JP2007030269A - Stretch shrink laminated film and manufacturing method thereof - Google Patents

Abstract

[PROBLEMS] To provide a stretch shrink laminated film having excellent low-temperature shrinkage and excellent packaging finish.
An ionomer-based mixture comprising at least three layers, wherein both surface layers are mainly composed of an ethylene-based polymer (A) component, and an intermediate layer is composed of the following components (B), (C) and (D): The resin composition is the main component, and the mixing mass ratio is (B) / (C) = 70-40 / 30-60, (B) / (D) = 95-70 / 5-30, and 80 ° C. oil. The total value of the heat shrinkage in the vertical and horizontal directions when immersed for 10 seconds in the bath is 30% or more.
(B) 10-20 parts by mass of unsaturated carboxylic acid, ionomer resin which is an ethylene / unsaturated carboxylic acid having a degree of neutralization by metal ions of 40-80%. (C) 5-20% by mass of unsaturated carboxylic acid. , Ethylene / unsaturated carboxylic acid copolymer (D) having a melt flow rate of 1 to 30 g / 10 min.

Description

  The present invention relates to a stretch shrink film and a method for producing the same, and more specifically, mainly prepackages of various trays and containers containing fresh foods and processed foods, stretch shrink laminated films used for overlap shrink film applications, and It relates to the manufacturing method.

  As a shrink film having heat shrinkability used mainly for pre-packages of various trays and containers containing fresh foods and processed foods, and for an overlap shrink film, it may be abbreviated as polyvinyl chloride (hereinafter referred to as PVC). ) Based films and polyolefin (hereinafter sometimes abbreviated as PO) based films are known. This is because a shrink film made of PVC or PO-based material satisfies the user's requirements relatively widely, including the main required characteristics such as mechanical strength, transparency, shrinkage characteristics, and other practical characteristics. .

  However, among these PVC-based films, there is a concern about the problem of waste disposal, and thus a shrink film made of a material other than PVC has been desired. Therefore, in the above applications, at present, the shrink film made of almost PO system occupies the market.

  Next, the shrink film in the application is roughly divided into two according to the container used mainly. One is a high-shrink type shrink film mainly used for overlapping shrink packaging of containers with lids such as lunch boxes and side dishes at convenience stores, and the other is expanded polystyrene used mainly for stretch packaging. It is a stretch shrink film used in a packaging method in which a lidless tray made of a polypropylene material is used as a container, and after this is stretch-wrapped, it is shrink-wrapped mainly to eliminate wrinkles and develop tight film tension.

  Here, in the packaging method using the high shrink type shrink film, a fusing seal type packaging machine called a horizontal pillow type is mainly used. In the present packaging method, first, a roll with a needle is passed through the film while it is being transported, and holes are formed in the film at a constant pitch. Next, a film is formed in a cylindrical shape so as to wrap the container, the film is pressure-bonded with a roller in the longitudinal direction at the bottom of the container and thermally sealed, and then the front and back of the container are fused and sealed. Thereafter, the film is passed through a shrink tunnel, and shrink wrapping is performed while air is released from the needle holes of the film formed earlier. In the packaging method, in order to obtain a tight packaging finish corresponding to containers of various shapes and sizes, physical properties such as a high shrinkage rate and a film that does not tear with a needle hole are required. For these reasons, various materials are combined in a specific amount to produce a multilayer structure, or a product is manufactured by a manufacturing method using a complex process such as crosslinking with an electron beam. It is difficult, and generally the manufacturing cost of the film is high (see, for example, Patent Documents 1 and 2).

  On the other hand, in the packaging method using stretch shrink, a tray used for normal stretch packaging is overlapped with a film, and the film is folded into the bottom of the tray and then shrink-wrapped. A wrapping machine in which a shrink tunnel is added to a subsequent process of a folding type wrapping machine called a horizontal pillow type or a push-up type is used. Here, the stretch wrapping is a wrapping method that expresses a wrapping finish such as wrinkle elimination and bottom sealability mainly due to viscoelastic properties such as a stress-strain curve and stress relaxation of the stretch film to be used. On the other hand, in packaging using stretch shrink film, a packaging method that develops packaging finish such as wrinkle elimination and bottom sealability after stretch packaging by passing the heat sealing process and shrink tunnel at the bottom after stretch packaging And the fact that a tight packaging finish can be manifested is a significant difference from ordinary stretch packaging.

  Among the packaging machines described above, the horizontal pillow method has a high packaging capacity (usually about 60 to 80 packs / minute), but the packaging line is long, so the efficiency of changeover operations such as size switching is poor. It is widely used in pack centers and food processing factories that are packed in large quantities and have relatively little changeover work, and products are arranged and displayed at each store after packaging. On the other hand, the push-up finger type has a low packaging capacity (usually about 25 to 50 packs / minute), but can accommodate a relatively large number of tray sizes with one size film (for example, a roll having a width of 350 mm), and is relatively compact. Because it requires less space, it has been introduced to pack centers and other places, but it is mainly used in supermarket in-stores (backyards).

  In this way, packaging of fresh products, etc. is broadly divided into those that are packaged at a pack center and delivered to each store, and those that are packaged at an in-store and displayed directly in the store. In terms of overall cost from the standpoint of efficiency, the in-store packaging ratio is decreasing, and the ratio of consolidation, large-volume, and high-speed packaging at pack centers is increasing. Here, in packaging at the pack center, about 2 to 4 packs of packed products are stacked, packed in a container, and delivered to each store by a cold car. For this reason, with normal stretch wrapping alone, film tearing or film sagging due to stacking may occur after delivery due to vibration during transportation or friction between products. There have been problems such as reducing the display effect and in some cases requiring repacking.

  In order to solve these problems, there is a tendency to increase the use of a stretch shrink film that can provide a tight film tension as compared with a stretch film. Since the packaging machine is the same as a normal stretch packaging machine, a shrink tunnel is added to the post-packaging process, and the tray shape does not vary. A high shrinkage rate is not required, and a sufficiently good packaging finish can be obtained with a relatively small shrinkage rate. However, the contents are often fresh foods, and heat shrinkage characteristics (hereinafter referred to as low temperature shrinkage in the present invention) at a relatively low temperature (usually about 80 ° C.) are required.

  Next, the conventional shrink wrapping film manufacturing method is a tenter method in which a raw film or a raw tube is collected by once cooling and solidifying a melt-extruded resin, and then reheated and stretched. Tubular method is mainly used. This is considered to be because desired heat shrinkage characteristics and film physical properties can be imparted relatively easily by adjusting mainly the temperature at the time of reheating, the draw ratio and the draw speed.

  On the other hand, the method for producing a film for stretch packaging is a method in which a melt-extruded resin is extruded into a cylindrical shape from an annular die without cooling and solidifying once, and air is blown into this cylinder to expand the molten cylinder. The law is mainly adopted. This is probably because the inflation method generally has a relatively wide condition setting range than the tenter method or the tubular method, can be stably produced, and the cost of manufacturing equipment is also low. In general, in the inflation method, the raw material resin is heated to a temperature equal to or higher than the melting point (Tm), extruded from a circular die into a cylindrical shape, and blown into a molten cylinder to be inflated to form a film. Drawing is performed in the longitudinal direction by taking-up. However, at the time of stretching, since the resin is in a high temperature region and has a low elastic modulus and viscosity, it is a substantially unstretched film from the viewpoint of imparting heat-shrinkable strain only by inflation molding. Although heat shrinkability is exhibited, it is usually difficult to obtain a film having a sufficient orientation that exhibits a shrinkage rate (low temperature shrinkability) at a relatively low temperature (about 80 ° C.).

  Therefore, if a stretch shrink film having excellent low-temperature shrinkage can be produced even with an inflation molding machine having a general good productivity and low manufacturing equipment costs, it is an effective means for solving the above-mentioned problems relating to the production cost. It is thought that it becomes. Here, an ionomer resin is mentioned as one of the resins having high elastic modulus and high viscosity when melted. Examples of known literature related to stretch films, wrap films, and shrink (heat-shrinkable) films using ionomer resins include the following Patents 3 to 5.

  Patent Document 3 proposes a stretch film for food packaging in which a layer made of an ethylene / vinyl acetate copolymer having a vinyl acetate content of 5 to 40% by mass is laminated on both surfaces of a layer made of an ionomer resin. . Such a film has properties similar to those of a PVC film and is also excellent in automatic packaging suitability. Specifically, Suron A1650 (base polymer: ethylene / methacrylic acid copolymer, methacrylic acid content: 9% by mass, neutralized metal ion species: zinc, MFR: 1.5 g / 10 as an ionomer resin) This is the only example in which a three-layer stretch film having a blow-up ratio of 5 times and a thickness of each layer of 12.5 μm / 5 μm / 12.5 μm is obtained with a multilayer inflation molding apparatus. Has been. However, in this patent, the ionomer resin is mainly intended to improve the heat resistance during heat sealing, and in order to obtain the necessary physical properties as a stretch film, the thickness of the intermediate layer should not exceed the thickness of each of the front and back layers. Is necessary. For these reasons, the patent is not intended to exhibit shrinkage characteristics with an ionomer resin, and even if shrinkage characteristics are manifested, the intermediate layer has a low thickness ratio and is sufficiently low temperature shrinkable. Is not suitable for a stretch shrink film.

  Patent Document 4 is not intended to provide a non-halogen multi-layer wrap film that can be manufactured by high-speed processing, and has excellent optical properties, adhesion to a packaging material, and cutability during use, and a method for producing the same. An ethylene / unsaturated ester copolymer is formed on both sides of a layer composed of an ethylene / unsaturated carboxylic acid copolymer ionomer having a saturated carboxylic acid content of 3 to 20% by mass and a degree of neutralization by metal ions of 0.1 to 10%. A multilayer wrap film in which layers composed of the above are laminated and a method for producing the same by a coextrusion T-die film forming machine have been proposed. However, this patent mainly aims at high-speed molding in a T-die molding machine, and is not intended to express shrinkage characteristics with an ionomer resin.

  In Patent Document 5, (a) one or two outer layers of a material selected from the group consisting of polyethylene, polypropylene, propylene / ethylene copolymers and blends thereof, and (b) necessary to orient the materials of the outer layer. An ethylene / acid copolymer and related ionomer; an ethylene / acid / acrylate terpolymer and related ionomer; any of the above and up to about 50% ethylene vinyl acetate; A multilayer heat-shrinkable film comprising: a blend of an ethylene / ester copolymer and up to about 50% ethylene vinyl acetate; and a core layer of a material selected from the group consisting of combinations of the above materials, The multilayer heat shrinkable film and the multilayer, wherein the core layer has a thickness comprising about 50-95% of the total thickness of the heat shrinkable film A method for producing a shrinkable film, wherein a multilayer film comprising one or two outer layers and the core layer is at least the orientation temperature of the substance in the one or two outer layers but less than the melting point of the substance A method of stretching at a temperature has been proposed. Here, the patent mainly aims to obtain a multilayer heat-shrinkable film having a high shrinkage rate and a low shrinkage force (shrinkage stress), and from the gist of the invention, the melting point of the substance in the outer layer ≧ The relationship of stretching temperature ≧ orientation temperature of the substance in the outer layer (generally 110 ° C. or higher) ≧ melting point of the substance in the core layer holds. Moreover, it describes that the substance which has a low friction coefficient is preferable for an outer layer. Furthermore, as a method for orienting the film, a known method can be adopted, but a preferable method is described as a “bubble” method (tubular stretching method), and a specific method is also described. Examples are shown in Method 1 as a tubular stretching method and as Method 2 as a tenter stretching method. That is, these methods are methods in which a melt-extruded resin is once rapidly cooled and solidified, and then a raw film or a raw tube is collected and then reheated and stretched.

Japanese Examined Patent Publication No. 1-47311 Japanese Patent Publication No. 5-64589 Japanese Patent Laid-Open No. 54-24982 JP 2000-135760 A Japanese Patent Publication No. 3-80627

  An object of the present invention is to provide a stretch shrink that is excellent in low-temperature shrinkage, tight film tension after shrinkage, and packaging finish in an automatic packaging machine, etc. It is to provide a laminated film.

As a result of intensive studies, the present inventors have found that the above problems can be solved by setting the ethylene-based polymer as both surface layers and the intermediate layer mainly composed of a specific mixed resin as a specific thickness ratio. The present invention has been completed.
That is, the present invention
(1) A laminated film composed of at least three layers, wherein both surface layers are composed mainly of the component (A) which is an ethylene polymer, and the intermediate layers are the following (B), (C) and (D The mixing mass ratio of the mixed resin composition comprising the ionomer-based mixed resin composition consisting of the components as the main component and forming the intermediate layer is (B) / (C) = 70-40 / 30-60, and (B) / (D) = 95-70 / 5-30, and the total value of the heat shrinkage in the vertical and horizontal directions when immersed in an oil bath at 80 ° C. for 10 seconds is 30% or more. Stretch shrink laminated film.
(B) An ionomer resin which is an ethylene / unsaturated carboxylic acid having an unsaturated carboxylic acid content of 10 to 30% by mass and a degree of neutralization by metal ions of 40 to 80%. (C) An unsaturated carboxylic acid content of 5 to 20% by mass. An ethylene / unsaturated carboxylic acid copolymer having a melt flow rate (JIS K7210 190 ° C., load 21.18 N) of 1 to 30 g / 10 min. (D) Crystalline polyamide having a melting point (JIS K7121) of 240 ° C. or less. 2) The ethylene / unsaturated carboxylic acid copolymer as component (C) is at least one ethylene polymer selected from ethylene-acrylic acid ester copolymers and ethylene-methacrylic acid ester copolymers. The stretch shrink laminated film according to (1), wherein
(3) Component (A) which is an ethylene polymer is low density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer and ethylene -The stretch shrink laminated film according to (1) or (2), which is at least one ethylene polymer selected from methacrylic acid ester copolymers.
(4) The component (A) which is an ethylene polymer has a vinyl acetate content of 8 to 30% by mass and a melt flow rate (JIS K7210, 190 ° C., load 21.18N) of 0.2 to 10 g / 10. The stretch shrink laminated film according to (1) or (2), wherein the stretch shrink laminated film is an ethylene-vinyl acetate copolymer.
(5) The total value of the shrinkage stress values in the longitudinal and transverse directions at 80 ° C. according to the stress / strain control TMA (TMA / SS) of the film is in the range of 0.5 to 3 MPa (1) to The stretch shrink laminated film according to any one of (4).
(6) The melt-extruded resin is manufactured by the inflation method, which is a method of extruding into a cylindrical shape from an annular die, and blowing the air into the cylinder without rapidly solidifying it. The stretch shrink laminated film according to any one of (1) to (5).

  Another object of the present invention is achieved by producing the stretch shrink laminated film according to any one of the above (1) to (5) by an inflation method.

  According to the present invention, there is provided a stretch shrink laminated film having excellent low-temperature shrinkability even in the inflation method, tight film tension after shrinkage and excellent packaging finish in an automatic packaging machine, and having mechanical properties suitable for packaging by an automatic machine. Can be provided.

Hereinafter, the present invention will be described in detail.
It should be noted that the upper and lower limits of the numerical range in the present invention are those of the present invention as long as they have the same operational effects as those in the numerical range even if they are slightly outside the numerical range specified by the present invention. It is included in the equivalent range. The main component in the present invention is a component containing at least 50% by mass, preferably 70% by mass or more, and more preferably 80% by mass or more.

The stretch shrink laminated film of the present invention is a laminated film composed of at least three layers, and both surface layers are composed mainly of the component (A) which is an ethylene polymer, and the intermediate layer is the following (B), (B) / (C) = 70-40 / 30- The mixing mass ratio of the mixed resin composition which has the ionomer type | system | group mixed resin composition which consists of (C) and (D) component as a main component, and forms an intermediate | middle layer. 60, and (B) / (D) = 95-70 / 5-30, and the total value of the heat shrinkage in the vertical and horizontal directions when immersed in an oil bath at 80 ° C. for 10 seconds is 30%. It is the above.
(B) An ionomer resin which is an ethylene / unsaturated carboxylic acid having an unsaturated carboxylic acid content of 10 to 30% by mass and a degree of neutralization by metal ions of 40 to 80%. (C) An unsaturated carboxylic acid content of 5 to 20% by mass. An ethylene / unsaturated carboxylic acid copolymer having a melt flow rate (JIS K7210 190 ° C., load 21.18 N) of 1 to 30 g / 10 min. (D) Crystalline polyamide having a melting point (JIS K7121) of 240 ° C. or less.

  Here, the component (A) which is an ethylene polymer as a main component used in the both surface layers is low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, medium density polyethylene, high density polyethylene and ethylene. An ethylene-based copolymer, that is, ethylene and an α-olefin having 3 to 10 carbon atoms such as propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1; vinyl acetate, Vinyl esters such as vinyl propionate; unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate; and ionomers thereof; among unsaturated compounds such as conjugated and non-conjugated dienes Copolymer or multi-component copolymer with one or more comonomers selected, or It mentioned mixed composition of. The ethylene unit content of the ethylene polymer is usually more than 50% by mass.

  Among these ethylene polymer (A) components, low density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer and At least one ethylene polymer selected from ethylene-methacrylic acid ester copolymers is preferred. Examples of the acrylate ester include methyl acrylate and ethyl acrylate. Examples of the methacrylic acid ester include methyl methacrylate and ethyl methacrylate.

  Moreover, in the component (A) which is the ethylene polymer, the vinyl acetate content is 8 to 30% by mass, and the melt flow rate (hereinafter sometimes abbreviated as MFR) (JIS K7210, 190 ° C., Most preferred is an ethylene-vinyl acetate copolymer having a load of 21.18 N) of 0.2 to 10 g / 10 min.

  Here, if the vinyl acetate content is 8% by mass or more, the resulting film will not be hard, the flexibility and elastic recovery will be good, the transparency and heat shrinkage characteristics of the entire film will not be impaired, It is preferable because surface tackiness is also easily exhibited. On the other hand, if it is 30% by weight or less, heat resistance, film strength and the like are sufficiently secured, and since the surface tackiness is not too strong, the film unwinding property and appearance are favorable. From these facts, the vinyl acetate content is preferably 10 to 28% by mass, more preferably 12 to 25% by mass.

  Also, if the MFR is 0.2 g / 10 min or more, the extrusion processability is stable, while if it is 10 g / 10 min or less, the film forming stability is obtained even in the inflation molding, and the thickness unevenness and the mechanical strength are improved. This is preferable because reduction, variation and the like are reduced. From these things, MFR becomes like this. Preferably it is 0.3-8, More preferably, it is 0.5-5.

  The method for producing the ethylene polymer (A) component is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite represented by a Ziegler-Natta type catalyst. Examples thereof include a slurry polymerization method, a solution polymerization method, a bulk polymerization method, a gas phase polymerization method and the like using a single site catalyst typified by a catalyst and a metallocene catalyst, and a bulk polymerization method using a radical initiator.

  In the component (A) which is an ethylene polymer constituting both the surface layers, various additives such as an antioxidant, an antifogging agent, an antistatic agent, a lubricant, and a nucleating agent are mixed as necessary. It doesn't matter.

  Next, the component (B), which is an ionomer resin used for the intermediate layer, contains at least a part of an unsaturated carboxylic acid component of a copolymer composed of ethylene, an unsaturated carboxylic acid, and optionally another unsaturated compound as a metal. It can be obtained by neutralizing at least one of ions and organic amines. The ionomer resin can also be obtained by saponifying at least a part of an unsaturated carboxylic acid ester component of a copolymer comprising ethylene, an unsaturated carboxylic acid ester, and other unsaturated compounds as optional components. .

  In the copolymer containing ethylene and an unsaturated carboxylic acid as a raw material for the ionomer resin and other unsaturated compounds as optional components, the unsaturated carboxylic acid preferably has about 3 to 8 carbon atoms, specifically, Acrylic acid, methacrylic acid, fumaric acid, itaconic acid, maleic anhydride, monomethyl maleate, monoethyl maleate and the like are used. Among these, acrylic acid or methacrylic acid is preferably used. Further, other typical unsaturated compounds as optional components are unsaturated esters, and specific examples thereof include unsaturated esters of saturated carboxylic acids such as vinyl acetate, acrylic esters and methacrylic esters. Can be mentioned. In addition, these can be used individually by 1 type or in combination of 2 or more types.

As the neutralization component of ^{copolymer, Na +, K +, Li} +, Ca 2+, Mg 2+, Zn 2+, Cu 2+, Co 2+, Ni 2+, Mn 2+ And monovalent to trivalent metal cations such as Al ³⁺ (hereinafter sometimes abbreviated as metal ions) or organic amines. In addition, these can be used individually by 1 type or in combination of 2 or more types. Of these, those neutralized with Zn ²⁺ are particularly preferred.

  In the present invention, in the copolymer as the ionomer raw material, the ethylene content is 50 to 97% by mass, preferably 60 to 95% by mass, and the unsaturated carboxylic acid content is 10 to 30% by mass, preferably 12 to 12%. 20% by mass and other unsaturated compounds having a polymerization composition of 0 to 40% by mass, preferably 0 to 20% by mass are suitably used. The neutralization degree is preferably obtained by neutralizing 40 to 80%, preferably 45 to 60% of the amount of unsaturated carboxylic acid in the copolymer component with the metal cation. Here, within the range of the polymerization composition and the degree of neutralization, the crystallinity of the ionomer resin is reduced to some extent, so that it is difficult to crystallize under cooling conditions during the molding process, and the transparency of the film can be maintained. Therefore, it is preferable. At the same time, mainly due to the cohesive strength of ionic crosslinks, it is possible to impart good low temperature heat shrinkage properties (low temperature shrinkability) by stretching in the cooling process from a molten state such as inflation molding. Therefore, it is preferable. In addition, an ionomer resin can be used individually by 1 type or in combination of 2 or more types.

  In the ionomer resin, when the carboxyl group in the copolymer is neutralized with a metal cation or the like, the neutralized portion is ionized. As the degree of neutralization increases, the ionized portion aggregates due to the ionic bond force to form ionic crosslinks. The ionic crosslinks are aggregated by ionic bonds, and when they are subjected to a force greater than the ionic bond strength, the agglomerated portion is broken, but at a force smaller than the ionic bond force, a pseudo-crosslinked state is obtained. Therefore, the melt viscosity increases with the amount of neutralization, and the effect of increasing the melt viscosity becomes greater when the melting point of the ionomer resin is close. Here, within the range of the polymerization composition and the degree of neutralization, there is no increase in extrusion performance, specifically an excessive melt viscosity due to these actions, for example, in the cooling process from a molten state such as inflation molding. At the time of stretching, the ionic crosslinking remains in a pseudo-crosslinked state, so that it is considered possible to impart a low temperature heat shrinkage property (low temperature shrinkability) suitable for the stretch shrink film.

  It is preferable that MFR (JIS K7210, 190 degreeC, load 21.18N) of (B) component which is an ionomer resin used for this invention is 0.2-5 g / 10min. Within such a range, back pressure or the like does not increase suddenly during extrusion molding, and it is possible to obtain inflation moldability such as bubble stability and mechanical properties suitable for a stretch shrink film. From these things, MFR becomes like this. Preferably it is 0.3-4.0, More preferably, it is 0.5-3.0.

    The production method of the component (B) that is an ionomer resin used in the present invention is not particularly limited, and for example, a known production method disclosed in Japanese Patent Publication No. 39-6810 can be used. In addition, a copolymer resin such as ethylene and acrylic acid or methacrylic acid that does not contain metal ions is used as a raw material, and after addition of acetylacetone metal complex, metal oxide, fatty acid metal salt, etc. Sometimes an ionomer resin can be obtained.

  In the present invention, commercially available raw materials can also be used. Specific products of ionomer resins include “High Milan”, a trade name of Mitsui DuPont Polychemicals. In addition, as specific products of copolymer resins such as ethylene and acrylic acid or methacrylic acid that do not contain metal ions, the product name “Nucleel” from Mitsui DuPont Polychemical Co., Ltd. and the product name “Novatech EAA” from Nippon Polychem Co., Ltd. Or the like.

  Next, (C) component which is ethylene and unsaturated carboxylic acid used for an intermediate | middle layer is at least 1 type or 2 types chosen from ethylene-acrylic acid ester copolymer and ethylene-methacrylic acid ester copolymer A mixed composition is mentioned. Examples of the acrylate ester include methyl acrylate and ethyl acrylate. Examples of the methacrylic acid ester include methyl methacrylate and ethyl methacrylate.

  In the present invention, in the ethylene-acrylic acid ester and / or ethylene-methacrylic acid ester copolymer, the acrylic acid and methacrylic acid content is preferably 5 to 20% by mass, preferably 5 to 18% by mass. It is done. Here, the range of the polymerization composition is preferable because the compatibility with the ionomer resin is good and the transparency of the film can be maintained. At the same time, it is preferable because mechanical characteristics suitable for packaging by an automatic machine can be obtained.

  It is preferable that MFR (JIS K7210, 190 degreeC, load 21.18N) of (C) component which is ethylene and unsaturated carboxylic acid used for this invention is 1-30 g / 10min. Within such a range, it is preferable because dispersion in the ionomer resin is good, and it is possible to obtain inflation moldability such as bubble stability and mechanical properties suitable for a stretch shrink film. From these things, MFR becomes like this. Preferably it is 1.5-25, More preferably, it is 2.0-20.

  The manufacturing method of (C) component which is ethylene and unsaturated carboxylic acid used for this invention is not specifically limited, Well-known manufacturing methods, such as a high pressure radical polymerization method, can be used.

  Next, the component (D) which is a crystalline polyamide used for the intermediate layer includes, for example, dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, dodecanoic acid, terephthalic acid, isophthalic acid, and 1,4-cyclohexyldicarboxylic acid. , Polycondensation with diamines such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, decamethylenediamine, 1,4-cyclohexyldiamine, m-xylenediamine, such as ε-caprolactam, ω-laurolactam Cyclic lactam ring-opening polymerization, polycondensation of aminocarboxylic acids such as 6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, 1,2-aminododecanoic acid, or the above-mentioned cyclic lactam, dicarboxylic acid and diamine Obtained from copolymers, etc. , Nylon 11, nylon 12, copolymer nylon, nylon MXD6, nylon 46, and the like. Here, in the application where transparency is regarded as important, it is preferable to employ a component having a refractive index close to that of the component (B), and nylon 12 can be preferably used in the present invention.

  In the present invention, the crystalline polyamide preferably has a melting point (conforming to JIS K7121) of 240 ° C. or less, more preferably a melting point of 200 ° C. or less, and particularly a melting point of less than 170 ° C. Is preferred. If the melting point is in the above range, it is not necessary to excessively increase the melt-kneading temperature for obtaining the ionomer-based mixed resin composition for forming the intermediate layer of the present invention, so that thermal degradation of the ionomer resin can be suppressed. . Moreover, since the extrusion temperature at the time of molding can be lowered as much as possible in accordance with the load of the extruder, it is possible to impart good heat shrinkage characteristics (low temperature shrinkability) at low temperatures as a result.

  The MFR (JIS K7210, compliant) of the component (B), which is a crystalline polyamide used in the present invention, is preferably 0.5 to 50 g / 10 minutes. Within such a range, it is preferable because dispersion in the ionomer resin is good and inflation moldability such as bubble stability can be obtained. From these things, MFR becomes like this. Preferably it is 2-40, More preferably, it is 5-30.

    The manufacturing method of (D) component which is crystalline polyamide used for this invention is not specifically limited, A well-known manufacturing method can be used.

  In the present invention, commercially available raw materials can also be used. Specific examples of crystalline polyamide products include Ube Industries 'product names “UBE Nylon” and “Uvesta”, Toray's product name “Amilan”, and Mitsubishi Engineering Plastics' product name “Novamid”. .

Moreover, the resin composition which forms an intermediate | middle layer is a mixed resin composition of the (B) component, (C) component, and (D) component which were mentioned above, (B) component and (D) component which were mentioned above are mixed mass. (B) / (C) = 70 to 40/30 to 60 in terms of ratio, and (B) / (D) = 95 to 70/5 to 30 in terms of mixing mass ratio of component (B) and component (D) It is important that
First, if the ratio of the component (C) to the component (B) is within the above range, the original characteristics of the ionomer, such as the melt viscosity characteristics and optical characteristics associated with ionic crosslinking, are not impaired, and heat shrinkage characteristics and after shrinkage The film tension of the film can be modified. In addition, when the ratio of the component (D) to the component (B) is within the above range, it is possible to impart mechanical properties suitable for packaging by an automatic machine.
When the resin composition forming the intermediate layer is the above-mentioned mixed resin composition of the component (B) and the component (C), depending on the molding conditions, it imparts heat shrinkage characteristics and tension after shrinkage. However, the tensile elongation characteristic of the obtained film is poor, and for example, the film is easily broken when packaged by an automatic machine. Moreover, when the resin composition which forms an intermediate | middle layer is a mixed resin composition of (B) component and (D) component, although it is influenced also by molding conditions, although the tensile elongation characteristic of the film obtained becomes favorable, The film has poor shrinkage characteristics and tension after shrinkage.

  The stretch shrink laminated film of the present invention preferably has a thickness ratio of 35 to 90% with respect to the thickness of the entire intermediate layer. If the ratio of the thickness of the intermediate layer to the thickness of the entire film is within such a range, low temperature heat shrinkage characteristics suitable as a stretch shrink film can be obtained. The thickness ratio of the intermediate layer to the entire film is preferably 40 to 90%, more preferably 45 to 90%.

Further, the heat shrinkage property of the food packaging film in the present invention is preferably such that the total of the heat shrinkage rate in the vertical and horizontal directions at 80 ° C. for 10 seconds measured in an oil bath is 30% or more, more preferably. It is 30 to 60% in both the vertical and horizontal directions. When the thermal shrinkage rate exceeds such a range, the longitudinal and lateral stretch ratios may be lowered within the range not impairing the present invention, or the cooling amount described above may be adjusted to lower the cooling efficiency. If it is less than the range, increase the stretching ratio in the longitudinal and lateral directions within the range not impairing the present invention, increase the cooling amount to increase the cooling efficiency, or cool from both the outer surface and the inner surface side of the film. Thus, it can be within the above range.
If the total shrinkage at 80 ° C in the vertical and horizontal directions is less than 30%, wrinkles generated after packaging cannot be removed even after passing through the shrink tunnel, and if it exceeds 70%, it depends on the shrinkage stress. It can be deformed or curled when the film woven into the bottom of the tray is heat sealed. If the heat shrinkage property is within the above range, a good finish without wrinkles can be obtained.

In addition, the components (A) and / or (B) and / or (C) and / or (D) are within the range not exceeding the gist of the present invention, and are antifogging, antistatic, slippery, self For the purpose of further improving various physical properties such as adhesiveness, various additives can be appropriately blended as necessary.
Examples of the various additives include aliphatic alcohols which are compounds of an aliphatic alcohol having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms and an aliphatic alcohol having 10 to 22 carbon atoms, preferably 12 to 18 carbon atoms. Specific examples include fatty acid esters, such as monoglycerin oleate, diglycerin monooleate, polyglycerin oleate, glycerin trilysylate, glycerin acetyl cinnolate, polyglycerin stearate, polyglycerin laurate, methyl acetyl ricinoleate, Ethyl acetyl ricinolate, butyl acetyl ricinolate, propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, polyethylene glycol oleate, polyethylene glycol sorbitan oleate, polyethylene glycol sorb And the like can be given Nraureto. Polyalkylene ether polyols can be used, and specific examples include polyethylene glycol and polypropylene glycol. Furthermore, at least one compound selected from paraffinic oils can be added. It is preferable to add these additives in an amount of 0.1 to 12 parts by mass, preferably 1 to 8 parts by mass with respect to 100 parts by mass of the resin component.

Further, the total value of the shrinkage stress values in the longitudinal direction and the transverse direction at 80 ° C. according to the stress / strain control TMA (TMA / SS) of the film is preferably in the range of 0.5 to 3 MPa, more preferably in the range of 0.6 to The range is 2.5 MPa.
Stress / strain control TMA (TMA / SS) is based on the structure of a conventional thermomechanical analyzer (TMA: thermal mechanical analyzer) and is loaded with a stress / strain controller that controls the relationship between displacement and force. Independent of the temperature control loop, the CPU gives a program related to stress or strain to the stress / strain control unit, and the stress / strain control unit controls based on this program, thereby controlling the temperature and strain of the sample. This is a device that can obtain the relationship of three signals of stress.
The shrinkage stress value can be set within this range by adjusting the molding conditions during inflation, specifically by appropriately adjusting the cooling conditions of the medium. Specifically, when the shrinkage stress value exceeds such a range, the stretching ratio in the longitudinal and lateral directions may be lowered within the range that does not impair the present invention, or the cooling amount described above may be adjusted to lower the cooling efficiency. If it is less than the range, increase the stretching ratio in the longitudinal and lateral directions within the range not impairing the present invention, increase the cooling amount to increase the cooling efficiency, or cool from both the outer surface and the inner surface side of the film. Thus, it can be within the above range. If the shrinkage stress value is less than 0.5 MPa, it may not be possible to give a packed product a sufficient tight feeling or tightness. On the other hand, when the pressure exceeds 3 MPa, particularly in a push-up packaging machine, a crack or deformation of the tray may occur at the time of packaging, or the tray may be twisted or warped after packaging, so that a satisfactory packaging finish may not be obtained.

Next, a film forming method will be described. In the present invention, for example, a resin is melted using a plurality of extruders, melt-extruded from a T die or I die, cooled by being guided to a cast roll, and formed into a flat so-called cast film, And the cast film is introduced into a roll or a heating furnace (such as a tenter), heated and stretched in a uniaxial direction or longitudinal and transverse biaxial directions, and stretched in a uniaxially oriented film or longitudinal and transverse biaxial directions, and uniaxially oriented film or biaxial Although a tenter method for forming an oriented film is also possible, in the present invention, a molten resin is extruded into a cylindrical shape from an annular (multilayer) die, and a certain amount of air is put into the cylindrical molten film and pressurized, In the process of cooling from the melted state without cooling once like the so-called inflation molding that continuously expands and then cools with a cooling device to obtain a cylindrical film continuously It is possible to obtain a suitable heat shrink properties in the stretch shrink film with stretching. In inflation molding, an effect of taking a molten resin from a die and cooling it with a medium works, and molecules constituting the film are oriented. The degree of this orientation varies depending on the difference between the melt viscosity of the resin and the solidification in the cooling process and the draw ratio that can be substituted for the blow ratio.
Here, the extrusion molding temperature is appropriately adjusted depending on the flow characteristics, film formability, and the like of the resin composition, but is generally about 240 ° C. or less, preferably 200 to 230 ° C.
In the present invention, at the time of inflation molding, it is important to subject the above-mentioned laminate of the surface layer / intermediate layer / back layer to a stretching process of at least 3.5 times in the longitudinal and lateral directions during the cooling process from the molten state. is there. Specifically, when a material resin is melt-extruded into a cylindrical shape from an annular (multi-layer) die with the above-described configuration and is blown by inflation, a certain amount of the resin is adjusted in the cylindrical molten film while adjusting the cooling amount with a medium. Stretching the entire film by adjusting the amount of pressure by introducing air, setting the blow-up ratio (diameter of the expanded cylindrical film / diameter of the annular die) to 3.5 or more, and adjusting the film take-up speed The magnification is preferably 12.3 times or more, and the blow-up ratio is preferably 4 to 10, and the stretching ratio of the entire film is preferably adjusted to 50 to 100 times. As a cooling method at that time, either a method of cooling from the outer surface side of the cylindrical film or a method of cooling from both the outer surface side and the inner surface side of the cylindrical film may be used.

  Generally, the thickness of the food packaging film of the present invention is in the same range as the thickness of a normal packaging stretch film, that is, in the range of about 8 to 30 μm, typically about 10 to 20 μm.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In addition, the various measured value and evaluation about the film displayed in this specification were performed as follows. Here, the flow direction from the extruder of the film is called the vertical direction, and the orthogonal direction is called the horizontal direction.

(1) Thermal contraction rate The thermal contraction rate was measured by the following method.
Cut the film into a size of length x width = 150 mm x 25 mm so that the measurement direction is the longitudinal direction in the vertical direction and the horizontal direction, create a sample, attach a marked line at 100 mm intervals in the sample measurement direction, It was immersed for 10 seconds in silicon oil adjusted to 80 ° C., calculated from the following formula, and the total of the heat shrinkage in the vertical and horizontal directions was determined.
(Expression 1) Shrinkage rate = {(100−L) / 100} × 100 (%)
(However, L is the distance between marked lines after contraction: Unit mm)

(2) Shrinkage stress The film was cut into a size of length × width = 10 mm × 3 mm so that the measurement direction was the longitudinal direction in the machine direction and the transverse direction, and a sample was prepared. Using control TMA (TMA / SS) and TMA / SS150C, the temperature range from 30 ° C to 100 ° C is measured at a heating rate of 5 ° C / min and a load of 9.8 kN / m2, at 80 ° C. The sum of the shrinkage stress values in the longitudinal and transverse directions was determined.

(3) Packaging test Using the following two types of packaging machines, pack samples for packaging tests using each film were prepared.
a: Pillow type manufactured by Omori Machinery Co., Ltd .: Horizontal pillow type packaging machine (STN7500)
b: Push-up type Ishida Co., Ltd .: Push-up type packaging machine (Wmin, ZERO1)
The tray was prepared by putting 200 g of viscosity (thickness 10 mm) into a normal foamed styrene tray (length x width x height = 200 x 150 x 15 mm).
Moreover, after pack packaging, it was shrunk using a shrink tunnel (C-300 type attached to a pillow packaging machine manufactured by Omori Machinery Co., Ltd.) under the conditions of a hot air temperature of 90 ° C. and a passage time of 3 seconds. (3-1) Automatic packaging machine suitability when packaged under the above conditions, (3-2) Finished after shrink wrapping, (3-3) Evaluation of film tension after shrink wrapping based on the following criteria did.
(3-1) Suitability for automatic packaging machine ×: The packaging operation was performed for 5 hours, and the film was broken three times or more.
Δ: The packaging work was performed for 5 hours, and film breaking trouble occurred 1 to 3 times. ○: The packaging work was performed for 5 hours, and no film breaking trouble occurred.
(3-2) Finished state after shrink wrapping.
X: A state in which a lot of wrinkles and slack are generated on the front surface, which is unsightly and problematic in practice.
Δ: Slight wrinkles and slack in the surroundings but no problem in practical use ○: No wrinkles or slacks in good appearance (3-3) Film tension after packaging About film tension after packaging Were visually evaluated based on the following criteria for the state of the upper surface of the bottom sample after standing for 10 hours at 5 ° C. in a state where three samples packed in the same condition were stacked.
X: A state in which a lot of slack is unsightly and causes a practical problem.
Δ: Some slack is observed, but there is no practical problem.
○: A state of good appearance without any slack.

(4) Comprehensive evaluation It evaluated comprehensively with the following references | standards as a stretch shrink film for food packaging from the evaluation result of said (1) to (4).
X: The packaging finish is poor and there are practical problems.
(Triangle | delta): The packaging finish is a little bad and may become a problem practically.
◯: Excellent packaging finish and excellent as a stretch shrink film.
A: The packaging finish is very good and it is very excellent as a stretch shrink film.

Example 1
As component (A), ethylene-vinyl acetate copolymer NUC-3758 (manufactured by Nihon Unicar Co., Ltd., vinyl acetate content = 15 mass%, MFR = 2.0 g / min) (hereinafter referred to as the ethylene copolymer) The resin composition consisting of 3.0 parts by mass of diglycerin monooleate as an antifogging agent was added to an extruder for forming the front and back layers with respect to 100 parts by mass of (abbreviated simply as A-1). As component (B), Hi-Millan 1706 (Mitsui / DuPont Polychemical Co., Ltd., Zn type, methacrylic acid content = 15 mass%, degree of neutralization = 58%), which is an ionomer resin, is 40 mass%, and as component (C) , Novatec EAA A210K (manufactured by Nippon Polyethylene Co., Ltd., acrylic acid content = 7% by mass, MFR = 3.0 g / min), which is an ethylene-acrylic acid copolymer, is 40% by mass. A resin composition comprising 20% by mass of amylan CM1017C (melting point = 226 ° C.) was charged into an extruder for forming an intermediate layer. Food packaging with an extrusion temperature of 190 ° C to 200 ° C, an annular die temperature of 200 ° C and a blow-up ratio of 10 and a thickness of 10 µm (surface layer / intermediate layer / surface layer = 2.0 µm / 6.0 µm / 2.0 µm) A film was obtained.

(Example 2)
Example 1 except that the component (C) was Nucrel AN4221C (Mitsui / Dupont Polychemical Co., Ltd., acrylic acid content = 12% by mass, MFR = 10.0 g / min), which is an ethylene-acrylic acid copolymer. A film for food packaging having a thickness of 10 μm (surface layer / intermediate layer / surface layer = 2.0 μm / 6.0 μm / 2.0 μm) was obtained by coextrusion inflation molding in the same manner as above.

(Example 3)
As component (D), a thickness of 10 μm (surface layer / intermediate layer / surface layer) was obtained by coextrusion inflation molding in the same manner as in Example 1 except that Uvesta 3035JU5 (manufactured by Ube Industries, melting point = 158 ° C.), which is nylon 12, was used. = 2.0 μm / 6.0 μm / 2.0 μm).

(Comparative Example 1)
As component (B), Hi-Millan 1706 (Mitsui / Dupont Polychemical Co., Ltd., Zn type, methacrylic acid content = 15 mass%, degree of neutralization = 58%), which is an ionomer resin, is 20 mass%, and as component (C) A resin composition comprising 80% by mass of Novatec EAA A210K (manufactured by Nippon Polyethylene Co., Ltd., acrylic acid content = 7% by mass, MFR = 3.0 g / min), which is an ethylene-acrylic acid copolymer, (D) A food packaging film having a thickness of 10 μm (surface layer / intermediate layer / surface layer = 2.5 μm / 5.0 μm / 2.5 μm) was obtained by coextrusion inflation molding in the same manner as in Example 1 except that the components were not used.

(Comparative Example 2)
As component (B), Himiran 1706 (Mitsui / DuPont Polychemical Co., Ltd., Zn type, methacrylic acid content = 15 mass%, degree of neutralization = 58%) is 90 mass% as component (D). Example 1 except that Uvesta 3035JU5 (manufactured by Ube Industries, melting point = 158 ° C.), which is nylon 12, is a resin composition comprising 10% by mass, the component (C) is not used, and the blow-up ratio is set to 5. A film for food packaging having a thickness of 10 μm (surface layer / intermediate layer / surface layer = 2.5 μm / 5.0 μm / 2.5 μm) was obtained by coextrusion inflation molding in the same manner as above.

From Table 1, it can be seen that the stretch shrink laminated film defined in the present invention is excellent in low-temperature shrinkage, tightness of the tight film after shrinkage, and packaging finish. Further, it can be confirmed that it can also be manufactured by inflation molding. In addition, the stretch shrink laminated film of Example 3 was excellent in transparency compared with Examples 1 and 2.

Claims (7)

It is a laminated film composed of at least three layers, and both surface layers are composed mainly of the component (A) which is an ethylene polymer, and the intermediate layer is composed of the following components (B), (C) and (D) The blending mass ratio of the mixed resin composition comprising the ionomer-based mixed resin composition as the main component and forming the intermediate layer is (B) / (C) = 70-40 / 30-60, and (B) / (D ) = 95-70 / 5-30, and further, the total value of the heat shrinkage ratio in the vertical direction and the horizontal direction when immersed in an oil bath at 80 ° C. for 10 seconds is 30% or more. Shrink laminated film.
(B) An ionomer resin which is an ethylene / unsaturated carboxylic acid having an unsaturated carboxylic acid content of 10 to 30% by mass and a degree of neutralization by metal ions of 40 to 80%. (C) An unsaturated carboxylic acid content of 5 to 20% by mass. An ethylene / unsaturated carboxylic acid copolymer having a melt flow rate (JIS K7210 190 ° C., load 21.18 N) of 1 to 30 g / 10 min. (D) Crystalline polyamide having a melting point (JIS K7121) of 240 ° C. or less. The ethylene / unsaturated carboxylic acid copolymer as component (C) is at least one ethylene polymer selected from ethylene-acrylic acid ester copolymers and ethylene-methacrylic acid ester copolymers. The stretch shrink laminated film according to claim 1. Component (A) which is an ethylene polymer is low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, and ethylene-methacrylic acid. The stretch shrink laminated film according to claim 1 or 2, wherein the stretch shrink laminated film is at least one ethylene polymer selected from ester copolymers. The ethylene-based polymer (A) component has an ethylene acetate content of 8 to 30% by mass and an ethylene melt flow rate (JIS K7210, 190 ° C., load 21.18 N) of 0.2 to 10 g / 10 min. 3. A stretch shrink laminated film according to claim 1 or 2, which is a vinyl acetate copolymer. 5. The total value of shrinkage stress values in the longitudinal and transverse directions at 80 ° C. according to the stress / strain control TMA (TMA / SS) of the film is in the range of 0.5 to 3 MPa. Stretch shrink laminated film The melt-extruded resin is manufactured by an inflation method, which is a method of extruding a cylindrical shape from an annular die without blowing and solidifying it once, blowing air into the cylinder, and expanding the molten cylinder. The stretch shrink laminated film in any one of claim | item 1 -5. It manufactures with an inflation molding machine, The manufacturing method of the stretch shrink laminated film in any one of Claims 1-5 characterized by the above-mentioned.