JP4345924B2 - Easy tear multilayer film or sheet - Google Patents

Description

  The present invention relates to a multilayer film or sheet excellent in low-temperature heat sealability and bag breaking strength and excellent in lateral and / or longitudinal tearability suitable as a packaging material.

  Low density ethylene / α-olefin copolymer, known as LLDPE, is transparent, tear resistant, low temperature heat seal, hot tack, interstitial seal, heat seal strength, bag breaking strength, boil Excellent heat resistance for processing, etc., when used as a sealant layer for packaging materials, the filling ability of the contents by the packaging machine is good, the reliability for sealing is high, and the strength as a packaging material is high, Widely used as packaging material. However, since the tear strength of the film itself is high, when it is used for a pouch or bag of the type that is opened by tearing, there is a problem that the tearability is poor and the tearing direction is not constant.

  Even when other ethylene polymers such as high-density low-density polyethylene or ethylene / vinyl acetate copolymer, whose tear strength is smaller than LLDPE, are used for similar purposes, tearing is satisfactory to some extent. It could not be said that it was at the level, and there was a problem in using it as a packaging material for tear opening.

  In order to improve the tearability of such an ethylene polymer, proposals have already been made to use ionomer resins in combination. For example, an easily tearable film made of a polyolefin layer and an ionomer resin, which is a coextrusion stretched multilayer film by an inflation method, has been proposed (Patent Document 1). Further, it is a co-extruded multilayer film by a T-die method, in which LLDPE, low density polyethylene, ethylene / vinyl acetate copolymer and the like are surface layers, olefin resin 40 to 95% by weight, ionomer resin 60 to 5% by weight An easily tearable film having a resin composition layer made of (Patent Document 2) has been proposed.

  In the former proposal, it is necessary to mold under special stretching conditions, and in the latter proposal, it is necessary to adopt a T-die method which is not only high in manufacturing cost but also difficult to express remarkable lateral cut property.

JP-A-6-55632 Japanese Unexamined Patent Publication No. 2000-169597

  Therefore, an object of the present invention is to provide an ethylene polymer multilayer film or sheet that is excellent in heat sealability, bag breaking strength, and easy tearability and can be produced at low cost.

That is, according to the present invention, it is a coextrusion multilayer film or sheet by an inflation method, wherein at least one surface layer is composed of an ethylene polymer or a layer (A) of a resin composition mainly composed of this, One layer is a layer (B) of a resin composition comprising 60 to 20 parts by weight of a polyolefin resin and 40 to 80 parts by weight of an ionomer resin containing magnesium as an ion source . A multilayer film or sheet excellent in tearability is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the low-temperature heat-sealing property and the bag breaking strength are excellent, and the laminated | multilayer film or sheet | seat excellent in the tearability of the horizontal and / or vertical direction can be provided.

  Utilizing such characteristics, the easily tearable multilayer film or sheet of the present invention is a package for water such as pickles and strawberries, liquid food packaging such as liquid soup and liquid seasoning, liquid shampoo, and other foods such as neutral detergents. Liquid packaging, powder soup, flour, salt, spices and other powder packaging, dry food packaging such as snacks, processed meat, meat packaging such as chilled beef and side dish packaging, syringe syringes, medical supplies packaging such as infusion bags, etc. It can be used for general light packaging applications. Further, it can be used for heavy packaging represented by industrial materials such as rice bags, fertilizers, cement, etc., or as a base material for adhesive plaster or binding tape, or as a stretch film or wrap film.

  The easily tearable multilayer film or sheet of the present invention is produced by coextrusion by an inflation method, and at least one layer is composed of an ethylene polymer or a resin composition layer (A) mainly composed of the ethylene polymer. . The ethylene polymer constituting the layer (A) is a homopolymer of ethylene or a copolymer mainly composed of ethylene and other α-olefin and / or a polar monomer, other than the ionomer resin described later Means things. Specifically, an ethylene homopolymer or ethylene and a small amount of an α-olefin having 3 to 10 carbon atoms such as propylene, 1-butene, 1-heptene, 1-hexene, 1-octene, 4-methyl-1 -Random copolymers with pentene, etc., which are so-called high pressure method low density polyethylene (HP-LDPE), linear or linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene ( HDPE), an ethylene homopolymer or ethylene / α-olefin copolymer, and a copolymer of ethylene and a small amount of polar monomer, such as ethylene / vinyl acetate copolymer, ethylene and unsaturated carboxylic acid For example, copolymers with acrylic acid, methacrylic acid, monoethyl maleate, maleic anhydride, ethylene, etc. And unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, dimethyl maleate and the like, ethylene and the above Such as a copolymer of unsaturated carboxylic acid and unsaturated carboxylic acid ester, a copolymer of ethylene and carbon monoxide, and optionally a copolymer of unsaturated carboxylic acid ester or vinyl acetate. . These ethylene polymers may be a single polymer or a composition (mixture) of two or more ethylene polymers.

  The ethylene polymer has a melt flow rate at 190 ° C. and a load of 2160 g in the range of 0.01 to 50 g / 10 min, particularly 0.1 to 10 g / 10 min in consideration of film strength, workability and the like. Is preferred.

  Examples of the ethylene polymer include polyethylene such as high-pressure low-density polyethylene and linear low-density polyethylene, ethylene / vinyl acetate copolymer having a vinyl acetate content of 20% by weight or less, and (meth) acrylic acid ester content of 20% by weight. It is preferable to select from the following ethylene / (meth) acrylic acid ester copolymers, and it is known as linear low density polyethylene (LLDPE), especially considering transparency, heat sealability, heat resistance, bag breaking strength, etc. It is preferable to use a copolymer of ethylene and an α-olefin, particularly a low density polyethylene produced by a metallocene catalyst.

As the LLDPE, particularly density 895~940kg / ^{m 3,} preferably suitable ones 900~930kg / ^{m 3.} Further, those having a molecular weight distribution (Mw / Mn) measured by gel permeation chromatography (GPC) are usually 1.5 to 4.0, particularly 1.8 to 3.5. The LLDPE also has one or more sharp endothermic peaks obtained from an endothermic curve measured with a differential scanning calorimeter (DSC) at a rate of temperature increase of 10 ° C./min. Those in the range of 90 to 130 ° C, preferably 100 to 120 ° C are preferred.

  LLDPE as described above can be produced by a conventionally known production method using a multi-site catalyst having a Ziegler type catalyst as a representative example and a single site catalyst having a metallocene catalyst as a representative example. As a Ziegler type catalyst, a combined catalyst comprising a highly active titanium catalyst component and an organoaluminum compound catalyst component can be exemplified. Moreover, as a metallocene catalyst, the combined catalyst which consists of a metallocene compound and an organoaluminum oxy compound can be illustrated.

  In the easily tearable multilayer film or sheet of the present invention, together with the ethylene polymer or the resin composition layer (A) mainly composed of the ethylene polymer, the polyolefin resin is 60 to 20 parts by weight, preferably 55 to 25 parts by weight. Preferably, the resin composition comprises 40 to 80 parts by weight, preferably 45 to 75 parts by weight, more preferably 50 to 70 parts by weight (a total of 100 parts by weight of both) of the ionomer resin with respect to 50 to 30 parts by weight. The layer (B) is provided.

  The polyolefin resin used for the layer (B) is a polymer mainly composed of an olefin selected from an olefin homopolymer, a copolymer of olefins, and a copolymer of an olefin and a polar monomer, and an ionomer Something other than resin. Specifically, in addition to the ethylene polymer described as the constituent material of the layer (A), a homopolymer or a co-polymer mainly composed of propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, etc. A coalescence can be illustrated. Among them, the layer (A) having an above-described physical property selected from polyethylene, ethylene / vinyl acetate copolymer and ethylene / (meth) acrylic acid ester copolymer suitable for the ethylene polymer is used. It is preferable to use the same ethylene polymer as that used in the layer (A). For example, when LLDPE is used as the layer (A), it is preferable to use LLDPE as the polyolefin resin in the layer (B). A particularly suitable LLDPE is low density polyethylene polymerized with a metallocene catalyst.

  The ionomer resin which is a constituent component of the layer (B) is a resinous polymer in which part or all of the ethylene / unsaturated carboxylic acid copolymer is neutralized with metal ions. The ethylene / unsaturated carboxylic acid copolymer used as the base polymer of the ionomer resin preferably has an unsaturated carboxylic acid content of 1 to 25% by weight, particularly preferably 3 to 23% by weight, and more preferably 4 to 20% by weight. % Copolymer, not only a binary copolymer of ethylene and unsaturated carboxylic acid but also a multi-component copolymer in which other monomers are arbitrarily copolymerized. If the unsaturated carboxylic acid content is too low, it is not easy to obtain an easily tearable laminated film. If the content of the unsaturated carboxylic acid is too high, the hygroscopicity is increased and molding problems may occur. Come.

  Examples of the unsaturated carboxylic acid constituting the base polymer include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, monomethyl maleate, monoethyl maleate and the like. be able to. Particularly preferred is acrylic acid or methacrylic acid.

  Other monomers that may be optionally copolymerized include vinyl acetate, vinyl esters such as vinyl propionate, methyl acrylate, ethyl acrylate, isopropyl acrylate, isobutyl acrylate, and n-butyl acrylate. Illustrative examples include unsaturated carboxylic acid esters such as isooctyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, dimethyl maleate and diethyl maleate, carbon monoxide and sulfur dioxide. Can do. These other monomers may be copolymerized in the range of, for example, 0 to 30% by weight, preferably 0 to 20% by weight, but are generally obtained when the content of such other monomers is increased. Since the tearability of the ionomer tends to be impaired, a monomer which does not contain such a monomer or is copolymerized in a slight amount, for example, 15% by weight or less is used. Is preferred.

  As the ionomer resin, a resin in which 10 to 100 mol%, preferably 10 to 80 mol% of the carboxyl group of the copolymer is neutralized with metal ions can be used. If the neutralization degree is too low, the tearability is impaired. Here, the metal ion is an alkali metal such as lithium, sodium or potassium, an alkaline earth metal such as magnesium or calcium, zinc or the like, preferably lithium, sodium, potassium, magnesium or zinc, particularly preferably Is preferable because it is easy to obtain a laminated film or sheet having desired tear characteristics when an ionomer using magnesium as an ion source is used.

  As the ionomer resin, in consideration of moldability and film physical properties in the production of a coextruded film, the melt flow rate at 190 ° C. and a load of 2160 g is 0.1 to 50 g / 10 minutes, particularly 0.5 to 20 g / 10 minutes. It is preferable to use one.

  In the easily tearable multilayer film or sheet of the present invention, arbitrary additives may be blended in all layers or arbitrary layers as long as the physical properties are not impaired. Examples of such additives include an antioxidant, a light stabilizer, a heat stabilizer, an ultraviolet absorber, an antistatic agent, an adhesive, a lubricant, an antiblocking agent, a pigment, and a dye.

  The easily tearable multilayer film or sheet in the present invention has a structure in which the layer (A) and the layer (B) are coextruded by an inflation method, and is mainly intended for a packaging material having the (A) layer as a heat seal layer. In that case, a two-layer structure such as (A) / (B), a three-layer structure such as (A) / (B) / (A), and particularly good surface characteristics. A three-layer structure such as (A) / (B) / (A) is preferred. However, a three-layer structure such as (B) / (A) / (B) can be used as desired.

  The easily tearable multilayer film of the present invention has a tear strength of 5 to 70 N / mm, preferably 10 to 50 N / mm in at least one of longitudinal and transverse directions, preferably both longitudinal and transverse directions, and is substantially displaced in the tearing direction. Does not occur. If either one of the tear strengths is smaller than the above range, the bag breaking strength is too small, which is not preferable. If the strength in both the vertical and horizontal directions exceeds 70 N / mm, the tearability is deteriorated, which is not preferable. .

  Such an easily tearable multilayer film or sheet having such properties can be obtained by appropriately selecting the properties of the raw materials used, the molding conditions of the coextruded film, the thickness ratio of each layer, and the like. In particular, the total thickness is preferably 3 to 500 μm, particularly preferably 10 to 200 μm, and the total thickness of the layer (B) is preferably 20 to 80%, particularly 30 to 70% of the total thickness of the film or sheet. . In an easily tearable multilayer film or sheet having a three-layer structure such as (A) / (B) / (A) as described above, or a three-layer structure such as (B) / (A) / (B) The thickness of the surface layer is 1 to 150 μm, particularly 5 to 100 μm, the thickness of the intermediate layer is 1 to 200 μm, particularly 5 to 150 μm, and the thickness ratio of the surface layer to the intermediate layer is 20/80 to 80/20, preferably 30 / 70 to 70/30 is preferable.

  The easily tearable multilayer film or sheet of the present invention can be used as it is as various packaging materials and tape materials. In addition, it is possible to use the easily tearable multilayer film or sheet of the present invention laminated on a substrate film for the purpose of imparting tearability or further low-temperature heat sealability, impact resistance, etc. to various substrate films. it can. By doing so, it is possible to obtain a laminated film or sheet exhibiting good tearability, preferably a laminated film or sheet having a transverse and / or longitudinal tear strength of 70 N / mm or less. In this case, in order to obtain an easily tearable laminated film or sheet, the thickness of the easily tearable multilayer film or sheet of the present invention is 0.5 times or more, preferably 1 to 20 times the thickness of the substrate film. It is preferable to do. Such a substrate film may be a single layer or a multilayer structure composed of two or more layers. Examples of the base film include, for example, polyester such as polyamide, polyethylene terephthalate, ethylene / vinyl alcohol copolymer, polyvinyl alcohol, polyacrylonitrile, polypropylene such as propylene homopolymer and propylene / α-olefin copolymer, Stretched or unstretched films of thermoplastic polymers such as polyethylene homopolymers and ethylene / α-olefin copolymers such as polyethylene, poly-4-methyl-1-pentene, and polyvinyl chloride, aluminum foil, aluminum vapor deposited film , Vapor deposition films of silica, alumina, magnesia and the like. In these, it is preferable to use the film of polyester, polyamide, or polypropylene, especially these stretched films. There is no particular limitation on the method of laminating the easily tearable multilayer film or sheet and the substrate of the present invention, but the sandwich lamination method or the dry lamination method is preferably used.

  When the easily tearable multilayer film obtained by the present invention is used as a packaging bag, by providing a cut portion, tearing in the cutting direction is facilitated, and it is possible to easily and cleanly cut the cut. . Moreover, the opening of the bag can be facilitated by providing the fine holes. The micropores can be formed by a method using a laser, a method of penetrating a diamond needle, a method of blending an inorganic filler in a film raw material, or the like. The portion to be provided with the fine holes may be only the seal portion, or may extend over the entire surface.

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, the composition and physical properties of the raw materials used in Examples and Comparative Examples, and the physical property measuring methods of the obtained stretched film are as follows.

1. Resin raw material (1) Metallocene catalyst linear low density polyethylene (mPE)
Evolue SP2320 manufactured by Sumitomo Mitsui Polyethylene Co., Ltd.
Density 919kg / m ³
Melt flow rate 1.9g / 10min Melting point (DSC method) 118 ° C
(2) Ethylene / methacrylic acid copolymer ionomer (Na ionomer)
Methacrylic acid content 10% by weight
Degree of neutralization 50% neutralization-sodium salt Melt flow rate 1.3 g / 10 min (3) Ethylene / methacrylic acid copolymer ionomer (Mg ionomer)
Methacrylic acid content 15% by weight
Degree of neutralization 15% neutralization-Magnesium salt Melt flow rate 0.7g / 10min

1. Physical property measuring method (1) Tear strength Tear strength in the vertical and horizontal directions was measured by a trouser tear method (JIS K7128-1).

[ Reference example ]
Using a multi-layer inflation film forming apparatus equipped with a three-layer inflation die, the mPE was passed through the outer layer extruder to the outer layer of the die, and 50 parts by weight of the mPE and the Na ionomer 50 were passed through the intermediate layer extruder. A part by weight of the pellet dry blend is supplied to the inner layer through the outer layer extruder at the condition of 180 ° C., and is bonded inside the die preheated to 180 ° C., the outer layer is 15 μm, the intermediate layer A three-layer blown film having a thickness of 30 μm and an inner layer of 15 μm was obtained. The evaluation results are shown in Table 1.

[Example 1 ]
A three-layer blown film was obtained in the same manner as in the reference example except that the composition of the resin composition of the intermediate layer was changed to 50 parts by weight of mPE and 50 parts by weight of Mg ionomer. The evaluation results are shown in Table 1.

[Example 2 ]
A three-layer blown film was obtained in the same manner as in the reference example except that the composition of the resin composition of the intermediate layer was changed to 30 parts by weight of mPE and 70 parts by weight of Mg ionomer. The evaluation results are shown in Table 1.

[Comparative Example 1]
A three-layer blown film was obtained in the same manner as in Example 1 except that mPE was used instead of the resin composition for the intermediate layer. The evaluation results are shown in Table 1.

Claims (7)

A co-extruded multilayer film or sheet by an inflation method, wherein at least one layer is composed of an ethylene polymer or a layer (A) of a resin composition mainly composed of this, and the other at least one layer is a polyolefin resin 60. A multilayer film excellent in lateral and / or longitudinal tearing, characterized in that it is a layer (B) of a resin composition comprising 20 to 80 parts by weight of ionomer resin containing magnesium as an ion source and 40 to 80 parts by weight Sheet. A layer (B) made of a resin composition comprising 60 to 20 parts by weight of a polyolefin resin and 40 to 80 parts by weight of an ionomer resin containing magnesium as an ion source is used as an intermediate layer, and an ethylene polymer or a resin composition mainly composed of this is used. The multilayer film or sheet excellent in tearability in the transverse and / or longitudinal direction according to claim 1 , wherein the layer (A) is both surface layers. It consists of a resin composition comprising an ethylene polymer or a resin composition layer (A) mainly comprising this as an intermediate layer, and an polyolefin resin 60-60 parts by weight and an ionomer resin 40-80 parts by weight of magnesium as an ion source. The multilayer film or sheet excellent in tearing property in the transverse and / or longitudinal direction according to claim 1 , wherein the layer (B) is both surface layers. The thickness ratio of the layer (B) to the layer (A) is 20/80 to 80/20. The multilayer film or sheet excellent in lateral and / or longitudinal tearability according to any one of claims 1 to 3. . The thickness of the both surface layers is 1-150 [mu] m, the thickness of the intermediate layer is 1 to 200 [mu] m, the horizontal and / or according to claim 2 or 3 thickness ratio of both surface layers and the intermediate layer is 20/80 to 80/20 Multilayer film or sheet with excellent longitudinal tearability The multilayer film or sheet excellent in lateral and / or longitudinal tearability according to any one of claims 1 to 5 , wherein the polyolefin resin of the layer (B) is a low-density polyethylene produced by a metallocene catalyst. The multilayer film or sheet excellent in lateral and / or longitudinal tearability according to any one of claims 1 to 6 , wherein the ethylene polymer of the layer (A) is a low-density polyethylene produced by a metallocene catalyst.