JP2008080744A - Stretch shrink laminated film and manufacturing method thereof - Google Patents

Abstract

Disclosed is a stretch shrink laminated film that can be manufactured even by an inflation molding machine that exhibits good productivity and has low manufacturing equipment costs, and has excellent low temperature shrinkage and finished packaging, and a method for manufacturing the same.
SOLUTION: A laminated film composed of at least three layers, wherein both surface layers are composed mainly of an (A) component that is an ethylene polymer, and an intermediate layer is a (B) component that is a lactic acid resin and an ionomer. A stretch shrink laminated film comprising as a main component a mixed resin composition with component (C) which is a resin.
[Selection figure] None

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. .

  Shrink films in the above applications are roughly classified into two types depending on 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. This 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 is stretch-wrapped, and then shrink-wrapped in order to develop wrinkle elimination and film tightness.

  In a packaging method using a 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.

  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.

  The packaging of fresh products, etc., is roughly 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 costs, the in-store packaging ratio is decreasing, and the ratio of consolidating, mass, 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 film with a tight feeling as compared with a stretch film and a tight product. 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 shrinkability in the present invention) at a relatively low temperature (usually about 80 ° C.) are required. A good stretch shrink film is desired.

  Here, the conventional manufacturing method of shrink wrapping film is a tenter method which is a method in which a melt-extruded resin is once cooled and solidified to collect a raw film or a raw tube 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.).

  Patent Document 1 proposes a stretch shrink film for food packaging in which a layer mainly composed of a polyolefin resin and a layer mainly composed of polylactic acid are laminated. Specifically, as polylactic acid, a material having a D-form weight of 4 mass% and a weight average molecular weight of about 200,000 is used, and the thickness of the layer mainly composed of polylactic acid in the total thickness of the film In the multilayer inflation molding apparatus, an example in which a film is obtained with a blow-up ratio of 6 times is shown such that the thermal shrinkage rate at 120 ° C. is 30% or more in the longitudinal direction of the film, A film having a lateral shrinkage of 40% or more is disclosed. However, in this application, although it has a heat shrink characteristic suitable for a high shrink type shrink film used for overlap shrink wrapping by inflation molding, a needle hole formed to allow internal air to escape during the heat shrink described above However, when the film is used for stretch stretch shrink applications, such as easy tearing of the film and insufficient low-temperature shrinkage characteristics and packaging finish, there are still problems to be solved.

JP 2002-019053 A

  An object of the present invention is to provide a stretch shrink laminated film that exhibits good productivity and can be manufactured even by an inflation molding machine with low manufacturing equipment costs, and has excellent low temperature shrinkage and packaging finish, and a method for manufacturing the same. There is to do.

As a result of intensive studies, the present inventors have found that the above problems can be solved by using an ethylene polymer as both surface layers and a mixed resin composition of a lactic acid resin and an ionomer resin as an intermediate layer. 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) that is an ethylene polymer, and the intermediate layer is a lactic acid resin (B) component and an ionomer system A stretch shrink laminated film comprising as a main component a mixed resin composition with a component (C) which is a resin.
(2) The mixed resin composition is composed of 10 to 90% by mass of component (B) which is a lactic acid resin and 90 to 10% by mass of component (C) which is an ionomer resin ( 1) The stretch shrink laminated film as described.
(3) Stretch shrink laminated film according to (1) or (2), wherein the thermal shrinkage in the vertical direction and the horizontal direction when immersed in an oil bath at 80 ° C. for 10 seconds is 20% or more, respectively. .
(4) 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 any one of (1) to (3), wherein the stretch shrink laminated film is at least one ethylene polymer selected from methacrylic acid ester copolymers.
(5) 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 any one of (1) to (3), wherein the stretch shrink laminated film is an ethylene-vinyl acetate copolymer.
(6) Melting | fusing point of (A) component which is an ethylene-type polymer is 65-100 degreeC, The stretch shrink laminated film in any one of (1) to (3) characterized by the above-mentioned.
(7) The component (C) which is an ionomer resin is an ethylene / unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of 10 to 30% by mass and a neutralization degree of 15 to 80% with metal ions. The stretch shrink laminated film according to any one of (1) to (6).
(8) 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, and blowing air into the cylinder to expand the molten cylinder. The stretch shrink laminated film according to any one of (1) to (7).

  Another object of the present invention is achieved by manufacturing the stretch shrink laminated film according to any one of the above (1) to (7) with an inflation molding machine.

  ADVANTAGE OF THE INVENTION According to this invention, the stretch shrink laminated | multilayer film excellent in low-temperature shrinkage | contraction property and packaging finish and its manufacturing method can be provided.

The present invention will be described in detail below.
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 is a lactic acid resin. The main component is a mixed resin composition of the component (B) and the component (C) which is an ionomer resin.

  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 has a function of expressing surface characteristics such as transparency and mechanical properties 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. 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 low-temperature shrinkage 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 and the like 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.

  Furthermore, the melting point of the component (A), which is an ethylene polymer, is 65 to 65 from the balance between the above-mentioned surface characteristics and mechanical characteristics of both surface layers and the heat shrinkability characteristics of the resulting stretch shrink laminated film, particularly low temperature shrinkage. 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 low-temperature shrinkage 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 component (B) will be described. It is important that the component (B) in the present invention is a lactic acid resin. It is preferable to use the lactic acid-based resin as the component (B) because the rigidity of the film at room temperature is increased, and it is difficult for the film to sag due to stacking during transportation during transportation of goods after packing. In addition, since the glass transition temperature exists between the film forming extrusion temperature and room temperature, the stretching deformation stops near the glass transition temperature during the stretching process in the cooling process from a molten state such as inflation molding, and the glass transition Since it is possible to leave the shrinkage strain received at a temperature higher than the temperature without relaxing, it is possible to impart a low temperature shrinkage characteristic (low temperature shrinkage characteristic) suitable for the stretch shrink film.

The lactic acid-based resin includes poly (L-lactic acid) whose structural unit is L-lactic acid, poly (D-lactic acid) whose structural unit is D-lactic acid, and poly (L-lactic acid and D-lactic acid whose structural units are L-lactic acid and D-lactic acid. DL-lactic acid) or a mixture thereof. The composition ratio of D-lactic acid (D-form) and L-lactic acid (L-form) of the lactic acid resin is essentially L-form: D-form = 100: 0 to 90:10, or L-form. : D-form = 0: 100 to 10:90, preferably L-form: D-form = 100: 0 to 94: 6, or L-form: D pair = 0: 100 to 6:94 In particular, L-form: D-form = 99.5: 0.5 to 94: 6, or L-form: D-form = 0.5: 99.5 to 6:94 is more preferable. When the composition ratio between the D body and the L body is within this range, the resulting film has high heat resistance and the application is not limited.
However, from the viewpoint of imparting low-temperature heat shrinkage properties, it is preferable that the crystallinity of the lactic acid resin is low, and L-form: D-form = 50: 50 to 94: 6, or L-form: D-form = 50: 50. ~ 6: 94 is preferred because it easily develops low-temperature heat shrinkage characteristics.
In addition, you may blend the lactic acid-type resin from which the copolymerization ratio of L body and D body differs. In this case, by blending a substantially homopolymer of L-form and D-form of a plurality of lactic acid resins and a copolymer, it is possible to balance the low temperature heat shrinkage characteristics and the expression of heat resistance.

As a polymerization method for the lactic acid-based resin, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed. For example, in the condensation polymerization method, L-lactic acid, D-lactic acid, or a mixture thereof can be directly subjected to dehydration condensation polymerization to obtain a lactic acid resin having an arbitrary composition.
In the ring-opening polymerization method (lactide method), lactide, which is a cyclic dimer of lactic acid, has an arbitrary composition and crystallinity using an appropriate catalyst while using a polymerization regulator or the like as necessary. A lactic acid resin can be obtained. The lactide includes DL-lactide composed of L-lactic acid and D-lactic acid. By mixing and polymerizing these as required, a lactic acid-based resin having a desired composition and crystallinity can be obtained.

  Furthermore, the lactic acid-based resin used in the present embodiment can be added with a small amount of a copolymerization component, if necessary, within a range not impairing the performance of the present invention, or a non-aliphatic carboxyl group such as terephthalic acid or the like. Non-aliphatic diols such as a hydroxyl group or an ethylene oxide adduct of both of them can also be used.

  The lactic acid resin used in the present embodiment preferably has a weight average molecular weight in the range of 50,000 to 400,000, and more preferably in the range of 100,000 to 300,000. As long as the polymerization average molecular weight of the acid resin is within such a range, mechanical properties and practical properties such as heat resistance can be secured, and good moldability can be secured because of an appropriate melt viscosity.

  As the lactic acid resin used in the present embodiment, a commercially available lactic acid resin can be used. For example, a trade name “Lacia” series (manufactured by Mitsui Chemicals), a trade name “Nature Works” series (Nature Works) And a product name “U'z series” (manufactured by Toyota Motor Corporation).

  The MFR (JIS K7210, 190 ° C., load: 21.18 N) of the component (B) used in the present invention is preferably 0.2 to 20 g / 10 minutes. 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.

  Next, the ionomer resin as the component (C) will be described. The ionomer resin neutralizes at least part of the saturated carboxylic acid component of the copolymer consisting of ethylene, unsaturated carboxylic acid, and other unsaturated compounds as optional components, with at least one of metal ions and organic amines. Can get to do. 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 unsaturated carboxylic acid as raw materials for the ionomer-based resin and other unsaturated compounds as optional components, the unsaturated carboxylic acid preferably has about 3 to 8 carbon atoms. 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. A typical example of the unsaturated compound as an optional component is an unsaturated ester. Specific examples thereof include vinyl acetate. In addition, these can be used individually by 1 type or in combination of 2 or more types.

As the neutralization component of the ^{copolymer, Na +, K +, Li} +, Ca 2+, Mg 2+, Zn 2+, Cu 2+, Co 2+, Ni 2+, Mn 2+, 1 , such as ^{Al 3+} Examples thereof include cation of trivalent to trivalent metal (hereinafter sometimes abbreviated as metal ion) or organic amine. 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 present invention, the copolymer as the above ionomer raw material has an ethylene content of 50 to 90% by mass, preferably 60 to 88% by mass, and an unsaturated carboxylic acid content of 10 to 30% by mass, preferably 12 to 20%. The mass% and other unsaturated compounds having a polymerization composition of 0 to 40 mass%, preferably 0 to 20 mass% are suitably used. Further, the neutralization degree is preferably obtained by neutralizing 15 to 80%, preferably 20 to 60% of the amount of unsaturated carboxylic acid in the copolymer component with the metal cation. Here, if it is within the range of the polymer 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 is maintained. 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 type resin can be used individually by 1 type or in combination of 2 or more types. In this case, it is also possible to use a combination of ionomer resins having different metal ions.

  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, ionized portions become ionic crosslinks in which they are aggregated by ionic bond strength. The ionic crosslinks are aggregated by ionic bonds, and when they are subjected to a force greater than the ionic bond strength, the aggregated portions are broken, but when the force is smaller than the ionic bond strength, 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. Here, as long as it is within the range of the polymerization composition and the degree of neutralization, there is no increase in extrusion performance, specifically, excessive melt viscosity due to these actions, and in the cooling process from a molten state such as inflation molding. At the time of stretching, the ionic crosslink remains in a pseudo-crosslinked structure, so that it is considered possible to impart a low temperature heat shrinkage property (low temperature shrinkage) suitable for the stretch shrink film.

  Regarding the degree of neutralization of the ionomer-based resin, the degree of neutralization can also be adjusted by blending an unneutralized copolymer with an ionomer resin having a high degree of neutralization. Specifically, for example, when the ionomer resin having a neutralization degree of 80% neutralized with a monovalent metal cation is set to 40%, the ionomer resin having a neutralization degree of 80% is obtained. This can be achieved by melt-kneading the unneutralized copolymer at a ratio of 50% by mass / 50% by mass.

  It is preferable that MFR (JIS K7210, 190 degreeC, load 21.18N) of (C) component which is an ionomer type resin 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 (C), which is an ionomer resin used in the present invention, is not particularly limited, and for example, a known production method shown in JP-B-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 may be obtained. Copolymer resins 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. Specific products of ionomer resins include “High Milan”, a trade name of Mitsui DuPont Polychemical Co., Ltd. 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 “Nuclele” of Mitsui-DuPont Polychemical Co., Ltd., the product of Nippon Polychem Co., Ltd. The name “Lex Pearl EAA” and the product name “Primacol” of Dow Chemical Co., Ltd. are listed.

  In the intermediate layer of the present invention, it is important that the mixed resin composition of the component (B) that is the lactic acid resin and the component (C) that is the ionomer resin is a main component. Here, the intermediate layer is mainly composed of a mixed resin composition of the component (B) that is a lactic acid resin and the component (C) that is an ionomer resin, so that, for example, from a molten state such as inflation molding. During the stretching process in the cooling process, the deformation stops near the glass transition temperature of the lactic acid-based resin, and it can be cooled while leaving the shrinkage distortion due to the deformation received at a temperature higher than the glass transition temperature, without being relaxed, In addition, the cohesive force of the ionomer resin's ionic crosslinks increases the internal pressure of the bubble and stabilizes the area where the deformation of the bubble stops (frost line). Improve film formation stability during molding (for example, bubble stability in inflation molding) while imparting properties (low temperature shrinkability) Possible, and therefore preferable.

  The mixed resin composition used for the intermediate layer of the present invention is not particularly limited as long as it satisfies the above-mentioned characteristics, but from the point that it can exert a function of expressing good low-temperature shrinkage and molding processability, The mixed resin composition in which the mixing ratio of the lactic acid resin as the component (B) and the ionomer resin as the component (C) is 10 to 90% by mass of the component (B) and 90 to 10% by mass of the component (C). More preferably, it is a mixed resin composition containing (B) component 30 to 70% by mass and (C) component 70 to 30% by mass.

  As described above, the stretch shrink laminated film of the present invention includes both surface layers mainly composed of the component (A) that is an ethylene polymer, the component (B) that is a lactic acid resin, and an ionomer resin ( C) A laminated film composed of at least three layers having an intermediate layer composed mainly of a mixed resin composition with component, but improved mechanical properties and interlayer adhesion within the scope of the present invention. For the purpose, other layers (hereinafter may be abbreviated as P layer) may be introduced as needed. Here, the surface layer (hereinafter sometimes abbreviated as S layer) may have the same layer in addition to the both surface layers, that is, the intermediate layer. The intermediate layer (hereinafter sometimes abbreviated as M layer) has a three-layer structure consisting of (S layer) / (M layer) / (S layer), (S layer) / (P layer) / (M Layer) / (S layer), (S layer) / (P layer) / (M layer) / (P layer) / (S layer), (S layer) / (M layer) / (P The structure of 5 layers or more which consists of (layer) / (M layer) / (S layer) etc. can also be mentioned typically. 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. It is possible to obtain a stretch shrink laminated film excellent in low temperature shrinkage and film forming stability during molding with good productivity and economy.

  The stretch shrink laminated film of the present invention preferably has a thickness ratio of 30 to 90% with respect to the thickness of the entire intermediate layer. If the thickness ratio of the intermediate layer to the entire film is within such a range, for example, as a film forming method, stable film formation can be achieved even if a stretching process method in a cooling process from a molten state such as inflation molding is used. Processability is obtained, and heat shrinkage characteristics such as low temperature shrinkage suitable for stretch shrink films, and mechanical characteristics such as transparency and flexibility can be imparted relatively easily including the material cost. From these facts, the thickness ratio is preferably 35 to 60%, more preferably 35 to 50%, when stable film forming workability, flexibility, and material cost are more important. Here, when the intermediate layer has two layers in the laminated structure as described above, the thickness ratio may be calculated using the total thickness of all the intermediate layers. The overall thickness of the stretch shrink laminate film of the present invention is not particularly limited, but is in the same range as the thickness of a normal stretch film, that is, about 5 to 30 μm, typically about 8 to 20 μm. It is in the range.

  The stretch shrink laminate film of the present invention preferably has a thermal shrinkage rate of 20% or more in the vertical direction and the horizontal direction when immersed in an oil bath at 80 ° C. for 10 seconds. More preferably, if it is 20 to 60%, especially 25 to 50%, it is often possible to eliminate the wrinkles after stretch-wrapping with the stretch shrink laminated film of the present invention by passing through the shrink tunnel, Deformation, curling when the film folded at the bottom of the tray is heat-sealed, or problems such as deformation due to tight tightening of roll film (rolled paper) over time due to natural shrinkage, etc. Since there is no, it is preferable.

  Furthermore, in this invention, although it changes with the magnitude | size relationship between the film width to be used, and the size of a tray, the total value of the heat contraction rate of the vertical direction and a horizontal direction when immersed for 10 second in an 80 degreeC oil bath is 40-. 120% or more, preferably 40 to 100%. Within such a range, the packaging finish on various sizes of trays and the change with time of the roll film are excellent, which is more preferable.

  The above-mentioned heat shrinkage ratio is mainly obtained by changing the thickness constitution ratio of both the surface layer and the intermediate layer, the draw ratio, the blow-up ratio (bubble diameter / die diameter), and the temperature conditions such as the draw temperature and the cooling condition. Can be adjusted to the range. For example, when the heat 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 distortion at a lower temperature, or the amount of cooling blower in the outer surface cooling. What is necessary is just to adjust cooling efficiency suitably, 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 distortion at a lower temperature, or the cooling blower in the outer surface cooling. The cooling efficiency, such as reducing the amount of DOWN or the inner surface cooling, may be appropriately adjusted.

  Next, in the intermediate layer of the stretch shrink laminated film of the present invention, in addition to the mixed resin composition of the component (B) and the component (C), the ethylene polymer as the component (A) described above is included in the present invention. It does not matter if it is mixed within the scope of the above. 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) + (C)} = 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 80% 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 scope of the present invention. Depending on the above, various additives and / or resins other than the above-described mixed resin composition of the component (A), the component (B) and the component (C) can be appropriately blended in the surface layer and / or the intermediate layer, respectively.

  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 resin other than the mixed resin composition of the component (A) and the component (B) and the component (C) is not particularly limited as long as it does not exceed the gist of the present invention. And styrene-based thermoplastic elastomers, various impact resistance improvers and compatibilizers, tackifier resins, plasticizers and the like. 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.

  As a method for imparting low-temperature shrinkage, which is one of the main objects of the present invention, a melt-extruded resin such as a commonly used tenter method or a tubular method is once cooled and solidified to be a raw film or an original film. 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 excellent in low-temperature shrinkage 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, it is preferable to adjust the deformation ratio of the resin extruded into a cylindrical shape from the annular die by adjusting the film take-up speed 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) Heat shrinkage rate The test piece which cut out the film from the obtained film to the strip shape of length 140mm * width 10mm each from the vertical direction and the horizontal direction, and wrote the mark line of 100 mm length in the middle is 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 thermal contraction 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.

(2) Packaging finish A horizontal pillow type packaging machine (STN7500 manufactured by Omori Machinery Co., Ltd.) using a film having a width of 400 mm.
) And a shrink tunnel (C-300 type attached to a pillow packaging machine manufactured by Omori Machinery Co., Ltd., hot air set temperature: 85 ° C., transit time: 3 seconds), and 200 g of clay (thickness 10 mm) An ordinary expanded polystyrene tray (length 200 mm, width 150 mm, height 15 mm) was packaged, and the obtained pack samples were evaluated according to the following criteria.
(◎): There is no wrinkles or sagging on the top surface of the tray, and the film has a sufficient tight feeling (○): There is almost no wrinkles or sagging on the top surface of the tray, and there is a tight feeling on the film (×): On the top surface of the tray No wrinkles or sagging or film tightness

(Example 1)
As the component (A) which is an ethylene polymer, an ethylene-vinyl acetate copolymer (manufactured by Nippon Polyethylene Co., Ltd .: 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 3.0 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) In addition, as component (B) which is a lactic acid-based resin, NW4032D (manufactured by NatureWorks: glass transition temperature: 55 ° C., MFR: 3.0 g / 10 min) (hereinafter sometimes abbreviated as B-1) 60 As a component (C) that is an ionomer-based resin by mass%, Himilan 1706 (manufactured by Mitsui DuPont Polychemical Co., Ltd .: Himilan 1706, density: 0.96 g / cm3, melting point: 8 ° C., MFR: 0.9 g / 10 min) (hereinafter may be abbreviated as C-1) 40% by mass as a mixed resin composition obtained by melt-kneading at an extrusion set temperature of 180 to 200 ° C. Combined from separate extruders, co-extruded inflation molding with annular three-layer die temperature of 185 ° C., lip gap of 1.2 mm, blow-up ratio of 5.0, total thickness of 10 μm (thickness ratio: 1/2/1) A stretch shrink laminated film was obtained. The results of evaluating the obtained film are shown in Table 1.

(Example 2)
In Example 1, the component (B) is 50% by mass of B-1, and the component (C) is C-1 of 30% by mass. An ethylene / acrylic acid copolymer (manufactured by Nippon Polyethylene Co., Ltd .: Lexpearl) A-210K, Acrylic acid content: 7% by mass, MFR: 3.0 g / 10 min, Melting point: 98 ° C. (hereinafter sometimes abbreviated as C-2) 20% by mass A shrink laminated film was obtained. The results of evaluating the obtained film are shown in Table 1.

(Example 3)
In Example 1, the composition of the intermediate layer was 50% by mass of B-1 as component (B), 20% by mass of C-1 as component (C), and ethylene-acetic acid as component (A). Vinyl copolymer (Mitsui DuPont Polychemical Co., Ltd .: Everflex EV360, vinyl acetate content: 25% by mass, density: 0.95 g / cm3, melting point: 77 ° C., MFR: 2.0 g / 10 min) ) (Sometimes abbreviated as A-2 below) was changed to 30% by mass, and a stretch shrink laminated film was obtained in the same manner. 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 intermediate layer was changed to A-1 used for the front and back layers, and a single layer film substantially consisting of A-1 was used. It was. 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 low-temperature shrinkage and packaging finish. Moreover, it can confirm that it can manufacture also by inflation molding (Examples 1-3). In contrast, in the case of a layer structure having no intermediate layer mainly composed of a mixed resin composition of the component (B) that is a lactic acid resin and the component (C) that is an ionomer resin (Comparative Example 1). ) Although the suitability of the automatic packaging machine is good, it can be confirmed that the low-temperature shrinkage is poor, wrinkles remain at the end of the packaging, and there is a problem with the tightness of the film.

Claims (9)

  A laminated film composed of at least three layers, wherein both surface layers are composed mainly of component (A) that is an ethylene polymer, and the intermediate layer is composed of component (B) that is a lactic acid resin and an ionomer resin. (C) The stretch shrink laminated film characterized by having a mixed resin composition with a component as a main component.   The mixed resin composition is composed of 10 to 90% by mass of component (B) that is a lactic acid resin and 90 to 10% by mass of component (C) that is an ionomer resin. Stretch shrink laminated film.   The stretch shrink laminated film according to claim 1 or 2, wherein the thermal shrinkage in the vertical direction and the horizontal direction when immersed in an oil bath at 80 ° C for 10 seconds is 20% or more, respectively.   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 any one of claims 1 to 3, 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 any one of claims 1 to 3, wherein the stretch shrink laminated film is a vinyl acetate copolymer.   The melting point of (A) component which is an ethylene-type polymer is 65-100 degreeC, The stretch shrink laminated film of any one of Claim 1 to 3 characterized by the above-mentioned.   Component (C) which is an ionomer resin is an ethylene / unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of 10 to 30% by mass and a neutralization degree of 15 to 80% with metal ions. The stretch shrink laminated film according to any one of claims 1 to 6.   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. Item 8. The stretch shrink laminated film according to any one of items 1 to 7. It manufactures with an inflation molding machine, The manufacturing method of the stretch shrink laminated film of any one of Claim 1 to 7 characterized by the above-mentioned.