JP4823663B2 - Stretch film for food packaging - Google Patents

Description

  The present invention relates to a stretch film for food packaging. More specifically, it has excellent requirements as a stretch film for food packaging, such as transparency, rebound, low shrinkage, cutability, heat sealability, stretchability, etc. In addition, the shrinkage after stretching is particularly slow, and automatic stretch packaging. The present invention relates to a stretch film for food packaging mainly composed of polyolefin resin having high suitability in a machine.

  A method of selling fruits and vegetables, fresh fish, meat, etc. in a tray, covering them with a stretch film and packaging them for sale is often used in supermarkets. For this stretch film, a soft polyvinyl chloride film has been used for a long time. In recent years, soft polyvinyl chloride films have begun to generate problems such as the generation of hydrogen chloride gas during incineration, and the contained plasticizer may be eluted. Development of alternative stretch films for food packaging, such as polyolefin films, is underway.

  In order to improve the working efficiency, the method of carrying out the packaging covered with the stretch film from the top of the tray by an automatic stretch packaging machine has been introduced. When packaging using this automatic stretch wrapping machine, if a film with a slow shrinkage rate after stretching, such as a soft polyvinyl chloride film, is used, stretch the film and allow it to overlap on the back of the bottom of the tray. The escape due to the shrinkage of the film is small before heat sealing, so heat sealing can be performed in a sufficiently overlapped state (so-called overlapping property is good). However, the polyolefin film is rubber-like, and the film tends to shrink in a short time from stretching to heat sealing, so it is not possible to heat seal in a sufficiently overlapped state, and the heat sealing part The amount of overlap is insufficient, and packaging defects are likely to occur.

  Conventionally, various polyolefin-based stretch films have been proposed for the purpose of providing the characteristics of a soft polyvinyl chloride film. Then, the adhesiveness of the front and back surfaces necessary for the stretch film is satisfied by forming it with an ethylene-vinyl acetate copolymer layer to which an antifogging agent is added, and the stretch film has suitability such as stretchability mainly composed of polyolefin. A stretch film for polyolefin food packaging having a three-layer structure filled with a central layer has been proposed, but a stretch film for polyolefin food packaging having sufficient performance has not yet been obtained. For example, although a stretch film for food packaging in which the central layer is an ethylene-α-olefin copolymer-containing resin has been proposed (Patent Document 1), this film has high elasticity and is necessary as a stretch film for food packaging. Inferior in physical properties and difficult to put into practical use. Then, the stretch film for food packaging whose center layer is a layer of resin compositions, such as hard polyolefin resin, an ethylene-alpha-olefin copolymer, and petroleum resin, is proposed (patent documents 2 and 3).

In addition, the stretch film for food packaging is examined from the physical properties, and has a specific storage elastic modulus (E ′) and loss tangent (tan δ), and the breaking elongation in the width direction is larger than the breaking elongation in the length direction. A stretch film for food packaging in which the total amount of tensile stress at the time of 100% elongation in the direction and the length direction is 1000 kg / cm ² or less has been proposed (Patent Document 4). Various food packaging stretch films having such physical properties have been proposed. For example, food packaging having a layer composed of a resin composition of a propylene polymer having a specific amount of crystallization heat or a mixture thereof and a petroleum resin. Stretch film for food packaging (Patent Document 5), a propylene resin, a stretch film for food packaging (Patent Document 6) having a layer composed of a resin composition of a vinyl aromatic compound and a conjugated diene, and a petroleum resin. Stretch film for food packaging having a layer composed of a resin composition comprising a main α-olefin repeating unit and a resin containing a cyclic olefin repeating unit bonded or not bonded to the α-olefin repeating unit The ratio between the stress ρ ₁₅₀ at 150% elongation and the stress ρ ₅₀ at 50% elongation (ρ ₁₅₀ / ρ ₅₀ ) Is known to affect packaging suitability (Patent Document 7).

The applicant has excellent physical properties as a stretch film for food packaging such as transparency, resolving property, low shrinkage force, cut property, heat seal property, stretch property, etc. For the purpose of providing a stretch film for food wrapping based on low-cost polyolefin-based resin, which has slow characteristics and is suitable for automatic stretch wrapping machines (especially overlap), the central layer and both outer surface layers A stretch film for food packaging comprising at least three layers, the central layer of which is (A) 20-40% by mass of homopolypropylene, (B) random co-polymerization of ethylene and an α-olefin having 3 to 6 carbon atoms a combined density 0.85~0.89g / cm ³ of ethylene -α- olefin copolymer 5 to 30 mass%, of the (C) 3 to 20 carbon atoms α- olefin A random copolymer of at least two olefins selected et, olefin copolymer 120 ° C. or less of the density 0.85~0.88g / cm ³ even if there if no melting point 5-30 And (D) a resin composition containing 15 to 40% by mass of at least one resin selected from petroleum resins, terpene resins, coumarone-indene resins, rosin resins, and hydrogenated resins thereof. ), (B), (C), and (D) is 100% by mass], and a stretch film for food packaging in which both outer surface layers are formed of a polyethylene resin has been proposed (Japanese Patent Application No. 2005-138026). ).
Japanese Patent Application Laid-Open No. 11-077927 JP-A-11-320785 JP 2003-220675 A JP-A-9-183458 JP-A-9-154479 Japanese Patent Laid-Open No. 9-165491 JP-A-8-259707

  The above-mentioned stretch film for food packaging proposed by the present applicant has excellent physical properties as a stretch film for food packaging such as transparency, rebound, low shrinkage, cut property, heat seal property, stretch property, etc. In addition, it is a stretch film for food packaging that is suitable for use in an automatic stretch packaging machine and is inexpensive. This stretch film for wrapping foods can be used smoothly with sufficient overlap for automatic packaging of trays of ordinary sizes and shapes that are usually used. However, there is a case where overlap is insufficient for automatic packaging of trays having a shape that requires strictly stretchability, such as a large tray or a deep tray. This invention aims at providing the stretch film for food packaging which improved this overlap property.

  As a result of various investigations on an inexpensive food packaging stretch film having a central layer formed of polyolefin, the present inventors mainly have polyolefin having moderate flexibility, such as random polypropylene or low-density polyethylene, and petroleum resin, The composition containing terpene resin, coumarone-indene resin, rosin resin and their hydrogenated resin as the central layer has rubber-like elastic properties, high shrinkage speed after stretching, and poor overlap On the other hand, it is mainly composed of a mixed resin in which a specific extremely hard polyolefin and a specific extremely soft polyolefin are mixed, and includes a petroleum resin, a terpene resin, a coumarone-indene resin, a rosin resin, and a hydrogenated resin thereof. The composition with the composition in the center layer is moderately flexible While maintaining was found that to obtain, may overlap with reducing the polyolefin-specific rubber-like elastic properties. And this time, petroleum resin, terpene resin, coumarone-indene resin, rosin resin, and those that contain aliphatic hydrocarbon resins or their hydrogenated resins instead of their hydrogenated resins further improve the overlap properties. As a result, the present invention has been completed.

That is, the present invention is a stretch film for food packaging comprising at least three layers of a center layer and both outer surface layers, and the center layer has the following components (A), (B), (C) and (D). :
(A) Homopolypropylene 20-40% by mass
(B) A random copolymer of ethylene and an α-olefin having 3 to 6 carbon atoms, and an ethylene-α-olefin copolymer having a density of 0.85 to 0.89 g / cm ³ and 5 to 30% by mass
(C) A random copolymer of at least two olefins selected from α-olefins having 3 to 20 carbon atoms, and a density of 0.85 to 0.88 g at 120 ° C. or less even if there is no melting point. / Cm ³ olefin copolymer 5-30% by mass
(D) 15-40% by mass of at least one resin selected from aliphatic hydrocarbon resins and hydrogenated resins thereof
(However, the total of (A), (B), (C), and (D) is 100% by mass), and both outer surface layers are formed of a polyethylene-based resin. It is a stretch film for food packaging.

  The stretch film for food packaging of the present invention has excellent physical properties as a stretch film for food packaging such as transparency, resolving property, low shrinkage force, cut property, heat seal property, and stretch property. In addition, the stretch film for food packaging of the present invention has a low shrinkage rate after stretching, so the film escapes due to shrinkage between the stretched film and the bottom back of the tray until it is heat sealed, It has the property of being heat-sealed in a sufficiently overlapped state, that is, it has excellent overlap properties, so it can be suitably used for packaging large and deep trays when packaging with automatic stretch packaging machines. . In addition, the olefin material is inexpensive.

  The component (A) of the center layer of the stretch film for food packaging of the present invention is homopolypropylene. This homopolypropylene (isotactic polypropylene) has high crystallinity and is widely used in general films, but has not been used in the past because it is too hard in the field of stretch films. This homopolypropylene is generally produced by a gas phase method using a Ziegler-Natta catalyst, a metallocene catalyst or the like. The homopolypropylene of component (A) has a physical property level as homopolypropylene, even if it contains a small amount of a copolymer component such as ethylene and 1-butene. Specifically, the heat of crystallization is 80 J / g. The above can be used, but is preferably pure homopolypropylene containing no copolymer component. (A) The compounding quantity of a component is 20-40 mass% of the total amount of (A) component, (B) component, (C) component, and (D) component, and 25-35 mass% has overlap property. It becomes the best and is more preferable. When the component (A) is 40% by mass or more, the stress at the time of stretching in the lateral direction increases, and the tray may be crushed when packaging with an automatic stretch packaging machine.

The component (B) of the center layer of the stretch film for food packaging of the present invention is a random copolymer of ethylene and an α-olefin having 3 to 6 carbon atoms, and has a density of 0.85 to 0.89 g / cm. ^{3 is} an ethylene-α-olefin copolymer. This random copolymer can be obtained by polymerizing ethylene and an α-olefin having 3 to 6 carbon atoms using a Ziegler-Natta catalyst or a metallocene catalyst by a gas phase method, a liquid phase method, or the like. When the component (B) has a density of 0.89 g / cm ³ or more, the hardness of the homopolypropylene of component (A) cannot be canceled, and the resulting film is a stretch film for food packaging. As it is too hard. The component (B) preferably has a density of 0.88 g / cm ³ or less, more preferably a density of 0.87 g / cm ³ or less, in terms of hardness adjustment. Specific examples of the component (B) include linear ultra-low density polyethylene obtained by copolymerizing ethylene and a small amount of propylene or 1-butene. In particular, an ethylene-propylene random copolymer having a density of 0.85 to 0.88 g / cm ³ polymerized by a liquid phase method using a metallocene catalyst is preferable. Further, the polymerization ratio of α-olefin is also an index of flexibility. When the polymerization ratio of α-olefin is 20% by mass or more, good flexibility is given. (B) The compounding quantity of a component is 5-30 mass% of the total amount of (A) component, (B) component, (C) component, and (D) component, and 10-25 mass% has overlap property. It becomes the best and is more preferable.

Component (C) of the present invention is a random copolymer of at least two olefins selected from α-olefins having 3 to 20 carbon atoms, and has a density of 120 ° C. or less even if there is no melting point. .85 to 0.88 g / cm ³ of olefin copolymer. When a random copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms is used, since the overlap property is inferior, no ethylene unit is present in the copolymer. Also, those having no melting point or having a melting point of 120 ° C. or lower are flexible, have a large tan δ near room temperature, and have an excellent damping property, which contributes to the improvement of the overlap property. Further, the component (C) preferably has a low crystallinity and is flexible, and a component having a density of 0.85 to 0.88 g / cm ³ is used from this viewpoint. A copolymer having no melting point is preferred. Examples of the α-olefin having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 4-methyl-1-pentene and 1-octene.

The component (C) is preferably a random copolymer of propylene and 1-butene, and particularly preferably has no melting point. Propylene and 1-butene are preferably used because they are inexpensive and can be efficiently synthesized by a gas phase method. It is a necessary condition in the present invention that the component (C) is flexible. Propylene and 1-butene are polymerized at a polymerization ratio that is not biased to one, and those synthesized at random have low crystallinity and become more flexible. A flexible α-olefin copolymer having low crystallinity has a low density. In the case of a propylene-1-butene random copolymer, the density is 0.88 g / cm ³ or less, more preferably 0.87 g / cm ³ or less from the viewpoint of adjusting the hardness by imparting flexibility. In particular, a propylene-1-butene random copolymer having no melting point and having a propylene monomer content of 30 to 70% by weight is excellent in damping property and is preferably used. (C) The compounding quantity of a component is 5-30 mass% of the total amount of (A) component, (B) component, (C) component, and (D) component, and 10-25 mass% has overlap property. It becomes the best and is more preferable.

  In this invention, said (B) component and said (C) component are used in combination, and it mix | blends with the homopolypropylene of (A) component, but this is moderate hardness as a stretch film for food packaging. This is to improve the overlap property. And when each of (B) component or (C) component is mix | blended independently, the direction when those mixtures are mix | blended is excellent, but the reason is unknown. In addition, when the above propylene-1-butene random copolymer is used as the component (C), a resin having a low density becomes sticky by adding a small amount of random polypropylene because the handling of resin pellets becomes troublesome due to stickiness. It is preferable to improve and make it easy to handle.

  The component (D) used in the present invention is at least one resin selected from aliphatic hydrocarbon resins and hydrogenated resins thereof. This aliphatic hydrocarbon resin is an alkyne (aliphatic hydrocarbon having a conjugated double bond) obtained by decomposition of petroleum, naphtha, for example, butadiene as a C4 fraction, 2-methyl- as a C5 fraction. 1,3 butadiene (isoprene), 1,3-pentadiene and the like are polymerized and are also called aliphatic petroleum resins. Of these, those obtained by polymerizing 1,3-pentadiene as a main raw material are preferred, and those obtained by polymerizing those containing 1,3-pentadiene of 80 mol% or more, particularly 95 mol% or more are preferred. The number average molecular weight of the aliphatic hydrocarbon resin is preferably 500 to 2000, and particularly preferably 1000 to 1500.

  This aliphatic hydrocarbon resin or its hydrogenated resin includes, for example, Quinton A100 (softening point 100 ° C., melt viscosity 240 mPas, number average molecular weight 1350), Quinton K100 (softening point 101 ° C., melt viscosity 170 mPas, number average) Molecular weight 1250), Quinton M100 (softening point 95 ° C., melt viscosity 100 mPas, number average molecular weight 1100), Quinton R100 (softening point 96 ° C., melt viscosity 120 mPas, number average molecular weight 1100), Quinton B170 (softening point 70 ° C., Trademarks of melt viscosity 50 mPas, number average molecular weight 950), quinton C200S (softening point 96 ° C., melt viscosity 140 mPas, number average molecular weight 1250), quinton C200H (softening point 101 ° C., melt viscosity 190 mPas, number average molecular weight 1350) It is commercially available from Nippon Zeon Co., Ltd. by name. This (D) component shows relatively good compatibility when mixed with the (A) component, (B) component and (C) component, but from the viewpoint of color tone, thermal stability, compatibility, etc. Is preferably used.

  In the present invention, the blended aliphatic hydrocarbon resin of component (D) or its hydrogenated resin is not compatible with the highly crystalline homopolypropylene of component (A), and the components (B) and (C ) Component is considered to be compatible with the low crystalline part and non-crystalline part. And the aliphatic hydrocarbon resin of component (D) or its hydrogenated resin can be used in soft polyvinyl chloride due to the compatibility of component (B) and component (C) in the low crystalline part and amorphous part. It is thought to impart reversible slip deformability similar to the action of a plasticizer. Therefore, the stretch film of the present invention exhibits a good overlap property similar to that of a soft polyvinyl chloride stretch film. In general, a resin having a small SP value (solubility parameter), such as polyolefin, is soft and soft when it has low crystallinity, and is unsuitable for a stretch film. Aliphatic hydrocarbon resin or its hydrogenated resin gives the above-mentioned sliding deformability to polyolefin as compared to alicyclic petroleum resin and aromatic petroleum resin, but also easily affects the crystallized portion thereof. . Therefore, in the present invention, homopolypropylene is used as the raw material polyolefin. Homopolypropylene has extremely high crystallinity and is compatible with an aliphatic hydrocarbon resin or a hydrogenated resin thereof, so that the highly crystalline portion does not deteriorate in crystallinity. (D) The compounding quantity of a component is 15-40 mass% of the total amount of (A) component, (B) component, (C) component, and (D) component. Preferably it is 20-40 mass% from the good overlap property.

  The aliphatic hydrocarbon resin of component (D) and its hydrogenated resin used in the present invention may be thermally decomposed during film forming processing such as extrusion, and this thermally decomposed product may generate a strange odor. In addition to the (A) component, the (B) component, the (C) component, and the (D) component of the center layer, a phosphite-based antioxidant is further added to suppress thermal decomposition during the film forming process. It is preferable to mix. As the phosphite antioxidant, phosphite or phosphonite is preferable. For example, commercially available brand name MARK PEP-36 [Asahi Denka Kogyo Co., Ltd .: bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite], trade name MARK PEP-10 [Asahi Denka Kogyo Co., Ltd .: 2,2-methylenebis (4,6-di-tert-butylphenyl) octyl phosphite], trade name MARK PEP-45 [Asahi Denka Kogyo Co., Ltd .: Bis (2,4-di-) tert-butylphenyl) pentaerythritol diphosphite], trade name Irgafos P-EPQ [manufactured by Ciba Specialty Chemicals: tetrakis (2,4-di-tert-butylphenyl) -4,4′-biphenylene-diphosphonite] Etc. The compounding quantity of a phosphite-type antioxidant is 0.03-0.5 mass part with respect to 100 mass parts of total amounts of (A) component, (B) component, (C) component, and (D) component. is there.

  In addition to the component (A), the component (B), the component (C) and the component (D), a small amount of random polypropylene or the like can be added to the resin composition forming the central layer of the present invention. In order to go in the direction where physical properties are bad, it is preferable to keep it to 10% or less with respect to the total amount of component (A), component (B), component (C) and component (D). Moreover, you may mix the cycle goods produced during a manufacturing process with a center layer. When the cycle product is mixed with the center layer, the resin of the outer surface layer, for example, ethylene-vinyl acetate copolymer is mixed into the center layer. In that case, the phase ratio is changed so that the ratio of the component (A), the component (B), the component (C) and the component (D) as the entire stretch film is within the range defined in the present invention. By doing so, changes in physical properties can be minimized.

  In the present invention, it is difficult to set appropriate heat sealability, adhesiveness, and antifogging property only with the center layer. Therefore, another resin layer is provided on both surfaces of the center layer. This resin layer may be a single layer or two or more layers. These resin layers are selected so as to be more flexible than the center layer and hardly affect the physical properties such as the overlap property. A layer made of a polyethylene resin is suitable for the surface layers on both sides of the stretch film for food packaging of the present invention, that is, both outer surface layers. Since the polyethylene resin is more flexible than the center layer, it hardly affects the physical properties such as the overlap property, and since the resin layer containing polypropylene in the center layer has a lower softening temperature, it becomes a suitable heat seal property. Preferably used.

  Examples of the polyethylene resin include ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-1-pentene copolymer, ethylene-hexene-1 copolymer, ethylene-vinyl acetate copolymer, ethylene -Methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl methacrylate copolymer, ethylene-methacrylic acid Ethylene, ethylene-methacrylic acid copolymer, ionomer resin, linear low density polyethylene, ultra low density polyethylene, and other ethylene-based ethylene copolymers and polyethylene such as low density polyethylene. is there. The ethylene-vinyl acetate copolymer has a particularly low softening temperature, is flexible, has almost no effect on physical properties such as overlap, has good heat-sealability, has suitable tackiness, and is mixed with an antifogging agent However, it is particularly preferable because it does not become so cloudy.

The total thickness of the stretch film for food packaging of the present invention is 7 to 15 μm. The ratio between the thickness of the center layer and both outer surface layers is preferably 1: 1.5 to 3: 1. Further, stretch film for food packaging of the present invention was measured at a temperature 20 ° C., the ratio between the stress [rho ₅₀ during elongation 50% stress ρ150 and lateral elongation of 150% in the transverse direction (lateral direction of the stress ratio : Ρ ₁₅₀ / ρ ₅₀ ) is preferably 1.0 to 1.3, particularly preferably 1.05 to 1.2. When using stretch films for food packaging on an automatic stretch wrapping machine, the overlap ratio is a problem because of the specifications that the wrapping machine stretches and wraps the film in the horizontal direction and the lateral stress ratio of the film. It becomes. In stretch films for food packaging, the smaller the stress ratio in the lateral direction, the better the overlap property. Further, when the stress ratio increases, workability is reduced because a strong force is required to stretch the film during the packaging operation, and the tray is easily deformed or crushed.

  The stress ratio in the lateral direction of the film is greatly affected by the production conditions together with the resin composition constituting the film. A multilayer film having a thickness of about 10 μm is generally produced by inflation molding using an extruder using a round die. The blow ratio (film diameter / die diameter) at this time is related to the stress ratio in the lateral direction. When a thin film having a thickness of about 10 μm is manufactured by inflation molding using a round die, the blow ratio is generally increased to about 5 to 6 to make it thin. In this conventional method, the stress ratio of the film becomes as large as about 1.5. Therefore, in the case of a stretch film for food packaging, the overlap property is inferior. For example, a conventional stretch film for food packaging represented by Patent Document 6 has a lateral stress ratio of about 1.5 at a blow ratio of 5 to 6, and a lateral stress ratio of about 1.3 at a blow ratio of 4. The stretch film for food packaging of the present invention has a basically small stress ratio in the transverse direction, and even if the stress ratio is small, partial stretch unevenness does not occur. Molding is performed at a blow ratio of about 5 to 8, and a lateral stress ratio of 1.0 to 1.3 is obtained, and a stretch film for food packaging showing good packaging suitability is obtained.

Examples 1-10, Comparative Examples 1-4
A composition obtained by kneading the components of Examples 1 to 10 and Comparative Examples 1 to 4 in Table 1 was used as a central layer, and an ethylene-vinyl acetate copolymer (vinyl acetate content 15% by mass, MFR at 190 ° C. = 2. (0 g / 10 min) A composition obtained by kneading 2 parts by mass of diglycerin monooleate as an antifogging agent in 100 parts by mass was formed into a front and back outer surface layer and molded with a co-extrusion inflation at a blow ratio of 6, and the total thickness A film having a thickness of 10 μm (outer surface layer 2.5 μm / center layer 5 μm / back outer surface layer 2.5 μm) was obtained.

In the composition of Table 1,
-Homopolypropylene is FS2011DG made by Sumitomo Chemical.
-Ethylene-propylene copolymer (1) is Sumitomo Chemical Co., Ltd. Esprene SPO V-0141 (propylene 27 mass%, density 0.86).
-Ethylene-propylene copolymer (2) is Sumitomo Chemical Co., Ltd. Esprene SPO V-0111 (propylene 22 mass%, density 0.87).
-The ethylene-1-butene copolymer (1) is Esprene SPO N-0441 (1-butene 30 mass%, density 0.86) by Sumitomo Chemical Co., Ltd.
-Ethylene-1-butene copolymer (2) is Esprene SPO N-0391 (1-butene 17 mass%, density 0.88) by Sumitomo Chemical Co., Ltd.
Propylene-1-butene copolymer is composed of 85% by mass of propylene-1-butene copolymer (Sumitomo Chemical Tuff Selenium T-1712: density 0.86) and random polypropylene (S-131, Sumitomo Chemical Co., Ltd.) 15 It is a mixture by weight.
The aliphatic hydrocarbon resin is Quinton A-100 manufactured by Nippon Zeon.
The alicyclic hydrocarbon resin is Alcon P-125 manufactured by Arakawa Chemical Industries.

About each obtained film, overlap property, transparency, resolving property, and the shrinkage force of the film were evaluated. Evaluation was based on the following method. The results are also shown in Tables 1 and 2.
Overlap property: Using a stretch automatic packaging machine AW-3600 manufactured by Teraoka Seiko Co., Ltd., a polystyrene foam tray having a length of 24 cm, a width of 24 cm, and a height of 4 cm was automatically packaged with each stretch film having a width of 350 mm. The overlap property was evaluated by measuring the distance of the polymerized portion of the film at the bottom of the tray.
Transparency: The transparency by bloom was evaluated. That is, each roll of stretch film was allowed to stand in an atmosphere of 50 ° C. for 10 days and then evaluated by haze measurement (measurement of light scattering according to JIS K7136-2000). The smaller the value, the better the transparency. O represents less than 3.0, Δ represents 3.0 or more and less than 4.0, and x represents 4.0 or more.
Detackability: Each stretch film roll having a width of 350 mm was left in an atmosphere of 50 ° C. for 10 days, then unraveled at a strograph speed of 500 mm / min, and the unraveling force at that time was measured and evaluated. ○ represents 200 g / 350 mm or less, and x represents 200 g / 350 mm or more.
Shrinkage force: Using a stretch automatic wrapping machine AW-3600, a polystyrene foam tray having a length of 20 cm, a width of 20 cm, and a height of 3 cm was automatically packaged with each stretch film having a width of 350 mm. The shrinkage of the stretch film was evaluated by visually observing the distortion of the tray at this time. The greater the shrinkage of the film, the greater the distortion of the tray. ○ indicates no distortion, Δ indicates low distortion, and x indicates large distortion. Note that “x” includes a case where the film cannot be pulled because it is hard, and the film is detached from the gripping portion of the machine.

Stress at elongation: The stress ρ ₅₀ at 50% elongation in the longitudinal direction measured at a temperature of 20 ° C. was 158 g / cm in Example 1, 162 g / cm in Example 2, and 158 g / cm in Comparative Example 2. . The stress ρ ₁₅₀ at 150% elongation in the longitudinal direction measured at a temperature of 20 ° C. was 237 g / cm in Example 1, 245 g / cm in Example 2, and 237 g / cm in Comparative Example 2. Further, the stress ρ ₅₀ at 50% elongation in the lateral direction measured at a temperature of 20 ° C. was 69 g / cm in Example 1, 72 g / cm in Example 2, and 69 g / cm in Comparative Example 2. The stress ρ ₁₅₀ at 150% elongation in the transverse direction measured at a temperature of 20 ° C. was 80 g / cm in Example 1, 83 g / cm in Example 2, and 80 g / cm in Comparative Example 2. When the lateral stress ratio (ρ ₁₅₀ / ρ ₅₀ ) is calculated from these values, Example 1 is 1.16, Example 2 is 1.15, and Comparative Example 2 is 1.16. When the stress ρ ₅₀ at 50% elongation in the lateral direction was 90 or more, the tray was crushed when packaging with an automatic stretch packaging machine.

  As can be seen from Table 1, the stretch films of Examples 1 to 10 in which the blending ratios of the (A) component, (B) component, (C) component and (D) component of the central layer are within the scope of the present invention. The overlap property, transparency, resolving property and shrinkage force were generally excellent, and it was practically usable. However, Comparative Examples 3 to 4 that do not satisfy the requirements of the present invention were not practically used because of any of the overlap properties, transparency, resolving properties, and shrinkage force. Comparative Examples 1 and 2 are examples in which an alicyclic hydrocarbon resin was blended in place of the aliphatic hydrocarbon resin of Examples 1 and 2. As can be seen by comparing Examples 1 and 2 with Comparative Examples 1 and 2, when the same amount of the aliphatic hydrocarbon resin and the alicyclic hydrocarbon resin are blended, when the aliphatic hydrocarbon resin is blended The stretch film excellent in the overlap property is obtained.

Examples 11-18
The composition obtained by kneading the components of Examples 11 to 18 in Table 2 was used as a central layer, and an ethylene-vinyl acetate copolymer (vinyl acetate content 15% by mass, MFR at 190 ° C. = 2.0 g / 10 min) 100 A composition obtained by kneading 2 parts by mass of diglycerin monooleate as an antifogging agent in parts by mass is formed into a front and back outer surface layer, molded with a co-extrusion inflation at a blow ratio of 6, and a total thickness of 10 μm (outer surface layer 2 500 μm of the film of 0.5 μm / center layer 5 μm / back outer surface layer 2.5 μm).

In Table 2, phosphite antioxidant (1) is MARK PEP-36 manufactured by Asahi Denka Kogyo Co., and phosphite ester antioxidant (2) is MARK PEP-10 manufactured by Asahi Denka Kogyo Co., Ltd. Irgafos P-EPQ manufactured by Ciba Specialty Chemicals was used as the acid ester antioxidant (3).
As for odor, a sensory test was conducted in which the above-scored film was left for 3 days and then opened 10 m to smell. The ones that were not worried about the odor were marked with ○, and those that were worried about the odor were marked with ×. Moreover, the same test and evaluation as Example 1 were followed about overlap property, transparency, rebound property, and shrinkage force. Examples 11 to 16 in which a phosphite-based antioxidant was blended were excellent in overlap property, transparency, resolving property and shrinkage, and had no odor. Although Examples 17-18 which do not mix | blend a phosphite-type antioxidant are excellent in overlap property, transparency, repelling property, and shrinkage | contraction force, the smell was worried.

Claims (7)

A stretch film for food packaging comprising at least three layers of a center layer and both outer surface layers, the center layer having the following components (A), (B), (C) and (D):
(A) Homopolypropylene 20-40% by mass
(B) A random copolymer of ethylene and an α-olefin having 3 to 6 carbon atoms, and an ethylene-α-olefin copolymer having a density of 0.85 to 0.89 g / cm ³ and 5 to 30% by mass
(C) A random copolymer of at least two olefins selected from α-olefins having 3 to 20 carbon atoms, and a density of 0.85 to 0.88 g at 120 ° C. or less even if there is no melting point. / Cm ³ olefin copolymer 5-30% by mass
(D) 15-40% by mass of at least one resin selected from aliphatic hydrocarbon resins and hydrogenated resins thereof
(However, the total of (A), (B), (C), and (D) is 100% by mass), and both outer surface layers are formed of a polyethylene-based resin. Stretch film for food packaging.   The stretch film for food packaging according to claim 1, wherein the component (B) is an ethylene-propylene random copolymer, and the component (C) is a propylene-1-butene random copolymer having no melting point.   The stretch film for food packaging according to claim 1, wherein the component (B) is an ethylene-1-butene random copolymer, and the component (C) is a propylene-1-butene random copolymer having no melting point.   The stretch film for food packaging according to any one of claims 1 to 3, wherein the component (D) is an aliphatic hydrocarbon resin produced using 1,3-pentadiene as a main raw material and a hydrogenated resin thereof.   The stretch film for food packaging according to any one of claims 1 to 4, further comprising a phosphite-based antioxidant added to the center layer.   The stretch film for food packaging according to any one of claims 1 to 5, wherein the polyethylene resin of both outer surface layers is an ethylene-vinyl acetate copolymer resin layer. The ratio (ρ ₁₅₀ / ρ ₅₀ ) between the stress ρ ₁₅₀ at 150% elongation in the transverse direction and the stress ρ ₅₀ at 50% elongation in the transverse direction, measured at a temperature of 20 ° C., is 1.0 to 1.3. It exists, The stretch film for food packaging in any one of Claims 1-6 characterized by the above-mentioned.