JP2008030858A - Wrapping film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wrapping film made of a lactic acid polymer as one of the main raw materials, particularly capable of functioning suitably as a wrapping film and preventing a blocking phenomenon even if it is kept in the rolled state. <P>SOLUTION: The wrapping film is formed as a laminated film composed of at least three layers, both surface layers of which include a polyolefin polymer A as a principal component, and the intermediate layer of which includes a lactic acid resin composition B as a principal component. The storage elastic modulus E' measured by dynamic viscoelastic measuring method at a frequency of 10 Hz and at a temperature of 20 °C is 1-4 GPa, the peak temperature of loss tangent tanδ is 20-60 °C, and the peak value is in the range of 0.1-0.8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a packaging film mainly comprising a lactic acid-based polymer, which is a resin derived from a natural plant, and can be suitably used as a small wrap film used particularly in homes. About.

A so-called “wrap film” (in the present invention, a “small roll wrap film” is used to distinguish a cooked food from a commercial packaging film as a packaging film that can be easily packaged on a ceramic dish. Also called).
Such a small roll wrap film is stored in a paper box provided with a cutter blade in a state of being wound around a cylinder, and when packaging, the film is drawn out from the paper box so as to cover the food, and the film is covered. The film is cut by pressing against the cutter blade provided in the paper box, perforating the film with this cutter blade and tearing the film so that the tear propagates in the width direction, and the end of the film It is common to pack the container in close contact with the container. For this reason, in addition to transparency, the small roll wrap film requires various properties such as adhesion to the container, drawability that allows the film to be pulled out smoothly from a paper box, and cutability when cutting the drawn film. It is said.

  The wrap film currently on the market includes a film mainly composed of a stretched polyvinylidene chloride resin, an extruded cast polyethylene resin, a plasticized polyvinyl chloride resin, and a poly-4-methylpentene-1 resin. And the like, etc., as a main component.

  In recent years, the effective use of depleting resources has become important due to increasing environmental problems, and natural plant-derived resins have attracted attention. Among them, lactic acid polymers are natural plant-derived resins obtained from starches such as corn and potato, and are not only mass-produced but also excellent in transparency, and are therefore attracting attention as raw materials for packaging films. Research and development of packaging films using lactic acid polymers as raw materials has been conducted.

  For example, in Patent Document 1, the outermost layer is a layer mainly composed of a polyolefin-based resin in order to provide a shrinkable sheet-like material that can obtain a high shrinkage rate at a relatively low temperature by an inflation method excellent in productivity. A shrinkable sheet-like material having at least one layer containing a lactic acid polymer as a main component between layers containing the polyolefin resin as a main component is disclosed.

  Further, in Patent Document 2, as a biodegradable wrap film having cut suitability, packaging suitability, and heat resistance, which are characteristics of a household wrap film, according to a dynamic viscoelasticity measurement method of JIS K-7198 A method, The value of storage elastic modulus at 40 ° C. measured at a frequency of 10 Hz and a strain of 0.1% is in the range of 100 MPa to 3 GPa, the value of storage elastic modulus at 100 ° C. is in the range of 30 MPa to 500 MPa, and the loss tangent (tan δ ) In the range of 0.1 to 0.8, for example, a lactic acid resin composition containing a lactic acid resin and a plasticizer in a mass ratio of 60: 1 to 99: 1. A biodegradable wrap film containing as a main component is disclosed.

JP 2002-19053 A WO / 2005/082981

  However, as in Patent Document 2, in a system in which a plasticizer is blended with a lactic acid polymer, the glass transition point (Tg) of the lactic acid polymer is lowered to around room temperature, so that it is rapidly cooled by a casting method or the like. When the wrap film is formed, the elastic modulus is lowered because the sheet is kept amorphous, and if it is wound as it is, the roll may be blocked due to the tightening force. It was.

  In addition, when the lactic acid polymer is exposed on the front and back layers of the wrap film, the molecular weight of the lactic acid polymer decreases with time due to hydrolysis, and thus there is a problem that blocking is more likely to occur.

  In addition, as described above, in order to function as a small roll wrap film, in addition to transparency, adhesion to the container, drawability that allows the film to be pulled out smoothly from the paper box, cut suitability when cutting the drawn film However, it is not easy to produce a packaging film satisfying such various characteristics using a lactic acid polymer as a main raw material. In a laminated film having a structure, it has been difficult to produce a film having excellent adhesion to a container.

  Therefore, the present invention provides a packaging film containing a lactic acid-based polymer as one of the main raw materials, and does not cause blocking even when the formed film is stored in a wound state, and further reduces the degree of molecular weight reduction of the lactic acid-based polymer. It is an object of the present invention to provide a packaging film that can be reduced and yet satisfy various properties required for a small roll wrap film.

  In view of such problems, the present invention is a laminated film composed of at least three layers, both surface layers containing the polyolefin polymer (A) as a main component, and the intermediate layer comprising a lactic acid resin composition. (B) as a main component, the storage elastic modulus (E ′) measured by dynamic viscoelasticity measurement at a frequency of 10 Hz and a temperature of 20 ° C. is 1 GPa to 4 GPa, and the loss tangent (tan δ) peak temperature is 20 to 20 A packaging film characterized by having a peak value in the range of 0.1 to 0.8 at 60 ° C is proposed.

The present invention is a laminated film composed of at least three layers, and both surface layers thereof are mainly composed of a polyolefin polymer (A), while the intermediate layer is mainly composed of a lactic acid resin composition (B). The storage elastic modulus (E ′) formed as a component and measured by dynamic viscoelasticity measurement at a frequency of 10 Hz and a temperature of 20 ° C. is 1 GPa to 4 GPa, and the peak temperature of loss tangent (tan δ) is 20 to 60 ° C. Then, by making the packaging film so that the peak value is in the range of 0.1 to 0.8, various properties required for the small roll wrap film, that is, transparency, adhesion to the container, It is possible to provide a wrapping film that can satisfy various properties such as the ability to pull out a film smoothly from a paper box and the suitability for cutting the drawn film. It can function suitably as Ppufirumu.
In addition, by forming both surface layers of the laminated film with the polyolefin polymer (A) as a main component, the molecular weight of the lactic acid resin composition is reduced even if the film thus formed is stored in a wound state. It is possible to suppress the blocking of the film, and to solve the problem that the films adhere to each other.
Furthermore, since the anti-fogging agent etc. can be included in both surface layers by setting it as the laminated film comprised from at least 3 layers, the anti-fogging property etc. of a film can also be improved.

In general, "film" is a thin flat product whose thickness is extremely small compared to the length and width and whose maximum thickness is arbitrarily limited, and is usually supplied in the form of a roll. (Japanese Industrial Standard JISK6900), and “sheet” generally refers to a product that is thin according to the definition in JIS, and usually has a thickness that is small instead of length and width. 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.
In addition, in the present invention, the expression “main component” includes the intention to allow other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified. Although the content ratio of the components is not specified, the main component (when two or more components are the main components, the total amount thereof) is 50% by mass or more, preferably 70% by mass or more, particularly in the composition. It preferably includes 80% by mass or more (including 100%).
In addition, when described as “X to Y” (X and Y are arbitrary numbers), “X to Y” is intended unless otherwise specified, and “preferably larger than X and smaller than Y”. The intention of

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

  The packaging film is a laminated film having at least three layers, and both surface layers thereof contain a polyolefin polymer (A) as a main component, and the intermediate layer thereof is a lactic acid resin composition (B). Is a laminated film containing as a main component.

<Surface layer>
In the packaging film, it is important that the main component of the inner and outer surface layers (hereinafter simply referred to as “surface layer”) is a polyolefin polymer.

(Polyolefin polymer (A))
Examples of polyolefin polymers include ethylene polymers, butylene polymers, propylene polymers such as polypropylene and ethylene-propylene copolymers, poly-4-methylpentene, polybutene, ethylene-vinyl acetate copolymers, and the like. be able to. These resins may be one type of the resins listed above, or may be a mixed resin composed of two or more types of resins.
Polyolefin thermoplastic elastomers in which ethylene / propylene rubber or the like is dispersed and combined with these polyolefin polymers can also be used.

  Among the above, the role of the surface layer, that is, blocking prevention of the packaging film, an appropriate balance between slip and surface adhesiveness, surface properties such as antifogging property, molding processing stability during film formation, and further hydrolysis Considering the role of suppressing the decrease in the molecular weight of the lactic acid-based polymer (C) with time, the main component of the surface layer is preferably an ethylene-based polymer.

The ethylene polymer may be one ethylene polymer selected from low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, medium density polyethylene and high density polyethylene, or a combination of two or more of these. Examples thereof include a mixed resin made of a combination, and a copolymer containing ethylene as a main component. More specifically, α-olefins having 3 to 10 carbon atoms such as propylene, butene-1, pentene-1, hexene-1, heptene-1 and octene-1, and vinyl such as vinyl acetate and vinyl propyleneate. One or two selected from esters and unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate, and unsaturated compounds such as conjugated and non-conjugated dienes A mixed resin comprising a copolymer or a multi-component copolymer of ethylene with at least one kind of comonomer and ethylene, or a combination of two or more of the ethylene-based polymer, the copolymer, and the multi-component copolymer. Can be mentioned. In these ethylene-based polymers, the ethylene unit content preferably exceeds 50% by mass.
Among them, 1 selected from low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer and ethylene-methacrylic acid ester copolymer A mixed resin composed of a seed ethylene polymer or a combination of two or more of these is particularly preferable.
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 the ethylene-based polymers, when importance is attached to surface properties such as balance of surface tackiness, antifogging properties, and molding processing stability during film formation, the vinyl acetate content is 10 to 60% by mass, The rate (hereinafter sometimes abbreviated as “MFR”. MFR measurement conditions are 190 ° C., load 21.18 N based on JIS K 7210, and other MFRs are also the same). An ethylene-vinyl acetate copolymer that is / 10 minutes is particularly preferred.
In this ethylene-vinyl acetate copolymer, if the vinyl acetate content is 10% by mass or more, the film is not hard because the crystallinity is low, the flexibility and elastic recovery are good, and surface tackiness is also exhibited. It is preferable in that it is easy. On the other hand, if it is 60% by mass or less, heat resistance, film strength, etc. can be secured, bleed-out can be suppressed even if an antifogging agent is added, and the film is unwound because the surface tackiness is not too strong. It is preferable at the point that property and an external appearance can be made favorable. From such a viewpoint, the vinyl acetate content of the ethylene-vinyl acetate copolymer is more preferably 10 to 58% by mass, and particularly preferably 12 to 56% by mass.
Further, if the MFR of the ethylene-vinyl acetate copolymer is 0.2 g / 10 min or more, the extrusion processability is stable, and if it is 20 g / 10 min or less, stable film formation at the time of molding becomes possible. It is preferable because thickness unevenness, decrease in mechanical strength, variation, and the like are reduced. From such a viewpoint, the MFR of the ethylene-vinyl acetate copolymer is more preferably 0.5 to 18 g / 10 minutes, and more preferably 1 to 15 g / 10 minutes.

On the other hand, when importance is attached to microwave heat resistance that can withstand microwave heating, linear low density polyethylene having a density of 0.90 to 0.95 g / cm ³ and an MFR of 0.2 to 20 g / 10 min is used. Particularly preferred.
If the density of the ethylene polymer is within such a range, the film does not become hard because it has appropriate crystallinity, and the flexibility and elastic recovery are good. Since the temperature is higher than the operating temperature range, specifically the atmospheric temperature when heated in a microwave oven, etc., when the food is packaged with this packaging film and heated in a microwave oven, etc., the film dissolves in the food container, etc. This is preferable because it does not cause a problem of sticking. From this point of view, particularly preferred that the density of the ethylene-based polymer is 0.90~0.94g / cm ^3, and even more preferably among them 0.91~0.94g / cm ^3.
Also, if the MFR of the ethylene polymer is 0.2 g / 10 min or more, the extrusion processability is stable, and if it is 20 g / 10 min or less, stable film formation is possible at the time of molding, and thickness unevenness and mechanical strength are increased. This is preferable because there is less decrease and variation. From such a viewpoint, the MFR of the ethylene polymer is particularly preferably 0.5 to 18 g / 10 minutes, and more preferably 1 to 15 g / 10 minutes.

  The method for producing the ethylene polymer is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. Examples thereof include a slurry polymerization method, a solution polymerization method, a bulk polymerization method, a gas phase polymerization method using a single site catalyst, and a bulk polymerization method using a radical initiator.

<Intermediate layer>
Next, constituent components of the intermediate layer will be described.

  The lactic acid resin composition (B) as the main component of the intermediate layer may be any material that contains the lactic acid polymer (C). For example, the lactic acid polymer (C) and the glycerin fatty acid ester (D) Is preferred.

(Lactic acid polymer (C))
As the lactic acid polymer (C), poly (L-lactic acid) whose structural unit is L-lactic acid, poly (D-lactic acid) whose structural unit is D-lactic acid, structural units that are L-lactic acid and D-lactic acid Poly (DL-lactic acid), a mixture thereof, or a copolymer containing these can be used. However, poly (L-lactic acid) or poly (D-lactic acid) referred to here is ideally a polymer comprising 100% of L-lactic acid or D-lactic acid, but inevitably different lactic acid is included in the polymerization. Since there is a possibility, it contains 98% or more of L-lactic acid or D-lactic acid.

The ratio (molar ratio) of D-lactic acid (D form) to L-lactic acid (L form) in the lactic acid polymer (C) is L form / D form = 100/0 to 85/15, or L form / D. It is preferable that it is 0 / 100-15 / 85, More preferably, L-form / D-form = 99.5 / 0.5-85 / 15 or L-form / D-form = 0.5 / 99.5 15/85. If it exists in this range, the heat resistance of the film obtained will not be impaired.
In addition, you may blend the lactic acid-type polymer from which the copolymerization ratio of L body and D body differs. In that case, it is preferable that the average value of the copolymerization ratios of the L-form and D-form of a plurality of lactic acid polymers falls within the above range.

  From the viewpoint of suppressing bleed-out of plasticizers and the like, it is preferable that the crystallinity of the lactic acid polymer is low. Therefore, polylactic acid having a lower crystallinity than poly (L-lactic acid), such as poly (D-lactic acid), It is preferable to use poly (DL-lactic acid) or a mixture thereof as a main component. The ratio of D-form to L-form in the poly (DL-lactic acid) or the mixture is L-form / D-form = 85/15 to 95/5, or L-form / D-form = 5/95 to 15/85. Is preferred. If it exists in this range, since the crystallinity of a lactic acid-type polymer is low, bleeding out, such as a plasticizer, can be suppressed.

  On the other hand, considering the balance between suppression of bleeding out of plasticizers and the like and heat resistance (depending on the type of polyolefin polymer (A) as the main component of both surface layers), the D-form content is 0. 5-5 mol% poly (L-lactic acid) (hereinafter sometimes abbreviated as “CI component”) and D-form content 10-15 mol% poly (D, L-lactic acid) (hereinafter “ The mixed resin composition may be abbreviated as “C-II component”). Among them, the mixing mass ratio of the (CI) component to the (C-II) component is (CI) / It is more preferable that the mixed resin composition is (C-II) = 10/90 to 60/40, among which (CI) / (C-II) = 20/80 to 55/45. The mixed resin composition is even more preferred.

  The lactic acid-based polymer may contain other hydroxycarboxylic acid or the like as a small amount of a copolymer component, and may contain a small amount of a chain extender residue.

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

  The weight average molecular weight of the lactic acid polymer is preferably in the range of 50,000 to 400,000, more preferably in the range of 100,000 to 250,000. If the weight average molecular weight of the lactic acid-based polymer is 50,000 or more, practical properties such as mechanical properties and heat resistance can be secured, and if it is 400,000 or less, the melt viscosity is too high and the molding processability may be inferior. Absent.

  As the lactic acid polymer used for the packaging film, a commercially available lactic acid polymer can be used. For example, a brand name “Lacia” series (manufactured by Mitsui Chemicals, Inc.), a brand name “Nature Works” series (manufactured by NatureWorks), a brand name “U′z series” (manufactured by Toyota Motor Corporation), and the like can be given.

(Glycerin fatty acid ester (D))
The glycerin fatty acid ester (D) can play a role of plasticizing the lactic acid polymer (C).
The type of glycerin fatty acid ester is not particularly limited. For example, in addition to monoglyceride, diglyceride, triglyceride, acetylated monoglyceride, polyglycerin fatty acid ester such as diglycerin, triglycerin, tetraglycerin, etc. Can be mentioned. Among these, an acetylated monoglyceride having a molecular structure represented by the following chemical formula (1) is particularly preferable from the viewpoint of good compatibility with lactic acid polymers and high plasticizing ability.

  In the chemical formula (1), R1 represents an alkyl group, and R2 and R3 each represents an acetyl group or hydrogen. The number of carbon atoms of these alkyl groups is not particularly limited, and may be appropriately selected so as to achieve the purpose of improving adhesion and flexibility. In general, it is preferably 6-20.

  In order to obtain good compatibility with the lactic acid polymer (C), the molecular weight of the glycerin fatty acid ester (D) is preferably 2,000 or less, more preferably 1,500 or less.

  The blending amount of the lactic acid polymer (C) and the glycerin fatty acid ester (D) is preferably blended so that (C) / (D) = 90 / 10-60 / 40 in terms of mass ratio. By being within the above range, flexibility can be imparted, and bleed-out in which the glycerin fatty acid ester (D) moves to the surface with time and becomes sticky can be suppressed.

(Other ingredients)
The intermediate layer of the packaging film may contain a polyolefin polymer (E) in addition to the lactic acid resin composition (B).

  The polyolefin polymer (E) may be the same polyolefin polymer as the polyolefin polymer (A) constituting the surface layer or may be a different polyolefin polymer, but preferably the same polyolefin polymer. It may be a polymer. If the polyolefin polymer (E) and the polyolefin polymer (A) constituting the surface layer are the same polyolefin polymer, the adhesion between the intermediate layer and the surface layer can be improved, In addition to improving mechanical properties, 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. The material cost can be reduced.

  As the most preferred polyolefin polymer (E), an ethylene-vinyl acetate copolymer having a vinyl acetate content of 10 to 60% by mass can be mentioned. This ethylene-vinyl acetate copolymer can be suitably used as a polyolefin polymer (A) which is a main component of the surface layer, and is transparent when a recycled resin generated from trimming loss is added. There are no practical problems in terms of properties, mechanical properties, and material costs, and they can be stably obtained as industrial materials.

  The blending ratio of the polyolefin polymer (E) is (C) :( E) = 1: 99 to 50:50, particularly 5:95 to 50 in the mass ratio with the lactic acid polymer (C) in the intermediate layer. : 50, particularly preferably 10:90 to 45:55.

In the intermediate layer of the packaging film, a heat stabilizer, an antioxidant, a UV absorber, an anti-blocking agent, a light stabilizer, a nucleating agent, a hydrolysis inhibitor, a deodorant, as long as the effects of the present invention are not impaired. Additives such as agents can be formulated.
For example, in order to maintain the practical properties of the packaging film, the carbodiimide compound is preferably 0.1 to 3 parts by mass, more preferably 0.5 to 100 parts by mass with respect to 100 parts by mass of the lactic acid resin composition (B). By blending 1 part by mass, the weight average molecular weight can be increased. Below this range, the effect of increasing the weight average molecular weight is often insignificant, and above this range, fish eyes and gels may be produced during film formation, which is not preferred.

In addition, the surface layer and / or the intermediate layer of the packaging film should contain the following various additives as appropriate in order to impart performance such as anti-fogging property, antistatic property, slipperiness, and adhesiveness. Can do.
For example, an aliphatic alcohol fatty acid ester which is a compound of an aliphatic 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, , Monoglycerin oleate, polyglycerin oleate, glycerin triricinoleate, glycerin acetyl ricinoleate, polyglyceryl stearate, polyglycerin laurate, methyl acetyl lysylate, ethyl acetyl lysylate, butyl acetyl lysylate, propylene glycol oleate, propylene glycol Laurate, pentaerythritol oleate, polyethylene glycol oleate, polypropylene glycol oleate, sorbitan oleate, sorbitan laurate, polyethylene glycol sorbitan oleate, polyethylene 100 masses of resin components constituting various kinds of at least one compound selected from glycol sorbitan laurate and the like, as well as polyalkylene ether polyols, specifically polyethylene glycol, polypropylene glycol and the like, and paraffinic oil, etc. 0.1 to 12 parts by mass with respect to part, and preferably 1 to 8 parts by mass is preferable.

<Characteristic value>
This packaging film has (1) a storage elastic modulus (E ′) measured by dynamic viscoelasticity measurement at a frequency of 10 Hz and a temperature of 20 ° C. of 1.0 to 4.0 GPa, and (2) loss tangent (tan δ). ) Having a peak temperature of 20 ° C. to 60 ° C., and (3) the peak value is in the range of 0.10 to 0.80. Such conditions (1), (2) ( It is important that the film is prepared so as to satisfy all of 3).

If the storage elastic modulus (E ′) is less than 1.0 GPa, the film is too soft and the stress is too small for deformation, so that, for example, the cutability when pulled out from a paper box and cut is deteriorated. On the other hand, when E ′ exceeds 4.0 GPa, the film becomes hard and hardly stretched, and the drawability when drawn from the paper box is deteriorated.
Further, if the peak temperature of tan δ is 60 ° C. or less and the peak value is 0.10 or more, the restoring behavior against deformation of the film does not occur instantaneously. It is preferable because the film is not restored and the adhesion to the container is improved. In addition, if the peak temperature of tan δ is 20 ° C. or higher and the peak value is 0.80 or lower, plastic deformation is not exhibited, and this is not a problem in a normal usage method.
The tan δ (loss tangent) is the ratio of the loss elastic modulus (E ″) to the storage elastic modulus (E ′), that is, the loss tangent (tan δ = E ″ / E ′). This means that the loss elastic modulus (E ″) of the material, that is, the contribution ratio of the viscosity is large among the viscoelastic properties. By evaluating the peak value and the peak temperature of tan δ, This is a great measure for judging the adhesiveness and stress relaxation behavior of the film in the packaging process.

  In order to produce a film that satisfies all of the above conditions (1) to (3), for example, selection of constituent components in the intermediate layer and the surface layer (the type of resin as the main component, its molecular weight and Tg, presence or absence of a plasticizer) And the type, mixing ratio of components, LD ratio of the lactic acid polymer), thickness ratio of the intermediate layer and the surface layer, film forming method, processing conditions (for example, heat treatment conditions after film formation, etc.) are appropriately balanced. It can be produced by adjusting.

<Laminated structure>
If this packaging film is a laminated film comprising three layers of both surface layers mainly composed of a polyolefin polymer (A) and an intermediate layer mainly composed of a lactic acid resin composition (B) Of course, other layers (hereinafter sometimes abbreviated as “P layer”) may be appropriately introduced as required, such as improvement of mechanical properties and interlayer adhesion. For example, a layer having the same composition as the surface layer (hereinafter sometimes abbreviated as “S layer”) may be interposed as an intermediate layer in addition to both surface layers, and the same composition as the intermediate layer Two or more layers (hereinafter sometimes abbreviated as “M layer”) may be interposed between both surface layers. Specifically, a three-layer configuration consisting of (S layer) / (M layer) / (S layer), a four-layer configuration consisting of (S layer) / (P layer) / (M layer) / (S layer), (S layer) / (P layer) / (M layer) / (P layer) / (S layer), (S layer) / (M layer) / (P layer) / (M layer) / (S layer), etc. A five-layer structure composed of In this case, the resin composition and thickness ratio of each layer may be the same or different.

In the packaging film, the thickness ratio of the intermediate layer to the thickness of the entire film is preferably 35 to 90%. If the thickness ratio of the intermediate layer is within such a range, it becomes easy to design a film that satisfies the above characteristic values (E ′, tan δ) due to the dynamic viscoelasticity. For example, when the film is formed by the T-die method Stable film-forming stability can be obtained, and mechanical properties for expressing a suitable cutting property for wrapping films for food packaging and relaxation properties for developing container adhesion can be imparted relatively easily. Can do.
Furthermore, in the case where more importance is attached to stable film forming workability and flexibility, the thickness ratio of the intermediate layer to the total film thickness is preferably 35 to 65%, more preferably 35 to 60%. preferable.
On the other hand, when more importance is attached to cutability and adhesion to a container, and further, the degree of planting, that is, CO ₂ reduction, the thickness ratio of the intermediate layer to the thickness of the entire film is preferably 60 to 90%. More preferably, it is 65 to 90%.
When there are two or more intermediate layers as described above, the thickness ratio may be calculated using the total thickness of all the intermediate layers.

  The thickness (whole) of the packaging film may be a range used as a food packaging wrap film, specifically 6 μm to 30 μm, and preferably 10 μm to 20 μm.

<Manufacturing method>
Although the manufacturing method of this packaging film is demonstrated, it is not limited to the following manufacturing method.

  First, when the constituent material of each layer is a mixed composition, the constituent material of each layer is preferably mixed in advance and pelletized as necessary. As a mixing method at this time, for example, it may be pre-compounded in advance using a same-direction twin-screw extruder, a kneader, a Hayshell mixer, or the like. You may make it throw in. In any mixing method, it is necessary to consider a decrease in molecular weight due to decomposition of the raw material, but pre-compounding is preferable for uniform mixing. For example, in the case of an intermediate layer, the lactic acid-based polymer and additives as necessary are sufficiently dried to remove moisture, and then melt-mixed using a twin screw extruder, and a plasticizer is removed from the vent port. What is necessary is just to produce a pellet by extruding into a strand shape while adding a predetermined amount.

Next, the constituent materials of each layer may be separately put into an extruder, melt extruded, and coextruded by T-die molding or inflation molding to be laminated.
At this time, it is preferable to form a film by practically pulling the melt extruded from the T die as it is while rapidly cooling it with a casting roll or the like.

When emphasizing the heat resistance and cutability of the film, after the melt-extruded sheet is cooled and solidified by a cooling roll, it is heated below the crystallization temperature of the resin, and the difference in speed between the nip rolls is used in the longitudinal direction of the film. It is preferable to adopt a longitudinal stretching method in which the film is stretched 1.2 to 5 times, or a flat stretching method in which biaxial stretching and / or simultaneous biaxial stretching is performed 1.2 to 5 times in both the longitudinal and transverse directions of the film.
As the stretching temperature, the temperature of the extruded sheet is preferably set in the range of 30 to 90 ° C, and more preferably in the range of 40 to 60 ° C. If the stretching temperature is within such a range, both the lactic acid resin composition (B) of the intermediate layer and the polyolefin polymer (A) of the surface layer can be brought close to the elastic modulus suitable for stretching. Further, the draw ratio is preferably in the range of 1.2 to 5.0 times, and more preferably in the range of 1.5 to 4.0 times. As long as the draw ratio is within this range, the cut property can be improved without causing troubles such as breakage and whitening of the extruded sheet.

  Moreover, when importance is attached to productivity and / or economy, it is preferable to melt-extrude the material resin from an annular die and perform inflation molding. Moreover, as a cooling method in that case, either the method of cooling from the outer surface of the tube, or the method of cooling from both the outer surface and the inner surface of the tube may be used.

The film thus obtained is reduced in heat shrinkage rate and natural shrinkage rate, depending on the purpose such as suppression of occurrence of width shrinkage, longitudinal stretching between heating rolls as required, various heat setting, Heat treatment such as aging may be performed.
As heat treatment conditions, the heat treatment temperature is preferably set in the range of 40 to 100 ° C, and more preferably in the range of 60 to 90 ° C. If the heat treatment temperature is 40 ° C. or higher, the effect of the heat treatment can be sufficiently obtained, and if it is 100 ° C. or lower, the problem of formability such as stickiness of the film on the roll does not occur.

  Further, for the purpose of imparting and promoting antifogging properties, antistatic properties, adhesiveness, and the like, treatments such as corona treatment and aging, and surface treatments and surface treatments such as printing and coating may be performed.

  It should be noted that the upper and lower limits of the numerical range in the present invention are those of the present invention as long as they have the same operational effects as those in the numerical range even if they are slightly outside the numerical range specified by the present invention. It is included in the equivalent range.

Hereinafter, although an Example and a comparative example demonstrate in more detail, this invention does not receive a restriction | limiting at all in the following Example.
In addition, the various measured value and evaluation about the film displayed in this specification were performed as follows. Here, the flow direction of the film from the extruder is referred to as the vertical direction (hereinafter sometimes referred to as “MD”), and the perpendicular direction thereof is referred to as the horizontal direction (hereinafter sometimes referred to as “TD”).

(1) E ′, tan δ
According to the dynamic viscoelasticity measurement method described in JIS K-7198 A method, using a viscoelastic spectrometer “VES-F3” manufactured by Iwamoto Seisakusho Co., Ltd., the vibration frequency is 10 Hz and the strain is 0 in the transverse direction (TD). .1%, measured from −50 ° C. to 150 ° C. at a rate of temperature increase of 1 ° C./min. From the obtained data, the storage elastic modulus (E ′) at a temperature of 20 ° C. and the loss tangent (tan δ) The peak temperature and its peak value were determined.

(2) Molecular weight retention (wet heat durability)
The obtained film was allowed to stand for 1 month in a constant temperature and humidity machine LH-112 manufactured by Tabay Espec adjusted to 40 ° C. × 90% by weight. The weight average molecular weight of the film before and after the test was mounted on a gel permeation chromatography HLS-8120GPC manufactured by Tosoh Corporation and a chromatographic column Shim-Pack series GPC-800CP manufactured by Shimadzu Corporation. Measurement was performed at a solution concentration of 0.2 wt / vol% by weight, a solution injection amount of 200 μl, a solvent flow rate of 1.0 ml / min, and a solvent temperature of 40 ° C., and a weight average molecular weight was calculated in terms of polystyrene. The weight average molecular weight of the standard polystyrene used is 20000, 670000, 110,000, 35000, 10,000, 4000, 600.
The molecular weight retention rate (% by weight) was calculated from the calculated weight average molecular weights before and after the test, and the following determinations were made.
○: The molecular weight retention is 60 to 100% by weight, and the molecular weight after aging is 100,000 or more. X: The molecular weight retention is 0 to 60% by weight, and the molecular weight after aging is 100,000 or less.

(3) Film-forming stability When a film was formed by the T-die forming method, the stability of casting and the degree of sticking to a roll were observed and evaluated according to the following criteria.
◎: Extremely stable ○: Stable △: Slightly unstable

(4) Blocking resistance The obtained roll of film is stored in a temperature-controlled room at a temperature of 43 ° C. and a relative humidity of 40% for 5 days, and the subsequent surface condition and roll-back property are observed and evaluated according to the following criteria. did.
◎: There is no blocking between films. ○: There is a little blocking between films, but there is no problem in practical use. △: A level where peeling is slightly more problematic due to blocking between films. Cannot be rolled back

(5) Adhesiveness of container Adhesion to a container when packaged in a bowl-shaped ceramic container having a diameter of 10 cm and a depth of 5 cm was evaluated according to the following criteria.
◎: Level that can be packaged moderately ○: Level that spreads slightly from the shape of the container, but there is no practical problem ×: The film spreads along the container and becomes a practical problem

(6) Anti-fogging property The film is pasted on the opening on one side of a cylinder made of SUS304 having a diameter of 50 mm and a height of 80 mm, and the film is pasted in an environment with an outside temperature of 0 to 5 ° C. The cylindrical end 30 mm on the open side was immersed in water at a water temperature of 20 ° C., and after 1 hour from the start of immersion, the antifogging property was visually observed and evaluated according to the following criteria.
◎: Water film with uniform moisture and no water droplets ○: Water film with uniform moisture content, but there are fine water droplets in some places △: Water droplets with a diameter of about 1 mm in some places ×: Water droplets with a diameter of about 3 mm

(Example 1)
About the resin composition which forms both surface layers, an ethylene-vinyl acetate copolymer “LV440” (vinyl acetate content: 15% by mass, MFR: 2.2 g / m) manufactured by Nippon Polyethylene Co., Ltd. as a polyolefin polymer (A). 10 minutes) 100 parts by mass (hereinafter abbreviated as “A-1”), and 5.0 parts by mass of diglycerin monooleate “DGO-1” manufactured by Riken Vitamin Co. It put into the same direction twin screw extruder set to 200 degreeC, and was melt-kneaded.
On the other hand, for the resin composition forming the intermediate layer, “NatureWorks 4050” (L-form / D-form = 94.5 / 5.5, weight average molecular weight: 200,000) manufactured by NatureWorks as the lactic acid polymer (C). (Hereinafter abbreviated as “C-1”) was introduced into a co-directional twin-screw extruder set at an extrusion set temperature of 180 ° C., and then acetylated monoglyceride “Riquemar PL019” manufactured by Riken Vitamin Co. ”(Hereinafter abbreviated as“ D-1 ”) from the first vent port of the extruder so that D-1 is 20 parts by mass with respect to C-1 (100 parts by mass). The mixture was melt-kneaded while pouring using the above.
Then, the resin composition for forming both surface layers melted and kneaded as described above and the resin composition for forming the intermediate layer are joined from separate extruders, respectively, and the three-layer T die temperature is 200 ° C. and the die gap is 2 mm. By co-extrusion and rapid cooling with a cast roll set at a temperature of 30 ° C., a packaging film having a total thickness of 12 μm (surface layer / intermediate layer / surface layer = 3 μm / 6 μm / 3 μm) was obtained. The results of evaluating the obtained film are shown in Table 1.

(Example 2)
In Example 1, instead of C-1, “NatureWorks 4032D” (L-form / D-form = 98.6 / 1.4, weight average molecular weight: 200,000) manufactured by NatureWorks, Inc. (hereinafter abbreviated as “C-2”) ) Was used in the same manner as in Example 1 to obtain a packaging film having a total thickness of 12 μm (surface layer / intermediate layer / surface layer = 3 μm / 6 μm / 3 μm). The results of evaluating the obtained film are shown in Table 1.

(Example 3)
In Example 1, instead of A-1, a linear low density polyethylene “NUCG5225” (density: 0.92 g / cm ³ , MFR: 2.0 g / 10 min) manufactured by Nippon Unicar Co., Ltd. (hereinafter “A-2”) And C-2 instead of C-1, and the thickness ratio of the surface layer to the intermediate layer is determined as follows: surface layer / intermediate layer / surface layer = 1.5 μm / 9 μm / 1.5 μm A packaging film having a total thickness of 12 μm was obtained in the same manner as in Example 1 except that the film was changed to. The results of evaluating the obtained film are shown in Table 1.

Example 4
In Example 3, as the lactic acid polymer (C), C-2 and NatureWorks 4060D ”(L-form / D-form = 97/13, weight average molecular weight: 200,000) (hereinafter abbreviated as“ C-3 ”) And a total thickness of 12 μm (surface layer / intermediate layer / surface layer = 1) in the same manner as in Example 3 except that a mixed resin containing C and C at a mass ratio of C-2 / C-3 = 30/70 was used. (5 μm / 9 μm / 1.5 μm). The results of evaluating the obtained film are shown in Table 1.

(Example 5)
In Example 1, as the resin composition for forming the intermediate layer, Example 1 is used except that a resin composition obtained by adding 25 parts by mass of A-1 to C-1 (100 parts by mass) is used. Similarly, a packaging film having a total thickness of 12 μm (front / back layer / intermediate layer / front / back layer = 3 μm / 6 μm / 3 μm) was obtained. The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 1)
In Example 1, except that the extrusion amount of each extruder was changed so that the thickness ratio of both the surface layer and the intermediate layer would be surface layer / intermediate layer / surface layer = 2/1/2. In the same manner as above, a packaging film having a total thickness of 15 μm (surface layer / intermediate layer / surface layer = 6 μm / 3 μm / 6 μm) was obtained. The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 2)
In Example 1, a resin composition having the same composition as the resin compositions (C-1 and D-1) forming the intermediate layer instead of A-1 and the antifogging agent as the resin composition forming both surface layers A pellet having a total thickness of 12 μm was prepared in the same manner as in Example 1 except that a pellet was prepared by precompounding the product, and the pellet was put into an extruder for both surface layers to form a substantially single-layer film. A film was obtained. The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 3)
In Example 3, a packaging film having a total thickness of 12 μm was obtained in the same manner as in Example 3 except that A-2 was charged into an intermediate layer extruder to obtain a substantially single layer film. The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 4)
In Example 1, D-1 was not injected from the first vent of the extruder, that is, melt-kneaded without containing D-1, and the total thickness was 12 μm (front / back layer / intermediate layer / A film for packaging having front and back layers = 3 μm / 6 μm / 3 μm) was obtained. The results of evaluating the obtained film are shown in Table 1.

From Table 1, the films obtained in Examples 1 to 5 can suppress the molecular weight of the packaging film from decreasing over time, and blocking occurs even when the film formed is stored in a wound state. Furthermore, it was confirmed that the antifogging property and the container adhesion were also good.
On the other hand, in the case of Comparative Example 1-4, since the thickness ratio of the intermediate layer to the entire film is low, the storage elastic modulus is lower than the range defined in the present invention (Comparative Example 1). In the case of not having an intermediate layer mainly composed of a lactic acid-based polymer resin composition (Comparative Example 3), blocking, antifogging properties, and film formation stability were good, but container adhesion was insufficient. Met. Further, when the front and back layers mainly composed of an ethylene polymer were not present (Comparative Example 2), the container adhesion was good, but the film-forming stability, blocking and antifogging properties were insufficient. In addition, the molecular weight decreased due to hydrolysis over time, which was a problem due to insufficient practical characteristics. Moreover, when the peak temperature of loss tangent was higher than the range prescribed | regulated by this invention (comparative example 4), although blocking and anti-fogging property were favorable, container adhesiveness was inadequate.

Claims (6)

It is a laminated film composed of at least three layers, both surface layers contain a polyolefin polymer (A) as a main component, and the intermediate layer contains a lactic acid resin composition (B) as a main component. ,
The storage elastic modulus (E ′) measured at a frequency of 10 Hz and a temperature of 20 ° C. by dynamic viscoelasticity measurement is 1 GPa to 4 GPa, the peak temperature of loss tangent (tan δ) is 20 to 60 ° C., and the peak value is A packaging film characterized by being in the range of 0.1 to 0.8.   The packaging film according to claim 1, wherein the polyolefin polymer (A) is an ethylene polymer.   Polyolefin polymers (A) are low density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, and ethylene-methacrylic acid ester copolymer. The packaging film according to claim 1 or 2, which is a mixed resin composed of at least one ethylene polymer selected from a coalescence or a combination of two or more of these.   The packaging film according to any one of claims 1 to 3, wherein the lactic acid resin composition (B) is a mixture of a lactic acid polymer (C) and a glycerin fatty acid ester (D).   The intermediate layer contains a polyolefin polymer (E) in addition to the lactic acid resin composition (B) containing the lactic acid polymer (C). Packaging film.   In the intermediate layer, the polyolefin polymer (E) is contained so that the mass ratio with the lactic acid polymer (C) is (C) :( E) = 1: 99 to 50:50. The packaging film according to claim 5.