JP2001219522A - Polylactic acid laminated biaxially stretched film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid laminated biaxially stretched film having heat salability and sufficient heat shrinkage resistance. SOLUTION: This polylactic acid laminated biaxially stretched film comprises at least two layers based on a polylactic acid polymer. A relation between the D-lactic acid containing ratio Da (%) of the crystalline polylactic acid polymer constituting one layer of the laminated film and the D-lactic acid containing ratio Db (%) of the polylactic acid polymer constituting the other one layer of the laminated film is Da <=7 and Db-Da >=3, and the other one layer is constituted of at least one outermost layer of the laminated film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a biodegradable polylactic acid-based laminated biaxially stretched film having good heat sealing properties.

[0002]

2. Description of the Related Art Conventionally, cellophane has been widely used as a packaging film, used for fiber packaging, confectionery packaging, medicine bags, etc., and has both moisture-proof and heat-sealing properties by coating polyvinylidene chloride on its surface. Used as a film. This cellophane is characterized by its degradability because it uses pulp obtained from wood as the main raw material.However, a manufacturing method called the casting method, in which pulp is chemically treated and dissolved once, and then formed into a film, is used. As a result, low productivity is required, and investment is needed to improve facilities in terms of wastewater treatment. For this reason, these days, most of the films are replaced by films made of polyethylene, polyolefin, or aromatic polyester made of petroleum-derived materials having low production costs. This petroleum-derived polyethylene, polyolefin and aromatic polyester are heat-resistant by various processing methods,
Films with shrinkage, heat sealability, printability, moisture resistance, antifogging properties, etc. have been produced, and are widely used not only for packaging materials but also as industrial materials.

[0003] However, the above cellophane has the property of not absorbing scents of perfume, tea, coffee and the like, is reviewed as a packaging material, and has a large amount of use while having the above-mentioned problems. In addition, a film made of a petroleum-derived material generates a large amount of heat during combustion, and may damage the combustion furnace during the combustion process. Furthermore, they are often landfilled, but remain almost undecomposed due to their scientific and biological stability, causing problems such as shortening the life of the landfill. For this reason, what decomposes in soil and water like cellophane is desired, and much research has been made.

[0004] Polylactic acid is an example of a material that is being developed today and decomposes in soil and water, that is, a biodegradable material. This polylactic acid has a calorific value of less than half that of polyethylene, and hydrolyses naturally in soil and water, and then becomes a harmless degradation product by microorganisms. At present, studies are being made to obtain molded articles, specifically films, sheets and containers such as bottles, using polylactic acid.

By the way, a non-stretched film of polylactic acid is
It is a brittle material with only a few percent elongation. For this reason, unstretched thin films are not practical for packaging. on the other hand,
By stretching polylactic acid uniaxially or biaxially,
It is already known that the film is oriented to increase the elongation, and further heat-treated to obtain a highly practical film with suppressed heat shrinkage. Another characteristic of the film made of the polylactic acid-based polymer is that it does not absorb scent components like cellophane. For this reason, it is expected that a polylactic acid-based film will be used in place of the conventionally used polyolefin-based heat sealant. This is because the polyolefin-based sealant material is superior in that it can be used with peace of mind, while the fragrance component may be sorbed and the contents may change depending on the packaging object. .

When used as a heat sealant,
Preferred characteristics include (1) an appropriate sealing temperature range, (2) easy lamination with other plastic films, paper, and metal foil, and (3) low shrinkage during sealing.

[0007] The above (1) can be used in a temperature range when it is compared with a sealant material made of polyethylene which is widely used today. This is because it can be flowed as it is to a bag making machine equipped with the above, and there is no need to introduce new equipment, which is economical. The sealing temperature range of polyethylene is as high as 130 ° C. or higher, and as low as 80 ° C. or higher, depending on the thickness, and serves as a guide as a heat sealant material. The above (2) indicates that it is necessary to be able to perform lamination with a known apparatus usually used in a dry lamination method and a wet lamination method. The laminating apparatus unwinds one of the films while applying a predetermined tension, applies heat as needed, applies an adhesive, and unwinds the other film while similarly applying a predetermined tension. Is an apparatus for laminating and bonding the films through an adhesive. Therefore, it is important that the film being unwound is not broken by the tension or a delicate change of the tension, and that the film size or the like does not change by the applied heat.

[0008]

In the case of a polylactic acid-based film, since a non-stretched film is brittle as described above, it is preferable to use a stretched and oriented polylactic acid-based film from the viewpoint of lamination suitability. However, in order to obtain a sufficient sealing strength such as a bag, for example, it is usually necessary to heat the film to a temperature range where the film is melted. The product does not satisfy the requirement of 3), and wrinkles, undulations, curls, and the like due to shrinkage are observed in the completed product, and if it is severe, the product may not be formed at all.

Accordingly, an object of the present invention is to provide a polylactic acid-based stretched film having heat sealing properties and sufficient heat shrink resistance.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a laminated film comprising at least two layers containing a polylactic acid-based polymer as a main component, wherein a crystalline polylactic acid-based material constituting one layer in the laminated film is provided. D-lactic acid content ratio Da of polymer
(%) And the content ratio Db (%) of D-lactic acid in the polylactic acid-based polymer constituting another layer of the laminated film is Da ≦ 7 and Db−Da> 3. The problem was solved by forming another layer from at least one outermost layer of the laminated film.

Since the layer made of the crystalline polylactic acid-based polymer having a predetermined D-lactic acid content is formed as one layer, shrinkage deformation hardly occurs and heat resistance shrinkage can be exhibited. In addition, since a layer made of a polylactic acid-based polymer having a predetermined D-lactic acid content is used as another layer, the layer has sufficient heat sealing properties, and the obtained laminate can be used as a heat sealant material. .

[0012]

Embodiments of the present invention will be described below.

The polylactic acid-based laminated biaxially stretched film according to the present invention is a laminated film composed of at least two layers containing a polylactic acid-based polymer as a main component.

The above-mentioned polylactic acid-based polymer is a polymer obtained by polycondensing a monomer containing lactic acid as a main component. The lactic acid includes two kinds of optical isomers, L-lactic acid and D-lactic acid, and the crystallinity differs depending on the ratio of these two types of structural units.
For example, the ratio of L-lactic acid to D-lactic acid is approximately 80: 2
There is no crystallinity in the random copolymer of 0 to 20:80,
It becomes a transparent complete non-crystalline polymer that softens near the glass transition point of 60 ° C. On the other hand, the ratio of L-lactic acid to D-lactic acid is approximately 100: 0 to 80:20, or 20:80 to 0:10.
The 0 random copolymer has crystallinity. The degree of crystallinity is determined by the ratio of L-lactic acid and D-lactic acid. The glass transition point of this copolymer is 60
It is a polymer of about ° C. This polymer becomes an amorphous material having excellent transparency by quenching immediately after melt extrusion, and becomes a crystalline material by cooling slowly. For example, a homopolymer composed of only L-lactic acid or D-lactic acid is a semi-crystalline polymer having a melting point of 180 ° C. or higher.

The polylactic acid-based polymer according to the present invention has D
It is a polymer of a lactic acid unit and an L-lactic acid unit, and may contain other hydroxycarboxylic acid units as a small amount of a copolymer component, or may contain a small amount of a chain extender residue.

As the polymerization method, known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed. For example, in the polycondensation method, L-lactic acid or D-lactic acid or a mixture thereof can be directly dehydrated and polycondensed to obtain a polylactic acid having an arbitrary composition.

In the ring-opening polymerization method (lactide method), lactide, which is a cyclic dimer of lactic acid, is converted to polylactic acid by using a selected catalyst while using a polymerization regulator or the like as necessary. be able to.

The other hydroxycarboxylic acid units copolymerized with polylactic acid include optical isomers of lactic acid (L-
D-lactic acid for lactic acid, L-lactic acid for D-lactic acid), glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3- Bifunctional aliphatic hydroxycarboxylic acids such as dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid and 2-hydroxycaproic acid, and caprolactone;
Lactones such as butyrolactone and valerolactone are exemplified.

If necessary, non-aliphatic dicarboxylic acids such as terephthalic acid and / or
Alternatively, a non-aliphatic diol such as an ethylene oxide adduct of bisphenol A, or lactic acid and / or a hydroxycarboxylic acid other than lactic acid may be used.

The preferred range of the weight average molecular weight of the polylactic acid polymer used in the present invention is from 60,000 to 70
10,000, more preferably 80,000 to 400,000, particularly preferably 100,000 to 300,000. If the molecular weight is too small, practical physical properties such as mechanical properties and heat resistance are hardly exhibited, and if it is too large, the melt viscosity is too high and molding processability is poor.

One layer (hereinafter, referred to as "first layer") in the laminated film according to the present invention is composed of a polylactic acid-based polymer and is preferably crystalline. Also,
Another layer of the laminated film (hereinafter, referred to as “second layer”) is composed of a polylactic acid-based polymer.

The content ratio of D-lactic acid in the crystalline polylactic acid polymer constituting the first layer (hereinafter referred to as "Da").
(%) And D of the polylactic acid-based polymer constituting the second layer.
-The lactic acid content ratio (hereinafter referred to as "Db") (%) preferably has a relationship of Da≤7 and Db-Da> 3.

That is, since the first layer is a support layer, the ratio (Da) of D-lactic acid in the crystalline polylactic acid-based polymer constituting the first layer is preferably 7% or less, more preferably 5% or less. Is more preferred. If it exceeds 7%, the crystallinity of the support layer is low, heat resistance cannot be obtained, and it tends to shrink and deform when heated.

Since the second layer is a heat-sealing layer, the proportion (Db) of D-lactic acid in the polylactic acid-based polymer constituting the second layer may be higher than Da by 3%. preferable. When the difference is 3% or less, both the crystallinity and the melting point are close to the polylactic acid-based polymer constituting the first layer, and it is necessary to seal at a high temperature. That is, in the case of a high-temperature seal, the support layer is also heated to cause heat shrinkage, which causes a problem such as waving or wrinkling of the product. Therefore, in order to lower the crystallinity and the melting point as compared with the support layer, it is preferable to set the above ranges.

The crystalline polylactic acid polymer constituting the first layer and the polylactic acid polymer constituting the second layer are a mixture of two or more different types of polylactic acid polymers. You may. In this case, the D-lactic acid ratios Da and Db are two or more types of D-lactic acid-based polymers, respectively.
It is an average value calculated from the mixing ratio of lactic acid.

Since the second layer has heat sealing properties, it constitutes at least one outermost layer of the laminated film.

The structure of the laminated film according to the present invention is as follows:
A three-layer structure of a second layer / first layer / second layer having a first layer having high heat resistance as an intermediate layer and a second layer having heat sealing properties on both surfaces is excellent in versatility. Also, the second layer / first layer /
Five-layer structure of second layer / first layer / second layer, and second layer / first layer
A multi-layer structure of layer / second layer / first layer /.../ second layer may be used. In consideration of the curl and heat resistance of the film, a two-layer structure of a second layer / first layer, or a four-layer structure of a second layer / first layer / second layer / first layer, in which only one side is a heat sealing layer. It may have a multi-layer structure of second layer / first layer /.../ first layer. The thickness of the second layer constituting the outermost layer of these final multilayer films is 2 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and the thickness of the final laminated film is 10 to 100 μm, preferably Is 15 to 80 μm.

Further, an adhesive layer, an adhesive resin layer, a recycled resin layer, or a resin layer having a thickness of 10 μm or less, preferably 5 μm or less, between the first and second layers within a range not to impair the effects of the present invention. An intermediate layer between the first layer and the second layer may be laminated.

The crystalline polylactic acid-based polymer constituting the first layer may be a mixture containing the polylactic acid-based polymer constituting the second layer. There may be.

To the polymer used in the present invention, a heat stabilizer, a light stabilizer, a light absorber, a lubricant, a plasticizer, an inorganic filler, a colorant, a pigment and the like are added for the purpose of adjusting various physical properties. You can also.

As a lamination method, a commonly used method can be adopted. For example, a method of so-called co-extrusion in which a plurality of extruders are connected to a single die in a feed block type or a multi-manifold type, and another type of film is heated and pressed on the surface of an unwound mixed film using a roll or a press plate. There is a way.

As a method for producing a biaxially stretched film containing a polylactic acid-based polymer as a main component, a sheet or a cylinder extruded from a T-die, an I-die, a round die or the like is cooled with a cooling cast roll, water, compressed air or the like. Or the like, followed by solidification in a state close to non-crystal, followed by biaxial stretching by a roll method, a tenter method, a tubular method, or the like.

Usually, in the production of a biaxially stretched film, a sequential biaxial stretching method in which longitudinal stretching is performed by a roll method and a transverse stretching is performed by a tenter method, and a simultaneous biaxial stretching method in which longitudinal and lateral stretching are simultaneously performed by a tenter are general.

The stretching conditions include a stretching temperature of 55 to 90.
° C, preferably 65 to 80 ° C, a longitudinal stretching ratio of 1.5 times, preferably 2 to 4 times, a transverse stretching ratio of 1.5 to 5 times, preferably 2 to 4 times, and a stretching speed of 10 to 100000% / min. Preferably it is 100 to 10000% / min. However, these suitability ranges vary depending on the composition of the polymer and the heat history of the unstretched sheet, so the strength of the film,
It is determined as appropriate while taking the elongation into consideration.

When the stretching ratio and the stretching temperature are not in the above ranges, the thickness accuracy of the obtained film is remarkably reduced, and this tendency is particularly remarkable in the film which is heat-treated after stretching. Such thickness fluctuations can be caused by printing a film, or by using other films or metal thin films,
In secondary processing such as lamination with paper, and further, bag making and the like, it is a factor that causes a product to have a bad appearance such as wrinkles and undulations.

In terms of suppressing thermal shrinkage of the film, heat treatment is performed while holding the film. In general, in the tenter method, the film is stretched while holding the film with a clip, so that the film is immediately heat-treated. In the secondary processing of the film, problems such as shrinkage of the film during processing are likely to occur.

For the purpose of adjusting various physical properties, a heat stabilizer, a light stabilizer, a light absorber, a lubricant, a plasticizer, an inorganic filler, a colorant, a pigment, and the like can be added to each of the above layers.

The shrinkage of the obtained polylactic acid-based laminated biaxially stretched film is preferably 5% or less after a water bath at 80 ° C. for 1 minute. If it exceeds 5%, factors that cause the appearance of the film to be wrinkled, wavy, etc., are badly caused.

The polylactic acid-based laminated biaxially stretched film produced according to the present invention is a polylactic acid-based film having a reduced shrinkage as much as possible and having a heat sealing property.
When this biaxially stretched film is used as a packaging material, it is necessary to satisfy the quality in the following cases. For example, for individual packaging and pillow packaging, it is necessary to heat seal the back affixed portion, the folded portion, and the like so that the packaging cannot be easily unraveled. In some cases, the film is heat-sealed to form a bag, the non-packaged body is put in this bag, and the opening is also heat-sealed to completely seal the bag. In such a case, the heat sealing strength needs to be 1 N or more with respect to the film 15 mm width. If it is less than 1N, the sealing strength of the film is low, and even if the package is heat-sealed, if external force or impact is applied, the package is easily released and the purpose of use is not achieved.

The polylactic acid-based laminated biaxially stretched film according to the present invention is suitable for individual packaging, pillow packaging, bag making, etc., in which conventional biaxially oriented polypropylene films and biaxially oriented polyester films have been used, and It is possible to provide a biodegradable polylactic acid-based laminated biaxially stretched film that can be a heat sealant layer when another plastic film is laminated, and can be used for fabric packaging, vegetable packaging, chocolate, caramel, candy, etc. There is a use as a film suitable for individual wrapping of confectionery, an overlap of an audio tape, an audio disk and the like. Further, it can be used by laminating it with another plastic film, paper, aluminum foil or the like.

[0041]

The present invention is not limited by the following examples. First, methods for measuring physical properties in Examples and Comparative Examples are shown below.

(1) Stretching ratio ・ Longitudinal stretching ratio = flow rate of film after longitudinal stretching / flow rate of original sheet before longitudinal stretching ・ Stretching ratio in the horizontal direction is determined by subtracting the width of the original sheet before longitudinal stretching from the clip of the tenter. The value obtained by subtracting the width of the part to be gripped from
This is a value obtained by assigning the length obtained by subtracting the width of the portion held by the clip from the width obtained after the transverse stretching. Lateral stretching ratio = {(film width after stretching) − (width held by clip)} / {(width of original sheet before stretching) − (width held by clip)}

(2) Shrinkage The film was cut into a length of 100 mm and a width of 100 mm along the MD and TD of the film, immersed in a hot water bath at 80 ° C. for 1 minute, and the dimensions after shrinkage were measured. The heat shrinkage was calculated. The shrinkage is measured along the stretching direction. In this test, both MD and TD are in the test direction. Shrinkage (%) = {(dimension before shrinkage) − (dimension after shrinkage)} × 100 / (dimension before shrinkage)

(3) Heat Seal Strength and Finish A film cut into a size of 170 mm MD × 130 mm TD is prepared, folded in two directions, overlapped so that the surfaces serving as a heat sealant material are in contact with each other, and sealed with a heat seal bar. A two-sided seal bag whose bottom was folded along the MD was produced. Sealing conditions are 80, 100 and 120 ° C
And then allowed to cool. The width of the heating bar is 10 mm and the pressure is 1.5 kgf / cm ² .

After sealing, the bag was observed, and those markedly marked with wrinkles, undulations, uneven shrinkage, etc. were marked with x. On the other hand, although these were slightly observed, those which were sufficiently finished as bags were marked with "O". The heat sealing strength was determined by a method described in JIS Z 1711 “Bag made of polyethylene film” at a width of 15 mm. Therefore, the film was cut to a width of 15 mm so that one end was on the seal side and perpendicular to the longitudinal direction of the seal (that is, along the MD of the film). The cut film was spread, and held by a chuck of a tensile tester to perform a test. Poorly finished bags have relatively poor seal strength and tend to vary. When the film was significantly shrunk, it could not be measured, and was indicated as unmeasurable.

(4) Comprehensive Evaluation In the above evaluations of shrinkage, heat seal strength, and finish, all of ○ were evaluated as ○, and at least one having X was evaluated as X. (Constituent Resin of Laminate) As a resin constituting the laminate, the first component shown in Table 1 alone or a mixture of the first component and the second component was used. The D-lactic acid ratio in the case of the mixture was calculated as an average value from both weight fractions.

[0047]

[Table 1]

Example 1 L-lactic acid: D-lactic acid = 80:
Polylactic acid 2 having 20 structural units, having a glass transition point (Tg) of 52 ° C. and 80% polylactic acid, having a structural unit of L-lactic acid: D-lactic acid = 95: 5, and having a glass transition point (Tg) of 56 ° C.
0%, and a total of 100 parts by weight of polylactic acid (Db =
17%, average particle size dried on resin 6) of Table 1 1.4 μm
0.1 part by weight of granular silica (trade name: Sylysia 100, manufactured by Fuji Silysia Chemical Ltd.) is mixed and extruded as a front and back layer from a multi-manifold type die at 220 ° C. using a 25 mmφ coaxial twin screw extruder. did.

Further, L-lactic acid: D-lactic acid = 99.5:
Polylactic acid polymer having a structural unit of 0.5 (Da = 0.5%) and a glass transition point (Tg) of 58 ° C. (resin 1 in Table 1)
Was extruded as an intermediate layer from the die using a 40 mmφ single screw extruder.

The thickness ratio of the surface layer, the intermediate layer and the back layer is 1:10:
The discharge amount of the molten resin was adjusted to be 1. This co-extruded sheet is rapidly cooled by a casting roll at about 43 ° C.
An unstretched sheet was obtained. Subsequently, it is 2.6 at 76 ° C in the longitudinal direction.
The film was stretched 3.2 times at a temperature of 72 ° C. with a tenter in the width direction. The temperature of the heat treatment zone in the tenter was set to 130 ° C. to produce a heat-treated film. The discharge amount of the molten resin from the extruder and the line speed were adjusted so that the film thickness was approximately 30 μm on average. Table 2 shows the evaluation results of the films.

(Examples 2 and 3 and Comparative Examples 1 to 5) As shown in Table 2 or Table 3, as shown in Table 2, polylactic acid polymers having different L-lactic acid and D-lactic acid (corresponding to each resin shown in Table 1) Were extruded into a surface layer, an intermediate layer and a back layer so as to have a predetermined thickness ratio as in Example 1, biaxially stretched and then heat-treated to prepare a film. Tables 2 and 3 show the evaluation results of each film.

In Comparative Example 2, the film was broken during the heat treatment. In Comparative Examples 1 and 4, the appearance of the sealed bag was poor, and a good finished bag could not be obtained. Further, Comparative Examples 3 and 5 could not obtain sufficient sealing strength to take a form as a bag. Table 2 or 3 shows the evaluation results of each film.

Example 4 L-lactic acid: D-lactic acid = 80:
Polylactic acid 2 having 20 structural units, having a glass transition point (Tg) of 52 ° C. and 80% polylactic acid, having a structural unit of L-lactic acid: D-lactic acid = 95: 5, and having a glass transition point (Tg) of 56 ° C.
0%, and a total of 100 parts by weight of polylactic acid (Db =
17%, average particle size dried on resin 6) of Table 1 1.4 μm
0.1 part by weight of granular silica (trade name: Sylysia 100, manufactured by Fuji Silysia Chemical Ltd.) was mixed and mixed with a 25 mmφ coaxial twin-screw extruder to form a surface layer of 210 ° C. from a two-layer multi-manifold type die. And extruded.

Further, L-lactic acid: D-lactic acid = 99.5:
Polylactic acid polymer having a structural unit of 0.5 (Da = 0.5%) and a glass transition point (Tg) of 58 ° C. (resin 1 in Table 1)
Dried silica having an average particle size of 1.4 μm (trade name:
(Sylysia 100, manufactured by Fuji Silysia Chemical Ltd.) 0.1
Parts by weight were mixed and extruded as an intermediate layer from the above die at 210 ° C. using a 40 mmφ single screw extruder. Since the obtained laminate has a two-layer structure, the intermediate layer directly forms the back layer.

The discharge amount of the molten resin was adjusted such that the thickness ratio of the laminate was 1: 2 for the surface layer: intermediate layer. This coextruded sheet was quenched with a casting roll at about 42 ° C. to obtain an unstretched sheet. Then 75 ° C in the longitudinal direction
And then stretched 2.6 times at a temperature of 74 ° C. with a tenter in the width direction. The temperature of the heat treatment zone in the tenter was set to 135 ° C. to produce a heat-treated film. The discharge amount of the molten resin from the extruder and the line speed were adjusted so that the film thickness was about 15 μm on average. Table 2 shows the evaluation results of the films.

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

The laminate according to the present invention has a support layer having heat shrink resistance and a heat seal layer having heat seal properties.

The laminate according to the present invention is suitable for individual wrapping, pillow wrapping, bag making and the like in which a biaxially stretched polypropylene film or a biaxially stretched polyester film has been used, and a laminate of another plastic film. In this case, a biodegradable polylactic acid-based laminated biaxially stretched film serving as a heat sealant layer can be provided.

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Claims (1)

[Claims] 1. A laminated film composed of at least two layers containing a polylactic acid-based polymer as a main component, wherein the content ratio of D-lactic acid in the polylactic acid-based polymer constituting one layer in the laminated film is Da. (%) And D- of the polylactic acid-based polymer constituting another layer of the laminated film.
The relation of the lactic acid content ratio Db (%) is as follows: Da ≦ 7 and Db−Da> 3, and the other one layer is a polylactic acid-based laminated biaxial member constituting at least one outermost layer of the laminated film. Stretched film.