JP2007237458A - Stretch shrink laminated film and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stretch shrink laminated film capable of being applied to inflation molding, having heat-shrinkable characteristics, not causing the deformation or breaking trouble at the time of thrust-up packaging and excellent in packaging finish, and its manufacturing method. <P>SOLUTION: The stretch shrink laminated film is constituted of at least three layers and both surface layers thereof are based on a component (A) being an ethylenic polymer while the intermediate layer thereof is based on a component (B) being an ionomer resin composition. The tensile elongation in the longitudinal direction of the laminated film is 100% or above and the sum total value of the heat shrinkage factors in the longitudinal and lateral directions of the laminated film when the laminated film is immersed in an oil bath of 80°C for 10 sec is 25% or above. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stretch shrink film and a method for producing the same, and more specifically, mainly relates to a stretch shrink laminated film suitably used for push-up packaging and a method for producing the same.

  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. Difficult or generally high production cost of film (for example, see 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 method has a low packaging capacity (usually about 25 to 50 packs / minute), but can handle a relatively large number of tray sizes with one size film (eg, a roll having a width of 350 mm), and is relatively compact and has a small installation space. However, it is also used in pack centers, but is mainly used in supermarket in-stores (backyards).

  In the case of a push-up packaging machine, the packaging mechanism is such that a film cut to a standard length is conveyed while its lateral end is held by a belt or the like, and is then held by a clamp to push the tray up from the bottom of the film. Can be folded in both the vertical and horizontal directions at the bottom of the tray. In this case, since the height of the bottom position of the tray needs to be pushed up to a height equal to or higher than the clamp for holding the film, the film is stretched by at least 20% or more. A conventional stretch shrink is a highly oriented film by so-called biaxial stretching basically by a tenter or tubular method in order to impart heat shrink properties, and the film has a high elastic modulus and is difficult to stretch in both the longitudinal and transverse directions. It is often a film. Therefore, when a conventional stretch shrink is used for packaging with a push-up wrapping machine, a large load is applied to the tray during the push-up, and the tray is cracked or deformed greatly. In particular, an excessive tension is applied, and a trouble that the film tears from the held clamp portion is likely to occur. That is, there is a problem in packaging using shrink, and a stretch shrink suitable for push-up packaging is desired.

  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 heat shrink characteristics suitable for stretch shrink.

  Therefore, if a stretch shrink film having excellent heat shrinkage characteristics 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, this patent is not intended to express shrinkage characteristics with an ionomer resin, and even if shrinkage characteristics are manifested, the thickness ratio of the intermediate layer is low so that sufficient heat shrinkage characteristics are obtained. 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

  SUMMARY OF THE INVENTION An object of the present invention is to provide a stretch shrink laminated film excellent in heat shrinkage characteristics and push-up packaging suitability that can be produced even with an inflation molding machine that is generally good in productivity and inexpensive in production equipment, and a method for producing the same. It is in.

As a result of intensive investigations, the present inventors have found that the ethylene polymer can be both surface layers, the ionomer resin composition as a main component, and the above problems can be solved by setting the mechanical properties to a specific value. The present invention has been completed.
That is, the present invention
(1) Consisting of at least three layers, both surface layers are composed mainly of component (A), which is an ethylene polymer, and the intermediate layer is composed mainly of component (B), which is an ionomer-based resin composition. It is a laminated film, and the tensile elongation in the machine direction is 100% or more, and the total value of the heat shrinkage in the machine direction and the transverse direction when immersed in an oil bath at 80 ° C. for 10 seconds is 25% or more. Stretch shrink laminated film characterized by
(2) The stretch shrink laminate film according to (1), wherein the tensile elastic modulus is in the range of 200 MPa to 400 MPa, and the 50% tensile elongation stress in the longitudinal direction and the transverse direction are both 40 MPa or less. .
(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), wherein the stretch shrink laminated film 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: 21.18 N) 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) Melting | fusing point of (A) component which is an ethylene-type polymer is 65-100 degreeC, The stretch shrink laminated film as described in (1) or (2) characterized by the above-mentioned.
(6) The (B) component which is an ionomer-based resin composition is a mixed resin composition containing (C) component 60 to 30% by mass and (D) component 40 to 70% by mass shown below. The stretch shrink laminated film according to (1) or (2).
(C) An ethylene / unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of 10 to 30% by mass and a degree of neutralization by metal ions of 30 to 80% (D) An unsaturated carboxylic acid content of 5 to 15% by mass (7) An ethylene / unsaturated carboxylic acid copolymer having a melt flow rate (JIS K7210, 190 ° C., load: 21.18 N) of 0.2 to 5 g / 10 min. (7) The melt-extruded resin is once cooled and solidified. (1) to (6), which is manufactured by an inflation method which is a method of extruding a cylindrical die from an annular die and blowing air into the cylinder to expand the molten cylinder. Stretch shrink laminated film.

  Another object of the present invention is achieved by producing the stretch shrink laminated film according to any one of the above (1) to (6) with an inflation molding machine.

  ADVANTAGE OF THE INVENTION According to this invention, the stretch shrink laminated | multilayer film excellent in the push-up packaging use with a favorable heat shrink property and its manufacturing method can be provided.

Hereinafter, the present invention will be described in detail.
It should be noted that the upper limit and lower limit of the numerical range in the present invention are the same as those in the present invention as long as they have the same effects as those in the numerical range, even if they are slightly outside the numerical range characterized by the present invention. It is included in the equivalent range. In addition, the main component in the present invention is a component that is contained in the largest amount, and is usually a component that is 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more. .

  First, the stretch shrink laminated film of the present invention is a laminated film composed of at least three layers, both surface layers are mainly composed of component (A) which is an ethylene polymer, and the intermediate layer has a specific heat. The component (B), which is an ionomer resin composition having characteristics, is the main component.

  Here, the component (A) that is an ethylene polymer that is 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 Copolymers having ethylene as a main component, 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 1 selected from vinyl esters such as vinyl propionate; unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate; and unsaturated compounds such as conjugated and non-conjugated dienes And a copolymer or a multi-component copolymer with two or more comonomers, or a mixed composition thereof. That. 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.

  In the present invention, both surface layers have a film-forming stability during molding (for example, bubble stability in inflation molding), a balance between appropriate slip properties and surface adhesiveness of the resulting stretch shrink laminated film, or antifogging properties. In the component (A) which is the ethylene polymer, the vinyl acetate content is 8 to 30% by mass, because it bears the function of expressing surface characteristics such as surface characteristics and mechanical characteristics such as transparency and flexibility. An ethylene-vinyl acetate copolymer having a melt flow rate (hereinafter sometimes abbreviated as MFR) (JISK7210, 190 ° C., load: 21.18 N) of 0.2 to 10 g / 10 min has these characteristics. It is most preferable because it can be adjusted relatively easily including the material cost.

  If the vinyl acetate content is 8% by mass or more, the resulting film is not hard because the crystallinity is low, the flexibility and elastic recovery are good, and the transparency and heat shrinkage characteristics of the entire film are impaired. This is preferable because it is easy to develop surface tackiness. On the other hand, if it is 30% by mass or less, heat resistance, film strength, etc. are sufficiently secured, and the bleedability and surface adhesiveness of the antifogging agent to be added are not too strong, so the unwinding property and appearance of the film are good. Therefore, it is preferable. Accordingly, 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. Therefore, the MFR is preferably 0.5 to 8 g / 10 minutes, more preferably 1 to 5 g / 10 minutes.

  Further, the balance between the above-described surface characteristics and mechanical characteristics of both surface layers and the heat shrinkability characteristics of the resulting stretch shrink laminated film, particularly from the heat shrink characteristics, the melting point of the component (A) which is an ethylene polymer is 65 to 65. Most preferably, it is 100 ° C.

  If the melting point is 65 ° C. or higher, the heat resistance, film strength, etc. are less likely to be a practical problem, and the antifogging agent to be added is not too bleed or surface adhesive. It is preferable because the unwinding property and appearance are good. On the other hand, if it is 100 ° C. or lower, the resulting film is not hard because the crystallinity is low, the flexibility and elastic recovery are good, and the transparency and heat shrinkage characteristics of the entire film are rarely impaired, Surface tackiness is also preferred because it is easy to develop. Therefore, the melting point is preferably 70 to 100 ° C, more preferably 75 to 98 ° C.

  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.

  Next, the ionomer resin comprises at least a part of an unsaturated carboxylic acid component of a copolymer comprising ethylene, an unsaturated carboxylic acid, and an optional other unsaturated compound as a minimum of a metal ion or an organic amine. It can be obtained by neutralizing either one. 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+, 1 monovalent such as ^{Al 3+} To trivalent metal cations (hereinafter sometimes abbreviated as metal ions) or organic amines. In the present invention, sodium or zinc is preferably used. In addition, these 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 this effect becomes greater near the melting point of the ionomer resin. Because of these effects, there is no excessive increase in extrusion performance, specifically melt viscosity, and ionic crosslinking remains in a pseudo-crosslinked state during stretching in the cooling process from a melted state such as inflation molding. It is thought that it becomes possible to give the heat shrink characteristic suitable for a stretch shrink film.

  Next, the (B) component which is an ionomer-based resin composition used in the present invention has a crystallization peak temperature of 60 to 90 ° C. when cooled at a cooling rate of 10 ° C./min by differential scanning calorimetry. Preferably there are at least two. Here, when the crystallization peak temperature is between 60 to 90 ° C., the stretch shrink film in a state where the bubble frost line is stable at the time of stretching in the cooling process from the melted state such as inflation molding. It is preferable because it is possible to impart suitable heat shrinkage characteristics. From these things, it is more preferable that it is 65 degreeC or more as a minimum of crystallization peak temperature. Moreover, as an upper limit, it is more preferable that it is 85 degrees C or less. In addition, since at least two crystallization peak temperatures exist in the temperature range, for example, during the stretching process in the cooling process from a molten state such as inflation molding, the crystallization peak temperature is excessively increased in the crystallization peak temperature region on the high temperature side. Strain that is suitable for imparting heat shrinkage properties up to the low temperature crystallization peak temperature range at the same time is less likely to cause vertical tearing and breakage troubles when packaging with an automatic packaging machine. It is thought that it becomes possible to give. Thus, when packaging with an automatic packaging machine, there are at least two crystallization peak temperatures between 60-90 ° C. when cooled at a cooling rate of 10 ° C./min by differential scanning calorimetry. Therefore, it is possible to achieve both a balance between the mechanical properties of preventing tearing and breakage troubles and the heat shrinkage properties suitable for stretch shrink films. In addition, if it is the range which does not exceed the main point of this invention, three or more crystallization peak temperature when it cools by differential scanning calorimetry may exist between 60-90 degreeC. The upper limit of the number of realistic crystallization peak temperatures is five.

  The crystallization peak temperature is measured as follows. That is, using a differential scanning calorimeter DSC-7 manufactured by PerkinElmer, approximately 10 mg of component (B), which is an ionomer resin composition, was accurately weighed in an aluminum pan for DSC measurement according to JIS K7121. Then, the temperature is raised from room temperature to 200 ° C. at a heating rate of 10 ° C./min, held at the same temperature for 2 minutes, and then cooled to 0 ° C. at a cooling rate of 10 ° C./min. The crystallization peak temperature (Tc) is determined from the thermogram in this cooling process. Here, the crystallization peak temperature is a temperature at which the first derivative of the variation with respect to the thermogram temperature becomes zero.

Further, an ionomer block copolymer or the like can also be used as the component (B) which is an ionomer resin composition. In the present invention, the component (B) has a function of exhibiting good heat shrinkage characteristics and mechanical properties such as tear resistance, which is a characteristic required for push-up packaging applications. The mixed resin composition containing -30 mass% and (D) component 40-70 mass% is used suitably, More preferably, (C) component 60-40 mass% and (D) component 40-60 It is a mixed resin composition containing 60 mass% of (C) component and 40-55 mass% of (D) component especially preferably.
(C) An ethylene / unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of 10 to 30% by mass and a degree of neutralization by metal ions of 30 to 80%. (D) An unsaturated carboxylic acid content of 5 to 15% by mass. An ethylene / unsaturated carboxylic acid copolymer having a melt flow rate (JIS K7210, 190 ° C., load: 21.18 N) of 0.2 to 5 g / 10 min.

  The component (C) described above has an ethylene content of 50 to 90% by mass, preferably 50 to 88% by mass, an unsaturated carboxylic acid content of 10 to 30% by mass, preferably 12 to 20% by mass, and other unsaturated compounds. Those having a polymerization composition of 0 to 40% by mass, preferably 0 to 20% are suitably used. Further, the neutralization degree is preferably obtained by neutralizing 30 to 80%, preferably 40 to 60%, of the amount of unsaturated carboxylic acid in the metal cationic copolymer component. Here, it is preferable that the component (C) is within the range of the polymerization composition and the degree of neutralization, since the crystallinity of the ionomer resin is reduced to some extent, so that the transparency of the film can be maintained. Also, for example, at the time of stretching in the cooling process from the melted state such as inflation molding, the ionic crosslinking remains in the pseudo-crosslinked state, and thus it is possible to impart suitable heat shrinkage characteristics to the stretch shrink film. .

  The component (D) has an ethylene content of 50 to 90% by mass, preferably 60 to 88% by mass, an unsaturated carboxylic acid content of 5 to 15% by mass, preferably 6 to 12% by mass, and other unsaturated components. A compound having a polymerization composition of 0 to 45% by mass, preferably 0 to 20% is suitably used. Here, if it is the range of the said polymerization composition, since compatibility with ionomer resin is comparatively favorable and it becomes possible to maintain the transparency of a film, it is preferable. At the same time, it is preferable because mechanical properties such as tear resistance suitable for packaging by an automatic machine can be imparted.

  It is preferable that MFR (JIS K7210, 190 degreeC, load: 21.18N) of (B) component which is an ionomer type resin composition used for this invention is 0.2-20 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. Therefore, the MFR is preferably 0.3 to 10 g / 10 minutes, more preferably 0.5 to 3 g / 10 minutes.

  The method for producing the component (B), which is an ionomer resin composition 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. . Also, starting from a copolymer resin such as ethylene and acrylic acid or methacrylic acid that does not contain metal ions, acetylacetone metal complex, metal oxide, aliphatic acid metal salt is added after the necessary amount to introduce ionic crosslinking, An ionomer resin may be obtained at the time of molding. Copolymers such as ethylene and acrylic acid or methacrylic acid can be polymerized with a post metallocene catalyst.

  In the present invention, commercially available raw materials can also be used. As a specific product of ionomer resin, trade name “HIMILAN” of Mitsui-DuPont Polychemical Co., Ltd. may be mentioned. 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 “Nucrel” of Mitsui-DuPont Polychemical Co., Ltd. and the product of Nippon Polyethylene Co., Ltd. Names such as “Lex Pearl”.

  As described above, the stretch shrink laminated film of the present invention is the component (B) that is an ionomer-based resin composition having both surface layers mainly composed of the component (A) that is an ethylene polymer and specific thermal characteristics. Although it is a laminated film composed of at least three layers having an intermediate layer containing as a main component, other layers (improvement of mechanical properties and interlayer adhesion, etc., if necessary within the range not exceeding the gist of the present invention) Hereinafter, it may be abbreviated as P layer). Here, the surface layer (hereinafter sometimes abbreviated as S layer) may have the same layer other than both surface layers, that is, an intermediate layer. Further, the intermediate layer (hereinafter sometimes abbreviated as “M layer”) may have at least one layer between both surface layers, and may have two or more layers. For example, a three-layer structure composed of (S layer) / (M layer) / (S layer), a four-layer structure composed of (S layer) / (P layer) / (M layer) / (S layer), (S layer) / (P layer) / (M layer) / (P layer) / (M layer) / (P layer) / (S layer), (S layer) / (M layer) / (P layer) / (M layer) A typical example is a five-layer structure including / (P layer) / (S layer), (S layer) / (M layer) / (S layer) / (M layer) / (S layer). In this case, the resin composition and thickness ratio of each layer may be the same or different.

  Here, the preferred laminated structure in the present invention is a three-layer structure composed of (S layer) / (M layer) / (S layer), and by adopting this layer structure, the object of the present invention is good. With excellent heat shrinkage characteristics, tight film tension after shrinkage, packaging finish by automatic packaging machine, etc., and no breakage trouble when packaging with the above-mentioned type of automatic packaging machine, and further regenerative additive properties (usually It is possible to obtain a stretch shrink laminated film excellent in productivity and economy, which is excellent in addition to the intermediate layer.

(Tensile modulus)
The stretch shrink laminated film of the present invention preferably has a tensile elastic modulus in the range of 200 MPa to 400 MPa. When the tensile elastic modulus is in the range of 200 MPa to 400 MPa, preferably 250 MPa to 350 MPa, when the stretch shrink laminated film of the present invention is stretch-wrapped using a push-up wrapping machine, an excessive force is not applied at the time of push-up. Since it stretches, there is no problem that the film comes off from the clamp or the problem that the tray is deformed, which is preferable.

(Tensile elongation)
The stretch shrink laminate film of the present invention is required to have a longitudinal tensile elongation of 100% or more. If the tensile elongation in the machine direction is 100% or more, preferably 110 to 200%, the film is not broken by deformation of the film that occurs during stretch packaging using a push-up packaging machine.

  Moreover, although it changes with the film width to be used, the size and size relationship of the tray, etc., if the tensile elongation in the transverse direction is 40% or more, preferably 50% to 150%, it will occur during stretch packaging using a push-up packaging machine. It is more preferable because the film is not broken by deformation of the film.

(50% tensile elongation stress)
The stretch shrink laminated film of the present invention preferably has a 50% tensile elongation stress of 40 MPa or less in both the longitudinal direction and the transverse direction. If the 50% tensile elongation stress is 40 MPa or less, preferably 20 to 35 MPa, when the stretch wrapping is performed using a push-up packaging machine, an excessive load is not applied to the tray when the film is stretched during push-up. This is preferable because it does not cause problems such as the occurrence of damage or damage to the tray.

  Next, in the stretch shrink laminated film of the present invention, it is important that the total value of the heat shrinkage ratio in the longitudinal direction and the transverse direction when immersed in an oil bath at 80 ° C. for 10 seconds is 25% or more. Furthermore, it is preferable that it is 30 to 100%. When the stretch shrink laminated film of the present invention is stretch-wrapped using a push-up wrapping machine, the film stretches slightly when pushed up, so that if there is a thermal shrinkage rate of 25% or more, the wrinkles afterwards will pass through the shrink tunnel. In many cases, the problem can be solved by the deformation of the tray, or the film folded on the bottom of the tray is curled when heat-sealed, or the film rolls up over time due to natural shrinkage. It is preferable because there are few occurrences of defects such as deformation due to.

  Furthermore, in the present invention, although it changes depending on the size relationship between the film width to be used and the size of the tray, the thermal contraction rate in the vertical direction and the horizontal direction when immersed in an oil bath at 80 ° C. for 10 seconds is 10 to 60 respectively. %. Within such a range, when a push-up packaging machine is used, the packaging finish on trays of various sizes and the temporal stability of the roll film are excellent, which is preferable.

  The above-mentioned heat shrinkage ratio is a predetermined range mainly by changing the thickness constitution of both surface layers and the intermediate layer, the stretching ratio, the blow-up ratio (bubble diameter / die diameter), and the temperature conditions such as the stretching temperature and the cooling condition. Can be adjusted. For example, when the thermal shrinkage rate is smaller than a desired value, the stretching ratio in the machine direction and / or the transverse direction is increased so as to increase the heat shrinkage strain at a lower temperature, or the amount of cooling blower in the outer surface cooling is increased. What is necessary is just to adjust suitably cooling efficiency, such as using UP and internal surface cooling together. On the other hand, when the heat shrinkage rate is larger than the desired value, the stretching ratio in the machine direction and / or the transverse direction is lowered so as to reduce the heat shrinkage strain at a lower temperature, or the cooling blower amount in the outer surface cooling. What is necessary is just to adjust cooling efficiency suitably, such as weakening DOWN of this and inner surface cooling.

  Next, in the intermediate layer of the stretch shrink laminate film of the present invention, the ionomer-based resin composition as the component (B) is contained as a main component, but in addition to the component (B), the component (A) described above A certain ethylene polymer may be mixed within a range not exceeding the gist of the present invention. For example, when the main purpose is to add recycled resin generated from trimming loss, etc., or to improve the mechanical properties of the resulting stretch shrink laminated film as a whole, especially properties such as elastic modulus (rigidity) and tear strength, and to reduce material costs It becomes an effective means. The mixing mass ratio in the case of mixing is (A) / (B) = 1-50 / 99-50, preferably 5-50 / 95-50, more preferably 10-45 / 90-55.

  Here, as the component (A) that can be most suitably mixed, an ethylene-vinyl acetate copolymer having a vinyl acetate content of 10 to 25% by mass can be used. This is suitable for use as both surface layers, and has no practical problems including transparency, mechanical properties and material cost when recycled resin generated from trimming loss etc. is added. This is because it is also available stably.

  The stretch shrink laminated film of the present invention is necessary for the purpose of further adjusting and improving various physical properties such as anti-fogging property, antistatic property, slipperiness, self-adhesiveness, mechanical properties, etc. within the range not exceeding the gist of the present invention. Depending on the above, various additives and / or resins other than the components (A) and (B) can be appropriately blended in the surface layer and / or the intermediate layer.

  Here, examples of the various additives include an antioxidant, an antifogging agent, an antistatic agent, a lubricant, and a nucleating agent, and are not particularly limited as long as the gist of the present invention is not exceeded. The additive suitably used in the present invention is a mixture of an aliphatic alcohol having 1 to 12 carbon atoms, preferably 1 to 6 carbons and an aliphatic alcohol having 10 to 22 carbon atoms, preferably 12 to 18 carbon atoms. Specific examples include aliphatic alcohol fatty esters such as monoglycerinolate, diglycerin monooleate, polyglycerin oleate, glyceryl trilysylate, glyceryl acetyl cinnolate, polyglyceryl stearate, polyglycerin laurate, methyl. Examples thereof include acetyl ricinolate, ethyl acetyl ricinolate, butyl acetyl ricinolate, propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, and polyethylene glycol sorbitan laurate. Furthermore, at least one compound selected from paraffinic oils can be added. A suitable addition amount of these additives is 0.1 to 12 parts by mass, preferably 2 to 8 parts by mass, more preferably 3 to 6 parts by mass, when the total of various resin components is 100 parts by mass. In the present invention, it is preferably added to at least the surface layer.

  Further, the resins other than the components (A) and (B) are not particularly limited as long as they do not exceed the gist of the present invention. For example, propylene-based and styrene-based thermoplastic elastomers, various resistances Examples include impact modifiers, compatibilizers, tackifying resins, and plasticizers. A suitable addition amount of these other resins is 0 to 20 parts by mass, preferably 0 to 15 parts by mass, more preferably 0 to 10 parts by mass, when the total of various resin components is 100 parts by mass. .

  Next, the manufacturing method of the stretch shrink laminated film of this invention is demonstrated. Various known production methods can be applied to the production method, and the production method is not particularly limited as long as it does not exceed the gist of the present invention. Examples of the film lamination method include a coextrusion lamination method, a lamination method, and a dry lamination method. Among these, in the present invention, a coextrusion lamination method in which melt bonding is performed is preferably used. Specifically, it is a method in which melt extrusion is performed using a plurality of extruders corresponding to the number of multilayers, and the molten resin is developed and laminated by a feed block, a multi-manifold or the like.

  One of the main objects of the present invention is to impart heat shrinkage properties by temporarily cooling and solidifying a melt-extruded resin, such as a commonly used tenter method or tubular method, to produce a raw film or raw material. A method of collecting the anti-tube and then reheating and stretching is also possible as appropriate. In the present invention, by adopting the above-mentioned laminated resin composition configuration, the melt-extruded resin is extruded into a cylindrical shape from an annular die without being once cooled and solidified, and air is blown into the cylinder. It has been found that a stretch shrink laminated film having excellent heat shrinkage characteristics can be obtained even by a so-called inflation method, which is a method of expanding a molten cylinder.

  The inflation method is a method in which the molten resin is taken from the annular die and the cooling effect works in the process of thinning, and the molecules constituting the film are oriented. The degree of orientation depends on the melt viscosity of the resin used and the solidification rate in the cooling process or It is considered that the change mainly depends on the difference in crystallization speed, blow-up ratio (bubble diameter / die diameter), bubble shape, and the like.

  In the present invention, when performing inflation molding, while adjusting the amount of cooling with a medium such as cold air, a fixed amount of air is introduced into the molten cylinder to adjust the amount of pressure, and the blow-up ratio is 3.5 or more, Preferably, 4 to 20, more preferably 5 to 15. Subsequently, by adjusting the film take-up speed, the deformation ratio of the resin extruded into a cylindrical shape from the annular ring is preferably adjusted to about 50 to 200 times, preferably 70 to 120 times for the entire film. Here, the deformation magnification is a value obtained by dividing the lip gap of the annular die by the thickness of the film. For example, when the lip gap of the annular die is 1 mm (1000 μm) and the thickness of the obtained film is 10 μm, the deformation magnification is 100 times. Further, when the lip gap of the annular die is 2 mm and the thickness of the obtained film is 10 μm, the deformation ratio is 200 times. The calculation of the deformation magnification is not affected by the blow-up ratio. As a cooling method at that time, either a method of cooling from the outer surface or inner surface side of the cylindrical film or a method of simultaneously cooling from both the outer surface side and the inner surface side of the cylindrical film may be adopted.

  The stretch shrink laminated film obtained by the above-described method is used for longitudinal stretching between heated rolls as necessary for adjusting the heat shrinkage rate, reducing the natural shrinkage rate and suppressing curling, etc. Heat treatment such as heat setting and aging can be performed. Further, for the purpose of imparting and promoting antifogging properties, antistatic properties, adhesiveness, etc., surface treatments such as corona discharge and aging, and surface treatments such as printing and coating can also be performed.

  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 values and evaluation about the film displayed on 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) Tensile modulus A strip-shaped film test piece having a length of 400 mm and a width of 5 mm was cut out from the longitudinal direction and the transverse direction, respectively, and a tensile tester (manufactured by Shimadzu Corporation, model number: AGS-H500N) was used. Measurement was performed at a chuck distance of 300 mm and a tensile speed of 5 mm / min, and the calculation was performed by the following formula using the linear portion at the beginning of the chart.
E = σ / ε
E: Tensile modulus,
σ: Difference in stress per unit area (average cross-sectional area of sample before tensile test) between two points on a straight line ε: Difference in strain between the same two points

(2) Tensile elongation, 50% tensile elongation stress A strip-shaped film test piece having a length of 100 mm and a width of 10 mm was cut out from the longitudinal direction and the transverse direction, respectively, and a tensile tester (manufactured by Shimadzu Corporation, model number: AGS-H500N) ) At a chucking distance of 40 mm and a tensile speed of 200 mm / min. The 50% tensile elongation stress was calculated by reading the 50% tensile elongation load from the chart obtained by the above measurement and converting it to 50% tensile elongation stress (MPa). Each measurement was performed three times, the average value was calculated, and the value rounded to the first decimal place was listed.

(3) Heat shrinkage rate The test piece which cut out the film in the strip shape of length 140mm x width 10mm from the obtained film from the lengthwise direction and the widthwise direction, respectively, and wrote the standard line of 100mm length in the middle, 80 The length between the marked lines after being immersed in an oil bath at 0 ° C. for 10 seconds and taken out was measured, and the shrinkage rate was determined in% from the length between the marked lines before and after immersion in the oil bath. In addition, the measurement was performed 10 times each, the average value was calculated, and the value rounded to the first decimal place was described.

(4) Suitability for automatic packaging machines (push-up suitability)
Using a film with a width of 400 mm, a push-up packaging machine (Fuji Machinery Co., Ltd .: FP-65A) + shrink tunnel (Omori Machinery Co., Ltd .: C-300 type, hot air set temperature: 105 ° C., transit time: 3 )), It is suitable for an automatic packaging machine when 1000 ordinary foamed polystyrene trays (length 100 mm, width 50 mm, height 50 mm) containing 200 g of viscosity (thickness 10 mm) are packaged at a speed of 70 packs / minute. Evaluation was made according to the following criteria.
(◎): No breakage trouble occurred (0 times / 1,000 pieces)
(◯): 1 to 3 times of tearing or breaking trouble occurred, but no problem in practical use (×): 4 or more times of tearing or breaking trouble occurred, causing practical problems

(5) Packaging Finish Similar to (4) above, ordinary foamed polystyrene trays (length 200 mm, width 150 mm, height 15 mm) were packaged, and the resulting pack samples were evaluated according to the following criteria.
(◎): There is almost no wrinkles or sagging on the top surface of the tray, and there is sufficient film tension (○): There is almost no wrinkles or sagging on the top surface of the tray, and there is film tension (×): Any slack or no film tension

Example 1
As component (A) which is an ethylene polymer, ethylene-vinyl acetate copolymer (manufactured by Nippon Polyethylene: LV-440, vinyl acetate content: 15% by mass, MFR: 2.2 g / 10 min, melting point: 95 ° C.) A resin composition obtained by melting and kneading 5.0 parts by mass of diglycerin monooleate as an antifogging agent at an extrusion set temperature of 180 to 200 ° C. in 100 parts by mass (hereinafter abbreviated as A-1) is used as both surface layers. As the component (B) that is an ionomer-based resin composition, the ionomer to be the component (C) (manufactured by Mitsui DuPont Polychemical: High Milan 1706, base polymer: ethylene / methacrylic acid copolymer, methacrylic acid content: 15% by mass , Neutralized metal ion species: zinc, degree of neutralization: 59%, MFR: 0.7 g / 10 min, melting point: 88 ° C.) (hereinafter abbreviated as C-1) 50% by mass, (D) As an ethylene / unsaturated carboxylic acid copolymer, an ethylene / acrylic acid copolymer (manufactured by Nippon Polyethylene: Lexpearl A-210K, acrylic acid content: 7% by mass, MFR: 3.0 g / 10 min, melting point: 98 ° C) (hereinafter abbreviated as D-1) 50% by mass of a resin composition obtained by melt-kneading at an extrusion set temperature of 180 to 200 ° C. is used as an intermediate layer, which is joined from separate extruders, and an annular three-layer die temperature of 185 ° C. Then, coextrusion inflation molding was performed at a lip gap of 1.2 mm and a blow-up ratio of 10.0 to obtain a stretch shrink laminated film having a total thickness of 13 μm (thickness ratio: 1/6/1). The results of evaluating the obtained film are shown in Table 1. The crystallization peak temperature (Tc) when cooled by differential scanning calorimetry of the component (B) which is an ionomer resin composition is such that the crystallization peak temperature derived from C-1 is 69.5 ° C. A crystallization peak temperature from 1 was observed at 80.4 ° C.

(Example 2)
In Example 1, a stretch shrink laminate film was obtained in the same manner as in Example 1 except that the thickness ratio was 1/3/1. The results of evaluating the obtained film are shown in Table 1.

(Example 3)
In Example 1, as the component (B) that is an ionomer-based resin composition, the ratio of C-1 and D-1 is C-1 / D-1 = 60% by mass / 40% by mass, and the total thickness is as follows. A stretch shrink laminated film was obtained in the same manner as in Example 1 except that the thickness was 13 μm (thickness ratio: 1/2/1). The results of evaluating the obtained film are shown in Table 1.

Example 4
In Example 1, as a component (B) which is an ionomer-based resin composition, the ratio of C-1 and D-1 was C-1 / D-1 = 40% by mass / 60% by mass, except for mass ratio. In the same manner as in Example 1, a stretch shrink laminated film was obtained. The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 1)
In Example 1, a stretch shrink laminated film was obtained in the same manner as in Example 1 except that the component (B) that is the ionomer resin composition was 100% by mass of C-1 as the component (C). . The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 2)
In Example 1, a stretch shrink laminate film was obtained in the same manner as in Example 1 except that D-1 serving as the (D) component was 100% by mass as the (B) component that is an ionomer resin composition. The results of evaluating the obtained film are shown in Table 1.

From Table 1, it can be seen that the stretch shrink laminated film defined in the present invention is excellent in packaging finish, without heat shrinkage characteristics and no problems of tearing and breaking during push-up packaging. Moreover, it can confirm that it can manufacture also by inflation molding (Examples 1-4). On the other hand, when the ionomer resin is used alone as the ionomer-based resin composition for the intermediate layer (Comparative Example 1), although the heat shrinkage rate is good, the elongation of the film is in the vertical and horizontal directions. Both of them are as low as 50% or less, and when a large amount (about 1000 pieces) is packed by push-up packaging, there are many problems of deformation and breakage of the tray, which causes a practical problem. Further, when an ethylene / unsaturated carboxylic acid copolymer is used alone as the resin composition for the intermediate layer (Comparative Example 2), the elongation of the film is 200% or more in both the vertical and horizontal directions. Although the packaging suitability is good, the heat shrinkage rate is small, and it can be confirmed that there is a problem in the finished packaging after shrink packaging by shrinker.

Claims (8)

  A laminated film composed of at least three layers, the surface layer of which is mainly composed of component (A), which is an ethylene-based polymer, and the intermediate layer of which is composed mainly of component (B), which is an ionomer-based resin composition. The tensile elongation in the machine direction is 100% or more, and the total value of the heat shrinkage in the machine direction and the transverse direction when immersed in an oil bath at 80 ° C. for 10 seconds is 25% or more. Stretch shrink laminated film.   The stretch shrink laminated film according to claim 1, wherein the tensile elastic modulus is in the range of 200 MPa to 400 MPa, and the 50% tensile elongation stress in the machine direction and the transverse direction are both 40 MPa or less.   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.   Component (A) which is an ethylene polymer 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. The stretch shrink laminated film according to claim 1, which is a vinyl acetate copolymer.   The stretch shrink laminated film according to claim 1 or 2, wherein the melting point of the component (A) which is an ethylene polymer is 65 to 100 ° C. The (B) component which is an ionomer-based resin composition is a mixed resin composition containing (C) component 60 to 30% by mass and (D) component 40 to 70% by mass shown below. Item 3. A stretch shrink laminated film according to item 1 or 2.
(C) An ethylene / unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of 10 to 30% by mass and a degree of neutralization by metal ions of 30 to 80% (D) An unsaturated carboxylic acid content of 5 to 15% by mass An ethylene / unsaturated carboxylic acid copolymer having a melt flow rate (JIS K7210, 190 ° C., load: 21.18 N) of 0.2 to 5 g / 10 min.   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 the resin, and blowing air into the cylinder to expand the molten cylinder. The stretch shrink laminated film in any one of claim | item 1 -6. It manufactures with an inflation molding machine, The manufacturing method of the stretch shrink laminated film in any one of Claims 1-6 characterized by the above-mentioned.