JP2006289986A - Polylactic acid-based laminated biaxially drawn film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid-based film having sufficient heat-shrinking resistance together with heat seal property. <P>SOLUTION: A laminated film, which comprises at least two layers having a polylactic acid polymer as a principal component, satisfies following relationships: Da≤7 and Db-Da>3; wherein Da is a proportion(%) of D-lactic acid content in the crystalline polylactic acid polymer constituting one of the layers in the laminated film, and Db is a proportion(%) of D-lactic acid content in a polylactic acid polymer constituting another layer in the laminated film. Said another layer is composed of at least one of the outermost layers of the laminated film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Conventionally, cellophane has been widely used as a packaging film, used for textile packaging, confectionery packaging, medicine bags, etc., and also used as a film having moisture resistance and heat sealability by coating polyvinylidene chloride on the surface. It was. This cellophane is characterized by its degradability because it is made from pulp that can be extracted from wood. However, the cellophane has a degradability. Therefore, the productivity is low and an investment is required to prepare facilities from the viewpoint of wastewater treatment. For this reason, today, most films are replaced with films made of polyethylene, polyolefins and aromatic polyesters, which are made of petroleum-derived raw materials with low production costs. This petroleum-derived polyethylene, polyolefin and aromatic polyester are manufactured with various processing methods to give heat resistance, shrinkage, heat sealability, printability, moisture proof and antifogging properties, etc. It is widely used not only as a material but also as an industrial material.

  However, the cellophane has a characteristic that it does not sorb perfume, tea, coffee, and other fragrances, has been reviewed as a packaging material, and has a large amount of use while having the above problems. In addition, films made of petroleum-derived raw materials have a large amount of heat generated during combustion, and there is a risk of damaging the combustion furnace during the combustion process. In addition, it is often landfilled, but due to its scientific and biological stability, it is hardly decomposed and remains, causing problems such as shortening the life of the landfill. For this reason, what decomposes | disassembles in soil and water like cellophane is desired, and many researches are made | formed.

  An example of a material that is being developed today and decomposes in soil and water, that is, a biodegradable material, is polylactic acid. This polylactic acid has a heat of combustion less than half that of polyethylene, and is naturally hydrolyzed in soil and water, and then becomes a harmless decomposition product by microorganisms. Currently, studies are being made to obtain molded articles, specifically containers such as films, sheets and bottles, using polylactic acid.

  By the way, an unstretched film of polylactic acid is a brittle material having only a few percent elongation. For this reason, an unstretched thin film is not practical for packaging. On the other hand, it is already known that a polylactic acid is stretched uniaxially or biaxially so that the film is oriented and stretched, and a heat-shrinkable and highly practical film can be obtained by heat treatment. . Further, as a feature of a film made of a polylactic acid polymer, there is a feature that a scent component is not sorbed like cellophane. For this reason, it is expected to use a polylactic acid film in place of the conventionally used polyolefin heat sealant material. This is because polyolefin-based sealant materials are advantageous in that they can be used with peace of mind, while depending on the object to be packaged, these scent components may be sorbed and the contents may change. .

When used as a heat sealant material, as a preferable characteristic,
(1) The seal temperature range is moderate.
(2) Easy to laminate with other plastic film, paper, metal foil,
(3) The shrinkage is low at the time of sealing.

  The above (1) can be used in a temperature range when compared with a polyethylene sealant material that is widely used today, and is equipped with a conventionally used secondary processing device, specifically a heat seal device. This is because it can flow directly to the bag making machine, and it is not necessary to introduce new equipment, which is economical. Depending on the thickness, the sealing temperature range of polyethylene is as high as 130 ° C. or higher, and as low as 80 ° C. or higher, which is a standard as a heat sealant material. The above (2) indicates that it is necessary to be able to be laminated by a known apparatus usually used in the dry laminating method and the wet laminating method. The laminating apparatus unwinds one film while applying a predetermined tension, applies heat after applying heat as necessary, and unwinds the other film while applying a predetermined tension. It is the apparatus which superposes | stacks the film of this through an adhesive agent, and crimps | bonds. Therefore, it is important that the film in the middle of unwinding does not break due to the tension or a slight change in the tension, and that the film size or the like does not change due to the applied heat.

  In the case of a polylactic acid-based film, the non-stretched film is fragile as described above. Therefore, it is preferable to use a stretched and oriented polylactic acid-based film in view of suitability for lamination. However, in order to obtain a sufficient sealing strength, for example, in a bag, it is usually necessary to heat to a temperature range where the film melts. However, when sealed under such conditions, the stretched film shrinks and the above ( Wrinkles due to shrinkage, undulations, curls, etc. are seen in the finished product that does not meet the requirement of 3), and if it is severe, it may not become a product at all.

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

The present invention is a laminated film comprising at least two layers mainly composed of a polylactic acid-based polymer, and the content ratio of D-lactic acid in the crystalline polylactic acid-based polymer constituting one layer in the laminated film The relationship between Da (%) and the D-lactic acid content ratio Db (%) of the polylactic acid polymer constituting the other layer of the laminated film is as follows:
Da ≦ 7 and Db-Da> 3
Thus, the above-mentioned problem is solved by configuring the other one layer from at least one outermost layer of the laminated film.

  Since the layer made of a crystalline polylactic acid polymer having a predetermined D-lactic acid content is one layer, shrinkage deformation is unlikely to occur and heat shrinkage resistance can be exhibited. Moreover, since the layer which consists of a polylactic acid-type polymer which has a predetermined D-lactic acid content rate is made into another one layer, it has sufficient heat seal characteristics, and the obtained laminated body can be used as a heat sealant material. .

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

  In addition, the laminate according to the present invention is suitable for individual packaging, pillow packaging, bag making, etc., in which a conventional biaxially stretched polypropylene film or biaxially stretched polyester film has been used, and when other plastic films are laminated. Can provide a biodegradable polylactic acid-based laminated biaxially stretched film serving as a heat sealant layer.

  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 mainly composed of a polylactic acid-based polymer.

  The polylactic acid polymer is a polymer formed by condensation polymerization of a monomer mainly composed of lactic acid. The lactic acid includes two kinds of optical isomers, L-lactic acid and D-lactic acid, and the crystallinity is different depending on the ratio of these two kinds of structural units. For example, a random copolymer having a ratio of L-lactic acid to D-lactic acid of approximately 80:20 to 20:80 has no crystallinity, and becomes a transparent, completely amorphous polymer that softens at around a glass transition temperature of 60 ° C. On the other hand, a random copolymer having a ratio of L-lactic acid to D-lactic acid of approximately 100: 0 to 80:20 or 20:80 to 0: 100 has crystallinity. The crystallinity is determined by the ratio of L-lactic acid and D-lactic acid, but the glass transition point of this copolymer is a polymer of about 60 ° C. as described above. This polymer becomes an amorphous material with excellent transparency by being rapidly cooled after melt extrusion, and becomes a crystalline material by slowly cooling. For example, a homopolymer composed of only L-lactic acid or only D-lactic acid is a semicrystalline polymer having a melting point of 180 ° C. or higher.

  The polylactic acid polymer according to the present invention is a polymer of D-lactic acid units and L-lactic acid units, and may contain other hydroxycarboxylic acid units as a small amount copolymerization component, and a small amount of chain extender. It may contain residues.

  As the polymerization method, a known method such as a condensation polymerization method or a ring-opening polymerization method can be employed. For example, in the condensation polymerization method, polylactic acid having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of L-lactic acid, D-lactic acid or a mixture thereof.

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

  Examples of the other hydroxycarboxylic acid units copolymerized with polylactic acid include optical isomers of lactic acid (D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid), glycolic acid, Such as 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, 2-hydroxycaproic acid, etc. Examples thereof include lactones such as bifunctional aliphatic hydroxycarboxylic acid, caprolactone, butyrolactone, and valerolactone.

  Further, if necessary, a non-aliphatic dicarboxylic acid such as terephthalic acid and / or 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 as a small amount copolymerization component. An acid may be used.

  The preferred range of the weight average molecular weight of the polylactic acid polymer used in the present invention is 60,000 to 700,000, more preferably 80,000 to 400,000, and 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 expressed, and if it is too large, the melt viscosity is too high and the 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 polymer and is preferably crystalline. The other layer of the laminated film (hereinafter referred to as “second layer”) is composed of a polylactic acid polymer.

The D-lactic acid content (hereinafter referred to as “Da”) (%) of the crystalline polylactic acid polymer constituting the first layer and the D-lactic acid polymer D- constituting the second layer. Lactic acid content (hereinafter referred to as “Db”) (%)
Da ≦ 7 and Db-Da> 3
It is good to have the relationship.

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

  In addition, since the second layer becomes a heat seal layer, the ratio (Db) of D-lactic acid in the polylactic acid polymer constituting the second layer is preferably higher than 3% than Da. When this difference is 3% or less, both the crystallinity and the melting point are close to the polylactic acid polymer constituting the first layer, and it is necessary to seal at a high temperature. That is, the support layer is also heated and heat shrinkage occurs at a high temperature seal, which causes problems such as undulations and wrinkles in 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 range.

  The crystalline polylactic acid polymer constituting the first layer and the polylactic acid polymer constituting the second layer may be a mixture of two or more different types of polylactic acid polymers. . In this case, the D-lactic acid ratios Da and Db are average values calculated from the blending ratio of D-lactic acid constituting two or more types of polylactic acid polymers.

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

  The laminated film according to the present invention has a three-layer constitution of a second layer / first layer / second layer comprising a second layer having a heat-resistant first layer as an intermediate layer and heat sealing properties on both sides. Is excellent in versatility. Also, a five-layer configuration of second layer / first layer / second layer / first layer / second layer, and second layer / first layer / second layer / first layer /... / Second layer The multi-layer structure may be used. In consideration of the curl and heat resistance of the film, the second layer / first layer has a two-layer structure in which only one side serves as a heat seal layer, or the second layer / first layer / second layer / first layer 4 The layer structure may be a multilayer structure of the 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 15-80 μm.

  Further, an adhesive layer, an adhesive resin layer, a recycled resin layer, or a first layer having a thickness of 10 μm or less, preferably 5 μm or less, between each layer between the first layer and the second layer as long as the effect of the present invention is not impaired. An intermediate layer of the second layer may be laminated.

  Further, the crystalline polylactic acid polymer constituting the first layer may be a mixture containing the polylactic acid polymer constituting the second layer, or may be recycling of the entire film layer. Good.

  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 can be added for the purpose of adjusting various physical properties. .

  As a laminating method, a commonly used method can be adopted. For example, so-called co-extrusion by connecting to a single die from a plurality of extruders in a feed block type or multi-manifold type, another type of film is heated and pressure-bonded on the surface of the unrolled mixed film using a roll or a press plate. There is a way.

  As a method for producing a biaxially stretched film mainly composed of a polylactic acid-based polymer, a sheet-like material or a cylindrical material extruded from a T die, I die, round die or the like is rapidly cooled by a cooling cast roll, water, compressed air, etc. Examples of the method include solidification in a state close to an amorphous state and then biaxial stretching by a roll method, a tenter method, a tubular method, or the like.

In general, 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 lateral stretching is performed by a tenter method, and a simultaneous biaxial stretching method in which stretching is performed by a tenter simultaneously in the longitudinal and lateral directions are generally used.

  As stretching conditions, the stretching temperature is 55 to 90 ° C, preferably 65 to 80 ° C, the longitudinal stretching ratio is 1.5 times, preferably 2 to 4 times, and the transverse stretching ratio is 1.5 to 5 times, preferably 2 to 4 times. The stretching speed is 10 to 100000% / min, preferably 100 to 10000% / min. However, these suitable ranges vary depending on the composition of the polymer and the thermal history of the unstretched sheet, and therefore can be appropriately determined in consideration of the strength and elongation of the film.

  When the film is not in the range of the draw ratio and the drawing temperature, the thickness accuracy of the obtained film is remarkably lowered, and this tendency is particularly remarkable in a film that is heat-treated after drawing. Such thickness fluctuations can cause the appearance of wrinkles, undulations, etc. in products during printing, filming, other film, metal thin film, lamination with paper, and secondary processing such as bag making. It becomes such a factor.

  In terms of suppressing thermal shrinkage of the film, heat treatment is performed with the film held. Usually, in the tenter method, since the film is stretched in a state where the film is held by a clip, it is immediately heat-treated. In the film secondary processing step, 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 ratio of the resulting polylactic acid-based laminated biaxially stretched film is preferably 5% or less after a water bath of 80 ° C./1 minute. This is because if it exceeds 5%, factors such as wrinkles and undulations on the film will be caused.

  The polylactic acid-based laminated biaxially stretched film produced according to the present invention is a polylactic acid-based film that is suppressed in shrinkage as much as possible and also has heat sealability. When this biaxially stretched film is used as a packaging material, it is necessary to satisfy quality in the following cases. For example, in individual packaging and pillow packaging, it is necessary to heat-seal the back-pasted part, the folded part, etc. so that the packaging cannot be easily unwound. Further, the film may be heat-sealed to form a bag, and after the non-wrapped body is put in the bag, the opening may be heat-sealed to be completely sealed. In such a case, the heat seal strength needs to be 1 N or more with respect to a film width of 15 mm. If it is less than 1 N, the sealing strength of the film is low, and even when heat sealed and packaged, if an external force or impact is applied, the packaging is easily unwound 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 a conventional biaxially stretched polypropylene film or biaxially stretched polyester film is used, and other plastics. Biodegradable polylactic acid laminated biaxially stretched film that can be used as a heat sealant layer when laminating films can be provided. Individual confectionery such as fiber packaging, vegetable packaging, chocolate, caramel, candy There is an application as a film suitable for packaging, overlapping of audio tapes and audio discs. It can also be used by laminating with other plastic films, paper, aluminum foil and the like.

  Examples are shown below, but the present invention is not limited by these. First, the physical property measuring method in this Example and a comparative example is shown below.

(1) Stretch ratio-Longitudinal stretch ratio = Flow rate of the film after longitudinal stretching / Flow rate of the original sheet before longitudinal stretching-The stretching ratio in the horizontal direction is gripped by the tenter clip from the width of the original sheet before longitudinal stretching. The value obtained by subtracting the width of the part is a value obtained by assigning the length obtained by subtracting the width of the part held by the clip from the width obtained after the transverse stretching.
Transverse stretching ratio = {(film width after stretching) − (width held by clip)} / {(original sheet width before stretching) − (width held by clip)}

(2) Shrinkage rate After cutting into a length of 100 mm and a width of 100 mm along the MD and TD of the film and immersing in a warm water bath at 80 ° C. for 1 minute, the dimensions after the shrinkage are measured, and the thermal shrinkage rate according to the following formula Was calculated. The shrinkage rate is measured along the stretching direction, and both MD and TD are in the test direction in this test.
Shrinkage rate (%) = {(dimension before shrinkage) − (dimension after shrinkage)} × 100 / (dimension before shrinkage)

(3) Heat seal strength and finish Prepare a film cut into MD170mm x TD130mm, fold it in two so that the surfaces to be heat sealant materials are in contact with each other, seal with a heat seal bar, and the bottom is MD A two-sided sealed bag was produced along the fold. The sealing conditions were 80, 100 and 120 ° C., pressing for about 5 seconds and then allowing 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 marked with x if wrinkles, undulations, shrinkage unevenness, etc. were noticeable. On the other hand, although some of these were observed, those that were sufficiently finished as bags were marked with “◯”.
The heat seal strength was determined by measuring the strength at a width of 15 mm according to the method described in JIS Z1711 “Polyethylene film bag”. 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 out film was spread and held on a chuck of a tensile tester for testing.
A poorly finished bag also has a relatively poor seal strength and tends to vary. When the film was significantly shrunk, it could not be measured and was described as being impossible to measure.

(4) Comprehensive evaluation In the above-described shrinkage rate, heat seal strength, and finish evaluation, all were evaluated as “good”, and even one having “×” was evaluated as “poor”.
(Constituent resin of laminate)
As the resin constituting the laminate, the first component alone shown in Table 1 or a mixture of the first component and the second component was used. The ratio of D-lactic acid in the case of the mixture was calculated as an average value from the weight fraction of both.

Example 1
L-lactic acid: D-lactic acid = 80: 20 structural unit, glass transition point (Tg) 52 ° C. polylactic acid 80%, L-lactic acid: D-lactic acid = 95: 5 structural unit, glass transition Point (Tg) Mixing 20% polylactic acid at 56 ° C. and drying to 100 parts by weight of polylactic acid (Db = 17%, resin 6 in Table 1) with an average particle size of 1.4 μm (trade name) : Silicia 100, manufactured by Fuji Silysia Chemical Co., Ltd.) 0.1 parts by weight were mixed and extruded as a front and back layer from a multi-manifold die at 220 ° C. with a 25 mmφ unidirectional twin screw extruder.

  Further, a polylactic acid polymer having a structural unit of L-lactic acid: D-lactic acid = 99.5: 0.5 (Da = 0.5%) and having 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 discharge amount of the molten resin was adjusted so that the thickness ratio of the surface layer, the intermediate layer, and the back layer was 1: 10: 1. This coextruded sheet was quenched with a casting roll at about 43 ° C. to obtain an unstretched sheet. Subsequently, the film was stretched 2.6 times at 76 ° C. in the longitudinal direction, and then 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 amount of molten resin discharged from the extruder and the line speed were adjusted so that the film thickness was approximately 30 μm on average. The evaluation results of the film are shown in Table 2.

(Examples 2 and 3 and Comparative Examples 1 to 5)
As shown in Table 2 or Table 3, a polylactic acid polymer (corresponding to each resin described in Table 1) of L-lactic acid and D-lactic acid different from each other as in Example 1 was used as a surface layer and an intermediate layer. And it was extruded so that it might become a predetermined thickness ratio as a back layer, and after biaxial stretching, it heat-processed and produced the film. The evaluation results of each film are shown in Table 2 and Table 3.

  In Comparative Example 2, the film broke during the heat treatment. In Comparative Examples 1 and 4, the bag produced by sealing was poor in appearance and could not be obtained with a good finish. Further, Comparative Examples 3 and 5 were unable to obtain sufficient sealing strength that could take a form as a bag. The evaluation results of each film are shown in Table 2 or Table 3.

Example 4
L-lactic acid: D-lactic acid = 80: 20 structural unit, glass transition point (Tg) 52 ° C. polylactic acid 80%, L-lactic acid: D-lactic acid = 95: 5 structural unit, glass transition Point (Tg) Mixing 20% polylactic acid at 56 ° C. and drying to 100 parts by weight of polylactic acid (Db = 17%, resin 6 in Table 1) with an average particle size of 1.4 μm (trade name) : Silicia 100, manufactured by Fuji Silysia Chemical Co., Ltd.) 0.1 parts by weight were mixed and extruded at 210 ° C. as a surface layer from a two-layer multi-manifold die using a 25 mmφ co-directional twin screw extruder.

  Further, a polylactic acid polymer having a structural unit of L-lactic acid: D-lactic acid = 99.5: 0.5 (Da = 0.5%) and having a glass transition point (Tg) of 58 ° C. (resin 1 in Table 1) And 0.1 parts by weight of dried granular silica having an average particle size of 1.4 μm (trade name: Siricia 100, manufactured by Fuji Silysia Chemical Co., Ltd.) and mixed with a 40 mmφ single screw extruder at 210 ° C. from the above die. Extruded as an intermediate layer. Since the obtained laminate has a two-layer structure, the intermediate layer forms the back layer as it is.

  The amount of molten resin discharged was adjusted so that the thickness ratio of the laminate was 1: 2 in the surface layer: intermediate layer. This coextruded sheet was quenched with a casting roll at about 42 ° C. to obtain an unstretched sheet. Subsequently, the film was stretched 2.6 times at 75 ° C. in the longitudinal direction, and then stretched 3.6 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 amount of molten resin discharged from the extruder and the line speed were adjusted so that the film thickness was approximately 15 μm on average. The evaluation results of the film are shown in Table 2.

Claims (1)

A laminated film comprising at least two layers mainly composed of a polylactic acid-based polymer,
The content ratio Da (%) of D-lactic acid in the polylactic acid polymer constituting one layer in the laminated film and the D-lactic acid in the polylactic acid polymer constituting another layer of the laminated film The relationship of the content ratio Db (%) of
Da ≦ 7 and Db-Da> 3
And
The other one layer is a polylactic acid-based laminated biaxially stretched film constituting at least one outermost layer of the laminated film.