JP2008221813A - Multilayered lactic acid-based soft film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayered lactic acid-based soft film excellent in restoration properties with respect to the deformation of a film at a room temperature and also enhanced in the close adhesiveness with a container held to a low temperature state. <P>SOLUTION: In a multilayered lactic acid-based soft film equipped with at least three layers, the intermediate layer contains a mixture of a lactic acid-based polymer (B), an aliphatic polyester (C) with a glass transmmition temperature of 0°C or below and a plasticizer (D) as main components and both surface layers contain a thermoplastic resin (A), which is different from the main component of the intermediate layer, as a main component and is characterized in that the value of loss tangent (tan δ) at 20°C measured under the condition of a vibration frequency of 10 Hz and a strain of 0.1% by the dynamic viscoelasticity measuring method described in the JIS K 7198 A method is 0.1-0.8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a lactic acid-based soft film mainly containing a lactic acid-based polymer, which is a resin derived from a natural plant, and more particularly to a lactic acid-based soft film that can be suitably used as a food packaging film or the like.

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 biodegradability. Attention has been paid. However, since the lactic acid-based polymer has high rigidity, a device for softening it was necessary.

  For example, Patent Document 1 discloses a polylactic acid resin composition comprising polylactic acid, a polymer component containing a biodegradable aliphatic polyester having a melting point of 80 to 250 ° C., and a biodegradable plasticizer. A polylactic acid containing 90 to 50% by weight and an aliphatic polyester of 10 to 50% by weight based on the total weight of the polylactic acid and the aliphatic polyester, and the composition ratio of the plasticizer is A polylactic acid resin composition is disclosed in which 5 to 25 parts by weight of a plasticizer is blended with 100 parts by weight of the polymer component.

JP-A-11-116788

  However, in the system in which a plasticizer is blended as in Patent Document 1, the glass transition temperature of polylactic acid (hereinafter sometimes referred to as “Tg”) is lowered to around room temperature, so that the casting method or the like is used. When the wrap film is formed by cooling rapidly, the elastic modulus is lowered by being seated in an amorphous state, and if it is wound as it is long, the scroll is blocked by the tightening force or the like. There was a problem that occurred. In addition, when a predetermined amount of plasticizer is blended with polylactic acid and aliphatic polyester, the viscosity is greatly reduced, which may cause difficulties in processability.

  In addition, as described above, in order to function as a wrap film, various conditions such as transparency, adhesion to a container, anti-fogging property, and drawability that allows the film to be pulled out smoothly are required. It has been difficult to produce a film satisfying such various conditions using a polymer as a main raw material.

  Therefore, the present invention is a lactic acid-based soft film using a lactic acid-based polymer, which has excellent recovery from deformation of the film even at a low temperature, and may cause blocking even when stored in a state where the formed film is wound. In addition, the present invention is to provide a lactic acid-based soft film that has satisfactory processability, can satisfy various conditions required for a wrap film, such as adhesion, antifogging properties, and film drawability.

  In view of this problem, the present invention is a multilayer lactic acid-based soft film having at least three layers, and the intermediate layer includes a lactic acid-based polymer (B) and an aliphatic polyester (C) having a glass transition temperature of 0 ° C. or lower. ) And a plasticizer (D) as a main component, both surface layers contain a thermoplastic resin (A) different from the main component of the intermediate layer as a main component, and comply with JIS K 7198 A method. A multilayer characterized in that a loss tangent (tan δ) value at 20 ° C. measured at a vibration frequency of 10 Hz and a strain of 0.1% is in the range of 0.1 to 0.8 by the described dynamic viscoelasticity measurement method. Propose a lactic acid-based soft film.

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 JIS K 6900), and “sheet” generally refers to a product that is thin by 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.
Further, in the present invention, the expression “main component” includes the intention to allow other components to be contained within a range that does not hinder 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 main components, the total amount thereof) is 50% by mass or more, preferably 70% by mass or more, particularly preferably 80%.
The meaning which occupies the mass% or more (100% is included) is included.
In addition, when “X to Y” (X and Y are arbitrary numbers) is described, “X” unless otherwise specified.
The above is intended to be “Y or less” and includes the intention of “greater than X and preferably smaller than Y”.

  The multilayer lactic acid-based soft film of the present invention has excellent recoverability against deformation of the film at room temperature, does not cause blocking even when stored in a state where the formed film is wound, has good workability, and Has high adhesion to containers at low temperatures. In addition, since the surface layer can contain an antifogging agent or the like, the antifogging property of the film can be improved.

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

  The present lactic acid-based soft film is a multilayer lactic acid-based soft film having at least three layers, and the intermediate layer includes a lactic acid-based polymer (B), an aliphatic polyester (C) having a glass transition temperature of 0 ° C. or less, and A multilayer lactic acid-based soft film containing a mixture with a plasticizer (D) as a main component and both surface layers containing a thermoplastic resin (A) different from the main component of the intermediate layer as a main component.

<Intermediate layer>
The intermediate layer of the lactic acid-based soft film contains as a main component a mixture of a lactic acid-based polymer (B), an aliphatic polyester (C) having a glass transition temperature of 0 ° C. or less, and a plasticizer (D).

(Lactic acid polymer (B))
As the lactic acid polymer (B), 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-based polymer (B) 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.

  In consideration of the balance between suppression of bleeding out of plasticizers and the like and heat resistance (depending on the type of thermoplastic resin (A) used for both surface layers), the D-form content is 0.5 to 5 Mol% poly (L-lactic acid) (hereinafter sometimes abbreviated as “BI component”) and D-form content of 10-15 mol% poly (D, L-lactic acid) (hereinafter “B-II component”) And the mixed mass ratio of the component (BI) and the component (B-II) is preferably (BI) / (B-II). ) = 10/90 to 60/40 is particularly preferable, and among them, a mixed resin composition in which (BI) / (B-II) = 20/80 to 55/45 is more preferable.

  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), 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.

(Aliphatic polyester (C))
As described above, the intermediate layer of the lactic acid-based soft film contains an aliphatic polyester (C) having a glass transition temperature (Tg) of 0 ° C. or lower in addition to the lactic acid-based polymer (B).

  Generally, the relaxation characteristics of the film are expressed in the vicinity of the Tg of the constituent resin, but in the case of the present lactic acid-based soft film, it is expressed in the vicinity of the Tg of the resin that forms the main component of the intermediate layer. By forming a film intermediate layer by polymer blending a polymer (B) and an aliphatic polyester (C) having a Tg of 0 ° C. or lower, a low temperature (0 ° C. in addition to relaxation properties near room temperature) The following relaxation properties can be imparted to the film. Moreover, impact resistance can also be improved by adding aliphatic polyester (C) whose Tg is 0 degreeC or less.

Here, as the aliphatic polyester (C) having a glass transition temperature (Tg) of 0 ° C. or lower, an aliphatic oxycarboxylic acid, an aliphatic or alicyclic diol, an aliphatic dicarboxylic acid or a derivative thereof was copolycondensed. Aliphatic polyester, aliphatic polyester obtained by polycondensation of aliphatic dicarboxylic acid and aliphatic diol as main components (50 to 100% by mass), aliphatic polyester obtained by ring-opening polymerization of cyclic lactones, synthetic aliphatic polyester, bacterial cells And a mixture of at least one or a combination of two or more selected from the aliphatic polyesters biosynthesized in (1), wherein Tg is 0 ° C. or lower, more preferably Tg is −20 ° C. or lower.

  In addition, the glass transition temperature (Tg) in this invention says the value calculated | required as follows. That is, by measuring with a differential scanning calorimeter (DSC), a sample cut to about 10 mg was heated from −100 ° C. to 200 ° C. at a heating rate of 10 ° C./min according to JIS K 7121, and at 250 ° C. After holding for 1 minute, the glass transition was determined from the thermogram when the temperature was lowered to −100 ° C. at a cooling rate of 10 ° C./minute, held at −100 ° C. for 1 minute, and then reheated at a heating rate of 10 ° C./minute. Temperature (Tg).

  Specific examples of the aliphatic oxycarboxylic acid in the copolycondensed aliphatic polyester include lactic acid, glycolic acid, 2-hydroxy-n-butyric acid, 2-hydroxycaproic acid, 2-hydroxy-3,3-dimethylbutyric acid, and 2-hydroxy-3-methyl. Examples include butyric acid, 2-hydroxyisocaproic acid, and mixtures thereof. Of these, lactic acid or glycolic acid is preferred, and particularly preferred is lactic acid or glycolic acid, which is particularly prominent in increasing the polymerization rate during use and is readily available. As a form, since the thing of 30-95% of aqueous solution can be obtained easily, it is preferable. These aliphatic oxycarboxylic acids can be used alone or as a mixture of two or more.

  Specific examples of the aliphatic or alicyclic diol in the copolycondensed aliphatic polyester include ethylene glycol, 1,3-propion glycol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol are preferred. In view of the physical properties of the obtained copolymer, 1,4-butanediol is particularly preferable.

  Specific examples of the aliphatic dicarboxylic acid or derivative thereof in the copolycondensed aliphatic polyester include oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, and their lower alcohols. And esters, succinic anhydride, adipic anhydride, and the like. From the viewpoint of the physical properties of the resulting copolymer, succinic acid, adipic acid, sebacic acid or their anhydrides, and their lower alcohols are preferred, and succinic acid, succinic anhydride, or a mixture thereof is particularly preferred. These can be used alone or in combination of two or more.

  Examples of aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones include ring-opening polymers selected from one or more cyclic monomers such as ε-caprolactone, δ-valerolactone, and β-methyl-δ-valerolactone. Can be mentioned.

  Examples of synthetic aliphatic polyesters include copolymers of succinic anhydride, cyclic acid anhydrides such as ethylene oxide and propylene oxide, and oxiranes.

  What is particularly preferably used as the aliphatic polyester (C) having a glass transition temperature (Tg) of 0 ° C. or lower is a copolycondensed aliphatic polyester which is considered to be relatively transparent among the above. Examples include polyethylene adipate, polypropylene adipate, polybutylene adipate, polyhexene adipate, polybutylene succinate, polybutylene succinate adipate, polybutylene succinate lactic acid, polybutylene succinate adipate lactic acid, polyethylene succinate and the like. Among them, aliphatic oxycarboxylic acids, aliphatic or cycloaliphatic diols, and aliphatic dicarboxylic acids such as polybutylene succinate lactic acid, polybutylene succinate adipate lactic acid and the like in the sense that a high molecular weight body can be easily obtained. It is preferable to select an aliphatic polyester obtained by copolycondensation of a derivative. This is because by copolymerizing an oxycarboxylic acid such as lactic acid, an aliphatic polyester having a number average molecular weight of 10,000 or more can be obtained very easily without using a chain extender. Further, by introducing the oxycarboxylic acid component, the crystallinity of the resulting polyester is lowered, and flexibility can be imparted.

  As a polymerization method of the aliphatic polyester (C), known methods such as a direct method and an indirect method can be employed. In the direct method, for example, polycondensation is performed by selecting the dicarboxylic acid compound anhydride or derivative thereof as the aliphatic dicarboxylic acid component, and selecting the diol compound or derivative thereof as the aliphatic diol component and performing polycondensation. A high molecular weight product can be obtained while removing the water generated at the time. Moreover, it becomes easy to obtain a high molecular weight body by copolymerizing oxycarboxylic acid like lactic acid as a 3rd component. The indirect method can be obtained by adding a small amount of chain extender, for example, a diisocyanate compound such as hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate to the oligomer polycondensed by the direct method to obtain a high molecular weight. .

  Commercially available aliphatic polyesters (C) include aliphatic polyesters that are polycondensed from aliphatic dicarboxylic acids and aliphatic diols as main components, “Bionole” series manufactured by Showa Polymer Co., Ltd., and aliphatic oxycarboxylic acids. As an aliphatic polyester obtained by copolycondensation of an aliphatic or alicyclic diol, and an aliphatic dicarboxylic acid or a derivative thereof, “GSPla” series manufactured by Mitsubishi Chemical Corporation is available.

  The weight average molecular weight of the aliphatic polyester (C) is preferably in the range of 20,000 to 500,000, more preferably in the range of 150,000 to 250,000. When the molecular weight is less than 20,000, practical physical properties such as mechanical strength cannot be obtained sufficiently, and when the molecular weight exceeds 500,000, there is a problem that molding processability is inferior.

  The blending ratio of the aliphatic polyester (C) having a glass transition temperature (Tg) of 0 ° C. or less is 100% by mass in total of the lactic acid polymer (B) and the aliphatic polyester (C), and Tg is 0 ° C. or less. It is preferable to mix | blend so that the aliphatic polyester (C) may occupy 30-90 mass%, and it is especially preferable to mix | blend so that 50-80 mass% may be occupied especially. In other words, the lactic acid polymer (B) is 10 to 70% by mass with respect to 100% by mass in total of the lactic acid copolymer (B) and the aliphatic polyester (C) having a glass transition temperature (Tg) of 0 ° C. or less. It is preferable to mix | blend so that it may occupy%, and it is especially preferable to mix | blend so that it may occupy 20-50 mass% especially. By making the blending ratio of the lactic acid-based polymer (B) 10% by mass or more, there is an effect that the glass transition temperature of the blend is expressed near room temperature and the relaxation property (tan δ peak value) is increased, Thus, by setting it to 70% by mass or less, there is an effect of increasing the relaxation characteristics (tan δ peak value) on the low temperature side.

(Plasticizer (D))
The plasticizer (D) can play a role of plasticizing the lactic acid polymer (B) and the aliphatic polyester (C) having a glass transition temperature (Tg) of 0 ° C. or lower. Among them, glycerin fatty acid ester is preferable, and the type thereof is not particularly limited. . In particular, an acetylated monoglyceride having a molecular structure represented by the following chemical formula (1) is preferable from the viewpoint of good compatibility with a lactic acid polymer 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 is appropriately selected so that the objectives of improving adhesion and flexibility are achieved, but generally 6 to 20 is preferable.

  In order to obtain good compatibility with the lactic acid polymer (B) and the aliphatic polyester (C) having a Tg of 0 ° C. or less, the plasticizer (D) preferably has a molecular weight of 2,000 or less. More preferably, it is 1,500 or less.

  The blending amount of the plasticizer (D) to the lactic acid polymer (B) and the aliphatic polyester (C) having a glass transition temperature of 0 ° C. or less is such that the lactic acid polymer (B) and the glass transition temperature are 0 ° C. or less. It is preferable to mix | blend so that it may become 10-30 mass parts with respect to a total of 100 mass parts with aliphatic polyester (C). By making it within the above range, flexibility can be imparted, bleed-out where the plasticizer (D) migrates to the surface over time and the surface becomes sticky can be suppressed, and the melt viscosity of the mixture decreases. Since it is not too much, workability is also improved.

(Other ingredients)
The intermediate layer of the present lactic acid-based soft film may contain a thermoplastic resin. This thermoplastic resin may be the same resin as the thermoplastic resin (A) constituting the surface layer or a different resin, but is preferably the same resin. If it is the same resin as the resin constituting the surface layer, the adhesion between the intermediate layer and the surface layer can be improved, the mechanical properties of the entire film can be improved, and for example, both ends of the formed film are cut. Thus, trimming loss that occurs when trimming is performed can be prepared by adding it as a constituent material of the intermediate layer, so that waste of material can be eliminated and material cost can be reduced.

  At this time, an ethylene polymer can be preferably used as the most suitable thermoplastic resin. Among these, 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 the thermoplastic resin (A) which is the main component of the surface layer, and is transparent when a recycled resin generated from trimming loss or the like is added. In addition, there are no practically significant problems including mechanical properties and material cost, and it can be stably obtained as an industrial material.

  Further, in the intermediate layer of the lactic acid-based soft film, a heat stabilizer, an antioxidant, a UV absorber, an anti-blocking agent, a light stabilizer, a nucleating agent, a hydrolysis inhibitor, as long as the effects of the present invention are not impaired. Additives such as deodorants can be formulated. For example, in order to maintain the practical properties of the present lactic acid-based soft film, the carbodiimide compound is preferably added in an amount of 0.1 to 3 parts by mass, more preferably 0.5 to 1 part by mass to increase the weight average molecular weight. Can do. 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.

<Surface layer>
It is important that both surface layers (that is, the front and back layers) of the lactic acid-based soft film contain a thermoplastic resin (A) different from the main component of the intermediate layer as a main component.

  In this lactic acid-based soft film, the surface layer secures hermeticity as a package by heat sealing and adhesion, and increases mechanical strength such as tear strength, piercing strength, impact strength, etc. In film forming by a stretching method or the like, in addition to enhancing stability during forming, it can also serve as an anti-blocking layer during film winding. Furthermore, by adding additives with various functions such as antifogging agents, antistatic agents, and lubricants, various functions can be imparted to the film, and additives such as plasticizers are added to the intermediate layer. If this happens, it will also prevent the bleeding out. Considering these functions, ethylene-based polymers are particularly preferable among the thermoplastic resins (A).

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. A mixed resin comprising a combination or a copolymer having ethylene as a main component, that is, ethylene and propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, etc. 10 α-olefins, vinyl esters such as vinyl acetate and vinyl propylene acid, unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate, and unsaturated such as conjugated and non-conjugated dienes A copolymer with one or more comonomers selected from compounds, or Terpolymer, or can include the ethylene polymer, the copolymer, two or more combinations mixed resin consisting of said multicomponent copolymer. The ethylene unit content of these ethylene polymers is usually more than 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 polymers, ethylene-vinyl acetate copolymers are preferable from the viewpoints of optical properties and adhesiveness. Among them, the vinyl acetate content is 5 to 25% by mass, and the melt flow rate (hereinafter referred to as “MFR”). The measurement conditions of MFR are 190 ° C., load 21.18 N based on JIS K7210, and the same applies to other MFRs.) Ethylene with 0.3 to 10 g / 10 min A vinyl acetate copolymer is particularly preferred.
In this ethylene-vinyl acetate copolymer, if the vinyl acetate content is 5% by mass or more, sufficient transparency can be secured. On the other hand, if it is 25 mass% or less, extrusion moldability can be ensured, acetic acid odor will not become strong, and stickiness will not occur. Further, if the MFR of the ethylene-vinyl acetate copolymer is 0.3 g / 10 min or more, the extrusion processability is stable, and if it is 10 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.

On the other hand, when importance is attached to microwave heat resistance that can withstand microwave heating, a 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. preferable.
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., the food is packaged with the resulting film, and even when heated in a microwave oven etc., the film melts and sticks to 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.
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. It is preferable because the decrease in strength, variation, and the like are reduced. 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.

(Other ingredients)
The surface layer and / or the intermediate layer of the lactic acid-based soft film may appropriately contain the following various additives in order to impart performance such as antifogging property, antistatic property, slipperiness, and adhesiveness. it can. 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.

<Laminated structure>
The lactic acid-based soft film comprises at least an intermediate layer containing as a main component a mixture of a lactic acid-based polymer (B), an aliphatic polyester (C) having a glass transition temperature of 0 ° C. or less, and a plasticizer (D); A laminated film having three layers composed of both surface layers containing the thermoplastic resin (A) as a main component may be used, and other layers (hereinafter, referred to as “improvement of mechanical properties and interlayer adhesion”). May be abbreviated as “P layer” as appropriate. 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.

  For example, an adhesive layer can be provided between the intermediate layer and the surface layer. In this case, as the adhesive layer, other resins other than those described above can be used singly or in combination. For example, partially saponified ethylene-vinyl acetate copolymer, ionomer resin, ethylene α-olefin copolymer, high pressure method low density polyethylene, high density polyethylene, X-ray method different from the above ethylene α-olefin copolymer Soft resin, polypropylene resin, polybutene resin, styrene-conjugated diene block copolymer, and hydrogenated at least part of the block copolymer, which is an α-olefin copolymer having a crystallinity of 30% or less Examples of these resins are those modified by acid modification and the like.

  In the lactic acid-based soft film, the thickness ratio between both surface layers and the intermediate layer is preferably 21:79 to 50:50. When the thickness ratio of both surface layers is less than 21%, not only the sealing strength is lowered, but it is difficult to improve the antifogging property. On the other hand, if it exceeds 50%, mechanical strength such as tear strength and puncture strength is lowered. In addition, when the thickness ratio of the intermediate layer is within such a range, it becomes easy to design a film that satisfies each characteristic value (E ′, tan δ) due to dynamic viscoelasticity. For example, when the film is formed by the T-die method Stable film-forming stability can be obtained, and it is relatively easy to impart mechanical properties for expressing cut properties suitable for food packaging films and relaxation properties for developing container adhesion. it can. 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 present lactic acid-based soft film is preferably within a range used as a food packaging film, specifically 6 μm to 30 μm, and more preferably 10 μm to 20 μm.

<Film characteristics>
Considering the use of this lactic acid-based soft film for food packaging films, storage 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 JIS K 7198 A method. The elastic modulus (E ′) is preferably in the range of 100 MPa to 4 GPa, more preferably 100 MPa to 800 MPa. When the film is used as a food packaging film, the value of the elastic modulus near room temperature is an index. Therefore, if the storage elastic modulus (E ′) at 20 ° C. is 100 MPa or more, the films do not adhere to each other or the film and other substances at room temperature due to excessive flexibility, and if it is 4 GPa or less, the film Is suitable for food packaging film applications because it does not become too hard and stretches appropriately.

  In the same measurement, it is important that the value of the loss tangent (tan δ) at 20 ° C. is in the range of 0.1 to 0.8, particularly preferably in the range of 0.1 to 0.3. The peak value of loss tangent (tan δ) is a physical property indicating a delay in deformation when a force is applied, and is one of parameters indicating a stress relaxation behavior. If the value of the loss tangent is small, the relaxation behavior of the film is fast, and conversely if the value is large, the stress relaxation is slow. If the loss tangent (tan δ) value at 20 ° C. is 0.1 or more, the restoring behavior against deformation of the film does not occur instantaneously, and if it is 0.8 or less, the restoring behavior is not too slow. It is suitable as a film for food packaging.

  More preferably, in the same measurement, a peak value of loss tangent (tan δ) is present in the range of −50 ° C. to 0 ° C. Further, the loss tangent (tan δ) value at −20 ° C. is preferably in the range of 0.1 to 0.8, and more preferably in the range of 0.1 to 0.3. If the loss tangent (tan δ) value at −20 ° C. is 0.1 or more, the restoring behavior against deformation of the film does not occur instantaneously even at a low temperature, and if it is 0.8 or less, the restoring behavior even at a low temperature. Is not too late, it is more suitable as a food packaging film.

  In order to produce a film satisfying the storage elastic modulus (E ′) and loss tangent (tan δ) as described above, 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, Tg, type of plasticizer, blending ratio of components, LD ratio of lactic acid polymer or lactic acid copolymer), thickness ratio of intermediate layer and surface layer, film forming method, processing conditions (for example, after film formation) It can be produced by appropriately adjusting the heat treatment conditions and the like in a well-balanced manner.

<Manufacturing method>
Next, the manufacturing method of this lactic acid type soft film is demonstrated.

  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 twin screw extruder, a kneader, a Henschel mixer, etc., or each raw material is dry blended and directly into a film extruder. 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 and melted, and co-extruded with a multilayer die and rapidly cooled and solidified to obtain a multilayer film original. As the extrusion method, a multi-layer T-die method, a multi-layer circular method, or the like can be adopted, but the latter is more preferable.

  The multilayer film original fabric thus obtained may be stretched under an appropriate temperature condition. The stretching temperature is usually preferably 120 ° C. or less, more preferably 100 ° C. or less, usually at the surface temperature at the stretching start point of the film (in the case of inflation, the position where expansion starts as a bubble). Examples of the stretching method include a roll stretching method, a tenter method, and inflation. Among these, a method of forming a film by simultaneous biaxial stretching is preferable in terms of stretching. Employing the inflation method is particularly preferable because it can be simultaneously biaxially stretched, can be produced at a relatively low cost with higher productivity, and can be formed into a bag shape (seamless shape). For example, it is particularly suitable for the production of bags and bags, such as take-out bags for supermarkets, bags for preventing dew condensation on low-temperature food packs such as frozen foods and meat, and bags for composting. By combining with the coextrusion method, a multilayer film can be produced with high productivity by using a plurality of resin compositions and / or other types of polymers according to the present invention having different properties.

  You may heat-process a film as needed. As for the heat treatment conditions, the temperature is preferably 40 ° C to 120 ° C, particularly preferably 50 ° C to 110 ° C. If the heat treatment temperature is 40 ° C. or higher, the effect of heat treatment can be easily obtained, and if it is 120 ° C. or lower, the elastic modulus will not be too low.

  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.

<Application>
This lactic acid-based soft film is a shopping bag, garbage bag, compost bag, food / confectionery packaging film, food packaging film, cosmetic / cosmetic packaging film, pharmaceutical packaging film, herbal medicine packaging film, stiff shoulders, sprains, etc. Surgical patch packaging film, sanitary materials (paper diapers, sanitary products) packaging film, agricultural / horticultural film, agricultural chemical packaging film, greenhouse film, fertilizer bag, video and audio, etc. Magnetic tape cassette product packaging film, floppy disk packaging film, plate-making film, adhesive tape, tape, waterproof sheet, sandbag bag, etc. In particular, it can be suitably used as a food packaging film.

  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.

  Examples are shown below, but the present invention is not limited by these. In addition, the result shown in an Example evaluated by the following method.

(Measurement and evaluation method)
(1) Dynamic Viscoelastic Properties Using a dynamic viscoelasticity measuring method described in JIS K 7198 A method, a dynamic viscoelasticity measuring device “DVA-200” manufactured by IT Measurement Control Co., Ltd. For the (flow direction from the extruder of the film), measured at a vibration frequency of 10 Hz, a strain of 0.1%, a temperature of 20 ° C., a storage elastic modulus (E ′) at a temperature of 20 ° C., and temperatures of 20 ° C. and −20 ° C. Loss tangent at (tan δ) was determined.

(2) Film formation 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.
A: Extremely stable.
○: Stable.
X: Slightly unstable.

(3) Container adhesion Water (50 cc) is placed in a bowl-shaped ceramic container having a diameter of 10 cm and a depth of 5 cm, and the entire container is packaged with the obtained film, and stored at 0 ° C. for 15 hours. The degree of adhesion was evaluated.
A: The film was in close contact with the container in a state where it was firm.
○: The film and the container were displaced, and some slack was generated.
X: Almost not adhered.

(4) Anti-fog property Water (50 cc) is put in a bowl-shaped ceramic container with a diameter of 10 cm and a depth of 5 cm, wrapped with a film so as to seal the opening of the bowl, and stored at 0 ° C for 30 minutes. The cloudiness was evaluated.
A: Transparent and clearly visible inside.
X: It was in a state of being clouded white.

(Example 1)
As the lactic acid-based polymer (B), “NatureWorks 4032D” manufactured by NatureWorks (L-form / D-form = 98.6 / 1.4, weight average molecular weight: 200,000) (hereinafter abbreviated as “B-1”) is used. It was.
As the aliphatic polyester (C), polybutylene succinate lactic acid (succinic acid-lactic acid-1,4-butanediol copolymer, weight average molecular weight: 160,000, Tg: -32 ° C., hereinafter referred to as “C-1”. Used).

  The lactic acid polymer (“B-1”) and the aliphatic polyester (C-1) are dry blended at a mass ratio of B-1: C-1 = 40: 60 and set to an extrusion set temperature of 180 ° C. Then, the acetylated monoglyceride “Likemar PL019” (hereinafter abbreviated as “D-1”) manufactured by Riken Vitamin Co., Ltd. as a plasticizer (D) was added to B-1 and C—. The intermediate layer is formed by melting and kneading while injecting from the first vent port of the extruder using a fixed liquid feed pump so that D-1 becomes 20 parts by mass with respect to the total of 1 (100 parts by mass) A pellet was prepared.

On the other hand, as the thermoplastic resin (A), an ethylene-vinyl acetate copolymer (manufactured by Nippon Polyethylene Co., Ltd., trade name “LV440”, vinyl acetate content: 15 mass%, MFR: 2.2 g / 10 minutes, hereinafter “A- 1 ”).
100 parts by mass of the ethylene polymer (A-1) and 2.0 parts by mass of diglycerin monooleate (manufactured by Riken Vitamin Co., Ltd., trade name “DGO-1”) as an antifogging agent are set at an extrusion set temperature of 180 to 200. The mixture was put into a co-directional twin-screw extruder set at 0 ° C., melted and kneaded, and extruded into a strand shape to produce pellets for forming a surface layer.

The pellets prepared as described above are put into separate extruders and merged, and formed by an inflation method at a three-layer T die temperature of 200 ° C., a die gap of 2 mm, an annular die temperature of 200 ° C., and a blow-up ratio of 10. A 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)
A film was obtained in the same manner as in Example 1 except that the mixing ratio of B-1 and C-1 in Example 1 was changed to the mass ratio B-1: C-1 = 20: 80.
The results of evaluating the obtained film are shown in Table 1.

(Example 3)
In Example 1, as aliphatic polyester (C), polybutylene succinate lactic acid (succinic acid-adipic acid-lactic acid-1,4-butanediol copolymer, weight average molecular weight: 160,000 instead of C-1) Tg: −45 ° C., hereinafter referred to as “C-2”), and the mixing ratio of B-1 and C-2 was set to mass ratio B-1: C-2 = 40: 60, A film was obtained in the same manner as in Example 1.
The results of evaluating the obtained film are shown in Table 1.

Example 4
A film was obtained in the same manner as in Example 3 except that the mixing ratio of B-1 and C-2 in Example 3 was changed to a mass ratio B-1: C-2 = 20: 80.
The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 1)
Example 1 is the same as Example 1 except that the pellets pre-compounded so as to have the same composition as the intermediate layer of Example 1 were put into an extruder for both surface layers to make a substantially single-layer film. Similarly, a film having a total thickness of 12 μm was obtained.
The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 2)
In Example 3, the pellets pre-compounded so as to have the same composition as the intermediate layer of Example 3 were put into an extruder for both surface layers, and substantially a single layer film was obtained. Similarly, a film having a total thickness of 12 μm was obtained.
The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 3)
Pellets prepared in advance so that B-1 is 100 parts by mass and D-1 is 20 parts by mass are put into an extruder, T die temperature 200 ° C., die gap 2 mm, annular die temperature 200 ° C., blow up Films were formed by an inflation method at a ratio of 10 to obtain a single layer film having a total thickness of 12 μm.
The results of evaluating the obtained film are shown in Table 1.

(Comparative Example 4)
Pellet prepared in advance so that C-1 is 100 parts by mass and D-1 is 20 parts by mass is put into an extruder, T die temperature 200 ° C., die gap 2 mm, annular die temperature 200 ° C., blow up Films were formed by an inflation method at a ratio of 10 to obtain a single layer film having a total thickness of 12 μm.
The results of evaluating the obtained film are shown in Table 1.

From the results of Table 1, the main component is a mixture of a lactic acid polymer (B) having a Tg greater than 0 ° C., an aliphatic polyester (C) having a Tg of 0 ° C. or less, and a glycerin fatty acid ester (D) having a molecular weight of 2000 or less. By forming the intermediate layer, it was confirmed that relaxation characteristics could be imparted to the film both at room temperature (20 ° C.) and at a low temperature of 0 ° C. or lower (−20 ° C.).
On the other hand, when there was no surface layer as in Comparative Examples 1 to 4, the stability during inflation molding was not maintained, and in Comparative Example 4, it was at a level that could not be molded without a surface layer. Further, it was confirmed that no effect was obtained with respect to the adhesion and antifogging property of the film when no surface layer was involved.

Claims (5)

  A multilayer lactic acid-based soft film comprising at least three layers, wherein the intermediate layer comprises a lactic acid-based polymer (B), an aliphatic polyester (C) having a glass transition temperature of 0 ° C. or less, and a plasticizer (D). As a main component, both surface layers contain a thermoplastic resin (A) that is different from the main component of the intermediate layer as a main component, according to the dynamic viscoelasticity measurement method described in JIS K 7198 A method. A multilayer lactic acid-based soft film having a loss tangent (tan δ) value at 20 ° C. measured at a vibration frequency of 10 Hz and a strain of 0.1% in the range of 0.1 to 0.8.   The thermoplastic resin (A) is low density polyethylene, linear low density polyethylene, linear ultra low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, and ethylene-methacrylic acid ester copolymer. The multilayer lactic acid-based soft film according to claim 1, wherein the multi-layered lactic acid-based soft film is a mixed resin composed of at least one ethylene polymer selected from the above or a combination of two or more thereof.   The multilayer lactic acid-based soft film according to claim 1 or 2, wherein the plasticizer (D) is a glycerin fatty acid ester having a molecular weight of 2000 or less.   The value of loss tangent (tan δ) at −20 ° C. measured at a vibration frequency of 10 Hz and strain of 0.1% by the dynamic viscoelasticity measurement method described in JIS K 7198 A method is in the range of 0.1 to 0.8. The multilayer lactic acid-based flexible film according to any one of claims 1 to 3, wherein the multilayer lactic acid-based flexible film is provided. According to the dynamic viscoelasticity measuring method described in JIS K 7198 A method, the vibration frequency is 10 Hz.
Storage elastic modulus (E ′) at 20 ° C. measured at a strain of 0.1% is 100 MPa to 4
The multilayer lactic acid-based soft film according to any one of claims 1 to 4, which is in a range of GPa.