JP2014076543A - Film for stretch packaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new non-chlorine based film for stretch packaging in which whitening is hard to be generated in the film after packaging even if being subjected to high stretching upon overlapping.SOLUTION: The film for stretch packaging is a laminated film composed of at least three layers having both surface layers comprising an ethylenic resin (A) as the main component and an intermediate layer comprising a propylene-based resin (B) as the main component, and simultaneously satisfies the following inequalities (1) to (3): Tc(Y)-Tc(X)≥30 (1)σ(X)-σ(Y)≤60 (2)σ(Y)≤60 (3)(in the above inequalities, Tc(X) denotes the crystallization temperature (°C) of the surface layers, Tc(Y) denotes the crystallization temperature(°C) of the intermediate layer, σ (X) denotes the generation stress (kgf/cm) in the longitudinal direction of the film in a 150% elongation percentage; and σ(Y) denotes the generation stress (kgf/cm) in the width direction of the film in a 150% elongation percentage).

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, Patent Document 1 has at least one layer containing a propylene resin having a crystallization calorific value of 10 to 60 J / g and a petroleum resin, a terpene resin, a coumarone-indene resin, a rosin resin, or a hydrogenated derivative thereof. And the stretch film for food packaging which has a specific storage elastic modulus is proposed.

  When a film for stretch packaging is set and packaged in an automatic packaging machine, a film having a predetermined width may be packaged by changing the degree of stretching according to the size of the tray. At this time, in order to wrap a large tray, the degree of stretching at the time of overlapping is increased and packaged (high stretch packaging).

  In the above-mentioned Patent Document 1, a new polyolefin-based stretch packaging film has been proposed as a non-chlorine-based stretch packaging film that does not contain chlorine or polyvinyl chloride plasticizer, but the film used an automatic packaging machine. Although the suitability of various packaging machines (cutability, packaging wrinkles, bottom folding stability, tearability) is good, whitening of the film after packaging that occurs when carrying out high stretch packaging as described above is an issue ing.

JP-A-9-154479

  This invention is made | formed in view of the said situation, The solution subject is providing the new film for non-chlorine type | system | group stretch packaging which is hard to produce whitening to the film after packaging even if it gives a high stretch when overlapping. There is.

  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. It is a laminated film, and the film is for a stretch wrapping film characterized by simultaneously satisfying the following formulas (1) to (3).

Tc (Y) −Tc (X) ≧ 30 (1)
σ (X) −σ (Y) ≦ 60 (2)
σ (Y) ≦ 60 (3)
(In the above formula, Tc (X) is the crystallization temperature (° C.) of the surface layer, Tc (Y) is the crystallization temperature (° C.) of the intermediate layer, and σ (X) is a film at 150% elongation. The generated stress in the longitudinal direction (kgf / cm ³ ), and σ (Y) is the generated stress in the film width direction at 150% elongation (kgf / cm ³ )

  According to the present invention, the suitability of various packaging machines when using an automatic packaging machine (cutability, packaging wrinkles, bottom folding stability, tearability) is good, and high stretch is applied when overlapping. In addition, it is possible to provide a non-chlorine stretch packaging film in which whitening of the post-packaging film hardly occurs, and the industrial value of the present invention is high.

  Hereinafter, the stretch packaging film as an example of the embodiment of the present invention (hereinafter sometimes abbreviated as the present stretch film) will be described, but the scope of the present invention is not limited to the embodiment described below. Absent.

  In the stretch film of the present invention, a surface layer mainly composed of an ethylene-based resin (A) component is formed and laminated on both sides, so that heat sealability (bottom sealability) at low temperatures and self Adhesiveness, moldability upon inflation, etc. 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, ethylene-vinyl acetate is a vinyl acetate unit content of 5 to 25% by mass and a melt flow rate (JIS K7210, temperature: 190 ° C., load: 21.18 N) of 0.2 to 10 g / 10 min. A polymer is preferable, and an ethylene-vinyl acetate copolymer is more preferable, particularly 0.5 to 8 g / 10 min, and particularly 1 to 6 g / 10 min.

  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 is too soft at room temperature or the strength is insufficient. . In addition, when the amount of heat of crystallization exceeds 60 J / g, a large force is required at the time of film extension, and only non-uniform elongation is exhibited, which may not be suitable for a stretch film.

  The method for adjusting the amount of crystallization heat (ΔHc) to a predetermined range is not particularly limited, but a method of mixing a resin different from the propylene-based resin (B) is preferably used. Among these, it is more preferable to mix resin (D) mentioned later in the point which provides various packaging machine aptitudes (cut property, packaging wrinkles, bottom folding stability, tearing property, 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, as the propylene resin (B), the resin (C), that is, a propylene-ethylene random copolymer, a propylene-ethylene-butene-1 copolymer, In addition, it is preferable to use one or two kinds of mixed components selected from reactor-type polypropylene elastomers and propylene-ethylene copolymers or propylene-α-olefin copolymers.

  In addition, in 1 type or 2 types of mixed components chosen from propylene-type resin (C), crystallization calorie | heat_amount ((DELTA) Hc) when it measures with a temperature-fall rate of 10 degree-C / min with a differential scanning calorimeter (DSC). If it is 30 J / g or more, strength and heat sealability 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.

  Moreover, when the peak of the crystallization curve when measured at a temperature decrease rate of 10 ° C./min with a differential scanning calorimeter (DSC) of the propylene-based resin (B) used in the present invention is not single, specifically, The case of a double peak will be described. When the peak of the crystallization curve is a double peak, there are regions with different crystallization speeds in the resin, i.e., it is inhomogeneous, resulting in reduced transparency, stickiness of raw material pellets and storage May cause blocking.

  The melt flow rate (MFR) of one or two kinds of mixed components selected from the propylene-based resin (B) is not particularly limited, but usually MFR (JISK7210, temperature: 230 ° C., load: 21.18N) is 0.2 g / 10 min or more, preferably 0.5 to 18 g / 10 min, and more preferably 1 to 15 g / 10 min. 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, trade names “Novatech PP” and “WINTEC” of Nippon Polypro Co., Ltd., trade names “Noblen” of Sumitomo Chemical Co., Ltd., and trade names “Prime Polypro” of Prime Polymer Co., Ltd. “Prime TPO”, trade name “Versify” of Dow Chemical Co., Ltd., and the like.

  Examples of the resin (D) include a block copolymer of a vinyl aromatic compound and a conjugated diene, or a hydrogenated derivative thereof. Since such a copolymer generally has rubber elasticity and is flexible, it provides an elastic recovery property to the film and effectively acts to reduce the tensile elastic modulus of the polypropylene resin (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 the conjugated diene may be contained. However, the thermal stability and weather resistance when a double bond mainly composed of vinyl bonds in the conjugated diene moiety remains are extremely poor. To improve this, 80% or more, preferably 95% of the double bonds. It is preferable to use one added with hydrogen.

  Moreover, it is preferable that the ratio of the vinyl aromatic-type compound and conjugated diene of such a copolymer 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 excessively lowered, and the polymerization productivity such as difficulty in pelletization tends to be lowered, while 40% by weight. If it exceeds 100%, the rigidity of the copolymer itself is increased, and it is likely that the effect of reducing the tensile elastic modulus and the like is imparted to the film which is the purpose of adding to the propylene-based resin (B). Tend.

  Specifically, styrene-butadiene block copolymer elastomer (Asahi Kasei Kogyo Co., Ltd. trade name “Tufprene”), hydrogenated derivative of styrene-butadiene block copolymer (Asahi Kasei Kogyo Co., Ltd. trade name “Tuftec”), styrene -Use of commercially available products such as hydrogenated derivatives of isoprene block copolymer (Kuraray brand name "Septon"), styrene-vinylisoprene block copolymer elastomer (Kuraray brand name "Hibler"), etc. it can.

  In the resin composition constituting the intermediate layer, the content of the resin (D) is preferably 1 to 50% by mass. If content of resin (D) 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 (D) 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 (D) is more preferably 40% by mass or less.

  The resin composition constituting the intermediate layer may contain a predetermined resin (E) component in addition to the component (B).

  Examples of the resin (E) include one resin selected from petroleum resin, terpene resin, coumarone-indene resin, rosin resin, and hydrogenated derivatives thereof. (Also referred to as “petroleum resins”).

  Such a resin (E) component effectively acts on further improvement in packaging suitability such as waist and cutability of the film, 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 (E) is preferably 1 to 40% by mass. If content of resin (E) 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 (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, 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 (E) 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 resin (F) in addition to the component (B) and the component (D).

  The ethylene resin (F) 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 (F) 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 (F), 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 soft and not only can maintain flexibility and elastic recovery, but also the ethylene resin (F) 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 (F) is a surface layer, for example, 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 (F) is preferably 1 to 40% by mass. If content of ethylene-type resin (F) 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 (F) 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 resin (F) 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.

  As various additives, for example, an aliphatic alcohol fatty acid ester 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, Specifically, monoglycerylate, polyglycerin oleate, glycerin triricinoleate, glyceryl acetyl ricinoleate, polyglyceryl stearate, glycerin laurate, polyglycerin laurate, methyl acetyl ricinoleate, ethyl acetyl ricinoleate, butyl acetyl ricin Norate, propylene glycol oleate, propylene glycol laurate, pentaerythritol oleate, polyethylene glycol oleate, polypropylene glycol oleate, sorbitan oleate, sorbitan laurate, polyethylene Glycol glycol sorbitan oleate, polyethylene glycol sorbitan laurate, and the like, and polyalkyl ether polyols, specifically, polyethylene glycol, polypropylene glycol, and the like, and paraffinic oils. 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 ranges of the thickness ratio of the surface layer and the intermediate layer are 10 to 65% of the front and back layers and 90 to 35% of 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 5 to 10. . 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.

  The crystallization temperature Tc (X) of the surface layer of the stretch film of the present invention and the crystallization temperature Tc (Y) of the intermediate layer need to have a relationship of Tc (Y) −Tc (X) ≧ 30 ° C. If the difference between the crystallization temperatures Tc (X) and Tc (Y) of the surface layer is within the above range, the intermediate layer starts to crystallize more quickly than the surface layer during molding. It is easy to be within the range of the generated stress in the MD direction and TD direction in%. When the relationship between Tc (X) and Tc (Y) is out of the above range, it becomes difficult to keep within the range of the generated stress in the MD direction and TD direction at an elongation rate of 150%, which will be described later. When a stretch film is subjected to high stretch wrapping in order to wrap a large tray, a large number of local stretching unevenness occurs on the stretch film, and the film after wrapping is whitened.

The generated stress σ (X) in the film longitudinal direction (MD direction) and the generated stress σ (Y) in the width direction (TD direction) perpendicular to the longitudinal direction (MD direction) when the stretch rate of the stretch film of the present invention is 150% are σ (X ) −σ (Y) ≦ 60 (kgf / cm ² ) and σ (Y) ≦ 60 (kgf / cm ² ). If it is in the above-mentioned range, when the stretch film is subjected to high stretch packaging for packaging a large tray, the film after packaging does not whiten. If the relationship between σ (X) and σ (Y) is out of the above range, when high stretch packaging is performed, a lot of local stretch unevenness occurs in the stretch film, and the film after packaging is whitened. End up.

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.
The flexibility of the stretch film is such that the 100% stretch 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 kgf / cm ^{2 to} 140 kgf. it is preferably in the range of / cm ^2, more preferably is ^{50kgf / cm 2 ~130kgf / cm 2} .

  In the present invention, the “stretch film” is meant to encompass a wide range of packaging films having stretchability and self-adhesiveness. Typically, a pre-packaging packaging film that overlaps fruits and vegetables, meat, side dish, etc. on a lightweight tray, or a packaging film that overlaps in order to fix the baggage during transportation. .

  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, let the flow direction from the extruder of a film be MD direction, and let the perpendicular direction be TD 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. And determining whether or not the peak of the crystallization temperature is single based on the obtained crystallization curve, and determining the crystallization peak temperature (Tc) and the crystallization heat quantity (ΔHc).

(2) Measurement of generated stress After the films obtained in Examples and Comparative Examples were cut into a 100 mm × 10 mm rectangular shape (longitudinal direction corresponds to each direction) along the MD direction and the TD direction, JISZ1702 was used. Accordingly, a tensile test was performed at a temperature of 20 ° C. and a tensile speed of 200 mm / min, and the tensile stress (kgf / cm ² ) generated in the MD and TD directions at an elongation of 150% was measured. The results are shown in Table 1. .

(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 carried out from −50 ° C. to 150 ° C. at a rate of temperature rise 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 is 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 TD direction is measured. The sex 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) Suitability for packaging machine Using the film (width 350 mm) obtained in Examples and Comparative Examples, with an automatic packaging machine (ISHIDA / Wmini-UNI manufactured by Ishida Co., Ltd.), expanded polystyrene tray (length 330 mm, width 230 mm, 38 mm in height) was packaged, and the transparency, cutability, packaging wrinkle, bottom folding stability and tearability after packing were evaluated according to the criteria shown in Table 2, and the results are shown in Table 1.

Example 1:
About the resin composition which forms both surface layers, EVA (vinyl acetate content: 15% by mass, crystallization heat amount: 84.8 J / g, crystallization peak temperature: component (A) as an ethylene polymer. 72.4 ° C., melt flow rate (JISK7210, temperature: 190 ° C., load: 21.18 N) 2.0 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, for the resin composition forming the intermediate layer, as component (B), propylene-based resin <1> (crystallization peak: single, crystallization heat amount: 62.5 J / g, crystallization peak temperature: 112.3 ° C, melt flow rate (JISK7210, temperature: 230 ° C, load: 21.18N) 7.0 g / 10 min) and propylene resin <2> (crystallization peak: single, crystallization heat amount: 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) to propylene resin <1> / propylene resin <2> = 64/36 A block copolymer of a kneaded product and a vinyl aromatic compound as component (C) and a conjugated diene or a hydrogenated derivative thereof (melt flow rate (JISK7210, Degree: 190 ° C., load: 21.18 N) 0.5 g / 10 min), and hydrogenated petroleum resin (softening temperature 125 ° C., Arakawa Chemical Industries, Ltd., Alcon P125) as a component (D) (B) / (C) / (D) = 60/20/20, and these melt-kneaded resins are co-extruded inflation molding with an annular three-layer die of 190 ° C. and a blow-up ratio of 8.5. Thus, a three-layer film having a total thickness of 12 μm (2 μm / 8 μm / 2 μm) was obtained.

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:
About the resin composition which forms both surface layers, EVA (vinyl acetate content: 15 mass%, crystallization heat amount: 81.4 J / g, crystallization peak temperature: component (A) as an ethylene-based polymer 73.0 ° C, 97 parts by mass of melt flow rate (JISK7210, temperature: 190 ° C, load: 21.18N) 2.3 g / 10 min) and 3 parts by mass of diglycerin oleate as an antifogging agent were melt-kneaded. . On the other hand, for the resin composition forming the intermediate layer, as the component (B), a propylene resin (crystallization peak: single, crystallization heat amount: 76.0 J / g, crystallization peak temperature: 13.2 ° C., melt A block copolymer of a flow rate (JISK7210, temperature: 230 ° C., load: 21.18N) 3.0 g / 10 min) and a vinyl aromatic compound and a conjugated diene as component (C) or a hydrogenated derivative thereof (Melt flow rate (JISK7210, temperature: 190 ° C, load: 21.18N) 0.5 g / 10 min) and hydrogenated petroleum resin (softening temperature 125 ° C, manufactured by Arakawa Chemical Industries, Ltd.) as component (D), Alcon P125) was melt-kneaded so that the mass ratio was (B) / (C) / (D) = 60/20/20, and these melt-kneaded resins were blown at a temperature of 190 ° C. in an annular three-layer die. By co-extrusion inflation molding in-up ratio of 5.0 to obtain a three-layer film having a total thickness of 12μm (2μm / 8μm / 2μm).

Comparative Example 2:
About the resin composition which forms both surface layers, EVA (vinyl acetate content: 15 mass%, crystallization heat amount: 81.4 J / g, crystallization peak temperature: component (A) as an ethylene-based polymer 73.0 ° C, 97 parts by mass of melt flow rate (JISK7210, temperature: 190 ° C, load: 21.18N) 2.3 g / 10 min) and 3 parts by mass of diglycerin oleate as an antifogging agent were melt-kneaded. . On the other hand, for the resin composition forming the intermediate layer, as the component (B), a propylene-based resin (crystallization peak: single, crystallization heat amount: 66.7 J / g, crystallization peak temperature: 103.3 ° C., melt A block copolymer of a flow rate (JISK7210, temperature: 230 ° C., load: 21.18 N) 7.0 g / 10 min) and a vinyl aromatic compound and a conjugated diene as component (C) or a hydrogenated derivative thereof (Melt flow rate (JISK7210, temperature: 190 ° C, load: 21.18N) 0.5 g / 10 min) and hydrogenated petroleum resin (softening temperature 125 ° C, manufactured by Arakawa Chemical Industries, Ltd.) as component (D), Alcon P125) is melt-kneaded so that the mass ratio is (B) / (C) / (D) = 60/20/20. By co-extrusion inflation molding at up ratio of 5.0 to obtain a three-layer film having a total thickness of 12μm (2μm / 8μm / 2μm).

Comparative Example 3:
About the resin composition which forms both surface layers, EVA (vinyl acetate content: 15 mass%, crystallization heat amount: 81.4 J / g, crystallization peak temperature: component (A) as an ethylene-based polymer 73.0 ° C, 97 parts by mass of melt flow rate (JISK7210, temperature: 190 ° C, load: 21.18N) 2.3 g / 10 min) and 3 parts by mass of diglycerin oleate as an antifogging agent were melt-kneaded. . On the other hand, for the resin composition forming the intermediate layer, as the component (B), a propylene-based resin (crystallization peak: single, crystallization heat amount: 62.5 J / g, crystallization peak temperature: 112.3 ° C., melt A block copolymer of a flow rate (JISK7210, temperature: 230 ° C., load: 21.18 N) 7.0 g / 10 min) and a vinyl aromatic compound and a conjugated diene as component (C) or a hydrogenated derivative thereof (Melt flow rate (JISK7210, temperature: 190 ° C, load: 21.18N) 0.5 g / 10 min) and hydrogenated petroleum resin (softening temperature 125 ° C, manufactured by Arakawa Chemical Industries, Ltd.) as component (D), Alcon P125) is melt-kneaded so that the mass ratio is (B) / (C) / (D) = 65/15/20. By co-extrusion inflation molding at up ratio 8.5, to obtain a three-layer film having a total thickness of 12μm (2μm / 8μm / 2μm).

From the results of Table 1, Examples 1 and 2 are (1) Tc (Y) −Tc (X) ≧ 30 ° C. and σ (X) −σ (Y) ≦ 60 (kgf / cm ² ). In addition, σ (Y) ≦ 60 (kgf / cm ² ), and (2) the peak of the crystallization curve when measured by a differential scanning calorimeter (DSC) at a temperature decrease rate of 10 ° C./min. By using an intermediate layer of component (B) that is single, has a crystallization peak temperature (Tc) of 70 ° C. or higher, and a crystallization heat quantity (ΔHc) of 10 J / g or more and 60 J / g or less, an automatic packaging machine Transparency after packing when a large tray is packaged in is good, and storage modulus (E ′) is within the specified range, so that it is good in packaging machine suitability, flexibility and low temperature suitability. It can be confirmed that the result is obtained.

In contrast, Tc (Y) −Tc (X) ≧ 30 ° C., but σ (X) −σ (Y) ≦ 60 (kgf / cm ² ) and σ (Y) ≦ 60 ( In Comparative Examples 1 and 3 where kgf / cm ² ) is not within the range, the transparency after packing when a large tray is packaged in an automatic packaging machine is good, but there is some difficulty in packaging suitability and practical performance. The result is not satisfied. Tc (Y) −Tc (X) ≧ 30 ° C. is out of range, σ (X) −σ (Y) ≦ 60 (kgf / cm ² ) and σ (Y) ≦ 60 (kgf / cm ² ) are in range Comparative Example 2, which was outside, had difficulty in transparency and packaging suitability when packing a large tray in an automatic packaging machine, and did not satisfy practical performance.

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

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, A film for stretch packaging, which satisfies the following formulas (1) to (3) simultaneously.
Tc (Y) −Tc (X) ≧ 30 (1)
σ (X) −σ (Y) ≦ 60 (2)
σ (Y) ≦ 60 (3)
(In the above formula, Tc (X) is the crystallization temperature (° C.) of the surface layer, Tc (Y) is the crystallization temperature (° C.) of the intermediate layer, and σ (X) is a film at 150% elongation. The generated stress in the longitudinal direction (kgf / cm ³ ), and σ (Y) is the generated stress in the film width direction at 150% elongation (kgf / cm ³ ) The film for stretch packaging according to claim 1, wherein the storage elastic modulus (E ') at 20 ° C measured by a dynamic viscoelasticity measurement method at a vibration frequency of 10 Hz and a strain of 0.1% is 100 MPa to 1 GPa. The crystallization curve when measured at a rate of temperature drop of 10 ° C / min with a stretch packaging film / differential scanning calorimeter (DSC) according to claim 1 or 2, wherein the intermediate layer simultaneously satisfies the following two conditions: The peak is single. The crystallization peak temperature (Tc) is 70 ° C. or higher, and the crystallization heat (ΔHc) is 10 J / g or more and 60 J / g or less. 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 film for stretch packaging according to any one of claims 1 to 4, wherein the intermediate layer contains two or more of the following components (C), (D), and (E).
(C) selected from propylene-ethylene copolymer, propylene-ethylene-butene-1 copolymer, and reactor type polypropylene elastomer, propylene-ethylene copolymer, and propylene-α-olefin copolymer One or more mixed components (D) Component consisting of block copolymer of vinyl aromatic compound and conjugated diene or hydrogenated derivative thereof (E) Petroleum resin, terpene resin, coumarone-indene resin, rosin Components comprising at least one resin selected from resins and hydrogenated derivatives thereof The ethylene resin (A) component is 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. And a film for stretch packaging according to any one of claims 1 to 5, comprising one or two or more kinds of mixed components selected from ionomer resins.