JP5208821B2 - Polylactic acid biaxially stretched film - Google Patents

Description

  The present invention relates to a polylactic acid-based stretched film having excellent transparency, flexibility, and bending resistance, and further provides a polylactic acid-based stretched film that can suppress bleed-out during production processes and long-term storage. .

  Films used as packaging materials for newspapers, magazines, foods and the like are desired to be formed from biodegradable polymers in accordance with the recent increase in social demand for environmental protection. Among them, polylactic acid, which is widely present in nature and harmless to animals, plants and animals, has a melting point of 140 to 175 ° C., sufficient heat resistance, extremely high transparency, and relatively inexpensive thermoplasticity. Since it is a resin and a plant-derived material, it has attracted a great deal of attention.

  However, since a film made of polylactic acid has a very hard and brittle property as it is, it has been difficult to use it in a field where impact resistance and bending resistance are required.

  Various studies have been conducted to improve the impact resistance of polylactic acid. For example, Patent Document 1 discloses a film made of a resin composition containing a lactic acid resin and a silicone acrylic composite rubber for the purpose of improving impact resistance. Patent Document 2 discloses a film having a weight average molecular weight of 50,000 or more. A polylactic acid resin and a poly (meth) acrylate and / or a polyvinyl compound having a glass transition temperature of 60 ° C. or higher are blended, and the poly (meth) acrylate and / or the glass transition temperature of 60 ° C. or higher is further impact resistant. A molded article comprising a resin composition to which an improving agent is added is disclosed.

  On the other hand, in Patent Document 3, based on polylactic acid, a resin composition containing an aliphatic dibasic acid diester as a plasticizer and further blended with a rubber polymer having a refractive index substantially equivalent to that of the polylactic acid. Is disclosed.

JP 2006-232929 A JP 2006-328369 A JP 2008-94878 A

  However, although the film obtained by the formulations described in Patent Documents 1 and 2 has improved impact resistance, it is poor in flexibility, inferior in texture, and further, transparency, which is an advantage of polylactic acid, is impaired. Therefore, it has been difficult to use for conventionally known applications such as food films and industrial films. Therefore, stretched films made of polylactic acid are required not only to improve impact resistance but also to improve flexibility and flex resistance.

  In addition, the resin composition according to the prescription in Patent Document 3 is improved in flexibility in an extruded product such as a transfer tube, but has not yet solved the deterioration of transparency, and further, during film production and long-term storage. In some cases, there is a problem that lactide and a low molecular weight plasticizer contained in the resin composition bleed out of the system.

  The present invention solves the above-mentioned problems of the prior art, and provides a stretched polylactic acid film that is excellent in transparency, flexibility, and bending resistance, and that can suppress bleed out during production processes and long-term storage. .

  The inventors of the present invention have arrived at the present invention as a result of intensive studies to solve the above problems. That is, a specific amount of a polylactic acid copolymer (B) containing a specific amount of a lactic acid component and a rubbery component (C) are blended in the polylactic acid (A), and the amount of lactide contained in the film is reduced to 0.0. It has been found that by adjusting the content to 5% by mass or less, a high degree of transparency, flexibility, and bending resistance can be imparted, and a polylactic acid-based stretched film excellent in operability during film formation is provided.

  That is, the gist of the present invention is composed of a resin composition containing polylactic acid (A), a polylactic acid copolymer (B) containing 30 to 70% by mass of a lactic acid component, and a rubbery component (C). A polylactic acid-based biaxially stretched film, wherein the mass ratio of the polylactic acid (A) and the polylactic acid-based copolymer (B) is 60 to 90/40 to 10, and the content of the rubbery component (C) is Polylactic acid based on polylactic acid (A) and polylactic acid copolymer (B) in a range of 5 to 30 parts by mass and lactide content of 0.5% by mass or less with respect to 100 parts by mass in total It is a biaxially stretched film.

  The polylactic acid biaxially stretched film of the present invention is obtained by blending a polylactic acid (A) with a highly compatible polylactic acid polymer (B) and a rubbery component (C). In addition to the originally obtained biaxially stretched film maintaining high transparency, it is excellent in flexibility and bending resistance, and bleed-out is suppressed. Furthermore, it is industrially advantageous because of its excellent operational stability during film production.

  Hereinafter, the present invention will be described in detail.

  The polylactic acid-based biaxially stretched film of the present invention needs to be formed of a resin composition comprising polylactic acid (A), polylactic acid-based copolymer (B), and rubbery component (C) as constituent components. .

  The polylactic acid (A) is a poly L-lactic acid in which the structural unit of lactic acid is L-lactic acid, a poly D-lactic acid in which the structural unit is D-lactic acid, or a copolymer of L-lactic acid and D-lactic acid. Examples include poly DL-lactic acid or a mixture thereof. The weight average molecular weight is preferably in the range of 150,000 to 300,000, more preferably 160,000 to 200,000. When the weight average molecular weight of polylactic acid, which is the main component, is less than 150,000, the resulting film is inferior in mechanical properties. When the weight average molecular weight exceeds 300,000, the melt viscosity becomes too high and melt extrusion is difficult. It becomes.

  As for polylactic acid (A), crystalline polylactic acid and amorphous polylactic acid can be used in combination. However, in consideration of ensuring film formation stability and heat resistance by crystallization of polylactic acid, It is preferable to use it. The crystalline polylactic acid as used herein refers to a polylactic acid resin having a melting point in the range of 140 to 175 ° C., and the amorphous polylactic acid refers to a polylactic acid resin that does not substantially have a melting point. The blending ratio of crystalline polylactic acid and amorphous polylactic acid is in the range of (crystalline polylactic acid) / (amorphous polylactic acid) = 80/20 to 100/0 (mass%) by mass ratio. Is preferred. If the blending ratio of the crystalline polylactic acid is less than 80% by mass, stable film formation cannot be performed because the polylactic acid is inferior in crystallization.

  The polylactic acid copolymer (B) needs to contain 30 to 70% by mass of a lactic acid component. When the lactic acid component exceeds 70% by mass, it is necessary to use a large amount of the polylactic acid copolymer (B) in order to impart flexibility of the resulting film, which is not preferable. When the lactic acid component is less than 30% by mass, the compatibility between the polylactic acid (A) and the polylactic acid copolymer (B) is lowered, and the transparency of the resulting film is deteriorated, which is not preferable.

  The lactic acid component constituting the polylactic acid-based copolymer (B) may be any of L-lactic acid, D-lactic acid, and DL-lactic acid, but the lactic acid resin that is the main component of the polylactic acid (A). Those having the same structure as the structural unit are particularly preferred.

  The copolymer component other than the lactic acid component is preferably a polyester composed of a dicarboxylic acid and a diol, or a polyether.

  The dicarboxylic acid component constituting the polyester is not particularly limited, but oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, dimer acid, terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalene Examples include dicarboxylic acids, 5-sodium sulfoisophthalic acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, cyclohexanedicarboxylic acid and other dicarboxylic acids, 4-hydroxybenzoic acid, and ε-caprolactone. Can do. From the aspect of compatibility with polylactic acid, dicarboxylic acids having 10 or less carbon atoms are preferred.

  The diol component constituting the polyester is not particularly limited, but ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, Examples include 1,6-hexanediol, cyclohexanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, ethylene oxide adducts of bisphenol A and bisphenol S, and the like. In view of compatibility with polylactic acid, glycol having 10 or less carbon atoms is preferred.

  Examples of the polyether include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. The weight average molecular weight of the polyether is preferably 200 to 5,000. Within this range, flexibility can be imparted to polylactic acid without lowering the compatibility with polylactic acid.

  The polylactic acid copolymer (B) may further contain a small amount of a trifunctional compound such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, and pentaerythritol.

  Two or more of the above-mentioned copolymerization components in the polylactic acid copolymer (B) may be used in combination.

  The weight average molecular weight of the polylactic acid copolymer (B) is preferably in the range of 10,000 to 100,000, more preferably 20,000 to 80,000. When the weight average molecular weight is less than 10,000, not only the strength of the resulting film is remarkably lowered, but also the melt viscosity difference is too large when the film is formed, and the kneadability may be poor. On the other hand, when the weight average molecular weight exceeds 100,000, the softening effect of the polylactic acid-based copolymer (B) is lowered, and sufficient stretch may not be imparted to the obtained stretched film.

  In consideration of flexibility, the glass transition temperature of the polylactic acid copolymer (B) is preferably 40 ° C. or less, and more preferably in the range of 0 to 30 ° C.

The blending ratio of the polylactic acid (A) and the polylactic acid copolymer (B) needs to be in the range of 60 to 90/40 to 10, preferably 70 to 85/30 to 15, 75 to 85/25 to 15 is a more preferable range.
When the polylactic acid copolymer (B) component is less than 10 parts by mass, the flexibility is insufficiently imparted and the texture of the obtained stretched film is inferior. When the polylactic acid copolymer (B) component exceeds 40 parts by mass, operability including stretchability and slipperiness is deteriorated. Further, when the stretched film roll is stored for a long period of time, there is a problem that a low molecular weight product of the polylactic acid copolymer (B) bleeds out on the film surface.

  In addition, you may add a plasticizer to the film of this invention to such an extent that bleeding property does not deteriorate. The plasticizer preferably has a low molecular weight of about 200 to 1000, and the blending amount of the plasticizer is preferably less than 5% by mass in the film, and more preferably less than 3% by mass. Specific examples of the plasticizer include Daihachi Chemical Industry's DAIFATTY 101, Company's MXA, and the like.

  The rubber-like component (C) used in the present invention is a rubber-like substance exhibiting rubber elasticity at room temperature. For example, ethylene-propylene copolymer, ethylene-propylene-nonconjugated diene copolymer, ethylene- Butene-1 copolymers, various acrylic rubbers, ethylene-acrylic acid copolymers and alkali metal salts thereof (so-called ionomers), ethylene-glycidyl (meth) acrylate copolymers, ethylene-acrylic acid alkyl ester copolymers (for example, , Ethylene-ethyl acrylate copolymer, ethylene butyl acrylate copolymer), acid-modified ethylene-propylene copolymer, diene rubber (eg, polybutadiene, polyisoprene, polychloroprene), copolymer of diene and vinyl monomer Polymers (for example, styrene-butadiene random copolymer, styrene- Tadiene block copolymer, styrene-butadiene-styrene block copolymer, styrene-isoprene random copolymer, styrene-isoprene block copolymer, styrene-isoprene-styrene block copolymer, graft copolymer of styrene with polybutadiene , Butadiene-acrylonitrile copolymer), polyisobutylene, copolymer of isobutylene and butadiene or isoprene, natural rubber, thiocol rubber, polysulfide rubber, acrylic rubber, silicone rubber, polyurethane rubber, polyether rubber, epichloro Examples include hydrin rubber, polyester elastomer, and polyamide elastomer.

As the rubbery component (C) in the present invention, those obtained by crosslinking a crosslinkable component such as a divinylbenzene unit, an allyl acrylate unit or a butylene glycol acrylate, those having a vinyl group, and other various structures, For example, those having a cis structure, a trans structure and the like can also be used.
Among the rubbery components, a polymer containing an acrylic monomer as a constituent unit is preferable, and a polymer containing a (meth) acrylic acid alkyl ester unit is more preferable. Preferable examples of this unit include a methyl acrylate unit, an ethyl acrylate unit, a butyl acrylate unit, a methyl methacrylate unit, an ethyl methacrylate unit, and a butyl methacrylate unit. These not only improve flex resistance as an elastomer, but also have excellent compatibility with polylactic acid and can improve the transparency of the resin.

  The rubbery component (C) is composed of a core layer and one or more shell layers covering the core layer, and a so-called core-shell type multilayer structure polymer in which adjacent layers are composed of different polymers. It is preferable that This multilayer structure polymer includes an elastomer component such as SBR rubber, butadiene, acrylonitrile-styrene copolymer, and a polymer (acrylic rubber) having a (meth) acrylic acid ester unit as a core layer, and as a shell layer, It is preferable that the polymer which has a polystyrene and a (meth) acrylic acid ester unit is included.

  When the rubber-like component is a core-shell type multilayer structure, the shell layer plays a role of maintaining the shape of the core layer, which is an elastomer component, and as a result, the elastomer component is uniformly finely dispersed in the resin, Excellent bending resistance can be expressed. Furthermore, it is possible to absorb an impact at the boundary between the core layer and the shell layer and at the boundary between the shell layer and the matrix, and therefore further improvement in bending resistance can be expected.

  The core layer is not particularly limited as long as it is composed of a polymer component having rubber elasticity. For example, a rubber constituted by polymerizing a (meth) acrylic component, a silicone component, a styrene component, a nitrile component, a conjugated diene component, a urethane component, an ethylenepropylene component, or the like can be given. Preferred rubbers include, for example, (meth) acrylic components such as ethyl (meth) acrylate units, butyl (meth) acrylate units, (meth) acrylic acid-2-ethylhexyl units and benzyl (meth) acrylate units, dimethyl Polymerize silicone components such as siloxane units and phenylmethylsiloxane units, styrene components such as styrene units and α-methylstyrene units, nitrile components such as acrylonitrile units and methacrylonitrile units, or conjugated diene components such as butanediene units and isoprene units. It is a rubber made of In addition to these components, a crosslinked rubber obtained by copolymerizing and crosslinking a crosslinkable component such as a divinylbenzene unit, an allyl (meth) acrylate unit, or a butylene glycol diacrylate unit is also preferable. Among these, from the viewpoint of transparency and bending resistance, the rubber layer is preferably a crosslinked rubber, and more preferably a crosslinked rubber having a glass transition temperature of 0 ° C. or less.

  The shell layer is not particularly limited, and is an unsaturated carboxylic acid alkyl ester unit, a glycidyl group-containing vinyl unit, an aliphatic vinyl unit, an aromatic vinyl unit, a vinyl cyanide unit, a maleimide unit. , Polymers containing unsaturated dicarboxylic acid units, unsaturated dicarboxylic acid anhydride units and / or other vinyl units, and the like, in terms of excellent transparency and flex resistance, methyl methacrylate units and It is preferably composed of a polymer containing methyl acrylate units.

  In the present invention, commercially available products that can be used as the rubber component (C) include, for example, “Metablene” manufactured by Mitsubishi Rayon, “Kane Ace” manufactured by Kaneka, “Paraloid” manufactured by Rohm and Haas, “Staffroid” manufactured by Gantz Kasei, Kuraray “Paraface” and the like can be mentioned, and these can be used alone or in combination of two or more. In particular, “Paralloid” BPM-500 manufactured by Rohm and Haas and “Metablene” S2001 manufactured by Mitsubishi Rayon are excellent in terms of transparency and bending resistance.

  In the present invention, it is necessary to use the polylactic acid copolymer (B) and the rubbery component (C) in combination. Only the polylactic acid copolymer (B) is inferior in the bending resistance of the film. Further, in order to obtain a predetermined flexibility, it is necessary to add a large amount of the polylactic acid copolymer (B), and the operability including the stretchability and the slipperiness is deteriorated. Further, when the stretched film roll is stored for a long period of time, there is a problem that a low molecular weight product of the polylactic acid copolymer (B) bleeds out on the film surface. The rubber-like component (C) alone is sufficient in bending resistance, but has a poor flexibility improvement effect, and is inferior in the texture of the stretched film. Moreover, when the compounding quantity of a rubber-like component (C) is increased, the transparency of a film will deteriorate.

  The content of the rubbery component (C) needs to be 5 to 30 parts by mass with respect to 100 parts by mass of the total amount of the polylactic acid (A) and the polylactic acid-based copolymer (B). 20 mass parts is preferable and 5-15 mass parts is a more preferable range.

  If the rubbery component (C) component is less than 5 parts by mass, the flex resistance and flexibility of the film tend to be insufficient. When the rubbery component (C) component exceeds 30 parts by mass, the flex resistance and flexibility improvement effect are sufficient, but the transparency of the film may deteriorate.

  In the present invention, the amount of lactide contained in the polylactic acid-based biaxially stretched film is required to be 0.5% by mass or less, and preferably 0.1 to 0.4% by mass. When the amount of lactide exceeds 0.5% by mass, smoke generation during film formation is remarkable, and equipment near the die is contaminated. In severe cases, the film is transferred to the film surface via a cast roll. Gets worse.

  As a method for reducing the amount of lactide, when polymerizing the polylactic acid (A) or the polylactic acid copolymer (B), it is removed by reducing the pressure at a temperature equal to or higher than the melting point, or polylactic acid (A) or polylactic acid. Examples include a method of gasifying and removing the pellets after polymerization of the system copolymer (B) under high temperature and reduced pressure, and a method of extracting and removing by immersion in warm water. In the present invention, the lactide content of the polylactic acid (A) or polylactic acid copolymer (B) used as the film raw material is preferably 1.0% by mass or less by the means described above.

  The polylactic acid biaxially stretched film used in the present invention preferably has a glass transition temperature of 40 to 55 ° C. From the viewpoint of flexibility, the glass transition temperature is preferably low, but in the present invention, it is not preferable to lower it to less than 40 ° C. When the glass transition temperature is lowered, the cast roll temperature during film formation needs to be lowered accordingly, but in the case of a polylactic acid resin, there are problems such as precipitation of lactide on the film surface and adhesion to the cast roll. Therefore, the temperature of the cast roll is preferably 30 ° C. or higher, and accordingly, the glass transition temperature is preferably 40 ° C. or higher. On the other hand, when the glass transition temperature exceeds 55 ° C., the softening effect of the polylactic acid film is small.

  The melting point of the polylactic acid-based biaxially stretched film of the present invention is preferably 140 ° C. or higher, and particularly preferably 150 ° C. or higher. When the melting point is less than 140 ° C., the heat resistance is insufficient.

  The polylactic acid-based biaxially stretched film of the present invention preferably has a haze of 5% or less, and more preferably 3% or less for practical use. When the haze exceeds 5%, the appearance of transparency is low, and the commercial value tends to decrease in applications such as packaging materials. In order to set the haze to 5% or less, the components (A) to (C) may be set to the above-described ranges.

  The polylactic acid-based biaxially stretched film of the present invention preferably has a tensile modulus of 3.0 GPa or less, and more preferably 2.8 GPa or less. In addition, the tensile elasticity modulus here is an average value of the measured value of MD direction and TD direction of a film. When the tensile modulus exceeds 3.0 GPa, the film becomes poor in flexibility, and the texture is inferior. Although the minimum of a tensile elasticity modulus is not specifically limited, It is preferable that it is 2.0 GPa or more from the reason for the intensity | strength of a film becoming scarce. In order to set the tensile elastic modulus to 3.0 GPa or less, the components (A) to (C) may be set to the above-described ranges.

  In addition, the resin composition constituting the polylactic acid-based biaxially stretched film is used in combination with a crosslinking agent such as an organic peroxide and a crosslinking aid for the purpose of suppressing a decrease in melt tension during film formation. Then, the resin composition may be subjected to slight crosslinking.

  In addition, the resin composition constituting the polylactic acid-based biaxially stretched film used in the present invention includes an ultraviolet ray preventive agent, a light stabilizer, an antifogging agent, an antifogging agent, a flame retardant, a color preventing agent, an oxidation agent, depending on the application Additives other than the above, such as inhibitors, fillers and pigments, can also be added.

  Next, the manufacturing method of the polylactic acid-type biaxially stretched film of this invention is demonstrated.

  The method for forming the resin composition into a film is not particularly limited, and examples thereof include a T-die method, an inflation method, a calendar method, and the like. Among these, the T-die method is preferable. In the T-die method, a resin composition containing polylactic acid (A), a polylactic acid-based copolymer (B), and a rubbery component (C) is supplied to an extruder hopper, melt-kneaded, extruded, and cast with a cast roll. An unstretched sheet is obtained by cooling. At this time, as temperature conditions, the cylinder temperature is suitably 180 to 250 ° C., and the T die temperature is suitably 200 to 250 ° C. The cast roll is suitably controlled at 20 to 40 ° C. According to this method, an unstretched sheet having a thickness of 100 to 600 μm is obtained.

  Although the method of blending the rubbery component (C) is not particularly limited, a master chip containing about 10 to 50% by mass in the polylactic acid (A) or the polylactic acid copolymer (B) is prepared in advance. A method of using this to add to a target content is preferable.

  A biaxially stretched film is obtained by biaxially stretching an unstretched sheet. Examples of the stretching method include a roll method and a tenter method, and either a sequential biaxial stretching method or a simultaneous biaxial stretching method may be employed. Moreover, it is preferable that the surface magnification in biaxial stretching is 6 to 16 times. If the surface magnification is less than 6 times, the mechanical properties of the resulting film, particularly the tensile strength, is low and may not be practically used. On the other hand, if the surface magnification exceeds 16 times, the film may not be able to withstand the stretching stress during stretching and may be broken.

  The thickness of the obtained stretched film is preferably 10 to 50 μm. When the thickness is less than 10 μm, the packaging bag is not stiff, and when it is thicker than 50 μm, it is disadvantageous in terms of cost, which is not preferable.

  As extending | stretching temperature, 50-90 degreeC is preferable and 60-80 degreeC is further more preferable. When the stretching temperature is less than 50 ° C., the film is broken at the initial stage of stretching due to insufficient heat for stretching. On the other hand, when the temperature exceeds 90 ° C., heat is excessively applied to the film, and draw stretching tends to occur, resulting in frequent occurrence of stretch spots.

  A coating agent can also be coated on the unstretched sheet before the stretching step, if necessary. The coating method is not particularly limited, and examples include gravure roll coating, reverse roll coating, wire bar coating, lip coating, air knife coating, curtain flow coating, spray coating, and dip coating.

  Moreover, you may implement a thermal relaxation process after extending | stretching in order to provide dimensional stability to a biaxially stretched film. As a method of thermal relaxation treatment, a method of blowing hot air, a method of irradiating infrared rays, a method of irradiating microwaves, a method of contacting on a heat roll, etc. can be selected, and a method of blowing hot air in that it can be heated uniformly and accurately Is preferred. In that case, it is preferable that it is 1 second or more in the range of 80-160 degreeC, and it is preferable to implement on the conditions of a 2-8% relaxation rate.

  Even if the film of the present invention is a single layer, a good package can be obtained, but other resins may be laminated in accordance with the contents, the storage method, and the bag making method. Examples of the lamination method include coating, direct lamination, extrusion lamination, and the like, and can be appropriately selected according to required performance.

  Hereinafter, the present invention will be described more specifically with reference to examples.

  The raw materials of the film and the method for measuring the characteristic values in the examples and comparative examples are as follows.

(A) Polylactic acid 4032D manufactured by Nature Works, D-form content 1.2 mol%, residual lactide amount 0.22 mass%, weight average molecular weight 200,000.

(B) Polylactic acid copolymer (B-1): Dainippon Ink Pramate PD350, lactic acid component content 50 mass%, melting point 158 ° C., glass transition temperature 18 ° C., weight average molecular weight 50,000, lactide content 2.02 mass%.
(B-2): B-1 was heat-treated at 110 ° C. under a reduced pressure of 0.5 mmHg or less for 24 hours to reduce the lactide amount to 0.54% by mass.

(C) Rubber component (C-1): Rohm and Haas Paraloid BPM-500, core shell type, acrylic rubber (C-2): Mitsubishi Rayon Co., Ltd. Metabrene S2001, core shell type, silicone rubber

(D) Plasticizer DAIFATTY101, manufactured by Daihachi Chemical Co., Ltd., adipic acid ester, molecular weight 338
(Measurement method)

(1) Amount of lactide Using a HP-6890 Series GC System manufactured by Hewlett Packard and a column 30 m × 0.25 mm ID DB-17 capillary column (0.25 μm ft.), Measurement was performed using helium as a carrier gas.

(2) Melting point, glass transition temperature (° C)
Using a differential scanning calorimeter DSC-7 manufactured by Perkin Elmer, the heating rate was measured at 20 ° C./min.

(3) Extrusion operability After the continuous film formation for 3 hours, the contamination near the T-die, the state of smoke generation, and the degree of contamination of the cast roll were visually evaluated according to the following criteria.
○: There is little contamination and smoke generation, and the cast roll is not soiled.
X: Contamination / smoke occurred and the cast roll was dirty.

(4) Haze (transparency)
In accordance with JIS-K7105, a film having a thickness of 25 μm was used as a sample, and measurement was performed using a haze meter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd. In the present invention, 5% or less was accepted. It is more preferable from a practical viewpoint to be 3% or less.

(5) Tensile modulus (GPa), tensile strength (MPa) and tensile elongation (%)
In accordance with the method described in JIS K-7127, a 25 mm-thick film made into a strip of 10 mm × 150 mm was used as a sample, and an autograph (tensile tester) AG-IS manufactured by Shimadzu Corporation was used. It was measured.

(6) Bleed property The stretched film was left in an atmosphere of 40 ° C. and 90% RH for 30 days, and judged according to the following criteria.
○: No stickiness on the film surface was observed.
Δ: Slight stickiness was observed on the film surface, but there were no practical problems such as blocking property and surface appearance.
X: Stickiness on the film surface was remarkably observed, and blocking and surface appearance were remarkably deteriorated.

(7) Bending resistance In accordance with ASTM F392, a 180 mm x 280 mm film that has been bent 200 times in a gel bot tester manufactured by Tester Sangyo in an atmosphere of 20 ° C is placed on white paper, coated with ink, and transferred to white paper. The number of inks counted was counted. Judgment was made based on the following criteria, and a score of ○ or higher was regarded as acceptable.
◎: Number of ink transferred to white paper is less than 10 ○: Number of ink transferred to white paper 10 to 30 ×: Number of ink transferred to white paper 30 to 100 ××: Ink transferred to white paper More than 100

Example 1
70 parts by weight of A, 30 parts by weight of B-2, and 5 parts by weight of C-1 were dry blended and melt-extruded at a T-die temperature of 230 ° C. with a 90 mmφ single-screw extruder and heated to 35 ° C. The film was tightly cooled to the controlled cast roll to obtain an unstretched sheet having a thickness of 240 μm. Next, the end of the unstretched film was held by a clip of a tenter type simultaneous biaxial stretching machine, and after running through a preheating zone at 70 ° C., the temperature was 68 ° C. and 3.0 times MD and 3.3 TD. At the same time biaxial stretching. Then, after a heat treatment for 4 seconds at a temperature of 140 ° C. with a TD relaxation rate of 5%, the film was cooled to room temperature and wound up to obtain a biaxially stretched film having a thickness of 25 μm. The obtained biaxially stretched film was evaluated by the measuring methods (1) to (7).

Examples 2-6, Comparative Examples 1-10
Various materials were obtained in the same manner as in Example 1 except that the raw resin, additives and stretching temperature were changed as shown in Table 1.

  As shown in Examples 1-6, what is in the range specified by the present invention is high in transparency with a haze of 5% or less, excellent in elasticity with a tensile elastic modulus of 3.0 GPa or less, and made of a film. The film obtained in Comparative Examples 1 to 7 did not satisfy all the above-mentioned performances, although the performance changes during storage such as operability during filming and bleeding were small.

  About Comparative Example 1, although the flex resistance is improved by adding the rubbery component (C), the lactic acid copolymer (B) is not blended, and the flexibility and the texture of the film are inferior. The transparency was poor.

  In Comparative Example 2, since the low molecular weight plasticizer was used instead of the lactic acid copolymer (B), the obtained film was satisfactory in flexibility, texture, and bending resistance, but was 50 ° C. The bleed-out was noticeable when stored in a 40% RH atmosphere.

  In Comparative Example 3, as in Comparative Example 1, although the flex resistance is improved by adding the rubber-like component (C), the lactic acid copolymer (B) is not blended and is flexible. It was inferior to the texture and texture of the film, and the transparency was poor.

  In Comparative Example 4, as in Comparative Examples 1 and 3, the rubber-like component (C) was added to improve the flex resistance, but the lactic acid copolymer (B) was added. The film was inferior in flexibility and film texture, and lacked transparency.

  In Comparative Example 5, since the content of the lactic acid-based copolymer (B) is large, the obtained film is satisfactory in flexibility, texture, and bending resistance, but at 40 ° C. and 90% RH atmosphere. The bleed-out was noticeable when stored in

  About the comparative example 6, since there was little content of the lactic acid-type copolymer polymer (B), it was inferior to the softness | flexibility and texture of the obtained film.

  About the comparative example 7, since there was little content of a rubber-like component (C), it was inferior to the softness | flexibility and bending resistance of the obtained film.

  About Comparative Example 8, since the content of the rubbery component (C) was large, the transparency of the obtained film was poor.

  In Comparative Example 9, since the lactic acid copolymer (B) and the rubbery component (C) were not contained, the obtained film was inferior in flexibility, texture and flex resistance.

In Comparative Example 10, since the amount of lactide in the film was large, the extrusion operability was inferior, and the bleed out was noticeably observed during storage in an atmosphere of 40 ° C. and 90% RH.

Claims (3)

A polylactic acid biaxially stretched film composed of a polylactic acid (A), a polylactic acid copolymer (B) containing 30 to 70% by mass of a lactic acid component, and a resin composition containing a rubbery component (C). The mass ratio of polylactic acid (A) to polylactic acid copolymer (B) is 60 to 90/40 to 10, and the content of rubbery component (C) is polylactic acid (A) and polylactic acid. The polylactic acid-type biaxially stretched film which is the range of 5-30 mass parts with respect to 100 mass parts of total amounts of a system copolymer polymer (B), and whose lactide amount is 0.5 mass% or less. The polylactic acid biaxially stretched film according to claim 1, wherein the film has a haze of 5% or less. The polylactic acid biaxially stretched film according to claim 1, wherein the film has a tensile modulus of 3.0 GPa or less.