JP2014111368A - Stretch wrapping film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-chlorine-based stretch wrapping film, which substantially prevents wrinkles in a wrapping film when a commercial product is wrapped, frozen and delivered to a shop and then thawed and displayed.SOLUTION: The stretch wrapping film is a laminate film comprising at least three layers including: outermost layers essentially comprising an ethylene-based resin (A) component; and a middle layer essentially comprising a propylene-based resin (B) component. The ethylene-based resin (A) component comprises a mixture component of one or more compounds selected from a low-density polyethylene, linear low-density polyethylene, linear ultralow-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-methacrylate copolymer and ionomer resin. According to a dynamic viscoelasticity measurement method, the film shows an average loss tangent (tanδ) of 0.1 to 0.5 in a temperature range from -40 to 0°C at a vibration frequency of 10 Hz and a strain of 0.1%.

Description

  The present invention relates to a stretch packaging film that is suitably used for food packaging, and more particularly to a stretch packaging film that does not contain chlorine or a plasticizer for polyvinyl chloride.

  Conventionally, a polyvinyl chloride film has been mainly used as a film that overlaps by placing fruits and vegetables, meat, side dish, etc. on a lightweight tray, that is, a stretch packaging film for so-called pre-packaging. The reason for this is that the polyvinyl chloride film has good packaging efficiency such as good packaging efficiency and a good packaging finish, and returns to its original state when the film after packaging is deformed by pressing with a finger. Quality recognized by both sellers and consumers that the product value does not decrease, such as excellent elasticity recovery, bottom folding stability, and film peeling during transportation display. It was because of having the advantage of.

  However, in recent years, with respect to polyvinyl chloride films, problems such as elution of hydrogen chloride gas generated during incineration and plasticizers contained in large quantities have been regarded as problems. For this reason, various alternatives to polyvinyl chloride films have been studied, and various stretch packaging films using polyolefin resins have been proposed. Above all, for reasons such as good surface properties as a stretch film, transparency, moderate heat resistance, freedom of material design, economy, etc., an ethylene-vinyl acetate copolymer is used as the main component for the front and back layers, and the intermediate layer In addition, a study is being actively made on a film for stretch packaging having two types and three layers comprising various polypropylene resins as main components.

  For example, the intermediate layer having the above-described two types and three layers is composed of a propylene-based resin (A) having a crystallization heat amount of 10 to 60 J / g, a petroleum resin, a terpene resin, a coumarone-indene resin, a rosin resin, or hydrogen thereof. A stretch film for food packaging which is a layer containing any of the additive derivatives (B) and has a specific storage elastic modulus has been proposed (Patent Document 1).

  However, fruits and vegetables, meat and side dishes have been packaged in stores in the past, but in recent years, large supermarkets and other places have gathered places for packaging fruits and vegetables, meat and side dishes (pack center). There is a tendency that the number of sales forms in which packaging is carried out in a batch and then transported while being frozen to each store is increasing, and there is a demand for the development of a film for stretch packaging that matches the sales form.

  When the film for stretch packaging is set in an automatic packaging machine and packaged, the film of a predetermined width is packaged with the degree of stretching changed according to the size of the tray. In order to deliver to each store later, it will be transported in a frozen state. In addition, since transportation efficiency is also considered, usually after being transported in a state of being stacked in a stack of about 2 to 3 packs, it will be displayed after thawing at each store. In the non-chlorine stretch packaging film as proposed, wrinkles and the like are generated in the packaging film after display, and there is a demand for improvement.

JP-A-9-154479

  The present invention has been made in view of the above circumstances, and the problem to be solved is that the packaging film is less likely to be wrinkled even if it is packed at a pack center and frozen and transported to each store and then thawed and displayed at each store. The object is to provide a new non-chlorine stretch packaging film.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is composed of at least three layers having both surface layers containing an ethylene resin (A) component as a main component and an intermediate layer containing a propylene resin (B) component as a main component. The ethylene resin (A) component is a low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylate ester copolymer It consists of one or two or more kinds of mixed components selected from a coalescence, an ethylene-methacrylic ester copolymer, and an ionomer resin, and was measured at a vibration frequency of 10 Hz and a strain of 0.1% by a dynamic viscoelasticity measurement method. Stretch packaging film characterized by having an average value of loss tangent (tan δ) at −40 to 0 ° C. of 0.1 to 0.5 It resides in the arm.

  According to the present invention, the suitability of various packaging machines (cutting properties, packaging wrinkles, bottom folding stability, tearability) when using an automatic packaging machine is good, and packaging at a pack center and freezing at each store. It is possible to provide a non-chlorine stretch packaging film that is less likely to be wrinkled on the film surface even after being thawed and displayed after transport.

  Hereinafter, a stretch packaging film (hereinafter, may be abbreviated as a stretch film) as an example of an embodiment of the present invention will be described. However, the scope of the present invention is not limited to the embodiments described below.

  The stretch film of the present invention forms a surface layer mainly composed of an ethylene-based resin (A) component and has a laminated structure, particularly heat sealability (bottom sealability) at low temperatures, self-adhesiveness, The formability at the time of inflation can be improved.

  Here, examples of the ethylene-based resin (A) include low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, and copolymers containing ethylene as a main component, for example Ethylene, α-olefins having 3 to 10 carbon atoms such as propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, heptene-1, octene-1, vinyl acetate, vinyl propionate, etc. One or two selected from unsaturated carboxylic acid esters such as vinyl esters, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and the like, and ionomers thereof, unsaturated compounds such as conjugated dienes and non-conjugated dienes Copolymers or multi-component copolymers with more than one comonomer, or their If the composition, and the like. The content of ethylene units in the ethylene polymer is usually more than 50% by mass.

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

  Among these, as the ethylene-based resin (A), the vinyl acetate unit content is 5 to 25% by mass, and the melt flow rate (JIS K7210, temperature: 190 ° C., load: 21.18 N) is 0.2 to 10 g / 10. Minute ethylene-vinyl acetate copolymer is preferred, especially 0.5 to 8 g / 10 min, especially 1 to 6 g / 10 min ethylene-vinyl acetate copolymer is more preferred.

  If the vinyl acetate unit content is 5% by mass or more, the resulting film is soft and not only can maintain flexibility and elastic recovery, but also can impart surface tackiness. On the other hand, if it is 25 mass% or less, surface tackiness will not be too strong and unwinding property and an external appearance can be maintained favorable. Moreover, if the melt flow rate is 0.2 g / 10 min or more, the extrudability can be maintained satisfactorily, while if it is 10 g / 10 min or less, the film forming stability can be maintained, This is preferable because it is possible to suppress the occurrence of thickness unevenness and variations in mechanical strength.

  The intermediate layer is a layer containing a predetermined propylene resin (B) component as a main component. In the present invention, it is preferable to set the crystallization heat amount (ΔHc) of the intermediate layer within a predetermined range (10 J / g or more and 60 J / g or less). If the heat of crystallization is less than 10 J / g, the crystallinity is too low and the film-forming property is deteriorated. In addition, the film may be too soft at room temperature or the strength may be insufficient. Moreover, when the amount of heat of crystallization exceeds 60 J / g, a large force is required at the time of stretching the film, and only non-uniform elongation is exhibited, which is not suitable for a stretch film. The method for adjusting the crystallization heat amount (ΔHc) to a predetermined range is not particularly limited, but a method of mixing a resin different from the propylene resin (B) is preferably used. Among them, it is more preferable to mix the later-described system resin (C) in terms of imparting various packaging machine aptitudes (cutting properties, packaging wrinkles, bottom folding stability, tearing properties, and transparency after packing).

  Examples of the propylene-based resin (B) include a propylene homopolymer, a random copolymer or a block copolymer of propylene and “another copolymerizable monomer”, and the like.

  By using such a propylene-based resin (B) as a main component of the intermediate layer, various packaging suitability such as bottom folding and cutability can be improved, and in addition to pellet storage stability, the resin composition constituting the intermediate layer The strength and heat resistance of the object can be increased.

  In this case, examples of other copolymerizable monomers include ethylene, 1-butene, 1-hexene, 4-methylpentene-1, 1-octene and other α-olefins having 4 to 20 carbon atoms and divinylbenzene, Although dienes, such as 1, 4- cyclohexadiene, dicyclopentadiene, cyclooctadiene, ethylidene norbornene, etc. are mentioned, 2 or more types of these may be copolymerized.

  From the viewpoint of imparting appropriate flexibility necessary for the stretch film, a propylene-ethylene random copolymer, a propylene-ethylene-butene-1 copolymer, a reactor type polypropylene elastomer, and a propylene-ethylene copolymer It is preferable to use one or two kinds of mixed components selected from a coalescence, a propylene-α-olefin copolymer, and a block polypropylene.

  In the case of the propylene resin (B), if the crystallization heat amount (ΔHc) measured at a temperature drop rate of 10 ° C./min with a differential scanning calorimeter (DSC) is 30 J / g or more, the strength and heat seal Sex can be maintained.

  Here, the amount of heat of crystallization (ΔHc) depends on the molecular weight, ethylene content (copolymerization ratio), randomness (dispersibility in the copolymer of ethylene components), stereoregularity, etc. of the propylene resin (B) used. Dependent. In general, it can be said that the higher the crystallization heat amount, the higher the peak temperature tends to increase, and the heat resistance is generally excellent. From such a viewpoint, the crystallization heat quantity (ΔHc) is preferably 30 J / g or more, more preferably 40 J / g or more, and particularly preferably 50 J / g or more. The upper limit is not particularly limited, but is practically 150 J / g or less.

  Further, when the propylene-based resin (B) is a block polypropylene, if the rubber component diameter contained is 1 μm or less, the impact generated during stretching is reduced without impairing transparency, which is preferable for stretch film applications. . In addition, when the rubber component diameter is 1 μm or more, there is a fear that it becomes a base point of breakage during stretching.

  The melt flow rate (MFR) of the propylene resin (B) is not particularly limited, but usually MFR (JISK7210, temperature: 230 ° C., load: 21.18 N) is 0.2 g / 10 min or more. Preferably, it is 0.5 to 18 g / 10 minutes, and more preferably 1 to 15 g / 10 minutes. If the MFR is 0.2 g / 10 min or more, the extrusion processability is stable. If the MFR is 20 g / 10 min or less, stable film formation is possible at the time of molding, as well as unevenness in thickness, decrease in mechanical strength, and variation. Etc. are preferable.

  Examples of the propylene-based resin (B) include, for example, the trade name “Novatech PP” of Nippon Polypro Co., Ltd., the trade name “Noblen” of Sumitomo Chemical Co., Ltd., and the trade names “Prime Polypro” and “Prime” of Prime Polymer Co., Ltd. TPO ", Sun Aroma Co., Ltd. trade name" Qualia "and the like can be mentioned.

  Examples of the resin (C) include a block copolymer of a vinyl aromatic compound and isobutylene. Since such a copolymer generally has rubber elasticity and is flexible, it gives an elastic recovery property to the film and effectively acts to reduce the tensile elastic modulus of the polypropylene resin as the component (B). .

  Here, styrene is a typical vinyl aromatic compound, but styrene homologues such as α-methylstyrene may also be used. Examples of the conjugated diene include 1,3-butadiene, isoprene, 1,3-pentadiene, and the like. These may be used alone or in combination of two or more. Further, as the third component, a small amount of components other than the vinyl aromatic compound and isobutylene may be contained.

  Moreover, it is preferable that the ratio of the vinyl aromatic compound of such a copolymer and isobutylene is 3 / 97-40 / 60 by weight ratio. Here, if the vinyl aromatic compound in the copolymer composition is less than 3% by weight, the rigidity of the copolymer itself is too low, and the polymerization productivity tends to be difficult, such as difficulty in pelletization. If the value exceeds 1, the rigidity of the copolymer itself becomes high, and it is easy to impart elasticity recovery properties to the film to which the component (B) is added, or the effect of reducing the tensile elastic modulus is insufficient. is there.

  Specifically, commercially available products such as a styrene-isobutylene copolymer elastomer (Kaneka Co., Ltd., trade name “SIBSTAR”) can be used.

  In the resin composition constituting the intermediate layer, the content of the resin (C) is preferably 1 to 50% by mass. If content of resin (C) is 1 mass% or more, the elastic recovery property of a film required for a stretch film can be provided. Especially, it is more preferable that content of resin (C) is 5 mass% or more, and it is further more preferable that it is 10 mass% or more. Moreover, if it is 50 mass% or less, compatibility with a propylene resin (B) will improve and transparency can be improved. Therefore, from the viewpoint of achieving both imparting elasticity and improving transparency, the content of the resin (C) is more preferably 40% by mass or less.

  The resin composition constituting the intermediate layer may contain a predetermined resin (D) component in addition to the component (B) and the component (C). Examples of the resin (D) include petroleum resins, terpene resins, coumarone-indene resins, rosin resins, and hydrogenated derivatives thereof. (Also referred to as “petroleum resins”).

Such a resin (D) component effectively acts on further improvement of packaging suitability such as film waist and cutability, bottom folding stability, and transparency.
Here, as the petroleum resin, cyclopentadiene or an alicyclic petroleum resin obtained from the dimer thereof, an aromatic petroleum resin obtained from the C9 component, or a copolymer of alicyclic and aromatic petroleum resin A petroleum resin etc. can be mentioned.

  Examples of the terpene resin include a terpene resin obtained from β-pinene and a terpene-phenol resin.

  Examples of the coumarone-indene resin include a thermoplastic synthetic resin obtained by purifying a 160 to 180 ° C. fraction of tar and polymerizing coumarone having 8 carbons and indene having 9 carbons as main monomers.

Examples of the rosin resin include rosin resins such as gum rosin and wood rosin, and esterified rosin resins modified with glycerin, pentaerythritol, and the like.
The petroleum resin as described above is preferably a hydrogenated derivative from the viewpoints of color tone, thermal stability, and compatibility.

  Moreover, although what has various softening temperatures mainly by molecular weight is obtained as said petroleum resin, what has a softening temperature in 100-150 degreeC, Preferably it is 110-140 degreeC is more suitable.

  Specifically, Mitsui Chemicals' product names “Hilets” and “Petrogin”, Arakawa Chemical Industries' product name “Arcon”, Yashara Chemicals' product name “Clearon”, Idemitsu Petrochemical Co., Ltd. ) And trade names “Escollets” and “Ligalite” of Eastman Chemical Co., Ltd. can be used.

  In the resin composition constituting the intermediate layer, the content of the resin (D) is preferably 1 to 40% by mass. If content of resin (D) is 1 mass% or more, the cut property and bottom folding stability required for a stretch film can be provided. Especially, it is more preferable that content of resin (D) is 5 mass% or more, and it is further more preferable that it is 10 mass% or more. Moreover, if it is 40 mass% or less, the low temperature aptitude required for a stretch film will not be spoiled with a raise of a glass transition temperature, and the blocking of the film by the bleed | bleed of a low molecular weight substance will not be caused easily. Therefore, from this viewpoint, the content of the resin (D) is more preferably 35% by mass or less, and further preferably 30% by mass or less.

  The resin composition constituting the intermediate layer may contain an ethylene-based resin (E) in addition to the component (B), the component (C), and the component (D).

  The ethylene resin (E) may be the same polyethylene polymer as the ethylene resin (A) constituting the surface layer or may be a different ethylene resin, but is preferably the same ethylene resin. It is good. If the ethylene-based resin (E) and the ethylene-based polymer (A) constituting the surface layer are the same ethylene-based polymer, the adhesion between the intermediate layer and the surface layer can be improved, and the dynamics of the entire film In addition to improving the characteristics, for example, trimming loss that occurs when trimming by trimming both ends of the formed film can be prepared by adding it as a constituent material of the intermediate layer, eliminating waste of materials, Material costs can be reduced.

As the most preferred ethylene-based resin (E), the vinyl acetate unit content is 5 to 25% by mass, and the melt flow rate (JISK7210, temperature: 190 ° C., load: 21.18 N) is 0.2 to 10 g / 10 min. The ethylene-vinyl acetate copolymer is preferably 0.5 to 8 g / 10 min, more preferably 1 to 6 g / 10 min.
Here, if the vinyl acetate unit content is 5% by mass or more, the resulting film is not only soft and can maintain flexibility and elastic recovery, but also when the ethylene resin (E) is a surface layer. Can be given surface tackiness. On the other hand, if it is 25 mass% or less, even if it is a case where ethylene-type resin (E) is a surface layer, it can maintain unwinding property and an external appearance favorably, without surface adhesiveness being too strong. it can. Moreover, if the melt flow rate is 0.2 g / 10 min or more, the extrudability can be maintained satisfactorily, while if it is 10 g / 10 min or less, the film forming stability can be maintained, This is preferable because it is possible to suppress the occurrence of thickness unevenness and variations in mechanical strength.

  In the resin composition constituting the intermediate layer, the content of the ethylene resin (E) is preferably 1 to 40% by mass. If content of ethylene-type resin (E) is 1 mass% or more, the low temperature aptitude required for a stretch film can be provided. Especially, it is more preferable that content of ethylene-type resin (E) is 5 mass% or more, and it is further more preferable that it is 10 mass% or more. Moreover, if it is 40 mass% or less, bottom folding stability and heat resistance are sufficient, and from this viewpoint, the content of the ethylene-based resin (E) is more preferably 35 mass% or less, and 30 mass% or less. More preferably.

  The surface layer and / or the intermediate layer of the stretch film of the present invention may be appropriately blended with various additives as described below in order to impart performance such as antifogging properties, antistatic properties, slipperiness, and tackiness. it can.

  Here, as various additives, for example, an aliphatic alcohol system which is a compound of a fatty acid alcohol having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, and a fatty acid having 10 to 22 carbon atoms, preferably 12 to 18 carbon atoms. Fatty acid esters, specifically, monoglycerylate, polyglycerin oleate, glycerin triricinoleate, glycerin acetylricinoleate, polyglycerin stearate, glycerin laurate, polyglycerin laurate, methylacetylricinoleate, ethylacetylricinoleate, Butylacetylricinoleate, propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, polyethylene glycol oleate, polypropylene glycol oleate, sorbitan oleate, sorbitan laurate, Reethylene glycol sorbitan oleate, polyethylene glycol sorbitan laurate, and the like, and polyalkyl ether polyols, specifically, polyethylene glycol, polypropylene glycol, etc., and paraffinic oils can be mentioned, one or two of these The above can be used together.

  These additives are preferably blended in an amount of 0.1 to 12 parts by weight, preferably 1 to 8 parts by weight with respect to 100 parts by weight of the resin component constituting the surface layer and / or the intermediate layer.

  In the stretch film of the present invention, the surface layer is an ethylene polymer (A), and the intermediate layer includes an intermediate layer made of a resin composition containing a predetermined propylene resin (B) component as a main component. It may be a laminated film composed of at least three layers, and other layers (hereinafter abbreviated as P layer) as necessary, such as improvement of mechanical properties and interlayer adhesion, within the scope of the present invention. May be introduced as appropriate. 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) 5 layers consisting of / (P layer) / (M layer) / (P layer) / (S layer), (S layer) / (M layer) / (P layer) / (M layer) / (S layer) A typical configuration can be given. In this case, the resin composition and thickness ratio of each layer may be the same or different.

  In the stretch film of the present invention, the preferred range of the thickness ratio between the surface layer and the intermediate layer is preferably 10 to 65% for the front and back layers and 90 to 35% for the intermediate layer. If the thickness ratio is within such a range, stable film forming stability can be obtained, and suitable surface tackiness can be imparted to the stretch film.

  Furthermore, when considering stable film forming processability, surface tackiness, various physical properties as a stretch wrapping film, and economic efficiency, it is more preferable that the front and back layers are 20 to 60% and the intermediate layer is 80 to 40%. .

  The thickness of the stretch film of the present invention may be in the range used as an ordinary stretch packaging film, that is, in the range of about 8 μm to 30 μm, typically about 9 μm to 20 μm.

The stretch film of the present invention can be produced, for example, by melt-extruding a material from an extruder and forming the material into a film by inflation molding or T-die molding.
When making a laminated film, it is preferable to co-extrusion with a multilayer die using a plurality of extruders. Practically, it is preferable to melt-extrude the material resin from an annular die and perform inflation molding, and the blow-up ratio (tube diameter / die diameter) at that time is preferably 3 or more, particularly preferably in the range of 4 to 7. . As a cooling method in that case, either a method of cooling from the outer surface of the tube, or a method of cooling from both the outer surface and the inner surface of the tube may be used.

  Further, the obtained film is heated to a temperature lower than the crystallization temperature of the resin, and stretched by about 1.2 to 5 times in the longitudinal direction of the film by utilizing a speed difference between nip rolls, or 1.2 in the longitudinal and lateral directions of the film. It may be biaxially stretched to about 5 times. Thereby, improvement of cut property, provision of heat shrinkability, etc. can be performed.

About the storage elastic modulus of the stretch film of the present invention, the loss tangent (tan δ) from −40 ° C. to 0 ° C. measured at a vibration frequency of 10 Hz and a strain of 0.1% by the dynamic viscoelasticity measurement method described in JIS K-7198A. Must be in the range of 0.1 to 0.5.
When the loss tangent (tan δ) is 0.1 or more, the stress relaxation property at low temperature is increased, and the stress applied to the film during loading at freezing and the volume of the contents packed by the film are reduced. It is possible to prevent the occurrence of wrinkles caused by the cause of In addition, when the loss tangent (tan δ) is 0.5 or less, the viscosity of the film at low temperature becomes small, and it becomes difficult for the tray and the film to stick to each other even when loaded at freezing. It is advantageous as a film application.
Each of the above physical properties is achieved by appropriately adjusting the blending ratio of the propylene-based resin (B), the resin (C), and the resin (D) used for the intermediate layer. This can be achieved by setting the content to 40% by mass.

The storage elastic modulus of the stretch film of the present invention is such that the storage elastic modulus (E ′) at 20 ° C. measured at a vibration frequency of 10 Hz and a strain of 0.1% by the dynamic viscoelasticity measurement method described in JISK-7198A is 100 MPa. It is preferably in the range of ˜1 GPa. When the film is used as a soft film, the value of the elastic modulus near room temperature is an index. When the storage elastic modulus (E ′) at 20 ° C. is 100 MPa or more, problems such as poor adhesion and workability are unlikely to occur at room temperature. On the other hand, if it is 1 GPa or less, the film does not become too hard and is appropriately stretched, which is advantageous for soft film applications.
Each of the above physical properties is achieved by appropriately adjusting the blending ratio of the propylene-based resin (B), the resin (C), and the resin (D) used for the intermediate layer. This can be achieved by setting the content to 40% by mass.

The flexibility of the stretch film of the present invention is such that a 100% elongation tensile stress in the transverse direction (TD) of the film measured by conducting a tensile test at a temperature of 20 ° C. and a tensile speed of 200 mm / min according to JIS Z1702 is 40 to 140 kgf / it is preferably in the range of cm ^2, more preferably 50~130kgf / cm ^2.
Each of the above physical properties is achieved by appropriately adjusting the blending ratio of the propylene-based resin (B), the resin (C), and the resin (D) used for the intermediate layer. The amount of crystallization (ΔHc) is 10 when measured at a rate of temperature decrease of 10 ° C./min with a differential scanning calorimeter (DSC) of the propylene-based resin (B) component used for the intermediate layer. It can be achieved by ˜60 J / g.

Regarding the haze of the stretch film of the present invention, the relationship between the light transmittance (%) measured according to JIS-K7105 and the film thickness (μm), the light transmittance (%) / film thickness (μm) is 0.1. % / Μm or less, more preferably 0.07% / μm or less. If the light transmittance (%) / film thickness (μm) is 0.1 or more, the haze of the entire film increases, which is not suitable as a stretch film for packaging.
Each of the physical properties described above has a crystallization heat amount (ΔHc) of 10 to 60 J when measured at a temperature decreasing rate of 10 ° C./min with a differential scanning calorimeter (DSC) of the propylene resin (B) component used for the intermediate layer. / G can be achieved.

  In the present invention, the “stretch film” is meant to encompass a wide range of packaging films having stretchability and self-adhesiveness. Typically, pre-packaging packaging films that overlap by placing fruits and vegetables, meat, side dishes, etc. on lightweight trays, and packaging films that overlap to secure the luggage during luggage transportation, etc. .

  In the present invention, the “main component” includes the meaning of allowing other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified. At this time, the content ratio of the main component is not specified, but the main component (when two or more components are main components, the total amount thereof) is 50% by mass or more, particularly 70% by mass in the composition. %, More preferably 90% by mass or more (including 100% by mass).

  In general, “sheet” is a thin product as defined by JIS, and generally its thickness is small and flat instead of length and width, and “film” is generally defined as length and width. A thin flat product having an extremely small thickness and an arbitrarily limited maximum thickness, usually supplied in the form of a roll (Japanese Industrial Standard JISK6900). For example, in terms of thickness, in the narrow sense, a film having a thickness of 100 μm or more is sometimes referred to as a sheet, and a film having a thickness of less than 100 μm is sometimes referred to as a film. However, since the boundary between the sheet and the film is not clear and it is not necessary to distinguish the two in terms of the present invention, in the present invention, even when the term “film” is used, the term “sheet” is included and the term “sheet” is used. In some cases, “film” is included.

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

(1) Crystallization peak temperature (Tc) and crystallization heat (ΔHc)
Using DSC-7 manufactured by PerkinElmer, Inc., according to JISK7121, JISK7122, the measurement sample was heated to 200 ° C at a temperature increase rate of 10 ° C / min, held for 1 minute, and then the temperature decrease rate was 10 ° C / min. The crystallization peak temperature (Tc) and the crystallization heat amount (ΔHc) were determined based on the obtained crystallization curve.

(2) Average value of loss tangent at -40 to 0 ° C. (tan δ)
According to the dynamic viscoelasticity measurement method described in the JISK-7198A method, using a dynamic viscoelasticity measurement device “DVA-200” manufactured by IT Measurement Control Co., Ltd., the vibration frequency is 10 Hz in the transverse direction (TD). Measurement was performed from −100 ° C. to 200 ° C. at a rate of temperature increase of 1 ° C./min at a strain of 0.1%, and the average value of loss tangent (tan δ) from −40 to 0 ° C. was calculated from the obtained data.

(3) Storage elastic modulus (E ')
According to the dynamic viscoelasticity measurement method described in the JISK-7198A method, using a dynamic viscoelasticity measurement device “DVA-200” manufactured by IT Measurement Control Co., Ltd., the vibration frequency is 10 Hz in the transverse direction (TD). Measurement was performed from −100 ° C. to 200 ° C. at a rate of temperature increase of 1 ° C./min at a strain of 0.1%, and the storage elastic modulus (E ′) at a temperature of 20 ° C. was determined from the obtained data.

(4) Flexibility According to JIS Z1702, a tensile test was performed at a temperature of 20 ° C. and a tensile speed of 200 mm / min, and a 100% elongation tensile stress (kgf / cm ² ) in the transverse direction of the film was measured. Flexibility was evaluated according to the following criteria.
A: Tensile stress value (kgf / cm ² ) is 50 or more and less than 80 B: Tensile stress value (kgf / cm ² ) is 40 or more and less than 50, or 80 or more and less than 90 Δ: Tensile stress value (kgf / cm ² ) is 20 or more and less than 40, or 90 or more and less than 140 ×: Tensile stress value (kgf / cm ² ) is less than 20, or 140 or more

(5) Packing machine suitability Using the films obtained in the examples and comparative examples (width 350 mm), the expanded polystyrene tray (length 330 mm, width 230 mm, height 38 mm) is packaged by a linear overlap shrink automatic packaging machine. According to the criteria shown in Table 2, transparency after packing, cut property, packaging wrinkle, bottom folding stability and tearability were evaluated, and Table 1 shows the results.

(6) Packing suitability after freezing and thawing (4) Samples packed with suitability for packaging machine were stored in 3 stages in a -20 ° C freezer for 24 hours and then thawed to cause wrinkles The case was evaluated based on the criterion of x when no wrinkle occurred, and the result is shown in Table 1.

(7) Haze After measuring the light transmittance of the intermediate layer using the haze / transmittance meter “HM-150” manufactured by Murakami Color Research Laboratory Co., Ltd., according to the light transmittance measuring method described in JIS-K7105, By dividing by the thickness (μm) of the intermediate layer, the value of light transmittance (%) / intermediate layer thickness (μm) was calculated, and the results are shown in Table 1.

Example 1:
About the resin composition which forms both surface layers, EVA (vinyl acetate content: 15 mass%, melt flow rate (JISK7210, temperature: 190 degreeC, load: 21.%) as an ethylene-type polymer which is (A) component. 18N) 2.3 g / 10 min) 97 parts by mass and 3 parts by mass of diglycerin oleate as an antifogging agent were melt-kneaded. On the other hand, about the resin composition which forms an intermediate | middle layer, (B) component propylene-type resin (Block polypropylene, crystallization calorie | heat amount: 67.0 J / g, crystallization peak temperature: 121.0 degreeC, melt flow rate ( JISK7210, temperature: 230 ° C., load: 21.18 N) 2.0 g / 10 min), and a block copolymer of a vinyl aromatic compound and isobutylene as component (C) (melt flow rate (JISK7210, temperature: 230 ° C., load: 21.18 N) 6.0 g / 10 min), and hydrogenated petroleum resin (softening temperature 125 ° C., Arakawa Chemical Industries, Ltd., Alcon P125) as a component (D) by mass ratio ( B) / (C) / (D) = 51.4 / 32.4 / 16 · 2 and kneaded so that these melt-kneaded resins have an annular three-layer die of 190 ° C. and a blow-up ratio of 5 0 by co-extrusion inflation molding, to obtain a three-layer film having a total thickness of 12μm (2μm / 8μm / 2μm).

Example 2:
A three-layer film was obtained in the same manner as in Example 1 except that the ratio of the total thickness of 12 μm in Example 1 was changed to (2.4 μm / 7.2 μm / 2.4 μm).

Comparative Example 1:
The propylene-based resin which is the component (B) of the intermediate layer in Example 1 was replaced with propylene-based resin <1> (propylene-ethylene random copolymer, crystallization heat amount: 60.0 J / g, crystallization peak temperature: 115. 9 ° C., melt flow rate (JISK7210, temperature: 230 ° C., load: 21.18 N) 2.0 g / 10 min) and propylene resin <2> (crystallization peak: single, crystallization heat: 8.9 J / g, crystallization peak temperature: 100.0 ° C., melt flow rate (JISK7210, temperature: 230 ° C., load: 21.18 N) 2 g / 10 min), propylene resin <1> / propylene resin <2> = 63 / 37 and kneaded in 37, and hydrogenated petroleum resin (softening temperature 125 ° C., Arakawa Chemical Industries, Ltd., Alcon P125) as a component (D) by mass ratio B) / (except for melt kneading so that D) = 83.8 / 16.2 was obtained a three-layer film in the same manner as in Example 1.

Comparative Example 2:
The propylene-based resin which is the component (B) of the intermediate layer in Example 1 is a propylene-based resin (propylene-ethylene random copolymer, crystallization heat amount: 60.0 J / g, crystallization peak temperature: 115.9 ° C., A three-layer film was obtained in the same manner as in Example 1 except that the melt flow rate was changed to a melt flow rate (JISK7210, temperature: 230 ° C., load: 21.18 N) 2.0 g / 10 min).

  From the results in Table 1, in Examples 1 and 2, the average value of loss tangent (tan δ) at −40 to 0 ° C. measured at a vibration frequency of 10 Hz and a strain of 0.1% by the dynamic viscoelasticity measurement method is 0.00. It is within 1 to 0.5, and the transparency after packing when packaging a large tray in an automatic packaging machine is also good, and the storage elastic modulus (E ′) is within the specified range, so that it is suitable for the packaging machine. It can be confirmed that good results are obtained in any of flexibility, packaging suitability after freezing / thawing, and haze. Further, in Example 1, in addition to the resin composition (B) component and the (C) component forming the intermediate layer, a hydrogenated petroleum resin is included as the (D) component, so that flexibility, packaging machine suitability, low temperature It is excellent in suitability and is a particularly preferred embodiment. In contrast, the average value of loss tangent (tan δ) at −40 to 0 ° C. measured at a vibration frequency of 10 Hz and a strain of 0.1% by a dynamic viscoelasticity measurement method is other than 0.1 to 0.5. When the intermediate layer was used, it was observed that wrinkles were generated on the film surface in the packaging suitability after freezing and thawing (Comparative Example 1), and the propylene-based resin (B) was mixed with propylene-ethylene random copolymer. When the intermediate layer changed to the polymer was used, it was found that the haze was significantly deteriorated (Comparative Example 2).

  The film of the present invention can be suitably used as a stretch film for food packaging, for example.

Claims (6)

A laminated film composed of at least three layers having both surface layers containing an ethylene-based resin (A) component as a main component and an intermediate layer containing a propylene-based resin (B) component as a main component, The ethylene resin (A) component is composed of low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid ester copolymer. Loss tangent at −40 to 0 ° C. measured at a vibration frequency of 10 Hz and a strain of 0.1% by dynamic viscoelasticity measurement method, comprising one or two or more mixed components selected from coalescence and ionomer resin A film for stretch packaging, wherein the average value of (tan δ) is 0.1 to 0.5. The film for stretch packaging according to claim 1, wherein the storage elastic modulus (E ') of the laminated film at 20 ° C measured at a vibration frequency of 10 Hz and a strain of 0.1% by a dynamic viscoelasticity measurement method is 100 MPa to 1 GPa. The film for stretch packaging according to claim 1 or 2, wherein the light transmittance (%) and the total thickness (µm) of the intermediate layer satisfy the following formula (1).
Light transmittance (%) / total thickness (μm) ≦ 0.1 The ethylene-based resin (A) component has a vinyl acetate unit content of 5 to 25% by mass and an ethylene melt flow rate (JIS K 7210, 190 ° C., load 21.18 N) of 0.2 to 10 g / 10 min. The film for stretch packaging according to any one of claims 1 to 3, which is a vinyl acetate copolymer. The intermediate layer has a heat of crystallization (ΔHc) of 10 J / g or more and 60 J / g or less when measured by a differential scanning calorimeter (DSC) at a temperature drop rate of 10 ° C / min. A film for stretch packaging as described in 1. The film for stretch packaging according to any one of claims 1 to 5, wherein the intermediate layer comprises two or more of the following components (B), (C), and (D).
(B) Propylene-ethylene copolymer, propylene-ethylene-butene-1 copolymer, reactor type polypropylene elastomer, propylene-ethylene copolymer, propylene-α-olefin copolymer, and block polypropylene One or two or more selected mixed components (C) Block copolymer of vinyl aromatic compound and isobutylene (D) Petroleum resin, terpene resin, coumarone-indene resin, rosin resin, and hydrogenation thereof A component comprising at least one resin selected from derivatives