in combination, so long as the total content is within the above range.
• resins other than the linear low density polyethylene may be used in combination within the range not impairing the effects of the present invention.
• examples of other resins that can be used in combination include polyethylene resins other than the linear low-density polyethylene resins exemplified for the surface layer (A) above, olefin resins such as polypropylene resins, and other resins.
• the olefin resin is used as the resin other than the linear low-density polyethylene, its content is preferably 30 mass% or less of the resin components contained in the sealing layer (C), more preferably 10 mass% or less, and even more preferably 5 mass% or less.
• a cyclic polyolefin resin may be used as the olefin resin, but the content of the cyclic polyolefin resin in the resin components contained in the sealing layer (C) of the multilayer film of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, and it is also preferable that substantially no cyclic polyolefin resin is used.
• the sealing layer (C) of the multilayer film of the present invention may contain resins other than those mentioned above.
• resins include the thermoplastic elastomers, ethylene-based copolymers, ionomers, etc. exemplified for the surface layer (A).
• their content is preferably 30 mass% or less of the resin components contained in the sealing layer (C), more preferably 10 mass% or less, and even more preferably 5 mass% or less.
• additives may be appropriately used in addition to the above resin components.
• the additives include antioxidants, weather stabilizers, antistatic agents, antifogging agents, antiblocking agents, lubricants, nucleating agents, pigments, and biodegradability-promoting additives.
• these additives are preferably used in an amount of 15 parts by mass or less, more preferably about 0.01 to 10 parts by mass, per 100 parts by mass of the resin component used in the sealing layer (C).
• the thickness ratio of the sealing layer (C) of the multilayer film of the present invention to the total thickness of the multilayer film is preferably 10 to 45%, and more preferably 20 to 40%, from the viewpoint of low-temperature impact resistance and in order to exhibit sufficient sealing strength when a heavy object is enclosed. If the thickness ratio of the sealing layer (C) to the total thickness of the multilayer film is 10% or more, sufficient sealing strength can be obtained, and if the thickness ratio is 20% or more, it is more preferable because it is easy to obtain sealing strength that can withstand the encapsulation of a heavy object.
• the thickness ratio is 45% or less, it is preferable because when mixed with a polypropylene film as a recycled material, the polyethylene/polypropylene ratio can be specified with a practical accuracy by simple measurement using IR, and if the thickness ratio is 40% or less, it is more preferable because the accuracy is improved.
• the sealing layer (C) of the multi-layer film of the present invention may be composed of multiple layers.
• the linear low-density polyethylene contained in each of the multiple sealing layers (C) is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more.
• each layer may have the same composition or different compositions, or may have different compositions only in terms of additives, as long as the composition is within the range of the composition.
• the total thickness of the sealing layer (C) is preferably 10 to 45%, more preferably 20 to 40%, of the total thickness of the multilayer film.
• the multilayer film of the present invention is a multilayer film in which the surface layer (A), intermediate layer (B) and seal layer (C) are laminated in the order of (A)/(B)/(C).
• another layer e.g., including a plurality of seal layers (C), other intermediate layers, adhesive layers, adhesive layers, etc.
• seal layer (C) may be included between the surface layer (A), intermediate layer (B) and seal layer (C).
• the layers are laminated in the order of (A)/(B)/(C), such as (A)/(B)/(C), (A)/(B)/(other layers)/(C), (A)/(other layers)/(B)/(C), etc.
• the multilayer film of the present invention can achieve suitable impact resistance even at low temperatures, particularly at temperatures as low as -20°C, which is significantly below 0°C.
• it has good film-forming properties, and can achieve favorable sealing properties and suitability for packaging machines.
• the multilayer film of the present invention is a multilayer film in which 90% by mass or more of the components contained therein are polyethylene-based resins. By making 90% by mass or more of the components contained in the multilayer film a polyethylene-based resin, the multilayer film becomes a mono-material film, and recyclability is improved.
• the components contained in the multilayer film include not only resins but also additives, adhesives, etc. From the viewpoint of recyclability, it is more preferable that 95% by mass or more of the components contained in the multilayer film is a polyethylene resin.
• the multi-layer film of the present invention preferably has a total thickness of 15 to 100 ⁇ m, more preferably 20 to 90 ⁇ m. If the total thickness of the film is within this range, it becomes easier to obtain excellent impact resistance, rigidity, sealability, suitability for packaging heavy items, suitability for use with packaging machines, and the like at low temperatures.
• each layer is not particularly limited, but for example, the thickness of the surface layer (A) is preferably from 2 to 25 ⁇ m, and more preferably from 4 to 20 ⁇ m.
• the thickness of the intermediate layer (B) is preferably from 10 to 40 ⁇ m, and more preferably from 12 to 38 ⁇ m.
• the thickness of the sealing layer (C) is preferably from 5 to 35 ⁇ m, and more preferably from 7 to 30 ⁇ m.
• the sealing layer (C) is made up of multiple layers, preferably in the configuration of surface layer (A)/intermediate layer (B)/sealing layer (C1)/sealing layer (C2), etc., it is preferable that the total thickness of the sealing layers (C1 and C2) is within the thickness range of the sealing layer (C).
• the multilayer film of the present invention preferably has a seal strength of 5 N/15 mm or more, and more preferably 10 N/15 mm or more, when the sealing layers (C) of the multilayer film are combined and heat sealed at 100°C, 0.2 MPa, for 1 second with a seal width of 10 mm.
• the multilayer film of the present invention preferably has an impact resistance strength of 0.5 J or more, more preferably 0.7 J or more, as measured by a film impact method.
• the impact strength was measured after conditioning a 40 ⁇ m multilayer film at ⁇ 20° C.
• the multilayer film of the present invention has a stiffness of preferably 200 to 400 MPa, and more preferably 220 to 380 MPa or more, because it is easy to obtain a suitable flexibility.
• the difference between the melting point of the surface layer (A) and the melting point of the seal layer (C) is preferably 10° C. or more, more preferably 20° C. or more. By ensuring the melting point difference, it becomes easier to obtain suitable packaging suitability.
• the melting points of the surface layer (A), intermediate layer (B) and seal layer (C) are melting points calculated from the content and melting point of each resin component used in each layer.
• the melting points of these resins are Ta, Tb, Tc, ...
• the masses of the resins used in the layers are Wa, Wb, Wc, ...
• the melting points are calculated as (TaWa+TbWb+TcWc%)/(Wa+Wb+Wc).
• the multilayer film of the present invention satisfies the following calculation formula.
• a ⁇ B > C By adjusting the melting points of each layer as described above, it is possible to obtain a difference in melting points between the surface layer (A) and the sealing layer (C), improving the suitability for packaging machines.
• the interlayer adhesion between the surface layer (A), the intermediate layer (B), and the sealing layer (C) is improved, improving low-temperature resistance and sealing strength.
• the multilayer film of the present invention has a high-density polyethylene content of 5 to 40% by mass relative to the entire multilayer film. This range of high-density polyethylene content is preferable because it provides suitable sealing strength and packaging suitability.
• the high-density polyethylene content of the entire multilayer film is preferably 7 to 35% by mass, more preferably 8 to 31% by mass, and even more preferably 10 to 26% by mass.
• the multilayer film of the present invention has a medium-density polyethylene content of 28 to 72% by mass relative to the entire multilayer film. This range of medium-density polyethylene content is preferable because it provides suitable sealing strength, packaging suitability, and impact resistance.
• the medium-density polyethylene content of the entire multilayer film is preferably 31 to 64% by mass, more preferably 34 to 56% by mass, and even more preferably 34 to 52% by mass.
• the multilayer film of the present invention has a specific range of high-density polyethylene and medium-density polyethylene content in the entire multilayer film, which allows the melting point and rigidity to be controlled while keeping the short-chain branching of polyethylene low. This improves the performance of the packaging material, such as seal strength, packaging suitability, and impact resistance, as well as the accuracy of measuring the polyethylene ratio by IR for recycled materials in which polypropylene resin and the multilayer film are mixed.
• the method for producing the multilayer film of the present invention is not particularly limited, but examples thereof include a coextrusion method in which each resin or resin mixture used for the surface layer (A), intermediate layer (B), and seal layer (C) is heated and melted in a separate extruder, and laminated in the molten state in the order of, for example, (A)/(B)/(C) by a method such as a coextrusion multilayer die method or a feed block method, and then molded into a film by an inflation method, a T-die chill roll method, or the like.
• This co-extrusion method is preferable because it allows relatively free adjustment of the thickness ratio of each layer, and it can provide a multi-layer film that is excellent in hygiene and cost performance.
• the multilayer film of the present invention may be a matte multilayer film in which an uneven structure is formed on the film surface by pressure molding using a chill roll having an uneven structure in the above-mentioned coextrusion method.
• the resins or resin mixtures used for the surface layer (A), intermediate layer (B), and seal layer (C) are heated and melted in separate extruders, and the thermoplastic resins extruded in a molten state from a T-die in the order of (A)/(B)/(C) by a method such as a coextrusion multilayer die method or a feed block method are pressure-molded by a chill roll having an uneven structure to form an uneven structure on the film surface, thereby making it possible to obtain a multilayer film having an uneven structure.
• This method imparts a matte design to the multilayer film while simplifying the manufacturing process and reducing costs by performing shaping simultaneously with film molding, with less environmental impact.
• the specific surface area of the surface of the seal layer (C) side of the multilayer film is preferably 1.02 or more.
• the specific surface area refers to the average value of the S/A specific surface area measured three times under the following measurement conditions using a non-contact surface/layer cross-sectional shape measurement system VertScan (registered trademark) 2.0 (model number: R3300G Lite, manufactured by Ryoka Systems Co., Ltd.).
• the specific surface area of the sealing layer (C) side surface of the multilayer film is preferably 1.02 or more, and more preferably 1.03 or more. There is no particular upper limit, but from the viewpoint of ease of manufacture, it is preferably 1.30 or less, and more preferably 1.10 or less. If the specific surface area is within the above range, pressure molding using a chill roll having an uneven structure may be performed on the sealing layer (C) side surface of the multilayer film, or on the surface layer (A) side surface of the multilayer film.
• the multilayer film of the present invention is obtained as a substantially unstretched multilayer film by the above manufacturing method, so secondary forming such as deep drawing by vacuum forming is also possible.
• the resin layer (A) in order to improve adhesion to printing ink and lamination suitability when used as a sealant film for lamination, it is preferable to subject the resin layer (A) to a surface treatment.
• surface treatments include surface oxidation treatments such as corona treatment, plasma treatment, chromic acid treatment, flame treatment, hot air treatment, and ozone/ultraviolet treatment, and surface roughening treatments such as sandblasting, with corona treatment being preferred.
• packaging materials made of the multilayer film of the present invention include packaging bags and packaging containers used for food, medicines, industrial parts, miscellaneous goods, magazines, etc.
• the film since the film has excellent impact resistance at very low temperatures, it can be suitably used for packaging materials for frozen foods, frozen lunches, refrigerated foods, and medical products that are distributed at low temperatures.
• the packaging bag is preferably a packaging bag formed by overlapping and sealing the seal layers (C) of the multilayer film of the present invention. It is also preferable that the packaging bag is a packaging bag formed by overlapping and sealing the seal layer (C) and the surface layer (A) of the multilayer film of the present invention.
• the packaging bag is a packaging bag formed by overlapping and sealing the seal layer (C) and the surface layer (A) of the multilayer film of the present invention.
• two sheets of the multilayer film can be cut to the desired size of a packaging bag, stacked on top of each other and sealed at three sides to form a bag, after which the contents can be filled in through the one unsealed side and the unsealed side can be sealed to form a hermetic bag, and the bag can be used as a packaging bag.
• the sealing method is not particularly limited, and may be heat sealing or ultrasonic sealing.
• the method of ultrasonic sealing is not particularly limited, and may be appropriately selected from known ultrasonic sealing methods and methods using known ultrasonic sealing devices according to the purpose.
• the other film to be used may be a film of LDPE, EVA or the like, which has a relatively weak mechanical strength.
• the multilayer film of the present invention can also be used by laminating it to another substrate.
• the other substrate that can be used in this case is not particularly limited, but from the viewpoint of easily realizing the effects of the present invention, it is preferable to use a plastic substrate having high rigidity and high gloss, in particular a stretched resin film.
• aluminum foil can be used alone or in combination.
• stretched resin film examples include biaxially oriented polyester (PET), easily tearable biaxially oriented polyester (PET), biaxially oriented polypropylene (OPP), biaxially oriented polyamide (PA), coextruded biaxially oriented polypropylene having an ethylene-vinyl alcohol copolymer (EVOH) as a central layer, biaxially oriented ethylene-vinyl alcohol copolymer (EVOH), and coextruded biaxially oriented polypropylene coated with polyvinylidene chloride (PVDC). These may be used alone or in combination.
• PET biaxially oriented polyester
• PET easily tearable biaxially oriented polyester
• OPP biaxially oriented polypropylene
• PA biaxially oriented polyamide
• EVOH coextruded biaxially oriented polypropylene having an ethylene-vinyl alcohol copolymer (EVOH) as a central layer
• EVOH biaxially oriented ethylene-vinyl alcohol copolymer
• Examples of lamination methods for laminating the above-mentioned substrate onto the multilayer film of the present invention obtained by the above-mentioned manufacturing method to form a laminate film include dry lamination, wet lamination, non-solvent lamination, extrusion lamination, etc.
• the layer of adhesive located between the multilayer film and the substrate is called the adhesive layer.
• Adhesives used in the dry lamination include, for example, solvent-based two-component curing adhesives.
• a "solvent-based” adhesive refers to a form used in the so-called dry lamination method, in which the adhesive is applied to a substrate, heated in an oven or the like to volatilize the organic solvent in the coating, and then bonded to another substrate, and includes a polyisocyanate composition, a polyol composition, and an organic solvent capable of dissolving (diluting) them.
• biomass raw materials plant-derived raw materials
• the biomass degree can be increased by appropriately using a biomass raw material.
• biomass raw material examples include castor oil-based polyols such as castor oil, dehydrated castor oil, hydrogenated castor oil, and 5 to 50 mole alkylene oxide adducts of castor oil, as well as aliphatic polybasic acids such as succinic acid, succinic anhydride, glutaric acid, adipic acid, azelaic acid, sebacic acid, and itaconic acid, and alkyl esters of the acids, and dimer acids.
• castor oil-based polyols such as castor oil, dehydrated castor oil, hydrogenated castor oil, and 5 to 50 mole alkylene oxide adducts of castor oil
• aliphatic polybasic acids such as succinic acid, succinic anhydride, glutaric acid, adipic acid, azelaic acid, sebacic acid, and itaconic acid, and alkyl esters of the acids, and dimer acids.
• the weight of the adhesive layer after drying is preferably 0.1 to 10 g/m 2 , more preferably 1 to 6 g/m 2 , and even more preferably 2 to 5 g/m 2.
• the thickness of the adhesive layer is preferably 0.1 to 10 ⁇ m, more preferably 1 to 7 ⁇ m, and even more preferably 2 to 5 ⁇ m.
• various adhesives can be used for the adhesive layer, but it is preferable to use a pressure-sensitive adhesive.
• pressure-sensitive adhesives include rubber-based adhesives obtained by dissolving polyisobutylene rubber, butyl rubber, or mixtures thereof in an organic solvent such as benzene, toluene, xylene, or hexane; or these rubber-based adhesives blended with tackifiers such as abiethylene acid rosin ester, terpene-phenol copolymer, or terpene-indene copolymer; and acrylic-based adhesives obtained by dissolving an acrylic copolymer having a glass transition point of ⁇ 20° C.
• any tear initiation portion such as a V notch, I notch, perforation, or microhole in the sealed portion in order to weaken the initial tear strength and improve the ease of opening.
• the multilayer film of the present invention may further have a printing layer on the surface layer (A).
• the printing layer is a layer in which a desired pattern is formed by liquid printing ink in order to impart aesthetics, various information about the contents, and functionality to the printed material.
• the printing layer is formed by printing a gravure printing ink or a flexographic printing ink (hereinafter referred to as liquid printing ink) containing a binder resin and a colorant, or an inkjet ink.
• the printing layer may be a single layer, or there may be multiple printing layers.
• the liquid printing ink used for each printing layer may be the same, or may be the same composition with only the colorant being different, or may be of different compositions.
• printing may be performed using a combination of liquid printing ink and inkjet ink.
• the above liquid printing inks are used as gravure printing inks and flexographic printing inks, and are broadly divided into organic solvent-based liquid printing inks that use organic solvents as the main solvent, and water-based liquid printing inks that use water as the main solvent. It is preferable that the printing layer formed on the multilayer film of the present invention be a general-purpose organic solvent-based liquid printing ink.
• the above organic solvent-based liquid printing ink is produced by dispersing a mixture of pigment, binder resin, organic solvent medium, dispersant, defoamer, etc., in a disperser to obtain a pigment dispersion.
• the resulting pigment dispersion is then mixed with resin, aqueous medium, and, if necessary, additives such as a leveling agent, and then stirred.
• Dispersers used in the production of gravure and flexographic printing inks include bead mills, Eiger mills, sand mills, gamma mills, and attritors.
• binder resins include cellulose-based resins such as cellulose acetate propionate (CAP) and cellulose acetate butyronate (CAB), polyamide-based resins, urethane-based resins, acrylic-based resins, vinyl chloride-vinyl acetate copolymer resins, chlorinated polypropylene resins, ethylene-vinyl acetate copolymer resins, vinyl acetate resins, polyvinyl chloride resins, and other vinyl chloride resins, polyester resins, alkyd resins, rosin-based resins, rosin-modified maleic acid resins, ketone resins, cyclized rubber, chlorinated rubber, butyral, and petroleum resins.
• cellulose-based resins such as cellulose acetate propionate (CAP) and cellulose acetate butyronate (CAB)
• polyamide-based resins such as cellulose acetate propionate (CAP) and cellulose acetate butyronate (CAB
• Pigments include inorganic and organic pigments that are commonly used in inks, paints, and recording agents.
• Organic pigments include soluble azo pigments, insoluble azo pigments, azo pigments, phthalocyanine pigments, halogenated phthalocyanine pigments, anthraquinone pigments, anthanthrone pigments, dianthraquinonyl pigments, anthrapyrimidine pigments, perylene pigments, perinone pigments, quinacridone pigments, thioindigo pigments, dioxazine pigments, isoindolinone pigments, quinophthalone pigments, azomethine azo pigments, flavanthrone pigments, diketopyrrolopyrrole pigments, isoindoline pigments, indanthrone pigments, and carbon black pigments.
• carmine 6B lake red C, permanent red 2B, disazo yellow, pyrazolone orange, carmine FB, chromophthalic yellow, chromophthalic red, phthalocyanine blue, phthalocyanine green, dioxazine violet, quinacridone magenta, quinacridone red, indanthrone blue, pyrimidine yellow, thioindigo bordeaux, thioindigo magenta, perylene red, perinone orange, isoindolinone yellow, aniline black, diketopyrrolopyrrole red, daylight fluorescent pigments, etc.
• both non-acid-treated pigments and acid-treated pigments can be used.
• inorganic pigments examples include white inorganic pigments such as titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, chromium oxide, silica, litbon, antimony white, and gypsum.
• white inorganic pigments such as titanium oxide, zinc oxide, zinc sulfide, barium sulfate, calcium carbonate, chromium oxide, silica, litbon, antimony white, and gypsum.
• titanium oxide is particularly preferred. Titanium oxide is white in color and is preferred in terms of coloring power, hiding power, chemical resistance, and weather resistance, and from the standpoint of printing performance, it is preferable that the titanium oxide has been treated with silica and/or alumina.
• inorganic pigments other than white examples include aluminum particles, mica, bronze powder, chrome vermilion, yellow lead, cadmium yellow, cadmium red, ultramarine, Prussian blue, red iron oxide, yellow iron oxide, iron oxide black, and zircon.
• Aluminum is in powder or paste form, but it is preferable to use it in paste form from the standpoint of ease of handling and safety, and whether leafing or non-leafing is used is selected appropriately from the standpoint of brightness and concentration.
• the organic solvent-based liquid printing ink has excellent adhesion to various substrates and can be used for printing on paper, synthetic paper, thermoplastic resin films, plastic products, steel plates, etc., and is useful as an ink for gravure printing using a gravure printing plate made by electronic engraving or the like, or for flexographic printing using a flexographic printing plate made by a resin plate or the like.
• the thickness of the liquid printing ink formed by the gravure printing method or the flexographic printing method using the organic solvent-based liquid printing ink is preferably 0.1 to 10 ⁇ m, more preferably 1 to 5 ⁇ m, and even more preferably 1 to 3 ⁇ m.
• the weight of the printed layer after drying is preferably 0.1 to 10 g/ m2 , more preferably 1 to 5 g/ m2 , and even more preferably 1 to 3 g/ m2 .
• liquid printing ink in consideration of the establishment of a recycling-based society that should develop in a sustainable manner (sustainability), it is preferable to use a liquid printing ink that uses raw materials derived from plants (biomass raw materials).
• plant-derived raw materials include cellulose resins such as cellulose acetate propionate resin and nitrocellulose; polyamide resins using dimer acids or polymerized fatty acids derived from natural oils such as soybean oil, palm oil, and rice bran oil; polycarboxylic acids such as succinic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, dimer acid, glutaric acid, and malic acid; polyols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, pentylene glycol, 1,10-dodecanediol, dimer diol, and
• Liquid printing inks using the above-mentioned plant-derived raw materials can also be commercially available products.
• Examples of commercially available products that can be used include inks listed in the Japan Organic Resources Association, such as Glossa BM, Raizin, Ultima, and Finart BM (all manufactured by DIC Corporation), Rotobio (manufactured by Sakata Inx Corporation), PANNECO, Real NEX BO, and FB King X (all manufactured by Toyo Ink Co., Ltd.), NT-VESTA, and PULPTECC (both manufactured by Tokyo Ink Co., Ltd.), etc.
• the above-mentioned printed layer may be printed directly onto the surface layer (A) of the multilayer film of the present invention by so-called surface printing, or may be printed onto another substrate by so-called reverse printing, and then the substrate and the multilayer film of the present invention may be laminated by dry lamination.
• the mixed ratio of recycled materials containing the multilayer film of the present invention and polypropylene-based resin can be determined by measuring with infrared spectroscopy (IR). Specifically, the polyethylene (multilayer film of the present invention) ratio in the recycled material can be calculated according to the following procedure, which is based on the method described in Gifu Prefectural Industrial Technology Center Research Report No. 13 pp10-13 (2019).
• the linear approximation formula described in Gifu Prefectural Industrial Technology Center Research Report No. 13 pp10-13 (2019) has been verified when the polyethylene ratio in a mixture of polyethylene and polypropylene is 5 to 50% by mass, but has not been verified when the polyethylene ratio exceeds 50% by mass.
• the inventors have found through their studies that the accuracy drops significantly when the polyethylene ratio is 70% by mass or more.
• the exponential approximation formula discovered by the inventors can specify the polyethylene ratio with good accuracy even when the polyethylene ratio is low, and can specify the polyethylene ratio with good accuracy even when the polyethylene ratio is 70 mass% or more.
• the multilayer film of the present invention uses a small amount of low-density polyethylene, which reduces the accuracy of measuring the polyethylene ratio of recycled materials mixed with polypropylene resins, and therefore the accuracy of measuring the polyethylene ratio of the recycled materials is relatively good.
• the multilayer film can achieve both packaging suitability and interlayer adhesive strength as well as excellent accuracy of measuring the polyethylene ratio by adjusting physical properties such as melting point and rigidity by using a combination of high-density polyethylene and medium-density polyethylene.
• Example 1 The following resins were used as the resin components forming each of the surface layer (A), intermediate layer (B) and seal layer (C) to prepare resins and resin mixtures forming each layer. These resins and resin mixtures were fed to three extruders and melted at 250°C. The molten resin was supplied to a T-die chill roll method coextrusion multilayer film manufacturing apparatus having a feed block (feed block and T-die temperature: 250°C) and co-melt extrusion was performed to obtain a multilayer film having a three-layer structure of surface layer (A)/middle layer (B)/seal layer (C), with each layer having a thickness of 10 ⁇ m/23 ⁇ m/17 ⁇ m (total 50 ⁇ m).
• Surface layer (A) 60 parts by mass of medium density polyethylene (density: 0.933 g/cm 3 , MFR (190° C., 21.18 N): 4 g/10 min, melting point: 122° C.) (hereinafter referred to as "MDPE (1)"), 40 parts by mass of high density polyethylene (density: 0.960 g/cm 3 , MFR (190° C., 21.18 N): 8 g/10 min, melting point: 134° C.) (hereinafter referred to as "HDPE").
• Sealing layer (C) 100 parts by mass of linear low density polyethylene (density: 0.905 g/cm 3 , MFR (190° C., 21.18 N): 4 g/10 min, melting point (peak with largest heat absorption): 89° C.) (hereinafter referred to as "LLDPE").
• Example 2 Multilayer films of Examples 2 to 6 were obtained in the same manner as in Example 1, except that the compounding ratio and layer thickness of each layer were changed as shown in Table 1.
• Example 7 After co-melt extrusion was carried out in the same manner as in Example 1, the film was pressurized and cooled by a chill roll having an uneven structure at 40° C. to obtain a matte multilayer film having a three-layer structure of a surface layer (A)/an intermediate layer (B)/a seal layer (C), with the average thicknesses of the layers being 10 ⁇ m/23 ⁇ m/17 ⁇ m (total 50 ⁇ m).
• Comparative Examples 1 to 2 A multilayer film of Comparative Example 1 was obtained in the same manner as in Example 1, except that the compounding ratio and layer thickness of each layer were changed as shown in Table 2.
• the surface roughness (RzJIS) of the surface of the seal layer (A) was measured (unit: ⁇ m) using a non-contact surface/layer cross-sectional shape measuring system VertScan (registered trademark) 2.0 (model number: R3300G Lite, manufactured by Ryoka Systems Co., Ltd.).
• the specific surface area (S/A) of the surface of the seal layer (A) was measured using a non-contact surface/layer cross-sectional shape measuring system VertScan (registered trademark) 2.0 (model number: R3300G Lite, manufactured by Ryoka Systems Co., Ltd.).
• the films obtained in the examples and comparative examples were cut into a size of 300 mm length x 25.4 mm width (200 mm interval between marks) with the longitudinal direction being the flow direction of the film (machine direction) to obtain test pieces with a thickness of 30 ⁇ m.
• the 1% tangent modulus (unit: MPa) at 23° C. was measured at a tensile speed of 500 mm/min in accordance with ASTM D-882 using a Tensilon tensile tester (manufactured by A&D Co., Ltd.).
• Heat seal strength Using the films obtained in the Examples and Comparative Examples, test pieces were prepared by heat sealing at 100°C, 0.2 MPa, and 1 second to a seal width of 10 mm. These were then cut to a width of 15 mm, and the heat seal strength (unit: N/15 mm) was measured using a tensile tester. The same evaluation was carried out three times, and the average value was used as the evaluation result.
• ⁇ Heat seal strength is 5N/15mm or more
• Heat seal strength is less than 5N/15mm
• ⁇ No shrinkage of the sealed part, no adhesion to the seal bar, no wrinkles, etc.
• ⁇ Some shrinkage of the sealed part, some adhesion to the seal bar, some wrinkles, etc.
• ⁇ Some shrinkage of the sealed part, some adhesion to the seal bar, some wrinkles, etc.
• ⁇ The measurement result of the polyethylene ratio of the recycled material is within ⁇ 10% by mass of the actual mixing ratio, exceeding ⁇ 5% by mass.
• ⁇ The measurement result of the polyethylene ratio of the recycled material is more than ⁇ 10% by mass of the actual mixing ratio. For example, when the actual mixing ratio of multilayer film:polypropylene is 50:50, if the measurement result of the polyethylene ratio of the recycled material is 65% by mass, it was evaluated as ⁇ .
• MDPE Medium density polyethylene (density: 0.933 g/cm 3 , MFR (190° C., 21.18 N): 4 g/10 min, melting point: 122° C.)
• MDPE (2) Medium density polyethylene (density: 0.931 g/cm 3 , MFR (190° C., 21.18 N): 4 g/10 min, melting point: 123° C.)
• HDPE High density polyethylene (density: 0.960 g/cm 3 , MFR (190° C., 21.18 N): 8 g/10 min, melting point: 134° C.)
• LLDPE Linear low density polyethylene (density: 0.905 g/cm 3 , MFR (190° C., 21.18 N): 4 g/10 min, melting point (peak with largest endothermic heat): 89° C.)
• LDPE low density polyethylene (density: 0.922 g/cm 3 , M
• the multilayer films of the present invention in Examples 1 to 10 had suitable rigidity and excellent impact resistance at a very low temperature of -20°C, and also had excellent suitability for packaging machines.
• they are monomaterials of polyethylene resins, they are easy to recycle.
• the polyethylene ratios measured by IR for the recycled materials consisting of mixtures of the multilayer films and polypropylene in Examples 1 and 5 to 7 were close to the actual mixture ratios, and even when mixed with polypropylene, the polyethylene ratio was easily identified by infrared spectroscopy, which was advantageous for the advanced utilization of the recycled materials.
• the multilayer film of Comparative Example 1 was a low-density polyethylene film, and therefore had poor suitability for packaging machines. Also, the polyethylene ratio measured by IR was far from the actual mixing ratio, and even when mixed with polypropylene, the polyethylene ratio could not be accurately determined by infrared spectroscopy. Also, the multilayer film of Comparative Example 2 had a low content of high-density polyethylene, and therefore the polyethylene ratio measured by IR was somewhat far from the actual mixing ratio, and even when mixed with polypropylene, the polyethylene ratio could not be accurately determined by infrared spectroscopy.

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