JP2003191425A - Flexible polylactic acid resin stretched film and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible biodegradable film and a production method thereof which is free from troubles in a film forming process such as tearing or roll wrap up or the like and also free from troubles such as blocking or the like after the film formation and is excellent in transparency, heat resistance and bleedout resistance. <P>SOLUTION: A flexible polylactic acid resin stretched film is obtained by laminating a layer A consisting of a resin component a' containing 10 to 200 pts.wt. of a plasticizer p to 100 pts.wt. of a polylactic acid resin a and a layer B consisting of a resin component b' containing 0 to 50 pts.wt. of a plasticizer p' to 100 pts.wt. of a crystalline polylactic acid resin b in the order of B/A/B. The thickness of the layer A in the entire film thickness is 30 to 99% and the layer B is stretched at least in one direction. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a stretched polylactic acid-based resin film softened by a plasticizer. More specifically, the present invention relates to a film having excellent properties such as transparency, heat resistance and bleed-out resistance and requiring particularly flexibility such as packaging material, agricultural film, laminating film, label and the like, and a manufacturing method thereof. In particular, the present invention relates to a film useful as a food packaging material, a compost bag, an agricultural mulch film, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, resins such as polyethylene, polypropylene, polyethylene terephthalate, soft polyvinyl chloride and polyvinylidene chloride have been widely used as film materials. However, it has been pointed out that such a resin does not have biodegradability and has an adverse effect on the environment when it is discarded in the natural environment. In particular, among these resin films, materials containing chlorine such as soft polyvinyl chloride and polyvinylidene chloride are problematic because they may cause generation of dioxins during soil burial or incineration.

Under these circumstances, studies on biodegradable resins have progressed, and many biodegradable polymers have been developed. However, some of them are less flexible than conventional resins, and are particularly used for packaging and agriculture. There is a resin that has problems when trying to develop into. Among them, polylactic acid resin is L-based by the fermentation method.
Lactic acid has become cheap, and the obtained polymer has high transparency and a relatively high melting point (about 170 degrees in the case of poly L-lactic acid). Is. On the other hand, as a method of softening such a biodegradable resin, for example, a method of improving flexibility by adding a softener or a plasticizer having a relatively low molecular weight to the biodegradable resin is widely known ( See, for example, Patent Documents 1 and 2.

However, a cast (unstretched) film of a polylactic acid-based resin softened by adding a plasticizer has a glass transition temperature lowered by the addition of the plasticizer, so that the films are apt to cause blocking and the glass transition temperature is increased. Above, there is a problem that the film shape cannot be maintained. Further, although the plasticized polylactic acid-based resin is transparent and flexible immediately after the film formation, there is a problem that the transparency is lowered due to the formation of crystals over time.

On the other hand, it is known that by stretching the resin, the degree of crystallinity is increased and heat resistance and transparency can be maintained. The above effects can be expected by stretching even a biodegradable resin containing a plasticizer. However, if the film temperature during film formation or during winding after film formation exceeds the glass transition temperature, it will easily stick to the stretching roll or the roll of the winder, which may cause process troubles such as film rupture or roll winding. In addition, since there is a possibility that blocking and other problems may occur due to bleeding out of the plasticizer on the film surface even in a wound film, a large amount of plasticizer is added to lower the glass transition temperature and soften it. It was difficult.

[0006]

[Patent Document 1] Japanese Patent No. 3096011

[0007]

[Patent Document 2] Japanese Patent Laid-Open No. 2000-72961

[0008]

The problem to be solved by the present invention is that there is no trouble in the film forming process such as film rupture or roll winding, and there is no problem such as blocking even after film formation, transparency, It is intended to provide a flexible biodegradable film having excellent heat resistance and bleed-out resistance, and a method for producing the film.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, have found that polylactic acid resin a
Layer A made of a resin composition a ′ containing 10 to 200 parts by weight of a plasticizer p with respect to 100 parts by weight, and resin containing 0 to 50 parts by weight of a plasticizer p ′ with respect to 100 parts by weight of a crystalline polylactic acid-based resin b. Layer B comprising composition b ′ is laminated in a B / A / B type, and the thickness of layer A is 30 to 9 of the thickness of the entire film.
9%, layer B is stretched in at least one direction, a softened polylactic acid-based resin stretched film,
There is no trouble in the above-mentioned film forming process, there is no problem such as blocking even after the film forming, and it is transparent and flexible and has excellent heat resistance and bleed-out resistance, packaging material, agricultural film, laminating film, It has been found that the film is useful as a film such as a label that requires particularly flexibility, particularly as a food packaging material such as a wrap film, a compost bag, and an agricultural mulch film. However, in the above, b'is characterized by a glass transition temperature higher by 3 ° C or more than a ', and the glass transition temperature of b'is 30 ° C or more, and p may be the same as or different from p'. It's good.

As a method for producing such a film, a layer A composed of a resin composition a'containing 10 to 200 parts by weight of a plasticizer p to 100 parts by weight of a polylactic acid resin a and a polylactic acid system. A layer B made of a resin composition b ′ containing 0 to 50 parts by weight of a plasticizer p ′ with respect to 100 parts by weight of a resin b is coextruded in a B / A / B type, and uniaxially or biaxially stretched to form a film. The inventors have found that a method for producing a stretched film of a softened polylactic acid-based resin, which is characterized, is effective, and completed the present invention.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The film of the present invention is manufactured by suppressing the bleeding of the plasticizer in the layer A and the central layer A mainly made of a polylactic acid resin plasticized by the plasticizer p which imparts flexibility. It is essential that the layer B has a B / A / B structure for controlling blocking after film formation and for improving film formability such as suppressing roll adhesion during film formation. In the present invention, having a structure of B / A / B means that the layer B exists in both outer layers of the layer A, and the B layer and the A layer are not necessarily in contact with each other.

Further, the layer B needs to be stretched in at least one direction. In so-called unstretched film or extruded sheet in which crystallization or orientation is not advanced, flexibility or flexibility decreases with time, or appearance or morphology changes, such as transparency, due to crystallization that greatly progresses during heating. Problems such as occur. In order to solve such a problem, the layer B needs to be stretched in at least one direction, and more preferably stretched in two directions (biaxial) and heat-fixed. The layer A is also preferably stretched in at least one direction when the resin composition a ′ constituting the layer A has crystallinity.

The polylactic acid resin used in the present invention is L
A homopolymer or a copolymer containing 50% by weight or more of a lactic acid residue or a D-lactic acid residue. Examples of the homopolylactic acid in the present invention include poly L-lactic acid having 0 to 50% by weight of D-lactic acid residue, poly D-lactic acid having 0 to 50% by weight of L-lactic acid residue, poly L-lactic acid and poly L-lactic acid. A blend of D-lactic acid may be mentioned. As a method for producing polylactic acid, there are a method of synthesizing a cyclic dimer lactide from lactic acid and obtaining a high molecular weight polylactic acid by ring-opening polymerization, and a method of obtaining polylactic acid by direct dehydration condensation of lactic acid. It can be used in the present invention regardless of the manufacturing method.

Further, the copolymer may be prepared by glycolic acid, 3-hydroxybutyric acid,
Hydroxycarboxylic acids such as 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid and 6-hydroxycaptonic acid, caprolactone, vinyl acetate, polyols such as polyethylene glycol and polypropylene glycol, ethylene terephthalate polymers, ethylene vinyl It can be obtained by adding one or more auxiliary components such as alcohol polymers and further advancing the polymerization. The form of the copolymer may be any form such as a block copolymer, a random copolymer and an alternating copolymer.

In the present invention, at least the polylactic acid resin b, which is a component constituting the layer B, is required to have crystallinity.

The crystal referred to herein means a poly L-lactic acid crystal, a poly D-lactic acid crystal, and a stereocomplex composed of poly L-lactic acid and poly D-lactic acid. The term "having crystallinity" as used herein means that these crystals have the property of being able to form a single species or a plurality of species. This crystalline polylactic acid-based resin can be used as the crystalline polylactic acid-based resin b forming the layer B, but from the viewpoint of heat resistance, poly-L-lactic acid and poly-D having a melting point of 150 ° C. or higher. -Lactic acid and a mixture thereof are preferable, and the melting point of poly-L-lactic acid and / or poly-D-lactic acid is 160 ° C.
The above is more preferable.

The polylactic acid resin a, which is a constituent of the layer A, may be crystalline or amorphous, but for applications requiring high flexibility, it is amorphous or has a low melting point of less than 150 ° C. It is preferable to use an organic resin and increase the content of the plasticizer p. Generally, when a plasticizer is mixed with a resin and used, the plasticizer molecule exists in a state of being mixed only in the amorphous portion of the resin. Therefore, when increasing the content of the plasticizer p to impart high flexibility, At the same time, in order to suppress bleed out of the plasticizer, it is particularly preferable to use an amorphous polylactic acid resin.

On the other hand, in order to ensure high flexibility and heat resistance at the same time, it is preferable to use a mixture of crystalline homopolylactic acid and an amorphous polylactic acid resin having a melting point of 150 ° C. or higher.

The plasticizers p and p'used in the present invention may be any ones which, when added to a polylactic acid type resin, lead to a decrease in glass transition temperature and a decrease in rigidity, for example, ester type derivatives and ethers. System derivatives,
More specific examples include ether ester derivatives, glycerin derivatives, phthalic acid derivatives, glycolic acid derivatives, citric acid derivatives, adipic acid derivatives, epoxy plasticizers, etc., but blends of two or more of these plasticizers are also possible. Including. In particular, we suppress bleed-out and maintain transparency,
To increase the plasticization efficiency, the solubility parameter of all plasticizers added to the film is 16-23 (MJ /
m ³ ) ^1/2 , preferably 17 to 21 (MJ / m
³ ) ^1/2 is more preferable. The method for calculating the solubility parameter is described in P. Small, J .; Appl.
Chem. , 3, 71 (1953). Further, among such plasticizers, a biodegradable plasticizer is preferable from the viewpoint of keeping the biodegradability of the entire film.

In addition, considering that it is used for food packaging and the possibility that undecomposed materials may remain on compost and farmland even temporarily, there is no problem in terms of food hygiene from the FDA or polyolefin hygiene council. It is preferably a certified plasticizer.

Examples of such plasticizers include triacetin, epoxidized soybean oil, epoxidized linseed oil, epoxidized linseed oil fatty acid butyl, adipic acid aliphatic polyester, acetyl citrate tributyl, acetylricinoleate, and sucrose fatty acid. Examples thereof include esters, sorbitan fatty acid esters, adipic acid dialkyl esters, bis (alkyldiglycol) adipates, and polyethylene glycols.

The plasticizer p may be the same as or different from the plasticizer p '.

Further, the molecular weight of the plasticizers p and p'is preferably 300 to 10,000, more preferably 400 to 10,000.
When it is 5000, bleed-out of the plasticizer on the film surface can be suppressed, which is preferable. When the plasticizers p and p ′ are polyethylene glycols, the molecular weight is preferably 300 to 30,000, more preferably 6
It is preferably set to 00 to 20000. The term "molecular weight" as used herein means that when p or p'is a blend of a plurality of types of plasticizers, it is preferable that each individual plasticizer be in the above molecular weight range.

The plasticizer may be added in an amount that provides flexibility according to the intended use, but the loop stiffness of the film is preferably 10 to 350 μN / cm, more preferably 50 to 250 μN / cm. As described above, the type and amount of the plasticizer and the thickness ratio of the layer A may be adjusted. When the loop stiffness is more than 350 μN / cm, the softening effect is insufficient and the usability may be deteriorated when used in applications such as packaging films. Further, if the loop stiffness is less than 10 μN / cm, the rigidity of the film will be insufficient, and defects in the film forming and processing processes are likely to occur, which is not preferable in some cases.

The amount of plasticizer added varies depending on the type of plasticizer and the type of polylactic acid resin used. Layer A comprises 10 to 200 parts by weight of polylactic acid resin a and 100 parts by weight of a,
More preferably, it comprises a resin composition a ′ containing 20 to 100 parts by weight of a plasticizer p. If the plasticizer p is less than 10 parts by weight with respect to 100 parts by weight, the flexibility of the film may be insufficient, and if it exceeds 200 parts by weight, the plasticizer cannot be uniformly dispersed in the resin or the plasticizer is evenly distributed. Even if dispersed, the strength may be insufficient, and bleed-out of the plasticizer from the end surface of the film may be a problem. Also, plasticizer p
Has a molecular weight of 300 to 10,000, preferably 400 to 5
A value of 000 is preferable because bleed-out of the plasticizer p on the film surface can be suppressed. If the molecular weight of the plasticizer p is less than 300, the plasticizer p is likely to bleed out to the film surface through the layer B, which is not preferable in some cases. In addition, the molecular weight of the plasticizer p is 1000
If it is larger than 0, the plasticizing effect may be reduced, or the film transparency may be lowered during stretching, which is not preferable.

Layer B is 0 to 50 parts by weight, preferably 0 to 20 parts by weight, based on 100 parts by weight of polylactic acid resin b and b.
More preferably, it comprises a resin composition b'containing 0 to 10 parts by weight of a plasticizer p '. When the plasticizer p ′ exceeds 50 parts by weight with respect to 100 parts by weight of b, bleed-out or blocking of the plasticizer p ′ on the film surface may be a problem. In the present invention, the content of the plasticizer p ′ may be 0 part by weight.

In the present invention, it is preferable that the resin composition b'forming the layer B has a glass transition temperature higher than that of the resin composition a'forming the layer A by 3 ° C. or more. Is necessary for.

The glass transition temperature of the resin composition b'forming the layer B must be 30 ° C. or higher, preferably 45 ° C. or higher for film-forming property and suppression of blocking. It is preferable to determine the type and the addition amount of the plasticizer p ′ in consideration of these points. Although it is possible to increase the glass transition temperature by adding an additive, for example, an acrylic compound such as polymethylmethacrylate to the polylactic acid resin, it is preferably 70 ° C. or lower from the viewpoint of film formability.

The thickness of the stretched film of the softened polylactic acid resin of the present invention is not particularly limited, but preferably 1 to 250.
Micron, more preferably 5-100 microns, most preferably 8-40 microns.

As described above, the softened polylactic acid resin-based stretched film of the present invention is laminated on the B / A / B type, but the layer A has a thickness of the whole film in order to impart sufficient flexibility. The thickness must be 30% or more, and preferably 70% or more. Further, in order to suppress the bleeding out of the plasticizer and to secure heat resistance and mechanical strength, the thickness of the layer A needs to be 99% or less, and preferably 95% or less, of the thickness of the entire film.

The film of the present invention has excellent transparency, and a haze value of 20% or less is preferably used as an index of transparency.

In the film of the present invention, stabilizers such as carbodiimide and oxazoline, 2,
6-di-tert-butyl-4-methylphenol (BH
T), antioxidants such as butyl hydroxyanisole (BHA), organic or inorganic antiblocking agents such as silica, talc, alumina, calcium carbonate, glycerin fatty acid esters, monostearyl citrate, alkyl sulfonates, etc. Various additives such as various antifogging agents and / or antistatic agents, titanium oxide, carbon black, and coloring agents such as various pigments and dyes may be contained.

In addition, a thin film layer is provided as the outermost layer of the film in order to impart antistatic property, antiblocking property, adhesive property with other materials, tackiness, etc. to the film and further suppress plasticizer bleed out. You can The formation of the thin film layer may be performed in-line during the film forming process before and after stretching, or may be performed offline after once obtaining the stretched film, but in-line is preferable from the viewpoint of manufacturing cost. In particular, among these, it is preferable to form the thin film layer in-line during the film formation by the successive stretching method because the flexibility is high and the stability is good.

Next, a method for producing the softened polylactic acid resin stretched film of the present invention will be described.

The softened polylactic acid-based resin stretched film of the present invention is combined with an existing stretched film production method such as an inflation method, a sequential biaxial stretching method or a simultaneous biaxial stretching method, and a lamination method if necessary. Can be obtained.

For example, layer A and layer B are co-extruded in a B / A / B type and stretched in at least one direction, preferably in two directions, or by casting or laminating in layer B stretched in one direction or in two directions. Layer A laminated, B / A / B
After the constitution, a method of further stretching can be adopted if necessary. As a method of adding a predetermined amount of the plasticizer to the polylactic acid-based resin, the resin and the plasticizer may be mixed in advance, but the plasticizer is added to the resin melted in the extruder using a biaxial extruder. Is preferably added while measuring.

The method for producing the softened polylactic acid-based resin stretched film of the present invention comprises a layer A comprising a resin composition a'containing 10 to 200 parts by weight of a plasticizer p to 100 parts by weight of the polylactic acid-based resin a. After coextruding a layer B consisting of a resin composition b'containing 0 to 50 parts by weight of a plasticizer p'to 100 parts by weight of a crystalline polylactic acid-based resin b on both sides, the B / A / B type was uniaxially Alternatively, a production method characterized by biaxially stretching and forming a film is preferable because it has high flexibility and good stability.

The softened polylactic acid resin stretched film of the present invention can be used in various applications by taking advantage of its biodegradability, flexibility, heat resistance, flexibility durability and the like.
In particular, it is preferable to use it for a food packaging material such as a packaging wrap film, a compost bag, or an agricultural mulch film, since the function can be sufficiently exhibited.

[0039]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited thereto. (Measurement of melting point and glass transition temperature of film forming raw material) About 5 mg of a dried sample is precisely weighed, packed in a predetermined sample pan, and made by a differential scanning calorimeter (DSC) RDC220 manufactured by Seiko Instruments Inc. Based on JIS-K7122, the temperature was raised from -50 ° C to 250 ° C at 20 ° C / min (first run), held at 250 ° C for 5 minutes, and then-
The temperature was lowered to −50 ° C. at 20 ° C./min, the temperature was kept at −50 ° C. for 5 minutes, and then the temperature was raised from −50 ° C. to 250 ° C. at 20 ° C./min (second run). The glass transition temperature of the raw material and the melting point in the case of a crystalline resin were determined from the thermograph of the second run. (Measurement method of loop stiffness) (1) Loop stiffness (bending strength index) M in terms of film thickness 10 μm M: sample has a length of 1 in the measurement direction.
Cut into 5 cm and 1 cm in width, and bend stress M1 using a loop stiffness tester manufactured by Toyo Seiki Seisaku-sho, Ltd.
(ΜN) was measured. The loop length was 50 mm and the crushing distance was 5 mm. Bending stress measurement value M1 (μN),
From the sample thickness t (μm), the thickness 1
The loop stiffness M (μN / cm) of 0 μm was determined.

M = M1 × (10 / t) ³ was measured by using 10 samples having different sampling positions, and the average value was obtained. For the biaxially stretched film, the average value in the longitudinal direction and the width direction was used, and for the uniaxially stretched film, the average value in the longitudinal direction was used as the loop stiffness of the film. (2) Evaluation of biodegradability: Based on ASTM D5338-92, the film was put in sludge and the temperature was set to 58 ° C to evaluate biodegradability. The degree of biodegradation was calculated by the following formula.

Biodegradability = (BOD−B) / TOD × 100 BOD: (sludge + test substance) system biochemical oxygen demand (mg) B: sludge blank system biochemical oxygen demand (mg) TOD: Theoretical oxygen demand (mg) required when the test substance is completely oxidized Further, in Examples 2, 3, and 7 to 9, as a accelerating test for bleeding out of the plasticizer, before and after hot water treatment. The weight loss rate was measured. The physical properties shown in Table 2 are values measured by the following methods. (3) Weight loss rate after hot water treatment: Temperature 23 in advance
The weight of the film sample, which had been conditioned for 1 day or more in an atmosphere of ℃ and humidity of 65% RH, was measured, treated in distilled water of 90 ° C. for 30 minutes, and then conditioned again under the same conditions as before treatment. The weight was measured from. The weight reduction rate was calculated as the ratio [%] of the weight change (reduction) before and after the treatment to the weight before the treatment. (4) Biodegradable resin: polylactic acid resin 1 (PLA1):
L-polylactic acid having a weight average molecular weight of about 200,000 (optical purity 99
% Or more, melting point 175 ° C.) was used. Raw material is 5 at 120 ℃
It was dried with a vacuum dryer for a certain period of time to sufficiently remove water before use.

Polylactic acid resin 2 (PLA2): DL-polylactic acid having a weight average molecular weight of about 180,000 (optical purity 92%, melting point 135 ° C.) was used. The raw material was dried at 80 ° C. for 12 hours in a vacuum dryer to remove water sufficiently before use.

Polylactic acid resin 3 (PLA3): DL-polylactic acid (optical purity 82%, amorphous) having a weight average molecular weight of about 160,000 was used. The raw material was dried at 50 ° C. for 24 hours in a vacuum dryer to remove water sufficiently before use. (5) Plasticizer: Table 1 shows the plasticizers used as examples.

[0044]

[Table 1]

Example 1 Regarding a polylactic acid resin composition containing a plasticizer, PLA1 (molecular weight 200,000, melting point 170 ° C.) was melted at 220 ° C. in a twin-screw extruder in advance, and as shown in Table 1 as a plasticizer. The compound shown was supplied while being metered so as to have the addition amount shown in Table 2, a plasticizer was added, and the mixture was extruded as a gut and rapidly cooled in liquid nitrogen to obtain pellets. The thermal characteristics were measured by DSC, and the melting point and glass transition temperature were measured. The polymer stream for layer A was melted at 220 ° C. using the main extruder and PLA1 containing no plasticizer was melted at the sub extruder to form the polymer stream for layer B. Combine these two polymer streams B / A
After forming a / B type laminated structure (lamination ratio 1/8/1),
Extruded into a film at a T-die base temperature of 210 ° C, and
An unstretched film was prepared by casting on a drum cooled to ℃. The film obtained was continuously stretched 3 times in the longitudinal direction between heating rolls at 60 ° C., then stretched 3.5 times in the width direction at 65 ° C., and then heat-treated at 120 ° C. to wind the film.

As a result, a film having good film-forming property, good flexibility, and a transparent and smooth surface was obtained without any trouble such as adhesion to a drawing roll or blocking or blocking during film-forming. . Table 2 shows the evaluation results of loop stiffness and biodegradability.

[0047]

[Table 2]

Examples 2, 4, 5 Composition and ratio of layer A to film thickness shown in Table 2 (ratio of layer A to film thickness is a (%), b =
Assuming that (100-a) / 2, the stacking ratio of B / A / B is b
An unstretched film was prepared in the same manner as in Example 1 except for / a / b).

Further, the film was obtained by continuously stretching it 3 times in the longitudinal direction between heating rolls at 70 ° C., then stretching 3.5 times in the width direction at 75 ° C., and then heat-treating at 120 ° C. Wound up. A film having good film-forming property, good flexibility, and a transparent and smooth surface was obtained without troubles such as adhesion to a stretching roll and blocking during film-forming. Table 2 shows the evaluation results of loop stiffness and biodegradability.

Example 3 The composition shown in Table 2, the ratio of the layer A to the film thickness, and the polylactic acid charged into the sub-extruder were set to 5 in advance.
An unstretched film was prepared in the same manner as in Example 1 except that parts by weight of the plasticizer p1 were mixed by a twin-screw extruder and made into pellets. The film was continuously stretched 3 times in the longitudinal direction between heating rolls at 70 ° C., then stretched 3.5 times in the width direction at 75 ° C., and then heat-treated at 120 ° C. to wind the film. A film having good film-forming property, good flexibility, and a transparent and smooth surface was obtained without troubles such as adhesion to a stretching roll and blocking during film-forming. Table 2 shows the evaluation results of loop stiffness and biodegradability.

Example 6 Up to the production of an unstretched film, the same procedure as in Example 2 was carried out. A film obtained by continuously stretching the film 3 times in the longitudinal direction between heating rolls at 60 ° C. and then heat-treating at 120 ° C. was wound. I took it.
A film having good film-forming property, good flexibility, and a transparent and smooth surface was obtained without troubles such as adhesion to a stretching roll and blocking during film-forming. Table 2 shows the evaluation results of loop stiffness and biodegradability.

Example 7 An unstretched film was prepared in the same manner as in Example 2 except that PLA2 was used as the resin a. Continuously stretched 3 times in the longitudinal direction between heating rolls at 70 ° C, and then 75
The film obtained was stretched 3.5 times in the width direction at 0 ° C. and then heat-treated at 120 ° C. to wind the film. A film having good film-forming property, good flexibility, and a transparent and smooth surface was obtained without troubles such as adhesion to a stretching roll and blocking during film-forming. Table 2 shows the evaluation results of loop stiffness, biodegradability and weight loss rate after hot water treatment.

Example 8 Example 3 was repeated except that PLA3 was used as the resin a and the ratio of the layer A to the film thickness was changed to the constitution shown in Table 2.
An unstretched film was prepared in the same manner as in. 70 in succession
The film obtained was stretched 3 times in the longitudinal direction between heating rolls at .degree. C., then stretched 3.5 times in the width direction at 75.degree. C., and then heat-treated at 120.degree. A film having good film-forming property, good flexibility, and a transparent and smooth surface was obtained without troubles such as adhesion to a stretching roll and blocking during film-forming. Table 2 shows the evaluation results of loop stiffness, biodegradability and weight loss rate after hot water treatment.

Example 9 PLA3 was used as the resin a, p2 was used as the plasticizer p, p3 was used as the plasticizer p ', and the proportions of the plasticizers p and p'were changed, respectively. Example 3 except that the ratio to the thickness was changed to the configuration shown in Table 2.
An unstretched film was prepared in the same manner as in.

Further, the film was obtained by continuously stretching the film 3 times in the longitudinal direction between heating rolls at 70 ° C., then 3.5 times in the width direction at 75 ° C., and then heat-treating at 120 ° C. Wound up. A film having good film-forming property, good flexibility, and a transparent and smooth surface was obtained without troubles such as adhesion to a stretching roll and blocking during film-forming. Table 2 shows the evaluation results of loop stiffness, biodegradability and weight loss rate after hot water treatment.

Comparative Example 1 An unstretched film was prepared in the same manner as in Example 1 except for the composition shown in Table 2. The film was continuously stretched 3 times in the longitudinal direction between heating rolls at 70 ° C., then stretched 3.5 times in the width direction at 75 ° C., and then heat-treated at 120 ° C. to wind the film. The film-forming property was good without problems such as adhesion to a stretching roll or blocking or blocking during film-forming, but a hard film without flexibility was obtained.

Comparative Examples 2 and 3 An unstretched film was prepared in the same manner as in Example 1 except for the composition shown in Table 2. In the stretching in the longitudinal direction, if the stretching temperature is lowered to such an extent that sticking of the stretching roll does not occur (about 20 to 30 ° C.), the stretching cannot be carried out, and the stretching temperature (6
When the stretching temperature was raised to 0 ° C. or higher), the film adhered to the heating roll and the stretching could not be performed.

Comparative Example 4 An unstretched film was prepared in the same manner as in Example 1 except that only the main extruder was used and the composition shown in Table 2 was used. In the longitudinal stretching, if the stretching temperature is lowered to such an extent that sticking of the heating roll does not occur (about 20 to 30 ° C.), the stretching cannot be performed, and if the stretching temperature is raised to a temperature (60 ° C. or higher), the heating roll becomes The film was sticky and could not be stretched.

Comparative Example 5 A stretched film was prepared in the same manner as in Example 2 except that the ratio of layer A to the whole film was 25%. The film-forming property was good without problems such as adhesion to a stretching roll or blocking or blocking during film-forming, but a hard film without flexibility was obtained.

Comparative Example 6 An unstretched film was prepared in the same manner as in Example 2 except that the amount of the plasticizer added to the resin composition a ′ was 220 parts. A biaxial extruder was used to prepare the plasticizer and the resin a. At the time of extruding, the plasticizer which could not be completely dispersed in the resin was extruded together with the resin from the extruder die, so that the resin composition a ′ could not be collected.

[0061]

According to the present invention, there are no troubles in the film forming process such as film rupture and roll winding, and there is no problem such as blocking even after the film forming, and the transparency, heat resistance and bleed-out resistance are excellent. A flexible biodegradable stretched film and a method for producing the same are provided. The film can be suitably used particularly for food packaging films, compost bags, and agricultural mulch films.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29L 9:00 B29L 9:00 (72) Inventor Futoshi Sasamoto 1-1-1, Sonoyama, Otsu, Shiga Prefecture Toray Stock company Shiga business site F-term (reference) 2B024 DB01 DB07 4F100 AK41A AK41B AK41C AK41H AK53A AK53B AK53H AK54A AK54B AK54H BA03 BA06 BA10 JA BA07 JA05 JA05 JA05 JA05 JA05 JA05A07 GB23B07CA05 JA04A07B23 JA04A07B23 JA04A07EJ23 202 EJ37BEJA202EJ04202 EJ37B EJ37B JJ03 JK13 JK20 JL00 JN01 YY00A YY00B YY00C YY00H 4F210 AA24 AA49 AB07 AB19 AG01 AG03 AH01 QC06 QG01 QG15 QG18

Claims (9)

[Claims] 1. A layer A comprising a resin composition a ′ containing 10 to 200 parts by weight of a plasticizer p with respect to 100 parts by weight of a polylactic acid resin a, and a plasticizer p ′ with respect to 100 parts by weight of a crystalline polylactic acid resin b. Resin composition b'containing 0 to 50 parts by weight
A layer B consisting of a B / A / B type is laminated, the thickness of the layer A is 30 to 99% of the total thickness of the film, and the layer B is stretched in at least one direction. Polylactic acid resin stretched film. (However, in the above,
b ′ has a glass transition temperature higher than that of a ′ by 3 ° C. or higher, and b ′ has a glass transition temperature of 30 ° C. or higher, and p may be the same as or different from p ′. ) 2. The softened polylactic acid resin stretched film according to claim 1, wherein the polylactic acid resin a has a melting point of less than 150 ° C. 3. The softened polylactic acid resin stretched film according to claim 1, wherein the polylactic acid resin a has a melting point of 150 ° C. or higher. 4. The plasticizers p and p'have a molecular weight of 300 to
10000 epoxidized soybean oil, epoxidized linseed oil,
Epoxidized linseed oil fatty acid butyl, adipic acid-based aliphatic polyester, acetyl citrate tributyl, acetylricinoleic acid ester, sucrose fatty acid ester, sorbitan fatty acid ester, adipic acid dialkyl ester,
The softened polylactic acid-based resin stretched film according to any one of claims 1 to 3, which is either bis (alkyldiglycol) adipate or polyethylene glycol having a molecular weight of 300 to 30,000. 5. The softened polylactic acid-based resin stretched film according to claim 1, which has a loop stiffness of 10 to 350 μN / cm in terms of film thickness of 10 μm. 6. The softened polylactic acid resin stretched film according to any one of claims 1 to 5, which is used as a food packaging film. 7. The softened polylactic acid resin stretched film according to any one of claims 1 to 5, which is used as a compost back. 8. The softened polylactic acid resin stretched film according to any one of claims 1 to 5, which is used as an agricultural mulch film. 9. A plasticizer for 100 parts by weight of a crystalline polylactic acid resin b on both sides of a layer A made of a resin composition a ′ containing 10 to 200 parts by weight of a plasticizer p for 100 parts by weight of a polylactic acid resin a. A layer B made of a resin composition b ′ containing 0 to 50 parts by weight of p ′ is coextruded into a B / A / B type, and then uniaxially or biaxially stretched to form a film. A method for producing a stretched film of a polylactic acid resin. (However, in the above, b ′ has a glass transition temperature higher by 3 ° C. or higher than a ′, the glass transition temperature of b ′ is 30 ° C. or higher, and p may be the same as or different from p ′.)