JP4440738B2 - Inflation molded biodegradable soft film - Google Patents

Description

  The present invention relates to a biodegradable soft film that can be suitably used as a small roll film for packaging, particularly at home, and is suitable for inflation molding.

  Plastics are now pervasive in every field of life and industry, with annual production of around 100 million tons worldwide. On the other hand, however, the problem of processing used plastics is increasing in proportion to the production volume.

Conventionally, most used plastics have been disposed of by landfill, but plastics are generally stable in nature for a long time and their bulk specific gravity is small. Problems such as damage to the living environment of wild plants have arisen.
In recent years, due to increasing interest in environmental issues, the effective use of depletable resources has become important, and biodegradable resins that do not adversely affect the natural environment, that is, disintegration and degradation by hydrolysis in soil and water. In the end, biodegradable resins that become harmless degradation products by the action of microorganisms are attracting attention.
Examples of biodegradable resins that are currently in practical use include polylactic acid resins, aliphatic polyesters, modified polyvinyl alcohol, cellulose ester compounds, starch modified products, and blends thereof.

  On the other hand, a small roll film used at home (hereinafter also referred to as “household wrap film”) is generally used in a form contained in a paper box equipped with a cutter blade. When packaging, pull the wrap film out of the paper box, press the film against the cutter blade provided in the paper box, open a perforated hole in the film with the cutter blade, and tear the film to propagate the tear in the width direction Cut the film and use the cut film so that it overlaps the food in the container. If the film is too soft in this cutting process, the film may stretch without being torn well in the width direction, or may be torn in an oblique direction. In addition, household wrap films are often used mainly when storing food in refrigerators or freezers or when heating in a microwave oven, and when heated in a microwave oven, the temperature of the film may be higher than 100 ° C. If the film does not have sufficient heat resistance to withstand heating at about 100 ° C, the film itself may be greatly deformed when heated in a microwave oven, resulting in excessive adhesion to the container or food in the container, or the film may melt during heating. This may cause problems such as holes being pierced.

  For this reason, the wrap film for home use is not only transparent, but also suitable for cutting when cut out from a paper box, moderate elasticity during packaging, storage and heating, and during heating in a microwave oven. In addition, special physical properties such as heat resistance are required which do not cause melt perforation, large deformation, close contact with the container, or alteration of itself.

Currently marketed household wrap films include films mainly composed of stretched polyvinylidene chloride resin, and then extrusion cast polyethylene resin, plasticized polyvinyl chloride resin, poly-4-methylpentene- A film mainly composed of a 1-series resin or the like is the mainstream.
Recently, a flexible film using a biodegradable resin material has also been proposed. For example, Patent Document 1 to Patent Document 5 disclose attempts to soften a film by adding a plasticizer to a lactic acid resin that is a transparent and hard material.

  Patent Document 1 discloses a composition in which a plasticizer is added to polylactic acid as a thermoplastic polymer composition having degradability in a natural environment that can be used as a packaging material or a medical material. Patent Document 2 discloses an acid comprising a lactic acid-based polymer containing polylactic acid as a main component, a repeating unit of a dibasic acid and a dihydric alcohol, and having a terminal capped with a monobasic acid and / or a monohydric alcohol. A lactic acid-based polymer resin composition containing a polyester-based plasticizer having a total number of hydroxyl value and hydroxyl value of 40 or less as an essential component is disclosed, and Patent Document 3 discloses sufficient thermal stability under use conditions. A lactic acid polymer composition comprising a flexible and transparent lactic acid polymer as a main component is disclosed. Patent Document 4 includes an aliphatic polyester resin having a crystallinity and a low crystallization speed and a plasticizer. resin A molded product in which flexibility and heat resistance are simultaneously imparted by molding the composition is disclosed. Patent Document 5 discloses a lactic acid composition having a high loss tangent and stable over time, and molding thereof. The product is disclosed.

JP-A-4-335060 Japanese Patent Laid-Open No. 7-118513 JP 2000-136300 A JP 2000-198908 A JP 2000-248164 A

  Conventionally proposed soft films with biodegradability have low shear viscosity at the time of molding processing, and also have poor strain-hardening properties, so that they are inferior in molding processability, especially because bubbles are not stable in inflation molding. In other words, it was difficult to form a film.

  An object of the present invention is to provide a biodegradable soft film that can be suitably produced by inflation molding, and can be suitably used for packaging, particularly as a household wrap film. is there.

  As a result of intensive studies in view of such problems, the present inventor made a polylactic acid resin composition having a specific composition as an intermediate layer, and a polyester resin having specific rheological properties on both sides of the intermediate layer. It was found that the above problems can be solved by laminating the front and back layers, and the present invention has been completed.

That is, the present invention contains a lactic acid resin component (A) and a plasticizer component (B) having a molecular weight of 2,000 or less, and the component (B) at a ratio of 10 to 20 parts by mass per 100 parts by mass of the component (A). An intermediate layer (β layer) made of a lactic acid resin composition containing
An inflation molded biodegradable soft film comprising front and back layers (α layer) made of a polyester resin composition on both sides of the intermediate layer (β layer),
The polyester resin composition forming the α layer has a strain of 0.1% at a temperature of 200 ° C., a shear viscosity of 500 to 1000 Pa · s measured at a frequency of 100 rad / s, and a uniaxial elongation rate of 1 at a temperature of 150 ° C. Inflation molding characterized by comprising a polyester resin composition having a strain hardening degree λ of uniaxial elongational viscosity measured at 0.0 sec ⁻¹ and uniaxial elongational strain of 1.0 to 3.0. Propose biodegradable soft film.

  ADVANTAGE OF THE INVENTION According to this invention, it is a biodegradable soft film which can be manufactured suitably by inflation molding, Comprising: The biodegradable soft film which can be used conveniently as a household wrap film can be obtained. In particular, at the time of inflation molding, since the thickness of the bubble can be produced uniformly and stably, a film having a stable quality can be produced industrially.

In addition, when it is described as “main component” in the present specification, it is intended to include the intention to allow other components to be contained within a range that does not hinder the function of the main component. Although the content ratio of the main component is not particularly specified, generally, the component accounts for 50% by mass, particularly 70% by mass or more in the composition.
The upper limit value and the lower limit value of the numerical range in the present invention are included in the scope of the present invention as long as they have the same operational effects as those in the numerical range, even when slightly deviating from the numerical range specified by the present invention. It is intended to include

  Hereinafter, although embodiment of this invention is described in detail, the scope of the present invention is not limited to embodiment described below.

  The biodegradable soft film according to this embodiment is a laminated film including an intermediate layer (β layer) and front and back layers (α layer) formed on both sides of the intermediate layer (β layer).

[Intermediate layer (β layer)]
An intermediate | middle layer ((beta) layer) is a layer formed from the lactic acid-type resin composition which has the following component (A) and the following component (B) as a main component.
(A) Polylactic acid resin (B) Plasticizer having a molecular weight of 2,000 or less

(Component A)
The polylactic acid resin constituting the component (A) includes poly (L-lactic acid) whose structural unit is L-lactic acid, poly (D-lactic acid) whose structural unit is D-lactic acid, and whose structural unit is L-lactic acid. And poly (DL-lactic acid) which is D-lactic acid, or a mixture thereof.
From the viewpoint of suppressing bleed-out of the plasticizer, it is preferable that the polylactic acid-based resin has low crystallinity. Therefore, polylactic acid having lower crystallinity than poly (L-lactic acid), such as poly (D-lactic acid), poly It is preferable to use (DL-lactic acid) or a mixture thereof.
However, poly (L-lactic acid) or poly (D-lactic acid) referred to here is ideally a polymer composed of 100% L-lactic acid or D-lactic acid, but inevitably different lactic acid is included in the polymerization. Since there is a possibility, the thing containing 98% or more of L-lactic acid or D-lactic acid is included.

In the polylactic acid resin, the composition ratio of D-lactic acid (D-form) and L-lactic acid (L-form) is L-form: D-form = 100: 0 to 84:16, or L-form: D-form = 0. : It is preferable that it is 100-16: 84. If the composition ratio of the D body and the L body is within this range, the heat resistance of the obtained molded product can be maintained high. Among them, L-form: D-form = 98: 2-86: 14, or L-form: D-form = 2: 98-14: 86, particularly 95: 5-88: 12 or 5: 95-12: 88.
In addition, you may blend the polylactic acid-type resin from which the copolymerization ratio of L body and D body differs. In this case, what is necessary is just to make it the average value of the copolymerization ratio of the L body and the D body of several polylactic acid-type resin fall in the said range. By blending the L and D homopolymers and the copolymer, it is possible to balance the difficulty of bleeding and the development of heat resistance.

Further, the polylactic acid resin used in the present embodiment is any one of L-lactic acid, D-lactic acid, and DL-lactic acid, and α-hydroxycarboxylic acid, aliphatic diol, aliphatic dicarboxylic acid, or Copolymers with two or more of these may be used.
In this case, α-hydroxycarboxylic acid includes glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methyl. Examples include bifunctional aliphatic hydroxy-carboxylic acids such as butyric acid, 2-methyllactic acid, and 2-hydroxycaproic acid, and lactones such as caprolactone, butyrolactone, and valerolactone.
Examples of the aliphatic diol include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like.
Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid.

  As a polymerization method for the polylactic acid-based resin, a condensation polymerization method, a ring-opening polymerization method, and other known polymerization methods can be employed. For example, in the condensation polymerization method, a polylactic acid resin having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of L-lactic acid, D-lactic acid, or a mixture thereof. 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 polylactic acid resin can be obtained. Examples of the lactide include L-lactide, which is a dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid, and DL-lactide composed of L-lactic acid and D-lactic acid. A polylactic acid resin having an arbitrary composition and arbitrary crystallinity can be obtained by mixing and polymerizing these as necessary.

  The mass average molecular weight of the polylactic acid resin used in the present embodiment is preferably in the range of 50,000 to 400,000, more preferably in the range of 100,000 to 250,000. If the polylactic acid resin has a mass average molecular weight of 50,000 or more, mechanical properties and practical physical properties such as heat resistance can be secured, and if it is 400,000 or less, the melt viscosity is too high and the molding processability is poor. Can be prevented.

  Note that a small amount of a copolymer component can be added to the polylactic acid resin used in the present embodiment according to the necessity for improving heat resistance, etc., and a non-aliphatic dicarboxylic acid such as terephthalic acid and / or Non-aliphatic diols such as ethylene oxide adducts of bisphenol A can also be used.

(Component B)
The plasticizer generally has a function of lowering the glass transition temperature (Tg) of the lactic acid-based resin and softening it. However, as the plasticizer constituting the component (B), compatibility and biodegradability are possible. In view of the above, those composed of one or a combination of two or more of molecular weights of 2,000 or less selected from the compounds shown in the following (1) to (9) are preferable, and in particular, the following (6), (7 ) Is preferred.

_{(1) H 5 C 3 (} OH) 3 -n (OOCCH 3) n ( where, 0 <n ≦ 3)
This is glycerol mono-, gee, or triacetate, and a mixture thereof may be used, but n is preferably close to 3.
(2) Glycerin alkylate (the alkyl group may have 2 to 20 carbon atoms and a hydroxyl group residue). Examples thereof include glycerin tripropionate and glycerin tributyrate.
(3) Ethylene glycol alkylate (an alkyl group having 1 to 20 carbon atoms and a hydroxyl group residue may be present). For example, ethylene glycol acetate etc. are mentioned.
(4) Polyethylene glycol alkylate having 5 or less ethylene repeating units (the alkyl group may have 1 to 12 carbon atoms and a hydroxyl group residue). Examples thereof include diethylene glycol monoacetate and diethylene glycol diacetate.
(5) Aliphatic monocarboxylic acid alkyl ester (the alkyl group has 1 to 20 carbon atoms). Examples thereof include butyl stearate. Among them, those having a number average molecular weight of 100 to 2000 are preferable.
(6) Aliphatic dicarboxylic acid alkyl ester (the alkyl group may be a residue having 1 to 20 carbon atoms and a carbosiyl group). Examples thereof include di (2-ethylhexyl) adipate and di (2-ethylhexyl) azelate. Among them, those having a number average molecular weight of 100 to 2000 are preferable.
(7) Aliphatic tricarboxylic acid alkyl ester (the alkyl group may have 1 to 20 carbon atoms and a carboxyl group residue). For example, citric acid trimethyl ester and the like can be mentioned.
(8) Natural fats and oils and their derivatives. For example, soybean oil, epoxidized soybean oil, castor oil, tung oil, rapeseed oil and the like can be mentioned. Among them, those having a number average molecular weight of 100 to 2000 are preferable.

 It is important to blend the component (B) so that the blending ratio of the component (A) and the component (B) is 10 to 20 parts by mass with respect to 100 parts by mass of the component (A). It is preferable to mix | blend a component (B) so that it may become a part. If the amount of the plasticizer is in the range of 10 to 20 parts by mass, suitable characteristics as a small roll film for home use can be imparted. On the other hand, when the amount is too small, the softening itself does not proceed. When the amount is too large, problems such as bleeding may occur over time.

[Front and back layers (α layer)]
The polyester resin composition constituting the front and back layers (α layer) has a shear viscosity of 500 to 1000 Pa · s measured at a strain of 0.1% and a frequency of 100 rad / s at a temperature of 200 ° C. and a temperature of 150 ° C. In which the rheological properties are such that the strain hardening degree λ of the uniaxial elongation viscosity measured at a uniaxial elongation rate of 1.0 sec ⁻¹ and a uniaxial elongation strain of 1.0 to 3.0 is 0.2 to 0.5. It is important for stabilizing the bubble in inflation molding.

If the shear viscosity at a temperature of 200 ° C. is 500 Pa · s or more, molding processability, particularly bubble stability at the time of inflation molding can be secured, and if it is 1000 Pa · s or less, the swell becomes large or melt extrusion occurs. It is possible to prevent a decrease in molding processability such as an increase in torque (extrusion load). In addition, the difference in viscosity between the polylactic acid resin composition constituting the intermediate layer (β layer) and the polyester resin composition constituting the front and back layers (α layer) becomes large, and the front and back layers do not develop well when laminated. Can be prevented.
From such a viewpoint, the shear viscosity measured at a temperature of 200 ° C. with a strain of 0.1% and a frequency of 100 rad / s is preferably 550 to 950 Pa · s, and more preferably 600 to 900 Pa · s.

Further, if the strain hardening degree λ of the uniaxial elongation viscosity measured at a temperature of 150 ° C. at a uniaxial elongation rate of 1.0 sec ⁻¹ and a uniaxial elongation strain of 1.0 to 3.0 is 0.2 to 0.5, Good molding processability can be obtained in molding.
From such a viewpoint, the strain hardening degree λ of the uniaxial elongation viscosity measured at a temperature of 150 ° C. at a uniaxial elongation rate of 1.0 sec ⁻¹ and a uniaxial elongation strain of 1.0 to 3.0 is 0.25 to 0.5. Is preferable, and 0.3 to 0.5 is even more preferable.

As shown in FIG. 1, the strain hardening degree λ of the uniaxial elongation viscosity is gradually increased as the uniaxial elongation strain (ε) increases after the start of measurement in the transient response of the uniaxial elongation viscosity measured by the uniaxial elongation viscometer. A region where the uniaxial elongation strain (ε) rises from a region where the uniaxial elongation viscosity increases (linear region) (nonlinear region) (in the plot of the uniaxial elongation rate of 1.0 sec ^{−1 in} FIG. 1, the uniaxial elongation strain (ε) Is an index indicating the degree to which the uniaxial elongational viscosity increases in the region of 1.0 or more), and can be calculated as follows.
In FIG. 1, the uniaxial elongation strain (ε) is expressed by multiplying the uniaxial elongation speed and time.

First, using a uniaxial extension viscometer (for example, product name: RME manufactured by TA Instruments Co., Ltd. (formerly Rheometric Scientific F.E.)), a uniaxial extension rate of 1. The transient response of uniaxial extensional viscosity at 0 sec ⁻¹ and 0.1 sec ⁻¹ is measured. Here, the uniaxial extension viscosities at the uniaxial extension speeds of 1.0 sec ⁻¹ and 0.1 sec ⁻¹ are η ₁ and η ₂ , respectively.
Incidentally, the uniaxial extension strain uniaxial elongation rate 1.0 sec ^-1 at a measuring time 1.0 to 3.0 seconds (epsilon) is 1.0 to 3.0, the uniaxial extension rate of 1 as shown in FIG. 1 The uniaxial elongational viscosity η ₁ in the range of uniaxial elongation strain (ε) 1.0 to 3.0 (time 1.0 to 3.0 seconds) at 0.0 sec ⁻¹ is a non-linear region. On the other hand, the uniaxial extension strain uniaxial elongation rate 0.1 sec ^-1 at a measuring time 1.0 to 3.0 seconds (epsilon) is 0.1 to 0.3, the uniaxial extension rate as shown in FIG. 1 The uniaxial elongation viscosity η ₂ in the range of uniaxial elongation strain (ε) 0.1 to 0.3 (time 1.0 to 3.0 seconds) at 0.1 sec ⁻¹ is a linear region.
Next, the eta _1, eta and ₂ η ₁ / η ₂ of the natural logarithm calculated from _{(ln (η 1 / η 2} )), uniaxial elongation strain at uniaxial extension rate 1.0 sec ^-1 (epsilon) is When obtained and plotted in the range of 1.0 to 3.0, the relationship shown in FIG. 2 is obtained.
Next, with respect to the plot (FIG. 2), the slope of the straight line is obtained by the least square method, and the strain hardening degree λ of the uniaxial elongational viscosity is obtained. Such strain hardening degree of uniaxial elongation viscosity and the measuring method thereof are described in, for example, Kiyamato Koyama, Journal of Japanese Rheological Society, vol. 19, pages 174 to 180 (1991).
The degree of increase in viscosity when the uniaxial elongation strain thus obtained is 1.0 or more is the strain hardening degree λ.
When the degree of strain hardening λ is large, for example, when the uniaxial elongation strain is 1.0 or more during inflation molding, the viscosity becomes large, so that bubbles are stabilized, and the film thickness accuracy is improved.

  Examples of the polyester resin constituting the front and back layers (α layer) include aliphatic polyesters obtained by condensation of aliphatic diols and aliphatic dicarboxylic acids, aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones, synthetic aliphatic polyesters, Aliphatic aromatic polyesters can be exemplified.

The above “aliphatic polyester obtained by condensing an aliphatic diol and an aliphatic dicarboxylic acid” includes aliphatic glycols such as ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol, Examples thereof include those obtained by condensation polymerization by selecting one or more of succinic acid, adipic acid, suberic acid, sebacic acid and dodecanoic acid, which are group dicarboxylic acids. Moreover, a desired resin can be obtained by a chain extension reaction with an isocyanate compound or the like as required.
Typical examples of the “aliphatic polyester obtained by ring-opening polymerization of cyclic lactones” include cyclic monomers such as ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone, and the like. More than one kind is selected and polymerized.
Examples of the “synthetic aliphatic polyester” include cyclic acid anhydrides and oxiranes such as copolymers of succinic anhydride with ethylene oxide, propylene oxide, and the like.

In addition, as the “aliphatic aromatic polyester”, the aliphatic aromatic polyester includes an aromatic aliphatic polyester having a biodegradability composed of an aromatic dicarboxylic acid component, an aliphatic dicarboxylic acid component, and an aliphatic diol component. Mention may be made of polyester.
In this case, examples of the aromatic dicarboxylic acid component include isophthalic acid, terephthalic acid, and 2,6-naphthalenedicarboxylic acid. Examples of the aliphatic dicarboxylic acid component include succinic acid, adipic acid, suberic acid, and sebacin. Examples of the aliphatic diol include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and the like. Two or more types of aromatic dicarboxylic acid components, aliphatic dicarboxylic acid components, and aliphatic diol components can be used. The aromatic dicarboxylic acid component that can be most preferably used is terephthalic acid, the aliphatic dicarboxylic acid component is adipic acid, and the aliphatic diol component is 1,4-butanediol.
Typical examples of the aromatic aliphatic polyester include a copolymer of polybutylene adipate and terephthalate, a copolymer of tetramethylene adipate and terephthalate, and the like.

  Among the polyester resins constituting the front and back layers (α layer), “aliphatic aromatic polyester” is preferable, and in order to increase heat resistance and mechanical strength, the aromatic monomer component as the dicarboxylic acid component is 50 mol%. In the following, it is particularly preferable to use an aliphatic aromatic polyester obtained by copolymerization with an aliphatic dicarboxylic acid component and an aliphatic diol component at a ratio of 50 to 30 mol%. As such aliphatic aromatic polyesters, the product name “Easter Bio” manufactured by Eastman Chemical Company, the product name “Ecoflex” manufactured by BASF Company, and the like are commercially available.

In addition, it is preferable to form a front and back layer (α layer) by mixing the above-described polyester resin with a “carbodiimide compound”.
By adding the “carbodiimide compound”, the melt flow characteristics and strain hardening characteristics of the polyester resin can be obtained.

  Examples of the “carbodiimide compound” used in this case include those having a basic structure of the following general formula.

-(N = C = N-R-) n-
(In the above formula, n represents an integer of 1 or more, and is usually appropriately determined between 1 and 50. R represents another organic bond unit. In these carbodiimide compounds, the R portion is aliphatic. , Alicyclic or aromatic.

Specifically, for example, bis (dipropylphenyl) carbodiimide, poly (4,4′-diphenylmethanecarbodiimide), poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide), poly (tolylcarbodiimide), poly ( Examples thereof include diisopropylphenylene carbodiimide), poly (methyl-diisopropylphenylene carbodiimide), poly (triisopropylphenylene carbodiimide), and the like.
The carbodiimide compound can be used alone or in combination of two or more of the above.

The mixing mass ratio of the polyester resin and the carbodiimide compound is not particularly limited, but is preferably mixed at the following ratio.
That is, the carbodiimide compound is 0.05 to 5 parts by mass, preferably 0.1 to 0.4 parts by mass, and more preferably 0.2 to 0.3 parts by mass with respect to 100 parts by mass of the polyester resin. Here, if content of a carbodiimide compound is 0.05 mass part or more, the improvement effect can be acquired in molding processability. On the other hand, if it is 0.4 parts by mass or less, the entire resin can be cross-linked to prevent deterioration of molding processability and heat resistance.

In the biodegradable soft film according to the present embodiment, regarding the ratio of the front and back layers (α layer) and the intermediate layer (β layer), the β layer accounts for 32 to 85% with respect to the total mass of the α layer and the β layer. A configuration is preferable.
If the proportion of the β layer is 32% by mass or more, it is possible to ensure the suitability for small winding wraps such as cutability, and if it is 85% by mass or less, the processability during film molding, particularly the inflation suitability is sufficiently secured. can do.

  The thickness of the film is preferably in the range used for ordinary small roll film, that is, about 8 to 30 μm, typically about 10 to 20 μm.

(Biodegradable soft film)
The biodegradable soft film obtained in the present embodiment has the following characteristics, and can be suitably used as a household wrap film that requires the following characteristics.
In addition, although the biodegradable soft film obtained by this embodiment is provided with the following characteristic, the following characteristic is also what identifies the use of the biodegradable soft film of this invention simultaneously.

A-1: The value of the storage elastic modulus at 20 ° C. measured by dynamic viscoelasticity at a frequency of 10 Hz and strain of 0.1% by the dynamic viscoelasticity measurement method of JIS K-7198 A method is in the range of 800 to 2000 MPa. Be in
A-2: The value of the storage elastic modulus at 100 ° C. is in the range of 10 to 100 MPa.
B-1: The value of loss tangent (tan δ) at 20 ° C. is in the range of 0.1 to 0.8.

  A-1: Biodegradability if the value of the storage elastic modulus at 20 ° C. measured at a frequency of 10 Hz and a strain of 0.1% by the dynamic viscoelasticity measurement method described in JIS K-7198 A method is 800 MPa or more. Since the flexible film has an appropriate waist, it can have the ability to wrap small rolls so that it can be successfully split in the width direction when the film is cut. Moreover, since the stress with respect to a deformation | transformation is not too small, when overlapping with a container etc., a film does not extend locally and can be packaged well. On the other hand, if the value of the storage elastic modulus at 20 ° C. is 2000 MPa or less, the film does not become too hard and can be appropriately stretched, so that it can be packaged well along the shape of a container or the like.

  A-2: If the value of the storage elastic modulus at 100 ° C. measured at a frequency of 10 Hz and a strain of 0.1% by the dynamic viscoelasticity measuring method described in JIS K-7198 A method is 10 MPa or more, a microwave oven or the like In the case where the film is heated, the film is not softened too much by heating, is not too close to the container or food, and the film itself is not melted and has no holes. On the other hand, if the value of the storage elastic modulus at 100 ° C. is 100 MPa or less, the storage elastic modulus at normal temperature will not be too high, and packaging suitability at normal temperature will not be a problem.

On the other hand, regarding loss tangent,
B-1: The value of loss tangent (tan δ) at 20 ° C. measured at a frequency of 10 Hz and a strain of 0.1% by a dynamic viscoelasticity measurement method of JIS K-7198 A method is 0.1 to 0. Must be in the range of 8. The peak value of loss tangent (tan δ) is a physical property value indicating a delay in deformation when a force is applied, and is one of parameters indicating a stress relaxation behavior. That is, when the loss tangent value is small, the stress relaxation is fast, and the restoring behavior with respect to film deformation occurs instantaneously. Conversely, when the loss tangent value is large, the stress relaxation is slow and the restoring behavior with respect to film deformation is slow.

  If the loss tangent (tan δ) value at 20 ° C. of the biodegradable soft film obtained in the present embodiment is 0.1 or more, the restoring behavior against deformation of the film does not occur instantaneously. When it is stretched and overlapped, it does not return to the original moment when the force to stretch is removed, and it can be packaged neatly without wrinkles. On the other hand, if it is 0.8 or less, the restoring behavior will not be too slow, and therefore, plastic deformation will not be exhibited for the amount of ordinary use.

(Production method)
Next, although the manufacturing method of the biodegradable soft film in this invention is demonstrated, it is not limited to the following manufacturing method.

The biodegradable soft film of the present invention can be produced by a film forming method by ordinary melt extrusion. In that case, as a method of obtaining a mixed composition by mixing a lactic acid resin, a plasticizer, and other additives as required, for example, a unidirectional twin-screw extruder, a kneader, a Hayshell mixer, etc. It may be possible to pre-compound using, or to dry blend each raw material and put it directly into the film extruder. 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. Specifically, for example, the lactic acid resin and other additives as necessary are sufficiently dried to remove moisture, and then melt-mixed using a twin-screw extruder, and the plasticizer is supplied from the vent port. While adding a predetermined amount, a pellet is extruded into a strand shape.
In this case, the lactic acid resin is appropriately selected for the melt extrusion temperature in consideration of the melting point changing depending on the composition ratio of the poly (L-lactic acid) structure, the poly (D-lactic acid) structure, and the poly (DL-lactic acid). It is preferable to do. In practice, one having a melting point temperature range of 160 to 230 ° C. is usually selected.

Next, after the pellet produced by the above method is sufficiently dried to remove moisture, film formation is performed by the following method.
A film can be obtained by melt-extruding the resin composition from a plurality of extruders and performing inflation molding. Practically, it is preferable to melt-extrude the material resin from the annular die and perform inflation, and the blow-up ratio (bubble diameter / die diameter) at that time is preferably 4 or more, particularly preferably in the range of 5-7.

When stretching is performed, for example, the film is pressed against the cutter blade, a perforated hole is opened in the film with the cutter blade, and the film is torn to propagate the tear in the width direction and cut, and the cut film is put into a container. It is preferable when further increasing the food quality when overlapping foods. When the degree of crystallinity increases, the plasticizer tends to bleed out, but even if the degree of crystallization increases due to stretching, the plasticizer bleedout is less likely to occur than when the degree of crystallization increases due to other factors. There are features.
The stretching conditions are preferably such that the temperature of the sheet is 20 to 100 ° C. and the stretching ratio is in the range of 1.0 to 5.0 times. Within such a range, there will be no troubles such as breakage or whitening of the sheet-like material, or the elastic modulus of the sheet-like material becomes too low, causing a draw-down in which the sheet-like material hangs down due to its own weight.

  In addition, if necessary, the sheet-like material may be stretched and then heat-treated with a fixed width within a range that does not impair the spirit of the present invention. The heat treatment conditions in this case are preferably a temperature of 50 ° C. to 120 ° C., particularly preferably 60 ° C. to 110 ° C. If the heat treatment temperature is set to 50 ° C. or higher, a heat treatment effect can be easily obtained, and if it is 120 ° C. or lower, drawdown hardly occurs. Further, if the heat treatment time is 5 seconds or more, the heat treatment effect is easily obtained, and if it is 5 minutes or less, the heat treatment equipment does not become long, so that the economy can be maintained.

The process of applying heat after film formation is performed by selecting appropriate conditions according to the type of lactic acid resin to be used, and by this process, the crystallinity of the film is increased so that ΔHm−ΔHc is 20 J / g or more. preferable.
When a lactic acid resin having a low crystallinity such as poly (DL-lactic acid) is used as a raw material, it is preferably stored and cured at a predetermined temperature for 6 hours or more after film formation. At this time, the curing temperature is generated along with the glass transition temperature when the film is heated at a heating rate of 10 ° C./min using a differential thermal scanning calorimeter according to JIS K-7121, and the crystallization during the heating. It is necessary to be between the peak temperatures of the heat of crystallization. Preferably, it is stored and cured at a temperature 30 ° C. or more higher than the glass transition temperature for 12 to 24 hours, more preferably 35 to 40 ° C. higher than the glass transition temperature.
That is, in the case of a lactic acid resin having a low crystallinity, it is necessary to increase the crystallinity over time under mild conditions.
On the other hand, in the case of a polymer blend of poly (DL-lactic acid) and poly (L-lactic acid) or poly (D-lactic acid), it is possible to increase the crystallinity by curing as described above. Since the degree of crystallinity is higher than that of (DL-lactic acid), the degree of crystallinity can be increased even by heat treatment at a high temperature for a short time. As heat treatment conditions at this time, for example, heat treatment at 60 to 120 ° C. for 1 to 200 seconds, 70 to 110 ° C. for 2 to 30 seconds, and 80 to 100 ° C. for 3 to 20 seconds is also possible. At this time, as a heating method, in addition to direct heating, a heating method using an energy wave such as a high frequency wave or an ultrasonic wave can be employed.

In order to increase ΔHm−ΔHc, it is possible to increase orientation crystallization by increasing the draw ratio. However, considering the usage of a wrap film for a microwave oven, the degree of crystallinity can be increased by curing or heat treatment. Is preferably increased.
In order to adjust the tensile stress ratio (σMD / TD) to the above range, in the inflation method, the take-up speed and the blow ratio are important, and the blow ratio should be in the range of 1.2 to 5.0. preferable. Further, in the casting method, it is preferable to set the extrusion pulling rate to 1.0 to 10.0. In the stretching method, it is preferable that the longitudinal stretching ratio is 1.5 to 5.0 and the lateral stretching ratio is 2.0 to 6.0.

  The resin composition constituting the biodegradable soft film of the present invention has an antifogging agent and a weather resistance for the purpose of improving and adjusting molding processability and physical properties of the molded product within a range that does not significantly impair the effects of the present invention. Additives such as stability stabilizers, heat resistance stabilizers, antistatic agents, antiblocking agents, lubricants, nucleating agents, antioxidants, colorants, pigments, inorganic fillers, etc. may be added as appropriate.

Examples of the present invention are shown below, but the present invention is not limited by these.
The MD direction of the film indicates the take-up direction (flow direction), and the TD direction indicates the direction perpendicular to the MD direction (width direction).
In addition, various measured values and evaluations of the polylactic acid resin composition and the molded product displayed in this specification were performed as follows.

(1) Strain hardening degree of uniaxial extensional viscosity (λ)
The pellet made of the aliphatic polyester resin composition constituting the front and back layers (α layer) was pressed at a set temperature of 150 ° C. for 10 minutes using a 100 t press machine, and then cooled by natural cooling to give a thickness of 1.5 mm. A plate was made. Next, a test piece having a width of 7 mm, a length of 55 mm, and a thickness of 1.5 mm was cut out from the plate.
This test piece was measured using a uniaxial extension viscometer (TA Instruments Co., Ltd. (formerly Rheometric Scientific F.E.), trade name: RME) at a measurement temperature of 150 ° C. and a uniaxial extension rate of 1. 0 sec ^-1, the transient response of the uniaxial elongation viscosity at 0.1 sec ^-1 was measured. Uniaxial extensional viscosity eta ₁ of the uniaxial elongation rate 1.0 sec ^-1 of from 1.0 seconds after the start of measurement until after 3.0 seconds, and a uniaxial elongation viscosity eta ₂ of the uniaxial elongation rate 0.1 sec ^-1 Then, the ratio η ₁ / η ₂ is calculated, and the linear gradient in the relationship between the natural logarithm ln (η ₁ / η ₂ ) and the uniaxial elongation strain (ε) of the ratio η ₁ / η ₂ is determined by the method of least squares. This value was taken as the strain hardening degree λ of the uniaxial elongational viscosity.

(2) Shear viscosity A cylindrical test piece having a diameter of 40 mm was cut out from the 1.5 mm-thick plate prepared in (1). This test piece was measured using a shear viscometer (TA Instruments Co., Ltd. (formerly Rheometric Scientific F.E., product name: ARES), measuring temperature 200 ° C., strain 0.1%, The shear viscosity at a frequency of 100 rad / s was measured.

(3) Dynamic Viscoelasticity Measurement A dynamic viscoelasticity measurement method described in JIS K-7198 A method was used, using a viscoelasticity spectrometer “VES-F3” manufactured by Iwamoto Seisakusho Co., Ltd. It was measured by MD of the film at 1%.

(4) Cut property The film was wound on a paper tube, put into a commercially available carton case with a saw blade, the film was pulled out from the carton case, and the saw blade cut property was evaluated according to the following criteria.
○: Good cutting properties.
(Triangle | delta): Although it can cut, a cut property is a little inferior.
X: The film is stretched and the cutting property is not good.

(5) Packaging suitability The packaging suitability when a film was wrapped on a ceramic dish was evaluated according to the following criteria.
○: Level that can be packaged moderately.
Δ: Some wrinkles enter.
X: Level at which the film spreads out of the container and causes a practical problem.

(6) Heat resistance Put two shrimp tempura (about 160mm in length) in a ceramic dish, wrap the film, put it in a 500W microwave oven, heat for 3 minutes, observe the tearing condition by heat, and Evaluated by criteria.
○: There was no hole.
Δ: Slightly perforated or deformed.
X: A large hole was formed or a large deformation occurred, resulting in a problem in use.

Example 1
In order to produce a β-layer pellet for forming an intermediate layer (β layer), as component (A), sufficiently dried polylactic acid A-1: NatureWorks 4032D (manufactured by Cargill Dow, L-lactic acid: D- Lactic acid = 98.6 / 1.4, molecular weight 200,000) 30% by mass, A-2: NatureWorks 4060 (manufactured by Cargill Dow, L-lactic acid: D-lactic acid = 85/15, molecular weight 190,000) 70 mass %, And this blend (component (A)) is melted at 200 ° C. using a φ40 mm twin screw extruder (L / D = 40), while the component (B) B-1: Adipic acid ester (PX-884 manufactured by Asahi Denka Kogyo Co., Ltd., molecular weight 650) was injected from the vent port of the extruder at a ratio of 17 parts by mass with respect to 100 parts by mass of the component (A), and melt-kneaded. β-layer pellets It was obtained.

  Moreover, in order to produce pellets for α layer forming front and back layers (α layer), α-2: carbodiimide compound with respect to 100 parts by mass of α-1: polybutylene terephthalate succinate (Ecoflex F manufactured by BASF Japan). (Nisshinbo Carbodilite HMV-8CA) was dry blended to 1 part by mass, and this blend was melt-kneaded at 200 ° C. using a φ40 mm twin screw extruder (L / D = 40) to form an α layer. Pellets were obtained.

  The α layer pellets and β layer pellets were put into separate φ60 mm single screw extruders (L / D = 35), melted and kneaded at 200 ° C., and the melts were joined in a round die die. A melt having a two-layer / three-layer structure of an intermediate layer / back layer was extruded so that the lamination ratio (mass ratio) was 1/6/1, and a 10 μm film was obtained by inflation molding.

(Example 2)
A 10 μm film was obtained in the same manner as in Example 1 except that the lamination ratio (mass ratio) of the surface layer / intermediate layer / back layer was 1/10/1.

(Reference Example 1)
A film was obtained in the same manner as in Example 1 except that a pellet made of α-3: polybutylene succinate (Bionole 1903, Showa Polymer Co., Ltd.) was used as the α layer pellet for forming the front and back layers (α layer).

(Comparative Example 1)
As component (A), fully dried polylactic acid NatureWorks 4032D (manufactured by Cargill Dow, L-lactic acid: D-lactic acid = 98.6 / 1.4) 30% by mass, and NatureWorks 4060 (Cargill Dow) L-lactic acid: D-lactic acid = 85/15) 70% by mass dry blended, and this blend (component (A)) is used in a φ40 mm twin screw extruder (L / D = 40). On the other hand, an adipic acid ester (PX-884, manufactured by Asahi Denka Kogyo Co., Ltd., molecular weight 650) as component (B) is extruded at a ratio of 17 parts by mass with respect to 100 parts by mass of component (A). The mixture was melted and kneaded while being injected from the vent port of to obtain pellets.
The pellets were melt-kneaded at 200 ° C., and inflation molding was attempted under the same conditions as in Example 1. However, the resin accumulated in the vicinity of the round die outlet and could not be blown.

(Comparative Example 2)
Dry blending is performed so that the carbodiimide compound (Nisshinbo Carbodilite HMV-8CA) is 1 part by mass with respect to 100 parts by mass of polybutylene terephthalate succinate (Ecoflex F, manufactured by BASF Japan). Pellets were prepared by melting and kneading at 200 ° C. using a machine (L / D = 40).
This pellet was melt-kneaded at 200 ° C. and subjected to inflation molding under the same conditions as in Example 1 to obtain a 10 μm film.

(Comparative Example 3)
Except that the pellet for α layer was produced only from polybutylene terephthalate succinate (Ecoflex F manufactured by BASF Japan), inflation molding was attempted in the same manner as in Example 1, but the bubble was not stabilized and the film was continuously formed. Could not be collected.

2 is a graph obtained by measuring the transient responsiveness of the uniaxial elongation viscosity of the polyester resin forming the front and back layers (α layer) of Example 1. FIG. 2 is a graph obtained by determining the strain hardening degree λ of the uniaxial elongation viscosity of the polyester resin forming the front and back layers (α layer) of Example 1 by the least square method.

Claims (5)

A lactic acid-based resin component (A) and a plasticizer component (B) having a molecular weight of 2,000 or less, and a component (B) in a proportion of 10 to 20 parts by mass with respect to 100 parts by mass of the component (A) An intermediate layer (β layer) made of a resin composition is provided,
An inflation molded biodegradable soft film comprising front and back layers (α layer) made of a polyester resin composition formed by mixing a carbodiimide compound on both sides of the intermediate layer (β layer),
The polyester resin composition forming the α layer has a strain of 0.1% at a temperature of 200 ° C., a shear viscosity of 500 to 1000 Pa · s measured at a frequency of 100 rad / s, and a uniaxial elongation rate of 1 at a temperature of 150 ° C. Inflation molding characterized by comprising a polyester resin composition having a strain hardening degree λ of uniaxial elongational viscosity measured at 0.0 sec ⁻¹ and uniaxial elongational strain of 1.0 to 3.0. Biodegradable soft film.   The inflation molded biodegradable flexible film according to claim 1, wherein the polyester resin composition forming the α layer comprises a mixture of an aliphatic aromatic polyester and a carbodiimide compound.   The aliphatic aromatic polyester constituting the α-layer polyester resin composition was obtained by copolymerizing an aromatic monomer component as a dicarboxylic acid component with an aliphatic dicarboxylic acid component and an aliphatic diol component at a ratio of 50 mol% or less. The inflation molded biodegradable soft film according to claim 2, which is an aliphatic aromatic polyester.   The inflation molded biodegradable soft film according to any one of claims 1 to 3, wherein the β layer accounts for 32 to 85% with respect to the total mass of the α layer and the β layer. The value of the storage elastic modulus at 20 ° C. measured by dynamic viscoelasticity at a frequency of 10 Hz and a strain of 0.1% is 800 to 2000 MPa, the value of the storage elastic modulus at 100 ° C. is in the range of 10 to 100 MPa, 20 The inflation molded biodegradable soft film according to any one of claims 1 to 4, wherein a value of loss tangent at ° C is in a range of 0.1 to 0.8.