JP5459535B2 - Coextruded multilayer film and packaging material comprising the film - Google Patents

Description

  The present invention relates to a packaging material for packaging foods, medicines, industrial parts, miscellaneous goods, magazines, etc. Specifically, the tearability by hand is good not only in the vertical direction of the film but also in the horizontal direction, and can be used alone. Furthermore, the present invention relates to a coextruded multilayer film having good heat seal strength, pinhole resistance, suitability for packaging machines, and low temperature impact resistance, and a packaging material comprising the film.

  Conventionally, a packaging material is required to have high heat seal strength and pinhole resistance from the viewpoint of protecting contents. On the other hand, with the trend toward universal design in recent years, easy opening and tearing are being emphasized in order to consider socially vulnerable people (old people, infants, people with disabilities, etc.). However, when trying to improve easy opening and easy tearing, there is a problem that the heat seal strength and pinhole resistance, which are the original functions of the packaging material, are lowered.

  In order to solve the above problems, the first layer formed from a cyclic olefin resin composition mainly composed of a cyclic olefin resin and an olefin (co) polymer or a composition containing the first layer is formed. Further, a polyolefin-based multilayer laminate in which at least two layers with the second layer are laminated has been proposed (for example, see Patent Document 1). However, the laminate provided in Patent Document 1 has a problem in pinhole resistance against bending because it has a cyclic olefin resin having poor flexibility as a main component. In addition, the thickness of the multilayer laminate manufactured in the examples is 100 μm or more, and even if it can be torn by hand, there is no linear cut property, and it is torn in an unexpected direction. There was a problem that the contents get dirty on hands and clothes.

  Further, a packaging film has been proposed in which layers made of other thermoplastic resins are laminated on both sides of a layer made of an alicyclic structure-containing polymer (see, for example, Patent Document 2). This packaging film has a good tearability because it is as thin as 20 to 40 μm. However, since it uses 100% cyclic olefin resin, it has poor flexibility and pinhole resistance like the above-mentioned polyolefin multilayer laminate. There was a problem.

  As a method for solving these problems, the present inventor has already laminated a resin layer mainly composed of low-density polyethylene on both surfaces of a resin layer formed by using a combination of low-density polyethylene and a cyclic olefin resin. In addition, the present invention provides a multilayer film excellent in flexibility and having good pinhole resistance and linear cutability (see, for example, Patent Documents 3 to 5). However, when these multilayer films are used alone and an automatic packaging machine is used, the heat seal layer and the surface layer are made of the same resin, so that the seal temperature and the seal pressure are sufficiently increased so as to sufficiently increase the seal strength. If it is changed, wrinkles or shrinkage may occur on the surface, and it is practically used as a thick film or laminate film having a large thickness. Further, when packaging heavy frozen meat and frozen marine products with a single film without lamination, there is a risk that the film may be broken or torn, and the seal part may be peeled off. From the viewpoint of environmental protection in recent years, considering that weight reduction and thinning of packaging materials are urgent issues, thinning is possible without impairing easy-cutting and pinhole resistance, and low-temperature impact resistance There is a need for packaging films that have good properties.

Japanese Patent Application Laid-Open No. 08-72210 JP 2000-334890 A JP 2007-055234 A Japanese Patent Laid-Open No. 2007-076300 JP 2007-245612 A

  An object of the present invention is made in view of the above problems, and can be used alone without using a stretched base material, and can be easily opened by having easy tearability in both the vertical and horizontal directions. By providing a coextruded multilayer film having excellent heat resistance, sufficient heat seal strength, good resistance to pinholes due to bending and good packaging machinery, and excellent low-temperature impact resistance, and a packaging material comprising the film. is there.

  As a result of diligent research to solve the above-mentioned problems, the present inventors have selected an ethylene-based resin having a specific density as a surface layer / heat seal layer, and a resin that contributes to easy tearing in the intermediate layer. Co-extruded multilayer film obtained by using in combination has heat-seal strength that can withstand heavy weight packaging to some extent, and is easy to tear with pinhole resistance and linear and vertical cut characteristics. In addition, the present inventors have found that the packaging machine suitability and low-temperature impact resistance are also good, and the present invention has been completed.

That is, the present invention has a density of 0.910 g / cm ² or more 0.945 g / cm ² less than the ethylene-based resin (a1) and 50 to 90 wt%, a density of 0.950 g / cm ² or more high-density polyethylene ( a2) a resin layer mainly composed of 10 to 50 wt% and comprises a mixture of resin with (a), density of 0.900 g / cm ² or more 0.940 g / cm ² less than the ethylene-based resin (b1) Mainly a resin formed by mixing 50 to 90% by mass with cyclic olefin resin (b2) and / or 10 to 50% by mass of high density polyethylene (b3) having a density of 0.950 g / cm ² or more. And (A) / (B) a resin layer (C) containing as a main component an ethylene-based resin (c1) having a density of 0.880 g / cm ² or more and less than 0.910 g / cm ^2. ) / (C) Coextruded multilayer film and, and is intended to provide a packaging material made of the film.

  The co-extruded multilayer film of the present invention has high straight-cut property and easy tearability in both the longitudinal direction and the transverse direction. Therefore, the coextruded multilayer film has an easy-opening property that can be easily torn even by a socially weak person without applying excessive force. In addition, it has a wide temperature range that can be sealed and excellent packaging machine suitability such as shrinkage of the seal part and resistance to wrinkles, resistance to pinholes caused by bending, and heat seal strength that can withstand heavy-weight packaging. It also has excellent low temperature impact resistance.

  Hereinafter, the present invention will be described in detail. In the present invention, “mainly comprising” specifically means that 70% by mass or more of the resin components used in each resin layer is made of the resin or resin mixture defined in the present invention. It is. From the viewpoint that the effects of the present invention can be easily expressed, the use ratio of the resin or resin mixture defined in the present invention in each resin layer is more preferably 90% by mass or more.

The ethylene resin (a1) used in the resin layer (A) of the coextruded multilayer film of the present invention may be an ethylene resin having a density of 0.910 / cm ³ or more and less than 0.945 g / cm ³ , for example , Linear low density polyethylene (LLDPE), linear medium density polyethylene (LMDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), and other polyethylene resins, ethylene-vinyl acetate copolymer (EVA), 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), ethylene-methacrylic acid copolymer Ethylene copolymers such as the body (EMAA); more ethylene - ionomer of acrylic acid copolymer, ethylene - ionomers of methacrylic acid copolymer. Among these, LDPE, LLDPE, LMDPE, and MDPE are preferable because of a good balance between easy tearing and pinhole resistance.

  The LDPE may be a branched or high-density polyethylene obtained by a high-pressure radical polymerization method, and is preferably a branched low-density polyethylene obtained by homopolymerizing ethylene by a high-pressure radical polymerization method.

  As LLDPE, an ethylene monomer is the main component by a low-pressure radical polymerization method using a single site catalyst, and an α-olefin such as butene-1, hexene-1, octene-1, 4-methylpentene is used as a comonomer. Are copolymerized. As a comonomer content rate in LLDPE, it is preferable that it is the range of 0.5-10 mol%, and it is more preferable that it is the range of 1-7 mol%. In addition, when butene-1 is used as a comonomer, it is preferable because transparency, impact resistance, easy tearing, and the like are improved. At this time, the content of the butene monomer is in the range of 1 to 5 mol%. Most preferred.

  Examples of the single-site catalyst include various single-site catalysts such as metallocene catalyst systems such as combinations of metallocene compounds of Group IV or V transition metals and organoaluminum compounds and / or ionic compounds. In addition, the single-site catalyst has a uniform active site, so the molecular weight distribution of the resulting resin is sharper than a multi-site catalyst with a non-uniform active site. This is preferable because a resin having physical properties excellent in stability of sealing strength and anti-blocking property can be obtained.

Although the density of the ethylene-based resin (a1) as mentioned above is less than 0.910 g / cm ³ or more 0.945 g / cm ^3, in the range of less than 0.915 g / cm ³ or more 0.940 g / cm ³ Is more preferable. When the density is less than 0.910 g / cm ³ , the difference in melting point from the resin layer (C) described later becomes small, so that the difference in melting point becomes small. If it is 0.945 g / cm ³ or more, the pinhole resistance and low temperature impact resistance of the film may be deteriorated. If the density is within this range, it has appropriate rigidity, excellent mechanical strength such as pinhole resistance, and film film formability and extrusion suitability are improved. Moreover, it is preferable that melting | fusing point is the range of 95-135 degreeC, and 100-130 degreeC is more preferable. When the melting point is within this range, the processing stability is improved. Moreover, it is preferable that MFR (190 degreeC, 21.18N) of the said ethylene-type resin (a1) is 2-20 g / 10min, and it is more preferable that it is 3-10 g / 10min. When the MFR is within this range, the extrusion moldability of the film is improved.

The high density polyethylene (a2) used in the resin layer (A) of the coextruded multilayer film of the present invention is used for improving easy tearability and packaging suitability, and is a polyethylene having a density of 0.950 g / cm ³ or more. is there.

  In addition, the high-density polyethylene (a2) is a high-density polyethylene generally used in extrusion molding such as film molding, for example, a high-density polyethylene having good flowability with a melt flow (190 ° C.) of 5 to 20 g / 10 min. It is preferable from the viewpoint of obtaining a film having a relatively smooth surface and good transparency when melt-kneaded and extrusion-molded with the ethylene resin (a1).

  Since such a high density polyethylene (a2) to be added has low mechanical strength, it is relatively brittle compared to other polyolefin resins and has good tearability and also has good compatibility with the ethylene resin (a1). The transparency when blended can also be maintained. Further, without using an adhesive resin or the like, the interlayer adhesive strength between the resin layer (A) and the resin layer (B) can be maintained, and since it has appropriate flexibility, the pinhole resistance is also improved. .

In the resin layer (A), the use ratio of the ethylene resin (a1) having a density of 0.910 g / cm ² or more and less than 0.945 g / cm ² and the high density polyethylene (a2) is (a1 ) Is 50 to 90% by mass, and (a2) is 10 to 50% by mass. If the usage rate of the high density polyethylene (a2) exceeds 50% by mass, the resulting multilayer film may be inferior in pinhole resistance and low temperature impact resistance, and the usage rate of the high density polyethylene (a2) is 10%. If it is less than mass%, the rigidity and heat resistance of the film will be insufficient.

As the ethylene-based resin (b1) used in the resin layer of the coextruded multilayer film of the present invention (B), as long density 0.900 g / cm ³ or more 0.940 g / cm ³ less than the ethylene-based resin, i.e., The difference from the ethylene resin (a1) used in the resin layer (A) is only in the density range. Therefore, the resin specifically mentioned is also the same as the ethylene resin (a1), for example, very low density polyethylene (VLDPE), linear low density polyethylene (LLDPE), linear medium density polyethylene (LMDPE), Low density polyethylene (LDPE), medium density polyethylene (MDPE), and other polyethylene resins, ethylene-vinyl acetate copolymer (EVA), 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), ethylene-methacrylic acid copolymer Ethylene copolymer such as polymer (EMAA); Down - ionomer of acrylic acid copolymer, ethylene - ionomers of methacrylic acid copolymer. Among these, LDPE, LLDPE, LMDPE, and MDPE are preferable because of a good balance between easy tearing and pinhole resistance.

Although the density of the ethylene-based resin (b1) as described above is less than 0.900 g / cm ³ or more 0.940 g / cm ^3, in the range of less than 0.905 g / cm ³ or more 0.935 g / cm ³ Is more preferable. As long as it corresponds to this density, two or more types of polyethylene resins may be blended. If the density is less than 0.900 g / cm ³ , the rigidity is lowered and the suitability of the packaging machine is deteriorated, and in addition, there is a problem in the cut property due to the increase in tear strength. On the other hand, if it is 0.940 g / cm ³ or more, the pinhole resistance may deteriorate. If the density is within this range, it has appropriate rigidity, excellent mechanical strength such as pinhole resistance, and film film formability and extrusion suitability are improved. Moreover, it is preferable that melting | fusing point is the range of 95-130 degreeC, and 100-125 degreeC is more preferable. If melting | fusing point is this range, kneading | mixing precision with process stability and the cyclic olefin resin (b2) mentioned later improves. Moreover, it is preferable that MFR (190 degreeC, 21.18N) of the said polyethylene-type resin (b1) is 2-20 g / 10min, and it is more preferable that it is 3-10 g / 10min. When the MFR is within this range, the extrusion moldability of the film is improved.

  By using such an ethylene-based resin (b1), mechanical strength can be maintained to some extent, low-temperature impact resistance is improved, and a phase with a cyclic olefin-based resin (b2) or high-density polyethylene (b3) described later is used. Since the solubility is good, the transparency when blended can be maintained. In addition, without using an adhesive resin or the like, the interlayer adhesive strength between the resin layer (A) and the resin layer (B) can be maintained, and since it has flexibility, the pinhole resistance is also improved.

  Examples of the cyclic olefin resin (b2) used in the resin layer (B) of the coextruded multilayer film of the present invention include a norbornene polymer, a vinyl alicyclic hydrocarbon polymer, a cyclic conjugated diene polymer, and the like. . Among these, norbornene-based polymers are preferable. The norbornene-based polymer includes a ring-opening polymer of a norbornene-based monomer (hereinafter referred to as “COP”), a norbornene-based copolymer obtained by copolymerizing a norbornene-based monomer and an olefin such as ethylene (hereinafter, referred to as “COP”). , “COC”). Furthermore, COP and COC hydrogenates are particularly preferred. In addition, the weight average molecular weight of the cyclic olefin resin (b2) is preferably 5,000 to 500,000, more preferably 7,000 to 300,000.

  The norbornene polymer and the norbornene monomer used as a raw material are alicyclic monomers having a norbornene ring. Examples of such norbornene-based monomers include norbornene, tetracyclododecene, ethylidene norbornene, vinyl norbornene, ethylidetetracyclododecene, dicyclopentadiene, dimethanotetrahydrofluorene, phenyl norbornene, methoxycarbonyl norbornene, methoxy And carbonyltetracyclododecene. These norbornene monomers may be used alone or in combination of two or more.

  The norbornene-based copolymer (COC) is obtained by copolymerizing an olefin copolymerizable with the norbornene-based monomer. Examples of such olefin include ethylene, propylene, and 1-butene. Examples thereof include olefins having 2 to 20 carbon atoms; cycloolefins such as cyclobutene, cyclopentene, and cyclohexene; non-conjugated dienes such as 1,4-hexadiene. These olefins can be used alone or in combination of two or more.

  In addition, the content ratio of the norbornene monomer in the norbornene copolymer (COC) is preferably 40 to 90 mol%, more preferably 50 to 80 mol%. If the content ratio is within this range, the rigidity, tearability and processing stability of the film are improved.

  As a commercially available product that can be used as the cyclic olefin resin (b2), examples of the ring-opening polymer (COP) of the norbornene monomer include “ZEONOR” manufactured by Nippon Zeon Co., Ltd. Examples of the system copolymer (COC) include “Apel” manufactured by Mitsui Chemicals, Inc., “TOPAS” manufactured by TICONA, and the like.

The high-density polyethylene (b3) used in the resin layer (B) of the coextruded multilayer film of the present invention is used for improving easy tearability and packaging suitability by increasing rigidity, and has a density of 0.950 g / cm ^3. It is the above polyethylene. Moreover, it may be the same as or different from the high-density polyethylene (a2) used in the resin layer (A).

  It is essential that the content of the ethylene-based resin (b1) in the resin layer (B) is 50 to 90% by mass, and it is preferably contained in an amount of 60 to 80% by mass from the viewpoint of better tearability. The content of the cyclic olefin-based resin (b2) in the resin layer (B) is 30% by mass or less from the viewpoint of flexibility of the resulting film, pinhole resistance, and low temperature impact resistance. Is preferred. Furthermore, the content of the high-density polyethylene (b3) in the resin layer (B) is 50% by mass or less from the viewpoints of transparency and smoothness and interlayer adhesion strength with the resin layers (A) and (C). It is preferable that it is 40 mass% or less.

Resin mixture used for the resin layer (B) in the present invention is a mixture of d styrene-based resin (b1) and a cyclic olefin resin (b2) and high density polyethylene (b3), the balance of physical properties obtained multi-layer film excellent, also the raw material cost of the point of view or RaYoshimi Masui. Moreover, you may use other resin together in the range which does not impair the effect of this invention.

The ethylene resin (c1) used in the resin layer (C) of the coextruded multilayer film of the present invention may be an ethylene resin having a density of 0.880 g / cm ³ or more and less than 0.910 g / cm ³ , Examples thereof include ultra-low density polyethylene, plastomer, elastomer, low density polyethylene, linear low density polyethylene, and linear ultra low density polyethylene. These may be used alone or in combination. Further, the ethylene resin (a1) and the ethylene resin (b1) are different only in density, and may be a copolymer of ethylene and another monomer described in each of them. When the density is less than 0.880 g / cm ³ , a sticky feeling is exhibited, so that the film formability and workability due to a significant deterioration in slipperiness are reduced. When the density is 0.910 g / cm ³ or more, the resin layer (A) Since the density of the ethylene-based resin (a1) used is close, wrinkles and shrinkage are likely to occur on the surface during heat sealing.

  The ethylene resin (c1) preferably has an MFR (190 ° C.) of 0.5 to 30.0 g / 10 minutes because it facilitates extrusion, and more preferably has an MFR of 2.0 to 2.0. 15.0 g / 10 min. Further, if the ethylene resin (c1) has a melting point of 80 to 135 ° C., the film is less likely to shrink during heat sealing, and the packaging suitability is improved. More preferably, the melting point is 80 to 110 ° C.

The ethylene resin (a1) has a higher density than the ethylene resin (c1), and the density difference is 0.02 to 0.07 g / cm ³ , more preferably 0.03 to 0.07 g / cm. A range of ³ is preferable. By using a resin having such a density difference for the resin layer (A) and the resin layer (C), the heat resistance of the resin layer (A) of the resulting multilayer film is improved, and the resin layer ( Since C) can be made into a low-temperature seal and heat seal strength can be increased, packaging suitability is improved, and it can be suitably used as a heavy-weight packaging material.

  The layer structure of the coextruded multilayer film of the present invention is a laminate of the resin layers (A), (B) and (C) in the order of (A) / (B) / (C). The thickness of the resin layer (B) is preferably in the range of 30 to 80%, more preferably 35 to 70% of the total thickness of the coextruded multilayer film. When the ratio of the thickness of the resin layer (B) to the total thickness of the coextruded multilayer film is within this range, transparency, tearability, pinhole resistance, and heat sealability are improved.

  In the layer structure (A) / (B) / (C) of the coextruded multilayer film, the thickness of the resin layer (C) is determined by the rigidity of the film, suitability for packaging machinery, transparency, low temperature impact resistance, and tearing. From the viewpoint of ease, it is preferably 5 to 35% of the total thickness of the coextruded multilayer film, more preferably 6 to 30%.

  Furthermore, the coextruded multilayer film of the present invention preferably has a film thickness of 15 to 90 μm, more preferably 20 to 80 μm. If the thickness of the film is within this range, stable sealing strength, suitability for packaging machinery, excellent pinhole resistance, easy tearing performance, and the like can be obtained.

  For each of the resin layers (A), (B), or (C), an antifogging agent, an antistatic agent, a thermal stabilizer, a nucleating agent, an antioxidant, a lubricant, and an antiblocking agent are added as necessary. In addition, components such as a release agent, an ultraviolet absorber, and a colorant can be added within a range that does not impair the object of the present invention. In particular, the resin layer (A) and (C) have a friction coefficient of 1.5 or less, preferably 1.0 or less in order to impart processing suitability during film forming and packaging suitability of the filling machine. It is preferable to add a lubricant or an antiblocking agent to the layers (A) and (C) as appropriate.

  Although it does not specifically limit as a manufacturing method of the co-extrusion multilayer film of this invention, For example, each resin or resin mixture used for a resin layer (A), a resin layer (B), and a resin layer (C) is respectively extruded separately. The film is heated and melted in a machine, laminated in the order of (A) / (B) / (C) in the melted state by a method such as a co-extrusion multi-layer die method or a feed block method, and then the film is formed by inflation, T-die chill roll method, etc. A co-extrusion method for forming into a shape. This coextrusion method is preferable because the thickness ratio of each layer can be adjusted relatively freely, and a multilayer film excellent in hygiene and cost performance can be obtained. Furthermore, since the difference in softening point (melting point) between the ethylene resin used in the resin layer (B) of the present invention and the high-density polyethylene or cyclic olefin resin is large, phase separation or gel may occur. In order to suppress the occurrence of such phase separation and gel, the T-die / chill roll method capable of performing melt extrusion at a relatively high temperature is preferable.

  Since the coextruded multilayer film of the present invention is obtained as a substantially unstretched multilayer film by the above production method, secondary molding such as deep drawing by vacuum molding is also possible.

  Furthermore, in order to improve the adhesiveness with the printing ink and the suitability for lamination, it is preferable to subject the resin layer (A) to a surface treatment. Examples of such surface treatment include corona treatment, plasma treatment, chromic acid treatment, flame treatment, hot air treatment, surface oxidation treatment such as ozone / ultraviolet treatment, and surface unevenness treatment such as sandblasting. Corona treatment is preferable.

  Examples of the packaging material composed of the coextruded multilayer film of the present invention include refrigerated foods, frozen foods, medicines, medical instruments, industrial parts, miscellaneous goods, packaging bags used for magazines, packaging containers, and the like.

  In the packaging bag, the resin layer (C) of the co-extruded multilayer film of the present invention is used as a heat seal layer, and the resin layers (C) are overlapped with each other to heat seal or the resin layer (A) and the resin layer (C). A packaging bag formed by overlapping and heat-sealing is preferable. For example, after cutting out the two coextruded multilayer films into a desired size of a packaging bag and overlapping them to heat-seal three sides to form a bag, the contents are removed from one side that is not heat-sealed. It can be used as a packaging bag by filling, heat sealing and sealing. Furthermore, it is also possible to form a packaging bag by sealing the top and bottom after sealing the end of a roll film into a cylindrical shape by an automatic packaging machine.

  Moreover, it is also possible to form a packaging bag and a container by heat-sealing a resin layer (C) and another heat-sealable film. At that time, as another film to be used, a film such as LDPE or EVA having relatively low mechanical strength can be used. In addition, a laminate film in which a film such as LDPE or EVA and a stretched film having relatively good tearability, for example, a biaxially stretched polyethylene terephthalate film (OPET), a biaxially stretched polypropylene film (OPP), or the like, is used. Can do.

  The packaging material using the coextruded multilayer film of the present invention has an arbitrary tear start portion such as a V-notch, an I-notch, a perforation, and a micro-porosity in the seal portion in order to weaken the initial tear strength and improve the openability. Is preferably formed.

  Next, the present invention will be described in more detail with reference to examples and comparative examples.

Example 1
As a resin for the resin layer (A), linear medium density polyethylene LMDPE (1) polymerized using a metallocene catalyst [Density: 0.935 g / cm ³ , MFR: 4 g / 10 min (230 ° C., 21.18 N] Hereinafter referred to as “LMDPE (1)”. ) 70 parts by mass and high-density polyethylene [Density: 0.955 g / cm ³ , MFR: 7 g / 10 min (190 ° C., 21.18 N); hereinafter referred to as “HDPE”. ) 30 parts by weight of resin mixture was used. Further, as a resin for the resin layer (B), a ring-opening polymer of a norbornene-based monomer [“ZEONOR 1060R” manufactured by Nippon Zeon Co., Ltd., MFR: 60 g / 10 min (280 ° C., 21.18 N), glass transition temperature: 100 ° C .; hereinafter referred to as “COP”. ] 20 parts by mass and linear medium density polyethylene [Density: 0.930 g / cm ³ , MFR: 5 g / 10 min (190 ° C., 21.18 N); hereinafter referred to as “LMDPE (2)”. A resin mixture of 70 parts by mass and 10 parts by mass of HDPE was used. As a resin for the resin layer (C), ultra-low density polyethylene VLLDPE polymerized using a metallocene catalyst [density: 0.890 g / cm ³ , MFR: 4 g / 10 min (230 ° C., 21.18 N), erucamide Contains 5000 ppm of a slip agent based on 7000 and 7000 ppm of an antiblocking agent based on a synthetic silica; hereinafter referred to as “VLLDPE”. ) Was used. These resins are supplied to an extruder for resin layer (A) (caliber 50 mm), an extruder for resin layer (B) (caliber 50 mm), and an extruder for resin layer (C) (caliber 50 mm), respectively. Melting at 230 ° C., and supplying the melted resin to a co-extruded multilayer film production apparatus (feed block and T-die temperature: 250 ° C.) of the T-die / chill roll method having a feed block, A coextruded multilayer film (X1) having a three-layer structure of (A) / (B) / (C) and a thickness of each layer of 10 μm / 14 μm / 6 μm (total 30 μm) was obtained.

(Example 2)
As the resin for the resin layer (B), a resin mixture of 13 parts by mass of COP, 70 parts by mass of LMDPE (2) and 17 parts by mass of HDPE was used. A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 7 μm / 20 μm / 3 μm (total 30 μm). A film (X2) was obtained.

(Example 3)
As the resin for the resin layer (B), a resin mixture of 13 parts by mass of COP, 60 parts by mass of LMDPE (2) and 27 parts by mass of HDPE was used. A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 10 μm / 14 μm / 6 μm (total 30 μm). A film (X3) was obtained.

Example 4
As resin for the resin layer (B), COP 13 parts by mass and LMDPE (2) 50 parts by mass and low density polyethylene [density: 0.920 g / cm ³ , MFR: 5 g / 10 min (190 ° C., 21.18 N); "LDPE (3)". A resin mixture of 10 parts by mass and 27 parts by mass of HDPE was used. A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 7 μm / 20 μm / 3 μm (total 30 μm). A film (X4) was obtained.

(Example 5)
As the resin for the resin layer (B), a resin mixture of 13 parts by mass of COP, 10 parts by mass of LMDPE (2), 50 parts by mass of LDPE (3), and 27 parts by mass of HDPE was used. A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 3 μm / 18 μm / 9 μm (total 30 μm). A film (X5) was obtained.

(Example 6 )
As the resin for the resin layer (A), a mixed resin of 70 parts by mass of LMDPE (1) and 30 parts by mass of HDPE was used. As a resin for the resin layer (B), 70 parts by mass of LMDPE (2) and a norbornene copolymer (“Topas” manufactured by Chicona, norbornene-ethylene copolymer, MFR: 50 g / 10 min (280 ° C., 21.18 N) ), Glass transition temperature: 80 ° C .; hereinafter referred to as “COC”.) A resin mixture of 20 parts by mass and 10 parts by mass of HDPE was used. A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 10 μm / 14 μm / 6 μm (total 30 μm). A film (X 6 ) was obtained.

(Comparative Example 1)
LMDPE (1) was used as the resin for the resin layer (A). As the resin for the resin layer (B), a resin mixture of 70 parts by mass of COP, 20 parts by mass of LMDPE (2) and 10 parts by mass of HDPE was used. LMDPE (1) resin was used as the resin for the resin layer (C). A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 10 μm / 14 μm / 6 μm (total 30 μm). A film (Y1) was obtained.

(Comparative Example 2)
As the resin for the resin layer (A), a mixed resin of 10 parts by mass of LMDPE (1) and 90 parts by mass of HDPE was used. As the resin for the resin layer (B), a resin mixture of 20 parts by mass of COP, 70 parts by mass of LMDPE (2) and 10 parts by mass of HDPE was used. LMDPE (1) resin was used as the resin for the resin layer (C). A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 10 μm / 14 μm / 6 μm (total 30 μm). A film (Y2) was obtained.

(Comparative Example 3)
As a resin for the resin layer (A), homopolypropylene resin [density: 0.900 g / cm ³ , MFR: 7 g / 10 min (230 ° C., 21.18 N); hereinafter referred to as “HOPP”. )
Was used. As the resin for the resin layer (B), a resin mixture of 13 parts by mass of COP, 37 parts by mass of LMDPE (2) and 50 parts by mass of HDPE was used. A resin of VLLDPE (4) was used as the resin for the resin layer (C). A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 16 μm / 8 μm / 6 μm (total 30 μm). A film (Y3) was obtained.

(Comparative Example 4)
As a resin for the resin layer (A), a mixed resin of 70 parts by mass of LMDPE (1) and 30 parts by mass of HDPE was used. As the resin for the resin layer (B), a resin mixture of 70 parts by mass of COP, 20 parts by mass of LMDPE (2) and 10 parts by mass of HDPE was used. A resin of VLLDPE (4) was used as the resin for the resin layer (C). A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 10 μm / 14 μm / 6 μm (total 30 μm). A film (Y4) was obtained.

(Comparative Example 5)
As a resin for the resin layer (A), linear low density polyethylene [density: 0.900 g / cm ³ , MFR: 4 g / 10 min (190 ° C., 21.18 N); hereinafter referred to as “LLDPE (5)” . A resin mixture of 80 parts by mass and 20 parts by mass of HDPE was used. As the resin for the resin layer (B), a resin mixture of 70 parts by mass of LMDPE (2), 13 parts by mass of COP and 17 parts by mass of HDPE was used. A resin of VLLDPE (4) was used as the resin for the resin layer (C). A coextruded multilayer film was prepared in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 4 μm / 14 μm / 12 μm (total 30 μm). A film (Y5) was obtained.

(Comparative Example 6)
As a resin for the resin layer (A), a mixed resin of 70 parts by mass of LMDPE (1) and 30 parts by mass of HDPE was used. As the resin for the resin layer (B), a resin mixture of 70 parts by mass of VLLDPE (4), 13 parts by mass of COP and 17 parts by mass of HDPE was used. A resin of VLLDPE (4) was used as the resin for the resin layer (C). A coextruded multilayer film was produced in the same manner as in Example 1 so that the thickness of each layer of the film was (A) / (B) / (C) = 10 μm / 14 μm / 6 μm (total 30 μm). A film (Y4) was obtained.

The following tests and evaluations were performed using the coextruded multilayer films obtained in Examples 1 to 6 and Comparative Examples 1 to 6 .

Tearability test The coextruded multilayer film obtained above was cut into test pieces each having a size of 63 mm x 76 mm in accordance with JIS K7128, and teared using an Elmendorf tear tester (manufactured by Tester Sangyo Co., Ltd.). Strength was measured. The tearability was evaluated from the obtained tear strength according to the following criteria.
○: Tear strength is less than 510.
X: Tear strength is 510 or more.

Pinhole resistance test The coextruded multilayer film obtained above was bent 100 times at a low temperature of −10 ° C. using a gelboflex tester (manufactured by Tester Sangyo Co., Ltd.), and then generated at the bent portion. Based on the number of pinholes, the pinhole resistance was evaluated according to the following criteria.
○: No pinhole.
X: There is a pinhole.

Suitability for packaging machine The films prepared in Examples and Comparative Examples were subjected to the following vertical pillow packaging with an automatic packaging machine to form a bag.
Packaging machine: Rika Kaken Co., Ltd. Unipacker NUV472

Horizontal (joint-pasted) seal: speed 30 bags / min, vertical heat seal temperature 150 ° C, air gauge pressure 4kg / cm ² , while changing from 10 ° C to 140 ° C in the horizontal heat seal temperature, the resin layer (C) Sealed each other. A flat bag measuring 200 mm long and 150 mm wide was used.

Vertical (envelope attached) seal: speed 30 bags / min, horizontal heat seal temperature 150 ° C, air gauge pressure 4kg / cm ² , resin layer (C) while changing from vertical heat seal temperature 120 ° C to 150 ° C in increments of 10 ° C And the resin layer (A) were sealed while being overlapped. A flat bag measuring 200 mm long and 150 mm wide was used.

Shrinkage / wrinkle test The film was fused to the heat-seal bar by shrinkage and heat seal bar by observing the appearance of the seal part of the flat bag with horizontal (gap-attached) seal and vertical (envelope-attached) seal. In addition, although the result of 110 degreeC is only a horizontal seal and the result of 150 degreeC is only a vertical seal, the result of 120, 130, and 140 degreeC has shown the result of both.
○: No shrinkage or wrinkles in seal part ×: There is shrinkage or wrinkles in seal part

Low Temperature Impact Resistance Impact strength at −10 ° C. was measured with an impact tester (Suga Test Co., Ltd.) according to ASTM D-256. From the obtained numerical values, the low temperature impact strength was evaluated according to the following criteria.
○: Numerical value 0.4J or more ×: Numerical value less than 0.4J

The film made under the above conditions was naturally cooled at 23 ° C., and then a test piece was cut into a strip shape having a width of 15 mm. This test piece was peeled 180 ° at a rate of 300 mm / min using a tensile tester (manufactured by A & D Co., Ltd.) in a thermostatic chamber at 23 ° C. and 50% RH, and the heat seal strength was measured. The heat sealability was evaluated according to the following criteria from the obtained heat seal strength value.
○: Heat seal strength is 300 g / 15 mm width or more.
X: Heat seal strength is less than 300 g / 15 mm width.

  The results obtained above are shown in Tables 1-2.

  From the results of Examples 1 to 10 in Table 1, the coextruded multilayer film of the present invention has a high easy-to-cut property in both the vertical direction and the horizontal direction. It was also found that the film has excellent suitability for packaging machinery, pinhole resistance due to bending, moderate heat seal strength, and excellent low-temperature impact resistance of the film.

  From the results of Comparative Examples 1 to 6 in Table 2, the following was found.

  The coextruded multilayer film of Comparative Example 1 is an example in which the resin layers (A) and (C) have the same resin composition and COP is used at a high concentration of 70%, but it is good without tearing, shrinkage and wrinkles. However, there was no difference in density between the resin (a1) and the resin (c1), and the heat seal (heat seal) start temperature was raised, so the heat seal strength was insufficient for both the horizontal and vertical seals. Furthermore, pinhole resistance and low temperature impact strength were found to be inferior.

  The coextruded multilayer film of Comparative Example 2 was obtained by using HDPE at a high concentration of 90% in the resin layer (A), but there was no tearing, shrinkage, or wrinkle, and the transverse sealability was relatively good. However, the pinhole resistance and the low temperature impact resistance were found to be inferior.

  The coextruded multilayer film of Comparative Example 3 was obtained by using HOPP 100% for the resin layer (A), but the rigidity was too high, and it was found that the pinhole resistance, the low temperature impact resistance, and the longitudinal sealability were inferior. .

  The co-extruded multilayer film of Comparative Example 4 is an example in which COP was used at a high concentration of 70% in the resin layer (B), but it was good without tearing, shrinkage and wrinkling, but pinhole resistance, It was found that the low-temperature impact strength was inferior.

  The coextruded multilayer film of Comparative Example 5 uses 80% linear low density polyethylene LLDPE (5) for the resin layer (A), but the tear strength is increased and the tearability is poor. Furthermore, it was found that shrinkage and wrinkling occurred at 130 ° C. or higher and the packaging machine suitability was poor.

  The coextruded multilayer film of Comparative Example 6 uses 70% ultra-linear low-density polyethylene VLLDPE (4) for the resin layer (B). It was found that the strength increased and the tearability was poor.

  The coextruded multilayer film of the present invention has high easy-cutting properties in both the vertical direction and the horizontal direction. In addition, it has excellent suitability for packaging machinery, low temperature pinhole resistance by bending, heat seal strength that can withstand heavy weight packaging, and excellent low temperature impact resistance of the film. Therefore, the coextruded multilayer film of the present invention is suitable for a packaging material for packaging foods, medicines, medical instruments, industrial parts, miscellaneous goods, magazines and the like.

Claims (9)

50-90 mass% of ethylene-based resin (a1) having a density of 0.910 g / cm ² or more and less than 0.945 g / cm ² and 10-50 mass of high-density polyethylene (a2) having a density of 0.950 g / cm ² or more. %, And a resin layer (A) mainly composed of a resin obtained by mixing
Density and 0.900 g / cm ² or more 0.940 g / cm ² less than the ethylene-based resin (b1) 50 to 90 wt% of density and cycloolefin resin (b2) is 0.950 g / cm ² or more high A resin layer (B) mainly composed of a resin obtained by mixing a total of 10 to 50% by mass of density polyethylene (b3);
A resin layer (C) mainly composed of an ethylene-based resin (c1) having a density of 0.880 g / cm ² or more and less than 0.910 g / cm ² ;
A coextruded multilayer film characterized by being laminated in the order of (A) / (B) / (C). The coextruded multilayer film according to claim 1, wherein the cyclic olefin resin (b2) is a norbornene polymer. The coextruded multilayer film according to claim 1 or 2, wherein the cyclic olefin-based resin (b2) in the resin layer (B) is used in an amount of 30% by mass or less. The coextruded multilayer film according to any one of claims 1 to 3, wherein a use ratio of the high-density polyethylene (b3) in the resin layer (B) is 40% by mass or less. The thickness of the said resin layer (B) is 30 to 80% of the total thickness of a coextruded multilayer film, The coextruded multilayer film in any one of Claims 1-4. The thickness of the said resin layer (C) is 5-35% of the total thickness of a coextruded multilayer film, The coextruded multilayer film in any one of Claims 1-5. The coextruded multilayer film according to any one of claims 1 to 6, wherein the total thickness of the coextruded multilayer film is 15 to 90 µm. A packaging material comprising the coextruded multilayer film according to any one of claims 1 to 7. The packaging material according to claim 8, wherein a tear start portion is provided in the seal portion.